Silva, Mateus X; Galvão, Breno R L; Belchior, Jadson C
2014-05-21
Genetic algorithm is employed to survey an empirical potential energy surface for small Na(x)K(y) clusters with x + y ≤ 15, providing initial conditions for electronic structure methods. The minima of such empirical potential are assessed and corrected using high level ab initio methods such as CCSD(T), CR-CCSD(T)-L and MP2, and benchmark results are obtained for specific cases. The results are the first calculations for such small alloy clusters and may serve as a reference for further studies. The validity and choice of a proper functional and basis set for DFT calculations are then explored using the benchmark data, where it was found that the usual DFT approach may fail to provide the correct qualitative result for specific systems. The best general agreement to the benchmark calculations is achieved with def2-TZVPP basis set with SVWN5 functional, although the LANL2DZ basis set (with effective core potential) and SVWN5 functional provided the most cost-effective results. PMID:24691391
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)
1997-01-01
The current methods of quantum chemical calculations will be reviewed. The accent will be on the accuracy that can be achieved with these methods. The basis set requirements and computer resources for the various methods will be discussed. The utility of the methods will be illustrated with some examples, which include the calculation of accurate bond energies for SiF$_n$ and SiF$_n^+$ and the modeling of chemical data storage.
Accurate quantum chemical calculations
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.
1989-01-01
An important goal of quantum chemical calculations is to provide an understanding of chemical bonding and molecular electronic structure. A second goal, the prediction of energy differences to chemical accuracy, has been much harder to attain. First, the computational resources required to achieve such accuracy are very large, and second, it is not straightforward to demonstrate that an apparently accurate result, in terms of agreement with experiment, does not result from a cancellation of errors. Recent advances in electronic structure methodology, coupled with the power of vector supercomputers, have made it possible to solve a number of electronic structure problems exactly using the full configuration interaction (FCI) method within a subspace of the complete Hilbert space. These exact results can be used to benchmark approximate techniques that are applicable to a wider range of chemical and physical problems. The methodology of many-electron quantum chemistry is reviewed. Methods are considered in detail for performing FCI calculations. The application of FCI methods to several three-electron problems in molecular physics are discussed. A number of benchmark applications of FCI wave functions are described. Atomic basis sets and the development of improved methods for handling very large basis sets are discussed: these are then applied to a number of chemical and spectroscopic problems; to transition metals; and to problems involving potential energy surfaces. Although the experiences described give considerable grounds for optimism about the general ability to perform accurate calculations, there are several problems that have proved less tractable, at least with current computer resources, and these and possible solutions are discussed.
NASA Astrophysics Data System (ADS)
Churakov, S. V.; Parrinello, M.
2003-04-01
The carbonation of brucite (Mg(OH)2) has been considered as a potential technology for cleaning industrial carbon dioxide waste. The kinetics of the reaction Mg(OH)2 + CO2 -> MgCO3 + H2O have been studied experimentally at 573°C by Bearat at al. [1]. Their experiments suggest that the carbonation of magnesium hydroxide proceeds by the reaction Mg(OH)2 -> MgO + H2O followed by the adsorption of CO2 molecules on the dehydrated brucite surface. Due to the large difference in volumes between Mg(OH)2 and MgO, dehydration causes the formation of dislocations and cracks, allowing water molecules to leave the brucite surface and facilitating the advance of the carbonation front in the bulk solid. The detailed mechanism of this process is however unknown. We used the Car-Parrinello ab initio molecular dynamics method to study the structure and dynamics of the (0001), (1-100) and (11-20) surfaces of brucit and calculated the enthalpy and activation barrier of H2O nucleation and dehydration on different surfaces. The results obtained are in agreement with previous studies of brucite dehydration by Masini and Bernasconi [2]. The reactive Car-Parrinello molecular dynamics method [3] has been applied to investigate the detailed mechanism of the dehydration-carbonation reaction at the (1-100) interface of brucite with the gas phase. Based on the results of our MD simulations and the calculated enthalpy of CO2 adsorption on the dehydrated brucite surfaces we propose a mechanism for the dehydration/carbonation reaction. [1] Bearat H, McKelvy MJ, Chizmeshya AVG, Sharma R, Carpenter RW (2002) J. Amer. Ceram. Soc. 85(4):742 [2] Masini P and Bernasconi M (2001) J. Phys. Cond. Mat. 13: 1-12 [3] Iannuzzi M, Laio A and Parrinello M (2003) Phys. Rev. Lett. (submitted)
Monari, Antonio; Rivail, Jean-Louis; Assfeld, Xavier
2013-02-19
Molecular mechanics methods can efficiently compute the macroscopic properties of a large molecular system but cannot represent the electronic changes that occur during a chemical reaction or an electronic transition. Quantum mechanical methods can accurately simulate these processes, but they require considerably greater computational resources. Because electronic changes typically occur in a limited part of the system, such as the solute in a molecular solution or the substrate within the active site of enzymatic reactions, researchers can limit the quantum computation to this part of the system. Researchers take into account the influence of the surroundings by embedding this quantum computation into a calculation of the whole system described at the molecular mechanical level, a strategy known as the mixed quantum mechanics/molecular mechanics (QM/MM) approach. The accuracy of this embedding varies according to the types of interactions included, whether they are purely mechanical or classically electrostatic. This embedding can also introduce the induced polarization of the surroundings. The difficulty in QM/MM calculations comes from the splitting of the system into two parts, which requires severing the chemical bonds that link the quantum mechanical subsystem to the classical subsystem. Typically, researchers replace the quantoclassical atoms, those at the boundary between the subsystems, with a monovalent link atom. For example, researchers might add a hydrogen atom when a C-C bond is cut. This Account describes another approach, the Local Self Consistent Field (LSCF), which was developed in our laboratory. LSCF links the quantum mechanical portion of the molecule to the classical portion using a strictly localized bond orbital extracted from a small model molecule for each bond. In this scenario, the quantoclassical atom has an apparent nuclear charge of +1. To achieve correct bond lengths and force constants, we must take into account the inner shell of
Quantum speed problem: Theoretical hints for control
NASA Astrophysics Data System (ADS)
Lisboa, Alexandre Coutinho; Piqueira, José Roberto Castilho
2016-06-01
The transition time between states plays an important role in designing quantum devices as they are very sensitive to environmental influences. Decoherence phenomenon is responsible for possible destructions of the entanglement that is a fundamental requirement to implement quantum information processing systems. If the time between states is minimized, the decoherence effects can be reduced, thus, it is advantageous to the designer to develop expressions for time performance measures. Quantum speed limit (QSL) problem has been studied from the theoretical point of view, providing general results. Considering the implementation of quantum control systems, as the decoherence phenomenon is unavoidable, it is important to apply these general results to particular cases, developing expressions and performance measures, to assist control engineering designers. Here, a minimum time performance measure is defined for quantum control problems, for time-independent or time-dependent Hamiltonians, and applied to some practical examples, providing hints that may be useful for researchers pursuing optimization strategies for quantum control systems.
Multiloop calculations in perturbative quantum field theory
NASA Astrophysics Data System (ADS)
Blokland, Ian Richard
This thesis deals with high-precision calculations in perturbative quantum field theory. In conjunction with detailed experimental measurements, perturbative quantum field theory provides the quantitative framework with which much of modern particle physics is understood. The results of three new theoretical calculations are presented. The first is a definitive resolution of a recent controversy involving the interaction of a muon with a magnetic field. Specifically, the light-by-light scattering contribution to the anomalous magnetic moment of the muon is shown to be of positive sign, thereby decreasing the discrepancy between theory and experiment. Despite this adjustment to the theoretical prediction, the remaining discrepancy might be a subtle signature of new kinds of particles. The second calculation involves the energy levels of a bound state formed from two charged particles of arbitrary masses. By employing recently developed mass expansion techniques, new classes of solutions are obtained for problems in a field of particle physics with a very rich history. The third calculation provides an improved prediction for the decay of a top quark. In order to obtain this result, a large class of multiloop integrals has been solved for the first time. Top quark decay is just one member of a family of interesting physical processes to which these new results apply. Since specialized calculational techniques are essential ingredients in all three calculations, they are motivated and explained carefully in this thesis. These techniques, once automated with symbolic computational software, have recently opened avenues of solution to a wide variety of important problems in particle physics.
Theoretical Calculations of Atomic Data for Spectroscopy
NASA Technical Reports Server (NTRS)
Bautista, Manuel A.
2000-01-01
Several different approximations and techniques have been developed for the calculation of atomic structure, ionization, and excitation of atoms and ions. These techniques have been used to compute large amounts of spectroscopic data of various levels of accuracy. This paper presents a review of these theoretical methods to help non-experts in atomic physics to better understand the qualities and limitations of various data sources and assess how reliable are spectral models based on those data.
Hybrid quantum teleportation: A theoretical model
Takeda, Shuntaro; Mizuta, Takahiro; Fuwa, Maria; Yoshikawa, Jun-ichi; Yonezawa, Hidehiro; Furusawa, Akira
2014-12-04
Hybrid quantum teleportation – continuous-variable teleportation of qubits – is a promising approach for deterministically teleporting photonic qubits. We propose how to implement it with current technology. Our theoretical model shows that faithful qubit transfer can be achieved for this teleportation by choosing an optimal gain for the teleporter’s classical channel.
Quantum transport calculations using periodic boundaryconditions
Wang, Lin-Wang
2004-06-15
An efficient new method is presented to calculate the quantum transports using periodic boundary conditions. This method allows the use of conventional ground state ab initio programs without big changes. The computational effort is only a few times of a normal groundstate calculations, thus is makes accurate quantum transport calculations for large systems possible.
Theoretical studies of graphene nanoribbon quantum dot qubits
NASA Astrophysics Data System (ADS)
Chen, Chih-Chieh; Chang, Yia-Chung
Graphene nanoribbon quantum dot qubits have been proposed as promising candidates for quantum computing applications to overcome the spin-decoherence problems associated with typical semiconductor (e.g., GaAs) quantum dot qubits. We perform theoretical studies of the electronic structures of graphene nanoribbon quantum dots by solving the Dirac equation with appropriate boundary conditions. We then evaluate the exchange splitting based on an unrestricted Hartree-Fock method for the Dirac particles. The electronic wave function and long-range exchange coupling due to the Klein tunneling and the Coulomb interaction are calculated for various gate configurations. It is found that the exchange coupling between qubits can be significantly enhanced by the Klein tunneling effect. The implications of our results for practical qubit construction and operation are discussed. This work was supported in part by the Ministry of Science and Technology, Taiwan, under Contract No. MOST 104-2112-M-001-009-MY2.
First principle thousand atom quantum dot calculations
Wang, Lin-Wang; Li, Jingbo
2004-03-30
A charge patching method and an idealized surface passivation are used to calculate the single electronic states of IV-IV, III-V, II-VI semiconductor quantum dots up to a thousand atoms. This approach scales linearly and has a 1000 fold speed-up compared to direct first principle methods with a cost of eigen energy error of about 20 meV. The calculated quantum dot band gaps are parametrized for future references.
Information-theoretic temporal Bell inequality and quantum computation
Morikoshi, Fumiaki
2006-05-15
An information-theoretic temporal Bell inequality is formulated to contrast classical and quantum computations. Any classical algorithm satisfies the inequality, while quantum ones can violate it. Therefore, the violation of the inequality is an immediate consequence of the quantumness in the computation. Furthermore, this approach suggests a notion of temporal nonlocality in quantum computation.
Multi-million atom electronic structure calculations for quantum dots
NASA Astrophysics Data System (ADS)
Usman, Muhammad
Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In the past decade or so, these nanostructures have attracted significant experimental and theoretical attention in the field of nanoscience. The new and tunable optical and electrical properties of these artificial atoms have been proposed in a variety of different fields, for example in communication and computing systems, medical and quantum computing applications. Predictive and quantitative modeling and simulation of these structures can help to narrow down the vast design space to a range that is experimentally affordable and move this part of nanoscience to nano-Technology. Modeling of such quantum dots pose a formidable challenge to theoretical physicists because: (1) Strain originating from the lattice mismatch of the materials penetrates deep inside the buffer surrounding the quantum dots and require large scale (multi-million atom) simulations to correctly capture its effect on the electronic structure, (2) The interface roughness, the alloy randomness, and the atomistic granularity require the calculation of electronic structure at the atomistic scale. Most of the current or past theoretical calculations are based on continuum approach such as effective mass approximation or k.p modeling capturing either no or one of the above mentioned effects, thus missing some of the essential physics. The Objectives of this thesis are: (1) to model and simulate the experimental quantum dot topologies at the atomistic scale; (2) to theoretically explore the essential physics i.e. long range strain, linear and quadratic piezoelectricity, interband optical transition strengths, quantum confined
Linear-scaling quantum Monte Carlo calculations.
Williamson, A J; Hood, R Q; Grossman, J C
2001-12-10
A method is presented for using truncated, maximally localized Wannier functions to introduce sparsity into the Slater determinant part of the trial wave function in quantum Monte Carlo calculations. When combined with an efficient numerical evaluation of these localized orbitals, the dominant cost in the calculation, namely, the evaluation of the Slater determinant, scales linearly with system size. This technique is applied to accurate total energy calculation of hydrogenated silicon clusters and carbon fullerenes containing 20-1000 valence electrons. PMID:11736525
A quantum theoretical study of polyimides
NASA Technical Reports Server (NTRS)
Burke, Luke A.
1987-01-01
One of the most important contributions of theoretical chemistry is the correct prediction of properties of materials before any costly experimental work begins. This is especially true in the field of electrically conducting polymers. Development of the Valence Effective Hamiltonian (VEH) technique for the calculation of the band structure of polymers was initiated. The necessary VEH potentials were developed for the sulfur and oxygen atoms within the particular molecular environments and the explanation explored for the success of this approximate method in predicting the optical properties of conducting polymers.
A Generalized Information Theoretical Model for Quantum Secret Sharing
NASA Astrophysics Data System (ADS)
Bai, Chen-Ming; Li, Zhi-Hui; Xu, Ting-Ting; Li, Yong-Ming
2016-07-01
An information theoretical model for quantum secret sharing was introduced by H. Imai et al. (Quantum Inf. Comput. 5(1), 69-80 2005), which was analyzed by quantum information theory. In this paper, we analyze this information theoretical model using the properties of the quantum access structure. By the analysis we propose a generalized model definition for the quantum secret sharing schemes. In our model, there are more quantum access structures which can be realized by our generalized quantum secret sharing schemes than those of the previous one. In addition, we also analyse two kinds of important quantum access structures to illustrate the existence and rationality for the generalized quantum secret sharing schemes and consider the security of the scheme by simple examples.
Sheaf-theoretic representation of quantum measure algebras
Zafiris, Elias
2006-09-15
We construct a sheaf-theoretic representation of quantum probabilistic structures, in terms of covering systems of Boolean measure algebras. These systems coordinatize quantum states by means of Boolean coefficients, interpreted as Boolean localization measures. The representation is based on the existence of a pair of adjoint functors between the category of presheaves of Boolean measure algebras and the category of quantum measure algebras. The sheaf-theoretic semantic transition of quantum structures shifts their physical significance from the orthoposet axiomatization at the level of events, to the sheaf-theoretic gluing conditions at the level of Boolean localization systems.
Theoretical Calculations of Equations of State
NASA Astrophysics Data System (ADS)
Prakash, Madappa
2016-07-01
The modeling of core-collapse supernovae, neutron stars from their birth to old age, and binary mergers of compact stars requires a detailed knowledge of the equation of state (EOS) of matter at finite temperature. Thermodynamic state variables such as the free energy, energy per baryon, pressure, entropy per baryon, specific heats, chemical potentials of the various species and their derivatives with respect to number densities, thermal and adiabatic indices, etc., all play distinct roles in large-scale computer simulations involving compact objects. In this talk, recent developments in the calculation of the thermal properties of dense matter will be reviewed. Recent results from beyond relativistic mean field theory will be discussed. Highlights will include the role of non-nucleonic degrees of freedom at finite temperature, and possible avenues for future investigations.
Quantum Theoretical Study of KCl and LiCl Clusters
NASA Astrophysics Data System (ADS)
Koetter, Ted; Hira, Ajit; Salazar, Justin; Jaramillo, Danelle
2014-03-01
This research focuses on the theoretical study of molecular clusters to examine the chemical properties of small KnClnandLinCln clusters (n = 2 - 20). The potentially important role of these molecular species in biochemical and medicinal processes is well known. This work applies the hybrid ab initio methods of quantum chemistry to derive the different alkali-halide (MnHn) geometries. Of particular interest is the competition between hexagonal ring geometries and rock salt structures. Electronic energies, rotational constants, dipole moments, and vibrational frequencies for these geometries are calculated. Magic numbers for cluster stability are identified and are related to the property of cluster compactness. Mapping of the singlet, triplet, and quintet, potential energy surfaces is performed. Calculations were performed to examine the interactions of these clusters with some atoms and molecules of biological interest, including O, O2, and Fe. Potential design of new medicinal drugs is explored.
Quantum Monte Carlo calculations of light nuclei
Pieper, S.C.
1998-12-01
Quantum Monte Carlo calculations using realistic two- and three-nucleon interactions are presented for nuclei with up to eight nucleons. We have computed the ground and a few excited states of all such nuclei with Greens function Monte Carlo (GFMC) and all of the experimentally known excited states using variational Monte Carlo (VMC). The GFMC calculations show that for a given Hamiltonian, the VMC calculations of excitation spectra are reliable, but the VMC ground-state energies are significantly above the exact values. We find that the Hamiltonian we are using (which was developed based on {sup 3}H,{sup 4}He, and nuclear matter calculations) underpredicts the binding energy of p-shell nuclei. However our results for excitation spectra are very good and one can see both shell-model and collective spectra resulting from fundamental many-nucleon calculations. Possible improvements in the three-nucleon potential are also be discussed. {copyright} {ital 1998 American Institute of Physics.}
Quantum Monte Carlo calculations of light nuclei
Pieper, Steven C.
1998-12-21
Quantum Monte Carlo calculations using realistic two- and three-nucleon interactions are presented for nuclei with up to eight nucleons. We have computed the ground and a few excited states of all such nuclei with Greens function Monte Carlo (GFMC) and all of the experimentally known excited states using variational Monte Carlo (VMC). The GFMC calculations show that for a given Hamiltonian, the VMC calculations of excitation spectra are reliable, but the VMC ground-state energies are significantly above the exact values. We find that the Hamiltonian we are using (which was developed based on {sup 3}H,{sup 4}He, and nuclear matter calculations) underpredicts the binding energy of p-shell nuclei. However our results for excitation spectra are very good and one can see both shell-model and collective spectra resulting from fundamental many-nucleon calculations. Possible improvements in the three-nucleon potential are also be discussed.
Quantum Monte Carlo calculations of light nuclei.
Pieper, S. C.
1998-08-25
Quantum Monte Carlo calculations using realistic two- and three-nucleon interactions are presented for nuclei with up to eight nucleons. We have computed the ground and a few excited states of all such nuclei with Greens function Monte Carlo (GFMC) and all of the experimentally known excited states using variational Monte Carlo (VMC). The GFMC calculations show that for a given Hamiltonian, the VMC calculations of excitation spectra are reliable, but the VMC ground-state energies are significantly above the exact values. We find that the Hamiltonian we are using (which was developed based on {sup 3}H, {sup 4}He, and nuclear matter calculations) underpredicts the binding energy of p-shell nuclei. However our results for excitation spectra are very good and one can see both shell-model and collective spectra resulting from fundamental many-nucleon calculations. Possible improvements in the three-nucleon potential are also be discussed.
Quantum Monte Carlo calculations for light nuclei.
Wiringa, R. B.
1998-10-23
Quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A {le} 8 are made using a realistic Hamiltonian that fits NN scattering data. Results for more than 40 different (J{pi}, T) states, plus isobaric analogs, are obtained and the known excitation spectra are reproduced reasonably well. Various density and momentum distributions and electromagnetic form factors and moments have also been computed. These are the first microscopic calculations that directly produce nuclear shell structure from realistic NN interactions.
Theoretical Studies of Classical and Quantum Systems
NASA Astrophysics Data System (ADS)
Wu, Jian
1995-01-01
Two implementations of the Backward Euler method for simulating molecular fluids are compared with brownian dynamics and molecular dynamics simulations. The four methods are used to compute equilibrium and time-dependent properties of a single diatomic molecule, liquid argon, a single butane molecule and liquid butane. We show that the Backward Euler simulation under-estimates the thermodynamic properties of the liquids, predicts liquid structures which are too solid-like, and incorrectly represents dynamical relaxation processes. Also, we show that any agreement between results from the Backward Euler simulation and quantum mechanics is accidental. Although the Backward Euler method allows longer time-steps to be used in simulations, the time-consuming energy minimization required at every time-step decreases significantly the overall computational efficiency. Even when time-steps more than 20 times larger than that required for energy and momentum conservation are used, neither implementation of the Backward Euler algorithm is more accurate than standard molecular dynamics calculations with the same time-step. We conclude that the new method offers no advantage over more usual methods for simulations and that it often predicts incorrect results. In particular, we see no evidence that the method will allow long-time dynamics of polymers and macromolecules to be simulated either accurately or efficiently. Neural and charged xenon in ^4 He clusters at zero temperature have been studied systematically for clusters of different size, up to a thousand particles, by employing variational and diffusion Monte Carlo methods with different choices of pairwise wave functions to describe the correlation between atoms. The static structure characterizing the atomic impurities is discussed with respect to helium density profiles and energy changes induced by adding helium atoms to a cluster one at a time. The effect of the uncertainty of the interaction potential between
Quantum number theoretic transforms on multipartite finite systems.
Vourdas, A; Zhang, S
2009-06-01
A quantum system composed of p-1 subsystems, each of which is described with a p-dimensional Hilbert space (where p is a prime number), is considered. A quantum number theoretic transform on this system, which has properties similar to those of a Fourier transform, is studied. A representation of the Heisenberg-Weyl group in this context is also discussed. PMID:19488175
Ligand Affinities Estimated by Quantum Chemical Calculations.
Söderhjelm, Pär; Kongsted, Jacob; Ryde, Ulf
2010-05-11
We present quantum chemical estimates of ligand-binding affinities performed, for the first time, at a level of theory for which there is a hope that dispersion and polarization effects are properly accounted for (MP2/cc-pVTZ) and at the same time effects of solvation, entropy, and sampling are included. We have studied the binding of seven biotin analogues to the avidin tetramer. The calculations have been performed by the recently developed PMISP approach (polarizable multipole interactions with supermolecular pairs), which treats electrostatic interactions by multipoles up to quadrupoles, induction by anisotropic polarizabilities, and nonclassical interactions (dispersion, exchange repulsion, etc.) by explicit quantum chemical calculations, using a fragmentation approach, except for long-range interactions that are treated by standard molecular-mechanics Lennard-Jones terms. In order to include effects of sampling, 10 snapshots from a molecular dynamics simulation are studied for each biotin analogue. Solvation energies are estimated by the polarized continuum model (PCM), coupled to the multipole-polarizability model. Entropy effects are estimated from vibrational frequencies, calculated at the molecular mechanics level. We encounter several problems, not previously discussed, illustrating that we are first to apply such a method. For example, the PCM model is, in the present implementation, questionable for large molecules, owing to the use of a surface definition that gives numerous small cavities in a protein. PMID:26615702
Quantum Monte Carlo calculations on positronium compounds
NASA Astrophysics Data System (ADS)
Jiang, Nan
The stability of compounds containing one or more positrons in addition to electrons and nuclei has been the focus of extensive scientific investigations. Interest in these compounds stems from the important role they play in the process of positron annihilation, which has become a useful technique in material science studies. Knowledge of these compounds comes mostly from calculations which are presently less difficult than laboratory experiments. Owing to the small binding energies of these compounds, quantum chemistry methods beyond the molecular orbital approximation must be used. Among them, the quantum Monte Carlo (QMC) method is most appealing because it is easy to implement, gives exact results within the fixed nodes approximation, and makes good use of existing approximate wavefunctions. Applying QMC to small systems like PsH for binding energy calculation is straightforward. To apply it to systems with heavier atoms, to systems for which the center-of-mass motion needs to be separated, and to calculate annihilation rates, special techniques must be developed. In this project a detailed study and several advancements to the QMC method are carried out. Positronium compounds PsH, Ps2, PsO, and Ps2O are studied with algorithms we developed. Results for PsH and Ps2 agree with the best accepted to date. Results for PsO confirm the stability of this compound, and are in fair agreement with an earlier calculation. Results for Ps2O establish the stability of this compound and give an approximate annihilation rate for the first time. Discussions will include an introduction to QMC methods, an in-depth discussion on the QMC formalism, presentation of new algorithms developed in this study, and procedures and results of QMC calculations on the above mentioned positronium compounds.
Collected Calculations in Quantum Gravity and QED
NASA Astrophysics Data System (ADS)
Sawhill, Bruce Kean
In the first part of this thesis, I present a calculation of the helicity amplitudes of electron-positron double bremsstrahlung in the massless limit. Using a representation for free photon polarizations developed by a group of European physicists, helicity amplitudes for double bremsstrahlung in the massless limit are calculated for all possible combinations of helicities in the two incoming and four outgoing particle states. The calculation is made possible by the vast simplification which occurs at the amplitude level because of the gauge cancellations caused by expressing the photon polarizations in terms of the fermion momenta to which they are attached. The results of the calculation are discussed in terms of possible use as a polarization monitor for future generations of colliding beam machines in which the beams could be polarized. It is found that, although the total cross-section is easily measured experimentally, the polarization asymmetry is very difficult to measure unless the flux is very high. The possibility of using double bremsstrahlung as a means of analyzing the zed-zero is discussed. The applications for this purpose are very promising, as the shape and amplitude of the cross-section are very dependent on the chiral structure of the mediating particle. In the second part of this work, I present a calculation of the cosmological constant to two loops in matterless quantum gravity. A quantization method originally developed by 't Hooft and Veltman and later modified by M. Mueller is used. This is the standard path integral formulation of gravity modified such that it takes into account the dependence of the action functional on the fluctuating metric, an effect which is normally discarded because dimensional regularization nullifies its contributions. The purpose of the calculation was to explore more fully an intriguing result found by Mark Mueller while performing the same calculation to one-loop order; namely, the quantum corrections to the
Quantum mechanical calculations to chemical accuracy
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.
1991-01-01
The accuracy of current molecular-structure calculations is illustrated with examples of quantum mechanical solutions for chemical problems. Two approaches are considered: (1) the coupled-cluster singles and doubles (CCSD) with a perturbational estimate of the contribution of connected triple excitations, or CCDS(T); and (2) the multireference configuration-interaction (MRCI) approach to the correlation problem. The MRCI approach gains greater applicability by means of size-extensive modifications such as the averaged-coupled pair functional approach. The examples of solutions to chemical problems include those for C-H bond energies, the vibrational frequencies of O3, identifying the ground state of Al2 and Si2, and the Lewis-Rayleigh afterglow and the Hermann IR system of N2. Accurate molecular-wave functions can be derived from a combination of basis-set saturation studies and full configuration-interaction calculations.
Limitations on information-theoretically-secure quantum homomorphic encryption
NASA Astrophysics Data System (ADS)
Yu, Li; Pérez-Delgado, Carlos A.; Fitzsimons, Joseph F.
2014-11-01
Homomorphic encryption is a form of encryption which allows computation to be carried out on the encrypted data without the need for decryption. The success of quantum approaches to related tasks in a delegated computation setting has raised the question of whether quantum mechanics may be used to achieve information-theoretically-secure fully homomorphic encryption. Here we show, via an information localization argument, that deterministic fully homomorphic encryption necessarily incurs exponential overhead if perfect security is required.
Linear Scaling Quantum Monte Carlo Calculations
NASA Astrophysics Data System (ADS)
Williamson, Andrew
2002-03-01
New developments to the quantum Monte Carlo approach are presented that improve the scaling of the time required to calculate the total energy of a configuration of electronic coordinates from N^3 to nearly linear[1]. The first factor of N is achieved by applying a unitary transform to the set of single particle orbitals used to construct the Slater determinant, creating a set of maximally localized Wannier orbitals. These localized functions are then truncated beyond a given cutoff radius to introduce sparsity into the Slater determinant. The second factor of N is achieved by evaluating the maximally localized Wannier orbitals on a cubic spline grid, which removes the size dependence of the basis set (e.g. plane waves, Gaussians) typically used to expand the orbitals. Application of this method to the calculation of the binding energy of carbon fullerenes and silicon nanostructures will be presented. An extension of the approach to deal with excited states of systems will also be presented in the context of the calculation of the excitonic gap of a variety of systems. This work was performed under the auspices of the U.S. Dept. of Energy at the University of California/LLNL under contract no. W-7405-Eng-48. [1] A.J. Williamson, R.Q. Hood and J.C. Grossman, Phys. Rev. Lett. 87 246406 (2001)
Quantum Monte Carlo calculations for carbon nanotubes
NASA Astrophysics Data System (ADS)
Luu, Thomas; Lähde, Timo A.
2016-04-01
We show how lattice quantum Monte Carlo can be applied to the electronic properties of carbon nanotubes in the presence of strong electron-electron correlations. We employ the path-integral formalism and use methods developed within the lattice QCD community for our numerical work. Our lattice Hamiltonian is closely related to the hexagonal Hubbard model augmented by a long-range electron-electron interaction. We apply our method to the single-quasiparticle spectrum of the (3,3) armchair nanotube configuration, and consider the effects of strong electron-electron correlations. Our approach is equally applicable to other nanotubes, as well as to other carbon nanostructures. We benchmark our Monte Carlo calculations against the two- and four-site Hubbard models, where a direct numerical solution is feasible.
Quantum Monte Carlo calculations of light nuclei.
Pieper, S. C.; Physics
2008-01-01
Variational Monte Carlo and Green's function Monte Carlo are powerful tools for cal- culations of properties of light nuclei using realistic two-nucleon (NN) and three-nucleon (NNN) potentials. Recently the GFMC method has been extended to multiple states with the same quantum numbers. The combination of the Argonne v18 two-nucleon and Illinois-2 three-nucleon potentials gives a good prediction of many energies of nuclei up to 12 C. A number of other recent results are presented: comparison of binding energies with those obtained by the no-core shell model; the incompatibility of modern nuclear Hamiltonians with a bound tetra-neutron; difficulties in computing RMS radii of very weakly bound nuclei, such as 6He; center-of-mass effects on spectroscopic factors; and the possible use of an artificial external well in calculations of neutron-rich isotopes.
