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.
Quantum Mechanics and physical calculations
NASA Astrophysics Data System (ADS)
Karayan, H. S.
2014-03-01
We suggest to realize the computer simulation and calculation by the algebraic structure built on the basis of the logic inherent to processes in physical systems (called physical computing). We suggest a principle for the construction of quantum algorithms of neuroinformatics of quantum neural networks. The role of academician Sahakyan is emphasized in the development of quantum physics in Armenia.
Theoretical calculation of polarizability isotope effects.
Moncada, Félix; Flores-Moreno, Roberto; Reyes, Andrés
2017-03-01
We propose a scheme to estimate hydrogen isotope effects on molecular polarizabilities. This approach combines the any-particle molecular orbital method, in which both electrons and H/D nuclei are described as quantum waves, with the auxiliary density perturbation theory, to calculate analytically the polarizability tensor. We assess the performance of method by calculating the polarizability isotope effect for 20 molecules. A good correlation between theoretical and experimental data is found. Further analysis of the results reveals that the change in the polarizability of a X-H bond upon deuteration decreases as the electronegativity of X increases. Our investigation also reveals that the molecular polarizability isotope effect presents an additive character. Therefore, it can be computed by counting the number of deuterated bonds in the molecule.
Local, nonlocal quantumness and information theoretic measures
NASA Astrophysics Data System (ADS)
Agrawal, Pankaj; Sazim, Sk; Chakrabarty, Indranil; Pati, Arun K.
2016-08-01
It has been suggested that there may exist quantum correlations that go beyond entanglement. The existence of such correlations can be revealed by information theoretic quantities such as quantum discord, but not by the conventional measures of entanglement. We argue that a state displays quantumness, that can be of local and nonlocal origin. Information theoretic measures not only characterize the nonlocal quantumness, but also the local quantumness, such as the “local superposition”. This can be a reason, why such measures are nonzero, when there is no entanglement. We consider a generalized version of the Werner state to demonstrate the interplay of local quantumness, nonlocal quantumness and classical mixedness of a state.
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
NASA Astrophysics Data System (ADS)
Suzuki, Shinji; Horii, Fumitaka; Kurosu, Hiromichi
2009-02-01
The γ- gauche effect on 13C chemical shifts that is produced by the O atoms located at the γ positions has been evaluated by quantum chemistry calculations based on the GAIO-CHF procedure. The γ- gauche effects produced by the O and Cl atoms in n-propanol and n-propyl chloride are found to be, respectively, +1.4 and -0.7 ppm, whereas that due to the C atom in n-butane is -3.0 ppm in good agreement of the values previously calculated. The apparent cause of such a difference in the γ- gauche effect is mainly relatively higher shielding of the CH 3 carbon in the trans conformation for the n-propanol and n-propyl chloride. Extending the n-propanol chain at both ends causes no significant change in the γ- gauche effect produced by the O atom. In 2-butanol and 2-methyl-2-butanol as examples of secondarily and tertiarily substituted compounds, the γ- gauche effects produced by the γ-OH groups are estimated to be -7 to -9 ppm. In addition, the γ- gauche effect due to the C atom is found to increase in n-butane, secondary, and tertiary butanols in this order. The γ- gauche effect produced by the O atom in hydroxyethylcyclohexane is as negligibly small as -0.7 ppm, whereas that produced by the C atom in ethylcyclohexane is about -5 ppm. These results suggest that the γ- gauche effect, including downfield shift, produced by the O atom in a compound greatly depends on its chemical structure, whereas upfield shifts of -3 to -7 ppm are induced in all examined compounds as the γ- gauche effect due to the C atom.
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 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.
Theoretical issues in silicon quantum dot qubits
NASA Astrophysics Data System (ADS)
Koh, Teck Seng
Electrically-gated quantum dots in semiconductors is an excellent architecture on which to make qubits for quantum information processing. Silicon is attractive because of the potential for excellent manipulability, scalability, and for integration with classical electronics. This thesis describes several aspects of the theoretical issues related to quantum dot qubits in silicon. It may be broadly divided into three parts — (1) the hybrid qubit and quantum gates, (2) decoherence and (3) charge transport. In the first part, we present a novel architecture for a double quantum dot spin qubit, which we term the hybrid qubit, and demonstrate that implementing this qubit in silicon is feasible. Next, we consider both AC and DC quantum gating protocols and compare the optimal fidelities for these protocols that can be achieved for both the hybrid qubit and the more traditional singlet-triplet qubit. In the second part, we present evidence that silicon offers superior coherence properties by analyzing experimental data from which charge dephasing and spin relaxation times are extracted. We show that the internal degrees of freedom of the hybrid qubit enhance charge coherence, and demonstrate tunable spin loading of a quantum dot. In the last part, we explain three key features of spin-dependent transport — spin blockade, lifetime-enhanced transport and spin-flip cotunneling. We explain how these features arise in the conventional two-electron as well as the unconventional three-electron regimes, using a theoretical model that captures the key characteristics observed in the 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 turbulence: Theoretical and numerical problems
NASA Astrophysics Data System (ADS)
Nemirovskii, Sergey K.
2013-03-01
The term “quantum turbulence” (QT) unifies the wide class of phenomena where the chaotic set of one dimensional quantized vortex filaments (vortex tangles) appear in quantum fluids and greatly influence various physical features. Quantum turbulence displays itself differently depending on the physical situation, and ranges from quasi-classical turbulence in flowing fluids to a near equilibrium set of loops in phase transition. The statistical configurations of the vortex tangles are certainly different in, say, the cases of counterflowing helium and a rotating bulk, but in all the physical situations very similar theoretical and numerical problems arise. Furthermore, quite similar situations appear in other fields of physics, where a chaotic set of one dimensional topological defects, such as cosmic strings, or linear defects in solids, or lines of darkness in nonlinear light fields, appear in the system. There is an interpenetration of ideas and methods between these scientific topics which are far apart in other respects. The main purpose of this review is to bring together some of the most commonly discussed results on quantum turbulence, focusing on analytic and numerical studies. We set out a series of results on the general theory of quantum turbulence which aim to describe the properties of the chaotic vortex configuration, starting from vortex dynamics. In addition we insert a series of particular questions which are important both for the whole theory and for the various applications. We complete the article with a discussion of the hot topic, which is undoubtedly mainstream in this field, and which deals with the quasi-classical properties of quantum turbulence. We discuss this problem from the point of view of the theoretical results stated in the previous sections. We also included section, which is devoted to the experimental and numerical suggestions based on the discussed theoretical models.
Computational approach for calculating bound states in quantum field theory
NASA Astrophysics Data System (ADS)
Lv, Q. Z.; Norris, S.; Brennan, R.; Stefanovich, E.; Su, Q.; Grobe, R.
2016-09-01
We propose a nonperturbative approach to calculate bound-state energies and wave functions for quantum field theoretical models. It is based on the direct diagonalization of the corresponding quantum field theoretical Hamiltonian in an effectively discretized and truncated Hilbert space. We illustrate this approach for a Yukawa-like interaction between fermions and bosons in one spatial dimension and show where it agrees with the traditional method based on the potential picture and where it deviates due to recoil and radiative corrections. This method permits us also to obtain some insight into the spatial characteristics of the distribution of the fermions in the ground state, such as the bremsstrahlung-induced widening.
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.
Domain theoretic structures in quantum information theory
NASA Astrophysics Data System (ADS)
Feng, Johnny
2011-12-01
In this thesis, we continue the study of domain theoretic structures in quantum information theory initiated by Keye Martin and Bob Coecke in 2002. The first part of the thesis is focused on exploring the domain theoretic properties of qubit channels. We discover that the Scott continuous qubit channels are exactly those that are unital or constant. We then prove that the unital qubit channels form a continuous dcpo, and identify various measurements on them. We show that Holevo capacity is a measurement on unital qubit channels, and discover the natural measurement in this setting. We find that qubit channels also form a continuous dcpo, but capacity fails to be a measurement. In the second part we focus on the study of exact dcpos, a domain theoretic structure, closely related to continuous dcpos, possessed by quantum states. Exact dcpos admit a topology, called the exact topology, and we show that the exact topology has an order theoretic characterization similar to the characterization of the Scott topology on continuous dcpos. We then explore the connection between exact and continuous dcpos; first, by identifying an important set of points, called the split points, that distinguishes between exact and continuous structures; second, by exploring a continuous completion of exact dcpos, and showing that we can recover the exact topology from the Scott topology of the completion.
Some Theoretical Studies of Disordered Quantum Systems.
NASA Astrophysics Data System (ADS)
Dobrosavljevic, Vladimir
1988-12-01
In the first part of the thesis, two examples of disordered electronic systems are considered. I first investigate the role of conformational disorder relevant to the electronic structure of conjugated polymers such as polydiacetylene. Both in a solid and in solution the polymer undergoes a conformational transition accompanied by color changes as the temperature is increased. A simple statistical mechanical model for the transition is presented and solved, with the result defining the effective distribution of disorder for the electronic system. Renormalization group methods are then used to calculate the density of states and localization length for the model. Next, I study the fate of a hydrogenic atom in a hard sphere fluid. In this case, the disorder comes from the distribution of open spaces in the fluid accommodating the electron on its way around the nucleus. Simplified models for the electronic propagation in limits of small and large orbitals are presented. Simple variational methods can then be used to calculate the shift and broadening of spectral lines as a function of solvent density. In the second part, I examine the effects of quantum fluctuations on phase transitions in disordered systems. An example where such effects are manifestly important is the proton glass--a random mixture of a ferroelectric and an antiferroelectric component. The system can be described using a quantum mechanical Ising spin glass model, and the mean-field theory is solved using a novel combination of discretized path integral methods and replica techniques. The results show that the glassy phase is more susceptible to destruction by tunneling than are the ordered phases. Finally, I also consider the role of randomness in the size of quantum fluctuations, on the example of an Ising model with randomly mixed classical and quantum spins. For this model, the existence of a critical concentration of quantum spins is demonstrated, below which tunneling cannot destroy the ordered
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
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.
Theoretical investigation of photonic quantum wells and defects
NASA Astrophysics Data System (ADS)
Jiang, Yuankai
In this dissertation, band gaps of photonic crystal slabs are calculated and single and multiple photonic quantum well systems are theoretically investigated. A comprehensive study of defects in the photonic crystal is also presented in the dissertation. The major milestones and current developments in the photonic crystal research are briefly outlined in the introduction. Four theoretical approaches most commonly applied in the photonic crystal studies are reviewed. They are the plane wave expansion method, finite difference time domain method, transfer matrix method and modal expansion with R-matrix propagation algorithm. A comparison of these theoretical methods is discussed and the R-matrix formalism is implemented in the present work. The modal expansion with R-matrix propagation algorithm is applied to calculate the band gap for two-dimensional photonic crystal slabs and the results are compared with experimental measurements and with other numerical calculations. Excellent agreement with experiments is found and the R-matrix formalism proves to be more advantageous than other approaches. These advantages include its stability, efficiency and the fact that it can deal with finite photonic crystal slabs. The effect of the finite photonic slab on the band gap is also discussed. It is demonstrated that the band gap for a photonic slab structure can be controlled by the dielectric contrast, filling factor, filling geometry, lattice structure and polarization of the electric field. A photonic quantum well structure is proposed and investigated by the R-matrix algorithm. The band gap of photonic materials with periodic spatial modulation of the refractive index greater than unity can actually be regarded as a potential barrier for photons. Similar to the semiconductor quantum well systems, a photonic quantum well can be constructed by sandwiching a uniform medium between two photonic barriers due to the photonic band gap mismatch. The transmission and reflection
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
2016-11-01
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.
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.
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.
Quantum Monte Carlo calculations with chiral effective field theory interactions.
Gezerlis, A; Tews, I; Epelbaum, E; Gandolfi, S; Hebeler, K; Nogga, A; Schwenk, A
2013-07-19
We present the first quantum Monte Carlo (QMC) calculations with chiral effective field theory (EFT) interactions. To achieve this, we remove all sources of nonlocality, which hamper the inclusion in QMC calculations, in nuclear forces to next-to-next-to-leading order. We perform auxiliary-field diffusion Monte Carlo (AFDMC) calculations for the neutron matter energy up to saturation density based on local leading-order, next-to-leading order, and next-to-next-to-leading order nucleon-nucleon interactions. Our results exhibit a systematic order-by-order convergence in chiral EFT and provide nonperturbative benchmarks with theoretical uncertainties. For the softer interactions, perturbative calculations are in excellent agreement with the AFDMC results. This work paves the way for QMC calculations with systematic chiral EFT interactions for nuclei and nuclear matter, for testing the perturbativeness of different orders, and allows for matching to lattice QCD results by varying the pion mass.
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 Monte Carlo calculations for light nuclei
Wiringa, R.B.
1998-08-01
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 30 different (j{sup {prime}}, 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.
Photophysical study and theoretical calculations of an ionic liquid crystal bearing oxadiazole
NASA Astrophysics Data System (ADS)
Pedro, Jorge A.; Mora, José R.; Westphal, Eduard; Gallardo, Hugo; Fiedler, Haidi D.; Nome, Faruk
2012-05-01
We report a detailed photophysical study of 1-dodecyl-4-[5-(4-dodecyloxyphenyl)-1,3,4-oxadiazole-2-yl]pyridinium bromide (454Do), a cationic amphiphile that behaves as a fluorescent liquid crystal. Excitation and emission spectra of the probe in different environments result in significant changes in quantum yields which are correlated with changes in lifetimes and theoretical calculations.
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 chemical calculations of glycine glutaric acid
NASA Astrophysics Data System (ADS)
Arioǧlu, ćaǧla; Tamer, Ömer; Avci, Davut; Atalay, Yusuf
2017-02-01
Density functional theory (DFT) calculations of glycine glutaric acid were performed by using B3LYP levels with 6-311++G(d,p) basis set. The theoretical structural parameters such as bond lengths and bond angles are in a good agreement with the experimental values of the title compound. HOMO and LUMO energies were calculated, and the obtained energy gap shows that charge transfer occurs in the title compound. Vibrational frequencies were calculated and compare with experimental ones. 3D molecular surfaces of the title compound were simulated using the same level and basis set. Finally, the 13C and 1H NMR chemical shift values were calculated by the application of the gauge independent atomic orbital (GIAO) method.
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.
Annular tautomerism: experimental observations and quantum mechanics calculations
NASA Astrophysics Data System (ADS)
Cruz-Cabeza, Aurora J.; Schreyer, Adrian; Pitt, William R.
2010-06-01
The use of MP2 level quantum mechanical (QM) calculations on isolated heteroaromatic ring systems for the prediction of the tautomeric propensities of whole molecules in a crystalline environment was examined. A Polarisable Continuum Model was used in the calculations to account for environment effects on the tautomeric relative stabilities. The calculated relative energies of tautomers were compared to relative abundances within the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB). The work was focussed on 84 annular tautomeric forms of 34 common ring systems. Good agreement was found between the calculations and the experimental data even if the quantity of these data was limited in many cases. The QM results were compared to those produced by much faster semiempirical calculations. In a search for other sources of the useful experimental data, the relative numbers of known compounds in which prototropic positions were often substituted by heavy atoms were also analysed. A scheme which groups all annular tautomeric transformations into 10 classes was developed. The scheme was designed to encompass a comprehensive set of known and theoretically possible tautomeric ring systems generated as part of a previous study. General trends across analogous ring systems were detected as a result. The calculations and statistics collected on crystallographic data as well as the general trends observed should be useful for the better modelling of annular tautomerism in the applications such as computer-aided drug design, small molecule crystal structure prediction, the naming of compounds and the interpretation of protein—small molecule crystal structures.
Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study
Michael, Stephan; Chow, Weng; Schneider, Hans
2016-05-01
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 can 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.
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
Quantum Monte Carlo Calculations Applied to Magnetic Molecules
Engelhardt, Larry
2006-01-01
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
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.
Density functional calculation of the structural and electronic properties of germanium quantum dots
NASA Astrophysics Data System (ADS)
Anas, M. M.; Gopir, G.
2015-04-01
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.
A Universal Operator Theoretic Framework for Quantum Fault Tolerance.
NASA Astrophysics Data System (ADS)
Gilbert, Gerald; Calderbank, Robert; Aggarwal, Vaneet; Hamrick, Michael; Weinstein, Yaakov
2008-03-01
We introduce a universal operator theoretic framework for quantum fault tolerance. This incorporates a top-down approach that implements a system-level criterion based on specification of the full system dynamics, applied at every level of error correction concatenation. This leads to more accurate determinations of error thresholds than could previously be obtained. The basis for the approach is the Quantum Computer Condition (QCC), an inequality governing the evolution of a quantum computer. In addition to more accurate determination of error threshold values, we show that the QCC provides a means to systematically determine optimality (or non-optimality) of different choices of error correction coding and error avoidance strategies. This is possible because, as we show, all known coding schemes are actually special cases of the QCC. We demonstrate this by introducing a new, operator theoretic form of entanglement assisted quantum error correction.
Theoretically extensible quantum digital signature with starlike cluster states
NASA Astrophysics Data System (ADS)
Yang, Yu-Guang; Liu, Zhi-Chao; Li, Jian; Chen, Xiu-Bo; Zuo, Hui-Juan; Zhou, Yi-Hua; Shi, Wei-Min
2017-01-01
Chen et al. (Phys Rev A 73:012303,
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.
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.
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.
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.
Calculation of Theoretical Isotropic Compton Profile for Many Particle Systems
NASA Astrophysics Data System (ADS)
Alzubadi, Ali A.; Albayati, Khalil H.
Theoretical isotropic (spherically symmetric) Compton profiles (ICP) have been calculated for many particle systems' He, Li, Be and B atoms in their ground states. Our calculations were performed using Roothan-Hartree-Fock (RHF) wave function, HF wave function of Thakkar and re-optimized HF wave function of Clementi-Roetti, taking into account the impulse approximation. The theoretical analysis included a decomposition of the various intra and inter shells and their contributions in the total ICP. A high momentum region of up to 4 a.u. was investigated and a non-negligible tail was observed in all ICP curves. The existence of a high momentum tail was mainly due to the electron-electron interaction. The ICP for the He atom has been compared with the available experimental data and it is found that the ICP values agree very well with them. A few low order radial momentum expectation values
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 ∗.
Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study
Michael, Stephan; Chow, Weng; Schneider, Hans
2016-05-01
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
Preliminary theoretical acoustic and rf sounding calculations for MILL RACE
Warshaw, S.I.; Dubois, P.F.
1981-11-02
As participant in DOE/ISA's Ionospheric Monitoring Program, LLNL has the responsibility of providing theoretical understanding and calculational support for experimental activities carried out by Los Alamos National Laboratory in using ionospheric sounders to remotely detect violent atmospheric phenomena. We have developed a system of interconnected computer codes which simulate the entire range of atmospheric and ionospheric processes involved in this remote detection procedure. We are able to model the acoustic pulse shape from an atmospheric explosion, the subsequent nonlinear transport of this energy to all parts of the immediate atmosphere including the ionosphere, and the propagation of high-frequency ratio waves through the acoustically perturbed ionosphere. Los Alamos' coverage of DNA's MILL RACE event provided an excellent opportunity to assess the credibility of the calculational system to correctly predict how ionospheric sounders would respond to a surface-based chemical explosion. In this experiment, 600 tons of high explosive were detonated at White Sands Missile Range at 12:35:40 local time on 16 September 1981. Vertical incidence rf phase sounders and bistatic oblique incidence rf sounders fielded by Los Alamos and SRI International throughout New Mexico and southern Colorado detected the ionospheric perturbation that ensued. A brief account of preliminary calculations of the acoustic disturbance and the predicted ionospheric sounder signatures for MILL RACE is presented. (WHK)
The theoretical shape of sucrose crystals from energy calculations
NASA Astrophysics Data System (ADS)
Saska, Michael; Myerson, Allan S.
1983-05-01
The surface energies of individual crystallographic faces of crystalline sucrose were calculated using two forms of the 6-exp (Buckingham) potential. Hydrogen bond energies were calculated as a sum of O-H, O…H and O…O interactions where the Lippincott-Schroeder short-range potential was used for O-H and O…H pairs and the 6-exp potential for the non-bonded O…O interactions. Assuming that the surface energy equals half of the cohesive energy of the crystal, the attachment and surface energies of most of the faces found on as sucrose crystal were calculated. A computer program was written to draw the theoretical shape of crystals given the positions (central distances) of its faces. The resulting sucrose shapes are elongated along the c-axis. It is argued that the c-axis elongated habit is an intrinsic shape for vapor grown sucrose crystals (if realizable) and it is suggested that the usual shapes of solution grown sucrose crystals can be explained in terms of solvent (water) adsorption.
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.
Some theoretical aspects of quantum mechanical equations in Rindler space
NASA Astrophysics Data System (ADS)
Mitra, Soma; Chakrabarty, Somenath
2017-03-01
In this article we have investigated theoretical aspects of the solutions of some of the quantum mechanical problems in Rindler space. We have developed formalisms for the exact analytical solutions for the relativistic equations, along with the approximate form of solutions for the Schrödinger equation. The Hamiltonian operator in Rindler space is found to be non-Hermitian in nature, whereas the energy eigen values are observed to be real in nature. We have noticed that the sole reason behind such real behavior is the PT -symmetric form of the Hamiltonian operator. We have also observed that the energy eigen values are negative, lineraly quantized and the quantum mechanical system becomes more and more bound with the increase in the strength of gravitational field strength produced by the strongly gravitating objects, e.g., black holes, which is classical in nature.
Quantum mechanical calculations and mineral spectroscopy
NASA Astrophysics Data System (ADS)
Kubicki, J. D.
2006-05-01
Interpretation of spectra in systems of environmental interest is not generally straightforward due to the lack of close analogs and a clear structure of some components of the system. Computational chemistry can be used as an objective method to test interpretations of spectra. This talk will focus on applying ab initio methods to complement vibrational, NMR, and EXAFS spectroscopic information. Examples of systems studied include phosphate/Fe-hydroxides, arsenate/Al- and Fe-hydroxide, fractured silica surfaces. Phosphate interactions with Fe-hydroxides are important in controlling nutrient availability in soils and transport within streams. In addition, organo-phosphate bonding may be a key attachment mechanism for bacteria at Fe-oxide surfaces. Interpretation of IR spectra is enhanced by model predictions of vibrational frequencies for various surface complexes. Ab initio calculations were used to help explain As(V) and As(III) adsorption behavior onto amorphous Al- and Fe-hydroxides in conjunction with EXAFS measurements. Fractured silica surfaces have been implicated in silicosis. These calculations test structures that could give rise to radical formation on silica surfaces. Calculations to simulate the creation of Si and SiO radical species on sufaces and their subsequent production of OH radicals will be discussed.
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.
Exact geometries from quantum chemical calculations
NASA Astrophysics Data System (ADS)
Cremer, Dieter; Kraka, Elfi; He, Yuan
2001-06-01
For seventeen molecules, complete basis set (CBS) geometries are obtained for Møller-Plesset perturbation methods at second (MP2), fourth (MP4), and sixth order (MP6) as well as for the Coupled Cluster methods CCD, CCSD, and CCSD( T). The correlation consistent basis sets cc-pVDZ, cc-pVTZ, and cc-pVQZ were systematically applied and calculated geometries extrapolated to the limit of an infinitely large basis set. MP6 equilibrium geometries are more accurate than MP2 or MP4 geometries at the CBS limit and provide AH bond lengths with an accuracy of 0.001 Å. However, AB bonds are always predicted too long because of the lack of sufficient coupling effects between p-electron correlation at MP6. CCSD( T) provides reasonable AB bond lengths although these are in general too short by 0.003 Å. Due to error cancellation very accurate geometries are obtained at the CCSD( T)/cc-pVTZ and CCSD( T)/cc-pVQZ level of theory. With the help of the accurate equilibrium geometries obtained in this work, several experimentally based geometries could be corrected. The effects of HF-optimized basis sets, diffuse functions or the frozen core approximation on geometry optimizations are discussed. It is emphasized that the use of the cc-pVDZ or any other VDZ+P basis set should be avoided in correlation corrected ab initio calculations.
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.
Infrared and theoretical calculations in 2-halocycloheptanones conformational analysis.
Rozada, Thiago C; Gauze, Gisele F; Favaro, Denize C; Rittner, Roberto; Basso, Ernani A
2012-08-01
2-Halocycloheptanones (Halo=F, Cl, Br and I) were synthesized and their conformational analysis was performed through infrared spectroscopy data. The corresponding conformers geometries and energies were obtained by theoretical calculations at B3LYP/aug-cc-pVDZ level of theory in the isolated state and in solution. It was observed, by both approaches, that the conformational preferences were very sensitive to the solvent polarity, since its increase led to an increase in the population of the more polar conformer. An analysis of these conformational equilibria showed they suffer also the influence of stereoelectronic effects, like hyperconjugation and steric effects. These results were interpreted using natural bond orbital (NBO) analysis, which indicated that the electronic delocalization to the orbital π*(C=O) is directly involved in the stability increase of conformers I and II. The relative effect of the period of the halogen can also be noted, with changes in the conformational preferences and in the energies involved in the interactions of NBO.
[Terahertz Absorption Spectra Simulation of Glutamine Based on Quantum-Chemical Calculation].
Zhang, Tian-yao; Zhang, Zhao-hui; Zhao, Xiao-yan; Zhang, Han; Yan, Fang; Qian, Ping
2015-08-01
With simulation of absorption spectra in THz region based on quantum-chemical calculation, the THz absorption features of target materials can be assigned with theoretical normal vibration modes. This is necessary for deeply understanding the origin of THz absorption spectra. The reliabilities of simulation results mainly depend on the initial structures and theoretical methods used throughout the calculation. In our study, we utilized THz-TDS to obtain the THz absorption spectrum of solid-state L-glutamine. Then three quantum-chemical calculation schemes with different initial structures commonly used in previous studies were proposed to study the inter-molecular interactions' contribution to the THz absorption of glutamine, containing monomer structure, dimer structure and crystal unit cell structure. After structure optimization and vibration modes' calculation based on density functional theory, the calculation results were converted to absorption spectra by Lorentzian line shape function for visual comparison with experimental spectra. The result of dimmer structure is better than monomer structure in number of absorption features while worse than crystal unit cell structure in position of absorption peaks. With the most reliable simulation result from crystal unit cell calculation, we successfully assigned all three experimental absorption peaks of glutamine ranged from 0.3 to 2.6 THz with overall vibration modes. Our study reveals that the crystal unit cell should be used as initial structure during theoretical simulation of solid-state samples' THz absorption spectrum which comprehensively considers not only the intra-molecular interactions but also inter-molecular interactions.
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.
Efficient free energy calculations of quantum systems through computer simulations
NASA Astrophysics Data System (ADS)
Antonelli, Alex; Ramirez, Rafael; Herrero, Carlos; Hernandez, Eduardo
2009-03-01
In general, the classical limit is assumed in computer simulation calculations of free energy. This approximation, however, is not justifiable for a class of systems in which quantum contributions for the free energy cannot be neglected. The inclusion of quantum effects is important for the determination of reliable phase diagrams of these systems. In this work, we present a new methodology to compute the free energy of many-body quantum systems [1]. This methodology results from the combination of the path integral formulation of statistical mechanics and efficient non-equilibrium methods to estimate free energy, namely, the adiabatic switching and reversible scaling methods. A quantum Einstein crystal is used as a model to show the accuracy and reliability the methodology. This new method is applied to the calculation of solid-liquid coexistence properties of neon. Our findings indicate that quantum contributions to properties such as, melting point, latent heat of fusion, entropy of fusion, and slope of melting line can be up to 10% of the calculated values using the classical approximation. [1] R. M. Ramirez, C. P. Herrero, A. Antonelli, and E. R. Hernández, Journal of Chemical Physics 129, 064110 (2008)
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
2013-12-30
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.
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.
Efficient method for the calculation of dissipative quantum transport in quantum cascade lasers.
Greck, Peter; Birner, Stefan; Huber, Bernhard; Vogl, Peter
2015-03-09
We present a novel and very efficient method for calculating quantum transport in quantum cascade lasers (QCLs). It follows the nonequilibrium Green's function (NEGF) framework but sidesteps the calculation of lesser self-energies by replacing them by a quasi-equilibrium expression. This method generalizes the phenomenological Büttiker probe model by taking into account individual scattering mechanisms. It is orders of magnitude more efficient than a fully self-consistent NEGF calculation for realistic devices. We apply this method to a new THz QCL design which works up to 250 K - according to our calculations.
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.
Quantum mechanical calculation of Rydberg-Rydberg autoionization rates
NASA Astrophysics Data System (ADS)
Kiffner, Martin; Ceresoli, Davide; Li, Wenhui; Jaksch, Dieter
2016-10-01
We present quantum mechanical calculations of autoionization rates for two rubidium Rydberg atoms with weakly overlapping electron clouds. We neglect exchange effects and consider tensor products of independent atom states forming an approximate basis of the two-electron state space. We consider large sets of two-atom states with randomly chosen quantum numbers and find that the charge overlap between the two Rydberg electrons allows one to characterise the magnitude of the autoionization rates. If the electron clouds overlap by more than one percent, the autoionization rates increase approximately exponentially with the charge overlap. This finding is independent of the energy of the initial state.
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 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
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.
Infinite variance in fermion quantum Monte Carlo calculations.
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.
Husimi-Wehrl entropy in the quantum chaotic system -An efficient calculational method-
NASA Astrophysics Data System (ADS)
Tsukiji, Hidekazu; Iida, Hideaki; Kunihiro, Teiji; Ohnishi, Akira
2014-09-01
Early thermalization in heavy ion collisions still remains a theoretical challenge. It was suggested in the hydrodynamical analyses of the relativistic heavy-ion collisions at RHIC and later at LHC. There are many proposals for pinning down the underlying mechanism for it. Quantum fluctuations on top of the classical configurations (glasma) are found to induce instabilities. It may trigger the chaotic behavior of the gauge field and eventually give rise to entropy production. In this work, we investigate thermalization of glasma by using the Husimi-Wehrl entropy. Quasi-distribution function defined in phase space should be useful to describe possible chaotic behavior of a quantum system. We adopt the Husimi distribution function to discuss entropy production of quantum systems. Husimi function is a minimally coarse-grained Wigner function and semi-positive definite. As a first stage of the study, we calculate the Husimi-Wehrl (H-W) entropy of a quantum Yang-Mills system [Tsai, Muller (2012)] with two-degrees of freedom. We propose a Monte-Carlo method to numerically calculate the time evolution of the Husimi function and the H-W entropy. We also discuss an extension of the method to quantum field theories.
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.
Quantum Monte Carlo Calculations of Nanostructure Optical Properties
NASA Astrophysics Data System (ADS)
Williamson, Andrew
2003-03-01
Near linear scaling Quantum Monte Carlo (QMC) calculations[1] are used to calculate the optical gaps, electron affinities, and ionization potentials of silicon and germanium quantum dots ranging in size from 0 to 2 nm[2]. These QMC results are used to examine the accuracy of semi-empirical and density functional (DFT) calculations. We find optical gaps are underestimated by DFT by 1-2 eV depending on choice of functional. Corrections introduced by the time dependent formalisms are found to be minimal in these systems. Our results also show that quantum confinement in germanium is significantly greater than in silicon leading to a crossover of their optical gaps in dots between 2 and 3 nm in size, verifying recent experiment observations. [1] A. J. Williamson, R.Q. Hood and J.C. Grossman, Phys. Rev. Lett. 87, 246406-1 (2001). [2] A.J. Williamson J.C. Grossman, R.Q. Hood, A. Puzder and Giulia Galli, Phys. Rev. Lett, 89, 196803 (2002).
Vibrational spectroscopic studies of Isoleucine by quantum chemical calculations.
Moorthi, P P; Gunasekaran, S; Ramkumaar, G R
2014-04-24
In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of Isoleucine (2-Amino-3-methylpentanoic acid). The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments, thermodynamics properties, NBO analyses, NMR chemical shifts and ultraviolet-visible spectral interpretation of Isoleucine have been studied by performing MP2 and DFT/cc-pVDZ level of theory. The FTIR, FT-Raman spectra were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. The UV-visible absorption spectra of the compound were recorded in the range of 200-800 nm. Computational calculations at MP2 and B3LYP level with basis set of cc-pVDZ is employed in complete assignments of Isoleucine molecule on the basis of the potential energy distribution (PED) of the vibrational modes, calculated using VEDA-4 program. The calculated wavenumbers are compared with the experimental values. The difference between the observed and calculated wavenumber values of most of the fundamentals is very small. (13)C and (1)H nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method and compared with experimental results. The formation of hydrogen bond was investigated in terms of the charge density by the NBO calculations. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands were carried out. Besides, molecular electrostatic potential (MEP) were investigated using theoretical calculations.
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.
Díaz, Natalia; Suárez, Dimas; Sordo, Tomás L
2003-11-30
Herein, we present theoretical results on the conformational properties of benzylpenicillin, which are characterized by means of quantum chemical calculations (MP2/6-31G* and B3LYP/6-31G*) and classical molecular dynamics simulations (5 ns) both in the gas phase and in aqueous solution. In the gas phase, the benzylpenicillin conformer in which the thiazolidine ring has the carboxylate group oriented axially is the most favored one. Both intramolecular CH. O and dispersion interactions contribute to stabilize the axial conformer with respect to the equatorial one. In aqueous solution, a molecular dynamics simulation predicts a relative population of the axial:equatorial conformers of 0.70:0.30 in consonance with NMR experimental data. Overall, the quantum chemical calculations as well as the simulations give insight into substituent effects, the conformational dynamics of benzylpenicillin, the frequency of ring-puckering motions, and the correlation of side chain and ring-puckering motions.
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.
Theoretical calculations of EPR parameters of gas phase hydracrylonitrile radical
NASA Astrophysics Data System (ADS)
Sarikaya, Ebru Karakaş; Dereli, Ömer
2017-02-01
As a result of detailed conformational search of the hydracrylonitrile, four different conformers of molecule have been obtained. For these conformations, eleven possible radicals were modelled by using density functional theory (DFT) computations with respect to molecular structure. Electron Paramagnetic Resonance parameters of these model radicals were calculated and then they were compared with the experimental ones. Geometry optimizations of the molecule and modeled radicals were calculated by B3LYP method using 6-311++G(d,p) basis sets in gas phase.
Banerjee, Subhashish; Alok, Ashutosh Kumar; Srikanth, R; Hiesmayr, Beatrix C
Correlations exhibited by neutrino oscillations are studied via quantum-information theoretic quantities. We show that the strongest type of entanglement, genuine multipartite entanglement, is persistent in the flavor changing states. We prove the existence of Bell-type nonlocal features, in both its absolute and genuine avatars. Finally, we show that a measure of nonclassicality, dissension, which is a generalization of quantum discord to the tripartite case, is nonzero for almost the entire range of time in the evolution of an initial electron-neutrino. Via these quantum-information theoretic quantities, capturing different aspects of quantum correlations, we elucidate the differences between the flavor types, shedding light on the quantum-information theoretic aspects of the weak force.
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.
Theoretical calculation of heat capacity by using third virial coefficient
NASA Astrophysics Data System (ADS)
Mamedov, Bahtiyar Akber; Somuncu, Elif
2017-02-01
We have presented a new formula to determine the heat capacity for real gaseous. This formula is a simple and more accurate analytical approximation for heat capacity using third virial coefficient over Lennard-Jones (12-6) potential. The calculation results of heat capacity show a good agreement with the data in the literature. The consistency of results demonstrates that the proposed formula is applicable to real gaseous.
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.
Surface Chemistry of Semiconducting Quantum Dots: Theoretical Perspectives.
Kilina, Svetlana V; Tamukong, Patrick K; Kilin, Dmitri S
2016-10-18
Colloidal quantum dots (QDs) are near-ideal nanomaterials for energy conversion and lighting technologies. However, their photophysics exhibits supreme sensitivity to surface passivation and defects, of which control is problematic. The role of passivating ligands in photodynamics remains questionable and is a focus of ongoing research. The optically forbidden nature of surface-associated states makes direct measurements on them challenging. Therefore, computational modeling is imperative for insights into surface passivation and its impact on light-driven processes in QDs. This Account discusses challenges and recent progress in understanding surface effects on the photophysics of QDs addressed via quantum-chemical calculations. We overview different methods, including the effective mass approximation (EMA), time-dependent density functional theory (TDDFT), and multiconfiguration approaches, considering their strengths and weaknesses relevant to modeling of QDs with a complicated surface. We focus on CdSe, PbSe, and Si QDs, where calculations successfully explain experimental trends sensitive to surface defects, doping, and ligands. We show that the EMA accurately describes both linear and nonlinear optical properties of large-sized CdSe QDs (>2.5 nm), while TDDFT is required for smaller QDs where surface effects dominate. Both approaches confirm efficient two-photon absorption enabling applications of QDs as nonlinear optical materials. TDDFT also describes the effects of morphology on the optical response of QDs: the photophysics of stoichiometric, magic-sized XnYn (X = Cd, Pb; Y = S, Se) QDs is less sensitive to their passivation compared with nonstoichiometric Xn≠mYm QDs. In the latter, surface-driven optically inactive midgap states can be eliminated by anionic ligands, explaining the better emission of metal-enriched QDs compared with nonmetal-enriched QDs. Ideal passivation of magic-sized QDs by amines and phosphine oxides leaves lower-energy transitions
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.
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.
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.
Calculation of exchange interaction for modified Gaussian coupled quantum dots
NASA Astrophysics Data System (ADS)
Khordad, R.
2017-03-01
A system of two laterally coupled quantum dots with modified Gaussian potential has been considered. Each quantum dot has an electron under electric and magnetic field. The quantum dots have been considered as hydrogen-like atoms. The physical picture has translated into the Heisenberg spin Hamiltonian. The Schrödinger equation using finite element method has been numerically solved. The exchange energy factor has been calculated as a functions of electric field, magnetic field, and the separation distance between the centers of the dots (d). According to the results, it is found that there is the transition from anti-ferromagnetic to ferromagnetic for constant electric field. Also, the transition occurs from ferromagnetic to anti-ferromagnetic for constant magnetic field (B>1 T). With decreasing the distance between the centers of the dots and increasing magnetic field, the transition occurs from anti-ferromagnetic to ferromagnetic. It is found that a switching of exchange energy factor is presented without canceling the interactions of the electric and magnetic fields on the system.
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)
Accelerating atomistic calculations of quantum energy eigenstates on graphic cards
NASA Astrophysics Data System (ADS)
Rodrigues, Walter; Pecchia, A.; Lopez, M.; Auf der Maur, M.; Di Carlo, A.
2014-10-01
Electronic properties of nanoscale materials require the calculation of eigenvalues and eigenvectors of large matrices. This bottleneck can be overcome by parallel computing techniques or the introduction of faster algorithms. In this paper we report a custom implementation of the Lanczos algorithm with simple restart, optimized for graphical processing units (GPUs). The whole algorithm has been developed using CUDA and runs entirely on the GPU, with a specialized implementation that spares memory and reduces at most machine-to-device data transfers. Furthermore parallel distribution over several GPUs has been attained using the standard message passing interface (MPI). Benchmark calculations performed on a GaN/AlGaN wurtzite quantum dot with up to 600,000 atoms are presented. The empirical tight-binding (ETB) model with an sp3d5s∗+spin-orbit parametrization has been used to build the system Hamiltonian (H).
Automated quantum conductance calculations using maximally-localised Wannier functions
NASA Astrophysics Data System (ADS)
Shelley, Matthew; Poilvert, Nicolas; Mostofi, Arash A.; Marzari, Nicola
2011-10-01
A robust, user-friendly, and automated method to determine quantum conductance in quasi-one-dimensional systems is presented. The scheme relies upon an initial density-functional theory calculation in a specific geometry after which the ground-state eigenfunctions are transformed to a maximally-localised Wannier function (MLWF) basis. In this basis, our novel algorithms manipulate and partition the Hamiltonian for the calculation of coherent electronic transport properties within the Landauer-Buttiker formalism. Furthermore, we describe how short-ranged Hamiltonians in the MLWF basis can be combined to build model Hamiltonians of large (>10,000 atom) disordered systems without loss of accuracy. These automated algorithms have been implemented in the Wannier90 code (Mostofi et al., 2008) [1], which is interfaced to a number of electronic structure codes such as Quantum-ESPRESSO, AbInit, Wien2k, SIESTA and FLEUR. We apply our methods to an Al atomic chain with a Na defect, an axially heterostructured Si/Ge nanowire and to a spin-polarised defect on a zigzag graphene nanoribbon.
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
Kasprzak, Maria; Fabijańska, Małgorzata; Chęcińska, Lilianna; Szmigiero, Leszek; Ochocki, Justyn
2016-04-13
This work presents the synthesis, spectroscopic properties and single-crystal X-ray examination of the structure of 3-hydroxyiminoflavanone and its palladium complex. It presents the results of NMR (Nuclear Magnetic Resonance) spectroscopy, electron-density studies based on X-ray wavefunction refinement and theoretical calculations combined with QTAIM (Quantum Theory of Atoms in Molecules) and ELI-D (Electron Localizability Indicator) analyses. These offer an interesting new insight into the structures and behavior of flavanone and its complex, in solid state and in solution. The study also examines the cytotoxicity of the ligand and its complex against three human ovarian and lung cancer cell lines.
