Wang, Jia-Nan; Jin, Jun-Ling; Geng, Yun; Sun, Shi-Ling; Xu, Hong-Liang; Lu, Ying-Hua; Su, Zhong-Min
2013-03-15
Recently, the extreme learning machine neural network (ELMNN) as a valid computing method has been proposed to predict the nonlinear optical property successfully (Wang et al., J. Comput. Chem. 2012, 33, 231). In this work, first, we follow this line of work to predict the electronic excitation energies using the ELMNN method. Significantly, the root mean square deviation of the predicted electronic excitation energies of 90 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives between the predicted and experimental values has been reduced to 0.13 eV. Second, four groups of molecule descriptors are considered when building the computing models. The results show that the quantum chemical descriptions have the closest intrinsic relation with the electronic excitation energy values. Finally, a user-friendly web server (EEEBPre: Prediction of electronic excitation energies for BODIPY dyes), which is freely accessible to public at the web site: http://202.198.129.218, has been built for prediction. This web server can return the predicted electronic excitation energy values of BODIPY dyes that are high consistent with the experimental values. We hope that this web server would be helpful to theoretical and experimental chemists in related research.
Zhang, Du; Yang, Weitao
2016-10-13
An efficient method for calculating excitation energies based on the particle-particle random phase approximation (ppRPA) is presented. Neglecting the contributions from the high-lying virtual states and the low-lying core states leads to the significantly smaller active-space ppRPA matrix while keeping the error to within 0.05 eV from the corresponding full ppRPA excitation energies. The resulting computational cost is significantly reduced and becomes less than the construction of the non-local Fock exchange potential matrix in the self-consistent-field (SCF) procedure. With only a modest number of active orbitals, the original ppRPA singlet-triplet (ST) gaps as well as the low-lying single and doublemore » excitation energies can be accurately reproduced at much reduced computational costs, up to 100 times faster than the iterative Davidson diagonalization of the original full ppRPA matrix. For high-lying Rydberg excitations where the Davidson algorithm fails, the computational savings of active-space ppRPA with respect to the direct diagonalization is even more dramatic. The virtues of the underlying full ppRPA combined with the significantly lower computational cost of the active-space approach will significantly expand the applicability of the ppRPA method to calculate excitation energies at a cost of O(K^{4}), with a prefactor much smaller than a single SCF Hartree-Fock (HF)/hybrid functional calculation, thus opening up new possibilities for the quantum mechanical study of excited state electronic structure of large systems.« less
Zhang, Du; Yang, Weitao
2016-10-13
An efficient method for calculating excitation energies based on the particle-particle random phase approximation (ppRPA) is presented. Neglecting the contributions from the high-lying virtual states and the low-lying core states leads to the significantly smaller active-space ppRPA matrix while keeping the error to within 0.05 eV from the corresponding full ppRPA excitation energies. The resulting computational cost is significantly reduced and becomes less than the construction of the non-local Fock exchange potential matrix in the self-consistent-field (SCF) procedure. With only a modest number of active orbitals, the original ppRPA singlet-triplet (ST) gaps as well as the low-lying single and double excitation energies can be accurately reproduced at much reduced computational costs, up to 100 times faster than the iterative Davidson diagonalization of the original full ppRPA matrix. For high-lying Rydberg excitations where the Davidson algorithm fails, the computational savings of active-space ppRPA with respect to the direct diagonalization is even more dramatic. The virtues of the underlying full ppRPA combined with the significantly lower computational cost of the active-space approach will significantly expand the applicability of the ppRPA method to calculate excitation energies at a cost of O(K^{4}), with a prefactor much smaller than a single SCF Hartree-Fock (HF)/hybrid functional calculation, thus opening up new possibilities for the quantum mechanical study of excited state electronic structure of large systems.
NASA Astrophysics Data System (ADS)
Zhang, Du; Yang, Weitao
2016-10-01
An efficient method for calculating excitation energies based on the particle-particle random phase approximation (ppRPA) is presented. Neglecting the contributions from the high-lying virtual states and the low-lying core states leads to the significantly smaller active-space ppRPA matrix while keeping the error to within 0.05 eV from the corresponding full ppRPA excitation energies. The resulting computational cost is significantly reduced and becomes less than the construction of the non-local Fock exchange potential matrix in the self-consistent-field (SCF) procedure. With only a modest number of active orbitals, the original ppRPA singlet-triplet (ST) gaps as well as the low-lying single and double excitation energies can be accurately reproduced at much reduced computational costs, up to 100 times faster than the iterative Davidson diagonalization of the original full ppRPA matrix. For high-lying Rydberg excitations where the Davidson algorithm fails, the computational savings of active-space ppRPA with respect to the direct diagonalization is even more dramatic. The virtues of the underlying full ppRPA combined with the significantly lower computational cost of the active-space approach will significantly expand the applicability of the ppRPA method to calculate excitation energies at a cost of O(K4), with a prefactor much smaller than a single SCF Hartree-Fock (HF)/hybrid functional calculation, thus opening up new possibilities for the quantum mechanical study of excited state electronic structure of large systems.
Gao, Ting; Sun, Shi-Ling; Shi, Li-Li; Li, Hui; Li, Hong-Zhi; Su, Zhong-Min; Lu, Ying-Hua
2009-05-14
Support vector machines (SVMs), as a novel type of learning machine, has been very successful in pattern recognition and function estimation problems. In this paper we introduce least-squares (LS) SVMs to improve the calculation accuracy of density functional theory. As a demonstration, this combined quantum mechanical calculation with LS-SVM correction approach has been applied to evaluate the electronic excitation energies of 160 organic molecules. The newly introduced LS-SVM approach reduces the root-mean-square deviation of the calculated electronic excitation energies of 160 organic molecules from 0.32 to 0.11 eV for the B3LYP/6-31G(d) calculation. Thus, the LS-SVM correction on top of B3LYP/6-31G(d) is a better method to correct electronic excitation energies and can be used as the approximation of experimental results which are impossible to obtain experimentally.
Riahi, Saleh; Rowley, Christopher N
2014-10-30
The quantum mechanical (QM)/molecular mechanical (MM) interface between Chemistry at HARvard Molecular Mechanics (CHARMM) and TURBOMOLE is described. CHARMM provides an extensive set of simulation algorithms, like molecular dynamics (MD) and free energy perturbation, and support for mature nonpolarizable and Drude polarizable force fields. TURBOMOLE provides fast QM calculations using density functional theory or wave function methods and excited state properties. CHARMM-TURBOMOLE is well-suited for extended QM/MM MD simulations using first principles methods with large (triple-ζ) basis sets. We demonstrate these capabilities with a QM/MM simulation of Mg(2+) (aq), where the MM outer sphere water molecules are represented using the SWM4-NDP Drude polarizable force field and the ion and inner coordination sphere are represented using QM PBE, PBE0, and MP2 methods. The relative solvation free energies of Mg(2+) and Zn(2+) were calculated using thermodynamic integration. We also demonstrate the features for excited state properties. We calculate the time-averaged solution absorption spectrum of indole, the emission spectrum of the indole 1La excited state, and the electronic circular dichroism spectrum of an oxacepham.
Pavanello, Michele; Van Voorhis, Troy; Visscher, Lucas; Neugebauer, Johannes
2013-02-07
Quantum-mechanical methods that are both computationally fast and accurate are not yet available for electronic excitations having charge transfer character. In this work, we present a significant step forward towards this goal for those charge transfer excitations that take place between non-covalently bound molecules. In particular, we present a method that scales linearly with the number of non-covalently bound molecules in the system and is based on a two-pronged approach: The molecular electronic structure of broken-symmetry charge-localized states is obtained with the frozen density embedding formulation of subsystem density-functional theory; subsequently, in a post-SCF calculation, the full-electron Hamiltonian and overlap matrix elements among the charge-localized states are evaluated with an algorithm which takes full advantage of the subsystem DFT density partitioning technique. The method is benchmarked against coupled-cluster calculations and achieves chemical accuracy for the systems considered for intermolecular separations ranging from hydrogen-bond distances to tens of Angstroms. Numerical examples are provided for molecular clusters comprised of up to 56 non-covalently bound molecules.
2017-01-01
Developing ab initio approaches able to provide accurate excited-state energies at a reasonable computational cost is one of the biggest challenges in theoretical chemistry. In that framework, the Bethe–Salpeter equation approach, combined with the GW exchange-correlation self-energy, which maintains the same scaling with system size as TD-DFT, has recently been the focus of a rapidly increasing number of applications in molecular chemistry. Using a recently proposed set encompassing excitation energies of many kinds [J. Phys. Chem. Lett.2016, 7, 586–591], we investigate here the performances of BSE/GW. We compare these results to CASPT2, EOM-CCSD, and TD-DFT data and show that BSE/GW provides an accuracy comparable to the two wave function methods. It is particularly remarkable that the BSE/GW is equally efficient for valence, Rydberg, and charge-transfer excitations. In contrast, it provides a poor description of triplet excited states, for which EOM-CCSD and CASPT2 clearly outperform BSE/GW. This contribution therefore supports the use of the Bethe–Salpeter approach for spin-conserving transitions. PMID:28301726
Jacquemin, Denis; Duchemin, Ivan; Blase, Xavier
2017-03-16
Developing ab initio approaches able to provide accurate excited-state energies at a reasonable computational cost is one of the biggest challenges in theoretical chemistry. In that framework the Bethe-Salpeter equation approach, combined with the GW exchange-correlation self-energy, that maintains the same scaling with system size as TD-DFT, has recently been the focus of a rapidly increasing number of applications in molecular chemistry. Using a recently-proposed set encompassing excitation energies of many kinds [J. Phys. Chem. Lett., 7 (2016), 586-591], we investigate here the performances of BSE/GW. We compare these results to CASPT2, EOM-CCSD, and TD-DFT data and show that BSE/GW provides an accuracy comparable to the two wavefunction methods. It is particularly remarkable that the BSE/GW is equally efficient for valence, Rydberg and charge-transfer excitations. In contrast, it provides a poor description of triplet excited-states, for which EOM-CCSD and CASPT2 clearly outperform BSE/GW. This contribution therefore supports the use of the Bethe-Salpeter approach for spin-conserving transitions.
Janke, Svenja M.; Auerbach, Daniel J.; Kandratsenka, Alexander; Wodtke, Alec M.
2015-09-28
We have constructed a potential energy surface (PES) for H-atoms interacting with fcc Au(111) based on fitting the analytic form of the energy from Effective Medium Theory (EMT) to ab initio energy values calculated with density functional theory. The fit used input from configurations of the H–Au system with Au atoms at their lattice positions as well as configurations with the Au atoms displaced from their lattice positions. It reproduces the energy, in full dimension, not only for the configurations used as input but also for a large number of additional configurations derived from ab initio molecular dynamics (AIMD) trajectories at finite temperature. Adiabatic molecular dynamics simulations on this PES reproduce the energy loss behavior of AIMD. EMT also provides expressions for the embedding electron density, which enabled us to develop a self-consistent approach to simulate nonadiabatic electron-hole pair excitation and their effect on the motion of the incident H-atoms. For H atoms with an energy of 2.7 eV colliding with Au, electron-hole pair excitation is by far the most important energy loss pathway, giving an average energy loss ≈3 times that of the adiabatic case. This increased energy loss enhances the probability of the H-atom remaining on or in the Au slab by a factor of 2. The most likely outcome for H-atoms that are not scattered also depends prodigiously on the energy transfer mechanism; for the nonadiabatic case, more than 50% of the H-atoms which do not scatter are adsorbed on the surface, while for the adiabatic case more than 50% pass entirely through the 4 layer simulation slab.
Janke, Svenja M; Auerbach, Daniel J; Wodtke, Alec M; Kandratsenka, Alexander
2015-09-28
We have constructed a potential energy surface (PES) for H-atoms interacting with fcc Au(111) based on fitting the analytic form of the energy from Effective Medium Theory (EMT) to ab initio energy values calculated with density functional theory. The fit used input from configurations of the H-Au system with Au atoms at their lattice positions as well as configurations with the Au atoms displaced from their lattice positions. It reproduces the energy, in full dimension, not only for the configurations used as input but also for a large number of additional configurations derived from ab initio molecular dynamics (AIMD) trajectories at finite temperature. Adiabatic molecular dynamics simulations on this PES reproduce the energy loss behavior of AIMD. EMT also provides expressions for the embedding electron density, which enabled us to develop a self-consistent approach to simulate nonadiabatic electron-hole pair excitation and their effect on the motion of the incident H-atoms. For H atoms with an energy of 2.7 eV colliding with Au, electron-hole pair excitation is by far the most important energy loss pathway, giving an average energy loss ≈3 times that of the adiabatic case. This increased energy loss enhances the probability of the H-atom remaining on or in the Au slab by a factor of 2. The most likely outcome for H-atoms that are not scattered also depends prodigiously on the energy transfer mechanism; for the nonadiabatic case, more than 50% of the H-atoms which do not scatter are adsorbed on the surface, while for the adiabatic case more than 50% pass entirely through the 4 layer simulation slab.
NASA Astrophysics Data System (ADS)
Brückner, Charlotte; Engels, Bernd
2017-01-01
Vertical and adiabatic singlet and triplet excitation energies of molecular p-type semiconductors calculated with various DFT functionals and wave-function based approaches are benchmarked against MS-CASPT2/cc-pVTZ reference values. A special focus lies on the singlet-triplet gaps that are very important in the process of singlet fission. Singlet fission has the potential to boost device efficiencies of organic solar cells, but the scope of existing singlet-fission compounds is still limited. A computational prescreening of candidate molecules could enlarge it; yet it requires efficient methods accurately predicting singlet and triplet excitation energies. Different DFT formulations (Tamm-Dancoff approximation, linear response time-dependent DFT, Δ-SCF) and spin scaling schemes along with several ab initio methods (CC2, ADC(2)/MP2, CIS(D), CIS) are evaluated. While wave-function based methods yield rather reliable singlet-triplet gaps, many DFT functionals are shown to systematically underestimate triplet excitation energies. To gain insight, the impact of exact exchange and correlation is in detail addressed.
Accurate Excited State Geometries within Reduced Subspace TDDFT/TDA.
Robinson, David
2014-12-09
A method for the calculation of TDDFT/TDA excited state geometries within a reduced subspace of Kohn-Sham orbitals has been implemented and tested. Accurate geometries are found for all of the fluorophore-like molecules tested, with at most all valence occupied orbitals and half of the virtual orbitals included but for some molecules even fewer orbitals. Efficiency gains of between 15 and 30% are found for essentially the same level of accuracy as a standard TDDFT/TDA excited state geometry optimization calculation.
Mean excitation energies for molecular ions
NASA Astrophysics Data System (ADS)
Jensen, Phillip W. K.; Sauer, Stephan P. A.; Oddershede, Jens; Sabin, John R.
2017-03-01
The essential material constant that determines the bulk of the stopping power of high energy projectiles, the mean excitation energy, is calculated for a range of smaller molecular ions using the RPA method. It is demonstrated that the mean excitation energy of both molecules and atoms increase with ionic charge. However, while the mean excitation energies of atoms also increase with atomic number, the opposite is the case for mean excitation energies for molecules and molecular ions. The origin of these effects is explained by considering the spectral representation of the excited state contributing to the mean excitation energy.
Collisional energy transfer from excited nitrogen dioxide
Patten, K.O.
1991-05-01
The radiative lifetimes of gaseous nitrogen dioxide excited by pulsed, tunable dye laser radiation are determined for excitation wavelengths ranging from 400 to 750 nm. When the data are expressed in the form of zero-pressure radiative rate constants (k{sub 0}/s{sup {minus}1}), they fit a linear equation with respect to excitation energy. This fit predicts a radiative lifetime of 64 {mu}s for 400 nm excitation and 102 {mu}s at 750 nm. The effects of pressure, observation delay time, and wavelength range of the fluorescence detection apparatus are determined for both radiative lifetime and quenching constant. Dispersed fluorescence spectra from excited nitrogen dioxide are analyzed into three-parameter functions that approximate the corresponding excited state population distributions. Energy transfer from nitrogen dioxide excited at 532 nm and colliding with thirteen buffer gases is studied by this population deconvolution method. The energy removal rate constants increase in the order Ne < Ar < Kr < Xe < He < CO < N{sub 2} < O{sub 2} < NO < NO{sub 2} < CO{sub 2} < SF{sub 6} < SO{sub 2}. The energy transfer rate constant is strongly correlated with the number of degrees of freedom of the buffer molecule and with low vibrational frequencies of the buffer molecule. Population deconvolution from excited nitrogen dioxide fluorescence spectra is again employed to find energy removal rate constants for the NO {sub 2}{sup *}-NO{sub 2} collisions, excited by dye laser at 475.34, 435.04, and 400.00 nm. The energy transfer rate constant increases with decreasing excitation wavelength. The energy removal rate constant between 400 and 532 nm excitation increases as the (3.6 {plus minus} 0.4) power of the excitation photon energy. 76 refs., 67 figs., 16 tabs.
Fast and Accurate Electronic Excitations in Cyanines with the Many-Body Bethe-Salpeter Approach.
Boulanger, Paul; Jacquemin, Denis; Duchemin, Ivan; Blase, Xavier
2014-03-11
The accurate prediction of the optical signatures of cyanine derivatives remains an important challenge in theoretical chemistry. Indeed, up to now, only the most expensive quantum chemical methods (CAS-PT2, CC, DMC, etc.) yield consistent and accurate data, impeding the applications on real-life molecules. Here, we investigate the lowest lying singlet excitation energies of increasingly long cyanine dyes within the GW and Bethe-Salpeter Green's function many-body perturbation theory. Our results are in remarkable agreement with available coupled-cluster (exCC3) data, bringing these two single-reference perturbation techniques within a 0.05 eV maximum discrepancy. By comparison, available TD-DFT calculations with various semilocal, global, or range-separated hybrid functionals, overshoot the transition energies by a typical error of 0.3-0.6 eV. The obtained accuracy is achieved with a parameter-free formalism that offers similar accuracy for metallic or insulating, finite size or extended systems.
Mean excitation energies for ions in gases and plasmas
NASA Astrophysics Data System (ADS)
Garbet, Xavier; Deutsch, Claude; Maynard, Gilles
1987-02-01
A variational approach yields accurate upper and lower bounds for mean excitation energies and other related parameters describing the stopping of nonrelativistic point charges by isolated species and ions embedded in dense and hot matter of relevance to particle-driven inertial fusion. The resulting I compares nicely with previous ones by Hartree-Fock-Slater and with experimental data when available. An efficient pseudo-analytic formula based on the Thomas-Fermi method is obtained, together with a cubic spline interpolation variationally improved. It is shown that in high temperature plasmas (kBT≥10 eV) mean excitation energies are significantly smaller than their cold homologue.
A highly accurate ab initio potential energy surface for methane
NASA Astrophysics Data System (ADS)
Owens, Alec; Yurchenko, Sergei N.; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter
2016-09-01
A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art ab initio theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects, and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of 12CH4 reproduced with a root-mean-square error of 0.70 cm-1. The computed ab initio equilibrium C-H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as J (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the equilibrium geometry. The PES represents the most accurate ab initio surface to date and will serve as a good starting point for empirical refinement.
Excitation energy transfer in the photosystem I
Webber, Andrew N
2012-09-25
Photosystem I is a multimeric pigment protein complex in plants, green alage and cyanobacteria that functions in series with Photosystem II to use light energy to oxidize water and reduce carbon dioxide. The Photosystem I core complex contains 96 chlorophyll a molecules and 22 carotenoids that are involved in light harvesting and electron transfer. In eucaryotes, PSI also has a peripheral light harvesting complex I (LHCI). The role of specific chlorophylls in excitation and electron transfer are still unresolved. In particular, the role of so-called bridging chlorophylls, located between the bulk antenna and the core electron transfer chain, in the transfer of excitation energy to the reaction center are unknown. During the past funding period, site directed mutagenesis has been used to create mutants that effect the physical properties of these key chlorophylls, and to explore how this alters the function of the photosystem. Studying these mutants using ultrafast absorption spectroscopy has led to a better understanding of the process by which excitation energy is transferred from the antenna chlorophylls to the electron transfer chain chlorophylls, and what the role of connecting chlorophylls and A_0 chlorophylls is in this process. We have also used these mutants to investigate whch of the central group of six chlorophylls are involved in the primary steps of charge separation and electron transfer.
Deng, Yan; Zhou, Bin; Xing, Chao; Zhang, Rong
2014-10-17
A novel multifrequency excitation (MFE) method is proposed to realize rapid and accurate dynamic testing of micromachined gyroscope chips. Compared with the traditional sweep-frequency excitation (SFE) method, the computational time for testing one chip under four modes at a 1-Hz frequency resolution and 600-Hz bandwidth was dramatically reduced from 10 min to 6 s. A multifrequency signal with an equal amplitude and initial linear-phase-difference distribution was generated to ensure test repeatability and accuracy. The current test system based on LabVIEW using the SFE method was modified to use the MFE method without any hardware changes. The experimental results verified that the MFE method can be an ideal solution for large-scale dynamic testing of gyroscope chips and gyroscopes.
Peculiarities of collisional excitation transfer with excited screened energy levels of atoms
Gerasimov, V. A.; Gerasimov, V. V.; Pavlinskiy, A. V.
2007-09-15
We report an experimental discovery of deviations from the known regularities in collisional excitation transfer processes for metal atoms. The collisional excitation transfer with excited screened energy levels of thulium and dysprosium atoms is studied. The selecting role of the screening 6s shell in collisional excitation transfer is shown.
New Accurate Oscillator Strengths and Electron Excitation Collision Strengths for N1
NASA Technical Reports Server (NTRS)
Tayal, S. S.
2006-01-01
The nonorthogonal orbitals technique in a multiconfiguration Hartree-Fock approach is used to calculate oscillator strengths and transition probabilities of N(I) lines. The relativistic effects are allowed by means of Breit-Pauli operators. The length and velocity forms of oscillator strengths show good agreement for most transitions. The B-spline R-matrix with pseudostates approach has been used to calculate electron excitation collision strengths and rates. The nonorthogonal orbitals are used for an accurate description of both target wave functions and the R-matrix basis functions. The 24 spectroscopic bound and autoionizing states together with 15 pseudostates are included in the close-coupling expansion. The collision strengths for transitions between fine-structure levels are calculated by transforming the LS-coupled K-matrices to K-matrices in an intermediate coupling scheme. Thermally averaged collision strengths have been determined by integrating collision strength over a Maxwellian distribution of electron energies over a temperature range suitable for the modeling of astrophysical plasmas. The oscillator strengths and thermally averaged collision strengths are presented for transitions between the fine-structure levels of the 2s(sup 2)p(sup 3) (sup 4)S(sup 0), (sup 2)D(sup 0), (sup 2)P(sup 0), 2s2p(sup 4) (sup 4)P, 2s(sup 2)2p(sup 2)3s (sup 4)P, and (sup 2)P terms and from these levels to the levels of the 2s(sup 2)2p(sup 2)3p (sup 2)S(sup 0), (sup 4)D(sup 0), (sup 4)P(sup 0), (sup 4)S(sup 0), (sup 2)D(sup 0), (sup 2)P(sup 0),2s(sup 2)2p(sup 2)3s(sup 2)D, 2s(sup 2)2p(sup 2)4s(sup 4)P, (sup 2)P, 2s(sup 2)2p(sup 2)3d(sup 2)P, (sup 4)F,(sup 2)F,(sup 4)P, (sup 4)D, and (sup 2)D terms. Thermally averaged collision strengths are tabulated over a temperature range from 500 to 50,000 K.
Low Energy Electron Impact Excitation of Water
NASA Astrophysics Data System (ADS)
Ralphs, Kevin; Serna, Gabriela; Hargreaves, Leigh R.; Khakoo, Murtadha A.; Winstead, Carl; McKoy, B. Vincent
2011-10-01
We present normalized absolute differential and integral cross-section measurements for the low energy electron impact excitation of the lowest dissociative 3B1, 1B1,3A1 and 1A1 states of H2O. The DCS were taken at incident energies of 9 eV, 10 eV, 12 eV, 15 eV and 20 eV and scattering angles of 15° to 130° and normalized to the elastic electron scattering measurements of. The DCS were obtained after a sophisticated unfolding of the electron energy loss spectrum of water using photoabsorption data in the literature as investigated by Thorn et al.. Our measurements extend those of to near-threshold energies. We find both important agreements and differences between our DCS and those of. Comparison to our theory (multi-channel Schwinger) and that of earlier work will also be presented. Funded by an NSF grant # RUI-PHY 0968874.
Electronic excitation of molecular hydrogen by low-energy electrons
NASA Astrophysics Data System (ADS)
Hargreaves, Leigh
2016-09-01
Molecular hydrogen is the most abundant element in the universe, particularly in interstellar plasmas such as atmospheres of gas giant planets and stars. Electron collision data for hydrogen is critical to interpreting the spectroscopy of interstellar objects, as well as being of applied value for modelling technological plasmas. Hydrogen is also fundamentally interesting, as while highly accurate wave functions for this simple molecule are available, providing an accurate, ab initio, treatment the collision dynamics has proven challenging, on account of the need to have a complete description of channel coupling and polarization effects. To date, no single theoretical approach has been able to replicate experimental results across all transitions and incident energies, while the experimental database that is available is far from complete and not all available measurements are in satisfactory agreement. In this talk, we present differential and integral cross section measurements for electronic excitation cross sections for molecular hydrogen by low-energy electron impact. The data were measured at incident energies below 20eV, using a well-tested crossed beam apparatus and employing a moveable gas source approach to ensure that background contributions to the scattering are accurately accounted for. These measurements are compared with new theoretical results employing the convergent close coupling approach.
Accurate nuclear radii and binding energies from a chiral interaction
Ekstrom, Jan A.; Jansen, G. R.; Wendt, Kyle A.; ...
2015-05-01
With the goal of developing predictive ab initio capability for light and medium-mass nuclei, two-nucleon and three-nucleon forces from chiral effective field theory are optimized simultaneously to low-energy nucleon-nucleon scattering data, as well as binding energies and radii of few-nucleon systems and selected isotopes of carbon and oxygen. Coupled-cluster calculations based on this interaction, named NNLOsat, yield accurate binding energies and radii of nuclei up to 40Ca, and are consistent with the empirical saturation point of symmetric nuclear matter. In addition, the low-lying collective Jπ=3- states in 16O and 40Ca are described accurately, while spectra for selected p- and sd-shellmore » nuclei are in reasonable agreement with experiment.« less
Accurate nuclear radii and binding energies from a chiral interaction
Ekstrom, Jan A.; Jansen, G. R.; Wendt, Kyle A.; Hagen, Gaute; Papenbrock, Thomas F.; Carlsson, Boris; Forssen, Christian; Hjorth-Jensen, M.; Navratil, Petr; Nazarewicz, Witold
2015-05-01
With the goal of developing predictive ab initio capability for light and medium-mass nuclei, two-nucleon and three-nucleon forces from chiral effective field theory are optimized simultaneously to low-energy nucleon-nucleon scattering data, as well as binding energies and radii of few-nucleon systems and selected isotopes of carbon and oxygen. Coupled-cluster calculations based on this interaction, named NNLO_{sat}, yield accurate binding energies and radii of nuclei up to ^{40}Ca, and are consistent with the empirical saturation point of symmetric nuclear matter. In addition, the low-lying collective J^{π}=3^{-} states in ^{16}O and ^{40}Ca are described accurately, while spectra for selected p- and sd-shell nuclei are in reasonable agreement with experiment.
NASA Astrophysics Data System (ADS)
Bačić, Z.
1991-09-01
We show that the triatomic adiabatic vibrational eigenstates (AVES) provide a convenient basis for accurate discrete variable representation (DVR) calculation and automatic assignment of highly excited, large amplitude motion vibrational states of floppy triatomic molecules. The DVR-AVES states are eigenvectors of the diagonal (in the stretch states) blocks of the adiabatically rearranged triatomic DVR-ray eigenvector (DVR-REV) Hamiltonian [J. C. Light and Z. Bačić, J. Chem. Phys. 87, 4008 (1987)]. The transformation of the full triatomic vibrational Hamiltonian from the DVR-REV basis to the new DVR-AVES basis is simple, and does not involve calculation of any new matrix elements. No dynamical approximation is made in the energy level calculation by the DVR-AVES approach; its accuracy and efficiency are identical to those of the DVR-REV method. The DVR-AVES states, as the adiabatic approximation to the vibrational states of a triatomic molecule, are labeled by three vibrational quantum numbers. Consequently, accurate large amplitude motion vibrational levels obtained by diagonalizing the full vibrational Hamiltonian transformed to the DVR-AVES basis, can be assigned automatically by the code, with the three quantum numbers of the dominant DVR-AVES state associated with the largest (by modulus) eigenvector element in the DVR-AVES basis. The DVR-AVES approach is used to calculate accurate highly excited localized and delocalized vibrational levels of HCN/HNC and LiCN/LiNC. A significant fraction of localized states of both systems, below and above the isomerization barrier, is assigned automatically, without inspection of wave function plots or separate approximate calculations.
Inverter Modeling For Accurate Energy Predictions Of Tracking HCPV Installations
NASA Astrophysics Data System (ADS)
Bowman, J.; Jensen, S.; McDonald, Mark
2010-10-01
High efficiency high concentration photovoltaic (HCPV) solar plants of megawatt scale are now operational, and opportunities for expanded adoption are plentiful. However, effective bidding for sites requires reliable prediction of energy production. HCPV module nameplate power is rated for specific test conditions; however, instantaneous HCPV power varies due to site specific irradiance and operating temperature, and is degraded by soiling, protective stowing, shading, and electrical connectivity. These factors interact with the selection of equipment typically supplied by third parties, e.g., wire gauge and inverters. We describe a time sequence model accurately accounting for these effects that predicts annual energy production, with specific reference to the impact of the inverter on energy output and interactions between system-level design decisions and the inverter. We will also show two examples, based on an actual field design, of inverter efficiency calculations and the interaction between string arrangements and inverter selection.
Accurate energy levels for singly ionized platinum (Pt II)
NASA Technical Reports Server (NTRS)
Reader, Joseph; Acquista, Nicolo; Sansonetti, Craig J.; Engleman, Rolf, Jr.
1988-01-01
New observations of the spectrum of Pt II have been made with hollow-cathode lamps. The region from 1032 to 4101 A was observed photographically with a 10.7-m normal-incidence spectrograph. The region from 2245 to 5223 A was observed with a Fourier-transform spectrometer. Wavelength measurements were made for 558 lines. The uncertainties vary from 0.0005 to 0.004 A. From these measurements and three parity-forbidden transitions in the infrared, accurate values were determined for 28 even and 72 odd energy levels of Pt II.
Accurate Energy Transaction Allocation using Path Integration and Interpolation
NASA Astrophysics Data System (ADS)
Bhide, Mandar Mohan
This thesis investigates many of the popular cost allocation methods which are based on actual usage of the transmission network. The Energy Transaction Allocation (ETA) method originally proposed by A.Fradi, S.Brigonne and B.Wollenberg which gives unique advantage of accurately allocating the transmission network usage is discussed subsequently. Modified calculation of ETA based on simple interpolation technique is then proposed. The proposed methodology not only increase the accuracy of calculation but also decreases number of calculations to less than half of the number of calculations required in original ETAs.
NASA Technical Reports Server (NTRS)
Wilson, J. W.; Xu, Y. J.; Kamaratos, E.; Chang, C. K.
1984-01-01
The local plasma model is used to study the effects of the chemical and physical state of a medium on its stopping power. The relationship between that model and a more exact quantum treatment of bound systems is elucidated by examining related quantities in both theories for the case of one and two-electron systems. Atomic mean excitation energies and straggling parameters in the local plasma model are compared with the accurate calculations of Inokuti et al. (1975, 1978, 1981). The use of the Gordon-Kim electron gas model of molecular bonding is used to determine the effects of covalent chemical bond shifts on the mean excitation energies for elements of the first two rows. Calculations of mean excitation energies of ionic bonded substances are presented, and the mean excitation energies of metals are discussed.
Energy Gap of Neutral Excitations Implies Vanishing Charge Susceptibility
NASA Astrophysics Data System (ADS)
Watanabe, Haruki
2017-03-01
In quantum many-body systems with a U(1) symmetry, such as particle number conservation and axial spin conservation, there are two distinct types of excitations: charge-neutral excitations and charged excitations. The energy gaps of these excitations may be independent from each other in strongly correlated systems. The static susceptibility of the U(1) charge vanishes when the charged excitations are all gapped, but its relation to the neutral excitations is not obvious. Here we show that a finite excitation gap of the neutral excitations is, in fact, sufficient to prove that the charge susceptibility vanishes (i.e., the system is incompressible). This result gives a partial explanation for why the celebrated quantization condition n (S -mz)∈Z at magnetization plateaus works even in spatial dimensions greater than one.
Accurate bond dissociation energies (D 0) for FHF- isotopologues
NASA Astrophysics Data System (ADS)
Stein, Christopher; Oswald, Rainer; Sebald, Peter; Botschwina, Peter; Stoll, Hermann; Peterson, Kirk A.
2013-09-01
Accurate bond dissociation energies (D 0) are determined for three isotopologues of the bifluoride ion (FHF-). While the zero-point vibrational contributions are taken from our previous work (P. Sebald, A. Bargholz, R. Oswald, C. Stein, P. Botschwina, J. Phys. Chem. A, DOI: 10.1021/jp3123677), the equilibrium dissociation energy (D e ) of the reaction ? was obtained by a composite method including frozen-core (fc) CCSD(T) calculations with basis sets up to cardinal number n = 7 followed by extrapolation to the complete basis set limit. Smaller terms beyond fc-CCSD(T) cancel each other almost completely. The D 0 values of FHF-, FDF-, and FTF- are predicted to be 15,176, 15,191, and 15,198 cm-1, respectively, with an uncertainty of ca. 15 cm-1.
Lee, Mi Kyung; Coker, David F
2016-08-18
An accurate approach for computing intermolecular and intrachromophore contributions to spectral densities to describe the electronic-nuclear interactions relevant for modeling excitation energy transfer processes in light harvesting systems is presented. The approach is based on molecular dynamics (MD) calculations of classical correlation functions of long-range contributions to excitation energy fluctuations and a separate harmonic analysis and single-point gradient quantum calculations for electron-intrachromophore vibrational couplings. A simple model is also presented that enables detailed analysis of the shortcomings of standard MD-based excitation energy fluctuation correlation function approaches. The method introduced here avoids these problems, and its reliability is demonstrated in accurate predictions for bacteriochlorophyll molecules in the Fenna-Matthews-Olson pigment-protein complex, where excellent agreement with experimental spectral densities is found. This efficient approach can provide instantaneous spectral densities for treating the influence of fluctuations in environmental dissipation on fast electronic relaxation.
Accurate ab initio vibrational energies of methyl chloride
Owens, Alec; Yurchenko, Sergei N.; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter
2015-06-28
Two new nine-dimensional potential energy surfaces (PESs) have been generated using high-level ab initio theory for the two main isotopologues of methyl chloride, CH{sub 3}{sup 35}Cl and CH{sub 3}{sup 37}Cl. The respective PESs, CBS-35{sup HL}, and CBS-37{sup HL}, are based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set (CBS) limit, and incorporate a range of higher-level (HL) additive energy corrections to account for core-valence electron correlation, higher-order coupled cluster terms, scalar relativistic effects, and diagonal Born-Oppenheimer corrections. Variational calculations of the vibrational energy levels were performed using the computer program TROVE, whose functionality has been extended to handle molecules of the form XY {sub 3}Z. Fully converged energies were obtained by means of a complete vibrational basis set extrapolation. The CBS-35{sup HL} and CBS-37{sup HL} PESs reproduce the fundamental term values with root-mean-square errors of 0.75 and 1.00 cm{sup −1}, respectively. An analysis of the combined effect of the HL corrections and CBS extrapolation on the vibrational wavenumbers indicates that both are needed to compute accurate theoretical results for methyl chloride. We believe that it would be extremely challenging to go beyond the accuracy currently achieved for CH{sub 3}Cl without empirical refinement of the respective PESs.
Fedorov, Dmitry A.; Varganov, Sergey A.; Derevianko, Andrei
2014-05-14
We calculate the potential energy curves, the permanent dipole moment curves, and the lifetimes of the ground and excited vibrational states of the heteronuclear alkali dimers XY (X, Y = Li, Na, K, Rb, Cs) in the X{sup 1}Σ{sup +} electronic state using the coupled cluster with singles doubles and triples method. All-electron quadruple-ζ basis sets with additional core functions are used for Li and Na, and small-core relativistic effective core potentials with quadruple-ζ quality basis sets are used for K, Rb, and Cs. The inclusion of the coupled cluster non-perturbative triple excitations is shown to be crucial for obtaining the accurate potential energy curves. A large one-electron basis set with additional core functions is needed for the accurate prediction of permanent dipole moments. The dissociation energies are overestimated by only 14 cm{sup −1} for LiNa and by no more than 114 cm{sup −1} for the other molecules. The discrepancies between the experimental and calculated harmonic vibrational frequencies are less than 1.7 cm{sup −1}, and the discrepancies for the anharmonic correction are less than 0.1 cm{sup −1}. We show that correlation between atomic electronegativity differences and permanent dipole moment of heteronuclear alkali dimers is not perfect. To obtain the vibrational energies and wave functions the vibrational Schrödinger equation is solved with the B-spline basis set method. The transition dipole moments between all vibrational states, the Einstein coefficients, and the lifetimes of the vibrational states are calculated. We analyze the decay rates of the vibrational states in terms of spontaneous emission, and stimulated emission and absorption induced by black body radiation. In all studied heteronuclear alkali dimers the ground vibrational states have much longer lifetimes than any excited states.
Fedorov, Dmitry A; Derevianko, Andrei; Varganov, Sergey A
2014-05-14
We calculate the potential energy curves, the permanent dipole moment curves, and the lifetimes of the ground and excited vibrational states of the heteronuclear alkali dimers XY (X, Y = Li, Na, K, Rb, Cs) in the X(1)Σ(+) electronic state using the coupled cluster with singles doubles and triples method. All-electron quadruple-ζ basis sets with additional core functions are used for Li and Na, and small-core relativistic effective core potentials with quadruple-ζ quality basis sets are used for K, Rb, and Cs. The inclusion of the coupled cluster non-perturbative triple excitations is shown to be crucial for obtaining the accurate potential energy curves. A large one-electron basis set with additional core functions is needed for the accurate prediction of permanent dipole moments. The dissociation energies are overestimated by only 14 cm(-1) for LiNa and by no more than 114 cm(-1) for the other molecules. The discrepancies between the experimental and calculated harmonic vibrational frequencies are less than 1.7 cm(-1), and the discrepancies for the anharmonic correction are less than 0.1 cm(-1). We show that correlation between atomic electronegativity differences and permanent dipole moment of heteronuclear alkali dimers is not perfect. To obtain the vibrational energies and wave functions the vibrational Schrödinger equation is solved with the B-spline basis set method. The transition dipole moments between all vibrational states, the Einstein coefficients, and the lifetimes of the vibrational states are calculated. We analyze the decay rates of the vibrational states in terms of spontaneous emission, and stimulated emission and absorption induced by black body radiation. In all studied heteronuclear alkali dimers the ground vibrational states have much longer lifetimes than any excited states.
Excitation energies of superdeformed states in the Pb isotopes
Wilson, A. N.; Byrne, A. P.; Dracoulis, G. D.; Davidson, P. M.; Lane, G. J.; Huebel, H.; Rossbach, D.; Schonwasser, G.; Korichi, A.; Hannachi, F.; Lopez-Martens, A.; Clark, R. M.; Fallon, P.; Macchiavelli, A. O.; Ward, D.
2006-04-26
Measurements of the excitation energies of superdeformed states via the observation of single-step linking transitions have now been made in three even-A Pb nuclei, with a quasicontinuum analysis providing a limit in a fourth, odd-A case. These results allow us to take the first steps towards establishing systematic trends in excitation energies and binding energies in the second minimum in Pb isotopes.
Roles of the Excitation in Harvesting Energy from Vibrations
Zhang, Hui; Ma, Tianwei
2015-01-01
The study investigated the role of excitation in energy harvesting applications. While the energy ultimately comes from the excitation, it was shown that the excitation may not always behave as a source. When the device characteristics do not perfectly match the excitation, the excitation alternately behaves as a source and a sink. The extent to which the excitation behaves as a sink determines the energy harvesting efficiency. Such contradictory roles were shown to be dictated by a generalized phase defined as the instantaneous phase angle between the velocity of the device and the excitation. An inductive prototype device with a diamagnetically levitated seismic mass was proposed to take advantage of the well established phase changing mechanism of vibro-impact to achieve a broader device bandwidth. Results suggest that the vibro-impact can generate an instantaneous, significant phase shift in response velocity that switches the role of the excitation. If introduced properly outside the resonance zone it could dramatically increase the energy harvesting efficiency. PMID:26496183
Accurate spectral numerical schemes for kinetic equations with energy diffusion
NASA Astrophysics Data System (ADS)
Wilkening, Jon; Cerfon, Antoine J.; Landreman, Matt
2015-08-01
We examine the merits of using a family of polynomials that are orthogonal with respect to a non-classical weight function to discretize the speed variable in continuum kinetic calculations. We consider a model one-dimensional partial differential equation describing energy diffusion in velocity space due to Fokker-Planck collisions. This relatively simple case allows us to compare the results of the projected dynamics with an expensive but highly accurate spectral transform approach. It also allows us to integrate in time exactly, and to focus entirely on the effectiveness of the discretization of the speed variable. We show that for a fixed number of modes or grid points, the non-classical polynomials can be many orders of magnitude more accurate than classical Hermite polynomials or finite-difference solvers for kinetic equations in plasma physics. We provide a detailed analysis of the difference in behavior and accuracy of the two families of polynomials. For the non-classical polynomials, if the initial condition is not smooth at the origin when interpreted as a three-dimensional radial function, the exact solution leaves the polynomial subspace for a time, but returns (up to roundoff accuracy) to the same point evolved to by the projected dynamics in that time. By contrast, using classical polynomials, the exact solution differs significantly from the projected dynamics solution when it returns to the subspace. We also explore the connection between eigenfunctions of the projected evolution operator and (non-normalizable) eigenfunctions of the full evolution operator, as well as the effect of truncating the computational domain.
Spectroscopic probes of vibrationally excited molecules at chemically significant energies
Rizzo, T.R.
1993-12-01
This project involves the application of multiple-resonance spectroscopic techniques for investigating energy transfer and dissociation dynamics of highly vibrationally excited molecules. Two major goals of this work are: (1) to provide information on potential energy surfaces of combustion related molecules at chemically significant energies, and (2) to test theoretical modes of unimolecular dissociation rates critically via quantum-state resolved measurements.
Low energy excitations of the neutron star core
NASA Astrophysics Data System (ADS)
Reddy, Sanjay
2017-01-01
I will summarize recent work on low energy excitations in cold dense matter and its implications for thermal and transport properties, and seismology of neutron stars. I argue that a low energy Lagrangian with a handful of low energy constants (LECs) provides an adequate framework for calculations. The LECs can be related to the equation of state of dense matter at zero temperature.
Vibration energy harvesting from random force and motion excitations
NASA Astrophysics Data System (ADS)
Tang, Xiudong; Zuo, Lei
2012-07-01
A vibration energy harvester is typically composed of a spring-mass system with an electromagnetic or piezoelectric transducer connected in parallel with a spring. This configuration has been well studied and optimized for harmonic vibration sources. Recently, a dual-mass harvester, where two masses are connected in series by the energy transducer and a spring, has been proposed. The dual-mass vibration energy harvester is proved to be able to harvest more power and has a broader bandwidth than the single-mass configuration, when the parameters are optimized and the excitation is harmonic. In fact, some dual-mass vibration energy harvesters, such as regenerative vehicle suspensions and buildings with regenerative tuned mass dampers (TMDs), are subjected to random excitations. This paper is to investigate the dual-mass and single-mass vibration harvesters under random excitations using spectrum integration and the residue theorem. The output powers for these two types of vibration energy harvesters, when subjected to different random excitations, namely force, displacement, velocity and acceleration, are obtained analytically with closed-form expressions. It is also very interesting to find that the output power of the vibration energy harvesters under random excitations depends on only a few parameters in very simple and elegant forms. This paper also draws some important conclusions on regenerative vehicle suspensions and buildings with regenerative TMDs, which can be modeled as dual-mass vibration energy harvesters. It is found that, under white-noise random velocity excitation from road irregularity, the harvesting power from vehicle suspensions is proportional to the tire stiffness and road vertical excitation spectrum only. It is independent of the chassis mass, tire-wheel mass, suspension stiffness and damping coefficient. Under random wind force excitation, the power harvested from buildings with regenerative TMD will depends on the building mass only, not
Egidi, Franco Segado, Mireia; Barone, Vincenzo; Koch, Henrik; Cappelli, Chiara
2014-12-14
In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π{sup *}, π-π{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.
NASA Astrophysics Data System (ADS)
Egidi, Franco; Segado, Mireia; Koch, Henrik; Cappelli, Chiara; Barone, Vincenzo
2014-12-01
In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π*, π-π*, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.
New accurate benchmark energies for large water clusters: DFT is better than expected.
Anacker, Tony; Friedrich, Joachim
2014-03-30
In this work, we use MP2 and coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] as well as their corresponding explicitly correlated (F12) counterparts to compute the interaction energies of water icosamers. The incremental scheme is used to compute benchmark energies at the CCSD(T)/CBS(45) and CCSD(T)(F12*)/cc-pVQZ-F12 level of theory. The four structures, dodecahedron, edge sharing, face sharing, and fused cubes, are part of the WATER27 test set and therefore, highly accurate interaction energies are required. All methods applied in this work lead to new benchmark energies for these four systems. To obtain these values, we carefully analyze the convergence of the interaction energies with respect to the basis set. Furthermore, we investigate the influence of the basis set superposition error and the core-valence correlation. The interaction energies are: dodecahedron -198.6 kcal/mol, edge sharing -209.7 kcal/mol, face sharing -208.0 kcal/mol, and fused cubes -208.0 kcal/mol. For water clusters, we recommend to use the PW6B95 density functional of Truhlar in combination with Grimme's dispersion correction (D3), as the mean absolute error is 0.9 and the root mean-squared deviation is only 1.4 kcal/mol.
Copan, Andreas V.; Wiens, Avery E.; Nowara, Ewa M.; Schaefer, Henry F.; Agarwal, Jay
2015-02-07
Peroxyacetyl radical [CH{sub 3}C(O)O{sub 2}] is among the most abundant peroxy radicals in the atmosphere and is involved in OH-radical recycling along with peroxyacetyl nitrate formation. Herein, the ground (X{sup ~}) and first (A{sup ~}) excited state surfaces of cis and trans peroxyacetyl radical are characterized using high-level ab initio methods. Geometries, anharmonic vibrational frequencies, and adiabatic excitation energies extrapolated to the complete basis-set limit are reported from computations with coupled-cluster theory. Excitation of the trans conformer is found to induce a symmetry-breaking conformational change due to second-order Jahn-Teller interactions with higher-lying excited states. Additional benchmark computations are provided to aid future theoretical work on peroxy radicals.
Raman active high energy excitations in URu2Si2
NASA Astrophysics Data System (ADS)
Buhot, Jonathan; Gallais, Yann; Cazayous, Maximilien; Sacuto, Alain; Piekarz, Przemysław; Lapertot, Gérard; Aoki, Dai; Méasson, Marie-Aude
2017-02-01
We have performed Raman scattering measurements on URu2Si2 single crystals on a large energy range up to ∼1300 cm-1 and in all the Raman active symmetries as a function of temperature down to 15 K. A large excitation, active only in the Eg symmetry, is reported. It has been assigned to a crystal electric field excitation on the Uranium site. We discuss how this constrains the crystal electric field scheme of the Uranium ions. Furthermore, three excitations in the A1g symmetry are observed. They have been associated to double Raman phonon processes consistently with ab initio calculations of the phonons dispersion.
Electric Discharge Excitation and Energy Source Integration.
1985-01-06
only one side of the machined bar connecting the mounting plate to the cathode. An electrical schematic of the PFN utilized for the discharge studies...for the initial charge voltage to be 2 VG for optimum energy transfer is still present. All arrangements of transmision lines studied showed the... side of the anode screen are used to achieve a smooth physical transition and, thereby, minimize flow-generated turbulence. With this arrangement the
Boothroyd, A.I. ); Dove, J.E.; Keogh, W.J. ); Martin, P.G. ); Peterson, M.R. )
1991-09-15
The interaction potential energy surface (PES) of H{sub 4} is of great importance for quantum chemistry, as a test case for molecule--molecule interactions. It is also required for a detailed understanding of certain astrophysical processes, namely, collisional excitation and dissociation of H{sub 2} in molecular clouds, at densities too low to be accessible experimentally. Accurate {ital ab} {ital initio} energies were computed for 6046 conformations of H{sub 4}, using a multiple reference (single and) double excitation configuration interaction (MRD-CI) program. Both systematic and random'' errors were estimated to have an rms size of 0.6 mhartree, for a total rms error of about 0.9 mhartree (or 0.55 kcal/mol) in the final {ital ab} {ital initio} energy values. It proved possible to include in a self-consistent way {ital ab} {ital initio} energies calculated by Schwenke, bringing the number of H{sub 4} conformations to 6101. {ital Ab} {ital initio} energies were also computed for 404 conformations of H{sub 3}; adding {ital ab} {ital initio} energies calculated by other authors yielded a total of 772 conformations of H{sub 3}. (The H{sub 3} results, and an improved analytic PES for H{sub 3}, are reported elsewhere.) {ital Ab} {ital initio} energies are tabulated in this paper only for a sample of H{sub 4} conformations; a full list of all 6101 conformations of H{sub 4} (and 772 conformations of H{sub 3} ) is available from Physics Auxiliary Publication Service (PAPS), or from the authors.
Combining MFD and PIE for accurate single-pair Förster resonance energy transfer measurements.
Kudryavtsev, Volodymyr; Sikor, Martin; Kalinin, Stanislav; Mokranjac, Dejana; Seidel, Claus A M; Lamb, Don C
2012-03-01
Single-pair Förster resonance energy transfer (spFRET) experiments using single-molecule burst analysis on a confocal microscope are an ideal tool to measure inter- and intramolecular distances and dynamics on the nanoscale. Different techniques have been developed to maximize the amount of information available in spFRET burst analysis experiments. Multiparameter fluorescence detection (MFD) is used to monitor a variety of fluorescence parameters simultaneously and pulsed interleaved excitation (PIE) employs direct excitation of the acceptor to probe its presence and photoactivity. To calculate accurate FRET efficiencies from spFRET experiments with MFD or PIE, several calibration measurements are usually required. Herein, we demonstrate that by combining MFD with PIE information regarding all calibration factors as well as an accurate determination of spFRET histograms can be performed in a single measurement. In addition, the quality of overlap of the different detection volumes as well as the detection of acceptor photophysics can be investigated with MFD-PIE. Bursts containing acceptor photobleaching can be identified and excluded from further investigation while bursts that contain FRET dynamics are unaffected by this analysis. We have employed MFD-PIE to accurately analyze the effects of nucleotides and substrate on the interdomain separation in DnaK, the major bacterial heat shock protein 70 (Hsp70). The interdomain distance increases from 47 Å in the ATP-bound state to 84 Å in the ADP-bound state and slightly contracts to 77 Å when a substrate is bound. This is in contrast to what was observed for the mitochondrial member of the Hsp70s, Ssc1, supporting the notion of evolutionary specialization of Hsp70s for different cellular functions in different organisms and cell organelles.
Fluorescent resonant excitation energy transfer in linear polyenes
NASA Astrophysics Data System (ADS)
Das, Mousumi; Ramasesha, S.
2010-03-01
We have studied the dynamics of excitation transfer between two conjugated polyene molecules whose intermolecular separation is comparable to the molecular dimensions. We have employed a correlated electron model that includes both the charge-charge, charge-bond, and bond-bond intermolecular electron repulsion integrals. We have shown that the excitation transfer rate varies as inverse square of donor-acceptor separation R-2 rather than as R-6, suggested by the Förster type of dipolar approximation. Our time-evolution study also shows that the orientational dependence on excitation transfer at a fixed short donor-acceptor separation cannot be explained by Förster type of dipolar approximation beyond a certain orientational angle of rotation of an acceptor polyene with respect to the donor polyene. The actual excitation transfer rate beyond a certain orientational angle is faster than the Förster type of dipolar approximation rate. We have also studied the excitation transfer process in a pair of push-pull polyenes for different push-pull strengths. We have seen that, depending on the push-pull strength, excitation transfer could occur to other dipole coupled states. Our study also allows for the excitation energy transfer to optically dark states which are excluded by Förster theory since the one-photon transition intensity to these states (from the ground state) is zero.
Yokono, Makio; Nagao, Ryo; Tomo, Tatsuya; Akimoto, Seiji
2015-10-01
Energy transfer dynamics in dimeric photosystem II (PSII) complexes isolated from four diatoms, Chaetoceros gracilis, Cyclotella meneghiniana, Thalassiosira pseudonana, and Phaeodactylum tricornutum, are examined. Time-resolved fluorescence measurements were conducted in the range of 0-80ns. Delayed fluorescence spectra showed a clear difference between PSII monomer and PSII dimer isolated from the four diatoms. The difference can be interpreted as reflecting suppressed energy transfer between PSII monomers in the PSII dimer for efficient energy trapping at the reaction center. The observation was especially prominent in C. gracilis and T. pseudonana. The pathways seem to be suppressed under a low pH condition in isolated PSII complexes from C. gracilis, and excitation energy may be quenched with fucoxanthin chlorophyll a/c-binding protein (FCP) that was closely associated with PSII in C. gracilis. The energy transfer between PSII monomers in the PSII dimer may play a role in excitation energy regulation in diatoms.
Resonant vibrational excitation of CO by low-energy electrons
Poparic, G. B.; Belic, D. S.; Vicic, M. D.
2006-06-15
Electron impact vibrational excitation of the CO molecule, via the {sup 2}{pi} resonance, in the 0-4 eV energy region has been investigated. The energy dependence of the resonant excitation of the first ten vibrational levels, v=1 to v=10, has been measured by use of a crossed-beams double trochoidal electron spectrometer. Obtained relative differential cross sections are normalized to the absolute values. Integral cross sections are determined by using our recent results on scattered electrons angular distributions, which demonstrate clear p-partial wave character of this resonance. Substructures appear in the {sup 2}{pi} resonant excitation of the CO molecule which have not been previously observed.
Complex fragment emission at low and high excitation energy
Moretto, L.G.
1986-08-01
Complex fragment emission has been certified as a compound nucleus process at low energies. An extension of the measurements to heavy ion reactions up to 50 MeV/u shows that most complex fragments are emitted by highly excited compound nuclei formed in incomplete fusion reactions. 12 refs., 26 figs.
On the Performances of the M06 Family of Density Functionals for Electronic Excitation Energies.
Jacquemin, Denis; Perpète, Eric A; Ciofini, Ilaria; Adamo, Carlo; Valero, Rosendo; Zhao, Yan; Truhlar, Donald G
2010-07-13
We assessed the accuracy of the four members of the M06 family of functionals (M06-L, M06, M06-2X, and M06-HF) for the prediction of electronic excitation energies of main-group compounds by time-dependent density functional theory. This is accomplished by comparing the predictions both to high-level theoretical benchmark calculations and some experimental data for gas-phase excitation energies of small molecules and to experimental data for midsize and large chromogens in liquid-phase solutions. The latter comparisons are carried out using implicit solvation models to include the electrostatic effects of solvation. We find that M06-L is one of the most accurate local functionals for evaluating electronic excitation energies, that M06-2X outperforms BHHLYP, and that M06-HF outperforms HF, although in each case, the compared functionals have the same or a similar amount of Hartree-Fock exchange. For the majority of investigated excited states, M06 emerges as the most accurate functional among the four tested, and it provides an accuracy similar to the best of the other global hybrids such as B3LYP, B98, and PBE0. For 190 valence excited states, 20 Rydberg states, and 16 charge transfer states, we try to provide an overall assessment by comparing the quality of the predictions to those of time-dependent Hartree-Fock theory and nine other density functionals. For the valence excited states, M06 yields a mean absolute deviation (MAD) of 0.23 eV, whereas B3LYP, B98, and PBE0 have MADs in the range 0.19-0.22 eV. Of the functionals tested, M05-2X, M06-2X, and BMK are found to perform best for Rydberg states, and M06-HF performs best for charge transfer states, but no single functional performs satisfactorily for all three kinds of excitation. The performance of functionals with no Hartree-Fock exchange is of great practical interest because of their high computational efficiency, and we find that M06-L predicts more accurate excitation energies than other such functionals.
NASA Astrophysics Data System (ADS)
Erturk, A.; Inman, D. J.
2009-02-01
Piezoelectric transduction has received great attention for vibration-to-electric energy conversion over the last five years. A typical piezoelectric energy harvester is a unimorph or a bimorph cantilever located on a vibrating host structure, to generate electrical energy from base excitations. Several authors have investigated modeling of cantilevered piezoelectric energy harvesters under base excitation. The existing mathematical modeling approaches range from elementary single-degree-of-freedom models to approximate distributed parameter solutions in the sense of Rayleigh-Ritz discretization as well as analytical solution attempts with certain simplifications. Recently, the authors have presented the closed-form analytical solution for a unimorph cantilever under base excitation based on the Euler-Bernoulli beam assumptions. In this paper, the analytical solution is applied to bimorph cantilever configurations with series and parallel connections of piezoceramic layers. The base excitation is assumed to be translation in the transverse direction with a superimposed small rotation. The closed-form steady state response expressions are obtained for harmonic excitations at arbitrary frequencies, which are then reduced to simple but accurate single-mode expressions for modal excitations. The electromechanical frequency response functions (FRFs) that relate the voltage output and vibration response to translational and rotational base accelerations are identified from the multi-mode and single-mode solutions. Experimental validation of the single-mode coupled voltage output and vibration response expressions is presented for a bimorph cantilever with a tip mass. It is observed that the closed-form single-mode FRFs obtained from the analytical solution can successfully predict the coupled system dynamics for a wide range of electrical load resistance. The performance of the bimorph device is analyzed extensively for the short circuit and open circuit resonance
Excitation energy dependent Raman spectrum of MoSe2
Nam, Dahyun; Lee, Jae-Ung; Cheong, Hyeonsik
2015-01-01
Raman investigation of MoSe2 was carried out with eight different excitation energies. Seven peaks, including E1g, A1g, E2g1, and A2u2 peaks are observed in the range of 100–400 cm−1. The phonon modes are assigned by comparing the peak positions with theoretical calculations. The intensities of the peaks are enhanced at different excitation energies through resonance with different optical transitions. The A1g mode is enhanced at 1.58 and 3.82 eV, which are near the A exciton energy and the band-to-band transition between higher energy bands, respectively. The E2g1 mode is strongly enhanced with respect to the A1g mode for the 2.71- and 2.81-eV excitations, which are close to the C exciton energy. The different enhancements of the A1g and E2g1 modes are explained in terms of the symmetries of the exciton states and the exciton-phonon coupling. Other smaller peaks including E1g and A2u2 are forbidden but appear due to the resonance effect near optical transition energies. PMID:26601614
The Calculation of Accurate Metal-Ligand Bond Energies
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W.; Partridge, Harry, III; Ricca, Alessandra; Arnold, James O. (Technical Monitor)
1997-01-01
The optimization of the geometry and calculation of zero-point energies are carried out at the B3LYP level of theory. The bond energies are determined at this level, as well as at the CCSD(T) level using very large basis sets. The successive OH bond energies to the first row transition metal cations are reported. For most systems there has been an experimental determination of the first OH. In general, the CCSD(T) values are in good agreement with experiment. The bonding changes from mostly covalent for the early metals to mostly electrostatic for the late transition metal systems.
Communication: An accurate global potential energy surface for the ground electronic state of ozone
Dawes, Richard E-mail: hguo@unm.edu; Lolur, Phalgun; Li, Anyang; Jiang, Bin; Guo, Hua E-mail: hguo@unm.edu
2013-11-28
We report a new full-dimensional and global potential energy surface (PES) for the O + O{sub 2} → O{sub 3} ozone forming reaction based on explicitly correlated multireference configuration interaction (MRCI-F12) data. It extends our previous [R. Dawes, P. Lolur, J. Ma, and H. Guo, J. Chem. Phys. 135, 081102 (2011)] dynamically weighted multistate MRCI calculations of the asymptotic region which showed the widely found submerged reef along the minimum energy path to be the spurious result of an avoided crossing with an excited state. A spin-orbit correction was added and the PES tends asymptotically to the recently developed long-range electrostatic model of Lepers et al. [J. Chem. Phys. 137, 234305 (2012)]. This PES features: (1) excellent equilibrium structural parameters, (2) good agreement with experimental vibrational levels, (3) accurate dissociation energy, and (4) most-notably, a transition region without a spurious reef. The new PES is expected to allow insight into the still unresolved issues surrounding the kinetics, dynamics, and isotope signature of ozone.
van Meer, R; Gritsenko, O V; Baerends, E J
2014-10-14
In recent years, several benchmark studies on the performance of large sets of functionals in time-dependent density functional theory (TDDFT) calculations of excitation energies have been performed. The tested functionals do not approximate exact Kohn-Sham orbitals and orbital energies closely. We highlight the advantages of (close to) exact Kohn-Sham orbitals and orbital energies for a simple description, very often as just a single orbital-to-orbital transition, of molecular excitations. Benchmark calculations are performed for the statistical average of orbital potentials (SAOP) functional for the potential [J. Chem. Phys. 2000, 112, 1344; 2001, 114, 652], which approximates the true Kohn-Sham potential much better than LDA, GGA, mGGA, and hybrid potentials do. An accurate Kohn-Sham potential does not only perform satisfactorily for calculated vertical excitation energies of both valence and Rydberg transitions but also exhibits appealing properties of the KS orbitals including occupied orbital energies close to ionization energies, virtual-occupied orbital energy gaps very close to excitation energies, realistic shapes of virtual orbitals, leading to straightforward interpretation of most excitations as single orbital transitions. We stress that such advantages are completely lost in time-dependent Hartree-Fock and partly in hybrid approaches. Many excitations and excitation energies calculated with local density, generalized gradient, and hybrid functionals are spurious. There is, with an accurate KS, or even the LDA or GGA potentials, nothing problematic about the "band gap" in molecules: the HOMO-LUMO gap is close to the first excitation energy (the optical gap).
Muñoz-Losa, A; Curutchet, C; Fdez Galván, I; Mennucci, B
2008-07-21
We present a comparative study on the influence of the quantum mechanical (QM) method (including basis set) on the evaluation of transition energies, transition densities and dipoles, and excitation energy transfer (EET) electronic couplings for a series of chromophores (and the corresponding pairs) typically found in organic electro-optical devices and photosynthetic systems. On these systems we have applied five different QM levels of description of increasing accuracy (ZINDO, CIS, TD-DFT, CASSCF, and SAC-CI). In addition, we have tested the effects of a surrounding environment (either mimicking a solvent or a protein matrix) on excitation energies, transition dipoles, and electronic couplings through the polarizable continuum model (PCM) description. Overall, the results obtained suggest that the choice of the QM level of theory affects the electronic couplings much less than it affects excitation energies. We conclude that reasonable estimates can be obtained using moderate basis sets and inexpensive methods such as configuration interaction of single excitations or time-dependent density functional theory when appropriately coupled to realistic solvation models such as PCM.
León-Montiel, Roberto de J; Kassal, Ivan; Torres, Juan P
2014-09-11
It has been argued that excitonic energy transport in photosynthetic complexes is efficient because of a balance between coherent evolution and decoherence, a phenomenon called environment-assisted quantum transport (ENAQT). Studies of ENAQT have usually assumed that the excitation is initially localized on a particular chromophore, and that it is transferred to a reaction center through a similarly localized trap. However, these assumptions are not physically accurate. We show that more realistic models of excitation and trapping can lead to very different predictions about the importance of ENAQT. In particular, although ENAQT is a robust effect if one assumes a localized trap, its effect can be negligible if the trapping is more accurately modeled as Förster transfer to a reaction center. Our results call into question the suggested role of ENAQT in the photosynthetic process of green sulfur bacteria and highlight the subtleties associated with drawing lessons for designing biomimetic light-harvesting complexes.
Entropy Driven Excitation Energy Sorting in Superfluid Fission Dynamics
Schmidt, Karl-Heinz; Jurado, Beatriz
2010-05-28
It is shown that the constant-temperature behavior of nuclei in the superfluid regime leads to an energy-sorting process if two nuclei are in thermal contact, as is the case in the fission process. This effect explains why an increase of the initial excitation energy leads an increase of the number of emitted neutrons from the heavy fission fragment, only. The observed essentially complete energy sorting may be seen as a new counterintuitive manifestation of quantum-mechanical properties of microscopic systems.
Vibration-assisted resonance in photosynthetic excitation-energy transfer
NASA Astrophysics Data System (ADS)
Irish, E. K.; Gómez-Bombarelli, R.; Lovett, B. W.
2014-07-01
Understanding how the effectiveness of natural photosynthetic energy-harvesting systems arises from the interplay between quantum coherence and environmental noise represents a significant challenge for quantum theory. Recently it has begun to be appreciated that discrete molecular vibrational modes may play an important role in the dynamics of such systems. Here we present a microscopic mechanism by which intramolecular vibrations may be able to contribute to the efficiency and directionality of energy transfer. Excited vibrational states create resonant pathways through the system, supporting fast and efficient energy transport. Vibrational damping together with the natural downhill arrangement of molecular energy levels gives intrinsic directionality to the energy flow. Analytical and numerical results demonstrate a significant enhancement of the efficiency and directionality of energy transport that can be directly related to the existence of resonances between vibrational and excitonic levels.
An accurate determination of the surface energy of solid selenium
NASA Astrophysics Data System (ADS)
Guisbiers, G.; Arscott, S.; Snyders, R.
2012-12-01
Selenium is currently a key element for developing nano and micro-technologies. Nevertheless, the surface energy of solid selenium (γSe) reported in the literature is still questionable. In this work, we have measured γSe = 0.291 ± 0.025 J/m2 at 293 K using the sessile drop technique with different probe liquids, namely ethylene glycol, de-ionized water, mercury, and gallium. This value is in excellent agreement with theoretical predictions.
An Accurate Potential Energy Surface for H2O
NASA Technical Reports Server (NTRS)
Schwenke, David W.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)
1997-01-01
We have carried out extensive high quality ab initio electronic structure calculations of the ground state potential energy surface (PES) and dipole moment function (DMF) for H2O. A small adjustment is made to the PES to improve the agreement of line positions from theory and experiment. The theoretical line positions are obtained from variational ro-vibrational calculations using the exact kinetic energy operator. For the lines being fitted, the root-mean-square error was reduced from 6.9 to 0.08 /cm. We were then able to match 30,092 of the 30,117 lines from the HITRAN 96 data base to theoretical lines, and 80% of the line positions differed less than 0.1 /cm. About 3% of the line positions in the experimental data base appear to be incorrect. Theory predicts the existence of many additional weak lines with intensities above the cutoff used in the data base. To obtain results of similar accuracy for HDO, a mass dependent correction to the PH is introduced and is parameterized by simultaneously fitting line positions for HDO and D2O. The mass dependent PH has good predictive value for T2O and HTO. Nonadiabatic effects are not explicitly included. Line strengths for vibrational bands summed over rotational levels usually agree well between theory and experiment, but individual line strengths can differ greatly. A high temperature line list containing about 380 million lines has been generated using the present PES and DMF
Accurate NMR structures through minimization of an extended hybrid energy.