Quantum Monte Carlo Calculations Applied to Magnetic Molecules
Larry Engelhardt
2006-08-09
We have calculated the equilibrium thermodynamic properties of Heisenberg spin systems using a quantum Monte Carlo (QMC) method. We have used some of these systems as models to describe recently synthesized magnetic molecules, and-upon comparing the results of these calculations with experimental data-have obtained accurate estimates for the basic parameters of these models. We have also performed calculations for other systems that are of more general interest, being relevant both for existing experimental data and for future experiments. Utilizing the concept of importance sampling, these calculations can be carried out in an arbitrarily large quantum Hilbert space, while still avoiding any approximations that would introduce systematic errors. The only errors are statistical in nature, and as such, their magnitudes are accurately estimated during the course of a simulation. Frustrated spin systems present a major challenge to the QMC method, nevertheless, in many instances progress can be made. In this chapter, the field of magnetic molecules is introduced, paying particular attention to the characteristics that distinguish magnetic molecules from other systems that are studied in condensed matter physics. We briefly outline the typical path by which we learn about magnetic molecules, which requires a close relationship between experiments and theoretical calculations. The typical experiments are introduced here, while the theoretical methods are discussed in the next chapter. Each of these theoretical methods has a considerable limitation, also described in Chapter 2, which together serve to motivate the present work. As is shown throughout the later chapters, the present QMC method is often able to provide useful information where other methods fail. In Chapter 3, the use of Monte Carlo methods in statistical physics is reviewed, building up the fundamental ideas that are necessary in order to understand the method that has been used in this work. With these
Quantum Biological Channel Modeling and Capacity Calculation
Djordjevic, Ivan B.
2012-01-01
Quantum mechanics has an important role in photosynthesis, magnetoreception, and evolution. There were many attempts in an effort to explain the structure of genetic code and transfer of information from DNA to protein by using the concepts of quantum mechanics. The existing biological quantum channel models are not sufficiently general to incorporate all relevant contributions responsible for imperfect protein synthesis. Moreover, the problem of determination of quantum biological channel capacity is still an open problem. To solve these problems, we construct the operator-sum representation of biological channel based on codon basekets (basis vectors), and determine the quantum channel model suitable for study of the quantum biological channel capacity and beyond. The transcription process, DNA point mutations, insertions, deletions, and translation are interpreted as the quantum noise processes. The various types of quantum errors are classified into several broad categories: (i) storage errors that occur in DNA itself as it represents an imperfect storage of genetic information, (ii) replication errors introduced during DNA replication process, (iii) transcription errors introduced during DNA to mRNA transcription, and (iv) translation errors introduced during the translation process. By using this model, we determine the biological quantum channel capacity and compare it against corresponding classical biological channel capacity. We demonstrate that the quantum biological channel capacity is higher than the classical one, for a coherent quantum channel model, suggesting that quantum effects have an important role in biological systems. The proposed model is of crucial importance towards future study of quantum DNA error correction, developing quantum mechanical model of aging, developing the quantum mechanical models for tumors/cancer, and study of intracellular dynamics in general. PMID:25371271
Density functional calculation of the structural and electronic properties of germanium quantum dots
Anas, M. M.; Gopir, G.
2015-04-24
We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation.
Surface Segregation Energies of BCC Binaries from Ab Initio and Quantum Approximate Calculations
NASA Technical Reports Server (NTRS)
Good, Brian S.
2003-01-01
We compare dilute-limit segregation energies for selected BCC transition metal binaries computed using ab initio and quantum approximate energy method. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent parameterization. Quantum approximate segregation energies are computed with and without atomistic relaxation. The ab initio calculations are performed without relaxation for the most part, but predicted relaxations from quantum approximate calculations are used in selected cases to compute approximate relaxed ab initio segregation energies. Results are discussed within the context of segregation models driven by strain and bond-breaking effects. We compare our results with other quantum approximate and ab initio theoretical work, and available experimental results.
NASA Astrophysics Data System (ADS)
Rusakova, I. L.; Rusakov, Yu Yu; Krivdin, L. B.
2016-04-01
The theoretical grounds of the modern relativistic methods for quantum chemical calculation of spin–spin coupling constants in nuclear magnetic resonance spectra are considered. Examples and prospects of application of relativistic calculations of these constants in the structural studies of organic and heteroorganic compounds are discussed. Practical recommendations on relativistic calculations of spin–spin coupling constants using the available software are given. The bibliography includes 622 references.
Quantum Monte Carlo calculations applied to magnetic molecules
NASA Astrophysics Data System (ADS)
Engelhardt, Larry Paul
In this dissertation, we have implemented a quantum Monte Carlo (QMC) algorithm, and have used it to perform calculations for a variety of finite Heisenberg spin systems. A detailed description of the QMC method has been provided, which is followed by applications of the method to various systems. These applications begin with a detailed analysis of the (calculated) equilibrium magnetization and magnetic susceptibility for a number of Heisenberg Hamiltonians. In particular, we have studied the dependence of these quantities on intrinsic spin s, and have quantified the approach to the classical (s → infinity) limit. These results are not specific to a particular physical system, but are potentially applicable to many systems. We have also analyzed four recently synthesized species of magnetic molecules, each of which is theoretically challenging to the methods that are normally used for such analyses. Using the QMC method, we have distinguished the microscopic (exchange) parameters that describe the interactions in each of these magnetic molecules, and, based upon these parameters, we have made predictions for future experiments. The well-known "negative sign problem" (NSP) can be problematic for QMC calculations. However, for some systems, our analysis was able to proceed despite the NSP. For other systems, this is not the cases, so we have clearly indicated when the NSP is, and is not, insurmountable for these types of calculations.
Using the Chebychev expansion in quantum transport calculations
Popescu, Bogdan; Rahman, Hasan; Kleinekathöfer, Ulrich
2015-04-21
Irradiation by laser pulses and a fluctuating surrounding liquid environment can, for example, lead to time-dependent effects in the transport through molecular junctions. From the theoretical point of view, time-dependent theories of quantum transport are still challenging. In one of these existing transport theories, the energy-dependent coupling between molecule and leads is decomposed into Lorentzian functions. This trick has successfully been combined with quantum master approaches, hierarchical formalisms, and non-equilibrium Green’s functions. The drawback of this approach is, however, its serious limitation to certain forms of the molecule-lead coupling and to higher temperatures. Tian and Chen [J. Chem. Phys. 137, 204114 (2012)] recently employed a Chebychev expansion to circumvent some of these latter problems. Here, we report on a similar approach also based on the Chebychev expansion but leading to a different set of coupled differential equations using the fact that a derivative of a zeroth-order Bessel function can again be given in terms of Bessel functions. Test calculations show the excellent numerical accuracy and stability of the presented formalism. The time span for which this Chebychev expansion scheme is valid without any restrictions on the form of the spectral density or temperature can be determined a priori.
Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study
Michael, Stephan; Chow, Weng; Schneider, Hans
2016-05-13
In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. We study the influence of two important quantum-dot material parameters, here, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density canmore » compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. By minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory.« less
Calorimetric determinations and theoretical calculations of polymorphs of thalidomide
NASA Astrophysics Data System (ADS)
Lara-Ochoa, F.; Pérez, G. Espinosa; Mijangos-Santiago, F.
2007-09-01
The analysis of the thermograms of thalidomide obtained for the two reported polymorphs α and β by differential scanning calorimetry (DSC) shows some inconsistencies that are discussed in the present work. The conception of a new polymorph form, named β ∗, allowed us to explain the observed thermal behavior more satisfactorily. This new polymorph shows enantiotropy with both α and β polymorphs, reflected in the unique endotherm obtained in the DSC-thermograms, when a heating rate of 10 °C/min is applied. Several additional experiments, such as re-melting of both polymorph forms, showed that there is indeed a new polymorph with an endotherm located between the endotherms of α and β. IR, Raman, and powder X-ray permit us to characterize the isolated compound, resulting from the re-melting of both polymorph forms. Mechanical calculations were performed to elucidate the conformations of each polymorph, and ab initio quantum chemical calculations were performed to determine the energy of the more stable conformers and the spatial cell energy for both polymorphs α and β. These results suggested a possible conformation for the newly discovered polymorph β ∗.
Magnetic rigid rotor in the quantum regime: Theoretical toolbox
NASA Astrophysics Data System (ADS)
Rusconi, Cosimo C.; Romero-Isart, Oriol
2016-02-01
We describe the quantum dynamics of a magnetic rigid rotor in the mesoscopic scale where the Einstein-De Haas effect is predominant. In particular, we consider a single-domain magnetic nanoparticle with uniaxial anisotropy in a magnetic trap. Starting from the basic Hamiltonian of the system under the macrospin approximation, we derive a bosonized Hamiltonian describing the center-of-mass motion, the total angular momentum, and the macrospin degrees of freedom of the particle treated as a rigid body. This bosonized Hamiltonian can be approximated by a simple quadratic Hamiltonian that captures the rich physics of a nanomagnet tightly confined in position, nearly not spinning, and with its macrospin antialigned to the magnetic field. The theoretical tools derived and used here can be applied to other quantum mechanical rigid rotors.
Maxwell's demon. (II) A quantum-theoretic exorcism
NASA Astrophysics Data System (ADS)
Gyftopoulos, Elias P.
2002-05-01
In Part II of this two-part paper we prove that Maxwell's demon is unable to accomplish his task of sorting air molecules into swift and slow because in air in a thermodynamic equilibrium state there are no such molecules. The proof is based on the principles of a unified quantum theory of mechanics and thermodynamics. The key idea of the unified theory is that von Neumann's concept of a homogeneous ensemble of identical systems, identically prepared, is valid not only for a density operator ρ equal to a projector (every member of the ensemble is assigned the same projector, ρi=| ψi> < ψi|= ρi2, or the same wave function ψ i as any other member) but also for a density operator that is not a projector (every member of the ensemble is assigned the same density operator, ρ>ρ 2, as any other member). So, the latter ensemble is not a statistical mixture of projectors. The broadening of the validity of the homogeneous ensemble is consistent with the quantum-theoretic postulates about observables, measurement results, and value of any observable. In the context of the unified theory, among the many novel results is the theorem that each molecule of a system in a thermodynamic equilibrium state has zero value of momentum, that is, each molecule is at a standstill and, therefore, there are no molecules to be sorted as swift and slow. Said differently, if Maxwell were cognizant of quantum theory, he would not have conceived of the idea of the demon. It is noteworthy that the zero value of momentum is not the result of averaging over different momenta of many molecules. Under the specified conditions, it is the quantum-theoretic value of the momentum of any one molecule, and the same result is valid even if the system consists of only one molecule.
Theoretical Investigations of Optical Origins of Fluorescent Graphene Quantum Dots
Wang, Jingang; Cao, Shuo; Ding, Yong; Ma, Fengcai; Lu, Wengang; Sun, Mengtao
2016-01-01
The optical properties of graphene quantum dots (GQDs) were investigated theoretically. We focused on the photoinduced charge transfer and electron-hole coherence of single-layer graphene in the electronic transitions in the visible regions. Surface functionalization with donor or acceptor groups produced a red shift in the absorption spectrum, and electrons and holes were highly delocalized. The recombination of excited, well-separated electron-hole (e–h) pairs can result in enhanced fluorescence. This fluorescence enhancement by surface functionalization occurs because of the decreased symmetry of the graphene resulting from the roughened structure of the surface-functionalized GQDs. PMID:27094439
Theoretical analysis of quantum ghost imaging through turbulence
Chan, Kam Wai Clifford; Simon, D. S.; Sergienko, A. V.; Hardy, Nicholas D.; Shapiro, Jeffrey H.; Dixon, P. Ben; Howland, Gregory A.; Howell, John C.; Eberly, Joseph H.; O'Sullivan, Malcolm N.; Rodenburg, Brandon; Boyd, Robert W.
2011-10-15
Atmospheric turbulence generally affects the resolution and visibility of an image in long-distance imaging. In a recent quantum ghost imaging experiment [P. B. Dixon et al., Phys. Rev. A 83, 051803 (2011)], it was found that the effect of the turbulence can nevertheless be mitigated under certain conditions. This paper gives a detailed theoretical analysis to the setup and results reported in the experiment. Entangled photons with a finite correlation area and a turbulence model beyond the phase screen approximation are considered.
Theoretical Investigations of Optical Origins of Fluorescent Graphene Quantum Dots
NASA Astrophysics Data System (ADS)
Wang, Jingang; Cao, Shuo; Ding, Yong; Ma, Fengcai; Lu, Wengang; Sun, Mengtao
2016-04-01
The optical properties of graphene quantum dots (GQDs) were investigated theoretically. We focused on the photoinduced charge transfer and electron-hole coherence of single-layer graphene in the electronic transitions in the visible regions. Surface functionalization with donor or acceptor groups produced a red shift in the absorption spectrum, and electrons and holes were highly delocalized. The recombination of excited, well-separated electron-hole (e–h) pairs can result in enhanced fluorescence. This fluorescence enhancement by surface functionalization occurs because of the decreased symmetry of the graphene resulting from the roughened structure of the surface-functionalized GQDs.
Role of information theoretic uncertainty relations in quantum theory
NASA Astrophysics Data System (ADS)
Jizba, Petr; Dunningham, Jacob A.; Joo, Jaewoo
2015-04-01
Uncertainty relations based on information theory for both discrete and continuous distribution functions are briefly reviewed. We extend these results to account for (differential) Rényi entropy and its related entropy power. This allows us to find a new class of information-theoretic uncertainty relations (ITURs). The potency of such uncertainty relations in quantum mechanics is illustrated with a simple two-energy-level model where they outperform both the usual Robertson-Schrödinger uncertainty relation and Shannon entropy based uncertainty relation. In the continuous case the ensuing entropy power uncertainty relations are discussed in the context of heavy tailed wave functions and Schrödinger cat states. Again, improvement over both the Robertson-Schrödinger uncertainty principle and Shannon ITUR is demonstrated in these cases. Further salient issues such as the proof of a generalized entropy power inequality and a geometric picture of information-theoretic uncertainty relations are also discussed.
Role of information theoretic uncertainty relations in quantum theory
Jizba, Petr; Dunningham, Jacob A.; Joo, Jaewoo
2015-04-15
Uncertainty relations based on information theory for both discrete and continuous distribution functions are briefly reviewed. We extend these results to account for (differential) Rényi entropy and its related entropy power. This allows us to find a new class of information-theoretic uncertainty relations (ITURs). The potency of such uncertainty relations in quantum mechanics is illustrated with a simple two-energy-level model where they outperform both the usual Robertson–Schrödinger uncertainty relation and Shannon entropy based uncertainty relation. In the continuous case the ensuing entropy power uncertainty relations are discussed in the context of heavy tailed wave functions and Schrödinger cat states. Again, improvement over both the Robertson–Schrödinger uncertainty principle and Shannon ITUR is demonstrated in these cases. Further salient issues such as the proof of a generalized entropy power inequality and a geometric picture of information-theoretic uncertainty relations are also discussed.
Macroscopic Quantum-Type Potentials in Theoretical Systems Biology
Nottale, Laurent
2014-01-01
We review in this paper the use of the theory of scale relativity and fractal space-time as a tool particularly well adapted to the possible development of a future genuine systems theoretical biology. We emphasize in particular the concept of quantum-type potentials, since, in many situations, the effect of the fractality of space—or of the underlying medium—can be reduced to the addition of such a potential energy to the classical equations of motion. Various equivalent representations—geodesic, quantum-like, fluid mechanical, stochastic—of these equations are given, as well as several forms of generalized quantum potentials. Examples of their possible intervention in high critical temperature superconductivity and in turbulence are also described, since some biological processes may be similar in some aspects to these physical phenomena. These potential extra energy contributions could have emerged in biology from the very fractal nature of the medium, or from an evolutive advantage, since they involve spontaneous properties of self-organization, morphogenesis, structuration and multi-scale integration. Finally, some examples of applications of the theory to actual biological-like processes and functions are also provided. PMID:24709901
Macroscopic quantum-type potentials in theoretical systems biology.
Nottale, Laurent
2013-01-01
We review in this paper the use of the theory of scale relativity and fractal space-time as a tool particularly well adapted to the possible development of a future genuine systems theoretical biology. We emphasize in particular the concept of quantum-type potentials, since, in many situations, the effect of the fractality of space-or of the underlying medium-can be reduced to the addition of such a potential energy to the classical equations of motion. Various equivalent representations-geodesic, quantum-like, fluid mechanical, stochastic-of these equations are given, as well as several forms of generalized quantum potentials. Examples of their possible intervention in high critical temperature superconductivity and in turbulence are also described, since some biological processes may be similar in some aspects to these physical phenomena. These potential extra energy contributions could have emerged in biology from the very fractal nature of the medium, or from an evolutive advantage, since they involve spontaneous properties of self-organization, morphogenesis, structuration and multi-scale integration. Finally, some examples of applications of the theory to actual biological-like processes and functions are also provided. PMID:24709901
Theoretical model for calculation of helicity in solar active regions
NASA Astrophysics Data System (ADS)
Chatterjee, P.
We (Choudhuri, Chatterjee and Nandy, 2005) calculate helicities of solar active regions based on the idea of Choudhuri (2003) that poloidal flux lines get wrapped around a toroidal flux tube rising through the convection zone, thereby giving rise to the helicity. Rough estimates based on this idea compare favourably with the observed magnitude of helicity. We use our solar dynamo model based on the Babcock--Leighton α-effect to study how helicity varies with latitude and time. At the time of solar maximum, our theoretical model gives negative helicity in the northern hemisphere and positive helicity in the south, in accordance with observed hemispheric trends. However, we find that, during a short interval at the beginning of a cycle, helicities tend to be opposite of the preferred hemispheric trends. Next we (Chatterjee, Choudhuri and Petrovay 2006) use the above idea along with the sunspot decay model of Petrovay and Moreno-Insertis, (1997) to estimate the distribution of helicity inside a flux tube as it keeps collecting more azimuthal flux during its rise through the convection zone and as turbulent diffusion keeps acting on it. By varying parameters over reasonable ranges in our simple 1-d model, we find that the azimuthal flux penetrates the flux tube to some extent instead of being confined to a narrow sheath outside.
Spectroscopic, quantum chemical calculation and molecular docking of dipfluzine
NASA Astrophysics Data System (ADS)
Srivastava, Karnica; Srivastava, Anubha; Tandon, Poonam; Sinha, Kirti; Wang, Jing
2016-12-01
Molecular structure and vibrational analysis of dipfluzine (C27H29FN2O) were presented using FT-IR and FT-Raman spectroscopy and quantum chemical calculations. The theoretical ground state geometry and electronic structure of dipfluzine are optimized by the DFT/B3LYP/6-311++G (d,p) method and compared with those of the crystal data. The 1D potential energy scan was performed by varying the dihedral angle using B3LYP functional at 6-31G(d,p) level of theory and thus the most stable conformer of the compound were determined. Molecular electrostatic potential surface (MEPS), frontier orbital analysis and electronic reactivity descriptor were used to predict the chemical reactivity of molecule. Energies of intra- and inter-molecular hydrogen bonds in molecule and their electronic aspects were investigated by natural bond orbital (NBO). To find out the anti-apoptotic activity of the title compound molecular docking studies have been performed against protein Fas.
Quantum mechanical cluster calculations of critical scintillationprocesses
Derenzo, Stephen E.; Klintenberg, Mattias K.; Weber, Marvin J.
2000-02-22
This paper describes the use of commercial quantum chemistrycodes to simu-late several critical scintillation processes. The crystalis modeled as a cluster of typically 50 atoms embedded in an array oftypically 5,000 point charges designed to reproduce the electrostaticfield of the infinite crystal. The Schrodinger equation is solved for theground, ionized, and excited states of the system to determine the energyand electron wavefunction. Computational methods for the followingcritical processes are described: (1) the formation and diffusion ofrelaxed holes, (2) the formation of excitons, (3) the trapping ofelectrons and holes by activator atoms, (4) the excitation of activatoratoms, and (5) thermal quenching. Examples include hole diffusion in CsI,the exciton in CsI, the excited state of CsI:Tl, the energy barrier forthe diffusion of relaxed holes in CaF2 and PbF2, and prompt hole trappingby activator atoms in CaF2:Eu and CdS:Te leading to an ultra-fast (<50ps) scintillation risetime.
NASA Technical Reports Server (NTRS)
Du, Ping
1993-01-01
As a theoretical component of the joint effort with the laboratory of Dr. Lou Allamandola to search for potential candidates for interstellar organic carbon compound that are responsible for the visible diffuse interstellar absorption bands (DIB's), quantum mechanical calculations were performed on the electron absorption spectra of selected polycyclic aromatic hydrocarbons (PAH) and derivatives. In the completed project, 15 different species of naphthalene, its hydrogen abstraction and addition derivatives, and corresponding cations and anions were studied. Using semiempirical quantum mechanical method INDO/S, the ground electronic state of each species was evaluated with restricted Hartree-Fock scheme and limited configuration interaction. The lowest energy spin state for each species was used for electron absorption calculations. Results indicate that these calculations are accurate enough to reproduce the spectra of naphthalene cation and anion observed in neon matrix. The spectral pattern of the hydrogen abstraction and addition derivatives predicted based on these results indicate that the electron configuration of the pi orbitals of these species is the dominant determinant. A combined list of 19 absorptions calculated from 4500 A to 10,400 A were compiled and suggested as potential candidates that are relevant for the DIB's absorptions. Continued studies on pyrene and derivatives revealed the ground state symmetries and multiplicities of its neutral, anionic, and cationic species. Spectral calculations show that the cation (B(sub 3g)-2) and the anion (A(sub u)-2) are more likely to have low energy absorptions in the regions between 10 kK and 20 kK, similar to naphthalene. These absorptions, together with those to be determined from the hydrogen abstraction and addition derivatives of pyrene, can be used to provide additional candidates and suggest experimental work in the search for interstellar compounds that are responsible for DIB's.
Quantum Parallelism as a Tool for Ensemble Spin Dynamics Calculations
NASA Astrophysics Data System (ADS)
Álvarez, Gonzalo A.; Danieli, Ernesto P.; Levstein, Patricia R.; Pastawski, Horacio M.
2008-09-01
Efficient simulations of quantum evolutions of spin-1/2 systems are relevant for ensemble quantum computation as well as in typical NMR experiments. We propose an efficient method to calculate the dynamics of an observable provided that the initial excitation is “local.” It resorts to a single entangled pure initial state built as a superposition, with random phases, of the pure elements that compose the mixture. This ensures self-averaging of any observable, drastically reducing the calculation time. The procedure is tested for two representative systems: a spin star (cluster with random long range interactions) and a spin ladder.
A theoretical and experimental study of λ>2 μm luminescence of quantum dots on InP substrate
NASA Astrophysics Data System (ADS)
Doré, F.; Even, J.; Cornet, C.; Schliwa, A.; Bertru, N.; Dehaese, O.; Alghoraibi, I.; Folliot, H.; Piron, R.; Le Corre, A.; Loualiche, S.
2007-04-01
Theoretical and experimental studies of the electronic properties of InAs(Sb) quantum dots (QDs) grown by molecular beam epitaxy (MBE) on InP(100) substrate are presented. Eight-band kṡp calculations including strain and piezoelectric effects are performed on InAs/InP(100) quantum dot (QD) structure to study the influence of the quantum dot height. Photoluminescence (PL) spectroscopy experiments show promising results. High arsine flow rate during the growth of InAs QDs makes possible long emission wavelength beyond 2 μm. Emission wavelength as long as 2.35 μm is observed with InAsSb QDs.
Detailed discussions and calculations of quantum Regge calculus of Einstein-Cartan theory
Xue Shesheng
2010-09-15
This article presents detailed discussions and calculations of the recent paper 'Quantum Regge calculus of Einstein-Cartan theory' in [9]. The Euclidean space-time is discretized by a four-dimensional simplicial complex. We adopt basic tetrad and spin-connection fields to describe the simplicial complex. By introducing diffeomorphism and local Lorentz invariant holonomy fields, we construct a regularized Einstein-Cartan theory for studying the quantum dynamics of the simplicial complex and fermion fields. This regularized Einstein-Cartan action is shown to properly approach to its continuum counterpart in the continuum limit. Based on the local Lorentz invariance, we derive the dynamical equations satisfied by invariant holonomy fields. In the mean-field approximation, we show that the averaged size of 4-simplex, the element of the simplicial complex, is larger than the Planck length. This formulation provides a theoretical framework for analytical calculations and numerical simulations to study the quantum Einstein-Cartan theory.
NASA Astrophysics Data System (ADS)
Kashinski, D. O.; Nelson, R. G.; Chase, G. M.; di Nallo, O. E.; Byrd, E. F. C.
2016-05-01
We are investigating the accuracy of theoretical models used to predict the visible, ultraviolet, and infrared spectra, as well as other properties, of product materials ejected from the muzzle of currently fielded systems. Recent advances in solid propellants has made the management of muzzle signature (flash) a principle issue in weapons development across the calibers. A priori prediction of the electromagnetic spectra of formulations will allow researchers to tailor blends that yield desired signatures and determine spectrographic detection ranges. Quantum chemistry methods at various levels of sophistication have been employed to optimize molecular geometries, compute unscaled harmonic frequencies, and determine the optical spectra of specific gas-phase species. Electronic excitations are being computed using Time Dependent Density Functional Theory (TD-DFT). Calculation of approximate global harmonic frequency scaling factors for specific DFT functionals is also in progress. A full statistical analysis and reliability assessment of computational results is currently underway. Work supported by the ARL, DoD-HPCMP, and USMA.
Theoretical Calculation and Validation of the Water Vapor Continuum Absorption
NASA Technical Reports Server (NTRS)
Ma, Qiancheng; Tipping, Richard H.
1998-01-01
The primary objective of this investigation is the development of an improved parameterization of the water vapor continuum absorption through the refinement and validation of our existing theoretical formalism. The chief advantage of our approach is the self-consistent, first principles, basis of the formalism which allows us to predict the frequency, temperature and pressure dependence of the continuum absorption as well as provide insights into the physical mechanisms responsible for the continuum absorption. Moreover, our approach is such that the calculated continuum absorption can be easily incorporated into satellite retrieval algorithms and climate models. Accurate determination of the water vapor continuum is essential for the next generation of retrieval algorithms which propose to use the combined constraints of multi-spectral measurements such as those under development for EOS data analysis (e.g., retrieval algorithms based on MODIS and AIRS measurements); current Pathfinder activities which seek to use the combined constraints of infrared and microwave (e.g., HIRS and MSU) measurements to improve temperature and water profile retrievals, and field campaigns which seek to reconcile spectrally-resolved and broad-band measurements such as those obtained as part of FIRE. Current widely used continuum treatments have been shown to produce spectrally dependent errors, with the magnitude of the error dependent on temperature and abundance which produces errors with a seasonal and latitude dependence. Translated into flux, current water vapor continuum parameterizations produce flux errors of order 10 W/ml, which compared to the 4 W/m' magnitude of the greenhouse gas forcing and the 1-2 W/m' estimated aerosol forcing is certainly climatologically significant and unacceptably large. While it is possible to tune the empirical formalisms, the paucity of laboratory measurements, especially at temperatures of interest for atmospheric applications, preclude tuning
Theoretical Calculation and Validation of the Water Vapor Continuum Absorption
NASA Technical Reports Server (NTRS)
Ma, Qiancheng; Tipping, Richard H.
1998-01-01
The primary objective of this investigation is the development of an improved parameterization of the water vapor continuum absorption through the refinement and validation of our existing theoretical formalism. The chief advantage of our approach is the self-consistent, first principles, basis of the formalism which allows us to predict the frequency, temperature and pressure dependence of the continuum absorption as well as provide insights into the physical mechanisms responsible for the continuum absorption. Moreover, our approach is such that the calculated continuum absorption can be easily incorporated into satellite retrieval algorithms and climate models. Accurate determination of the water vapor continuum is essential for the next generation of retrieval algorithms which propose to use the combined constraints of multispectral measurements such as those under development for EOS data analysis (e.g., retrieval algorithms based on MODIS and AIRS measurements); current Pathfinder activities which seek to use the combined constraints of infrared and microwave (e.g., HIRS and MSU) measurements to improve temperature and water profile retrievals, and field campaigns which seek to reconcile spectrally-resolved and broad-band measurements such as those obtained as part of FIRE. Current widely used continuum treatments have been shown to produce spectrally dependent errors, with the magnitude of the error dependent on temperature and abundance which produces errors with a seasonal and latitude dependence. Translated into flux, current water vapor continuum parameterizations produce flux errors of order 10 W/sq m, which compared to the 4 W/sq m magnitude of the greenhouse gas forcing and the 1-2 W/sq m estimated aerosol forcing is certainly climatologically significant and unacceptably large. While it is possible to tune the empirical formalisms, the paucity of laboratory measurements, especially at temperatures of interest for atmospheric applications, preclude
Theoretical and experimental studies of (In,Ga)As/GaP quantum dots
2012-01-01
(In,Ga)As/GaP(001) quantum dots (QDs) are grown by molecular beam epitaxy and studied both theoretically and experimentally. The electronic band structure is simulated using a combination of k·p and tight-binding models. These calculations predict an indirect to direct crossover with the In content and the size of the QDs. The optical properties are then studied in a low-In-content range through photoluminescence and time-resolved photoluminescence experiments. It suggests the proximity of two optical transitions of indirect and direct types. PMID:23176537
Accelerating quantum instanton calculations of the kinetic isotope effects.