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…
A theoretical study of blue phosphorene nanoribbons based on first-principles calculations
Xie, Jiafeng; Si, M. S. Yang, D. Z.; Zhang, Z. Y.; Xue, D. S.
2014-08-21
Based on first-principles calculations, we present a quantum confinement mechanism for the band gaps of blue phosphorene nanoribbons (BPNRs) as a function of their widths. The BPNRs considered have either armchair or zigzag shaped edges on both sides with hydrogen saturation. Both the two types of nanoribbons are shown to be indirect semiconductors. An enhanced energy gap of around 1 eV can be realized when the ribbon's width decreases to ∼10 Å. The underlying physics is ascribed to the quantum confinement effect. More importantly, the parameters to describe quantum confinement are obtained by fitting the calculated band gaps with respect to their widths. The results show that the quantum confinement in armchair nanoribbons is stronger than that in zigzag ones. This study provides an efficient approach to tune the band gap in BPNRs.
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.
Open Quantum Dynamics Calculations with the Hierarchy Equations of Motion on Parallel Computers.
Strümpfer, Johan; Schulten, Klaus
2012-08-14
Calculating the evolution of an open quantum system, i.e., a system in contact with a thermal environment, has presented a theoretical and computational challenge for many years. With the advent of supercomputers containing large amounts of memory and many processors, the computational challenge posed by the previously intractable theoretical models can now be addressed. The hierarchy equations of motion present one such model and offer a powerful method that remained under-utilized so far due to its considerable computational expense. By exploiting concurrent processing on parallel computers the hierarchy equations of motion can be applied to biological-scale systems. Herein we introduce the quantum dynamics software PHI, that solves the hierarchical equations of motion. We describe the integrator employed by PHI and demonstrate PHI's scaling and efficiency running on large parallel computers by applying the software to the calculation of inter-complex excitation transfer between the light harvesting complexes 1 and 2 of purple photosynthetic bacteria, a 50 pigment system.
NASA Astrophysics Data System (ADS)
Brandsema, Matthew J.; Narayanan, Ram M.; Lanzagorta, Marco
2017-01-01
The concept of the quantum radar cross section (QRCS) has generated interest due to its promising feature of enhanced side lobe target visibility in comparison to the classical radar cross section. Researchers have simulated the QRCS for very limited geometries and even developed approximations to reduce the computational complexity of the simulations. This paper develops an alternate theoretical framework for calculating the QRCS. This new framework yields an alternative form of the QRCS expression in terms of Fourier transforms. This formulation is much easier to work with mathematically and allows one to derive analytical solutions for various geometries, which provides an explanation for the aforementioned sidelobe advantage. We also verify the resulting equations by comparing with numerical simulations, as well as provide an error analysis of these simulations to ensure the accuracy of the results. Comparison of our simulation results with the analytical solutions reveal that they agree with one another extremely well.
Molecular thermodynamics of metabolism: quantum thermochemical calculations for key metabolites.
Hadadi, N; Ataman, M; Hatzimanikatis, V; Panayiotou, C
2015-04-28
The present work is the first of a series of papers aiming at a coherent and unified development of the thermodynamics of metabolism and the rationalization of feasibility analysis of metabolic pathways. The focus in this part is on high-level quantum chemical calculations of the thermochemical quantities of relatively heavy metabolites such as amino acids/oligopeptides, nucleosides, saccharides and their derivatives in the ideal gas state. The results of this study will be combined with the corresponding hydration/solvation results in subsequent parts of this work in order to derive the desired thermochemical quantities in aqueous solutions. The above metabolites exist in a vast conformational/isomerization space including rotational conformers, tautomers or anomers exhibiting often multiple or cooperative intramolecular hydrogen bonding. We examine the challenges posed by these features for the reliable estimation of thermochemical quantities. We discuss conformer search, conformer distribution and averaging processes. We further consider neutral metabolites as well as protonated and deprotonated metabolites. In addition to the traditional presentation of gas-phase acidities, basicities and proton affinities, we also examine heats and free energies of ionic species. We obtain simple linear relations between the thermochemical quantities of ions and the formation quantities of their neutral counterparts. Furthermore, we compare our calculations with reliable experimental measurements and predictive calculations from the literature, when available. Finally, we discuss the next steps and perspectives for this work.
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
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.
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.
Quantum plasmonics: from jellium models to ab initio calculations
NASA Astrophysics Data System (ADS)
Varas, Alejandro; García-González, Pablo; Feist, Johannes; García-Vidal, F. J.; Rubio, Angel
2016-08-01
Light-matter interaction in plasmonic nanostructures is often treated within the realm of classical optics. However, recent experimental findings show the need to go beyond the classical models to explain and predict the plasmonic response at the nanoscale. A prototypical system is a nanoparticle dimer, extensively studied using both classical and quantum prescriptions. However, only very recently, fully ab initio time-dependent density functional theory (TDDFT) calculations of the optical response of these dimers have been carried out. Here, we review the recent work on the impact of the atomic structure on the optical properties of such systems. We show that TDDFT can be an invaluable tool to simulate the time evolution of plasmonic modes, providing fundamental understanding into the underlying microscopical mechanisms.
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
A quantum theoretical explanation for probability judgment errors.
Busemeyer, Jerome R; Pothos, Emmanuel M; Franco, Riccardo; Trueblood, Jennifer S
2011-04-01
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 spaces defined by features and similarities between vectors to determine probability judgments. On the other hand, quantum probability theory is a generalization of Bayesian probability theory because it is based on a set of (von Neumann) axioms that relax some of the classic (Kolmogorov) axioms. The quantum model is compared and contrasted with other competing explanations for these judgment errors, including the anchoring and adjustment model for probability judgments. In the quantum model, a new fundamental concept in cognition is advanced--the compatibility versus incompatibility of questions and the effect this can have on the sequential order of judgments. We conclude that quantum information-processing principles provide a viable and promising new way to understand human judgment and reasoning.
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.
1991-06-28
AD-A238 853 ANOMALOUS DISPERSION IN GASES DERIVED FROM THE OPTICAL DEPTH. THEORETICAL TREATMENT; LINE BY LINE CALCULATIONS BY EGIL BINGEN . BJ0RNAR...06054 917 1 04 ANOMALOUS DISPERSION IN GASES DERIVED FROM THE OPTICAL DEPTH. THEORETICAL TREATMENT; LINE BY LINE CALCULATIONS by - EGII, BINGEN . BJORNAR... BINGEN Egil, YSTAD Bjornar 61 DISTRIBUTION STATEMENT Approved for pub’ic release. Distribution unlimited (Offentlig tilgjengelig) 7) INDEXING TERMS IN
Theoretical realization and application of parity-time-symmetric oscillators in a quantum regime
NASA Astrophysics Data System (ADS)
Li, Wenlin; Li, Chong; Song, Heshan
2017-02-01
In the existing parity-time (PT ) symmetry with the balanced gain and loss, the gain is derived from semiclassical but not full quantum theories, which significantly restricts the applications of PT symmetry in quantum fields. In this work, we propose and analyze a theoretical scheme to realize full quantum oscillator PT symmetry. The quantum gain is provided by a dissipation optical cavity with a blue-detuned laser field. After adiabatically eliminating the cavity modes, we give an effective master equation, which is a complete quantum description compared with the non-Hermitian Hamiltonian, to reveal the quantum behaviors of such a gain oscillator. This kind of PT symmetry can eliminate the dissipation effect in the quantum regime. As an example, we apply PT -symmetric oscillators to enhance optomechanically induced transparency.
NASA Astrophysics Data System (ADS)
Lakshmi, A.; Balachandran, V.
2013-02-01
FT-IR and FT-Raman spectra of N-(2-hydroxyethyl)phthalimide (NHEP) have been recorded and analyzed. The stable isomer of NHEP is determined. The optimization geometry, intermolecular hydrogen bonding, and harmonic vibrational wavenumber of NHEP have been investigated with the help of B3LYP scaled quantum mechanical (SQM) method. The infrared and Raman spectra were predicted theoretically from the calculated intensities. Natural bond orbital (NBO) analysis indicates the presence of Cdbnd O⋯H in the molecule. The calculated HOMO and LUMO are important in determining such properties as molecular reactivity. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with electrostatic potential (ESP).
Theoretical discussion for quantum computation in biological systems
NASA Astrophysics Data System (ADS)
Baer, Wolfgang
2010-04-01
Analysis of the brain as a physical system, that has the capacity of generating a display of every day observed experiences and contains some knowledge of the physical reality which stimulates those experiences, suggests the brain executes a self-measurement process described by quantum theory. Assuming physical reality is a universe of interacting self-measurement loops, we present a model of space as a field of cells executing such self-measurement activities. Empty space is the observable associated with the measurement of this field when the mass and charge density defining the material aspect of the cells satisfy the least action principle. Content is the observable associated with the measurement of the quantum wave function ψ interpreted as mass-charge displacements. The illusion of space and its content incorporated into cognitive biological systems is evidence of self-measurement activity that can be associated with quantum operations.
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.
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...
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.
Theoretical calculation of Joule-Thomson coefficient by using third virial coefficient
NASA Astrophysics Data System (ADS)
Mamedov, Bahtiyar Akber; Somuncu, Elif; Askerov, Iskender M.
2017-02-01
The Joule-Thomson coefficient has been theoretical investigated by using third virial coefficient. Established expressions enable us accurate and rapid calculations of Joule-Thomson coefficient. As seen from numerical results the analytical expressions for third virial coefficients are a very useful, giving a very fast method to calculate other thermodynamics properties of gasses. As an example, the calculation results have been successfully tested by using various literature data.
Calculation of the axion mass based on high-temperature lattice quantum chromodynamics.
Borsanyi, S; Fodor, Z; Guenther, J; Kampert, K-H; Katz, S D; Kawanai, T; Kovacs, T G; Mages, S W; Pasztor, A; Pittler, F; Redondo, J; Ringwald, A; Szabo, K K
2016-11-03
Unlike the electroweak sector of the standard model of particle physics, quantum chromodynamics (QCD) is surprisingly symmetric under time reversal. As there is no obvious reason for QCD being so symmetric, this phenomenon poses a theoretical problem, often referred to as the strong CP problem. The most attractive solution for this requires the existence of a new particle, the axion-a promising dark-matter candidate. Here we determine the axion mass using lattice QCD, assuming that these particles are the dominant component of dark matter. The key quantities of the calculation are the equation of state of the Universe and the temperature dependence of the topological susceptibility of QCD, a quantity that is notoriously difficult to calculate, especially in the most relevant high-temperature region (up to several gigaelectronvolts). But by splitting the vacuum into different sectors and re-defining the fermionic determinants, its controlled calculation becomes feasible. Thus, our twofold prediction helps most cosmological calculations to describe the evolution of the early Universe by using the equation of state, and may be decisive for guiding experiments looking for dark-matter axions. In the next couple of years, it should be possible to confirm or rule out post-inflation axions experimentally, depending on whether the axion mass is found to be as predicted here. Alternatively, in a pre-inflation scenario, our calculation determines the universal axionic angle that corresponds to the initial condition of our Universe.
Calculation of the axion mass based on high-temperature lattice quantum chromodynamics
NASA Astrophysics Data System (ADS)
Borsanyi, S.; Fodor, Z.; Guenther, J.; Kampert, K.-H.; Katz, S. D.; Kawanai, T.; Kovacs, T. G.; Mages, S. W.; Pasztor, A.; Pittler, F.; Redondo, J.; Ringwald, A.; Szabo, K. K.
2016-11-01
Unlike the electroweak sector of the standard model of particle physics, quantum chromodynamics (QCD) is surprisingly symmetric under time reversal. As there is no obvious reason for QCD being so symmetric, this phenomenon poses a theoretical problem, often referred to as the strong CP problem. The most attractive solution for this requires the existence of a new particle, the axion—a promising dark-matter candidate. Here we determine the axion mass using lattice QCD, assuming that these particles are the dominant component of dark matter. The key quantities of the calculation are the equation of state of the Universe and the temperature dependence of the topological susceptibility of QCD, a quantity that is notoriously difficult to calculate, especially in the most relevant high-temperature region (up to several gigaelectronvolts). But by splitting the vacuum into different sectors and re-defining the fermionic determinants, its controlled calculation becomes feasible. Thus, our twofold prediction helps most cosmological calculations to describe the evolution of the early Universe by using the equation of state, and may be decisive for guiding experiments looking for dark-matter axions. In the next couple of years, it should be possible to confirm or rule out post-inflation axions experimentally, depending on whether the axion mass is found to be as predicted here. Alternatively, in a pre-inflation scenario, our calculation determines the universal axionic angle that corresponds to the initial condition of our Universe.
Group Theoretical Approach for Controlled Quantum Mechanical Systems
2007-11-06
evolution equation with Hamiltonians which may possess discrete , continuous, and mixed spectrum. For such a quantum system, the Hamiltonian operator...study of classical linear and nonlinear systems, which proves to be very useful in understanding the design problems such as disturbance decoupling...developed by Kunita can then be implemented to establish controllability conditions for the original time-dependent Schrodinger control problem. The end
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.
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.
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.
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.
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.
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.
Theoretical Study of Solid State Quantum Information Processing
2013-08-28
odd effects of Heisenberg chains on long-range interaction and entanglement, Physical Review B, (10 2010): 140403. doi: 10.1103/PhysRevB.82.140403 08...interface-bound electrons in silicon: An effective mass study, Physical Review B, (10 2011): 0. doi: 10.1103/PhysRevB.84.155320 08/31/2012 18.00 Xuedong...Xuedong Hu. Effect of randomness on quantum data buses of Heisenberg spin chains, Physical Review B, (06 2012): 0. doi: 10.1103/PhysRevB.85.224418
Tantillo, Dean J
2013-08-01
This Highlight describes applications of quantum chemical calculations to problems in natural products chemistry, including the elucidation of natural product structures (distinguishing between constitutional isomers, distinguishing between diastereomers, and assigning absolute configuration) and determination of reasonable mechanisms for their formation.
Theoretical calculation of electronic stopping power of water vapor by proton impact
Olivera, G.H.; Martinez, A.E.; Rivarola, R.D.
1995-11-01
The energy loss of proton beams in water vapor is analyzed with a full quantum-mechanical treatment, the distorted-wave model. This model takes into account distortion effects due to the long-range Coulomb potential. Projectile energies from 10 keV up to 1 MeV are considered. Mean stopping power and equilibrium charge-state fractions are calculated and compared with experimental data. The validity of Bragg`s additivity rule is investigated. 35 refs., 5 figs.
On the Notion of Truth in Quantum Mechanics: a Category-Theoretic Standpoint
NASA Astrophysics Data System (ADS)
Karakostas, Vassilios; Zafiris, Elias
The category-theoretic representation of quantum event structures provides a canonical setting for confronting the fundamental problem of truth valuation in quantum mechanics as exemplified, in particular, by Kochen-Specker's theorem. In the present study, this is realized on the basis of the existence of a categorical adjunction between the category of sheaves of variable local Boolean frames, constituting a topos, and the category of quantum event algebras. We show explicitly that the latter category is equipped with an object of truth values, or classifying object, which constitutes the appropriate tool for assigning truth values to propositions describing the behavior of quantum systems. Effectively, this category-theoretic representation scheme circumvents consistently the semantic ambiguity with respect to truth valuation that is inherent in conventional quantum mechanics by inducing an objective contextual account of truth in the quantum domain of discourse. The philosophical implications of the resulting account are analyzed. We argue that it subscribes neither to a pragmatic instrumental nor to a relative notion of truth. Such an account essentially denies that there can be a universal context of reference or an Archimedean standpoint from which to evaluate logically the totality of facts of nature. In this light, the transcendence condition of the usual conception of correspondence truth is superseded by a reflective-like transcendental reasoning of the proposed account of truth that is suitable to the quantum domain of discourse.
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.
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.
Glushkov, Alexander V.; Gurnitskaya, E.P.; Loboda, A.V.
2005-10-26
Advanced quantum approach to calculation of spectra for superheavy ions with an account of relativistic, correlation, nuclear, radiative effects is developed and based on the gauge invariant quantum electrodynamics (QED) perturbation theory (PT). The Lamb shift polarization part is calculated in the Ueling approximation, self-energy part is defined within a new non-PT procedure of Ivanov-Ivanova. Calculation results for energy levels, hyperfine structure parameters of some heavy elements ions are presented.
NASA Astrophysics Data System (ADS)
Hung, Hsiang-Hsuan; Chua, Victor; Wang, Lei; Fiete, Gregory A.
2014-06-01
We theoretically study topological phase transitions in four generalized versions of the Kane-Mele-Hubbard model with up to 2×182 sites. All models are free of the fermion-sign problem allowing numerically exact quantum Monte Carlo (QMC) calculations to be performed to extremely low temperatures. We numerically compute the Z2 invariant and spin Chern number Cσ directly from the zero-frequency single-particle Green's functions, and study the topological phase transitions driven by the tight-binding parameters at different on-site interaction strengths. The Z2 invariant and spin Chern number, which are complementary to each another, characterize the topological phases and identify the critical points of topological phase transitions. Although the numerically determined phase boundaries are nearly identical for different system sizes, we find strong system-size dependence of the spin Chern number, where quantized values are only expected upon approaching the thermodynamic limit. For the Hubbard models we considered, the QMC results show that correlation effects lead to shifts in the phase boundaries relative to those in the noninteracting limit, without any spontaneously symmetry breaking. The interaction-induced shift is nonperturbative in the interactions and cannot be captured within a "simple" self-consistent calculation either, such as Hartree-Fock. Furthermore, our QMC calculations suggest that quantum fluctuations from interactions stabilize topological phases in systems where the one-body terms preserve the D3 symmetry of the lattice, and destabilize topological phases when the one-body terms break the D3 symmetry.
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.
Physics in one dimension: theoretical concepts for quantum many-body systems.
Schönhammer, K
2013-01-09
Various sophisticated approximation methods exist for the description of quantum many-body systems. It was realized early on that the theoretical description can simplify considerably in one-dimensional systems and various exact solutions exist. The focus in this introductory paper is on fermionic systems and the emergence of the Luttinger liquid concept.
Theoretical method for full ab initio calculation of DNA/RNA-ligand interaction energy
NASA Astrophysics Data System (ADS)
Chen, Xi H.; Zhang, John Z. H.
2004-06-01
In this paper, we further develop the molecular fractionation with conjugate caps (MFCC) scheme for quantum mechanical computation of DNA-ligand interaction energy. We study three oligonuclear acid interaction systems: dinucleotide dCG/water, trinucleotide dCGT/water, and a Watson-Crick paired DNA segment, dCGT/dGCA. Using the basic MFCC approach, the nucleotide chains are cut at each phosphate group and a pair of conjugate caps (concaps) are inserted. Five cap molecules have been tested among which the dimethyl phosphate anion is proposed to be the standard concap for application. For each system, one-dimensional interaction potential curves are computed using the MFCC method and the calculated interaction energies are found to be in excellent agreement with corresponding results obtained from the full system ab initio calculations. The current study extends the application of the MFCC method to ab initio calculations for DNA- or RNA-ligand interaction energies.
Eigenvector Approximation Leading to Exponential Speedup of Quantum Eigenvalue Calculation
NASA Astrophysics Data System (ADS)
Jaksch, Peter; Papageorgiou, Anargyros
2003-12-01
We present an efficient method for preparing the initial state required by the eigenvalue approximation quantum algorithm of Abrams and Lloyd. Our method can be applied when solving continuous Hermitian eigenproblems, e.g., the Schrödinger equation, on a discrete grid. We start with a classically obtained eigenvector for a problem discretized on a coarse grid, and we efficiently construct, quantum mechanically, an approximation of the same eigenvector on a fine grid. We use this approximation as the initial state for the eigenvalue estimation algorithm, and show the relationship between its success probability and the size of the coarse grid.
A perspective on quantum mechanics calculations in ADMET predictions.
Bowen, J Phillip; Güner, Osman F
2013-01-01
Understanding the molecular basis of drug action has been an important objective for pharmaceutical scientists. With the increasing speed of computers and the implementation of quantum chemistry methodologies, pharmacodynamic and pharmacokinetic problems have become more computationally tractable. Historically the former has been the focus of drug design, but within the last two decades efforts to understand the latter have increased. It takes about fifteen years and over $1 billion dollars for a drug to go from laboratory hit, through lead optimization, to final approval by the U.S. Food and Drug Administration. While the costs have increased substantially, the overall clinical success rate for a compound to emerge from clinical trials is approximately 10%. Most of the attrition rate can be traced to ADMET (absorption, distribution, metabolism, excretion, and toxicity) problems, which is a powerful impetus to study these issues at an earlier stage in drug discovery. Quantum mechanics offers pharmaceutical scientists the opportunity to investigate pharmacokinetic problems at the molecular level prior to laboratory preparation and testing. This review will provide a perspective on the use of quantum mechanics or a combination of quantum mechanics coupled with other classical methods in the pharmacokinetic phase of drug discovery. A brief overview of the essential features of theory will be discussed, and a few carefully selected examples will be given to highlight the computational methods.
NASA Astrophysics Data System (ADS)
Borkowski, Eduardo J.; Cecati, Francisco M.; Suvire, Fernando D.; Ruiz, Diego M.; Ardanaz, Carlos E.; Romanelli, Gustavo P.; Enriz, Ricardo D.
2015-08-01
In this study we have performed CID mass spectrometry measurements and theoretical calculations in a selected series of coumarins. Our theoretical and experimental results indicate that there is room for reasonable doubts about the fragmentation way previously proposed by Shapiro and Djerassi (1965). A complementary explanation about the fragmentation way of the methyl loss from methoxy coumarins has been reported in this work. Our results demonstrated that different theoretical models are very useful to explain the fragmentation occurred in MS, supporting the usual rules of fragmentation. Although the QTAIM analysis gives a good correlation in order to explain the formation of p-quinoid resonance forms; however, the best correlation has been obtained using the NBO approximation as well as from the Wiberg indexes.
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)
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.
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.
Jooya, Hossein Z.; Reihani, Kamran; Chu, Shih-I
2016-01-01
We propose a graph-theoretical formalism to study generic circuit quantum electrodynamics systems consisting of a two level qubit coupled with a single-mode resonator in arbitrary coupling strength regimes beyond rotating-wave approximation. We define colored-weighted graphs, and introduce different products between them to investigate the dynamics of superconducting qubits in transverse, longitudinal, and bidirectional coupling schemes. The intuitive and predictive picture provided by this method, and the simplicity of the mathematical construction, are demonstrated with some numerical studies of the multiphoton resonance processes and quantum interference phenomena for the superconducting qubit systems driven by intense ac fields. PMID:27869230
NASA Astrophysics Data System (ADS)
Jooya, Hossein Z.; Reihani, Kamran; Chu, Shih-I.
2016-11-01
We propose a graph-theoretical formalism to study generic circuit quantum electrodynamics systems consisting of a two level qubit coupled with a single-mode resonator in arbitrary coupling strength regimes beyond rotating-wave approximation. We define colored-weighted graphs, and introduce different products between them to investigate the dynamics of superconducting qubits in transverse, longitudinal, and bidirectional coupling schemes. The intuitive and predictive picture provided by this method, and the simplicity of the mathematical construction, are demonstrated with some numerical studies of the multiphoton resonance processes and quantum interference phenomena for the superconducting qubit systems driven by intense ac fields.
NASA Astrophysics Data System (ADS)
Alaşalvar, Can; Demircan, Aydın; Koşar, Başak; Pekacar, Ali İhsan; Büyükgüngör, Orhan
2016-11-01
The crystal structure and spectroscopic properties of (3aR,6S,7aR)-7a-bromo-6-methyl-2-[(4-methylphenyl)sulfonyl]-1,2,3,6,7,7a-hexahydro-3a,6-epoxyisoindole were determined by X-ray diffraction, IR and 13CNMR and 1H NMR spectroscopy techniques. We investigate molecular and crystal structure of the new sulfonamide, which was derived from an environmental friendly cyclization reaction in water. This work allow to the development of a stereo-selective tandem allylamine isomerization/Diels Alder cyclo-addition sequence led to rapid assembly of complex nitrogen containing heterocycles. The molecular geometry from X-ray determination, vibrational frequencies and NMR shifts values of the title compound in the ground state have been calculated by using CAM-B3LYP and B3LYP methods with 6-311++G(d,p) basis sets. The calculated results show that the optimized geometry can well regenerate the crystal structure and theoretical vibrational frequencies and chemical shift data are in good agreement with experimental data. Besides, it is examined nonlinear optic properties, molecular electrostatic potential map and HOMO-LUMO orbitals of the molecule.
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.
Theoretical calculation of positron affinities of solute clusters in aluminum alloys
NASA Astrophysics Data System (ADS)
Mizuno, Masataka; Araki, Hideki; Shirai, Yasuharu
2016-01-01
We have performed theoretical calculations of positron states for solute clusters in aluminum alloys to estimate the positron affinity of solute clusters. Positron states of solute clusters in aluminum alloys were calculated under the electronic structures obtained by first- principles molecular orbital calculations using Al158-X13 clusters. We defined the positron affinity of the solute clusters by the difference in the lowest potential sensed by positrons between the solute clusters and Al bulk. With increasing atomic number of 3d metals, the annihilation fraction of the solute clusters rapidly increases at Mn and shows a maximum at Ni. A similar trend is observed for 4d metals. The localization of positron at the solute clusters mainly arises from charge transfer from Al matrix to solute clusters. The positron affinity defined in this work well represents the localization of positron at the solute clusters in aluminum alloys.
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.
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.
Theoretical calculation of mid-infrared spectra from hypersonic non-ablative sphere
NASA Astrophysics Data System (ADS)
Wu, Jie; Yu, Xilong; Zhu, Xijuan; Ma, Jing; Mao, Hongxia
2016-10-01
Hypersonic body moving in the atmosphere will suffer high temperature reacting flows which will emit complex radiation. Theoretical calculation was taken in this paper for a hypersonic non-ablative sphere. Hypersonic flow around the sphere was simulated using 9 species chemical kinetic and two temperature thermal non-equilibrium model. Based on this simulated flow field, the LOS method is used to solve radiative transfer and line-by-line model is used to calculate the spectrum from molecular and atoms in mid-infrared. The spectra from different components have been analyzed one by one. The calculation founds out that atom N and O diatomic molecule NO and bremsstrahlung will be important radiation source in this pure air hypersonic flow field. The radiation from hypersonic flow field has been analyzed in both high pressure environment and low pressure environment.
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.
Theoretical calculation and experimental study of acousto-optically Q-switched CO2 laser.
Xie, Jijang; Guo, Ruhai; Li, Dianjun; Zhang, Chuansheng; Yang, Guilong; Geng, Yumin
2010-06-07
Using resonator inserted with acousto-optically modulator, the experiments of the compacted CO(2) laser were performed with Q-switch. According to various factors that influenced the output of laser, the theoretical calculation of its main parameters was conducted by Q-switched pulsed laser rate equations. Based on the results, the technical route and approach were presented for optimization design of this laser. The measured peak power of this laser device was more than 4000W and pulsed width was 180ns which agreed well with the theoretical calculation. The range of repetition frequency could adjust from 1 Hz to 100 kHz. The theoretical analyzes and experimental results showed that the acoustic traveling time of ultrasonic field could not influence the pulse width of laser so that it did not require inserting optical lens in the cavity to reduce the diameter of beam. The acoustic traveling time only extended the establishingtime of laser pulse. The optimum working frequency of laser is about 1 kHz, which it matched with the radiation life time (1 ms) of CO(2) molecular upper energy level. When the frequency is above 1 kHz, the pulse width of laser increased with the frequency. The full band of wavelength tuning between 9.2 microm and 10.8 microm was obtained by grating selection one by one which the measured spectrum lines were over 30 in the condition of Q-switch.
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.
Quantum-Theoretical Methods and Studies Relating to Properties of Materials
1989-12-19
V. B.; Halow, I.; Bailey, S. M.; Schumm, R. H. Selected Values of Chemical Thermodynamic Properties , NBS Technical Note 270-3, Nat]. Bur. Stands... Thermodynamic Properties of Individual Substances (in Russian); Glyshko, W. P., Ed.; Science: Moscow, 1982. (14) Shimanouchi, T. J. Phys. Chem. Ref. Data...Theoretical Methods and Studies Relating to Properties of Materials. -’This research concerned-the development of new ab initio nonempirical quantum
Black hole state counting in loop quantum gravity: a number-theoretical approach.
Agulló, Iván; Barbero G, J Fernando; Díaz-Polo, Jacobo; Fernández-Borja, Enrique; Villaseñor, Eduardo J S
2008-05-30
We give an efficient method, combining number-theoretic and combinatorial ideas, to exactly compute black hole entropy in the framework of loop quantum gravity. Along the way we provide a complete characterization of the relevant sector of the spectrum of the area operator, including degeneracies, and explicitly determine the number of solutions to the projection constraint. We use a computer implementation of the proposed algorithm to confirm and extend previous results on the detailed structure of the black hole degeneracy spectrum.
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.
Confidence and efficiency scaling in variational quantum Monte Carlo calculations
NASA Astrophysics Data System (ADS)
Delyon, F.; Bernu, B.; Holzmann, Markus
2017-02-01
Based on the central limit theorem, we discuss the problem of evaluation of the statistical error of Monte Carlo calculations using a time-discretized diffusion process. We present a robust and practical method to determine the effective variance of general observables and show how to verify the equilibrium hypothesis by the Kolmogorov-Smirnov test. We then derive scaling laws of the efficiency illustrated by variational Monte Carlo calculations on the two-dimensional electron gas.
Theoretical calculation of the melting curve of Cu-Zr binary alloys
Gunawardana, K. G.S.H.; Wilson, S. R.; Mendelev, M. I.; ...
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.
García-Granados, A; Melguizo, E; Parra, A; Simeó, Y; Viseras, B; Dobado, J A; Molina, J; Arias, J M
2000-12-01
Different lipase enzymes have been tested in order to perform regioselective acetylations on the eudesmane tetrol from vulgarin. High yields (95%) of 1,12-diacetoxy derivative (4) were achieved in 1 h with Candida antarctica lipase (CAL). However, only the 12-acetyl derivative (6) was obtained in similar yield with Mucor miehei (MML) or Candida cylindracea (CCL) lipases. The enzymatic protection at C-1 and C-12 has been used to form eudesmane cyclic-sulfites between C-6 and C-4 atoms. The R/S-sulfur configuration has been assigned by means of the experimental and theoretical (13)C and (1)H NMR chemical shifts. The theoretical shifts were calculated using the GIAO method, with a MM+ geometry optimization followed by a single-point calculation at the B3LYP/6-31G(*) level (B3LYP/6-31G(*)//MM+). Moreover, B3LYP/6-31G(*) geometry optimizations were carried out to test the B3LYP/6-31G(*)//MM+ results, for the deacetylated sulfites (12 and 15). In addition to the delta(C) and delta(H) shifts, the (3)J(HH) coupling constants were also calculated and compared with the experimental values when available. Finally, different reactivities have been checked in both sulfites by biotransformation with Rhizopus nigricans. While the R-sulfite gave 2 alpha- and 11 beta-hydroxylated metabolites, the S-sulfite yielded only regioselective deacetylations. Furthermore, both sulfites showed different reactivities in redox processes.
NASA Astrophysics Data System (ADS)
Belyakov, Alexander V.; Nikolaenko, Kirill O.; Davidovich, Pavel B.; Ivanov, Anatolii D.; Garabadzhiu, Alexander V.; Rykov, Anatolii N.; Shishkov, Igor F.
2017-03-01
The molecular structure of isatin, indole-2,3-dione, was studied by gas-phase electron diffraction (GED) and quantum chemical calculations (M062X and MP2 methods with aug-cc-pVTZ basis set). The best fit of the experimental scattering intensities (R-factor = 4.4%) was obtained for a molecular model of Cs symmetry. The structure of the benzene ring deviates from a regular hexagon due to the adjacent pyrrole heterocycle. The small differences between similar geometric parameters were constrained at the values calculated at the M062X level. The experimental structural parameters agree well with the results of theoretical calculations. The bonds in the benzene moiety are in agreement with their standard values. The (Odbnd)Csbnd C(dbnd O) carbon-carbon bond of the pyrrole moiety (1.573(7) Å) is remarkably lengthened in comparison with standard C(sp2)sbnd C(sp2) value, 1.425(11) Å for N-methylpyrrole. According to NBO analysis of isatin, glyoxal and pyrrole-2,3-dione molecules this lengthening cannot be attributed to the steric interactions of Cdbnd O bonds alone and is, mainly, due to the electrostatic repulsion and hyperconjugation that is delocalization of oxygen lone pairs of π-type into the corresponding carbon-carbon antibonding orbital, nπ(O) → σ∗(Csbnd C). Deletion of σ∗(Csbnd C) orbital followed by subsequent geometry optimization led to shortening of the corresponding Csbnd C bond by 0.06 Å. According to different aromaticity descriptors, aromaticity of benzene moiety of isatin is smaller in comparison with benzene molecule. External magnetic field induces diatropic ring current in benzene moiety of isatin.
Order-N Electronic Structure Calculation of n-TYPE GaAs Quantum Dots
NASA Astrophysics Data System (ADS)
Nomura, S.; Iitaka, T.
2008-10-01
A linear scale method for calculating electronic properties of large and complex systems is introduced within a local density approximation. The method is based on the Chebyshev polynomial expansion and the time-dependent method, which is tested in calculating the electronic structure of a model n-type GaAs quantum dot.
Kadmensky, S. G. Titova, L. V.; Pen'kov, N. V.
2006-08-15
In the framework of quantum-mechanical fission theory, the method of calculation for partial fission width amplitudes and asymptotic behavior of the fissile nucleus wave function with strong channel coupling taken into account has been suggested. The method allows one to solve the calculation problem of angular and energy distribution countation for binary and ternary fission.
Fast and accurate calculation of dilute quantum gas using Uehling-Uhlenbeck model equation
NASA Astrophysics Data System (ADS)
Yano, Ryosuke
2017-02-01
The Uehling-Uhlenbeck (U-U) model equation is studied for the fast and accurate calculation of a dilute quantum gas. In particular, the direct simulation Monte Carlo (DSMC) method is used to solve the U-U model equation. DSMC analysis based on the U-U model equation is expected to enable the thermalization to be accurately obtained using a small number of sample particles and the dilute quantum gas dynamics to be calculated in a practical time. Finally, the applicability of DSMC analysis based on the U-U model equation to the fast and accurate calculation of a dilute quantum gas is confirmed by calculating the viscosity coefficient of a Bose gas on the basis of the Green-Kubo expression and the shock layer of a dilute Bose gas around a cylinder.
Theoretical examination of quantum coherence in a photosynthetic system at physiological temperature
Ishizaki, Akihito; Fleming, Graham R.
2009-01-01
The observation of long-lived electronic coherence in a photosynthetic pigment–protein complex, the Fenna–Matthews–Olson (FMO) complex, is suggestive that quantum coherence might play a significant role in achieving the remarkable efficiency of photosynthetic electronic energy transfer (EET), although the data were acquired at cryogenic temperature [Engel GS, et al. (2007) Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems. Nature 446:782–786]. In this paper, the spatial and temporal dynamics of EET through the FMO complex at physiological temperature are investigated theoretically. The numerical results reveal that quantum wave-like motion persists for several hundred femtoseconds even at physiological temperature, and suggest that the FMO complex may work as a rectifier for unidirectional energy flow from the peripheral light-harvesting antenna to the reaction center complex by taking advantage of quantum coherence and the energy landscape of pigments tuned by the protein scaffold. A potential role of quantum coherence is to overcome local energetic traps and aid efficient trapping of electronic energy by the pigments facing the reaction center complex. PMID:19815512
Matsunaga, Katsuyuki; Murata, Hidenobu; Shitara, Kazuki
2010-09-29
Defect formation energies in materials generally depend on chemical potentials determined by a chemical equilibrium condition. In particular, an aqueous solution environment is important for biomaterials such as hydroxyapatite studied here. Therefore, a methodology to obtain ionic chemical potentials under chemical equilibrium between solid and aqueous solution was introduced, and was applied to substitutional divalent cations formed via ion exchange with Ca(2+) in hydroxyapatite. The calculated ranking of the stability of substitutional cations in HAp was in good agreement with the experimentally observed trend. The present theoretical approach would be useful to explore the thermodynamic stability of defects in materials subjected to an aqueous solution environment.
Quantum Monte Carlo calculations of two neutrons in finite volume
Klos, P.; Lynn, J. E.; Tews, I.; ...
2016-11-18
Ab initio calculations provide direct access to the properties of pure neutron systems that are challenging to study experimentally. In addition to their importance for fundamental physics, their properties are required as input for effective field theories of the strong interaction. In this work, we perform auxiliary-field diffusion Monte Carlo calculations of the ground state and first excited state of two neutrons in a finite box, considering a simple contact potential as well as chiral effective field theory interactions. We compare the results against exact diagonalizations and present a detailed analysis of the finite-volume effects, whose understanding is crucial formore » determining observables from the calculated energies. Finally, using the Lüscher formula, we extract the low-energy S-wave scattering parameters from ground- and excited-state energies for different box sizes.« less
Quantum Monte Carlo calculations of two neutrons in finite volume
Klos, P.; Lynn, J. E.; Tews, I.; Gandolfi, Stefano; Gezerlis, A.; Hammer, H. -W.; Hoferichter, M.; Schwenk, A.
2016-11-18
Ab initio calculations provide direct access to the properties of pure neutron systems that are challenging to study experimentally. In addition to their importance for fundamental physics, their properties are required as input for effective field theories of the strong interaction. In this work, we perform auxiliary-field diffusion Monte Carlo calculations of the ground state and first excited state of two neutrons in a finite box, considering a simple contact potential as well as chiral effective field theory interactions. We compare the results against exact diagonalizations and present a detailed analysis of the finite-volume effects, whose understanding is crucial for determining observables from the calculated energies. Finally, using the Lüscher formula, we extract the low-energy S-wave scattering parameters from ground- and excited-state energies for different box sizes.
NASA Astrophysics Data System (ADS)
Walters, Wendell W.; Michalski, Greg
2015-09-01
The nitrogen stable isotope ratio (15N/14N) of nitrogen oxides (NOx = NO + NO2) and its oxidation products (NOy = NOx + PAN (peroxyacetyl nitrate = C2H3NO5) + HNO3 + NO3 + HONO + N2O5 + ⋯ + particulate nitrates) has been suggested as a tool for partitioning NOx sources; however, the impact of nitrogen (N) equilibrium isotopic fractionation on 15N/14N ratios during the conversion of NOx to NOy must also be considered, but few fractionation factors for these processes have been determined. To address this limitation, computational quantum chemistry calculations of harmonic frequencies, reduced partition function ratios (15β), and N equilibrium isotope exchange fractionation factors (αA/B) were performed for various gaseous and aqueous NOy molecules in the rigid rotor and harmonic oscillator approximations using the B3LYP and EDF2 density functional methods for the mono-substitution of 15N. The calculated harmonic frequencies, 15β, and αA/B are in good agreement with available experimental measurements, suggesting the potential to use computational methods to calculate αA/B values for N isotope exchange processes that are difficult to measure experimentally. Additionally, the effects of solvation (water) on 15β and αA/B were evaluated using the IEF-PCM model, and resulted in lower 15β and αA/B values likely due to the stabilization of the NOy molecules from dispersion interactions with water. Overall, our calculated 15β and αA/B values are accurate in the rigid rotor and harmonic oscillator approximations and will allow for the estimation of αA/B involving various NOy molecules. These calculated αA/B values may help to explain the trends observed in the N stable isotope ratio of NOy molecules in the atmosphere.
Petsalakis, I.D.; Theodorakopoulos, G.; Wright, J.S.
1988-12-01
MRD-CI calculations have been carried out on the ground and excited electronic states of H/sub 3/ for D/sub 3//sub h/, D/sub infinity//sub h/, C/sub infinity//sub v/, and C/sub 2//sub v/ geometries. Dipole transition moments between the various electronic states have been also obtained at the different geometries calculated. The present work provides accurate theoretical information relevant to the transition state spectroscopy of H+H/sub 2/ along a collinear path and also along a perpendicular path. In addition, the present work is the first all-electron configuration interaction treatment of the Rydberg states of H/sub 3/, and the results are in excellent agreement with the observed spectra.
NASA Astrophysics Data System (ADS)
Vagena, E.; Stoulos, S.