Nilges, Michael; Bernard, Aymeric; Bardiaux, Benjamin; Malliavin, Thérèse; Habeck, Michael; Rieping, Wolfgang
2008-09-10
The use of generous distance bounds has been the hallmark of NMR structure determination. However, bounds necessitate the estimation of data quality before the calculation, reduce the information content, introduce human bias, and allow for major errors in the structures. Here, we propose a new rapid structure calculation scheme based on Bayesian analysis. The minimization of an extended energy function, including a new type of distance restraint and a term depending on the data quality, results in an estimation of the data quality in addition to coordinates. This allows for the determination of the optimal weight on the experimental information. The resulting structures are of better quality and closer to the X-ray crystal structure of the same molecule. With the new calculation approach, the analysis of discrepancies from the target distances becomes meaningful. The strategy may be useful in other applications-for example, in homology modeling.
NASA Astrophysics Data System (ADS)
Chong, C.; Kim, E.; Charalampidis, E. G.; Kim, H.; Li, F.; Kevrekidis, P. G.; Lydon, J.; Daraio, C.; Yang, J.
2016-05-01
This article explores the excitation of different vibrational states in a spatially extended dynamical system through theory and experiment. As a prototypical example, we consider a one-dimensional packing of spherical particles (a so-called granular chain) that is subject to harmonic boundary excitation. The combination of the multimodal nature of the system and the strong coupling between the particles due to the nonlinear Hertzian contact force leads to broad regions in frequency where different vibrational states are possible. In certain parametric regions, we demonstrate that the nonlinear Schrödinger equation predicts the corresponding modes fairly well. The electromechanical model we apply predicts accurately the conversion from the obtained mechanical energy to the electrical energy observed in experiments.
Excitation-energy dependence of the giant dipole resonance width
NASA Astrophysics Data System (ADS)
Enders, G.; Berg, F. D.; Hagel, K.; Kühn, W.; Metag, V.; Novotny, R.; Pfeiffer, M.; Schwalb, O.; Charity, R. J.; Gobbi, A.; Freifelder, R.; Henning, W.; Hildenbrand, K. D.; Holzmann, R.; Mayer, R. S.; Simon, R. S.; Wessels, J. P.; Casini, G.; Olmi, A.; Stefanini, A. A.
1992-07-01
High-energy γ rays have been measured in coincidence with heavy fragents in deeply inelastic reactions of 136Xe+48Ti at 18.5 MeV/nucleon. The giant dipole resonance (GDR) strength function is deduced from an analysis of the photon spectra within the statistical model. The GDR width Γ is studied as a function of the fragment excitation energy E*. A saturation at about Γ=10 MeV is observed for E*/A>=1.0 MeV/nucleon.
Rotary bistable and Parametrically Excited Vibration Energy Harvesting
NASA Astrophysics Data System (ADS)
Kurmann, L.; Jia, Y.; Hoffmann, D.; Manoli, Y.; Woias, P.
2016-11-01
Parametric resonance is a type of nonlinear vibration phenomenon [1], [2] induced from the periodic modulation of at least one of the system parameters and has the potential to exhibit interesting higher order nonlinear behaviour [3]. Parametrically excited vibration energy harvesters have been previously shown to enhance both the power amplitude [4] and the frequency bandwidth [5] when compared to the conventional direct resonant approach. However, to practically activate the more profitable regions of parametric resonance, additional design mechanisms [6], [7] are required to overcome a critical initiation threshold amplitude. One route is to establish an autoparametric system where external direct excitation is internally coupled to parametric excitation [8]. For a coupled two degrees of freedom (DoF) oscillatory system, principal autoparametric resonance can be achieved when the natural frequency of the first DoF f1 is twice that of the second DoF f2 and the external excitation is in the vicinity of f1. This paper looks at combining rotary and translatory motion and use autoparametric resonance phenomena.
Beck, Warren F; Bishop, Michael M; Roscioli, Jerome D; Ghosh, Soumen; Frank, Harry A
2015-04-15
A consideration of the excited state potential energy surfaces of carotenoids develops a new hypothesis for the nature of the conformational motions that follow optical preparation of the S2 (1(1)Bu(+)) state. After an initial displacement from the Franck-Condon geometry along bond length alternation coordinates, it is suggested that carotenoids pass over a transition-state barrier leading to twisted conformations. This hypothesis leads to assignments for several dark intermediate states encountered in femtosecond spectroscopic studies. The Sx state is assigned to the structure reached upon the onset of torsional motions near the transition state barrier that divides planar and twisted structures on the S2 state potential energy surface. The X state, detected recently in two-dimensional electronic spectra, corresponds to a twisted structure well past the barrier and approaching the S2 state torsional minimum. Lastly, the S(∗) state is assigned to a low lying S1 state structure with intramolecular charge transfer character (ICT) and a pyramidal conformation. It follows that the bent and twisted structures of carotenoids that are found in photosynthetic light-harvesting proteins yield excited-state structures that favor the development of an ICT character and optimized energy transfer yields to (bacterio)chlorophyll acceptors.
Excitation of phonons in medium-energy electron diffraction
NASA Astrophysics Data System (ADS)
Alvarez, M. A. Vicente; Ascolani, H.; Zampieri, G.
1996-03-01
The ``elastic'' backscattering of electrons from crystalline surfaces presents two regimes: a low-energy regime, in which the characteristic low-energy electron diffraction (LEED) pattern is observed, and a medium-energy regime, in which the diffraction pattern is similar to those observed in x-ray photoemission diffraction (XPD) and Auger electron diffraction (AED) experiments. We present a model for the electron scattering which, including the vibrational degrees of freedom of the crystal, contains both regimes and explains the passage from one regime to the other. Our model is based on a separation of the electron and atomic motions (adiabatic approximation) and on a cluster-type formulation of the multiple scattering of the electron. The inelastic scattering events (excitation and/or absorption of phonons) are treated as coherent processes and no break of the phase relation between the incident and the exit paths of the electron is assumed. The LEED and the medium-energy electron diffraction regimes appear naturally in this model as the limit cases of completely elastic scattering and of inelastic scattering with excitation and/or absorption of multiple phonons. Intensity patterns calculated with this model are in very good agreement with recent experiments of electron scattering on Cu(001) at low and medium energies. We show that there is a correspondence between the type of intensity pattern and the mean number of phonons excited and/or absorbed during the scattering: a LEED-like pattern is observed when this mean number is less than 2, LEED-like and XPD/AED-like features coexist when this number is 3-4, and a XPD/AED-like pattern is observed when this number is greater than 5-6.
Magnetic Excitations and the Exchange Energy Available for Superconductivity
NASA Astrophysics Data System (ADS)
Dahm, Thomas
2007-03-01
We have made detailed comparisons of theoretical calculations and experimental neutron scattering results in absolute units in order to determine the temperature change of the nearest neighbor spin correlations in optimally doped YBCO as one goes from the normal to the superconducting state [1]. This allows us to estimate the magnetic exchange energy change that becomes available for superconducting condensation. Our results show that the available magnetic energy change is about 10-15 times larger than the energy necessary for superconducting condensation [1]. We discuss the issue of the spin sum rule and implications for a spin fluctuation driven pairing interaction as well as implications for low energy excitations in angular photoemission spectroscopy [2]. [1] H. Woo et al, Nature Physics 2, 600 (2006). [2] T. Dahm et al, Phys. Rev. B 72, 214512 (2005).
Phonon-assisted excitation energy transfer in photosynthetic systems
NASA Astrophysics Data System (ADS)
Chen, Hao; Wang, Xin; Fang, Ai-Ping; Li, Hong-Rong
2016-09-01
The phonon-assisted process of energy transfer aiming at exploring the newly emerging frontier between biology and physics is an issue of central interest. This article shows the important role of the intramolecular vibrational modes for excitation energy transfer in the photosynthetic systems. Based on a dimer system consisting of a donor and an acceptor modeled by two two-level systems, in which one of them is coupled to a high-energy vibrational mode, we derive an effective Hamiltonian describing the vibration-assisted coherent energy transfer process in the polaron frame. The effective Hamiltonian reveals in the case that the vibrational mode dynamically matches the energy detuning between the donor and the acceptor, the original detuned energy transfer becomes resonant energy transfer. In addition, the population dynamics and coherence dynamics of the dimer system with and without vibration-assistance are investigated numerically. It is found that, the energy transfer efficiency and the transfer time depend heavily on the interaction strength of the donor and the high-energy vibrational mode, as well as the vibrational frequency. The numerical results also indicate that the initial state and dissipation rate of the vibrational mode have little influence on the dynamics of the dimer system. Results obtained in this article are not only helpful to understand the natural photosynthesis, but also offer an optimal design principle for artificial photosynthesis. Project supported by the National Natural Science Foundation of China (Grant No. 11174233).
Modeling coherent excitation energy transfer in photosynthetic light harvesting systems
NASA Astrophysics Data System (ADS)
Huo, Pengfei
2011-12-01
Recent non-linear spectroscopy experiments suggest the excitation energy transfer in some biological light harvesting systems initially occurs coherently. Treating such processes brings significant challenge for conventional theoretical tools that usually involve different approximations. In this dissertation, the recently developed Iterative Linearized Density Matrix (ILDM) propagation scheme, which is non-perturbative and non-Markovian is extended to study coherent excitation energy transfer in various light harvesting complexes. It is demonstrated that the ILDM approach can successfully describe the coherent beating of the site populations on model systems and gives quantitative agreement with both experimental results and the results of other theoretical methods have been developed recently to going beyond the usual approximations, thus providing a new reliable theoretical tool to study this phenomenon. This approach is used to investigate the excited energy transfer dynamics in various experimentally studied bacteria light harvesting complexes, such as Fenna-Matthews-Olsen (FMO) complex, Phycocyanin 645 (PC645). In these model calculations, quantitative agreement is found between computed de-coherence times and quantum beating pattens observed in the non-linear spectroscopy. As a result of these studies, it is concluded that the stochastic resonance behavior is important in determining the optimal throughput. To begin addressing possible mechanics for observed long de-coherence time, various models which include correlation between site energy fluctuations as well as correlation between site energy and inter-site coupling are developed. The influence of both types of correlation on the coherence and transfer rate is explored using with a two state system-bath hamiltonian parametrized to model the reaction center of Rhodobacter sphaeroides bacteria. To overcome the disadvantages of a fully reduced approach or a full propagation method, a brownian dynamics
Fluctuations, Saturation, and Diffractive Excitation in High Energy Collisions
Flensburg, Christoffer
2011-07-15
Diffractive excitation is usually described by the Good-Walker formalism for low masses, and by the triple-Regge formalism for high masses. In the Good-Walker formalism the cross section is determined by the fluctuations in the interaction. By taking the fluctuations in the BFKL ladder into account, it is possible to describe both low and high mass excitation in the Good-Walker formalism. In high energy pp collisions the fluctuations are strongly suppressed by saturation, which implies that pomeron exchange does not factorise between DIS and pp collisions. The Dipole Cascade Model reproduces the expected triple-Regge form for the bare pomeron, and the triple-pomeron coupling is estimated.
Low-energy Coulomb excitation of Sr,9896 beams
NASA Astrophysics Data System (ADS)
Clément, E.; Zielińska, M.; Péru, S.; Goutte, H.; Hilaire, S.; Görgen, A.; Korten, W.; Doherty, D. T.; Bastin, B.; Bauer, C.; Blazhev, A.; Bree, N.; Bruyneel, B.; Butler, P. A.; Butterworth, J.; Cederkäll, J.; Delahaye, P.; Dijon, A.; Ekström, A.; Fitzpatrick, C.; Fransen, C.; Georgiev, G.; Gernhäuser, R.; Hess, H.; Iwanicki, J.; Jenkins, D. G.; Larsen, A. C.; Ljungvall, J.; Lutter, R.; Marley, P.; Moschner, K.; Napiorkowski, P. J.; Pakarinen, J.; Petts, A.; Reiter, P.; Renstrøm, T.; Seidlitz, M.; Siebeck, B.; Siem, S.; Sotty, C.; Srebrny, J.; Stefanescu, I.; Tveten, G. M.; Van de Walle, J.; Vermeulen, M.; Voulot, D.; Warr, N.; Wenander, F.; Wiens, A.; De Witte, H.; Wrzosek-Lipska, K.
2016-11-01
The structure of neutron-rich Sr,9896 nuclei was investigated by low-energy safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. A rich set of transitional and diagonal E 2 matrix elements, including those for non-yrast structures, has been extracted from the differential Coulomb-excitation cross sections. The results support the scenario of a shape transition at N =60 , giving rise to the coexistence of a highly deformed prolate and a spherical configuration in 98Sr, and are compared to predictions from several theoretical calculations. The experimental data suggest a significant contribution of the triaxal degree of freedom in the ground state of both isotopes. In addition, experimental information on low-lying states in 98Rb has been obtained.
Excitation energy and nuclear dissipation probed with evaporation-residue cross sections
Ye, W.
2011-04-15
Using a Langevin equation coupled with a statistical decay model, we calculate the excess of evaporation-residue cross sections over its standard statistical-model value as a function of nuclear dissipation strength for {sup 200}Hg compound nuclei (CNs) under two distinct types of initial conditions for populated CNs: (i) high excitation energy but low angular momentum (produced via proton-induced spallation reactions at GeV energies and via peripheral heavy-ion collisions at relativistic energies) and (ii) high angular momentum but low excitation energy (produced through fusion mechanisms). We find that the conditions of case (ii) not only amplify the effect of dissipation on the evaporation residues, but also substantially increase the sensitivity of this excess to nuclear dissipation. These results suggest that, in experiments, to obtain accurate information of presaddle nuclear dissipation strength by measuring evaporation-residue cross sections, it is best to choose the heavy-ion-induced fusion reaction approach to yield excited compound nuclei.
Pšenčík, Jakub; Ma, Ying-Zhong; Arellano, Juan B.; Hála, Jan; Gillbro, Tomas
2003-01-01
The excited-state relaxation within bacteriochlorophyll (BChl) e and a in chlorosomes of Chlorobium phaeobacteroides has been studied by femtosecond transient absorption spectroscopy at room temperature. Singlet-singlet annihilation was observed to strongly influence both the isotropic and anisotropic decays. Pump intensities in the order of 1011 photons × pulse−1 × cm−2 were required to obtain annihilation-free conditions. The most important consequence of applied very low excitation doses is an observation of a subpicosecond process within the BChl e manifold (∼200–500 fs), manifesting itself as a rise in the red part of the Qy absorption band of the BChl e aggregates. The subsequent decay of the kinetics measured in the BChl e region and the corresponding rise in the baseplate BChl a is not single-exponential, and at least two components are necessary to fit the data, corresponding to several BChl e→BChl a transfer steps. Under annihilation-free conditions, the anisotropic kinetics show a generally slow decay within the BChl e band (10–20 ps) whereas it decays more rapidly in the BChl a region (∼1 ps). Analysis of the experimental data gives a detailed picture of the overall time evolution of the energy relaxation and energy transfer processes within the chlorosome. The results are interpreted within an exciton model based on the proposed structure. PMID:12547796
Munafò, A; Panesi, M; Magin, T E
2014-02-01
A Boltzmann rovibrational collisional coarse-grained model is proposed to reduce a detailed kinetic mechanism database developed at NASA Ames Research Center for internal energy transfer and dissociation in N(2)-N interactions. The coarse-grained model is constructed by lumping the rovibrational energy levels of the N(2) molecule into energy bins. The population of the levels within each bin is assumed to follow a Boltzmann distribution at the local translational temperature. Excitation and dissociation rate coefficients for the energy bins are obtained by averaging the elementary rate coefficients. The energy bins are treated as separate species, thus allowing for non-Boltzmann distributions of their populations. The proposed coarse-grained model is applied to the study of nonequilibrium flows behind normal shock waves and within converging-diverging nozzles. In both cases, the flow is assumed inviscid and steady. Computational results are compared with those obtained by direct solution of the master equation for the rovibrational collisional model and a more conventional multitemperature model. It is found that the proposed coarse-grained model is able to accurately resolve the nonequilibrium dynamics of internal energy excitation and dissociation-recombination processes with only 20 energy bins. Furthermore, the proposed coarse-grained model provides a superior description of the nonequilibrium phenomena occurring in shock heated and nozzle flows when compared with the conventional multitemperature models.
Dependence of the energy transfer to graphene on the excitation energy
Mackowski, Sebastian Kamińska, Izabela
2015-07-13
Fluorescence studies of natural photosynthetic complexes on a graphene layer demonstrate pronounced influence of the excitation wavelength on the energy transfer efficiency to graphene. Ultraviolet light yields much faster decay of fluorescence, with average efficiencies of the energy transfer equal to 87% and 65% for excitation at 405 nm and 640 nm, respectively. This implies that focused light changes locally the properties of graphene affecting the energy transfer dynamics, in an analogous way as in the case of metallic nanostructures. Demonstrating optical control of the energy transfer is important for exploiting unique properties of graphene in photonic and sensing architectures.
Oyedepo, Gbenga A; Wilson, Angela K
2010-08-26
The correlation consistent Composite Approach, ccCA [ Deyonker , N. J. ; Cundari , T. R. ; Wilson , A. K. J. Chem. Phys. 2006 , 124 , 114104 ] has been demonstrated to predict accurate thermochemical properties of chemical species that can be described by a single configurational reference state, and at reduced computational cost, as compared with ab initio methods such as CCSD(T) used in combination with large basis sets. We have developed three variants of a multireference equivalent of this successful theoretical model. The method, called the multireference correlation consistent composite approach (MR-ccCA), is designed to predict the thermochemical properties of reactive intermediates, excited state species, and transition states to within chemical accuracy (e.g., 1 kcal/mol for enthalpies of formation) of reliable experimental values. In this study, we have demonstrated the utility of MR-ccCA: (1) in the determination of the adiabatic singlet-triplet energy separations and enthalpies of formation for the ground states for a set of diradicals and unsaturated compounds, and (2) in the prediction of energetic barriers to internal rotation, in ethylene and its heavier congener, disilene. Additionally, we have utilized MR-ccCA to predict the enthalpies of formation of the low-lying excited states of all the species considered. MR-ccCA is shown to give quantitative results without reliance upon empirically derived parameters, making it suitable for application to study novel chemical systems with significant nondynamical correlation effects.
Amino Acid Mean Excitation Energies and Directional Dependencies from Core and Bond Calculations
Sabin, John R.; Oddershede, Jens; Sauer, Stephan P. A.
2008-12-08
We determine the mean excitation energies of several amino acids using a Bragg Rule developed for molecular fragments or functional groups. As the composition of the amino acids is very similar, we find that the amino acids have similar mean excitation energies (approximately 70 eV). Differences arise from variation of the side chains (-R); addition of-CH2-groups decreases the mean excitation energy. We also speculate concerning the directional dependence of the amino acid mean excitation energies.
Population shuffling between ground and high energy excited states
Sabo, T Michael; Trent, John O; Lee, Donghan
2015-01-01
Stochastic processes powered by thermal energy lead to protein motions traversing time-scales from picoseconds to seconds. Fundamental to protein functionality is the utilization of these dynamics for tasks such as catalysis, folding, and allostery. A hierarchy of motion is hypothesized to connect and synergize fast and slow dynamics toward performing these essential activities. Population shuffling predicts a “top-down” temporal hierarchy, where slow time-scale conformational interconversion leads to a shuffling of the free energy landscape for fast time-scale events. Until now, population shuffling was only applied to interconverting ground states. Here, we extend the framework of population shuffling to be applicable for a system interconverting between low energy ground and high energy excited states, such as the SH3 domain mutants G48M and A39V/N53P/V55L from the Fyn tyrosine kinase, providing another tool for accessing the structural dynamics of high energy excited states. Our results indicate that the higher energy gauche− rotameric state for the leucine χ2 dihedral angle contributes significantly to the distribution of rotameric states in both the major and minor forms of the SH3 domain. These findings are corroborated with unrestrained molecular dynamics (MD) simulations on both the major and minor states of the SH3 domain demonstrating high correlations between experimental and back-calculated leucine χ2 rotameric populations. Taken together, we demonstrate how fast time-scale rotameric side-chain population distributions can be extracted from slow time-scale conformational exchange data further extending the scope and the applicability of the population shuffling model. PMID:26316263
Population shuffling between ground and high energy excited states.
Sabo, T Michael; Trent, John O; Lee, Donghan
2015-11-01
Stochastic processes powered by thermal energy lead to protein motions traversing time-scales from picoseconds to seconds. Fundamental to protein functionality is the utilization of these dynamics for tasks such as catalysis, folding, and allostery. A hierarchy of motion is hypothesized to connect and synergize fast and slow dynamics toward performing these essential activities. Population shuffling predicts a "top-down" temporal hierarchy, where slow time-scale conformational interconversion leads to a shuffling of the free energy landscape for fast time-scale events. Until now, population shuffling was only applied to interconverting ground states. Here, we extend the framework of population shuffling to be applicable for a system interconverting between low energy ground and high energy excited states, such as the SH3 domain mutants G48M and A39V/N53P/V55L from the Fyn tyrosine kinase, providing another tool for accessing the structural dynamics of high energy excited states. Our results indicate that the higher energy gauche - rotameric state for the leucine χ2 dihedral angle contributes significantly to the distribution of rotameric states in both the major and minor forms of the SH3 domain. These findings are corroborated with unrestrained molecular dynamics (MD) simulations on both the major and minor states of the SH3 domain demonstrating high correlations between experimental and back-calculated leucine χ2 rotameric populations. Taken together, we demonstrate how fast time-scale rotameric side-chain population distributions can be extracted from slow time-scale conformational exchange data further extending the scope and the applicability of the population shuffling model.
Piezoelectric compliant mechanism energy harvesters under large base excitations
NASA Astrophysics Data System (ADS)
Ma, Xiaokun; Trolier-McKinstry, Susan; Rahn, Christopher D.
2016-09-01
A piezoelectric compliant mechanism (PCM) energy harvester is designed, modeled, and analyzed that consists of a polyvinylidene diflouoride, PVDF unimorph clamped at its base and attached to a compliant mechanism at its tip. The compliant hinge stiffness is carefully tuned to approach a low frequency first mode with an efficient (nearly quadratic) shape that provides a uniform strain distribution. A nonlinear model of the PCM energy harvester under large base excitation is derived to determine the maximum power that can be generated by the device. Experiments with a fabricated PCM energy harvester prototype show that the compliant mechanism introduces a stiffening effect and a much wider bandwidth than a benchmark proof mass cantilever design. The PCM bridge structure self-limits the displacement and maximum strain at large excitations compared with the proof mass cantilever, improving the device robustness. The PCM outperforms the cantilever in both average power and power-strain sensitivity at high accelerations due to the PCM axial stretching effect and its more uniform strain distribution.
Excitation energy transfer: Study with non-Markovian dynamics
Liang Xianting
2010-11-15
In this paper, we investigate the non-Markovian dynamics of a model to mimic the excitation energy transfer (EET) between chromophores in photosynthesis systems. The numerical path integral method is used. This method includes the non-Markovian effects of the environmental affects, and it does not need the perturbation approximation in solving the dynamics of systems of interest. It implies that the coherence helps the EET between chromophores through lasting the transfer time rather than enhancing the transfer rate of the EET. In particular, the non-Markovian environment greatly increases the efficiency of the EET in the photosynthesis systems.
Patten, K.O. Jr.; Johnston, H.S. Lawrence Berkeley Lab., CA )
1993-09-30
We follow the collisional deactivation of laser-excited nitrogen dioxide through its dispersed fluorescence. The energy acceptor gases are NO[sub 2] at four excitation energies ranging from 18828 to 24989 cm[sup [minus]1] and five monatomic gases, four diatomic gases, and three polyatomic gases with 18828-cm[sup [minus]1] excitation energy. The nominal products are the shapes of the internal energy distributions, which are obtained and plotted for several representative cases. From these distributions, the first three moments of the internal energy distributions are derived as a function of molecular collisions and tabulated as (i) the average internal energy, (ii) energy spread, and (iii) skewness. These quantities are plotted against c(M)t, the product of buffer gas concentration c(M) and delay time after laser excitation t(0.5-2 [mu]s), which is a quantity proportional to number of collisions. The negative slope of average energy vs c(M)t is the macroscopic energy-transfer rate constant, k[sub [epsilon
Nonradiative excitation energy transport in one-component disordered systems.
Bojarski, P; Kulak, L; Bojarski, C; Kawski, A
1995-12-01
High-accuracy Monte Carlo simulations of the time-dependent excitation probabilityG (s) (t) and steady-state emission anisotropyr M /r 0M for one-component three-dimensional systems were performed. It was found that the values ofr M /r 0M obtained for the averaged orientation factor[Formula: see text] only slightly overrate those obtained for the real values of the orientation factor κ ik (2) . This result is essentially different from that previously reported. Simulation results were compared with the probability coursesG (s) (t) andR(t) obtained within the frameworks of diagrammatic and two-particle Huber models, respectively. The results turned out to be in good agreement withR(t) but deviated visibly fromG (s) (t) at long times and/or high concentrations. Emission anisotropy measurements on glycerolic solutions of Na-fluorescein and rhodamine 6G were carried out at different excitation wavelengths. Very good agreement between the experimental data and the theory was found, with λex≈λ0-0 for concentrations not exceeding 3.5·10(-2) and 7.5·10(-3) M in the case of Na-fluorescein and rhodamine 6G, respectively. Up to these concentrations, the solutions investigated can be treated as one-component systems. The discrepancies observed at higher concentrations are caused by the presence of dimers. It was found that forλ ex <λ0-0 (Stokes excitation) the experimental emission anisotropies are lower than predicted by the theory. However, upon anti-Stokes excitation (λex>λ0-0), they lie higher than the respective theoretical values. Such a dispersive character of the energy migration can be explained qualitatively by the presence of fluorescent centers with 0-0 transitions differing from the "mean" at λ0-0.
Limit on rotational energy available to excite Jovian aurora
NASA Technical Reports Server (NTRS)
Eviatar, A.; Siscoe, G. L.
1980-01-01
There is a fundamental relationship between the power that is extracted from Jupiter's rotation to drive magnetospheric processes and the rate at which mass is injected into the Io plasma torus. Half of this power is consumed by bulk motion of the plasma and the other half represents an upper limit on the energy from rotation available for dissipation and in particular to excite the Jovian aurora. Since the rotation of the planet is the only plausible source of energy, the power inferred from the observed auroral intensities requires a plasma injection rate of 2.6 x 10 to the 29th AMU/sec or greater. This in turn leads to a residence time of a torus particle of 48 days or less. These results raise doubts about the applicability of equilibrium thermodynamics to the determination of plasma parameters in the Io torus.
NASA Astrophysics Data System (ADS)
Kosumi, Daisuke; Yanagi, Kazuhiro; Nishio, Tomohiro; Hashimoto, Hideki; Yoshizawa, Masayuki
2005-06-01
Ultrafast relaxation kinetics in β-carotene and lycopene has been investigated by femtosecond absorption and fluorescence spectroscopies using tunable excitation pulses. The transient signals induced by the photoexcitation with larger excess energy have broader bands and longer lifetimes both in the 11Bu+and21Ag- excited states. The excess vibrational energy remains longer than several picoseconds and slows the relaxation kinetics in carotenoids.
Excitation energy transfer in covalently bonded porphyrin heterodimers
NASA Astrophysics Data System (ADS)
Paschenko, V. Z.; Konovalova, N. V.; Bagdashkin, A. L.; Gorokhov, V. V.; Tusov, V. B.; Yuzhakov, V. I.
2012-04-01
We describe the photophysical properties of heterodimers that are formed by the free base 2-(2-carboxyvinyl)-5,10,15,20-tetraphenylporphyrin and the zinc complex of 5-( p-aminophenyl)-10,15,20-triphenylporphyrin and that are covalently bonded by the amide link. These dimers differ in the configuration of the double bond in the spacer group. We determine fluorescence quantum yields of heterodimers and their porphyrin components. The energy transfer rate constants have been estimated from the measured fluorescence lifetimes and fluorescence excitation spectra and, also, they have been calculated from the steady-state absorption and fluorescence spectra according to the Förster theory. We have found that the efficiency of the intramolecular energy transfer in heterodimers is 0.97-0.99, and the energy migration rate constants have been found to be (1.82-4.49) × 1010 s-1. The results of our investigation show that synthesized heterodimers can be used as efficient light-harvesting elements in solar energy conversion devices.
Energies of low-lying excited states of linear polyenes.
Christensen, Ronald L; Galinato, Mary Grace I; Chu, Emily F; Howard, Jason N; Broene, Richard D; Frank, Harry A
2008-12-11
Room temperature absorption and emission spectra of the all-trans isomers of decatetraene, dodecapentaene, tetradecahexaene, and hexadecaheptaene have been obtained in a series of nonpolar solvents. The resolved vibronic features in the optical spectra of these model systems allow the accurate determination of S(0) (1(1)A(g)(-)) --> S(2) (1(1)B(u)(+)) and S(1) (2(1)A(g)(-)) --> S(0) (1(1)A(g)(-)) electronic origins as a function of solvent polarizability. These data can be extrapolated to predict the transition energies in the absence of solvent perturbations. The effects of the terminal methyl substituents on the transition energies also can be estimated. Franck-Condon maxima in the absorption and emission spectra were used to estimate differences between S(0) (1(1)A(g)(-)) --> S(1) (2(1)A(g)(-)) and S(0) (1(1)A(g)(-)) --> S(2) (1(1)B(u)(+)) electronic origins and "vertical" transition energies. Experimental estimates of the vertical transition energies of unsubstituted, all-trans polyenes in vacuum as a function of conjugation length are compared with long-standing multireference configuration interaction (MRCI) treatments and with more recent ab initio calculations of the energies of the 2(1)A(g)(-) (S(1)) and 1(1)B(u)(+) (S(2)) states.
Metallic bond effects on mean excitation energies for stopping powers
NASA Technical Reports Server (NTRS)
Wilson, J. W.; Xu, Y. J.
1982-01-01
Mean excitation energies for first row metals are evaluated by means of the local plasma approximation. Particle corrections based on Pines' (1953) procedure and the Wigner Seitz (1934) model of the metallic state are included. The agreement with experimental values is remarkably good. In contrast to previous work, the calculations given here estimate shifts in the plasma frequency according to the theory for plane wave states in an extended plasma as calculated by Pines. It is demonstrated that the effects of the metallic bond in lithium and beryllium are quite large and that they appear mainly as a result of collective oscillations in the 'free' electron gas formed from the valence electrons. The usefulness of the plasma frequency shift derived for a degenerate electron gas in predicting the plasma frequency shift within the ion core is considered surprising.
Variational calculation of highly excited rovibrational energy levels of H2O2.
Polyansky, Oleg L; Kozin, Igor N; Ovsyannikov, Roman I; Małyszek, Paweł; Koput, Jacek; Tennyson, Jonathan; Yurchenko, Sergei N
2013-08-15
Results are presented for highly accurate ab initio variational calculation of the rotation-vibration energy levels of H2O2 in its electronic ground state. These results use a recently computed potential energy surface and the variational nuclear-motion programs WARV4, which uses an exact kinetic energy operator, and TROVE, which uses a numerical expansion for the kinetic energy. The TROVE calculations are performed for levels with high values of rotational excitation, J up to 35. The purely ab initio calculations of the rovibrational energy levels reproduce the observed levels with a standard deviation of about 1 cm(-1), similar to that of the J = 0 calculation, because the discrepancy between theory and experiment for rotational energies within a given vibrational state is substantially determined by the error in the vibrational band origin. Minor adjustments are made to the ab initio equilibrium geometry and to the height of the torsional barrier. Using these and correcting the band origins using the error in J = 0 states lowers the standard deviation of the observed-calculated energies to only 0.002 cm(-1) for levels up to J = 10 and 0.02 cm(-1) for all experimentally known energy levels, which extend up to J = 35.
NASA Astrophysics Data System (ADS)
Bohr, Henrik G.; Malik, F. Bary
2013-11-01
The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin-chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used Förster-Dexter theory, which does not allow for charge transfer, is a special case of B-A theory. The latter could, under appropriate circumstances, lead to excimers.
NASA Astrophysics Data System (ADS)
Lu-Lu, Zhang; Yu-Zhi, Song; Shou-Bao, Gao; Yuan, Zhang; Qing-Tian, Meng
2016-05-01
A globally accurate single-sheeted double many-body expansion potential energy surface is reported for the first excited state of HS2 by fitting the accurate ab initio energies, which are calculated at the multireference configuration interaction level with the aug-cc-pVQZ basis set. By using the double many-body expansion-scaled external correlation method, such calculated ab initio energies are then slightly corrected by scaling their dynamical correlation. A grid of 2767 ab initio energies is used in the least-square fitting procedure with the total root-mean square deviation being 1.406 kcal·mol-1. The topographical features of the HS2(A2A‧) global potential energy surface are examined in detail. The attributes of the stationary points are presented and compared with the corresponding ab initio results as well as experimental and other theoretical data, showing good agreement. The resulting potential energy surface of HS2(A2A‧) can be used as a building block for constructing the global potential energy surfaces of larger S/H molecular systems and recommended for dynamic studies on the title molecular system. Project supported by the National Natural Science Foundation of China (Grant No. 11304185), the Taishan Scholar Project of Shandong Province, China, the Shandong Provincial Natural Science Foundation, China (Grant No. ZR2014AM022), the Shandong Province Higher Educational Science and Technology Program, China (Grant No. J15LJ03), the China Postdoctoral Science Foundation (Grant No. 2014M561957), and the Post-doctoral Innovation Project of Shandong Province, China (Grant No. 201402013).
NASA Astrophysics Data System (ADS)
Harne, R. L.; Zhang, Chunlin; Li, Bing; Wang, K. W.
2016-07-01
Impulsive energies are abundant throughout the natural and built environments, for instance as stimulated by wind gusts, foot-steps, or vehicle-road interactions. In the interest of maximizing the sustainability of society's technological developments, one idea is to capture these high-amplitude and abrupt energies and convert them into usable electrical power such as for sensors which otherwise rely on less sustainable power supplies. In this spirit, the considerable sensitivity to impulse-type events previously uncovered for bistable oscillators has motivated recent experimental and numerical studies on the power generation performance of bistable vibration energy harvesters. To lead to an effective and efficient predictive tool and design guide, this research develops a new analytical approach to estimate the electroelastic response and power generation of a bistable energy harvester when excited by an impulse. Comparison with values determined by direct simulation of the governing equations shows that the analytically predicted net converted energies are very accurate for a wide range of impulse strengths. Extensive experimental investigations are undertaken to validate the analytical approach and it is seen that the predicted estimates of the impulsive energy conversion are in excellent agreement with the measurements, and the detailed structural dynamics are correctly reproduced. As a result, the analytical approach represents a significant leap forward in the understanding of how to effectively leverage bistable structures as energy harvesting devices and introduces new means to elucidate the transient and far-from-equilibrium dynamics of nonlinear systems more generally.
NASA Technical Reports Server (NTRS)
Wilson, J. W.; Xu, Y. J.; Kamaratos, E.; Chang, C. K.
1984-01-01
The basic model of Lindhard and Scharff, known as the local plasma model, is used to study the effects on stopping power of the chemical and physical state of the medium. Unlike previous work with the local plasma model, in which individual electron shifts in the plasma frequency were estimated empirically, he Pines correction derived for a degenerate Fermi gas is shown herein to provide a reasonable estimate, even on the atomic scale. Thus, the model is moved to a complete theoretical base requiring no empirical adjustments, as characteristic of past applications. The principal remaining error is in the overestimation of the low-energy absorption properties that are characteristic of the plasma model in the region of the atomic discrete spectrum, although higher-energy phenomena are accurately represented, and even excitation-to-ionization ratios are given to fair accuracy. Mean excitation energies for covalent-bonded gases and solids, for ionic gases and crystals, and for metals are calculated using first-order models of the bonded states.
Modeling excitation energy transfer in multi-BODIPY architectures.
Azarias, Cloé; Russo, Roberto; Cupellini, Lorenzo; Mennucci, Benedetta; Jacquemin, Denis
2017-02-15
The excitation energy transfer (EET) allowing the concentration of the energy has been investigated in several multi-BODIPY architectures with the help of an approach coupling time dependent density functional theory to an implicit solvation scheme, the polarizable continuum model. We have first considered several strategies to compute the electronic coupling in a dyad varying the size of the donor/acceptor units, the bridge, the geometries and conformations. We have next studied the electronic coupling in three different architectures for which the EET rate constants have been experimentally measured both from luminescence and transient absorption data and from Förster theory. A good agreement with experimental values was obtained. Finally, in an effort to further improve these systems, we have designed several series of BODIPY triads, investigating the effect of acidochromism, core modifications, the position of the linkage and chemical substitutions on the EET coupling and rate constant. We show that several architectures allow us to increase the EET rate by one order of magnitude compared to the original compound.
Energy harvesting from human motion: exploiting swing and shock excitations
NASA Astrophysics Data System (ADS)
Ylli, K.; Hoffmann, D.; Willmann, A.; Becker, P.; Folkmer, B.; Manoli, Y.
2015-02-01
Modern compact and low power sensors and systems are leading towards increasingly integrated wearable systems. One key bottleneck of this technology is the power supply. The use of energy harvesting techniques offers a way of supplying sensor systems without the need for batteries and maintenance. In this work we present the development and characterization of two inductive energy harvesters which exploit different characteristics of the human gait. A multi-coil topology harvester is presented which uses the swing motion of the foot. The second device is a shock-type harvester which is excited into resonance upon heel strike. Both devices were modeled and designed with the key constraint of device height in mind, in order to facilitate the integration into the shoe sole. The devices were characterized under different motion speeds and with two test subjects on a treadmill. An average power output of up to 0.84 mW is achieved with the swing harvester. With a total device volume including the housing of 21 cm3 a power density of 40 μW cm-3 results. The shock harvester generates an average power output of up to 4.13 mW. The power density amounts to 86 μW cm-3 for the total device volume of 48 cm3. Difficulties and potential improvements are discussed briefly.
NASA Astrophysics Data System (ADS)
Msezane, A. Z.; Eure, A.; Felfli, Z.; Sokolovski, D.
2009-11-01
The recent Regge-pole methodology has been benchmarked [1] on the accurately measured binding energies of the excited Ge= and Sn= anions [2] through the binding energies (BEs) extracted from the Regge-pole calculated elastic total cross sections (TCSs). Here the methodology is applied together with a Thomas-Fermi type potential that incorporates the vital core polarization interaction to investigate the possibility of forming excited Au= and Pt= anions in low-energy electron elastic collisions with Au and Pt atoms. From the positions of the characteristic extremely narrow resonances in the total cross sections, we extract the binding energies of the excited Au= and Pt= anions formed as Regge resonances during the collisions. The angular life of the complexes thus formed is used to differentiate the stable excited bound states of the anions from the shape resonances [3]. The BEs for the excited Au= and Pt= anions are found to be 0.475eVand 0.543eV, respectively, challenging both theory and experiment to verify. [1] A. Msezane et al, Phys. Rev. A, Submitted (2009) [2] M. Scheer et al, Phys. Rev. A 58, 2844 (1998) [3] Z. Felfli et al, Phys. Rev. A 79, 012714 (2009)
Excitation energy transfer in photosynthetic protein-pigment complexes
NASA Astrophysics Data System (ADS)
Yeh, Shu-Hao
Quantum biology is a relatively new research area which investigates the rules that quantum mechanics plays in biology. One of the most intriguing systems in this field is the coherent excitation energy transport (EET) in photosynthesis. In this document I will discuss the theories that are suitable for describing the photosynthetic EET process and the corresponding numerical results on several photosynthetic protein-pigment complexes (PPCs). In some photosynthetic EET processes, because of the electronic coupling between the chromophores within the system is about the same order of magnitude as system-bath coupling (electron-phonon coupling), a non-perturbative method called hierarchy equation of motion (HEOM) is applied to study the EET dynamics. The first part of this thesis includes brief introduction and derivation to the HEOM approach. The second part of this thesis the HEOM method will be applied to investigate the EET process within the B850 ring of the light harvesting complex 2 (LH2) from purple bacteria, Rhodopseudomonas acidophila. The dynamics of the exciton population and coherence will be analyzed under different initial excitation configurations and temperatures. Finally, how HEOM can be implemented to simulate the two-dimensional electronic spectra of photosynthetic PPCs will be discussed. Two-dimensional electronic spectroscopy is a crucial experimental technique to probe EET dynamics in multi-chromophoric systems. The system we are interested in is the 7-chromophore Fenna-Matthews-Olson (FMO) complex from green sulfur bacteria, Prosthecochloris aestuarii. Recent crystallographic studies report the existence of an additional (eighth) chromophore in some of the FMO monomers. By applying HEOM we are able to calculate the two-dimensional electronic spectra of the 7-site and 8-site FMO complexes and investigate the functionality of the eighth chromophore.
Theoretical Studies on Excitation Energy Fluctuations of Pigments in a Light-Harvesting Complex
NASA Astrophysics Data System (ADS)
Higashi, Masahiro; Saito, Shinji
2014-03-01
Excitation energy fluctuations of pigments in light-harvesting complexes play an important role in the excitation energy transfer dynamics. It is considered that protein environment controls the excitation energy fluctuation to maximize the efficiency of excitation energy transfer. However, the detailed mechanism is still unknown. The high computational cost of reliable electronic structure calculations for excited states prevents us from carrying out a large number of sampling needed to evaluate the excitation energy fluctuations. To overcome this difficulty, we develop a new method called molecular mechanics with Shepard interpolation corrections (MMSIC), which enable us to generate potential energy surfaces for pigments in light-harvesting complexes efficiently. We illustrate the new method by application to bacteriochlorophyll a pigments in the Fenna-Matthews-Olson complex. The MMSIC calculations are more than a million times faster than the direct electronic structure calculations, and the calculated results are in good agreement with the experimental results.
Mustafa, Sanam; Hannagan, John; Rigby, Paul; Pfleger, Kevin; Corry, Ben
2013-02-01
Accurate quantification of Förster resonance energy transfer (FRET) using intensity-based methods is difficult due to the overlap of fluorophore excitation and emission spectra. Consequently, mechanisms are required to remove bleedthrough of the donor emission into the acceptor channel and direct excitation of the acceptor when aiming to excite only the donor fluorophores. Methods to circumvent donor bleedthrough using the unmixing of emission spectra have been reported, but these require additional corrections to account for direct excitation of the acceptor. Here we present an alternative method for robust quantification of FRET efficiencies based upon the simultaneous spectral unmixing of both excitation and emission spectra. This has the benefit over existing methodologies in circumventing the issue of donor bleedthrough and acceptor cross excitation without the need for additional corrections. Furthermore, we show that it is applicable with as few as two excitation wavelengths and so can be used for quantifying FRET efficiency in microscope images as easily as for data collected on a spectrofluorometer. We demonstrate the accuracy of the approach by reproducing efficiency values in well characterized FRET standards: HEK cells expressing a variety of linked cerulean and venus fluorescent proteins. Finally we describe simple ImageJ plugins that can be used to calculate and create images of FRET efficiencies from microscope images.
Electron-Excited X-Ray Microanalysis at Low Beam Energy: Almost Always an Adventure!
Newbury, Dale E; Ritchie, Nicholas W M
2016-08-01
Scanning electron microscopy with energy-dispersive spectrometry has been applied to the analysis of various materials at low-incident beam energies, E 0≤5 keV, using peak fitting and following the measured standards/matrix corrections protocol embedded in the National Institute of Standards and Technology Desktop Spectrum Analyzer-II analytical software engine. Low beam energy analysis provides improved spatial resolution laterally and in-depth. The lower beam energy restricts the atomic shells that can be ionized, reducing the number of X-ray peak families available to the analyst. At E 0=5 keV, all elements of the periodic table except H and He can be measured. As the beam energy is reduced below 5 keV, elements become inaccessible due to lack of excitation of useful characteristic X-ray peaks. The shallow sampling depth of low beam energy microanalysis makes the technique more sensitive to surface compositional modification due to formation of oxides and other reaction layers. Accurate and precise analysis is possible with the use of appropriate standards and by accumulating high count spectra of unknowns and standards (>1 million counts integrated from 0.1 keV to E 0).
Bang, Junhyeok; Meng, Sheng; Sun, Yi-Yang; West, Damien; Wang, Zhiguo; Gao, Fei; Zhang, S. B.
2013-01-01
Understanding and controlling of excited carrier dynamics is of fundamental and practical importance, particularly in photochemistry and solar energy applications. However, theory of energy relaxation of excited carriers is still in its early stage. Here, using ab initio molecular dynamics (MD) coupled with time-dependent density functional theory, we show a coverage-dependent energy transfer of photoexcited carriers in hydrogenated graphene, giving rise to distinctively different ion dynamics. Graphene with sparsely populated H is difficult to dissociate due to inefficient transfer of the excitation energy into kinetic energy of the H. In contrast, H can easily desorb from fully hydrogenated graphane. The key is to bring down the H antibonding state to the conduction band minimum as the band gap increases. These results can be contrasted to those of standard ground-state MD that predict H in the sparse case should be much less stable than that in fully hydrogenated graphane. Our findings thus signify the importance of carrying out explicit electronic dynamics in excited-state simulations. PMID:23277576
Bang, Junhyeok; Meng, Sheng; Sun, Yi-Yang; West, Damien; Wang, Zhiguo; Gao, Fei; Zhang, Shengbai
2013-01-15
Understanding and controlling of excited carrier dynamics is of fundamental and practical importance, particularly in photochemistry and solar energy applications. However, theory of energy relaxation of excited carriers is still in its early stage. Here, using ab-initio molecular dynamics (MD) coupled with time-dependent density functional theory, we show a coverage-dependent energy transfer of photoexcited carriers in hydrogenated graphene, giving rise to distinctively different ion dynamics. Graphene with sparsely populated H is difficult to dissociate due to inefficient transfer of the excitation energy into kinetic energy of the H. In contrast, H can easily desorb from fully hydrogenated graphane. The key is to bring down the H antibonding state to the conduction band minimum as the band gap increases. These results can be contrasted to those of standard ground-state MD which predicts H in the sparse case should be much less stable than that in fully hydrogenated graphane. Our findings thus signify the importance of carrying out explicit electronic dynamics in excited-state simulations.
Suess, Christian J; Hirst, Jonathan D; Besley, Nicholas A
2017-04-01
The development of optical multidimensional spectroscopic techniques has opened up new possibilities for the study of biological processes. Recently, ultrafast two-dimensional ultraviolet spectroscopy experiments have determined the rates of tryptophan → heme electron transfer and excitation energy transfer for the two tryptophan residues in myoglobin (Consani et al., Science, 2013, 339, 1586). Here, we show that accurate prediction of these rates can be achieved using Marcus theory in conjunction with time-dependent density functional theory. Key intermediate residues between the donor and acceptor are identified, and in particular the residues Val68 and Ile75 play a critical role in calculations of the electron coupling matrix elements. Our calculations demonstrate how small changes in structure can have a large effect on the rates, and show that the different rates of electron transfer are dictated by the distance between the heme and tryptophan residues, while for excitation energy transfer the orientation of the tryptophan residues relative to the heme is important. © 2017 The Authors Journal of Computational Chemistry Published by Wiley Periodicals, Inc.
Safronova, U. I.; Johnson, W. R.; Safronova, M. S.
2007-10-15
Relativistic many-body perturbation theory is applied to study properties of ions of the francium isoelectronic sequence. Specifically, energies of the 7s, 7p, 6d, and 5f states of Fr-like ions with nuclear charges Z=87-100 are calculated through third order; reduced matrix elements, oscillator strengths, transition rates, and lifetimes are determined for 7s-7p, 7p-6d, and 6d-5f electric-dipole transitions; and 7s-6d, 7s-5f, and 5f{sub 5/2}-5f{sub 7/2} multipole matrix elements are evaluated to obtain the lifetimes of low-lying excited states. Moreover, for the ions Z=87-92 calculations are also carried out using the relativistic all-order single-double method, in which single and double excitations of Dirac-Fock wave functions are included to all orders in perturbation theory. With the aid of the single-double wave functions, we obtain accurate values of energies, transition rates, oscillator strengths, and the lifetimes of these six ions. Ground state scalar polarizabilities in Fr I, Ra II, Ac III, and Th IV are calculated using relativistic third-order and all-order methods. Ground state scalar polarizabilities for other Fr-like ions are calculated using a relativistic second-order method. These calculations provide a theoretical benchmark for comparison with experiment and theory.
Peng, Bo; Lestrange, Patrick J; Goings, Joshua J; Caricato, Marco; Li, Xiaosong
2015-09-08
Single-reference techniques based on coupled-cluster (CC) theory, in the forms of linear response (LR) or equation of motion (EOM), are highly accurate and widely used approaches for modeling valence absorption spectra. Unfortunately, these equations with singles and doubles (LR-CCSD and EOM-CCSD) scale as O(N⁶), which may be prohibitively expensive for the study of high-energy excited states using a conventional eigensolver. In this paper, we present an energy-specific non-Hermitian eigensolver that is able to obtain high-energy excited states (e.g., XAS K-edge spectrum) at low computational cost. In addition, we also introduce an improved trial vector for iteratively solving the EOM-CCSD equation with a focus on high-energy eigenstates. The energy-specific EOM-CCSD approach and its low-scaling alternatives are applied to calculations of carbon, nitrogen, oxygen, and sulfur K-edge excitations. The results are compared to other implementations of CCSD for excited states, energy-specific linear response time-dependent density functional theory (TDDFT), and experimental results with multiple statistical metrics are presented and evaluated.
Kearns, F L; Hudson, P S; Boresch, S; Woodcock, H L
2016-01-01
Enzyme activity is inherently linked to free energies of transition states, ligand binding, protonation/deprotonation, etc.; these free energies, and thus enzyme function, can be affected by residue mutations, allosterically induced conformational changes, and much more. Therefore, being able to predict free energies associated with enzymatic processes is critical to understanding and predicting their function. Free energy simulation (FES) has historically been a computational challenge as it requires both the accurate description of inter- and intramolecular interactions and adequate sampling of all relevant conformational degrees of freedom. The hybrid quantum mechanical molecular mechanical (QM/MM) framework is the current tool of choice when accurate computations of macromolecular systems are essential. Unfortunately, robust and efficient approaches that employ the high levels of computational theory needed to accurately describe many reactive processes (ie, ab initio, DFT), while also including explicit solvation effects and accounting for extensive conformational sampling are essentially nonexistent. In this chapter, we will give a brief overview of two recently developed methods that mitigate several major challenges associated with QM/MM FES: the QM non-Boltzmann Bennett's acceptance ratio method and the QM nonequilibrium work method. We will also describe usage of these methods to calculate free energies associated with (1) relative properties and (2) along reaction paths, using simple test cases with relevance to enzymes examples.
Accurate Hartree-Fock energy of extended systems using large Gaussian basis sets
NASA Astrophysics Data System (ADS)
Paier, Joachim; Diaconu, Cristian V.; Scuseria, Gustavo E.; Guidon, Manuel; Vandevondele, Joost; Hutter, Jürg
2009-11-01
Calculating highly accurate thermochemical properties of condensed matter via wave-function-based approaches (such as, e.g., Hartree-Fock or hybrid functionals) has recently attracted much interest. We here present two strategies providing accurate Hartree-Fock energies for solid LiH in a large Gaussian basis set and applying periodic boundary conditions. The total energies were obtained using two different approaches, namely, a supercell evaluation of Hartree-Fock exchange using a truncated Coulomb operator and an extrapolation toward the full-range Hartree-Fock limit of a Padé fit to a series of short-range screened Hartree-Fock calculations. These two techniques agreed to significant precision. We also present the Hartree-Fock cohesive energy of LiH (converged to within sub-millielectron volt) at the experimental equilibrium volume as well as the Hartree-Fock equilibrium lattice constant and bulk modulus.
A Cavity Corrected 3D-RISM Functional for Accurate Solvation Free Energies
2014-01-01
We show that an Ng bridge function modified version of the three-dimensional reference interaction site model (3D-RISM-NgB) solvation free energy method can accurately predict the hydration free energy (HFE) of a set of 504 organic molecules. To achieve this, a single unique constant parameter was adjusted to the computed HFE of single atom Lennard-Jones solutes. It is shown that 3D-RISM is relatively accurate at predicting the electrostatic component of the HFE without correction but requires a modification of the nonpolar contribution that originates in the formation of the cavity created by the solute in water. We use a free energy functional with the Ng scaling of the direct correlation function [Ng, K. C. J. Chem. Phys.1974, 61, 2680]. This produces a rapid, reliable small molecule HFE calculation for applications in drug design. PMID:24634616
Margraf, Johannes T; Ranasinghe, Duminda S; Bartlett, Rodney J
2017-03-31
In this contribution, we discuss how reaction energy benchmark sets can automatically be created from arbitrary atomization energy databases. As an example, over 11 000 reaction energies derived from the W4-11 database, as well as some relevant subsets are reported. Importantly, there is only very modest computational overhead involved in computing >11 000 reaction energies compared to 140 atomization energies, since the rate-determining step for either benchmark is performing the same 140 quantum chemical calculations. The performance of commonly used electronic structure methods for the new database is analyzed. This allows investigating the relationship between the performances for atomization and reaction energy benchmarks based on an identical set of molecules. The atomization energy is found to be a weak predictor for the overall usefulness of a method. The performance of density functional approximations in light of the number of empirically optimized parameters used in their design is also discussed.
Excitation Energy and Temperature Dependence of the Phase Coherent Photorefractive Effect
NASA Astrophysics Data System (ADS)
Kabir, A.; Wagner, H. P.
2011-12-01
We investigate the influence of excitation energy and temperature on the phase coherent photorefractive (PCP) effect in ZnSe quantum wells. At temperatures below 35 K and nearly exciton resonant excitation the formation of trions suppresses the PCP effect. At lower excitation energies increasing space-charge-fields reduce the trion binding energy which leads to an enhanced thermal ionization of trions resulting in a PCP signal. Due to the thermal dissociation of trions at temperatures exceeding 40 K a strong PCP effect occurs even at nearly resonant excitation.
Vincent, Mark A; Hillier, Ian H
2014-08-25
The accurate prediction of the adsorption energies of unsaturated molecules on graphene in the presence of water is essential for the design of molecules that can modify its properties and that can aid its processability. We here show that a semiempirical MO method corrected for dispersive interactions (PM6-DH2) can predict the adsorption energies of unsaturated hydrocarbons and the effect of substitution on these values to an accuracy comparable to DFT values and in good agreement with the experiment. The adsorption energies of TCNE, TCNQ, and a number of sulfonated pyrenes are also predicted, along with the effect of hydration using the COSMO model.
Xiao, Jing-Lin
2009-03-01
In an asymmetry quantum dot, the properties of the electron, which is strongly coupled with phonon, were investigated. The variational relations of the first internal excited state energy, the excitation energy and the frequency of transition spectral line between the first internal excited state and the ground state of the electron which is strongly coupled with phonon in an asymmetry quantum dot with the transverse and longituainal effective confinement length of quantum dot and the electron-phonon coupling strength were studied by using a linear combination operator and the unitary transformation methods. Numerical calculations for the variational relations of the first internal excited state energy, the excitation energy and the frequency of transition spectral line between the first internal excited state and the ground state of the electron which is strongly coupled with phonon in an asymmetry quantum dot with the transverse and longituainal effective confinement length of quantum dot and the electron-phonon coupling strength were performed and the results show that the first internal excited state energy, the excitation energy and the frequency of transition spectral line between the first internal excited state and the ground state of the electron which is strongly coupled with phonon in an asymmetry quantum dot will strongly increase with decreasing the transverse and longitudinal effective confinement length. The first internal excited state energy of the electron which is strongly coupled with phonon in an asymmetry quantum dot will decrease with increasing the electron-phonon coupling strength. The excitation energy and the frequency of transition spectral line between the first internal excited state and the ground state of the electron which is strongly coupled with phonon in an asymmetry quantum dot will increase with increasing the electron-phonon coupling strength.
Han, Huixian; Li, Anyang; Guo, Hua
2014-12-28
A new full-dimensional global potential energy surface (PES) for the acetylene-vinylidene isomerization on the ground (S{sub 0}) electronic state has been constructed by fitting ∼37 000 high-level ab initio points using the permutation invariant polynomial-neural network method with a root mean square error of 9.54 cm{sup −1}. The geometries and harmonic vibrational frequencies of acetylene, vinylidene, and all other stationary points (two distinct transition states and one secondary minimum in between) have been determined on this PES. Furthermore, acetylene vibrational energy levels have been calculated using the Lanczos algorithm with an exact (J = 0) Hamiltonian. The vibrational energies up to 12 700 cm{sup −1} above the zero-point energy are in excellent agreement with the experimentally derived effective Hamiltonians, suggesting that the PES is approaching spectroscopic accuracy. In addition, analyses of the wavefunctions confirm the experimentally observed emergence of the local bending and counter-rotational modes in the highly excited bending vibrational states. The reproduction of the experimentally derived effective Hamiltonians for highly excited bending states signals the coming of age for the ab initio based PES, which can now be trusted for studying the isomerization reaction.
Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics
Deyne, Andy Van Yperen-De; Pauwels, Ewald; Ghysels, An; Waroquier, Michel; Van Speybroeck, Veronique; Hemelsoet, Karen; De Meyer, Thierry; De Clerck, Karen
2014-04-07
A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed.
NASA Astrophysics Data System (ADS)
Wu, Xiaonan; Tseng, C. K.
1992-12-01
The excitation energy transfer from phycobiliproteins to thylakoid PSII of higher plants was investigated. When incubated with spinach thylakoids, phycobiliproteins isolated from red and blue-green algae transferred light energy absorbed to spinach PSII. The efficiency of energy transfer was dependent on the kind of phycobiliproteins used. If spinach thylakoids were replaced by the thylakoids of Brassica chinensis, R-phycoerythin or C-phycocyanin did not transfer their excitation energy to PSII of Brassica chinensis unless allophycocyanin was present.
Properties of high-energy isoscalar monopole excitations in medium-heavy mass spherical nuclei
Gorelik, M. L. Shlomo, Sh. Tulupov, B. A. Urin, M. H.
2015-07-15
The recently developed particle-hole dispersive optical model is applied to describe properties of high-energy isoscalar monopole excitations in medium-heavy mass spherical nuclei. In particular, the double transition density averaged over the energy of the isoscalar monopole excitations is considered for {sup 208}Pb in a wide energy interval, which includes the isoscalar giant monopole resonance and its overtone. The energy-averaged strength functions of these resonances are also analyzed.
Fractionally Charged Zero-Energy Single-Particle Excitations in a Driven Fermi Sea
NASA Astrophysics Data System (ADS)
Moskalets, Michael
2016-07-01
A voltage pulse of a Lorentzian shape carrying half of the flux quantum excites out of a zero-temperature Fermi sea an electron in a mixed state, which looks like a quasiparticle with an effectively fractional charge e /2 . A prominent feature of such an excitation is a narrow peak in the energy distribution function lying exactly at the Fermi energy μ . Another spectacular feature is that the distribution function has symmetric tails around μ , which results in a zero-energy excitation. This sounds improbable since at zero temperature all available states below μ are fully occupied. The resolution lies in the fact that such a voltage pulse also excites electron-hole pairs, which free some space below μ and thus allow a zero-energy quasiparticle to exist. I discuss also how to address separately electron-hole pairs and a fractionally charged zero-energy excitation in an experiment.
Observation of low- and high-energy Gamow-Teller phonon excitations in nuclei.
Fujita, Y; Fujita, H; Adachi, T; Bai, C L; Algora, A; Berg, G P A; von Brentano, P; Colò, G; Csatlós, M; Deaven, J M; Estevez-Aguado, E; Fransen, C; De Frenne, D; Fujita, K; Ganioğlu, E; Guess, C J; Gulyás, J; Hatanaka, K; Hirota, K; Honma, M; Ishikawa, D; Jacobs, E; Krasznahorkay, A; Matsubara, H; Matsuyanagi, K; Meharchand, R; Molina, F; Muto, K; Nakanishi, K; Negret, A; Okamura, H; Ong, H J; Otsuka, T; Pietralla, N; Perdikakis, G; Popescu, L; Rubio, B; Sagawa, H; Sarriguren, P; Scholl, C; Shimbara, Y; Shimizu, Y; Susoy, G; Suzuki, T; Tameshige, Y; Tamii, A; Thies, J H; Uchida, M; Wakasa, T; Yosoi, M; Zegers, R G T; Zell, K O; Zenihiro, J
2014-03-21
Gamow-Teller (GT) transitions in atomic nuclei are sensitive to both nuclear shell structure and effective residual interactions. The nuclear GT excitations were studied for the mass number A = 42, 46, 50, and 54 "f-shell" nuclei in ((3)He, t) charge-exchange reactions. In the (42)Ca → (42)Sc reaction, most of the GT strength is concentrated in the lowest excited state at 0.6 MeV, suggesting the existence of a low-energy GT phonon excitation. As A increases, a high-energy GT phonon excitation develops in the 6-11 MeV region. In the (54)Fe → (54)Co reaction, the high-energy GT phonon excitation mainly carries the GT strength. The existence of these two GT phonon excitations are attributed to the 2 fermionic degrees of freedom in nuclei.
NASA Technical Reports Server (NTRS)
Lee, Timothy J.; Dateo, Christopher E.; Schwenke, David W.; Chaban, Galina M.
2005-01-01
Accurate quartic force fields have been determined for the CCH- and NH2- molecular anions using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, CCSD(T). Very large one-particle basis sets have been used including diffuse functions and up through g-type functions. Correlation of the nitrogen and carbon core electrons has been included, as well as other "small" effects, such as the diagonal Born-Oppenheimer correction, and basis set extrapolation, and corrections for higher-order correlation effects and scalar relativistic effects. Fundamental vibrational frequencies have been computed using standard second-order perturbation theory as well as variational methods. Comparison with the available experimental data is presented and discussed. The implications of our research for the astronomical observation of molecular anions will be discussed.
2015-01-01
Herein, we report chemistry that enables excitation energy transfer (EET) to be accurately measured via action spectroscopy on gaseous ions in an ion trap. It is demonstrated that EET between tryptophan or tyrosine and a disulfide bond leads to excited state, homolytic fragmentation of the disulfide bond. This phenomenon exhibits a tight distance dependence, which is consistent with Dexter exchange transfer. The extent of fragmentation of the disulfide bond can be used to determine the distance between the chromophore and disulfide bond. The chemistry is well suited for the examination of protein structure in the gas phase because native amino acids can serve as the donor/acceptor moieties. Furthermore, both tyrosine and tryptophan exhibit unique action spectra, meaning that the identity of the donating chromophore can be easily determined in addition to the distance between donor/acceptor. Application of the method to the Trpcage miniprotein reveals distance constraints that are consistent with a native-like fold for the +2 charge state in the gas phase. This structure is stabilized by several salt bridges, which have also been observed to be important previously in proteins that retain native-like structures in the gas phase. The ability of this method to measure specific distance constraints, potentially at numerous positions if combined with site-directed mutagenesis, significantly enhances our ability to examine protein structure in the gas phase. PMID:25174489
Hendricks, Nathan G; Lareau, Nichole M; Stow, Sarah M; McLean, John A; Julian, Ryan R
2014-09-24
Herein, we report chemistry that enables excitation energy transfer (EET) to be accurately measured via action spectroscopy on gaseous ions in an ion trap. It is demonstrated that EET between tryptophan or tyrosine and a disulfide bond leads to excited state, homolytic fragmentation of the disulfide bond. This phenomenon exhibits a tight distance dependence, which is consistent with Dexter exchange transfer. The extent of fragmentation of the disulfide bond can be used to determine the distance between the chromophore and disulfide bond. The chemistry is well suited for the examination of protein structure in the gas phase because native amino acids can serve as the donor/acceptor moieties. Furthermore, both tyrosine and tryptophan exhibit unique action spectra, meaning that the identity of the donating chromophore can be easily determined in addition to the distance between donor/acceptor. Application of the method to the Trpcage miniprotein reveals distance constraints that are consistent with a native-like fold for the +2 charge state in the gas phase. This structure is stabilized by several salt bridges, which have also been observed to be important previously in proteins that retain native-like structures in the gas phase. The ability of this method to measure specific distance constraints, potentially at numerous positions if combined with site-directed mutagenesis, significantly enhances our ability to examine protein structure in the gas phase.
Whittleton, Sarah R; Otero-de-la-Roza, A; Johnson, Erin R
2017-02-14
Accurate energy ranking is a key facet to the problem of first-principles crystal-structure prediction (CSP) of molecular crystals. This work presents a systematic assessment of B86bPBE-XDM, a semilocal density functional combined with the exchange-hole dipole moment (XDM) dispersion model, for energy ranking using 14 compounds from the first five CSP blind tests. Specifically, the set of crystals studied comprises 11 rigid, planar compounds and 3 co-crystals. The experimental structure was correctly identified as the lowest in lattice energy for 12 of the 14 total crystals. One of the exceptions is 4-hydroxythiophene-2-carbonitrile, for which the experimental structure was correctly identified once a quasi-harmonic estimate of the vibrational free-energy contribution was included, evidencing the occasional importance of thermal corrections for accurate energy ranking. The other exception is an organic salt, where charge-transfer error (also called delocalization error) is expected to cause the base density functional to be unreliable. Provided the choice of base density functional is appropriate and an estimate of temperature effects is used, XDM-corrected density-functional theory is highly reliable for the energetic ranking of competing crystal structures.
Accurate studies of dissociation energies and vibrational energies on alkali metals
NASA Astrophysics Data System (ADS)
Liu, Xiu-Ying; Sun, Wei-Guo; Fan, Qun-Chao
2008-06-01
This paper studies full vibrational spectra {Ev} and molecular dissociation energies De by using conventional least-squares (LS) fitting and an algebraic method (AM) proposed recently for 10 diatomic electronic states of 7Li2, Na2, NaK and NaLi molecules based on some known experimental vibrational energies in a subset [Evexpt] respectively. Studies show that: (1) although both the full AM spectrum {EvAM} and the LS spectrum {EvLS} can reproduce the known experimental energies in [Evexpt], the {EvAM} is superior to the {EvLS} in that the high-lying AM vibrational energies which may not be available experimentally have better or much better accuracy than those LS counterparts in {EvLS}, and so is the AM dissociation energy DeAM; (2) the main source of the errors in the data obtained by using the LS fitting is that the fitting which is just a pure mathematical process does not use any physical criteria that must be satisfied by the full vibrational spectrum, while the AM method does. This study suggests that when fitting or solving a physical equation using a set of source data, it is important not only to apply a proper mathematical tool, but also to use correct physical criteria which measure the physical properties of the data, kick out those data having bigger errors, and impose conditional convergence on the numerical process.