Karandashev, Konstantin; Vaníček, Jiří
2015-11-21
Path integral implementation of the quantum instanton approximation currently belongs among the most accurate methods for computing quantum rate constants and kinetic isotope effects, but its use has been limited due to the rather high computational cost. Here, we demonstrate that the efficiency of quantum instanton calculations of the kinetic isotope effects can be increased by orders of magnitude by combining two approaches: The convergence to the quantum limit is accelerated by employing high-order path integral factorizations of the Boltzmann operator, while the statistical convergence is improved by implementing virial estimators for relevant quantities. After deriving several new virial estimators for the high-order factorization and evaluating the resulting increase in efficiency, using ⋅Hα + HβHγ → HαHβ + ⋅ Hγ reaction as an example, we apply the proposed method to obtain several kinetic isotope effects on CH4 + ⋅ H ⇌ ⋅ CH3 + H2 forward and backward reactions. PMID:26590524
Quantum-field-theoretic analysis of inflation dynamics in a (2+1)-dimensional universe
Samiullah, M. ); Eboli, O. ); Pi, S. )
1991-10-15
We reexamine inflationary scenarios based on slow-rollover transitions, which occur under various initial conditions of the inflation-driving scalar field. We examine inflation dynamics using a recently developed calculational technique for studying a quantum-field-theoretic system in an external environment that is itself changing with time. This method, based on the functional Schroedinger picture, uses a self-consistent Gaussian approximation that, unlike ordinary perturbation theory, reflects some of the nonlinearities of the full quantum theory. Our treatment is confined to planar universes, where the approximation techniques do not suffer from well-known problems associated with scalar field self-interactions in four-dimensional space-time. However, for these toy models we can present concrete and explicit results.
Simulation of Quantum-Mechanical Measurements with Programmable Pocket Calculators.
ERIC Educational Resources Information Center
Sauer, G.
1979-01-01
Described is a method for the illustration of the statistical nature of measurements in quantum physics by means of simulation with pocket calculators. The application to examples like the double-slit experiment, Mott scattering, and the demonstration of the uncertainty relation is discussed. (Author/HM)
NASA Astrophysics Data System (ADS)
Dey, Swayandipta; Zhou, Yadong; Tian, Xiangdong; Jenkins, Julie A.; Chen, Ou; Zou, Shengli; Zhao, Jing
2015-04-01
In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs of appropriate sizes were chosen so that the plasmon resonance overlaps with the absorption and emission of the QDs. We observed that in the regime of a low excitation power, the photon antibunching and blinking properties of single QDs were modified significantly when the QDs were on the Au@SiO2 substrates compared to those on glass. Most significantly, second-order photon intensity correlation data show that the presence of plasmons increases the ratio of the biexciton quantum yield over the exciton quantum yield (QYBX/QYX). An electrodynamics model was developed to quantify the effect of plasmons on the lifetime, quantum yield, and emission intensity of the biexcitons for the QDs. Good agreement was obtained between the experimentally measured and calculated changes in QYBX/QYX due to Au@SiO2 NPs, showing the validity of the developed model. The theoretical studies also indicated that the relative position of the QDs to the Au NPs and the orientation of the electric field are important factors that regulate the emission properties of the excitons and biexcitons of QDs. The study suggests that the multiexciton emission efficiency in QD systems can be manipulated by employing properly designed plasmonic structures.In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs of appropriate sizes were chosen so that the plasmon resonance
Theoretical calculations and vibrational potential energy surface of 4-silaspiro(3,3)heptane
Ocola, Esther J.; Medders, Cross; Laane, Jaan; Meinander, Niklas
2014-04-28
Theoretical computations have been carried out on 4-silaspiro(3,3)heptane (SSH) in order to calculate its molecular structure and conformational energies. The molecule has two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. Energy calculations were carried out for different conformations of SSH. These results allowed the generation of a two-dimensional ring-puckering potential energy surface (PES) of the form V = a(x{sub 1}{sup 4} + x{sub 2}{sup 4}) – b(x{sub 1}{sup 2} + x{sub 2}{sup 2}) + cx{sub 1}{sup 2}x{sub 2}{sup 2}, where x{sub 1} and x{sub 2} are the ring-puckering coordinates for the two rings. The presence of sufficiently high potential energy barriers prevents the molecule from undergoing pseudorotation. The quantum states, wave functions, and predicted spectra resulting from the PESs were calculated.
Efficient hybrid-symbolic methods for quantum mechanical calculations
NASA Astrophysics Data System (ADS)
Scott, T. C.; Zhang, Wenxing
2015-06-01
We present hybrid symbolic-numerical tools to generate optimized numerical code for rapid prototyping and fast numerical computation starting from a computer algebra system (CAS) and tailored to any given quantum mechanical problem. Although a major focus concerns the quantum chemistry methods of H. Nakatsuji which has yielded successful and very accurate eigensolutions for small atoms and molecules, the tools are general and may be applied to any basis set calculation with a variational principle applied to its linear and non-linear parameters.
A combined experimental and theoretical quantum chemical studies on 4-morpholinecarboxaldehyde
NASA Astrophysics Data System (ADS)
Arjunan, V.; Rani, T.; Santhanalakshmi, K.; Mohan, S.
2011-09-01
Extensive spectroscopic investigations have been carried out by recording the Fourier transform infrared (FTIR) and FT-Raman spectra and carrying out the theoretical quantum chemical studies on 4-morpholinecarboxaldehyde (4MC). From the ab initio and DFT analysis using HF, B3LYP and B3PW91 methods with 6-31G(d,p) and 6-311G++(d,p) basis sets the energies, structural, thermodynamical and vibrational characteristics of the compound were determined. The energy difference between the chair equatorial and chair axial conformers of 4MC have been calculated by density functional theory (DFT) method. The optimised geometrical parameters, theoretical wavenumbers and thermodynamic properties of the molecule were compared with the experimental values. The effect of carbonyl group on the characteristic frequencies of the morpholine ring has been analysed. The mixing of the fundamental modes with the help of potential energy distribution (PED) through normal co-ordinate analysis has been discussed.
Infinite variance in fermion quantum Monte Carlo calculations
NASA Astrophysics Data System (ADS)
Shi, Hao; Zhang, Shiwei
2016-03-01
For important classes of many-fermion problems, quantum Monte Carlo (QMC) methods allow exact calculations of ground-state and finite-temperature properties without the sign problem. The list spans condensed matter, nuclear physics, and high-energy physics, including the half-filled repulsive Hubbard model, the spin-balanced atomic Fermi gas, and lattice quantum chromodynamics calculations at zero density with Wilson Fermions, and is growing rapidly as a number of problems have been discovered recently to be free of the sign problem. In these situations, QMC calculations are relied on to provide definitive answers. Their results are instrumental to our ability to understand and compute properties in fundamental models important to multiple subareas in quantum physics. It is shown, however, that the most commonly employed algorithms in such situations have an infinite variance problem. A diverging variance causes the estimated Monte Carlo statistical error bar to be incorrect, which can render the results of the calculation unreliable or meaningless. We discuss how to identify the infinite variance problem. An approach is then proposed to solve the problem. The solution does not require major modifications to standard algorithms, adding a "bridge link" to the imaginary-time path integral. The general idea is applicable to a variety of situations where the infinite variance problem may be present. Illustrative results are presented for the ground state of the Hubbard model at half-filling.
Information-theoretical meaning of quantum-dynamical entropy
Alicki, Robert
2002-11-01
The theories of noncommutative dynamical entropy and quantum symbolic dynamics for quantum-dynamical systems are analyzed from the point of view of quantum information theory. Using a general quantum-dynamical system as a communication channel, one can define different classical capacities depending on the character of resources applied for encoding and decoding procedures and on the type of information sources. It is shown that for Bernoulli sources, the entanglement-assisted classical capacity, which is the largest one, is bounded from above by the quantum-dynamical entropy defined in terms of operational partitions of unity. Stronger results are proved for the particular class of quantum-dynamical systems--quantum Bernoulli shifts. Different classical capacities are exactly computed and the entanglement-assisted one is equal to the dynamical entropy in this case.
Dey, Swayandipta; Zhou, Yadong; Tian, Xiangdong; Jenkins, Julie A; Chen, Ou; Zou, Shengli; Zhao, Jing
2015-04-21
In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs of appropriate sizes were chosen so that the plasmon resonance overlaps with the absorption and emission of the QDs. We observed that in the regime of a low excitation power, the photon antibunching and blinking properties of single QDs were modified significantly when the QDs were on the Au@SiO2 substrates compared to those on glass. Most significantly, second-order photon intensity correlation data show that the presence of plasmons increases the ratio of the biexciton quantum yield over the exciton quantum yield (QYBX/QYX). An electrodynamics model was developed to quantify the effect of plasmons on the lifetime, quantum yield, and emission intensity of the biexcitons for the QDs. Good agreement was obtained between the experimentally measured and calculated changes in QYBX/QYX due to Au@SiO2 NPs, showing the validity of the developed model. The theoretical studies also indicated that the relative position of the QDs to the Au NPs and the orientation of the electric field are important factors that regulate the emission properties of the excitons and biexcitons of QDs. The study suggests that the multiexciton emission efficiency in QD systems can be manipulated by employing properly designed plasmonic structures. PMID:25806486
Potential theoretic methods for far field sound radiation calculations
NASA Technical Reports Server (NTRS)
Hariharan, S. I.; Stenger, Edward J.; Scott, J. R.
1995-01-01
In the area of computational acoustics, procedures which accurately predict the far-field sound radiation are much sought after. A systematic development of such procedures are found in a sequence of papers by Atassi. The method presented here is an alternate approach to predicting far field sound based on simple layer potential theoretic methods. The main advantages of this method are: it requires only a simple free space Green's function, it can accommodate arbitrary shapes of Kirchoff surfaces, and is readily extendable to three-dimensional problems. Moreover, the procedure presented here, though tested for unsteady lifting airfoil problems, can easily be adapted to other areas of interest, such as jet noise radiation problems. Results are presented for lifting airfoil problems and comparisons are made with the results reported by Atassi. Direct comparisons are also made for the flat plate case.
Quantum Monte Carlo Calculations in Solids with Downfolded Hamiltonians
NASA Astrophysics Data System (ADS)
Ma, Fengjie; Purwanto, Wirawan; Zhang, Shiwei; Krakauer, Henry
2015-06-01
We present a combination of a downfolding many-body approach with auxiliary-field quantum Monte Carlo (AFQMC) calculations for extended systems. Many-body calculations operate on a simpler Hamiltonian which retains material-specific properties. The Hamiltonian is systematically improvable and allows one to dial, in principle, between the simplest model and the original Hamiltonian. As a by-product, pseudopotential errors are essentially eliminated using frozen orbitals constructed adaptively from the solid environment. The computational cost of the many-body calculation is dramatically reduced without sacrificing accuracy. Excellent accuracy is achieved for a range of solids, including semiconductors, ionic insulators, and metals. We apply the method to calculate the equation of state of cubic BN under ultrahigh pressure, and determine the spin gap in NiO, a challenging prototypical material with strong electron correlation effects.
The focus of light - theoretical calculation and experimental tomographic reconstruction
NASA Astrophysics Data System (ADS)
Quabis, S.; Dorn, R.; Eberler, M.; Glöckl, O.; Leuchs, G.
2001-01-01
We present numerical calculations on the field distribution in the focus of an optical system with high numerical aperture. The diffraction integrals which are based on the Debye approximation are derived and evaluated for a radially polarized input field with a doughnut-shaped intensity distribution. It is shown that this mode focusses down to a spot size significantly smaller as compared to the case of linear polarization. An experimental setup to measure the three-dimensional intensity distribution in the focal region is presented, which is based on the knife-edge method and on tomographic reconstruction.
Theoretical calculation of spectra of dibutyl phthalate and dioctyl phthalate
NASA Astrophysics Data System (ADS)
Du, Jian-Bin; Tang, Yan-Lin; Long, Zheng-Wen; Hu, Shuang-Hui; Li, Tao
2014-05-01
Dibutyl phthalate DBP and dioctyl phthalate DOP are the main components of the plasticizers. In order to investigate their molecular structure, chemical bond and spectrum, the geometrical parameters of the ground state and infrared (IR) spectrum are calculated using the density functional theory B3LYP method at the level of 6-311++G( d, p). On this basis, the first twenty-six excited states and the UV-Vis absorption spectra of DBP and DOP are studied using the time-dependent density functional theory (TDDFT) in the same fundamental group and compared with the ultraviolet absorption peak of the molecules measured with UNICO UV-Vis spectrophotometer. The two kinds of molecular spectra are then classified and compared with that in reference. The results show that the strong absorption of IR spectra of DOP and DBP are produced by C-H bending in-plane vibration and C=O telescopic vibration producing. The most absorption of UV-Vis absorption spectra appears in the end absorption belt from n to σ* transition, and the stronger absorption in the E belt of benzene electronic transition from π to π*. There are blue shift for DOP end absorption belt from n to σ* transition and red shift for DOP E absorption belt from π to π* transition relative to that of DBP. This calculation results are better in accord with the spectral data measured by UNICO ultraviolet and visible spectrophotometer.
Plasmon spectroscopy: Theoretical and numerical calculations, and optimization techniques
NASA Astrophysics Data System (ADS)
Rodríguez-Oliveros, Rogelio; Paniagua-Domínguez, Ramón; Sánchez-Gil, José A.; Macías, Demetrio
2016-02-01
We present an overview of recent advances in plasmonics, mainly concerning theoretical and numerical tools required for the rigorous determination of the spectral properties of complex-shape nanoparticles exhibiting strong localized surface plasmon resonances (LSPRs). Both quasistatic approaches and full electrodynamic methods are described, providing a thorough comparison of their numerical implementations. Special attention is paid to surface integral equation formulations, giving examples of their performance in complicated nanoparticle shapes of interest for their LSPR spectra. In this regard, complex (single) nanoparticle configurations (nanocrosses and nanorods) yield a hierarchy of multiple-order LSPR s with evidence of a rich symmetric or asymmetric (Fano-like) LSPR line shapes. In addition, means to address the design of complex geometries to retrieve LSPR spectra are commented on, with special interest in biologically inspired algorithms. Thewealth of LSPRbased applications are discussed in two choice examples, single-nanoparticle surface-enhanced Raman scattering (SERS) and optical heating, and multifrequency nanoantennas for fluorescence and nonlinear optics.
Accelerating quantum instanton calculations of the kinetic isotope effects
Karandashev, Konstantin; Vaníček, Jiří
2015-11-21
Path integral implementation of the quantum instanton approximation currently belongs among the most accurate methods for computing quantum rate constants and kinetic isotope effects, but its use has been limited due to the rather high computational cost. Here, we demonstrate that the efficiency of quantum instanton calculations of the kinetic isotope effects can be increased by orders of magnitude by combining two approaches: The convergence to the quantum limit is accelerated by employing high-order path integral factorizations of the Boltzmann operator, while the statistical convergence is improved by implementing virial estimators for relevant quantities. After deriving several new virial estimators for the high-order factorization and evaluating the resulting increase in efficiency, using ⋅H{sub α} + H{sub β}H{sub γ} → H{sub α}H{sub β} + ⋅ H{sub γ} reaction as an example, we apply the proposed method to obtain several kinetic isotope effects on CH{sub 4} + ⋅ H ⇌ ⋅ CH{sub 3} + H{sub 2} forward and backward reactions.
A Quantum Theoretical Explanation for Probability Judgment Errors
ERIC Educational Resources Information Center
Busemeyer, Jerome R.; Pothos, Emmanuel M.; Franco, Riccardo; Trueblood, Jennifer S.
2011-01-01
A quantum probability model is introduced and used to explain human probability judgment errors including the conjunction and disjunction fallacies, averaging effects, unpacking effects, and order effects on inference. On the one hand, quantum theory is similar to other categorization and memory models of cognition in that it relies on vector…
Aryl sulfoxide radical cations. Generation, spectral properties, and theoretical calculations.
Baciocchi, Enrico; Del Giacco, Tiziana; Gerini, Maria Francesca; Lanzalunga, Osvaldo
2006-08-17
Aromatic sulfoxide radical cations have been generated by pulse radiolysis and laser flash photolysis techniques. In water (pulse radiolysis) the radical cations showed an intense absorption band in the UV region (ca. 300 nm) and a broad less intense band in the visible region (from 500 to 1000 nm) whose position depends on the nature of the ring substituent. At very low pulse energy, the radical cations decayed by first-order kinetics, the decay rate increasing as the pH increases. It is suggested that the decay involves a nucleophilic attack of H(2)O or OH(-) (in basic solutions) to the positively charged sulfur atom to give the radical ArSO(OH)CH(3)(*). By sensitized [N-methylquinolinium tetrafluoborate (NMQ(+))] laser flash photolysis (LFP) the aromatic sulfoxide radical cations were generated in acetonitrile. In these experiments, however, only the band of the radical cation in the visible region could be observed, the UV band being covered by the UV absorption of NMQ(+). The lambda(max) values of the bands in the visible region resulted almost identical to those observed in water for the same radical cations. In the LFP experiments the sulfoxide radical cations decayed by second-order kinetics at a diffusion-controlled rate, and the decay is attributed to the back electron transfer between the radical cation and NMQ(*). DFT calculations were also carried out for a number of 4-X ring substituted (X = H, Me, Br, OMe, CN) aromatic sulfoxide radical cations (and their neutral parents). In all radical cations, the conformation with the S-O bond almost coplanar with the aromatic ring is the only one corresponding to the energy minimum. The maximum of energy corresponds to the conformation where the S-O bond is perpendicular to the aromatic ring. The rotational energy barriers are not very high, ranging from 3.9 to 6.9 kcal/mol. In all radical cations, the major fraction of charge and spin density is localized on the SOMe group. However, a substantial delocalization
NASA Astrophysics Data System (ADS)
Kripal, Ram; Yadav, Awadhesh Kumar
2015-06-01
Zero field splitting parameters (ZFSPs) D and E of Cr3+ ion doped ammonium oxalate monohydrate (AOM) are calculated with formula using the superposition model. The theoretically calculated ZFSPs for Cr3+ in AOM crystal are compared with the experimental value obtained by electron paramagnetic resonance (EPR). Theoretical ZFSPs are in good agreement with the experimental ones. The energy band positions of optical absorption spectra of Cr3+ in AOM crystal calculated with CFA package are in good match with the experimental values.
Delay time calculation for dual-wavelength quantum cascade lasers
Hamadou, A.; Lamari, S.; Thobel, J.-L.
2013-11-28
In this paper, we calculate the turn-on delay (t{sub th}) and buildup (Δt) times of a midinfrared quantum cascade laser operating simultaneously on two laser lines having a common upper level. The approach is based on the four-level rate equations model describing the variation of the electron number in the states and the photon number present within the cavity. We obtain simple analytical formulae for the turn-on delay and buildup times that determine the delay times and numerically apply our results to both the single and bimode states of a quantum cascade laser, in addition the effects of current injection on t{sub th} and Δt are explored.
Ab initio quantum transport calculations using plane waves
NASA Astrophysics Data System (ADS)
Garcia-Lekue, A.; Vergniory, M. G.; Jiang, X. W.; Wang, L. W.
2015-08-01
We present an ab initio method to calculate elastic quantum transport at the nanoscale. The method is based on a combination of density functional theory using plane wave nonlocal pseudopotentials and the use of auxiliary periodic boundary conditions to obtain the scattering states. The method can be applied to any applied bias voltage and the charge density and potential profile can either be calculated self-consistently, or using an approximated self-consistent field (SCF) approach. Based on the scattering states one can straightforwardly calculate the transmission coefficients and the corresponding electronic current. The overall scheme allows us to obtain accurate and numerically stable solutions for the elastic transport, with a computational time similar to that of a ground state calculation. This method is particularly suitable for calculations of tunneling currents through vacuum, that some of the nonequilibrium Greens function (NEGF) approaches based on atomic basis sets might have difficulty to deal with. Several examples are provided using this method from electron tunneling, to molecular electronics, to electronic devices: (i) On a Au nanojunction, the tunneling current dependence on the electrode-electrode distance is investigated. (ii) The tunneling through field emission resonances (FERs) is studied via an accurate description of the surface vacuum states. (iii) Based on quantum transport calculations, we have designed a molecular conformational switch, which can turn on and off a molecular junction by applying a perpendicular electric field. (iv) Finally, we have used the method to simulate tunnel field-effect transistors (TFETs) based on two-dimensional transition-metal dichalcogenides (TMDCs), where we have studied the performance and scaling limits of such nanodevices and proposed atomic doping to enhance the transistor performance.
NASA Astrophysics Data System (ADS)
Montgomery, Jason
2007-12-01
Scattering resonances play a key role in many chemical processes, including unimolecular and bimolecular reactions and photodissociation. A significant theoretical emphasis over the past several decades has been placed on accurate resonance calculations for polyatomic systems. In spite of such efforts, a quantum treatment of molecular systems which exhibit a high density of states and strong coordinate coupling near dissociation remains a formidable task. The research described herein employs improved quantum mechanical methods to calculate a representation of nuclear motion, both bound and unbound, which is used subsequently to calculate accurate resonance energies and lifetimes for two triatomic systems: the neon trimer and ozone. Specifically, theory and results are given regarding the construction of an optimal, L2 eigenbasis using techniques such as the discrete variable representation, the energy selected basis (ESB) method, and iterative diagonalization methods. A new energy selection method is also developed and implemented for the neon trimer. Subsequent resonance calculations are described which make use of the artificial boundary inhomogeneity (ABI) method, adapted to work with the above mentioned ESB and hyperspherical coordinates. The ABI method is used to calculate a set of linearly independent wavefunctions (LIWs) at a given energy for the representation of the scattering wavefunction. Resonance parameters are obtained by imposing scattering boundary conditions on a linear combination of LIWs and solving for the S-matrix, S, its energy derivative, dS/dE, and the Smith lifetime matrix, Q. When available, comparisons are made with previously reported calculations.
The actual content of quantum theoretical kinematics and mechanics
NASA Technical Reports Server (NTRS)
Heisenberg, W.
1983-01-01
First, exact definitions are supplied for the terms: position, velocity, energy, etc. (of the electron, for instance), such that they are valid also in quantum mechanics. Canonically conjugated variables are determined simultaneously only with a characteristic uncertainty. This uncertainty is the intrinsic reason for the occurrence of statistical relations in quantum mechanics. Mathematical formulation is made possible by the Dirac-Jordan theory. Beginning from the basic principles thus obtained, macroscopic processes are understood from the viewpoint of quantum mechanics. Several imaginary experiments are discussed to elucidate the theory.
The Nature of Infinity in Quantum Field Calculations
NASA Astrophysics Data System (ADS)
Kriske, Richard
2011-05-01
In many textbooks on Quantum Field Theory it has been noted that an infinity is taken a circle and the flux is calculated from the A field in that manner. There are of course many such examples of this sort of calculation using infinity as a circle. This author would like to point out that if the three dimensions of space are curved and the one dimension of time is not, in say a four space, infinity is the horizon, which is not a circle but rather a sphere; as long as space-time is curved uniformly, smoothly and has positive curvature. This author believes the math may be in error, since maps of the CMBR seem to indicate a ``Swiss-Cheese'' type of topology, wherein the Sphere at infinity (the Horizon of the Universe), has holes in it that can readily be seen. This author believes that these irregularities most certainly have a calculable effect on QED, QCD and Quantum Field Theory.
Quantum Monte Carlo calculations of {Alpha} = 8 nuclei.
Wiringa, R. B.; Pieper, S. C.; Carlson, J.; Pandharipande, V. R.; Physics; LANL; Univ. of Illinois
2000-07-01
We report quantum Monte Carlo calculations of ground and low-lying excited states for {Alpha}=8 nuclei using a realistic Hamiltonian containing the Argonne v{sub 18} two-nucleon and Urbana IX three-nucleon potentials. The calculations begin with correlated eight-body wave functions that have a filled {alpha}-like core and four p-shell nucleons LS coupled to the appropriate (J{sup {pi}},T) quantum numbers for the state of interest. After optimization, these variational wave functions are used as input to a Green's function Monte Carlo calculation made with a new constrained path algorithm. We find that the Hamiltonian produces a {sup 8}Be ground state that is within 2 MeV of the experimental resonance, but the other eight-body energies are progressively worse as the neutron-proton asymmetry increases. The {sup 8}Li ground state is stable against breakup into subclusters, but the {sup 8}He ground state is not. The excited state spectra are in fair agreement with experiment, with both the single-particle behavior of {sup 8}He and {sup 8}Li and the collective rotational behavior of {sup 8}Be being reproduced. We also examine energy differences in the T=1,2 isomultiplets and isospin-mixing matrix elements in the excited states of {sup 8}Be. Finally, we present densities, momentum distributions, and studies of the intrinsic shapes of these nuclei, with {sup 8}Be exhibiting a definite 2{alpha} cluster structure.
Quantum chemistry calculation of resveratrol and related stilbenes
NASA Astrophysics Data System (ADS)
Del Nero, J.; de Melo, C. P.
2003-01-01
We report a semiempirical investigation of the first excited states and of the spectroscopic properties of resveratrol, a phytoalexin with well-known antioxidative properties, and of structurally related stilbenes. The analysis of the calculated bond length and charge rearrangements resulting from the photoexcitation and of the corresponding theoretical spectra gives us some insight of how chemical modifications of these molecules could affect the possible physiological properties of resveratrol.
Theoretical study of spin relaxation in a carbon nanotube quantum dot
NASA Astrophysics Data System (ADS)
Bezanson, Brian; Hu, Xuedong
2008-03-01
Carbon nanotubes offer an attractive environment for coherent spin manipulation due to the small population of nuclear spins and weak spin-orbit interaction. While a couple of specific spin relaxation mechanisms have been investigated theoretically[1][2], there is still no comprehensive study of spin lifetimes in carbon nanotubes. In the present study we calculate the spin decay rate for electrons in gate-defined quantum dots on carbon nanotubes due to the spin-orbit and electron-phonon interactions. More specifically, we explore effects of magnetic field strength and orientation, tube diameter and chirality, and confinement. [1] Y. G. Semenov, K. W. Kim, G. J. Iafrate, Phys. Rev. B 75, 045429 (2007) [2] K. M. Borysenko, Y. G. Semenov, K. W. Kim, J. M. Zavada, arXiv 0710.3382 (2007)
[Large scale quantum chemical calculation for drug discovery].
Kitaura, Kazuo
2011-01-01
Due to the increase in computer power and the development of computational methods, it becomes possible to perform quantum mechanical calculations of very large molecules such as proteins that were previously exclusively treated with classical force field methods. We have developed the fragment molecular orbital (FMO) method aimed at biomolecular applications. One of the important applications of the method is in structure-based drug design because it provides accurate descriptions of various non-bonded interactions between a protein and its ligand. In this article, the FMO method will be described as well as its applications to the analysis of protein-ligand binding. PMID:21804319
Importance of parametrizing constraints in quantum-mechanical variational calculations
NASA Technical Reports Server (NTRS)
Chung, Kwong T.; Bhatia, A. K.
1992-01-01
In variational calculations of quantum mechanics, constraints are sometimes imposed explicitly on the wave function. These constraints, which are deduced by physical arguments, are often not uniquely defined. In this work, the advantage of parametrizing constraints and letting the variational principle determine the best possible constraint for the problem is pointed out. Examples are carried out to show the surprising effectiveness of the variational method if constraints are parameterized. It is also shown that misleading results may be obtained if a constraint is not parameterized.
Ramabhadran, Raghunath O; Raghavachari, Krishnan
2014-12-16
CONSPECTUS: Quantum chemistry and electronic structure theory have proven to be essential tools to the experimental chemist, in terms of both a priori predictions that pave the way for designing new experiments and rationalizing experimental observations a posteriori. Translating the well-established success of electronic structure theory in obtaining the structures and energies of small chemical systems to increasingly larger molecules is an exciting and ongoing central theme of research in quantum chemistry. However, the prohibitive computational scaling of highly accurate ab initio electronic structure methods poses a fundamental challenge to this research endeavor. This scenario necessitates an indirect fragment-based approach wherein a large molecule is divided into small fragments and is subsequently reassembled to compute its energy accurately. In our quest to further reduce the computational expense associated with the fragment-based methods and overall enhance the applicability of electronic structure methods to large molecules, we realized that the broad ideas involved in a different area, theoretical thermochemistry, are transferable to the area of fragment-based methods. This Account focuses on the effective merger of these two disparate frontiers in quantum chemistry and how new concepts inspired by theoretical thermochemistry significantly reduce the total number of electronic structure calculations needed to be performed as part of a fragment-based method without any appreciable loss of accuracy. Throughout, the generalized connectivity based hierarchy (CBH), which we developed to solve a long-standing problem in theoretical thermochemistry, serves as the linchpin in this merger. The accuracy of our method is based on two strong foundations: (a) the apt utilization of systematic and sophisticated error-canceling schemes via CBH that result in an optimal cutting scheme at any given level of fragmentation and (b) the use of a less expensive second
NASA Astrophysics Data System (ADS)
Hagiwara, Yohsuke; Tateno, Masaru
2010-10-01
We review the recent research on the functional mechanisms of biological macromolecules using theoretical methodologies coupled to ab initio quantum mechanical (QM) treatments of reaction centers in proteins and nucleic acids. Since in most cases such biological molecules are large, the computational costs of performing ab initio calculations for the entire structures are prohibitive. Instead, simulations that are jointed with molecular mechanics (MM) calculations are crucial to evaluate the long-range electrostatic interactions, which significantly affect the electronic structures of biological macromolecules. Thus, we focus our attention on the methodologies/schemes and applications of jointed QM/MM calculations, and discuss the critical issues to be elucidated in biological macromolecular systems.
Quantum Monte Carlo Calculations of Nucleon-Nucleus Scattering
NASA Astrophysics Data System (ADS)
Wiringa, R. B.; Nollett, Kenneth M.; Pieper, Steven C.; Brida, I.
2009-10-01
We report recent quantum Monte Carlo (variational and Green's function) calculations of elastic nucleon-nucleus scattering. We are adding the cases of proton-^4He, neutron-^3H and proton-^3He scattering to a previous GFMC study of neutron-^4He scattering [1]. To do this requires generalizing our methods to include long-range Coulomb forces and to treat coupled channels. The two four-body cases can be compared to other accurate four-body calculational methods such as the AGS equations and hyperspherical harmonic expansions. We will present results for the Argonne v18 interaction alone and with Urbana and Illinois three-nucleon potentials. [4pt] [1] K.M. Nollett, S. C. Pieper, R.B. Wiringa, J. Carlson, and G.M. Hale, Phys. Rev. Lett. 99, 022502 (2007)
Quantum states of confined hydrogen plasma species: Monte Carlo calculations
NASA Astrophysics Data System (ADS)
Micca Longo, G.; Longo, S.; Giordano, D.