2017-01-01
Bremsstrahlung photon beam delivered by a linear electron accelerator has been used to experimentally determine the near threshold photonuclear cross section data of nuclides. For the first time, (γ, n) cross section data was obtained for the astrophysical important nucleus 162Er. Moreover, theoretical calculations have been applied using the TALYS 1.6 code. The effect of the gamma ray strength function on the cross section calculations has been studied. A satisfactorily reproduction of the available experimental data of photonuclear cross section at the energy region below 20 MeV could be achieved. The photon flux was monitored by measuring the photons yield from seven well known (γ, n) reactions from the threshold energy of each reaction up to the end-point energy of the photon beam used. An integrated cross-section 87 ± 14 mb is calculated for the photonuclear reaction 162Er (γ, n) at the energy 9.2-14 MeV. The effective cross section estimated using the TALYS code range between 89 and 96 mb depending on the γ-strength function used. To validate the method for the estimation of the average cross-section data of 162Er (γ, n) reaction, the same procedure has been performed to calculate the average cross-section data of 197Au (γ, n) and 55Mn (γ, n) reactions. In this case, the photons yield from the rest well known (γ, n) reactions was used in order to monitoring the photon flux. The results for 162Er (γ, n), 197Au (γ, n) and 55Mn (γ, n) are found to be in good agreement with the theoretical values obtained by TALYS 1.6. So, the present indirect process could be a valuable tool to estimate the effective cross section of (γ, n) reaction for various isotopes using bremsstrahlung beams.
A quantum fluid of metallic hydrogen suggested by first-principles calculations.
Bonev, Stanimir A; Schwegler, Eric; Ogitsu, Tadashi; Galli, Giulia
2004-10-07
It is generally assumed that solid hydrogen will transform into a metallic alkali-like crystal at sufficiently high pressure. However, some theoretical models have also suggested that compressed hydrogen may form an unusual two-component (protons and electrons) metallic fluid at low temperature, or possibly even a zero-temperature liquid ground state. The existence of these new states of matter is conditional on the presence of a maximum in the melting temperature versus pressure curve (the 'melt line'). Previous measurements of the hydrogen melt line up to pressures of 44 GPa have led to controversial conclusions regarding the existence of this maximum. Here we report ab initio calculations that establish the melt line up to 200 GPa. We predict that subtle changes in the intermolecular interactions lead to a decline of the melt line above 90 GPa. The implication is that as solid molecular hydrogen is compressed, it transforms into a low-temperature quantum fluid before becoming a monatomic crystal. The emerging low-temperature phase diagram of hydrogen and its isotopes bears analogies with the familiar phases of 3He and 4He (the only known zero-temperature liquids), but the long-range Coulomb interactions and the large component mass ratio present in hydrogen would result in dramatically different properties.
NASA Astrophysics Data System (ADS)
Kumar, Jitendra; Kapoor, Sheetal; Gupta, Saral K.; Sen, Pranay K.
2006-09-01
The effect of size and shape anisotropy on the optical properties of Stranski-Krastanov quantum dots (QDs) is theoretically investigated. The QD is modeled using anisotropic parabolic confinement potential. The complex structure of the valence band is described by Luttinger Hamiltonian. The energy spectra and eigenfunctions of hole states are calculated by numerical diagonalization of the Hamiltonian. The dipole matrix elements are obtained for the interband transitions and hence the degree of linear polarization is calculated. The formulation is applied to self-assembled CdSe quantum dots for numerical analysis. The variation of energy eigenvalues with the QD shape anisotropy parameter is studied and the effect of valence subband mixing is clearly identified. The crossings and anticrossings of the valence subbands have been explained in terms of the symmetries of the corresponding eigenstates. It is worthy to note that these symmetry properties of the energy states are responsible for the specific types of dipole selection rules for the anisotropic QDs. The degree of linear polarization is found to increase almost linearly with anisotropy parameter for the transitions from heavy-hole ground states. On the contrary, for the excited hole states, the change is nonmonotonic due to strong anisotropy-dependent mixing effects.
Foltran, Stéphanie; Méreau, Raphaël; Tassaing, Thierry
2011-05-28
The nature and strength of the interactions occurring between epoxides and CO(2) have been investigated by combining infrared spectroscopy with quantum chemistry calculations. A series of infrared absorption experiments on four model epoxide molecules highly diluted in supercritical CO(2) have been performed at constant temperature T = 40 °C for various CO(2) pressures varying from 1 to 30 MPa. Then, we carried out a theoretical analysis based on quantum chemistry calculations using Density Functional Theory (B3PW91 and CAM-B3LYP) and ab initio (MP2) computational methods. A very good agreement between experimental and calculated vibrational frequency shifts of the epoxide ring vibrations group was obtained using the CAM-B3LYP functional, hence validating the calculated optimized geometries of the epoxide-CO(2) complexes. Whatever the epoxide considered, CO(2) is found to be on average above the oxygen atom of the epoxy ring and interacts with the carbon atom of CO(2) through a Lewis acid-Lewis base type of interaction. The substituents on the epoxide ring are found to influence the stability of the epoxide-CO(2) complexes mainly because of the partial charge on the oxygen atom that is sensitive to the nature of the substituent.
Wehrle, Marius; Sulc, Miroslav; Vanícek, Jirí
2011-01-01
We explore three specific approaches for speeding up the calculation of quantum time correlation functions needed for time-resolved electronic spectra. The first relies on finding a minimum set of sufficiently accurate electronic surfaces. The second increases the time step required for convergence of exact quantum simulations by using different split-step algorithms to solve the time-dependent Schrödinger equation. The third approach lowers the number of trajectories needed for convergence of approximate semiclassical dynamics methods.
Uncertainties Associated with Theoretically Calculated N2-Broadened Half-Widths of H2O Lines
NASA Technical Reports Server (NTRS)
Ma, Q.; Tipping, R. H.; Gamache, R. R.
2010-01-01
With different choices of the cut-offs used in theoretical calculations, we have carried out extensive numerical calculations of the N2-broadend Lorentzian half-widths of the H2O lines using the modified Robert-Bonamy formalism. Based on these results, we are able to thoroughly check for convergence. We find that, with the low-order cut-offs commonly used in the literature, one is able to obtain converged values only for lines with large half-widths. Conversely, for lines with small half-widths, much higher cut-offs are necessary to guarantee convergence. We also analyse the uncertainties associated with calculated half-widths, and these are correlated as above. In general, the smaller the half-widths, the poorer the convergence and the larger the uncertainty associated with them. For convenience, one can divide all H2O lines into three categories, large, intermediate, and small, according to their half-width values. One can use this division to judge whether the calculated half-widths are converged or not, based on the cut-offs used, and also to estimate how large their uncertainties are. We conclude that with the current Robert- Bonamy formalism, for lines in category lone can achieve the accuracy requirement set by HITRAN, whereas for lines in category 3, it 'is impossible to meet this goal.
NASA Astrophysics Data System (ADS)
Balasubramanian, T. K.; Mishra, A. P.
2011-11-01
D. A. Long [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.80.042513 80, 042513 (2009)] recently reported accurate measurements on the ultraweak electric quadrupole (E2) transitions in the O2 A band. They also presented elegant theoretical calculation of the line intensities based on Hund's case (b) formulation. However, their theoretical elucidation fails to relate to a highly relevant previous work by Balasubramanian and Narayanan [Acta Phys. Hung 74, 341 (1994)] in which closed-form expressions for the E2 branch line strengths for the eight possible rotational branches of the b1Σg+-X3Σg- transition, in intermediate coupling, are derived. The complete equivalence of the two methods is proven through direct calculation. A second point of concern is that the magnetic dipole (M1) transition moment M1 = 0.0687 μB deduced by Long from the previously measured transition intensities is ˜2.7 times the ab initio value of 0.0255 μB computed by Minaev [Chem. Phys.CMPHC20301-010410.1016/0301-0104(96)00126-7 208, 299 (1996)]. Since the latter reproduces closely the measured Einstein's spontaneous emission coefficient of the A band, this large discrepancy is intriguing.
NASA Astrophysics Data System (ADS)
Xie, Yunfei; Li, Yan; Sun, Yingying; Wang, Heya; Qian, He; Yao, Weirong
2012-10-01
Ponceau 4R is used as a coloring agent in many different products, such as food, drinks, medicines, cosmetics and tobacco. However, ponceau 4R also shows carcinogenic, teratogenic and mutagenic behavior in high doses. In this work, standard Raman, theoretical Raman and surface-enhanced Raman scattering (SERS) spectra have been used to investigate ponceau 4R. More specifically, density functional theory (DFT) calculations have been used to calculate the optimized Raman spectrum of ponceau 4R at the B3LYP/6-31G(d) level. This has provided a better understanding of the optimized geometry and vibrational frequencies of this dye. In addition, the experimental spectrum of ponceau 4R has been compared with the theoretical spectrum; good agreement was obtained. Finally, it has shown that using SERS the detection limit of the ponceau 4R solution can be as low as 5 μg/mL. This has been achieved by SERS measurements of ponceau 4R on a substrate of gold nanoparticles. The SERS peaks at 1030, 1236, 1356 and 1502 cm-1 were chosen as index for semi-quantitative analysis, showing that the SERS technique provided a useful ultrasensitive method for the detection of ponceau 4R.
Calculating two-dimensional spectra with the mixed quantum-classical Ehrenfest method.
van der Vegte, C P; Dijkstra, A G; Knoester, J; Jansen, T L C
2013-07-25
We present a mixed quantum-classical simulation approach to calculate two-dimensional spectra of coupled two-level electronic model systems. We include the change in potential energy of the classical system due to transitions in the quantum system using the Ehrenfest method. We study how this feedback of the quantum system on the classical system influences the shape of two-dimensional spectra. We show that the feedback leads to the expected Stokes shift of the energy levels in the quantum system. This subsequently leads to changes in the population transfer between quantum sites, which in turn influence the intensities of the peaks in two-dimensional spectra. The obtained spectra are compared with spectra calculated using the Hierarchical Equations of Motion method which is exact. While the spectra match perfectly for short waiting times, clear differences are found for longer waiting times. This is attributed to a violation of detailed balance between the quantum states in the Ehrenfest method. The energy of the total quantum-classical system however does obey a Boltzmann distribution, when coupled to a stochastic heat bath.
Machine Learning of Parameters for Accurate Semiempirical Quantum Chemical Calculations
2015-01-01
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 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. PMID:26146493
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.
Machine Learning of Parameters for Accurate Semiempirical Quantum Chemical Calculations.
Dral, Pavlo O; von Lilienfeld, O Anatole; Thiel, Walter
2015-05-12
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 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.
Quantum Monte Carlo Calculations of Transition Metal Oxides
NASA Astrophysics Data System (ADS)
Wagner, Lucas
2006-03-01
Quantum Monte Carlo is a powerful computational tool to study correlated systems, allowing us to explicitly treat many-body interactions with favorable scaling in the number of particles. It has been regarded as a benchmark tool for first and second row condensed matter systems, although its accuracy has not been thoroughly investigated in strongly correlated transition metal oxides. QMC has also historically suffered from the mixed estimator error in operators that do not commute with the Hamiltonian and from stochastic uncertainty, which make small energy differences unattainable. Using the Reptation Monte Carlo algorithm of Moroni and Baroni(along with contributions from others), we have developed a QMC framework that makes these previously unavailable quantities computationally feasible for systems of hundreds of electrons in a controlled and consistent way, and apply this framework to transition metal oxides. We compare these results with traditional mean-field results like the LDA and with experiment where available, focusing in particular on the polarization and lattice constants in a few interesting ferroelectric materials. This work was performed in collaboration with Lubos Mitas and Jeffrey Grossman.
Efficient method for calculating electronic bound states in arbitrary one-dimensional quantum wells
NASA Astrophysics Data System (ADS)
de Aquino, V. M.; Iwamoto, H.; Dias, I. F. L.; Laureto, E.; da Silva, M. A. T.; da Silva, E. C. F.; Quivy, A. A.
2017-01-01
In the present paper it is demonstrated that the bound electronic states of multiple quantum wells structures may be calculated very efficiently by expanding their eigenstates in terms of the eigenfunctions of a particle in a box. The bound states of single and multiple symmetric or nonsymmetric wells are calculated within the single-band effective mass approximation. A comparison is then made between the results obtained for simple cases with exact calculations. We also apply our approach to a GaAs/AlGaAs multiple quantum well structure composed of forty periods each one with seven quantum wells. The method may be very useful to design narrow band quantum cascade photodetectors to work without applied bias in a photovoltaic mode. With the presented method the effects of a electric field may also be easily included which is very important if one desires study quantum well structures for application to the development of quantum cascade lasers. The advantages of the method are also presented.
Quantum noise in the mirror-field system: A field theoretic approach
Hsiang, Jen-Tsung; Wu, Tai-Hung; Lee, Da-Shin; King, Sun-Kun; Wu, Chun-Hsien
2013-02-15
We revisit the quantum noise problem in the mirror-field system by a field-theoretic approach. Here a perfectly reflecting mirror is illuminated by a single-mode coherent state of the massless scalar field. The associated radiation pressure is described by a surface integral of the stress-tensor of the field. The read-out field is measured by a monopole detector, from which the effective distance between the detector and mirror can be obtained. In the slow-motion limit of the mirror, this field-theoretic approach allows to identify various sources of quantum noise that all in all leads to uncertainty of the read-out measurement. In addition to well-known sources from shot noise and radiation pressure fluctuations, a new source of noise is found from field fluctuations modified by the mirror's displacement. Correlation between different sources of noise can be established in the read-out measurement as the consequence of interference between the incident field and the field reflected off the mirror. In the case of negative correlation, we found that the uncertainty can be lowered than the value predicted by the standard quantum limit. Since the particle-number approach is often used in quantum optics, we compared results obtained by both approaches and examine its validity. We also derive a Langevin equation that describes the stochastic dynamics of the mirror. The underlying fluctuation-dissipation relation is briefly mentioned. Finally we discuss the backreaction induced by the radiation pressure. It will alter the mean displacement of the mirror, but we argue this backreaction can be ignored for a slowly moving mirror. - Highlights: Black-Right-Pointing-Pointer The quantum noise problem in the mirror-field system is re-visited by a field-theoretic approach. Black-Right-Pointing-Pointer Other than the shot noise and radiation pressure noise, we show there are new sources of noise and correlation between them. Black-Right-Pointing-Pointer The noise correlations can
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.
NASA Astrophysics Data System (ADS)
Arnold, A.; Weigend, F.; Evers, F.
2007-05-01
Modern quantum chemistry calculations are usually implemented for isolated systems—big molecules or atom clusters; total energy and particle number are fixed. However, in many situations, like quantum transport calculations or molecules in a electrochemical environment, the molecule can exchange particles (and energy) with a reservoir. Calculations for such cases require to switch from the canonical to a grand canonical description, where one fixes the chemical potential rather than particle number. To achieve this goal, the authors propose an implementation in standard quantum chemistry packages. An application to the nonlinear charge transport through 1,4-benzenedithiol will be presented. They explain the leading finite bias effect on the transmission as a consequence of a nonequilibrium Stark effect and discuss the relation to earlier work.
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
Equation of State of Al Based on Quantum Molecular Dynamics Calculations
NASA Astrophysics Data System (ADS)
Minakov, Dmitry V.; Levashov, Pavel R.; Khishchenko, Konstantin V.
2011-06-01
In this work, we present quantum molecular dynamics calculations of the shock Hugoniots of solid and porous samples as well as release isentropes and values of isentropic sound velocity behind the shock front for aluminum. We use the VASP code with an ultrasoft pseudopotential and GGA exchange-correlation functional. Up to 108 particles have been used in calculations. For the Hugoniots of Al we solve the Hugoniot equation numerically. To calculate release isentropes, we use Zel'dovich's approach and integrate an ordinary differential equation for the temperature thus restoring all thermodynamic parameters. Isentropic sound velocity is calculated by differentiation along isentropes. The results of our calculations are in good agreement with experimental data. Thus, quantum molecular dynamics results can be effectively used for verification or calibration of semiempirical equations of state under conditions of lack of experimental information at high energy densities. This work is supported by RFBR, grants 09-08-01129 and 11-08-01225.
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.
Wickham, Jason R; Halye, Jeffrey L; Kashtanov, Stepan; Khandogin, Jana; Rice, Charles V
2009-02-19
Teichoic acids are essential components of the Gram-positive bacterial cell wall. One of their many functions is metal binding, a vital process for bacterial growth. With the combination of phosphorus-31 solid-state NMR spectroscopy and theoretical calculations using density functional theory (DFT), we have determined that the binding mode between teichoic acids and magnesium involves bidentate coordination by the phosphate groups of teichoic acid. Measurement of chemical shift anisotropy tensors gave a reduced anisotropy (delta) of 49.25 ppm and an asymmetry (eta) of 0.7. DFT calculations with diglycerol phosphate and triglycerol diphosphate model compounds were completed with Mg(2+) in anhydrous as well as partially hydrated bidentate and fully hydrated monodentate, bidentate, and bridging binding modes. (31)P CSA tensors were calculated from the energy-minimized model compounds using the combined DFT and GIAO methods, resulting in dramatically different tensor values for each binding mode. The anhydrous bidentate chelation mode was found to be a good approximation of the experimental data, an observation that alters the current monodentate paradigm for metal chelation by teichoic acids.
Kumar, Sumit; Singh, Santosh Kumar; Vaishnav, Jamuna Kanaram; Hill, J Grant; Das, Aloke
2017-01-26
π-hydrogen bonding interactions are ubiquitous in both materials and biology. Despite their relatively weak nature great progress has been made in their investigation by experimental and theoretical methods, but this becomes significantly more complicated when secondary intermolecular interactions are present. In this study the effect of successive methyl substitution on the supramolecular structure and interaction energy of indole⋯methylated benzene (ind⋯n-mb, n = 1-6) complexes is probed through a combination of supersonic jet experiment and benchmark quality quantum chemical calculations. It is demonstrated that additional secondary interactions introduce a subtle interplay among electrostatic and dispersion forces, as well as steric repulsion, which fine-tunes the overall structural motif. Resonant Two-Photon Ionization (R2PI) and IR-UV double resonance spectroscopy techniques were used to probe jet-cooled ind⋯n-mb (n = 2, 3, 6) complexes, with red-shifting of the N-H IR stretching frequency showing that increasing the degree of methyl substitution increases the strength of the primary N-H⋯π interaction. Ab initio harmonic frequency and binding energy calculations confirm this trend for all six complexes. Electronic spectra of the three dimers are broad and structureless, with quantum chemical calculations revealing that this is likely due to multiple tilted conformations of each dimer possessing similar stabilization energies.
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.
Theoretical calculations of a compound formed by Fe(+3) and tris(catechol).
Kara, İzzet; Kara, Yeşim; Öztürk Kiraz, Aslı; Mammadov, Ramazan
2015-01-01
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.
Quantum Monte Carlo calculations of the dimerization energy of borane.
Fracchia, Francesco; Bressanini, Dario; Morosi, Gabriele
2011-09-07
Accurate thermodynamic data are required to improve the performance of chemical hydrides that are potential hydrogen storage materials. Boron compounds are among the most interesting candidates. However, different experimental measurements of the borane dimerization energy resulted in a rather wide range (-34.3 to -39.1) ± 2 kcal/mol. Diffusion Monte Carlo (DMC) simulations usually recover more than 95% of the correlation energy, so energy differences rely less on error cancellation than other methods. DMC energies of BH(3), B(2)H(6), BH(3)CO, CO, and BH(2)(+) allowed us to predict the borane dimerization energy, both via the direct process and indirect processes such as the dissociation of BH(3)CO. Our D(e) = -43.12(8) kcal/mol, corrected for the zero point energy evaluated by considering the anharmonic contributions, results in a borane dimerization energy of -36.59(8) kcal/mol. The process via the dissociation of BH(3)CO gives -34.5(2) kcal/mol. Overall, our values suggest a slightly less D(e) than the most recent W4 estimate D(e) = -44.47 kcal/mol [A. Karton and J. M. L. Martin, J. Phys. Chem. A 111, 5936 (2007)]. Our results show that reliable thermochemical data for boranes can be predicted by fixed node (FN)-DMC calculations.
Molecular docking, spectroscopic studies and quantum calculations on nootropic drug.
Uma Maheswari, J; Muthu, S; Sundius, Tom
2014-04-05
A systematic vibrational spectroscopic assignment and analysis of piracetam [(2-oxo-1-pyrrolidineacetamide)] have been carried out using FT-IR and FT-Raman spectral data. The vibrational analysis was aided by an electronic structure calculation based on the hybrid density functional method B3LYP using a 6-311G++(d,p) basis set. Molecular equilibrium geometries, electronic energies, IR and Raman intensities, and harmonic vibrational frequencies have been computed. The assignments are based on the experimental IR and Raman spectra, and a complete assignment of the observed spectra has been proposed. The UV-visible spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies and the maximum absorption wavelengths λmax were determined by the time-dependent DFT (TD-DFT) method. The geometrical parameters, vibrational frequencies and absorption wavelengths were compared with the experimental data. The complete vibrational assignments are performed on the basis of the potential energy distributions (PED) of the vibrational modes in terms of natural internal coordinates. The simulated FT-IR, FT-Raman, and UV spectra of the title compound have been constructed. Molecular docking studies have been carried out in the active site of piracetam by using Argus Lab. In addition, the potential energy surface, HOMO and LUMO energies, first-order hyperpolarizability and the molecular electrostatic potential have been computed.
Theoretical study and rate constant calculation of the CH2O+CH3 reaction
NASA Astrophysics Data System (ADS)
Liu, Jing-yao; Li, Ze-sheng; Wu, Jia-yan; Wei, Zhi-gang; Zhang, Gang; Sun, Chia-chung
2003-10-01
The potential energy surface of the CH2O+CH3 reaction is explored at the MP2/6-311++G(d,p), MP4SDQ/6-311G(d,p), and QCISD(T)/6-311+G(3df,2p) (single point) levels of theory. Theoretical calculations suggest that the major product channel (R1) is the hydrogen abstraction leading to the product P1 CHO+CH4 (R1), while the addition process leading to P2H+CH3CHO (R2) appears to be negligibly small. The calculated enthalpies and dissociation activation energies for CH3CH2O and CH3OCH2 radicals involved in the reaction are in line with the experimental values. Dual-level dynamics calculation is carried out for the direct hydrogen abstraction channel. The energy profile of (R1) is refined with the interpolated single-point energies (ISPE) method at the QCISD(T)//MP2 level. The rate constants, which are evaluated by canonical variational transition-state theory (CVT) including small-curvature tunneling (SCT) correction, are in good agreement with the available experimental data. It is shown that tunneling effect plays a significant role in the rate constant calculation; and as a result, the CVT/SCT rate constants exhibit typical non-Arrhenius behavior over a wide temperature range 300-2000 K. The three parameter expression is k=6.35×10-26 T4.4 exp(-2450/T) cm3 molecule-1 s-1.
Quantum calculations for the photodetachment cross sections of H- located between two walls
NASA Astrophysics Data System (ADS)
Zhao, H. J.; Ma, Z. J.; Du, M. L.
2015-06-01
We re-investigate the photodetachment cross sections of H- in a quantum well consisting of two parallel hard walls using a quantum approach. The formulas for the cross sections are explicitly derived and compared with those derived by using closed-orbit theory (G.C. Yang, et al., Physica B 404 (2009) 1576 [15]). The present quantum results confirm the staircase pattern of the cross sections obtained earlier when the polarization of photons is parallel to the normal direction of the walls. However, we find that when the polarization is perpendicular to the normal direction of the walls, oscillations in the cross sections in the present quantum calculations are still present in contrast to the predictions of closed-orbit theory. The differences in the two results are large enough to be observable.
Semenov, Alexander; Babikov, Dmitri
2014-01-16
For computational treatment of rotationally inelastic scattering of molecules, we propose to use the mixed quantum/classical theory, MQCT. The old idea of treating translational motion classically, while quantum mechanics is used for rotational degrees of freedom, is developed to the new level and is applied to Na + N2 collisions in a broad range of energies. Comparison with full-quantum calculations shows that MQCT accurately reproduces all, even minor, features of energy dependence of cross sections, except scattering resonances at very low energies. The remarkable success of MQCT opens up wide opportunities for computational predictions of inelastic scattering cross sections at higher temperatures and/or for polyatomic molecules and heavier quenchers, which is computationally close to impossible within the full-quantum framework.
NASA Astrophysics Data System (ADS)
Afifi, Mahmoud S.; Farag, Rabei S.; Shaaban, Ibrahim A.; Wilson, Lee D.; Zoghaib, Wajdi M.; Mohamed, Tarek A.
2013-07-01
The infrared (4000-200 cm-1) spectrum for 4-amino-5-pyrimidinecarbonitrile (APC, C5H4N4) was acquired in the solid phase. In addition, the 1H and 13C NMR spectra of APC were obtained in DMSO-d6 along with its mass spectrum. Initially, six isomers were hypothesized and then investigated by means of DFT/B3LYP and MP2(full) quantum mechanical calculations using a 6-31G(d) basis set. Moreover, the 1H and 13C NMR chemical shifts were predicted using a GIAO approximation at the 6-311+G(d,p) basis set and the B3LYP method with (and without) solvent effects using PCM method. The correlation coefficients showed good agreement between the experimental/theoretical chemical shift values of amino tautomers (1 and 2) rather than the eliminated imino tautomers (3-6), in agreement with the current quantum mechanical calculations. Structures 3-6 are less stable than the amino tautomers (1 and 2) by about 5206-8673 cm-1 (62.3-103.7 kJ/mol). The MP2(full)/6-31G(d) computational results favor the amino structure 1 with a pyramidal NH2 moiety and calculated real vibrational frequencies, however; structure 2 is considered a transition state owing to the calculated imaginary frequency. It is worth mentioning that, the calculated structural parameters suggest a strong conjugation between the amino nitrogen and pyrimidine ring. Aided by frequency calculations, normal coordinate analysis, force constants and potential energy distributions (PEDs), a complete vibrational assignment for the observed bands is proposed herein. Finally, NH2 internal rotation barriers for the stable non-planar isomer (1) were carried out using MP2(full)/6-31G(d) optimized structural parameters. Our results are discussed herein and compared to structural parameters for similar molecules whenever appropriate.
NASA Astrophysics Data System (ADS)
He, Xing; Wang, Yang; Liu, Weilong; Yang, Zhenling; Du, Xin; Liu, Yuqiang; Yang, Yanqiang
2011-01-01
The excited states of a symmetric D- π-D structure two-photon excited fluorescence material 1,4-di (4'- N, N-diphenylaminostyryl) benzene (DPA-DSB) have been investigated by spectroscopic experiments and quantum chemical calculations. The solvent polarity dependent fluorescence properties indicate that upon photoexcitation, a radiative intramolecular charge-transfer (ICT) state is formed resulting from the ICT process. The molecular structure does not have large change during the ICT process, which is confirmed by the quantum chemical calculations performed by G AUSSIAN 03 software. The planar structure of the fluorescent ICT state results in the high fluorescence quantum yield which is important in the two-photon excited fluorescence application.
NASA Astrophysics Data System (ADS)
Zhang, Huan; Bo, Tian-Li; Zheng, Xiaojing
2017-03-01
Dusty phenomena, such as wind-blown sand, dust devils, and dust storms, play key roles in Earth's climate and geological processes. Dust electrification considerably affects the lifting and transport of dust particles. However, the electrical properties of dust storms remain poorly understood. Here, we conducted multi-parameter measurements and theoretical calculations to investigate the electrical properties of dust storms and their application to dust storm prediction. The results show that the vertical electric field (E-field) decreases first, then increases, and finally decreases with the height above the ground, reversing its direction at two heights, ∼ 8- 12 and ∼ 24 m. This suggests that the charge polarity of dust particles changes from negative to positive and back to negative again as the height increases. By carefully analyzing the E-field and dust concentration data, we further found that there is a significant positive linear relationship between the measured E-field intensity and dust concentration at the given ambient conditions. In addition, measurements and calculations demonstrate that a substantial enhancement in the vertical E-field can be observed several hours before the arrival of the external-source dust storms, indicating that the E-field can be used to provide an early warning of external-source dust storms.
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...
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
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.
Underwriting information-theoretic accounts of quantum mechanics with a realist, psi-epistemic model
NASA Astrophysics Data System (ADS)
Stuckey, W. M.; Silberstein, Michael; McDevitt, Timothy
2016-05-01
We propose an adynamical interpretation of quantum theory called Relational Blockworld (RBW) where the fundamental ontological element is a 4D graphical amalgam of space, time and sources called a “spacetimesource element.” These are fundamental elements of space, time and sources, not source elements in space and time. The transition amplitude for a spacetimesource element is computed using a path integral with discrete graphical action. The action for a spacetimesource element is constructed from a difference matrix K and source vector J on the graph, as in lattice gauge theory. K is constructed from graphical field gradients so that it contains a non-trivial null space and J is then restricted to the row space of K, so that it is divergence-free and represents a conserved exchange of energy-momentum. This construct of K and J represents an adynamical global constraint between sources, the spacetime metric and the energy-momentum content of the spacetimesource element, rather than a dynamical law for time-evolved entities. To illustrate this interpretation, we explain the simple EPR-Bell and twin-slit experiments. This interpretation of quantum mechanics constitutes a realist, psi-epistemic model that might underwrite certain information-theoretic accounts of the quantum.
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
NASA Astrophysics Data System (ADS)
Yalçin, C.
2017-02-01
The theoretical cross section calculations for the astrophysical p process are very crucial due to the most of the related reactions are technically very difficult to measure at the laboratory. On the other hand, the theoretical cross sections are not in agreement with the experimental results, especially for the (α,γ) reactions. One of the main reason of the difference between theoretical and experimental cross section is description of the α+nucleus optical model potential. In order to understand current situation and improvement of the theoretical calculations, the 112Sn(α,γ)116Te reaction were investigated for different global optical model potentials at the astrophysically interested energies. Astrophysical S factors were also calculated and compared with experimental data available at EXFOR database.
Walker, R.B.; Hayes, E.F.
1983-03-31
Detailed quantum-dynamical calculations on the Siegbahn-Liu-Truhlar-Horowitz (SLTH) surface reported for a rotating linear model (RLM) approximation with and without corrections for bending zero-point energy. These dynamical results predict that there are substantial prethreshold quantum contributions to state-selected cross sections and rate constants for both of the title reactions. However, the mechanisms for these prethreshold quantum effects are not the same. For H/sub 2/(v=1)+H, a threshold resonance is responsible for the large prethreshold quantum contribution: 65% of the total rate of 300K. For H/sub 2/(v=1)+D, tunneling is found to be large, leading to a 66% prethreshold quantum contribution at 300K. These large quantum corrections are not large enough to provide an explanation for the previously identified discrepancy between the experimental and classical theoretical rate constants for these reactions.
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.
NASA Astrophysics Data System (ADS)
Landry, E. S.; McGaughey, A. J. H.
2009-10-01
The accuracies of two theoretical expressions for thermal boundary resistance are assessed by comparing their predictions to independent predictions from molecular dynamics (MD) simulations. In one expression (RE) , the phonon distributions are assumed to follow the equilibrium, Bose-Einstein distribution, while in the other expression (RNE) , the phonons are assumed to have nonequilibrium, but bulk-like distributions. The phonon properties are obtained using lattice dynamics-based methods, which assume that the phonon interface scattering is specular and elastic. We consider (i) a symmetrically strained Si/Ge interface, and (ii) a series of interfaces between Si and “heavy-Si,” which differs from Si only in mass. All of the interfaces are perfect, justifying the assumption of specular scattering. The MD-predicted Si/Ge thermal boundary resistance is temperature independent and equal to 3.1×10-9m2-K/W below a temperature of ˜500K , indicating that the phonon scattering is elastic, as required for the validity of the theoretical calculations. At higher-temperatures, the MD-predicted Si/Ge thermal boundary resistance decreases with increasing temperature, a trend we attribute to inelastic scattering. For the Si/Ge interface and the Si/heavy-Si interfaces with mass ratios greater than two, RE is in good agreement with the corresponding MD-predicted values at temperatures where the interface scattering is elastic. When applied to a system containing no interface, RE is erroneously nonzero due to the assumption of equilibrium phonon distributions on either side of the interface. While RNE is zero for a system containing no interface, it is 40%-60% less than the corresponding MD-predicted values for the Si/Ge interface and the Si/heavy-Si interfaces at temperatures where the interface scattering is elastic. This inaccuracy is attributed to the assumption of bulk-like phonon distributions on either side of the interface.
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
NASA Astrophysics Data System (ADS)
Schulz, S.; Caro, M. A.; O'Reilly, E. P.; Marquardt, O.
2011-09-01
We present expressions for the elastic and first-order piezoelectric tensor in (111)-oriented III-V zinc-blende semiconductors. Moreover, an equation for the second-order piezoelectric polarization vector in these systems is derived. Together these expressions provide an efficient route to calculate built-in potentials and strain fields in (111)-oriented zinc-blende nanostructures. Our detailed analysis provides insight into the key parameters that modify strain and built-in fields in a (111)-oriented zinc-blende system compared to a conventional (001) structure. We show that the calculated strain field in a (111)-oriented quantum dot displays the correct C3v symmetry of the underlying crystal structure, even though we use a continuum-based approach and the quantum dot geometry is higher in symmetry than C3v, e.g., C∞v. This behavior originates from an in-plane angle dependence of certain elastic tensor components in the (111)-zinc-blende system. In addition, we compare the elastic and the first-order piezoelectric tensor of the (111)-zinc-blende systems with the corresponding quantities in a wurtzite structure and point out similarities and differences. This comparison provides, for example, insight into the sign of the shear piezoelectric coefficient e15 in the wurtzite system, which is still under debate in the literature. Our analysis indicates e15<0, in accordance with recent experimental and theoretical results.
NASA Astrophysics Data System (ADS)
Vyas, P. B.; Naquin, C.; Edwards, H.; Lee, M.; Vandenberghe, W. G.; Fischetti, M. V.
2017-01-01
We present a theoretical study of the negative differential transconductance (NDT) recently observed in the lateral-quantum-well Si n-channel field-effect transistors [J. Appl. Phys. 118, 124505 (2015)]. In these devices, p+ doping extensions are introduced at the source-channel and drain-channel junctions, thus creating two potential barriers that define the quantum well across whose quasi-bound states resonant/sequential tunneling may occur. Our study, based on the quantum transmitting boundary method, predicts the presence of a sharp NDT in devices with a nominal gate length of 10-to-20 nm at low temperatures ( ˜10 K). At higher temperatures, the NDT weakens and disappears altogether as a result of increasing thermionic emission over the p+ potential barriers. In larger devices (with a gate length of 30 nm or longer), the NDT cannot be observed because of the low transmission probability and small energetic spacing (smaller than kBT ) of the quasi-bound states in the quantum well. We speculate that the inability of the model to predict the NDT observed in 40 nm gate-length devices may be due to an insufficiently accurate knowledge of the actual doping profiles. On the other hand, our study shows that NDT suitable for novel logic applications may be obtained at room temperature in devices of the current or near-future generation (sub-10 nm node), provided an optimal design can be found that minimizes the thermionic emission (requiring high p+ potential-barriers) and punch-through (that meets the opposite requirement of potential-barriers low enough to favor the tunneling current).
Quantum mechanical calculation of spectral statistics of a modified Kepler problem.
Ma, Tao; Serota, R A
2012-03-01
For a modified Kepler problem, we reexamine jumps in the saturation spectral rigidity and large oscillations of the level number variance with near zero minima. Earlier discrepancy between the periodic orbit theory and numerical calculation is cleared by a quantum mechanical calculation. A new class of radial periodic orbits is included establishing a complete correspondence between the periodic orbit theory and the quantum mechanical approach. We show that the diagonal approximation for the level density in the periodic orbit theory already gives a good fit with the numerical calculation. Even greater accuracy is achieved by considering coherent interference between the classical periodic orbits term and the Balian-Bloch term. This procedure produces improved results for the hard-wall rectangular billiards as well.
NASA Astrophysics Data System (ADS)
Roginsky, Jacob
1987-09-01
In 1982 Gotta et al^1, experimentally observed the branching ratios for n + D, n + D^', where D ^' represents the virtual S _{0} np state, and the probability density for three-body (n + n + p) events following absorption of stopped (pi) ^{-} in ^3He. The purpose of the thesis was to calculate theoretically the particle spectrum following the absorption, using the two-nucleon model of pion absorption ^2 and to compare it to the results obtained in the Gotta experiment. The ^3 He pionic atom is unique in that it is the simplest nucleus which provides an opportunity for the verification of the two-nucleon absorption model. For this calculation the effective two-nucleon Hamiltonian^{3,4,5} was chosen as the T-matrix for low energy pion scattering from one nucleon followed by absorption on the second nucleon. The constants g_{0} and g _1 are obtained from the corresponding two-nucleon interaction processes resulting in the pion production with the first one corresponding to the spin triplet and the second to the spin singlet nucleon interactions. The initial bound-state momentum-space wave function was chosen ^6 to be consistent with the charge radius of the ^3He nucleus and to have the correct singularities generated by the asymptotic two- and three-body channels. The final-state wave functions are characterized by non-interacting n + D, non-interacting n + D^', and a non-interacting n + n + p states (when the energy is roughly equally shared between the nucleons). The results of the calculation turned out to be in a fairly good agreement with those obtained in ^1. The branching ratio of singlet deuteron rate of transition to the corresponding rate into deuteron differed from the result in the former by less than one percent. As a check some of the results obtained in ^6 were reproduced, giving a very good agreement with it as well. The calculation indicates that the two-nucleon absorption model gives a good result when used for a simple system like ^3He. Those
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.
Algorithmic differentiation and the calculation of forces by quantum Monte Carlo.
Sorella, Sandro; Capriotti, Luca
2010-12-21
We describe an efficient algorithm to compute forces in quantum Monte Carlo using adjoint algorithmic differentiation. This allows us to apply the space warp coordinate transformation in differential form, and compute all the 3M force components of a system with M atoms with a computational effort comparable with the one to obtain the total energy. Few examples illustrating the method for an electronic system containing several water molecules are presented. With the present technique, the calculation of finite-temperature thermodynamic properties of materials with quantum Monte Carlo will be feasible in the near future.
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.
Efficiency of free-energy calculations of spin lattices by spectral quantum algorithms
Master, Cyrus P.; Yamaguchi, Fumiko; Yamamoto, Yoshihisa
2003-03-01
Ensemble quantum algorithms are well suited to calculate estimates of the energy spectra for spin-lattice systems. Based on the phase estimation algorithm, these algorithms efficiently estimate discrete Fourier coefficients of the density of states. Their efficiency in calculating the free energy per spin of general spin lattices to bounded error is examined. We find that the number of Fourier components required to bound the error in the free energy due to the broadening of the density of states scales polynomially with the number of spins in the lattice. However, the precision with which the Fourier components must be calculated is found to be an exponential function of the system size.
NASA Astrophysics Data System (ADS)
Marrouni, Karim El; Abou-Rachid, Hakima; Kaliaguine, Serge
This work investigates the chemical reactivity of four linear symmetrical monoethers with molecular oxygen. Such oxygenated compounds may be considered as potential diesel fuel additives in order to reduce the ignition delay in diesel fuel engines. For this purpose, a kinetic study is proposed to clarify the relation between the molecular structure of the fuel molecule and its ignition properties. To this end, DFT calculations were performed for these reactions using B3LYP/6-311G(d,p) and BH&HLYP/6-311G(d,p) to determine structures, energies, and vibrational frequencies of stationary points as well as activated complexes involved in each gas-phase combustion initiation reaction of the monoethers CH3OCH3, C2H5OC2H5, C3H7OC3H7, or C4H9OC4H9 with molecular oxygen. This theoretical kinetic study was carried out using electronic structure results and the transition state theory, to assess the rate constants for all studied combustion reactions. As it has been shown in our previous work [Abou-Rachid et al., J Mol Struct (Theochem) 2003, 621, 293], the cetane number (CN) of a pure organic molecule depends on the initiation rate of its homogeneous gas-phase reaction with molecular oxygen. Indeed, the calculated initiation rate constants of the H-abstraction process of linear monoethers with O2 show a very good correlation with experimental CN data of these pure compounds at T D 1,000 K. This temperature is representative of the operating conditions of a diesel fuel engine.0
Poulain-Paul, Agnieszka; Nassour, Ayoub; Jelsch, Christian; Guillot, Benoit; Kubicki, Maciej; Lecomte, Claude
2012-11-01
Three models of charge-density distribution - Hansen-Coppens multipolar, virtual atom and kappa - of different complexities, different numbers of refined parameters, and with variable levels of restraints, were tested against theoretical and high-resolution X-ray diffraction structure factors for 2-methyl-4-nitro-1-phenyl-1H-imidazole-5-carbonitrile. The influence of the model, refinement strategy, multipole level and treatment of the H atoms on the dipole moment was investigated. The dipole moment turned out to be very sensitive to the refinement strategy. Also, small changes in H-atom treatment can greatly influence the calculated magnitude and orientation of the dipole moment. The best results were obtained when H atoms were kept in positions determined by neutron diffraction and anisotropic displacement parameters (obtained by SHADE, in this case) were used. Also, constraints on kappa values of H atoms were found to be superior to the free refinement of these parameters. It is also shown that the over-parametrization of the multipolar model, although possibly leading to better residuals, in general gives worse dipole moments.