Validation of local hybrid functionals for TDDFT calculations of electronic excitation energies
NASA Astrophysics Data System (ADS)
Maier, Toni M.; Bahmann, Hilke; Arbuznikov, Alexei V.; Kaupp, Martin
2016-02-01
The first systematic evaluation of local hybrid functionals for the calculation of electronic excitation energies within linear-response time-dependent density functional theory (TDDFT) is reported. Using our recent efficient semi-numerical TDDFT implementation [T. M. Maier et al., J. Chem. Theory Comput. 11, 4226 (2015)], four simple, thermochemically optimized one-parameter local hybrid functionals based on local spin-density exchange are evaluated against a database of singlet and triplet valence excitations of organic molecules, and against a mixed database including also Rydberg, intramolecular charge-transfer (CT) and core excitations. The four local hybrids exhibit comparable performance to standard global or range-separated hybrid functionals for common singlet valence excitations, but several local hybrids outperform all other functionals tested for the triplet excitations of the first test set, as well as for relative energies of excited states. Evaluation for the combined second test set shows that local hybrids can also provide excellent Rydberg and core excitations, in the latter case rivaling specialized functionals optimized specifically for such excitations. This good performance of local hybrids for different excitation types could be traced to relatively large exact-exchange (EXX) admixtures in a spatial region intermediate between valence and asymptotics, as well as close to the nucleus, and lower EXX admixtures in the valence region. In contrast, the tested local hybrids cannot compete with the best range-separated hybrids for intra- and intermolecular CT excitation energies. Possible directions for improvement in the latter category are discussed. As the used efficient TDDFT implementation requires essentially the same computational effort for global and local hybrids, applications of local hybrid functionals to excited-state problems appear promising in a wide range of fields. Influences of current-density dependence of local kinetic-energy
Two-photon excited quantum dots as energy donors for photosensitizer chlorin e6.
Skripka, Artiom; Valanciunaite, Jurga; Dauderis, Gediminas; Poderys, Vilius; Kubiliute, Reda; Rotomskis, Ricardas
2013-07-01
The excitation-related problems in photodynamic therapy of cancer might be solved by combining two-photon (TP) irradiation and quantum dots (QDs) as effective energy donors for conventional photosensitizers (PS). Here, it is demonstrated for the first time that QD-chlorin e6 (Ce6) complex formed due to the hydrophobic interaction between Ce6 molecules and lipid coating of QDs can be effectively excited via TP irradiation at 1030 nm, which spectrally coincides with the biological tissue optical window. TP absorption cross-section for free QDs and Ce6 at 1030 nm was 3325 and 13 Goeppert-Mayer, respectively. Upon TP excitation of QD-Ce6 solution, the fluorescence band of bound Ce6 molecules was observed via energy transfer from excited QDs. Increasing concentration of Ce6 resulted in quenching of the photoluminescence of QDs and an increase in the fluorescence intensity of bound Ce6 molecules. These intensity changes coincided well with those observed upon single-photon excitation of QD-Ce6 solution when QDs alone are excited. The efficiency of energy transfer in QD-Ce6 complex upon TP excitation was about 80% (QD∶Ce61∶5). These results indicate that the effective excitation of PS with a low TP absorption cross-section is possible in such type noncovalent complexes via energy transfer from TP excited QDs.
A pair natural orbital implementation of the coupled cluster model CC2 for excitation energies.
Helmich, Benjamin; Hättig, Christof
2013-08-28
We demonstrate how to extend the pair natural orbital (PNO) methodology for excited states, presented in a previous work for the perturbative doubles correction to configuration interaction singles (CIS(D)), to iterative coupled cluster methods such as the approximate singles and doubles model CC2. The original O(N(5)) scaling of the PNO construction is reduced by using orbital-specific virtuals (OSVs) as an intermediate step without spoiling the initial accuracy of the PNO method. Furthermore, a slower error convergence for charge-transfer states is analyzed and resolved by a numerical Laplace transformation during the PNO construction, so that an equally accurate treatment of local and charge-transfer excitations is achieved. With state-specific truncated PNO expansions, the eigenvalue problem is solved by combining the Davidson algorithm with deflation to project out roots that have already been determined and an automated refresh with a generation of new PNOs to achieve self-consistency of the PNO space. For a large test set, we found that truncation errors for PNO-CC2 excitation energies are only slightly larger than for PNO-CIS(D). The computational efficiency of PNO-CC2 is demonstrated for a large organic dye, where a reduction of the doubles space by a factor of more than 1000 is obtained compared to the canonical calculation. A compression of the doubles space by a factor 30 is achieved by a unified OSV space only. Moreover, calculations with the still preliminary PNO-CC2 implementation on a series of glycine oligomers revealed an early break even point with a canonical RI-CC2 implementation between 100 and 300 basis functions.
A pair natural orbital implementation of the coupled cluster model CC2 for excitation energies
NASA Astrophysics Data System (ADS)
Helmich, Benjamin; Hättig, Christof
2013-08-01
We demonstrate how to extend the pair natural orbital (PNO) methodology for excited states, presented in a previous work for the perturbative doubles correction to configuration interaction singles (CIS(D)), to iterative coupled cluster methods such as the approximate singles and doubles model CC2. The original O(N^5) scaling of the PNO construction is reduced by using orbital-specific virtuals (OSVs) as an intermediate step without spoiling the initial accuracy of the PNO method. Furthermore, a slower error convergence for charge-transfer states is analyzed and resolved by a numerical Laplace transformation during the PNO construction, so that an equally accurate treatment of local and charge-transfer excitations is achieved. With state-specific truncated PNO expansions, the eigenvalue problem is solved by combining the Davidson algorithm with deflation to project out roots that have already been determined and an automated refresh with a generation of new PNOs to achieve self-consistency of the PNO space. For a large test set, we found that truncation errors for PNO-CC2 excitation energies are only slightly larger than for PNO-CIS(D). The computational efficiency of PNO-CC2 is demonstrated for a large organic dye, where a reduction of the doubles space by a factor of more than 1000 is obtained compared to the canonical calculation. A compression of the doubles space by a factor 30 is achieved by a unified OSV space only. Moreover, calculations with the still preliminary PNO-CC2 implementation on a series of glycine oligomers revealed an early break even point with a canonical RI-CC2 implementation between 100 and 300 basis functions.
Electron-impact excitation and ionization of atomic boron at low and intermediate energies
NASA Astrophysics Data System (ADS)
Wang, Kedong; Zatsarinny, Oleg; Bartschat, Klaus
2016-05-01
We present a comprehensive study of electron collisions with neutral boron atoms. The calculations were performed with the B-Spline R-matrix (close-coupling) method, by employing a parallelized version of the associated computer code. Elastic, excitation, and ionization cross sections were obtained for all transitions involving the lowest 11 states of boron, for incident electron energies ranging from threshold to 100 eV. A multiconfiguration Hartree-Fock method with nonorthogonal term-dependent orbitals was used to generate accurate wave functions for the target states. Close-coupling expansions including 13, 51, and 999 physical and pseudo states were set up to check the sensitivity of the predictions to variations in the theoretical model. The cross-section dataset generated in this work is expected to be the most accurate one available today and should be sufficiently comprehensive for most modeling applications involving neutral boron. Work supported by the China Scholarship Council and the United States National Science Foundation under Grants PHY-1403245 and PHY-1520970, and by the XSEDE allocation PHY-090031.
Pulsed laser excitation power dependence of photoluminescence peak energies in bulk ZnO
NASA Astrophysics Data System (ADS)
Dang, Giang T.; Kanbe, Hiroshi; Kawaharamura, Toshiyuki; Taniwaki, Masafumi
2011-10-01
Photoluminescence (PL) spectra of hydrothermal bulk ZnO were measured in the temperature range from 5 to 298 K. The sample was excited by means of the 266-nm line of an Nd3+: YAG Q-switched pulsed laser with numerous average excitation powers in the range from 0.33 to 7.50 mW. At constant temperatures, the most intense PL peak red-shifts with average excitation power, whereas positions of other near-band-edge peaks remain unchanged. It was experimentally proven that the red-shift is not due to local heating at the excited spot. Rather, it is due to relaxation of photoexcited carriers to lower energy transitions as the most intense transition is saturated by high excitation photon density. Furthermore, the temperature dependence of energy of the most intense PL peak was fitted with the Varshni equation. The Varshni coefficients α and β decrease with increasing pulsed laser excitation power.
NASA Astrophysics Data System (ADS)
Krieger, J. B.; Chen, Jiqiang; Iafrate, G. J.; Savin, A.
1998-03-01
We have obtained an analytic approximation to E_c(r_g, ζ,G) where G is an energy gap separating the occupied and unoccupied states of a homogeneous electron gas for ζ=3D0 and ξ=3D1. When G=3D0, E_c(r_g, ζ) reduces to the usual LSD result. This functional is employed in calculating correlation energies for unpolarized atoms and ions for Z <= 18 by taking G[n]=3D1/8|nabla ln n|^2, which reduces to the ionization energy in the large r limit in an exact Kohn-Sham (KS) theory. The resulting functional is self-interaction-corrected employing a method which is invariant under a unitary transformation. We find that the application of this approach to the calculation of the Ec functional reduces the error in the LSD result by more than 95%. When the value of G is approximately corrected to include the effect of higher lying unoccupied localized states, the resulting values of Ec are within a few percent of the exact results.
Strasser, R J; Butler, W L
1977-05-11
Equations are derived from our model of the photochemical apparatus of photosynthesis to show that the yield of energy transfer from Photosystem II to Photosystem I, phi T(II leads to I), can be obtained from measurements on an individual sample of chloroplasts frozen to -196 degrees C by comparing the sum of two specifically defined fluorescence excitation spectra with the absorption spectrum of the sample. Then, given that value of phiT(II leads to I), the fraction of the quanta absorbed by the photochemical apparatus which is distributed initially to Photosystem I, alpha, can be determined as a function of the wavelength of excitation from the same fluorescence excitation spectra. The results obtained in this study of individual samples of chloroplasts frozen to -196 degrees C in the absence of divalent cations, namely, that phi T(II leads to I)varies from a minimum value of 0.10 when the Photosystem II reaction centers are all open to a maximum value of 0.25 when the centers are all closed and that alpha has a value of about 0.30 which is almost independent of wavelength for wavelength shorter than 675 nm (alpha increases rapidly toward unity at wavelength longer than 675 nm), agrees quite well with results obtained previously from comparative measurements of chloroplasts frozen to -196 degrees C in the presence and absence of divalent cations.
Fraccarollo, Alberto; Canti, Lorenzo; Marchese, Leonardo; Cossi, Maurizio
2017-03-07
The force fields used to simulate the gas adsorption in porous materials are strongly dominated by the van der Waals (vdW) terms. Here we discuss the delicate problem to estimate these terms accurately, analyzing the effect of different models. To this end, we simulated the physisorption of CH4, CO2, and Ar into various Al-free microporous zeolites (ITQ-29, SSZ-13, and silicalite-1), comparing the theoretical results with accurate experimental isotherms. The vdW terms in the force fields were parametrized against the free gas densities and high-level quantum mechanical (QM) calculations, comparing different methods to evaluate the dispersion energies. In particular, MP2 and DFT with semiempirical corrections, with suitable basis sets, were chosen to approximate the best QM calculations; either Lennard-Jones or Morse expressions were used to include the vdW terms in the force fields. The comparison of the simulated and experimental isotherms revealed that a strong interplay exists between the definition of the dispersion energies and the functional form used in the force field; these results are fairly general and reproducible, at least for the systems considered here. On this basis, the reliability of different models can be discussed, and a recipe can be provided to obtain accurate simulated adsorption isotherms.
Ab Initio Potential Energy Surfaces and the Calculation of Accurate Vibrational Frequencies
NASA Technical Reports Server (NTRS)
Lee, Timothy J.; Dateo, Christopher E.; Martin, Jan M. L.; Taylor, Peter R.; Langhoff, Stephen R. (Technical Monitor)
1995-01-01
Due to advances in quantum mechanical methods over the last few years, it is now possible to determine ab initio potential energy surfaces in which fundamental vibrational frequencies are accurate to within plus or minus 8 cm(exp -1) on average, and molecular bond distances are accurate to within plus or minus 0.001-0.003 Angstroms, depending on the nature of the bond. That is, the potential energy surfaces have not been scaled or empirically adjusted in any way, showing that theoretical methods have progressed to the point of being useful in analyzing spectra that are not from a tightly controlled laboratory environment, such as vibrational spectra from the interstellar medium. Some recent examples demonstrating this accuracy will be presented and discussed. These include the HNO, CH4, C2H4, and ClCN molecules. The HNO molecule is interesting due to the very large H-N anharmonicity, while ClCN has a very large Fermi resonance. The ab initio studies for the CH4 and C2H4 molecules present the first accurate full quartic force fields of any kind (i.e., whether theoretical or empirical) for a five-atom and six-atom system, respectively.
Accurate nonrelativistic ground-state energies of 3d transition metal atoms
Scemama, A.; Applencourt, T.; Giner, E.; Caffarel, M.
2014-12-28
We present accurate nonrelativistic ground-state energies of the transition metal atoms of the 3d series calculated with Fixed-Node Diffusion Monte Carlo (FN-DMC). Selected multi-determinantal expansions obtained with the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) method and including the most prominent determinants of the full configuration interaction expansion are used as trial wavefunctions. Using a maximum of a few tens of thousands determinants, fixed-node errors on total DMC energies are found to be greatly reduced for some atoms with respect to those obtained with Hartree-Fock nodes. To the best of our knowledge, the FN-DMC/(CIPSI nodes) ground-state energies presented here are the lowest variational total energies reported so far. They differ from the recently recommended non-variational values of McCarthy and Thakkar [J. Chem. Phys. 136, 054107 (2012)] only by a few percents of the correlation energy. Thanks to the variational property of FN-DMC total energies, our results provide exact lower bounds for the absolute value of all-electron correlation energies, |E{sub c}|.
Sansone, Giuseppe; Maschio, Lorenzo; Usvyat, Denis; Schütz, Martin; Karttunen, Antti
2016-01-07
The black phosphorus (black-P) crystal is formed of covalently bound layers of phosphorene stacked together by weak van der Waals interactions. An experimental measurement of the exfoliation energy of black-P is not available presently, making theoretical studies the most important source of information for the optimization of phosphorene production. Here, we provide an accurate estimate of the exfoliation energy of black-P on the basis of multilevel quantum chemical calculations, which include the periodic local Møller-Plesset perturbation theory of second order, augmented by higher-order corrections, which are evaluated with finite clusters mimicking the crystal. Very similar results are also obtained by density functional theory with the D3-version of Grimme's empirical dispersion correction. Our estimate of the exfoliation energy for black-P of -151 meV/atom is substantially larger than that of graphite, suggesting the need for different strategies to generate isolated layers for these two systems.
Lan, C. B.; Qin, W. Y.
2014-09-15
This letter investigates the energy harvesting from the horizontal coherent resonance of a vertical cantilever beam subjected to the vertical base excitation. The potential energy of the system has two symmetric potential wells. So, under vertical excitation, the system can jump between two potential wells, which will lead to the large vibration in horizontal direction. Two piezoelectric patches are pasted to harvest the energy. From experiment, it is found that the vertical excitation can make the beam turn to be bistable. The system can transform vertical vibration into horizontal vibration of low frequency when excited by harmonic motion. The horizontal coherence resonance can be observed when excited by a vertical white noise. The corresponding output voltages of piezoelectric films reach high values.
Energy Excitation Transfer in a Single Molecule of Poly(p-phenylene vinylene)
NASA Astrophysics Data System (ADS)
Claudio, Gil; Bittner, Eric
2002-03-01
Energy excitation transfer has been shown to occur in conducting polymers such as MEH-PPV [Synth. Met. 116, 35 (2001)]. Initially excited chromophores, which are short oligomers of the polymer, non-radiatively transfer their excitation to longer oligomers of lower energy. We calculate the dynamics of this migration in an ensemble of PPV chains generated by a random growth algorithm [J. Chem. Phys. 115, 9585 (2001)] using the rates described by Förster theory. The proximity of nearby chromophores within the polymer allows for the efficient non-radiative within a single polymer. The great difference in rates between interchain and intrachain transfer also impedes the isolated chromophore from further transfering its excitation to and thus fluoresce with an energy that is red-shifted from the initial excitation.
NASA Astrophysics Data System (ADS)
Seleznev, Alexey O.; Khrustov, Vladimir F.; Stepanov, Nikolay F.
2013-11-01
The attainability of a uniform precision level for estimates of electronic transition characteristics through the multireference first-order polarization propagator approximation (MR-FOPPA) was examined under extension of a basis set, using the CH ion as an example. The transitions from the ground electronic state to the 19 excited electronic terms were considered. Balanced approximations for (i) transition energies to the studied excited states and (ii) forms and relative dispositions of their potential energy curves were attained in the 3-21G and 6-311G (d,p) basis sets. In both the basis sets, a balanced approximation for the corresponding transition moments was not achieved.
Spectroscopic probes of vibrationally excited molecules at chemically significant energies
Rizzo, T.R.
1993-04-01
Infrared-optical double resonance is being used to study the unimolecular dissociation dynamics of hydrazoic acid (HN[sub 3]). 6[nu][sub NH] vibrational overtone excitation spectra are given for HN[sub 3]. Work was begun to determine the feasibility of extending the infrared-optical double resonance photofragment spectroscopy to small free radicals, and to be able to monitor atomic dissociation fragments via laser induced fluorescence in the VUV spectrum. 1 fig.
Do Bond Functions Help for the Calculation of Accurate Bond Energies?
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W., Jr.; Arnold, James (Technical Monitor)
1998-01-01
The bond energies of 8 chemically bound diatomics are computed using several basis sets with and without bond functions (BF). The bond energies obtained using the aug-pVnZ+BF basis sets (with a correction for basis set superposition error, BSSE) tend to be slightly smaller that the results obtained using the aug-pV(n+I)Z basis sets, but slightly larger than the BSSE corrected aug-pV(n+I)Z results. The aug-cc-pVDZ+BF and aug-cc-pVTZ+BF basis sets yield reasonable estimates of bond energies, but, in most cases, these results cannot be considered highly accurate. Extrapolation of the results obtained with basis sets including bond functions appears to be inferior to the results obtained by extrapolation using atom-centered basis sets. Therefore bond functions do not appear to offer a path for obtaining highly accurate results for chemically bound systems at a lower computational cost than atom centered basis sets.
Chatterji, Tapan; Jalarvo, Niina
2013-04-17
We have investigated the low energy excitations in metallic Ho by high resolution neutron spectroscopy. We found at T = 3 K clear inelastic peaks in the energy loss and energy gain sides, along with the central elastic peak. The energy of this low energy excitation, which is 26.59 ± 0.02 μeV at T = 3 K, decreased continuously and became zero at TN ≈ 130 K. By fitting the data in the temperature range 100-127.5 K with a power law we obtained the power-law exponent β = 0.37 ± 0.02, which agrees with the expected value β = 0.367 for a three-dimensional Heisenberg model. Thus the energy of the low energy excitations can be associated with the order parameter.
Accurate structures and binding energies for small water clusters: The water trimer
Nielsen, I.M.; Seidl, E.T.; Janssen, C.L.
1999-05-01
The global minimum on the water trimer potential energy surface has been investigated by means of second-order Mo/ller-Plesset (MP2) perturbation theory employing the series of correlation-consistent basis sets aug-cc-pVXZ (X = D, T, Q, 5, 6), the largest of which contains 1329 basis functions. Definitive predictions are made for the binding energy and equilibrium structure, and improved values are presented for the harmonic vibrational frequencies. A value of 15.82{plus_minus}0.05 kcal mol{sup {minus}1} is advanced for the infinite basis set frozen core MP2 binding energy, obtained by extrapolation of MP2 correlation energies computed at the aug-cc-pVQZ MP2 geometry. Inclusion of core correlation, using the aug-cc-pCV5Z basis set, has been found to increase the binding energy by 0.08 kcal mol{sup {minus}1}, and after consideration of core correlation and higher-order correlation effects, the classical binding energy for the water trimer is estimated to be 15.9{plus_minus}0.2 kcal mol{sup {minus}1}. A zero-point vibrational correction of {minus}5.43 kcal mol{sup {minus}1} has been computed from aug-cc-pVTZ MP2 harmonic vibrational frequencies. The accuracy of different computational schemes for obtaining the binding energies of the water dimer and trimer has been investigated, and computationally feasible methods are suggested for obtaining accurate structures and binding energies for larger water clusters.{copyright} {ital 1999 American Institute of Physics.}
Esque, Jeremy; Cecchini, Marco
2015-04-23
The calculation of the free energy of conformation is key to understanding the function of biomolecules and has attracted significant interest in recent years. Here, we present an improvement of the confinement method that was designed for use in the context of explicit solvent MD simulations. The development involves an additional step in which the solvation free energy of the harmonically restrained conformers is accurately determined by multistage free energy perturbation simulations. As a test-case application, the newly introduced confinement/solvation free energy (CSF) approach was used to compute differences in free energy between conformers of the alanine dipeptide in explicit water. The results are in excellent agreement with reference calculations based on both converged molecular dynamics and umbrella sampling. To illustrate the general applicability of the method, conformational equilibria of met-enkephalin (5 aa) and deca-alanine (10 aa) in solution were also analyzed. In both cases, smoothly converged free-energy results were obtained in agreement with equilibrium sampling or literature calculations. These results demonstrate that the CSF method may provide conformational free-energy differences of biomolecules with small statistical errors (below 0.5 kcal/mol) and at a moderate computational cost even with a full representation of the solvent.
Extensive and accurate energy levels and transition rates for Al-like Zn XVIII
NASA Astrophysics Data System (ADS)
Si, R.; Zhang, C. Y.; Liu, Y. W.; Chen, Z. B.; Guo, X. L.; Li, S.; Yan, J.; Chen, C. Y.; Wang, K.
2017-03-01
Energy levels and transition rates for electric-dipole (E1), electric-quadrupole (E2), magnetic-dipole (M1), and magnetic-quadrupole (M2) transitions of the lowest 393 levels arising from the 3l3 (0 ≤ l ⩽ 2), 3s2 4 l (0 ≤ l ⩽ 3), 3 s 3 p 4 l (0 ≤ l ⩽ 3), 3p2 4 l (0 ≤ l ⩽ 2), 3 s 3 d 4 l (0 ≤ l ⩽ 1), and 3s2 5 l (0 ≤ l ⩽ 4) configurations in Al-like Zn are calculated through the multi-configuration Dirac-Hartree-Fock (MCDHF) method and second-order many-body perturbation theory (MBPT). In the MCDHF calculation, valence-valence and core-valence correlations with the 2 p and 2 s electrons are taken into account. The effect of Breit interaction and quantum electrodynamics corrections on excitation level energies and level lifetimes are assessed though the MCDHF and MBPT calculations. The two sets of level energies are in excellent agreement of better than 0.1%, while the level lifetimes mostly agree to within 2%. Comparisons are also made with experimental measurements and other theoretical results to assess the accuracy of our calculations.
Hyperfine structure in 229gTh3+ as a probe of the 229gTh→ 229mTh nuclear excitation energy.
Beloy, K
2014-02-14
We identify a potential means to extract the 229gTh→ 229mTh nuclear excitation energy from precision microwave spectroscopy of the 5F(5/2,7/2) hyperfine manifolds in the ion 229gTh3+. The hyperfine interaction mixes this ground fine structure doublet with states of the nuclear isomer, introducing small but observable shifts to the hyperfine sublevels. We demonstrate how accurate atomic structure calculations may be combined with the measurement of the hyperfine intervals to quantify the effects of this mixing. Further knowledge of the magnetic dipole decay rate of the isomer, as recently reported, allows an indirect determination of the nuclear excitation energy.
Ultrafast Non-Förster Intramolecular Donor-Acceptor Excitation Energy Transfer.
Athanasopoulos, Stavros; Alfonso Hernandez, Laura; Beljonne, David; Fernandez-Alberti, Sebastian; Tretiak, Sergei
2017-04-06
Ultrafast intramolecular electronic energy transfer in a conjugated donor-acceptor system is simulated using nonadiabatic excited-state molecular dynamics. After initial site-selective photoexcitation of the donor, transition density localization is monitored throughout the S2 → S1 internal conversion process, revealing an efficient unidirectional donor → acceptor energy-transfer process. Detailed analysis of the excited-state trajectories uncovers several salient features of the energy-transfer dynamics. While a weak temperature dependence is observed during the entire electronic energy relaxation, an ultrafast initially temperature-independent process allows the molecular system to approach the S2-S1 potential energy crossing seam within the first ten femtoseconds. Efficient energy transfer occurs in the absence of spectral overlap between the donor and acceptor units and is assisted by a transient delocalization phenomenon of the excited-state wave function acquiring Frenkel-exciton character at the moment of quantum transition.
Huang, Xinchuan; Schwenke, David W; Lee, Timothy J
2008-12-07
A global potential energy surface (PES) that includes short and long range terms has been determined for the NH(3) molecule. The singles and doubles coupled-cluster method that includes a perturbational estimate of connected triple excitations and the internally contracted averaged coupled-pair functional electronic structure methods have been used in conjunction with very large correlation-consistent basis sets, including diffuse functions. Extrapolation to the one-particle basis set limit was performed and core correlation and scalar relativistic contributions were included directly, while the diagonal Born-Oppenheimer correction was added. Our best purely ab initio PES, denoted "mixed," is constructed from two PESs which differ in whether the ic-ACPF higher-order correlation correction was added or not. Rovibrational transition energies computed from the mixed PES agree well with experiment and the best previous theoretical studies, but most importantly the quality does not deteriorate even up to 10 300 cm(-1) above the zero-point energy (ZPE). The mixed PES was improved further by empirical refinement using the most reliable J=0-2 rovibrational transitions in the HITRAN 2004 database. Agreement between high-resolution experiment and rovibrational transition energies computed from our refined PES for J=0-6 is excellent. Indeed, the root mean square (rms) error for 13 HITRAN 2004 bands for J=0-2 is 0.023 cm(-1) and that for each band is always
Sevy, Eric T.; Michaels, Chris A.; Tapalian, H. Charles; Flynn, George W.
2000-04-01
CO{sub 2} bath molecules scattered into J=72 of the 00{sup 0}0 vibrational state at short times after 248 or 266 nm UV excitation of pyrazine are probed using high resolution time resolved IR diode laser spectroscopy as a function of UV laser fluence from {approx}3 to 80 mJ/cm2. The implications of pyrazine photodissociation for the interpretation of these collisional energy transfer experiments are considered. Specifically, the possibility that translationally hot HCN resulting from pyrazine dissociation may be the source of excitation for collisions that impart a large amount of rotational and translational energy to CO{sub 2} molecules is examined. Transient absorption measurements probing rotationally and translationally excited CO{sub 2} molecules produced following excitation of pyrazine are analyzed within the context of a kinetic scheme incorporating pyrazine photodissociation, as well as excitation of CO{sub 2} by both translationally hot HCN and vibrationally excited pyrazine. This analysis indicates that vibrationally hot pyrazine, which has sufficient energy to dissociate, is the source of excitation in collisions imparting large amounts of rotational and translational energy to CO{sub 2}. (c) 2000 American Institute of Physics.
NASA Astrophysics Data System (ADS)
Schneckenburger, Herbert; Gschwend, Michael H.; Bauer, Manfred; Strauss, Wolfgang S. L.; Steiner, Rudolf W.
1996-12-01
Mitochondrial malfunction may be concomitant with changes of the redox states of the coenzymes nicotinamide adenine dinucleotide (NAD+/NADH), as well as flavin.mononucleotide or dinucleotide. The intrinsic fluorescence of these coenzymes was therefore proposed to be a measure of malfunction. Since mitochondrial fluorescence is strongly superposed by autofluorescence from various cytoplasmatic fluorophores, cultivated endothelial cells were incubated with the mitochondrial marker rhodamine 123 (R123), and after excitation of flavin molecules, energy transfer to R123 was investigated. Due to spectral overlap of flavin and R123 fluorescence, energy transfer flavin yields R123 could not be detected from their emission spectra. Therefore, the method of microscopic fluorescence excitation spectroscopy was established. When detecting R123 fluorescence, excitation maxima at 370 - 390 nm and 420-460 nm were assigned to flavins, whereas a pronounced excitation band at 465 - 490 nm was attributed to R123. Therefore, excitation at 475 nm reflected the intracellular concentration of R123, whereas excitation at 385 nm reflected flavin excitation with a subsequent energy transfer to R123 molecules. An enhanced energy transfer after inhibition of specific enzyme complexes of the respiratory chain is discussed in the present article.
Low-energy structures of benzene clusters with a novel accurate potential surface.
Bartolomei, M; Pirani, F; Marques, J M C
2015-12-05
The benzene-benzene (Bz-Bz) interaction is present in several chemical systems and it is known to be crucial in understanding the specificity of important biological phenomena. In this work, we propose a novel Bz-Bz analytical potential energy surface which is fine-tuned on accurate ab initio calculations in order to improve its reliability. Once the Bz-Bz interaction is modeled, an analytical function for the energy of the Bzn clusters may be obtained by summing up over all pair potentials. We apply an evolutionary algorithm (EA) to discover the lowest-energy structures of Bzn clusters (for n=2-25), and the results are compared with previous global optimization studies where different potential functions were employed. Besides the global minimum, the EA also gives the structures of other low-lying isomers ranked by the corresponding energy. Additional ab initio calculations are carried out for the low-lying isomers of Bz3 and Bz4 clusters, and the global minimum is confirmed as the most stable structure for both sizes. Finally, a detailed analysis of the low-energy isomers of the n = 13 and 19 magic-number clusters is performed. The two lowest-energy Bz13 isomers show S6 and C3 symmetry, respectively, which is compatible with the experimental results available in the literature. The Bz19 structures reported here are all non-symmetric, showing two central Bz molecules surrounded by 12 nearest-neighbor monomers in the case of the five lowest-energy structures.
Galindo, Johan F; Atas, Evrim; Altan, Aysun; Kuroda, Daniel G; Fernandez-Alberti, Sebastian; Tretiak, Sergei; Roitberg, Adrian E; Kleiman, Valeria D
2015-09-16
Solar energy conversion starts with the harvest of light, and its efficacy depends on the spatial transfer of the light energy to where it can be transduced into other forms of energy. Harnessing solar power as a clean energy source requires the continuous development of new synthetic materials that can harvest photon energy and transport it without significant losses. With chemically-controlled branched architectures, dendrimers are ideally suited for these initial steps, since they consist of arrays of chromophores with relative positioning and orientations to create energy gradients and to spatially focus excitation energies. The spatial localization of the energy delimits its efficacy and has been a point of intense research for synthetic light harvesters. We present the results of a combined theoretical experimental study elucidating ultrafast, unidirectional, electronic energy transfer on a complex molecule designed to spatially focus the initial excitation onto an energy sink. The study explores the complex interplay between atomic motions, excited-state populations, and localization/delocalization of excitations. Our findings show that the electronic energy-transfer mechanism involves the ultrafast collapse of the photoexcited wave function due to nonadiabatic electronic transitions. The localization of the wave function is driven by the efficient coupling to high-frequency vibrational modes leading to ultrafast excited-state dynamics and unidirectional efficient energy funneling. This work provides a long-awaited consistent experiment-theoretical description of excited-state dynamics in organic conjugated dendrimers with atomistic resolution, a phenomenon expected to universally appear in a variety of synthetic conjugated materials.
Multireference Excitation Energies for Bacteriochlorophylls A within Light Harvesting System 2.
Anda, André; Hansen, Thorsten; De Vico, Luca
2016-03-08
Light-harvesting system 2 (LH2) of purple bacteria is one of the most popular antenna complexes used to study Nature's way of collecting and channeling solar energy. The dynamics of the absorbed energy is probed by ultrafast spectroscopy. Simulation of these experiments relies on fitting a range of parameters to reproduce the spectra. Here, we present a method that can determine key parameters to chemical accuracy. These will eliminate free variables in the modeling, thus reducing the problem. Using MS-RASPT2/RASSCF calculations, we compute excitation energies and transition dipole moments of all bacteriochlorophylls in LH2. We find that the excitation energies vary among the bacteriochlorophyll monomers and that they are regulated by the curvature of the macrocycle ring and the dihedral angle of an acetyl moiety. Increasing the curvature lifts the ground state energy, which causes a red shift of the excitation energy. Increasing the torsion of the acetyl moiety raises the excited state energy, resulting in a blue shift of the excitation energy. The obtained results mark a giant leap for multiconfigurational multireference quantum chemical methods in the photochemistry of biological systems, which can prove instrumental in exposing the underlying physics of photosynthetic light-harvesting.
Peach, Megan L; Cachau, Raul E; Nicklaus, Marc C
2017-02-24
In this review, we address a fundamental question: What is the range of conformational energies seen in ligands in protein-ligand crystal structures? This value is important biophysically, for better understanding the protein-ligand binding process; and practically, for providing a parameter to be used in many computational drug design methods such as docking and pharmacophore searches. We synthesize a selection of previously reported conflicting results from computational studies of this issue and conclude that high ligand conformational energies really are present in some crystal structures. The main source of disagreement between different analyses appears to be due to divergent treatments of electrostatics and solvation. At the same time, however, for many ligands, a high conformational energy is in error, due to either crystal structure inaccuracies or incorrect determination of the reference state. Aside from simple chemistry mistakes, we argue that crystal structure error may mainly be because of the heuristic weighting of ligand stereochemical restraints relative to the fit of the structure to the electron density. This problem cannot be fixed with improvements to electron density fitting or with simple ligand geometry checks, though better metrics are needed for evaluating ligand and binding site chemistry in addition to geometry during structure refinement. The ultimate solution for accurately determining ligand conformational energies lies in ultrahigh-resolution crystal structures that can be refined without restraints.
Lee, M.W.; Meuwly, M.
2013-01-01
The evaluation of hydration free energies is a sensitive test to assess force fields used in atomistic simulations. We showed recently that the vibrational relaxation times, 1D- and 2D-infrared spectroscopies for CN(-) in water can be quantitatively described from molecular dynamics (MD) simulations with multipolar force fields and slightly enlarged van der Waals radii for the C- and N-atoms. To validate such an approach, the present work investigates the solvation free energy of cyanide in water using MD simulations with accurate multipolar electrostatics. It is found that larger van der Waals radii are indeed necessary to obtain results close to the experimental values when a multipolar force field is used. For CN(-), the van der Waals ranges refined in our previous work yield hydration free energy between -72.0 and -77.2 kcal mol(-1), which is in excellent agreement with the experimental data. In addition to the cyanide ion, we also study the hydroxide ion to show that the method used here is readily applicable to similar systems. Hydration free energies are found to sensitively depend on the intermolecular interactions, while bonded interactions are less important, as expected. We also investigate in the present work the possibility of applying the multipolar force field in scoring trajectories generated using computationally inexpensive methods, which should be useful in broader parametrization studies with reduced computational resources, as scoring is much faster than the generation of the trajectories.
Potential energy surface of excited semiconductors: Graphene quantum dot and BODIPY
NASA Astrophysics Data System (ADS)
Colherinhas, Guilherme; Fileti, Eudes Eterno; Chaban, Vitaly V.
2016-08-01
Binding energy (BE) is an important descriptor in chemistry, which determines thermodynamics and phase behavior of a given substance. BE between two molecules is not directly accessible from the experiment. It has to be reconstructed from cohesive energies, vaporization heats, etc. We report BE for the excited states of two semiconductor molecules - boron-dipyrromethene (BODIPY) and graphene quantum dot (GQD) - with water. We show, for the first time, that excitation increases BE twofold at an optimal separation (energy minimum position), whereas higher separations lead to higher differences. Interestingly, the effects of excitation are similar irrespective of the dominant binding interactions (van der Waals or electrostatic) in the complex. This new knowledge is important for simulations of the excited semiconductors by simplified interaction functions.
Energy transfer in strained graphene assisted by discrete breathers excited by external ac driving
NASA Astrophysics Data System (ADS)
Evazzade, Iman; Lobzenko, Ivan P.; Korznikova, Elena A.; Ovid'ko, Ilya A.; Roknabadi, Mahmood Rezaee; Dmitriev, Sergey V.
2017-01-01
In the present molecular-dynamics study, external ac driving is used at frequencies outside the phonon spectrum to excite gap DBs in uniformly strained graphene nanoribbon. Harmonic displacement or harmonic force is applied to a zigzag atomic chain of graphene. In the former case, nonpropagating DBs are excited on the atoms next to the driven atoms, while in the latter case the excited DBs propagate along the nanoribbon. The energy transfer along the nanoribbon assisted by the DBs is investigated in detail, and the differences between harmonic displacement driving and harmonic force driving are discussed. It is concluded that the amplitude of external driving at out-of-phonon spectrum frequencies should not necessarily be large to obtain a noticeable energy transfer to the system. Overall, our results suggest that external harmonic driving even at relatively small driving amplitudes can be used to control excitation of DBs and consequently the energy transfer to the system.
Accurate potential energy surfaces with a DFT+U(R) approach.
Kulik, Heather J; Marzari, Nicola
2011-11-21
We introduce an improvement to the Hubbard U augmented density functional approach known as DFT+U that incorporates variations in the value of self-consistently calculated, linear-response U with changes in geometry. This approach overcomes the one major shortcoming of previous DFT+U studies, i.e., the use of an averaged Hubbard U when comparing energies for different points along a potential energy surface is no longer required. While DFT+U is quite successful at providing accurate descriptions of localized electrons (e.g., d or f) by correcting self-interaction errors of standard exchange correlation functionals, we show several diatomic molecule examples where this position-dependent DFT+U(R) provides a significant two- to four-fold improvement over DFT+U predictions, when compared to accurate correlated quantum chemistry and experimental references. DFT+U(R) reduces errors in binding energies, frequencies, and equilibrium bond lengths by applying the linear-response, position-dependent U(R) at each configuration considered. This extension is most relevant where variations in U are large across the points being compared, as is the case with covalent diatomic molecules such as transition-metal oxides. We thus provide a tool for deciding whether a standard DFT+U approach is sufficient by determining the strength of the dependence of U on changes in coordinates. We also apply this approach to larger systems with greater degrees of freedom and demonstrate how DFT+U(R) may be applied automatically in relaxations, transition-state finding methods, and dynamics.
Excitation energy dependence of the level density parameter close to the doubly magic 208Pb
NASA Astrophysics Data System (ADS)
Roy, Pratap; Banerjee, K.; Bhattacharya, C.; Pandey, R.; Sen, A.; Manna, S.; Kundu, S.; Rana, T. K.; Ghosh, T. K.; Mukherjee, G.; Roy, T.; Dhal, A.; Dey, A.; Meena, J. K.; Saha, A. K.; Pandit, Deepak; Mukhopadhyay, S.; Bhattacharya, S.
2016-12-01
Neutron evaporation spectra have been measured from 4He+208Pb and 4He+209Bi reactions by using 4He-ion beams of several bombarding energies. Excitation-energy dependence of the level density parameter has been studied for the two systems in the excitation energy range of ˜18 -50 MeV. For both the reactions an overall reduction of the asymptotic level density parameter with increasing excitation energy (temperature) is observed. The trend of the data was compared with the Thomas-Fermi model predictions and found to be in reasonable agreement. The value of the shell damping parameter has been extracted from the lowest-energy data in the case of Po,211210 and At,212211 nuclei close to the Z =82 and N =126 shell closure, and it was found to be consistent with the recent measurement in the vicinity of doubly magic 208Pb nucleus.
NASA Astrophysics Data System (ADS)
Nakano, K.; Su, D.; Zheng, R.; Cartmell, M.
2016-09-01
Vibrational energy harvesters are often excited by band-limited noise excitations. In this paper, the influence of the stiffness nonlinearity on the transduction of the energy harvester and the relative performance of linear, monostable hardening-type and bistable energy harvesters are compared and investigated. The performance is experimentally compared under band-limited noise excitations of different levels, bandwidths, and centre frequencies at first. The rms output power delivered to the same load resistance is measured and compared under the same excitation levels, which indicts the constant electrical damping level. It is shown that the effect of nonlinearities is strongly dependent on the excitation parameters. Under a moderate excitation level it is shown that the monostable hardening-type oscillator performs worse than its linear counterpart under band-limited excitation. However, the results also illustrate that for the most part of the frequency and bandwidth range considered, the bistable harvester can outperforms the linear variant but for around the peak output area. Moreover, the comparison is also numerically conducted with the consideration of the optimised electrical damping level and the displacement constraint of the device. General conclusions are drawn based on the experimental observations.
NASA Astrophysics Data System (ADS)
Roberts, Benjamin; Dzuba, Vladimir; Flambaum, Victor; Gribakin, Gleb; Pospelov, Maxim; Stadnik, Yevgeny
2017-01-01
Atoms can become ionised during the scattering of a slow, heavy particle off a bound electron. Such an interaction involving leptophilic WIMP dark matter is a potential explanation for the anomalous 9 sigma annual modulation in the DAMA direct detection experiment. We show that due to non-analytic, cusp-like behavior of Coulomb functions close to the nucleus leads to an effective atomic structure enhancement. Crucially, we also show that electron relativistic effects are important. With this in mind, we perform high-accuracy relativistic calculations of atomic ionisation. We scan the parameter space: the DM mass, the mediator mass, and the effective coupling strength, to determine if there is any region that could potentially explain the DAMA signal. While we find that the modulation fraction of all events with energy deposition above 2 keV in NaI can be quite significant, reaching 50%, the relevant parts of the parameter space are excluded by the XENON10 and XENON100 experiments.
Mezei, Pál D; Csonka, Gábor I; Ruzsinszky, Adrienn; Sun, Jianwei
2015-01-13
A correct description of the anion-π interaction is essential for the design of selective anion receptors and channels and important for advances in the field of supramolecular chemistry. However, it is challenging to do accurate, precise, and efficient calculations of this interaction, which are lacking in the literature. In this article, by testing sets of 20 binary anion-π complexes of fluoride, chloride, bromide, nitrate, or carbonate ions with hexafluorobenzene, 1,3,5-trifluorobenzene, 2,4,6-trifluoro-1,3,5-triazine, or 1,3,5-triazine and 30 ternary π-anion-π' sandwich complexes composed from the same monomers, we suggest domain-based local-pair natural orbital coupled cluster energies extrapolated to the complete basis-set limit as reference values. We give a detailed explanation of the origin of anion-π interactions, using the permanent quadrupole moments, static dipole polarizabilities, and electrostatic potential maps. We use symmetry-adapted perturbation theory (SAPT) to calculate the components of the anion-π interaction energies. We examine the performance of the direct random phase approximation (dRPA), the second-order screened exchange (SOSEX), local-pair natural-orbital (LPNO) coupled electron pair approximation (CEPA), and several dispersion-corrected density functionals (including generalized gradient approximation (GGA), meta-GGA, and double hybrid density functional). The LPNO-CEPA/1 results show the best agreement with the reference results. The dRPA method is only slightly less accurate and precise than the LPNO-CEPA/1, but it is considerably more efficient (6-17 times faster) for the binary complexes studied in this paper. For 30 ternary π-anion-π' sandwich complexes, we give dRPA interaction energies as reference values. The double hybrid functionals are much more efficient but less accurate and precise than dRPA. The dispersion-corrected double hybrid PWPB95-D3(BJ) and B2PLYP-D3(BJ) functionals perform better than the GGA and meta
NASA Astrophysics Data System (ADS)
Sun, Jianwei
The accuracy and computational efficiency of the widely used Kohn-Sham density functional theory (DFT) are limited by the approximation to its exchange-correlation energy Exc. The earliest local density approximation (LDA) overestimates the strengths of all bonds near equilibrium (even the vdW bonds). By adding the electron density gradient to model Exc, generalized gradient approximations (GGAs) generally soften the bonds to give robust and overall more accurate descriptions, except for the vdW interaction which is largely lost. Further improvement for covalent, ionic, and hydrogen bonds can be obtained by the computationally more expensive hybrid GGAs, which mix GGAs with the nonlocal exact exchange. Meta-GGAs are still semilocal in computation and thus efficient. Compared to GGAs, they add the kinetic energy density that enables them to recognize and accordingly treat different bonds, which no LDA or GGA can. We show here that the recently developed non-empirical strongly constrained and appropriately normed (SCAN) meta-GGA improves significantly over LDA and the standard Perdew-Burke-Ernzerhof GGA for geometries and energies of diversely-bonded materials (including covalent, metallic, ionic, hydrogen, and vdW bonds) at comparable efficiency. Often SCAN matches or improves upon the accuracy of a hybrid functional, at almost-GGA cost. This work has been supported by NSF under DMR-1305135 and CNS-09-58854, and by DOE BES EFRC CCDM under DE-SC0012575.
Accurate Cross-section Calculations for Low-Energy Electron-Atom Collisions
Zatsarinny, Oleg; Bartschat, Klaus
2011-05-11
We describe a recently developed fully relativistic B-spline R-matrix method for atomic structure as well as calculations for electron and photon collision with atoms and ions. The method is based on the solution of the many-electron Fock-Dirac equation and allows to employ non-orthogonal sets of atomic orbitals. A B-spline basis is used to generate both the target description and the R-matrix basis functions in the inner region. Employing B-splines of different orders for the large and small components prevents the appearance of spurious states in the spectrum of the Dirac equation. Using term-dependent and thus nonorthogonal sets of one-electron functions enables us to generate accurate and flexible representations of the target states and the scattering function. Our method is based upon the Dirac-Coulomb Hamiltonian and thus may be employed for any complex atom or ion, without the use of phenomenological core potentials. Example results from recent applications of the method for accurate calculations of low-energy electron scattering from noble gases are presented. In most cases we obtained a substantial improvement over results obtained in previous Breit-Pauli R-matrix calculations.
NASA Astrophysics Data System (ADS)
Sun, Jianwei; Remsing, Richard C.; Zhang, Yubo; Sun, Zhaoru; Ruzsinszky, Adrienn; Peng, Haowei; Yang, Zenghui; Paul, Arpita; Waghmare, Umesh; Wu, Xifan; Klein, Michael L.; Perdew, John P.
2016-09-01
One atom or molecule binds to another through various types of bond, the strengths of which range from several meV to several eV. Although some computational methods can provide accurate descriptions of all bond types, those methods are not efficient enough for many studies (for example, large systems, ab initio molecular dynamics and high-throughput searches for functional materials). Here, we show that the recently developed non-empirical strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA) within the density functional theory framework predicts accurate geometries and energies of diversely bonded molecules and materials (including covalent, metallic, ionic, hydrogen and van der Waals bonds). This represents a significant improvement at comparable efficiency over its predecessors, the GGAs that currently dominate materials computation. Often, SCAN matches or improves on the accuracy of a computationally expensive hybrid functional, at almost-GGA cost. SCAN is therefore expected to have a broad impact on chemistry and materials science.
Szewczyk, Sebastian; Giera, Wojciech; D'Haene, Sandrine; van Grondelle, Rienk; Gibasiewicz, Krzysztof
2017-05-01
Excitation energy transfer in monomeric and trimeric forms of photosystem I (PSI) from the cyanobacterium Synechocystis sp. PCC 6803 in solution or immobilized on FTO conducting glass was compared using time-resolved fluorescence. Deposition of PSI on glass preserves bi-exponential excitation decay of ~4-7 and ~21-25 ps lifetimes characteristic of PSI in solution. The faster phase was assigned in part to photochemical quenching (charge separation) of excited bulk chlorophylls and in part to energy transfer from bulk to low-energy (red) chlorophylls. The slower phase was assigned to photochemical quenching of the excitation equilibrated over bulk and red chlorophylls. The main differences between dissolved and immobilized PSI (iPSI) are: (1) the average excitation decay in iPSI is about 11 ps, which is faster by a few ps than for PSI in solution due to significantly faster excitation quenching of bulk chlorophylls by charge separation (~10 ps instead of ~15 ps) accompanied by slightly weaker coupling of bulk and red chlorophylls; (2) the number of red chlorophylls in monomeric PSI increases twice-from 3 in solution to 6 after immobilization-as a result of interaction with neighboring monomers and conducting glass; despite the increased number of red chlorophylls, the excitation decay accelerates in iPSI; (3) the number of red chlorophylls in trimeric PSI is 4 (per monomer) and remains unchanged after immobilization; (4) in all the samples under study, the free energy gap between mean red (emission at ~710 nm) and mean bulk (emission at ~686 nm) emitting states of chlorophylls was estimated at a similar level of 17-27 meV. All these observations indicate that despite slight modifications, dried PSI complexes adsorbed on the FTO surface remain fully functional in terms of excitation energy transfer and primary charge separation that is particularly important in the view of photovoltaic applications of this photosystem.
Numerical and experimental study of a compressive-mode energy harvester under random excitations
NASA Astrophysics Data System (ADS)
Li, H. T.; Yang, Z.; Zu, J.; Qin, W. Y.
2017-03-01
Piezoelectric energy harvester working in compressive mode has shown outstanding performance under harmonic excitation. However, it is still not clear if the compressive-mode energy harvester can sustain its superiority under random excitations. This paper presents a theoretical and experimental study on a nonlinear compressive-mode piezoelectric energy harvester under random excitations. First, a comprehensive distributed parameter electro-elastic model is developed using the extended Hamilton’s principle and the Euler–Bernoulli beam theory. The embedded force amplification effect of the flexural motion is analytically predicted. Then, the model is numerically solved under random excitations. Strong nonlinear responses was observed in both mechanical and electrical responses. Furthermore, a prototype was fabricated and tested. The experimental data show a good agreement with the model estimations under different level excitations and resistances. The results under random excitation demonstrate that the compressive-mode energy harvester significantly outperforms the state-of-the-art systems in terms of output voltage and normalized power density. If the optimal resistance is chosen in the harvesting circuit, the root mean square power of the prototype will reach three times higher than that of the counterparts.
High-energy electron-impact excitation process: The generalized oscillator strengths of helium
NASA Astrophysics Data System (ADS)
Han, Xiao-Ying; Li, Jia-Ming
2006-12-01
The high-energy electron impact excitation cross sections are directly proportional to the generalized oscillator strengths (GOSs) of the target (an atom or molecule). In the present work, the GOSs of helium from the ground state to nS1 , nP1 , nD1 (n→∞) and adjacent continuum excited states are calculated by a modified R -matrix code within the first Born approximation. In order to treat the bound-bound and bound-continuum transitions in a unified manner, the GOS density (GOSD) is defined based on the quantum defect theory. The GOSD surfaces of S1 , P1 , and D1 channels are calculated and tested stringently by the recent experiments. With the recommended GOSD surfaces with sufficient accuracy, the GOSDs (i.e., GOSs) from the ground state into all nS1 , nP1 , and nD1 excited states of helium can be obtained by interpolation. Thus, the high-energy electron impact excitation cross sections of all these excited states can be readily obtained. In addition to the high-energy electron impact excitation cross sections, a scheme to calculate the cross sections in the entire incident energy range is discussed.
Brandenburg, Jan Gerit; Caldeweyher, Eike; Grimme, Stefan
2016-06-21
We extend the recently introduced PBEh-3c global hybrid density functional [S. Grimme et al., J. Chem. Phys., 2015, 143, 054107] by a screened Fock exchange variant based on the Henderson-Janesko-Scuseria exchange hole model. While the excellent performance of the global hybrid is maintained for small covalently bound molecules, its performance for computed condensed phase mass densities is further improved. Most importantly, a speed up of 30 to 50% can be achieved and especially for small orbital energy gap cases, the method is numerically much more robust. The latter point is important for many applications, e.g., for metal-organic frameworks, organic semiconductors, or protein structures. This enables an accurate density functional based electronic structure calculation of a full DNA helix structure on a single core desktop computer which is presented as an example in addition to comprehensive benchmark results.
NASA Astrophysics Data System (ADS)
Zou, Wenlong; Cai, Zhijian; Zhou, Hongwu; Wu, Jianhong
2013-12-01
Raman spectroscopy is fast and nondestructive, and it is widely used in chemistry, biomedicine, food safety and other areas. However, Raman spectroscopy is often hampered by strong fluorescence background, especially in food additives detection and biomedicine researching. In this paper, one efficient technique was the multi-excitation Raman difference spectroscopy (MERDS) which incorporated a series of small wavelength-shift wavelengths as excitation sources. A modified multi-energy constrained iterative deconvolution (MMECID) algorithm was proposed to reconstruct the Raman Spectroscopy. Computer simulation and experiments both demonstrated that the Raman spectrum can be well reconstructed from large fluorescence background. The more excitation sources used, the better signal to noise ratio got. However, many excitation sources were equipped on the Raman spectrometer, which increased the complexity of the experimental system. Thus, a trade-off should be made between the number of excitation frequencies and experimental complexity.
Nganou, C; David, L; Adir, N; Mkandawire, M
2016-01-01
We applied a femtosecond flash method, using induced transient absorption changes, to obtain a time-resolved view of excitation energy transfer in intact phycobilisomes of Thermosynechococcus vulcanus at room temperature. Our measurement of an excitation energy transfer rate of 888 fs in phycobilisomes shows the existence of ultrafast kinetics along the phycocyanin rod subcomplex to the allophycocyanin core that is faster than expected for previous excitation energy transfer based on Förster theory in phycobilisomes. Allophycocyanin in the core further transfers energy to the terminal emitter(s) in 17 ps. In the phycobilisome, rod doublets composed of hexameric phycocyanin discs and internal linker proteins are arranged in a parallel fashion, facilitating direct rod-rod interactions. Excitonic splitting likely drives rod absorption at 635 nm as a result of strong coupling between β84 chromophores (20 ± 1 Å) in adjacent hexamers. In comparison to the absorbance of the phycobilisome antenna system of the cyanobacterium Acaryochloris marina, which possesses a single rod structure, the linkers in T. vulcanus rods induce a 17 nm red shift in the absorbance spectrum. Furthermore, the kinetics of 888 fs indicates that the presence of the linker protein induces ultrafast excitation energy transfer between phycocyanin and allophycocyanin inside the phycobilisome, which is faster than all previous excitation energy transfer in phycobilisome subunits or sub-complexes reported to date.
NASA Astrophysics Data System (ADS)
Mead, A. J.; Heymans, C.; Lombriser, L.; Peacock, J. A.; Steele, O. I.; Winther, H. A.
2016-06-01
We present an accurate non-linear matter power spectrum prediction scheme for a variety of extensions to the standard cosmological paradigm, which uses the tuned halo model previously developed in Mead et al. We consider dark energy models that are both minimally and non-minimally coupled, massive neutrinos and modified gravitational forces with chameleon and Vainshtein screening mechanisms. In all cases, we compare halo-model power spectra to measurements from high-resolution simulations. We show that the tuned halo-model method can predict the non-linear matter power spectrum measured from simulations of parametrized w(a) dark energy models at the few per cent level for k < 10 h Mpc-1, and we present theoretically motivated extensions to cover non-minimally coupled scalar fields, massive neutrinos and Vainshtein screened modified gravity models that result in few per cent accurate power spectra for k < 10 h Mpc-1. For chameleon screened models, we achieve only 10 per cent accuracy for the same range of scales. Finally, we use our halo model to investigate degeneracies between different extensions to the standard cosmological model, finding that the impact of baryonic feedback on the non-linear matter power spectrum can be considered independently of modified gravity or massive neutrino extensions. In contrast, considering the impact of modified gravity and massive neutrinos independently results in biased estimates of power at the level of 5 per cent at scales k > 0.5 h Mpc-1. An updated version of our publicly available HMCODE can be found at https://github.com/alexander-mead/hmcode.
Do, T. P. T.; Lopes, M. C. A.; Konovalov, D. A.; White, R. D.; Brunger, M. J. E-mail: darryl.jones@flinders.edu.au; Jones, D. B. E-mail: darryl.jones@flinders.edu.au
2015-03-28
We report differential cross sections (DCSs) for electron-impact vibrational-excitation of tetrahydrofuran, at intermediate incident electron energies (15-50 eV) and over the 10°-90° scattered electron angular range. These measurements extend the available DCS data for vibrational excitation for this species, which have previously been obtained at lower incident electron energies (≤20 eV). Where possible, our data are compared to the earlier measurements in the overlapping energy ranges. Here, quite good agreement was generally observed where the measurements overlapped.
Nogami, Keisuke; Sakai, Yasuhiro; Mineta, Shota; Kato, Daiji; Murakami, Izumi; Sakaue, Hiroyuki A.; Kenmotsu, Takahiro; Furuya, Kenji; Motohashi, Kenji
2015-11-15
Visible emission spectra were acquired from neutral atoms sputtered by 35–60 keV Kr{sup +} ions from a polycrystalline tungsten surface. Mean velocities of excited tungsten atoms in seven different 6p states were also obtained via the dependence of photon intensities on the distance from the surface. The average velocities parallel to the surface normal varied by factors of 2–4 for atoms in the different 6p energy levels. However, they were almost independent of the incident ion kinetic energy. The 6p-level energy dependence indicated that the velocities of the excited atoms were determined by inelastic processes that involve resonant charge exchange.
NASA Astrophysics Data System (ADS)
Paşca, H.; Andreev, A. V.; Adamian, G. G.; Antonenko, N. V.
2016-12-01
Using the improved scission-point model, the isotopic trends of the charge distribution of fission fragments are studied in induced fission of even-even Th isotopes. The calculated results are in good agreement with available experimental data. With increasing neutron number the transition from symmetric to asymmetric fission mode is shown to be related to the change of the potential energy surface. The change of the shape of mass distribution with increasing excitation energy is discussed for fissioning ATh nuclei. At high excitation energies, there are unexpected large asymmetric modes in the fission of neutron-deficient Th isotopes considered.
On the spin excitation energy of the nucleon in the Skyrme model
NASA Astrophysics Data System (ADS)
Adam, C.; Sanchez-Guillen, J.; Wereszczynski, A.
2016-11-01
In the Skyrme model of nucleons and nuclei, the spin excitation energy of the nucleon is traditionally calculated by a fit of the rigid rotor quantization of spin/isospin of the fundamental Skyrmion (the hedgehog) to the masses of the nucleon and the Delta resonance. The resulting, quite large spin excitation energy of the nucleon of about 73MeV is, however, rather difficult to reconcile with the small binding energies of physical nuclei, among other problems. Here, we argue that a more reliable interval of values for the spin excitation energy of the nucleon, compatible with many physical constraints is between 15MeV and 30MeV. The fit of the rigid rotor to the Delta, on the other hand, is problematic in any case, because it implies the use of a nonrelativistic method for a highly relativistic system.
Effects of introducing nonlinear components for a random excited hybrid energy harvester
NASA Astrophysics Data System (ADS)
Zhou, Xiaoya; Gao, Shiqiao; Liu, Haipeng; Guan, Yanwei
2017-01-01
This work is mainly devoted to discussing the effects of introducing nonlinear components for a hybrid energy harvester under random excitation. For two different types of nonlinear hybrid energy harvesters subjected to random excitation, the analytical solutions of the mean output power, voltage and current are derived from Fokker-Planck (FP) equations. Monte Carlo simulation exhibits qualitative agreement with FP theory, showing that load values and excitation’s spectral density have an effect on the total mean output power, piezoelectric (PE) power and electromagnetic power. Nonlinear components affect output characteristics only when the PE capacitance of the hybrid energy harvester is non-negligible. Besides, it is also demonstrated that for this type of nonlinear hybrid energy harvesters under random excitation, introducing nonlinear components can improve output performances effectively.
Electron energy-loss spectroscopy of excited states of the pyridine molecules
NASA Astrophysics Data System (ADS)
Linert, Ireneusz; Zubek, Mariusz
2016-04-01
Electron energy-loss spectra of the pyridine, C5H5N, molecules in the gas phase have been measured to investigate electronic excitation in the energy range 3.5-10 eV. The applied wide range of residual electron energy and the scattering angle range from 10° to 180° enabled to differentiate between optically-allowed and -forbidden transitions. These measurements have allowed vertical excitation energies of the triplet excited states of pyridine to be determined and tentative assignments of these states to be proposed. Some of these states have not been identified in the previous works. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.
Low-energy electron elastic scattering cross sections for excited Au and Pt atoms
NASA Astrophysics Data System (ADS)
Felfli, Zineb; Eure, Amanda R.; Msezane, Alfred Z.; Sokolovski, Dmitri
2010-05-01
Electron elastic total cross sections (TCSs) and differential cross sections (DCSs) in both impact energy and scattering angle for the excited Au and Pt atoms are calculated in the electron impact energy range 0 ⩽ E ⩽ 4.0 eV. The cross sections are found to be characterized by very sharp long-lived resonances whose positions are identified with the binding energies of the excited anions formed during the collisions. The recent novel Regge-pole methodology wherein is embedded through the Mulholland formula the electron-electron correlations is used together with a Thomas-Fermi type potential incorporating the crucial core-polarization interaction for the calculations of the TCSs. The DCSs are evaluated using a partial wave expansion. The Ramsauer-Townsend minima, the shape resonances and the binding energies of the excited Au - and Pt - anions are extracted from the cross sections, while the critical minima are determined from the DCSs.
Finite strain effects in piezoelectric energy harvesters under direct and parametric excitations
NASA Astrophysics Data System (ADS)
Mam, Koliann; Peigney, Michaël; Siegert, Dominique
2017-02-01
This paper addresses the dynamic behavior of piezoelectric cantilevers under base excitations. Such devices are frequently used for applications in energy harvesting. An Euler-Bernoulli model that accounts for large-deflection effects and piezoelectric nonlinearities is proposed. Closed-form expressions of the frequency response are derived, both for direct excitation (i.e. with a base acceleration transverse to the axis of the cantilever) and parametric excitation (i.e. with a base acceleration along the axis of the cantilever). Experimental results are reported and used for assessing the validity of the proposed model. Building on the model presented, some critical issues related to energy-harvesting are investigated, such as the influence of nonlinearities on the optimal load resistance, the limits of validity of linear models, and hysteresis effects in the electrical power. The efficiency of direct and parametric excitation is also compared in detail.
Generating Excitement: Build Your Own Generator to Study the Transfer of Energy
ERIC Educational Resources Information Center
Fletcher, Kurt; Rommel-Esham, Katie; Farthing, Dori; Sheldon, Amy
2011-01-01
The transfer of energy from one form to another can be difficult to understand. The electrical energy that turns on a lamp may come from the burning of coal, water falling at a hydroelectric plant, nuclear reactions, or gusts of wind caused by the uneven heating of the Earth. The authors have developed and tested an exciting hands-on activity to…
Numerical and experimental comparison of the energy transfer in a parametrically excited system
NASA Astrophysics Data System (ADS)
Fichtinger, Andreas; Ecker, Horst
2016-09-01
This study is based on experimental results obtained from a test rig for a 2-DOF vibrational system. The main feature of this test rig is an electromechanical actuator which enables the variation of a mechanical stiffness parameter. The vibrational system is excited by this device, resulting in a parametrically excited system. In this study, the test rig is operated such that an initial deflection is applied to the masses, but no external excitation acts on the system. The actuator coils are driven by a current following a harmonic function defined by amplitude and frequency. The latter defines the parametric excitation frequency (PEF). When the mechanical system performs free vibrations, the parametric excitation may initiate an energy transfer between the two vibrational modes of the system. This transfer depends primarily on the PEF. For certain values of the PEF only one of the vibrational modes is affected. At other frequencies both modes are influenced and a continuous intermodal energy transfer is observed. A numerical model for the test rig was established and allows a comparison of experimental and numerical results. The total system energy as well as the modal energies are calculated from the measured and from the simulated signals. Interesting experimental observations are reported concerning the transfer of energy, and are in good agreement with simulated results.
Excited-State Energies and Electronic Couplings of DNA Base Dimers
Kozak, Christopher R.; Kistler, Kurt A.; Lu, Zhen; Matsika, Spiridoula
2010-02-04
The singlet excited electronic states of two π-stacked thymine molecules and their splittings due to electronic coupling have been investigated with a variety of computational methods. Focus has been given on the effect of intermolecular distance on these energies and couplings. Single-reference methods, CIS, CIS(2), EOMCCSD, TDDFT, and the multireference method CASSCF, have been used, and their performance has been compared. It is found that the excited-state energies are very sensitive to the applied method but the couplings are not as sensitive. Inclusion of diffuse functions in the basis set also affects the excitation energies significantly but not the couplings. TDDFT is inadequate in describing the states and their coupling, while CIS(2) gives results very similar to EOM-CCSD. Excited states of cytosine and adenine π-stacked dimers were also obtained and compared with those of thymine dimers to gain a more general picture of excited states in π-stacked DNA base dimers. The coupling is very sensitive to the relative position and orientation of the bases, indicating great variation in the degree of delocalization of the excited states between stacked bases in natural DNA as it fluctuates.
NASA Astrophysics Data System (ADS)
Komsa, Hannu-Pekka; Berseneva, Natalia; Krasheninnikov, Arkady V.; Nieminen, Risto M.
2014-07-01
Impurities and defects frequently govern materials properties, with the most prominent example being the doping of bulk semiconductors where a minute amount of foreign atoms can be responsible for the operation of the electronic devices. Several computational schemes based on a supercell approach have been developed to get insights into types and equilibrium concentrations of point defects, which successfully work in bulk materials. Here, we show that many of these schemes cannot directly be applied to two-dimensional (2D) systems, as formation energies of charged point defects are dominated by large spurious electrostatic interactions between defects in inhomogeneous environments. We suggest two approaches that solve this problem and give accurate formation energies of charged defects in 2D systems in the dilute limit. Our methods, which are applicable to all kinds of charged defects in any 2D system, are benchmarked for impurities in technologically important h-BN and MoS2 2D materials, and they are found to perform equally well for substitutional and adatom impurities.
Dupuy, Nicolas; Bouaouli, Samira; Mauri, Francesco; Sorella, Sandro; Casula, Michele
2015-06-07
We study the ionization energy, electron affinity, and the π → π(∗) ((1)La) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO → LUMO one, which underlies the (1)La excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in π-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral (1)La excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account.
Dupuy, Nicolas; Bouaouli, Samira; Mauri, Francesco Casula, Michele; Sorella, Sandro
2015-06-07
We study the ionization energy, electron affinity, and the π → π{sup ∗} ({sup 1}L{sub a}) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO → LUMO one, which underlies the {sup 1}L{sub a} excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in π-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral {sup 1}L{sub a} excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account.
Wang, Zhifan; Tu, Zheyan; Wang, Fan
2014-12-09
Excitation energies of closed-shell systems based on the equation-of-motion (EOM) coupled-cluster theory at the singles and doubles (CCSD) level with spin-orbit coupling (SOC) included in the post-Hartree-Fock treatment are implemented in the present work. SOC can be included in both the CC and EOM steps (EOM-SOC-CCSD) or only in the EOM part (SOC-EOM-CCSD). The latter approach is an economical way to account for SOC effects, but excitation energies with this approach are not size-intensive. When the unlinked term in the latter approach is neglected (cSOC-EOM-CCSD), size-intensive excitation energies can be obtained. Time-reversal symmetry and spatial symmetry are exploited to reduce the computational effort. Imposing time-reversal symmetry results in a real matrix representation for the similarity-transformed Hamiltonian, which facilitates the requirement of time-reversal symmetry for new trial vectors in Davidson's algorithm. Results on some closed-shell atoms and molecules containing heavy elements show that EOM-SOC-CCSD can provide excitation energies and spin-orbit splittings with reasonable accuracy. On the other hand, the SOC-EOM-CCSD approach is able to afford accurate estimates of SOC effects for valence electrons of systems containing elements up to the fifth row, while cSOC-EOM-CCSD is less accurate for spin-orbit splittings of transitions involving p1/2 spinors, even for Kr.