2015-12-01
The diffusion Monte Carlo method with symmetry-based state selection is used to calculate the quantum energy states of \\text{H}2+ confined into potential barriers of atomic dimensions (a model for these ions in solids). Special solutions are employed, permitting one to obtain satisfactory results with rather simple native code. As a test case, {{}2}{{\\Pi}u} and {{}2}{{\\Pi}g} states of \\text{H}2+ ions under spherical confinement are considered. The results are interpreted using the correlation of \\text{H}2+ states to atomic orbitals of H atoms lying on the confining surface and perturbation calculations. The method is straightforwardly applied to cavities of any shape and different hydrogen plasma species (at least one-electron ones, including H) for future studies with real crystal symmetries.
Nuclear-magnetic-resonance quantum calculations of the Jones polynomial
Marx, Raimund; Spoerl, Andreas; Pomplun, Nikolas; Schulte-Herbrueggen, Thomas; Glaser, Steffen J.; Fahmy, Amr; Kauffman, Louis; Lomonaco, Samuel; Myers, John M.
2010-03-15
The repertoire of problems theoretically solvable by a quantum computer recently expanded to include the approximate evaluation of knot invariants, specifically the Jones polynomial. The experimental implementation of this evaluation, however, involves many known experimental challenges. Here we present experimental results for a small-scale approximate evaluation of the Jones polynomial by nuclear magnetic resonance (NMR); in addition, we show how to escape from the limitations of NMR approaches that employ pseudopure states. Specifically, we use two spin-1/2 nuclei of natural abundance chloroform and apply a sequence of unitary transforms representing the trefoil knot, the figure-eight knot, and the Borromean rings. After measuring the nuclear spin state of the molecule in each case, we are able to estimate the value of the Jones polynomial for each of the knots.
Self-consistent calculations of optical properties of type I and type II quantum heterostructures
NASA Astrophysics Data System (ADS)
Shuvayev, Vladimir A.
In this Thesis the self-consistent computational methods are applied to the study of the optical properties of semiconductor nanostructures with one- and two-dimensional quantum confinements. At first, the self-consistent Schrodinger-Poisson system of equations is applied to the cylindrical core-shell structure with type II band alignment without direct Coulomb interaction between carriers. The electron and hole states and confining potential are obtained from a numerical solution of this system. The photoluminescence kinetics is theoretically analyzed, with the nanostructure size dispersion taken into account. The results are applied to the radiative recombination in the system of ZnTe/ZnSe stacked quantum dots. A good agreement with both continuous wave and time-resolved experimental observations is found. It is shown that size distribution results in the photoluminescence decay that has essentially non-exponential behavior even at the tail of the decay where the carrier lifetime is almost the same due to slowly changing overlap of the electron and hole wavefunctions. Also, a model situation applicable to colloidal core-shell nanowires is investigated and discussed. With respect to the excitons in type I quantum wells, a new computationally efficient and flexible approach of calculating the characteristics of excitons, based on a self-consistent variational treatment of the electron-hole Coulomb interaction, is developed. In this approach, a system of self-consistent equations describing the motion of an electron-hole pair is derived. The motion in the growth direction of the quantum well is separated from the in-plane motion, but each of them occurs in modified potentials found self-consistently. This approach is applied to a shallow quantum well with the delta-potential profile, for which analytical expressions for the exciton binding energy and the ground state eigenfunctions are obtained, and to the quantum well with the square potential profile with several
Quantum cognition: a new theoretical approach to psychology.
Bruza, Peter D; Wang, Zheng; Busemeyer, Jerome R
2015-07-01
What type of probability theory best describes the way humans make judgments under uncertainty and decisions under conflict? Although rational models of cognition have become prominent and have achieved much success, they adhere to the laws of classical probability theory despite the fact that human reasoning does not always conform to these laws. For this reason we have seen the recent emergence of models based on an alternative probabilistic framework drawn from quantum theory. These quantum models show promise in addressing cognitive phenomena that have proven recalcitrant to modeling by means of classical probability theory. This review compares and contrasts probabilistic models based on Bayesian or classical versus quantum principles, and highlights the advantages and disadvantages of each approach. PMID:26058709
Wu, Yunhu; Zhang, Guoping; Guo, Ling; Qi, Guoqun; Li, Xiaoming
2014-06-14
Based on Auger scattering mechanism, carrier-carrier scattering dynamics between the two-dimensional carrier reservoir (also called wetting layer, i.e., WL) and the confined quantum dot ground and first excited state in quantum-dot semiconductor optical amplifiers (QD-SOAs) are investigated theoretically in this paper. The scattering rates for independent electron and hole densities are calculated. The results show an ultra-fast carrier capture (relaxation) rate up to 1 ps{sup −1}, and there is a complex dependence of the Coulomb scattering rates on the WL electron and hole densities. In addition, due to the different effective mass and the level distribution, the scattering rates for electron and hole are very different. Finally, in order to provide a direction to control (increase or decrease) the input current in realistic QD-SOA systems, a simple method is proposed to determine the trends of the carrier recovery rates with the WL carrier densities in the vicinity of the steady-state.
Quantum Monte Carlo calculations of A=8 nuclei
Wiringa, R. B.; Pieper, Steven C.; Carlson, J.; Pandharipande, V. R.
2000-07-01
We report quantum Monte Carlo calculations of ground and low-lying excited states for A=8 nuclei using a realistic Hamiltonian containing the Argonne v{sub 18} two-nucleon and Urbana IX three-nucleon potentials. The calculations begin with correlated eight-body wave functions that have a filled {alpha}-like core and four p-shell nucleons LS coupled to the appropriate (J{sup {pi}};T) quantum numbers for the state of interest. After optimization, these variational wave functions are used as input to a Green's function Monte Carlo calculation made with a new constrained path algorithm. We find that the Hamiltonian produces a {sup 8}Be ground state that is within 2 MeV of the experimental resonance, but the other eight-body energies are progressively worse as the neutron-proton asymmetry increases. The {sup 8}Li ground state is stable against breakup into subclusters, but the {sup 8}He ground state is not. The excited state spectra are in fair agreement with experiment, with both the single-particle behavior of {sup 8}He and {sup 8}Li and the collective rotational behavior of {sup 8}Be being reproduced. We also examine energy differences in the T=1,2 isomultiplets and isospin-mixing matrix elements in the excited states of {sup 8}Be. Finally, we present densities, momentum distributions, and studies of the intrinsic shapes of these nuclei, with {sup 8}Be exhibiting a definite 2{alpha} cluster structure. (c) 2000 The American Physical Society.
Number-theoretic nature of communication in quantum spin systems.
Godsil, Chris; Kirkland, Stephen; Severini, Simone; Smith, Jamie
2012-08-01
The last decade has witnessed substantial interest in protocols for transferring information on networks of quantum mechanical objects. A variety of control methods and network topologies have been proposed, on the basis that transfer with perfect fidelity-i.e., deterministic and without information loss-is impossible through unmodulated spin chains with more than a few particles. Solving the original problem formulated by Bose [Phys. Rev. Lett. 91, 207901 (2003)], we determine the exact number of qubits in unmodulated chains (with an XY Hamiltonian) that permit transfer with a fidelity arbitrarily close to 1, a phenomenon called pretty good state transfer. We prove that this happens if and only if the number of nodes is n = p - 1, 2p - 1, where p is a prime, or n = 2(m) - 1. The result highlights the potential of quantum spin system dynamics for reinterpreting questions about the arithmetic structure of integers and, in this case, primality. PMID:23006153
A quantum theoretical approach to information processing in neural networks
NASA Astrophysics Data System (ADS)
Barahona da Fonseca, José; Barahona da Fonseca, Isabel; Suarez Araujo, Carmen Paz; Simões da Fonseca, José
2000-05-01
A reinterpretation of experimental data on learning was used to formulate a law on data acquisition similar to the Hamiltonian of a mechanical system. A matrix of costs in decision making specifies values attributable to a barrier that opposed to hypothesis formation about decision making. The interpretation of the encoding costs as frequencies of oscillatory phenomena leads to a quantum paradigm based in the models of photoelectric effect as well as of a particle against a potential barrier. Cognitive processes are envisaged as complex phenomena represented by structures linked by valence bounds. This metaphor is used to find some prerequisites to certain types of conscious experience as well as to find an explanation for some pathological distortions of cognitive operations as they are represented in the context of the isolobal model. Those quantum phenomena are understood as representing an analogue programming for specific special purpose computations. The formation of complex chemical structures within the context of isolobal theory is understood as an analog quantum paradigm for complex cognitive computations.
Variational quantum Monte Carlo calculations for solid surfaces
Bahnsen, R.; Eckstein, H.; Schattke, W.; Fitzer, N.; Redmer, R.
2001-06-15
Quantum Monte Carlo methods have proven to predict atomic and bulk properties of light and nonlight elements with high accuracy. Here we report on variational quantum Monte Carlo (VMC) calculations for solid surfaces. Taking the boundary condition for the simulation from a finite-layer geometry, the Hamiltonian, including a nonlocal pseudopotential, is cast in a layer-resolved form and evaluated with a two-dimensional Ewald summation technique. The exact cancellation of all jellium contributions to the Hamiltonian is ensured. The many-body trial wave function consists of a Slater determinant with parametrized localized orbitals and a Jastrow factor with a common two-body term plus an additional confinement term representing further variational freedom to take into account the existence of the surface. We present results for the ideal (110) surface of gallium arsenide for different system sizes. With the optimized trial wave function, we determine some properties related to a solid surface to illustrate that VMC techniques provide reasonable results under full inclusion of many-body effects at solid surfaces.
Technology Transfer Automated Retrieval System (TEKTRAN)
Determination of absolute configuration (AC) is one of the most challenging features in the structure elucidation of chiral natural products, especially those with complex structures. With revolutionary advancements in the area of quantum chemical calculations of chiroptical spectroscopy over the pa...
Pseudopotentials for quantum Monte Carlo calculations of transition metal oxides
NASA Astrophysics Data System (ADS)
Krogel, Jaron; Santana, Juan; Kent, Paul; Reboredo, Fernando
2015-03-01
Quantum Monte Carlo calculations of transition metal oxides are partially limited by the availability of high quality pseudopotentials that are both accurate in QMC and compatible with major electronic structure codes, e.g. by not being overly hard in the standard planewave basis. Following insight gained from recent GW calculations, a set of neon core pseudopotentials with small cutoff radii have been created for the early transition metal elements Sc to Zn within the local density approximation of DFT. The pseudopotentials have been tested for energy consistency within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (TM) atoms and the binding curve of each TM-O dimer. The vast majority of the ionization potentials fall within 0.3 eV of the experimental values, with exceptions occurring mainly for atoms with multiple unpaired d electrons where multireference effects are the strongest. The equilibrium bond lengths of the dimers are within 1% of experimental values and the binding energy errors are typically less than 0.3 eV. Given the uniform treatment of the core, the larger deviations occasionally observed may primarily reflect the limitations of a Slater-Jastrow trial wavefunction. This work is supported by the Materials Sciences & Engineering Division of the Office of Basic Energy Sciences, U.S. DOE. Research by PRCK was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
Performance of quantum Monte Carlo for calculating molecular bond lengths
NASA Astrophysics Data System (ADS)
Cleland, Deidre M.; Per, Manolo C.
2016-03-01
This work investigates the accuracy of real-space quantum Monte Carlo (QMC) methods for calculating molecular geometries. We present the equilibrium bond lengths of a test set of 30 diatomic molecules calculated using variational Monte Carlo (VMC) and diffusion Monte Carlo (DMC) methods. The effect of different trial wavefunctions is investigated using single determinants constructed from Hartree-Fock (HF) and Density Functional Theory (DFT) orbitals with LDA, PBE, and B3LYP functionals, as well as small multi-configurational self-consistent field (MCSCF) multi-determinant expansions. When compared to experimental geometries, all DMC methods exhibit smaller mean-absolute deviations (MADs) than those given by HF, DFT, and MCSCF. The most accurate MAD of 3 ± 2 × 10-3 Å is achieved using DMC with a small multi-determinant expansion. However, the more computationally efficient multi-determinant VMC method has a similar MAD of only 4.0 ± 0.9 × 10-3 Å, suggesting that QMC forces calculated from the relatively simple VMC algorithm may often be sufficient for accurate molecular geometries.
Frka, Sanja; Šala, Martin; Kroflič, Ana; Huš, Matej; Čusak, Alen; Grgić, Irena
2016-06-01
Methylnitrocatechols (MNCs) are secondary organic aerosol (SOA) tracers and major contributors to atmospheric brown carbon; however, their formation and aging processes in atmospheric waters are unknown. To investigate the importance of aqueous-phase electrophilic substitution of 3-methylcatechol with nitronium ion (NO2(+)), we performed quantum calculations of their favorable pathways. The calculations predicted the formation of 3-methyl-5-nitrocatechol (3M5NC), 3-methyl-4-nitrocatechol (3M4NC), and a negligible amount of 3-methyl-6-nitrocatechol (3M6NC). MNCs in atmospheric PM2 samples were further inspected by LC/(-)ESI-MS/MS using commercial as well as de novo synthesized authentic standards. We detected 3M5NC and, for the first time, 3M4NC. In contrast to previous reports, 3M6NC was not observed. Agreement between calculated and observed 3M5NC/3M4NC ratios cannot unambiguously confirm the electrophilic mechanism as the exclusive formation pathway of MNCs in aerosol water. However, the examined nitration by NO2(+) is supported by (1) the absence of 3M6NC in the ambient aerosols analyzed and (2) the constant 3M5NC/3M4NC ratio in field aerosol samples, which indicates their common formation pathway. The magnitude of error one could make by incorrectly identifying 3M4NC as 3M6NC in ambient aerosols was also assessed, suggesting the importance of evaluating the literature regarding MNCs with special care. PMID:27136117
QTAIM Analysis in the Context of Quasirelativistic Quantum Calculations.
Pilmé, Julien; Renault, Eric; Bassal, Fadel; Amaouch, Mohamed; Montavon, Gilles; Galland, Nicolas
2014-11-11
Computational chemistry currently lacks ad hoc tools for probing the nature of chemical bonds in heavy and superheavy-atom systems where the consideration of spin-orbit coupling (SOC) effects is mandatory. We report an implementation of the Quantum Theory of Atoms-In-Molecules in the framework of two-component relativistic calculations. Used in conjunction with the topological analysis of the Electron Localization Function, we show for astatine (At) species that SOC significantly lowers At electronegativity and boosts its propensity to make charge-shift bonds. Relativistic spin-dependent effects are furthermore able to change some bonds from mainly covalent to charge-shift type. The implication of the disclosed features regarding the rationalization of the labeling protocols used in nuclear medicine for (211)At radioisotope nicely illustrates the potential of the introduced methodology for investigating the chemistry of (super)heavy elements. PMID:26584370
Vibrational spectra and quantum mechanical calculations of antiretroviral drugs: Nevirapine
NASA Astrophysics Data System (ADS)
Ayala, A. P.; Siesler, H. W.; Wardell, S. M. S. V.; Boechat, N.; Dabbene, V.; Cuffini, S. L.
2007-02-01
Nevirapine (11-cyclopropyl-5,11-dihydro-4-methyl-6H-dipyrido[3,2-b:2',3'e][1,4]diazepin-6-one) is an antiretroviral drug belonging to the class of the non-nucleoside inhibitors of the HIV-1 virus reverse transcriptase. As most of this kind of antiretroviral drugs, nevirapine displays a butterfly-like conformation which is preserved in complexes with the HIV-1 reverse transcriptase. In this work, we present a detailed vibrational spectroscopy investigation of nevirapine by using mid-infrared, near-infrared, and Raman spectroscopies. These data are supported by quantum mechanical calculations, which allow us to characterize completely the vibrational spectra of this compound. Based on these results, we discuss the correlation between the vibrational modes and the crystalline structure of the most stable form of nevirapine.
Conformational analysis of small molecules: NMR and quantum mechanics calculations.
Tormena, Cláudio F
2016-08-01
This review deals with conformational analysis in small organic molecules, and describes the stereoelectronic interactions responsible for conformational stability. Conformational analysis is usually performed using NMR spectroscopy through measurement of coupling constants at room or low temperature in different solvents to determine the populations of conformers in solution. Quantum mechanical calculations are used to address the interactions responsible for conformer stability. The conformational analysis of a large number of small molecules is described, using coupling constant measurements in different solvents and at low temperature, as well as recent applications of through-space and through-hydrogen bond coupling constants JFH as tools for the conformational analysis of fluorinated molecules. Besides NMR parameters, stereoelectronic interactions such as conjugative, hyperconjugative, steric and intramolecular hydrogen bond interactions involved in conformational preferences are discussed. PMID:27573182
NASA Astrophysics Data System (ADS)
Moreira, Rafael Y. O.; Brasil, Davi S. B.; Alves, Cláudio N.; Guilhon, Giselle M. S. P.; Santos, Lourivaldo S.; Arruda, Mara S. P.; Müller, Adolfo H.; Barbosa, Patrícia S.; Abreu, Alcicley S.; Silva, Edilene O.; Rumjanek, Victor M.; Souza, Jaime, Jr.; da Silva, Albérico B. F.; Santos, Regina H. De A.
Julocrotine, N-(2,6-dioxo-1-phenethyl-piperidin-3-yl)-2-methyl-butyramide, is a potent antiproliferative agent against the promastigote and amastigote forms of Leishmania amazonensis (L.). In this work, the crystal structure of Julocrotine was solved by X-ray diffraction, and its geometrical parameters were compared with theoretical calculations at the B3LYP and HF level of theory. IR and NMR spectra also have been obtained and compared with theoretical calculations. IR absorptions calculated with the B3LYP level of theory employed together with the 6-311G+(d,p) basis set, are close to those observed experimentally. Theoretical NMR calculations show little deviation from experimental results. The results show that the theory is in accordance with the experimental data.0
Fragment quantum mechanical calculation of proteins and its applications.
He, Xiao; Zhu, Tong; Wang, Xianwei; Liu, Jinfeng; Zhang, John Z H
2014-09-16
Conspectus The desire to study molecular systems that are much larger than what the current state-of-the-art ab initio or density functional theory methods could handle has naturally led to the development of novel approximate methods, including semiempirical approaches, reduced-scaling methods, and fragmentation methods. The major computational limitation of ab initio methods is the scaling problem, because the cost of ab initio calculation scales nth power or worse with system size. In the past decade, the fragmentation approach based on chemical locality has opened a new door for developing linear-scaling quantum mechanical (QM) methods for large systems and for applications to large molecular systems such as biomolecules. The fragmentation approach is highly attractive from a computational standpoint. First, the ab initio calculation of individual fragments can be conducted almost independently, which makes it suitable for massively parallel computations. Second, the electron properties, such as density and energy, are typically combined in a linear fashion to reproduce those for the entire molecular system, which makes the overall computation scale linearly with the size of the system. In this Account, two fragmentation methods and their applications to macromolecules are described. They are the electrostatically embedded generalized molecular fractionation with conjugate caps (EE-GMFCC) method and the automated fragmentation quantum mechanics/molecular mechanics (AF-QM/MM) approach. The EE-GMFCC method is developed from the MFCC approach, which was initially used to obtain accurate protein-ligand QM interaction energies. The main idea of the MFCC approach is that a pair of conjugate caps (concaps) is inserted at the location where the subsystem is divided by cutting the chemical bond. In addition, the pair of concaps is fused to form molecular species such that the overcounted effect from added concaps can be properly removed. By introducing the electrostatic
Large Scale Electronic Structure Calculations using Quantum Chemistry Methods
NASA Astrophysics Data System (ADS)
Scuseria, Gustavo E.
1998-03-01
This talk will address our recent efforts in developing fast, linear scaling electronic structure methods for large scale applications. Of special importance is our fast multipole method( M. C. Strain, G. E. Scuseria, and M. J. Frisch, Science 271), 51 (1996). (FMM) for achieving linear scaling for the quantum Coulomb problem (GvFMM), the traditional bottleneck in quantum chemistry calculations based on Gaussian orbitals. Fast quadratures(R. E. Stratmann, G. E. Scuseria, and M. J. Frisch, Chem. Phys. Lett. 257), 213 (1996). combined with methods that avoid the Hamiltonian diagonalization( J. M. Millam and G. E. Scuseria, J. Chem. Phys. 106), 5569 (1997) have resulted in density functional theory (DFT) programs that can be applied to systems containing many hundreds of atoms and ---depending on computational resources or level of theory-- to many thousands of atoms.( A. D. Daniels, J. M. Millam and G. E. Scuseria, J. Chem. Phys. 107), 425 (1997). Three solutions for the diagonalization bottleneck will be analyzed and compared: a conjugate gradient density matrix search (CGDMS), a Hamiltonian polynomial expansion of the density matrix, and a pseudo-diagonalization method. Besides DFT, our near-field exchange method( J. C. Burant, G. E. Scuseria, and M. J. Frisch, J. Chem. Phys. 105), 8969 (1996). for linear scaling Hartree-Fock calculations will be discussed. Based on these improved capabilities, we have also developed programs to obtain vibrational frequencies (via analytic energy second derivatives) and excitation energies (through time-dependent DFT) of large molecules like porphyn or C_70. Our GvFMM has been extended to periodic systems( K. N. Kudin and G. E. Scuseria, Chem. Phys. Lett., in press.) and progress towards a Gaussian-based DFT and HF program for polymers and solids will be reported. Last, we will discuss our progress on a Laplace-transformed \\cal O(N^2) second-order pertubation theory (MP2) method.
Double Exponential Relativity Theory Coupled Theoretically with Quantum Theory?
Montero Garcia, Jose de la Luz; Novoa Blanco, Jesus Francisco
2007-04-28
Here the problem of special relativity is analyzed into the context of a new theoretical formulation: the Double Exponential Theory of Special Relativity with respect to which the current Special or Restricted Theory of Relativity (STR) turns to be a particular case only.
Auxiliary-field quantum Monte Carlo calculations of the molybdenum dimer
NASA Astrophysics Data System (ADS)
Purwanto, Wirawan; Zhang, Shiwei; Krakauer, Henry
2016-06-01
Chemical accuracy is difficult to achieve for systems with transition metal atoms. Third row transition metal atoms are particularly challenging due to strong electron-electron correlation in localized d-orbitals. The Cr2 molecule is an outstanding example, which we previously treated with highly accurate auxiliary-field quantum Monte Carlo (AFQMC) calculations [W. Purwanto et al., J. Chem. Phys. 142, 064302 (2015)]. Somewhat surprisingly, computational description of the isoelectronic Mo2 dimer has also, to date, been scattered and less than satisfactory. We present high-level theoretical benchmarks of the Mo2 singlet ground state (X1Σg+) and first triplet excited state (a3Σu+), using the phaseless AFQMC calculations. Extrapolation to the complete basis set limit is performed. Excellent agreement with experimental spectroscopic constants is obtained. We also present a comparison of the correlation effects in Cr2 and Mo2.
The information-theoretical entropy of some quantum oscillators
Popov, D. Pop, N.; Popov, M.
2014-11-24
The Wehrl entropy or the 'classical' entropy associated with a quantum system is the entropy of the probability distribution in phase space, corresponding to the Husimi Q-function in terms of coherent states. In the present paper, we shall focus our attention on the examination of the Wehrl entropy for both the pure and the mixed (thermal) states of the pseudoharmonic oscillator (PHO). The choice of the PHO is interesting because this oscillator is an intermediate between the ideal one-dimensional harmonic oscillator (HO-1D) and the more practical anharmonicone.
NASA Astrophysics Data System (ADS)
Mastour, N.; Mejatty, M.; Bouchriha, H.
2015-06-01
A theoretical approach based on the rate equation of exciton density for the electroluminescence quenching in (polymers-quantum dots) nanocomposite is developed. It is shown that the light intensity observed in the nanocomposite depends respectively on the quantum dots concentration, the injected charge carriers, the exciton density, and the Förster energy transfer between polymer and quantum dots. We have found that the significant reduction of the light intensity is related to the exciton density profiles which exhibit a monotonic decrease with the increase of Förster transfer mechanism. Our theoretical approach for the electroluminescence agrees with experimental results observed in hybrid structure (MEH-PPV) with CdSe quantum dots. The maximum of exciton density is also estimated and we have obtained a value for the exciton diffusion length of 10 nm which is consistent with the available experimental results.
NASA Technical Reports Server (NTRS)
Carder, K. L.; Lee, Z. P.; Marra, John; Steward, R. G.; Perry, M. J.
1995-01-01
The quantum yield of photosynthesis (mol C/mol photons) was calculated at six depths for the waters of the Marine Light-Mixed Layer (MLML) cruise of May 1991. As there were photosynthetically available radiation (PAR) but no spectral irradiance measurements for the primary production incubations, three ways are presented here for the calculation of the absorbed photons (AP) by phytoplankton for the purpose of calculating phi. The first is based on a simple, nonspectral model; the second is based on a nonlinear regression using measured PAR values with depth; and the third is derived through remote sensing measurements. We show that the results of phi calculated using the nonlinear regreesion method and those using remote sensing are in good agreement with each other, and are consistent with the reported values of other studies. In deep waters, however, the simple nonspectral model may cause quantum yield values much higher than theoretically possible.
Theoretical Model for the Calculation of Optical Properties of Gold Nanoparticles
NASA Astrophysics Data System (ADS)
Mendoza-García, A.; Romero-Depablos, A.; Ortega, M. A.; Paz, J. L.; Echevarría, L.
We have developed an analytical method to describe the optical properties of nanoparticles, whose results are in agreement with the observed experimental behavior according to the size of the nanoparticle under analysis. Our considerations to describe plasmonic absorption and dispersion are based on the combination of the two-level molecular system and the two-dimensional quantum box models. Employing the optical stochastic Bloch equations, we have determined the system's coherence, from which we have calculated expressions for the absorption coefficient and refractive index. The innovation of this methodology is that it allows us to take into account the solvent environment, which induce quantum effects not considered by classical treatments.
Classical and Quantum Conditioning:. Mathematical and Information Theoretical Aspects
NASA Astrophysics Data System (ADS)
Accardi, Luigi
2010-01-01
The different notions of stochastic independences, introduced in quantum probability open new fascinating possibilities to deepen our intuition on what a composite system. In the present note we propose a general mathematical definition of composite system which emphasizes the fact that the naive idea, that a physical system is composed of a multiplicity of sub-systems, can be substantiated by a multiplicity of inequivalent mathematical models. This wealth of possibilities can considerably enrich the present approach to the theory of open systems, with potential implications for the theory of measurement and the theory of complex systems, such as biological or economical ones. The standard approach to composite system strongly privileges the tensor product construction and the corresponding notion of stochastic independence. But there are a multiplicity of other possibilities whose mathematical and physical investigation is only at the beginning. In particular, to any notion of statistical independence it is canonically associated a corresponding notion of entanglement.
Theoretical calculation of light-induced forces and torques on complex microrotors
NASA Astrophysics Data System (ADS)
Liu, Yuxiang; Zhu, Anding; Huang, Wenhao
2004-12-01
In this letter, we propose the new theoretical investigation on the optical forces and torques on complex microrotors. On the basis of R. C. Gauthier"s hybrid ray-wave model, the optical forces and toques on two complex asymmetric micro-objects, the conical microrotor and the helical microrotor, are analyzed. The viscous drag torque is estimated by Stokes flow to obtain the rotational speed. The results of our computation agree well with the previously published experimental results, which indicates that our approach of the optical torque calculation is suitable for other complex microrotors and that the theoretical calculation is very helpful to optimum design of light-driven microrotors.
Kuwada, Takeshi; Fukui, Miyako; Hata, Toshiyuki; Choshi, Tominari; Nobuhiro, Junko; Ono, Yukio; Hibino, Satoshi
2003-01-01
The specific optical rotations of (R)-oxopropaline D calculated by two ab initio MO methods were +52+/-31 degrees and +61+/-29 degrees, respectively, and (+)-oxopropaline D (3) was presumed to have an R-configuration. On the basis of this theoretical result, the reaction of 1-litio-beta-carboline with (R)-glyceraldehyde acetonide followed by oxidation with MnO(2) gave (R)-oxopropaline D acetonide (4a), which was consistent with the previously synthesized (+)-oxopropaline D acetonide (4) in all respects. From the results of theoretical calculations and the experimental synthesis, we determined that natural (+)-oxopropaline D (3) has an R-configuration. PMID:12520122
NASA Astrophysics Data System (ADS)
Orwat, Justyna; Mielimaka, Ryszard
2016-06-01
The article demonstrates the comparison of prognosed values of deformation indicators with their values obtained from geodetic measurements. The value of correlation coefficient R between its theoretical and practical values was calculated for each indicator. Following the measured values as basic ones, the evaluation of efficiency of prognosis via the use of Knothe`s theory (a mathematical model, in which lowering of point is calculated as a double integral from Gauss error function with adequate parameters).
Quantum Monte Carlo calculations for point defects in semiconductors
NASA Astrophysics Data System (ADS)
Hennig, Richard
2010-03-01
Point defects in silicon have been studied extensively for many years. Nevertheless the mechanism for self diffusion in Si is still debated. Direct experimental measurements of the selfdiffusion in silicon are complicated by the lack of suitable isotopes. Formation energies are either obtained from theory or indirectly through the analysis of dopant and metal diffusion experiments. Density functional calculations predict formation energies ranging from 3 to 5 eV depending on the approximations used for the exchange-correlation functional [1]. Analysis of dopant and metal diffusion experiments result in similar broad range of diffusion activation energies of 4.95 [2], 4.68 [3], 2.4 eV [4]. Assuming a migration energy barrier of 0.1-0.3 eV [5], the resulting experimental interstitial formation energies range from 2.1 - 4.9 eV. To answer the question of the formation energy of Si interstitials we resort to a many-body description of the wave functions using quantum Monte Carlo (QMC) techniques. Previous QMC calculations resulted in formation energies for the interstitials of around 5 eV [1,6]. We present a careful analysis of all the controlled and uncontrolled approximations that affect the defect formation energies in variational and diffusion Monte Carlo calculations. We find that more accurate trial wave functions for QMC using improved Jastrow expansions and most importantly a backflow transformation for the electron coordinates significantly improve the wave functions. Using zero-variance extrapolation, we predict interstitial formation energies in good agreement with hybrid DFT functionals [1] and recent GW calculations [7]. [4pt] [1] E. R. Batista, J. Heyd, R. G. Hennig, B. P. Uberuaga, R. L. Martin, G. E. Scuseria, C. J. Umrigar, and J. W. Wilkins. Phys. Rev. B 74, 121102(R) (2006).[0pt] [2] H. Bracht, E. E. Haller, and R. Clark-Phelps, Phys. Rev. Lett. 81, 393 (1998). [0pt] [3] A. Ural, P. B. Griffin, and J. D. Plummer, Phys. Rev. Lett. 83, 3454 (1999). [0pt
NASA Astrophysics Data System (ADS)
Chen, Xin
2014-04-01
Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.