Vivas, M G; Silva, D L; Misoguti, L; Zaleśny, R; Bartkowiak, W; Mendonca, C R
2010-03-18
In this work we investigate the degenerate two-photon absorption spectrum of all-trans retinal in ethanol employing the Z-scan technique with femtosecond pulses. The two-photon absorption (2PA) spectrum presents a monotonous increase as the excitation wavelength approaches the one-photon absorption band and a peak at 790 nm. We attribute the 2PA band to the mixing of states (1)B(u)(+)-like and |S(1)>, which are strongly allowed by one- and two-photon, respectively. We modeled the 2PA spectrum by using the sum-over-states approach and obtained spectroscopic parameters of the electronic transitions to |S(1)>, |S(2)> ("(1)B(u)(+)"), |S(3)>, and |S(4)> singlet-excited states. The results were compared with theoretical predictions of one- and two-photon transition calculations using the response functions formalism within the density functional theory framework with the aid of the CAM-B3LYP functional.
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.
García-Granados, Andrés; López, Pilar E; Melguizo, Enrique; Moliz, Juan N; Parra, Andrés; Simeó, Yolanda; Dobado, José A
2003-06-13
Several triterpenic derivatives, with the A-ring functionalized, were semisynthesized from oleanolic and maslinic acids. The reactivities of sulfites, sulfate, and epoxides in these triterpene compounds were investigated under different reaction conditions. Moreover, contracted A-ring triterpenes (five-membered rings) were obtained, by different treatments of the sulfate 7. From the epoxide 8, deoxygenated and halohydrin derivatives were semisynthesized with several nucleophiles. Ozonolysis and Beckmann reactions were used to yield 4-aza compounds, from five-membered ring olanediene triterpenes. The X-ray structure of sulfate 7 is given and compared with density functional theory geometries. Theoretical (13)C and (1)H chemical shifts (gauge-invariant atomic orbital method at the B3LYP/6-31G*//B3LYP/6-31G* level) and (3)J(H,H) coupling constants were calculated for compounds 5-9 and 34-36, identifying the (R)- or (S)-sulfur and alpha- or beta-epoxide configurations together with 4-aza or 3-aza structures.
Theoretical study of atomic oxygen on gold surface by Hückel theory and DFT calculations.
Sun, Keju; Kohyama, Masanori; Tanaka, Shingo; Takeda, Seiji
2012-09-27
It is fundamental to understand the behavior of atomic oxygen on gold surfaces so as to elucidate the mechanism of nano gold catalysts for low-temperature CO oxidation reactions since the atomic oxygen on gold system is an important intermediate involved in both the processes of O(2) dissociation and CO oxidation. We performed theoretical analysis of atomic oxygen adsorption on gold by using Hückel theory. It is found that formation of linear O-Au-O structure on Au surfaces greatly stabilizes the atomic oxygen adsorption due to stronger bond energy and bond order, which is confirmed subsequently by density functional theory (DFT) calculations. The linear O-Au-O structure may explain the surprising first order kinetics behavior of O(2) desorption from gold surfaces. This view of the linear O-Au-O structure as the natural adsorption status is quite different from the conventional view, which may lead to new understanding toward the reaction mechanism of low-temperature CO oxidation reaction on nano gold catalysts.
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.
NASA Astrophysics Data System (ADS)
Schulz, S.; Tanner, D. S. P.; O'Reilly, E. P.; Caro, M. A.; Tang, F.; Griffiths, J. T.; Oehler, F.; Kappers, M. J.; Oliver, R. A.; Humphreys, C. J.; Sutherland, D.; Davies, M. J.; Dawson, P.
2016-11-01
We present a combined theoretical and experimental analysis of the optical properties of m-plane InGaN/GaN quantum wells. The sample was studied by photoluminescence and photoluminescence excitation spectroscopy at low temperature. The spectra show a large Stokes shift between the lowest exciton peak in the excitation spectra and the peak of the photoluminescence spectrum. This behavior is indicative of strong carrier localization effects. These experimental results are complemented by tight-binding calculations, accounting for random alloy fluctuations and Coulomb effects. The theoretical data explain the main features of the experimental spectra. Moreover, by comparison with calculations based on a virtual crystal approximation, the importance of carrier localization effects due to random alloy fluctuations is explicitly shown.
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.
Ceriotti, Michele; Manolopoulos, David E
2012-09-07
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.
Fang, Jingtian Vandenberghe, William G.; Fu, Bo; Fischetti, Massimo V.
2016-01-21
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.
NASA Astrophysics Data System (ADS)
Zhang, Dawei
2017-03-01
Molecular fractionation with conjugate caps (MFCC) method is introduced for the efficient estimation of quantum mechanical (QM) interaction energies between nanomaterial (carbon nanotube, fullerene, and graphene surface) and ligand (charged and neutral). In the calculations, nanomaterials are partitioned into small fragments and conjugated caps that are properly capped, and the interaction energies can be obtained through the summation of QM calculations of the fragments from which the contribution of the conjugated caps is removed. All the calculations were performed by density functional theory (DFT) and dispersion contributions for the attractive interactions were investigated by dispersion corrected DFT method. The predicted interaction energies by MFCC at each computational level are found to give excellent agreement with full system (FS) calculations with the mean energy deviation just a fractional kcal/mol. The accurate determination of nanomaterial-ligand interaction energies by MFCC suggests that it is an effective method for performing QM calculations on nanomaterial-ligand systems.
Zhang, Dawei
2017-01-01
Molecular fractionation with conjugate caps (MFCC) method is introduced for the efficient estimation of quantum mechanical (QM) interaction energies between nanomaterial (carbon nanotube, fullerene, and graphene surface) and ligand (charged and neutral). In the calculations, nanomaterials are partitioned into small fragments and conjugated caps that are properly capped, and the interaction energies can be obtained through the summation of QM calculations of the fragments from which the contribution of the conjugated caps is removed. All the calculations were performed by density functional theory (DFT) and dispersion contributions for the attractive interactions were investigated by dispersion corrected DFT method. The predicted interaction energies by MFCC at each computational level are found to give excellent agreement with full system (FS) calculations with the mean energy deviation just a fractional kcal/mol. The accurate determination of nanomaterial-ligand interaction energies by MFCC suggests that it is an effective method for performing QM calculations on nanomaterial-ligand systems. PMID:28300179
Shock Hugoniot calculations of polymers using quantum mechanics and molecular dynamics
NASA Astrophysics Data System (ADS)
Chantawansri, Tanya L.; Sirk, Timothy W.; Byrd, Edward F. C.; Andzelm, Jan W.; Rice, Betsy M.
2012-11-01
Using quantum mechanics (QM) and classical force-field based molecular dynamics (FF), we have calculated the principle shock Hugoniot curves for numerous amorphous polymers including poly[methyl methacrylate] (PMMA), poly[styrene], polycarbonate, as well as both the amorphous and crystalline forms of poly[ethylene]. In the FF calculations, we considered a non-reactive force field (i.e., polymer consistent FF). The QM calculations were performed with density functional theory (DFT) using dispersion corrected atom centered pseudopotentials. Overall, results obtained by DFT show much better agreement with available experimental data than classical force fields. In particular, DFT calculated Hugoniot curves for PMMA up to 74 GPa are in very good agreement with experimental data, where a preliminary study of chain fracture and association was also performed. Structure analysis calculations of the radius of gyration and carbon-carbon radial distribution function were also carried out to elucidate contraction of the polymer chains with increasing pressure.
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
"Shut up and calculate": the available discursive positions in quantum physics courses
NASA Astrophysics Data System (ADS)
Johansson, Anders; Andersson, Staffan; Salminen-Karlsson, Minna; Elmgren, Maja
2016-08-01
Educating new generations of physicists is often seen as a matter of attracting good students, teaching them physics and making sure that they stay at the university. Sometimes, questions are also raised about what could be done to increase diversity in recruitment. Using a discursive perspective, in this study of three introductory quantum physics courses at two Swedish universities, we instead ask what it means to become a physicist, and whether certain ways of becoming a physicist and doing physics is privileged in this process. Asking the question of what discursive positions are made accessible to students, we use observations of lectures and problem solving sessions together with interviews with students to characterize the discourse in the courses. Many students seem to have high expectations for the quantum physics course and generally express that they appreciate the course more than other courses. Nevertheless, our analysis shows that the ways of being a "good quantum physics student" are limited by the dominating focus on calculating quantum physics in the courses. We argue that this could have negative consequences both for the education of future physicists and the discipline of physics itself, in that it may reproduce an instrumental "shut up and calculate"-culture of physics, as well as an elitist physics education. Additionally, many students who take the courses are not future physicists, and the limitation of discursive positions may also affect these students significantly.
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.
Band like Electronic Structures in Square Hollow Quantum Dots by 3D-MHFKS Calculation
NASA Astrophysics Data System (ADS)
Takizawa, Tokihiro; Okada, Hoshihito; Matsuse, Takehiro
To find novel aspects of the electronic structures in quantum dots (QD) from a view point of spatial broken symmetry, 3-dimensional-mesh Hartree-Fock-Kohn-Sham (3D-MHFKS) calculations1 are applied to the interacting electron system of electron number N in a symmetry broken hollow QD. For the case of a square hollow quantum dot confined in square hard wall (HW) potential (SSHQD), the magnetic (B) field dependence of the obtained single particle energy levels and chemical potentials in B-N diagram are shown to have a band like electronic structures over the wide B-field range up to 20T. To clarify the origin of the band like electronic structures in SSHQD, 3D-MHFKS calculations are also applied for the mixed symmetry QD's with a circular hollow in square HW potential (SCHQD) and with a square hollow in circular HW potential (CSHQD).
Calculation of spontaneous emission and gain spectra for quantum cascade lasers
NASA Astrophysics Data System (ADS)
Yang, Q. K.; Li, A. Z.
2000-02-01
In this paper, a quantum cascade laser has been treated as a three-level system, and the calculation of the spontaneous emission and gain spectra has been given. In the calculation, the conduction band nonparabolicity and the injection and exit of electrons have been considered. Results have shown that with increasing injection current, the spontaneous emission peak blue shifts, and the peak intensity increases near linearly with current. With increasing temperatures, the broadening of the spontaneous emission spectra has been attributed to the electron-optical phonon interactions. The peak gain of the stimulated emission has been shown to be determined mainly by the subband lifespans. We have pointed out that it is essential to obtain a long lifespan for the second excited state and short lifespan for the first excited state in order to obtain efficient population inversion and high peak gain for quantum cascade lasers.
Information-theoretic security proof for quantum-key-distribution protocols
NASA Astrophysics Data System (ADS)
Renner, Renato; Gisin, Nicolas; Kraus, Barbara
2005-07-01
We present a technique for proving the security of quantum-key-distribution (QKD) protocols. It is based on direct information-theoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with one-way classical post-processing. We show that, in order to analyze the full security of these protocols, it suffices to consider collective attacks. Indeed, we give new lower and upper bounds on the secret-key rate which only involve entropies of two-qubit density operators and which are thus easy to compute. As an illustration of our results, we analyze the Bennett-Brassard 1984, the six-state, and the Bennett 1992 protocols with one-way error correction and privacy amplification. Surprisingly, the performance of these protocols is increased if one of the parties adds noise to the measurement data before the error correction. In particular, this additional noise makes the protocols more robust against noise in the quantum channel.
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.
Usman, Muhammad; Tasco, Vittorianna; Todaro, Maria Teresa; De Giorgi, Milena; O'Reilly, Eoin P; Klimeck, Gerhard; Passaseo, Adriana
2012-04-27
III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed in an effort to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two-layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows us to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response.
Information-theoretic security proof for quantum-key-distribution protocols
Renner, Renato; Gisin, Nicolas; Kraus, Barbara
2005-07-15
We present a technique for proving the security of quantum-key-distribution (QKD) protocols. It is based on direct information-theoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with one-way classical post-processing. We show that, in order to analyze the full security of these protocols, it suffices to consider collective attacks. Indeed, we give new lower and upper bounds on the secret-key rate which only involve entropies of two-qubit density operators and which are thus easy to compute. As an illustration of our results, we analyze the Bennett-Brassard 1984, the six-state, and the Bennett 1992 protocols with one-way error correction and privacy amplification. Surprisingly, the performance of these protocols is increased if one of the parties adds noise to the measurement data before the error correction. In particular, this additional noise makes the protocols more robust against noise in the quantum channel.
Helium trimer calculations with a public quantum three-body code
Kolganova, E. A.; Roudnev, V.; Cavagnero, M.
2012-10-15
We present an illustration of using a quantumthree-body code being prepared for public release. The code is based on iterative solving of the three-dimensional Faddeev equations. The code is easy to use and allows users to perform highly-accurate calculations of quantum three-body systems. The previously known results for He{sub 3} ground state are well reproduced by the code.
Multi-state Approach to Chemical Reactivity in Fragment Based Quantum Chemistry Calculations.
Lange, Adrian W; Voth, Gregory A
2013-09-10
We introduce a multistate framework for Fragment Molecular Orbital (FMO) quantum mechanical calculations and implement it in the context of protonated water clusters. The purpose of the framework is to address issues of nonuniqueness and dynamic fragmentation in FMO as well as other related fragment methods. We demonstrate that our new approach, Fragment Molecular Orbital Multistate Reactive Molecular Dynamics (FMO-MS-RMD), can improve energetic accuracy and yield stable molecular dynamics for small protonated water clusters undergoing proton transfer reactions.
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)
Niquet, Yann-Michel; Nguyen, Viet-Hung; Triozon, François; Duchemin, Ivan; Nier, Olivier; Rideau, Denis
2014-02-01
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 μM associated with a given elastic scattering mechanism "M," taking phonons (PH) as a reference (μM-1=μPH+M-1-μPH-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.
Reptation Quantum Monte Carlo Calculation of Charge Transfer in The Na-Cl Dimer
NASA Astrophysics Data System (ADS)
Yao, Yi; Kanai, Yosuke
2015-03-01
Reptation Quantum Monte Carlo (QMC) calculations are performed to describe the charge transfer behavior in a NaCl dimer. Influence of fixed node approximation on the charge transfer was examined by obtaining electron density via reputation QMC. We employ Slater-Jastrow wavefunction as the trial wavefunction, and the fermion nodes are obtained from single particle orbitals of Hartree-Fock and Density Functional Theory (DFT) with several exchange-correlation approximations. We will discuss our QMC results together with DFT calculations to give insights into observed dependence of the charge transfer behavior on the fixed-node approximation.
Dai, Peng; Jiang, Nan; Tan, Ren-Xiang
2016-01-01
Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.
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.
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.
SU-E-T-191: First Principle Calculation of Quantum Yield in Photodynamic Therapy
Abolfath, R; Guo, F; Chen, Z; Nath, R
2014-06-01
Purpose: We present a first-principle method to calculate the spin transfer efficiency in oxygen induced by any photon fields especially in MeV energy range. The optical pumping is mediated through photosensitizers, e.g., porphyrin and/or ensemble of quantum dots. Methods: Under normal conditions, oxygen molecules are in the relatively non-reactive triplet state. In the presence of certain photosensitizer compounds such as porphyrins, electromagnetic radiation of specific wavelengths can excite oxygen to highly reactive singlet state. With selective uptake of photosensitizers by certain malignant cells, photon irradiation of phosensitized tumors can lead to selective killing of cancer cells. This is the basis of photodynamic therapy (PDT). Despite several attempts, PDT has not been clinically successful except in limited superficial cancers. Many parameters such as photon energy, conjugation with quantum dots etc. can be potentially combined with PDT in order to extend the role of PDT in cancer management. The key quantity for this optimization is the spin transfer efficiency in oxygen by any photon field. The first principle calculation model presented here, is an attempt to fill this need. We employ stochastic density matrix description of the quantum jumps and the rate equation methods in quantum optics based on Markov/Poisson processes and calculate time evolution of the population of the optically pumped singlet oxygen. Results: The results demonstrate the feasibility of our model in showing the dependence of the optical yield in generating spin-singlet oxygen on the experimental conditions. The adjustable variables can be tuned to maximize the population of the singlet oxygen hence the efficacy of the photodynamic therapy. Conclusion: The present model can be employed to fit and analyze the experimental data and possibly to assist researchers in optimizing the experimental conditions in photodynamic therapy.
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.
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.
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.
Quantum computing applied to calculations of molecular energies: CH2 benchmark.
Veis, Libor; Pittner, Jiří
2010-11-21
Quantum computers are appealing for their ability to solve some tasks much faster than their classical counterparts. It was shown in [Aspuru-Guzik et al., Science 309, 1704 (2005)] that they, if available, would be able to perform the full configuration interaction (FCI) energy calculations with a polynomial scaling. This is in contrast to conventional computers where FCI scales exponentially. We have developed a code for simulation of quantum computers and implemented our version of the quantum FCI algorithm. We provide a detailed description of this algorithm and the results of the assessment of its performance on the four lowest lying electronic states of CH(2) molecule. This molecule was chosen as a benchmark, since its two lowest lying (1)A(1) states exhibit a multireference character at the equilibrium geometry. It has been shown that with a suitably chosen initial state of the quantum register, one is able to achieve the probability amplification regime of the iterative phase estimation algorithm even in this case.
Yamamoto, Daisuke; Marmorini, Giacomo; Danshita, Ippei
2015-01-16
Magnetization processes of spin-1/2 layered triangular-lattice antiferromagnets (TLAFs) under a magnetic field H are studied by means of a numerical cluster mean-field method with a scaling scheme. We find that small antiferromagnetic couplings between the layers give rise to several types of extra quantum phase transitions among different high-field coplanar phases. Especially, a field-induced first-order transition is found to occur at H≈0.7H_{s}, where H_{s} is the saturation field, as another common quantum effect of ideal TLAFs in addition to the well-established one-third plateau. Our microscopic model calculation with appropriate parameters shows excellent agreement with experiments on Ba_{3}CoSb_{2}O_{9} [T. Susuki et al., Phys. Rev. Lett. 110, 267201 (2013)]. Given this fact, we suggest that the Co^{2+}-based compounds may allow for quantum simulations of intriguing properties of this simple frustrated model, such as quantum criticality and supersolid states.
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) =
Calculation of strain compensation thickness for III-V semiconductor quantum dot superlattices
NASA Astrophysics Data System (ADS)
Polly, S. J.; Bailey, C. G.; Grede, A. J.; Forbes, D. V.; Hubbard, S. M.
2016-11-01
Models based on continuum elasticity theory are discussed to calculate the necessary thickness of a strain compensation (SC) layer for a superlattice (SL) of strained quantum wells (QW) or quantum dots (QD). These models are then expanded to cover material systems (substrates, QW or QD, and SC) composed of AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, or InSb, as well as the ternary, quaternary, and higher order material alloys possible in the Al/Ga/In/P/As/Sb systems. SC thickness calculation methods were compared against dynamical scattering simulations and experimental X-ray diffraction measurements of the InAs/GaP/GaAs QD/SC/Substrate superlattices of varying SC thickness. Based on the reduced (but not eliminated) strain present, a further modified strain compensation thickness is calculated to maximize the number of SL repeat units before the onset of misfit dislocations is also calculated. These models have been assembled into a free application on nanoHUB for use by the community.
Fox, Stephen J; Pittock, Chris; Fox, Thomas; Tautermann, Christofer S; Malcolm, Noj; Skylaris, Chris-Kriton
2011-12-14
Biomolecular simulations with atomistic detail are often required to describe interactions with chemical accuracy for applications such as the calculation of free energies of binding or chemical reactions in enzymes. Force fields are typically used for this task but these rely on extensive parameterisation which in cases can lead to limited accuracy and transferability, for example for ligands with unusual functional groups. These limitations can be overcome with first principles calculations with methods such as density functional theory (DFT) but at a much higher computational cost. The use of electrostatic embedding can significantly reduce this cost by representing a portion of the simulated system in terms of highly localised charge distributions. These classical charge distributions are electrostatically coupled with the quantum system and represent the effect of the environment in which the quantum system is embedded. In this paper we describe and evaluate such an embedding scheme in which the polarisation of the electronic density by the embedding charges occurs self-consistently during the calculation of the density. We have implemented this scheme in a linear-scaling DFT program as our aim is to treat with DFT entire biomolecules (such as proteins) and large portions of the solvent. We test this approach in the calculation of interaction energies of ligands with biomolecules and solvent and investigate under what conditions these can be obtained with the same level of accuracy as when the entire system is described by DFT, for a variety of neutral and charged species.
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.
Laref, A; Alshammari, Nuyer; Laref, S; Luo, S J
2014-04-14
We have performed a theoretical study of silicon carbide nanowires (SiCNWs) within the framework of first-principles calculations by incorporating the size effect and hydrogen terminated surface. Specifically, the variation of the energy gap and optical absorption spectra for hydrogen passivated SiCNWs and pristine wires are examined with respect to the wire diameter. All the [001]-orientated SiCNWs derived from the parent zinc-blende (3C) exhibit semiconducting behavior. Our study demonstrates that the saturated 3C-SiCNWs grown along the [001] direction with larger wire sizes are energetically more favorable than the wires with a smaller diameter. Additionally, the energy gaps are reduced with the increment of wire size because of the quantum-confinement effects. The unsaturated SiCNWs possess smaller band gaps than those of saturated ones when the Si- and C-dangling bonds are passivated by hydrogen atoms. Interestingly, the surface terminated by hydrogen atoms substantially alters the onset of absorption as well as the spectrum behavior at upper energies. Moreover, some pronounced fine structures in the absorption peak are conspicuous at the lower energy region of hydrogen saturated SiCNWs as the wire size increases. We find that the distributions of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals are uniform along the wire axis, which reveals that the SiCNWs are exceptional candidates in producing nano-optoelectronic devices.
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.
Li Xiufeng; Li Xi
1996-08-01
Using the Tang-Toennies potential model and a set of expressions given by J. Kestin et al., we calculate the transport properties of the two noble gases He and Ne and of their binary mixtures, based upon the calculation of the interaction potential. Our calculated results for the transport properties are restricted to low densities but cover the full temperature interval extending from 50 K to the onset of ionization; the mole fraction of the binary mixtures is x{sub 1}:x{sub 2} = 0.25:0.75. Our results are comparable to the best theoretical results given by J. Kestin et al.
Puzzarini, Cristina; Barone, Vincenzo
2011-04-21
The equilibrium structure of uracil has been investigated using both theoretical and experimental data. With respect to the former, quantum-chemical calculations at the coupled-cluster level in conjunction with a triple-zeta basis set have been carried out. Extrapolation to the basis set limit, performed employing the second-order Møller-Plesset perturbation theory, and inclusion of core-correlation and diffuse-function corrections have also been considered. Based on the available rotational constants for various isotopic species together with corresponding computed vibrational corrections, the semi-experimental equilibrium structure of uracil has been determined for the first time. Theoretical and semi-experimental structures have been found in remarkably good agreement, thus pointing out the limitations of previous experimental determinations. Molecular and spectroscopic properties of uracil have then been studied by means of the composite computational approach introduced for the molecular structure evaluation. Among the results achieved, we mention the revision of the dipole moment. On the whole, it has been proved that the computational procedure presented is able to provide parameters with the proper accuracy to support experimental investigations of large molecules of biological interest.
NASA Astrophysics Data System (ADS)
Carmeli, Benny; Metiu, Horia
1987-02-01
We calculate the equilibrium properties of a system consisting of two strongly interacting quantum and classical subsystems, by using a fast Fourier transform method to evaluate the quantum contribution and a Monte Carlo method to evaluate the contribution of the classical part. The method is applied to a model relevant to tunneling problems.
Gurvits, L.
2002-01-01
Classical matching theory can be defined in terms of matrices with nonnegative entries. The notion of Positive operator, central in Quantum Theory, is a natural generalization of matrices with non-negative entries. Based on this point of view, we introduce a definition of perfect Quantum (operator) matching. We show that the new notion inherits many 'classical' properties, but not all of them. This new notion goes somewhere beyound matroids. For separable bipartite quantum states this new notion coinsides with the full rank property of the intersection of two corresponding geometric matroids. In the classical situation, permanents are naturally associated with perfects matchings. We introduce an analog of permanents for positive operators, called Quantum Permanent and show how this generalization of the permanent is related to the Quantum Entanglement. Besides many other things, Quantum Permanents provide new rational inequalities necessary for the separability of bipartite quantum states. Using Quantum Permanents, we give deterministic poly-time algorithm to solve Hidden Matroids Intersection Problem and indicate some 'classical' complexity difficulties associated with the Quantum Entanglement. Finally, we prove that the weak membership problem for the convex set of separable bipartite density matrices is NP-HARD.
Calculating work in weakly driven quantum master equations: Backward and forward equations
NASA Astrophysics Data System (ADS)
Liu, Fei
2016-01-01
I present a technical report indicating that the two methods used for calculating characteristic functions for the work distribution in weakly driven quantum master equations are equivalent. One involves applying the notion of quantum jump trajectory [Phys. Rev. E 89, 042122 (2014), 10.1103/PhysRevE.89.042122], while the other is based on two energy measurements on the combined system and reservoir [Silaev et al., Phys. Rev. E 90, 022103 (2014), 10.1103/PhysRevE.90.022103]. These represent backward and forward methods, respectively, which adopt a very similar approach to that of the Kolmogorov backward and forward equations used in classical stochastic theory. The microscopic basis for the former method is also clarified. In addition, a previously unnoticed equality related to the heat is also revealed.
NASA Astrophysics Data System (ADS)
Kim, Han Seul; Kim, Yong-Hoon
2015-03-01
We report on the development of a novel first-principles method for the calculation of non-equilibrium quantum transport process. Within the scheme, non-equilibrium situation and quantum transport within the open-boundary condition are described by the region-dependent Δ self-consistent field method and matrix Green's function theory, respectively. We will discuss our solutions to the technical difficulties in describing bias-dependent electron transport at complicated nanointerfaces and present several application examples. Global Frontier Program (2013M3A6B1078881), Basic Science Research Grant (2012R1A1A2044793), EDISON Program (No. 2012M3C1A6035684), and 2013 Global Ph.D fellowship program of the National Research Foundation. KISTI Supercomputing Center (KSC-2014-C3-021).
Kamachi, Takashi; Yoshizawa, Kazunari
2016-02-22
A conformational search program for finding low-energy conformations of large noncovalent complexes has been developed. A quantitatively reliable semiempirical quantum mechanical PM6-DH+ method, which is able to accurately describe noncovalent interactions at a low computational cost, was employed in contrast to conventional conformational search programs in which molecular mechanical methods are usually adopted. Our approach is based on the low-mode method whereby an initial structure is perturbed along one of its low-mode eigenvectors to generate new conformations. This method was applied to determine the most stable conformation of transition state for enantioselective alkylation by the Maruoka and cinchona alkaloid catalysts and Hantzsch ester hydrogenation of imines by chiral phosphoric acid. Besides successfully reproducing the previously reported most stable DFT conformations, the conformational search with the semiempirical quantum mechanical calculations newly discovered a more stable conformation at a low computational cost.
FragBuilder: an efficient Python library to setup quantum chemistry calculations on peptides models.
Christensen, Anders S; Hamelryck, Thomas; Jensen, Jan H
2014-01-01
We present a powerful Python library to quickly and efficiently generate realistic peptide model structures. The library makes it possible to quickly set up quantum mechanical calculations on model peptide structures. It is possible to manually specify a specific conformation of the peptide. Additionally the library also offers sampling of backbone conformations and side chain rotamer conformations from continuous distributions. The generated peptides can then be geometry optimized by the MMFF94 molecular mechanics force field via convenient functions inside the library. Finally, it is possible to output the resulting structures directly to files in a variety of useful formats, such as XYZ or PDB formats, or directly as input files for a quantum chemistry program. FragBuilder is freely available at https://github.com/jensengroup/fragbuilder/ under the terms of the BSD open source license.
Roos, K P; Leung, A F
1987-08-01
Sarcomere striation positions have been obtained throughout the volumes of calcium-tolerant resting heart cells by direct computer interfaced high-resolution optical imaging. Each sarcomere position is stored in a three-dimensional (3-D) matrix array from which Fraunhofer light diffraction patterns have been calculated using numerical methods based on Fourier transforms. Diffraction patterns have been calculated from heart cell data arrays oriented normal to a theoretical laser beam. Twelve characteristic features have been identified and described from these diffraction patterns that correlate to diffraction phenomena observed from both cardiac and skeletal muscle. This numerical approach provides the means to directly assess diffraction pattern formulation, the precision of layer line angular separation, layer-line intensity and angular asymmetries, line widths and fine structures in terms of the known diffracting source structures. These results confirm that theoretical calculations can predict real muscle diffraction patterns and their asymmetries.
Fox, Stephen J; Pittock, Chris; Tautermann, Christofer S; Fox, Thomas; Christ, Clara; Malcolm, N O J; Essex, Jonathan W; Skylaris, Chris-Kriton
2013-08-15
Schemes of increasing sophistication for obtaining free energies of binding have been developed over the years, where configurational sampling is used to include the all-important entropic contributions to the free energies. However, the quality of the results will also depend on the accuracy with which the intermolecular interactions are computed at each molecular configuration. In this context, the energy change associated with the rearrangement of electrons (electronic polarization and charge transfer) upon binding is a very important effect. Classical molecular mechanics force fields do not take this effect into account explicitly, and polarizable force fields and semiempirical quantum or hybrid quantum-classical (QM/MM) calculations are increasingly employed (at higher computational cost) to compute intermolecular interactions in free-energy schemes. In this work, we investigate the use of large-scale quantum mechanical calculations from first-principles as a way of fully taking into account electronic effects in free-energy calculations. We employ a one-step free-energy perturbation (FEP) scheme from a molecular mechanical (MM) potential to a quantum mechanical (QM) potential as a correction to thermodynamic integration calculations within the MM potential. We use this approach to calculate relative free energies of hydration of small aromatic molecules. Our quantum calculations are performed on multiple configurations from classical molecular dynamics simulations. The quantum energy of each configuration is obtained from density functional theory calculations with a near-complete psinc basis set on over 600 atoms using the ONETEP program.
Quantum calculation of disordered length in fcc single crystals using channelling techniques
NASA Astrophysics Data System (ADS)
Abu-Assy, M. K.
2006-04-01
Lattices of face-centred cubic crystals (fcc), due to irradiation processes, may become disordered in stable configurations like the dumb-bell configuration (DBC) or body-centred interstitial (BCI). In this work, a quantum mechanical treatment for the calculation of transmission coefficients of channelled positrons from their bound states in the normal lattice regions into the allowed bound states in the disordered regions is given as a function of the length of the disordered regions. In order to obtain more reliable results, higher anharmonic terms in the planar channelling potential are considered in the calculations by using first-order perturbation theory where new bound states have been found. The calculations were executed in the energy range 10 200 MeV of the incident positron on a copper single crystal in the planar direction (100).
Wu, Xin; Koslowski, Axel; Thiel, Walter
2012-07-10
In this work, we demonstrate that semiempirical quantum chemical calculations can be accelerated significantly by leveraging the graphics processing unit (GPU) as a coprocessor on a hybrid multicore CPU-GPU computing platform. Semiempirical calculations using the MNDO, AM1, PM3, OM1, OM2, and OM3 model Hamiltonians were systematically profiled for three types of test systems (fullerenes, water clusters, and solvated crambin) to identify the most time-consuming sections of the code. The corresponding routines were ported to the GPU and optimized employing both existing library functions and a GPU kernel that carries out a sequence of noniterative Jacobi transformations during pseudodiagonalization. The overall computation times for single-point energy calculations and geometry optimizations of large molecules were reduced by one order of magnitude for all methods, as compared to runs on a single CPU core.
Quantum chemical calculation of the equilibrium structures of small metal atom clusters
NASA Technical Reports Server (NTRS)
Kahn, L. R.
1981-01-01
The application of ab initio quantum mechanical approaches in the study of metal atom clusters requires simplifying techniques that do not compromise the reliability of the calculations. Various aspects of the implementation of the effective core potential (ECP) technique for the removal of the metal atom core electrons from the calculation were examined. The ECP molecular integral formulae were modified to bring out the shell characteristics as a first step towards fulfilling the increasing need to speed up the computation of the ECP integrals. Work on the relationships among the derivatives of the molecular integrals that extends some of the techniques pioneered by Komornicki for the calculation of the gradients of the electronic energy was completed and a formulation of the ECP approach that quite naturally unifies the various state-of-the-art "shape- and Hamiltonian-consistent" techniques was discovered.
NASA Astrophysics Data System (ADS)
Skone, Jonathan H.
Development of quantum mechanical methods for the calculation of proton tunneling splittings and proton-coupled electron transfer vibronic couplings is presented in this thesis. The fundamental physical principles underlying proton transfer in the electronically adiabatic and nonadiabatic limits are illustrated by applying the quantum mechanical methods we developed to chemical systems exemplary of the electronically adiabatic and nonadiabatic proton-tunneling regimes. Overall, this thesis emphasizes the need for quantum chemical methods that avoid the adiabatic separation of the quantum proton and electron, are computationally tractable, and treat all quantum particles three-dimensionally. The nuclear-electronic orbital nonorthogonal configuration interaction (NEO-NOCI) approach is presented for calculating proton tunneling splittings and vibronic couplings. The NEO approach is a molecular orbital based method that avoids the Born-Oppenheimer separation of the select protons and electrons, thereby making methods developed within this scheme, such as NEO-NOCI, applicable to electronically nonadiabatic proton transfer. In the two-state NEO-NOCI approach, the ground and excited state delocalized nuclear-electronic wavefunctions are expressed as linear combinations of two nonorthogonal localized nuclear-electronic wavefunctions obtained at the NEO-Hartree-Fock level. The advantages of the NEO-NOCI approach are the removal of the adiabatic separation between the electrons and the quantum nuclei, the computational efficiency, the potential for systematic improvement by enhancing the basis sets and number of configurations, and the applicability to a broad range of chemical systems. The tunneling splitting is determined by the energy difference between these two delocalized vibronic states. The proton tunneling splittings calculated with the NEO-NOCI approach for the [He-H-He]+ model system with a range of fixed He-He distances are shown to be in excellent agreement with
NASA Astrophysics Data System (ADS)
Laptyeva, T. V.; Kozinov, E. A.; Meyerov, I. B.; Ivanchenko, M. V.; Denisov, S. V.; Hänggi, P.
2016-04-01
We present a numerical approach to calculate non-equilibrium eigenstates of a periodically time-modulated quantum system. The approach is based on the use of a chain of single-step propagating operators. Each operator is time-specific and constructed by combining the Magnus expansion of the time-dependent system Hamiltonian with the Chebyshev expansion of an operator exponent. The construction of the unitary Floquet operator, which evolves a system state over the full modulation period, is performed by propagating the identity matrix over the period. The independence of the evolution of basis vectors makes the propagation stage suitable for realization on a parallel cluster. Once the propagation stage is completed, a routine diagonalization of the Floquet matrix is performed. Finally, an additional propagation round, now involving the eigenvectors as the initial states, allows to resolve the time-dependence of the Floquet states and calculate their characteristics. We demonstrate the accuracy and scalability of the algorithm by applying it to calculate the Floquet states of two quantum models, namely (i) a synthesized random-matrix Hamiltonian and (ii) a many-body Bose-Hubbard dimer, both of the size up to 104 states.
Yang, Sandy; Yamamoto, Takeshi; Miller, William H.
2005-11-28
The quantum instanton approximation is a type of quantum transition state theory that calculates the chemical reaction rate using the reactive flux correlation function and its low order derivatives at time zero. Here we present several path-integral estimators for the latter quantities, which characterize the initial decay profile of the flux correlation function. As with the internal energy or heat capacity calculation, different estimators yield different variances (and therefore different convergence properties) in a Monte Carlo calculation. Here we obtain a virial(-type) estimator by using a coordinate scaling procedure rather than integration by parts, which allows more computational benefits. We also consider two different methods for treating the flux operator, i.e., local-path and global-path approaches, in which the latter achieves a smaller variance at the cost of using second-order potential derivatives. Numerical tests are performed for a one-dimensional Eckart barrier and a model proton transfer reaction in a polar solvent, which illustrates the reduced variance of the virial estimator over the corresponding thermodynamic estimator.
NASA Technical Reports Server (NTRS)
Burr, D. M.; Emery, J. P.; Lorenz, R. D.
2005-01-01
The Cassini Imaging Science System (ISS) has been returning images of Titan, along with other Saturnian satellites. Images taken through the 938 nm methane window see down to Titan's surface. One of the purposes of the Cassini mission is to investigate possible fluid cycling on Titan. Lemniscate features shown recently and radar evidence of surface flow prompted us to consider theoretically the creation by methane fluid flow of streamlined forms on Titan. This follows work by other groups in theoretical consideration of fluid motion on Titan's surface.
Trail-Needs pseudopotentials in quantum Monte Carlo calculations with plane-wave/blip basis sets
NASA Astrophysics Data System (ADS)
Drummond, N. D.; Trail, J. R.; Needs, R. J.
2016-10-01
We report a systematic analysis of the performance of a widely used set of Dirac-Fock pseudopotentials for quantum Monte Carlo (QMC) calculations. We study each atom in the periodic table from hydrogen (Z =1 ) to mercury (Z =80 ), with the exception of the 4 f elements (57 ≤Z ≤70 ). We demonstrate that ghost states are a potentially serious problem when plane-wave basis sets are used in density functional theory (DFT) orbital-generation calculations, but that this problem can be almost entirely eliminated by choosing the s channel to be local in the DFT calculation; the d channel can then be chosen to be local in subsequent QMC calculations, which generally leads to more accurate results. We investigate the achievable energy variance per electron with different levels of trial wave function and we determine appropriate plane-wave cutoff energies for DFT calculations for each pseudopotential. We demonstrate that the so-called "T-move" scheme in diffusion Monte Carlo is essential for many elements. We investigate the optimal choice of spherical integration rule for pseudopotential projectors in QMC calculations. The information reported here will prove crucial in the planning and execution of QMC projects involving beyond-first-row elements.
NASA Astrophysics Data System (ADS)
Shlykov, Sergey A.; Phien, Tran D.; Gao, Yan; Weber, Peter M.
2017-03-01
Molecular structure and conformational behavior of N-phenylpiperidine (NPhP) were investigated by synchronous gas-phase electron diffraction/mass spectrometry (GED/MS) and quantum chemistry. Due to influence of steric repulsion and hyperconjugation, NPhP may exist in two conformers, equatorial and axial chair forms. Both experiment and theoretical calculations suggest a C1 symmetry of the conformers, with the plane perpendicular to the phenyl group turned by ca. 30-40° (equatorial) and 0-20° (axial) about the plane perpendicular to the piperidine ring symmetry plane. According to the QC calculations, NPhP may exist as two conformers, equatorial and axial, with a ratio of Eq:Ax = 92:8 (B3LYP), 87:13 (B3LYP-GD3), 84:16 (M06-2X), 83:17 (MP2/6-311G**) and 76:24% (MP2/cc-pVTZ). Except for the latter, these values are in good agreement with the experimental GED data of 90(10):10(10)%. A comparative analysis of similar compounds, phenylcyclohexane and 1-phenylheterocyclohexanes, was performed. Conformational properties depend on the CPhsbnd X bond distance and hyperconjugation between the phenyl ring and the lone pair on the heteroatom. The contribution of the axial form of 1-phenylcyclohexane derivatives increases in the series of the heteroatom X in the cyclohexane ring: C → N → Si → P.
NASA Astrophysics Data System (ADS)
de Guzman, C. P.; Andrianarijaona, M.; Lee, Y. S.; Andrianarijaona, V.
An extensive knowledge of the ionization energies of amino acids can provide vital information on protein sequencing, structure, and function. Acidic and basic amino acids are unique because they have three ionizable groups: the C-terminus, the N-terminus, and the side chain. The effects of multiple ionizable groups can be seen in how Aspartate's ionizable side chain heavily influences its preferred conformation (J Phys Chem A. 2011 April 7; 115(13): 2900-2912). Theoretical and experimental data on the ionization energies of many of these molecules is sparse. Considering each atom of the amino acid as a potential departing site for the electron gives insight on how the three ionizable groups affect the ionization process of the molecule and the dynamic coupling between the vibrational modes. In the following study, we optimized the structure of each acidic and basic amino acid then exported the three dimensional coordinates of the amino acids. We used ORCA to calculate single point energies for a region near the optimized coordinates and systematically went through the x, y, and z coordinates of each atom in the neutral and ionized forms of the amino acid. With the calculations, we were able to graph energy potential curves to better understand the quantum dynamic properties of the amino acids. The authors thank Pacific Union College Student Association for providing funds.