Tensor numerical methods in quantum chemistry: from Hartree-Fock to excitation energies.
Khoromskaia, Venera; Khoromskij, Boris N
2015-12-21
We resume the recent successes of the grid-based tensor numerical methods and discuss their prospects in real-space electronic structure calculations. These methods, based on the low-rank representation of the multidimensional functions and integral operators, first appeared as an accurate tensor calculus for the 3D Hartree potential using 1D complexity operations, and have evolved to entirely grid-based tensor-structured 3D Hartree-Fock eigenvalue solver. It benefits from tensor calculation of the core Hamiltonian and two-electron integrals (TEI) in O(n log n) complexity using the rank-structured approximation of basis functions, electron densities and convolution integral operators all represented on 3D n × n × n Cartesian grids. The algorithm for calculating TEI tensor in a form of the Cholesky decomposition is based on multiple factorizations using algebraic 1D "density fitting" scheme, which yield an almost irreducible number of product basis functions involved in the 3D convolution integrals, depending on a threshold ε > 0. The basis functions are not restricted to separable Gaussians, since the analytical integration is substituted by high-precision tensor-structured numerical quadratures. The tensor approaches to post-Hartree-Fock calculations for the MP2 energy correction and for the Bethe-Salpeter excitation energies, based on using low-rank factorizations and the reduced basis method, were recently introduced. Another direction is towards the tensor-based Hartree-Fock numerical scheme for finite lattices, where one of the numerical challenges is the summation of electrostatic potentials of a large number of nuclei. The 3D grid-based tensor method for calculation of a potential sum on a L × L × L lattice manifests the linear in L computational work, O(L), instead of the usual O(L(3) log L) scaling by the Ewald-type approaches.
Relativistic Energy Density Functionals: Exotic modes of excitation
Vretenar, D.; Paar, N.; Marketin, T.
2008-11-11
The framework of relativistic energy density functionals has been applied to the description of a variety of nuclear structure phenomena, not only in spherical and deformed nuclei along the valley of {beta}-stability, but also in exotic systems with extreme isospin values and close to the particle drip-lines. Dynamical aspects of exotic nuclear structure have been investigated with the relativistic quasiparticle random-phase approximation. We present results for the evolution of low-lying dipole (pygmy) strength in neutron-rich nuclei, and charged-current neutrino-nucleus cross sections.
NASA Astrophysics Data System (ADS)
Pfeiffer, Florian; Rauhut, Guntram; Feller, David; Peterson, Kirk A.
2013-01-01
Anharmonic zero point vibrational energies (ZPVEs) calculated using both conventional CCSD(T) and MP2 in combination with vibrational second-order perturbation theory (VPT2) are compared to explicitly correlated CCSD(T)-F12 and MP2-F12 results that utilize vibrational configuration interaction (VCI) theory for 26 molecules of varying size. Sequences of correlation consistent basis sets are used throughout. It is found that the explicitly correlated methods yield results close to the basis set limit even with double-zeta quality basis sets. In particular, the anharmonic contributions to the ZPVE are accurately recovered at just the MP2 (or MP2-F12) level of theory. Somewhat surprisingly, the best vibrational CI results agreed with the VPT2 values with a mean unsigned deviation of just 0.09 kJ/mol and a standard deviation of just 0.11 kJ/mol. The largest difference was observed for C4H4O (0.34 kJ/mol). A simplified version of the vibrational CI procedure that limited the modal expansion to at most 2-mode coupling yielded anharmonic corrections generally within about 0.1 kJ/mol of the full 3- or 4-mode results, except in the cases of C3H8 and C4H4O where the contributions were underestimated by 1.3 and 0.8 kJ/mol, respectively (34% and 40%, respectively). For the molecules considered in this work, accurate anharmonic ZPVEs are most economically obtained by combining CCSD(T)-F12a/cc-pVDZ-F12 harmonic frequencies with either MP2/aug-cc-pVTZ/VPT2 or MP2-F12/cc-pVDZ-F12/VCI anharmonic corrections.
No Galaxy Left Behind: Accurate Measurements with the Faintest Objects in the Dark Energy Survey
Suchyta, E.
2016-01-27
Accurate statistical measurement with large imaging surveys has traditionally required throwing away a sizable fraction of the data. This is because most measurements have have relied on selecting nearly complete samples, where variations in the composition of the galaxy population with seeing, depth, or other survey characteristics are small. We introduce a new measurement method that aims to minimize this wastage, allowing precision measurement for any class of stars or galaxies detectable in an imaging survey. We have implemented our proposal in Balrog, a software package which embeds fake objects in real imaging in order to accurately characterize measurement biases. We also demonstrate this technique with an angular clustering measurement using Dark Energy Survey (DES) data. We first show that recovery of our injected galaxies depends on a wide variety of survey characteristics in the same way as the real data. We then construct a flux-limited sample of the faintest galaxies in DES, chosen specifically for their sensitivity to depth and seeing variations. Using the synthetic galaxies as randoms in the standard LandySzalay correlation function estimator suppresses the effects of variable survey selection by at least two orders of magnitude. Now our measured angular clustering is found to be in excellent agreement with that of a matched sample drawn from much deeper, higherresolution space-based COSMOS imaging; over angular scales of 0.004° < θ < 0.2 ° , we find a best-fit scaling amplitude between the DES and COSMOS measurements of 1.00 ± 0.09. We expect this methodology to be broadly useful for extending the statistical reach of measurements in a wide variety of coming imaging surveys.
No galaxy left behind: accurate measurements with the faintest objects in the Dark Energy Survey
NASA Astrophysics Data System (ADS)
Suchyta, E.; Huff, E. M.; Aleksić, J.; Melchior, P.; Jouvel, S.; MacCrann, N.; Ross, A. J.; Crocce, M.; Gaztanaga, E.; Honscheid, K.; Leistedt, B.; Peiris, H. V.; Rykoff, E. S.; Sheldon, E.; Abbott, T.; Abdalla, F. B.; Allam, S.; Banerji, M.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Burke, D. L.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Eifler, T. F.; Estrada, J.; Evrard, A. E.; Flaugher, B.; Fosalba, P.; Frieman, J.; Gerdes, D. W.; Gruen, D.; Gruendl, R. A.; James, D. J.; Jarvis, M.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Lima, M.; Maia, M. A. G.; March, M.; Marshall, J. L.; Miller, C. J.; Miquel, R.; Neilsen, E.; Nichol, R. C.; Nord, B.; Ogando, R.; Percival, W. J.; Reil, K.; Roodman, A.; Sako, M.; Sanchez, E.; Scarpine, V.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, D.; Vikram, V.; Walker, A. R.; Wechsler, R. H.; Zhang, Y.; DES Collaboration
2016-03-01
Accurate statistical measurement with large imaging surveys has traditionally required throwing away a sizable fraction of the data. This is because most measurements have relied on selecting nearly complete samples, where variations in the composition of the galaxy population with seeing, depth, or other survey characteristics are small. We introduce a new measurement method that aims to minimize this wastage, allowing precision measurement for any class of detectable stars or galaxies. We have implemented our proposal in BALROG, software which embeds fake objects in real imaging to accurately characterize measurement biases. We demonstrate this technique with an angular clustering measurement using Dark Energy Survey (DES) data. We first show that recovery of our injected galaxies depends on a variety of survey characteristics in the same way as the real data. We then construct a flux-limited sample of the faintest galaxies in DES, chosen specifically for their sensitivity to depth and seeing variations. Using the synthetic galaxies as randoms in the Landy-Szalay estimator suppresses the effects of variable survey selection by at least two orders of magnitude. With this correction, our measured angular clustering is found to be in excellent agreement with that of a matched sample from much deeper, higher resolution space-based Cosmological Evolution Survey (COSMOS) imaging; over angular scales of 0.004° < θ < 0.2°, we find a best-fitting scaling amplitude between the DES and COSMOS measurements of 1.00 ± 0.09. We expect this methodology to be broadly useful for extending measurements' statistical reach in a variety of upcoming imaging surveys.
No Galaxy Left Behind: Accurate Measurements with the Faintest Objects in the Dark Energy Survey
Suchyta, E.
2016-01-27
Accurate statistical measurement with large imaging surveys has traditionally required throwing away a sizable fraction of the data. This is because most measurements have have relied on selecting nearly complete samples, where variations in the composition of the galaxy population with seeing, depth, or other survey characteristics are small. We introduce a new measurement method that aims to minimize this wastage, allowing precision measurement for any class of stars or galaxies detectable in an imaging survey. We have implemented our proposal in Balrog, a software package which embeds fake objects in real imaging in order to accurately characterize measurement biases.more » We also demonstrate this technique with an angular clustering measurement using Dark Energy Survey (DES) data. We first show that recovery of our injected galaxies depends on a wide variety of survey characteristics in the same way as the real data. We then construct a flux-limited sample of the faintest galaxies in DES, chosen specifically for their sensitivity to depth and seeing variations. Using the synthetic galaxies as randoms in the standard LandySzalay correlation function estimator suppresses the effects of variable survey selection by at least two orders of magnitude. Now our measured angular clustering is found to be in excellent agreement with that of a matched sample drawn from much deeper, higherresolution space-based COSMOS imaging; over angular scales of 0.004° < θ < 0.2 ° , we find a best-fit scaling amplitude between the DES and COSMOS measurements of 1.00 ± 0.09. We expect this methodology to be broadly useful for extending the statistical reach of measurements in a wide variety of coming imaging surveys.« less
Time-resolved observation of interatomic excitation-energy transfer in argon dimers.
Mizuno, Tomoya; Cörlin, Philipp; Miteva, Tsveta; Gokhberg, Kirill; Kuleff, Alexander; Cederbaum, Lorenz S; Pfeifer, Thomas; Fischer, Andreas; Moshammer, Robert
2017-03-14
The ultrafast transfer of excitation energy from one atom to its neighbor is observed in singly charged argon dimers in a time-resolved extreme ultraviolet (XUV)-pump IR-probe experiment. In the pump step, bound 3s-hole states in the dimer are populated by single XUV-photon ionization. The excitation-energy transfer at avoided crossings of the potential-energy curves leads to dissociation of the dimer, which is experimentally observed by further ionization with a time-delayed IR-probe pulse. From the measured pump-probe delay-dependent kinetic-energy release of coincident Ar(+) + Ar(+) ions, we conclude that the transfer of energy occurs on a time scale of about 800fs. This mechanism represents a fast relaxation process below the energy threshold for interatomic Coulombic decay.
Selective excitation, relaxation, and energy channeling in molecular systems
Rhodes, W.C.
1993-08-01
Research involves theoretical studies of response, relaxation, and correlated motion in time-dependent behavior of large molecular systems ranging from polyatomic molecules to protein molecules in their natural environment. Underlying theme is subsystem modulation dynamics. Main idea is that quantum mechanical correlations between components of a system develop with time, playing a major role in determining the balance between coherent and dissipative forces. Central theme is interplay of coherence and dissipation in determining the nature of dynamic structuring and energy flow in molecular transformation mechanisms. Subsystem equations of motion are being developed to show how nonlinear, dissipative dynamics of a particular subsystem arise from correlated interactions with the rest of the system (substituent groups, solvent, lattice modes, etc.); one consequence is resonance structures and networks. Quantum dynamics and thermodynamics are being applied to understand control and energy transfer mechanisms in biological functions of protein molecules; these mechanisms are both global and local. Besides the above theory, the research deals with phenomenological aspects of molecular systems.
Nagesh, Jayashree; Frisch, Michael J; Brumer, Paul; Izmaylov, Artur F
2016-12-28
We extend the localized operator partitioning method (LOPM) [J. Nagesh, A. F. Izmaylov, and P. Brumer, J. Chem. Phys. 142, 084114 (2015)] to the time-dependent density functional theory framework to partition molecular electronic energies of excited states in a rigorous manner. A molecular fragment is defined as a collection of atoms using Becke's atomic partitioning. A numerically efficient scheme for evaluating the fragment excitation energy is derived employing a resolution of the identity to preserve standard one- and two-electron integrals in the final expressions. The utility of this partitioning approach is demonstrated by examining several excited states of two bichromophoric compounds: 9-((1- naphthyl)- methyl)- anthracene and 4-((2- naphthyl)- methyl)- benzaldehyde. The LOPM is found to provide nontrivial insights into the nature of electronic energy localization that is not accessible using a simple density difference analysis.
NASA Astrophysics Data System (ADS)
González Ureña, A.; Telle, H. H.; Tornero, J.
2013-01-01
A simple, inelastic electron-scattering dynamical model is presented to account for vibrational excitation in molecular adsorbates. The basic two ingredients of the theoretical model are: (i) the conservation of the total angular momentum, and (ii) the requirement of a critical time to allow for the intra-molecular energy re-arrangement of the transient negative-ion complex. The model is applied to the vibrational excitation dynamics of molecules chemisorbed at sub-monolayer conditions on ordered metal surfaces. This was exemplified for Acrylonitrile adsorbed on Cu(1 0 0), whose vibrational excitation was studied via energy loss spectra of low-energy two-photon photoemission (2PPE) electrons, and for ammonia (NH3 and ND3) adsorbed on Cu(1 0 0), being probed in a STM experiment. Fits of the model to the data allowed for deducing the energy threshold of the vibrational excitation of the Cdbnd C and Ctbnd N bonds of the ACN adsorbate molecules, and the threshold for the symmetric ν1-stretch mode excitation of adsorbed NH3/ND3. Also, information about the temporal dynamics underlying the inelastic electron scattering was gained.
Triplet-state energies and substituent effects of excited aroyl compounds in the gas phase.
Lin, Z P; Aue, W A
2000-01-01
Triplet-state energy values obtained from the gas phase are still scarce. In this study, the triplet-state energies of 58 aroyl compounds, introduced as gas chromatographic peaks at atmospheric pressure and typically 473 K, have been determined from the 0-0 bands of their n --> pi* type phosphorescence spectra in excited nitrogen. Correlations of those gas-phase triplet-state energies with Hammett constants could be observed for substituted acetophenones, benzaldehydes and benzophenones.
Blancafort, Lluis; Gatti, Fabien; Meyer, Hans-Dieter
2011-10-07
The double bond photoisomerization of fulvene has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method. Fulvene is a test case to develop optical control strategies based on the knowledge of the excited state decay mechanism. The decay takes place on a time scale of several hundred femtoseconds, and the potential energy surface is centered around a conical intersection seam between the ground and excited state. The competition between unreactive decay and photoisomerization depends on the region of the seam accessed during the decay. The dynamics are carried out on a four-dimensional model surface, parametrized from complete active space self-consistent field calculations, that captures the main features of the seam (energy and locus of the seam and associated branching space vectors). Wave packet propagations initiated by single laser pulses of 5-25 fs duration and 1.85-4 eV excitation energy show the principal characteristics of the first 150 fs of the photodynamics. Initially, the excitation energy is transferred to a bond stretching mode that leads the wave packet to the seam, inducing the regeneration of the reactant. The photoisomerization starts after the vibrational energy has flowed from the bond stretching to the torsional mode. In our propagations, intramolecular energy redistribution (IVR) is accelerated for higher excess energies along the bond stretch mode. Thus, the competition between unreactive decay and isomerization depends on the rate of IVR between the bond stretch and torsion coordinates, which in turn depends on the excitation energy. These results set the ground for the development of future optical control strategies.
Low-energy electron attachment and detachment in vibrationally excited oxygen
NASA Astrophysics Data System (ADS)
Aleksandrov, N. L.; Anokhin, E. M.
2009-11-01
Three-body electron attachment to O2 molecules and electron detachment from O_{2}^{-} ions have been theoretically studied in vibrationally excited oxygen and O2-containing mixtures. Assuming that electron attachment and detachment proceed via the formation of vibrationally excited temporary O_{2}^{-} ions, the rates of these processes were determined on the basis of the statistical approach for the vibrational transfer and relaxation in collisions between O_{2}^{-} ions and O2 molecules. The calculated attachment and detachment rate constants turned out to agree well with available measurements in unexcited oxygen. This method was extended to calculate attachment and detachment rates in vibrationally excited oxygen. It was shown that the effect of vibrational excitation on electron detachment is profound, whereas attachment of low-energy electrons to vibrationally excited O2 is inefficient. The calculated vibrational distribution of stable O_{2}^{-} ions turned out to be non-equilibrium in an excited gas and the effective vibrational temperature of the ions was much lower than the vibrational temperature of molecules. An analytical method was suggested to determine this distribution and the effective vibrational temperature. The calculated rate constants were used to simulate the formation and decay of an electron-beam-generated plasma in N2 : O2 mixtures at elevated vibrational temperatures. The calculations showed that vibrational excitation of molecules leads to orders of magnitude increase in the plasma density and in the plasma lifetime, in agreement with available observations.
Optimum forward scattering zone for intermediate-energy Coulomb excitation experiments
NASA Astrophysics Data System (ADS)
Kumar, Rajiv; Singh, Pardeep; Kharab, Rajesh
2015-08-01
Here we present a comparative study of various schemes commonly used for the determination of the safe minimum value of the impact parameter, which decides the maximum value of forward laboratory scattering angle, in intermediate-energy Coulomb excitation experiments. We have found that these are special cases of the recently proposed parameterization scheme in Kumar Rajiv et al., Phys. Rev. C, 81 (2010) 037602. The scheme may be used to demarcate the absorption-free as well as no-flux loss zone for intermediate-energy Coulomb excitation experiments.
Variety in excitation energy transfer processes from phycobilisomes to photosystems I and II.
Ueno, Yoshifumi; Aikawa, Shimpei; Niwa, Kyosuke; Abe, Tomoko; Murakami, Akio; Kondo, Akihiko; Akimoto, Seiji
2017-02-09
The light-harvesting antennas of oxygenic photosynthetic organisms capture light energy and transfer it to the reaction centers of their photosystems. The light-harvesting antennas of cyanobacteria and red algae, called phycobilisomes (PBSs), supply light energy to both photosystem I (PSI) and photosystem II (PSII). However, the excitation energy transfer processes from PBS to PSI and PSII are not understood in detail. In the present study, the energy transfer processes from PBS to PSs in various cyanobacteria and red algae were examined in vivo by selectively exciting their PSs or PBSs, and measuring the resulting picosecond to nanosecond time-resolved fluorescences. By observing the delayed fluorescence spectrum of PBS-selective excitation in Arthrospira platensis, we demonstrated that energy transfer from PBS to PSI via PSII (PBS→PSII→PSI transfer) occurs even for PSI trimers. The contribution of PBS→PSII→PSI transfer was species dependent, being largest in the wild-type of red alga Pyropia yezoensis (formerly Porphyra yezoensis) and smallest in Synechococcus sp. PCC 7002. Comparing the time-resolved fluorescence after PSs- and PBS-selective excitation, we revealed that light energy flows from CP43 to CP47 by energy transfer between the neighboring PSII monomers in PBS-PSII supercomplexes. We also suggest two pathways of energy transfer: direct energy transfer from PBS to PSI (PBS→PSI transfer) and indirect transfer through PSII (PBS→PSII→PSI transfer). We also infer that PBS→PSI transfer conveys light energy to a lower-energy red chlorophyll than PBS→PSII→PSI transfer.
Bulut, Niyazi; Kłos, Jacek; Alexander, Millard H
2012-03-14
We present converged exact quantum wave packet calculations of reaction probabilities, integral cross sections, and thermal rate coefficients for the title reaction. Calculations have been carried out on the ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged wave packet reaction probabilities at selected values of the total angular momentum up to a partial wave of J = 140 with the HCl reagent initially selected in the v = 0, j = 0-16 rovibrational states have been obtained for the collision energy range from threshold up to 0.8 eV. The present calculations confirm an important enhancement of reactivity with rotational excitation of the HCl molecule. First, accurate integral cross sections and rate constants have been calculated and compared with the available experimental data.
NASA Astrophysics Data System (ADS)
Clary, David C.; Meijer, Anthony J. H. M.
2002-06-01
Quantum dynamical calculations have been carried out on the excitation of the torsional vibrations of a protein by collision with a solvent molecule. This energy transfer process represents the first step in the unfolding of the protein. The method developed for this purpose is the torsional close coupling, infinite order sudden approximation. Both time-independent and time dependent methods are used to solve the scattering problem and individual excitation of all the torsional modes of the protein is treated. The method is applied to the excitation of the HIV protein gp41 colliding with a water molecule. This protein has 1101 atoms, 56 amino acids, and 452 torsional modes. A major mode-selective effect is found in the computations: it is much easier to excite backbone torsions than sidechain torsions in the protein. In addition, resonances arise in the collisional process and these complexes involve temporary trapping of the water molecule inside the pockets of the protein.
Synthesis of silver nanorods by low energy excitation of spherical plasmonic seeds.
Zhang, Jian; Langille, Mark R; Mirkin, Chad A
2011-06-08
Plasmon excitation of Ag seed particles with 600-750 nm light in the presence of Ag(+) and trisodium citrate was used to synthesize penta-twinned nanorods. Importantly, the excitation wavelength can be used to control the reaction rate and, consequently, the aspect ratio of the nanorods. When the excitation wavelength is red-shifted from the surface plasmon resonance of the spherical seed particles, the rate of Ag(+) reduction becomes slower and more kinetically controlled. Such conditions favor the deposition of silver onto the tips of the growing nanorods as compared to their sides, resulting in the generation of higher aspect ratio rods. However, control experiments reveal that there is only a range of low energy excitation wavelengths (between 600 and 750 nm) that yields monodisperse nanorods. This study further highlights the utility of using wavelength to control the size and shape of growing nanoparticles using plasmon-mediated methods.
Double-well potential energy curve of cadmium-krypton molecule in the B1(5(3)P1) excited state.
Lukomski, M; Koperski, J; Czajkowski, M
2002-06-01
The real shape of a double-well B1(5(3)P1)-state potential in CdKr van der Waals molecule was reconstructed applying both the experimental data, using a Birge-Sponer method-based analysis of the B1 <-- X0+(5(1)S0) transition in excitation spectrum, and theoretical result of recent ab initio calculation. An inverse perturbation approach method was used for defining an accurate B1-state potential energy curve.
High spin spectroscopy near the N=Z line: Channel selection and excitation energy systematics
Svensson, C.E.; Cameron, J.A.; Flibotte, S.
1996-12-31
The total {gamma}-ray and charged-particle energies emitted in fusion-evaporation reactions leading to N=Z compound systems in the A = 50-70 mass region have been measured with the 8{pi} {gamma}-ray spectrometer and the miniball charged-particle detector array. A new method of channel selection has been developed which combines particle identification with these total energy measurements and greatly improves upon the selectivity possible with particle detection alone. In addition, the event by event measurement of total {gamma}-ray energies using the BGO ball of the 8{pi} spectrometer has allowed a determination of excitation energies following particle evaporation for a large number of channels in several different reactions. The new channel selection procedure and excitation energy systematics are illustrated with data from the reaction of {sup 24}Mg on {sup 40}Ca at E{sub lab} = 80MeV.
NASA Astrophysics Data System (ADS)
Froese, Robert D. J.; Morokuma, Keiji
1996-12-01
The recently proposed integrated MO + MO (IMOMO) and MO + MM (IMOMM) methods have been applied to excited states of large molecules, i.e., the adiabatic triplet excitation energies of cyclic alkenes and enones. The IMOMO methods with G2MS as High level and HF or MP2 as Low level agree well with pure MO benchmarks and experiments. The substituent shifts have been discussed in the IMOMO analysis. The geometries of a testosterone derivative with more than 50 atoms were optimized for the lower triplet excited states with the IMOMM(HF:MM3) method and their energies were calculated using IMOMO and IMOMM methods.
Excitation functions of {sup 6,7}Li+{sup 7}Li reactions at low energies
Prepolec, L.; Soic, N.; Blagus, S.; Miljanic, D.; Siketic, Z.; Skukan, N.; Uroic, M.; Milin, M.
2009-08-26
Differential cross sections of {sup 6,7}Li+{sup 7}Li nuclear reactions have been measured at forward angles (10 deg. and 20 deg.), using particle identification detector telescopes, over the energy range 2.75-10.00 MeV. Excitation functions have been obtained for low-lying residual-nucleus states. The well pronounced peak in the excitation function of {sup 7}Li({sup 7}Li,{sup 4}He){sup 10}Be(3.37 MeV,2{sup +}) at beam energy about 8 MeV, first observed by Wyborny and Carlson in 1971 at 0 deg., has been observed at 10 deg., but is less evident at 20 deg. The cross section obtained for the {sup 7}Li({sup 7}Li,{sup 4}He){sup 10}Be(g.s,0{sup +}) reaction is about ten times smaller. The well pronounced peak in the excitation function of {sup 7}Li({sup 7}Li,{sup 4}He){sup 10}Be(3.37 MeV,2{sup +}) reaction could correspond to excited states in {sup 14}C, at excitation energies around 30 MeV.
Ginagunta, Saroja; Bucher, Götz
2011-02-03
We have performed a computational study on the properties of a series of heterocycles bearing two adjacent heteroatoms, focusing on the structures and electronic properties of their first excited triplet states. If the heteroatoms are both heavy chalcogens (S, Se, or Te) or isoelectronic species, then the lowest excited triplet state usually has (π*, σ*) character. The triplet energies are fairly low (30-50 kcal mol(-1)). The (π*, σ*) triplet states are characterized by a significantly lengthened bond between the two heteroatoms. Thus, in 1,2-dithiolane (1b), the S-S bond length is calculated to be 2.088 Å in the singlet ground state and 2.568 Å in the first triplet excited state. The spin density is predicted to be localized almost exclusively on the sulfur atoms. Replacing one heavy chalcogen atom by an oxygen atom or an NR group results in a significant destabilization of the (π*, σ*) triplet excited state, which then no longer is lower in energy than an open-chain biradical. The size of the heterocyclic ring also contributes to the stability of the (π*, σ*) triplet state, with five-membered rings being more favorable than six-membered rings. Benzoannulation, finally, usually lowers the energy of the (π*, σ*) triplet excited states. If one of the heteroatoms is an oxygen or nitrogen atom, however, the corresponding lowest triplet states are better described as σ,π-biradicals.
Fujita, Takatoshi; Huh, Joonsuk; Saikin, Semion K; Brookes, Jennifer C; Aspuru-Guzik, Alán
2014-06-01
We present a theoretical study of excitation dynamics in the chlorosome antenna complex of green photosynthetic bacteria based on a recently proposed model for the molecular assembly. Our model for the excitation energy transfer (EET) throughout the antenna combines a stochastic time propagation of the excitonic wave function with molecular dynamics simulations of the supramolecular structure and electronic structure calculations of the excited states. We characterized the optical properties of the chlorosome with absorption, circular dichroism and fluorescence polarization anisotropy decay spectra. The simulation results for the excitation dynamics reveal a detailed picture of the EET in the chlorosome. Coherent energy transfer is significant only for the first 50 fs after the initial excitation, and the wavelike motion of the exciton is completely damped at 100 fs. Characteristic time constants of incoherent energy transfer, subsequently, vary from 1 ps to several tens of ps. We assign the time scales of the EET to specific physical processes by comparing our results with the data obtained from time-resolved spectroscopy experiments.
Airflow energy harvesters of metal-based PZT thin films by self-excited vibration
NASA Astrophysics Data System (ADS)
Suwa, E.; Tsujiura, Y.; Kurokawa, F.; Hida, H.; Kanno, I.
2014-11-01
We developed self-excited vibration energy harvesters of Pb(Zr,Ti)O3 (PZT) thin films using airflow. To enhance the self-excited vibration, we used 30-μm-thick stainless steel (SS304) foils as base cantilevers on which PZT thin films were deposited by rf-magnetron sputtering. To compensate for the initial bending of PZT/SS304 unimorph cantilever due to the thermal stress, we deposited counter PZT thin films on the back of the SS304 cantilever. We evaluated power-generation performance and vibration mode of the energy harvester in the airflow. When the angle of attack (AOA) was 20° to 30°, large vibration was generated at wind speeds over 8 m/s. By FFT analysis, we confirmed that stable self-excited vibration was generated. At the AOA of 30°, the output power reached 19 μW at wind speeds of 12 m/s.
Howell, R.B.; Fonck, R.J.; Knize, R.J.; Jaehnig, K.P.
1988-08-01
The use of charge exchange spectrocopy to determine plasma rotation speeds and ion temperature is complicated by the energy dependence of the excitation cross sections. The Doppler-broadened spectral line shape is distorted by the relative velocity between the neutral hydrogen atoms of the injected beam and impurity ions. The asymmetric nature of the energy dependence of this cross section causes a non-motional shift of the line center and a non-thermal change in the line width. These effects vary with the angles between the beam direction, rotation velocity direction, and direction of the viewing sightline. When viewing two neutral beams at different angles on TFTR, the two measurements of v/sub phi/(r) show discrepancies about 20 to 30% with each other. The calculation of the spectral intensity profiles, using the excitation rates available, overcorrects these discrepancies and indicates the need for better excitation coefficients. 10 refs., 5 figs.
Linear-response theory for Mukherjee's multireference coupled-cluster method: excitation energies.
Jagau, Thomas-C; Gauss, Jürgen
2012-07-28
The recently presented linear-response function for Mukherjee's multireference coupled-cluster method (Mk-MRCC) [T.-C. Jagau and J. Gauss, J. Chem. Phys. 137, 044115 (2012)] is employed to determine vertical excitation energies within the singles and doubles approximation (Mk-MRCCSD-LR) for ozone as well as for o-benzyne, m-benzyne, and p-benzyne, which display increasing multireference character in their ground states. In order to assess the impact of a multireference ground-state wavefunction on excitation energies, we compare all our results to those obtained at the single-reference coupled-cluster level of theory within the singles and doubles as well as within the singles, doubles, and triples approximation. Special attention is paid to the artificial splitting of certain excited states which arises from the redundancy intrinsic to Mk-MRCC theory and hinders the straightforward application of the Mk-MRCC-LR method.
Hackman, G.; Khoo, T.L.; Carpenter, M.P.; Lauritsen, T.; Calderin, I.J.; Janssens, R.V.; Ackermann, D.; Ahmad, I.; Agarwala, S.; Blumenthal, D.J.; Fischer, S.M.; Nisius, D.; Reiter, P.; Young, J.; Amro, H.; Lopez-Martens, A.; Hannachi, F.; Korichi, A.; Amro, H.; Moore, E.F.; Lee, I.Y.; Macchiavelli, A.O.; Do Nakatsukasa, T.
1997-11-01
An excited superdeformed band in {sup 194}Hg , observed to decay directly to both normal-deformed and superdeformed yrast states, is proposed to be a K{sup {pi}}=2{sup {minus}} octupole vibrational band, based on its excitation energies, spins, and likely parity. The transition energies are identical to those of the yrast superdeformed band in {sup 192}Hg , but originate from levels with different spins and parities. The evolution of transition energies with spin suggests that cancellations between pairing and particle alignment are partly responsible for the identical transition energies. {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Lau, K.-C.; Ng, C. Y.
2006-01-01
The ionization energies (IEs) for the 2-propyl (2-C3H7), phenyl (C6H5), and benzyl (C6H5CH2) radicals have been calculated by the wave-function-based ab initio CCSD(T)/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level with single and double excitations plus quasiperturbative triple excitation [CCSD(T)]. The zero-point vibrational energy correction, the core-valence electronic correction, and the scalar relativistic effect correction have been also made in these calculations. Although a precise IE value for the 2-C3H7 radical has not been directly determined before due to the poor Franck-Condon factor for the photoionization transition at the ionization threshold, the experimental value deduced indirectly using other known energetic data is found to be in good accord with the present CCSD(T)/CBS prediction. The comparison between the predicted value through the focal-point analysis and the highly precise experimental value for the IE(C6H5CH2) determined in the previous pulsed field ionization photoelectron (PFI-PE) study shows that the CCSD(T)/CBS method is capable of providing an accurate IE prediction for C6H5CH2, achieving an error limit of 35 meV. The benchmarking of the CCSD(T)/CBS IE(C6H5CH2) prediction suggests that the CCSD(T)/CBS IE(C6H5) prediction obtained here has a similar accuracy of 35 meV. Taking into account this error limit for the CCSD(T)/CBS prediction and the experimental uncertainty, the CCSD(T)/CBS IE(C6H5) value is also consistent with the IE(C6H5) reported in the previous HeI photoelectron measurement. Furthermore, the present study provides support for the conclusion that the CCSD(T)/CBS approach with high-level energy corrections can be used to provide reliable IE predictions for C3-C7 hydrocarbon radicals with an uncertainty of +/-35 meV. Employing the atomization scheme, we have also computed the 0 K (298 K) heats of formation in kJ/mol at the CCSD(T)/CBS level for 2-C3H7
NASA Astrophysics Data System (ADS)
Dubois, Jonathan; Lee, Donghwa; Kanai, Yosuke
2013-03-01
Charge separation of excitons in materials is one of the most important physical processes to utilize the solar energy in diverse devices including solar cells and photo-catalysts. Heterogeneous interfaces with the so-called type-II character are often employed to infer the interfacial charge transfer in this context. As a simple criterion for designing such an interface, the energy alignment of the quasi-particle states together with the exciton binding energy of electron-donating materials is often discussed in the literature. However, an accurate description of the effect of exciton binding at the interface has not been investigated extensively. Although density functional theory (DFT) is a powerful method to investigate various electronic properties of materials, incomplete description of many-body interactions can lead to an incorrect interpretation of the energy level alignment. While Many-Body Perturbation Theory and Quantum Monte Carlo are promising in this context, much more work is necessary to assess how well these methods perform in practice. In this talk, we will discuss our preliminary results using diffusion Quantum Monte Carlo to calculate the excited states and energy-level alignment at an Oligomer/Quantum-Dot interface - a system that is often discussed in context of solar energy conversion. This work is Prepared by LLNL under Contract DE-AC52-07NA27344.
The role of the individual Lhcas in photosystem I excitation energy trapping.
Wientjes, Emilie; van Stokkum, Ivo H M; van Amerongen, Herbert; Croce, Roberta
2011-08-03
In this work, we have investigated the role of the individual antenna complexes and of the low-energy forms in excitation energy transfer and trapping in Photosystem I of higher plants. To this aim, a series of Photosystem I (sub)complexes with different antenna size/composition/absorption have been studied by picosecond fluorescence spectroscopy. The data show that Lhca3 and Lhca4, which harbor the most red forms, have similar emission spectra (λ(max) = 715-720 nm) and transfer excitation energy to the core with a relative slow rate of ∼25/ns. Differently, the energy transfer from Lhca1 and Lhca2, the "blue" antenna complexes, occurs about four times faster. In contrast to what is often assumed, it is shown that energy transfer from the Lhca1/4 and the Lhca2/3 dimer to the core occurs on a faster timescale than energy equilibration within these dimers. Furthermore, it is shown that all four monomers contribute almost equally to the transfer to the core and that the red forms slow down the overall trapping rate by about two times. Combining all the data allows the construction of a comprehensive picture of the excitation-energy transfer routes and rates in Photosystem I.
Highly correlated systems. Excitation energies of first row transition metals Sc-Cu
NASA Astrophysics Data System (ADS)
Raghavachari, Krishnan; Trucks, Gary W.
1989-07-01
The low-lying dns2→dn+1s1 excitation energies of the first row transition metal atoms Sc-Cu are calculated using fourth-order M≂ller-Plesset perturbation theory (MP4) as well as quadratic configuration interaction (QCI) techniques with large spd and spdf basis sets. The MP4 method performs well for Sc-Mn but fails dramatically for Fe-Cu. In contrast, the QCI technique performs uniformly for all excitation energies with a mean deviation from experiment of only 0.14 eV after including relativistic corrections. f functions contribute 0.1-0.4 eV to the excitation energies for these systems. The highly correlated d10 state of the Ni atom is also considered in detail. The QCI technique obtains the d9s1→d10 splitting of the Ni atom with an error of only 0.13 eV. The results show that single-configuration Hartree-Fock based methods can be successful in calculating excitation energies of transition metal atoms.
Ionic bond effects on the mean excitation energy for stopping power
NASA Technical Reports Server (NTRS)
Wilson, J. W.; Chang, C. K.; Kamaratos, E.; Xu, Y. J.
1982-01-01
Molecular mean excitation energies for ionic bonded molecules calculated according to the local plasma approximation are compared to the Bragg rule. Adjustments of 15% are calculated for LiF in agreement with experiments while 6% adjustments are predicted for HF and 3% for LiH.
Schultz, D.R.; Krstic, P.S.
1996-12-31
Due to the present interest in modeling and diagnosing the edge and divertor plasma regions in magnetically confined fusion devices, we have sought to provide new calculations regarding the elastic, excitation, ionization, and charge transfer cross sections in collisions among relevant ions, neutrals, and isotopes in the low- to intermediate-energy regime. We summarize here some of our recent work.
Megow, Jörg
2016-09-07
The gas-to-crystal-shift denotes the shift of electronic excitation energies, i.e., the difference between ground and excited state energies, for a molecule transferred from the gas to the bulk phase. The contributions to the gas-to-crystal-shift comprise electrostatic as well as inductive polarization and dispersive energy shifts of the molecular excitation energies due to interaction with environmental molecules. For the example of 3,4,9,10-perylene-tetracarboxylic-diimide (PTCDI) bulk, the contributions to the gas-to-crystal shift are investigated. In the present work, electrostatic interaction is calculated via Coulomb interaction of partial charges while inductive and dispersive interactions are obtained using respective sum over states expressions. The coupling of higher transition densities for the first 4500 excited states of PTCDI was computed using transition partial charges based on an atomistic model of PTCDI bulk obtained from molecular dynamics simulations. As a result it is concluded that for the investigated model system of a PTCDI crystal, the gas to crystal shift is dominated by dispersive interaction.
Highly correlated systems. Excitation energies of first row transition metals Sc--Cu
Raghavachari, K.; Trucks, G. W.
1989-07-15
The low-lying /ital d//sup /ital n/s//sup 2//r arrow//ital d//sup /ital n/+1//ital s//sup 1/ excitation energies of the first row transition metal atoms Sc--Cu are calculated using fourth-order M/congruent/ller--Plesset perturbation theory (MP4) as well as quadratic configuration interaction (QCI) techniques with large /ital spd/ and /ital spdf/ basis sets. The MP4 method performs well for Sc--Mn but fails dramatically for Fe--Cu. In contrast, the QCI technique performs uniformly for all excitation energies with a mean deviation from experiment of only 0.14 eV after including relativistic corrections. /ital f/ functions contribute 0.1--0.4 eV to the excitation energies for these systems. The highly correlated /ital d//sup 10/ state of the Ni atom is also considered in detail. The QCI technique obtains the /ital d//sup 9//ital s1//r arrow//ital d10/ splitting of the Ni atom with an error of only 0.13 eV. The results show that single-configuration Hartree--Fock based methods can be successful in calculating excitation energies of transition metal atoms.
Excitation energies and spins of the yrast superdeformed band in {sup 191}Hg
Siem, S.; Reiter, P.; Khoo, T.L.; Lauritsen, T.; Carpenter, M.P.; Ahmad, I.; Calderin, I.J.; Duguet, T.; Fischer, S.M.; Gassmann, D.; Hackman, G.; Janssens, R.V.F.; Nisius, D.; Heenen, P.-H.; Amro, H.; Moore, E.F.; Doessing, T.; Garg, U.; Kharraja, B.; Hannachi, F.
2004-07-01
The excitation energies and spins of the levels in the yrast superdeformed band of {sup 191}Hg have been determined from two single-step {gamma} transitions and the quasicontinuum spectrum connecting the superdeformed and normal-deformed states. The results are compared with those from theoretical mean-field calculations with different interactions. A discussion of pairing in superdeformed states is also included.
High-energy collective electronic excitations in free-standing single-layer graphene
NASA Astrophysics Data System (ADS)
Wachsmuth, P.; Hambach, R.; Kinyanjui, M. K.; Guzzo, M.; Benner, G.; Kaiser, U.
2013-08-01
In this joint experimental and theoretical work, we investigate collective electronic excitations (plasmons) in free-standing, single-layer graphene. The energy- and momentum-dependent electron energy-loss function was measured up to 50eV along two independent in-plane symmetry directions (ΓM and ΓK) over the first Brillouin zone by momentum-resolved electron energy-loss spectroscopy in a transmission electron microscope. We compare our experimental results with corresponding time-dependent density-functional theory calculations. For finite momentum transfers, good agreement with experiments is found if crystal local-field effects are taken into account. In the limit of small and vanishing momentum transfers, we discuss differences between calculations and the experimentally obtained electron energy-loss functions of graphene due to a finite momentum resolution and out-of-plane excitations.
Fukuda, Ryoichi Ehara, Masahiro
2014-10-21
Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2{sup ′}-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy.
Oyeyemi, Victor B; Keith, John A; Carter, Emily A
2014-09-04
Accurate bond dissociation energies (BDEs) are important for characterizing combustion chemistry, particularly the initial stages of pyrolysis. Here we contribute to evaluating the thermochemistry of biodiesel methyl ester molecules using ab initio BDEs derived from a multireference averaged coupled-pair functional (MRACPF2)-based scheme. Having previously validated this approach for hydrocarbons and a variety of oxygenates, herein we provide further validation for bonds within carboxylic acids and methyl esters, finding our scheme predicts BDEs within chemical accuracy (i.e., within 1 kcal/mol) for these molecules. Insights into BDE trends with ester size are then analyzed for methyl formate through methyl crotonate. We find that the carbonyl group in the ester moiety has only a local effect on BDEs. C═C double bonds in ester alkyl chains are found to increase the strengths of bonds adjacent to the double bond. An important exception are bonds beta to C═C or C═O bonds, which produce allylic-like radicals upon dissociation. The observed trends arise from different degrees of geometric relaxation and resonance stabilization in the radicals produced. We also compute BDEs in various small alkanes and alkenes as models for the long hydrocarbon chain of actual biodiesel methyl esters. We again show that allylic bonds in the alkenes are much weaker than those in the small methyl esters, indicating that hydrogen abstractions are more likely at the allylic site and even more likely at bis-allylic sites of alkyl chains due to more electrons involved in π-resonance in the latter. Lastly, we use the BDEs in small surrogates to estimate heretofore unknown BDEs in large methyl esters of biodiesel fuels.
NASA Astrophysics Data System (ADS)
Peng, Degao; Yang, Yang; Zhang, Peng; Yang, Weitao
2014-12-01
In this article, we develop systematically second random phase approximations (RPA) and Tamm-Dancoff approximations (TDA) of particle-hole and particle-particle channels for calculating molecular excitation energies. The second particle-hole RPA/TDA can capture double excitations missed by the particle-hole RPA/TDA and time-dependent density-functional theory (TDDFT), while the second particle-particle RPA/TDA recovers non-highest-occupied-molecular-orbital excitations missed by the particle-particle RPA/TDA. With proper orbital restrictions, these restricted second RPAs and TDAs have a formal scaling of only O(N4). The restricted versions of second RPAs and TDAs are tested with various small molecules to show some positive results. Data suggest that the restricted second particle-hole TDA (r2ph-TDA) has the best overall performance with a correlation coefficient similar to TDDFT, but with a larger negative bias. The negative bias of the r2ph-TDA may be induced by the unaccounted ground state correlation energy to be investigated further. Overall, the r2ph-TDA is recommended to study systems with both single and some low-lying double excitations with a moderate accuracy. Some expressions on excited state property evaluations, such as < hat{S}2rangle are also developed and tested.
Peng, Degao; Yang, Yang; Zhang, Peng; Yang, Weitao
2014-12-07
In this article, we develop systematically second random phase approximations (RPA) and Tamm-Dancoff approximations (TDA) of particle-hole and particle-particle channels for calculating molecular excitation energies. The second particle-hole RPA/TDA can capture double excitations missed by the particle-hole RPA/TDA and time-dependent density-functional theory (TDDFT), while the second particle-particle RPA/TDA recovers non-highest-occupied-molecular-orbital excitations missed by the particle-particle RPA/TDA. With proper orbital restrictions, these restricted second RPAs and TDAs have a formal scaling of only O(N{sup 4}). The restricted versions of second RPAs and TDAs are tested with various small molecules to show some positive results. Data suggest that the restricted second particle-hole TDA (r2ph-TDA) has the best overall performance with a correlation coefficient similar to TDDFT, but with a larger negative bias. The negative bias of the r2ph-TDA may be induced by the unaccounted ground state correlation energy to be investigated further. Overall, the r2ph-TDA is recommended to study systems with both single and some low-lying double excitations with a moderate accuracy. Some expressions on excited state property evaluations, such as 〈S{sup ^2}〉 are also developed and tested.
Peng, Degao; Yang, Yang; Zhang, Peng; Yang, Weitao
2014-12-07
In this article, we develop systematically second random phase approximations (RPA) and Tamm-Dancoff approximations (TDA) of particle-hole and particle-particle channels for calculating molecular excitation energies. The second particle-hole RPA/TDA can capture double excitations missed by the particle-hole RPA/TDA and time-dependent density-functional theory (TDDFT), while the second particle-particle RPA/TDA recovers non-highest-occupied-molecular-orbital excitations missed by the particle-particle RPA/TDA. With proper orbital restrictions, these restricted second RPAs and TDAs have a formal scaling of only O(N(4)). The restricted versions of second RPAs and TDAs are tested with various small molecules to show some positive results. Data suggest that the restricted second particle-hole TDA (r2ph-TDA) has the best overall performance with a correlation coefficient similar to TDDFT, but with a larger negative bias. The negative bias of the r2ph-TDA may be induced by the unaccounted ground state correlation energy to be investigated further. Overall, the r2ph-TDA is recommended to study systems with both single and some low-lying double excitations with a moderate accuracy. Some expressions on excited state property evaluations, such as ⟨Ŝ(2)⟩ are also developed and tested.
Energy-Looping Nanoparticles: Harnessing Excited-State Absorption for Deep-Tissue Imaging.
Levy, Elizabeth S; Tajon, Cheryl A; Bischof, Thomas S; Iafrati, Jillian; Fernandez-Bravo, Angel; Garfield, David J; Chamanzar, Maysamreza; Maharbiz, Michel M; Sohal, Vikaas S; Schuck, P James; Cohen, Bruce E; Chan, Emory M
2016-09-27
Near infrared (NIR) microscopy enables noninvasive imaging in tissue, particularly in the NIR-II spectral range (1000-1400 nm) where attenuation due to tissue scattering and absorption is minimized. Lanthanide-doped upconverting nanocrystals are promising deep-tissue imaging probes due to their photostable emission in the visible and NIR, but these materials are not efficiently excited at NIR-II wavelengths due to the dearth of lanthanide ground-state absorption transitions in this window. Here, we develop a class of lanthanide-doped imaging probes that harness an energy-looping mechanism that facilitates excitation at NIR-II wavelengths, such as 1064 nm, that are resonant with excited-state absorption transitions but not ground-state absorption. Using computational methods and combinatorial screening, we have identified Tm(3+)-doped NaYF4 nanoparticles as efficient looping systems that emit at 800 nm under continuous-wave excitation at 1064 nm. Using this benign excitation with standard confocal microscopy, energy-looping nanoparticles (ELNPs) are imaged in cultured mammalian cells and through brain tissue without autofluorescence. The 1 mm imaging depths and 2 μm feature sizes are comparable to those demonstrated by state-of-the-art multiphoton techniques, illustrating that ELNPs are a promising class of NIR probes for high-fidelity visualization in cells and tissue.
Wilson, A.N.; Singh, A.K.; Huebel, H.; Rossbach, D.; Schonwasser, G.; Davidson, P.M.; Dracoulis, G.D.; Lane, G.J.; Goergen, A.; Buforn, N.; Redon, N.
2005-10-28
The excitation energy of the lowest-energy superdeformed band in {sup 196}Pb is established using the techniques of time-correlated {gamma}-ray spectroscopy. Together with previous measurements on {sup 192}Pb and {sup 194}Pb, this result allows superdeformed excitation energies, binding energies, and two-proton and two-neutron separation energies to be studied systematically, providing stringent tests for current nuclear models. The results are examined for evidence of a 'superdeformed shell gap'.
Wilson, A N; Singh, A K; Hübel, H; Davidson, P M; Görgen, A; Rossbach, D; Korichi, A; Astier, A; Azaiez, F; Bazzacco, D; Bourgeois, C; Buforn, N; Byrne, A P; Dracoulis, G D; Hannachi, F; Hauschild, K; Korten, W; Kröll, T; Lane, G J; Lopez-Martens, A; Redon, N; Reiter, P; Rossi-Alvarez, C; Schonwasser, G; Stezowski, O; Thirolf, P G
2005-10-28
The excitation energy of the lowest-energy superdeformed band in 196Pb is established using the techniques of time-correlated gamma-ray spectroscopy. Together with previous measurements on 192Pb and 194Pb, this result allows superdeformed excitation energies, binding energies, and two-proton and two-neutron separation energies to be studied systematically, providing stringent tests for current nuclear models. The results are examined for evidence of a "superdeformed shell gap."
An accurate potential energy curve for helium based on ab initio calculations
NASA Astrophysics Data System (ADS)
Janzen, A. R.; Aziz, R. A.
1997-07-01
Korona, Williams, Bukowski, Jeziorski, and Szalewicz [J. Chem. Phys. 106, 1 (1997)] constructed a completely ab initio potential for He2 by fitting their calculations using infinite order symmetry adapted perturbation theory at intermediate range, existing Green's function Monte Carlo calculations at short range and accurate dispersion coefficients at long range to a modified Tang-Toennies potential form. The potential with retardation added to the dipole-dipole dispersion is found to predict accurately a large set of microscopic and macroscopic experimental data. The potential with a significantly larger well depth than other recent potentials is judged to be the most accurate characterization of the helium interaction yet proposed.
NASA Astrophysics Data System (ADS)
Safronova, U. I.; Safronova, A. S.; Beiersdorfer, P.
2016-11-01
Energy levels, radiative transition probabilities, and autoionization rates for [Ni]4{s}24{p}6{nl}, [Ni]4{s}24{p}54l\\prime {nl} (l\\prime =d,f,n = 4-7), [Ni]4s4{p}64l\\prime {nl}, (l\\prime =d,f,n = 4-7), [Ni]4{s}24{p}55l\\prime {nl} (n = 5-7), and [Ni]4s4{p}66l\\prime {nl} (n = 6-7) states in Rb-like tungsten (W37+) are calculated using the relativistic many-body perturbation theory method (RMBPT code) and the Hartree-Fock-relativistic method (COWAN code). Autoionizing levels above the [Ni]4{s}24{p}6 threshold are considered. It is found that configuration mixing among [Ni]4{s}24{p}54l\\prime {nl} and [Ni]4s4{p}64l\\prime {nl} plays an important role for all atomic characteristics. Branching ratios relative to the first threshold and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are determined for the [Ni]4{s}24{p}6{nl} (n = 4-7) singly excited states, as well as the [Ni]4{s}24{p}54{dnl}, [Ni]4{s}24{p}54{fnl}, [Ni]4s4{p}64{dnl}, [Ni]4{s}24{p}64{fnl}, (n = 4-6), and [Ni]4{s}24{p}55l\\prime 5l doubly excited nonautoionizing states in Rb-like W37+ ion. Contributions from the [Ni]4s24{p}64{fnl} (n = 6-7), [Ni]4{s}24{p}55l\\prime {nl} (n = 5-6), and [Ni]4{s}24{p}56l\\prime {nl} (n = 6-7) doubly excited autoionizing states are evaluated numerically. The high-n state (with n up to 500) contributions are very important for high temperatures. These contributions are determined by using a scaling procedure. Synthetic dielectronic satellite spectra from Rb-like W are simulated in a broad spectral range from 8 to 70 Å. These calculations provide highly accurate values for a number of W37+ properties useful for a variety of applications including for fusion applications.
[Selective excitation spectra and energy level structure of Dy3+:ThO2 crystal].
Yin, M; Krupa, J C
2001-08-01
Dy3+:ThO2 crystal was grown by the flux technique for the first time. The emission spectra, excitation spectra and fluorescence decay curves were measured and discussed. By using emission spectra obtained under selective dye laser excitation at 12 K, together with the crystal-field theory, the site symmetry of Dy3+ ions in ThO2 was determined as C3 nu and its energy level structure was tabulated. The lifetime of radiative level 4F9/2 was also determined as 0.40 ms.
NASA Technical Reports Server (NTRS)
Kofsky, I. L.; Barrett, J. L.
1985-01-01
Laboratory experiments in which recombined CO, CO2, D2O, OH, N2, H2, and O2 molecules desorb from surfaces in excited internal and translational states are briefly reviewed. Unequilibrated distributions predominate from the principally catalytic metal substrates so far investigated. Mean kinetic energies have been observed up to approx. 3x, and in some cases less than, wall-thermal; the velocity distributions generally vary with emission angle, with non-Lambertian particle fluxes. The excitation state populations are found to depend on surface impurities, in an as yet unexplained way.
Baudin, Pablo; Bykov, Dmytro; Liakh, Dmitry I.; ...
2017-02-22
Here, the recently developed Local Framework for calculating Excitation energies (LoFEx) is extended to the coupled cluster singles and doubles (CCSD) model. In the new scheme, a standard CCSD excitation energy calculation is carried out within a reduced excitation orbital space (XOS), which is composed of localised molecular orbitals and natural transition orbitals determined from time-dependent Hartree–Fock theory. The presented algorithm uses a series of reduced second-order approximate coupled cluster singles and doubles (CC2) calculations to optimise the XOS in a black-box manner. This ensures that the requested CCSD excitation energies have been determined to a predefined accuracy compared tomore » a conventional CCSD calculation. We present numerical LoFEx-CCSD results for a set of medium-sized organic molecules, which illustrate the black-box nature of the approach and the computational savings obtained for transitions that are local compared to the size of the molecule. In fact, for such local transitions, the LoFEx-CCSD scheme can be applied to molecular systems where a conventional CCSD implementation is intractable.« less
Excitation-energy dependence of solvation dynamics in room-temperature ionic liquids
NASA Astrophysics Data System (ADS)
Kim, Daekeon; Park, Sang-Won; Shim, Youngseon; Kim, Hyung J.; Jung, YounJoon
2016-07-01
Influence of the excitation energy of a probe solute molecule on its solvation dynamics and emission spectrum in 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI+PF6-) is studied via molecular dynamics simulations using a coarse-grained model description. By exciting the probe at different energies, each with an extremely narrow distribution, ensuing solvent relaxation and its dynamic variance are monitored using the isoconfigurational ensemble method. Resulting Stokes shift function, S(t), indicates that long-time solvent relaxation becomes slower with the decreasing excitation energy and approaches the equilibrium correlation function, C(t), of solvent fluctuations. This suggests that the system excited at the red-edge of the spectrum observes linear response better than that at the blue-edge. A detailed analysis of nonequilibrium trajectories shows that the effect of initial configurations on variance of relaxation dynamics is mainly confined to short times; it reaches a maximum around 0.1 ≲ t ≲ 1 ps and diminishes as time further increases. The influence of the initial velocity distribution, on the other hand, tends to grow with time and dominates the long-time variations of dynamics. The emission spectrum shows the red-edge effect in accord with previous studies.
Excited-state energies and fine structure of highly charged lithiumlike ions
NASA Astrophysics Data System (ADS)
Li, Jin-ying; Ding, Da-jun; Wang, Zhi-wen
2013-10-01
The full-core-plus-correlation method (FCPC) is extended to calculate the energies and fine structures of 1s2nd and 1s2nf (n≤5) states for the lithiumlike systems with high nuclear charge from Z = 41 to 50. In calculating energy, the higher-order relativistic contribution is estimated under a hydrogenic approximation. The nonrelativistic energies and wave functions are calculated by the Rayleigh-Ritz method. The mass polarization and the relativistic corrections including the kinetic energy correction, the Darwin term, the electron-electron contact term, and the orbit-orbit interaction are calculated perturbatively as the first-order correction. The quantum-electrodynamics contributions to the energy and to the fine-structure splitting are estimated by using the effective nuclear charge formula. The excited energies, the fine structures, and other relevant term energies are given and compared with the data available in the literature.
Effect of collision energy and vibrational excitation on endothermic ion-molecule reactions
Turner, T.P.
1984-07-01
This thesis is divided into two major parts. In the first part an experimental study of proton and deuteron transfer in H/sub 2//sup +/ + He and HD/sup +/ + He has been carried out as a function of kinetic and vibrational energy. The data gives evidence that at lower kinetic energies, the spectator stripping mechanism indeed plays an important role when H/sub 2//sup +/ or HD/sup +/ is vibrationally excited. The second half of this thesis examines the relative efficiencies between the excitation of C-C stretching vibration and collision energy on the promotion of the H atom transfer reaction of C/sub 2/H/sub 2//sup +/ + H/sub 2/ ..-->.. C/sub 2/H/sub 3//sup +/ + H.
Khan, Ahsan U.
1980-01-01
Phosphorus chemiluminescence under ambient conditions of a phosphorus oxidation flame is found to offer an efficient electronic energy transferring system to alkali metal atoms. The lowest resonance lines, 2P3 / 2,½→2S½, of potassium and sodium are excited by energy transfer when an argon stream at 80°C carrying potassium or sodium atoms intersects a phosphorus vapor stream, either at the flame or in the postflame region. The lowest electronically excited metastable 4IIi state of PO or the (PO[unk]PO)* excimer is considered to be the probable energy donor. The (PO[unk]PO)* excimer results from the interaction of the 4IIi state of one PO molecule with the ground 2IIr state of another. Metastability of the donor state is strongly indicated by the observation of intense sensitized alkali atom fluorescence in the postflame region. PMID:16592925
Duque, H. V.; Chiari, L.; Jones, D. B.; Pettifer, Z.; Silva, G. B. da; Limão-Vieira, P.; Blanco, F.; García, G.; White, R. D.; Lopes, M. C. A.; Brunger, M. J.
2014-06-07
Differential and integral cross section measurements, for incident electron energies in the 20–50 eV range, are reported for excitation of several composite vibrational modes in α-tetrahydrofurfuryl alcohol (THFA). Optimisation and frequency calculations, using GAUSSIAN 09 at the B3LYP/aug-cc-pVDZ level, were also undertaken for the two most abundant conformers of THFA, with results being reported for their respective mode classifications and excitation energies. Those calculations assisted us in the experimental assignments of the composite features observed in our measured energy loss spectra. There are, to the best of our knowledge, no other experimental or theoretical data currently available in the literature against which we can compare the present results.
Fusion excitation function measurement for 6Li+64Ni at near-barrier energies
NASA Astrophysics Data System (ADS)
Moin Shaikh, Md.; Roy, Subinit; Rajbanshi, S.; Pradhan, M. K.; Mukherjee, A.; Basu, P.; Pal, S.; Nanal, V.; Pillay, R. G.; Shrivastav, A.
2015-01-01
Total fusion excitation function has been measured for the reaction of weakly bound 6Li projectile on medium mass 64Ni target at energies near the Coulomb barrier of the system. Online characteristic γ-ray detection method has been used to identify and determine the cross sections of the residues. No suppression of total fusion cross section (σTF) is observed at above barrier energies. But enhancement of measured cross section with respect to the one-dimensional barrier penetration model (1-DBPM) calculation is observed at below barrier energies. The enhancement can not be explained by coupled channels calculation with dominant projectile and target excitations as well as one-neutron stripping reaction.
Self-energy correction to the hyperfine splitting for excited states
Wundt, B. J.; Jentschura, U. D.
2011-05-15
The self-energy corrections to the hyperfine splitting is evaluated for higher excited states in hydrogenlike ions using an expansion in the binding parameter Z{alpha}, where Z is the nuclear-charge number and {alpha} is the fine-structure constant. We present analytic results for D, F, and G states, and for a number of highly excited Rydberg states, with principal quantum numbers in the range 13{<=}n{<=}16, and orbital angular momenta l=n-2 and l=n-1. A closed-form analytic expression is derived for the contribution of high-energy photons, valid for any state with l{>=}2 and arbitrary n, l, and total angular momentum j. The low-energy contributions are written in the form of generalized Bethe logarithms and evaluated for selected states.
Intermediate energy electron impact excitation of composite vibrational modes in phenol.
Neves, R F C; Jones, D B; Lopes, M C A; Nixon, K L; de Oliveira, E M; da Costa, R F; Varella, M T do N; Bettega, M H F; Lima, M A P; da Silva, G B; Brunger, M J
2015-05-21
We report differential cross section results from an experimental investigation into the electron impact excitation of a number of the low-lying composite (unresolved) vibrational modes in phenol (C6H5OH). The measurements were carried out at incident electron energies in the range 15-40 eV and for scattered-electron angles in the range 10-90°. The energy resolution of those measurements was typically ∼80 meV. Calculations, using the GAMESS code, were also undertaken with a B3LYP/aug-cc-pVDZ level model chemistry, in order to enable us to assign vibrational modes to the features observed in our energy loss spectra. To the best of our knowledge, the present cross sections are the first to be reported for vibrational excitation of the C6H5OH molecule by electron impact.
Energy transport in weakly nonlinear wave systems with narrow frequency band excitation.
Kartashova, Elena
2012-10-01
A novel discrete model (D model) is presented describing nonlinear wave interactions in systems with small and moderate nonlinearity under narrow frequency band excitation. It integrates in a single theoretical frame two mechanisms of energy transport between modes, namely, intermittency and energy cascade, and gives the conditions under which each regime will take place. Conditions for the formation of a cascade, cascade direction, conditions for cascade termination, etc., are given and depend strongly on the choice of excitation parameters. The energy spectra of a cascade may be computed, yielding discrete and continuous energy spectra. The model does not require statistical assumptions, as all effects are derived from the interaction of distinct modes. In the example given-surface water waves with dispersion function ω(2)=gk and small nonlinearity-the D model predicts asymmetrical growth of side-bands for Benjamin-Feir instability, while the transition from discrete to continuous energy spectrum, excitation parameters properly chosen, yields the saturated Phillips' power spectrum ~g(2)ω(-5). The D model can be applied to the experimental and theoretical study of numerous wave systems appearing in hydrodynamics, nonlinear optics, electrodynamics, plasma, convection theory, etc.
NASA Astrophysics Data System (ADS)
Sahu, B. B.; Han, Jeon G.
2016-12-01
Argon (Ar) plasma characteristics in a single and dual-frequency (DF), capacitively coupled plasma processing system are compared for drive frequencies 13.56 MHz, 320 MHz and their mixture as dual frequencies (DF). We present frequency dependent changes that occur in discharges in terms of plasma parameters such as plasma density, electron temperature, electron energy distribution function, optical emission, gas temperature, and metastable Ar density in a pressure range of 10-150 mTorr. Additionally, this work also presents the formulation and characterization of energy fluxes from plasma to a substrate/probe during the plasma generation. By variation of the operating pressure and plasma excitation frequency, the different contributions originating from the kinetic energy, the recombination of charge carriers such as electrons and ions at the surface along with the contributions from the neutral and excited species are determined. Data reveals that Ar metastable density in low-frequency radio frequency (RF) plasma is not a strong function of operating pressure even though plasma ionization increases with pressure. However, in the case of high-frequency and DF, the excitation of Ar metastable decreases and ionization increases due to enhanced collisions and efficient electron-neutral momentum/energy transfer. Also, data reveals that energy flux in the low-frequency RF plasmas is very high compared to that of high-frequency and DF operations.
Energy expenditure during level human walking: seeking a simple and accurate predictive solution.
Ludlow, Lindsay W; Weyand, Peter G
2016-03-01
Accurate prediction of the metabolic energy that walking requires can inform numerous health, bodily status, and fitness outcomes. We adopted a two-step approach to identifying a concise, generalized equation for predicting level human walking metabolism. Using literature-aggregated values we compared 1) the predictive accuracy of three literature equations: American College of Sports Medicine (ACSM), Pandolf et al., and Height-Weight-Speed (HWS); and 2) the goodness-of-fit possible from one- vs. two-component descriptions of walking metabolism. Literature metabolic rate values (n = 127; speed range = 0.4 to 1.9 m/s) were aggregated from 25 subject populations (n = 5-42) whose means spanned a 1.8-fold range of heights and a 4.2-fold range of weights. Population-specific resting metabolic rates (V̇o2 rest) were determined using standardized equations. Our first finding was that the ACSM and Pandolf et al. equations underpredicted nearly all 127 literature-aggregated values. Consequently, their standard errors of estimate (SEE) were nearly four times greater than those of the HWS equation (4.51 and 4.39 vs. 1.13 ml O2·kg(-1)·min(-1), respectively). For our second comparison, empirical best-fit relationships for walking metabolism were derived from the data set in one- and two-component forms for three V̇o2-speed model types: linear (∝V(1.0)), exponential (∝V(2.0)), and exponential/height (∝V(2.0)/Ht). We found that the proportion of variance (R(2)) accounted for, when averaged across the three model types, was substantially lower for one- vs. two-component versions (0.63 ± 0.1 vs. 0.90 ± 0.03) and the predictive errors were nearly twice as great (SEE = 2.22 vs. 1.21 ml O2·kg(-1)·min(-1)). Our final analysis identified the following concise, generalized equation for predicting level human walking metabolism: V̇o2 total = V̇o2 rest + 3.85 + 5.97·V(2)/Ht (where V is measured in m/s, Ht in meters, and V̇o2 in ml O2·kg(-1)·min(-1)).
Low-Energy Excitation Spectra in the Excitonic Phase of Cobalt Oxides
NASA Astrophysics Data System (ADS)
Yamaguchi, Tomoki; Sugimoto, Koudai; Ohta, Yukinori
2017-04-01
We study the excitonic phase and low-energy excitation spectra of perovskite cobalt oxides. Constructing the five-orbital Hubbard model defined on the three-dimensional cubic lattice for the 3d bands of Pr0.5Ca0.5CoO3, we calculate the excitonic susceptibility in the normal state in the random-phase approximation (RPA) to show the presence of the instability toward excitonic condensation. On the basis of the excitonic ground state with a magnetic multipole obtained in the mean-field approximation, we calculate the dynamical susceptibility of the excitonic phase in the RPA and find that there appear a gapless collective excitation in the spin-transverse mode (Goldstone mode) and a gapful collective excitation in the spin-longitudinal mode (Higgs mode). The experimental relevance of our results is discussed.
NASA Astrophysics Data System (ADS)
Zhukov, A. A.; Shapiro, D. S.; Remizov, S. V.; Pogosov, W. V.; Lozovik, Yu. E.