Chen, Xin
2014-04-21
Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.
NASA Astrophysics Data System (ADS)
Ghazzali, Mohamed; Khattab, Sherine A. N.; Elnakady, Yasser A.; Al-Mekhlafi, Fahd A.; Al-Farhan, Khalid; El-Faham, Ayman
2013-08-01
A series of naphthyl and tolyl sulfonate ester were synthesized and characterized by H NMR. X-ray single crystal diffraction experiments established the molecular structure of three new sulfonate esters derivatives, and spectral data agree with these in solution. The observed hydrogen bonding is discussed on the basis of crystal structural analyses and DFT/MP2 geometry optimization quantum calculations. Antimicrobial activities were screened for selected compounds against three human cancer cell lines and Mosquito Culex pipiens larvae.
Quantum Monte Carlo Algorithms for Diagrammatic Vibrational Structure Calculations
NASA Astrophysics Data System (ADS)
Hermes, Matthew; Hirata, So
2015-06-01
Convergent hierarchies of theories for calculating many-body vibrational ground and excited-state wave functions, such as Møller-Plesset perturbation theory or coupled cluster theory, tend to rely on matrix-algebraic manipulations of large, high-dimensional arrays of anharmonic force constants, tasks which require large amounts of computer storage space and which are very difficult to implement in a parallel-scalable fashion. On the other hand, existing quantum Monte Carlo (QMC) methods for vibrational wave functions tend to lack robust techniques for obtaining excited-state energies, especially for large systems. By exploiting analytical identities for matrix elements of position operators in a harmonic oscillator basis, we have developed stochastic implementations of the size-extensive vibrational self-consistent field (MC-XVSCF) and size-extensive vibrational Møller-Plesset second-order perturbation (MC-XVMP2) theories which do not require storing the potential energy surface (PES). The programmable equations of MC-XVSCF and MC-XVMP2 take the form of a small number of high-dimensional integrals evaluated using Metropolis Monte Carlo techniques. The associated integrands require independent evaluations of only the value, not the derivatives, of the PES at many points, a task which is trivial to parallelize. However, unlike existing vibrational QMC methods, MC-XVSCF and MC-XVMP2 can calculate anharmonic frequencies directly, rather than as a small difference between two noisy total energies, and do not require user-selected coordinates or nodal surfaces. MC-XVSCF and MC-XVMP2 can also directly sample the PES in a given approximation without analytical or grid-based approximations, enabling us to quantify the errors induced by such approximations.
Charge transport in conjugated materials: insight from quantum chemical calculations
NASA Astrophysics Data System (ADS)
Beljonne, David; Cornil, J. P.; Calbert, J. P.; Bredas, Jean-Luc
2001-06-01
The electronic structure of neutral and singly charged conjugated molecular clusters is investigated by means of quantum-chemical calculations. We first assess the influence of interchain interactions on the nature of the singly charged species (polarons) in organic conjugated polymers. In a two- chain model aggregate, the polaron is found to be delocalized over the two conjugated chains for short interchain separation. Such a delocalization strongly affects the geometric and electronic relaxation phenomena induced by charge injection, which in turn lead to a dramatic spectral redistribution of the linear absorption cross section. We then consider pentacene clusters built from the experimental crystal structure and compute the HOMO and LUMO bandwidths, which are decisive parameters for charge transport in the limiting case of band-like motion (i.e., complete delocalization of the excess charge over a large number of interacting molecules). Very large bandwidths are obtained, in agreement with the remarkable electron and hole charge-carrier mobilities reported recently for ultrahigh purity pentacene single crystals.
Microcomputer Calculation of Theoretical Pre-Exponential Factors for Bimolecular Reactions.
ERIC Educational Resources Information Center
Venugopalan, Mundiyath
1991-01-01
Described is the application of microcomputers to predict reaction rates based on theoretical atomic and molecular properties taught in undergraduate physical chemistry. Listed is the BASIC program which computes the partition functions for any specific bimolecular reactants. These functions are then used to calculate the pre-exponential factor of…
Technology Transfer Automated Retrieval System (TEKTRAN)
Time-dependent density functional theory (TDDFT) was employed for theoretical calculation of electronic circular dichroism (ECD) of a hexahydroxydiphenoyl (HHDP)-containing flavanone glycoside, mattucinol-7-O-[4'',6''-O-(aS)-hexahydroxydiphenoyl]-ß-d-glucopyranoside (2). It identified the roles of t...
Efficiency and power loss in d. c. chopper circuits. [Theoretical calculation
Beck, M.O.
1981-01-01
The object of this paper was to investigate the efficiency and source of power losses of various classes of dc chopper circuits. The study involved a theoretical calculation of the power losses, supported by a considerable amount of practical work on full power-rated traction motor test bed. 3 refs.
Invariant-theoretic method for calculating Clebsch-Gordan coefficients for space groups
Aizenberg, A.Ya.; Gufan, Yu.M.
1995-03-01
A new invariant-theoretic method to directly calculate Clebsch-Gordan coefficients for space and point groups representations is proposed. The method is exemplified with the space groups O{sub h}{sup 5} and D{sub 6h}{sup 1}. 34 refs.
Heats of Segregation of BCC Binaries from ab Initio and Quantum Approximate Calculations
NASA Technical Reports Server (NTRS)
Good, Brian S.
2004-01-01
We compare dilute-limit heats of segregation for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent LMTO-based parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation, while the ab initio calculations are performed without relaxation. Results are discussed within the context of a segregation model driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.
Theoretical basis for two-phase disengagement and vapor fraction calculations
Sheppard, C.M.
1995-12-31
This paper reviews the theoretical basis for disengagement calculations. That is the assumptions of pseudo-steady-state, volumetric gas production and applicable drift-flux correlations. Using these an axial void fraction profile can be calculated. The use of graphical, analytical, and simplified-equation-based correlations for vertical cylinders, horizontal cylinders, and spheres are covered. Before disengagement occurs the vent stream void fraction can be estimated using the coupling equation. The implications of the converging cross-sectional area of horizontal cylinders and spheres are discussed for both disengagement and two-phase flow calculations. 22 refs., 9 figs., 5 tabs.
Theoretical methods for the calculation of Bragg curves and 3D distributions of proton beams
NASA Astrophysics Data System (ADS)
Ulmer, W.; Matsinos, E.
2010-12-01
The well-known Bragg-Kleeman rule RCSDA = A ṡ E has become a pioneer work in radiation physics of charged particles and is still a useful tool to estimate the range RCSDA of approximately monoenergetic protons with initial energy E0 in a homogeneous medium. The rule is based on the continuous-slowing-down-approximation (CSDA). It results from a generalized (nonrelativistic) Langevin equation and a modification of the phenomenological friction term. The complete integration of this equation provides information about the residual energy E(z) and dE(z)/dz at each position z(0 ≦ z ≦ RCSDA). A relativistic extension of the generalized Langevin equation yields the formula RCSDA = A ṡ (E0 + E/2M ṡ c2)p. The initial energy of therapeutic protons satisfies E0 ≪ 2M ṡ c2(M ṡ c2 = 938.276 MeV), which enables us to consider the relativistic contributions as correction terms. Besides this phenomenological starting-point, a complete integration of the Bethe-Bloch equation (BBE) is developed, which also provides the determination of RCSDA, E(z) and dE(z)/dz and uses only those parameters given by the BBE itself (i.e., without further empirical parameters like modification of friction). The results obtained in the context of the aforementioned methods are compared with Monte-Carlo calculations (GEANT4); this Monte-Carlo code is also used with regard to further topics such as lateral scatter, nuclear interactions, and buildup effects. In the framework of the CSDA, the energy transfer from protons to environmental atomic electrons does not account for local fluctuations. Based on statistical quantum mechanics, an analysis of the Gaussian convolution and the Landau-Vavilov distribution function is carried out to describe these fluctuations. The Landau tail is derived as Hermite polynomial corrections of a Gaussian convolution. It is experimentally confirmed that proton Bragg curves with E0 ≧ 120 MeV show a buildup, which increases with the proton energy. This
Theoretical analysis of on-chip linear quantum optical information processing networks
NASA Astrophysics Data System (ADS)
Hach, Edwin E.; Preble, Stefan F.; Steidle, Jeffrey A.
2015-05-01
We present a quantum optical analysis of waveguides directionally coupled to ring resonators, an architecture realizable using silicon nanophotonics. The innate scalability of the silicon platform allows for the possibility of "on-chip" quantum computation and information processing. In this paper, we briefly review a comprehensive method for analyzing the quantum mechanical output of such a network for an arbitrary input state of the quantized, traveling electromagnetic field in the continuous wave (cw) limit. Specifically, we briefly review a recent theoretical result identifying a particular device topology that yields, via Passive Quantum Optical Feedback (PQOF), dramatic and unexpected enhancements of the Hong-Ou-Mandel Effect, an effect central to the operation of many quantum information processing systems. Next, we extend the analysis to our proposal for a scalable, on-chip realization of the Nonlinear Sign (NS) shifter essential for implementation of the Knill-Laflamme-Milburn (KLM) protocol for Linear Optical Quantum Computing (LOQC). Finally, we discuss generalizations to arbitrary networks of directionally coupled ring resonators along with possible applications is the areas of quantum metrology and sensitive photon detection.
Hyperon Puzzle: Hints from Quantum Monte Carlo Calculations
NASA Astrophysics Data System (ADS)
Lonardoni, Diego; Lovato, Alessandro; Gandolfi, Stefano; Pederiva, Francesco
2015-03-01
The onset of hyperons in the core of neutron stars and the consequent softening of the equation of state have been questioned for a long time. Controversial theoretical predictions and recent astrophysical observations of neutron stars are the grounds for the so-called hyperon puzzle. We calculate the equation of state and the neutron star mass-radius relation of an infinite systems of neutrons and Λ particles by using the auxiliary field diffusion Monte Carlo algorithm. We find that the three-body hyperon-nucleon interaction plays a fundamental role in the softening of the equation of state and for the consequent reduction of the predicted maximum mass. We have considered two different models of three-body force that successfully describe the binding energy of medium mass hypernuclei. Our results indicate that they give dramatically different results on the maximum mass of neutron stars, not necessarily incompatible with the recent observation of very massive neutron stars. We conclude that stronger constraints on the hyperon-neutron force are necessary in order to properly assess the role of hyperons in neutron stars.
Hyperon puzzle: hints from quantum Monte Carlo calculations.
Lonardoni, Diego; Lovato, Alessandro; Gandolfi, Stefano; Pederiva, Francesco
2015-03-01
The onset of hyperons in the core of neutron stars and the consequent softening of the equation of state have been questioned for a long time. Controversial theoretical predictions and recent astrophysical observations of neutron stars are the grounds for the so-called hyperon puzzle. We calculate the equation of state and the neutron star mass-radius relation of an infinite systems of neutrons and Λ particles by using the auxiliary field diffusion Monte Carlo algorithm. We find that the three-body hyperon-nucleon interaction plays a fundamental role in the softening of the equation of state and for the consequent reduction of the predicted maximum mass. We have considered two different models of three-body force that successfully describe the binding energy of medium mass hypernuclei. Our results indicate that they give dramatically different results on the maximum mass of neutron stars, not necessarily incompatible with the recent observation of very massive neutron stars. We conclude that stronger constraints on the hyperon-neutron force are necessary in order to properly assess the role of hyperons in neutron stars. PMID:25793808
NASA Astrophysics Data System (ADS)
Santos, Marcela F.; Braga, Carolyne B.; Rozada, Thiago C.; Basso, Ernani A.; Fiorin, Barbara C.
2014-08-01
The geometries involved in the conformational equilibria of 2,2-dichloro-N-cyclohexyl-N-methyl-acetamide (DCCMA) and 2-chloro-N,N-dicyclohexylacetamide (CDCA) were investigated. Theoretical calculations at the B3LYP/cc-pVDZ level of theory showed that gauche forms (Clsbnd Csbnd Cdbnd O) are the most stable and the predominant conformers in isolated phase. Both compounds had the conformational behavior in solvents of different polarities estimated from theoretical calculations with the PCM (Polarizable Continuum Model), at the same level of theory, using infrared data from deconvolution of the carbonyl absorption bands and 13C NMR spectra. Their IR spectra showed two carbonyl absorptions and that the conformer with the highest dipole moment had its population increased when the most polar solvents were used, in accordance with the theoretical calculation in solution. 1JCH coupling constants were obtained from their NMR spectra, and revealed that there was population variation of conformers with solvent exchange. Experimental data (NMR and IR) as well as calculations including the solvent effects followed the same trend.
Heats of Segregation of BCC Binaries from Ab Initio and Quantum Approximate Calculations
NASA Technical Reports Server (NTRS)
Good, Brian S.
2003-01-01
We compare dilute-limit segregation energies for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation. Results are discussed within the context of segregation models driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.
NASA Astrophysics Data System (ADS)
Fedorov, V. M.
2016-05-01
Based on the astronomical ephemerides DE-406, theoretical calculations have been performed of the interannual variability of the Earth's insolation related to celestial-mechanical processes for 365 points of a tropical year in the time period from 1900 to 2050. It has been determined that the average amplitude of variations of the interannual insolation is 0.310 W/m2 (0.023% of the solar constant). The calculated variations are characterized by strict periodicity that corresponds with the length of a synodic month. Connection between the extreme values of the calculated insolation variability and syzygies has been defined. The average amplitude of the calculated variability exceeds by 1.7 times (0.01% of the solar constant) the amplitude of the interannual variability in the 11-year variation of the total Earth's insolation.
Nuclear radii calculations in various theoretical approaches for nucleus-nucleus interactions
Merino, C.; Novikov, I. S.; Shabelski, Yu.
2009-12-15
The information about sizes and nuclear density distributions in unstable (radioactive) nuclei is usually extracted from the data on interaction of radioactive nuclear beams with a nuclear target. We show that in the case of nucleus-nucleus collisions the values of the parameters depend somewhat strongly on the considered theoretical approach and on the assumption about the parametrization of the nuclear density distribution. The obtained values of root-mean-square radii (R{sub rms}) for stable nuclei with atomic weights A=12-40 vary by approximately 0.1 fm when calculated in the optical approximation, in the rigid target approximation, and using the exact expression of the Glauber theory. We present several examples of R{sub rms} radii calculations using these three theoretical approaches and compare these results with the data obtained from electron-nucleus scattering.
NASA Astrophysics Data System (ADS)
Sievänen, Elina; Toušek, Jaromír; Lunerová, Kamila; Marek, Jaromír; Jankovská, Dagmar; Dvorská, Margita; Marek, Radek
2010-08-01
In this article we present a detailed structural investigation for five homoisoflavonoids, molecules important from the pharmacological point of view. For studying the electron distribution as well as its influence on the physicochemical properties, NMR spectroscopy, X-ray diffraction, and theoretical calculations have been used. Nuclear magnetic shieldings obtained by using DFT calculations for optimized molecular geometries are correlated with the experimentally determined chemical shifts. The theoretical data are well in agreement with the experimental values. The single crystal X-ray structures of homoisoflavonoid derivatives 1, 3, and 4 have been solved. The molecular geometries and crystal packing determined by X-ray diffraction are used for characterizing the intermolecular interactions. Electron distribution is crucial for the stability of radicals and hence the antioxidant efficiency of flavonoid structures. The hydrogen bonding governs the formation of complexes of homoisoflavonoids with biological targets.
NASA Astrophysics Data System (ADS)
Tosto, Sebastiano
1997-04-01
The presentation aims to show the basic features of an "ab initio" approach to calculate the energy levels of quantum systems. The purpose of the model is not to furtherly increase the accuracy of some already existing computational method or to develop a new mathematical algorithm but rather to examine the consequences of introducing since the beginning the quantum uncertainty in the energy equations of atoms and molecules. Without any hypothesis on the state of motion of the electrons but merely concerning the number of states allowed in the phase space as a function of momentum and space uncertainty ranges, one obtains simple formulae enabling to calculate the enegy levels of multielectron atoms in a good agreement with the experimental data. The same theoretical approach has been also utilized to describe the diatomic molecules in terms of anharmonic oscillators. Also in this case, simple formulae enable to correlate dissociation energy, vibrational frequency and bond length in a good agreement with the experimental data
NASA Astrophysics Data System (ADS)
Komatsu, Yu; Umemura, Masayuki; Shoji, Mitsuo; Kayanuma, Megumi; Yabana, Kazuhiro; Shiraishi, Kenji
For detecting life from reflectance spectra on extrasolar planets, several indicators called surface biosignatures have been proposed. One of them is the vegetation red edge (VRE) which derives from surface vegetation. VRE is observed in 700-750 nm on the Earth, but there is no guarantee that exovegetation show the red edge in this wavelength. Therefore it is necessary to check the validity of current standards of VRE as the signatures. In facts, M stars (cooler than Sun) will be the main targets in future missions, it is significantly important to know on the fundamental mechanisms in photosynthetic organism such as purple bacteria which absorb longer wavelength radiation. We investigated light absorptions and excitation energy transfers (EETs) in light harvesting complexes in purple bacteria (LH2s) by using quantum dynamics simulations. In LH2, effective EET is accomplished by corporative electronic excitation of the pigments. In our theoretical model, a dipole-dipole approximation was used for the electronic interactions between pigment excitations. Quantum dynamics simulations were performed according to Liouville equation to examine the EET process. The calculated oscillator strength and the transfer time between LH2 were good agreement with the experimental values. As the system size increases, the absorption bands shifted longer and the transfer velocities became larger. When two pigments in a LHC were exchanged to another pigments with lower excitation energy, faster and intensive light collection were observed.
Ab initio quantum Monte Carlo calculations of ground-state properties of manganese's oxides
NASA Astrophysics Data System (ADS)
Sharma, Vinit; Krogel, Jaron T.; Kent, P. R. C.; Reboredo, Fernando A.
One of the critical scientific challenges of contemporary research is to obtain an accurate theoretical description of the electronic properties of strongly correlated systems such as transition metal oxides and rare-earth compounds, since state-of-art ab-initio methods based on approximate density functionals are not always sufficiently accurate. Quantum Monte Carlo (QMC) methods, which use statistical sampling to evaluate many-body wave functions, have the potential to answer this challenge. Owing to the few fundamental approximations made and the direct treatment of electron correlation, QMC methods are among the most accurate electronic structure methods available to date. We assess the accuracy of the diffusion Monte Carlo method in the case of rocksalt manganese oxide (MnO). We study the electronic properties of this strongly-correlated oxide, which has been identified as a suitable candidate for many applications ranging from catalysts to electronic devices. ``This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.'' Ab initio quantum Monte Carlo calculations of ground-state properties of manganese's oxides.
Theoretical calculation of plane wave speeds for alkali metals under pressure.
NASA Technical Reports Server (NTRS)
Eftis, J.; Macdonald, D. E.; Arkilic, G. M.
1971-01-01
Theoretical calculations of the variation with pressure of small amplitude plane wave speeds are performed for sodium and potassium at zero temperature. The results obtained for wave speeds associated with volume dependent second-order elastic coefficients show better agreement with experimental data than for wave speeds associated with shear dependent coefficients. This result is believed to be due to omission of the band structure correction to the strain energy density.
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms
Song, Lei; Avoird, Ad van der; Karman, Tijs; Groenenboom, Gerrit C.; Balakrishnan, N.
2015-05-28
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 − 30 to v′ = 0, j′ are calculated using the close coupling method for collision energies between 0.1 and 15 000 cm{sup −1} based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ≥ 3 to v′ = 0, j′ are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H–CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H–CO collisions in astrophysical models.
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms
NASA Astrophysics Data System (ADS)
Song, Lei; Balakrishnan, N.; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C.
2015-05-01
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 - 30 to v' = 0, j' are calculated using the close coupling method for collision energies between 0.1 and 15 000 cm-1 based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ≥ 3 to v' = 0, j' are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H-CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H-CO collisions in astrophysical models.
NASA Astrophysics Data System (ADS)
Loued, W.; Wéry, J.; Dorlando, A.; Alimi, K.
2015-02-01
In this paper, the significance of annealing, in two different atmospheres (air and vacuum), on the surface characteristics of poly (lactic acid) (PLA) films was investigated. X-ray diffraction (XRD) measurements correlated to atomic force microscopy (AFM) observations of the cast PLA films show that thermal treatment under air atmosphere is responsible for a significant increase of crystallinity with the increase of temperature. However, band gap energy of the title compound is slightly affected by annealing at different temperatures. As for the untreated PLA, the molecular geometry was optimized using density functional theory (DFT/B3LYP) method with 6-31g (d) basis set in ground state. From the optimized geometry, HOMO and LUMO energies and quantum chemical parameters were performed at B3LYP/6-31g (d). The theoretical results, applied to simulated optical spectra of the compound, were compared to the observed ones. On the basis of theoretical vibrational analyses, the thermodynamic properties were calculated at different temperatures, revealing the correlation between internal energy (U), enthalpy (H), entropy (S), Free energy (G) and temperatures.
NASA Technical Reports Server (NTRS)
Richards, P. G.; Torr, D. G.
1981-01-01
A simplified method for the evaluation of theoretical photoelectron fluxes in the upper atmosphere resulting from the solar radiation at 304 A is presented. The calculation is based on considerations of primary and cascade (secondary) photoelectron production in the two-stream model, where photoelectron transport is described by two electron streams, one moving up and one moving down, and of loss rates due to collisions with neutral gases and thermal electrons. The calculation is illustrated for the case of photoelectrons at an energy of 24.5 eV, and it is noted that the 24.5-eV photoelectron flux may be used to monitor variations in the solar 304 A flux. Theoretical calculations based on various ionization and excitation cross sections of Banks et al. (1974) are shown to be in generally good agreement with AE-E measurements taken between 200 and 235 km, however the use of more recent, larger cross sections leads to photoelectron values a factor of two smaller than observations but in agreement with previous calculations. It is concluded that a final resolution of the photoelectron problem may depend on a reevaluation of the inelastic electron collision cross sections.
NASA Astrophysics Data System (ADS)
He, C.; Liou, K. N.; Takano, Y.; Li, Q.; Yang, P.; Zhang, R.
2014-12-01
The optical properties of black carbon (BC) are significantly affected by its aging process in the atmosphere. We have built a conceptual model defining three BC aging stages, including freshly emitted BC aggregates, coating by soluble material and hygroscopic growth. We apply an improved geometric-optics surface-wave approach (Liou et al., 2011; Takano et al., 2013) to calculate the absorption and scattering properties of BC at each stage and compare the theoretical results with those obtained from laboratory experiments (Zhang et al., 2008; Khalizov et al., 2009). Preliminary results show a general agreement between calculated and measured BC absorption cross sections (bias < 10%) and scattering cross sections (bias < 30%) for BC aerosols with mobility diameters of 155, 245 and 320 nm at Stages 1 and 2, where BC is coated by sulfuric acid and its water solution, respectively. We find that the calculated scattering and absorption cross sections for fresh BC aggregates (Stage 0) with different sizes are invariably larger than experimental results partly because of the uncertainty in theoretical calculations for BC with size parameters less than 1. It appears that the uncertainty in the experiment could also contribute to the discrepancy, considering that the measuring instrument missed some scattering in certain angles (0-7° and 170-180°). Finally, we will apply the conceptual model and the single-scattering results to assess the effects of BC aging processes on direct radiative forcing using observed BC vertical profiles.
NASA Technical Reports Server (NTRS)
Zhang, Kuanshou; Xie, Changde; Peng, Kunchi
1996-01-01
The dependence of the quantum fluctuation of the output fundamental and second-harmonic waves upon cavity configuration has been numerically calculated for the intracavity frequency-doubled laser. The results might provide a direct reference for the design of squeezing system through the second-harmonic-generation.
Lundahl, Gunnel
2007-01-01
When calculating of the physical F121.1 degrees c-value by the equation F121.1 degrees C = t x 10(T-121.1/z the temperature (T), in combination with the z-value, influences the F121.1 degrees c-value exponentially. Because the z-value for spores of Geobacillus stearothermophilus often varies between 6 and 9, the biological F-value (F(Bio) will not always correspond to the F0-value based on temperature records from the sterilization process calculated with a z-value of 10, even if the calibration of both of them are correct. Consequently an error in calibration of thermocouples and difference in z-values influences the F121.1 degrees c-values logarithmically. The paper describes how results from measurements with different z-values can be compared. The first part describes the mathematics of a calculation program, which makes it easily possible to compare F0-values based on temperature records with the F(BIO)-value based on analysis of bioindicators such as glycerin-water-suspension sensors. For biological measurements, a suitable bioindicator with a high D121-value can be used (such a bioindicator can be manufactured as described in the article "A Method of Increasing Test Range and Accuracy of Bioindicators-Geobacillus stearothermophilus Spores"). By the mathematics and calculations described in this macro program it is possible to calculate for every position the theoretical temperature difference (deltaT(th)) needed to explain the difference in results between the thermocouple and the biointegrator. Since the temperature difference is a linear function and constant all over the process this value is an indication of the magnitude of an error. A graph and table from these calculations gives a picture of the run. The second part deals with product characteristics, the sterilization processes, loading patterns. Appropriate safety margins have to be chosen in the development phase of a sterilization process to achieve acceptable safety limits. Case studies are
Theoretical performance of solar cell based on mini-bands quantum dots
Aly, Abou El-Maaty M. E-mail: ashraf.nasr@gmail.com; Nasr, A. E-mail: ashraf.nasr@gmail.com
2014-03-21
The tremendous amount of research in solar energy is directed toward intermediate band solar cell for its advantages compared with the conventional solar cell. The latter has lower efficiency because the photons have lower energy than the bandgap energy and cannot excite mobile carriers from the valence band to the conduction band. On the other hand, if mini intermediate band is introduced between the valence and conduction bands, then the smaller energy photons can be used to promote charge carriers transfer to the conduction band and thereby the total current increases while maintaining a large open circuit voltage. In this article, the influence of the new band on the power conversion efficiency for structure of quantum dots intermediate band solar cell is theoretically investigated and studied. The time-independent Schrödinger equation is used to determine the optimum width and location of the intermediate band. Accordingly, achievement of a maximum efficiency by changing the width of quantum dots and barrier distances is studied. Theoretical determination of the power conversion efficiency under the two different ranges of QD width is presented. From the obtained results, the maximum power conversion efficiency is about 70.42%. It is carried out for simple cubic quantum dot crystal under fully concentrated light. It is strongly dependent on the width of quantum dots and barrier distances.
NASA Technical Reports Server (NTRS)
Avrett, E. H.
1984-01-01
Models and spectra of sunspots were studied, because they are important to energy balance and variability discussions. Sunspot observations in the ultraviolet region 140 to 168 nn was obtained by the NRL High Resolution Telescope and Spectrograph. Extensive photometric observations of sunspot umbrae and prenumbrae in 10 chanels covering the wavelength region 387 to 3800 nm were made. Cool star opacities and model atmospheres were computed. The Sun is the first testcase, both to check the opacity calculations against the observed solar spectrum, and to check the purely theoretical model calculation against the observed solar energy distribution. Line lists were finally completed for all the molecules that are important in computing statistical opacities for energy balance and for radiative rate calculations in the Sun (except perhaps for sunspots). Because many of these bands are incompletely analyzed in the laboratory, the energy levels are not well enough known to predict wavelengths accurately for spectrum synthesis and for detailed comparison with the observations.
NASA Astrophysics Data System (ADS)
McCann, Kathleen; Laane, Jaan
2008-11-01
The Raman and infrared spectra of dipicolinic acid (DPA) and dinicotinic acid (DNic) and their salts (CaDPA, Na 2DPA, and CaDNic) have been recorded and the spectra have been assigned. Ab initio and DFT calculations were carried out to predict the structures and vibrational spectra and were compared to the experimental results. Because of extensive intermolecular hydrogen bonding in the crystals of these molecules, the calculated structures and spectra for the individual molecules agree only moderately well with the experimental values. Theoretical calculations were also carried out for DPA dimers and DPA·2H 2O to better understand the intermolecular interactions. The spectra do show that DPA and its calcium salt, which are present in anthrax spores, can be distinguished from the very similar DNic and CaDNic.
Vasiltsova, Tatiana; Heintz, Andreas
2007-12-21
A recently developed statistical mechanical model for calculating Kirkwood correlation factors gK in self associating liquids and liquid mixtures has been applied for the simultaneous description of gK, the molar enthalpy of mixing HEM and the infrared absorption of monomer alcoholic species as function of the composition in alkanol + hexane and alkanol + pentane mixtures (alkanol: butan-1-ol, pentan-1-ol, hexan-1-ol, heptan-1-ol, sec-butanol, tert-butanol). The majority of parameters involved into the theory are obtained by independent quantum mechanical ab initio calculations of molecular clusters consisting of up to four alcohol molecules. As a consequence only two parameters have to be adjusted freely to each binary system, a third parameter responsible for the non specific intermolecular dispersion interaction has been adjusted within a limited range of possible values given by physical arguments. Excellent agreement between theory and experimental data of gK, HEM and IR absorbance is obtained covering the whole range of concentration including the temperature dependence of these properties without adjusting further parameters. The Kirkwood correlation factor gK turns out to be a sensitive response to peculiarities of the molecular structure of hydrogen bonded systems in the condensed liquid state. The successful application of the theoretical model opens a new way of a deeper and more reliable understanding of such liquid structures. PMID:18046469
Quantum entanglement of identical particles by standard information-theoretic notions
Lo Franco, Rosario; Compagno, Giuseppe
2016-01-01
Quantum entanglement of identical particles is essential in quantum information theory. Yet, its correct determination remains an open issue hindering the general understanding and exploitation of many-particle systems. Operator-based methods have been developed that attempt to overcome the issue. Here we introduce a state-based method which, as second quantization, does not label identical particles and presents conceptual and technical advances compared to the previous ones. It establishes the quantitative role played by arbitrary wave function overlaps, local measurements and particle nature (bosons or fermions) in assessing entanglement by notions commonly used in quantum information theory for distinguishable particles, like partial trace. Our approach furthermore shows that bringing identical particles into the same spatial location functions as an entangling gate, providing fundamental theoretical support to recent experimental observations with ultracold atoms. These results pave the way to set and interpret experiments for utilizing quantum correlations in realistic scenarios where overlap of particles can count, as in Bose-Einstein condensates, quantum dots and biological molecular aggregates. PMID:26857475
Quantum entanglement of identical particles by standard information-theoretic notions.