NASA Astrophysics Data System (ADS)
Wang, Chao; Xiao, Jun; Luo, Xiaobing
2016-10-01
The neutron inelastic scattering cross section of 115In has been measured by the activation technique at neutron energies of 2.95, 3.94, and 5.24 MeV with the neutron capture cross sections of 197Au as an internal standard. The effects of multiple scattering and flux attenuation were corrected using the Monte Carlo code GEANT4. Based on the experimental values, the 115In neutron inelastic scattering cross sections data were theoretically calculated between the 1 and 15 MeV with the TALYS software code, the theoretical results of this study are in reasonable agreement with the available experimental results.
Vibrational analysis of 4-chloro-3-nitrobenzonitrile by quantum chemical calculations.
Sert, Yusuf; Çırak, Çağrı; Ucun, Fatih
2013-04-15
In the present study, the experimental and theoretical harmonic and anharmonic vibrational frequencies of 4-chloro-3-nitrobenzonitrile were investigated. The experimental FT-IR (400-4000 cm(-1)) and μ-Raman spectra (100-4000 cm(-1)) of the molecule in the solid phase were recorded. Theoretical vibrational frequencies and geometric parameters (bond lengths and bond angles) were calculated using ab initio Hartree Fock (HF), density functional B3LYP and M06-2X methods with 6-311++G(d,p) basis set by Gaussian 09 W program, for the first time. The assignments of the vibrational frequencies were performed by potential energy distribution (PED) analysis by using VEDA 4 program. The theoretical optimized geometric parameters and vibrational frequencies were compared with the corresponding experimental data, and they were seen to be in a good agreement with each other. Also, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies were found.
Vibrational analysis of 4-chloro-3-nitrobenzonitrile by quantum chemical calculations
NASA Astrophysics Data System (ADS)
Sert, Yusuf; Çırak, Çağrı; Ucun, Fatih
2013-04-01
In the present study, the experimental and theoretical harmonic and anharmonic vibrational frequencies of 4-chloro-3-nitrobenzonitrile were investigated. The experimental FT-IR (400-4000 cm-1) and μ-Raman spectra (100-4000 cm-1) of the molecule in the solid phase were recorded. Theoretical vibrational frequencies and geometric parameters (bond lengths and bond angles) were calculated using ab initio Hartree Fock (HF), density functional B3LYP and M06-2X methods with 6-311++G(d,p) basis set by Gaussian 09 W program, for the first time. The assignments of the vibrational frequencies were performed by potential energy distribution (PED) analysis by using VEDA 4 program. The theoretical optimized geometric parameters and vibrational frequencies were compared with the corresponding experimental data, and they were seen to be in a good agreement with each other. Also, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies were found.
NASA Astrophysics Data System (ADS)
Hsieh, Tiane-Jye; Su, Chia-Ching; Chen, Chung-Yi; Liou, Chyong-Huey; Lu, Li-Hwa
2005-05-01
Three natural products, Coumarin ( 1), p-hydroxybenzoic acid ( 2), trans-cinnamic acid ( 3) were isolated from the natural plant of indigenous cinnamon and the structures including relative stereochemistry were elucidated on the basis of spectroscopic data and theoretical calculations. Their sterochemical structures were determined by NMR spectroscopy, mass spectroscopy, and X-ray crystallography. The p-hydroxybenzoic acid complex with water is reported to show the existence of two hydrogen bonds. The two hydrogen bonds are formed in the water molecule of two hydrogen-accepting oxygen of carbonyl group of the p-hydroxybenzoic acid. The intermolecular interaction two hydrogen bond of the model system of the water- p-hydroxybenzoic acid was investigated. An experimental study and a theoretical analysis using the B3LYP/6-31G* method in the GAUSSIAN-03 package program were conducted on the three natural products. The theoretical results are supplemented by experimental data. Optimal geometric structures of three compounds were also determined. The calculated molecular mechanics compared quite well with those obtained from the experimental data. The ionization potentials, highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy, energy gaps, heat of formation, atomization energies, and vibration frequencies of the compounds were also calculated. The results of the calculations show that three natural products are stable molecules with high reactive and various other physical properties. The study also provided an explicit understanding of the sterochemical structure and thermodynamic properties of the three natural products.
An approximate framework for quantum transport calculation with model order reduction
Chen, Quan; Li, Jun; Yam, Chiyung; Zhang, Yu; Wong, Ngai; Chen, Guanhua
2015-04-01
A new approximate computational framework is proposed for computing the non-equilibrium charge density in the context of the non-equilibrium Green's function (NEGF) method for quantum mechanical transport problems. The framework consists of a new formulation, called the X-formulation, for single-energy density calculation based on the solution of sparse linear systems, and a projection-based nonlinear model order reduction (MOR) approach to address the large number of energy points required for large applied biases. The advantages of the new methods are confirmed by numerical experiments.
Forming NCO– in Dense Molecular Clouds: Possible Gas-Phase Chemical Paths From Quantum Calculations
2015-01-01
The existence of NCO– anions in the interstellar medium (ISM) has been suggested and searched for over the years but without any formal definitive sighting of that molecule. We discuss in this work the possible formation of either NCO– directly or of NCO neutral as a precursor to NCO– formation by electron attachment. We follow simple, gas-phase chemical reactions for which the general features are obtained from accurate quantum calculations. The results are shedding some additional light on the likely presence of this anion in the ISM environment, drawing further information from the specific features of the considered reactions on the additional chemical options that exist for its formation. PMID:26696323
Path-integral calculation of the third virial coefficient of quantum gases at low temperatures
Garberoglio, Giovanni; Harvey, Allan H.
2011-04-07
We derive path-integral expressions for the second and third virial coefficients of monatomic quantum gases. Unlike previous work that considered only Boltzmann statistics, we include exchange effects (Bose-Einstein or Fermi-Dirac statistics). We use state-of-the-art pair and three-body potentials to calculate the third virial coefficient of {sup 3}He and {sup 4}He in the temperature range 2.6-24.5561 K. We obtain uncertainties smaller than those of the limited experimental data. Inclusion of exchange effects is necessary to obtain accurate results below about 7 K.
Path-integral calculation of the third virial coefficient of quantum gases at low temperatures.
Garberoglio, Giovanni; Harvey, Allan H
2011-04-07
We derive path-integral expressions for the second and third virial coefficients of monatomic quantum gases. Unlike previous work that considered only Boltzmann statistics, we include exchange effects (Bose-Einstein or Fermi-Dirac statistics). We use state-of-the-art pair and three-body potentials to calculate the third virial coefficient of (3)He and (4)He in the temperature range 2.6-24.5561 K. We obtain uncertainties smaller than those of the limited experimental data. Inclusion of exchange effects is necessary to obtain accurate results below about 7 K.
Electric-field control of magnetism in graphene quantum dots: Ab initio calculations
Agapito, Luis A.; Kioussis, Nicholas; Kaxiras, Efthimios
2011-01-01
Employing ab initio calculations we predict that the magnetic states of hydrogenated diamond-shaped zigzag graphene quantum dots (GQDs), each exhibiting unique electronic structure, can be selectively tuned with gate voltage, through Stark or hybridization electric-field modulation of the spatial distribution and energy of the spin-polarized molecular orbitals, leading to transitions between these states. Electrical read-out of the GQD magnetic state can be accomplished by exploiting the distinctive electrical properties of the various magnetic configurations. PMID:21765631
Diffusion Rates for Hydrogen on Pd(111) from Molecular Quantum Dynamics Calculations.
Firmino, Thiago; Marquardt, Roberto; Gatti, Fabien; Dong, Wei
2014-12-18
The van Hove formula for the dynamical structure factor (DSF) related to particle scattering at mobile adsorbates is extended to include the relaxation of the adsorbates' vibrational states. The total rate obtained from the DSF is assumed to be the sum of a diffusion and a relaxation rate. A simple kinetic model to support this assumption is presented. To illustrate its potential applicability, the formula is evaluated using wave functions, energies, and lifetimes of vibrational states obtained for H/Pd(111) from first-principle calculations. Results show that quantum effects can be expected to be important even at room temperature.
Playing the quantum shuffling game with programmable pocket calculators and microcomputers
NASA Astrophysics Data System (ADS)
Sauer, G.
1981-03-01
The utilisation of programmable calculators or microcomputers in the classroom for the quantum shuffling game may reinforce the study of statistical physics in unit 9 of the Nuffield advanced physics course since the students are themselves able to work out much more sophisticated applications of the game. Because of the higher speed of computation and the possibilities of graphical representation on the computer screen preference is given to the application of microcomputer games. Copies of the programs described may be obtained from Professor P J Black, Chelsea College Centre for Science Education, Bridges Place, London SW6 4HR or directly from the author at Tulpenweg 3, 6301 Linden, W Germany.
Superchi, Stefano; Scafato, Patrizia; Górecki, Marcin; Pescitelli, Gennaro
2017-03-10
The application of quantum mechanical simulation of chiroptical properties, i.e. electronic circular dichroism (ECD), optical rotation (OR), and vibrational circular dichroism (VCD), to the assignment of the absolute configuration of chiral naturally occurring metabolites of fungal origin, is reviewed. The fundamentals of such chiroptical spectroscopies as well as the specific experimental and computational issues allied to the application of their ab initio calculation is reported. Some examples, related to the use of the ECD, VCD, and OR techniques and highlighting the practical application of the methods, are also described.
tRNA structure from a graph and quantum theoretical perspective.
Galindo, Johan F; Bermúdez, Clara I; Daza, Edgar E
2006-06-21
One of the objectives of theoretical biochemistry is to find a suitable representation of molecules allowing us to encode what we know about their structures, interactions and reactivity. Particularly, tRNA structure is involved in some processes like aminoacylation and genetic code translation, and for this reason these molecules represent a biochemical object of the utmost importance requiring characterization. We propose here two fundamental aspects for characterizing and modeling them. The first takes into consideration the connectivity patterns, i.e. the set of linkages between atoms or molecular fragments (a key tool for this purpose is the use of graph theory), and the second one requires the knowledge of some properties related to the interactions taking place within the molecule, at least in an approximate way, and perhaps of its reactivity in certain means. We used quantum mechanics to achieve this goal; specifically, we have used partial charges as a manifestation of the reply to structural changes. These charges were appropriately modified to be used as weighted factors for elements constituting the molecular graph. This new graph-tRNA context allow us to detect some structure-function relationships.
Structure and properties of electronic and hole centers in CsBr from theoretical calculations
Halliday, Matthew T.; Hess, Wayne P.; Shluger, Alexander L.
2015-06-24
The electronic structure, geometry, diffusion barriers and optical properties of fundamental defects of CsBr are calculated using hybrid functional DFT and TD- DFT methods. The B3LYP functional with a modified exchange contribution has been used in an embedded cluster scheme to model the structure and spectroscopic properties of self-trapped triplet exciton, interstitial Br atoms and ions, self-trapped holes and Br vacancies. The calculated migration barriers and positions of maxima of optical absorption bands are in good agreement with experiment, justifying the obtained defect geometries. The o*-center triplet exciton luminescence energy is also accurately calculated.
NASA Technical Reports Server (NTRS)
Gamache, Robert R.; Pollack, James B.
1995-01-01
Halfwidths were calculated for H2O with H2 as a broadening gas and were estimated for He as the broadening species. The calculations used the model of Robert and Bonamy with parabolic trajectories and all relevant terms in the interaction potential. The calculations investigated the dependence of the halfwidth on the order of the atom-atom expansion, the rotational states, and the temperature in the range 200 to 400K. Finally, calculations were performed for many transitions of interest in the 5 micrometer window region of the spectrum. The resulting data will be supplied to Dr. R. Freedman for extracting accurate water mixing ratios from the analysis of the thermal channels for the Net Flux experiment on the Galileo probe.
NASA Astrophysics Data System (ADS)
Kılınç, F.; Karpuz, N.; ćetin, B.
2017-02-01
In medical physics, radionuclides are needed to diagnose functional disorders of organs and to diagnose and treat many diseases. Nuclear reactions are significant for the productions of radionuclides. It is important to analyze the cross sections for much different energy. In this study, reactional cross sections calculations on 13N, 18F radioisotopes are with TALYS 1.6 nuclear reaction simulation code. Cross sections calculated and experimental data taken from EXFOR library were compared
NASA Astrophysics Data System (ADS)
Stanke, Monika; Jurkowski, Jacek; Adamowicz, Ludwik
2017-03-01
Algorithms for calculating the quantum electrodynamics Araki–Sucher correction for n-electron explicitly correlated molecular Gaussian functions with shifted centers are derived and implemented. The algorithms are tested in calculations concerning the H2 molecule and applied in ground-state calculations of LiH and {{{H}}}3+ molecules. The implementation will significantly increase the accuracy of the calculations of potential energy surfaces of small diatomic and triatomic molecules and their rovibrational spectra.
Parallelizing the QUDA Library for Multi-GPU Calculations in Lattice Quantum Chromodynamics
Ronald Babich, Michael Clark, Balint Joo
2010-11-01
Graphics Processing Units (GPUs) are having a transformational effect on numerical lattice quantum chromodynamics (LQCD) calculations of importance in nuclear and particle physics. The QUDA library provides a package of mixed precision sparse matrix linear solvers for LQCD applications, supporting single GPUs based on NVIDIA's Compute Unified Device Architecture (CUDA). This library, interfaced to the QDP++/Chroma framework for LQCD calculations, is currently in production use on the "9g" cluster at the Jefferson Laboratory, enabling unprecedented price/performance for a range of problems in LQCD. Nevertheless, memory constraints on current GPU devices limit the problem sizes that can be tackled. In this contribution we describe the parallelization of the QUDA library onto multiple GPUs using MPI, including strategies for the overlapping of communication and computation. We report on both weak and strong scaling for up to 32 GPUs interconnected by InfiniBand, on which we sustain in excess of 4 Tflops.
A new method to calculate Berry phase in one-dimensional quantum anomalous Hall insulator
NASA Astrophysics Data System (ADS)
Liao, Yi
2016-08-01
Based on the residue theorem and degenerate perturbation theory, we derive a new, simple and general formula for Berry phase calculation in a two-level system for which the Hamiltonian is a real symmetric matrix. The special torus topology possessed by the first Brillouin zone (1 BZ) of this kind of systems ensures the existence of a nonzero Berry phase. We verify the correctness of our formula on the Su-Schrieffer-Heeger (SSH) model. Then the Berry phase of one-dimensional quantum anomalous Hall insulator (1DQAHI) is calculated analytically by applying our method, the result being -π/2 -π/4 sgn (B) [ sgn (Δ - 4 B) + sgn (Δ) ]. Finally, illuminated by this idea, we investigate the Chern number in the two-dimensional case, and find a very simple way to determine the parameter range of the non-trivial Chern number in the phase diagram.
NASA Astrophysics Data System (ADS)
Szyczewski, A.; Hołderna-Natkaniec, K.; Natkaniec, I.
2004-05-01
Inelastic incoherent neutron scattering spectra of progesterone and testosterone measured at 20 and 290 K were compared with the IR spectra measured at 290 K. The Phonon Density of States spectra display well resolved peaks of low frequency internal vibration modes up to 1200 cm -1. The quantum chemistry calculations were performed by semiempirical PM3 method and by the density functional theory method with different basic sets for isolated molecule, as well as for the dimer system of testosterone. The proposed assignment of internal vibrations of normal modes enable us to conclude about the sequence of the onset of the torsion movements of the CH 3 groups. These conclusions were correlated with the results of proton molecular dynamics studies performed by NMR method. The GAUSSIAN program had been used for calculations.
Theoretical calculations of emission of wolframite and scheelite-type tungstate crystals
Nikolaenko, T.; Hizhnyi, Y.; Nedilko, S.
2009-01-21
Tungstate crystals AWO{sub 4} (A = Zn,Cd,Pb) are well-known scintillation materials for various applications in science and technology. In recent years the optical properties of these crystals were intensively studied experimentally and theoretically. However, the origin of luminescence in lead, cadmium and zinc tungstates is still the subject of discussion. According to generally accepted view, the centers of luminescence in AWO{sub 4} crystals are in some or other way related to the tungstate anionic groups. We developed a cluster approach in theoretical investigation of the electronic structure of AWO{sub 4} tungstate crystals based on the configuration interaction (CI) computation in which the lattice vibrations were taken into account.
NASA Technical Reports Server (NTRS)
Mccluney, W. R.
1974-01-01
The development is considered of procedures for measuring a number of subsurface oceanographic parameters using remotely sensed ocean color data. It is proposed that the first step in this effort should be the development of adequate theoretical models relating the desired oceanographic parameters to the upwelling radiances to be observed. A portion of a contributory theoretical model is shown to be described by a modified single scattering approach based upon a simple treatment of multiple scattering. The resulting quasi-single scattering model can be used to predict the upwelling distribution of spectral radiance emerging from the sea. The shape of the radiance spectrum predicted by this model for clear ocean water shows encouraging agreement with measurments made at the edge of the Sargasso Sea off Cape Hatteras.
Jacob, D; Palacios, J J
2011-01-28
We study the performance of two different electrode models in quantum transport calculations based on density functional theory: parametrized Bethe lattices and quasi-one-dimensional wires or nanowires. A detailed account of implementation details in both the cases is given. From the systematic study of nanocontacts made of representative metallic elements, we can conclude that the parametrized electrode models represent an excellent compromise between computational cost and electronic structure definition as long as the aim is to compare with experiments where the precise atomic structure of the electrodes is not relevant or defined with precision. The results obtained using parametrized Bethe lattices are essentially similar to the ones obtained with quasi-one-dimensional electrodes for large enough cross-sections of these, adding a natural smearing to the transmission curves that mimics the true nature of polycrystalline electrodes. The latter are more demanding from the computational point of view, but present the advantage of expanding the range of applicability of transport calculations to situations where the electrodes have a well-defined atomic structure, as is the case for carbon nanotubes, graphene nanoribbons, or semiconducting nanowires. All the analysis is done with the help of codes developed by the authors which can be found in the quantum transport toolbox ALACANT and are publicly available.
Tilborg, Anaëlle; Jacquemin, Denis; Norberg, Bernadette; Perpète, Eric; Michaux, Catherine; Wouters, Johan
2011-12-01
Pharmaceutical compounds are mostly developed as solid dosage forms containing a single-crystal form. It means that the selection of a particular crystal state for a given molecule is an important step for further clinical outlooks. In this context, piracetam, a pharmaceutical molecule known since the sixties for its nootropic properties, is considered in the present work. This molecule is analyzed using several experimental and theoretical approaches. First, the conformational space of the molecule has been systematically explored by performing a quantum mechanics scan of the two most relevant dihedral angles of the lateral chain. The predicted stable conformations have been compared to all the reported experimental geometries retrieved from the Cambridge Structural Database (CSD) covering polymorphs and cocrystals structures. In parallel, different batches of powders have been recrystallized. Under specific conditions, single crystals of polymorph (III) of piracetam have been obtained, an outcome confirmed by crystallographic analysis.
Quantum Monte Carlo calculations of neutron matter with chiral three-body forces
NASA Astrophysics Data System (ADS)
Tews, I.; Gandolfi, S.; Gezerlis, A.; Schwenk, A.
2016-02-01
Chiral effective field theory (EFT) enables a systematic description of low-energy hadronic interactions with controlled theoretical uncertainties. For strongly interacting systems, quantum Monte Carlo (QMC) methods provide some of the most accurate solutions, but they require as input local potentials. We have recently constructed local chiral nucleon-nucleon (NN) interactions up to next-to-next-to-leading order (N2LO ). Chiral EFT naturally predicts consistent many-body forces. In this paper, we consider the leading chiral three-nucleon (3N) interactions in local form. These are included in auxiliary field diffusion Monte Carlo (AFDMC) simulations. We present results for the equation of state of neutron matter and for the energies and radii of neutron drops. In particular, we study the regulator dependence at the Hartree-Fock level and in AFDMC and find that present local regulators lead to less repulsion from 3N forces compared to the usual nonlocal regulators.
Quantum Monte Carlo calculations of neutron matter with chiral three-body forces
Tews, I.; Gandolfi, Stefano; Gezerlis, A.; Schwenk, A.
2016-02-02
Chiral effective field theory (EFT) enables a systematic description of low-energy hadronic interactions with controlled theoretical uncertainties. For strongly interacting systems, quantum Monte Carlo (QMC) methods provide some of the most accurate solutions, but they require as input local potentials. We have recently constructed local chiral nucleon-nucleon (NN) interactions up to next-to-next-to-leading order (N^{2}LO). Chiral EFT naturally predicts consistent many-body forces. In this paper, we consider the leading chiral three-nucleon (3N) interactions in local form. These are included in auxiliary field diffusion Monte Carlo (AFDMC) simulations. We present results for the equation of state of neutron matter and for the energies and radii of neutron drops. Specifically, we study the regulator dependence at the Hartree-Fock level and in AFDMC and find that present local regulators lead to less repulsion from 3N forces compared to the usual nonlocal regulators.
NASA Astrophysics Data System (ADS)
Heusler, Stefan
2006-12-01
The main focus of the second, enlarged edition of the book Mathematica for Theoretical Physics is on computational examples using the computer program Mathematica in various areas in physics. It is a notebook rather than a textbook. Indeed, the book is just a printout of the Mathematica notebooks included on the CD. The second edition is divided into two volumes, the first covering classical mechanics and nonlinear dynamics, the second dealing with examples in electrodynamics, quantum mechanics, general relativity and fractal geometry. The second volume is not suited for newcomers because basic and simple physical ideas which lead to complex formulas are not explained in detail. Instead, the computer technology makes it possible to write down and manipulate formulas of practically any length. For researchers with experience in computing, the book contains a lot of interesting and non-trivial examples. Most of the examples discussed are standard textbook problems, but the power of Mathematica opens the path to more sophisticated solutions. For example, the exact solution for the perihelion shift of Mercury within general relativity is worked out in detail using elliptic functions. The virial equation of state for molecules' interaction with Lennard-Jones-like potentials is discussed, including both classical and quantum corrections to the second virial coefficient. Interestingly, closed solutions become available using sophisticated computing methods within Mathematica. In my opinion, the textbook should not show formulas in detail which cover three or more pages—these technical data should just be contained on the CD. Instead, the textbook should focus on more detailed explanation of the physical concepts behind the technicalities. The discussion of the virial equation would benefit much from replacing 15 pages of Mathematica output with 15 pages of further explanation and motivation. In this combination, the power of computing merged with physical intuition
NASA Astrophysics Data System (ADS)
Pang, Sumei; Zhao, Yanying; Xin, Liu; Xue, Jiadan; Zheng, Xuming
2017-01-01
The vibration spectra of 5-(methylthio)-1,3,4-thiadiazole-2(3H)-thione (MTTN) in acetonitrile (CH3CN), methanol (CH3OH) and water (H2O) solvents were collected and evaluated via deuterium isotopic substitution Raman spectroscopic experiments. These experiments were combined with the quantum chemical theoretical calculations using the PCM solvent model and normal mode analysis. The results confirmed that the MTTN in CH3CN, CH3OH and H2O have hydrogen bonding (H-bonding) MTTN(solvent)n clusters that produce significantly different Raman intensity patterns in different solvents. Combined with the normal Raman assignment, most resonance Raman spectra were assigned to the vibration modes of the H-bonding MTTN(CH3CN), MTTN(CH3OH)3 and MTTN(H2O)3 clusters in CH3CN, CH3OH and H2O. The theoretically-predicted frequencies and intensities in different surrounding environments enabled reliable assignments of Raman bands. The intermolecular > NH ⋯ O and > NH ⋯ N H-bonding interactions are key constituents of stable thione structures in MTTN. This underlines the significant structural differences of MTTN in CH3CN, CH3OH and H2O. H-bonding perturbation of MTTN reveal important insights about the intermolecular excited state proton transfer (ESPT) reaction mechanisms in the Franck-Condon region structural dynamics of the thione → thiol tautomer in CH3OH and H2O.
NASA Astrophysics Data System (ADS)
Koparir, Pelin; Sarac, Kamiran; Orek, Cahit; Koparir, Metin
2016-11-01
This study acquaints the 8-t-buthyl-4-methyl-2H-chromen 2-one (II) of by quantum chemical calculations and spectral ways. The molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) 1H and 13C NMR chemical shift values of II in the ground state have been calculated utilizing the density functional method (B3LYP) with the 6-31G(d) basis set. The theoretical vibrational frequencies and chemical shift values display well agreement with experimental values. On the other hand, DFT calculations of molecular electrostatic potentials and frontier molecular orbitals of II were implemented at the B3LYP/6-31G(d) level of theory.
The Calculation of Theoretical Chromospheric Models and the Interpretation of the Solar Spectrum
NASA Technical Reports Server (NTRS)
Avrett, Eugene H.
1998-01-01
Since the early 1970s we have been developing the extensive computer programs needed to construct models of the solar atmosphere and to calculate detailed spectra for use in the interpretation of solar observations. This research involves two major related efforts: work by Avrett and Loeser on the Pandora computer program for non-LTE modeling of the solar atmosphere including a wide range of physical processes, and work by Rurucz on the detailed synthesis of the solar spectrum based on opacity data or over 58 million atomic and molecular lines. our goals are: to determine models of the various features observed on the Sun (sunspots, different components of quiet and active regions, and flares) by means of physically realistic models, and to calculate detailed spectra at all wavelengths that match observations of those features. These two goals are interrelated: discrepancies between calculated and observed spectra are used to determine improvements in the structure of the models, and in the detailed physical processes used in both the model calculations and the spectrum calculations. The atmospheric models obtained in this way provide not only the depth variation of various atmospheric parameters, but also a description of the internal physical processes that are responsible for non-radiative heating, and for solar activity in general.
The calculation of theoretical chromospheric models and the interpretation of the solar spectrum
NASA Technical Reports Server (NTRS)
Avrett, Eugene H.
1994-01-01
Since the early 1970s we have been developing the extensive computer programs needed to construct models of the solar atmosphere and to calculate detailed spectra for use in the interpretation of solar observations. This research involves two major related efforts: work by Avrett and Loeser on the Pandora computer program for non-LTE modeling of the solar atmosphere including a wide range of physical processes, and work by Kurucz on the detailed synthesis of the solar spectrum based on opacity data for over 58 million atomic and molecular lines. Our goals are to determine models of the various features observed on the sun (sunspots, different components of quiet and active regions, and flares) by means of physically realistic models, and to calculate detailed spectra at all wavelengths that match observations of those features. These two goals are interrelated: discrepancies between calculated and observed spectra are used to determine improvements in the structure of the models, and in the detailed physical processes used in both the model calculations and the spectrum calculations. The atmospheric models obtained in this way provide not only the depth variation of various atmospheric parameters, but also a description of the internal physical processes that are responsible for nonradiative heating, and for solar activity in general.
Automated Routines for Calculating Whole-Stream Metabolism: Theoretical Background and User's Guide
Bales, Jerad D.; Nardi, Mark R.
2007-01-01
In order to standardize methods and facilitate rapid calculation and archival of stream-metabolism variables, the Stream Metabolism Program was developed to calculate gross primary production, net ecosystem production, respiration, and selected other variables from continuous measurements of dissolved-oxygen concentration, water temperature, and other user-supplied information. Methods for calculating metabolism from continuous measurements of dissolved-oxygen concentration and water temperature are fairly well known, but a standard set of procedures and computation software for all aspects of the calculations were not available previously. The Stream Metabolism Program addresses this deficiency with a stand-alone executable computer program written in Visual Basic.NET?, which runs in the Microsoft Windows? environment. All equations and assumptions used in the development of the software are documented in this report. Detailed guidance on application of the software is presented, along with a summary of the data required to use the software. Data from either a single station or paired (upstream, downstream) stations can be used with the software to calculate metabolism variables.
NASA Astrophysics Data System (ADS)
Saritas, Kayahan; Grossman, Jeffrey C.
2015-03-01
Molecules that undergo pericyclic isomerization reactions find interesting optical and energy storage applications, because of their usually high quantum yields, large spectral shifts and small structural changes upon light absorption. These reactions induce a drastic change in the conjugated structure such that substituents that become a part of the conjugated system upon isomerization can play an important role in determining properties such as enthalpy of isomerization and HOMO-LUMO gap. Therefore, theoretical investigations dealing with such systems should be capable of accurately capturing the interplay between electron correlation and exchange effects. In this work, we examine the dihydroazulene isomerization as an example conjugated system. We employ the highly accurate quantum Monte Carlo (QMC) method to predict thermochemical properties and to benchmark results from density functional theory (DFT) methods. Although DFT provides sufficient accuracy for similar systems, in this particular system, DFT predictions of ground state and reaction paths are inconsistent and non-systematic errors arise. We present a comparison between QMC and DFT results for enthalpy of isomerization, HOMO-LUMO gap and charge densities with a range of DFT functionals.
Theoretical calculation of the p-emitter length for snapback-free reverse-conducting IGBT
NASA Astrophysics Data System (ADS)
Liheng, Zhu; Xingbi, Chen
2014-06-01
A physically based equation for predicting required p-emitter length of a snapback-free reverse-conducting insulated gate bipolar transistor (RC-IGBT) with field-stop structure is proposed. The n-buffer resistances above the p-emitter region with anode geometries of linear strip, circular and annular type are calculated, and based on this, the minimum p-emitter lengths of those three geometries are given and verified by simulation. It is found that good agreement was achieved between the numerical calculation and simulation results. Moreover, the calculation results show that the annular case needs the shortest p-emitter length for RC-IGBT to be snapback-free.
Hybrid theory and calculation of e-N2 scattering. [quantum mechanics - nuclei (nuclear physics)
NASA Technical Reports Server (NTRS)
Chandra, N.; Temkin, A.
1975-01-01
A theory of electron-molecule scattering was developed which was a synthesis of close coupling and adiabatic-nuclei theories. The theory is shown to be a close coupling theory with respect to vibrational degrees of freedom but is a adiabatic-nuclei theory with respect to rotation. It can be applied to any number of partial waves required, and the remaining ones can be calculated purely in one or the other approximation. A theoretical criterion based on fixed-nuclei calculations and not on experiment can be given as to which partial waves and energy domains require the various approximations. The theory allows all cross sections (i.e., pure rotational, vibrational, simultaneous vibration-rotation, differential and total) to be calculated. Explicit formulae for all the cross sections are presented.
Theoretical Calculation for the Ionization of Molecules by Short Strong Laser Pulses
Nagy, L.; Borbely, S.
2011-10-03
We have developed several calculation methods for the ionization of atoms and molecules by strong and ultrashort laser pulses, based on the numerical solution of the time dependent Schroedinger equation (TDSE) in the momentum space. We have performed calculations within the strong field approximation (Volkov) and using iterative and direct methods for solving the TDSE. The investigated molecules are H{sub 2}{sup +} and H{sub 2}O. In case of the ionization of diatomic molecules the interference effects in the ejected electron spectra due to the coherent addition of the waves associated to the electrons ejected from the vicinity of different nuclei were also analysed.
Quantum Monte Carlo calculation of the binding energy of the beryllium dimer
Deible, Michael J.; Kessler, Melody; Gasperich, Kevin E.; Jordan, Kenneth D.
2015-08-28
The accurate calculation of the binding energy of the beryllium dimer is a challenging theoretical problem. In this study, the binding energy of Be{sub 2} 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 Be{sub 2} 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 Be{sub 2}, obtained by using configuration interaction trial functions and extrapolating in the threshold for the configurations retained in the trial function, is 908 cm{sup −1}, only slightly below the 935 cm{sup −1} value derived from experiment.
Theoretical investigation of intersubband hole transitions in Si/SiGe/Si quantum wells
NASA Astrophysics Data System (ADS)
Boujdaria, K.; Ridene, S.; Radhia, S. Ben; Zitouni, O.; Bouchriha, H.; Fishman, G.
2002-09-01
We study the effects of the pc-pc coupling in intersubband hole optical transitions in SiGe/Si quantum wells for x and z polarizations. We have used a k[middle dot]p model taking into account both the p-like first conduction band and the s-like second conduction band. First, we have found a unitary transformation that block diagonalizes the 14 x14 Hamiltonian (or 12 x12 Hamiltonian) into two 7 x7 (or 6 x6) blocks that are real symmetric in the finite difference formulation. We find that pc-pc interaction plays a minimal role in intersubband optical transition for x and z polarizations. Moreover, our calculations clearly confirm that the pc-pv coupling favors intersubband transitions for an optical polarization parallel to the layer plane (x polarization). In addition, for z polarization, both s-pv and pc-pv interactions play an equal footing role in intervalence band transitions.
Theoretical calculation of electron-positron momentum density in YBa 2Cu 3O 7-δ
NASA Astrophysics Data System (ADS)
Massidda, S.
1990-07-01
We present calculations of the electron-positron momentum density for the high- Tc superconductor YBa 2Cu 3O 7-δ for δ=0 and for the insulating parent compound YBa 2Cu 3O 6, based on first-principle electronic structure calculations performed within the local density approximation (LDA) using the full potential linearized augmented plane wave (FLAPW) method. Our results indicate a small overlap of the positron wave function with the CuO 2 plane electrons and, as a consequence, relatively small signals due to the related Fermi surfaces. By contrast, the present calculations show, after the folding of Umklapp terms according to Lock, Crisp and West, clear Fermi surface breaks arising from the Cu-O chain bands. No general agreement with existing experiments allows a clear definition of Fermi surface structures in the latter. A comparison of the calculated momentum with the experimental two-dimensional angular correlation of annihilation radiation (2D-ACAR) recently measured in Geneva shows an overall agreement for the insulating compound, despite the spurious LDA metallic state, and possibly suggests the importance of O vacancies in experiments performed on non-stoichiometric YBa 2Cu 3O 7-δ samples.
Theoretical calculation of low-lying states of NaAr and NaXe
NASA Technical Reports Server (NTRS)
Laskowski, B. C.; Langhoff, S. R.; Stallcop, J. R.
1981-01-01
Potential curves as well as dipole moments and linking transition moments are calculated for the ground X 2 Sigma + and low lying excited A 2 Pi, B 2 Sigma +, C 2 Sigma +, (4) 2 Sigma +, (2) 2 Pi and (1) 2 Delta states of NaAr and NaXe. Calculations are performed using a self-consistent field plus configuration-interaction procedure with the core electrons replaced by an ab initio effective core potential. The potential curves obtained are found to be considerably less repulsive than the semiempirical curves of Pascale and Vandeplanque (1974) and to agree well with existing experimental data, although the binding energies of those states having potential minima due to van der Waals interactions are underestimated. Emission bands are also calculated for the X 2 Sigma + - C 2 Sigma + excimer transitions of NaAr and NaXe using the calculated transition moments and potential curves, and shown to agree well with experiment on the short-wavelength side of the maximum.
Calculation of theoretical lubrication regimes in two-piece first metatarsophalangeal prostheses.
Joyce, T J
2008-01-01
The key joint of the forefoot during gait is the first metatarsophalangeal joint. It plays an important role in propelling the human form but can be subject to a number of diseases which can lead to its replacement with an artificial joint. Some of these designs of prosthesis employ a two-piece ball and socket arrangement and are available with a range of biomaterial couples including ceramic-on-ceramic, metal-on-metal and metal-on-polymer. Calculation of predicted lubrication regimes applicable to these implant designs was undertaken. Modelling the ball and socket implant as an equivalent ball-on-plane model and employing elastohydrodynamic theory allowed the minimum film thickness to be calculated and in turn the lambda ratio to indicate the lubrication regime. The calculations were undertaken for a 50 to 1500 N range of loading values, a 0 to 30 mm/s range of entraining velocities, and a 3 to 15 mm radius range of sizes. Calculations showed that the ceramic-on-ceramic and metal-on-metal implants could operate under fluid film lubrication, whereas the metal-on-polymer combination operated in the boundary lubrication regime. It was also recognized that manufacturing capabilities are critical to the radial clearances and values of surface roughness that can be achieved, and thus the predicted lubrication regime.
Menapace, E.; Birattari, C.; Bonardi, M.L.; Groppi, F.; Morzenti, S.; Zona, C.
2005-05-24
The radionuclide production for biomedical applications has been brought up in the years, as a special nuclear application, at INFN LASA Laboratory, particularly in co-operation with the JRC-Ispra of EC. Mainly scientific aspects concerning radiation detection and the relevant instruments, the measurements of excitation functions of the involved nuclear reactions, the requested radiochemistry studies and further applications have been investigated. On the side of the nuclear data evaluations, based on nuclear model calculations and critically selected experimental data, the appropriate competence has been developed at ENEA Division for Advanced Physics Technologies. A series of high specific activity accelerator-produced radionuclides in no-carrier-added (NCA) form, for uses in metabolic radiotherapy and for PET radiodiagnostics, are investigated. In this work, last revised measurements and model calculations are reviewed for excitation functions of natZn(d,X)64Cu, 66Ga reactions, referring to irradiation experiments at K=38 variable energy Cyclotron of JRC-Ispra. Concerning the reaction data for producing 186gRe and 211At/211gPo (including significant emission spectra) and 210At, most recent and critically selected experimental results are considered and discussed in comparison with model calculations paying special care to pre-equilibrium effects estimate and to the appropriate overall parameterization. Model calculations are presented for 226Ra(p,2n)225Ac reaction, according to the working program of the ongoing IAEA CRP on the matter.
Technology Transfer Automated Retrieval System (TEKTRAN)
Several flux-calculation (FC) schemes are available for determining soil-to-atmosphere emissions of nitrous oxide (N2O) and other trace gases using data from non-steady-state flux chambers. Recently developed methods claim to provide more accuracy in estimating the true pre-deployment flux (f0) comp...
About some of the theoretical approaches used in double-beta decay calculations
Civitarese, O.
2007-10-12
The calculations of nuclear matrix elements, corresponding to nuclear double beta decay transitions, rely upon several approximations. The impact of these approximations upon final estimations of the nuclear matrix elements is illustrated. We pay attention to mean field (symmetry violations) and to approximate diagonalizations (pn-QRPA, renormalized pn-QRPA and fully renormalized pn-QRPA)
About some of the theoretical approaches used in double-beta decay calculations
NASA Astrophysics Data System (ADS)
Civitarese, O.
2007-10-01
The calculations of nuclear matrix elements, corresponding to nuclear double beta decay transitions, rely upon several approximations. The impact of these approximations upon final estimations of the nuclear matrix elements is illustrated. We pay attention to mean field (symmetry violations) and to approximate diagonalizations (pn-QRPA, renormalized pn-QRPA and fully renormalized pn-QRPA).
Jia, Xiangyu; Wang, Meiting; Shao, Yihan; König, Gerhard; Brooks, Bernard R; Zhang, John Z H; Mei, Ye
2016-02-09
In this work, the solvation free energies of 20 organic molecules from the 4th Statistical Assessment of the Modeling of Proteins and Ligands (SAMPL4) have been calculated. The sampling of phase space is carried out at a molecular mechanical level, and the associated free energy changes are estimated using the Bennett Acceptance Ratio (BAR). Then the quantum mechanical (QM) corrections are computed through the indirect Non-Boltzmann Bennett's acceptance ratio (NBB) or the thermodynamics perturbation (TP) method. We show that BAR+TP gives a minimum analytic variance for the calculated solvation free energy at the Gaussian limit and performs slightly better than NBB in practice. Furthermore, the expense of the QM calculations in TP is only half of that in NBB. We also show that defining the biasing potential as the difference of the solute-solvent interaction energy, instead of the total energy, can converge the calculated solvation free energies much faster but possibly to different values. Based on the experimental solvation free energies which have been published before, it is discovered in this study that BLYP yields better results than MP2 and some other later functionals such as B3LYP, M06-2X, and ωB97X-D.
Bulut, N; Castillo, J F; Bañares, L; Aoiz, F J
2009-12-31
The dynamics and kinetics of the Li + H2(+) reaction have been studied by means of quantum mechanical (QM) real wave packet, wave packet with flux operator, and quasiclassical trajectory (QCT) calculations on the ab initio potential energy surface of Martinazzo et al. [J. Chem. Phys., 2003, 119, 21]. Total initial state-selected reaction probabilities for the title reaction have been calculated for total angular momentum J = 0 at collision energies from threshold up to 1 eV. Wave packet reaction probabilities at selected values of the total angular momentum up to J = 60 are obtained using the centrifugal sudden approximation (CSA). Integral cross sections and rate constants have been calculated from the wave packet reactions probabilities by means of a refined J-shifting method and the separable rotation approximation in combination with the CSA for J > 0. The calculated rate constants as function of temperature show an Arrhenius type behavior. The QM results are found to be in overall good agreement with the corresponding QCT data.
Ushakov, D V; Manak, I S; Kononenko, V K
2010-05-26
The energy levels, wave functions, and matrix elements of optical dipole transitions are calculated numerically for superlattice quantum-cascade structures. The effect of spectral broadening on the shape of emission spectra is estimated and semiphenomenological asymmetric profiles of emission line broadening are proposed. It is shown that the electroluminescence spectra well agree with the calculated spontaneous recombination spectra. (lasers)
A Comparison of Two Topos-Theoretic Approaches to Quantum Theory
NASA Astrophysics Data System (ADS)
Wolters, Sander A. M.