2017-02-01
We consider a superconducting qubit coupled to the nonstationary transmission line cavity with modulated frequency taking into account energy dissipation. Previously, it was demonstrated that in the case of a single nonadiabatical modulation of a cavity frequency there are two channels of a two-level system excitation which are due to the absorption of Casimir photons and due to the counterrotating wave processes responsible for the dynamical Lamb effect. We show that the parametric periodical modulation of the resonator frequency can increase dramatically the excitation probability. Remarkably, counterrotating wave processes under such a modulation start to play an important role even in the resonant regime. Our predictions can be used to control qubit-resonator quantum states as well as to study experimentally different channels of a parametric qubit excitation.
Boström, Jonas; Delcey, Mickaël G; Aquilante, Francesco; Serrano-Andrés, Luis; Pedersen, Thomas Bondo; Lindh, Roland
2010-03-09
The accuracy of auxiliary basis sets derived from Cholesky decomposition of two-electron integrals is assessed for excitation energies calculated at the state-average complete active space self-consistent field (CASSCF) and multiconfigurational second order perturbation theory (CASPT2) levels of theory using segmented as well as generally contracted atomic orbital basis sets. Based on 196 valence excitations in 26 organic molecules and 72 Rydberg excitations in 3 organic molecules, the results show that Cholesky auxiliary basis sets can be used without compromising the accuracy of the multiconfigurational methods. Specifically, with a decomposition threshold of 10(-4) au, the mean error due to the Cholesky auxiliary basis set is 0.001 eV, or smaller, decreasing with increasing atomic orbital basis set quality.
NASA Astrophysics Data System (ADS)
Ahnen, Sandra; Hehn, Anna-Sophia; Vogiatzis, Konstantinos D.; Trachsel, Maria A.; Leutwyler, Samuel; Klopper, Wim
2014-09-01
Using explicitly-correlated coupled-cluster theory with single and double excitations, the intermolecular distances and interaction energies of the T-shaped imidazole⋯benzene and pyrrole⋯benzene complexes have been computed in a large augmented correlation-consistent quadruple-zeta basis set, adding also corrections for connected triple excitations and remaining basis-set-superposition errors. The results of these computations are used to assess other methods such as Møller-Plesset perturbation theory (MP2), spin-component-scaled MP2 theory, dispersion-weighted MP2 theory, interference-corrected explicitly-correlated MP2 theory, dispersion-corrected double-hybrid density-functional theory (DFT), DFT-based symmetry-adapted perturbation theory, the random-phase approximation, explicitly-correlated ring-coupled-cluster-doubles theory, and double-hybrid DFT with a correlation energy computed in the random-phase approximation.
NASA Astrophysics Data System (ADS)
Czakó, Gábor
2013-04-01
Chemically accurate full-dimensional non-spin-orbit and spin-orbit (SO) ground-state potential energy surfaces (PESs) are obtained for the Br + CH4 → HBr + CH3 reaction by fitting 21 574 composite ab initio energy points. The composite method considers electron correlation methods up to CCSD(T), basis sets up to aug-cc-pwCVTZ-PP, correlation of the core electrons, scalar relativistic effects via an effective core potential (ECP), and SO corrections, thereby achieving an accuracy better than 0.5 kcal/mol. Benchmark structures and relative energies are computed for the stationary points using the ab initio focal-point analysis (FPA) scheme based on both ECP and Douglas-Kroll approaches providing all-electron relativistic CCSDT(Q)/complete-basis-set quality energies. The PESs accurately describe the saddle point of the abstraction reaction and the van der Waals complexes in the entrance and product channels. The SO-corrected PES provides a classical barrier height of 7285(7232 ± 50) cm-1, De values of 867(799 ± 10) and 399(344 ± 10) cm-1 for the complexes CH3-HBr and CH3-BrH, respectively, and reaction endothermicity of 7867(7857 ± 50) cm-1, in excellent agreement with the new, FPA-based benchmark data shown in parentheses. The difference between the Br + CH4 asymptotes of the non-SO and SO PESs is 1240 cm-1, in good agreement with the experiment (1228 cm-1). Quasiclassical trajectory calculations based on more than 13 million trajectories for the late-barrier Br + CH4(vk = 0, 1) [k = 1, 2, 3, 4] reactions show that the vibrational energy, especially the excitation of the stretching modes, activates the reaction much more efficiently than translational energy, in agreement with the extended Polanyi rules. Angular distributions show dominant backward scattering for the ground-state reaction and forward scattering for the stretching-excited reactions. The reactivity on the non-SO PES is about 3-5 times larger than that on the SO PES in a wide collision energy
Czakó, Gábor
2013-04-07
Chemically accurate full-dimensional non-spin-orbit and spin-orbit (SO) ground-state potential energy surfaces (PESs) are obtained for the Br + CH4 → HBr + CH3 reaction by fitting 21 574 composite ab initio energy points. The composite method considers electron correlation methods up to CCSD(T), basis sets up to aug-cc-pwCVTZ-PP, correlation of the core electrons, scalar relativistic effects via an effective core potential (ECP), and SO corrections, thereby achieving an accuracy better than 0.5 kcal∕mol. Benchmark structures and relative energies are computed for the stationary points using the ab initio focal-point analysis (FPA) scheme based on both ECP and Douglas-Kroll approaches providing all-electron relativistic CCSDT(Q)∕complete-basis-set quality energies. The PESs accurately describe the saddle point of the abstraction reaction and the van der Waals complexes in the entrance and product channels. The SO-corrected PES provides a classical barrier height of 7285(7232 ± 50) cm(-1), De values of 867(799 ± 10) and 399(344 ± 10) cm(-1) for the complexes CH3-HBr and CH3-BrH, respectively, and reaction endothermicity of 7867(7857 ± 50) cm(-1), in excellent agreement with the new, FPA-based benchmark data shown in parentheses. The difference between the Br + CH4 asymptotes of the non-SO and SO PESs is 1240 cm(-1), in good agreement with the experiment (1228 cm(-1)). Quasiclassical trajectory calculations based on more than 13 million trajectories for the late-barrier Br + CH4(vk = 0, 1) [k = 1, 2, 3, 4] reactions show that the vibrational energy, especially the excitation of the stretching modes, activates the reaction much more efficiently than translational energy, in agreement with the extended Polanyi rules. Angular distributions show dominant backward scattering for the ground-state reaction and forward scattering for the stretching-excited reactions. The reactivity on the non-SO PES is about 3-5 times larger than that on the SO PES in a wide
Piecuch, Piotr; Hansen, Jared A.; Ajala, Adeayo O.
2015-09-15
When vertical energies are excited for a comprehensive test set of about 150 singlet excited states of 28 medium-sized organic molecules computed using two variants of the completely renormalised (CR) equation-of-motion (EOM) coupled-cluster (CC) method with singles, doubles, and non-iterative triples, abbreviated as δ-CR-EOMCCSD(T), and the analogous two variants of the newer, left-eigenstate δ-CR-EOMCC(2,3) approach are benchmarked against the previously published CASPT2, CC3, and EOMCCSDT-3 results, as well as the suggested theoretical best estimate (TBE) values. The δ-CR-EOMCC approaches are also used to identify and characterise about 50 additional excited states, including several states having substantial two-electron excitation components, which have not been found in the previous work and which can be used in future benchmark studies. We demonstrated that the non-iterative triples corrections to the EOMCCSD excitation energies defining the relatively inexpensive, single-reference, black-box δ-CR-EOMCC approaches provide significant improvements in the EOMCCSD data, while closely matching the results of the iterative and considerably more expensive CC3 and EOMCCSDT-3 calculations and their CASPT2 and TBE counterparts. It is also shown that the δ-CR-EOMCC methods, especially δ-CR-EOMCC(2,3), are capable of bringing the results of the CC3 and EOMCCSDT-3 calculations to a closer agreement with the CASPT2 and TBE data, demonstrating the utility of the cost-effective δ-CR-EOMCC methods in applications involving molecular electronic spectra. Finally, we show that there may exist a relationship between the magnitude of the triples corrections defining δ-CR-EOMCC approaches and the reduced excitation level diagnostic resulting from EOMCCSD.
Piecuch, Piotr; Hansen, Jared A.; Ajala, Adeayo O.
2015-09-15
When vertical energies are excited for a comprehensive test set of about 150 singlet excited states of 28 medium-sized organic molecules computed using two variants of the completely renormalised (CR) equation-of-motion (EOM) coupled-cluster (CC) method with singles, doubles, and non-iterative triples, abbreviated as δ-CR-EOMCCSD(T), and the analogous two variants of the newer, left-eigenstate δ-CR-EOMCC(2,3) approach are benchmarked against the previously published CASPT2, CC3, and EOMCCSDT-3 results, as well as the suggested theoretical best estimate (TBE) values. The δ-CR-EOMCC approaches are also used to identify and characterise about 50 additional excited states, including several states having substantial two-electron excitation components, whichmore » have not been found in the previous work and which can be used in future benchmark studies. We demonstrated that the non-iterative triples corrections to the EOMCCSD excitation energies defining the relatively inexpensive, single-reference, black-box δ-CR-EOMCC approaches provide significant improvements in the EOMCCSD data, while closely matching the results of the iterative and considerably more expensive CC3 and EOMCCSDT-3 calculations and their CASPT2 and TBE counterparts. It is also shown that the δ-CR-EOMCC methods, especially δ-CR-EOMCC(2,3), are capable of bringing the results of the CC3 and EOMCCSDT-3 calculations to a closer agreement with the CASPT2 and TBE data, demonstrating the utility of the cost-effective δ-CR-EOMCC methods in applications involving molecular electronic spectra. Finally, we show that there may exist a relationship between the magnitude of the triples corrections defining δ-CR-EOMCC approaches and the reduced excitation level diagnostic resulting from EOMCCSD.« less
NASA Astrophysics Data System (ADS)
Weeraddana, Dilusha; Premaratne, Malin; Gunapala, Sarath D.; Andrews, David L.
2016-08-01
A fundamental theory is developed for describing laser-driven resonance energy transfer (RET) in dimensionally constrained nanostructures within the framework of quantum electrodynamics. The process of RET communicates electronic excitation between suitably disposed emitter and detector particles in close proximity, activated by the initial excitation of the emitter. Here, we demonstrate that the transfer rate can be significantly increased by propagation of an auxiliary laser beam through a pair of nanostructure particles. This is due to the higher order perturbative contribution to the Förster-type RET, in which laser field is applied to stimulate the energy transfer process. We construct a detailed picture of how excitation energy transfer is affected by an off-resonant radiation field, which includes the derivation of second and fourth order quantum amplitudes. The analysis delivers detailed results for the dependence of the transfer rates on orientational, distance, and laser intensity factor, providing a comprehensive fundamental understanding of laser-driven RET in nanostructures. The results of the derivations demonstrate that the geometry of the system exercises considerable control over the laser-assisted RET mechanism. Thus, under favorable conformational conditions and relative spacing of donor-acceptor nanostructures, the effect of the auxiliary laser beam is shown to produce up to 70% enhancement in the energy migration rate. This degree of control allows optical switching applications to be identified.
Estimation of excitation energy of diatomic molecules in expanding nonequilibrium flows
NASA Technical Reports Server (NTRS)
Park, Chul
1992-01-01
The energy contained in the highly excited vibrational and rotational states in a diatomic gas in a thermochemical nonequilibrium state during expansion is estimated. The estimation is made on the assumption that the populations of the vibrational and rotational states, when normalized by their respective equilibrium values, are describable by simple functions containing no more than four arbitrary parameters. A cubic polynomial, a logarithmic-cubic polynomial, and a bimodal step function are used for this purpose. The four parameters are determined by imposing conditions known at the ground state and the dissociation limit and the mass conservation law. The energy in excess of that accounted for by assuming a Boltzmann distribution of these states, defined here as excess excitation energy, is calculated for N2, O2, NO, CO, OH, and H2. A calculation made for a typical nozzle flow shows that the excess energy may reach 6 percent of the total enthalpy of the flow, and that the flow velocity may decrease by as much as 4 percent due to the nonequilibrium excitation phenomenon.
B1-based specific energy absorption rate determination for nonquadrature radiofrequency excitation.
Katscher, Ulrich; Findeklee, Christian; Voigt, Tobias
2012-12-01
The current gold standard to estimate local and global specific energy absorption rate for MRI involves numerically modeling the patient and the transmit radiofrequency coil. Recently, a patient-individual method was presented, which estimated specific energy absorption rate from individually measured B(1) maps. This method, however, was restricted to quadrature volume coils due to difficulties distinguishing phase contributions from radiofrequency transmission and reception. In this study, a method separating these two phase contributions by comparing the electric conductivity reconstructed from different transmit channels of a parallel radiofrequency transmission system is presented. This enables specific energy absorption rate estimation not only for quadrature excitation but also for the nonquadrature excitation of the single elements of the transmit array. Though the contributions of the different phases are known, unknown magnetic field components and tissue boundary artifacts limit the technique. Nevertheless, the high agreement between simulated and experimental results found in this study is promising. B(1)-based specific energy absorption rate determination might become possible for arbitrary radiofrequency excitation on a patient-individual basis.
NASA Astrophysics Data System (ADS)
Shahab, S.; Erturk, A.
2014-04-01
Low-power electronic systems are used in various underwater applications ranging from naval sensor networks to ecological monitoring for sustainability. In this work, underwater base excitation of cantilevers made of Macro-Fiber Composite (MFC) piezoelectric structures is explored experimentally and theoretically to harvest energy for such wireless electronic components toward enabling self-powered underwater systems. Bimorph cantilevers made of MFCs with different length-to-width ratios and same thickness are tested in air and under water to characterize the change in natural frequency and damping with a focus on the fundamental bending mode. The real and imaginary parts of hydrodynamic frequency response functions are identified and corrected based on this set of experiments. An electrohydroelastic model is developed and experimentally validated for predicting the power delivered to an electrical load as well as the shunted underwater vibration response under base excitation. Variations of the electrical power output with excitation frequency and load resistance are obtained for different length-to-width ratios. Underwater power density results are reported and compared with their in-air counterparts. Specifically a nonlinear dependence of the power density to the cantilever width is reported for energy harvesting from underwater base excitation.
Ultrafast excited-state deactivation and energy transfer in guanine-cytosine DNA double helices.
Miannay, François-Alexandre; Bányász, Akos; Gustavsson, Thomas; Markovitsi, Dimitra
2007-11-28
The DNA double helix poly(dGdC).poly(dGdC) is studied by fluorescence upconversion spectroscopy with femtosecond resolution. It is shown that the excited-state relaxation of the duplex is faster than that of the monomeric components dGMP and dCMP. This contrasts with the behavior of duplexes composed exclusively of adenine-thymine base pairs, for which an overall lengthening of the fluorescence lifetimes with respect to that of an equimolar mixture of dAMP and TMP was reported previously. Despite the difference in the excited-state deactivation rate between the two types of duplexes, the signature of ultrafast energy transfer is present in both of them. It is attested by the decrease of fluorescence anisotropy decay of the duplexes on the subpicosecond time scale, where molecular motions are inhibited, and is corroborated by the fact that their steady-state fluorescence spectra do not change with the excitation wavelength. Energy transfer involves excited states delocalized over at least two bases, whose existence is revealed by the UV absorption spectrum of the duplex, clearly different from that of an equimolar spectrum of dGMP and dCMP.
Excitation Mechanisms in Moderate-Energy Na+-He and K+-He Collisions
NASA Astrophysics Data System (ADS)
Kita, Shigetomo; Hattori, Takehito; Shimakura, Noriyuki
2015-01-01
Excitation mechanisms in Na+-He and K+-He collisions were studied at laboratory collision energies of 1000 ≤ Elab ≤ 1500 eV by differential scattering spectroscopy. Extensive measurements were performed at Elab = 1500 eV. Double differential cross sections σ(Θ)k were measured over a wide range of center-of-mass scattering angles, 7.3 ≤ Θ ≤ 173°, by detecting all the scattered particles (Na+, Na, K+, K, He+, and He), where the subscript k denotes the number of exit channels in the reactions. At the collision energy of Elab = 1500 eV, one- and two-electron excitations were observed appreciably for the Na+-He collisions, while only one-electron excitations were observed in the K+-He collisions. The analyses of the experimental results for these collision systems indicate that the electronic transitions in the Na+-He and K+-He collisions take place at the internuclear distances of R < RC = 0.63 × 10-10 m [potential height V(R) > 49 eV] and R < RC = 0.80 × 10-10 m [V(R) > 36 eV], respectively. For these asymmetric systems, at Elab= 1500 eV, the electronic transition probabilities around the threshold angles are so small that the integral excitation cross sections have small values of Sex < 1.2 × 10-21 m2.
A model for energy transfer in collisions of atoms with highly excited molecules.
Houston, Paul L; Conte, Riccardo; Bowman, Joel M
2015-05-21
A model for energy transfer in the collision between an atom and a highly excited target molecule has been developed on the basis of classical mechanics and turning point analysis. The predictions of the model have been tested against the results of trajectory calculations for collisions of five different target molecules with argon or helium under a variety of temperatures, collision energies, and initial rotational levels. The model predicts selected moments of the joint probability distribution, P(Jf,ΔE) with an R(2) ≈ 0.90. The calculation is efficient, in most cases taking less than one CPU-hour. The model provides several insights into the energy transfer process. The joint probability distribution is strongly dependent on rotational energy transfer and conservation laws and less dependent on vibrational energy transfer. There are two mechanisms for rotational excitation, one due to motion normal to the intermolecular potential and one due to motion tangential to it and perpendicular to the line of centers. Energy transfer is found to depend strongly on the intermolecular potential and only weakly on the intramolecular potential. Highly efficient collisions are a natural consequence of the energy transfer and arise due to collisions at "sweet spots" in the space of impact parameter and molecular orientation.
Technology Transfer Automated Retrieval System (TEKTRAN)
The three evapotranspiration (ET) measurement/retrieval techniques used in this study, lysimeter, scintillometer and remote sensing vary in their level of complexity, accuracy, resolution and applicability. The lysimeter with its point measurement is the most accurate and direct method to measure ET...
Excitation energy-transfer in functionalized nanoparticles: Going beyond the Förster approach
NASA Astrophysics Data System (ADS)
Gil, G.; Corni, S.; Delgado, A.; Bertoni, A.; Goldoni, G.
2016-02-01
We develop a novel approach to treat excitation energy transfer in hybrid nanosystems composed by an organic molecule attached to a semiconductor nanoparticle. Our approach extends the customary Förster theory by considering interaction between transition multipole moments of the nanoparticle at all orders and a point-like transition dipole moment representing the molecule. Optical excitations of the nanoparticle are described through an envelope-function configuration interaction method for a single electron-hole pair. We applied the method to the prototypical case of a core/shell CdSe/ZnS semiconductor quantum dot which shows a complete suppression of the energy transfer for specific transitions which could not be captured by Förster theory.
NASA Technical Reports Server (NTRS)
Brinca, A. L.; Tsurutani, B. T.
1987-01-01
The characteristics of electromagnetic waves excited by cometary newborn ions with large perpendicular energies are examined using a model of solar wind permeated by dilute drifting ring distributions of electrons and oxygen ions with finite thermal spreads. The model has parameters compatible with the ICE observations at the Giacobini-Zinner comet. It is shown that cometary newborn ions with large perpendicular energies can excite a wave mode with rest frame frequencies in the order of the heavy ion cyclotron frequency, Omega(i), and unusual propagation characteristics at small obliquity angles. For parallel propagation, the mode is left-hand circularly polarized, might be unstable in a frequency range containing Omega(i), and moves in the direction of the newborn ion drift along the static magnetic field.
Sedelnikova, O. V. Bulusheva, L. G.; Okotrub, A. V.; Asanov, I. P.; Yushina, I. V.
2014-04-21
Effect of corrugation of hexagonal carbon network on the collective electron excitations has been studied using optical absorption and X-ray photoelectron spectroscopy in conjunction with density functional theory calculations. Onion-like carbon (OLC) was taken as a material, where graphitic mantle enveloping agglomerates of multi-shell fullerenes is strongly curved. Experiments showed that positions of π and π + σ plasmon modes as well as π → π* absorption peak are substantially redshifted for OLC as compared with those of highly ordered pyrolytic graphite and thermally exfoliated graphite consisted of planar sheets. This effect was reproduced in behavior of dielectric functions of rippled graphite models calculated within the random phase approximation. We conclude that the energy of electron excitations in graphitic materials could be precisely tuned by a simple bending of hexagonal network without change of topology. Moreover, our investigation suggests that in such materials optical exciton can transfer energy to plasmon non-radiatively.
Li, Yongqing; Yuan, Jiuchuang; Chen, Maodu; Ma, Fengcai; Sun, Mengtao
2013-07-15
An accurate single-sheeted double many-body expansion potential energy surface is reported for the title system. A switching function formalism has been used to warrant the correct behavior at the H2(X1Σg+)+N(2D) and NH (X3Σ-)+H(2S) dissociation channels involving nitrogen in the ground N(4S) and first excited N(2D) states. The topographical features of the novel global potential energy surface are examined in detail, and found to be in good agreement with those calculated directly from the raw ab initio energies, as well as previous calculations available in the literature. The novel surface can be using to treat well the Renner-Teller degeneracy of the 12A″ and 12A' states of NH 2. Such a work can both be recommended for dynamics studies of the N(2D)+H2 reaction and as building blocks for constructing the double many-body expansion potential energy surface of larger nitrogen/hydrogen-containing systems. In turn, a test theoretical study of the reaction N(2D)+H2(X1Σg+)(ν=0,j=0)→NH (X3Σ-)+H(2S) has been carried out with the method of quantum wave packet on the new potential energy surface. Reaction probabilities, integral cross sections, and differential cross sections have been calculated. Threshold exists because of the energy barrier (68.5 meV) along the minimum energy path. On the curve of reaction probability for total angular momentum J = 0, there are two sharp peaks just above threshold. The value of integral cross section increases quickly from zero to maximum with the increase of collision energy, and then stays stable with small oscillations. The differential cross section result shows that the reaction is a typical forward and backward scatter in agreement with experimental measurement result.
Transient energy excitation in shortcuts to adiabaticity for the time-dependent harmonic oscillator
Chen Xi; Muga, J. G.
2010-11-15
We study for the time-dependent harmonic oscillator the transient energy excitation in speed-up processes ('shortcuts to adiabaticity') designed to reproduce the initial populations at some predetermined final frequency and time. We provide lower bounds and examples. Implications for the limits imposed to the process times and for the principle of unattainability of the absolute zero, in a single expansion or in quantum refrigerator cycles, are drawn.
NASA Technical Reports Server (NTRS)
Rosen, G.
1973-01-01
A survey is presented of free radicals and electronically excited metastable species as high energy propellants for rocket engines. Nascent or atomic forms of diatomic gases are considered free radicals as well as the highly reactive diatomic triatomic molecules that posess unpaired electrons. Manufacturing and storage problems are described, and a review of current experimental work related to the manufacture of atomic hydrogen propellants is presented.
NASA Technical Reports Server (NTRS)
Papailiou, D. D. (Editor)
1975-01-01
Concepts are described that presently appear to have the potential for propulsion applications in the post-1990 era of space technology. The studies are still in progress, and only the current status of investigation is presented. The topics for possible propulsion application are lasers, nuclear fusion, matter-antimatter annihilation, electronically excited helium, energy exchange through the interaction of various fields, laser propagation, and thermonuclear fusion technology.
NASA Astrophysics Data System (ADS)
Wilhelm, Michael J.; Dai, Hai-Lung
2013-06-01
Time-resolved IR emission spectroscopy has previously been used to characterize the 193 nm photodissociation dynamics of vinyl cyanide, H_{2}CC(H)CN. Of significance, it was observed that the major molecular elimination channels generated ro-vibrationally excited photofragments consisting of: HCN + H_{2}CC: and HNC + HCCH, for which the HCN / HNC branching ratio was deduced to be 3.3 to 1. In the present study, we examine the collisional deactivation of the vibrationally excited (E_{vib}=15 kcal mole^{-1} above the zero-point energy) ν_{1} NH and ν_{3} NC stretches of HNC, in response to collisions with a series of inert rare-gas atoms: Rg=He, Ar, Kr, and Xe. Spectral modeling of the IR emission allows direct determination of the time-dependent average internal energy of HNC, and therefore a quantification of the average energy lost per collision, as a function of the internal energy. Similar to vibrationally excited radicals, collisional deactivation of HNC is shown to be remarkably efficient, likely due to comparatively strong HNC / Rg intermolecular attractive interactions. Subsequently, depending upon the relative rates, excited HNC can either isomerize to the energetically more stable HCN, or be rapidly quenched and kinetically trapped as HNC. Potential implications for the astrophysical HNC / HCN abundance ratio problem will be discussed. M. J. Wilhelm, M. Nikow, L. Letendre, and H. L. Dai J. Chem. Phys. 130, 044307 (2009). M. J. Wilhelm, M. Nikow, J. M. Smith, and H. L. Dai J. Phys. Chem. Lett. 4, 23 (2013).
Supporting middle school students' development of an accurate and applicable energy concept
NASA Astrophysics Data System (ADS)
Nordine, Jeffrey Carl
Energy is a fundamental unifying concept of science, yet common approaches to energy instruction in middle school have shown little success with helping students develop their naive ideas about energy into more sophisticated understandings that are useful for making sense of their experiences. While traditional approaches to energy focus on performing calculations in idealized systems, our development team produced a new middle school energy unit that focuses qualitatively on the energy transformations that occur in everyday, non-idealized, systems. This approach uses project-based pedagogy to contextualize instruction with the driving question, "How can I use trash to power my stereo?" In this study, I investigate the effectiveness of our approach by tracking 8th grade students' conceptual development during the unit, following up with students who participated in the unit a year previously, and comparing the energy conceptions and content knowledge between energy unit participants and older students in the same school who learned about energy in an approach that did not emphasize energy transformations in non-idealized systems. Results indicate that during instruction, students' energy conceptions progress from a set of disconnected ideas toward a coherent understanding that is organized around the principle of transformation. After instruction, students who participated in the energy unit were generally more capable of using their understanding of energy to make sense of everyday scenarios than were older non-participants. Furthermore, 9th grade students who participated in the energy unit in their 8th grade year continued to develop more sophisticated understandings of energy during their 9th grade biology course. These 9th grade students seemed better prepared to learn about energy content in their biology course than 10th graders, who did not participate in the energy unit, but took the same biology course during their 9th grade year. Overall, my results
Light absorption and excitation energy transfer calculations in primitive photosynthetic bacteria
NASA Astrophysics Data System (ADS)
Komatsu, Yu; Kayanuma, Megumi; Shoji, Mitsuo; Yabana, Kazuhiro; Shiraishi, Kenji; Umemura, Masayuki
2015-06-01
In photosynthetic organisms, light energy is converted into chemical energy through the light absorption and excitation energy transfer (EET) processes. These processes start in light-harvesting complexes, which contain special photosynthetic pigments. The exploration of unique mechanisms in light-harvesting complexes is directly related to studies, such as artificial photosynthesis or biosignatures in astrobiology. We examined, through ab initio calculations, the light absorption and EET processes using cluster models of light-harvesting complexes in purple bacteria (LH2). We evaluated absorption spectra and energy transfer rates using the LH2 monomer and dimer models to reproduce experimental results. After the calibration tests, a LH2 aggregation model, composed of 7 or 19 LH2s aligned in triangle lattice, was examined. We found that the light absorption is red shifted and the energy transfer becomes faster as the system size increases. We also found that EET is accelerated by exchanging the central pigments to lower energy excited pigments. As an astrobiological application, we calculated light absorptions efficiencies of the LH2 in different photoenvironments.
Excited state potential energy surfaces of bistridentate RuII complexes - A TD-DFT study
NASA Astrophysics Data System (ADS)
Österman, Tomas; Persson, Petter
2012-10-01
Time-dependent density functional theory (TD-DFT) calculations have been used to investigate low-energy singlet and triplet excited state potential energy surfaces (PES) of two prototype RuII-bistridentate complexes: [RuII(tpy)2]2+ (tpy is 2,2':6',2''-terpyridine) and [RuII(dqp)2]2+ (dqp is 2,6-di(quinolin-8-yl)pyridine). Solvent effects were considered using a self-consistent reaction field scheme. The calculations provide information about the excited state manifold along pathways for activated decay of metal-to-ligand charge-transfer (MLCT) excited states via metal-centered (MC) states for the two complexes. Significant differences in the energy profiles of the investigated PESs are explained through characterization of the electronic properties of the involved states calculated by the TD-DFT calculations. Finally, implications of the computational results for the design of octahedral metal complexes utilizing ligand field splitting (LFS) strategies for efficient light-harvesting in photochemical applications such as artificial photosynthesis are discussed.
Moroz, Pavel; Razgoniaeva, Natalia; He, Yufan; Jensen, Gregory; Eckard, Holly; Lu, H Peter; Zamkov, Mikhail
2017-03-23
Tracking the energy flow in nanoscale materials is an important yet challenging goal. Experimental methods for probing the intermolecular energy transfer (ET) are often burdened by the spectral crosstalk between donor and acceptor species, which complicates unraveling their individual contributions. This issue is particularly prominent in inorganic nanoparticles and biological macromolecules featuring broad absorbing profiles. Here, we demonstrate a general spectroscopic strategy for measuring the ET efficiency between nanostructured or molecular dyes exhibiting a significant donor-acceptor spectral overlap. The reported approach is enabled through spectral shaping of the broadband excitation light with solutions of donor molecules, which inhibits the excitation of respective donor species in the sample. The resulting changes in the acceptor emission induced by the spectral modulation of the excitation beam are then used to determine the quantum efficiency and the rate of ET processes between arbitrary fluorophores (molecules, nanoparticles, polymers) with high accuracy. The feasibility of the reported method was demonstrated using a control donor-acceptor system utilizing a protein-bridged Cy3-Cy5 dye pair and subsequently applied for studying the energy flow in a CdSe560-CdSe600 binary nanocrystal film.
Excited State Potential Energy Surfaces of Polyenes and Protonated Schiff Bases.
Send, Robert; Sundholm, Dage; Johansson, Mikael P; Pawłowski, Filip
2009-09-08
The potential energy surface of the (1)Bu and (1)A' states of all-trans-polyenes and the corresponding protonated Schiff bases have been studied at density functional theory and coupled cluster levels. Linear polyenes and protonated Schiff bases with 4 to 12 heavy atoms have been investigated. The calculations show remarkable differences in the excited state potential energy surfaces of the polyenes and the protonated Schiff bases. The excited states of the polyenes exhibit high torsion barriers for single-bond twists and low torsion barriers for double-bond twists. The protonated Schiff bases, on the other hand, are very flexible molecules in the first excited state with low or vanishing torsion barriers for both single and double bonds. Calculations at density functional theory and coupled cluster levels yield qualitatively similar potential energy surfaces. However, significant differences are found for some single-bond torsions in longer protonated Schiff bases, which indicate a flaw of the employed time-dependent density functional theory methods. The close agreement between the approximate second and third order coupled cluster levels indicates that for these systems calculations at second order coupled cluster level are useful in the validation of results based on time-dependent density functional theory.
Low-energy Coulomb excitation of neutron-rich zinc isotopes
NASA Astrophysics Data System (ADS)
van de Walle, J.; Aksouh, F.; Behrens, T.; Bildstein, V.; Blazhev, A.; Cederkäll, J.; Clément, E.; Cocolios, T. E.; Davinson, T.; Delahaye, P.; Eberth, J.; Ekström, A.; Fedorov, D. V.; Fedosseev, V. N.; Fraile, L. M.; Franchoo, S.; Gernhauser, R.; Georgiev, G.; Habs, D.; Heyde, K.; Huber, G.; Huyse, M.; Ibrahim, F.; Ivanov, O.; Iwanicki, J.; Jolie, J.; Kester, O.; Köster, U.; Kröll, T.; Krücken, R.; Lauer, M.; Lisetskiy, A. F.; Lutter, R.; Marsh, B. A.; Mayet, P.; Niedermaier, O.; Pantea, M.; Raabe, R.; Reiter, P.; Sawicka, M.; Scheit, H.; Schrieder, G.; Schwalm, D.; Seliverstov, M. D.; Sieber, T.; Sletten, G.; Smirnova, N.; Stanoiu, M.; Stefanescu, I.; Thomas, J.-C.; Valiente-Dobón, J. J.; Duppen, P. Van; Verney, D.; Voulot, D.; Warr, N.; Weisshaar, D.; Wenander, F.; Wolf, B. H.; Zielińska, M.
2009-01-01
At the radioactive ion beam facility REX-ISOLDE, neutron-rich zinc isotopes were investigated using low-energy Coulomb excitation. These experiments have resulted in B(E2,21+→01+) values in Zn74-80, B(E2,41+→21+) values in Zn74,76 and the determination of the energy of the first excited 21+ states in Zn78,80. The zinc isotopes were produced by high-energy proton- (A=74,76,80) and neutron- (A=78) induced fission of U238, combined with selective laser ionization and mass separation. The isobaric beam was postaccelerated by the REX linear accelerator and Coulomb excitation was induced on a thin secondary target, which was surrounded by the MINIBALL germanium detector array. In this work, it is shown how the selective laser ionization can be used to deal with the considerable isobaric beam contamination and how a reliable normalization of the experiment can be achieved. The results for zinc isotopes and the N=50 isotones are compared to collective model predictions and state-of-the-art large-scale shell-model calculations, including a recent empirical residual interaction constructed to describe the present experimental data up to 2004 in this region of the nuclear chart.
NASA Astrophysics Data System (ADS)
Zhang, Zhongyang; Berti, Emanuele; Cardoso, Vitor
2013-08-01
The analytical understanding of quasinormal mode ringing requires an accurate knowledge of the Green’s function describing the response of the black hole to external perturbations. We carry out a comprehensive study of quasinormal mode excitation for Kerr black holes. Relying on the formalism developed by Mano, Suzuki, and Takasugi, we improve and extend previous calculations of the quasinormal mode residues in the complex frequency plane (“excitation factors Bq”). Using these results we compute the “excitation coefficients” Cq (essentially the mode amplitudes) in the special case where the source of the perturbations is a particle falling into the black hole along the symmetry axis. We compare this calculation with numerical integrations of the perturbation equations, and we show quantitatively how the addition of higher overtones improves the agreement with the numerical waveforms. Our results should find applications in models of the ringdown stage and in the construction of semianalytical template banks for gravitational-wave detectors, especially for binaries with large mass ratios and/or fast-spinning black holes.
Exact kinetic energy enables accurate evaluation of weak interactions by the FDE-vdW method
Sinha, Debalina; Pavanello, Michele
2015-08-28
The correlation energy of interaction is an elusive and sought-after interaction between molecular systems. By partitioning the response function of the system into subsystem contributions, the Frozen Density Embedding (FDE)-vdW method provides a computationally amenable nonlocal correlation functional based on the adiabatic connection fluctuation dissipation theorem applied to subsystem density functional theory. In reproducing potential energy surfaces of weakly interacting dimers, we show that FDE-vdW, either employing semilocal or exact nonadditive kinetic energy functionals, is in quantitative agreement with high-accuracy coupled cluster calculations (overall mean unsigned error of 0.5 kcal/mol). When employing the exact kinetic energy (which we term the Kohn-Sham (KS)-vdW method), the binding energies are generally closer to the benchmark, and the energy surfaces are also smoother.
Exact kinetic energy enables accurate evaluation of weak interactions by the FDE-vdW method.
Sinha, Debalina; Pavanello, Michele
2015-08-28
The correlation energy of interaction is an elusive and sought-after interaction between molecular systems. By partitioning the response function of the system into subsystem contributions, the Frozen Density Embedding (FDE)-vdW method provides a computationally amenable nonlocal correlation functional based on the adiabatic connection fluctuation dissipation theorem applied to subsystem density functional theory. In reproducing potential energy surfaces of weakly interacting dimers, we show that FDE-vdW, either employing semilocal or exact nonadditive kinetic energy functionals, is in quantitative agreement with high-accuracy coupled cluster calculations (overall mean unsigned error of 0.5 kcal/mol). When employing the exact kinetic energy (which we term the Kohn-Sham (KS)-vdW method), the binding energies are generally closer to the benchmark, and the energy surfaces are also smoother.
NASA Astrophysics Data System (ADS)
Chiarelli, Antonio M.; Maclin, Edward L.; Low, Kathy A.; Mathewson, Kyle E.; Fabiani, Monica; Gratton, Gabriele
2016-03-01
Diffuse optical tomography (DOT) provides data about brain function using surface recordings. Despite recent advancements, an unbiased method for estimating the depth of absorption changes and for providing an accurate three-dimensional (3-D) reconstruction remains elusive. DOT involves solving an ill-posed inverse problem, requiring additional criteria for finding unique solutions. The most commonly used criterion is energy minimization (energy constraint). However, as measurements are taken from only one side of the medium (the scalp) and sensitivity is greater at shallow depths, the energy constraint leads to solutions that tend to be small and superficial. To correct for this bias, we combine the energy constraint with another criterion, minimization of spatial derivatives (Laplacian constraint, also used in low resolution electromagnetic tomography, LORETA). Used in isolation, the Laplacian constraint leads to solutions that tend to be large and deep. Using simulated, phantom, and actual brain activation data, we show that combining these two criteria results in accurate (error <2 mm) absorption depth estimates, while maintaining a two-point spatial resolution of <24 mm up to a depth of 30 mm. This indicates that accurate 3-D reconstruction of brain activity up to 30 mm from the scalp can be obtained with DOT.
Chiarelli, Antonio M; Maclin, Edward L; Low, Kathy A; Mathewson, Kyle E; Fabiani, Monica; Gratton, Gabriele
2016-03-01
Diffuse optical tomography (DOT) provides data about brain function using surface recordings. Despite recent advancements, an unbiased method for estimating the depth of absorption changes and for providing an accurate three-dimensional (3-D) reconstruction remains elusive. DOT involves solving an ill-posed inverse problem, requiring additional criteria for finding unique solutions. The most commonly used criterion is energy minimization (energy constraint). However, as measurements are taken from only one side of the medium (the scalp) and sensitivity is greater at shallow depths, the energy constraint leads to solutions that tend to be small and superficial. To correct for this bias, we combine the energy constraint with another criterion, minimization of spatial derivatives (Laplacian constraint, also used in low resolution electromagnetic tomography, LORETA). Used in isolation, the Laplacian constraint leads to solutions that tend to be large and deep. Using simulated, phantom, and actual brain activation data, we show that combining these two criteria results in accurate (error <2 mm) absorption depth estimates, while maintaining a two-point spatial resolution of <24 mm up to a depth of 30 mm. This indicates that accurate 3-D reconstruction of brain activity up to 30 mm from the scalp can be obtained with DOT.
Chiarelli, Antonio M.; Maclin, Edward L.; Low, Kathy A.; Mathewson, Kyle E.; Fabiani, Monica; Gratton, Gabriele
2016-01-01
Abstract. Diffuse optical tomography (DOT) provides data about brain function using surface recordings. Despite recent advancements, an unbiased method for estimating the depth of absorption changes and for providing an accurate three-dimensional (3-D) reconstruction remains elusive. DOT involves solving an ill-posed inverse problem, requiring additional criteria for finding unique solutions. The most commonly used criterion is energy minimization (energy constraint). However, as measurements are taken from only one side of the medium (the scalp) and sensitivity is greater at shallow depths, the energy constraint leads to solutions that tend to be small and superficial. To correct for this bias, we combine the energy constraint with another criterion, minimization of spatial derivatives (Laplacian constraint, also used in low resolution electromagnetic tomography, LORETA). Used in isolation, the Laplacian constraint leads to solutions that tend to be large and deep. Using simulated, phantom, and actual brain activation data, we show that combining these two criteria results in accurate (error <2 mm) absorption depth estimates, while maintaining a two-point spatial resolution of <24 mm up to a depth of 30 mm. This indicates that accurate 3-D reconstruction of brain activity up to 30 mm from the scalp can be obtained with DOT. PMID:26987429
Excitation energies of double isobar-analog states in heavy nuclei
Poplavskii, I. V.
1988-12-01
Several new relationships are established for isomultiplets on the basis of a theory in which the Coulomb coupling constant (CCC) is allowed to be complex. In particular, the following rule is formulated: the energies for fission or decay of members of an isomultiplet into a charged cluster and members of the corresponding daughter isomultiplet are equidistant. This relationship is well satisfied for isomultiplets with /ital A/less than or equal to60. By extrapolating the rule for fission and decay energies to the region of heavy nuclei, the excitation energies /ital E//sub /ital x// of double isobar-analog states (DIASs) are found for the nuclei /sup 197,199/Hg, /sup 205/Pb, /sup 205 - -209/Po, /sup 209/At, and /sup 238/Pu. A comparison of the computed energies /ital E//sub /ital x// with the experimentally measured values for /sup 208/Po attest to the reliability and good accuracy of the method proposed here when used to determine the excitation energies of DIASs in heavy nuclei.
Zhang, Yijing Moore, Keegan J.; Vakakis, Alexander F.; McFarland, D. Michael
2015-12-21
We study passive pulse redirection and nonlinear targeted energy transfer in a granular network composed of two semi-infinite, ordered homogeneous granular chains mounted on linear elastic foundations and coupled by weak linear stiffnesses. Periodic excitation in the form of repetitive half-sine pulses is applied to one of the chains, designated as the “excited chain,” whereas the other chain is initially at rest and is regarded as the “absorbing chain.” We show that passive pulse redirection and targeted energy transfer from the excited to the absorbing chain can be achieved by macro-scale realization of the spatial analog of the Landau-Zener quantum tunneling effect. This is realized by finite stratification of the elastic foundation of the excited chain and depends on the system parameters (e.g., the percentage of stratification) and on the parameters of the periodic excitation. Utilizing empirical mode decomposition and numerical Hilbert transforms, we detect the existence of two distinct nonlinear phenomena in the periodically forced network; namely, (i) energy localization in the absorbing chain due to sustained 1:1 resonance capture leading to irreversible pulse redirection from the excited chain, and (ii) continuous energy exchanges in the form of nonlinear beats between the two chains in the absence of resonance capture. Our results extend previous findings of transient passive energy redirection in impulsively excited granular networks and demonstrate that steady state passive pulse redirection in these networks can be robustly achieved under periodic excitation.
Erol, Ayse; Akalin, Elif; Sarcan, Fahrettin; Donmez, Omer; Akyuz, Sevim; Arikan, Cetin M; Puustinen, Janne; Guina, Mircea
2012-11-28
The excitation energy-dependent nature of Raman scattering spectrum, vibration, electronic or both, has been studied using different excitation sources on as-grown and annealed n- and p-type modulation-doped Ga1 - xInxNyAs1 - y/GaAs quantum well structures. The samples were grown by molecular beam technique with different N concentrations (y = 0%, 0.9%, 1.2%, 1.7%) at the same In concentration of 32%. Micro-Raman measurements have been carried out using 532 and 758 nm lines of diode lasers, and the 1064 nm line of the Nd-YAG laser has been used for Fourier transform-Raman scattering measurements. Raman scattering measurements with different excitation sources have revealed that the excitation energy is the decisive mechanism on the nature of the Raman scattering spectrum. When the excitation energy is close to the electronic band gap energy of any constituent semiconductor materials in the sample, electronic transition dominates the spectrum, leading to a very broad peak. In the condition that the excitation energy is much higher than the band gap energy, only vibrational modes contribute to the Raman scattering spectrum of the samples. Line shapes of the Raman scattering spectrum with the 785 and 1064 nm lines of lasers have been observed to be very broad peaks, whose absolute peak energy values are in good agreement with the ones obtained from photoluminescence measurements. On the other hand, Raman scattering spectrum with the 532 nm line has exhibited only vibrational modes. As a complementary tool of Raman scattering measurements with the excitation source of 532 nm, which shows weak vibrational transitions, attenuated total reflectance infrared spectroscopy has been also carried out. The results exhibited that the nature of the Raman scattering spectrum is strongly excitation energy-dependent, and with suitable excitation energy, electronic and/or vibrational transitions can be investigated.
Jara-Cortés, Jesús; Guevara-Vela, José Manuel; Martín Pendás, Ángel; Hernández-Trujillo, Jesús
2017-05-15
This work provides a novel interpretation of elementary processes of photophysical relevance from the standpoint of the electron density using simple model reactions. These include excited states of H2 taken as a prototype for a covalent bond, excimer formation of He2 to analyze non-covalent interactions, charge transfer by an avoided crossing of electronic states in LiF and conical interesections involved in the intramolecular scrambling in C2 H4 . The changes of the atomic and interaction energy components along the potential energy profiles are described by the interacting quantum atoms approach and the quantum theory of atoms in molecules. Additionally, the topological analysis of one- and two-electron density functions is used to explore basic reaction mechanisms involving excited and degenerate states in connection with the virial theorem. This real space approach allows to describe these processes in a unified way, showing its versatility and utility in the study of chemical systems in excited states. © 2017 Wiley Periodicals, Inc.
Guo, Lifen; Han, Huixian; Ma, Jianyi; Guo, Hua
2015-08-06
Vinylidene is a high-energy isomer of acetylene, and the rearrangement of bonds in the two species serves as a prototype for isomerization reactions. Here, a full-dimensional quantum mechanical study of the vinylidene vibration is carried out on a recently developed global acetylene-vinylidene potential energy surface by simulating the photodetachment dynamics of the vinylidene anion. Several low-lying vibrational levels of the anion were first determined on a new ab initio based potential energy surface, and their photoelectron spectra were obtained within the Condon approximation. The vibrational features of the vinylidene isomer are found to agree well with the experiment in both positions and intensities, validating the global acetylene-vinylidene potential energy surface.
Asmadi, Aldi; Neumann, Marcus A; Kendrick, John; Girard, Pascale; Perrin, Marc-Antoine; Leusen, Frank J J
2009-12-24
In the 2007 blind test of crystal structure prediction hosted by the Cambridge Crystallographic Data Centre (CCDC), a hybrid DFT/MM method correctly ranked each of the four experimental structures as having the lowest lattice energy of all the crystal structures predicted for each molecule. The work presented here further validates this hybrid method by optimizing the crystal structures (experimental and submitted) of the first three CCDC blind tests held in 1999, 2001, and 2004. Except for the crystal structures of compound IX, all structures were reminimized and ranked according to their lattice energies. The hybrid method computes the lattice energy of a crystal structure as the sum of the DFT total energy and a van der Waals (dispersion) energy correction. Considering all four blind tests, the crystal structure with the lowest lattice energy corresponds to the experimentally observed structure for 12 out of 14 molecules. Moreover, good geometrical agreement is observed between the structures determined by the hybrid method and those measured experimentally. In comparison with the correct submissions made by the blind test participants, all hybrid optimized crystal structures (apart from compound II) have the smallest calculated root mean squared deviations from the experimentally observed structures. It is predicted that a new polymorph of compound V exists under pressure.
Excitation of vibrational quanta in furfural by intermediate-energy electrons.
Jones, D B; Neves, R F C; Lopes, M C A; da Costa, R F; Varella, M T do N; Bettega, M H F; Lima, M A P; García, G; Blanco, F; Brunger, M J
2015-12-14
We report cross sections for electron-impact excitation of vibrational quanta in furfural, at intermediate incident electron energies (20, 30, and 40 eV). The present differential cross sections are measured over the scattered electron angular range 10°-90°, with corresponding integral cross sections subsequently being determined. Furfural is a viable plant-derived alternative to petrochemicals, being produced via low-temperature plasma treatment of biomass. Current yields, however, need to be significantly improved, possibly through modelling, with the present cross sections being an important component of such simulations. To the best of our knowledge, there are no other cross sections for vibrational excitation of furfural available in the literature, so the present data are valuable for this important molecule.
Excitation of vibrational quanta in furfural by intermediate-energy electrons
Jones, D. B.; Neves, R. F. C.; Lopes, M. C. A.; Costa, R. F. da; Varella, M. T. do N.; Bettega, M. H. F.; Lima, M. A. P.; García, G.; and others
2015-12-14
We report cross sections for electron-impact excitation of vibrational quanta in furfural, at intermediate incident electron energies (20, 30, and 40 eV). The present differential cross sections are measured over the scattered electron angular range 10°–90°, with corresponding integral cross sections subsequently being determined. Furfural is a viable plant-derived alternative to petrochemicals, being produced via low-temperature plasma treatment of biomass. Current yields, however, need to be significantly improved, possibly through modelling, with the present cross sections being an important component of such simulations. To the best of our knowledge, there are no other cross sections for vibrational excitation of furfural available in the literature, so the present data are valuable for this important molecule.
Intermediate energy cross sections for electron-impact vibrational-excitation of pyrimidine
Jones, D. B.; Ellis-Gibbings, L.; García, G.; Nixon, K. L.; Lopes, M. C. A.; Brunger, M. J.
2015-09-07
We report differential cross sections (DCSs) and integral cross sections (ICSs) for electron-impact vibrational-excitation of pyrimidine, at incident electron energies in the range 15–50 eV. The scattered electron angular range for the DCS measurements was 15°–90°. The measurements at the DCS-level are the first to be reported for vibrational-excitation in pyrimidine via electron impact, while for the ICS we extend the results from the only previous condensed-phase study [P. L. Levesque, M. Michaud, and L. Sanche, J. Chem. Phys. 122, 094701 (2005)], for electron energies ⩽12 eV, to higher energies. Interestingly, the trend in the magnitude of the lower energy condensed-phase ICSs is much smaller when compared to the corresponding gas phase results. As there is no evidence for the existence of any shape-resonances, in the available pyrimidine total cross sections [Baek et al., Phys. Rev. A 88, 032702 (2013); Fuss et al., ibid. 88, 042702 (2013)], between 10 and 20 eV, this mismatch in absolute magnitude between the condensed-phase and gas-phase ICSs might be indicative for collective-behaviour effects in the condensed-phase results.
Energies, radiative and Auger transitions of the core-excited states for the boron atom
NASA Astrophysics Data System (ADS)
Chen, Chao; Sun, Yan; Cong Gou, Bing
2014-09-01
Energies, radiative and Auger transitions of the 1s vacancy resonances 1s2s22p2, 1s2s22p3p, 1s2s2p3, 1s2p4, and 1s2p33p, 4L (L=S, P, D) for the neutral boron atom are calculated using the saddle-point variation and saddle-point complex-rotation methods. Large-scale wave functions are used to obtain reliable results. Relativistic and mass polarization corrections are included by the first-order perturbation theory. The calculated term energies, x-ray wavelengths, and Auger electron energies for these core-excited states are compared with available theoretical and experimental results. Auger electron energies and branching ratios are used to identify high-resolution B Auger spectrum produced in 300 keV B+ on CH4 collision experiment. It is found that the Auger decay of core-excited states of the boron atom gives significant contributions to Auger spectrum in the range of 165-210 eV, and many previously unknown line identifications are presented.
Oyeyemi, Victor B.; Krisiloff, David B.; Keith, John A.; Libisch, Florian; Pavone, Michele; Carter, Emily A.
2014-01-28
Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs.
NASA Astrophysics Data System (ADS)
Oyeyemi, Victor B.; Krisiloff, David B.; Keith, John A.; Libisch, Florian; Pavone, Michele; Carter, Emily A.
2014-01-01
Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs.
Interplay between vibrational energy transfer and excited state deactivation in DNA components.
West, Brantley A; Womick, Jordan M; Moran, Andrew M
2013-07-25
Femtosecond laser spectroscopies are used to examine a thymine family of systems chosen to expose the interplay between excited state deactivation and two distinct vibrational energy transfer (VET) pathways: (i) VET from the base to the deoxyribose ring; (ii) VET between neighboring units in a dinucleotide. We find that relaxation in the ground electronic state accelerates markedly as the molecular sizes increase from the nucleobase to the dinucleotide. This behavior directly reflects growth in the density of vibrational quantum states on the substituent of the base. Excited state lifetimes are studied at temperatures ranging from 100 to 300 K to characterize the thermal fluctuations that connect the Franck-Condon geometries and the conical intersections leading back to the ground state. An Arrhenius analysis yields an approximate excited state energy barrier of 13 meV in the thymine dinucleotide. In addition, we find that the transfer of vibrational energy from the base to the substituent suppresses thermal fluctuations across this energy barrier. The possibility that the solvent viscosity imposes friction on the reaction coordinate is examined by comparing thymine and adenine systems. Experiments suggest that the solvent viscosity has little effect on barrier crossing dynamics in thymine because the conical intersection is accessed through relatively small out-of-plane atomic displacements. Overall, we conclude that the transfer of vibrational quanta from thymine to the deoxyribose ring couples significantly to the internal conversion rate, whereas the neighboring unit in the dinucleotide serves as a secondary heat bath. In natural DNA, it follows that (local) thermal fluctuations in the geometries of subunits involving the base and deoxyribose ring are most important to this subpicosecond relaxation process.
Statistics of low energy excitations for the directed polymer in a random medium.
Monthus, Cécile; Garel, Thomas
2006-05-01
We consider a directed polymer of length L in a random medium of space dimension d = 1,2,3. The statistics of low energy excitations as a function of their size l is numerically evaluated. These excitations can be divided into bulk and boundary excitations, with respective densities rho(bulk)(L) (E = 0,l) and rho(boundary)(L)(E=0,l). We find that both densities follow the scaling behavior rho(bulk, boundary)(L)(E = 0,l)=L(-1-theta)(d)R(bulk,boundary)(x = l/L), where theta(d) is the exponent governing the energy fluctuations at zero temperature (with the well-known exact value theta(1)= 1/3 in one dimension). In the limit x = l/L --> 0, both scaling functions R(bulk)(x) and R(boundary)(x) behave as R(bulk,boundary)(x) approximately x(-1-theta)(d), leading to the droplet power law rho(bulk, boundary)(L) (E = 0,l) approximately l(-1-theta)(d) in the regime 1 < l < L. Beyond their common singularity near x --> 0, the two scaling functions R(bulk,boundary)(x) are very different: whereas R(bulk)(x) decays monotonically for 0 < x < 1, the function R(boundary)(x) first decays for 0 < x < x(min), then grows for x(min) < x < 1, and finally presents a power law singularity R(boundary)(x) approximately (1-x)(-sigma)(d) near x -->1. The density of excitations of length l = L accordingly decays as rho(boundary)(L)(E = 0,l = L) approximately L(-lambda)(d) where gamma(d) = 1+ theta(d) - lambda(d). We obtain lambda(1) approximately 10.67, lambda(2) = 0.53, and lambda(3) approximately 0.39, suggesting the possible relation lambda(d) = 2theta(d).
Conte, Riccardo; Houston, Paul L; Bowman, Joel M
2014-09-11
The influence of rotational excitation on energy transfer in single collisions of allyl with argon and on allyl dissociation is investigated. About 90,000 classical scattering simulations are performed in order to determine collision-induced changes in internal energy and in allyl rotational angular momentum. Dissociation is studied by means of about 50,000 additional trajectories evolved for the isolated allyl under three different conditions: allyl with no angular momentum (J = 0); allyl with the same microcanonically sampled initial conditions used for the collisions (J*); allyl evolving from the corresponding exit conditions after the collision. The potential energy surface is the sum of an intramolecular potential and an interaction one, and it has already been used in a previous work on allyl-argon scattering (Conte, R.; Houston, P. L.; Bowman, J. M. J. Phys. Chem. A 2013, 117, 14028-14041). Energy transfer data show that increased initial rotation favors, on average, increased relaxation of the excited molecule. The availability of a high-level intramolecular potential energy surface permits us to study the dependence of energy transfer on the type of starting allyl isomer. A turning point analysis is presented, and highly efficient collisions are detected. Collision-induced variations in the allyl rotational angular momentum may be quite large and are found to be distributed according to three regimes. The roles of rotational angular momentum, collision, and type of isomer on allyl unimolecular dissociation are considered by looking at dissociations times, kinetic energies of the fragments, and branching ratios. Generally, rotational angular momentum has a strong influence on the dissociation dynamics, while the single collision and the type of starting isomer are less influential.
Revised Charge Equilibration Parameters for More Accurate Hydration Free Energies of Alkanes.
Davis, Joseph E; Patel, Sandeep
2010-01-01
We present a refined alkane charge equilibration (CHEQ) force field, improving our previously reported CHEQ alkane force field[1] to better reproduce experimental hydration free energies. Experimental hydration free energies of ethane, propane, butane, pentane, hexane, and heptane are reproduced to within 3.6% on average. We demonstrate that explicit polarization results in a shift in molecular dipole moment for water molecules associated with the alkane molecule. We also show that our new parameters do not have a significant effect on the alkane-water interactions as measured by the radial distribution function (RDF).
NASA Astrophysics Data System (ADS)
Haruyama, Jun; Suzuki, Takahiro; Hu, Chunping; Watanabe, Kazuyuki
2012-01-01
We present a simple and computationally efficient method to calculate excited-state nuclear forces on adiabatic potential-energy surfaces (APES) from linear-response time-dependent density-functional theory within a real-space framework. The Casida ansatz, which has been validated for computing first-order nonadiabatic couplings in previous studies, was applied to the calculation of the excited-state forces. Our method is validated by the consistency of results in the lower excited states, which reproduce well those obtained by the numerical derivative of each APES. We emphasize the usefulness of this technique by demonstrating the excited-state molecular-dynamics simulation.
Excited-state charging energies in quantum dots investigated by terahertz photocurrent spectroscopy
NASA Astrophysics Data System (ADS)
Zhang, Y.; Shibata, K.; Nagai, N.; Ndebeka-Bandou, C.; Bastard, G.; Hirakawa, K.
2016-06-01
We have investigated the excited-state (ES) charging energies in quantum dots (QDs) by measuring a terahertz (THz)-induced photocurrent in a single-electron transistor (SET) geometry that contains a single InAs QD between metal nanogap electrodes. A photocurrent is produced in the QD SETs through THz intersublevel transitions and the subsequent resonant tunneling. We have found that the photocurrent exhibits stepwise change even within one Coulomb blockaded region as the electrochemical potential in the QD is swept by the gate voltage. From the threshold for the photocurrent generation, we have determined the charging energies for adding an electron in the photoexcited state in the QD. Furthermore, the charging energies for the ESs with different electron configurations are clearly resolved. The present THz photocurrent measurements are essentially dynamical experiments and allow us to analyze electronic properties in off-equilibrium states in the QD.
Neutron Scattering Study of Low Energy Magnetic Excitation in FeTeSe System
NASA Astrophysics Data System (ADS)
Xu, Zhijun; Wen, Jinsheng; Schneeloch, John; Matsuda, Masaaki; Christianson, A. D.; Gu, Genda; Zaliznyak, I. A.; Xu, Guangyong; Tranquada, J. M.; Birgeneau, R. J.
2014-03-01
We have performed neutron scattering and magnetization/transport measurements on a series of FeTe1-xSex system single crystals to study the interplay between magnetism and superconductivity. Comparing to pure FeTe1-xSex compounds, extra Fe and Ni/Cu doping on Fe-site can change physics properties of these samples, including resistivity, magnetization and superconducting properties. Our neutron scattering studies also show the Fe-site doping change low energy magnetic spectrum, including the magnetic excitations intensity, position and magnetic correlation length in these samples. On the other hand, the temperature dependence of the low energy magnetic fluctuations are also found to be different depending on the composition. This work is supported by the Office of Basic Energy Sciences, DOE.
High excitation transfer efficiency from energy relay dyes in dye-sensitized solar cells.
Hardin, Brian E; Yum, Jun-Ho; Hoke, Eric T; Jun, Young Chul; Péchy, Peter; Torres, Tomás; Brongersma, Mark L; Nazeeruddin, Md Khaja; Grätzel, Michael; McGehee, Michael D
2010-08-11
The energy relay dye, 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), was used with a near-infrared sensitizing dye, TT1, to increase the overall power conversion efficiency of a dye-sensitized solar cell (DSC) from 3.5% to 4.5%. The unattached DCM dyes exhibit an average excitation transfer efficiency (ETE) of 96% inside TT1-covered, mesostructured TiO(2) films. Further performance increases were limited by the solubility of DCM in an acetonitrile based electrolyte. This demonstration shows that energy relay dyes can be efficiently implemented in optimized dye-sensitized solar cells, but also highlights the need to design highly soluble energy relay dyes with high molar extinction coefficients.
Absolute cross sections for electronic excitations of cytosine by low energy electron impact
Bazin, M.; Michaud, M.; Sanche, L.
2013-01-01
The absolute cross sections (CS) for electronic excitations of cytosine by electron impact between 5 and 18 eV were measured by electron-energy loss (EEL) spectroscopy of the molecule deposited at low coverage on an inert Ar substrate. The lowest EEL features found at 3.55 and 4.02 eV are ascribed to transitions from the ground state to the two lowest triplet 1 3A′(π→π*) and 2 3A′(π→π*) valence states of the molecule. Their energy dependent CS exhibit essentially a common maximum at about 6 eV with a value of 1.84 × 10−17 cm2 for the former and 4.94 × 10−17 cm2 for the latter. In contrast, the CS for the next EEL feature at 4.65 eV, which is ascribed to the optically allowed transition to the 2 1A′(π→π*) valence state, shows only a steep rise to about 1.04 × 10−16 cm2 followed by a monotonous decrease with the incident electron energy. The higher EEL features at 5.39, 6.18, 6.83, and 7.55 eV are assigned to the excitations of the 3 3, 1A′(π→π*), 4 1A′(π→π*), 5 1A′(π→π*), and 6 1A′(π→π*) valence states, respectively. The CS for the 3 3, 1A′ and 4 1A′ states exhibit a common enhancement at about 10 eV superimposed on a more or less a steep rise, reaching respectively a maximum of 1.27 and 1.79 × 10−16 cm2, followed by a monotonous decrease. This latter enhancement and the maximum seen at about 6 eV in the lowest triplet states correspond to the core-excited electron resonances that have been found by dissociative electron attachment experiments with cytosine in the gas phase. The weak EEL feature found at 5.01 eV with a maximum CS of 3.8 × 10−18 cm2 near its excitation threshold is attributed to transitions from the ground state to the 1 3, 1A″(n→π*) states. The monotonous rise of the EEL signal above 8 eV is attributed to the ionization of the molecule. It is partitioned into four excitation energy regions at about 8.55, 9.21, 9.83, and 11.53 eV, which correspond closely to the ionization energies of
Yoshidome, Takashi; Ekimoto, Toru; Matubayasi, Nobuyuki; Harano, Yuichi; Kinoshita, Masahiro; Ikeguchi, Mitsunori
2015-05-07
The hydration free energy (HFE) is a crucially important physical quantity to discuss various chemical processes in aqueous solutions. Although an explicit-solvent computation with molecular dynamics (MD) simulations is a preferable treatment of the HFE, huge computational load has been inevitable for large, complex solutes like proteins. In the present paper, we propose an efficient computation method for the HFE. In our method, the HFE is computed as a sum of 〈UUV〉/2 (〈UUV〉 is the ensemble average of the sum of pair interaction energy between solute and water molecule) and the water reorganization term mainly reflecting the excluded volume effect. Since 〈UUV〉 can readily be computed through a MD of the system composed of solute and water, an efficient computation of the latter term leads to a reduction of computational load. We demonstrate that the water reorganization term can quantitatively be calculated using the morphometric approach (MA) which expresses the term as the linear combinations of the four geometric measures of a solute and the corresponding coefficients determined with the energy representation (ER) method. Since the MA enables us to finish the computation of the solvent reorganization term in less than 0.1 s once the coefficients are determined, the use of the MA enables us to provide an efficient computation of the HFE even for large, complex solutes. Through the applications, we find that our method has almost the same quantitative performance as the ER method with substantial reduction of the computational load.
Optimising speed and energy expenditure in accurate visually directed upper limb movements.
Elliott, Digby; Hansen, Steve; Grierson, Lawrence E M
2009-04-01
Traditional models of speed-accuracy relations and limb control are steady-state models that fail to consider the learning history and strategic approach of the performer. Work from this laboratory indicates that a performer adjusts his/her behaviour from trial-to-trial to optimise not only the speed and accuracy of performance, but also energy expenditure. Because some errors have greater temporal and energy costs than others, most performers execute movements that are prepared such that potential errors are of minimal expense. The trajectories and subsequent endpoint distributions of rapid aiming movements depend on advance knowledge about the availability of afferent information for online control, as well as the costs associated with undershooting or overshooting the target position with the initial impulse. With practice, a performer is able to reduce the trial-to-trial variability associated with goal-directed movement through more consistent movement planning processes and more rapid online control. Part of the optimisation process is related to the development of an internal model of performance against which early afferent feedback can be evaluated. This framework for examining speed, accuracy and energy expenditure in goal-directed reaching can be used to help understand the breakdown of efficient limb control due to fatigue, ageing and pathology.
NASA Astrophysics Data System (ADS)
Renner, F.; Schwab, A.; Kapsch, R.-P.; Makowski, Ch; Jannek, D.
2014-03-01
At the national metrology institute of Germany, the Physikalisch-Technische Bundesanstalt, a research accelerator for dosimetry in radiation therapy has been installed. Magnetic spectrometry is used to determine the spectrum of high-energy electrons generated by this accelerator. Regarding the intended experiments at the accelerator, a high accuracy for the energy determination of the electron beam is required. For this purpose, an experimental setup is used that has a number of additional devices assembled around the spectrometer to determine geometric characteristics of the electron beam, which influence the energy analysis. For the analysis of the acquired data, a software was developed which meets specific needs. One important aspect is that the software is based on an algorithm for energy determination which considers the measured magnetic flux density of the spectrometer and geometric details of the beam and the spectrometer. The software also meets the demand that it can be used to estimate the uncertainty assigned to the energy. This paper covers the experimental and analytical background of magnetic spectrometry at the high-energy beamline of PTB's research accelerator. A comparison of results calculated with the specific algorithm for energy determination which was developed for this experimental setup and with well-known algorithms is given to show the advantage of the specific method. Results of measurements and their analysis with the algorithm are presented as well.
Measurement of the fusion excitation function for 19O + 12C at near barrier energies
NASA Astrophysics Data System (ADS)
Singh, Varinderjit; Steinbach, T. K.; Vadas, J.; Wiggins, B. B.; Hudan, S.; Desouza, R. T.; Baby, L. T.; Tripathi, V.; Kuvin, S. A.; Wiedenhover, I.
2015-10-01
Fusion of neutron-rich light nuclei in the outer crust of an accreting neutron star has been proposed as responsible for triggering X-ray super-bursts. The underlying hypothesis in this proposition is that the fusion of neutron-rich nuclei is enhanced as compared to stable nuclei. To investigate this hypothesis, an experiment has been performed to measure the fusion excitation function for 18O and 19O nuclei incident on a 12C target. A beam of 19O was produced by the 18O(d,p) reaction at Florida State University and separated using the RESOLUT mass spectrometer. The resulting 19O beam bombarded a 100 μg/cm2 12C target at an intensity of 2-4 × 103 p/s. Evaporation residues resulting from the de-excitation of the fusion product were distinguished by measuring their energy and time-of-flight. Using silicon detectors, micro-channel plate detectors, and an ionization chamber, evaporation residues were detected in the angular range θlab <= 23° with high efficiency. Initial experimental results including measurement of the fusion cross-section to approximately the 100 mb level will be presented. The measured excitation function will be compared to theoretical predictions. Supported by the US DOE under Grand No. DEFG02-88ER-40404.