Lo Franco, Rosario; Compagno, Giuseppe
2016-01-01
Quantum entanglement of identical particles is essential in quantum information theory. Yet, its correct determination remains an open issue hindering the general understanding and exploitation of many-particle systems. Operator-based methods have been developed that attempt to overcome the issue. Here we introduce a state-based method which, as second quantization, does not label identical particles and presents conceptual and technical advances compared to the previous ones. It establishes the quantitative role played by arbitrary wave function overlaps, local measurements and particle nature (bosons or fermions) in assessing entanglement by notions commonly used in quantum information theory for distinguishable particles, like partial trace. Our approach furthermore shows that bringing identical particles into the same spatial location functions as an entangling gate, providing fundamental theoretical support to recent experimental observations with ultracold atoms. These results pave the way to set and interpret experiments for utilizing quantum correlations in realistic scenarios where overlap of particles can count, as in Bose-Einstein condensates, quantum dots and biological molecular aggregates. PMID:26857475
Quantum entanglement of identical particles by standard information-theoretic notions
NASA Astrophysics Data System (ADS)
Lo Franco, Rosario; Compagno, Giuseppe
2016-02-01
Quantum entanglement of identical particles is essential in quantum information theory. Yet, its correct determination remains an open issue hindering the general understanding and exploitation of many-particle systems. Operator-based methods have been developed that attempt to overcome the issue. Here we introduce a state-based method which, as second quantization, does not label identical particles and presents conceptual and technical advances compared to the previous ones. It establishes the quantitative role played by arbitrary wave function overlaps, local measurements and particle nature (bosons or fermions) in assessing entanglement by notions commonly used in quantum information theory for distinguishable particles, like partial trace. Our approach furthermore shows that bringing identical particles into the same spatial location functions as an entangling gate, providing fundamental theoretical support to recent experimental observations with ultracold atoms. These results pave the way to set and interpret experiments for utilizing quantum correlations in realistic scenarios where overlap of particles can count, as in Bose-Einstein condensates, quantum dots and biological molecular aggregates.
Aarset, Kirsten; Page, Elizabeth M; Rice, David A
2006-07-20
The structures of benzoic acid (C6H5COOH) and 2-hydroxybenzoic acid (C6H4OHCOOH) have been determined in the gas phase by electron diffraction using results from quantum chemical calculations to inform restraints used on the structural parameters. Theoretical methods (HF and MP2/6-311+G(d,p)) predict two conformers for benzoic acid, one which is 25.0 kJ mol(-1) (MP2) lower in energy than the other. In the low-energy form, the carboxyl group is coplanar with the phenyl ring and the O-H group eclipses the C=O bond. Theoretical calculations (HF and MP2/6-311+G(d,p)) carried out for 2-hydroxybenzoic acid gave evidence for seven stable conformers but one low-energy form (11.7 kJ mol(-1) lower in energy (MP2)) which again has the carboxyl group coplanar with the phenyl ring, the O-H of the carboxyl group eclipsing the C=O bond and the C=O of the carboxyl group oriented toward the O-H group of the phenyl ring. The effects of internal hydrogen bonding in 2-hydroxybenzoic acid can be clearly observed by comparison of pertinent structural parameters between the two compounds. These differences for 2-hydroxybenzoic acid include a shorter exocyclic C-C bond, a lengthening of the ring C-C bond between the substituents, and a shortening of the carboxylic single C-O bond. PMID:16836466
NASA Astrophysics Data System (ADS)
Latgé, A.; Porras-Montenegro, N.; de Dios-Leyva, M.; Oliveira, L. E.
1997-05-01
The acceptor-related photoluminescence of a GaAs-(Ga,Al)As superlattice, under the influence of a magnetic field applied parallel to the interfaces, is theoretically studied following a variational procedure within the effective-mass approximation. Electron and hole magnetic Landau levels and envelope wave functions were obtained by an expansion in terms of sine functions, whereas for the impurity levels the envelope functions were taken as products of sine and hydrogenic-like variational functions. Impurity binding energies and wave functions are obtained for acceptors at a general position in the superlattice and for different in-plane magnetic fields. Theoretical results corresponding to transitions from the conduction subband to states of acceptors (miniband-to-acceptor e-A0 transitions) at the edge and center positions of the GaAs quantum well compare well with available experimental data by Skromme et al. [Phys. Rev. Lett. 65, 2050 (1990)] on the magnetic-field dependence of the photoluminescence peak position of conduction miniband-to-acceptor transitions for different temperatures and values of the superlattice period.
Quantum chemical calculation of the equilibrium structures of small metal atom clusters
NASA Technical Reports Server (NTRS)
Kahn, L. R.
1982-01-01
Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.
Theoretical calculation of the melting curve of Cu-Zr binary alloys
Gunawardana, K. G.S.H.; Wilson, S. R.; Mendelev, M. I.; Song, Xueyu
2014-11-14
Helmholtz free energies of the dominant binary crystalline solids found in the Cu-Zr system at high temperatures close to the melting curve are calculated. This theoretical approach combines fundamental measure density functional theory (applied to the hard-sphere reference system) and a perturbative approach to include the attractive interactions. The studied crystalline solids are Cu(fcc), Cu51Zr14(β), CuZr(B2), CuZr2(C11b), Zr(hcp), and Zr(bcc). The calculated Helmholtz free energies of crystalline solids are in good agreement with results from molecular-dynamics (MD) simulations. Using the same perturbation approach, the liquid phase free energies are calculated as a function of composition and temperature, from which themore » melting curve of the entire composition range of this system can be obtained. Phase diagrams are determined in this way for two leading embedded atom method potentials, and the results are compared with experimental data. Furthermore, theoretical melting temperatures are compared both with experimental values and with values obtained directly from MD simulations at several compositions.« less
Theoretical calculation of the melting curve of Cu-Zr binary alloys
Gunawardana, K. G.S.H.; Wilson, S. R.; Mendelev, M. I.; Song, Xueyu
2014-11-14
Helmholtz free energies of the dominant binary crystalline solids found in the Cu-Zr system at high temperatures close to the melting curve are calculated. This theoretical approach combines fundamental measure density functional theory (applied to the hard-sphere reference system) and a perturbative approach to include the attractive interactions. The studied crystalline solids are Cu(fcc), Cu_{51}Zr_{14}(β), CuZr(B_{2}), CuZr_{2}(C11b), Zr(hcp), and Zr(bcc). The calculated Helmholtz free energies of crystalline solids are in good agreement with results from molecular-dynamics (MD) simulations. Using the same perturbation approach, the liquid phase free energies are calculated as a function of composition and temperature, from which the melting curve of the entire composition range of this system can be obtained. Phase diagrams are determined in this way for two leading embedded atom method potentials, and the results are compared with experimental data. Furthermore, theoretical melting temperatures are compared both with experimental values and with values obtained directly from MD simulations at several compositions.
Theoretical study of the electronic structure with dipole moment calculations of barium monofluoride
NASA Astrophysics Data System (ADS)
Tohme, Samir N.; Korek, Mahmoud
2015-12-01
The potential energy curves have been investigated for the 41 lowest doublet and quartet electronic states in the 2s+1Λ± representation below 55,000 cm-1 of the molecule BaF via CASSCF and MRCI (single and double excitations with Davidson correction) calculations. Twenty-five electronic states have been studied here theoretically for the first time. The crossing and avoided crossing of 20 doublet electronic states have been studied in the region 30,000-50,000 cm-1. The harmonic frequency ωe, the internuclear distance Re, the rotational constant Be, the electronic energy with respect to the ground state Te, and the permanent and transition dipole moments have been calculated in addition to static dipole polarizability of the ground state. By using the canonical functions approach, the eigenvalue Ev, the rotational constant Bv, and the abscissas of the turning points Rmin and Rmax have been calculated for the electronic states up to the vibrational level v=98. The comparison of these values with the theoretical results available in the literature shows a very good agreement.
NASA Astrophysics Data System (ADS)
Kajiya, Daisuke; Saitow, Ken-ichi
2013-08-01
Carbonyl compounds are solutes that are highly soluble in supercritical CO2 (scCO2). Their solubility governs the efficiency of chemical reactions, and is significantly increased by changing a chromophore. To effectively use scCO2 as solvent, it is crucial to understand the high solubility of carbonyl compounds, the solvation structure, and the solute-solvent intermolecular interactions. We report Raman spectroscopic data, for three prototypical ketones dissolved in scCO2, and four theoretical analyses. The vibrational Raman spectra of the C=O stretching modes of ketones (acetone, acetophenone, and benzophenone) were measured in scCO2 along the reduced temperature Tr = T/Tc = 1.02 isotherm as a function of the reduced density ρr = ρ/ρc in the range 0.05-1.5. The peak frequencies of the C=O stretching modes shifted toward lower energies as the fluid density increased. The density dependence was analyzed by using perturbed hard-sphere theory, and the shift was decomposed into attractive and repulsive energy components. The attractive energy between the ketones and CO2 was up to nine times higher than the repulsive energy, and its magnitude increased in the following order: acetone < acetophenone < benzophenone. The Mulliken charges of the three solutes and CO2 molecules obtained by using quantum chemistry calculations described the order of the magnitude of the attractive energy and optimized the relative configuration between each solute and CO2. According to theoretical calculations for the dispersion energy, the dipole-induced-dipole interaction energy, and the frequency shift due to their interactions, the experimentally determined attractive energy differences in the three solutes were attributed to the dispersion energies that depended on a chromophore attached to the carbonyl groups. It was found that the major intermolecular interaction with the attractive shift varied from dipole-induced dipole to dispersion depending on the chromophore in the ketones in
A Calculation of Cosmological Scale from Quantum Coherence
Lindesay, J
2004-07-23
We use general arguments to examine the energy scales for which a quantum coherent description of gravitating quantum energy units is necessary. The cosmological dark energy density is expected to decouple from the Friedman-Lemaitre energy density when the Friedman-Robertson-Walker scale expansion becomes sub-luminal at R = c, at which time the usual microscopic interactions of relativistic quantum mechanics (QED, QCD, etc) open new degrees of freedom. We assume that these microscopic interactions cannot signal with superluminal exchanges, only superluminal quantum correlations. The expected gravitational vacuum energy density at that scale would be expected to freeze out due to the loss of gravitational coherence. We define the vacuum energy which generates this cosmological constant to be that of a zero temperature Bose condensate at this gravitational de-coherence scale. We presume a universality throughout the universe in the available degrees of freedom determined by fundamental constants during its evolution. Examining the reverse evolution of the universe from the present, long before reaching Planck scale dynamics one expects major modifications from the de-coherent thermal equations of state, suggesting that the pre-coherent phase has global coherence properties. Since the arguments presented involve primarily counting of degrees of freedom, we expect the statistical equilibrium states of causally disconnected regions of space to be independently identical. Thus, there is no horizon problem associated with the lack of causal influences between spatially separated regions in this approach. The scale of the amplitude of fluctuations produced during de-coherence of cosmological vacuum energy are found to evolve to values consistent with those observed in cosmic microwave background radiation and galactic clustering.
Experimental investigation and theoretical calculation for 3He induced nuclear reactions on vanadium
NASA Astrophysics Data System (ADS)
Ali, B. M.; Al-Abyad, M.; Seddik, U.; El-Kameesy, S. U.; Ditrói, F.; Takács, S.; Tárkányi, F.
2016-04-01
Using stacked-foil activation technique and gamma-ray spectrometry, excitation functions for 3He induced nuclear reactions on natV were measured. Cross-sections for natV(3He, xn)52m,gMn and natV(3He, pxn)51Cr nuclear reactions were measured up to 27 MeV utilizing the MGC-20E cyclotron of ATOMKI. The measurements establish for the first time consistent excitation curves. Comparisons with results for values derived from different theoretical codes were included. Integral yield were calculated.
NASA Technical Reports Server (NTRS)
Brainerd, J. J.; Petrosian, V.
1987-01-01
Calculations are performed numerically and analytically of synchrotron spectra for thermal and power-law electron distributions using the single-particle synchrotron power spectrum derived from quantum electrodynamics. It is found that the photon energy at which quantum effects appear is proportional to temperature and independent of field strength for thermal spectra; quantum effects introduce an exponential roll-off away from the classical spectra. For power law spectra, the photon energy at which quantum effects appear is inversely proportional to the magnetic field strength; quantum effects produce a steeper power law than is found classically. The results are compared with spectra derived from the classical power spectrum with an energy cutoff ensuring conservation of energy. It is found that an energy cutoff is generally an inadequate approximation of quantum effects for low photon energies and for thermal spectra, but gives reasonable results for high-energy emission from power-law electron distributions.
NASA Astrophysics Data System (ADS)
Michalska, Katarzyna; Mizera, Mikołaj; Lewandowska, Kornelia; Cielecka-Piontek, Judyta
2016-07-01
Tedizolid is the newest antibacterial agent from the oxazolidinone class. For its identification, FT-IR (2000-400 cm-1) and Raman (2000-400 cm-1) analyses were proposed. Studies of the enantiomeric purity of tedizolid were conducted based on ultraviolet-circular dichroism (UV-CD) analysis. Density functional theory (DFT) with the B3LYP hybrid functional and 6-311G(2df,2pd) basis set was used for support of the analysis of the FT-IR and Raman spectra. Theoretical methods made it possible to conduct HOMO and LUMO analysis, which was used to determine the charge transfer for two tedizolid enantiomers. Molecular electrostatic potential maps were calculated with the DFT method for both tedizolid enantiomers. The relationship between the results of ab initio calculations and knowledge about the chemical-biological properties of R- and S-tedizolid enantiomers is also discussed.
Calculation of membrane bending rigidity using field-theoretic umbrella sampling.
Smirnova, Y G; Müller, M
2015-12-28
The free-energy change of membrane shape transformations can be small, e.g., as in the case of membrane bending. Therefore, the calculation of the free-energy difference between different membrane morphologies is a challenge. Here, we discuss a computational method - field-theoretic umbrella sampling - to compute the local chemical potential of a non-equilibrium configuration and illustrate how one can apply it to study free-energy changes of membrane transformations using simulations. Specifically, the chemical potential profile of the bent membrane and the bending rigidity of membrane are calculated for a soft, coarse-grained amphiphile model and the MARTINI model of a dioleoylphosphatidylcholine (DOPC) membrane. PMID:26723640
Hoff, R.W.; Gardner, D.G.; Gardner, M.A.
1984-10-05
A technique for modeling quasiparticle excitation energies and rotational parameters in odd-odd deformed nuclei has been used to construct sets of discrete states with energy 0 to 1.5 MeV in /sup 176/Lu and /sup 236/Np. These data were used as part of the input for calculation of isomer production cross-section ratios in the /sup 175/Lu(n,..gamma..)/sup 176/Lu and /sup 237/Np(n,2n)/sup 236/Np reactions. In order to achieve agreement with experiment, it has been found necessary to include in the modeled set many rotational bands (35 to 95), which are comprised of hundreds of levels with their gamma-ray branching ratios. It is essential that enough bands be included to produce a representative selection of K quantum numbers in the de-excitation cascade. 20 refs., 3 figs., 3 tabs.
The implementation of ab initio quantum chemistry calculations on transporters.
Cooper, M D; Hillier, I H
1991-06-01
The RHF and geometry optimization sections of the ab initio quantum chemistry code, GAMESS, have been optimized for a network of parallel microprocessors, Inmos T800-20 transputers, using both indirect and direct SCF techniques. The results indicate great scope for implementation of such codes on small parallel computer systems, very high efficiencies having been achieved, particularly in the cases of direct SCF and geometry optimization with large basis sets. The work, although performed upon one particular parallel system, the Meiko Computing Surface, is applicable to a wide range of parallel systems with both shared and distributed memory. PMID:1919615
Synthesis, characterization, optical properties and theoretical calculations of 6-fluoro coumarin
NASA Astrophysics Data System (ADS)
Bai, Yihui; Du, Jinyan; Weng, Xuexiang
6-Fluoro coumarin is synthesized and characterized by 1H NMR and 13C NMR. The optical properties of the title compound are investigated by UV-vis absorption and fluorescence emission spectra, the results show the title compound can absorb UV-vis light at 319, 269 and 215 nm, moreover it exhibits blue-purple fluorescence emission at 416 nm. Theoretical studies on molecular structure, infrared spectra (IR), nuclear magnetic resonance (1H NMR, 13C NMR) chemical shifts, UV-vis absorption and fluorescence emission of the synthesized compound have been worked out. Most chemical calculations were performed by density functional theory (DFT) method at the B3LYP/6-311G(d,p) level (NMR at B3LYP/Aug-CC-Pvdz level) using Gaussian 09 program. The compared results reveal that the scaled theoretical vibrational frequencies are in good accordance with the observed spectra; computational chemical shifts are consistent with the experimental values in most parts, except for some minor deviations; the UV-vis absorption calculated matches the experimental one very well, and the fluorescence emission spectrum is in good agreement with the experimental one when the solute-solvent hydrogen-bonding interaction is considered. These good coincidences prove that the computational methods selected can be used to predict these properties of other similar materials where it is difficult to arrive at experimental results.
Investigation on the Gas-Phase Decomposition of Trichlorfon by GC-MS and Theoretical Calculation
Jiang, Kezhi; Zhang, Ningwen; Zhang, Hu; Wang, Jianmei; Qian, Mingrong
2015-01-01
The gas phase pyrolysis of trichlorfon was investigated by the on-line gas chromatography – mass spectrometry (GC-MS) pyrolysis and theoretical calculations. Two reaction channels were proposed in the pyrolytic reaction, by analyzing the detected pyrolytic products in the total ion chromatography, including 2,2,2-trichloroacetaldehyde, dimethyl phosphite, and dichlorvos. Theoretical calculations showed that there is an intramolecular hydrogen bond between the hydroxyl group and the phosphate O atom in trichlorfon, through which the hydroxyl H atom can be easily transferred to phosphate O atom to trigger two pyrolytic channels. In path-a, migration of H atom results in direct decomposition of trichlorfon to give 2,2,2-trichloroacetaldehyde and dimethyl phosphite in one step. In path-b, migration of H atom in trichlorfon is combined with formation of the O-P bond to give an intermediate, followed by HCl elimination to afford dichlorvos. Path-a is kinetically more favorable than path-b, which is consistent with the GC-MS results. PMID:25856549
Plimak, L.I.; Fleischhauer, M.; Olsen, M.K.; Collett, M.J.
2003-01-01
We present an introduction to phase-space techniques (PST) based on a quantum-field-theoretical (QFT) approach. In addition to bridging the gap between PST and QFT, our approach results in a number of generalizations of the PST. First, for problems where the usual PST do not result in a genuine Fokker-Planck equation (even after phase-space doubling) and hence fail to produce a stochastic differential equation (SDE), we show how the system in question may be approximated via stochastic difference equations (S{delta}E). Second, we show that introducing sources into the SDE's (or S{delta}E's) generalizes them to a full quantum nonlinear stochastic response problem (thus generalizing Kubo's linear reaction theory to a quantum nonlinear stochastic response theory). Third, we establish general relations linking quantum response properties of the system in question to averages of operator products ordered in a way different from time normal. This extends PST to a much wider assemblage of operator products than are usually considered in phase-space approaches. In all cases, our approach yields a very simple and straightforward way of deriving stochastic equations in phase space.
Quantum chemical calculations for polymers and organic compounds
NASA Technical Reports Server (NTRS)
Lopez, J.; Yang, C.
1982-01-01
The relativistic effects of the orbiting electrons on a model compound were calculated. The computational method used was based on 'Modified Neglect of Differential Overlap' (MNDO). The compound tetracyanoplatinate was used since empirical measurement and calculations along "classical" lines had yielded many known properties. The purpose was to show that for large molecules relativity effects could not be ignored and that these effects could be calculated and yield data in closer agreement to empirical measurements. Both the energy band structure and molecular orbitals are depicted.
Miao, Qingyuan; Zhou, Qunjie; Cui, Jun; He, Ping-An; Huang, Dexiu
2014-12-29
Characteristics of polarization insensitivity of carrier-induced refractive index change of 1.55 μm tensile-strained multiple quantum well (MQW) are theoretically investigated. A comprehensive MQW model is proposed to effectively extend the application range of previous models. The model considers the temperature variation as well as the nonuniform distribution of injected carrier in MQW. Tensile-strained MQW is expected to achieve polarization insensitivity of carrier-induced refractive index change over a wide wavelength range as temperature varies from 0°C to 40°C, while the magnitude of refractive index change keeps a large value (more than 3 × 10^{-3}). And that the polarization insensitivity of refractive index change can maintain for a wide range of carrier concentration. Multiple quantum well with different material and structure parameters is anticipated to have the similar polarization insensitivity of refractive index change, which shows the design flexibility. PMID:25607157
Morales, Giovanni; Martínez, Ramiro
2009-07-30
This research's main goals were to analyze ketene dimers' relative stability and expand group additivity value (GAV) methodology for estimating the thermochemical properties of high-weight ketene polymers (up to tetramers). The CBS-Q multilevel procedure and statistical thermodynamics were used for calculating the thermochemical properties of 20 cyclic structures, such as diketenes, cyclobutane-1,3-diones, cyclobut-2-enones and pyran-4-ones, as well as 57 acyclic base compounds organized into five groups. According to theoretical heat of formation predictions, diketene was found to be thermodynamically favored over cyclobutane-1,3-dione and its enol-tautomeric form (3-hydroxycyclobut-2-enone). This result did not agree with old combustion experiments. 3-Hydroxycyclobut-2-enone was found to be the least stable dimer and its reported experimental detection in solution may have been due to solvent effects. Substituted diketenes had lower stability than substituted cyclobutane-1,3-diones with an increased number of methyl substituents, suggesting that cyclobutane-1,3-dione type dimers are the major products because of thermodynamic control of alkylketene dimerization. Missing GAVs for the ketene dimers and related structures were calculated through linear regression on the 57 acyclic base compounds. Corrections for non next neighbor interactions (such as gauche, eclipses, and internal hydrogen bond) were needed for obtaining a highly accurate and precise regression model. To the best of our knowledge, the hydrogen bond correction for GAV methodology is the first reported in the literature; this correction was correlated to MP2/6-31Gdagger and HF/6-31Gdagger derived geometries to facilitate its application. GAVs assessed by the linear regression model were able to reproduce acyclic compounds' theoretical thermochemical properties and experimental heat of formation for acetylacetone. Ring formation and substituent position corrections were calculated by consecutively
NASA Astrophysics Data System (ADS)
Lu, Hua; Zhang, Shushu; Liu, Hanzhuang; Wang, Yanwei; Shen, Zhen; Liu, Chungen; You, Xiaozeng
2009-12-01
A boron-dipyrromethene (BODIPY)-based fluorescence probe with a N,N'-(pyridine-2, 6-diylbis(methylene))-dianiline substituent (1) has been prepared by condensation of 2,6-pyridinedicarboxaldehyde with 8-(4-amino)-4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene and reduction by NaBH4. The sensing properties of compound 1 toward various metal ions are investigated via fluorometric titration in methanol, which show highly selective fluorescent turn-on response in the presence of Hg2+ over the other metal ions, such as Li+, Na+, K+, Ca2+, Mg2+, Pb2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ag+, and Mn2+. Computational approach has been carried out to investigate the mechanism why compound 1 provides different fluorescent signal for Hg2+ and other ions. Theoretic calculations of the energy levels show that the quenching of the bright green fluorescence of boradiazaindacene fluorophore is due to the reductive photoinduced electron transfer (PET) from the aniline subunit to the excited state of BODIPY fluorophore. In metal complexes, the frontier molecular orbital energy levels changes greatly. Binding Zn2+ or Cd2+ ion leads to significant decreasing of both the HOMO and LUMO energy levels of the receptor, thus inhibit the reductive PET process, whereas an oxidative PET from the excited state fluorophore to the receptor occurs, vice versa, which also quenches the fluorescence. However, for 1-Hg2+ complex, both the reductive and oxidative PETs are prohibited; therefore, strong fluorescence emission from the fluorophore can be observed experimentally. The agreement of the experimental results and theoretic calculations suggests that our calculation method can be applicable as guidance for the design of new chemosensors for other metal ions.
NASA Astrophysics Data System (ADS)
Gnanasambandan, T.; Gunasekaran, S.; Seshadri, S.
2013-11-01
The complete vibrational assignment and analysis of the fundamental modes of carbimazole (CBZ) was carried out using the experimental FTIR, FT-Raman and UV-Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of CBZ have been computed using B3LYP quantum chemical calculation. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.
Bounces and the calculation of quantum tunneling effects
NASA Astrophysics Data System (ADS)
Liang, Jiu-Qing; Müller-Kirsten, H. J. W.
1992-04-01
The imaginary part of the energy of the metastable ground state for the inverted double-well potential is calculated by using the path-integral method. The tunneling process is dominated by bounces. It is shown that the evaluation of the determinant of the second variation of the action at the bounce can be avoided, and that the imaginary part of the energy results directly from characteristic properties of the bounce itself, namely, the antisymmetry of its first time derivative under time reversal. The imaginary part of the result is in exact agreement with that of the well-known WKB calculation of Bender and Wu.
NASA Astrophysics Data System (ADS)
Çakır, Bekir; Atav, Ülfet; Yakar, Yusuf; Özmen, Ayhan
2016-08-01
In this study we report a detailed theoretical investigation of the effect of an external magnetic field on the 1s-, 2p-, 3d- and 4f-energy states of a spherical quantum dot. We treat the contribution of the diamagnetic term as a perturbation and discuss the effect of the diamagnetic term on the 1s-, 2p-, 3d- and 4f-energy states. We also have calculated the Zeeman transition energies between 2p → 1s and 3d → 2p states with m = 0, ±1 and 0, ±1, ±2 as a function of dot radius and the magnetic field strength. The results show that the magnetic field, impurity charge and dot radius have a strong influence on the energy states and the Zeeman transitions. It is found that the energies of the electronic states with m < 0 addition of the diamagnetic term firstly decrease toward a minimum, and then increase with the increasing magnetic field strength. We have seen that as magnetic field intensity is adjusted, frequency of the emitted light can be changed for Zeeman transitions.
Quantum robots and quantum computers
Benioff, P.
1998-07-01
Validation of a presumably universal theory, such as quantum mechanics, requires a quantum mechanical description of systems that carry out theoretical calculations and systems that carry out experiments. The description of quantum computers is under active development. No description of systems to carry out experiments has been given. A small step in this direction is taken here by giving a description of quantum robots as mobile systems with on board quantum computers that interact with different environments. Some properties of these systems are discussed. A specific model based on the literature descriptions of quantum Turing machines is presented.
Theoretical calculations of a compound formed by Fe(+3) and tris(catechol).
Kara, İzzet; Kara, Yeşim; Öztürk Kiraz, Aslı; Mammadov, Ramazan
2015-10-01
Phenolic compounds generally have special smell, easily soluble in water, organic solvents (alcohols, esters, chloroform, ethyl acetate), in aqueous solutions of bases, colorless or colorful, crystalline and amorphous materials. Phenols form colorful complexes when they form compounds with heavy metals. In this study, the structural properties of a compound formed by catechol and Fe(+3) are investigated theoretically. The electronic and thermodynamic properties of the complex were also investigated in gas phase and organic solvents at B3LYP/6-31+G(d,p) and B3LYP/6-311++G(d,p) basis set. The formation of Fe-tris(catechol) complex compound is exothermic, and it is difficult to obtain the complex as the temperature increases. The observed and calculated FT-IR and geometric parameters spectra are in good agreement with empirical. PMID:25983060
NASA Astrophysics Data System (ADS)
da Silva, Julio Cesar A.; Ducati, Lucas C.; Rittner, Roberto
2012-05-01
NMR solvent effects and theoretical calculations showed muscarinic agonists present a large stability for their near synclinal conformations, indicating the presence of significant stabilization factors. Analysis of the results clearly indicated that this stability is not determined by the dihedral around the substituted C-C ethane bond, as stated by some authors, but a consequence of the geometry adopted in order to maximize N+/O interactions in this type of molecules. It can be assumed that acetylcholine and its muscarinic agonists exhibit their biologic activity when the positively charged nitrogen and the oxygen atoms are in the same side of the molecule within an interatomic distance ranging from 3.0 to 6.0 Å.
Rokhina, Ekaterina V; Lahtinen, Manu; Makarova, Katerina; Jegatheesan, Veeriah; Virkutyte, Jurate
2012-06-01
The nitric acid-functionalized commercial carbon nanofibers (CNFs) were comprehensively studied by instrumental (XRD, BET, SEM, TGA) and theoretical (DFT calculations) methods. The detailed surface study revealed the variation in the characteristics of functionalized CNFs, such as a decreased (up to 34%) surface area and impacted structural, electronic and chemical properties. The effects of functional groups were studied by comparison with pristine nanofibers. The results showed that the C-C bond lengths of the modified CNFs varied significantly. Chemical functionalization altered the frontier orbitals of the pristine material, and therefore altered the nature of their interactions with other substances. Moreover, the pristine and modified CNFs were tested for the removal of phenol from aqueous solutions. It was observed that surface modification tuned the adsorption capacity of carbon nanofibers (up to 0.35 mmol g(-1)), whereas original fibers did not demonstrate any adsorption capacity of phenol. PMID:22209137
Isodesmic reaction for accurate theoretical pKa calculations of amino acids and peptides.