2013-01-01
The aim of this paper is to compare the two topos-theoretic approaches to quantum mechanics that may be found in the literature to date. The first approach, which we will call the contravariant approach, was originally proposed by Isham and Butterfield, and was later extended by Döring and Isham. The second approach, which we will call the covariant approach, was developed by Heunen, Landsman and Spitters. Motivated by coarse-graining and the Kochen-Specker theorem, the contravariant approach uses the topos of presheaves on a specific context category, defined as the poset of commutative von Neumann subalgebras of some given von Neumann algebra. In particular, the approach uses the spectral presheaf. The intuitionistic logic of this approach is given by the (complete) Heyting algebra of closed open subobjects of the spectral presheaf. We show that this Heyting algebra is, in a natural way, a locale in the ambient topos, and compare this locale with the internal Gelfand spectrum of the covariant approach. In the covariant approach, a non-commutative C*-algebra (in the topos Set) defines a commutative C*-algebra internal to the topos of covariant functors from the context category to the category of sets. We give an explicit description of the internal Gelfand spectrum of this commutative C*-algebra, from which it follows that the external spectrum is spatial. Using the daseinisation of self-adjoint operators from the contravariant approach, we give a new definition of the daseinisation arrow in the covariant approach and compare it with the original version. States and state-proposition pairing in both approaches are compared. We also investigate the physical interpretation of the covariant approach.
Hahn, Seungsoo; Lee, Hochan; Cho, Minhaeng
2004-07-22
Infrared absorption, vibrational circular dichroism, and two-dimensional infrared pump-probe and photon echo spectra of acetylproline solutions are theoretically calculated and directly compared with experiments. In order to quantitatively determine interpeptide interaction-induced amide I mode frequency shifts, high-level quantum chemistry calculations were performed. The solvatochromic amide I mode frequency shift and fluctuation were taken into account by carrying out molecular dynamics simulations of acetylproline dissolved in liquids water and chloroform and by using the extrapolation method developed recently. We first studied correlation time scales of the two amide I vibrational frequency fluctuations, cross correlation between the two fluctuating local mode frequencies, ensemble averaged conformations of the acetylproline molecule in liquids water and chloroform. The corresponding conformations of the acetylproline in liquids water and chloroform are close to the ideal 3(10) helix and the C(7) structure, respectively. A few methods proposed to determine the angle between the two transition dipoles associated with the amide I vibrations were tested and their limitations are discussed.
Theoretical Calculations of Refractive Properties for Hg3Te2Cl2 Crystals
NASA Astrophysics Data System (ADS)
Bokotey, O. V.
2016-05-01
This paper reviews the optical properties, such as refractive index, optical dielectric constant, and reflection coefficient of the Hg3Te2Cl2 crystals. The applications of the Hg3X2Y2 crystals as electronic, optical, and optoelectronic devices are very much determined by the nature and magnitude of these fundamental material properties. The origin of chemical bonding in the crystals is very important for definition of the physical and chemical properties. The main structural feature of the Hg3X2Y2 crystals is the presence of covalent pyramids [XHg3] and linear X-Hg-X groups. Optical properties are calculated according to the model proposed by Harrison. The refractive index in the spectral region far from the absorption edge is determined within the generalized single-oscillator model. The calculated results are found to be in good agreement with experimental data.
A theoretical model for calculation of molecular stopping power. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Xu, Y. J.
1984-01-01
A modified local plasma model is established. The Gordon-Kim's molecular charged density model is employed to obtain a formula to evaluate the stopping power of many useful molecular systems. The stopping power of H2 and He gas was calculated for incident proton energy ranging from 100 keV to 2.5 MeV. The stopping power of O2, N2, and water vapor was also calculated for incident proton energy ranging from 40 keV. to 2.5 MeV. Good agreement with experimental data was obtained. A discussion of molecular effects leading to department from Bragg's rule is presented. The equipartition rule and the effect of nuclear momentum recoiling in stopping power are also discussed.
Huang, Jianhua
2012-07-01
There are three methods for calculating thermal insulation of clothing measured with a thermal manikin, i.e. the global method, the serial method, and the parallel method. Under the condition of homogeneous clothing insulation, these three methods yield the same insulation values. If the local heat flux is uniform over the manikin body, the global and serial methods provide the same insulation value. In most cases, the serial method gives a higher insulation value than the global method. There is a possibility that the insulation value from the serial method is lower than the value from the global method. The serial method always gives higher insulation value than the parallel method. The insulation value from the parallel method is higher or lower than the value from the global method, depending on the relationship between the heat loss distribution and the surface temperatures. Under the circumstance of uniform surface temperature distribution over the manikin body, the global and parallel methods give the same insulation value. If the constant surface temperature mode is used in the manikin test, the parallel method can be used to calculate the thermal insulation of clothing. If the constant heat flux mode is used in the manikin test, the serial method can be used to calculate the thermal insulation of clothing. The global method should be used for calculating thermal insulation of clothing for all manikin control modes, especially for thermal comfort regulation mode. The global method should be chosen by clothing manufacturers for labelling their products. The serial and parallel methods provide more information with respect to the different parts of clothing.
Theoretical Calculation of Prompt Neutron Spectra from Fission of Curium Isotopes
NASA Astrophysics Data System (ADS)
Ohsawa, Takaaki; Tani, Kazuhiro; Kishimoto, Yasufumi
2003-06-01
Prompt neutron spectra for Cm-isotopes (242Cm, 243Cm, 244Cm, 245Cm, 246Cm, 248Cm) were calculated on the basis of a modified version of the Madland-Nix model combined with a multimodal fission model. The predicted spectra were found to be in fair agreement with recent data. A slight enhancement of the low-energy component of the spectrum was interpreted in terms of neutron emission during fragment acceleration.
NASA Astrophysics Data System (ADS)
Chavda, Bhavin R.; Gandhi, Sahaj A.; Dubey, Rahul P.; Patel, Urmila H.; Barot, Vijay M.
2016-05-01
The novel chalcone derivatives have widespread applications in material science and medicinal industries. The density functional theory (DFT) is used to optimized the molecular structure of the three chalcone derivatives (M-I, II, III). The observed discrepancies between the theoretical and experimental (X-ray data) results attributed to different environments of the molecules, the experimental values are of the molecule in solid state there by subjected to the intermolecular forces, like non-bonded hydrogen bond interactions, where as isolated state in gas phase for theoretical studies. The lattice energy of all the molecules have been calculated using PIXELC module in Coulomb -London -Pauli (CLP) package and is partitioned into corresponding coulombic, polarization, dispersion and repulsion contributions. Lattice energy data confirm and strengthen the finding of the X-ray results that the weak but significant intermolecular interactions like C-H…O, Π- Π and C-H… Π plays an important role in the stabilization of crystal packing.
NASA Astrophysics Data System (ADS)
Jin, Na; Yang, Yanqing; Luo, Xian; Li, Jian; Huang, Bin; Liu, Shuai; Xiao, Zhiyuan
2014-09-01
The β-SiC(1 1 1)/α-W(1 1 0) interfaces were studied by first-principles calculations based on density functional theory (DFT). The ideal work of adhesion (Wad) and interface energy (γint) were calculated for six different interfacial structures, taking into account both Si- and C-terminations of β-SiC(1 1 1) surfaces, and three different stacking sequences. The interfacial electronic structures including charge density distribution and difference, and density of states (DOS) were simulated to determine the nature of SiC/W bonding. The results show that the Si-terminated top-site interface is the most stable interface, yielding the highest Wad and the lowest γint. During the optimization, the Si-terminated top-site interface will transform into the center-site structure, resulting in the interaction among the interfacial W and Si atoms, and subinterfacial C atoms. In addition, the calculated interface energies show that an interdiffusion layer will form on the SiC/W interface. The experimental results also have verified the existence of an interdiffusion layer on the SiC/W interface in a CVD-SiC fiber.
NASA Astrophysics Data System (ADS)
Jacak, Monika; Jacak, Janusz; Jóźwiak, Piotr; Jóźwiak, Ireneusz
2016-06-01
The overview of the current status of quantum cryptography is given in regard to quantum key distribution (QKD) protocols, implemented both on nonentangled and entangled flying qubits. Two commercial R&D platforms of QKD systems are described (the Clavis II platform by idQuantique implemented on nonentangled photons and the EPR S405 Quelle platform by AIT based on entangled photons) and tested for feasibility of their usage in commercial TELECOM fiber metropolitan networks. The comparison of systems efficiency, stability and resistivity against noise and hacker attacks is given with some suggestion toward system improvement, along with assessment of two models of QKD.
Tscherbul, T V; Dalgarno, A
2010-11-14
An efficient method is presented for rigorous quantum calculations of atom-molecule and molecule-molecule collisions in a magnetic field. The method is based on the expansion of the wave function of the collision complex in basis functions with well-defined total angular momentum in the body-fixed coordinate frame. We outline the general theory of the method for collisions of diatomic molecules in the (2)Σ and (3)Σ electronic states with structureless atoms and with unlike (2)Σ and (3)Σ molecules. The cross sections for elastic scattering and Zeeman relaxation in low-temperature collisions of CaH((2)Σ(+)) and NH((3)Σ(-)) molecules with (3)He atoms converge quickly with respect to the number of total angular momentum states included in the basis set, leading to a dramatic (>10-fold) enhancement in computational efficiency compared to the previously used methods [A. Volpi and J. L. Bohn, Phys. Rev. A 65, 052712 (2002); R. V. Krems and A. Dalgarno, J. Chem. Phys. 120, 2296 (2004)]. Our approach is thus well suited for theoretical studies of strongly anisotropic molecular collisions in the presence of external electromagnetic fields.
Wood, R. M.; Saha, D.; McCarthy, L. A.; ...
2014-10-29
A combined experimental-theoretical study of optically pumped NMR (OPNMR) has been performed in a GaAs/Al0.1Ga0.9As quantum well film with thermally induced biaxial strain. The photon energy dependence of the Ga-71 OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from differential absorption to spin-up and spin-down states of the conduction band using a modified Pidgeon Brown model. Reasonable agreement between theory and experiment is obtained, facilitating assignment of features in the OPNMR energy dependence to specific interband transitions. Despite the approximationsmore » made in the quantum-mechanical model and the inexact correspondence between the experimental and calculated observables, the results provide insight into how effects of strain and quantum confinement are manifested in OPNMR signals« less
Wood, R. M.; Saha, D.; McCarthy, L. A.; Tokarski, III, J. T.; Sanders, G. D.; Kuhns, P. L.; McGill, S. A.; Reyes, A. P.; Reno, J. L.; Stanton, C. J.; Bowers, C. R.
2014-10-29
A combined experimental-theoretical study of optically pumped NMR (OPNMR) has been performed in a GaAs/Al_{0.1}Ga_{0.9}As quantum well film with thermally induced biaxial strain. The photon energy dependence of the Ga-71 OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from differential absorption to spin-up and spin-down states of the conduction band using a modified Pidgeon Brown model. Reasonable agreement between theory and experiment is obtained, facilitating assignment of features in the OPNMR energy dependence to specific interband transitions. Despite the approximations made in the quantum-mechanical model and the inexact correspondence between the experimental and calculated observables, the results provide insight into how effects of strain and quantum confinement are manifested in OPNMR signals
Accuracy of Theoretical Calculations for Electron-Impact Ionization of atoms and Molecules
NASA Astrophysics Data System (ADS)
Madison, Don
2015-09-01
In the last two decades, there have been several close-coupling approaches developed which can accurately calculate the triply differential cross sections for electron impact ionization of effective one and two electron atoms. The agreement between experiment and theory is not particularly good for more complicated atoms and molecules. Very recently, a B-spline R-matrix with pseudostates (BSRPS) approach was used to investigate low energy electron impact ionization of neon and very good agreement with experiment was found. The perturbative 3-body distorted wave (3DW) approach which includes the exact final state electron-electron interaction (post collision interaction - PCI) gave comparably good agreement with experiment. For ionization of molecules, there have been numerous studies of high-energy electron impact. These studies are called EMS (Electron Momentum Spectroscopy) and they were very valuable in determining the accuracy of molecular wavefunctions since the measured cross sections were proportional to the momentum space molecular wavefunction. More recently, lower energy collisions have started to be measured and these cross sections are much more difficult for theory since the detailed kinematics of the experiment become important. So far, the only close coupling calculation reported for ionization of molecules is the time-dependent close-coupling calculation (TDCC) which has been developed for ionization of H2 and it yields relative good agreement with experiment. Again the molecular 3-body distorted wave (M3DW) gave equally good agreement with experiment. For polyatomic molecules, the only theory available is the M3DW. In this talk, I will show the current status of agreement between experiment and theory for low and intermediate energy single ionization of atoms and molecules. Work supported by the NSF and XSEDE.
Munson, D.E.; Holcomb, D.J.; DeVries, K.L.; Brodsky, N.S.
1994-12-31
Cross-hole ultrasonic measurements were made in the immediate wall of the Air Intake Shaft of the Waste Isolation Pilot Plant facility. These measurements show that compressional wave speed markedly decreases at the shaft wall and then increases with radial distance from the shaft to eventually become that of solid or undamaged salt. This behavior is indicative of deformation damage or microfractures in the salt. These in situ data are compared to both laboratory measurements of wave speed as a function of volume dilatancy and to calculations based on the Multimechanism Deformation Coupled Fracture model, with reasonable agreement.
Hoff, R.W.; Gardner, D.G.; Gardner, M.A.
1985-05-01
A technique for modeling level structures of odd-odd nuclei has been used to construct sets of discrete states with energies in the range 0 to 1.5 MeV for several nuclei in the rare-earth and actinide regions. The accuracy of the modeling technique was determined by comparison with experimental data. Examination was made of what effect the use of these new, more complete sets of discrete states has on the calculation of level densities, total reaction cross sections, and isomer ratios. 9 refs.
NASA Astrophysics Data System (ADS)
Arroudj, S.; Bouchouit, M.; Bouchouit, K.; Bouraiou, A.; Messaadia, L.; Kulyk, B.; Figa, V.; Bouacida, S.; Sofiani, Z.; Taboukhat, S.
2016-06-01
This paper explores the synthesis, structure characterization and optical properties of two new schiff bases. These compounds were obtained by condensation of o-tolidine with salicylaldehyde and cinnamaldehyde. The obtained ligands were characterized by UV, 1H and NMR. Their third-order NLO properties were measured using the third harmonic generation technique on thin films at 1064 nm. The electric dipole moment (μ), the polarizability (α) and the first hyperpolarizability (β) were calculated using the density functional B3LYP method with the lanl2dz basis set. For the results, the title compound shows nonzero β value revealing second order NLO behaviour.
NASA Astrophysics Data System (ADS)
Kostko, Oleg; Troy, Tyler P.; Bandyopadhyay, Biswajit; Ahmed, Musahid
2015-03-01
Acetaldehyde, a probable human carcinogen and of environmental importance, upon solvation provides a test bed for understanding proton transfer pathways and catalytic mechanisms. In this study, we report on single photon vacuum ultraviolet photoionization of small acetaldehyde and acetaldehyde-water clusters. Appearance energies of protonated clusters are extracted from the experimental photoionization efficiency curves and compared to electronic structure calculations. The comparison of experimental data to computational results provides mechanistic insight into the fragmentation mechanisms of the observed mass spectra. Using deuterated water for isotopic tagging, we observe that proton transfer is mediated via acetaldehyde and not water in protonated acetaldehyde-water clusters.
NASA Technical Reports Server (NTRS)
Avrett, E. H.
1985-01-01
Solar chromospheric models are described. The models included are based on the observed spectrum, and on the assumption of hydrostatic equilibrium. The calculations depend on realistic solutions of the radiative transfer and statistical equilibrium equations for optically thick lines and continua, and on including the effects of large numbers of lines throughout the spectrum. Although spectroheliograms show that the structure of the chromosphere is highly complex, one-dimensional models of particular features are reasonably successful in matching observed spectra. Such models were applied to the interpretation of chromospheric observations.
Romanov, Alexey N; Gularyan, Samvel K; Polyak, Boris M; Sakovich, Ruslan A; Dobretsov, Gennady E; Sarkisov, Oleg M
2011-05-28
Quantum-chemical calculations of ground and excited states for membrane fluorescent probe 4-dimethylaminochalcone (DMAC) in vacuum were performed. Optimized geometries and dipole moments for lowest-lying singlet and triplet states were obtained. The nature of these electronic transitions and the relaxation path in the excited states were determined; changes in geometry and charge distribution were assessed. It was shown that in vacuum the lowest existed level is of (n, π*) nature, and the closest to it is the level of (π, π*) nature; the energy gap between them is narrow. This led to an effective (1)(π, π*) →(1)(n, π*) relaxation. After photoexcitation the molecule undergoes significant transformations, including changes in bond orders, pyramidalization angle of the dimethylamino group, and planarity of the molecule. Its dipole moment rises from 5.5 Debye in the ground state to 17.1 Debye in the (1)(π, π*) state, and then falls to 2 Debye in the (1)(n, π*) state. The excited (1)(n, π*) state is a short living state; it has a high probability of intersystem crossing into the (3)(π, π*) triplet state. This relaxation path explains the low quantum yield of DMAC fluorescence in non-polar media. It is possible that (3)(π, π*) is responsible for observed DMAC phosphorescence.
Quantum mechanical calculations related to ionization and charge transfer in DNA
NASA Astrophysics Data System (ADS)
Cauët, E.; Valiev, M.; Weare, J. H.; Liévin, J.
2012-07-01
Ionization and charge migration in DNA play crucial roles in mechanisms of DNA damage caused by ionizing radiation, oxidizing agents and photo-irradiation. Therefore, an evaluation of the ionization properties of the DNA bases is central to the full interpretation and understanding of the elementary reactive processes that occur at the molecular level during the initial exposure and afterwards. Ab initio quantum mechanical (QM) methods have been successful in providing highly accurate evaluations of key parameters, such as ionization energies (IE) of DNA bases. Hence, in this study, we performed high-level QM calculations to characterize the molecular energy levels and potential energy surfaces, which shed light on ionization and charge migration between DNA bases. In particular, we examined the IEs of guanine, the most easily oxidized base, isolated and embedded in base clusters, and investigated the mechanism of charge migration over two and three stacked guanines. The IE of guanine in the human telomere sequence has also been evaluated. We report a simple molecular orbital analysis to explain how modifications in the base sequence are expected to change the efficiency of the sequence as a hole trap. Finally, the application of a hybrid approach combining quantum mechanics with molecular mechanics brings an interesting discussion as to how the native aqueous DNA environment affects the IE threshold of nucleobases.
NASA Astrophysics Data System (ADS)
Greenman, Loren; Whitley, Heather D.; Whaley, K. Birgitta
2013-10-01
We present density functional theory calculations of phosphorus dopants in bulk silicon and of several properties relating to their use as spin qubits for quantum computation. Rather than a mixed pseudopotential or a Heitler-London approach, we have used an explicit treatment for the phosphorus donor and examined the detailed electronic structure of the system as a function of the isotropic doping fraction, including lattice relaxation due to the presence of the impurity. Doping electron densities (ρdoped-ρbulk) and spin densities (ρ↑-ρ↓) are examined in order to study the properties of the dopant electron as a function of the isotropic doping fraction. Doping potentials (Vdoped-Vbulk) are also calculated for use in calculations of the scattering cross sections of the phosphorus dopants, which are important in the understanding of electrically detected magnetic resonance experiments. We find that the electron density around the dopant leads to nonspherical features in the doping potentials, such as trigonal lobes in the (001) plane at energy scales of +12 eV near the nucleus and of -700 meV extending away from the dopants. These features are generally neglected in effective mass theory and will affect the coupling between the donor electron and the phosphorus nucleus. Our density functional calculations reveal detail in the densities and potentials of the dopants which are not evident in calculations that do not include explicit treatment of the phosphorus donor atom and relaxation of the crystal lattice. These details can also be used to parametrize tight-binding models for simulation of large-scale devices.
Quantum close coupling calculation of transport and relaxation properties for Hg-H2 system
NASA Astrophysics Data System (ADS)
Nemati-Kande, Ebrahim; Maghari, Ali
2016-11-01
Quantum mechanical close coupling calculation of the state-to-state transport and relaxation cross sections have been done for Hg-H2 molecular system using a high-level ab initio potential energy surface. Rotationally averaged cross sections were also calculated to obtain the energy dependent Senftleben-Beenakker cross sections at the energy range of 0.005-25,000 cm-1. Boltzmann averaging of the energy dependent Senftleben-Beenakker cross sections showed the temperature dependency over a wide temperature range of 50-2500 K. Interaction viscosity and diffusion coefficients were also calculated using close coupling cross sections and full classical Mason-Monchick approximation. The results were compared with each other and with the available experimental data. It was found that Mason-Monchick approximation for viscosity is more reliable than diffusion coefficient. Furthermore, from the comparison of the experimental diffusion coefficients with the result of the close coupling and Mason-Monchick approximation, it was found that the Hg-H2 potential energy surface used in this work can reliably predict diffusion coefficient data.
Thorwirth, Sven; Mück, Leonie Anna; Gauss, Jürgen; Tamassia, Filippo; Lattanzi, Valerio; McCarthy, Michael C
2011-06-02
Silicon oxysulfide, OSiS, and seven of its minor isotopic species have been characterized for the first time in the gas phase at high spectral resolution by means of Fourier transform microwave spectroscopy. The equilibrium structure of OSiS has been determined from the experimental data using calculated vibration-rotation interaction constants. The structural parameters (rO-Si = 1.5064 Å and rSi-S = 1.9133 Å) are in very good agreement with values from high-level quantum chemical calculations using coupled-cluster techniques together with sophisticated additivity and extrapolation schemes. The bond distances in OSiS are very short in comparison with those in SiO and SiS. This unexpected finding is explained by the partial charges calculated for OSiS via a natural population analysis. The results suggest that electrostatic effects rather than multiple bonding are the key factors in determining bonding in this triatomic molecule. The data presented provide the spectroscopic information needed for radio astronomical searches for OSiS.
NASA Astrophysics Data System (ADS)
Gonta, Svetlana; Utinans, Maris; Kirilov, Georgii; Belyakov, Sergey; Ivanova, Irena; Fleisher, Mendel; Savenkov, Valerij; Kirilova, Elena
2013-01-01
Several new substituted amidine derivatives of benzanthrone were synthesized by a condensation reaction from 3-aminobenzo[de]anthracen-7-one and appropriate aromatic and aliphatic amides. The obtained derivatives have a bright yellow or orange fluorescence in organic solvents and in solid state. The novel benzanthrone derivatives were characterized by TLC analysis, 1H NMR, IR, MS, UV/vis, and fluorescence spectroscopy. The solvent effect on photophysical behaviors of these dyes was investigated, and the results showed that the Stoke's shift increased, whereas quantum yield decreased with the growth of the solvent polarity. The structure of some dyes was confirmed by the X-ray single crystal structure analysis. AM1, ZINDO/S and ab initio calculations using Gaussian software were carried out to estimate the electron system of structures. The calculations show planar configurations for the aromatic core of these compounds and two possible orientations of amidine substituents. The calculation results correlate well with red-shifted absorption and emission spectra of compounds.
Optimized Non-Orthogonal Localized Orbitals for Linear Scaling Quantum Monte Carlo calculations
NASA Astrophysics Data System (ADS)
Williamson, Andrew; Reboredo, Fernando; Galli, Giulia
2004-03-01
It has been shown [1] that Quantum Monte Carlo calculations of total energies of interacting systems can be made to scale nearly linearly with the number of electrons (N), by using localized single particle orbitals to construct Slater determinants. Here we propose a new way of defining the localized orbitals required for O(N)-QMC calculation, by minimizing an appropriate cost function yielding a set of N non-orthogonal (NO) localized orbitals considerably smoother in real space than Maximally localized Wannier functions (MLWF). These NO orbitals have better localization properties than MLWFs. We show that for semiconducting systems NO orbitals can be localized in a much smaller region of space than orthogonal orbitals (typically, one eighth of the volume) and give total energies with the same accuracy, thus yielding a linear scaling QMC algorithm which is 5 times faster than the one originally proposed [1]. We also discuss the extension of O(N)-QMC with NO orbitals to the calculations of total energies of metallic systems. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [1] A. J. Williamson, R.Q. Hood and J.C. Grossman, Phys. Rev. Lett. 87, 246406 (2001)
First principles calculation of thermo-mechanical properties of thoria using Quantum ESPRESSO
NASA Astrophysics Data System (ADS)
Malakkal, Linu; Szpunar, Barbara; Zuniga, Juan Carlos; Siripurapu, Ravi Kiran; Szpunar, Jerzy A.
2016-05-01
In this work, we have used Quantum ESPRESSO (QE), an open source first principles code, based on density-functional theory, plane waves, and pseudopotentials, along with quasi-harmonic approximation (QHA) to calculate the thermo-mechanical properties of thorium dioxide (ThO2). Using Python programming language, our group developed qe-nipy-advanced, an interface to QE, which can evaluate the structural and thermo-mechanical properties of materials. We predicted the phonon contribution to thermal conductivity (kL) using the Slack model. We performed the calculations within local density approximation (LDA) and generalized gradient approximation (GGA) with the recently proposed version for solids (PBEsol). We employed a Monkhorst-Pack 5 × 5 × 5 k-points mesh in reciprocal space with a plane wave cut-off energy of 150 Ry to obtain the convergence of the structure. We calculated the dynamical matrices of the lattice on a 4 × 4 × 4 mesh. We have predicted the heat capacity, thermal expansion and the phonon contribution to thermal conductivity, as a function of temperature up to 1400K, and compared them with the previous work and known experimental results.
Rafiee, Marjan; Javaheri, Masoumeh
2015-01-01
Tyrosinase is a multifunctional copper-containing enzyme. It can catalyze two distinct reactions of melanin synthesis and benzaldehyde derivatives, which are potential tyrosinase inhibitors. To find the relationships between charge distributions of benzaldehyde and their pharmaceutical behavior, the present study aimed at investigating nuclear quadrupole coupling constants of quadrupolare nuclei in the functional benzaldehyde group and calculating some its derivatives. In addition, the differences between the electronic structures of various derivatives of this depigmenting drug were examined. All ab initio calculations were carried out using Gaussian 03. The results predicted benzaldehyde derivatives to be bicentral inhibitors; nevertheless, the oxygen or hydrogen contents of the aldehyde group were not found to be the only active sites. Furthermore with the presence of the aldehyde group, the terminal methoxy group in C4 was found to contribute to tyrosinase inhibitory activities. In addition, an oxygen atom with high charge density in the side chain was found to play an important role in its inhibitory effect. PMID:27844007
NASA Astrophysics Data System (ADS)
Barabash, Sergey V.; Pramanik, Dipankar
2015-03-01
Development of low-leakage dielectrics for semiconductor industry, together with many other areas of academic and industrial research, increasingly rely upon ab initio tunneling and transport calculations. Complex band structure (CBS) is a powerful formalism to establish the nature of tunneling modes, providing both a deeper understanding and a guided optimization of materials, with practical applications ranging from screening candidate dielectrics for lowest ``ultimate leakage'' to identifying charge-neutrality levels and Fermi level pinning. We demonstrate that CBS is prone to a particular type of spurious ``phantom'' solution, previously deemed true but irrelevant because of a very fast decay. We demonstrate that (i) in complex materials, phantom modes may exhibit very slow decay (appearing as leading tunneling terms implying qualitative and huge quantitative errors), (ii) the phantom modes are spurious, (iii) unlike the pseudopotential ``ghost'' states, phantoms are an apparently unavoidable artifact of large numerical basis sets, (iv) a presumed increase in computational accuracy increases the number of phantoms, effectively corrupting the CBS results despite the higher accuracy achieved in resolving the true CBS modes and the real band structure, and (v) the phantom modes cannot be easily separated from the true CBS modes. We discuss implications for direct transport calculations. The strategy for dealing with the phantom states is discussed in the context of optimizing high-quality high- κ dielectric materials for decreased tunneling leakage.
Teki, Yoshio; Matsumoto, Takafumi
2011-04-07
The mechanism of the unique dynamic electron polarization of the quartet (S = 3/2) high-spin state via a doublet-quartet quantum-mixed state and detail theoretical calculations of the population transfer are reported. By the photo-induced electron transfer, the quantum-mixed charge-separate state is generated in acceptor-donor-radical triad (A-D-R). This mechanism explains well the unique dynamic electron polarization of the quartet state of A-D-R. The generation of the selectively populated quantum-mixed state and its transfer to the strongly coupled pure quartet and doublet states have been treated both by a perturbation approach and by exact numerical calculations. The analytical solutions show that generation of the quantum-mixed states with the selective populations after de-coherence and/or accompanying the (complete) dephasing during the charge-recombination are essential for the unique dynamic electron polarization. Thus, the elimination of the quantum coherence (loss of the quantum information) is the key process for the population transfer from the quantum-mixed state to the quartet state. The generation of high-field polarization on the strongly coupled quartet state by the charge-recombination process can be explained by a polarization transfer from the quantum-mixed charge-separate state. Typical time-resolved ESR patterns of the quantum-mixed state and of the strongly coupled quartet state are simulated based on the generation mechanism of the dynamic electron polarization. The dependence of the spectral pattern of the quartet high-spin state has been clarified for the fine-structure tensor and the exchange interaction of the quantum-mixed state. The spectral pattern of the quartet state is not sensitive towards the fine-structure tensor of the quantum-mixed state, because this tensor contributes only as a perturbation in the population transfer to the spin-sublevels of the quartet state. Based on the stochastic Liouville equation, it is also
NASA Astrophysics Data System (ADS)
Vojta, Danijela; Dominković, Katarina; Miljanić, Snežana; Spanget-Larsen, Jens
2017-03-01
The molecular structures of myricetin (3,3‧,4‧,5,5‧,7-hexahydroxyflavone; MCE) and myricitrin (myricetin 3-O-rhamnoside; MCI) are investigated by quantum chemical calculations (B3LYP/6-311G**). Two preferred molecular rotamers of MCI are predicted, corresponding to different conformations of the O-rhamnoside subunit. The rotamers are characterized by different hydrogen bonded cross-links between the hydroxy groups of the rhamnoside substituent and the parent MCE moiety. The predicted OH stretching frequencies are compared with vibrational spectra of MCE and MCI recorded for the sake of this investigation (IR and Raman). In addition, a reassignment of the Cdbnd O stretching bands is suggested.
Dwyer, Donard S
2005-01-01
Background Electronic properties of amino acid side chains such as inductive and field effects have not been characterized in any detail. Quantum mechanics (QM) calculations and fundamental equations that account for substituent effects may provide insight into these important properties. PM3 analysis of electron distribution and polarizability was used to derive quantitative scales that describe steric factors, inductive effects, resonance effects, and field effects of amino acid side chains. Results These studies revealed that: (1) different semiempirical QM methods yield similar results for the electronic effects of side chain groups, (2) polarizability, which reflects molecular deformability, represents steric factors in electronic terms, and (3) inductive effects contribute to the propensity of an amino acid for α-helices. Conclusion The data provide initial characterization of the substituent effects of amino acid side chains and suggest that these properties affect electron density along the peptide backbone. PMID:16078995
Quantum three-body calculation of nonresonant triple-{alpha} reaction rate at low temperatures
Ogata, Kazuyuki; Kan, Masataka; Kamimura, Masayasu
2010-08-12
Triple-{alpha} reaction rate is re-evaluated by directly solving the three-body Schroedinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. An accurate description of the {alpha}-{alpha} nonresonant states significantly quenches the Coulomb barrier between the first two {alpha}-particles and the third {alpha}-particle. Consequently, the{alpha}-{alpha} nonresonant continuum states give a markedly larger contribution at low temperatures than that reported in previous studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find an increase in triple-{alpha} reaction rate by about 20 orders of magnitude around 10{sup 7} K compared with the rate of NACRE.
Quantum three-body calculation of nonresonant triple-alpha reaction rate at low temperatures
Ogata, Kazuyuki; Kan, Masataka; Kamimura, Masayasu
2010-06-01
Triple-alpha reaction rate is re-evaluated by directly solving the three-body Schroedinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. An accurate description of the alpha-alpha nonresonant states significantly quenches the Coulomb barrier between the first two alpha-particles and the third alpha-particle. Consequently, the alpha-alpha nonresonant continuum states give a markedly larger contribution at low temperatures than that reported in previous studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find an increase in triple-alpha reaction rate by 26 orders of magnitude around 10{sup 7} K compared with the rate of NACRE.
One-loop calculations in quantum field theory: from Feynman diagrams to unitarity cuts
Ellis, R. Keith; Kunszt, Zoltan; Melnikov, Kirill; Zanderighi, Giulia
2012-09-01
The success of the experimental program at the Tevatron re-inforced the idea that precision physics at hadron colliders is desirable and, indeed, possible. The Tevatron data strongly suggests that one-loop computations in QCD describe hard scattering well. Extrapolating this observation to the LHC, we conclude that knowledge of many short-distance processes at next-to-leading order may be required to describe the physics of hard scattering. While the field of one-loop computations is quite mature, parton multiplicities in hard LHC events are so high that traditional computational techniques become inefficient. Recently new approaches based on unitarity have been developed for calculating one-loop scattering amplitudes in quantum field theory. These methods are especially suitable for the description of multi-particle processes in QCD and are amenable to numerical implementations. We present a systematic pedagogical description of both conceptual and technical aspects of the new methods.
Lee, Chien-Wei; Hwu, Jenn-Gwo
2013-10-15
We derive a statistical physics model of two-dimensional electron gas (2DEG) and propose an accurate approximation method for calculating the quantum-mechanical effects of metal-oxide-semiconductor (MOS) structure in accumulation and strong inversion regions. We use an exponential surface potential approximation in solving the quantization energy levels and derive the function of density of states in 2D to 3D transition region by applying uncertainty principle and Schrödinger equation in k-space. The simulation results show that our approximation method and theory of density of states solve the two major problems of previous researches: the non-negligible error caused by the linear potential approximation and the inconsistency of density of states and carrier distribution in 2D to 3D transition region.
Optical Properties Of Ice And Snow In The Polar Oceans. II: Theoretical Calculations
NASA Astrophysics Data System (ADS)
Grenfell, Thomas C.; Perovich, Donald K.
1986-08-01
Radiative transfer models of sea ice applied to date range from a simple Bouguer-Lambert representation for net downwelling irradiance through 16 stream models which takes into account detailed variations in ice microstructure. Both sea ice and snow are strongly multiple scattering media with single scattering albedos well above 0.9 through the visible and into the near infrared. Parameter studies indicate that the optical properties of sea ice are controlled by the density of brine and vapor inclusions which in general undergo substantial seasonal changes. Melting and brine drainage are the principal causes of these variations. For ice below -5°C, temperature effects are relatively weak unless the Tice drops below the eutectic point. The optical properties of snow depend primarily on grain size, the bulk density, and the presence of impurities such as carbon soot. The theoretical models appear to be able to reproduce observations quite well and have revealed that soot or dust contamination of snow appears to be prevalent even in the Arctic.
Seravalli, L.; Trevisi, G.; Frigeri, P.
2013-11-14
In this work, we calculate the two-dimensional quantum energy system of the In(Ga)As wetting layer that arises in InAs/InGaAs/GaAs metamorphic quantum dot structures. Model calculations were carried on the basis of realistic material parameters taking in consideration their dependence on the strain relaxation of the metamorphic buffer; results of the calculations were validated against available literature data. Model results confirmed previous hypothesis on the extrinsic nature of the disappearance of wetting layer emission in metamorphic structures with high In composition. We also show how, by adjusting InGaAs metamorphic buffer parameters, it could be possible: (i) to spatially separate carriers confined in quantum dots from wetting layer carriers, (ii) to create an hybrid 0D-2D system, by tuning quantum dot and wetting layer levels. These results are interesting not only for the engineering of quantum dot structures but also for other applications of metamorphic structures, as the two design parameters of the metamorphic InGaAs buffer (thickness and composition) provide additional degrees of freedom to control properties of interest.
Mulliner, Denis; Wondrousch, Dominik; Schüürmann, Gerrit
2011-12-21
The electrophilic reactivity of Michael acceptors is an important determinant of their toxicity. For a set of 35 α,β-unsaturated aldehydes, ketones and esters with experimental rate constants of their reaction with glutathione (GSH), k(GSH), quantum chemical transition-state calculations of the corresponding Michael addition of the model nucleophile methane thiol (CH(3)SH) have been performed at the B3LYP/6-31G** level, focusing on the 1,2-olefin addition pathway without and with initial protonation. Inclusion of Boltzmann-weighting of conformational flexibility yields intrinsic reaction barriers ΔE(‡) that for the case of initial protonation correctly reflect the structural variation of k(GSH) across all three compound classes, except that they fail to account for a systematic (essentially incremental) decrease in reactivity upon α-substitution. By contrast, the reduction in k(GSH) through β-substitution is well captured by ΔE(‡). Empirical correction for the α-substitution effect yields a high squared correlation coefficient (r(2) = 0.96) for the quantum chemical prediction of log k(GSH), thus enabling an in silico screening of the toxicity-relevant electrophilicity of α,β-unsaturated carbonyls. The latter is demonstrated through application of the calculation scheme for a larger set of 46 Michael-acceptor aldehydes, ketones and esters with experimental values for their toxicity toward the ciliates Tetrahymena pyriformis in terms of 50% growth inhibition values after 48 h exposure (EC(50)). The developed approach may add in the predictive hazard evaluation of α,β-unsaturated carbonyls such as for the European REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) Directive, enabling in particular an early identification of toxicity-relevant Michael-acceptor reactivity.
Gao, Ting; Shi, Li-Li; Li, Hai-Bin; Zhao, Shan-Shan; Li, Hui; Sun, Shi-Ling; Su, Zhong-Min; Lu, Ying-Hua
2009-07-07
The combination of genetic algorithm and back-propagation neural network correction approaches (GABP) has successfully improved the calculation accuracy of absorption energies. In this paper, the absorption energies of 160 organic molecules are corrected to test this method. Firstly, the GABP1 is introduced to determine the quantitative relationship between the experimental results and calculations obtained by using quantum chemical methods. After GABP1 correction, the root-mean-square (RMS) deviations of the calculated absorption energies reduce from 0.32, 0.95 and 0.46 eV to 0.14, 0.19 and 0.18 eV for B3LYP/6-31G(d), B3LYP/STO-3G and ZINDO methods, respectively. The corrected results of B3LYP/6-31G(d)-GABP1 are in good agreement with experimental results. Then, the GABP2 is introduced to determine the quantitative relationship between the results of B3LYP/6-31G(d)-GABP1 method and calculations of the low accuracy methods (B3LYP/STO-3G and ZINDO). After GABP2 correction, the RMS deviations of the calculated absorption energies reduce to 0.20 and 0.19 eV for B3LYP/STO-3G and ZINDO methods, respectively. The results show that the RMS deviations after GABP1 and GABP2 correction are similar for B3LYP/STO-3G and ZINDO methods. Thus, the B3LYP/6-31G(d)-GABP1 is a better method to predict absorption energies and can be used as the approximation of experimental results where the experimental results are unknown or uncertain by experimental method. This method may be used for predicting absorption energies of larger organic molecules that are unavailable by experimental methods and by high-accuracy theoretical methods with larger basis sets. The performance of this method was demonstrated by application to the absorption energy of the aldehyde carbazole precursor.
Jin, R Y; Sun, X H; Liu, Y F; Long, W; Chen, B; Shen, S Q; Ma, H X
2016-01-05
Series of isoxazole derivatives were synthesized by substituted chalcones and 2-chloro-6-fluorobenzene formaldehyde oxime with 1,3-dipolar cycloaddition. The target compounds were determined by melting point, IR, (1)H NMR, elemental analyses and HRMS. The crystal structure of compound 3a was detected by X-ray diffraction and it crystallizes in the triclinic space group p2(1)/c with z=4. The molecular geometry of compound 3a was optimized using density functional theory (DFT/B3LYP) method with the 6-31G+(d,p) basis set in the ground state. From the optimized geometry of the molecule, FT-IR, FT-Raman, HOMO-LUMO and natural bond orbital (NBO) were calculated at B3LYP/6-31G+(d,p) level. Finally, the antifungal activity of the synthetic compounds were evaluated against Pythium solani, Gibberella nicotiancola, Fusarium oxysporium f.sp. niveum and Gibberella saubinetii.
NASA Technical Reports Server (NTRS)
Binienda, W. K.; Arnold, S. M.; Tan, H. Q.
1992-01-01
An essential part of describing the damage state and predicting the damage growth in a multicracked plate is the accurate calculation of stress intensity factors (SIF's). Here, a methodology and rigorous solution formulation for SIF's of a multicracked plate, with fully interacting cracks, subjected to a far-field arbitrary stress state is presented. The fundamental perturbation problem is derived, and the steps needed to formulate the system of singular integral equations whose solution gives rise to the evaluation of the SIF's are identified. This analytical derivation and numerical solution are obtained by using intelligent application of symbolic computations and automatic FORTRAN generation capabilities (described in the second part of this paper). As a result, a symbolic/FORTRAN package, named SYMFRAC, that is capable of providing accurate SIF's at each crack tip was developed and validated.