Energy spectra of 2D gravity and capillary waves with narrow frequency band excitation
NASA Astrophysics Data System (ADS)
Kartashova, E.
2012-02-01
In this letter we present a new method, called increment chain equation method (ICEM), for computing a cascade of distinct modes in a two-dimensional weakly nonlinear wave system generated by narrow frequency band excitation. The ICEM is a means for computing the quantized energy spectrum as an explicit function of frequency ω0 and stationary amplitude A0 of excitation. The physical mechanism behind the generation of the quantized cascade is modulation instability. The ICEM can be used in numerous 2D weakly nonlinear wave systems with narrow frequency band excitation appearing in hydrodynamics, nonlinear optics, electrodynamics, convection theory etc. In this letter the ICEM is demonstrated with examples of gravity and capillary waves with dispersion functions ω(k)~k1/2 and ω(k)~k3/2, respectively, and for two different levels of nonlinearity ɛ=A0k0: small (ɛ~0.1 to 0.25) and moderate (ɛ~0.25 to 0.4).
Mechanisms for production of doubly excited states in low energies Iq+-He collisions
NASA Astrophysics Data System (ADS)
Harel, C.; Jouin, H.; Pons, B.
1993-06-01
We present a theoretical study of the mechanisms leading to the formation of doubly excited states of the series 3l3l' (or 4l') and 2lnl' in N7+, O8+ and C6+-He low energy collisions. The importance of both direct transitions from the entry channel (involving electron-electron interaction couplings) and transitions through a single electron capture channel has been analyzed for a range of impact velocities between 0.2 and 0.6 a.u.
Atomic mean excitation energies for stopping powers from local plasma oscillator strengths
NASA Technical Reports Server (NTRS)
Wilson, J. W.; Xu, Y. J.; Chang, C. K.; Kamaratos, E.
1984-01-01
The stopping of a charged particle by isolated atoms is investigated theoretically using an 'atomic plasma' model in which atomic oscillator strengths are replaced by the plasma frequency spectrum. The plasma-frequency correction factor for individual electron motion proposed by Pines (1953) is incorporated, and atomic mean excitation energies are calculated for atoms through Sr. The results are compared in a graph with those obtained theoretically by Inokuti et al. (1978, 1981) and Dehmer et al. (1975) and with the experimental values compiled by Seltzer and Berger (1982): good agreement is shown.
Effect of the initial excitation energy on the average fission lifetime of nuclei
Gontchar, I. I. Ponomarenko, N. A. Litnevsky, A. L.
2008-07-15
The dependence of the fission time on the initial nuclear excitation energy E{sub tot0}* is studied on the basis of a refined combined dynamical and statistical model. It is shown that this dependence may be nonmonotonic, in which case it features a broad maximum. It turns out that the form of the average fission time
Quadrupole collectivity beyond N = 28: intermediate-energy Coulomb excitation of (47,48)Ar.
Winkler, R; Gade, A; Baugher, T; Bazin, D; Brown, B A; Glasmacher, T; Grinyer, G F; Meharchand, R; McDaniel, S; Ratkiewicz, A; Weisshaar, D
2012-05-04
We report on the first experimental study of quadrupole collectivity in the very neutron-rich nuclei (47,48)Ar using intermediate-energy Coulomb excitation. These nuclei are located along the path from doubly magic Ca to collective S and Si isotopes, a critical region of shell evolution and structural change. The deduced B(E2) transition strengths are confronted with large-scale shell-model calculations in the sdpf shell using the state-of-the-art SDPF-Uand EPQQM effective interactions. The comparison between experiment and theory indicates that a shell-model description of Ar isotopes around N=28 remains a challenge.
Quadrupole Collectivity beyond N=28: Intermediate-Energy Coulomb Excitation of Ar47,48
NASA Astrophysics Data System (ADS)
Winkler, R.; Gade, A.; Baugher, T.; Bazin, D.; Brown, B. A.; Glasmacher, T.; Grinyer, G. F.; Meharchand, R.; McDaniel, S.; Ratkiewicz, A.; Weisshaar, D.
2012-05-01
We report on the first experimental study of quadrupole collectivity in the very neutron-rich nuclei Ar47,48 using intermediate-energy Coulomb excitation. These nuclei are located along the path from doubly magic Ca to collective S and Si isotopes, a critical region of shell evolution and structural change. The deduced B(E2) transition strengths are confronted with large-scale shell-model calculations in the sdpf shell using the state-of-the-art SDPF-Uand EPQQM effective interactions. The comparison between experiment and theory indicates that a shell-model description of Ar isotopes around N=28 remains a challenge.
Theorectical Studies of Excitation in Low-Energy Electron-Polyatomic Molecule Collisions
Rescigno, T N; McCurdy, C W; Isaacs, W A; Orel, A E; Meyer, H D
2001-08-13
This paper focuses on the channeling of energy from electronic to nuclear degrees of freedom in electron-polyatomic molecule collisions. We examine the feasibility of attacking the full scattering problem, both the fixed-nuclei electronic problem and the post-collision nuclear dynamics, entirely from first principles. The electron-CO{sub 2} system is presented as an example. We study resonant vibrational excitation, showing how a6 initio, fixed-nuclei electronic cross sections can provide the necessary input for a multi-dimensional treatment of the nuclear vibrational dynamics.
NASA Astrophysics Data System (ADS)
Argenti, L.; Plésiat, E.; Kukk, E.; Ueda, K.; Decleva, P.; Martín, F.
2012-11-01
Distinct oscillations in vibrationally resolved cross section ratios for the photoionization of CH4 from the C 1s orbital at photon energies as high as 1keV are predicted. The oscillations are attributed to the different relative vibrational excitation due to the scattering of the photoelectron by the peripheral hydrogen atoms. The latter effect is also responsible for the well known EXAFS oscillations in the integrated photoelectron spectrum. The calculations are performed with an ab-initio DFT method [1], as well as with a single-particle semi-analytical model, which incorporate both the effect of the nuclear recoil and of the Coulomb corrections.
Wolter, Tino; Welke, Kai; Phatak, Prasad; Bondar, Ana-Nicoleta; Elstner, Marcus
2013-08-14
The first proton transfer in the bacteriorhodopsin photocycle takes place during the L → M transition. Structural details of the pre proton transfer L intermediate have been investigated using experiments and computations. Here, we assess L-state structural models by performing hybrid quantum mechanical/molecular mechanical molecular dynamics and excitation energy calculations. The computations suggest that a water-bridged twisted retinal structure gives the closest agreement with the experimental L/bR shift in the excitation energy.
NASA Astrophysics Data System (ADS)
Djamo, V.; Teillet-Billy, D.; Gauyacq, J. P.
1995-02-01
Molecules adsorbed on a metal surface can be excited by low-energy electron impact. Resonant processes in which an intermediate negative ion is formed during the collision are very efficient. The resonant vibrational excitation of N2 molecules physisorbed on Ag by low-energy electrons is studied theoretically with the coupled-angular-mode method. The influence of the neighboring surface on the excitation process (including the excitation of overtones) is analyzed. The results are compared with the experimental results of Demuth, Schmeisser, and Avouris. It is found that in a scattering experiment, most of the vibrational excitation concerns electrons that are inelastically scattered into the metal and are thus not observed experimentally.
Hasegawa, Jun-ya; Yanai, Kazuma; Ishimura, Kazuya
2015-01-01
Intermolecular interactions regulate the molecular properties in proteins and solutions such as solvatochromic systems. Some of the interactions have to be described at an electronic-structure level. In this study, a commutator for calculating the excitation energy is used for deriving a first-order interacting space (FOIS) to describe the environmental response to solute excitation. The FOIS wave function for a solute-in-solvent cluster is solved by second-order perturbation theory. The contributions to the excitation energy are decomposed into each interaction and for each solvent. PMID:25393373
Accurate Human Tissue Characterization for Energy-Efficient Wireless On-Body Communications
Vallejo, Mónica; Recas, Joaquín; del Valle, Pablo García; Ayala, José L.
2013-01-01
The demand for Wireless Body Sensor Networks (WBSNs) is rapidly increasing due to the revolution in wearable systems demonstrated by the penetration of on-the-body sensors in hospitals, sports medicine and general health-care practices. In WBSN, the body acts as a communication channel for the propagation of electromagnetic (EM) waves, where losses are mainly due to absorption of power in the tissue. This paper shows the effects of the dielectric properties of biological tissues in the signal strength and, for the first time, relates these effects with the human body composition. After a careful analysis of results, this work proposes a reactive algorithm for power transmission to alleviate the effect of body movement and body type. This policy achieves up to 40.8% energy savings in a realistic scenario with no performance overhead. PMID:23752565
Accurate electron affinity of Pb and isotope shifts of binding energies of Pb-
NASA Astrophysics Data System (ADS)
Chen, Xiaolin; Ning, Chuangang
2016-08-01
Lead (Pb) was the last element of the group IVA whose electron affinity had a low accuracy around 10 meV before the present work. This was due to the generic threshold photodetachment measurement that cannot extent well below 0.5 eV due to the light source limitation. In the present work, the electron affinity of Pb was determined to be 2877.33(13) cm-1 or 0.356 743(16) eV for the isotope m = 208. The accuracy was improved by a factor of 500 with respect to the previous laser photodetachment electron spectroscopy. Moreover, remarkable isotope shifts of the binding energy of Pb- 6p3 4S3/2 - Pb 6p2 3P2 were observed for m = 206, 207, and 208.
Accurate electron affinity of Pb and isotope shifts of binding energies of Pb(.).
Chen, Xiaolin; Ning, Chuangang
2016-08-28
Lead (Pb) was the last element of the group IVA whose electron affinity had a low accuracy around 10 meV before the present work. This was due to the generic threshold photodetachment measurement that cannot extent well below 0.5 eV due to the light source limitation. In the present work, the electron affinity of Pb was determined to be 2877.33(13) cm(-1) or 0.356 743(16) eV for the isotope m = 208. The accuracy was improved by a factor of 500 with respect to the previous laser photodetachment electron spectroscopy. Moreover, remarkable isotope shifts of the binding energy of Pb(-) 6p(3) (4)S3/2 - Pb 6p(2) (3)P2 were observed for m = 206, 207, and 208.
Accurate human tissue characterization for energy-efficient wireless on-body communications.
Vallejo, Mónica; Recas, Joaquín; del Valle, Pablo García; Ayala, José L
2013-06-10
The demand for Wireless Body Sensor Networks (WBSNs) is rapidly increasing due to the revolution in wearable systems demonstrated by the penetration of on-the-body sensors in hospitals, sports medicine and general health-care practices. In WBSN, the body acts as a communication channel for the propagation of electromagnetic (EM) waves, where losses are mainly due to absorption of power in the tissue. This paper shows the effects of the dielectric properties of biological tissues in the signal strength and, for the first time, relates these effects with the human body composition. After a careful analysis of results, this work proposes a reactive algorithm for power transmission to alleviate the effect of body movement and body type. This policy achieves up to 40.8% energy savings in a realistic scenario with no performance overhead.
Excited state absorption and energy transfer in Ho3+-doped indium fluoride glass
NASA Astrophysics Data System (ADS)
Gomes, Laercio; Fortin, Vincent; Bernier, Martin; Maes, Frédéric; Vallée, Réal; Poulain, Samuel; Poulain, Marcel; Jackson, Stuart D.
2017-04-01
This investigation examines in detail the rates of energy transfer relevant to the 5I5 → 5I6 transition (at 3930 nm) in Ho3+-doped InF3 glass as a function of the Ho3+ concentration. The decay times, branching ratios and rate parameters for energy transfer were measured in this investigation for Ho3+ (x)-doped InF3 glass with x = 2, 4 and 10 mol.% and they were used as the input parameters for a rate equation analysis. Excited state absorption (ESA) initiating from the lower laser level is included in the study. Numerical simulation of CW laser emission at 3.9 μm was performed using two pump wavelengths, one for upper laser level excitation (i.e., 5I8 → 5I5 = λP1) and the other for lower laser level de-excitation (i.e., 5I6 → 5S2 = λP2). The pump wavelength λP2 = 962 nm was chosen based on the measurements of ESA and the application of the McCumber method. Critically, the estimated ESA cross section at λP2 = 962 nm (σESA = 7.1 × 10-21 cm2) is approximately sixteen times larger than ground state (5I8) absorption cross section (σGSA = 4.3 × 10-22 cm2) and ESA does not overlap with any ground state absorption process. Our calculations suggest that even for high Ho3+ concentration in which cross relaxation has been shown in a previous study to quench the 5I5 level, ESA is nevertheless strong enough to allow a sufficient population inversion required for practical CW emission.
Towards More Accurate Measurements of the Ionization Energy of Molecular Hydrogen
NASA Astrophysics Data System (ADS)
Sprecher, D.; Beyer, M.; Liu, J.; Merkt, F.; Salumbides, E.; Eikema, K. S. E.; Ubachs, W.; Jungen, Ch.
2013-06-01
With two electrons and two protons, molecular hydrogen is the simplest molecule displaying all features of a chemical bond. H_2 is therefore a fundamental system for testing molecular quantum mechanics and quantum electrodynamics in molecules. The test can be performed by comparing measured and calculated intervals between different rovibronic states of H_2. Two further quantities that can be used for this test are the dissociation and ionization energies of H_2, and considerable efforts have been invested over more than 80 years to improve the precision and accuracy of experimental and theoretical determination of these two quantities. The current status of the comparison is that the theoretical and experimental values of the ionization and dissociation energies of H_2 agree within the combined uncertainty of 30 MHz (see also). The factors currently limiting the precision of the experimental determination will be discussed and the strategies that are being implemented towards overcoming these limitations will be presented. A long-term goal is to achieve a precision of better than 15 kHz, which is the ultimate limit imposed on the accuracy of the theoretical determination by the current uncertainty of the proton-to-electron mass ratio. E. J. Salumbides, G. D. Dickenson, T. I. Ivanov and W. Ubachs, {Phys. Rev. Lett.} 107 (4), 043005 (2011). K. Piszczatowski, G. Lach, M. Przybytek, J. Komasa, K. Pachuckiand and B. Jeziorski, {J. Chem. Theory Comput.} 5 (11), 3039 (2009). J. Liu, E. J. Salumbides, U. Hollenstein, J. C. J. Koelemeij, K. S. E. Eikema, W. Ubachs and F. Merkt, {J. Chem. Phys.} 130 (17), 174306 (2009). D. Sprecher, Ch. Jungen, W. Ubachs and F. Merkt, {Faraday Discuss.} 150, 51 (2011).
NASA Astrophysics Data System (ADS)
Majumder, Moumita; Dawes, Richard; Wang, Xiao-Gang; Carrington, Tucker; Li, Jun; Guo, Hua; Manzhos, Sergei
2014-06-01
New potential energy surfaces for methane were constructed, represented as analytic fits to about 100,000 individual high-level ab initio data. Explicitly-correlated multireference data (MRCI-F12(AE)/CVQZ-F12) were computed using Molpro [1] and fit using multiple strategies. Fits with small to negligible errors were obtained using adaptations of the permutation-invariant-polynomials (PIP) approach [2,3] based on neural-networks (PIP-NN) [4,5] and the interpolative moving least squares (IMLS) fitting method [6] (PIP-IMLS). The PESs were used in full-dimensional vibrational calculations with an exact kinetic energy operator by representing the Hamiltonian in a basis of products of contracted bend and stretch functions and using a symmetry adapted Lanczos method to obtain eigenvalues and eigenvectors. Very close agreement with experiment was produced from the purely ab initio PESs. References 1- H.-J. Werner, P. J. Knowles, G. Knizia, 2012.1 ed. 2012, MOLPRO, a package of ab initio programs. see http://www.molpro.net. 2- Z. Xie and J. M. Bowman, J. Chem. Theory Comput 6, 26, 2010. 3- B. J. Braams and J. M. Bowman, Int. Rev. Phys. Chem. 28, 577, 2009. 4- J. Li, B. Jiang and Hua Guo, J. Chem. Phys. 139, 204103 (2013). 5- S Manzhos, X Wang, R Dawes and T Carrington, JPC A 110, 5295 (2006). 6- R. Dawes, X-G Wang, A.W. Jasper and T. Carrington Jr., J. Chem. Phys. 133, 134304 (2010).
Dependence of Fission-Fragment Properties On Excitation Energy For Neutron-Rich Actinides
NASA Astrophysics Data System (ADS)
Ramos, D.; Rodríguez-Tajes, C.; Caamaño, M.; Farget, F.; Audouin, L.; Benlliure, J.; Casarejos, E.; Clement, E.; Cortina, D.; Delaune, O.; Derkx, X.; Dijon, A.; Doré, D.; Fernández-Domínguez, B.; de France, G.; Heinz, A.; Jacquot, B.; Navin, A.; Paradela, C.; Rejmund, M.; Roger, T.; Salsac, M. D.; Schmitt, C.
2016-03-01
Experimental access to full isotopic fragment distributions is very important to determine the features of the fission process. However, the isotopic identification of fission fragments has been, in the past, partial and scarce. A solution based on the use of inverse kinematics to study transfer-induced fission of exotic actinides was carried out at GANIL, resulting in the first experiment accessing the full identification of a collection of fissioning systems and their corresponding fission fragment distribution. In these experiments, a 238U beam at 6.14 AMeV impinged on a carbon target to produce fissioning systems from U to Am by transfer reactions, and Cf by fusion reactions. Isotopic fission yields of 250Cf, 244Cm, 240Pu, 239Np and 238U are presented in this work. With this information, the average number of neutrons as a function of the atomic number of the fragments is calculated, which reflects the impact of nuclear structure around Z=50, N=80 on the production of fission fragments. The characteristics of the Super Long, Standard I, Standard II, and Standard III fission channels were extracted from fits of the fragment yields for different ranges of excitation energy. The position and contribution of the fission channels as function of excitation energy are presented.
Calculation of excitation energies from the CC2 linear response theory using Cholesky decomposition
Baudin, Pablo; Marín, José Sánchez; Cuesta, Inmaculada García; Sánchez de Merás, Alfredo M. J.
2014-03-14
A new implementation of the approximate coupled cluster singles and doubles CC2 linear response model is reported. It employs a Cholesky decomposition of the two-electron integrals that significantly reduces the computational cost and the storage requirements of the method compared to standard implementations. Our algorithm also exploits a partitioning form of the CC2 equations which reduces the dimension of the problem and avoids the storage of doubles amplitudes. We present calculation of excitation energies of benzene using a hierarchy of basis sets and compare the results with conventional CC2 calculations. The reduction of the scaling is evaluated as well as the effect of the Cholesky decomposition parameter on the quality of the results. The new algorithm is used to perform an extrapolation to complete basis set investigation on the spectroscopically interesting benzylallene conformers. A set of calculations on medium-sized molecules is carried out to check the dependence of the accuracy of the results on the decomposition thresholds. Moreover, CC2 singlet excitation energies of the free base porphin are also presented.
Velasco, A. M.; Lavín, C.; Dolgounitcheva, O.; Ortiz, J. V.
2014-08-21
Vertical excitation energies of the methyl and silyl radicals were inferred from ab initio electron propagator calculations on the electron affinities of CH{sub 3}{sup +} and SiH{sub 3}{sup +}. Photoionization cross sections and angular distribution of photoelectrons for the outermost orbitals of both CH{sub 3} and SiH{sub 3} radicals have been obtained with the Molecular Quantum Defect Orbital method. The individual ionization cross sections corresponding to the Rydberg channels to which the excitation of the ground state's outermost electron gives rise are reported. Despite the relevance of methyl radical in atmospheric chemistry and combustion processes, only data for the photon energy range of 10–11 eV seem to be available. Good agreement has been found with experiment for photoionization cross section of this radical. To our knowledge, predictions of the above mentioned photoionization parameters on silyl radical are made here for the first time, and we are not aware of any reported experimental measurements. An analysis of our results reveals the presence of a Cooper minimum in the photoionization of the silyl radical. The adequacy of the two theoretical procedures employed in the present work is discussed.
Excitation energy transfer in chlorosomes of green bacteria: theoretical and experimental studies.
Fetisova, Z; Freiberg, A; Mauring, K; Novoderezhkin, V; Taisova, A; Timpmann, K
1996-01-01
A theory of excitation energy transfer within the chlorosomal antennae of green bacteria has been developed for an exciton model of aggregation of bacteriochlorophyll (BChl) c (d or e). This model of six exciton-coupled BChl chains with low packing density, approximating that in vivo, and interchain distances of approximately 2 nm was generated to yield the key spectral features found in natural antennae, i.e., the exciton level structure revealed by spectral hole burning experiments and polarization of all the levels parallel to the long axis of the chlorosome. With picosecond fluorescence spectroscopy it was demonstrated that the theory explains the antenna-size-dependent kinetics of fluorescence decay in chlorosomal antenna, measured for intact cells of different cultures of the green bacterium C. aurantiacus, with different chlorosomal antenna size determined by electron microscopic examination of the ultrathin sections of the cells. The data suggest a possible mechanism of excitation energy transfer within the chlorosome that implies the formation of a cylindrical exciton, delocalized over a tubular aggregate of BChl c chains, and Forster-type transfer of such a cylindrical exciton between the nearest tubular BChl c aggregates as well as to BChl a of the baseplate. PMID:8842237
Live-cell visualization of excitation energy dynamics in chloroplast thylakoid structures
Iwai, Masakazu; Yokono, Makio; Kurokawa, Kazuo; Ichihara, Akira; Nakano, Akihiko
2016-01-01
The intricate molecular processes underlying photosynthesis have long been studied using various analytic approaches. However, the three-dimensional (3D) dynamics of such photosynthetic processes remain unexplored due to technological limitations related to investigating intraorganellar mechanisms in vivo. By developing a system for high-speed 3D laser scanning confocal microscopy combined with high-sensitivity multiple-channel detection, we visualized excitation energy dynamics in thylakoid structures within chloroplasts of live Physcomitrella patens cells. Two distinct thylakoid structures in the chloroplast, namely the grana and stroma lamellae, were visualized three-dimensionally in live cells. The simultaneous detection of the shorter (than ~670 nm) and longer (than ~680 nm) wavelength regions of chlorophyll (Chl) fluorescence reveals different spatial characteristics—irregular and vertical structures, respectively. Spectroscopic analyses showed that the shorter and longer wavelength regions of Chl fluorescence are affected more by free light-harvesting antenna proteins and photosystem II supercomplexes, respectively. The high-speed 3D time-lapse imaging of the shorter and longer wavelength regions also reveals different structural dynamics—rapid and slow movements within 1.5 seconds, respectively. Such structural dynamics of the two wavelength regions of Chl fluorescence would indicate excitation energy dynamics between light-harvesting antenna proteins and photosystems, reflecting the energetically active nature of photosynthetic proteins in thylakoid membranes. PMID:27416900
Holland, Alexandra D; Rückerl, Florian; Dragavon, Joseph M; Rekiki, Abdessalem; Tinevez, Jean-Yves; Tournebize, Régis; Shorte, Spencer L
2014-03-15
Energy transfer mechanisms represent the basis for an array of valuable tools to infer interactions in vitro and in vivo, enhance detection or resolve interspecies distances such as with resonance. Based upon our own previously published studies and new results shown here we present a novel framework describing for the first time a model giving a view of the biophysical relationship between Fluorescence by Unbound Excitation from Luminescence (FUEL), a conventional radiative excitation-emission process, and bioluminescence resonance energy transfer. We show here that in homogeneous solutions and in fluorophore-targeted bacteria, FUEL is the dominant mechanism responsible for the production of red-shifted photons. The minor resonance contribution was ascertained by comparing the intensity of the experimental signal to its theoretical resonance counterpart. Distinctive features of the in vitro FUEL signal include a macroscopic depth dependency, a lack of enhancement upon targeting at a constant fluorophore concentration cf and a non-square dependency on cf. Significantly, FUEL is an important, so far overlooked, component of all resonance phenomena which should guide the design of appropriate controls when elucidating interactions. Last, our results highlight the potential for FUEL as a means to enhance in vivo and in vitro detection through complex media while alleviating the need for targeting.
Time dependent thermal lensing measurements of V-T energy transfer from highly excited NO2
NASA Astrophysics Data System (ADS)
Toselli, Beatriz M.; Walunas, Theresa L.; Barker, John R.
1990-04-01
The vibrational relaxation of NO2 (excited at 21,631/cm) by Ar, Kr, and Xe is investigated experimentally using the time-dependent thermal lensing (TDTL) apparatus and methods described by Barker and Rothem (1982) and Barker and Toselli (1989). The theoretical basis of TDTL is reviewed; the techniques used to analyze the TDTL signals and determine the beam size are discussed; and the results are presented in extensive tables and graphs and characterized in detail. The bulk average energy transfer per collision is shown to depend strongly on the vibrational energy, and a sharp increase above about 10,000/cm is tentatively attributed to large-amplitude vibration associated with coupled electronic states. Ar deactivation of NO2 (010) is found to have a V-T rate constant of (5.1 + or - 1.0) x 10 to the -14th cu cm/sec.
Mass-number and excitation-energy dependence of the spin cutoff parameter
Grimes, S. M.; Voinov, A. V.; Massey, T. N.
2016-07-12
Here, the spin cutoff parameter determining the nuclear level density spin distribution ρ(J) is defined through the spin projection as < J^{2}_{z} > ^{1/2} or equivalently for spherical nuclei, (< J(J+1) >/3)^{1/2}. It is needed to divide the total level density into levels as a function of J. To obtain the total level density at the neutron binding energy from the s-wave resonance count, the spin cutoff parameter is also needed. The spin cutoff parameter has been calculated as a function of excitation energy and mass with a super-conducting Hamiltonian. Calculations have been compared with two commonly used semiempirical formulas. A need for further measurements is also observed. Some complications for deformed nuclei are discussed. The quality of spin cut off parameter data derived from isomeric ratio measurement is examined.
Mass-number and excitation-energy dependence of the spin cutoff parameter
Grimes, S. M.; Voinov, A. V.; Massey, T. N.
2016-07-12
Here, the spin cutoff parameter determining the nuclear level density spin distribution ρ(J) is defined through the spin projection as < J2z > 1/2 or equivalently for spherical nuclei, (< J(J+1) >/3)1/2. It is needed to divide the total level density into levels as a function of J. To obtain the total level density at the neutron binding energy from the s-wave resonance count, the spin cutoff parameter is also needed. The spin cutoff parameter has been calculated as a function of excitation energy and mass with a super-conducting Hamiltonian. Calculations have been compared with two commonly used semiempirical formulas.more » A need for further measurements is also observed. Some complications for deformed nuclei are discussed. The quality of spin cut off parameter data derived from isomeric ratio measurement is examined.« less
Energy exchange and localization in a modular metastructure under impulsive excitation
NASA Astrophysics Data System (ADS)
Wu, Z.; Harne, R. L.; Wang, K. W.
2016-04-01
Recent investigations on the concept of modular metastructures have demonstrated remarkable adaptivity of properties as a synergistic product of assembling together metastable modules, modules that exhibit coexisting states for the same topology. It has been found that such modularity provides an accessible pathway for unprecedented massive property adaptation. Despite the extensive report on the static or quasistatic characteristics of modular metastructures, much remains to be explored regarding their dynamic characteristics. This research initiates the study on transient response of a modular metastructure under impulsive excitation. Numerical studies characterize the adaptability of energy exchange and localization characteristics afforded by metastable states. It is found that responses of internal bistable masses of the metastable modules play an important role in determining energy distribution of the overall system. It is discovered that low internal bistable mass and high impulsive energy level are beneficial for energy to be localized and dissipated internally. Additionally, mechanism behind effective energy absorption is disclosed. Overall, this investigation provides opportunities to tailor dynamical responses using modular metastructures and opens potential avenues for designing transient vibration absorbers.
The excitation of electronic transverse energy levels in an intense magnetic field
NASA Technical Reports Server (NTRS)
Bussard, R. W.
1978-01-01
Observations of the X-ray pulsar Hercules X-1 show a line emission feature at about 60 keV, which has been interpreted as the fundamental electron cyclotron line in a magnetic field of around six trillion gauss. In this interpretation, the line radiation results from transitions between transverse energy levels, which are quantized by the field. The expected line luminosity from the excitation of these levels by protons which are falling into the polar cap of a neutron star are calculated. They are assumed to attain kinetic energies up to around 200 MeV, the gravitational potential energy at the surface. The cross sections for high energy Coulomb encounters between small pitch angle protons and electrons in a strong field are measured and used to calculate the energy loss rate of the infalling protons. This rate, together with the rate of elastic nuclear proton collisions, is then used to calculate the number of line photons an infalling proton can be expected to produce, directly or indirectly. The results are applied to Hercules X-1.
NASA Astrophysics Data System (ADS)
Manser, Joseph S.
travel 220 nm over the course of 2 ns after photoexcitation, with an extrapolated diffusion length greater than one micrometer over the full excited state lifetime. The solution-processability of metal halide perovskites necessarily raises questions as to the properties of the solvated precursors and their connection to the final solid-state perovskite phase. Through structural and steady-state and time-resolved absorption studies, the important link between the excited state properties of the precursor components, composed of solvated and solid-state halometallate complexes, and CH3NH3PbI3 is evinced. This connection provides insight into optical nonlinearities and electronic properties of the perovskite phase. Fundamental studies of CH 3NH3PbI3 ultimately serve as a foundation for application of this and other related materials in high-performance devices. In the final chapter, the operation of CH3NH3PbI 3 solar cells in a tandem architecture is presented. The quest for economic, large scale hydrogen production has motivated the search for new materials and device designs capable of splitting water using only energy from the sun. In light of this, we introduce an all solution-processed tandem water splitting assembly composed of a BiVO4 photoanode and a single-junction CH3NH3PbI3 hybrid perovskite solar cell. This unique configuration allows efficient solar photon management, with the metal oxide photoanode selectively harvesting high energy visible photons and the underlying perovskite solar cell capturing lower energy visible-near IR wavelengths in a single-pass excitation. Operating without external bias under standard terrestrial one sun illumination, the photoanode-photovoltaic architecture, in conjunction with an earthabundant cobalt phosphate catalyst, exhibits a solar-to-hydrogen conversion efficiency of 2.5% at neutral pH. The design of low-cost tandem water splitting assemblies employing single-junction hybrid perovskite materials establishes a potentially
Spatial Pattern Classification for More Accurate Forecasting of Variable Energy Resources
NASA Astrophysics Data System (ADS)
Novakovskaia, E.; Hayes, C.; Collier, C.
2014-12-01
The accuracy of solar and wind forecasts is becoming increasingly essential as grid operators continue to integrate additional renewable generation onto the electric grid. Forecast errors affect rate payers, grid operators, wind and solar plant maintenance crews and energy traders through increases in prices, project down time or lost revenue. While extensive and beneficial efforts were undertaken in recent years to improve physical weather models for a broad spectrum of applications these improvements have generally not been sufficient to meet the accuracy demands of system planners. For renewables, these models are often used in conjunction with additional statistical models utilizing both meteorological observations and the power generation data. Forecast accuracy can be dependent on specific weather regimes for a given location. To account for these dependencies it is important that parameterizations used in statistical models change as the regime changes. An automated tool, based on an artificial neural network model, has been developed to identify different weather regimes as they impact power output forecast accuracy at wind or solar farms. In this study, improvements in forecast accuracy were analyzed for varying time horizons for wind farms and utility-scale PV plants located in different geographical regions.
Chawla, Mohit; Oliva, Romina; Bujnicki, Janusz M; Cavallo, Luigi
2015-08-18
Posttranscriptional modifications greatly enhance the chemical information of RNA molecules, contributing to explain the diversity of their structures and functions. A significant fraction of RNA experimental structures available to date present modified nucleobases, with half of them being involved in H-bonding interactions with other bases, i.e. 'modified base pairs'. Herein we present a systematic investigation of modified base pairs, in the context of experimental RNA structures. To this end, we first compiled an atlas of experimentally observed modified base pairs, for which we recorded occurrences and structural context. Then, for each base pair, we selected a representative for subsequent quantum mechanics calculations, to find out its optimal geometry and interaction energy. Our structural analyses show that most of the modified base pairs are non Watson-Crick like and are involved in RNA tertiary structure motifs. In addition, quantum mechanics calculations quantify and provide a rationale for the impact of the different modifications on the geometry and stability of the base pairs they participate in.
NASA Astrophysics Data System (ADS)
Alborzpour, Jonathan P.; Tew, David P.; Habershon, Scott
2016-11-01
Solution of the time-dependent Schrödinger equation using a linear combination of basis functions, such as Gaussian wavepackets (GWPs), requires costly evaluation of integrals over the entire potential energy surface (PES) of the system. The standard approach, motivated by computational tractability for direct dynamics, is to approximate the PES with a second order Taylor expansion, for example centred at each GWP. In this article, we propose an alternative method for approximating PES matrix elements based on PES interpolation using Gaussian process regression (GPR). Our GPR scheme requires only single-point evaluations of the PES at a limited number of configurations in each time-step; the necessity of performing often-expensive evaluations of the Hessian matrix is completely avoided. In applications to 2-, 5-, and 10-dimensional benchmark models describing a tunnelling coordinate coupled non-linearly to a set of harmonic oscillators, we find that our GPR method results in PES matrix elements for which the average error is, in the best case, two orders-of-magnitude smaller and, in the worst case, directly comparable to that determined by any other Taylor expansion method, without requiring additional PES evaluations or Hessian matrices. Given the computational simplicity of GPR, as well as the opportunities for further refinement of the procedure highlighted herein, we argue that our GPR methodology should replace methods for evaluating PES matrix elements using Taylor expansions in quantum dynamics simulations.
Effective approach for accurately calculating individual energy of polar heterojunction interfaces
NASA Astrophysics Data System (ADS)
Akiyama, Toru; Nakane, Harunobu; Nakamura, Kohji; Ito, Tomonori
2016-09-01
We propose a direct approach for calculating individual energy of polar semiconductor interfaces using density functional theory calculations. This approach is applied to polar interfaces between group-III nitrides (AlN and GaN) and SiC and clarifies the interplay of chemical bonding and charge neutrality at the interface, which is crucial for the stability and polarity of group-III nitrides on SiC substrates. The ideal interface is stabilized among various atomic arrangements over the wide range of the chemical potential on Si-face SiC, whereas those with intermixing are favorable on C-face SiC. The stabilization of the ideal interfaces resulting in Ga-polar GaN and Al-polar AlN films on Si-face SiC is consistent with experiments, suggesting that our approach is versatile to evaluate various polar heterojunction interfaces as well as group-III nitrides on semiconductor substrates.
Excitation energies, oscillator strengths and lifetimes in Mg-like vanadium
NASA Astrophysics Data System (ADS)
Gupta, G. P.; Msezane, A. Z.
2013-08-01
Excitation energies from the ground state for 86 fine-structure levels as well as oscillator strengths and radiative decay rates for all fine-structure transitions among the levels of the terms (1s22s22p6)3s2(1S), 3s3p(1,3Po), 3s3d(1,3D), 3s4s(1,3S), 3s4p(1,3Po), 3s4d(1,3D), 3s4f(1,3Fo), 3p2(1S, 3P, 1D), 3p3d(1,3Po, 1,3Do, 1,3Fo), 3p4s(1,3Po), 3p4p(1,3S, 1,3P, 1,3D), 3p4d(1,3Po, 1,3Do, 1,3Fo), 3p4f(1,3D, 1,3F, 1,3G) and 3d2(1S, 3P, 1D,3F,1G) of V XII are calculated using extensive configuration-interaction wave functions obtained with the configuration-interaction version 3 computer code of Hibbert. The important relativistic effects in intermediate coupling are included through the Breit-Pauli approximation. In order to keep our calculated energy splittings as close as possible to the corresponding experimental values, we have made small adjustments to the diagonal elements of the Hamiltonian matrices. The mixing among several fine-structure levels is found to be very strong. Our fine-tuned excitation energies, including their ordering, are in excellent agreement (better than 0.25%) with the available experimental results. From our calculated radiative decay rates, we have also calculated the radiative lifetimes of fine-structure levels. Generally, our calculated data for the excitation energies and radiative decay rates are found to agree reasonably well with other available calculations. However, significant differences between our calculated lifetimes and those from the calculation of Froese Fischer et al (2006 At. Data Nucl. Data Tables 92 607) for a few fine-structure levels, mainly those belonging to the 3p4d configuration, are noted and discussed. Also, our calculated lifetime for the longer-lived level 3s3p(3P1) is found to be in excellent agreement with the corresponding value of Curtis (1991 Phys. Scr. 43 137). ) for all 1108 transitions in V XII are available with the first author (
NASA Astrophysics Data System (ADS)
Zhang, Zhisen; Wu, Tao; Wang, Qi; Pan, Haihua; Tang, Ruikang
2014-01-01
The interactions between proteins/peptides and materials are crucial to research and development in many biomedical engineering fields. The energetics of such interactions are key in the evaluation of new proteins/peptides and materials. Much research has recently focused on the quality of free energy profiles by Jarzynski's equality, a widely used equation in biosystems. In the present work, considerable discrepancies were observed between the results obtained by Jarzynski's equality and those derived by umbrella sampling in biomaterial-water model systems. Detailed analyses confirm that such discrepancies turn up only when the target molecule moves in the high-density water layer on a material surface. Then a hybrid scheme was adopted based on this observation. The agreement between the results of the hybrid scheme and umbrella sampling confirms the former observation, which indicates an approach to a fast and accurate estimation of adsorption free energy for large biomaterial interfacial systems.
NASA Astrophysics Data System (ADS)
Chatterjee, Koushik; Pernal, Katarzyna
2012-11-01
Starting from Rowe's equation of motion we derive extended random phase approximation (ERPA) equations for excitation energies. The ERPA matrix elements are expressed in terms of the correlated ground state one- and two-electron reduced density matrices, 1- and 2-RDM, respectively. Three ways of obtaining approximate 2-RDM are considered: linearization of the ERPA equations, obtaining 2-RDM from density matrix functionals, and employing 2-RDM corresponding to an antisymmetrized product of strongly orthogonal geminals (APSG) ansatz. Applying the ERPA equations with the exact 2-RDM to a hydrogen molecule reveals that the resulting ^1Σ _g^+ excitation energies are not exact. A correction to the ERPA excitation operator involving some double excitations is proposed leading to the ERPA2 approach, which employs the APSG one- and two-electron reduced density matrices. For two-electron systems ERPA2 satisfies a consistency condition and yields exact singlet excitations. It is shown that 2-RDM corresponding to the APSG theory employed in the ERPA2 equations yields excellent singlet excitation energies for Be and LiH systems, and for the N2 molecule the quality of the potential energy curves is at the coupled cluster singles and doubles level. ERPA2 nearly satisfies the consistency condition for small molecules that partially explains its good performance.
Zeng, Qiao; Liang, WanZhen
2015-10-07
The time-dependent density functional theory (TDDFT) has become the most popular method to calculate the electronic excitation energies, describe the excited-state properties, and perform the excited-state geometric optimization of medium and large-size molecules due to the implementation of analytic excited-state energy gradient and Hessian in many electronic structure software packages. To describe the molecules in condensed phase, one usually adopts the computationally efficient hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) models. Here, we extend our previous work on the energy gradient of TDDFT/MM excited state to account for the mutual polarization effects between QM and MM regions, which is believed to hold a crucial position in the potential energy surface of molecular systems when the photoexcitation-induced charge rearrangement in the QM region is drastic. The implementation of a simple polarizable TDDFT/MM (TDDFT/MMpol) model in Q-Chem/CHARMM interface with both the linear response and the state-specific features has been realized. Several benchmark tests and preliminary applications are exhibited to confirm our implementation and assess the effects of different treatment of environmental polarization on the excited-state properties, and the efficiency of parallel implementation is demonstrated as well.
Analytic model for low energy excitation states and phase transitions in spin-ice systems
NASA Astrophysics Data System (ADS)
López-Bara, F. I.; López-Aguilar, F.
2017-04-01
Low energy excitation states in magnetic structures of the so-called spin-ices are produced via spin flips among contiguous tetrahedra of their crystal structure. These spin flips generate entities which mimic magnetic dipoles in every two tetrahedra according to the dumbbell model. When the temperature increases, the spin-flip processes are transmitted in the lattice, generating so-called Dirac strings, which constitute structural entities that can present mimetic behavior similar to that of magnetic monopoles. In recent studies of both specific heat and ac magnetic susceptibility, two (even possibly three) phases have been shown to vary the temperature. The first of these phases presents a sharp peak in the specific heat and another phase transition occurs for increasing temperature whose peak is broader than that of the former phase. The sharp peak occurs when there are no free individual magnetic charges and temperature of the second phase transition coincides with the maximum proliferation of free deconfined magnetic charges. In the present paper, we propose a model for analyzing the low energy excitation many-body states of these spin-ice systems. We give analytical formulas for the internal energy, specific heat, entropy and their temperature evolution. We study the description of the possible global states via the nature and structure of their one-body components by means of the thermodynamic functions. Below 0.37 K, the Coulomb-like magnetic charge interaction can generate a phase transition to a condensation of pole–antipole pairs, possibly having Bose–Einstein structure which is responsible for the sharp peak of the first phase transition. When there are sufficient free positive and negative charges, the system tends to behave as a magnetic plasma, which implies the broader peak in the specific heat appearing at higher temperature than the sharper experimental peak.
Liu, Lingzhi; Dong, Xiaohu; Lian, Wenlong; Peng, Xiaoniu; Liu, Zhihong; He, Zhike; Wang, Ququan
2010-02-15
Recently, we have successfully developed a two-photon excitation fluorescence resonance energy transfer (TPE-FRET)-based homogeneous immunoassay using two-photon excitable small organic molecule as the energy donor. In the present work, the newly emerging TPE-FRET technique was extended to the determination of oligonucleotide. A new TPE molecule with favorable two-photon action cross section was synthesized [2-(2,5-bis(4-(dimethylamino)styryl)-1H-pyrrol-1-yl)acetic acid, abbreviated as TP-COOH], with the tagged reactive carboxyl group allowing facile conjugation with streptavidin (SA). Employing the TP-COOH molecule as energy donor and black hole quencher 1 (BHQ-1) as acceptor, a TPE-FRET-based homogeneous competitive hybridization model was constructed via a biotin-streptavidin bridge. Through the hybridization between a biotinylated single-stranded DNA (ssDNA) and a BHQ-1-linked ssDNA, and the subsequent capture of the as-formed hybrid by TP-COOH labeled SA, the donor fluorescence was quenched due to the FRET between TP-COOH and BHQ-1. Upon the competition between a target ssDNA and the quencher-linked ssDNA toward the biotinylated oligonucleotide, the donor fluorescence was recovered in a target-dependent manner. Good linearity was obtained with the target oligonucleotide ranging from 0.08 to 1.52 microM. The method was applied to spiked serum and urine samples with satisfying recoveries obtained. The results of this work verified the applicability of TPE-FRET technique in hybridization assay and confirmed the advantages of TPE-FRET in complicated matrix.
Yuan, Bing; Yu, Zijun; Bernstein, Elliot R.
2014-01-21
Decomposition of energetic material 3,4-dinitropyrazole (DNP) and two model molecules 4-nitropyrazole and 1-nitropyrazole is investigated both theoretically and experimentally. The initial decomposition mechanisms for these three nitropyrazoles are explored with complete active space self-consistent field (CASSCF) level. The NO molecule is observed as an initial decomposition product from all three materials subsequent to UV excitation. Observed NO products are rotationally cold (<50 K) for all three systems. The vibrational temperature of the NO product from DNP is (3850 ± 50) K, 1350 K hotter than that of the two model species. Potential energy surface calculations at the CASSCF(12,8)/6-31+G(d) level illustrate that conical intersections plays an essential role in the decomposition mechanism. Electronically excited S{sub 2} nitropyraozles can nonradiatively relax to lower electronic states through (S{sub 2}/S{sub 1}){sub CI} and (S{sub 1}/S{sub 0}){sub CI} conical intersection and undergo a nitro-nitrite isomerization to generate NO product either in the S{sub 1} state or S{sub 0} state. In model systems, NO is generated in the S{sub 1} state, while in the energetic material DNP, NO is produced on the ground state surface, as the S{sub 1} decomposition pathway is energetically unavailable. The theoretically predicted mechanism is consistent with the experimental results, as DNP decomposes in a lower electronic state than do the model systems and thus the vibrational energy in the NO product from DNP should be hotter than from the model systems. The observed rotational energy distributions for NO are consistent with the final structures of the respective transition states for each molecule.
Wallace, Jason A; Wang, Yuhang; Shi, Chuanyin; Pastoor, Kevin J; Nguyen, Bao-Linh; Xia, Kai; Shen, Jana K
2011-12-01
Proton uptake or release controls many important biological processes, such as energy transduction, virus replication, and catalysis. Accurate pK(a) prediction informs about proton pathways, thereby revealing detailed acid-base mechanisms. Physics-based methods in the framework of molecular dynamics simulations not only offer pK(a) predictions but also inform about the physical origins of pK(a) shifts and provide details of ionization-induced conformational relaxation and large-scale transitions. One such method is the recently developed continuous constant pH molecular dynamics (CPHMD) method, which has been shown to be an accurate and robust pK(a) prediction tool for naturally occurring titratable residues. To further examine the accuracy and limitations of CPHMD, we blindly predicted the pK(a) values for 87 titratable residues introduced in various hydrophobic regions of staphylococcal nuclease and variants. The predictions gave a root-mean-square deviation of 1.69 pK units from experiment, and there were only two pK(a)'s with errors greater than 3.5 pK units. Analysis of the conformational fluctuation of titrating side-chains in the context of the errors of calculated pK(a) values indicate that explicit treatment of conformational flexibility and the associated dielectric relaxation gives CPHMD a distinct advantage. Analysis of the sources of errors suggests that more accurate pK(a) predictions can be obtained for the most deeply buried residues by improving the accuracy in calculating desolvation energies. Furthermore, it is found that the generalized Born implicit-solvent model underlying the current CPHMD implementation slightly distorts the local conformational environment such that the inclusion of an explicit-solvent representation may offer improvement of accuracy.
Response analysis of a nonlinear magnetoelectric energy harvester under harmonic excitation
NASA Astrophysics Data System (ADS)
Naifar, S.; Bradai, S.; Viehweger, C.; Kanoun, O.
2015-11-01
Magnetostrictive (MS) piezoelectric composites provide interesting possibilities to harvest energy from low amplitude and low frequency vibrations with a relative high energy outcome. In this paper a magnetoelectric (ME) vibration energy harvester has been designed, which consists of two ME transducers a magnetic circuit and a magnetic spring. The ME transducers consist of three layered Terfenol-D and Lead Zirconate Titanate (PZT) laminated composites. The outcoming energy is collected directly from the piezo layer to avoid electrical losses. In the system under consideration, the magnetic forces between the ME transducers and the magnetic circuit introduce additional stiffness on the magnetic spring. The one degree of freedom system is analysed analytically and the corresponding governing equation is solved with the Lindstedt-Poincaré method. The effects of the structure parameters, such as the nonlinear magnetic forces and the magnetic field distribution, are analysed based on finite element analysis for optimization of electric output performances. Investigations demonstrate that 1.56 mW output power across 8 MΩ load resistance can be harvested for an excitation amplitude of 1 mm at 21.84 Hz.
Dissipation of excess excitation energy of the needle leaves in Pinus trees during cold winters
NASA Astrophysics Data System (ADS)
Zhang, AO; Cui, Zhen-Hai; Yu, Jia-Lin; Hu, Zi-Ling; Ding, Rui; Ren, Da-Ming; Zhang, Li-Jun
2016-12-01
Photooxidative damage to the needle leaves of evergreen trees results from the absorption of excess excitation energy. Efficient dissipation of this energy is essential to prevent photodamage. In this study, we determined the fluorescence transients, absorption spectra, chlorophyll contents, chlorophyll a/ b ratios, and relative membrane permeabilities of needle leaves of Pinus koraiensis, Pinus tabulaeformis, and Pinus armandi in both cold winter and summer. We observed a dramatic decrease in the maximum fluorescence ( F m) and substantial absorption of light energy in winter leaves of all three species. The F m decline was not correlated with a decrease in light absorption or with changes in chlorophyll content and chlorophyll a/ b ratio. The results suggested that the winter leaves dissipated a large amount of excess energy as heat. Because the cold winter leaves had lost normal physiological function, the heat dissipation depended solely on changes in the photosystem II supercomplex rather than the xanthophyll cycle. These findings imply that more attention should be paid to heat dissipation via changes in the photosystem complex structure during the growing season.
Qiao, Yan; Polzer, Frank; Kirmse, Holm; Steeg, Egon; Kühn, Sergei; Friede, Sebastian; Kirstein, Stefan; Rabe, Jürgen P
2015-02-24
Resonant coupling between distinct excitons in organic supramolecular assemblies and inorganic semiconductors is supposed to offer an approach to optoelectronic devices. Here, we report on colloidal nanohybrids consisting of self-assembled tubular J-aggregates decorated with semiconductor quantum dots (QDs) via electrostatic self-assembly. The role of QDs in the energy transfer process can be switched from a donor to an acceptor by tuning its size and thereby the excitonic transition energy while keeping the chemistry unaltered. QDs are located within a close distance (<4 nm) to the J-aggregate surface, without harming the tubular structures and optical properties of J-aggregates. The close proximity of J-aggregates and QDs allows the strong excitation energy transfer coupling, which is around 92% in the case of energy transfer from the QD donor to the J-aggregate acceptor and approximately 20% in the reverse case. This system provides a model of an organic-inorganic light-harvesting complex using methods of self-assembly in aqueous solution, and it highlights a route toward hierarchical synthesis of structurally well-defined supramolecular objects with advanced functionality.
Orf, Gregory S.; Saer, Rafael G.; Niedzwiedzki, Dariusz M.; Zhang, Hao; McIntosh, Chelsea L.; Schultz, Jason W.; Mirica, Liviu M.; Blankenship, Robert E.
2016-01-01
Light-harvesting antenna complexes not only aid in the capture of solar energy for photosynthesis, but regulate the quantity of transferred energy as well. Light-harvesting regulation is important for protecting reaction center complexes from overexcitation, generation of reactive oxygen species, and metabolic overload. Usually, this regulation is controlled by the association of light-harvesting antennas with accessory quenchers such as carotenoids. One antenna complex, the Fenna–Matthews–Olson (FMO) antenna protein from green sulfur bacteria, completely lacks carotenoids and other known accessory quenchers. Nonetheless, the FMO protein is able to quench energy transfer in aerobic conditions effectively, indicating a previously unidentified type of regulatory mechanism. Through de novo sequencing MS, chemical modification, and mutagenesis, we have pinpointed the source of the quenching action to cysteine residues (Cys49 and Cys353) situated near two low-energy bacteriochlorophylls in the FMO protein from Chlorobaculum tepidum. Removal of these cysteines (particularly removal of the completely conserved Cys353) through N-ethylmaleimide modification or mutagenesis to alanine abolishes the aerobic quenching effect. Electrochemical analysis and electron paramagnetic resonance spectra suggest that in aerobic conditions the cysteine thiols are converted to thiyl radicals which then are capable of quenching bacteriochlorophyll excited states through electron transfer photochemistry. This simple mechanism has implications for the design of bio-inspired light-harvesting antennas and the redesign of natural photosynthetic systems. PMID:27335466
NASA Astrophysics Data System (ADS)
Beiersdorfer, P.; Safronova, U. I.; Safronova, A. S.
2012-06-01
Energy levels, radiative transition probabilities, and autoionization rates for [Cd]4f^145p^65l'nl, [Cd]4f^145p^66l''nl, [Cd]4f^145p^55d^2nl, [Cd]4f^145p^55d6l''nl, [Cd]4f^135p^65d^2nl, and [Cd]4f^135p^65d6l''nl (l'=d, f, g , l''=s,p,d,f, g, n=5-7) states of Yb-like tungsten (W^4+) are calculated using the RMBPT, HULLAC, and COWAN codes. Branching ratios relative to the [Cd]4f^145p^65d, [Cd]4f^145p^66s, and [Cd]4f^145p^66p thresholds in Tm-like tungsten and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are determined for the singly excited, as well as non-autoionizing core-excited states in Yb-like tungsten. Contributions from the autoionizing doubly excited states and core-excited states (with n up to 100), which are particulary important for calculating total DR rates, are estimated. Synthetic dielectronic satellite spectra from Yb-like W are simulated in a broad spectral range from 200 to 1400 å. These calculations provide recommended values critically evaluated for their accuracy for a number of W^4+ properties useful for a variety of applications including for fusion applications.
Rhee, Young Min; Head-Gordon, Martin
2007-02-01
Two modifications of the perturbative doubles correction to configuration interaction with single substitutions (CIS(D)) are suggested, which are excited state analogs of ground state scaled second order Moeller-Plesset (MP2) methods. The first approach employs two parameters to scale the two spin components of the direct term of CIS(D), starting from the two-parameter spin-component scaled (SCS) MP2 ground state, and is termed SCS-CIS(D). An efficient resolution-of-the-identity (RI) implementation of this approach is described. The second approach employs a single parameter to scale only the opposite-spin direct term of CIS(D), starting from the one-parameter scaled opposite spin (SOS) MP2 ground state, and is called SOS-CIS(D). By utilizing auxiliary basis expansions and a Laplace transform, a fourth order algorithm for SOS-CIS(D) is described and implemented. The parameters describing SCS-CIS(D) and SOS-CIS(D) are optimized based on a training set including valence excitations of various organic molecules and Rydberg transitions of water and ammonia, and they significantly improve upon CIS(D) itself. The accuracy of the two methods is found to be comparable. This arises from a strong correlation between the same-spin and opposite-spin portions of the excitation energy terms. The methods are successfully applied to the zincbacteriochlorin-bacteriochlorin charge transfer transition, for which time-dependent density functional theory, with presently available exchange-correlation functionals, is known to fail. The methods are also successfully applied to describe various electronic transitions outside of the training set. The efficiency of SOS-CIS(D) and the auxiliary basis implementation of CIS(D) and SCS-CIS(D) are confirmed with a series of timing tests.
NASA Astrophysics Data System (ADS)
Gorelik, M. L.; Shlomo, S.; Tulupov, B. A.; Urin, M. H.
2016-11-01
The particle-hole dispersive optical model, developed recently, is applied to study properties of high-energy isoscalar monopole excitations in medium-heavy mass spherical nuclei. The energy-averaged strength functions of the isoscalar giant monopole resonance and its overtone in 208Pb are analyzed. In particular, we analyze the energy-averaged isoscalar monopole double transition density, the key quantity in the description of the hadron-nucleus inelastic scattering, and studied the validity of the factorization approximation using semi classical and microscopic one body transition densities, respectively, in calculating the cross sections for the excitation of isoscalar giant resonances by inelastic alpha scattering.
NASA Astrophysics Data System (ADS)
Teillet-Billy, D.; Stibbe, D. T.; Tennyson, J.; Gauyacq, J. P.
1999-12-01
The electron impact vibrational excitation of H 2 molecules physisorbed on a free-electron metal surface is studied theoretically at collision energies of a few eV. The role of the short-lived low-lying 2Σ u resonance is investigated. The electron scattering by a free H 2 molecule is described by the R-matrix method and the corresponding results are used to model the electron scattering by the physisorbed molecule with the coupled angular mode (CAM) method. The strength of the vibrational excitation and, in particular, the overtone vibrational excitation ratio are found to be smaller for the physisorbed molecule than for the free molecule. However, the energy dependence of the vibrational excitation process is found to be weakly influenced by the physisorption, as observed experimentally by Demuth et al. [Phys. Rev. Lett. 47 (1981) 1166].
Jennings, Robert C; Zucchelli, Giuseppe
2014-01-01
We examine ergodicity and configurational entropy for a dilute pigment solution and for a suspension of plant photosystem particles in which both ground and excited state pigments are present. It is concluded that the pigment solution, due to the extreme brevity of the excited state lifetime, is non-ergodic and the configurational entropy approaches zero. Conversely, due to the rapid energy transfer among pigments, each photosystem is ergodic and the configurational entropy is positive. This decreases the free energy of the single photosystem pigment array by a small amount. On the other hand, the suspension of photosystems is non-ergodic and the configurational entropy approaches zero. The overall configurational entropy which, in principle, includes contributions from both the single excited photosystems and the suspension which contains excited photosystems, also approaches zero. Thus the configurational entropy upon photon absorption by either a pigment solution or a suspension of photosystem particles is approximately zero.
NASA Astrophysics Data System (ADS)
Kharchenko, V. A.; Lewkow, N.; Gacesa, M.
2014-12-01
Formation and evolution of neutral fluxes of atoms and molecules escaping from the Mars atmosphere have been investigated for the sputtering and photo-chemical mechanisms. Energy and momentum transfer in collisions between the atmospheric gas and fast atoms and molecules have been considered using our recently obtained angular and energy dependent cross sections[1]. We have showed that accurate angular dependent collision cross sections are critical for the description of the energy relaxation of precipitating keV energetic ions/ENAs and for computations of altitude profiles of the fast atom and molecule production rates in recoil collisions. Upward and escape fluxes of the secondary energetic He and O atoms and H2, N2, CO and CO2 molecules, induced by precipitating ENAs, have been determined and their non-thermal energy distribution functions have been computed at different altitudes for different solar conditions. Precipitation and energy deposition of the energetic H2O molecules and products of their dissociations into the Mars atmosphere in the Comet C/2013 A1 (Siding Spring) - Mars interaction have been modeled using accurate cross sections. Reflection of precipitating ENAs by the Mars atmosphere has been analyzed in detail. [1] N. Lewkow and V. Kharchenko, "Precipitation of Energetic Neutral Atoms and Escape Fluxes induced from the Mars Atmosphere, ApJ, v.790, p.98 (2014).
Accurate Analytic Potential Energy Function and Spectroscopic Study for G1Πg State of Dimer 7Li2
NASA Astrophysics Data System (ADS)
Shi, De-Heng; Ma, Heng; Sun, Jin-Feng; Zhu, Zun-Lue
2007-06-01
The reasonable dissociation limit for the G1Πg state of dimer 7Li2 is determined. The equilibrium internuclear distance, dissociation energy, harmonic frequency, vibrational zero energy, and adiabatic excitation energy are calculated using a symmetry-adapted-cluster configuration-interaction method in complete active space in Gaussian03 program package at such numerous basis sets as 6-311++G, 6-311++G(2df,2pd), 6-311++G(2df,p), cc-PVTZ, 6-311++G(3df,3pd), CEP-121G, 6-311++G(2df,pd), 6-311++G(d,p),6-311G(3df,3pd), D95(3df,3pd), 6-311++G(3df,2p), 6-311++G(2df), 6-311++G(df,pd) D95V++, and DGDZVP. The complete potential energy curves are obtained at these sets over a wide internuclear distance range and have least squares fitted to Murrell-Sorbie function. The conclusion shows that the basis set 6-311++G(2df,p) is a most suitable one for the G1Πg state. At this basis set, the calculated spectroscopic constants Te, De, E0, Re, ωe, ωeχe, αe, and Be are of 3.9523 eV, 0.813 06 eV, 113.56 cm-1, 0.320 15 nm, 227.96 cm-1, 1.6928 cm-1, 0.004 436 cm-1, and 0.4689 cm-1, respectively, which are in good agreement with measurements whenever available. The total 50 vibrational levels and corresponding inertial rotation constants are for the first time calculated and compared with available RKR data. And good agreement with measurements is obtained.
Excited baryon form-factors at high momentum transfer at CEBAF at higher energies
Stoler, P.
1994-04-01
The possibilities of measuring the properties of excited nucleons at high Q{sup 2} by means of exclusive single meson production at CEBAF with an electron energy of 8 GeV is considered. The motivation is to access short range phenomena in baryon structure, and to investigate the transition from the low Q{sup 2} non-perturbative QCD regime, where constituent quark models are valid, to higher Q{sup 2} where it is believed perturbative QCD plays an increasingly important role. It is found that high quality baryon decay angular distributions can be obtained for the most prominent states up to Q{sup 2} {approximately} 12 GeV{sup 2}/c{sup 2} using a set of moderate resolution, large solid angle magnetic spectrometers.
Logarithmic mean excitation energies: II. Helium, lithium, beryllium, and the 2s state of hydrogen
NASA Astrophysics Data System (ADS)
Rosendorff, S.; Schlaile, H. G.
1993-10-01
The four logarithmic excitation eneriges I(ν) for ν=-1, 0, 1, and 2 have been calculated for helium, lithium, beryllium, and the 2s state of hydrogen. They appear in the expressions of the total cross section, the stopping power, and the straggling effect for fast charged particles, and in the expressions of the Lamb shift of atomic energy levels. The method was introduced some years ago [Rosendorff and Birman, Phys. Rev. A 31, 612 (1985)]. For hydrogen the method is rigorous. Exact one-particle wave functions given by Clementi were used. Thus, correlation and symmetrization effects were neglected. For the nonhydrogen states, the relevant differential equations were solved by using a computer. An effective charge was defined which has interesting features. It is helpful in gaining some physical insight into the results obtained for helium and the 1s and 2s states of lithium and beryllium.
Chen, T. E-mail: henning@fysik.su.se; Gatchell, M.; Stockett, M. H.; Schmidt, H. T.; Cederquist, H.; Zettergren, H. E-mail: henning@fysik.su.se; Delaunay, R.; Rousseau, P.; Adoui, L.; Domaracka, A.; Huber, B. A.; Tielens, A. G. G. M.
2015-04-14
We have investigated the effectiveness of molecular hydrogen (H{sub 2}) formation from Polycyclic Aromatic Hydrocarbons (PAHs) which are internally heated by collisions with keV ions. The present and earlier experimental results are analyzed in view of molecular structure calculations and a simple collision model. We estimate that H{sub 2} formation becomes important for internal PAH temperatures exceeding about 2200 K, regardless of the PAH size and the excitation agent. This suggests that keV ions may effectively induce such reactions, while they are unlikely due to, e.g., absorption of single photons with energies below the Lyman limit. The present analysis also suggests that H{sub 2} emission is correlated with multi-fragmentation processes, which means that the [PAH-2H]{sup +} peak intensities in the mass spectra may not be used for estimating H{sub 2}-formation rates.
Nesbitt, D.J. |; Field, R.W.
1996-08-01
A pedagogical overview of intramolecular vibrational redistribution (IVR) phenomena in vibrationally excited molecules is presented. In the interest of focus and simplicity, the topics covered deal primarily with IVR in the ground electronic state, relying on examples from the literature to illustrate key points. The experimental topics discussed attempt to sample systematically three different energy regimes on the full potential surface corresponding to (i) `low`, e.g., moderate- to high-resolution vibrational spectroscopies, (ii) `intermediate`, e.g., stimulated emission pumping and high overtone spectroscopies, and (iii) `high`, e.g., photofragment/predissociation dynamical spectroscopies. The interplay between experiment and theory is highlighted here because it has facilitated enormous advances in the field over the past decade. 183 refs., 13 figs., 2 tabs.
Low-energy d-d excitations in MnO studied by resonant x-ray fluorescence spectroscopy
Butorin, S.M.; Guo, J.; Magnuson, M.
1997-04-01
Resonant soft X-ray emission spectroscopy has been demonstrated to possess interesting abilities for studies of electronic structure in various systems, such as symmetry probing, alignment and polarization dependence, sensitivity to channel interference, etc. In the present abstract the authors focus on the feasibility of resonant soft X-ray emission to probe low energy excitations by means of resonant electronic X-ray Raman scattering. Resonant X-ray emission can be regarded as an inelastic scattering process where a system in the ground state is transferred to a low excited state via a virtual core excitation. The energy closeness to a core excitation of the exciting radiation enhances the (generally) low probability for inelastic scattering at these wavelengths. Therefore soft X-ray emission spectroscopy (in resonant electronic Raman mode) can be used to study low energy d-d excitations in transition metal systems. The involvement of the intermediate core state allows one to use the selection rules of X-ray emission, and the appearance of the elastically scattered line in the spectra provides the reference to the ground state.
Sub-barrier fusion excitation function data and energy dependent Woods-Saxon potential
NASA Astrophysics Data System (ADS)
Gautam, Manjeet Singh
2016-07-01
This paper analyzed the role of intrinsic degrees of freedom of colliding nuclei in the enhancement of sub-barrier fusion cross-section data of various heavy ion fusion reactions. The influences of inelastic surface vibrations of colliding pairs are found to be dominant and their couplings result in the significantly larger fusion enhancement over the predictions of the one dimensional barrier penetration model at sub-barrier energies. The theoretical calculations are performed by using energy dependent Woods-Saxon potential model (EDWSP model) in conjunction with the one dimensional Wong formula. The effects of dominant intrinsic channels are entertained within framework of the coupled channel calculations obtained by using the code CCFULL. It is quite interesting to note that the energy dependence in Woods-Saxon potential simulates the effects of inelastic surface vibrational states of reactants wherein significantly larger value of diffuseness parameter ranging from a = 0.85 fm to a = 0.95 fm is required to address the observed fusion excitation function data of the various heavy ion fusion reactions.
Praveen, Vakayil K; Ranjith, Choorikkat; Bandini, Elisa; Ajayaghosh, Ayyappanpillai; Armaroli, Nicola
2014-06-21
Oligo(phenylenevinylene)s (OPVs) are extensively investigated π-conjugated molecules that exhibit absorption and fluorescence in the UV-Vis spectral region, which can be widely tuned by chemical functionalisation and external control (e.g. solvent, temperature, pH). Further modulation of the optoelectronic properties of OPVs is possible by supramolecular aggregation, primarily driven by hydrogen bonding or π-stacking interactions. In recent years, extensive research work has been accomplished in exploiting the unique combination of the structural and electronic properties of OPVs, most of which has been targeted at the preparation of molecules and materials featuring photoinduced energy transfer. This review intends to offer an overview of the multicomponent arrays and self-assembled materials based on OPV which have been designed to undergo energy transfer by means of a thorough choice of excitation donor-acceptor partners. We present a few selected examples of photoactive dyads and triads containing organic moieties (e.g. fullerene, phenanthroline) as well as coordination compounds (Cu(I) complexes). We then focus more extensively on self-assembled materials containing suitably functionalised OPVs that lead to hydrogen bonded aggregates, helical structures, gels, nanoparticles, vesicles, mesostructured organic-inorganic hybrid films, functionalised nanoparticles and quantum dots. In most cases, these materials exhibit luminescence whose colour and intensity is related to the efficiency and direction of the energy transfer processes.
Jun, Sunhong; Yang, Cheolhee; Kim, Tae Wu; Isaji, Megumi; Tamiaki, Hitoshi; Ihee, Hyotcherl; Kim, Jeongho
2015-07-21
Chlorosomes are the largest light harvesting complexes in nature and consist of many bacteriochlorophyll pigments forming self-assembled J-aggregates. In this work, we use two-dimensional electronic spectroscopy (2D-ES) to investigate ultrafast dynamics of excitation energy transfer (EET) in chlorosomes and their temperature dependence. From time evolution of the measured 2D electronic spectra of chlorosomes, we directly map out the distribution of the EET rate among the manifold of exciton states in a 2D energy space. In particular, it is found that the EET rate varies gradually depending on the energies of energy-donor and energy-acceptor states. In addition, from comparative 2D-ES measurements at 77 K and room temperature, we show that the EET rate exhibits subtle dependence on both the exciton energy and temperature, demonstrating the effect of thermal excitation on the EET rate. This observation suggests that active thermal excitation at room temperature prevents the excitation trapping at low-energy states and thus promotes efficient exciton diffusion in chlorosomes at ambient temperature.