Sastre, S; Casasnovas, R; Muñoz, F; Frau, J
2016-04-20
Theoretical and quantitative prediction of pKa values at low computational cost is a current challenge in computational chemistry. We report that the isodesmic reaction scheme provides semi-quantitative predictions (i.e. mean absolute errors of 0.5-1.0 pKa unit) for the pKa1 (α-carboxyl), pKa2 (α-amino) and pKa3 (sidechain groups) of a broad set of amino acids and peptides. This method fills the gaps of thermodynamic cycles for the computational pKa calculation of molecules that are unstable in the gas phase or undergo proton transfer reactions or large conformational changes from solution to the gas phase. We also report the key criteria to choose a reference species to make accurate predictions. This method is computationally inexpensive and makes use of standard density functional theory (DFT) and continuum solvent models. It is also conceptually simple and easy to use for researchers not specialized in theoretical chemistry methods. PMID:27052591
Machine learning of parameters for accurate semiempirical quantum chemical calculations
Dral, Pavlo O.; von Lilienfeld, O. Anatole; Thiel, Walter
2015-04-14
We investigate possible improvements in the accuracy of semiempirical quantum chemistry (SQC) methods through the use of machine learning (ML) models for the parameters. For a given class of compounds, ML techniques require sufficiently large training sets to develop ML models that can be used for adapting SQC parameters to reflect changes in molecular composition and geometry. The ML-SQC approach allows the automatic tuning of SQC parameters for individual molecules, thereby improving the accuracy without deteriorating transferability to molecules with molecular descriptors very different from those in the training set. The performance of this approach is demonstrated for the semiempiricalmore » OM2 method using a set of 6095 constitutional isomers C7H10O2, for which accurate ab initio atomization enthalpies are available. The ML-OM2 results show improved average accuracy and a much reduced error range compared with those of standard OM2 results, with mean absolute errors in atomization enthalpies dropping from 6.3 to 1.7 kcal/mol. They are also found to be superior to the results from specific OM2 reparameterizations (rOM2) for the same set of isomers. The ML-SQC approach thus holds promise for fast and reasonably accurate high-throughput screening of materials and molecules.« less
Machine learning of parameters for accurate semiempirical quantum chemical calculations
Dral, Pavlo O.; von Lilienfeld, O. Anatole; Thiel, Walter
2015-04-14
We investigate possible improvements in the accuracy of semiempirical quantum chemistry (SQC) methods through the use of machine learning (ML) models for the parameters. For a given class of compounds, ML techniques require sufficiently large training sets to develop ML models that can be used for adapting SQC parameters to reflect changes in molecular composition and geometry. The ML-SQC approach allows the automatic tuning of SQC parameters for individual molecules, thereby improving the accuracy without deteriorating transferability to molecules with molecular descriptors very different from those in the training set. The performance of this approach is demonstrated for the semiempirical OM2 method using a set of 6095 constitutional isomers C_{7}H_{10}O_{2}, for which accurate ab initio atomization enthalpies are available. The ML-OM2 results show improved average accuracy and a much reduced error range compared with those of standard OM2 results, with mean absolute errors in atomization enthalpies dropping from 6.3 to 1.7 kcal/mol. They are also found to be superior to the results from specific OM2 reparameterizations (rOM2) for the same set of isomers. The ML-SQC approach thus holds promise for fast and reasonably accurate high-throughput screening of materials and molecules.
Quantum Monte Carlo calculations of neutron-alpha scattering.
Nollett, K. M.; Pieper, S. C.; Wiringa, R. B.; Carlson, J.; Hale, G. M.; Physics
2007-07-13
We describe a new method to treat low-energy scattering problems in few-nucleon systems, and we apply it to the five-body case of neutron-alpha scattering. The method allows precise calculations of low-lying resonances and their widths. We find that a good three-nucleon interaction is crucial to obtain an accurate description of neutron-alpha scattering.
Quantum Monte Carlo Calculations of Neutron-{alpha} Scattering
Nollett, Kenneth M.; Pieper, Steven C.; Wiringa, R. B.; Carlson, J.; Hale, G. M.
2007-07-13
We describe a new method to treat low-energy scattering problems in few-nucleon systems, and we apply it to the five-body case of neutron-alpha scattering. The method allows precise calculations of low-lying resonances and their widths. We find that a good three-nucleon interaction is crucial to obtain an accurate description of neutron-alpha scattering.
A 3-D Theoretical Model for Calculating Plasma Effects in Germanium Detectors
NASA Astrophysics Data System (ADS)
Wei, Wenzhao; Liu, Jing; Mei, Dongming; Cubed Collaboration
2015-04-01
In the detection of WIMP-induced nuclear recoil with Ge detectors, the main background source is the electron recoil produced by natural radioactivity. The capability of discriminating nuclear recoil (n) from electron recoil (γ) is crucial to WIMP searches. Digital pulse shape analysis is an encouraging approach to the discrimination of nuclear recoil from electron recoil since nucleus is much heavier than electron and heavier particle generates ionization more densely along its path, which forms a plasma-like cloud of charge that shields the interior from the influence of the electric field. The time needed for total disintegration of this plasma region is called plasma time. The plasma time depends on the initial density and radius of the plasma-like cloud, diffusion constant for charge carriers, and the strength of electric field. In this work, we developed a 3-D theoretical model for calculating the plasma time in Ge detectors. Using this model, we calculated the plasma time for both nuclear recoils and electron recoils to study the possibility for Ge detectors to realize n/ γ discrimination and improve detector sensitivity in detecting low-mass WIMPs. This work is supported by NSF in part by the NSF PHY-0758120, DOE Grant DE-FG02-10ER46709, and the State of South Dakota.
Theoretical study of light-emission properties of amorphous silicon quantum dots
NASA Astrophysics Data System (ADS)
Nishio, Kengo; Kōga, Junichiro; Yamaguchi, Toshio; Yonezawa, Fumiko
2003-05-01
In order to clarify the mechanism of the photoluminescence (PL) from amorphous silicon quantum dots (a-Si QDs), we calculate, in the tight-binding scheme, the emission spectra and the radiative recombination rate P of the direct band-to-band recombination process. For a-Si QDs smaller than 2.4 nm in diameter, our calculations beautifully reproduce the peak energy EPL of the experimental PL peak [N.-M. Park et al., Phys. Rev. Lett. 86, 1355 (2001)]. Our analysis also show that (i) the emission energy can be tuned into the visible range of light from red to blue by controlling the sizes of a-Si QDs, and that (ii) P calculated for a-Si QDs is higher by two to three orders of magnitude than that for crystalline Si QDs. From these results, we assert that a-Si QDs are promising candidates for visible, tunable, and high-performance light-emitting devices.
Kotani, Teruhisa; Birner, Stefan; Lugli, Paolo; Hamaguchi, Chihiro
2014-04-14
We present theoretical investigations of miniband structures and optical properties of InAs/GaAs one-dimensional quantum dot superlattices (1D-QDSLs). The calculation is based on the multi-band k·p theory, including the conduction and valence band mixing effects, the strain effect, and the piezoelectric effect; all three effects have periodic boundary conditions. We find that both the electronic and optical properties of the 1D-QDSLs show unique states which are different from those of well known single quantum dots (QDs) or quantum wires. We predict that the optical absorption spectra of the 1D-QDSLs strongly depend on the inter-dot spacing because of the inter-dot carrier coupling and changing strain states, which strongly influence the conduction and valence band potentials. The inter-miniband transitions form the absorption bands. Those absorption bands can be tuned from almost continuous (closely stacked QD case) to spike-like shape (almost isolated QD case) by changing the inter-dot spacing. The polarization of the lowest absorption peak for the 1D-QDSLs changes from being parallel to the stacking direction to being perpendicular to the stacking direction as the inter-dot spacing increases. In the case of closely stacked QDs, in-plane anisotropy, especially [110] and [11{sup ¯}0] directions also depend on the inter-dot spacing. Our findings and predictions will provide an additional degree of freedom for the design of QD-based optoelectronic devices.
NASA Astrophysics Data System (ADS)
Predoi-Cross, Adriana; Holladay, Christopher; Heung, Henry; Bouanich, Jean-Pierre; Mellau, Georg Ch.; Keller, Reimund; Hurtmans, Daniel R.
2008-09-01
We report measurements for N 2-broadening, pressure-shift and line mixing coefficients for 55 oxygen transitions in the A-band retrieved using a multispectrum fitting technique. Nineteen laboratory absorption spectra were recorded at 0.02 cm -1 resolution using a multi-pass absorption cell with path length of 1636.9 cm and the IFS 120 Fourier transform spectrometer located at Justus-Liebig-University in Giessen, Germany. The total sample pressures ranged from 8.8 to 3004.5 Torr with oxygen volume mixing ratios in nitrogen ranging between 0.057 and 0.62. An Exponential Power Gap (EPG) scaling law was used to calculate the N 2-broadening and N 2-line mixing coefficients. The line broadening and shift coefficients for the A-band of oxygen self-perturbed and perturbed by N 2 are modeled using semiclassical calculations based on the Robert-Bonamy formalism and two intermolecular potentials. These potentials involve electrostatic contributions including the hexadecapole moment of the molecules and (a) a simple dispersion contribution with one adjustable parameter to fit the broadening coefficients or (b) the atom-atom Lennard-Jones model without such adjustable parameters. The first potential leads to very weak broadening coefficients for high J transitions whereas the second potential gives much more improved results at medium and large J values, in reasonable agreement with the experimental data. For the line shifts which mainly arise in our calculation from the electronic state dependence of the isotropic potential, their general trends with increasing J values can be well predicted, especially from the first potential. From the theoretical results, we have derived air-broadening and air-induced shift coefficients with an agreement comparable to that obtained for O 2-O 2 and O 2-N 2.
Duan, Yuhua
2012-11-02
Since current technologies for capturing CO{sub 2} to fight global climate change are still too energy intensive, there is a critical need for development of new materials that can capture CO{sub 2} reversibly with acceptable energy costs. Accordingly, solid sorbents have been proposed to be used for CO{sub 2} capture applications through a reversible chemical transformation. By combining thermodynamic database mining with first principles density functional theory and phonon lattice dynamics calculations, a theoretical screening methodology to identify the most promising CO{sub 2} sorbent candidates from the vast array of possible solid materials has been proposed and validated. The calculated thermodynamic properties of different classes of solid materials versus temperature and pressure changes were further used to evaluate the equilibrium properties for the CO{sub 2} adsorption/desorption cycles. According to the requirements imposed by the pre- and post- combustion technologies and based on our calculated thermodynamic properties for the CO{sub 2} capture reactions by the solids of interest, we were able to screen only those solid materials for which lower capture energy costs are expected at the desired pressure and temperature conditions. Only those selected CO{sub 2} sorbent candidates were further considered for experimental validations. The ab initio thermodynamic technique has the advantage of identifying thermodynamic properties of CO{sub 2} capture reactions without any experimental input beyond crystallographic structural information of the solid phases involved. Such methodology not only can be used to search for good candidates from existing database of solid materials, but also can provide some guidelines for synthesis new materials. In this presentation, we first introduce our screening methodology and the results on a testing set of solids with known thermodynamic properties to validate our methodology. Then, by applying our computational method
Quantum Monte Carlo calculation of the properties of atomic carbon and diamond
Fahy, S.; Wang, X.W.; Louie, S.G.
1988-06-01
A new method of calculating total energies of solids using non-local pseudopotentials in conjunction with the variational quantum Monte Carlo approach is presented. By using pseudopotentials, the large fluctuations of the energies in the core region of the atoms which occur in quantum Monte Carlo all-electron schemes are avoided. The method is applied to calculate the cohesive energy and structural properties of diamond and the first ionization energy and electron affinity of the carbon atom. Results are in excellent agreement with experiment. 8 refs., 1 fig., 2 tabs.
Quantum Monte Carlo calculations of neutron and nuclear matter
NASA Astrophysics Data System (ADS)
Gandolfi, Stefano
2014-09-01
Recent advances in experiments of the symmetry energy of nuclear matter and in neutron star observations yield important new insights on the equation of state of neutron matter at nuclear densities. In this regime the EOS of neutron matter plays a critical role in determining the mass-radius relationship for neutron stars. We show how microscopic calculations of neutron matter, based on realistic two- and three-nucleon forces, make clear predictions for the relation between the isospin-asymmetry energy of nuclear matter and its density dependence, and the maximum mass and radius for a neutron star. We will also discuss the recent extension of the Auxiliary Field Diffusion Monte Carlo method to study the equation of state of nuclear matter using two-body nucleon interactions. The equation of state of isospin-asymmetric nuclear matter will also be discussed.
Rice, Betsy M; Byrd, Edward F C
2016-03-01
Quantum and classical molecular dynamics simulations are used to explore whether chemical reactivity of shocked formic acid occurs at pressures greater than 15 GPa, a question arising from results of different shock compression experiments. The classical molecular dynamics simulations were performed using a quantum-based nonreactive pair additive interaction potential whereas the full resolution quantum mechanical molecular dynamics simulations allow chemical reactions. Although the shock Hugoniot curve calculated using nonreactive classical MD for formic acid is in reasonable agreement with one set of experimental results, shock Hugoniot points calculated using Born-Oppenheimer MD at 30 GPa are in agreement with the set of experimental data that suggests chemical reactivity at these elevated temperatures and pressures. Examination of atomic positions throughout the Born-Oppenheimer MD trajectories clearly indicates extensive and complex chemical reaction, chiefly involving hydrogen-atom transfer and intermolecular complexation. PMID:26654191
NASA Astrophysics Data System (ADS)
Pavlov, A. V.; Sitnov, Iu. S.
1985-10-01
Pavlov's (1984) method is used to determine the relative errors (due to errors in measuring the input parameters of the model) in theoretical calculations of the main parameters of the daytime F2-layer under quiet conditions. The parameters calculated are the height of the F2-layer maximum and the electron density.
Habegger, Maria L; Motta, Philip J; Huber, Daniel R; Dean, Mason N
2012-12-01
Evaluations of bite force, either measured directly or calculated theoretically, have been used to investigate the maximum feeding performance of a wide variety of vertebrates. However, bite force studies of fishes have focused primarily on small species due to the intractable nature of large apex predators. More massive muscles can generate higher forces and many of these fishes attain immense sizes; it is unclear how much of their biting performance is driven purely by dramatic ontogenetic increases in body size versus size-specific selection for enhanced feeding performance. In this study, we investigated biting performance and feeding biomechanics of immature and mature individuals from an ontogenetic series of an apex predator, the bull shark, Carcharhinus leucas (73-285cm total length). Theoretical bite force ranged from 36 to 2128N at the most anterior bite point, and 170 to 5914N at the most posterior bite point over the ontogenetic series. Scaling patterns differed among the two age groups investigated; immature bull shark bite force scaled with positive allometry, whereas adult bite force scaled isometrically. When the bite force of C. leucas was compared to those of 12 other cartilaginous fishes, bull sharks presented the highest mass-specific bite force, greater than that of the white shark or the great hammerhead shark. A phylogenetic independent contrast analysis of anatomical and dietary variables as determinants of bite force in these 13 species indicated that the evolution of large adult bite forces in cartilaginous fishes is linked predominantly to the evolution of large body size. Multiple regressions based on mass-specific standardized contrasts suggest that the evolution of high bite forces in Chondrichthyes is further correlated with hypertrophication of the jaw adductors, increased leverage for anterior biting, and widening of the head. Lastly, we discuss the ecological significance of positive allometry in bite force as a possible
Path integral calculation of free energies: quantum effects on the melting temperature of neon.
Ramírez, R; Herrero, C P; Antonelli, A; Hernández, E R
2008-08-14
The path integral formulation has been combined with several methods to determine free energies of quantum many-body systems, such as adiabatic switching and reversible scaling. These techniques are alternatives to the standard thermodynamic integration method. A quantum Einstein crystal is used as a model to demonstrate the accuracy and reliability of these free energy methods in quantum simulations. Our main interest focuses on the calculation of the melting temperature of Ne at ambient pressure, taking into account quantum effects in the atomic dynamics. The free energy of the solid was calculated by considering a quantum Einstein crystal as reference state, while for the liquid, the reference state was defined by the classical limit of the fluid. Our findings indicate that, while quantum effects in the melting temperature of this system are small, they still amount to about 6% of the melting temperature, and are therefore not negligible. The particle density as well as the melting enthalpy and entropy of the solid and liquid phases at coexistence is compared to results obtained in the classical limit and also to available experimental data. PMID:18715054
Quantum-Chemical Calculation of Carbododecahedron Formation in Carbon Plasma.
Poklonski, Nikolai A; Ratkevich, Sergey V; Vyrko, Sergey A
2015-08-27
The ground state of the molecule consisting of 10 carbon atoms in C10(rg) "ring" conformation and the energy of its metastable C10(st) "star" conformation are reported. The reaction coordinate for the isomeric transition C10(st) → C10(rg) was calculated using density functional theory (DFT) with UB3LYP/6-31G(d,p). It was established that a 5-fold symmetry axis is conserved in this isomeric transition. The total energy of the ring isomer is by 10.33 eV (9.16 eV as zero-point energy corrected) lower than that of the star isomer. The energy barrier for the transition from the metastable star state to the ring state is 2.87 eV (3.57 eV as zero-point energy corrected). An analysis of possible chemical reactions in carbon plasma involving C10(st) and C10(rg) and leading to the formation of C20 fullerenes was performed. It was revealed that the presence of the C10(st) conformation in the reaction medium is a necessary condition for C20 fullerene formation. It was shown that the presence of hydrogen atoms in carbon plasma and UV radiation accelerate the C10(st) → C10(rg) transition and thus suppress the C20 fullerene formation. PMID:26267290
NASA Astrophysics Data System (ADS)
Fang, Jingtian; Vandenberghe, William G.; Fu, Bo; Fischetti, Massimo V.
2016-01-01
We present a formalism to treat quantum electronic transport at the nanometer scale based on empirical pseudopotentials. This formalism offers explicit atomistic wavefunctions and an accurate band structure, enabling a detailed study of the characteristics of devices with a nanometer-scale channel and body. Assuming externally applied potentials that change slowly along the electron-transport direction, we invoke the envelope-wavefunction approximation to apply the open boundary conditions and to develop the transport equations. We construct the full-band open boundary conditions (self-energies of device contacts) from the complex band structure of the contacts. We solve the transport equations and present the expressions required to calculate the device characteristics, such as device current and charge density. We apply this formalism to study ballistic transport in a gate-all-around (GAA) silicon nanowire field-effect transistor with a body-size of 0.39 nm, a gate length of 6.52 nm, and an effective oxide thickness of 0.43 nm. Simulation results show that this device exhibits a subthreshold slope (SS) of ˜66 mV/decade and a drain-induced barrier-lowering of ˜2.5 mV/V. Our theoretical calculations predict that low-dimensionality channels in a 3D GAA architecture are able to meet the performance requirements of future devices in terms of SS swing and electrostatic control.
Theoretical calculations of nonlinear refraction and absorption coefficients of doped graphene
NASA Astrophysics Data System (ADS)
Margulis, Vl A.; Muryumin, E. E.; Gaiduk, E. A.
2014-12-01
In this study, we present the first theoretical predictions concerning the nonlinear refractive and absorptive properties of the doped graphene in which the Fermi energy {{E}F} of charge carriers (noninteracting massless Dirac fermions) is controlled by an external gate voltage. We base our study on the original perturbation theory technique developed by Genkin and Mednis (1968 Sov. Phys. JETP 27 609) for calculating the nonlinear-optical (NLO) response coefficients of bulk crystalline semiconductors with partially filled bands. Using a simple tight-binding model for the π-electron energy bands of graphene, we obtain analytic expressions for the nonlinear refractive index {{n}2}(ω ) and the nonlinear absorption coefficient {{α }2}(ω ) of the doped graphene at photon energies above twice the value of the Fermi energy (\\hbar ω \\gt 2{{E}F}). We show that in this spectral region, both the nonlinear refraction ant the nonlinear absorption are determined predominantly by the combined processes which simultaneously involve intraband and interband motion of π-electrons. Our calculations indicate that extremely large negative values of n2 (of the order of -{{10}-6} cm2 W-1) can be achieved in the graphene at a relatively low doping level (of about 1012 cm-2) provided that the excitation frequency slightly exceeds the threshold frequency corresponding to the onset of interband transitions. With a further increase of the radiation frequency, the {{n}2}(ω ) becomes positive and begins to decrease in its absolute magnitude. The peculiar frequency dispersion of n2 and a negative sign of the {{α }2} (absorption bleaching), as predicted by our theory, suggest that the doped graphene is a prospective NLO material to be used in practical optical switching applications.
Elucidating the interaction of H2O2 with polar amino acids - Quantum chemical calculations
NASA Astrophysics Data System (ADS)
Karmakar, Tarak; Balasubramanian, Sundaram
2014-10-01
Quantum chemical calculations have been carried out to investigate the interaction motifs of H2O2 with polar amino acid residues. Binding energies obtained from gas phase and continuum solvent phase calculations range between 2 and 30 kcal/mol. H2O2 interacts with the side chain of polar amino acids chiefly through the formation of hydrogen bonds. The sbnd CH group in side chains of a few residues provides additional stabilization to H2O2.
Holderna-Natkaniec, K.; Natkaniec, I.; Khavryutchenko, V. D.
1999-06-15
The observed and calculated INS vibrational densities of states for globular molecules of norbornane, norborneole and borneole are compared in the frequency range up to 600 cm{sup -1}. Inelastic incoherent neutron scattering (IINS) spectra were measured at ca. 20 K on the high resolution NERA spectrometer at the IBR-2 pulsed reactor. The IINS intensities were calculated by semi-empirical quantum chemistry method and the assignments of the low-frequency internal modes were proposed.
NASA Technical Reports Server (NTRS)
Cohen, S. C.
1979-01-01
A model of viscoelastic deformations associated with earthquakes is presented. A strike-slip fault is represented by a rectangular dislocation in a viscoelastic layer (lithosphere) lying over a viscoelastic half-space (asthenosphere). Deformations occur on three time scales. The initial response is governed by the instantaneous elastic properties of the earth. A slower response is associated with viscoelastic relaxation of the lithosphere and a yet slower response is due to viscoelastic relaxation of the asthenosphere. The major conceptual contribution is the inclusion of lithospheric viscoelastic properties into a dislocation model of earthquake related deformations and stresses. Numerical calculations using typical fault parameters reveal that the postseismic displacements and strains are small compared to the coseismic ones near the fault, but become significant further away. Moreover, the directional sense of the deformations attributable to the elastic response, the lithospheric viscoelastic softening, and the asthenospheric viscoelastic flow may differ and depend on location and model details. The results and theoretical arguments suggest that the stress changes accompanying lithospheric relaxation may also be in a different sense than and be larger than the strain changes.
Wu, Yanlin; Shi, Jin; Chen, Hongche; Zhao, Jianfu; Dong, Wenbo
2016-10-01
4-tert-butylphenol (4-t-BP), an endocrine disrupting chemical, is widely distributed in natural bodies of water but is difficult to biodegrade. In this study, we focused on the transformation of 4-t-BP in photo-initiated degradation processes. The steady-state photolysis and laser flash photolysis (LFP) experiments were conducted in order to elucidate its degradation mechanism. Identification of products was performed using the GC-MS, LC-MS and theoretical calculation techniques. The oxidation pathway of 4-t-BP by hydroxyl radical (HO) was also studied and H2O2 was added to produce HO. 4-tert-butylcatechol and 4-tert-butylphenol dimer were produced in 4-t-BP direct photolysis. 4-tert-butylcatechol and hydroquinone were produced by the oxidation of HO. But the formation mechanism of 4-tert-butylcatechol in the two processes was different. The benzene ring was fractured in 4-t-BP oxidation process and 29% of TOC was degraded after 16h irradiation. PMID:27213674
Young’s modulus calculations for cellulose Iß by MM3 and quantum mechanics
Technology Transfer Automated Retrieval System (TEKTRAN)
Quantum mechanics (QM) and molecular mechanics (MM) calculations were performed to elucidate Young’s moduli for a series of cellulose Iß models. Computations using the second generation empirical force field MM3 with a disaccharide cellulose model, 1,4'-O-dimethyl-ß-cellobioside (DMCB), and an analo...
Theoretical studies for experimental implementation of quantum computing with trapped ions
NASA Astrophysics Data System (ADS)
Yoshimura, Bryce T.
Certain quantum many-body physics problems, such as the transverse field Ising model are intractable on a classical computer, meaning that as the number of particles grows, or spins, the amount of memory and computational time required to solve the problem exactly increases faster than a polynomial behavior. However, quantum simulators are being developed to efficiently solve quantum problems that are intractable via conventional computing. Some of the most successful quantum simulators are based on ion traps. Their success depends on the ability to achieve long coherence time, precise spin control, and high fidelity in state preparation. In this work, I present calculations that characterizes the oblate Paul trap that creates two-dimensional Coulomb crystals in a triangular lattice and phonon modes. We also calculate the spin-spin Ising-like interaction that can be generated in the oblate Paul trap using the same techinques as the linear radiofrequency Paul trap. In addition, I discuss two possible challenges that arise in the Penning trap: the effects of defects ( namely when Be+ → BeH+) and the creation of a more uniform spin-spin Ising-like interaction. We show that most properties are not significantly influenced by the appearance of defects, and that by adding two potentials to the Penning trap a more uniform spin-spin Ising-like interaction can be achieved. Next, I discuss techniques tfor preparing the ground state of the Ising-like Hamiltonian. In particular, we explore the use of the bang-bang protocol to prepare the ground state and compare optimized results to conventional adiabatic ramps ( the exponential and locally adiabatic ramp ). The bang-bang optimization in general outperforms the exponential; however the locally adiabatic ramp consistently is somewhat better. However, compared to the locally adiabatic ramp, the bang-bang optimization is simpler to implement, and it has the advantage of providingrovide a simple procedure for estimating the
Quantum Humor: The Playful Side of Physics at Bohr's Institute for Theoretical Physics
NASA Astrophysics Data System (ADS)
Halpern, Paul
2012-09-01
From the 1930s to the 1950s, a period of pivotal developments in quantum, nuclear, and particle physics, physicists at Niels Bohr's Institute for Theoretical Physics in Copenhagen took time off from their research to write humorous articles, letters, and other works. Best known is the Blegdamsvej Faust, performed in April 1932 at the close of one of the Institute's annual conferences. I also focus on the Journal of Jocular Physics, a humorous tribute to Bohr published on the occasions of his 50th, 60th, and 70th birthdays in 1935, 1945, and 1955. Contributors included Léon Rosenfeld, Victor Weisskopf, George Gamow, Oskar Klein, and Hendrik Casimir. I examine their contributions along with letters and other writings to show that they offer a window into some issues in physics at the time, such as the interpretation of complementarity and the nature of the neutrino, as well as the politics of the period.
NASA Astrophysics Data System (ADS)
Takeshima, Tsuguhide; Takeuchi, Hiroshi; Egawa, Toru; Konaka, Shigehiro
2005-01-01
The molecular structure of arecoline (methyl 1,2,5,6-tetrahydro-1-methylnicotinate, ? has been determined by gas electron diffraction. Diffraction patterns were taken at about 370 K. Structural constraints for the data analysis were obtained from MP2/6-31G** calculations. Vibrational mean amplitudes and shrinkage corrections were calculated from the force constants obtained from the gas-phase vibrational frequencies and the B3LYP/6-31G** calculations. The electron diffraction data were well reproduced by assuming the mixture of four conformers. The determined structural parameters ( rg (Å) and ∠ (°)) for the main conformer with 3 σ in parentheses are as follows: < rg(N-C ring)>=1.456(4); rg(N-C methyl)=1.451 (d.p.); rg(C dbnd6 C)=1.339(9); < rg(C-C)>=1.512(3); rg(O-C methyl)=1.434(5); rg(C(O)-O)=1.355 (d.p.); rg(C dbnd6 O)=1.209(4); the out-of-plane angle of the methyl group=50.3(23); ∠C ringN ringC ring=112.8(30); ∠N ringC ringC ring(H 2)=110.5(16); <∠C ringC ringC ring>=118.4(5); ∠C dbnd6 CC(O)=116.8(7); ∠CC dbnd6 O=127.6(9); ∠CC-O=109.8(8), where the angle brackets denote averaged values and d.p. denotes dependent parameters. Fixing the abundances of the minor conformers, Ax-s- cis and Ax-s- trans, at the theoretical values (13% in total), those of the Eq-s- cis and Eq-s- trans conformers were determined to be 46(16) and 41(16)%, respectively. Here Ax and Eq denote the axial and equatorial directions of the N-CH 3 bond and s- cis and s- trans show the orientation of the methoxycarbonyl group expressed by the configuration of the C dbnd6 O and C dbnd6 C bonds. The N⋯O carbonyl distances of the Eq-s- cis and Ax-s- cis conformers are 4.832(13) and 4.874(16) Å, respectively. They are close to the N⋯N distance of the most abundant conformer of nicotine, 4.885(6) Å, suggesting that the Eq-s- cis and Ax-s- cis conformers have nicotinic activity.
Semiclassical and quantum field theoretic bounds for traversable Lorentzian stringy wormholes
Nandi, Kamal Kanti; Zhang Yuanzhong; Kumar, K.B. Vijaya
2004-09-15
A lower bound on the size of a Lorentzian wormhole can be obtained by semiclassically introducing the Planck cutoff on the magnitude of tidal forces (Horowitz-Ross constraint). Also, an upper bound is provided by the quantum field theoretic constraint in the form of the Ford-Roman Quantum Inequality for massless minimally coupled scalar fields. To date, however, exact static solutions belonging to this scalar field theory have not been worked out to verify these bounds. To fill this gap, we examine the wormhole features of two examples from the Einstein frame description of the vacuum low energy string theory in four dimensions which is the same as the minimally coupled scalar field theory. Analyses in this paper support the conclusion of Ford and Roman that wormholes in this theory can have sizes that are indeed only a few order of magnitudes larger than the Planck scale. It is shown that the two types of bounds are also compatible. In the process, we point out a 'wormhole' analog of naked black holes.