NASA Astrophysics Data System (ADS)
Jin, R. Y.; Sun, X. H.; Liu, Y. F.; Long, W.; Chen, B.; Shen, S. Q.; Ma, H. X.
2016-01-01
Series of isoxazole derivatives were synthesized by substituted chalcones and 2-chloro-6-fluorobenzene formaldehyde oxime with 1,3-dipolar cycloaddition. The target compounds were determined by melting point, IR, 1H NMR, elemental analyses and HRMS. The crystal structure of compound 3a was detected by X-ray diffraction and it crystallizes in the triclinic space group p2(1)/c with z = 4. The molecular geometry of compound 3a was optimized using density functional theory (DFT/B3LYP) method with the 6-31G+(d,p) basis set in the ground state. From the optimized geometry of the molecule, FT-IR, FT-Raman, HOMO-LUMO and natural bond orbital (NBO) were calculated at B3LYP/6-31G+(d,p) level. Finally, the antifungal activity of the synthetic compounds were evaluated against Pythium solani, Gibberella nicotiancola, Fusarium oxysporium f.sp. niveum and Gibberella saubinetii.
NASA Astrophysics Data System (ADS)
Sarikaya, Ebru Karakaş; Dereli, Ömer
2017-02-01
To obtain liquid phase molecular structure, conformational analysis of Orotic acid was performed and six conformers were determined. For these conformations, eight possible radicals were modelled by using Density Functional Theory computations with respect to molecular structure. Electron Paramagnetic Resonance parameters of these model radicals were calculated and then they were compared with the experimental ones. Geometry optimizations of the molecule and modeled radicals were performed using Becke's three-parameter hybrid-exchange functional combined with the Lee-Yang-Parr correlation functional of Density Functional Theory and 6-311++G(d,p) basis sets in p-dioxane solution. Because Orotic acid can be mutagenic in mammalian somatic cells and it is also mutagenic for bacteria and yeast, it has been studied.
Buryak, Ilya; Frommhold, Lothar; Vigasin, Andrey A.
2014-04-21
We compare calculations of the translational collision-induced spectra and their integrated intensities of both He–Ar and Ne–Ar collisional complexes, using the quantum mechanical and a semiclassical formalism. Advanced potential energy and induced dipole functions are used for the calculations. The quantum method used is as described previously [L. Frommhold, Collision-induced Absorption in Gases (Cambridge University Press, 1993 and 2006)]. The semiclassical method is based on repeated classical atom-atom scattering calculations to simulate an ensemble average; subsequent Fourier transform then renders the binary absorption coefficient as a function of frequency. The problem of classical calculations is the violation of the principle of detailed balance, which may be introduced only artificially in classical calculations. Nevertheless, it is shown that the use of classical trajectories permits a fairly accurate reproduction of the experimental spectra, comparable to the quantum mechanical results at not too low temperatures and for collisional pairs of not too small reduced mass. Inexpensive classical calculations may thus be promising to compute spectra also of molecular pairs, or even of polyatomic collisional pairs with anisotropic intermolecular interactions, for which the quantum approach is still inefficient or impractical.
Quantum-Mechanical Calculation of Ionization-Potential Lowering in Dense Plasmas
NASA Astrophysics Data System (ADS)
Son, Sang-Kil; Thiele, Robert; Jurek, Zoltan; Ziaja, Beata; Santra, Robin
2014-07-01
The charged environment within a dense plasma leads to the phenomenon of ionization-potential depression (IPD) for ions embedded in the plasma. Accurate predictions of the IPD effect are of crucial importance for modeling atomic processes occurring within dense plasmas. Several theoretical models have been developed to describe the IPD effect, with frequently discrepant predictions. Only recently, first experiments on IPD in Al plasma have been performed with an x-ray free-electron laser, where their results were found to be in disagreement with the widely used IPD model by Stewart and Pyatt. Another experiment on Al, at the Orion laser, showed disagreement with the model by Ecker and Kröll. This controversy shows a strong need for a rigorous and consistent theoretical approach to calculate the IPD effect. Here, we propose such an approach: a two-step Hartree-Fock-Slater model. With this parameter-free model, we can accurately and efficiently describe the experimental Al data and validate the accuracy of standard IPD models. Our model can be a useful tool for calculating atomic properties within dense plasmas with wide-ranging applications to studies on warm dense matter, shock experiments, planetary science, inertial confinement fusion, and nonequilibrium plasmas created with x-ray free-electron lasers.
Mezei, Pál D; Csonka, Gábor I; Ruzsinszky, Adrienn; Sun, Jianwei
2015-01-13
A correct description of the anion-π interaction is essential for the design of selective anion receptors and channels and important for advances in the field of supramolecular chemistry. However, it is challenging to do accurate, precise, and efficient calculations of this interaction, which are lacking in the literature. In this article, by testing sets of 20 binary anion-π complexes of fluoride, chloride, bromide, nitrate, or carbonate ions with hexafluorobenzene, 1,3,5-trifluorobenzene, 2,4,6-trifluoro-1,3,5-triazine, or 1,3,5-triazine and 30 ternary π-anion-π' sandwich complexes composed from the same monomers, we suggest domain-based local-pair natural orbital coupled cluster energies extrapolated to the complete basis-set limit as reference values. We give a detailed explanation of the origin of anion-π interactions, using the permanent quadrupole moments, static dipole polarizabilities, and electrostatic potential maps. We use symmetry-adapted perturbation theory (SAPT) to calculate the components of the anion-π interaction energies. We examine the performance of the direct random phase approximation (dRPA), the second-order screened exchange (SOSEX), local-pair natural-orbital (LPNO) coupled electron pair approximation (CEPA), and several dispersion-corrected density functionals (including generalized gradient approximation (GGA), meta-GGA, and double hybrid density functional). The LPNO-CEPA/1 results show the best agreement with the reference results. The dRPA method is only slightly less accurate and precise than the LPNO-CEPA/1, but it is considerably more efficient (6-17 times faster) for the binary complexes studied in this paper. For 30 ternary π-anion-π' sandwich complexes, we give dRPA interaction energies as reference values. The double hybrid functionals are much more efficient but less accurate and precise than dRPA. The dispersion-corrected double hybrid PWPB95-D3(BJ) and B2PLYP-D3(BJ) functionals perform better than the GGA and meta
Quantum Calculations on Salt Bridges with Water: Potentials, Structure, and Properties
Liao, Sing; Green, Michael E.
2011-01-01
Salt bridges are electrostatic links between acidic and basic amino acids in a protein; quantum calculations are used here to determine the energetics and other properties of one form of these species, in the presence of water molecules. The acidic groups are carboxylic acids (aspartic and glutamic acids); proteins have two bases with pK above physiological pH: one, arginine, with a guanidinium basic group, the other lysine, which is a primary amine. Only arginine is modeled here, by ethyl guanidinium, while propionic acid is used as a model for either carboxylic acid. The salt bridges are accompanied by 0-12 water molecules; for each of the 13 systems, the energy-bond distance relation, natural bond orbitals (NBO), frequency calculations allowing thermodynamic corrections to room temperature, and dielectric constant dependence, were all calculated. The water molecules were found to arrange themselves in hydrogen bonded rings anchored to the oxygens of the salt bridge components. This was not surprising in itself, but it was found that the rings lead to a periodicity in the energy, and to a 'water addition' rule. The latter shows that the initial rings, with four oxygen atoms, become five member rings when an additional water molecule becomes available, with the additional water filling in at the bond with the lowest Wiberg index, as calculated using NBO. The dielectric constant dependence is the expected hyperbola, and the fit of the energy to the inverse dielectric constant is determined. There is an energy periodicity related to ring formation upon addition of water molecules. When 10 water molecules have been added, all spaces near the salt bridge are filled, completing the first hydration shell, and a second shell starts to form. The potentials associated with salt bridges depend on their hydration, and potentials assigned without regard to local hydration are likely to cause errors as large as or larger than kBT, thus suggesting a serious problem if these
NASA Astrophysics Data System (ADS)
Sethi, Arun; Singh, Ranvijay Pratap; Prakash, Rohit; Amandeep
2017-02-01
In the present research paper corticosteroids prodrugs of hydrocortisone acetate (1) have been synthesized, which was isolated from the flowers of Allamanda Violacea. The hydrocortisone acetate (1) was hydrolyzed to hydrocortisone (2) which was subsequently converted to prednisolone (3). Both the hydrocortisone (1) and prednisolone (2) underwent Steglich esterification with naproxen and Ibuprofen yielding compounds 11, 17 dihydroxy-21-(2-(6-methoxynaphthalene-2yl) propionoxy)-pregn-4-ene-3, 20-dione (4), 11, 17-dihydroxy-21-(2-(4-isobutylphenyl) propionoxy)-pregn-4-ene-3, 20-dione (5), 21-(2-(6-methoxynaphthalene-2-yl) propionoxy) 11,17-di-hydroxy-3,20-diketo-pregn-1,4-diene (6) and 11,17-di-hydroxy-3,20-diketo-pregn-1,4-diene-21-yl-2-(4-isobutylphenyl) propanoate (7). The synthesized compounds have been characterized with the help of spectroscopic techniques like 1H, 13C NMR, FT-IR spectroscopy and mass spectrometry. Density functional theory (DFT) with B3LYP functional and 6-31G (d, p) basis set has been used for the Quantum chemical calculations. The electronic properties such as frontier orbitals and band gap energies were calculated by TD-DFT approach. Intramolecular interactions have been identified by AIM (Atoms in Molecule) approach and vibrational wavenumbers have been calculated using DFT method. The reactivity and reactive site within the synthesized prodrugs have been examined with the help of reactivity descriptors. Dipole moment, polarizability and first static hyperpolarizability have been calculated to get a better insight of the properties of synthesized prodrugs. The molecular electrostatic potential (MEP) surface analysis has also been carried out.
NASA Astrophysics Data System (ADS)
Prytz, Ø.; Løvvik, O. M.; Taftø, J.
2006-12-01
We explore the possibility of combining density functional theory (DFT) and electron energy loss spectroscopy (EELS) to determine the dielectric function of materials. As model systems we use the skutterudites CoP3 , CoAs3 , and CoSb3 which are prototypes for thermoelectric materials. We achieve qualitative agreement between the theoretically and experimentally obtained low energy-loss spectra and dielectric function. Some of the remaining discrepancies may be caused by the challenge of refining the experimental spectra before Kramers-Kronig analysis. However, contrary to what is the case for some crystals with less complicated electronic structure, the DFT calculated plasmon energies deviate significantly from the experimental values. The great accuracy with which the plasmon energy can be determined by EELS, suggests that this technique may provide valuable inputs in further efforts to improve DFT calculations. The use of EELS as the experimental technique may become particularly powerful in studies of small volumes of materials.
NASA Astrophysics Data System (ADS)
San, Xiaojiao; Wang, Liancheng; Ma, Yanming; Liu, Zhiming; Cui, Tian; Liu, Bingbing; Zou, Guangtian
2008-04-01
The structural stability and optical properties of solid iodine under pressure have been studied using the ab initio pseudopotential plane-wave method. The dependence of lattice parameters on pressure indicates that the first structural phase transition from phase I to phase V occurs at about 20 GPa. From the pressure dependence of our elastic constants for solid iodine in phase I, it is found that the first structural transformation from molecular phase I to the intermediate phase V occurs at about 20 GPa due to the softening of the elastic constant C44, which is very close to the transition pressure of 20 GPa obtained by geometry optimizations and 23.2 GPa obtained by experimental measurements. The optimized structure for phase V is a face-centered orthorhombic (fco) phase with equal interatomic distances d1 = d2 = d3, but this fco structure is mechanically unstable, with shear elastic stiffness coefficient C44<0. To understand the modulated phase V, we use a periodic crystal structure to mimic the incommensurate phase V and obtain some quantitative information. In our calculation, the modulated phase is thermodynamically and mechanically stable. It is believed that phase V is not a monatomic phase but an intermediate state between a molecular and a monatomic state.
Hashem, Joseph; Schneider, Erich; Pryor, Mitch; ...
2017-01-01
Our paper describes how to use MCNP to evaluate the rate of material damage in a robot incurred by exposure to a neutron flux. The example used in this work is that of a robotic manipulator installed in a high intensity, fast, and collimated neutron radiography beam port at the University of Texas at Austin's TRIGA Mark II research reactor. Our effort includes taking robotic technologies and using them to automate non-destructive imaging tasks in nuclear facilities where the robotic manipulator acts as the motion control system for neutron imaging tasks. Simulated radiation tests are used to analyze the radiationmore » damage to the robot. Once the neutron damage is calculated using MCNP, several possible shielding materials are analyzed to determine the most effective way of minimizing the neutron damage. Furthermore, neutron damage predictions provide users the means to simulate geometrical and material changes, thus saving time, money, and energy in determining the optimal setup for a robotic system installed in a radiation environment.« less
Hashem, Joseph; Schneider, Erich; Pryor, Mitch; Landsberger, Sheldon
2017-01-01
Our paper describes how to use MCNP to evaluate the rate of material damage in a robot incurred by exposure to a neutron flux. The example used in this work is that of a robotic manipulator installed in a high intensity, fast, and collimated neutron radiography beam port at the University of Texas at Austin's TRIGA Mark II research reactor. Our effort includes taking robotic technologies and using them to automate non-destructive imaging tasks in nuclear facilities where the robotic manipulator acts as the motion control system for neutron imaging tasks. Simulated radiation tests are used to analyze the radiation damage to the robot. Once the neutron damage is calculated using MCNP, several possible shielding materials are analyzed to determine the most effective way of minimizing the neutron damage. Furthermore, neutron damage predictions provide users the means to simulate geometrical and material changes, thus saving time, money, and energy in determining the optimal setup for a robotic system installed in a radiation environment.
Dalal, Namita; Buckner, Ira S; Wildfong, Peter L D
2017-02-22
Cefuroxime axetil (CFA), an ester prodrug of cefuroxime exists as a pair of diastereoemers, namely isomer A and isomer B. To enable phase diagram construction, crystallization of the diastereomers of CFA from the commercially available amorphous drug substance was carried out. Isomer A was separated with a purity approaching 100% whereas the maximum purity of isomer B was 85% as confirmed by solution state proton NMR spectroscopy. The crystalline forms of isomer A and isomer B were confirmed as forms AI and BI, respectively, based on differential scanning calorimetry (DSC) analysis and powder X-ray diffraction. DSC analysis was used to observe the melting behavior of different diastereomer mixture compositions. The binary solid-liquid phase diagram for mixture compositions ranging from 0 to 85% w/w isomer B indicated the formation of a eutectic mixture having a melting temperature of 124.7 ± 0.4°C and a composition of 75% w/w (+/-5% wt.) isomer B. The eutectic composition was calculated using an index based on the van't Hoff equation for melting point depression and was found to be 75% isomer B and 25% isomer A. As CFA is present in commercial preparations as a mixture of diastereomers, the formation of a eutectic mixture between the diastereomers may impact the solubility and stability of the commercial product. Eutectic formation can be explained on the basis of the chemical similarity of diastereomers that favor miscibility in the liquid state.
Theoretical investigation of lead vapor adsorption on kaolinite surfaces with DFT calculations.
Wang, Xinye; Huang, Yaji; Pan, Zhigang; Wang, Yongxing; Liu, Changqi
2015-09-15
Kaolinite can be used as the in-furnace sorbent/additive to adsorb lead (Pb) vapor at high temperature. In this paper, the adsorptions of Pb atom, PbO molecule and PbCl2 molecule on kaolinie surfaces were investigated by density functional theory (DFT) calculation. Si surface is inert to Pb vapor adsorption while Al surfaces with dehydroxylation are active for the unsaturated Al atoms and the O atoms losing H atoms. The adsorption energy of PbO is much higher than that of Pb atom and PbCl2. Considering the energy barriers, it is easy for PbO and PbCl2 to adsorb on Al surfaces but difficult to escape. The high energy barriers of de-HCl process cause the difficulties of PbCl2 to form PbO·Al2O3·2SiO2 with kaolinite. Considering the inertia of Si atoms and the activity of Al atoms after dehydroxylation, calcination, acid/alkali treatment and some other treatment aiming at amorphous silica producing and Al activity enhancement can be used as the modification measures to improve the performance of kaolinite as the in-furnace metal capture sorbent.
Kudrawiec, R. Kopaczek, J.; Polak, M. P.; Scharoch, P.; Gladysiewicz, M.; Misiewicz, J.; Richards, R. D.; Bastiman, F.; David, J. P. R.
2014-12-21
Band gap alignment in GaAs{sub 1−x}Bi{sub x}/GaAs quantum wells (QWs) was studied experimentally by photoreflectance (PR) and theoretically, ab initio, within the density functional theory in which the supercell based calculations are combined with the alchemical mixing approximation applied to a single atom in a supercell. In PR spectra, the optical transitions related to the excited states in the QW (i.e., the transition between the second heavy-hole and the second electron subband) were clearly observed in addition to the ground state QW transition and the GaAs barrier transition. This observation is clear experimental evidence that this is a type I QW with a deep quantum confinement in the conduction and valence bands. From the comparison of PR data with calculations of optical transitions in GaAs{sub 1−x}Bi{sub x}/GaAs QW performed for various band gap alignments, the best agreement between experimental data and theoretical calculations has been found for the valence band offset of 52 ± 5%. A very similar valence band offset was obtained from ab initio calculations. These calculations show that the incorporation of Bi atoms into GaAs host modifies both the conduction and the valence band. For GaAs{sub 1−x}Bi{sub x} with 0 < x < 0.074, the conduction band shifts lineary at a rate of ∼33 meV per % Bi, which only slightly decreases with Bi concentration. Whereas the valance band shift is clearly non-linear. Reducing initially at a rate of ∼51 meV per % Bi for low concentrations of Bi and then at a significantly reduced rate of ∼20 meV per % Bi near the end of the studied composition range. The overall reduction rate of the band gap is parabolic and the reduction rates change from ∼84 to ∼53 meV per % Bi for lower and higher Bi concentrations, respectively. The calculated shifts of valence and conduction bands give the variation of valence (conduction) band offset between GaAs{sub 1−x}Bi{sub x} and GaAs in the range of ∼60
Novotny, O.; Hahn, M.; Lestinsky, M.; Savin, D. W.; Badnell, N. R.; Bernhardt, D.; Mueller, A.; Schippers, S.; Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A.
2012-07-01
We have measured electron-ion recombination for Fe XII forming Fe XI using a merged-beam configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The measured merged-beam recombination rate coefficient (MBRRC) for collision energies from 0 to 1500 eV is presented. This work uses a new method for determining the absolute MBRRC based on a comparison of the ion beam decay rate with and without the electron beam on. For energies below 75 eV, the spectrum is dominated by dielectronic recombination (DR) resonances associated with 3s {yields} 3p and 3p {yields} 3d core excitations. At higher energies, we observe contributions from 3 {yields} N' and 2 {yields} N' core excitation DR. We compare our experimental results to state-of-the-art multi-configuration Breit-Pauli (MCBP) calculations and find significant differences, both in resonance energies and strengths. We have extracted the DR contributions from the measured MBRRC data and transformed them into a plasma recombination rate coefficient (PRRC) for temperatures in the range of 10{sup 3}-10{sup 7} K. We show that the previously recommended DR data for Fe XII significantly underestimate the PRRC at temperatures relevant for both photoionized plasmas (PPs) and collisionally ionized plasmas (CPs). This is contrasted with our MCBP PRRC results, which agree with the experiment to within 30% at PP temperatures and even better at CP temperatures. We find this agreement despite the disagreement shown by the detailed comparison between our MCBP and experimental MBRRC results. Last, we present a simple parameterized form of the experimentally derived PRRC for easy use in astrophysical modeling codes.
Ortiz-Sanchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel; Lluch, José M
2006-04-13
The proton-transfer dynamics in the aromatic Schiff base salicylidene methylamine has been theoretically analyzed in the ground and first singlet (pi,pi) excited electronic states by density functional theory calculations and quantum wave-packet dynamics. The potential energies obtained through electronic calculations that use the time-dependent density functional theory formalism, which predict a barrierless excited-state intramolecular proton transfer, are fitted to a reduced three-dimensional potential energy surface. The time evolution in this surface is solved by means of the multiconfiguration time-dependent Hartree algorithm applied to solve the time-dependent Schrödinger equation. It is shown that the excited-state proton transfer occurs within 11 fs for hydrogen and 25 fs for deuterium, so that a large kinetic isotope effect is predicted. These results are compared to those of the only previous theoretical work published on this system [Zgierski, M. Z.; Grabowska, A. J. Chem. Phys. 2000, 113, 7845], reporting a configuration interaction singles barrier of 1.6 kcal mol(-1) and time reactions of 30 and 115 fs for the hydrogen and deuterium transfers, respectively, evaluated with the semiclassical instanton approach.
Calculations of the time taken for excitons to form in GaAs quantum wells
NASA Astrophysics Data System (ADS)
Zhang, M. H.; Huang, Q.; Zhou, J. M.
1997-11-01
The time taken for excitons to form has been calculated by solving the Boltzmann equation for an 80 Å GaAs quantum well. Our results show that longitudinal acoustic phonon emission is the most important relaxation mechanism for exciton formation from free-electron - hole pairs at low lattice temperatures. The time taken for excitons to form is found to depend on the excitation conditions: the excitation density, the electron - hole plasma temperature and the lattice temperature, and is approximately proportional to 0953-8984/9/46/016/img1 (where 0953-8984/9/46/016/img2 is the electron - hole plasma temperature and 0953-8984/9/46/016/img3 is the exciton binding energy) at a fixed lattice temperature. For the excitation conditions used by Kumar et al (Kumar R, Vengurlekar A S, Prabhu S S, Shah J and Pfeiffer L N 1996 Phys. Rev. B 54 4891), the calculated time is 108 ps, which is of the same order of magnitude as the experimentally deduced one of 50 ps. We find that the approximation in which the wave-vector component 0953-8984/9/46/016/img4 of the LA phonon is taken as zero can lead to underestimation of the rate of exciton formation. A longer time of 150 ps for the exciton formation can be obtained using this approximation.
NASA Astrophysics Data System (ADS)
Moosavi-Tekyeh, Zainab; Taherian, Fatemeh; Tayyari, Sayyed Faramarz
2016-05-01
The structural parameters, and vibrational frequencies of 5-nitrosalicylaldehyde (5NSA) were studied by the FT-IR and Raman spectra and the quantum chemical calculations carried out at the B3LYP/6-311++G(d,p) level of theory in order to investigate the intramolecular hydrogen bonding (IHB) present in its structure. The strength and nature of IHB in the optimized structure of 5NSA were studied in detail by means of the atoms in molecules (AIM) and the natural bond orbital (NBO) approaches. The results obtained were then compared with the corresponding data for its parent molecule, salicylaldehyde (SA). Comparisons made between the geometrical structures for 5NSA and SA, their OH/OD stretching and out-of-plane bending modes, their enthalpies for the hydrogen bond, and their AIM parameters demonstrated a stronger H-bonding in 5NSA compared with that in SA. The calculated binding enthalpy (ΔHbind) for 5NSA was -10.92 kcal mol-1. The observed νOH and γOH appeared at about 3120 cm-1 and 786 cm-1 respectively. The stretching frequency shift of H-bond formation was 426 cm-1 which is consistent with ΔHbind and the strength of H-bond in 5NSA. The delocalization energies and electron delocalization indices derived by the NBO and AIM approaches indicate that the resonance effects were responsible for the stronger IHB in 5NSA than in SA.
NASA Astrophysics Data System (ADS)
Holderna-Natkaniec, K.; Szyczewski, A.; Natkaniec, I.; Khavryutchenko, V. D.; Pawlukojc, A.
Inelastic incoherent neutron scattering (IINS) and neutron diffraction spectra of progesterone and testosterone were measured simultaneously on the NERA spectrometer at the IBR-2 pulsed reactor in Dubna. Both studied samples do not indicate any phase transition in the temperature range from 20 to 290K. The IINS spectra have been transformed to the phonon density of states (PDS) in the one-phonon scattering approximation. The PDS spectra display well-resolved peaks of low-frequency internal vibration modes up to 600cm-1. The assignment of these modes was proposed taking into account the results of calculations of the structure and dynamics of isolated molecules of the investigated substances. The quantum chemistry calculations were performed by the semi-empirical PM3 method and at the restricted Hartree-Fock level with the 6-31* basis set. The lower internal modes assigned to torsional vibration of the androstane skeleton mix with the lattice vibrations. The intense bands in the PDS spectra in the frequency range from 150 to 300cm-1 are related to librations of structurally inequivalent methyl groups.
Gu, Zhenyan; Lei, Wu; Shi, Wenyan; Hao, Qingli; Si, Weimeng; Xia, Xifeng; Wang, Fengxiang
2014-11-11
The interaction between 9-fluorenylmethyl chloroformate (FMOC-Cl) and Fe3+ and Cu2+ ions was investigated using fluorescence, UV/Vis absorption spectroscopies and theoretical calculation. The optical property of FMOC-Cl was studied in detail in absence and presence of various transition metal ions with particular affinity to Fe3+ and Cu2+ ions. With the fluorescence characteristic band centered at 307 and 315 nm for FMOC-Cl, the introduction of Fe3+ or Cu2+ ions leads to the fluorescence quenching of FMOC-Cl with different shift and intensities of two fluorescent bands. It allows us to differentiate between FMOC-Cl and Fe3+ and Cu2+ ions interaction behavior. The study on fluorescent kinetics confirms that the fluorescence quenching of FMOC-Cl with Fe3+ and Cu2+ ions is based on the formation of non-fluorescent material, that is, static quenching. Further analyses of bond lengths, Mulliken atomic charges and the frontier orbital compositions for FMOC-Cl and its complexes with Fe3+ and Cu2+ ions were carried out. The theoretical calculations prove the fluorescence quenching originates from the formation of coordination bonds between the oxygen atom of the carbonyl group of FMOC-Cl and Fe3+ and Cu2+ ions. The commercially available FMOC-Cl can be used as excellent fluorescent probe toward Fe3+ and Cu2+ ions with high sensitivity.
Jiang, He; Chen, Changshui
2015-04-23
Most material properties can be traced to electronic structures. Black silicon produced from SF6 or sulfur powder via irradiation with femtosecond laser pulses displays decreased infrared absorption after annealing, with almost no corresponding change in visible light absorption. The high-intensity laser pulses destroy the original crystal structure, and the doping element changes the material performance. In this work, the structural and electronic properties of several sulfur-doped silicon systems are investigated using first principle calculations. Depending on the sulfur concentration (level of doping) and the behavior of the sulfur atoms in the silicon lattice, different states or an absence of states are exhibited, compared with the undoped system. Moreover, the visible-infrared light absorption intensities are structure specific. The results of our theoretical calculations show that the conversion efficiency of sulfur-doped silicon solar cells depends on the sulfur concentrations. Additionally, two types of defect configurations exhibit light absorption characteristics that differ from the other configurations. These two structures produce a rapid increase in the theoretical photoelectric conversion efficiency in the range of the specific chemical potential studied. By controlling the positions of the atomic sulfur and the sulfur concentration in the preparation process, an efficient photovoltaic (PV) material may be obtainable.
NASA Astrophysics Data System (ADS)
Gu, Zhenyan; Lei, Wu; Shi, Wenyan; Hao, Qingli; Si, Weimeng; Xia, Xifeng; Wang, Fengxiang
2014-11-01
The interaction between 9-fluorenylmethyl chloroformate (FMOC-Cl) and Fe3+ and Cu2+ ions was investigated using fluorescence, UV/Vis absorption spectroscopies and theoretical calculation. The optical property of FMOC-Cl was studied in detail in absence and presence of various transition metal ions with particular affinity to Fe3+ and Cu2+ ions. With the fluorescence characteristic band centered at 307 and 315 nm for FMOC-Cl, the introduction of Fe3+ or Cu2+ ions leads to the fluorescence quenching of FMOC-Cl with different shift and intensities of two fluorescent bands. It allows us to differentiate between FMOC-Cl and Fe3+ and Cu2+ ions interaction behavior. The study on fluorescent kinetics confirms that the fluorescence quenching of FMOC-Cl with Fe3+ and Cu2+ ions is based on the formation of non-fluorescent material, that is, static quenching. Further analyses of bond lengths, Mulliken atomic charges and the frontier orbital compositions for FMOC-Cl and its complexes with Fe3+ and Cu2+ ions were carried out. The theoretical calculations prove the fluorescence quenching originates from the formation of coordination bonds between the oxygen atom of the carbonyl group of FMOC-Cl and Fe3+ and Cu2+ ions. The commercially available FMOC-Cl can be used as excellent fluorescent probe toward Fe3+ and Cu2+ ions with high sensitivity.
Quantum Monte Carlo calculations of neutron matter with chiral three-body forces
Tews, I.; Gandolfi, Stefano; Gezerlis, A.; ...
2016-02-02
Chiral effective field theory (EFT) enables a systematic description of low-energy hadronic interactions with controlled theoretical uncertainties. For strongly interacting systems, quantum Monte Carlo (QMC) methods provide some of the most accurate solutions, but they require as input local potentials. We have recently constructed local chiral nucleon-nucleon (NN) interactions up to next-to-next-to-leading order (N2LO). Chiral EFT naturally predicts consistent many-body forces. In this paper, we consider the leading chiral three-nucleon (3N) interactions in local form. These are included in auxiliary field diffusion Monte Carlo (AFDMC) simulations. We present results for the equation of state of neutron matter and for themore » energies and radii of neutron drops. Specifically, we study the regulator dependence at the Hartree-Fock level and in AFDMC and find that present local regulators lead to less repulsion from 3N forces compared to the usual nonlocal regulators.« less
Welsch, Ralph Manthe, Uwe
2014-08-07
The mode-selective chemistry of the title reaction is studied by full-dimensional quantum dynamics simulation on an accurate ab initio potential energy surface for vanishing total angular momentum. Using a rigorous transition state based approach and multi-configurational time-dependent Hartree wave packet propagation, initial state-selected reaction probabilities for many ro-vibrational states of methane are calculated. The theoretical results are compared with experimental trends seen in reactions of methane. An intuitive interpretation of the ro-vibrational control of the chemical reactivity provided by a sudden model based on the quantum transition state concept is discussed.
NASA Astrophysics Data System (ADS)
ten Kate, O. M.; de Jong, M.; Hintzen, H. T.; van der Kolk, E.
2013-08-01
Solar cells of which the efficiency is not limited by the Shockley-Queisser limit can be obtained by integrating a luminescent spectral conversion layer into the cell structure. We have calculated the maximum efficiency of state-of-the-art c-Si, pc-Si, a-Si, CdTe, GaAs, CIS, CIGS, CGS, GaSb, and Ge solar cells with and without an integrated spectral shifting, quantum cutting, or quantum tripling layer using their measured internal quantum efficiency (IQE) curves. Our detailed balance limit calculations not only take into account light in-coupling efficiency of the direct AM1.5 spectral irradiance but also wavelength dependence of the refractive index and the IQEs of the cells and the angular dependent light in-coupling of the indirect spectral irradiance. An ideal quantum cutting layer enhances all cell efficiencies ranging from a modest 2.9% for c-Si to much larger values of 4.0%, 7.7%, and 11.2% for CIGS, Ge, and GaSb, respectively. A quantum tripling layer also enhances cell efficiencies, but to a lesser extent. These efficiency enhancements are largest for small band gap cells like GaSb (7.5%) and Ge (3.8%). Combining a quantum tripling and a quantum cutting layer would enhance efficiency of these cells by a factor of two. Efficiency enhancement by a simple spectral shifting layer is limited to less than 1% in case the IQE is high for blue and UV lights. However, for CdTe and GaSb solar cells, efficiency enhancements are as high as 4.6% and 3.5%, respectively. A shifting layer based on available red LED phosphors like Sr2Si5N8:Eu will raise CdTe efficiency by 3.0%.
NASA Astrophysics Data System (ADS)
Subramanian, Ramachandran; Schultz, Andrew J.; Kofke, David A.
2017-03-01
We develop an orientation sampling algorithm for rigid diatomic molecules, which allows direct generation of rings of images used for path-integral calculation of nuclear quantum effects. The algorithm treats the diatomic molecule as two independent atoms as opposed to one (quantum) rigid rotor. Configurations are generated according to a solvable approximate distribution that is corrected via the acceptance decision of the Monte Carlo trial. Unlike alternative methods that treat the systems as a quantum rotor, this atom-based approach is better suited for generalization to multi-atomic (more than two atoms) and flexible molecules. We have applied this algorithm in combination with some of the latest ab initio potentials of rigid H2 to compute fully quantum second virial coefficients, for which we observe excellent agreement with both experimental and simulation data from the literature.
NASA Astrophysics Data System (ADS)
Bester, Gabriel
2006-03-01
The optical spectrum and the charging energies of semiconductor quantum dots have been recently measured with high accuracy. Both of these experimental techniques probe many-body states that are not directly described by independent particle theories such as the density functional theory. On the other hand, quasi- particle theories that can in principle address the problem, such as GW, are computationally too demanding for the study of nanostructures (as opposed to clusters) where many thousands of atoms are involved. One way to approach this problem is to use the effective mass approximation or the k.p method and choose a confinement potential that reproduces a few known experimental facts (e.g. the splitting between confined levels). These methods can provide a good initial guess but were shown to be too crude to enable a quantitative comparision with recent experiments. We therefore adopt a bottom-up atomistic approach where instead of starting from a simplified approach, such as effective mass, and progressively increase the complexity by adding parameters, we start from the accurate atomistic description (LDA or GW) and work ourselves up using a few well controlled approximations.I will first present the method, namely (i) the scheme that is used to derive the empirical pseudopotentials including the piezoelectric effect, (ii) the choices that have to be made for the basis used to expand the wave functions, (iii) the inclusion of corelations through Bethe-Salpeter-like treatment. I will then present recent applications of the theory to calculate the fine-structure [1] of excitons and charged excitons, the charging spectra of holes [2] and the degree or entanglement stored in a quantum dot molecule [3].[1] G. Bester, S.V. Nair, A. Zunger, prb 67, 161306 (2003). [2] L. He, G. Bester, A. Zunger, PRL (in press). [3] G. Bester, J. Shumway, A. Zunger, PRL 93, 047401 (2004)
An efficient method for the calculation of quantum mechanics/molecular mechanics free energies
NASA Astrophysics Data System (ADS)
Woods, Christopher J.; Manby, Frederick R.; Mulholland, Adrian J.
2008-01-01
The combination of quantum mechanics (QM) with molecular mechanics (MM) offers a route to improved accuracy in the study of biological systems, and there is now significant research effort being spent to develop QM/MM methods that can be applied to the calculation of relative free energies. Currently, the computational expense of the QM part of the calculation means that there is no single method that achieves both efficiency and rigor; either the QM/MM free energy method is rigorous and computationally expensive, or the method introduces efficiency-led assumptions that can lead to errors in the result, or a lack of generality of application. In this paper we demonstrate a combined approach to form a single, efficient, and, in principle, exact QM/MM free energy method. We demonstrate the application of this method by using it to explore the difference in hydration of water and methane. We demonstrate that it is possible to calculate highly converged QM/MM relative free energies at the MP2/aug-cc-pVDZ/OPLS level within just two days of computation, using commodity processors, and show how the method allows consistent, high-quality sampling of complex solvent configurational change, both when perturbing hydrophilic water into hydrophobic methane, and also when moving from a MM Hamiltonian to a QM/MM Hamiltonian. The results demonstrate the validity and power of this methodology, and raise important questions regarding the compatibility of MM and QM/MM forcefields, and offer a potential route to improved compatibility.
NASA Astrophysics Data System (ADS)
Schwerdtfeger, Christine A.; Mazziotti, David A.
2012-12-01
Treatment of two-electron excitations is a fundamental but computationally expensive part of ab initio calculations of many-electron correlation. In this paper we develop a low-rank spectral expansion of two-electron excitations for accelerated electronic-structure calculations. The spectral expansion differs from previous approaches by relying upon both (i) a sum of three expansions to increase the rank reduction of the tensor and (ii) a factorization of the tensor into geminal (rank-two) tensors rather than orbital (rank-one) tensors. We combine three spectral expansions from the three distinct forms of the two-electron reduced density matrix (2-RDM), (i) the two-particle 2D, (ii) the two-hole 2Q, and the (iii) particle-hole 2G matrices, to produce a single spectral expansion with significantly accelerated convergence. While the resulting expansion is applicable to any quantum-chemistry calculation with two-particle excitation amplitudes, it is employed here in the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], 10.1103/PhysRevLett.101.253002. The low-rank parametric 2-RDM method scales quartically with the basis-set size, but like its full-rank version it can capture multi-reference correlation effects that are difficult to treat efficiently by traditional single-reference wavefunction methods. Applications are made to computing potential energy curves of HF and triplet OH+, equilibrium bond distances and frequencies, the HCN-HNC isomerization, and the energies of hydrocarbon chains. Computed 2-RDMs nearly satisfy necessary N-representability conditions. The low-rank spectral expansion has the potential to expand the applicability of the parametric 2-RDM method as well as other ab initio methods to large-scale molecular systems that are often only treatable by mean-field or density functional theories.
NASA Astrophysics Data System (ADS)
Roehl, Jason L.
Diffusion of point defects on crystalline surfaces and in their bulk is an important and ubiquitous phenomenon affecting film quality, electronic properties and device functionality. A complete understanding of these diffusion processes enables one to predict and then control those processes. Such understanding includes knowledge of the structural, energetic and electronic properties of these native and non-native point defect diffusion processes. Direct experimental observation of the phenomenon is difficult and microscopic theories of diffusion mechanisms and pathways abound. Thus, knowing the nature of diffusion processes, of specific point defects in given materials, has been a challenging task for analytical theory as well as experiment. The recent advances in computing technology have been a catalyst for the rise of a third mode of investigation. The advent of tremendous computing power, breakthroughs in algorithmic development in computational applications of electronic density functional theory now enables direct computation of the diffusion process. This thesis demonstrates such a method applied to several different examples of point defect diffusion on the (001) surface of gallium arsenide (GaAs) and the bulk of cadmium telluride (CdTe) and cadmium sulfide (CdS). All results presented in this work are ab initio, total-energy pseudopotential calculations within the local density approximation to density-functional theory. Single particle wavefunctions were expanded in a plane-wave basis and reciprocal space k-point sampling was achieved by Monkhorst-Pack generated k-point grids. Both surface and bulk computations employed a supercell approach using periodic boundary conditions. Ga adatom adsorption and diffusion processes were studied on two reconstructions of the GaAs(001) surface including the c(4x4) and c(4x4)-heterodimer surface reconstructions. On the GaAs(001)- c(4x4) surface reconstruction, two distinct sets of minima and transition sites were
Calzado, Carmen J; Ben Amor, Nadia; Maynau, Daniel
2014-07-14
This paper reports a theoretical analysis of the electronic structure and magnetic properties of a ferromagnetic Cu(II) [3×3] grid. A two-step strategy, combining calculations on the whole grid and on binuclear fragments, has been employed to evaluate all the magnetic interactions in the grid. The calculations confirm an S = 7/2 ground state, which is in accordance with the magnetisation versus field curve and the thermal dependence of the magnetic moment data. Only the first-neighbour coupling terms present non-negligible amplitudes, all of them in agreement with the structure and arrangement of the Cu 3d magnetic orbitals. The results indicate that the dominant interaction in the system is the antiferromagnetic coupling between the ring and the central Cu sites (J3 = J4 ≈ -31 cm(-1)). In the ring two different interactions can be distinguished, J1 = 4.6 cm(-1) and J2 = -0.1 cm(-1), in contrast to the single J model employed in the magnetic data fit. The calculated J values have been used to determine the energy level distribution of the Heisenberg magnetic states. The effective magnetic moment versus temperature plot resulting from this ab initio energy profile is in good agreement with the experimental curve and the fitting obtained with the simplified spin model, despite the differences between these two spin models. This study underlines the role that the theoretical evaluations of the coupling constants can play on the rationalisation of the magnetic properties of these complex polynuclear systems.
Mishra, Sandeep Kumar; Suryaprakash, N
2015-06-21
The rare examples of intramolecular hydrogen bonds (HB) of the type the N-H∙∙∙F-C, detected in a low polarity solvent in the derivatives of hydrazides, by utilizing one and two-dimensional solution state multinuclear NMR techniques, are reported. The observation of through-space couplings, such as, (1h)JFH, and (1h)JFN, provides direct evidence for the existence of intra-molecular HB. Solvent induced perturbations and the variable temperature NMR experiments unambiguously establish the presence of intramolecular HB. The existence of multiple conformers in some of the investigated molecules is also revealed by two dimensional HOESY and (15)N-(1)H HSQC experiments. The (1)H DOSY experimental results discard any possibility of self or cross dimerization of the molecules. The derived NMR experimental results are further substantiated by Density Function Theory (DFT) based Non Covalent Interaction (NCI), and Quantum Theory of Atom in Molecule (QTAIM) calculations. The NCI calculations served as a very sensitive tool for detection of non-covalent interactions and also confirm the presence of bifurcated HBs.