Szabó, István; Telekes, Hajnalka; Czakó, Gábor
2015-06-28
We develop a full-dimensional global analytical potential energy surface (PES) for the F(-) + CH3F reaction by fitting about 50 000 energy points obtained by an explicitly correlated composite method based on the second-order Møller-Plesset perturbation-F12 and coupled-cluster singles, doubles, and perturbative triples-F12a methods and the cc-pVnZ-F12 [n = D, T] basis sets. The PES accurately describes the (a) back-side attack Walden inversion mechanism involving the pre- and post-reaction (b) ion-dipole and (c) hydrogen-bonded complexes, the configuration-retaining (d) front-side attack and (e) double-inversion substitution pathways, as well as (f) the proton-abstraction channel. The benchmark quality relative energies of all the important stationary points are computed using the focal-point analysis (FPA) approach considering electron correlation up to coupled-cluster singles, doubles, triples, and perturbative quadruples method, extrapolation to the complete basis set limit, core-valence correlation, and scalar relativistic effects. The FPA classical(adiabatic) barrier heights of (a), (d), and (e) are -0.45(-0.61), 46.07(45.16), and 29.18(26.07) kcal mol(-1), respectively, the dissociation energies of (b) and (c) are 13.81(13.56) and 13.73(13.52) kcal mol(-1), respectively, and the endothermicity of (f) is 42.54(38.11) kcal mol(-1). Quasiclassical trajectory computations of cross sections, scattering (θ) and initial attack (α) angle distributions, as well as translational and internal energy distributions are performed for the F(-) + CH3F(v = 0) reaction using the new PES. Apart from low collision energies (Ecoll), the SN2 excitation function is nearly constant, the abstraction cross sections rapidly increase with Ecoll from a threshold of ∼40 kcal mol(-1), and retention trajectories via double inversion are found above Ecoll = ∼ 30 kcal mol(-1), and at Ecoll = ∼ 50 kcal mol(-1), the front-side attack cross sections start to increase very rapidly. At
NASA Astrophysics Data System (ADS)
Szabó, István; Telekes, Hajnalka; Czakó, Gábor
2015-06-01
We develop a full-dimensional global analytical potential energy surface (PES) for the F- + CH3F reaction by fitting about 50 000 energy points obtained by an explicitly correlated composite method based on the second-order Møller-Plesset perturbation-F12 and coupled-cluster singles, doubles, and perturbative triples-F12a methods and the cc-pVnZ-F12 [n = D, T] basis sets. The PES accurately describes the (a) back-side attack Walden inversion mechanism involving the pre- and post-reaction (b) ion-dipole and (c) hydrogen-bonded complexes, the configuration-retaining (d) front-side attack and (e) double-inversion substitution pathways, as well as (f) the proton-abstraction channel. The benchmark quality relative energies of all the important stationary points are computed using the focal-point analysis (FPA) approach considering electron correlation up to coupled-cluster singles, doubles, triples, and perturbative quadruples method, extrapolation to the complete basis set limit, core-valence correlation, and scalar relativistic effects. The FPA classical(adiabatic) barrier heights of (a), (d), and (e) are -0.45(-0.61), 46.07(45.16), and 29.18(26.07) kcal mol-1, respectively, the dissociation energies of (b) and (c) are 13.81(13.56) and 13.73(13.52) kcal mol-1, respectively, and the endothermicity of (f) is 42.54(38.11) kcal mol-1. Quasiclassical trajectory computations of cross sections, scattering (θ) and initial attack (α) angle distributions, as well as translational and internal energy distributions are performed for the F- + CH3F(v = 0) reaction using the new PES. Apart from low collision energies (Ecoll), the SN2 excitation function is nearly constant, the abstraction cross sections rapidly increase with Ecoll from a threshold of ˜40 kcal mol-1, and retention trajectories via double inversion are found above Ecoll = ˜ 30 kcal mol-1, and at Ecoll = ˜ 50 kcal mol-1, the front-side attack cross sections start to increase very rapidly. At low Ecoll, the
Excited state potential energy surfaces and their interactions in Fe(IV)=O active sites.
Srnec, Martin; Wong, Shaun D; Solomon, Edward I
2014-12-21
The non-heme ferryl active sites are of significant interest for their application in biomedical and green catalysis. These sites have been shown to have an S = 1 or S = 2 ground spin state; the latter is functional in biology. Low-temperature magnetic circular dichroism (LT MCD) spectroscopy probes the nature of the excited states in these species including ligand-field (LF) states that are otherwise difficult to study by other spectroscopies. In particular, the temperature dependences of MCD features enable their unambiguous assignment and thus determination of the low-lying excited states in two prototypical S = 1 and S = 2 NHFe(IV)[double bond, length as m-dash]O complexes. Furthermore, some MCD bands exhibit vibronic structures that allow mapping of excited-state interactions and their effects on the potential energy surfaces (PESs). For the S = 2 species, there is also an unusual spectral feature in both near-infrared absorption and MCD spectra - Fano antiresonance (dip in Abs) and Fano resonance (sharp peak in MCD) that indicates the weak spin-orbit coupling of an S = 1 state with the S = 2 LF state. These experimental data are correlated with quantum-chemical calculations that are further extended to analyze the low-lying electronic states and the evolution of their multiconfigurational characters along the Fe-O PESs. These investigations show that the lowest-energy states develop oxyl Fe(III) character at distances that are relevant to the transition state (TS) for H-atom abstraction and define the frontier molecular orbitals that participate in the reactivity of S = 1 vs. S = 2 non-heme Fe(IV)[double bond, length as m-dash]O active sites. The S = 1 species has only one available channel that requires the C-H bond of a substrate to approach perpendicular to the Fe-oxo bond (the π channel). In contrast, there are three channels (one σ and two π) available for the S = 2 non-heme Fe(IV)[double bond, length as m-dash]O system allowing C-H substrate approach
Trivedi, Evan R; Eliseeva, Svetlana V; Jankolovits, Joseph; Olmstead, Marilyn M; Petoud, Stéphane; Pecoraro, Vincent L
2014-01-29
Near-infrared (NIR) luminescent lanthanide complexes hold great promise for practical applications, as their optical properties have several complementary advantages over organic fluorophores and semiconductor nanoparticles. The fundamental challenge for lanthanide luminescence is their sensitization through suitable chromophores. The use of the metallacrown (MC) motif is an innovative strategy to arrange several organic sensitizers at a well-controlled distance from a lanthanide cation. Herein we report a series of lanthanide “encapsulated sandwich” MC complexes of the form Ln3+ [12-MC(Zn(II),quinHA)-4]2[24-MC(Zn(II),quinHA)-8] (Ln3+ [Zn(II)MC(quinHA)]) in which the MC framework is formed by the self-assembly of Zn2+ ions and tetradentate chromophoric ligands based on quinaldichydroxamic acid (quinHA). A first-generation of luminescent MCs was presented previously but was limited due to excitation wavelengths in the UV. We report here that through the design of the chromophore of the MC assembly, we have significantly shifted the absorption wavelength toward lower energy (450 nm). In addition to this near-visible inter- and/or intraligand charge transfer absorption, Ln3+ [Zn(II)MC(quinHA)] exhibits remarkably high quantum yields, long luminescence lifetimes (CD3OD; Yb3+, QLn(L) = 2.88(2)%, τobs = 150.7(2) μs; Nd3+, QLn(L) = 1.35(1)%, τobs = 4.11(3) μs; Er3+, QLn(L) = 3.60(6)·10–2%, τobs = 11.40(3) μs), and excellent photostability. Quantum yields of Nd3+ and Er3+ MCs in the solid state and in deuterated solvents, upon excitation at low energy, are the highest values among NIR-emitting lanthanide complexes containing C–H bonds. The versatility of the MC strategy allows modifications in the excitation wavelength and absorptivity through the appropriate design of the ligand sensitizer, providing a highly efficient platform with tunable properties.
Beste, Ariana; Vazquez-Mayagoitia, Alvaro; Ortiz, J. Vincent
2013-01-01
A direct method (D-Delta-MBPT(2)) to calculate second-order ionization potentials (IPs), electron affinities (EAs), and excitation energies is developed. The Delta-MBPT(2) method is defined as the correlated extension of the Delta-HF method. Energy differences are obtained by integrating the energy derivative with respect to occupation numbers over the appropriate parameter range. This is made possible by writing the second-order energy as a function of the occupation numbers. Relaxation effects are fully included at the SCF level. This is in contrast to linear response theory, which makes the D-Delta-MBPT(2) applicable not only to single excited but also higher excited states. We show the relationship of the D-Delta-MBPT(2) method for IPs and EAs to a second-order approximation of the effective Fock-space coupled-cluster Hamiltonian and a second-order electron propagator method. We also discuss the connection between the D-Delta-MBPT(2) method for excitation energies and the CIS-MP2 method. Finally, as a proof of principle, we apply our method to calculate ionization potentials and excitation energies of some small molecules. For IPs, the Delta-MBPT(2) results compare well to the second-order solution of the Dyson equation. For excitation energies, the deviation from EOM-CCSD increases when correlation becomes more important. When using the numerical integration technique, we encounter difficulties that prevented us from reaching the Delta-MBPT(2) values. Most importantly, relaxation beyond the Hartree Fock level is significant and needs to be included in future research.
NASA Astrophysics Data System (ADS)
Pislari, Tatiana; Enaki, Nicolae
2016-12-01
The energy transferring between three q-bits system flying simultaneously through an optical cavity, is discussed. It is observed the migration of energy from one excited radiator with dipole forbidden transitions relatively to another two- radiators with half excitation energy of first atom. Photon entangled state between distinct atoms and their transfer is studied. These atoms in our interpretations are named, D - dipole forbidden atom, S1 and S2 - two dipole active atoms with summer energy ћɷ1 + ћɷ2 = ћɷn, ɷ1 observe the periodical transfer of energy from D- atom to ensemble of two S- atoms. This effect may be used for quantum gates processing in which the energy transfer depends on the input information. The quantum discord and entanglement for this system of q-bits was explored.
Accurate double many-body expansion potential energy surface for the 2(1)A' state of N2O.
Li, Jing; Varandas, António J C
2014-08-28
An accurate double many-body expansion potential energy surface is reported for the 2(1)A' state of N2O. The new double many-body expansion (DMBE) form has been fitted to a wealth of ab initio points that have been calculated at the multi-reference configuration interaction level using the full-valence-complete-active-space wave function as reference and the cc-pVQZ basis set, and subsequently corrected semiempirically via double many-body expansion-scaled external correlation method to extrapolate the calculated energies to the limit of a complete basis set and, most importantly, the limit of an infinite configuration interaction expansion. The topographical features of the novel potential energy surface are then examined in detail and compared with corresponding attributes of other potential functions available in the literature. Exploratory trajectories have also been run on this DMBE form with the quasiclassical trajectory method, with the thermal rate constant so determined at room temperature significantly enhancing agreement with experimental data.
NASA Astrophysics Data System (ADS)
Lee, Myeong H.; Troisi, Alessandro
2017-02-01
It has been reported in recent years that vibronic resonance between vibrational energy of the intramolecular nuclear mode and excitation-energy difference is crucial to enhance excitation energy transport in light harvesting proteins. Here we investigate how vibronic enhancement induced by vibronic resonance is influenced by the details of local and non-local exciton-phonon interactions. We study a heterodimer model with parameters relevant to the light-harvesting proteins with the surrogate Hamiltonian quantum dynamics method in a vibronic basis. In addition, the impact of field-driven excitation on the efficiency of population transfer is compared with the instantaneous excitation, and the effect of multi-mode vibronic coupling is presented in comparison with the coupling to a single effective vibrational mode. We find that vibronic enhancement of site population transfer is strongly suppressed with the increase of non-local exciton-phonon interaction and increasing the number of strongly coupled high-frequency vibrational modes leads to a further decrease in vibronic enhancement. Our results indicate that vibronic enhancement is present but may be much smaller than previously thought and therefore care needs to be taken when interpreting its role in excitation energy transport. Our results also suggest that non-local exciton-phonon coupling, which is related to the fluctuation of the excitonic coupling, may be as important as local exciton-phonon coupling and should be included in any quantum dynamics model.
McCarthy, Shane P; Thakkar, Ajit J
2011-01-28
All-electron correlation energies E(c) are not very well-known for atoms with more than 18 electrons. Hence, coupled-cluster calculations in carefully designed basis sets are combined with fully converged second-order Møller-Plesset perturbation theory (MP2) computations to obtain fairly accurate, nonrelativistic E(c) values for the 12 closed-shell atoms from Ar to Rn. These energies will be useful for the evaluation and parameterization of density functionals. The results show that MP2 overestimates ∣E(c)∣ for heavy atoms. Spin-component scaling of the MP2 correlation energy is used to provide a simple explanation for this overestimation.
Issack, Bilkiss B; Roy, Pierre-Nicholas
2005-08-22
An approach for the inclusion of geometric constraints in semiclassical initial value representation calculations is introduced. An important aspect of the approach is that Cartesian coordinates are used throughout. We devised an algorithm for the constrained sampling of initial conditions through the use of multivariate Gaussian distribution based on a projected Hessian. We also propose an approach for the constrained evaluation of the so-called Herman-Kluk prefactor in its exact log-derivative form. Sample calculations are performed for free and constrained rare-gas trimers. The results show that the proposed approach provides an accurate evaluation of the reduction in zero-point energy. Exact basis set calculations are used to assess the accuracy of the semiclassical results. Since Cartesian coordinates are used, the approach is general and applicable to a variety of molecular and atomic systems.
NASA Astrophysics Data System (ADS)
Dixit, V. K.; Porwal, S.; Singh, S. D.; Sharma, T. K.; Ghosh, Sandip; Oak, S. M.
2014-02-01
Temperature dependence of the photoluminescence (PL) peak energy of bulk and quantum well (QW) structures is studied by using a new phenomenological model for including the effect of localized states. In general an anomalous S-shaped temperature dependence of the PL peak energy is observed for many materials which is usually associated with the localization of excitons in band-tail states that are formed due to potential fluctuations. Under such conditions, the conventional models of Varshni, Viña and Passler fail to replicate the S-shaped temperature dependence of the PL peak energy and provide inconsistent and unrealistic values of the fitting parameters. The proposed formalism persuasively reproduces the S-shaped temperature dependence of the PL peak energy and provides an accurate determination of the exciton localization energy in bulk and QW structures along with the appropriate values of material parameters. An example of a strained InAs0.38P0.62/InP QW is presented by performing detailed temperature and excitation intensity dependent PL measurements and subsequent in-depth analysis using the proposed model. Versatility of the new formalism is tested on a few other semiconductor materials, e.g. GaN, nanotextured GaN, AlGaN and InGaN, which are known to have a significant contribution from the localized states. A quantitative evaluation of the fractional contribution of the localized states is essential for understanding the temperature dependence of the PL peak energy of bulk and QW well structures having a large contribution of the band-tail states.
Lin, Shi Ying; Sun, Zhigang; Guo, Hua; Zhang, Dong Hui; Honvault, Pascal; Xie, Daiqian; Lee, Soo-Y
2008-01-31
We present accurate quantum calculations of the integral cross section and rate constant for the H + O2 --> OH + O combustion reaction on a recently developed ab initio potential energy surface using parallelized time-dependent and Chebyshev wavepacket methods. Partial wave contributions up to J = 70 were computed with full Coriolis coupling, which enabled us to obtain the initial state-specified integral cross sections up to 2.0 eV of the collision energy and thermal rate constants up to 3000 K. The integral cross sections show a large reaction threshold due to the quantum endothermicity of the reaction, and they monotonically increase with the collision energy. As a result, the temperature dependence of the rate constant is of the Arrhenius type. In addition, it was found that reactivity is enhanced by reactant vibrational excitation. The calculated thermal rate constant shows a significant improvement over that obtained on the DMBE IV potential, but it still underestimates the experimental consensus.
Bayrakceken, Fuat
2005-04-01
In principle, the optical energy absorbed by a complex molecule raises that molecule to one of its excited states, and afterwards this excitation energy decays through the relaxation channels. Initially, electronically excited naphthalene emits photons and these emitted photons are absorbed by the acceptor molecule biacetyl, then excited biacetyl fluoresces. In this investigation radiative energy transfer-time is measured in cyclohexane by one and two-photon excitations. The UV-vis spectrum of biacetyl vapor at room temperature conditions was broad and structureless.
Gatti, Matteo; Panaccione, Giancarlo; Reining, Lucia
2015-03-20
The effects of electron interaction on spectral properties can be understood in terms of coupling between excitations. In transition-metal oxides, the spectral function close to the Fermi level and low-energy excitations between d states have attracted particular attention. In this work we focus on photoemission spectra of vanadium dioxide over a wide (10 eV) range of binding energies. We show that there are clear signatures of the metal-insulator transition over the whole range due to a cross coupling of the delocalized s and p states with low-energy excitations between the localized d states. This coupling can be understood by advanced calculations based on many-body perturbation theory in the GW approximation. We also advocate the fact that tuning the photon energy up to the hard-x-ray range can help to distinguish fingerprints of correlation from pure band-structure effects.
FAMBE-pH: a fast and accurate method to compute the total solvation free energies of proteins.
Vorobjev, Yury N; Vila, Jorge A; Scheraga, Harold A
2008-09-04
A fast and accurate method to compute the total solvation free energies of proteins as a function of pH is presented. The method makes use of a combination of approaches, some of which have already appeared in the literature; (i) the Poisson equation is solved with an optimized fast adaptive multigrid boundary element (FAMBE) method; (ii) the electrostatic free energies of the ionizable sites are calculated for their neutral and charged states by using a detailed model of atomic charges; (iii) a set of optimal atomic radii is used to define a precise dielectric surface interface; (iv) a multilevel adaptive tessellation of this dielectric surface interface is achieved by using multisized boundary elements; and (v) 1:1 salt effects are included. The equilibrium proton binding/release is calculated with the Tanford-Schellman integral if the proteins contain more than approximately 20-25 ionizable groups; for a smaller number of ionizable groups, the ionization partition function is calculated directly. The FAMBE method is tested as a function of pH (FAMBE-pH) with three proteins, namely, bovine pancreatic trypsin inhibitor (BPTI), hen egg white lysozyme (HEWL), and bovine pancreatic ribonuclease A (RNaseA). The results are (a) the FAMBE-pH method reproduces the observed pK a's of the ionizable groups of these proteins within an average absolute value of 0.4 p K units and a maximum error of 1.2 p K units and (b) comparison of the calculated total pH-dependent solvation free energy for BPTI, between the exact calculation of the ionization partition function and the Tanford-Schellman integral method, shows agreement within 1.2 kcal/mol. These results indicate that calculation of total solvation free energies with the FAMBE-pH method can provide an accurate prediction of protein conformational stability at a given fixed pH and, if coupled with molecular mechanics or molecular dynamics methods, can also be used for more realistic studies of protein folding, unfolding, and
Morrison, Adrian F; Herbert, John M
2015-11-05
We introduce a charge-embedding scheme for an excited-state quantum chemistry method aimed at weakly interacting molecular aggregates. The Hamiltonian matrix for the aggregate is constructed in a basis of direct products of configuration-state functions for the monomers, and diagonalization of this matrix affords excitation energies within ∼0.2 eV of the corresponding supersystem calculation. Both the basis states and the coupling matrix elements can be computed in a distributed way, resulting in an algorithm whose time-to-solution is independent of the number of chromophores, and we report calculations on systems with almost 55 000 basis functions using fewer than 450 processors. In a semiconducting organic nanotube, we find evidence of ultrafast, coherent dynamics followed by energy localization driven by static disorder. Truncation of the model system has a qualitative effect on the energy-transfer dynamics, demonstrating the importance of simulating an extended portion of the nanotube, which is not feasible using traditional quantum chemistry.
Bertrand, F.E.; Beene, J.R.; Horen, D.J.
1988-01-01
Inelastic scattering of medium energy heavy ions provides very large cross sections and peak-to-continuum ratios for excitation of giant resonances. For energies above about 50 MeV/nucleon, giant resonances are excited primarily through Coulomb excitation, which is indifferent to isospin, thus providing a good probe for the study of isovector giant resonances. The extremely large cross sections available from heavy ion excitation permit the study of rare decay modes of the photon decay of giant resonances following excitation by 22 and 84 MeV/nucleon /sup 17/O projectiles. The singles results at 84 MeV/nucleon yield peak cross sections for the isoscalar giant quadrupole resonance and the isovector giant dipole resonance of approximately 0.8 and 3 barns/sr, respectively. Data on the ground state decay of the isoscalar giant quadrupole and isovector giant dipole resonances are presented and compared with calculations. Decays to low-lying excited states are also discussed. Preliminary results from an experiment to isolate the /sup 208/Pb isovector quadrupole resonance using its gamma decay are presented.
Vibrational excitation in CO by electron impact in the energy range 10-90 eV.
NASA Technical Reports Server (NTRS)
Chutjian, A.; Truhlar, D. G.; Williams, W.; Trajmar, S.
1972-01-01
The ratio of the scattering intensity for the v double prime = 1 excitation to the elastic scattering intensity at 40- and 80-deg scattering angles has been determined for 10- to 90-eV impact energies for electron scattering by CO. These ratio curves exhibit broad peaks near 20-eV impact energy which cannot be accounted for by plane-wave calculations based on potential scattering models. The peaks are indicative of a resonant excitation process (or processes) in the v double prime = 1 channel in the range from 15 to 25 eV.
Sun Yan; Gou Bingcong; Chen Feng
2011-09-28
Energy levels, Auger branching ratios, and radiative rates of the core-excited states of B-like carbon are calculated by the saddle-point variation and saddle-point complex-rotation methods. Relativistic and mass polarization corrections are included using first-order perturbation theory. Calculated Auger channel energies and branching ratios are used to identify high-resolution Auger spectrum in the 300-keV C{sup +}{yields} CH{sub 4} collision experiment. It is found that Auger decay of these five-electron core-excited states gives significant contributions to Auger spectrum in the range of 238-280 eV.
NASA Astrophysics Data System (ADS)
Huo, Pengfei; Coker, David F.
2012-03-01
Two-dimensional photon-echo experiments indicate that excitation energy transfer between chromophores near the reaction center of the photosynthetic purple bacterium Rhodobacter sphaeroides occurs coherently with decoherence times of hundreds of femtoseconds, comparable to the energy transfer time scale in these systems. The original explanation of this observation suggested that correlated fluctuations in chromophore excitation energies, driven by large scale protein motions could result in long lived coherent energy transfer dynamics. However, no significant site energy correlation has been found in recent molecular dynamics simulations of several model light harvesting systems. Instead, there is evidence of correlated fluctuations in site energy-electronic coupling and electronic coupling-electronic coupling. The roles of these different types of correlations in excitation energy transfer dynamics are not yet thoroughly understood, though the effects of site energy correlations have been well studied. In this paper, we introduce several general models that can realistically describe the effects of various types of correlated fluctuations in chromophore properties and systematically study the behavior of these models using general methods for treating dissipative quantum dynamics in complex multi-chromophore systems. The effects of correlation between site energy and inter-site electronic couplings are explored in a two state model of excitation energy transfer between the accessory bacteriochlorophyll and bacteriopheophytin in a reaction center system and we find that these types of correlated fluctuations can enhance or suppress coherence and transfer rate simultaneously. In contrast, models for correlated fluctuations in chromophore excitation energies show enhanced coherent dynamics but necessarily show decrease in excitation energy transfer rate accompanying such coherence enhancement. Finally, for a three state model of the Fenna-Matthews-Olsen light
Excitation energy transfer in the LHC-II trimer: from carotenoids to chlorophylls in space and time.
Martiskainen, Jari; Kananavičius, Robertas; Linnanto, Juha; Lehtivuori, Heli; Keränen, Mika; Aumanen, Viivi; Tkachenko, Nikolai; Korppi-Tommola, Jouko
2011-02-01
Exciton model for description of experimentally determined excitation energy transfer from carotenoids to chlorophylls in the LHC-II trimer of spinach is presented. Such an approach allows connecting the excitonic states to the spatial structure of the complex and hence descriptions of advancements of the initially created excitations in space and time. Carotenoids were excited at 490 nm and at 500 nm and induced absorbance changes probed in the Chl Q(y) region to provide kinetic data that were interpreted by using the results from exciton calculations. Calculations included the 42 chlorophylls and the 12 carotenoids of the complex, Soret, Q(x) and Q(y) states of the chlorophylls, and the main absorbing S(2) state of the carotenoids. According to the calculations excitation at 500 nm populates mostly a mixed Lut S(2) Chl a Soret state, from where excitation is transferred to the Q(x) and Q(y) states of the Chl a's on the stromal side. Internal conversion of the mixed state to a mixed Lut S(1) and Chl a Q(y) state provides a channel for Lut S(1) to Chl a Q(y) energy transfer. The results from the calculations support a picture where excitation at 490 nm populates primarily a mixed neoxanthin S(2) Chl b Soret state. From this state excitation from neoxanthin is transferred to iso-energetic Chl b Soret states or via internal conversion to S(1) Chl b Q(y) states. From the Soret states excitation proceeds via internal conversion to Q(y) states of Chl b's mostly on the lumenal side. A rapid Chl b to Chl a transfer and subsequent transfer to the stromal side Chl a's and to the final state completes the process after 490 nm excitation. The interpretation is further supported by the fact that excitation energy transfer kinetics after excitation of neoxanthin at 490 nm and the Chl b Q(y) band at 647 nm (Linnanto et al., Photosynth Res 87:267-279, 2006) are very similar.
The effect of electron beams on cyclotron maser emission excited by lower-energy cutoffs
NASA Astrophysics Data System (ADS)
Zhao, G. Q.; Feng, H. Q.; Wu, D. J.
2016-05-01
Electron-cyclotron maser (ECM) is one of the most important emission mechanisms in astrophysics and can be excited efficiently by lower-energy cutoffs of power-law electrons. These non-thermal electrons probably propagate as a directed collimated beam along ambient magnetic fields. This paper investigates the ECM, in which the effect of electron beams is emphasized. Results show the dependence of emission properties of the ECM on the beam feature. The maximum growth rate of the extraordinary mode (X2) rapidly decreases as the beam momentum increases, while the growth rate of the ordinary mode (O1) changes slightly. In particular, the ordinary mode can overcome the extraordinary mode and becomes the fastest growth mode once the beam momentum is large enough. This research presents an extension of the conventional studies on ECM driven by lower-energy cutoffs and may be helpful to understand better the emission process of solar type I radio bursts, which are dominated by the ordinary mode emission.
Ground state spin and excitation energies in half-filled Lieb lattices
NASA Astrophysics Data System (ADS)
Ţolea, M.; Niţǎ, M.
2016-10-01
We present detailed spectral calculations for small Lieb lattices having up to N =4 number of cells, in the regime of half-filling, an instance of particular relevance for the nanomagnetism of discrete systems such as quantum dot arrays, due to the degenerate levels at midspectrum. While for the Hubbard interaction model—and even number of sites—the ground state spin is given by the Lieb theorem, the inclusion of long-range interaction—or odd number of sites—makes the spin state not known a priori, which justifies our approach. We calculate also the excitation energies, which are of experimental importance, and find significant variation induced by the interaction potential. One obtains insights on the mechanisms involved that impose as ground state the Lieb state with lower spin rather than the Hund one with maximum spin for the degenerate levels, showing this in the first and second orders of the interaction potential for the smaller lattices. The analytical results agree with the numerical ones, which are performed by exact diagonalization calculations or by a combined mean-field and configuration interaction method. While the Lieb state is always lower in energy than the Hund state, for strong long-range interaction, when possible, another minimal spin state is imposed as ground state.
Bhatt, Sudhir; Pulpytel, Jérome; Ceccone, Giacomo; Lisboa, Patricia; Rossi, François; Kumar, Virendra; Arefi-Khonsari, Farzaneh
2011-12-06
Statistically designed amphiphilic copolymer coatings were deposited onto Thermanox, Si wafer, and quartz crystal microbalance (QCM) substrates via Plasma Enhanced Chemical Vapor Deposition of 1H,1H,2H,2H-perfluorodecyl acrylate and diethylene glycol vinyl ether in an Inductively Excited Low Pressure Plasma reactor. Plasma deposited amphiphilic coatings were characterized by Field Emission Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy, Atomic Force Microscopy, and Water Contact Angle techniques. The surface energy of the coatings can be adjusted between 12 and 70 mJ/m(2). The roughness of the coatings can be tailored depending on the plasma mode used. A very smooth coating was deposited with a CW (continuous wave) power, whereas a rougher surface with R(a) in the range of 2 to 12 nm was deposited with the PW (pulsed wave) mode. The nanometer scale roughness of amphiphilic PFDA-co-DEGVE coatings was found to be in the range of the size of the two proteins namely BSA and lysozyme used to examine for the antifouling properties of the surfaces. The results show that the statistically designed surfaces, presenting a surface energy around 25 mJ/m(2), present no adhesion with respect to both proteins measured by QCM.
Delcorte, Arnaud
2005-10-07
This article reviews the recent progress in the understanding of kiloelectronvolt particle interactions with organic solids, including atomic displacements in a light organic medium, vibrational excitation and desorption of fragments and entire molecules. This new insight is the result of a combination of theoretical and experimental approaches, essentially molecular dynamics (MD) simulations and secondary ion mass spectrometry (SIMS). Classical MD simulations provide us with a detailed microscopic view of the processes occurring in the bombarded target, from the collision cascade specifics to the scenarios of molecular emission. Time-of-flight SIMS measures the mass and energy distributions of sputtered ionized fragments and molecular species, a precious source of information concerning their formation, desorption, ionization and delayed unimolecular dissociation in the gas phase. The mechanisms of energy transfer and sputtering are compared for bulk molecular solids, organic overlayers on metal and large molecules embedded in a low-molecular weight matrix. These comparisons help understand some of the beneficial effects of metal substrates and matrices for the analysis of molecules by SIMS. In parallel, I briefly describe the distinct ionization channels of molecules sputtered from organic solids and overlayers. The specific processes induced by polyatomic projectile bombardment, especially fullerenes, are discussed on the basis of new measurements and calculations. Finally, the perspective addresses the state-of-the-art and potential developments in the fields of surface modification and analysis of organic materials by kiloelectronvolt ion beams.
YIELDS OF IONS AND EXCITED STATES IN NONPOLAR LIQUIDS EXPOSED TO X-RAYS OF 1 TO 30 KEV ENERGY
HOLROYD,R.A.
1999-08-18
When x-rays from a synchrotron source are absorbed in a liquid, the x-ray energy (E{sub x}) is converted by the photoelectric effect into the kinetic energy of the electrons released. For hydrocarbons, absorption by the K-electrons of carbon dominates. Thus the energy of the photoelectron (E{sub pe}) is E{sub x}-E{sub b}, where E{sub b} is the K-shell binding energy of carbon. Additional electrons with energy equal to E{sub b} is released in the Auger process that fills the hole in the K-shell. These energetic electrons will produce many ionizations, excitations and products. The consequences of the high density of ionizations and excitations along the track of the photoelectron and special effects near the K-edge are examined here.
NASA Technical Reports Server (NTRS)
Lee, Timothy J.; Dateo, Christopher E.
2001-01-01
Vertical electronic excitation energies for single states have been computed for the high energy density material (HEDM) Td N4 in order to assess possible synthetic routes that originate from excited electronic states of N2 molecules. Several ab initio theoretical approaches have been used, including complete active space self-consistent field (CASSCF), state averaged CASSCF (SA-CASSCF), singles configuration interaction (CIS), CIS with second-order and third-order correlation corrections [CIS(D)) and CIS(3)], and linear response singles and doubles coupled-cluster (LRCCSD), which is the highest level of theory employed. Standard double zeta polarized (DZP) and triple zeta double polarized (TZ2P) one-particle basis sets were used. The CASSCF calculations are found to overestimate the excitation energies, while the SA-CASSCF approach rectifies this error to some extent, but not completely. The accuracy of the CIS calculations varied depending on the particular state, while the CIS(D), CIS(3), and LRCCSD results are in generally good agreement. Based on the LRCCSD calculations, the lowest six excited singlet states are 9.35(l(sup)T1), 10.01(l(sup)T2), 10.04(1(sup)A2), 10.07(1(sup)E), 10.12(2(sup)T1), and 10.42(2(sup)T2) eV above the ground state, respectively. Comparison of these excited state energies with the energies of possible excited states of N2+N2 fragments, leads us to propose that the most likely synthetic route for Td N4 involving this mechanism arises from combination of two bound quintet states of N2.
NASA Astrophysics Data System (ADS)
Safronova, U. I.; Safronova, A. S.; Beiersdorfer, P.
2012-04-01
Energy levels, radiative transition probabilities and autoionization rates for [Cd]4f145p65l‧nl, [Cd]4f145p66l″nl, [Cd]4f145p55d2nl, [Cd]4f145p55d6l″nl, [Cd]4f135p65d2nl and [Cd]4f135p65d6l″nl (l‧ = d, f, g, l″ = s, p, d, l = s, p, d, f, g and n = 5-7) states of Yb-like tungsten (W4 +) are calculated using the relativistic many-body perturbation theory method (RMBPT code), the multiconfiguration relativistic Hebrew University-Lawrence Livermore Atomic Code (HULLAC code) and the Hartree-Fock relativistic method (COWAN code). Branching ratios relative to the [Cd]4f145p65d, [Cd]4f145p66s and [Cd]4f145p66p thresholds in Tm-like tungsten and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are determined for the singly excited, as well as non-autoionizing core-excited states in Yb-like tungsten. Contributions from the autoionizing doubly excited states [Cd]4f145p65fnl, [Cd]4f145p66l″nl and core-excited [Cd]4f145p55d2nl, [Cd]4f145p55d6l″nl, [Cd]4f135p65d2nl, [Cd]4f135p65d6l″nl states (with n up to 100), which are particulary important for calculating the total DR rates, are estimated. Synthetic dielectronic satellite spectra from Yb-like W are simulated in a broad spectral range from 200 to 1400 Å. These calculations provide recommended values critically evaluated for their accuracy for a number of W4 + properties useful for a variety of applications including for fusion applications.
Collado, Daniel; Remón, Patricia; Vida, Yolanda; Najera, Francisco; Sen, Pratik; Pischel, Uwe; Perez-Inestrosa, Ezequiel
2014-03-01
Aminonaphthalimide-BODIPY energy transfer cassettes were found to show very fast (kEET ≈ 10(10)-10(11) s(-1) and efficient BODIPY fluorescence sensitization. This was observed upon one- and two-photon excitation, which extends the application range of the investigated bichromophoric dyads in terms of accessible excitation wavelengths. In comparison with the direct excitation of the BODIPY chromophore, the two-photon absorption cross-section δ of the dyads is significantly incremented by the presence of the aminonaphthalimide donor [δ ≈ 10 GM for the BODIPY versus 19-26 GM in the dyad at λ(exc)=840 nm; 1 GM (Goeppert-Mayer unit)=10(-50) cm(4) smolecule(-1) photon-(1)]. The electronic decoupling of the donor and acceptor, which is a precondition for the energy transfercassette concept, was demonstrated by time-dependent density functional theory calculations. The applicability of the new probes in the one- and twophoton excitation mode was demonstrated in a proof-of-principle approach in the fluorescence imaging of HeLa cells. To the best of our knowledge, this is the first demonstration of the merging of multiphoton excitation with the energy transfer cassette concept for a BODIPY-containing dyad.
NASA Astrophysics Data System (ADS)
Tsuchida, Toshinori; Odagiri, Takeshi; Ishikawa, Lisa; Yachi, Kazufumi; Shigemura, Keisuke; Ohno, Naruhito; Hosaka, Kouichi; Kitajima, Masashi; Kouchi, Noriyuki
2011-09-01
The electron energy loss spectrum of H2O in coincidence with detecting Lyman-α photons (CoEELS) has been measured at the incident electron energy of 100 eV and electron scattering angle of 8° in the inner valence range in order to investigate the formation and decay of the doubly excited states. The present CoEELS has been compared with that at the infinite incident electron energy and 0° electron scattering angle, which was derived from the density of the dipole oscillator strength of H2O for the emission of the Lyman-α photons against the incident photon energy (Nakano et al 2010 J. Phys. B: At. Mol. Opt. Phys. 43 215206). It is remarkable that there exists a large difference in shape between these CoEELSs. This difference has turned out to be attributed to the noticeable contribution of the forbidden doubly excited states at 100 eV incident electron energy and 8° scattering angle. They lie at 25.0 and 27.4 eV and have been found out in this study. The differential cross sections for the excitation to the superexcited states resulting in H(2p) formation have been obtained at 100 eV and 8° and compared with those at the infinite energy and 0°. The electron collisions at 100 eV and 8° enhance the dissociative double excitation against the dissociative single excitation as compared with the electron collision at the infinite energy and 0°.
Send, Robert; Kaila, Ville R I; Sundholm, Dage
2011-06-07
We investigate how the reduction of the virtual space affects coupled-cluster excitation energies at the approximate singles and doubles coupled-cluster level (CC2). In this reduced-virtual-space (RVS) approach, all virtual orbitals above a certain energy threshold are omitted in the correlation calculation. The effects of the RVS approach are assessed by calculations on the two lowest excitation energies of 11 biochromophores using different sizes of the virtual space. Our set of biochromophores consists of common model systems for the chromophores of the photoactive yellow protein, the green fluorescent protein, and rhodopsin. The RVS calculations show that most of the high-lying virtual orbitals can be neglected without significantly affecting the accuracy of the obtained excitation energies. Omitting all virtual orbitals above 50 eV in the correlation calculation introduces errors in the excitation energies that are smaller than 0.1 eV. By using a RVS energy threshold of 50 eV, the CC2 calculations using triple-ζ basis sets (TZVP) on protonated Schiff base retinal are accelerated by a factor of 6. We demonstrate the applicability of the RVS approach by performing CC2/TZVP calculations on the lowest singlet excitation energy of a rhodopsin model consisting of 165 atoms using RVS thresholds between 20 eV and 120 eV. The calculations on the rhodopsin model show that the RVS errors determined in the gas-phase are a very good approximation to the RVS errors in the protein environment. The RVS approach thus renders purely quantum mechanical treatments of chromophores in protein environments feasible and offers an ab initio alternative to quantum mechanics/molecular mechanics separation schemes.
NASA Astrophysics Data System (ADS)
Deguchi, Daiki; Sato, Kazunori; Kino, Hiori; Kotani, Takao
2016-05-01
We have recently implemented a new version of the quasiparticle self-consistent GW (QSGW) method in the ecalj package released at http://github.com/tkotani/ecalj. Since the new version of the ecalj package is numerically stable and more accurate than the previous versions, we can perform calculations easily without being bothered with tuning input parameters. Here we examine its ability to describe energy band properties, e.g., band-gap energy, eigenvalues at special points, and effective mass, for a variety of semiconductors and insulators. We treat C, Si, Ge, Sn, SiC (in 2H, 3C, and 4H structures), (Al, Ga, In) × (N, P, As, Sb), (Zn, Cd, Mg) × (O, S, Se, Te), SiO2, HfO2, ZrO2, SrTiO3, PbS, PbTe, MnO, NiO, and HgO. We propose that a hybrid QSGW method, where we mix 80% of QSGW and 20% of LDA, gives universally good agreement with experiments for these materials.
Time-resolved X-ray measurements of energy relaxation in ultrafast laser excited semiconductors
NASA Astrophysics Data System (ADS)
Lee, Soo Heyong
In semiconductors, the properties and dynamics of photoexcited carriers and subsequent energy relaxation through lattice vibrations are quite complex and occur on a variety of time scales. Typically the transient dynamics involving transitions of electrons from lower energy states to higher ones upon photoexcitation take place almost instantaneously. The electrons eventually recombine with holes while losing most of their kinetic energy to the lattice through various routes at different time scales. The lattice relaxation processes, especially at high photoexcitation levels, have been subjected to numerous experimental and theoretical investigations during past decades. Time-resolved X-ray diffraction (TRXD) method provides a novel tool for studying these dynamics because X-rays have short wavelength, long material penetration depth and relatively strong interaction with core electrons. In my work, femtosecond laser pulses excite electrons in opaque materials, and subsequent carrier relaxation process and coherent/incoherent lattice dynamics are investigated using TRXD. My thesis covers quantitative detail of the generation and propagation of ultrafast laser induces acoustic strain waves in bulk semiconductor materials as well as at the heterostructure interface. In particular propagation of strain waves, which are comprised of broadband low wave vector phonons, is studied in an AlGaAs/GaAs multilayer structure. The spatial and temporal profiles of the acoustic waves at varying photoexcitation density are characterized. We are able to distinguish thermal from carrier-induced strain and measure the free-carrier absorption cross-section. The approximation that impulsively generated acoustic waves are uniaxial is found to break down. The research also demonstrates a novel approach to explore laser induced acoustic phonon dynamics at high wavevector, near the Brillouin zone-boundary, the details of which are inaccessible to optical pump-probe methods. Throughout this
New Fluorescence Parameters for the Determination of QA Redox State and Excitation Energy Fluxes.
Kramer, David M; Johnson, Giles; Kiirats, Olavi; Edwards, Gerald E
2004-02-01
A number of useful photosynthetic parameters are commonly derived from saturation pulse-induced fluorescence analysis. We show, that qP, an estimate of the fraction of open centers, is based on a pure 'puddle' antenna model, where each Photosystem (PS) II center possesses its own independent antenna system. This parameter is incompatible with more realistic models of the photosynthetic unit, where reaction centers are connected by shared antenna, that is, the so-called 'lake' or 'connected units' models. We thus introduce a new parameter, qL, based on a Stern-Volmer approach using a lake model, which estimates the fraction of open PS II centers. We suggest that qL should be a useful parameter for terrestrial plants consistent with a high connectivity of PS II units, whereas some marine species with distinct antenna architecture, may require the use of more complex parameters based on intermediate models of the photosynthetic unit. Another useful parameter calculated from fluorescence analysis is ΦII, the yield of PS II. In contrast to qL, we show that the ΦII parameter can be derived from either a pure 'lake' or pure 'puddle' model, and is thus likely to be a robust parameter. The energy absorbed by PS II is divided between the fraction used in photochemistry, ΦII, and that lost non-photochemically. We introduce two additional parameters that can be used to estimate the flux of excitation energy into competing non-photochemical pathways, the yield induced by downregulatory processes, ΦNPQ, and the yield for other energy losses, ΦNO.
Nuclear level densities below 40 MeV excitation energy in the mass region A ≃ 50
NASA Astrophysics Data System (ADS)
Avrigeanu, M.; Ivaşcu, M.; Avrigeanu, V.
1990-09-01
Consistent pre-equilibrium emission and statistical model calculations of fast neutron induced reaction cross sections are used to validate nuclear level densities for excitation energies up to 40 MeV in the mass region A ≃50. A “composed” level density approach has been employed by using the back-shifted Fermi gas model for excitation energies lower than 12 MeV and a realistic analytical formula for higher excitations. In the transition region from the BSFG model range to that of full applicability of the realistic formula, an interpolation between the predictions of the two models is adopted. The interpolation rule, suggested by microscopic level density calculations, has been validated through the comparison of the calculated and experimental cross sections.
NASA Astrophysics Data System (ADS)
van Grondelle, Rienk
2011-03-01
The success of photosynthesis relies on two ultrafast processes: excitation energy transfer in the light-harvesting antenna followed by charge separation in the reaction center. LHCII, the peripheral light-harvesting complex of Photosystem II, plays a major role. At the same time, the same light-harvesting system can be `switched' into a quenching state, which effectively protects the reaction center of Photosystem II from over-excitation and photodamage. In this talk I will demonstrate how LHCII collects and transfers excitation energy. Using single molecule spectroscopy we have discovered how LHCII can switch between this light-harvesting state, a quenched state and a red-shifted state. We show that the switching properties between the light-harvesting state and the quenched state depend strongly on the environmental conditions, where the quenched state is favoured under `NPQ-like' conditions. It is argued that this is the mechanism of non-photochemical quenching in plants.
NASA Astrophysics Data System (ADS)
Collins, Sean M.; Midgley, Paul A.
2013-06-01
In previous publications, qualitative agreement between studies of surface plasmon excitations in nanoparticles by near-field light scattering and electron energy-loss spectroscopy (EELS) has been found for experiments and simulations. Here, we present a quantitative method for the comparison of light scattering and EELS for surface plasmons in metal spheres. Defining the Fourier transform of the modal component of the scattered electric field along the equivalent electron trajectory enables a direct evaluation of the relative weighting factor for light- and electron-excited surface plasmon modes. This common quantity for light scattering and EELS is examined for size, composition, and trajectory dependencies, facilitating the analysis of key differences between light and electron excitation. A single functional dependence on Drude model plasmon energies is identified to explain the relative modal weighting factors for light scattering and EELS. This method represents an important step toward the complete spectral and spatial reconstruction of EELS maps from near-field light scattering calculations.
MLCT excited states at interfaces and in rigid media: Applications in energy conversion
Meyer, Thomas J.; Papanikolas, John M.
2014-10-31
In this proposal for continued support from the DOE, we propose to build on our understanding of light-driven electron transfer by molecules and molecular assemblies on oxide surfaces. We will conduct a systematic investigation of injection and back electron transfer dynamics on the surfaces of thin (1-10 μm), mesoporous, transparent conducting oxide films consisting of 10-20 nm tin-doped indium oxide (Sn:In2O3, ITO)) nanoparticles. These materials are unique because they mimic the morphology, surface area, and oxide nature of conventional mesoporous, nanocrystalline metal oxide thin films such as TiO_{2}, SnO2, and NiO used in DSSC and DSPEC applications but they are conductive with high electron mobilities (0.1-10 cm2 V-1 s-1) and conductivities (101-104 Ω-1 cm-1) over a wide range of applied potentials. Their high conductivities and metallic behavior allow the Fermi level at nanoparticle surfaces to be tuned systematically by varying an applied bias. We will investigate injection, intra-assembly, and back electron transfer dynamics on nanoITO by transient absorption measurements on the picosecond to millisecond timescales. One series of experiments will build on initial results from DOE-supported research and focus on the bias- and medium-dependence of interfacial electron transfer by surface-bound molecular chromophores to investigate: i) the bias dependence of injection and back electron transfer, ii) injection by short-lived, otherwise inaccessible excited-states, and iii) medium effects. In parallel, we will investigate the dynamic interfacial properties of nanoITO-bound molecular assemblies designed for photogalvanic solar energy conversion. These studies will focus on surface-prepared, layer-by-layer donor-chromophore-acceptor assemblies in which inter-molecular excited-state quenching leads to redox separation as opposed to interfacial electron transfer quenching by the semiconductor material. Transient absorption measurements performed on nano
Amarie, Sergiu; Lupo, Domenico; Lenz, Martin O; Saegesser, Rudolf; Ghosh, Robin; Wachtveitl, Josef
2010-03-01
Light-induced reaction dynamics of isolated photosynthetic membranes obtained from wild-type (WT) and reaction center (RC)-subunit deletion strains SPUHK1 (an H-subunit deletion mutant) and SK Delta LM (an (L+M) deletion mutant) of the purple non-sulphur bacterium Rhodospirillum rubrum have been investigated by femtosecond transient absorption spectroscopy. Upon excitation of the spirilloxanthin (Spx) S(2) state at 546 nm, of the bacteriochlorophyll Soret band at 388 nm and probing spectral regions, which are characteristic for carotenoids, similar dynamics in the SPUHK1, SK Delta LM and WT strains could be observed. The excitation of Spx S(2) is followed by the simultaneous population of the lower singlet excited states S(1) and S* which decay with lifetimes of 1.4 and 5 ps, respectively for the mutants, and 1.4 and 4 ps, respectively, for the wild-type. The excitation of the BChl Soret band is followed by relaxation into BChl lower excited states which compete with excitation energy transfer BChl-to-Spx. The deexcitation pathway BChl(Soret) --> Spx(S(2)) --> Spx(S(1)) occurs with the same transition rate for all investigated samples (WT, SPUHK1 and SK Delta LM). The kinetic traces measured for the Spx S(1) --> S(N) transition display similar behaviour for all samples showing a positive signal which increases within the first 400 fs (i.e. the time needed for the excitation energy to reach the Spx S(1) excited state) and decays with a lifetime of about 1.5 ps. This suggests that the Spx excited state dynamics in the investigated complexes do not differ significantly. Moreover, a longer excited state lifetime of BChl for SPUHK1 in comparison to WT was observed, consistent with a photochemical quenching channel present in the presence of RC. For long delay times, photobleaching of the RC special pair and an electrochromic blue shift of the monomeric BChl a can be observed only for the WT but not for the mutants. The close similarity of the excited state decay
Lombardi, Andrea; Faginas-Lago, Noelia; Pacifici, Leonardo; Costantini, Alessandro
2013-11-14
We present extended applications of an established theoretical and computational machinery suitable for the study of the dynamics of CO2+CO2 collisions, focusing on vibrational energy exchange, considered over a wide range of energies and rotational temperatures. Calculations are based on quasi-classical trajectories on a potential energy function (a critical component of dynamics simulations), tailored to accurately describe the intermolecular interactions, modeled by the recently proposed bond-bond semiempirical formulation that allows the colliding molecules to be stretchable, rather than frozen at their equilibrium geometry. In a previous work, the same potential energy surface has been used to show that modifications in the geometry (and in physical properties such as polarizability and charge distribution) of the colliding partners affect the intermolecular interaction and determine the features of the energy exchange, to a large extent driven by long-range forces. As initial partitioning of the energy among the molecular degrees of freedom, we consider the excitation of the vibrational bending mode, assuming an initial rotational distribution and a rotational temperature. The role of the vibrational angular momentum is also carefully assessed. Results are obtained by portable implementations of this approach in a Grid-computing framework and on high performance platforms. Cross sections are basic ingredients to obtain rate constants of use in advanced state-to-state kinetic models, under equilibrium or nonequilibrium conditions, and this approach is suitable for gas dynamics applications to plasmas and modeling of hypersonic flows.
Thomas, Ryan A; Tsai, Chia Nung; Mazumder, Shivnath; Lu, I Chen; Lord, Richard L; Schlegel, H Bernhard; Chen, Yuan Jang; Endicott, John F
2015-06-18
The variations in band shape with excited state energy found for the triplet metal to ligand charge transfer ((3)MLCT) emission spectra of ruthenium-bipyridine (Ru-bpy) chromophores at 77 K have been postulated to arise from excited state/excited state configurational mixing. This issue is more critically examined through the determination of the excited state energy dependence of the radiative rate constants (kRAD) for these emissions. Experimental values for kRAD were determined relative to known literature references for Ru-bpy complexes. When the lowest energy excited states are metal centered, kRAD can be anomalously small and such complexes have been identified using density functional theory (DFT) modeling. When such complexes are removed from the energy correlation, there is a strong (3)MLCT energy-dependent contribution to kRAD in addition to the expected classical energy cubed factor for complexes with excited state energies greater than 10 000 cm(-1). This correlates with the DFT calculations which show significant excited state electronic delocalization between a π(bpy-orbital) and a half-filled dπ*-(Ru(III)-orbital) for Ru-bpy complexes with (3)MLCT excited state energies greater than about 16 000 cm(-1). Overall, this work implicates the "stealing" of emission bandshapes as well as intensity from the higher energy, strongly allowed bpy-centered singlet ππ* excited state.
Xu, Xuefei; Yang, Ke R; Truhlar, Donald G
2014-05-13
Conventional time-dependent density functional theory (TDDFT) is based on a closed-shell Kohn-Sham (KS) singlet ground state with the adiabatic approximation, using either linear response (KS-LR) or the Tamm-Dancoff approximation (KS-TDA); these methods can only directly predict singly excited states. This deficiency can be overcome by using a triplet state as the reference in the KS-TDA approximation and "exciting" the singlet by a spin flip (SF) from the triplet; this is the method suggested by Krylov and co-workers, and we abbreviate this procedure as SF-KS-TDA. SF-KS-TDA can be applied either with the original collinear kernel of Krylov and co-workers or with a noncollinear kernel, as suggested by Wang and Ziegler. The SF-KS-TDA method does bring some new practical difficulties into play, but it can at least formally model doubly excited states and states with double-excitation character, so it might be more useful than conventional TDDFT (both KS-LR and KS-TDA) for photochemistry if these additional difficulties can be surmounted and if it is accurate with existing approximate exchange-correlation functionals. In the present work, we carried out calculations specifically designed to understand better the accuracy and limitations of the conventional TDDFT and SF-KS-TDA methods; we did this by studying closed-shell atoms and closed-shell monatomic cations because they provide a simple but challenging testing ground for what we might expect in studying the photochemistry of molecules with closed-shell ground states. To test their accuracy, we applied conventional KS-LR and KS-TDA and 18 versions of SF-KS-TDA (nine collinear and nine noncollinear) to the same set of vertical excitation energies (including both Rydberg and valence excitations) of Be, B(+), Ne, Na(+), Mg, and Al(+). We did this for 10 exchange-correlation functionals of various types, both local and nonlocal. We found that the GVWN5 and M06 functionals with nonlocal kernels in spin-flip calculations
Dynamics of Rovibrational Energy Transfer from Excited Molecular - Crossed Beam Studies
NASA Astrophysics Data System (ADS)
Du, Hong
1990-01-01
Rovibrational inelastic scattering has been studied for the collisions between helium and excited molecular iodine (I_2) in a crossed beam apparatus. I _2 was initially prepared in two vibrational states, upsilon' = 15 and 35, in the B O_{rm u }^ + electronic state. Dispersed single vibrational level fluorescence spectra revealed the vibrational inelastic scattering. The collision energy (Ecm) was varied from 35meV to 190meV. Vibrational state changes up to | Deltaupsilon| = 6 in upsilon' = 35 and | Deltaupsilon| = 3 in upsilon' = 15 were observed. Nearly 200 relative vibrational state-to-state inelastic scattering cross sections were measured. At each Ecm, all the cross sections for both upsilon' = 15 and 35 can be fitted by a single exponential function sigma ~ exp(-| Delta rm E|/beta). At high Ecm, beta_{rm Vto T} is equal to beta_{rm Tto V}. At low ECM, beta _{rm Vto T} is larger than beta_{rm Tto V}. However, all beta's are linear functions of Ecm. Also the cross sections for the Deltaupsilon = +/-1 scattering are nearly independent of Ecm. Considering that the collisions are not adiabatic, these results are not consistent with the well-known Landau-Teller theory. Using the empirical dependence of the cross sections on Ecm, we calculated the thermal rate constants. The calculation at 300K agrees with the bulb experiment for V to T but not for T to V transitions. The calculation also shows that the bulb energy transfer is mainly induced by collisions with velocities ~2 times larger than the most probable velocity. From the cross sections, mean energy transfer per vibrationally inelastic collision, < Deltarm E>, was also obtained. The results show that < Deltarm E> increases linearly with Ecm and levels off to near-zero at high collision energy. At low Ecm, < Deltarm E> in upsilon' = 15 is larger than that in upsilon' = 35. The average rotational energy transfered increases almost linearly with Ecm but is small, only ~ 2% of the Ecm. This is a direct result of
Schmiedt, Hanno; Schlemmer, Stephan; Yurchenko, Sergey N; Yachmenev, Andrey; Jensen, Per
2017-01-18
We report a new semi-classical method to compute highly excited rotational energy levels of an asymmetric-top molecule. The method forgoes the idea of a full quantum mechanical treatment of the ro-vibrational motion of the molecule. Instead, it employs a semi-classical Green's function approach to describe the rotational motion, while retaining a quantum mechanical description of the vibrations. Similar approaches have existed for some time, but the method proposed here has two novel features. First, inspired by the path integral method, periodic orbits in the phase space and tunneling paths are naturally obtained by means of molecular symmetry analysis. Second, the rigorous variational method is employed for the first time to describe the molecular vibrations. In addition, we present a new robust approach to generating rotational energy surfaces for vibrationally excited states; this is done in a fully quantum-mechanical, variational manner. The semi-classical approach of the present work is applied to calculating the energies of very highly excited rotational states and it reduces dramatically the computing time as well as the storage and memory requirements when compared to the fullly quantum-mechanical variational approach. Test calculations for excited states of SO2 yield semi-classical energies in very good agreement with the available experimental data and the results of fully quantum-mechanical calculations.
Schmiedt, Hanno; Schlemmer, Stephan; Yurchenko, Sergey N.; Yachmenev, Andrey
2017-01-01
We report a new semi-classical method to compute highly excited rotational energy levels of an asymmetric-top molecule. The method forgoes the idea of a full quantum mechanical treatment of the ro-vibrational motion of the molecule. Instead, it employs a semi-classical Green's function approach to describe the rotational motion, while retaining a quantum mechanical description of the vibrations. Similar approaches have existed for some time, but the method proposed here has two novel features. First, inspired by the path integral method, periodic orbits in the phase space and tunneling paths are naturally obtained by means of molecular symmetry analysis. Second, the rigorous variational method is employed for the first time to describe the molecular vibrations. In addition, we present a new robust approach to generating rotational energy surfaces for vibrationally excited states; this is done in a fully quantum-mechanical, variational manner. The semi-classical approach of the present work is applied to calculating the energies of very highly excited rotational states and it reduces dramatically the computing time as well as the storage and memory requirements when compared to the fullly quantum-mechanical variational approach. Test calculations for excited states of SO2 yield semi-classical energies in very good agreement with the available experimental data and the results of fully quantum-mechanical calculations. PMID:28000807
The structure of the high-energy spin excitations in YBa2Cu3O6+x
NASA Astrophysics Data System (ADS)
Hayden, Stephen
2005-03-01
The most obvious feature in the magnetic excitations of high-Tc superconductors is the so-called `resonance-mode'. This mode is strongly coupled to the superconductivity, however, it has not been found in the La2-x(Ba,Sr)xCuO4 family and is not universally present in Bi2Sr2CaCu2O8+δ. Here we use inelastic neutron scattering to characterize other excitations at higher energies which may be relevant to the superconductive pairing in YBa2Cu3O6.6. We observe a square-shaped continuum of excitations in reciprocal space [1]. These excitations have energies greater than the superconducting pairing energy, are present at Tc, and have spectral weight far exceeding that of the `resonance'. The discovery of similar excitations in La2-xBaxCuO4 [2] suggests that they are a general property of the copper oxides, and a candidate for mediating the electron pairing. Our data show that the high-energy magnetic excitations in the high-temperature superconductor YBa2Cu3O6.6 consists of a continuum of scattering bounded by a square and peaked at wavevector positions Qɛ =(1/2±ɛ,1/2±ɛ) and (1/2±ɛ,1/2ɛ). A similar structure is observed in the high-energy magnetic excitations of the magnetically ordered but weakly superconducting compound La1.85Ba0.125CuO4 [2]. This suggests there is universality, both in the low-energy and the high-energy spin dynamics between two very different classes of high-Tc superconductor. [1] S.M. Hayden, H.A. Mook, P.C. Dai, T.G. Perring, and F. Dogan, Nature 429, 531-534 (2004) [2] J.M. Tranquada, H. Woo, T.G. Perring, H. Goka, G.D. Gu , G. Xu, M. Fujita, K.Yamada K, Nature 429, 534-538 (2004).
NASA Astrophysics Data System (ADS)
Kumar, Ashok; Thakkar, Ajit J.
2011-11-01
Experimental photoabsorption cross-sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule and the high-energy behavior of the dipole-oscillator-strength density are used to construct dipole oscillator strength distributions for buckminsterfullerene (C60). The distributions are used to predict dipole sum rules Sk, mean excitation energies Ik, the frequency dependent polarizability, and C6 coefficients for the long-range dipole-dipole interactions of C60 with a variety of atoms and molecules.
Tang, J. F.; Wu, D. J.; Yan, Y. H. E-mail: djwu@pmo.ac.cn
2011-02-01
The electron-cyclotron maser (ECM) conventionally driven by velocity anisotropies of energetic electrons trapped in magnetic fields is one of the most important radio-emission mechanisms in astrophysics. Recently, Wu and Tang proposed that a proper lower energy cutoff behavior of power-law electrons can effectively excite the ECM emission. This paper considers effects of temperature anisotropy on this new ECM mechanism. The results show that the growth rates of the ECM emissions increase with {beta}{sub perpendicular0} and {beta}{sub ||0}, where {beta}{sub perpendicular0} and {beta}{sub ||0} are the perpendicular and parallel velocity spreads (in units of the light velocity c) of the energetic electron beam, respectively. Moreover, the growth rates of O1 and X2 modes both sensitively depend on the ratio of the electron-cyclotron frequency to the plasma frequency {Omega} and reach their extremum values at {Omega} {approx_equal} 1.5 for the O1 mode and at {Omega} {approx_equal} 1.0 for the X2 mode. Meanwhile, as the mean velocity of the electron beam {beta}{sub s} (in units of c) increases, the growth rate of the O1 mode remains approximately constant and that of the X2 mode decreases considerably.
Potential energy curves for the ground and low-lying excited states of CuAg
Alizadeh, Davood; Shayesteh, Alireza E-mail: ashayesteh@ut.ac.ir; Jamshidi, Zahra E-mail: ashayesteh@ut.ac.ir
2014-10-21
The ground and low-lying excited states of heteronuclear diatomic CuAg are examined by multi-reference configuration interaction (MRCI) method. Relativistic effects were treated and probed in two steps. Scalar terms were considered using the spin-free DKH Hamiltonian as a priori and spin-orbit coupling was calculated perturbatively via the spin-orbit terms of the Breit-Pauli Hamiltonian based on MRCI wavefunctions. Potential energy curves of the spin-free states and their corresponding Ω components correlating with the separated atom limits {sup 2}S(Cu) + {sup 2}S(Ag) and {sup 2}D(Cu) + {sup 2}S(Ag) are obtained. The results are in fine agreement with the experimental measurements and tentative conclusions for the ion-pair B0{sup +} state are confirmed by our theoretical calculations. Illustrative results are presented to reveal the relative importance and magnitude of the scalar and spin-orbit effects on the spectroscopic properties of this molecule. Time dependent density functional theory calculations, using the LDA, BLYP, B3LYP, and SAOP functionals have been carried out for CuAg and the accuracy of TD-DFT has been compared with ab initio results.
Solhaug, Knut Asbjørn; Xie, Li; Gauslaa, Yngvar
2014-08-01
Photosynthesis was compared in two cyanobacterial lichens (Lobaria hallii and Peltigera praetextata) and two green algal lichens (Lobaria pulmonaria and Peltigera leucophlebia) exposed to red, green or blue light. Cyanolichens had substantially lower photosynthetic CO(2) uptake and O(2) evolution than the green algal lichens in blue light, but slightly higher photosynthesis in red and green light. The effective quantum yield of photosystem (PS) II (Φ(PSII)) decreased with increasing red and green light for all species, but in blue light this response occurred in green algal lichens only. Cyanolichen Φ(PSII) increased with increasing blue light at low irradiances, but decreased at stronger exposures. However, after adding red light the efficiency of blue light for photosynthetic O(2) evolution increased by 2.4 times. Because phycobilisomes associated with PSII have a low blue light absorption, our results are consistent with blue light absorption mainly by Chl in PSI. Thereby, unequal allocation of excitation energy between PSII and PSI results in low cyanolichen photosynthesis under blue light. This is new knowledge in the science of lichenology with important implications for e.g. the reliability of using Chl fluorometers with blue light for cyanolichens.
NASA Astrophysics Data System (ADS)
Tian, Y. P.; Wang, Y.; Jin, X. L.; Huang, Z. L.
2014-09-01
A nonlinear electromagnetic energy harvester directly powering a load resistance is considered in this manuscript. The nonlinearity includes the cubic stiffness and the unavoidable Coulomb friction, and the base excitation is confined to Gaussian white noise. Directly starting from the coupled equations, a novel procedure to evaluate the random responses and the mean output power is developed through the generalized harmonic transformation and the equivalent non-linearization technique. The dependence of the optimal ratio of the load resistance to the internal resistance and the associated optimal mean output power on the internal resistance of the coil is established. The principle of impedance matching is correct only when the internal resistance is infinity, and the optimal mean output power approaches an upper limit as the internal resistance is close to zero. The influence of the Coulomb friction on the optimal resistance ratio and the optimal mean output power is also investigated. It is proved that the Coulomb friction almost does not change the optimal resistance ratio although it prominently reduces the optimal mean output power.
Gutten, Ondrej; Beššeová, Ivana; Rulíšek, Lubomír
2011-10-20
To address fundamental questions in bioinorganic chemistry, such as metal ion selectivity, accurate computational protocols for both the gas-phase association of metal-ligand complexes and solvation/desolvation energies of the species involved are needed. In this work, we attempt to critically evaluate the performance of the ab initio and DFT electronic structure methods available and recent solvation models in calculations of the energetics associated with metal ion complexation. On the example of five model complexes ([M(II)(CH(3)S)(H(2)O)](+), [M(II)(H(2)O)(2)(H(2)S)(NH(3))](2+), [M(II)(CH(3)S)(NH(3))(H(2)O)(CH(3)COO)], [M(II)(H(2)O)(3)(SH)(CH(3)COO)(Im)], [M(II)(H(2)S)(H(2)O)(CH(3)COO)(PhOH)(Im)](+) in typical coordination geometries) and four metal ions (Fe(2+), Cu(2+), Zn(2+), and Cd(2+); representing open- and closed-shell and the first- and second-row transition metal elements), we provide reference values for the gas-phase complexation energies, as presumably obtained using the CCSD(T)/aug-cc-pVTZ method, and compare them with cheaper methods, such as DFT and RI-MP2, that can be used for large-scale calculations. We also discuss two possible definitions of interaction energies underlying the theoretically predicted metal-ion selectivity and the effect of geometry optimization on these values. Finally, popular solvation models, such as COSMO-RS and SMD, are used to demonstrate whether quantum chemical calculations can provide the overall free enthalpy (ΔG) changes in the range of the expected experimental values for the model complexes or match the experimental stability constants in the case of three complexes for which the experimental data exist. The data presented highlight several intricacies in the theoretical predictions of the experimental stability constants: the covalent character of some metal-ligand bonds (e.g., Cu(II)-thiolate) causing larger errors in the gas-phase complexation energies, inaccuracies in the treatment of solvation of the
Meng, Qing-Hao; Yao, Zhen-Jing; Peng, Han-Yang
2009-12-01
Both the energy efficiency and correlation characteristics are important in airborne sonar systems to realize multichannel ultrasonic transducers working together. High energy efficiency can increase echo energy and measurement range, and sharp autocorrelation and flat cross correlation can help eliminate cross-talk among multichannel transducers. This paper addresses energy efficiency optimization under the premise that cross-talk between different sonar transducers can be avoided. The nondominated sorting genetic algorithm-II is applied to optimize both the spectrum and correlation characteristics of the excitation sequence. The central idea of the spectrum optimization is to distribute most of the energy of the excitation sequence within the frequency band of the sonar transducer; thus, less energy is filtered out by the transducers. Real experiments show that a sonar system consisting of eight-channel Polaroid 600 series electrostatic transducers excited with 2 ms optimized pulse-position-modulation sequences can work together without cross-talk and can measure distances up to 650 cm with maximal 1% relative error.