NASA Astrophysics Data System (ADS)
Zakharenko, Olena; Aviles Moreno, Juan-Ramon; Imane, Haykal; Motiyenko, R. A.; Huet, T. R.; Pirali, Olivier
2014-06-01
Methacrolein, CH_2=C(CH_3)CHO or MAC, is an important atmospheric molecule because it is a major product of the isoprene-OH reaction. Meanwhile the spectroscopic information on MAC is very scarse. On the theoretical side, we have performed quantum calculations at different levels of theory (DFT and ab initio) to model the structure of the two conformers, the large amplitude motion associated with the methyl top, and the anharmonic vibrational structure. On the experimental side, we have at first characterized the millimeter-wave spectrum of MAC in the 150-465 GHz range using the Lille frequency multiplication chain spectrometer. In particular the ground state has been analyzed up to J, K_a = 37, 17 and the first excited states are currently investigated. Secondly, FTIR spectra have been recorded on the AILES beamline of SOLEIL using a long path cell, between 30 and 3500 wn at medium resolution (0.5 wn). A few bands of atmospheric interest have also been recorded at higher resolution (0.001 wn). We will report the details of the vibrational analysis, as well as the molecular parameters derived from the analysis of the high resolution spectrum of the c-type band located around 930 wn. Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged. The experiment on the AILES beam-line of the synchrotron SOLEIL was performed under project number 20130192. M. Suzuki and K. Kozima, J. Molec. Spectrosc. 38 (1971) 314 J. R. Durig, J. Qiu, B. Dehoff and T. S. Little, Spectrochimica Acta 42A (1986) 89
Tucker, Jon R.; Magyar, Rudolph J.
2012-02-01
High explosives are an important class of energetic materials used in many weapons applications. Even with modern computers, the simulation of the dynamic chemical reactions and energy release is exceedingly challenging. While the scale of the detonation process may be macroscopic, the dynamic bond breaking responsible for the explosive release of energy is fundamentally quantum mechanical. Thus, any method that does not adequately describe bonding is destined to lack predictive capability on some level. Performing quantum mechanics calculations on systems with more than dozens of atoms is a gargantuan task, and severe approximation schemes must be employed in practical calculations. We have developed and tested a divide and conquer (DnC) scheme to obtain total energies, forces, and harmonic frequencies within semi-empirical quantum mechanics. The method is intended as an approximate but faster solution to the full problem and is possible due to the sparsity of the density matrix in many applications. The resulting total energy calculation scales linearly as the number of subsystems, and the method provides a path-forward to quantum mechanical simulations of millions of atoms.
Ab initio no core calculations of light nuclei and preludes to Hamiltonian quantum field theory
Vary, J. P.; Maris, P.; Honkanen, H.; Li, J.; Shirokov, A. M.; Brodsky, S. J.; Harindranath, A.
2009-12-17
Recent advances in ab initio quantum many-body methods and growth in computer power now enable highly precise calculations of nuclear structure. The precision has attained a level sufficient to make clear statements on the nature of 3-body forces in nuclear physics. Total binding energies, spin-dependent structure effects, and electroweak properties of light nuclei play major roles in pinpointing properties of the underlying strong interaction. Eventually, we anticipate a theory bridge with immense predictive power from QCD through nuclear forces to nuclear structure and nuclear reactions. Light front Hamiltonian quantum field theory offers an attractive pathway and we outline key elements.
Ab initio no core calculations of light nuclei and preludes to Hamiltonian quantum field theory
Vary, J.P.; Maris, P.; Shirokov, A.M.; Honkanen, H.; li, J.; Brodsky, S.J.; Harindranath, A.; Teramond, G.F.de; /Costa Rica U.
2009-08-03
Recent advances in ab initio quantum many-body methods and growth in computer power now enable highly precise calculations of nuclear structure. The precision has attained a level sufficient to make clear statements on the nature of 3-body forces in nuclear physics. Total binding energies, spin-dependent structure effects, and electroweak properties of light nuclei play major roles in pinpointing properties of the underlying strong interaction. Eventually,we anticipate a theory bridge with immense predictive power from QCD through nuclear forces to nuclear structure and nuclear reactions. Light front Hamiltonian quantum field theory offers an attractive pathway and we outline key elements.
Roaming dynamics in the MgH + H→Mg + H 2 reaction: Quantum dynamics calculations
NASA Astrophysics Data System (ADS)
Takayanagi, Toshiyuki; Tanaka, Tomokazu
2011-03-01
Reaction mechanisms of the MgH + H→Mg + H 2 reaction have been investigated using quantum reactive scattering methods on a global ab initio potential energy surface. There exist two microscopic mechanisms in the dynamics of this reaction. One is a direct hydrogen abstraction reaction and the other proceeds via initial formation of a HMgH complex in the deep potential well. The result of the present quantum dynamics calculations suggests that the HMgH complex formed in the reaction mainly decays into the Mg + H 2 channel via a 'roaming mechanism' without going through the saddle point region.
Systematic study of finite-size effects in quantum Monte Carlo calculations of real metallic systems
Azadi, Sam Foulkes, W. M. C.
2015-09-14
We present a systematic and comprehensive study of finite-size effects in diffusion quantum Monte Carlo calculations of metals. Several previously introduced schemes for correcting finite-size errors are compared for accuracy and efficiency, and practical improvements are introduced. In particular, we test a simple but efficient method of finite-size correction based on an accurate combination of twist averaging and density functional theory. Our diffusion quantum Monte Carlo results for lithium and aluminum, as examples of metallic systems, demonstrate excellent agreement between all of the approaches considered.
Chen, Xiao-bo; Wang, Ce; Li, Song; Naruhito, Sawanobori; Kang, Dong-guo
2010-07-01
A photonic phenomenon of fluorescence intensity reverse between red and green fluorescence was studied theoretically and experimentally in the present article. It was found by experiment that Er(0.5) Yb(9.5) : FOV oxyfluoride vitroceramics exhibits strong fluorescence intensity reverse phenomenon. The range of the intensity reverse of Er(0.5) Yb(9.5) : FOV was measured to be 877. Moreover, all basic spectroscopic parameters were calculated. The theoretical basis of numerical calculation for dynamics processes of all levels was established. PMID:20827959
Matthew Mihelic, F.
2010-12-22
Nucleic acids theoretically possess a Szilard engine function that can convert the energy associated with the Shannon entropy of molecules for which they have coded recognition, into the useful work of geometric reconfiguration of the nucleic acid molecule. This function is logically reversible because its mechanism is literally and physically constructed out of the information necessary to reduce the Shannon entropy of such molecules, which means that this information exists on both sides of the theoretical engine, and because information is retained in the geometric degrees of freedom of the nucleic acid molecule, a quantum gate is formed through which multi-state nucleic acid qubits can interact. Entangled biophotons emitted as a consequence of symmetry breaking nucleic acid Szilard engine (NASE) function can be used to coordinate relative positioning of different nucleic acid locations, both within and between cells, thus providing the potential for quantum coherence of an entire biological system. Theoretical implications of understanding biological systems as such 'quantum adaptive systems' include the potential for multi-agent based quantum computing, and a better understanding of systemic pathologies such as cancer, as being related to a loss of systemic quantum coherence.
Shakib, Farnaz; Hanna, Gabriel
2016-07-12
In this work, we derive a general mixed quantum-classical formula for calculating thermal proton-coupled electron-transfer (PCET) rate constants, starting from the time integral of the quantum flux-flux correlation function. This formula allows for the direct simulation of PCET reaction dynamics via the mixed quantum-classical Liouville approach. Owing to the general nature of the derivation, this formula does not rely on any prior mechanistic assumptions and can be applied across a wide range of electronic and protonic coupling regimes. To test the validity of this formula, we applied it to a reduced model of a condensed-phase PCET reaction. Good agreement with the numerically exact rate constant is obtained, demonstrating the accuracy of our formalism. We believe that this approach constitutes a solid foundation for future investigations of the rates and mechanisms of a wide range of PCET reactions. PMID:27232936
Ceriotti, Michele; Manolopoulos, David E
2012-09-01
Light nuclei at room temperature and below exhibit a kinetic energy which significantly deviates from the predictions of classical statistical mechanics. This quantum kinetic energy is responsible for a wide variety of isotope effects of interest in fields ranging from chemistry to climatology. It also furnishes the second moment of the nuclear momentum distribution, which contains subtle information about the chemical environment and has recently become accessible to deep inelastic neutron scattering experiments. Here, we show how, by combining imaginary time path integral dynamics with a carefully designed generalized Langevin equation, it is possible to dramatically reduce the expense of computing the quantum kinetic energy. We also introduce a transient anisotropic Gaussian approximation to the nuclear momentum distribution which can be calculated with negligible additional effort. As an example, we evaluate the structural properties, the quantum kinetic energy, and the nuclear momentum distribution for a first-principles simulation of liquid water. PMID:23005275
Theoretical Study of All-Electrical Quantum Wire Valley Filters in Bilayer Graphene
NASA Astrophysics Data System (ADS)
Wu, Yu-Shu; Lue, Ning-Yuan; Chen, Yen-Chun; Jiang, Jia-Huei; Chou, Mei-Yin
Graphene electrons carry valley pseudospin, due to the double valley degeneracy in graphene band structure. In gapped graphene, the pseudospin is coupled to an in-plane electric field, through the mechanism of valley-orbit interaction (VOI), Based on the VOI, a family of electrically-controlled valleytronic devices have been proposed. Here, we report the theoretical study of a recently proposed valley filter consisting of a Q1D channel in bilayer graphene defined and controlled by electrical gates. We discuss two types of calculations - those of energy subband structure in the channel and electron transmission through a valley valve consisting of two proposed filters. For the former, we have developed a tight binding formulation in the continuum limit. For the latter, we employ the recursive Green's function method. Results from the calculations will be presented. Financial support by MoST, Taiwan, ROC is acknowledged.
Theoretical studies of excitons in type II CdSe/CdTe quantum dots
NASA Astrophysics Data System (ADS)
Miloszewski, Jacek M.; Tomić, Stanko; Binks, David
2014-06-01
We present a method for calculating exciton and bi-exciton energies in type-II colloidal quantum dots. Our methodology is based on an 8-band k · p Hamiltonian of the zinc- blend structure, which incorporates the effects of spin-orbit interaction, strain between the core and the shell and piezoelectric potentials. Exciton states are found using the configuration interaction (CI) method that explicitly includes the effects of Coulomb interaction, as well as exchange and correlation between many-electron configurations. We pay particular attention to accurate modelling of the electrostatic interaction between quasiparticles. The model includes surface polarization and self-polarization effects due to the large difference in dielectric constants at the boundary of the QD.
NASA Astrophysics Data System (ADS)
Legler, C. R.; Brown, N. R.; Dunbar, R. A.; Harness, M. D.; Nguyen, K.; Oyewole, O.; Collier, W. B.
2015-06-01
The Scaled Quantum Mechanical (SQM) method of scaling calculated force constants to predict theoretically calculated vibrational frequencies is expanded to include a broad array of polarized and augmented basis sets based on the split valence 6-31G and 6-311G basis sets with the B3LYP density functional. Pulay's original choice of a single polarized 6-31G(d) basis coupled with a B3LYP functional remains the most computationally economical choice for scaled frequency calculations. But it can be improved upon with additional polarization functions and added diffuse functions for complex molecular systems. The new scale factors for the B3LYP density functional and the 6-31G, 6-31G(d), 6-31G(d,p), 6-31G+(d,p), 6-31G++(d,p), 6-311G, 6-311G(d), 6-311G(d,p), 6-311G+(d,p), 6-311G++(d,p), 6-311G(2d,p), 6-311G++(2d,p), 6-311G++(df,p) basis sets are shown. The double d polarized models did not perform as well and the source of the decreased accuracy was investigated. An alternate system of generating internal coordinates that uses the out-of plane wagging coordinate whenever it is possible; makes vibrational assignments via potential energy distributions more meaningful. Automated software to produce SQM scaled vibrational calculations from different molecular orbital packages is presented.
Chikayama, Eisuke; Shimbo, Yudai; Komatsu, Keiko; Kikuchi, Jun
2016-04-14
NMR spectroscopy is a powerful method for analyzing metabolic mixtures. The information obtained from an NMR spectrum is in the form of physical parameters, such as chemical shifts, and construction of databases for many metabolites will be useful for data interpretation. To increase the accuracy of theoretical chemical shifts for development of a database for a variety of metabolites, the effects of sets of conformations (structural ensembles) and the levels of theory on computations of theoretical chemical shifts were systematically investigated for a set of 29 small molecules in the present study. For each of the 29 compounds, 101 structures were generated by classical molecular dynamics at 298.15 K, and then theoretical chemical shifts for 164 (1)H and 123 (13)C atoms were calculated by ab initio quantum chemical methods. Six levels of theory were used by pairing Hartree-Fock, B3LYP (density functional theory), or second order Møller-Plesset perturbation with 6-31G or aug-cc-pVDZ basis set. The six average fluctuations in the (1)H chemical shift were ±0.63, ± 0.59, ± 0.70, ± 0.62, ± 0.75, and ±0.66 ppm for the structural ensembles, and the six average errors were ±0.34, ± 0.27, ± 0.32, ± 0.25, ± 0.32, and ±0.25 ppm. The results showed that chemical shift fluctuations with changes in the conformation because of molecular motion were larger than the differences between computed and experimental chemical shifts for all six levels of theory. In conclusion, selection of an appropriate structural ensemble should be performed before theoretical chemical shift calculations for development of an accurate database for a variety of metabolites. PMID:26963288
Reeves, Kyle G.; Kanai, Yosuke
2014-07-14
Oxidation state is a powerful concept that is widely used in chemistry and materials physics, although the concept itself is arguably ill-defined quantum mechanically. In this work, we present impartial comparison of four, well-recognized theoretical approaches based on Lowdin atomic orbital projection, Bader decomposition, maximally localized Wannier function, and occupation matrix diagonalization, for assessing how well transition metal oxidation states can be characterized. Here, we study a representative molecular complex, tris(bipyridine)ruthenium. We also consider the influence of water solvation through first-principles molecular dynamics as well as the improved electronic structure description for strongly correlated d-electrons by including Hubbard correction in density functional theory calculations.
NASA Astrophysics Data System (ADS)
Reeves, Kyle G.; Kanai, Yosuke
2014-07-01
Oxidation state is a powerful concept that is widely used in chemistry and materials physics, although the concept itself is arguably ill-defined quantum mechanically. In this work, we present impartial comparison of four, well-recognized theoretical approaches based on Lowdin atomic orbital projection, Bader decomposition, maximally localized Wannier function, and occupation matrix diagonalization, for assessing how well transition metal oxidation states can be characterized. Here, we study a representative molecular complex, tris(bipyridine)ruthenium. We also consider the influence of water solvation through first-principles molecular dynamics as well as the improved electronic structure description for strongly correlated d-electrons by including Hubbard correction in density functional theory calculations.
Poirier, Bill; Salam, A
2004-07-22
In a previous paper [J. Theo. Comput. Chem. 2, 65 (2003)], one of the authors (B.P.) presented a method for solving the multidimensional Schrodinger equation, using modified Wilson-Daubechies wavelets, and a simple phase space truncation scheme. Unprecedented numerical efficiency was achieved, enabling a ten-dimensional calculation of nearly 600 eigenvalues to be performed using direct matrix diagonalization techniques. In a second paper [J. Chem. Phys. 121, 1690 (2004)], and in this paper, we extend and elaborate upon the previous work in several important ways. The second paper focuses on construction and optimization of the wavelength functions, from theoretical and numerical viewpoints, and also examines their localization. This paper deals with their use in representations and eigenproblem calculations, which are extended to 15-dimensional systems. Even higher dimensionalities are possible using more sophisticated linear algebra techniques. This approach is ideally suited to rovibrational spectroscopy applications, but can be used in any context where differential equations are involved. PMID:15260721
NASA Astrophysics Data System (ADS)
Takeshima, Tsuguhide; Takeuchi, Hiroshi; Egawa, Toru; Konaka, Shigehiro
2007-09-01
The molecular structure of cotinine (( S)-1-methyl-5-(3-pyridinyl)-2-pyrrolidinone), the major metabolite of nicotine, has been determined at about 182 °C by gas electron diffraction combined with MP2 and DFT calculations. The diffraction data are consistent with the existence of the (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers, where ax and eq indicate the configuration of the pyrrolidinone ring by means of the position (axial and equatorial) of the pyridine ring, and sc, sp and ap distinguish the isomers arising from the internal rotation around the bond connecting the two rings. The (CH 3)NCCC(N) dihedral angles, ϕ, of the (ax, sc) and (eq, sp) conformers were determined independently to be 158(12)° and 129(13)°, respectively, where the numbers in parentheses are three times the standard errors, 3 σ. According to the MP2 calculations, the corresponding dihedral angles for the (ax, ap) and (eq, ap) conformers were assumed to differ by 180° from their syn counterparts. The ratios x(ax, sc)/ x(ax, ap) and x(eq, sp)/ x(eq, ap) were taken from the theoretically estimated free energy differences, Δ G, where x is the abundance of the conformer. The resultant abundances of (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers are 34(6)%, 21% (d.p.), 28% (d.p.), and 17% (d.p.), respectively, where d.p. represents dependent parameters. The determined structural parameters ( rg (Å) and ∠ α (°)) of the most abundant conformer, (ax, sc), are as follows: r(N sbnd C) pyrrol = 1.463(5); r(N sbnd C methyl) = 1.457(←); r(N sbnd C( dbnd O)) = 1.384(12); r(C dbnd O) = 1.219(5); < r(C sbnd C) pyrrol> = 1.541(3); r(C pyrrolsbnd C pyrid) = 1.521(←); < r(C sbnd C) pyrid> = 1.396(2); < r(C sbnd N) pyrid> = 1.343(←); ∠(CNC) pyrrol = 113.9(11); ∠CCC pyrrol(-C pyrid) = 103.6(←); ∠NCO = 124.1(13); ∠NC pyrrolC pyrid = 113.1(12); ∠C pyrrolC pyrrolC pyrid = 113.3(←); ∠(CNC) pyrid = 117.1(2); <∠(NCC) pyrid> = 124.4(←); ∠C methylNC( dbnd O) =
Schiffmann, Christoph; Sebastiani, Daniel
2011-05-10
We present an algorithmic extension of a numerical optimization scheme for analytic capping potentials for use in mixed quantum-classical (quantum mechanical/molecular mechanical, QM/MM) ab initio calculations. Our goal is to minimize bond-cleavage-induced perturbations in the electronic structure, measured by means of a suitable penalty functional. The optimization algorithm-a variant of the artificial bee colony (ABC) algorithm, which relies on swarm intelligence-couples deterministic (downhill gradient) and stochastic elements to avoid local minimum trapping. The ABC algorithm outperforms the conventional downhill gradient approach, if the penalty hypersurface exhibits wiggles that prevent a straight minimization pathway. We characterize the optimized capping potentials by computing NMR chemical shifts. This approach will increase the accuracy of QM/MM calculations of complex biomolecules. PMID:26610125
NASA Astrophysics Data System (ADS)
Ticknor, Christopher; Kendrick, Brian
2016-05-01
We report progress towards including excited vibrational states in quantum scattering calculations of NaK-NaK at ultracold temperatures. We systematically use all pair potentials to build a complete 4 body potential energy surface. We study this 4-body potential and the asymptotic ro-vibrational 2-body basis. This allows for a more complete interaction as two molecules approach each other. We study where and how vibrationally excited states influence the asymptotic 2-body ro-vibrational scattering potentials. This work is an intermediate step in performing the complete scattering calculations as we develop tools to bring together the long range, ultracold 2-body scattering problem and the short range 4-body quantum chemistry problem.
Yamamoto, Atsushi; Matsui, Yasunori; Asada, Toshio; Kumeda, Motoki; Takagi, Kenichiro; Suenaga, Yu; Nagae, Kunihiko; Ohta, Eisuke; Sato, Hiroyasu; Koseki, Shiro; Naito, Hiroyoshi; Ikeda, Hiroshi
2016-04-15
The p-type organic semiconductor (OSC) material tetrathieno[2,3-a:3',2'-c:2″,3″-f:3‴,2‴-h]naphthalene (2TTN) and its alkyl-substituted derivatives Cn-2TTNs (n = 6, 8, and 10) have been developed based on the results of theoretical calculation-inspired investigation. A hole mobility for amorphous Cn-2TTNs (10(-2)-10(-3) cm(2) V(-1) s(-1)) was accurately predicted by using a novel statistical method in which the geometric mean of the mobilities for many individual small molecular flocks in an amorphous solid was obtained by using molecular mechanical molecular dynamics simulations and quantum chemical calculations. The simulation also suggests that upon increasing the length of alkyl chains in Cn-2TTNs the mobilities become smaller as a consequence of a decrease in transfer integral values. Cn-2TTNs are synthesized in a microflow reactor through photoreactions of the corresponding precursors. Cn-2TTNs are then utilized in the fabrication of organic field-effect transistors (OFETs). Although spin-coated thin films of Cn-2TTNs are crystalline, the hole mobilities (10(-2)-10(-3) cm(2) V(-1) s(-1)) of trial OFETs decrease upon elongation of the alkyl chains. This finding parallels the results of theoretical simulation. The simulation method for amorphous solids developed in this effort should become a useful tool in studies aimed at designing new OSC materials. PMID:27010327
Payne, Walter A.; Harding, Lawrence B.; Stief, Louis J.; Parker, James F. , 1925-; Klippenstein, Stephen J.; Nesbitt, Fred L.; Cody, Regina J.
2004-10-01
The rate coefficient has been measured under pseudo-first-order conditions for the Cl + CH{sub 3} association reaction at T = 202, 250, and 298 K and P = 0.3-2.0 Torr helium using the technique of discharge-flow mass spectrometry with low-energy (12-eV) electron-impact ionization and collision-free sampling. Cl and CH{sub 3} were generated rapidly and simultaneously by reaction of F with HCl and CH{sub 4}, respectively. Fluorine atoms were produced by microwave discharge in an approximately 1% mixture of F{sub 2} in He. The decay of CH{sub 3} was monitored under pseudo-first-order conditions with the Cl-atom concentration in large excess over the CH{sub 3} concentration ([Cl]{sub 0}/[CH{sub 3}]{sub 0} = 9-67). Small corrections were made for both axial and radial diffusion and minor secondary chemistry. The rate coefficient was found to be in the falloff regime over the range of pressures studied. For example, at T = 202 K, the rate coefficient increases from 8.4 x 10{sup -12} at P = 0.30 Torr He to 1.8 x 10{sup -11} at P = 2.00 Torr He, both in units of cm{sup 3} molecule{sup -1} s{sup -1}. A combination of ab initio quantum chemistry, variational transition-state theory, and master-equation simulations was employed in developing a theoretical model for the temperature and pressure dependence of the rate coefficient. Reasonable empirical representations of energy transfer and of the effect of spin-orbit interactions yield a temperature- and pressure-dependent rate coefficient that is in excellent agreement with the present experimental results. The high-pressure limiting rate coefficient from the RRKM calculations is k{sub 2} = 6.0 x 10{sup -11} cm{sup 3} molecule{sup -1} s{sup -1}, independent of temperature in the range from 200 to 300 K.
Nalli, Nicholas R; Minnett, Peter J; van Delst, Paul
2008-07-20
Although published sea surface infrared (IR) emissivity models have gained widespread acceptance for remote sensing applications, discrepancies have been identified against field observations obtained from IR Fourier transform spectrometers at view angles approximately > 40 degrees. We therefore propose, in this two-part paper, an alternative approach for calculating surface-leaving IR radiance that treats both emissivity and atmospheric reflection in a systematic yet practical manner. This first part presents the theoretical basis, development, and computations of the proposed model. PMID:18641735
Niquet, Yann-Michel Nguyen, Viet-Hung; Duchemin, Ivan; Nier, Olivier; Rideau, Denis
2014-02-07
We discuss carrier mobilities in the quantum Non-Equilibrium Green's Functions (NEGF) framework. We introduce a method for the extraction of the mobility that is free from contact resistance contamination and with minimal needs for ensemble averages. We focus on silicon thin films as an illustration, although the method can be applied to various materials such as semiconductor nanowires or carbon nanostructures. We then introduce a new paradigm for the definition of the partial mobility μ{sub M} associated with a given elastic scattering mechanism “M,” taking phonons (PH) as a reference (μ{sub M}{sup −1}=μ{sub PH+M}{sup −1}−μ{sub PH}{sup −1}). We argue that this definition makes better sense in a quantum transport framework as it is free from long range interference effects that can appear in purely ballistic calculations. As a matter of fact, these mobilities satisfy Matthiessen's rule for three mechanisms [e.g., surface roughness (SR), remote Coulomb scattering (RCS) and phonons] much better than the usual, single mechanism calculations. We also discuss the problems raised by the long range spatial correlations in the RCS disorder. Finally, we compare semi-classical Kubo-Greenwood (KG) and quantum NEGF calculations. We show that KG and NEGF are in reasonable agreement for phonon and RCS, yet not for SR. We discuss the reasons for these discrepancies.
NASA Astrophysics Data System (ADS)
Blanco, R.; Pesquera, L.; Santos, E.
1987-08-01
An oscillator with a small, but otherwise arbitrary, perturbing potential is considered immersed in a random cavity radiation. Classical (stochastic) calculations are done when the radiation has a Rayleigh-Jeans spectrum and a complete Planck spectrum (i.e., with zero point). These are compared with the results obtained by a quantum calculation. First, a comparison is made of stationary values, in particular, the energy. Then the emission and the absorption spectra are calculated, in particular, the absorption spectrum for an arbitrary incoming radiation. Finally, a detailed comparison is made of the absorption bands when the perturbing potential has the form λx2K (K=2,3,...). In all cases, it is explicitly shown that the quantum and the classical behavior agree in the limit of high temperatures. It is also shown that the classical system immersed in a radiation with complete Planck spectrum is much closer to the quantum system than the fully classical system (with a Rayleigh-Jeans spectrum).
Quantum Monte Carlo calculation of the binding energy of the beryllium dimer
NASA Astrophysics Data System (ADS)
Deible, Michael J.; Kessler, Melody; Gasperich, Kevin E.; Jordan, Kenneth D.
2015-08-01
The accurate calculation of the binding energy of the beryllium dimer is a challenging theoretical problem. In this study, the binding energy of Be2 is calculated using the diffusion Monte Carlo (DMC) method, using single Slater determinant and multiconfigurational trial functions. DMC calculations using single-determinant trial wave functions of orbitals obtained from density functional theory calculations overestimate the binding energy, while DMC calculations using Hartree-Fock or CAS(4,8), complete active space trial functions significantly underestimate the binding energy. In order to obtain an accurate value of the binding energy of Be2 from DMC calculations, it is necessary to employ trial functions that include excitations outside the valence space. Our best estimate DMC result for the binding energy of Be2, obtained by using configuration interaction trial functions and extrapolating in the threshold for the configurations retained in the trial function, is 908 cm-1, only slightly below the 935 cm-1 value derived from experiment.
NASA Astrophysics Data System (ADS)
Punegov, V. I.; Sivkov, D. V.
2015-03-01
Two independent approaches to calculate the angular distribution of X-ray diffusion scattering from a crystalline medium with spheroidal quantum dots (QDs) have been proposed. The first method is based on the analytical solution involving the multipole expansion of elastic strain fields beyond QDs. The second approach is based on calculations of atomic displacements near QDs by the Green's function method. An analysis of the diffuse scattering intensity distribution in the reciprocal space within these two approaches shows that both methods yield similar results for the chosen models of QD spatial distribution.
Dynamical basis sets for algebraic variational calculations in quantum-mechanical scattering theory
NASA Technical Reports Server (NTRS)
Sun, Yan; Kouri, Donald J.; Truhlar, Donald G.; Schwenke, David W.
1990-01-01
New basis sets are proposed for linear algebraic variational calculations of transition amplitudes in quantum-mechanical scattering problems. These basis sets are hybrids of those that yield the Kohn variational principle (KVP) and those that yield the generalized Newton variational principle (GNVP) when substituted in Schlessinger's stationary expression for the T operator. Trial calculations show that efficiencies almost as great as that of the GNVP and much greater than the KVP can be obtained, even for basis sets with the majority of the members independent of energy.
Auxiliary-field quantum Monte Carlo calculations for systems with long-range repulsive interactions
Silvestrelli, P.L.; Baroni, S.; Car, R. Scuola Internazionale Superiore di Studi Avanzati , via Beirut 2/4, I-34014 Trieste Institut Romand de Recherche Numerique en Physique des Materiaux , PHB Ecublens, CH-1015 Lausanne )
1993-08-23
We report on the first successful attempt to apply the auxiliary-field quantum Monte Carlo technique to the calculation of ground-state properties of systems of many electrons interacting via a Coulomb potential. We have been able to substantially reduce the huge statistical fluctuations arising from the repulsive, long-range character of the interactions, which had so far hindered the application of this method to [ital realistic] Hamiltonians for atoms, molecules, and solids. Our technique is demonstrated with calculations of ground-state properties of the simplest molecular and solid-state systems, i.e., the H[sub 2] molecule and the homogeneous electron gas.
NASA Astrophysics Data System (ADS)
Freeman, Will
2016-05-01
Dephasing in terahertz quantum cascade structures is studied within a density matrix formalism. We self-consistently calculate the pure dephasing time from the intrasubband interactions within the upper and lower lasing states. Interface roughness and ionized impurity scattering interactions are included in the calculation. Dephasing times are shown to be consistent with measured spontaneous emission spectra, and the lattice temperature dependence of the device output power is consistent with experiment. The importance of including multiple optical transitions when a lower miniband continuum is present and the resulting multi-longitudinal modes within the waveguide resonant cavity are also shown.
Finite element basis for the expansion of radial wavefunction in quantum scattering calculations
NASA Astrophysics Data System (ADS)
Hwang, Woonglin; Sup Lee, Yoon; Park, Seung C.
1991-11-01
Radial wavefunctions in quantum scattering calculations are expanded in terms of two shape functions for each finite element. This approach is the R matrix version of Kohn's variational method and also directly applicable to S matrix in the log-derivative version. The linear algebra involved amounts to solving definite banded systems. In this basis set method, R matrix or log-derivative matrix is greatly simplified and the computational effort is linearly proportional to the number of radial basis functions, promising computational efficiencies for large scale calculations. Convergences for test vases are also reasonably rapid.