Rivera, Eva; Montemayor, Daniel; Masia, Marco; Coker, David F
2013-05-09
A site-dependent spectral density system-bath model of the Fenna-Matthews-Olsen (FMO) pigment-protein complex is developed using results from ground-state molecular mechanics simulations together with a partial charge difference model for how the long-range contributions to the chromophore excitation energies fluctuate with environmental configuration. A discussion of how best to consistently process the chromophore excitation energy fluctuation correlation functions calculated in these classical simulations to obtain reliable site-dependent spectral densities is presented. The calculations reveal that chromophores that are close to the protein-water interface can experience strongly dissipative environmental interactions characterized by reorganization energies that can be as much as 2-3 times those of chromophores that are buried deep in the hydrophobic protein scaffolding. Using a linearized density matrix quantum propagation method, we demonstrate that the inhomogeneous system-bath model obtained from our site-dependent spectral density calculations gives results consistent with experimental dissipation and dephasing rates. Moreover, we show that this model can simultaneously enhance the energy-transfer rate and extend the decoherence time. Finally, we explore the influence of initially exciting different chromophores and mutating local environments on energy transfer through the network. These studies suggest that different pathways, selected by varying initial photoexcitation, can exhibit significantly different relaxation times depending on whether the energy-transfer path involves chromophores at the protein-solvent interface or if all chromophores in the pathway are buried in the protein.
NASA Astrophysics Data System (ADS)
Lee, Yu Ran; Kang, Do Won; Kim, Hong Lae; Kwon, Chan Ho
2014-11-01
Ionization energies and cationic structures of pyridine were intensively investigated utilizing one-photon mass-analyzed threshold ionization (MATI) spectroscopy with vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. The present one-photon high-resolution MATI spectrum of pyridine demonstrated a much finer and richer vibrational structure than that of the previously reported two-photon MATI spectrum. From the MATI spectrum and photoionization efficiency curve, the accurate ionization energy of the ionic ground state of pyridine was confidently determined to be 73 570 ± 6 cm-1 (9.1215 ± 0.0007 eV). The observed spectrum was almost completely assigned by utilizing Franck-Condon factors and vibrational frequencies calculated through adjustments of the geometrical parameters of cationic pyridine at the B3LYP/cc-pVTZ level. A unique feature unveiled through rigorous analysis was the prominent progression of the 10 vibrational mode, which corresponds to in-plane ring bending, and the combination of other totally symmetric fundamentals with the ring bending overtones, which contribute to the geometrical change upon ionization. Notably, the remaining peaks originate from the upper electronic state (2A2), as predicted by high-resolution photoelectron spectroscopy studies and symmetry-adapted cluster configuration interaction calculations. Based on the quantitatively good agreement between the experimental and calculated results, it was concluded that upon ionization the pyridine cation in the ground electronic state should have a planar structure of C2v symmetry through the C-N axis.
Arcon, Juan Pablo; Defelipe, Lucas A; Modenutti, Carlos P; López, Elias D; Alvarez-Garcia, Daniel; Barril, Xavier; Turjanski, Adrián G; Martí, Marcelo A
2017-03-31
One of the most important biological processes at the molecular level is the formation of protein-ligand complexes. Therefore, determining their structure and underlying key interactions is of paramount relevance and has direct applications in drug development. Because of its low cost relative to its experimental sibling, molecular dynamics (MD) simulations in the presence of different solvent probes mimicking specific types of interactions have been increasingly used to analyze protein binding sites and reveal protein-ligand interaction hot spots. However, a systematic comparison of different probes and their real predictive power from a quantitative and thermodynamic point of view is still missing. In the present work, we have performed MD simulations of 18 different proteins in pure water as well as water mixtures of ethanol, acetamide, acetonitrile and methylammonium acetate, leading to a total of 5.4 μs simulation time. For each system, we determined the corresponding solvent sites, defined as space regions adjacent to the protein surface where the probability of finding a probe atom is higher than that in the bulk solvent. Finally, we compared the identified solvent sites with 121 different protein-ligand complexes and used them to perform molecular docking and ligand binding free energy estimates. Our results show that combining solely water and ethanol sites allows sampling over 70% of all possible protein-ligand interactions, especially those that coincide with ligand-based pharmacophoric points. Most important, we also show how the solvent sites can be used to significantly improve ligand docking in terms of both accuracy and precision, and that accurate predictions of ligand binding free energies, along with relative ranking of ligand affinity, can be performed.
Lee, Yu Ran; Kang, Do Won; Kim, Hong Lae E-mail: hlkim@kangwon.ac.kr; Kwon, Chan Ho E-mail: hlkim@kangwon.ac.kr
2014-11-07
Ionization energies and cationic structures of pyridine were intensively investigated utilizing one-photon mass-analyzed threshold ionization (MATI) spectroscopy with vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. The present one-photon high-resolution MATI spectrum of pyridine demonstrated a much finer and richer vibrational structure than that of the previously reported two-photon MATI spectrum. From the MATI spectrum and photoionization efficiency curve, the accurate ionization energy of the ionic ground state of pyridine was confidently determined to be 73 570 ± 6 cm{sup −1} (9.1215 ± 0.0007 eV). The observed spectrum was almost completely assigned by utilizing Franck-Condon factors and vibrational frequencies calculated through adjustments of the geometrical parameters of cationic pyridine at the B3LYP/cc-pVTZ level. A unique feature unveiled through rigorous analysis was the prominent progression of the 10 vibrational mode, which corresponds to in-plane ring bending, and the combination of other totally symmetric fundamentals with the ring bending overtones, which contribute to the geometrical change upon ionization. Notably, the remaining peaks originate from the upper electronic state ({sup 2}A{sub 2}), as predicted by high-resolution photoelectron spectroscopy studies and symmetry-adapted cluster configuration interaction calculations. Based on the quantitatively good agreement between the experimental and calculated results, it was concluded that upon ionization the pyridine cation in the ground electronic state should have a planar structure of C{sub 2v} symmetry through the C-N axis.
Two-photon excitation into low-energy singlet states of anthracene in mixed crystals
NASA Astrophysics Data System (ADS)
Bree, A.; Leyderman, A.; Taliani, C.
1985-08-01
The two-photon excitation spectrum of the first excited state of anthracene in fluorene and biphenyl at 4.2 K has been measured. Intensity is induced into the origin by the static dipole moment of fluorene, and into b 1u vibrons through coupling to an A g state near 29400 cm -1; the nature of this A g state is discussed.
Crowell, B.; Carpenter, M.; Janssens, R.; Blumenthal, D.; Timar, J.; Wilson, A.; Sharpey-Schafer, J. |; Nakatsukasa, T.; Ahmad, I.; Astier, A.; Azaiez, F.; du Croux, L.; Gall, B.; Hannachi, F.; Khoo, T.; Korichi, A.; Lauritsen, T.; Lopez-Martens, A.
1995-04-01
An experiment using the Eurogam phase II {gamma}-ray spectrometer confirms the existence of an excited superdeformed (SD) band in {sup 190}Hg and its very unusual decay into the lowest SD band over 3--4 transitions. The energies of the transitions linking the two SD bands have been firmly established, and their angular distributions are consistent with a dipole character. Comparisons with calculations using random-phase approximation indicate that the excited SD band can be interpreted as an octupole-vibrational structure.
Energies and Auger widths of the high-lying triply excited states for Li-like beryllium
Gou Bingcong; Zhu Jingjing; Sun Yan
2009-12-15
The energies, fine-structure splittings, Auger channel energies, and the Auger widths of the high-lying triply excited 2l2l{sup '}nl{sup ''} (n>=2) states of {sup 2}S, {sup 2}D, and {sup 2}P{sup o} resonances for Be{sup +} are studied using the saddle-point variational method and saddle-point complex-rotation method. The relativistic corrections and mass polarization are included using the first-order perturbation theory. Restricted variational method is carried out to extrapolate better energies. The partial Auger widths are calculated for the individual open channels and the total Auger widths are obtained by coupling the important open channels and summing over the other channels. The configuration mixings of the triply excited resonances are described and differences in the literature on the designation of the intershell states are pointed out. These results are compared with other theoretical and experimental data in the literature.
NASA Astrophysics Data System (ADS)
Huo, Y.; Zhou, C.; Sun, L.; Chui, S. T.; Wu, Y. Z.
2016-11-01
Magnetization excitation in micron sized FeNi disks with different diameters is studied by broadband ferromagnetic resonance (FMR) measurement. Except the main FMR peak, additional adsorption peaks with lower energies are observed. Both micromagnetic simulation and quantum spin wave calculation confirm that the low-energy excitation states are attributed to backward volume magnetostatic (BVM) spin waves. The size dependence of the low-energy states is systematically studied in 50-nm-thick Py disks with diameters larger than 500 nm, and the linewidth of the first BVM state is found to be obviously smaller than that of the FMR absorption peak. Through a quantitative comparison with experimental results, the quantum spin wave calculation is proven to be a reliable method to get the susceptibility and is much faster than the classical micromagnetic simulations.
The low-energy, charge-transfer excited states of 4-amino-4-prime-nitrodiphenyl sulfide
NASA Technical Reports Server (NTRS)
O'Connor, Donald B.; Scott, Gary W.; Tran, Kim; Coulter, Daniel R.; Miskowski, Vincent M.; Stiegman, Albert E.; Wnek, Gary E.
1992-01-01
Absorption and emission spectra of 4-amino-4-prime-nitrodiphenyl sulfide in polar and nonpolar solvents were used to characterize and assign the low-energy excited states of the molecule. Fluorescence-excitation anisotropy spectra and fluorescence quantum yields were also used to characterize the photophysics of these states. The lowest-energy fluorescent singlet state was determined to be an intramolecular charge transfer (ICT) state involving transfer of a full electron charge from the amino to the nitro group yielding a dipole moment of about 50 D. A low-energy, intense absorption band is assigned as a transition to a different ICT state involving a partial electron charge transfer from sulfur to the nitro group.
Durrant, James R
2013-08-13
This review starts with a brief overview of the technological potential of molecular-based solar cell technologies. It then goes on to focus on the core scientific challenge associated with using molecular light-absorbing materials for solar energy conversion, namely the separation of short-lived, molecular-excited states into sufficiently long-lived, energetic, separated charges capable of generating an external photocurrent. Comparisons are made between different molecular-based solar cell technologies, with particular focus on the function of dye-sensitized photoelectrochemical solar cells as well as parallels with the function of photosynthetic reaction centres. The core theme of this review is that generating charge carriers with sufficient lifetime and a high quantum yield from molecular-excited states comes at a significant energetic cost-such that the energy stored in these charge-separated states is typically substantially less than the energy of the initially generated excited state. The role of this energetic loss in limiting the efficiency of solar energy conversion by such devices is emphasized, and strategies to minimize this energy loss are compared and contrasted.
NASA Astrophysics Data System (ADS)
Xing, Jing Tang; Sun, Zhe; Zhou, Sulian; Tan, Mingyi
2017-03-01
An investigation is undertaken of an integrated mechanical-electromagnetic coupling system consisting of a rigid vehicle with heave, roll, and pitch motions, four electromagnetic energy harvesters and four tires subject to uneven road excitations in order to improve the passengers' riding comfort and harvest the lost engine energy due to uneven roads. Following the derived mathematical formulations and the proposed solution approaches, the numerical simulations of this interaction system subject to a continuous sinusoidal road excitation and a single ramp impact are completed. The simulation results are presented as the dynamic response curves in the forms of the frequency spectrum and the time history, which reveals the complex interaction characteristics of the system for vibration reductions and energy harvesting performance. It has addressed the coupling effects on the dynamic characteristics of the integrated system caused by: (1) the natural modes and frequencies of the vehicle; (2) the vehicle rolling and pitching motions; (3) different road excitations on four wheels; (4) the time delay of a road ramp to impact both the front and rear wheels, etc., which cannot be tackled by an often used quarter vehicle model. The guidelines for engineering applications are given. The developed coupling model and the revealed concept provide a means with analysis idea to investigate the details of four energy harvester motions for electromagnetic suspension designs in order to replace the current passive vehicle isolators and to harvest the lost engine energy. Potential further research directions are suggested for readers to consider in the future.
NASA Astrophysics Data System (ADS)
Huang, Xinchuan; Schwenke, David W.; Lee, Timothy J.
2014-03-01
A purely ab initio potential energy surface (PES) was refined with selected 32S16O2 HITRAN data. Compared to HITRAN, the root-mean-squares error (σRMS) for all J = 0-80 rovibrational energy levels computed on the refined PES (denoted Ames-1) is 0.013 cm-1. Combined with a CCSD(T)/aug-cc-pV(Q+d)Z dipole moment surface (DMS), an infrared (IR) line list (denoted Ames-296K) has been computed at 296 K and covers up to 8000 cm-1. Compared to the HITRAN and CDMS databases, the intensity agreement for most vibrational bands is better than 85%-90%. Our predictions for 34S16O2 band origins, higher energy 32S16O2 band origins and missing 32S16O2 IR bands have been verified by most recent experiments and available HITRAN data. We conclude that the Ames-1 PES is able to predict 32/34S16O2 band origins below 5500 cm-1 with 0.01-0.03 cm-1 uncertainties, and the Ames-296K line list provides continuous, reliable and accurate IR simulations. The Ka-dependence of both line position and line intensity errors is discussed. The line list will greatly facilitate SO2 IR spectral experimental analysis, as well as elimination of SO2 lines in high-resolution astronomical observations.
NASA Technical Reports Server (NTRS)
Huang, Xinchuan; Schwenke, David W.; Lee, Timothy J.
2014-01-01
A purely ab initio potential energy surface (PES) was refined with selected (32)S(16)O2 HITRAN data. Compared to HITRAN, the root-mean-squares error (RMS) error for all J=0-80 rovibrational energy levels computed on the refined PES (denoted Ames-1) is 0.013 cm(exp -1). Combined with a CCSD(T)/aug-cc-pV(Q+d)Z dipole moment surface (DMS), an infrared (IR) line list (denoted Ames-296K) has been computed at 296K and covers up to 8,000 cm(exp -1). Compared to the HITRAN and CDMS databases, the intensity agreement for most vibrational bands is better than 85-90%. Our predictions for (34)S(16)O2 band origins, higher energy (32)S(16)O2 band origins and missing (32)S(16)O2 IR bands have been verified by most recent experiments and available HITRAN data. We conclude that the Ames-1 PES is able to predict (32/34)S(16)O2 band origins below 5500 cm(exp -1) with 0.01-0.03 cm(exp -1) uncertainties, and the Ames-296K line list provides continuous, reliable and accurate IR simulations. The Ka-dependence of both line position and line intensity errors is discussed. The line list will greatly facilitate SO2 IR spectral experimental analysis, as well as elimination of SO2 lines in high-resolution astronomical observations.
NASA Technical Reports Server (NTRS)
Lee, Timothy J.; Martin, Jan M. L.; Kwak, Dochan (Technical Monitor)
2002-01-01
The CCSD(T) method has been used to compute a highly accurate quartic force field and fundamental frequencies for all N-14 and N-15 isotopomers of the high energy density material T(sub d)N(sub 4). The computed fundamental frequencies show beyond doubt that the bands observed in a matrix isolation experiment by Radziszewski and coworkers are not due to different isotopomers of T(sub d)N(sub 4). The most sophisticated thermochemical calculations to date yield a N(sub 4) -> 2N(sub 2) heat of reaction of 182.22 +/- 0.5 kcal/mol at 0 K (180.64 +/- 0.5 at 298 K). It is hoped that the data reported herein will aid in the ultimate detection of T(sub d)N(sub 4).
NASA Astrophysics Data System (ADS)
Kozich, V.; Szyc, Ł.; Nibbering, E. T. J.; Werncke, W.; Elsaesser, T.
2009-04-01
Vibrational relaxation after spectrally selective excitation within the NH stretching band of adenine-thymine base pairs in DNA oligomers was studied by subpicosecond infrared-pump/anti-Stokes Raman-probe spectroscopy. The decay of the different NH stretching vibrations populates distinct accepting modes in the NH bending range with a rise time of 0.6 ps that is close to the NH stretching decay times. The population of thymine fingerprint modes after excitation of the adenine antisymmetric NH 2 stretching mode points to an ultrafast excitation transfer to the thymine NH stretching vibration before relaxation. The nonequilibrium fingerprint populations decay on a time scale of several picoseconds.
NASA Technical Reports Server (NTRS)
Nash-Stevenson, S. K.; Reddy, B. R.; Venkateswarlu, P.
1994-01-01
A summary is presented of the spectroscopic study of three systems: LaF3:Ho(3+), LaF3:Er(3+) and CaF2:Nd(3+). When the D levels of Ho(3+) in LaF3 were resonantly excited with a laser beam of 640 nm, upconverted emissions were detected from J (416 nm), F (485 nm), and E (546 nm) levels. Energy upconverted emissions were also observed from F and E levels of Ho(3+) when the material was excited with an 800 nm near infrared laser. When the D levels of Er(3+) in LaF3 were resonantly excited with a laser beam of 637 nm, upconverted emissions were detected from the E (540 nm) and P (320, 400, and 468 nm) levels. Energy upconverted emissions were also observed from F, E, and D levels of Er(3+) when the material was resonantly excited with an 804 nm near infrared laser. When the D levels of Nd(3+) in CaF2 were resonantly excited with a laser beam of 577 nm, upconverted emissions were detected from the L (360 and 382 nm), K (418 nm), and I (432 nm) levels. Very weak upconverted emissions were detected when this system was irradiated with a near infrared laser. The numbers in parentheses are the wavelengths of the emissions.
On the correlation between photoelectron energy and bending excitation in molecular photoionization
NASA Astrophysics Data System (ADS)
Miller, J. Scott; Poliakoff, E. D.
2000-07-01
We report on excitation of the bending vibration following 3σu-1 photoionization of CO2. Dispersed fluorescence is used to determine the v+=(0,1,0)/v+=(0,0,0) ratio over the range 18⩽hνexc⩽190 eV. The results demonstrate that the bending excitation varies over this wide range, and is influenced by the photoelectron.
Passive broadband targeted energy transfers and control of self-excited vibrations
NASA Astrophysics Data System (ADS)
Lee, Young S.
This work consists of the three main parts---Nonlinear energy pumping (that is, passive broadband targeted energy transfers---TETs), and its applications to theoretical and experimental suppression of aeroelastic instabilities. In the first part, nonlinear energy pumping (or TETs) in coupled oscillators is studied. The system is composed of a primary linear subsystem coupled through an essentially nonlinear stiffness and a linear viscous damper to an additional mass (which is called, as a whole, a nonlinear energy sink---NES). By considering the linear damping as a perturbation to the system, periodic solutions of the underlying Hamiltonian system are formulated by means of the non-smooth temporal transformation and solved numerically by a shooting method. The special periodic orbits, which are corresponding to the impulsive initial conditions for the primary subsystem, bear their importance as baits for initiating localized transfers of a significant portion of energy to the NES. The second part theoretically deals with suppression of limit cycle oscillations (LCOs) in self-excited systems by means of passive energy localizations. As a pilot scheme, suppression or even complete elimination of the LCO in a van der Pol (VDP) oscillator coupled with two types of NESS---grounded and ungrounded---is studied. Computational parametric study proves the efficacy of LCO elimination by means of passive nonlinear energy pumping from the VDP oscillator to appropriately designed NESs. The numerical study of the transient dynamics of the system showed that the dynamical mechanism for LCO suppression is a series of 1:1 and 1:3 transient resonance captures, with the damped transient dynamics following closely corresponding resonant manifolds of the underlying Hamiltonian system. It is through the TRCs that energy gets transferred from the VDP oscillator to the NES, thus causing LCO suppression. By performing an additional bifurcation analysis of the steady state responses through
NASA Astrophysics Data System (ADS)
Maruani, J.; Khoudir, A.; Kuleff, A.; Tronc, M.; Giorgi, G.; Bonnelle, C.
Core excitation energies (CEs) are known to depend on the chemical environment mostly through the charge transfered from or to the would-be excited atom in the ground-state molecule. We have made use of this peculiarity to set up a combined method for evaluating the CEs of molecules involving heavy atoms, where cumulated handicaps make direct calculations very difficult. We have evaluated the CEs of np levels in chromium, molybdenum and tungsten hexafluorides and compared the contributions of relaxation and relativity. In a first step, various approximate methods were used to evaluate the amount of charge transfered in the three hexafluorides, using the experimental geometries and testing different definitions of the charge. Results show the following trends: i) the calculated charge transfer increases as CrF6 << MoF6 < WF6; ii) Mulliken (balanced) charges vary in the order REX >> RHF > CISD > DFT, and Weinhold (natural) charges tend to be slightly larger; iii) our best (CISD) calculations give a natural percentage of electron transfer from the metal atom to the bonded fluorines of about 45% for CrF6, 56% for MoF6, and 59% for WF6. In a second step, numerical ab-initio, relativistic, [Delta]DF calculations of the total and orbital energies were performed on the ground-state and core-excited metal ions involving 1 to 5 valence ionizations. Core excitation energies were deduced and the relative importance of relaxation and relativity effects was discussed. In a last step, the core excitation energies for the molecules were evaluated by interpolating between values previously obtained for the free ions, using the net atomic charges derived for the ground-state molecules in our best previous approximation. The results are particularly striking for WF6: 1) for core excitations from the 2p1/2, 2p3/2 and 3p1/2, 3p3/2 levels, experimental energies are reproduced within 0.4-1.2 eV; 2) there is a relaxation alteration of the charge transfer stronger for the 3p than for the 2
NASA Technical Reports Server (NTRS)
Mckenzie, R. L.
1976-01-01
A semiclassical collision model is applied to the study of energy transfer rates between a vibrationally excited diatomic molecule and a structureless atom. The molecule is modeled as an anharmonic oscillator with a multitude of dynamically coupled vibrational states. Three main aspects in the prediction of vibrational energy transfer rates are considered. The applicability of the semiclassical model to an anharmonic oscillator is first evaluated for collinear encounters. Second, the collinear semiclassical model is applied to obtain numerical predictions of the vibrational energy transfer rate dependence on the initial vibrational state quantum number. Thermally averaged vibration-translation rate coefficients are predicted and compared with CO-He experimental values for both ground and excited initial states. The numerical model is also used as a basis for evaluating several less complete but analytic models. Third, the role of rational motion in the dynamics of vibrational energy transfer is examined. A three-dimensional semiclassical collision model is constructed with coupled rotational motion included. Energy transfer within the molecule is shown to be dominated by vibration-rotation transitions with small changes in angular momentum. The rates of vibrational energy transfer in molecules with rational frequencies that are very small in comparison to their vibrational frequency are shown to be adequately treated by the preceding collinear models.
NASA Astrophysics Data System (ADS)
Ge, Zi-Ming; Wang, Zhi-Wen; Zhou, Ya-Jun; He, Li-Ming; Liu, Guo-Guang
2003-05-01
In this paper, the full-core plus correlation (FCPC) and the Ritz method is extended to calculate the non-relativistic energies of 1s2ns (n=3,4,5) and 1s2nf (n=4,5) states and the wavefunctions of the lithium-like systems from Z=11-20. The mass-polarization and the relativistic correction including the kinetic-energy correction, the Darwin term, the electron-electron contact term and the orbit-orbit interaction are evaluated perturbatively as the first-order correction. The contribution from quantum electrodynamic is also included by using the effective nuclear charge formula. The excited energies, the term-energy and fine structure, are given and compared with the other theoretical calculation and experimental results. It is shown that the correlative wave in the FCPC method embodies well the strong correlation between the 1s2 core and the valence electron.
Wang, Fan; Ziegler, Tom
2005-10-15
In the present work we have proposed an approximate time-dependent density-functional theory (TDDFT) formalism to deal with the influence of spin-orbit coupling effect on the excitation energies for closed-shell systems. In this formalism scalar relativistic TDDFT calculations are first performed to determine the lowest single-group excited states and the spin-orbit coupling operator is applied to these single-group excited states to obtain the excitation energies with spin-orbit coupling effects included. The computational effort of the present method is much smaller than that of the two-component TDDFT formalism and this method can be applied to medium-size systems containing heavy elements. The compositions of the double-group excited states in terms of single-group singlet and triplet excited states are obtained automatically from the calculations. The calculated excitation energies based on the present formalism show that this formalism affords reasonable excitation energies for transitions not involving 5p and 6p orbitals. For transitions involving 5p orbitals, one can still obtain acceptable results for excitations with a small truncation error, while the formalism will fail for transitions involving 6p orbitals, especially 6p1/2 spinors.
Calculated low-energy electron-impact vibrational excitation cross sections for CO2 molecule
NASA Astrophysics Data System (ADS)
Laporta, V.; Tennyson, J.; Celiberto, R.
2016-12-01
Vibrational-excitation cross sections of ground electronic states of a carbon dioxide molecule by electron-impact through CO2-≤ft({{}2}{{\\Pi}u}\\right) shape resonance is considered in the separation of the normal modes approximation. Resonance curves and widths are computed for each vibrational mode. The calculations assume a decoupling between normal modes and employ the local complex potential model for the treatment of nuclear dynamics, usually adopted for electron-scattering involving diatomic molecules. Results are presented for excitation up to 10 vibrational levels in each mode and a comparison with data present in the literature is discussed.
Song, Yu-Zhi; Zhang, Lu-Lu; Gao, Shou-Bao; Meng, Qing-Tian
2016-01-01
A globally accurate many-body expansion potential energy surface is reported for HCS(X2A′) by fitting a wealth of accurate ab initio energies calculated at the multireference configuration interaction level using aug-cc-pVQZ and aug-cc-pV5Z basis sets via extrapolation to the complete basis set limit. The topographical features of the present potential energy surface are examined in detail and is in good agreement with the raw ab initio results, as well as other theoretical results available in literatures. By utilizing the potential energy surface of HCS(X2A′), the dynamic studies of the C(3P) + SH(X2Π) → H(2S) + CS(X1∑+) reaction has been carried out using quasi-classical trajectory method. PMID:27898106
Kim, Kilyoung; Johnson, Alan M; Powell, Amber L; Mitchell, Deborah G; Sevy, Eric T
2014-12-21
Collisional energy transfer between vibrational ground state CO2 and highly vibrationally excited monofluorobenzene (MFB) was studied using narrow bandwidth (0.0003 cm(-1)) IR diode laser absorption spectroscopy. Highly vibrationally excited MFB with E' = ∼41,000 cm(-1) was prepared by 248 nm UV excitation followed by rapid radiationless internal conversion to the electronic ground state (S1→S0*). The amount of vibrational energy transferred from hot MFB into rotations and translations of CO2 via collisions was measured by probing the scattered CO2 using the IR diode laser. The absolute state specific energy transfer rate constants and scattering probabilities for single collisions between hot MFB and CO2 were measured and used to determine the energy transfer probability distribution function, P(E,E'), in the large ΔE region. P(E,E') was then fit to a bi-exponential function and extrapolated to the low ΔE region. P(E,E') and the biexponential fit data were used to determine the partitioning between weak and strong collisions as well as investigate molecular properties responsible for large collisional energy transfer events. Fermi's Golden rule was used to model the shape of P(E,E') and identify which donor vibrational motions are primarily responsible for energy transfer. In general, the results suggest that low-frequency MFB vibrational modes are primarily responsible for strong collisions, and govern the shape and magnitude of P(E,E'). Where deviations from this general trend occur, vibrational modes with large negative anharmonicity constants are more efficient energy gateways than modes with similar frequency, while vibrational modes with large positive anharmonicity constants are less efficient at energy transfer than modes of similar frequency.
Giannetti, Claudio; Cilento, Federico; Conte, Stefano Dal; Coslovich, Giacomo; Ferrini, Gabriele; Molegraaf, Hajo; Raichle, Markus; Liang, Ruixing; Eisaki, Hiroshi; Greven, Martin; Damascelli, Andrea; van der Marel, Dirk; Parmigiani, Fulvio
2011-01-01
In strongly correlated systems the electronic properties at the Fermi energy (EF) are intertwined with those at high-energy scales. One of the pivotal challenges in the field of high-temperature superconductivity (HTSC) is to understand whether and how the high-energy scale physics associated with Mott-like excitations (|E−EF|>1 eV) is involved in the condensate formation. Here, we report the interplay between the many-body high-energy CuO2 excitations at 1.5 and 2 eV, and the onset of HTSC. This is revealed by a novel optical pump-supercontinuum-probe technique that provides access to the dynamics of the dielectric function in Bi2Sr2Ca0.92Y0.08Cu2O8+δ over an extended energy range, after the photoinduced suppression of the superconducting pairing. These results unveil an unconventional mechanism at the base of HTSC both below and above the optimal hole concentration required to attain the maximum critical temperature (Tc). PMID:21673674
Giannetti, Claudio; Cilento, Federico; Dal Conte, Stefano; Coslovich, Giacomo; Ferrini, Gabriele; Molegraaf, Hajo; Raichle, Markus; Liang, Ruixing; Eisaki, Hiroshi; Greven, Martin; Damascelli, Andrea; van der Marel, Dirk; Parmigiani, Fulvio
2011-06-14
In strongly correlated systems the electronic properties at the Fermi energy (E(F)) are intertwined with those at high-energy scales. One of the pivotal challenges in the field of high-temperature superconductivity (HTSC) is to understand whether and how the high-energy scale physics associated with Mott-like excitations (|E-E(F)|>1 eV) is involved in the condensate formation. Here, we report the interplay between the many-body high-energy CuO(2) excitations at 1.5 and 2 eV, and the onset of HTSC. This is revealed by a novel optical pump-supercontinuum-probe technique that provides access to the dynamics of the dielectric function in Bi(2)Sr(2)Ca(0.92)Y(0.08)Cu(2)O(8+δ) over an extended energy range, after the photoinduced suppression of the superconducting pairing. These results unveil an unconventional mechanism at the base of HTSC both below and above the optimal hole concentration required to attain the maximum critical temperature (T(c)).
NASA Astrophysics Data System (ADS)
Remick, Kevin; Dane Quinn, D.; Michael McFarland, D.; Bergman, Lawrence; Vakakis, Alexander
2016-05-01
The authors investigate a vibration-based energy harvesting system utilizing essential (nonlinearizable) nonlinearities and electromagnetic coupling elements. The system consists of a grounded, weakly damped linear oscillator (primary system) subjected to a single impulsive load. This primary system is coupled to a lightweight, damped oscillating attachment (denoted as nonlinear energy sink, NES) via a neodymium magnet and an inductance coil, and a piano wire, which generates an essential geometric cubic stiffness nonlinearity. Under impulsive input, the transient damped dynamics of this system exhibit transient resonance captures (TRCs) causing intentional large-amplitude and high-frequency instabilities in the response of the NES. These TRCs result in strong energy transfer from the directly excited primary system to the light-weight attachment. The energy is harvested by the electromagnetic elements in the coupling and, in the present case, dissipated in a resistive element in the electrical circuit. The primary goal of this work is to numerically, analytically, and experimentally demonstrate the efficacy of employing this type of intentional high-frequency dynamic instability to achieve enhanced vibration energy harvesting under impulsive excitation.
Positron-electron decay of 28Si at an excitation energy of 50 MeV
NASA Astrophysics Data System (ADS)
Buda, A.; Bacelar, J. C.; Balanda, A.; van der Ploeg, H.; Sujkowski, Z.; van der Woude, A.
1993-03-01
The electron-position pair decay of 28Si at 50 MeV excitation produced by the isospin T=0 (α + 24Mg) and the mixed isospin T=0,1 (3He + 25Mg) reactions has been studied using a special designed Positron-Electron pair spectrometer PEPSI.
Debreczeny, M.P.; Sauer, K.; Zhou, J.; Bryant, D.A.
1995-05-18
Rate constants for excitation energy transfer in light-harvesting protein, C-phycocyanin (PC), in the monomeric aggregation state, isolated from the cyanobacterium cynechococcus sp. PCC 7002, are calculated, using Foerster theory and compared with the results of time-resolved fluorescence measurements. The assignments of the energy-transfer rate constants in PC monomers are confirmed here by time-resolved fluorescence anisotropy measurements of the PC monomers isolated from both the wild-type and a mutant strain (cpcB/C155S) whose PC is missing the {beta}{sub 155} chromophore. It is concluded that the Foerster model of resonant energy transfer in the weak coupling limit successfully describes the dominant energy-transfer processes in this protein in the monomeric state. 31 refs., 3 figs., 4 tabs.
Mancini, Joshua A; Kodali, Goutham; Jiang, Jianbing; Reddy, Kanumuri Ramesh; Lindsey, Jonathan S; Bryant, Donald A; Dutton, P Leslie; Moser, Christopher C
2017-02-01
Synthetic proteins designed and constructed from first principles with minimal reference to the sequence of any natural protein have proven robust and extraordinarily adaptable for engineering a range of functions. Here for the first time we describe the expression and genetic fusion of a natural photosynthetic light-harvesting subunit with a synthetic protein designed for light energy capture and multi-step transfer. We demonstrate excitation energy transfer from the bilin of the CpcA subunit (phycocyanin α subunit) of the cyanobacterial photosynthetic light-harvesting phycobilisome to synthetic four-helix-bundle proteins accommodating sites that specifically bind a variety of selected photoactive tetrapyrroles positioned to enhance energy transfer by relay. The examination of combinations of different bilin, chlorin and bacteriochlorin cofactors has led to identification of the preconditions for directing energy from the bilin light-harvesting antenna into synthetic protein-cofactor constructs that can be customized for light-activated chemistry in the cell.
NASA Astrophysics Data System (ADS)
Amerikheirabadi, Fatemeh; Basurto, Luis; Zope, Rajendra; Baruah, Tunna
2015-03-01
Organic donor-acceptor (D-A) moieties make up the main component of organic photovoltaics (OPVs). It has been proved that the open circuit voltage of these devices which is a parameter in efficiency determination, is directly related to the charge transfer excited states of the D-A pairs. Fullerenes having lots of interesting acceptor properties and porphyrins as well as phthalocyanines possessing intriguing donor characteristics, are shown to be promising nominees. In this work, we computationally analyze three donor-acceptor dyads of Zn-tetraphenyl porphyrin and Zn-phthalocyanine with novel endohedral fullerenes: Sc3N@C80_ZnTPP, Y3N@C80_ZnTPPandSc3N@C80_ZnPc.TheSc3N@C80_and Y3N@C80 belong to a particular class of fullerenes called trimetallic nitride endohedral fullerenes where the trimellatic nitrides form the endohedral units. Density functional theory, as implemented in NRLMOL code, is used to study the electronic structure and the related properties of these D-A complexes. The charge transfer excitation energies are calculated using the perturbative delta self-consistent field method recently developed in our group. We find that the CT excitation energies are larger for endohedral fullerene based dyads compared to similar C60 based dyads.
Bauer, P.; Dufour, C.; Jaouen, C.; Marchal, G.; Pacaud, J.; Grilhe, J.; Jousset, J.C.
1997-01-01
M{umlt o}ssbauer spectroscopy ({sup 57}Fe) shows evidence for mixing effects induced by electronic energy deposition in nanoscale Fe/Si multilayers irradiated with swift heavy ions. A decrease in the mixing efficiency with electronic stopping power is reported; a threshold is found, under which iron environment modifications no longer occur. The kinetics of Fe{endash}Si phase formation after irradiation suggests the existence of three regimes: (i) for high excitation levels, a magnetic amorphous phase is formed directly in the wake of the incoming ion and an almost complete mixing is reached at low fluence (10{sup 13} U/cm{sup 2}); (ii) for low excitation levels, a paramagnetic Si-rich amorphous phase is favored at the interface while crystalline iron subsists at high fluences; (iii) for intermediate excitation levels, saturation effects are observed and the formation rate of both magnetic and paramagnetic phases points to direct mixing in the ion wake but with a reduced track length in comparison to U irradiation. The measured interfacial mixing cross section induced by electronic energy deposition suggests that a thermal diffusion process is mainly involved in addition to damage creation. {copyright} {ital 1997 American Institute of Physics.}
Excitation Energies from Real-Time Propagation of the Four-Component Dirac-Kohn-Sham Equation.
Repisky, Michal; Konecny, Lukas; Kadek, Marius; Komorovsky, Stanislav; Malkin, Olga L; Malkin, Vladimir G; Ruud, Kenneth
2015-03-10
We report the first implementation of real-time time-dependent density functional theory (RT-TDDFT) at the relativistic four-component level of theory. In contrast to the perturbative linear-response TDDFT approach (LR-TDDFT), the RT-TDDFT approach performs an explicit time propagation of the Dirac-Kohn-Sham density matrix, offering the possibility to simulate molecular spectroscopies involving strong electromagnetic fields while, at the same time, treating relativistic scalar and spin-orbit corrections variationally. The implementation is based on the matrix representation of the Dirac-Coulomb Hamiltonian in the basis of restricted kinetically balanced Gaussian-type functions, exploiting the noncollinear Kramers unrestricted formalism implemented in the program ReSpect. We also present an analytic form for the delta-type impulse commonly used in RT-TDDFT calculations, as well as a dipole-weighted transition matrix analysis, facilitating the interpretation of spectral transitions in terms of ground-state molecular orbitals. The possibilities offered by the methodology are illustrated by investigating vertical excitation energies and oscillator strengths for ground-state to excited-state transitions in the Group 12 atoms and in heavy-element hydrides. The accuracy of the method is assessed by comparing the excitation energies obtained with earlier relativistic linear response TDDFT results and available experimental data.
NASA Astrophysics Data System (ADS)
Zhang, Yinan; Birch, David J. S.; Chen, Yu
2011-09-01
We have demonstrated energy transfer between 4'-6-Diamidino-2-phenylindole (DAPI), a commonly used DNA label, and gold nanoparticles under two-photon excitation in solution using fluorescence lifetime imaging microscopy (FLIM). With comparable size and concentration, gold nanorods (GNRs) are shown to provide more efficient energy transfer than gold nanospheres (GNSs). We attribute this transfer enhancement effect to the longitudinal surface plasmon mode of GNRs overlapping with the excitation wavelength. Energy transfer under two-photon excitation between GNRs and DAPI has also been observed in cell culture and found to be in accord with the solution phase results.
NASA Astrophysics Data System (ADS)
Venhart, M.; Wood, J. L.; Boston, A. J.; Cocolios, T. E.; Harkness-Brennan, L. J.; Herzberg, R.-D.; Joss, D. T.; Judson, D. S.; Kliman, J.; Matoušek, V.; Motyčák, Š.; Page, R. D.; Patel, A.; Petrík, K.; Sedlák, M.; Veselský, M.
2017-03-01
A technique for elucidating β-decay schemes of isotopes with a large density of states at low excitation energy has been developed, in which a Broad Energy Germanium (BEGe) detector is used in conjunction with coaxial hyper-pure germanium detectors. The power of this technique is demonstrated using the example of 183Hg decay. Mass-separated samples of 183Hg were produced by a deposition of the low-energy radioactive-ion beam delivered by the ISOLDE facility at CERN. The excellent energy resolution of the BEGe detector allowed γ-ray energies to be determined with a precision of a few tens of eV, which was sufficient for the analysis of the Rydberg-Ritz combinations (in conjunction with γ-γ coincidences) in the level scheme. The timestamped structure of the data was used for unambiguous separation of γ rays arising from the decay of 183Hg from those due to the daughter decays.
Loco, Daniele; Polack, Étienne; Caprasecca, Stefano; Lagardère, Louis; Lipparini, Filippo; Piquemal, Jean-Philip; Mennucci, Benedetta
2016-08-09
A fully polarizable implementation of the hybrid quantum mechanics/molecular mechanics approach is presented, where the classical environment is described through the AMOEBA polarizable force field. A variational formalism, offering a self-consistent relaxation of both the MM induced dipoles and the QM electronic density, is used for ground state energies and extended to electronic excitations in the framework of time-dependent density functional theory combined with a state specific response of the classical part. An application to the calculation of the solvatochromism of the pyridinium N-phenolate betaine dye used to define the solvent ET(30) scale is presented. The results show that the QM/AMOEBA model not only properly describes specific and bulk effects in the ground state but it also correctly responds to the large change in the solute electronic charge distribution upon excitation.
NASA Astrophysics Data System (ADS)
Surzhikov, V. P.; Demikhova, A. A.
2017-01-01
Results of research of influence of the excitation pulse duration on the parameters of the electromagnetic response of epoxy samples with filler the quartz sand presented in the paper. The electric component of a response was registered by the capacitive sensors using a differential amplifier. Measurements were carried out at two frequencies of the master generator of 65 kHz and 74 kHz. The pulse duration was changing from 10 to 100 microseconds. The stepped sort of dependence of the integrated oscillations energy in the response from duration of the excitation pulse was discovered. The conclusion was made about the determining role of the normal oscillations in formation of such dependence.
Brøndsted Nielsen, Steen; Brøndsted Nielsen, Mogens; Rubio, Angel
2014-04-15
In a charge-transfer (CT) transition, electron density moves from one end of the molecule (donor) to the other end (acceptor). This type of transition is of paramount importance in nature, for example, in photosynthesis, and it governs the excitation of several protein biochromophores and luminophores such as the oxyluciferin anion that accounts for light emission from fireflies. Both transition energy and oscillator strength are linked to the coupling between the donor and acceptor groups: The weaker the coupling, the smaller the excitation energy. But a weak coupling necessarily also causes a low oscillator strength possibly preventing direct excitation (basically zero probability in the noncoupling case). The coupling is determined by the actual spacer between the two groups, and whether the spacer acts as an insulator or a conductor. However, it can be difficult or even impossible to distinguish the effect of the spacer from that of local solvent molecules that often cause large solvent shifts due to different ground-state and excited-state stabilization. This calls for gas-phase spectroscopy experiments where absorption by the isolated molecule is identified to unequivocally establish the intrinsic molecular properties with no perturbations from a microenvironment. From such insight, the effect of a protein microenvironment on the CT excited state can be deduced. In this Account, we review our results over the last 5 years from mass spectroscopy experiments using specially designed apparatus on several charged donor-acceptor ions that are based on the nitrophenolate moiety and π-extended derivatives, which are textbook examples of donor-acceptor chromophores. The phenolate oxygen is the donor, and the nitro group is the acceptor. The choice of this system is also based on the fact that phenolate is a common structural motif of biochromophores and luminophores, for example, it is a constituent of the oxyluciferin anion. A presentation of the setups used for
Chatterji, T; Jalarvo, N; Kumar, C M N; Xiao, Y; Brückel, Th
2013-07-17
We have investigated low energy nuclear spin excitations in the strongly correlated electron compound HoCrO3. We observe clear inelastic peaks at E = 22.18 ± 0.04 μeV in both energy loss and gain sides. The energy of the inelastic peaks remains constant in the temperature range 1.5-40 K at which they are observed. The intensity of the inelastic peak increases at first with increasing temperature and then decreases at higher temperatures. The temperature dependence of the energy and intensity of the inelastic peaks is very unusual compared to that observed in other Nd, Co, V and also simple Ho compounds. Huge quasielastic scattering appears at higher temperatures presumably due to the fluctuating electronic moments of the Ho ions that get increasingly disordered at higher temperatures. The strong quasielastic scattering may also originate in the first Ho crystal-field excitations at about 1.5 meV.
Joung, Joonyoung F; Kim, Sangin; Park, Sungnam
2015-12-17
Coumarin 183 (C183) was used as a photoacid to study excited-state proton transfer (ESPT) reactions. Here, we studied the effect of ions on the ESPT of C183 in aqueous NaCl solutions using a steady-state fluorescence spectroscopy and time-correlated single photon counting (TCSPC) method. The acid dissociation equilibrium of excited-state C183 and the activation energy for the ESPT of C183 were determined as a function of NaCl concentration. The change in the equilibrium constant was found to be correlated with the solvation energy of deprotonated C183. Frequency-resolved TCSPC signals measured at several temperatures were analyzed by using a global fitting analysis method which enabled us to extract all the rate constants involving the ESPT reaction and the spectra of individual species. The activation energy for the ESPT reaction of C183 was highly dependent on NaCl concentration. Quantum chemical calculations were used to calculate the local hydrogen-bond (H-bond) configurations around C183 in aqueous NaCl solutions. It was found that the activation energy for the ESPT was determined by the local H-bond configurations around C183 which were significantly influenced by the dissolved ions.
Denis-Alpizar, Otoniel; Kalugina, Yulia; Stoecklin, Thierry; Vera, Mario Hernández; Lique, François
2013-12-14
We present a new four-dimensional potential energy surface for the collisional excitation of HCN by H2. Ab initio calculations of the HCN-H2 van der Waals complex, considering both molecules as rigid rotors, were carried out at the explicitly correlated coupled cluster with single, double, and perturbative triple excitations [CCSD(T)-F12a] level of theory using an augmented correlation-consistent triple zeta (aVTZ) basis set. The equilibrium structure is linear HCN-H2 with the nitrogen pointing towards H2 at an intermolecular separation of 7.20 a0. The corresponding well depth is -195.20 cm(-1). A secondary minimum of -183.59 cm(-1) was found for a T-shape configuration with the H of HCN pointing to the center of mass of H2. We also determine the rovibrational energy levels of the HCN-para-H2 and HCN-ortho-H2 complexes. The calculated dissociation energies for the para and ortho complexes are 37.79 cm(-1) and 60.26 cm(-1), respectively. The calculated ro-vibrational transitions in the HCN-H2 complex are found to agree by more than 0.5% with the available experimental data, confirming the accuracy of the potential energy surface.
Johnson, Matthew P; Ruban, Alexander V
2009-08-28
Non-photochemical quenching (NPQ), a mechanism of energy dissipation in higher plants protects photosystem II (PSII) reaction centers from damage by excess light. NPQ involves a reduction in the chlorophyll excited state lifetime in the PSII harvesting antenna (LHCII) by a quencher. Yet, little is known about the effect of the quencher on chlorophyll excited state energy and dynamics. Application of picosecond time-resolved fluorescence spectroscopy demonstrated that NPQ involves a red-shift (60 +/- 5 cm(-1)) and slight enhancement of the vibronic satellite of the main PSII lifetime component present in intact chloroplasts. Whereas this fluorescence red-shift was enhanced by the presence of zeaxanthin, it was not dependent upon it. The red-shifted fluorescence of intact chloroplasts in the NPQ state was accompanied by red-shifted chlorophyll a absorption. Nearly identical absorption and fluorescence changes were observed in isolated LHCII complexes quenched in a low detergent media, suggesting that the mechanism of quenching is the same in both systems. In both cases, the extent of the fluorescence red-shift was shown to correlate with the lifetime of a component. The alteration in the energy of the emitting chlorophyll(s) in intact chloroplasts and isolated LHCII was also accompanied by changes in lutein 1 observed in their 77K fluorescence excitation spectra. We suggest that the characteristic red-shifted fluorescence emission reflects an altered environment of the emitting chlorophyll(s) in LHCII brought about by their closer interaction with lutein 1 in the quenching locus.
Ichou, Farid; Schwarzenberg, Adrian; Lesage, Denis; Alves, Sandra; Junot, Christophe; Machuron-Mandard, Xavier; Tabet, Jean-Claude
2014-06-01
Reproducibility among different types of excitation modes is a major bottleneck in the field of tandem mass spectrometry library development in metabolomics. In this study, we specifically evaluated the influence of collision voltage and activation time parameters on tandem mass spectrometry spectra for various excitation modes [collision-induced dissociation (CID), pulsed Q dissociation (PQD) and higher-energy collision dissociation (HCD)] of Orbitrap-based instruments. For this purpose, internal energy deposition was probed using an approach based on Rice-Rampserger-Kassel-Marcus modeling with three thermometer compounds of different degree of freedom (69, 228 and 420) and a thermal model. This model treats consecutively the activation and decomposition steps, and the survival precursor ion populations are characterized by truncated Maxwell-Boltzmann internal energy distributions. This study demonstrates that the activation time has a significant impact on MS/MS spectra using the CID and PQD modes. The proposed model seems suitable to describe the multiple collision regime in the PQD and HCD modes. Linear relationships between mean internal energy and collision voltage are shown for the latter modes and the three thermometer molecules. These results suggest that a calibration based on the collision voltage should provide reproducible for PQD, HCD to be compared with CID in tandem in space instruments. However, an important signal loss is observed in PQD excitation mode whatever the mass of the studied compounds, which may affect not only parent ions but also fragment ions depending on the fragmentation parameters. A calibration approach for the CID mode based on the variation of activation time parameter is more appropriate than one based on collision voltage. In fact, the activation time parameter in CID induces a modification of the collisional regime and thus helps control the orientation of the fragmentation pathways (competitive or consecutive dissociations).
NASA Technical Reports Server (NTRS)
Parusel, A. B.; Pohorille, A.
2001-01-01
The electronic ground and first excited states of retinal and its Schiff base are optimized for the first time using the semiempirical AM1 Hamiltonian. The barrier for rotation about the C(11)-C(12) double bond is characterized by variation of both the twist angle delta(C(10)-C(11)-C(12)-C(13)) and the bond length d(C(11)-C(12)). The potential energy surface is obtained by varying these two parameters. The calculated ground state rotational barrier is equal to 15.6 kcal/mol for retinal and 20.5 kcal/mol for its Schiff base. The all-trans conformation is more stable by 3.7 kcal/mol than the 11-cis geometry. For the first excited state, S(1,) the 90 degrees twisted geometry represents a saddle point for retinal with the rotational barrier of 14.6 kcal/mol. In contrast, this conformation is an energy minimum for the Schiff base. It can be easily reached at room temperature from the planar minima since it is separated from them by a barrier of only 0.6 kcal/mol. The 90 degrees minimum conformation is more stable than the all-trans by 8.6 kcal/mol. We are thus able to present a reaction path on the S(1) surface of the retinal Schiff base with an almost barrier-less geometrical relaxation into a twisted minimum geometry, as observed experimentally. The character of the ground and first excited singlet states underscores the need for the inclusion of double excitations in the calculations.
Fujisawa, Jun-Ichi; Osawa, Ayumi; Hanaya, Minoru
2016-08-10
Photoinduced carrier injection from dyes to inorganic semiconductors is a crucial process in various dye-sensitized solar energy conversions such as photovoltaics and photocatalysis. It has been reported that an energy offset larger than 0.2-0.3 eV (threshold value) is required for efficient electron injection from excited dyes to metal-oxide semiconductors such as titanium dioxide (TiO2). Because the energy offset directly causes loss in the potential of injected electrons, it is a crucial issue to minimize the energy offset for efficient solar energy conversions. However, a fundamental understanding of the energy offset, especially the threshold value, has not been obtained yet. In this paper, we report the origin of the threshold value of the energy offset, solving the long-standing questions of why such a large energy offset is necessary for the electron injection and which factors govern the threshold value, and suggest a strategy to minimize the threshold value. The threshold value is determined by the sum of two reorganization energies in one-electron reduction of semiconductors and typically-used donor-acceptor (D-A) dyes. In fact, the estimated values (0.21-0.31 eV) for several D-A dyes are in good agreement with the threshold value, supporting our conclusion. In addition, our results reveal that the threshold value is possible to be reduced by enlarging the π-conjugated system of the acceptor moiety in dyes and enhancing its structural rigidity. Furthermore, we extend the analysis to hole injection from excited dyes to semiconductors. In this case, the threshold value is given by the sum of two reorganization energies in one-electron oxidation of semiconductors and D-A dyes.
Excited Li and Na in He(n): influence of the dimer potential energy curves.
Dell'Angelo, David; Guillon, Grégoire; Viel, Alexandra
2012-03-21
The X(2)Σ ground and the A(2)Π and B(2)Σ first two excited states of Li-He and Na-He are determined using high level complete active space self-consistent field-multireference configuration interaction ab initio method. The obtained potentials differ from the ones proposed by Pascale [Phys. Rev. A 28, 632 (1983)], more strongly for the ground than for the excited states. Quantum diffusion Monte Carlo studies of small Li(∗)He(n) and Na(∗)He(n) with n ≤ 5 are performed using a diatomics-in-molecule approach to model the non-pair additive interaction potential. The sensitivity of our results to the A(2)Π and B(2)Σ potentials used is assessed by an analysis of the structure and of the energetics of the clusters. For these small clusters, the physical conclusions are essentially independent of the diatomic curves employed.
Multi-Index Nonlinear Coordinated Control for Battery Energy Storage System and Generator Excitation
NASA Astrophysics Data System (ADS)
Lingyi, Kong; Liying, Liao
A multi-index nonlinear coordinated control scheme for BESS and generator excitation is proposed. The proposed multi-index nonlinear coordinated controller can effectively coordinate the dynamic and steady-state performance of the controlled system. It can enhance the stability of the system, improve the dynamic characteristics of state variables, and can improve the control accuracy of output variables such as terminal voltage, active power output of the generator. Simulation results show that to control BESS and generator coordinately has the advantage of enhancing the stability of the system. With the ability of BESS to control the active power and reactive power, and the regulate of generator excitation, the dynamic characteristics of state variables can changes more smoothness, responds more speediness.
NASA Astrophysics Data System (ADS)
Deur, Killian; Mazouin, Laurent; Fromager, Emmanuel
2017-01-01
Ensemble density functional theory (eDFT) is an exact time-independent alternative to time-dependent DFT (TD-DFT) for the calculation of excitation energies. Despite its formal simplicity and advantages in contrast to TD-DFT (multiple excitations, for example, can be easily taken into account in an ensemble), eDFT is not standard, which is essentially due to the lack of reliable approximate exchange-correlation (x c ) functionals for ensembles. Following Smith et al. [Phys. Rev. B 93, 245131 (2016), 10.1103/PhysRevB.93.245131], we propose in this work to construct an exact eDFT for the nontrivial asymmetric Hubbard dimer, thus providing more insight into the weight dependence of the ensemble x c energy in various correlation regimes. For that purpose, an exact analytical expression for the weight-dependent ensemble exchange energy has been derived. The complementary exact ensemble correlation energy has been computed by means of Legendre-Fenchel transforms. Interesting features like discontinuities in the ensemble x c potential in the strongly correlated limit have been rationalized by means of a generalized adiabatic connection formalism. Finally, functional-driven errors induced by ground-state density-functional approximations have been studied. In the strictly symmetric case or in the weakly correlated regime, combining ensemble exact exchange with ground-state correlation functionals gives better ensemble energies than when calculated with the ground-state exchange-correlation functional. However, when approaching the asymmetric equiensemble in the strongly correlated regime, the former approximation leads to highly curved ensemble energies with negative slope which is unphysical. Using both ground-state exchange and correlation functionals gives much better results in that case. In fact, exact ensemble energies are almost recovered in some density domains. The analysis of density-driven errors is left for future work.
Half-life and excitation energy of the Iπ=13/2+ isomer in Ra209
NASA Astrophysics Data System (ADS)
Hauschild, K.; Lopez-Martens, A.; Yeremin, A. V.; Dorvaux, O.; Belozerov, A. V.; Chelnokov, M. L.; Chepigin, V. I.; Gall, B.; Gorshkov, V. A.; Guttormsen, M.; Jones, P.; Kabachenko, A. P.; Khouaja, A.; Larsen, A. C.; Malyshev, O. N.; Minkova, A.; Nyhus, H. T.; Oganessian, Yu. Ts.; Pantelica, D.; Popeko, A. G.; Rotaru, F.; Saro, S.; Shutov, A. V.; Siem, S.; Svirikhin, A. I.; Syed, N. U. H.
2008-04-01
An isomeric state in Ra209 has been observed for the first time, using the GABRIELA setup at the focal plane of VASSILISSA, to decay to the ground state of Ra209 via a cascade of 238-keV (M2) and 644-keV transitions. The half-life of the isomer has been measured to be 117(5)μs and from systematics is assigned as a neutron i13/2-1 excitation.
2009-08-26
Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 15. SUBJECT TERMS superconducting qubits, quasiparticles, coherence John ...ARO 8. PERFORMING ORGANIZATION REPORT NUMBER 19a. NAME OF RESPONSIBLE PERSON 19b. TELEPHONE NUMBER John Martinis 805-893-3910 3. DATES...Junction Qubits from Nonequilibrium Quasiparticle Excitations John M. Martinis,1 M. Ansmann,1 and J. Aumentado2 1Department of Physics, University of
Berman, P. R.; Le Goueet, J.-L.
2011-03-15
Scully and coworkers [M. O. Scully, E. S. Fry, C. H. R. Oii, and K. Wodkiewicz, Phys. Rev. Lett. 96, 010501 (2006)] demonstrated that there is directional, phase-matched emission following the excitation of an ensemble of atoms by a single-photon pulse. While the phase-matched emission intensity is proportional to the the number of atoms, for optically thin samples the total energy emitted in the phase-matched direction is much less than that radiated in other directions. Moreover, even for optically thin samples, it is necessary to take into account effects related to cooperative decay if energy is to be conserved in the overall emission process. An analytic calculation is presented to show explicitly how cooperative decay reduces the incoherent emission and restores energy conservation in this low-density limit.
Ferreira, Rute A S; Nolasco, Mariela; Roma, Ana C; Longo, Ricardo L; Malta, Oscar L; Carlos, Luis D
2012-09-17
In many Eu(III)-based materials, the presence of an intermediate energy level, such as ligand-to-metal charge transfer (LMCT) states or defects, that mediates the energy transfer mechanisms can strongly affect the lifetime of the (5)D(0) state, mainly at near-resonance (large transfer rates). We present results for the dependence of the (5)D(0) lifetime on the excitation wavelength for a wide class of Eu(III)-based compounds: ionic salts, polyoxometalates (POMs), core/shell inorganic nanoparticles (NPs) and nanotubes, coordination polymers, β-diketonate complexes, organic-inorganic hybrids, macro-mesocellular foams, functionalized mesoporous silica, and layered double hydroxides (LDHs). This yet unexplained behavior is successfully modelled by a coupled set of rate equations with seven states, in which the wavelength dependence is simulated by varying the intramolecular energy transfer rates. In addition, the simulations of the rate equations for four- and three-level systems show a strong dependence of the emission lifetime upon the excitation wavelength if near-resonant non-radiative energy transfer processes are present, indicating that the proposed scheme can be generalized to other trivalent lanthanide ions, as observed for Tb(III)/Ce(III). Finally, the proper use of lifetime definition in the presence of energy transfer is emphasized.
NASA Astrophysics Data System (ADS)
Koh, Yang Wei
2016-04-01
We present an extensive numerical study of the Sherrington-Kirkpatrick model in a transverse field. Recent numerical studies of quantum spin glasses have focused on exact diagonalization of the full Hamiltonian for small systems (≈20 spins). However, such exact numerical treatments are difficult to apply on larger systems. We propose making an approximation by using only a subspace of the full Hilbert space spanned by low-lying excitations consisting of one-spin-flipped and two-spin-flipped states. The approximation procedure is carried out within the theoretical framework of the Hartree-Fock approximation and configuration interaction. Although not exact, our approach allows us to study larger system sizes comparable to that achievable by state-of-the-art quantum Monte Carlo simulations. We calculate two quantities of interest due to recent advances in quantum annealing, the ground-state energy and the energy gap between the ground and first excited states. For the energy gap, we derive a formula that enables it to be calculated using just the ground-state wave function, thereby circumventing the need to diagonalize the Hamiltonian. We calculate the scalings of the energy gap and the leading correction to the extensive part of the ground-state energy with system size, which are difficult to obtain with current methods.
Li, Y Q; Zhang, P Y; Han, K L
2015-03-28
A global many-body expansion potential energy surface is reported for the electronic ground state of CH2 (+) by fitting high level ab initio energies calculated at the multireference configuration interaction level with the aug-cc-pV6Z basis set. The topographical features of the new global potential energy surface are examined in detail and found to be in good agreement with those calculated directly from the raw ab initio energies, as well as previous calculations available in the literature. In turn, in order to validate the potential energy surface, a test theoretical study of the reaction CH(+)(X(1)Σ(+))+H((2)S)→C(+)((2)P)+H2(X(1)Σg (+)) has been carried out with the method of time dependent wavepacket on the title potential energy surface. The total integral cross sections and the rate coefficients have been calculated; the results determined that the new potential energy surface can both be recommended for dynamics studies of any type and as building blocks for constructing the potential energy surfaces of larger C(+)/H containing systems.
Guan, Jingang; Wang, Fan; Ziegler, Tom; Cox, Hazel
2006-07-28
Orbital energies, ionization potentials, molecular constants, potential energy curves, and the excitation spectrum of O(2) are calculated using time-dependent density functional theory (TDDFT) with Tamm-Dancoff approximation (TDA). The calculated negative highest occupied molecular orbital energy (-epsilon(HOMO)) is compared with the energy difference ionization potential for five exchange correlation functionals consisting of the local density approximation (LDAxc), gradient corrected Becke exchange plus Perdew correlation (B(88X)+P(86C)), gradient regulated asymptotic correction (GRAC), statistical average of orbital potentials (SAOP), and van Leeuwen and Baerends asymptotically correct potential (LB94). The potential energy curves calculated using TDDFT with the TDA at internuclear distances from 1.0 to 1.8 A are divided into three groups according to the electron configurations. The 1pi(u) (4)1pi(g) (2) electron configuration gives rise to the X (3)Sigma(g) (-), a (1)Delta(g), and b (1)Sigma(g) (+) states; the 1pi(u) (3)1pi(g) (3) electron configuration gives rise to the c (1)Sigma(u) (-), C (3)Delta(u), and A (3)Sigma(u) (+) states; and the B (3)Sigma(u) (-), A (1)Delta(u), and f (1)Sigma(u) (+) states are determined by the mixing of two or more electron configurations. The excitation spectrum of the oxygen molecule, calculated with the aforementioned exchange correlation functionals, shows that the results are quite sensitive to the choice of functional. The LDAxc and the B(88X)+P(86C) functionals produce similar spectroscopic patterns with a single strongly absorbing band positioned at 19.82 and 19.72 eV, respectively, while the asymptotically corrected exchange correlation functionals of the SAOP and the LB94 varieties yield similar excitation spectra where the computed strongly absorbing band is located at 16.09 and 16.42 eV, respectively. However, all of the exchange correlation functionals yield only one strongly absorbing band (oscillator strength
Wlodarczyk, Lucyna M; Dinc, Emine; Croce, Roberta; Dekker, Jan P
2016-06-01
The efficient use of excitation energy in photosynthetic membranes is achieved by a dense network of pigment-protein complexes. These complexes fulfill specific functions and interact dynamically with each other in response to rapidly changing environmental conditions. Here, we studied how in the intact cells of Chlamydomonas reinhardtii (C.r.) the lack of the photosystem I (PSI) core or the photosystem II (PSII) core affects these interactions. To that end the mutants F15 and M18 (both PSI-deficient) and FUD7 (PSII-deficient) were incubated under conditions known to promote state transitions in wild-type. The intact cells were then instantly frozen to 77K and the full-spectrum time-resolved fluorescence emission of the cells was measured by means of streak camera. In the PSI-deficient mutants excitation energy transfer (EET) towards light-harvesting complexes of PSI (Lhca) occurs in less than 0.5 ns, and fluorescence from Lhca decays in 3.1 ns. Decreased trapping by PSII and increased fluorescence of Lhca upon state 1 (S1)→state 2 (S2) transition appears in the F15 and less in the M18 mutant. In the PSII-deficient mutant FUD7, quenched (0.5 ns) and unquenched (2 ns) light-harvesting complexes of PSII (LHCII) are present in both states, with the quenched form more abundant in S2 than in S1. Moreover, EET of 0.4 ns from the remaining LHCII to PSI increases upon S1→S2 transition. We relate the excitation energy kinetics observed in F15, M18 and FUD7 to the remodeling of the photosynthetic apparatus in these mutants under S1 and S2 conditions.
Tanaka, Kazunori; Iida, Satoko; Takaichi, Shinichi; Mimuro, Mamoru; Murakami, Akio; Akimoto, Seiji
2016-12-01
Photosynthetic light-harvesting complexes, found in aquatic photosynthetic organisms, contain a variety of carotenoids and chlorophylls. Most of the photosynthetic dinoflagellates possess two types of light-harvesting antenna complexes: peridinin (Peri)-chlorophyll (Chl) a/c-protein, as an intrinsic thylakoid membrane complex protein (iPCP), and water-soluble Peri-Chl a-protein, as an extrinsic membrane protein (sPCP) on the inner surface of the thylakoid. Peri is a unique carotenoid that has eight C=C bonds and one C=O bond, which results in a characteristic absorption band in the green wavelength region. In the present study, excitation relaxation dynamics of Peri in solution and excitation energy transfer processes of sPCP and the thylakoid membranes, prepared from the photosynthetic dinoflagellate, Symbiodinium sp., are investigated by ultrafast time-resolved fluorescence spectroscopy. We found that Peri-to-Chl a energy transfer occurs via the Peri S1 state with a time constant of 1.5 ps or 400 fs in sPCP or iPCP, respectively, and that Chl c-to-Chl a energy transfer occurs in the time regions of 350-400 fs and 1.8-2.6 ps.
Marinakis, Sarantos; Dean, Indigo Lily; Kłos, Jacek; Lique, François
2015-09-07
We present a new set of potential energy surfaces (PESs) for the CH(X(2)Π)-He van der Waals system. Ab initio calculations of the CH-He PES were carried out using the open-shell single- and double-excitation coupled cluster approach with non-iterative perturbational treatment of triple excitations [RCCSD(T)]. The augmented correlation-consistent polarized valence quadruple-zeta (aug-cc-pVQZ) basis set was employed augmented by mid-bond functions. Integral cross sections for the rotational excitation in CH-He collisions were calculated using the new PES and compared with available experimental results. The newly constructed PES reproduces the available experimental results for CH(X(2)Π, v = 0)-He collisions better than any previously available PES. Differential cross sections (DCS) are presented for the first time for this system and discussed within the context of rotational rainbows. Finally, our work provides the first rate thermal coefficients for this system that are crucially needed for astrochemical modelling and future anticipated experiments in CH(X(2)Π)-He collisions.
Li, Jian-Hao; Zuehlsdorff, T J; Payne, M C; Hine, N D M
2015-05-14
We show that the transition origins of electronic excitations identified by quantified natural transition orbital (QNTO) analysis can be employed to connect potential energy surfaces (PESs) according to their character across a wide range of molecular geometries. This is achieved by locating the switching of transition origins of adiabatic potential surfaces as the geometry changes. The transition vectors for analysing transition origins are provided by linear response time-dependent density functional theory (TDDFT) calculations under the Tamm-Dancoff approximation. We study the photochemical CO ring opening of oxirane as an example and show that the results corroborate the traditional Gomer-Noyes mechanism derived experimentally. The knowledge of specific states for the reaction also agrees well with that given by previous theoretical work using TDDFT surface-hopping dynamics that was validated by high-quality quantum Monte Carlo calculations. We also show that QNTO can be useful for considerably larger and more complex systems: by projecting the excitations to those of a reference oxirane molecule, the approach is a