Hache, F
2010-09-23
Quantum calculation of the hyperpolarizabilty tensor is carried out for chiral molecules displaying a "one-electron" chirality. Calculation is made possible by introducing a chiral perturbation term in the potential energy surface. We show that a one-electron chiral molecule is intrinsically nonlinear and diplays a nonzero electric chiral hyperpolarizability. Existence of magnetic contributions is discussed, and it is shown that higher-order perturbation terms are necessary to introduce such magnetic effects in the second-order hyperpolarizability.
Ramanantoanina, Harry; Urland, Werner; Cimpoesu, Fanica; Daul, Claude
2013-09-07
Herein we present a Ligand Field Density Functional Theory (LFDFT) based methodology for the analysis of the 4f(n)→ 4f(n-1)5d(1) transitions in rare earth compounds and apply it for the characterization of the 4f(2)→ 4f(1)5d(1) transitions in the quantum cutter Cs2KYF6:Pr(3+) with the elpasolite structure type. The methodological advances are relevant for the analysis and prospection of materials acting as phosphors in light-emitting diodes. The positions of the zero-phonon energy corresponding to the states of the electron configurations 4f(2) and 4f(1)5d(1) are calculated, where the praseodymium ion may occupy either the Cs(+)-, K(+)- or the Y(3+)-site, and are compared with available experimental data. The theoretical results show that the occupation of the three undistorted sites allows a quantum-cutting process. However size effects due to the difference between the ionic radii of Pr(3+) and K(+) as well as Cs(+) lead to the distortion of the K(+)- and the Cs(+)-site, which finally exclude these sites for quantum-cutting. A detailed discussion about the origin of this distortion is also described.
Dong, Bing; Zhou, Xiao-Lin E-mail: lkworld@126.com; Chang, Jing; Liu, Ke E-mail: lkworld@126.com
2014-08-07
The structural and elastic properties of RuN{sub 2} were investigated through the first-principles calculation using generalized gradient approximation (GGA) and local density approximation (LDA) within the plane-wave pseudopotential density functional theory. The obtained equilibrium structure and mechanical properties are in excellent agreement with other theoretical results. Then we compared the elastic modulus of RuN{sub 2} with several other isomorphic noble metal nitrides. Results show that RuN{sub 2} can nearly rival with OsN{sub 2} and IrN{sub 2}, which indicate RuN{sub 2} is a potentially ultra-incompressible and hard material. By the elastic stability criteria, it is predicted that RuN{sub 2} is stable in our calculations (0–100 GPa). The calculated B/G ratios indicate that RuN{sub 2} possesses brittle nature at 0 GPa and when the pressure increases to 13.4 GPa (for LDA) or 20.8 GPa (for GGA), it begins to prone to ductility. Through the quasi-harmonic Debye model, we also investigated the thermodynamic properties of RuN{sub 2}.
Quantum Darwinism Requires an Extra-Theoretical Assumption of Encoding Redundancy
NASA Astrophysics Data System (ADS)
Fields, Chris
2010-10-01
Observers restricted to the observation of pointer states of apparatus cannot conclusively demonstrate that the pointer of an apparatus mathcal{A} registers the state of a system of interest S without perturbing S. Observers cannot, therefore, conclusively demonstrate that the states of a system S are redundantly encoded by pointer states of multiple independent apparatus without destroying the redundancy of encoding. The redundancy of encoding required by quantum Darwinism must, therefore, be assumed from outside the quantum-mechanical formalism and without the possibility of experimental demonstration.
Chan, Bun; Kawashima, Yukio; Katouda, Michio; Nakajima, Takahito; Hirao, Kimihiko
2016-02-03
We have carried out large-scale computational quantum chemistry calculations on the K computer to obtain heats of formation for C60 and some higher fullerenes with the DSD-PBE-PBE/cc-pVQZ double-hybrid density functional theory method. Our best estimated values are 2520.0 ± 20.7 (C60), 2683.4 ± 17.7 (C70), 2862.0 ± 18.5 (C76), 2878.8 ± 13.3 (C78), 2946.4 ± 14.5 (C84), 3067.3 ± 15.4 (C90), 3156.6 ± 16.2 (C96), 3967.7 ± 33.4 (C180), 4364 (C240) and 5415 (C320) kJ mol(-1). In our assessment, we also find that the B3-PW91-D3BJ and BMK-D3(BJ) functionals perform reasonably well. Using the convergence behavior for the calculated per-atom heats of formation, we obtained the formula ΔfH per carbon = 722n(-0.72) + 5.2 kJ mol(-1) (n = the number of carbon atoms), which enables an estimation of ΔfH for higher fullerenes more generally. A slow convergence to the graphene limit is observed, which we attribute to the relatively small proportion of fullerene carbons that are in "low-strain" regions. We further propose that it would take tens, if not hundreds, of thousands of carbons for a fullerene to roughly approach the limit. Such a distinction may be a contributing factor to the discrete properties between the two types of nanomaterials. During the course of our study, we also observe a fairly reliable means for the theoretical calculation of heats of formation for medium-sized fullerenes. This involves the use of isodesmic-type reactions with fullerenes of similar sizes to provide a good balance of the chemistry and to minimize the use of accompanying species.
NASA Astrophysics Data System (ADS)
Shoji, Mitsuo; Isobe, Hiroshi; Yamanaka, Shusuke; Umena, Yasufumi; Kawakami, Keisuke; Kamiya, Nobuo; Shen, Jian-Ren; Nakajima, Takahito; Yamaguchi, Kizashi
2015-02-01
Quantum mechanical (QM)/molecular mechanics (MM) calculations by the use of a large-scale QM model (QM Model V) have been performed to elucidate hydrogen-bonding networks and proton wires for proton release pathways (PRP) of water oxidation reaction in the oxygen evolving complex (OEC) of photosystem II (PSII). Full geometry optimisations of PRP by the QM/MM model have been carried out starting from the geometry of heavy atoms determined by the recent high-resolution X-ray diffraction (XRD) experiment of PSII refined to 1.9 Å resolution. Computational results by the QM/MM calculations have elucidated the hydrogen-bonding O...O(N) and O...H distances and O(N)-H...O angles in PRP, together with the Cl-O(N) and Cl...H distances and O(N)-H...Cl angles for chloride anions. The optimised hydrogen-bonding networks are well consistent with the XRD results and available experiments such as extended X-ray absorption fine structure, showing the reliability of channel structures of OEC of PSII revealed by the XRD experiment. The QM/MM computations have elucidated possible roles of chloride anions in the OEC of PSII. The QM/MM computational results have provided useful information for understanding and explanation of accumulated mutation experiments of key amino acid residues in the OEC of PSII. Implications of the present results are discussed in relation to three steps for theoretical modelling of water oxidation in the OEC of PSII and bio-inspired working hypotheses for developments of artificial water oxidation systems by use of 3d transition-metal complexes.
Treatment of dilute clusters of methanol and water by ab initio quantum mechanical calculations.
Ruckenstein, Eli; Shulgin, Ivan L; Tilson, Jeffrey L
2005-02-10
Large molecular clusters can be considered as intermediate states between gas and condensed phases, and information about them can help us understand condensed phases. In this paper, ab initio quantum mechanical methods have been used to examine clusters formed of methanol and water molecules. The main goal was to obtain information about the intermolecular interactions and the structure of methanol/water clusters at the molecular level. The large clusters (CH(4)O...(H(2)O)(12) and H(2)O...(CH(4)O)(10)) containing one molecule of one component (methanol or water) and many (12, 10) molecules of the other component were considered. Møller-Plesset perturbation theory (MP2) was used in the calculations. Several representative cluster geometries were optimized, and nearest-neighbor interaction energies were calculated for the geometries obtained in the first step. The results of the calculations were compared to the available experimental information regarding the liquid methanol/water mixtures and to the molecular dynamics and Monte Carlo simulations, and good agreement was found. For the CH(4)O...(H(2)O)(12) cluster, it was shown that the molecules of water can be subdivided into two classes: (i) H bonded to the central methanol molecule and (ii) not H bonded to the central methanol molecule. As expected, these two classes exhibited striking energy differences. Although they are located almost the same distance from the carbon atom of the central methanol molecule, they possess very different intermolecular interaction energies with the central molecule. The H bonding constitutes a dominant factor in the hydration of methanol in dilute aqueous solutions. For the H(2)O...(CH(4)O)(10) cluster, it was shown that the central molecule of water has almost three H bonds with the methanol molecules; this result differs from those in the literature that concluded that the average number of H bonds between a central water molecule and methanol molecules in dilute solutions of
NASA Astrophysics Data System (ADS)
Ferres, Lynn; Stahl, Wolfgang; Nguyen, Ha Vinh Lam
2016-06-01
A pulsed molecular beam Fourier transform microwave spectrometer operating in the frequency range 2 - 26.5 GHz was used to measure the spectrum of phenetole (ethyl phenyl ether or ethoxybenzene, C6H5OC2H5). The conformational landscape is completely determined by the orientations of the phenyl ring and the ethyl group. A two-dimensional potential energy surface was calculated at the MP2/6-311++G(d,p) level of theory. Two conformers were found: The trans conformer has a Cs symmetry, and the gauche conformer has the ethyl group tilted out of the phenyl plane by about 70°. Totally 186 rotational transitions were assigned to the more stable planar trans conformer, and fitted using a semi-rigid rotor model to measurement accuracy of 2 kHz. Highly accurate rotational and centrifugal distortion constants were determined. Several method and basis set combinations were applied to check for convergence and to compare with the experimentally deduced molecular parameters. The inertial defect of the observed conformer Δc = (Ic - Ia - Ib) = -6.718 uÅ2 confirms that the heavy atom skeleton is planar with two pairs of hydrogen atoms out of plane. All lines in the spectrum could be assigned to the trans conformer, which confirms that the gauche conformer cannot be observed under our measurement conditions. In agreement with the rather high torsional barrier of the methyl group (V3 = 1168 wn) calculated by quantum chemical methods, all assigned lines appeared sharp and no signs of splittings were observed for the methyl internal rotation.
A Monte Carlo Resampling Approach for the Calculation of Hybrid Classical and Quantum Free Energies.
Cave-Ayland, Christopher; Skylaris, Chris-Kriton; Essex, Jonathan W
2017-02-14
Hybrid free energy methods allow estimation of free energy differences at the quantum mechanics (QM) level with high efficiency by performing sampling at the classical mechanics (MM) level. Various approaches to allow the calculation of QM corrections to classical free energies have been proposed. The single step free energy perturbation approach starts with a classically generated ensemble, a subset of structures of which are postprocessed to obtain QM energies for use with the Zwanzig equation. This gives an estimate of the free energy difference associated with the change from an MM to a QM Hamiltonian. Owing to the poor numerical properties of the Zwanzig equation, however, recent developments have produced alternative methods which aim to provide access to the properties of the true QM ensemble. Here we propose an approach based on the resampling of MM structural ensembles and application of a Monte Carlo acceptance test which in principle, can generate the exact QM ensemble or intermediate ensembles between the MM and QM states. We carry out a detailed comparison against the Zwanzig equation and recently proposed non-Boltzmann methods. As a test system we use a set of small molecule hydration free energies for which hybrid free energy calculations are performed at the semiempirical Density Functional Tight Binding level. Equivalent ensembles at this level of theory have also been generated allowing the reverse QM to MM perturbations to be performed along with a detailed analysis of the results. Additionally, a previously published nucleotide base pair data set simulated at the QM level using ab initio molecular dynamics is also considered. We provide a strong rationale for the use of the Monte Carlo Resampling and non-Boltzmann approaches by showing that configuration space overlaps can be estimated which provide useful diagnostic information regarding the accuracy of these hybrid approaches.
Busch, Anna; González-García, Núria; Lendvay, György; Olzmann, Matthias
2015-07-16
The thermal decomposition of cyanonitrene, NCN, was studied behind reflected shock waves in the temperature range 1790-2960 K at pressures near 1 and 4 bar. Highly diluted mixtures of NCN3 in argon were shock-heated to produce NCN, and concentration-time profiles of C atoms as reaction product were monitored with atomic resonance absorption spectroscopy at 156.1 nm. Calibration was performed with methane pyrolysis experiments. Rate coefficients for the reaction (3)NCN + M → (3)C + N2 + M (R1) were determined from the initial slopes of the C atom concentration-time profiles. Reaction R1 was found to be in the low-pressure regime at the conditions of the experiments. The temperature dependence of the bimolecular rate coefficient can be expressed with the following Arrhenius equation: k1(bim) = (4.2 ± 2.1) × 10(14) exp[-242.3 kJ mol(-1)/(RT)] cm(3) mol(-1) s(-1). The rate coefficients were analyzed by using a master equation with specific rate coefficients from RRKM theory. The necessary molecular data and energies were calculated with quantum chemical methods up to the CCSD(T)/CBS//CCSD/cc-pVTZ level of theory. From the topography of the potential energy surface, it follows that reaction R1 proceeds via isomerization of NCN to CNN and subsequent C-N bond fission along a collinear reaction coordinate without a tight transition state. The calculations reproduce the magnitude and temperature dependence of the rate coefficient and confirm that reaction R1 is in the low-pressure regime under our experimental conditions.
Derivation of the Rules of Quantum Mechanics from Information-Theoretic Axioms
NASA Astrophysics Data System (ADS)
Fivel, Daniel I.
2012-02-01
Conventional quantum mechanics with a complex Hilbert space and the Born Rule is derived from five axioms describing experimentally observable properties of probability distributions for the outcome of measurements. Axioms I, II, III are common to quantum mechanics and hidden variable theories. Axiom IV recognizes a phenomenon, first noted by von Neumann (in Mathematical Foundations of Quantum Mechanics, Princeton University Press, Princeton, 1955) and independently by Turing (Teuscher and Hofstadter, Alan Turing: Life and Legacy of a Great Thinker, Springer, Berlin, 2004), in which the increase in entropy resulting from a measurement is reduced by a suitable intermediate measurement. This is shown to be impossible for local hidden variable theories. Axiom IV, together with the first three, almost suffice to deduce the conventional rules but allow some exotic, alternatives such as real or quaternionic quantum mechanics. Axiom V recognizes a property of the distribution of outcomes of random measurements on qubits which holds only in the complex Hilbert space model. It is then shown that the five axioms also imply the conventional rules for any finite dimension.
Smith, Kyle K. G.; Poulsen, Jens Aage Nyman, Gunnar; Rossky, Peter J.
2015-06-28
We develop two classes of quasi-classical dynamics that are shown to conserve the initial quantum ensemble when used in combination with the Feynman-Kleinert approximation of the density operator. These dynamics are used to improve the Feynman-Kleinert implementation of the classical Wigner approximation for the evaluation of quantum time correlation functions known as Feynman-Kleinert linearized path-integral. As shown, both classes of dynamics are able to recover the exact classical and high temperature limits of the quantum time correlation function, while a subset is able to recover the exact harmonic limit. A comparison of the approximate quantum time correlation functions obtained from both classes of dynamics is made with the exact results for the challenging model problems of the quartic and double-well potentials. It is found that these dynamics provide a great improvement over the classical Wigner approximation, in which purely classical dynamics are used. In a special case, our first method becomes identical to centroid molecular dynamics.
The Impact of Quantum Theoretical Models of Consciousness on the Study of Education.
ERIC Educational Resources Information Center
Andris, James F.
This paper abstracts and discusses the approaches of five educational theorists who have used quantum theory as a model for educational phenomena, sets forth and uses metatheoretical criteria to evaluate the work of these theorists, and states guidelines for further work in this domain. The paper abstracts and discusses the works of the following…
Smith, Kyle K G; Poulsen, Jens Aage; Nyman, Gunnar; Rossky, Peter J
2015-06-28
We develop two classes of quasi-classical dynamics that are shown to conserve the initial quantum ensemble when used in combination with the Feynman-Kleinert approximation of the density operator. These dynamics are used to improve the Feynman-Kleinert implementation of the classical Wigner approximation for the evaluation of quantum time correlation functions known as Feynman-Kleinert linearized path-integral. As shown, both classes of dynamics are able to recover the exact classical and high temperature limits of the quantum time correlation function, while a subset is able to recover the exact harmonic limit. A comparison of the approximate quantum time correlation functions obtained from both classes of dynamics is made with the exact results for the challenging model problems of the quartic and double-well potentials. It is found that these dynamics provide a great improvement over the classical Wigner approximation, in which purely classical dynamics are used. In a special case, our first method becomes identical to centroid molecular dynamics.
Concepts and their dynamics: a quantum-theoretic modeling of human thought.
Aerts, Diederik; Gabora, Liane; Sozzo, Sandro
2013-10-01
We analyze different aspects of our quantum modeling approach of human concepts and, more specifically, focus on the quantum effects of contextuality, interference, entanglement, and emergence, illustrating how each of them makes its appearance in specific situations of the dynamics of human concepts and their combinations. We point out the relation of our approach, which is based on an ontology of a concept as an entity in a state changing under influence of a context, with the main traditional concept theories, that is, prototype theory, exemplar theory, and theory theory. We ponder about the question why quantum theory performs so well in its modeling of human concepts, and we shed light on this question by analyzing the role of complex amplitudes, showing how they allow to describe interference in the statistics of measurement outcomes, while in the traditional theories statistics of outcomes originates in classical probability weights, without the possibility of interference. The relevance of complex numbers, the appearance of entanglement, and the role of Fock space in explaining contextual emergence, all as unique features of the quantum modeling, are explicitly revealed in this article by analyzing human concepts and their dynamics.
Aquilante, Francesco; Autschbach, Jochen; Carlson, Rebecca K; Chibotaru, Liviu F; Delcey, Mickaël G; De Vico, Luca; Fdez Galván, Ignacio; Ferré, Nicolas; Frutos, Luis Manuel; Gagliardi, Laura; Garavelli, Marco; Giussani, Angelo; Hoyer, Chad E; Li Manni, Giovanni; Lischka, Hans; Ma, Dongxia; Malmqvist, Per Åke; Müller, Thomas; Nenov, Artur; Olivucci, Massimo; Pedersen, Thomas Bondo; Peng, Daoling; Plasser, Felix; Pritchard, Ben; Reiher, Markus; Rivalta, Ivan; Schapiro, Igor; Segarra-Martí, Javier; Stenrup, Michael; Truhlar, Donald G; Ungur, Liviu; Valentini, Alessio; Vancoillie, Steven; Veryazov, Valera; Vysotskiy, Victor P; Weingart, Oliver; Zapata, Felipe; Lindh, Roland
2016-02-15
In this report, we summarize and describe the recent unique updates and additions to the Molcas quantum chemistry program suite as contained in release version 8. These updates include natural and spin orbitals for studies of magnetic properties, local and linear scaling methods for the Douglas-Kroll-Hess transformation, the generalized active space concept in MCSCF methods, a combination of multiconfigurational wave functions with density functional theory in the MC-PDFT method, additional methods for computation of magnetic properties, methods for diabatization, analytical gradients of state average complete active space SCF in association with density fitting, methods for constrained fragment optimization, large-scale parallel multireference configuration interaction including analytic gradients via the interface to the Columbus package, and approximations of the CASPT2 method to be used for computations of large systems. In addition, the report includes the description of a computational machinery for nonlinear optical spectroscopy through an interface to the QM/MM package Cobramm. Further, a module to run molecular dynamics simulations is added, two surface hopping algorithms are included to enable nonadiabatic calculations, and the DQ method for diabatization is added. Finally, we report on the subject of improvements with respects to alternative file options and parallelization.
Photodissociation dynamics of the pyridinyl radical: Time-dependent quantum wave-packet calculations
NASA Astrophysics Data System (ADS)
Ehrmaier, Johannes; Picconi, David; Karsili, Tolga N. V.; Domcke, Wolfgang
2017-03-01
The H-atom photodissociation reaction from the pyridinyl radical (C5H5NH ) via the low-lying π σ* excited electronic state is investigated by nonadiabatic time-dependent quantum wave-packet dynamics calculations. A model comprising three electronic states and three nuclear coordinates has been constructed using ab initio multi-configurational self-consistent-field and multi-reference perturbation theory methods. Two conical intersections among the three lowest electronic states have been characterized in the framework of the linear vibronic-coupling model. Time-dependent wave-packet simulations have been performed using the multi-configuration time-dependent Hartree method. The population dynamics of the diabatic and adiabatic electronic states and the time-dependent dissociation behavior are analyzed for various vibrational initial conditions. The results provide detailed mechanistic insight into the photoinduced H-atom dissociation process from a hypervalent aromatic radical and show that an efficient dissociation reaction through two conical intersections is possible.
Auxiliary-field-based trial wave functions in quantum Monte Carlo calculations
NASA Astrophysics Data System (ADS)
Chang, Chia-Chen; Rubenstein, Brenda M.; Morales, Miguel A.
2016-12-01
Quantum Monte Carlo (QMC) algorithms have long relied on Jastrow factors to incorporate dynamic correlation into trial wave functions. While Jastrow-type wave functions have been widely employed in real-space algorithms, they have seen limited use in second-quantized QMC methods, particularly in projection methods that involve a stochastic evolution of the wave function in imaginary time. Here we propose a scheme for generating Jastrow-type correlated trial wave functions for auxiliary-field QMC methods. The method is based on decoupling the two-body Jastrow into one-body projectors coupled to auxiliary fields, which then operate on a single determinant to produce a multideterminant trial wave function. We demonstrate that intelligent sampling of the most significant determinants in this expansion can produce compact trial wave functions that reduce errors in the calculated energies. Our technique may be readily generalized to accommodate a wide range of two-body Jastrow factors and applied to a variety of model and chemical systems.
Maia, Julio Daniel Carvalho; Urquiza Carvalho, Gabriel Aires; Mangueira, Carlos Peixoto; Santana, Sidney Ramos; Cabral, Lucidio Anjos Formiga; Rocha, Gerd B
2012-09-11
In this study, we present some modifications in the semiempirical quantum chemistry MOPAC2009 code that accelerate single-point energy calculations (1SCF) of medium-size (up to 2500 atoms) molecular systems using GPU coprocessors and multithreaded shared-memory CPUs. Our modifications consisted of using a combination of highly optimized linear algebra libraries for both CPU (LAPACK and BLAS from Intel MKL) and GPU (MAGMA and CUBLAS) to hasten time-consuming parts of MOPAC such as the pseudodiagonalization, full diagonalization, and density matrix assembling. We have shown that it is possible to obtain large speedups just by using CPU serial linear algebra libraries in the MOPAC code. As a special case, we show a speedup of up to 14 times for a methanol simulation box containing 2400 atoms and 4800 basis functions, with even greater gains in performance when using multithreaded CPUs (2.1 times in relation to the single-threaded CPU code using linear algebra libraries) and GPUs (3.8 times). This degree of acceleration opens new perspectives for modeling larger structures which appear in inorganic chemistry (such as zeolites and MOFs), biochemistry (such as polysaccharides, small proteins, and DNA fragments), and materials science (such as nanotubes and fullerenes). In addition, we believe that this parallel (GPU-GPU) MOPAC code will make it feasible to use semiempirical methods in lengthy molecular simulations using both hybrid QM/MM and QM/QM potentials.
NASA Astrophysics Data System (ADS)
Yu, Hua-Gen
2009-08-01
An exact variational algorithm is presented for calculating vibrational energy levels of pentaatomic molecules without any dynamical approximation. The quantum mechanical Hamiltonian of the system is expressed in a set of orthogonal coordinates defined by four scattering vectors in the body-fixed frame. The eigenvalue problem is solved using a two-layer Lanczos iterative diagonalization method in a mixed grid/basis set. A direct product potential-optimized discrete variable representation (PO-DVR) basis is used for the radial coordinates while a non-direct product finite basis representation (FBR) is employed for the angular variables. The two-layer Lanczos method requires only the actions of the Hamiltonian operator on the Lanczos vectors, where the potential-vector products are accomplished via a pseudo-spectral transform technique. By using Jacobi, Radau and orthogonal satellite vectors, we have proposed 21 types of orthogonal coordinate systems so that the algorithm is capable of describing most five-atom systems with small and/or large amplitude vibrational motions. Finally, an universal program ( PetroVib) has been developed. Its applications to the molecules CH and HO2-, and the van der Waals cluster HeCl are also discussed.
Wang, Se; Song, Xuedan; Hao, Ce; Gao, Zhanxian; Chen, Jingwen; Qiu, Jieshan
2015-03-01
Sulfadiazine (SDZ) mainly proceeds triplet-sensitized photolysis with dissolved organic matter (DOM) in the aquatic environment. However, the mechanisms underlying the triplet-sensitized photolysis of SDZ with DOM have not been fully worked out. In this study, we investigated the mechanisms of triplet-sensitized photolysis of SDZ(0) (neutral form) and SDZ(-) (anionic form) with four DOM analogues, i.e., fluorenone (FL), thioxanthone (TX), 2-acetonaphthone (2-AN), and 4-benzoylbenzoic acid (CBBP), and three metal ions (i.e., Mg(2+), Ca(2+), and Zn(2+)) effects using quantum chemical calculations. Results indicated that the triplet-sensitized photolysis mechanism of SDZ(0) with FL, TX, and 2-AN was hydrogen transfer, and with CBBP was electron transfer along with proton transfer (for complex SDZ(0)-CBBP2) and hydrogen transfer (for complex SDZ(0)-CBBP1). The triplet-sensitized photolysis mechanisms of SDZ(-) with FL, TX, and CBBP was electron transfer along with proton transfer, and with 2-AN was hydrogen transfer. The triplet-sensitized photolysis product of both SDZ(0) and SDZ(-) was a sulfur dioxide extrusion product (4-(2-iminopyrimidine-1(2H)-yl)aniline), but the formation routs of the products for SDZ(0) and SDZ(-) were different. In addition, effects of the metal ions on the triplet-sensitized photolysis of SDZ(0) and SDZ(-) were different. The metal ions promoted the triplet-sensitized photolysis of SDZ(0), but inhibited the triplet-sensitized photolysis of SDZ(-).
NASA Astrophysics Data System (ADS)
Enrique-Romero, J.; Rimola, A.; Ceccarelli, C.; Balucani, N.
2016-06-01
Complex Organic Molecules (COMs) have been detected in the interstellar medium (ISM). However, it is not clear whether their synthesis occurs on the icy surfaces of interstellar grains or via a series of gas-phase reactions. As a test case of the COMs synthesis in the ISM, we present new quantum chemical calculations on the formation of acetaldehyde (CH3CHO) from the coupling of the HCO and CH3 radicals, both in gas phase and on water ice surfaces. The binding energies of HCO and CH3 on the amorphous water ice were also computed (2333 and 734 K, respectively). Results indicate that, in gas phase, the products could be either CH3CHO, CH4 + CO, or CH3OCH, depending on the relative orientation of the two radicals. However, on the amorphous water ice, only the CH4 + CO product is possible due to the geometrical constraints imposed by the water ice surface. Therefore, acetaldehyde cannot be synthesized by the CH3 + HCO coupling on the icy grains. We discuss the implications of these results and other cases, such as ethylene glycol and dimethyl ether, in which similar situations can occur, suggesting that formation of these molecules on the grain surfaces might be unlikely.
Plaschke, M; Rothe, J; Armbruster, M K; Denecke, M A; Naber, A; Geckeis, H
2010-03-01
Humic acids (HA) have a high binding capacity towards traces of toxic metal cations, thus affecting their transport in aquatic systems. Eu(III)-HA aggregates are studied by synchrotron-based scanning transmission X-ray microscopy (STXM) at the carbon K-edge and laser scanning luminescence microscopy (LSLM) at the (5)D(0) --> (7)F(1,2) fluorescence emission lines. Both methods provide the necessary spatial resolution in the sub-micrometre range to resolve characteristic aggregate morphologies: optically dense zones embedded in a matrix of less dense material in STXM images correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. In the C 1s-NEXAFS of metal-loaded polyacrylic acid (PAA), used as a HA model compound, a distinct complexation effect is identified. This effect is similar to trends observed in the dense fraction of HA/metal cation aggregates. The strongest complexation effect is observed for the Zr(IV)-HA/PAA system. This effect is confirmed by quantum chemical calculations performed at the ab initio level for model complexes with different metal centres and complex geometries. Without the high spatial resolution of STXM and LSLM and without the combination of molecular modelling with experimental results, the different zones indicating a ;pseudo'-phase separation into strong complexing domains and weaker complexing domains of HA would never have been identified. This type of strategy can be used to study metal interaction with other organic material.
Auxiliary-field-based trial wave functions in quantum Monte Carlo calculations
Chang, Chia -Chen; Rubenstein, Brenda M.; Morales, Miguel A.
2016-12-19
Quantum Monte Carlo (QMC) algorithms have long relied on Jastrow factors to incorporate dynamic correlation into trial wave functions. While Jastrow-type wave functions have been widely employed in real-space algorithms, they have seen limited use in second-quantized QMC methods, particularly in projection methods that involve a stochastic evolution of the wave function in imaginary time. Here we propose a scheme for generating Jastrow-type correlated trial wave functions for auxiliary-field QMC methods. The method is based on decoupling the two-body Jastrow into one-body projectors coupled to auxiliary fields, which then operate on a single determinant to produce a multideterminant trial wavemore » function. We demonstrate that intelligent sampling of the most significant determinants in this expansion can produce compact trial wave functions that reduce errors in the calculated energies. Lastly, our technique may be readily generalized to accommodate a wide range of two-body Jastrow factors and applied to a variety of model and chemical systems.« less
Auxiliary-field-based trial wave functions in quantum Monte Carlo calculations
Chang, Chia -Chen; Rubenstein, Brenda M.; Morales, Miguel A.
2016-12-19
Quantum Monte Carlo (QMC) algorithms have long relied on Jastrow factors to incorporate dynamic correlation into trial wave functions. While Jastrow-type wave functions have been widely employed in real-space algorithms, they have seen limited use in second-quantized QMC methods, particularly in projection methods that involve a stochastic evolution of the wave function in imaginary time. Here we propose a scheme for generating Jastrow-type correlated trial wave functions for auxiliary-field QMC methods. The method is based on decoupling the two-body Jastrow into one-body projectors coupled to auxiliary fields, which then operate on a single determinant to produce a multideterminant trial wave function. We demonstrate that intelligent sampling of the most significant determinants in this expansion can produce compact trial wave functions that reduce errors in the calculated energies. Lastly, our technique may be readily generalized to accommodate a wide range of two-body Jastrow factors and applied to a variety of model and chemical systems.
Swails, Jason; Zhu, Tong; He, Xiao; Case, David A
2015-10-01
We evaluate the performance of the automated fragmentation quantum mechanics/molecular mechanics approach (AF-QM/MM) on the calculation of protein and nucleic acid NMR chemical shifts. The AF-QM/MM approach models solvent effects implicitly through a set of surface charges computed using the Poisson-Boltzmann equation, and it can also be combined with an explicit solvent model through the placement of water molecules in the first solvation shell around the solute; the latter substantially improves the accuracy of chemical shift prediction of protons involved in hydrogen bonding with solvent. We also compare the performance of AF-QM/MM on proteins and nucleic acids with two leading empirical chemical shift prediction programs SHIFTS and SHIFTX2. Although the empirical programs outperform AF-QM/MM in predicting chemical shifts, the differences are in some cases small, and the latter can be applied to chemical shifts on biomolecules which are outside the training set employed by the empirical programs, such as structures containing ligands, metal centers, and non-standard residues. The AF-QM/MM described here is implemented in version 5 of the SHIFTS software, and is fully automated, so that only a structure in PDB format is required as input.
Accurate quantum calculation of the bound and resonant rovibrational states of Li-(H2)
NASA Astrophysics Data System (ADS)
Xiao, Yingsheng; Poirier, Bill
2005-03-01
In a recent paper [B. Poirier, Chem. Phys. 308, 305 (2005)] a full-dimensional quantum method for computing the rovibrational dynamics of triatomic systems was presented, incorporating three key features: (1) exact analytical treatment of Coriolis coupling, (2) three-body "effective potential," and (3) a single bend angle basis for all rotational states. In this paper, these ideas are applied to the Li-(H2) electrostatic complex, to compute all of the rovibrational bound state energies, and a number of resonance energies and widths, to very high accuracy (thousandths of a wave number). This application is very challenging, owing to the long-range nature of the interaction and to narrow level spacings near dissociation. Nevertheless, by combining the present method with a G4 symmetry-adapted phase-space-optimized representation, only modest basis sizes are required for which the matrices are amenable to direct diagonalization. Several new bound levels are reported, as compared with a previous calculation [D. T. Chang, G. Surratt, G. Ristroff, and G. I. Gellene, J. Chem. Phys. 116, 9188 (2002)]. The resonances exhibit a clear-cut separation into shape and Feshbach varieties, with the latter characterized by extremely long lifetimes (microseconds or longer).
New Insights To Simulate the Luminescence Properties of Pt(II) Complexes Using Quantum Calculations.
Massuyeau, Florian; Faulques, Eric; Latouche, Camille
2017-03-24
The present manuscript reports a thorough quantum investigation on the luminescence properties of three monoplatinum(II) complexes. First, the simulated bond lengths at the ground state are compared to the observed ones, and the simulated electronic transitions are compared to the reported ones in the literature in order to assess our methodology. In a second time we show that geometries from the first triplet excited state are similar to the ground state ones. Simulations of the phosphorescence spectra from the first triplet excited states have been performed taking into account the vibronic coupling effects together with mode-mixing (Dushinsky) and solvent effects. Our simulations are compared with the observed ones already reported in the literature and are in good agreement. The calculations demonstrate that the normal modes of low energy are of great importance on the phosphorescence signature. When temperature effects are taken into account, the simulated phosphorescence spectra are drastically improved. An analysis of the computational time shows that the vibronic coupling simulation is cost-effective and thus can be extended to treat large transition metal complexes. In addition to the intrinsic importance of the investigated targets, this work provides a robust method to simulate phosphorescence spectra and to increase the duality experiment-theory.
Gagnon, Jean-Sebastien; Jeon, Sangyong
2007-01-15
Using diagrammatic methods, we show how the Ward identity can be used to constrain the ladder kernel in transport coefficient calculations. More specifically, we use the Ward identity to determine the necessary diagrams that must be resummed using an integral equation. One of our main results is an equation relating the kernel of the integral equation with functional derivatives of the full self-energy; it is similar to what is obtained with two-particle irreducible (2PI) effective action methods. However, since we use the Ward identity as our starting point, gauge invariance is preserved. Using power counting arguments, we also show which self-energies must be included in the resummation at leading order, including 2 to 2 scatterings and 1 to 2 collinear scatterings with the Landau-Pomeranchuk-Migdal effect. We show that our quantum field theory result is equivalent to the one of Arnold, Moore, and Yaffe obtained using effective kinetic theory. In this paper we restrict our discussion to electrical conductivity in hot QED, but our method can in principle be generalized to other transport coefficients and other theories.
NASA Technical Reports Server (NTRS)
Dickerson, R. R.; Stedman, D. H.; Chameides, W. L.; Crutzen, P. J.; Fishman, J.
1979-01-01
The paper presents an experimental technique which measures j/O3-O(1-D)/, the rate of solar photolysis of ozone to singlet oxygen atoms. It is shown that a flow actinometer carries dilute O3 in N2O into direct sunlight where the O(1D) formed reacts with N2O to form NO which chemiluminescence detects, with a time resolution of about one minute. Measurements indicate a photolysis rate of 1.2 (+ or - .2) x 10 to the -5/s for a cloudless sky, 45 deg zenith angle, 0.345 cm ozone column and zero albedo. Finally, ground level results compare with theoretical calculations based on the UV actinic flux as a function of ozone column and solar zenith angle.
Hahn, M.; Novotný, O.; Savin, D. W.; Badnell, N. R.; Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A.; Lestinsky, M.; Müller, A.; Schippers, S.
2014-06-10
We have measured dielectronic recombination (DR) for Fe{sup 12+} forming Fe{sup 11+} using the heavy ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Using our results, we have calculated a plasma rate coefficient from these data that can be used for modeling astrophysical and laboratory plasmas. For the low temperatures characteristic of photoionized plasmas, the experimentally derived rate coefficient is orders of magnitude larger than the previously recommended atomic data. The existing atomic data were also about 40% smaller than our measurements at temperatures relevant for collisionally ionized plasmas. Recent state-of-the-art theory has difficulty reproducing the detailed energy dependence of the DR spectrum. However, for the Maxwellian plasma rate coefficient, recent theoretical results agree with our measurements to within about 30% for both photoionized and collisionally ionized plasmas.
NASA Astrophysics Data System (ADS)
Egawa, Toru; Kachi, Yukari; Takeshima, Tsuguhide; Takeuchi, Hiroshi; Konaka, Shigehiro
2003-10-01
The molecular structure and conformation of carvone, a compound with a minty odor, were investigated by means of gas electron diffraction supported by theoretical calculations. Electron diffraction patterns were recorded by heating the nozzle up to 128 °C to obtain enough scattering intensity. The infrared spectrum was also measured by using an absorption cell with a path length of 10 m. The obtained molecular scattering intensities were analyzed with the aid of theoretical calculations and infrared spectroscopy. It was revealed that the experimental data are well reproduced by assuming that carvone consists of a mixture of three conformers that have the isopropenyl group in the equatorial position and mutually differ in the torsional angle around the single bond connecting the ring and the isopropenyl group. It was also found that the puckering amplitude of the ring of carvone is close to those of menthol and isomenthol, a minty compound and its nonminty isomer. The determined structural parameters ( rg and ∠ α) of the most abundant conformer of carvone are as follows: < r(C-C)>=1.520(3) Å; < r(CC)>=1.360(5) Å; r(CO)=1.225(5) Å; < r(C-H)>=1.104(4)Å; <∠CC-C>=121.1(5)°; <∠C-C-C>=110.4(5)°; ∠C-CO-C=117.1(14)°; <∠C-C-H>=111.1(13)°. Angle brackets denote average values and parenthesized values are the estimated limits of error (3 σ) referring to the last significant digit.
NASA Astrophysics Data System (ADS)
Finkelstein, Noah; Hoehn, Jessica
2017-01-01
Learning quantum mechanics requires students to develop not only new mathematical skills and conceptual understanding, but also has students reason about what these mean and how to organize understanding of quantum mechanical principles, tools and concepts. Towards this instructional goal, we present current research that examines how students make interpretations, probes understanding of student ontologies, and curricula that explicitly addresses interpretation of quantum phenomena and student reasoning structures (ontologies).
Jiang, Junhang; Zheng, Canhui; Zhu, Kongkai; Liu, Jia; Sun, Nannan; Wang, Chongqing; Jiang, Hualiang; Zhu, Ju; Luo, Cheng; Zhou, Youjun
2015-03-12
A potent combretastatin A-4 (CA-4) like tubulin polymerization inhibitor 22b was found with strong antitumor activity previously. However, it easily undergoes cis-trans isomerization under natural light, and the resulting decrease in activity limits its further applications. In this study, we used quantum chemistry calculations to explore the molecular basis of its instability. Aided by the calculations, two rounds of structural optimization of 22b were conducted. Accelerated quantitative light stability testing confirmed that the stability of these designed compounds was significantly improved as predicted. Among them, compounds 1 and 3b displayed more potent inhibitory activity on tumor cell growth than 22b. In addition, the potent in vivo antitumor activity of compound 1 was confirmed. Quantum chemistry calculations were used in the optimization of stilbene-like molecules, providing new insight into stilbenoid optimization and important implications for the future development of novel CA-4-like tubulin polymerization inhibitors.
NASA Technical Reports Server (NTRS)
Thibault, Franck; Boulet, Christian; Ma, Qiancheng
2014-01-01
We present quantum calculations of the relaxation matrix for the Q branch of N2 at room temperature using a recently proposed N2-N2 rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility. This has been done using complementary calculations based on the energy corrected sudden formalism. Agreement of these quantum predictions with experimental data is good, but the main goal of this work is to provide a benchmark relaxation matrix for testing more approximate methods which remain of a great utility for complex molecular systems at room (and higher) temperatures.
Thibault, Franck; Boulet, Christian; Ma, Qiancheng
2014-01-28
We present quantum calculations of the relaxation matrix for the Q branch of N{sub 2} at room temperature using a recently proposed N{sub 2}-N{sub 2} rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10 200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility. This has been done using complementary calculations based on the energy corrected sudden formalism. Agreement of these quantum predictions with experimental data is good, but the main goal of this work is to provide a benchmark relaxation matrix for testing more approximate methods which remain of a great utility for complex molecular systems at room (and higher) temperatures.
Bovino, S.; Gianturco, F. A.; Stoecklin, T.
2010-01-10
To better understand the overall role of lithium chemistry in the early universe, reactive quantum calculations involving LiH{sup +} have been carried out and rate coefficients have been obtained. The reactive quantum calculations have been performed using a negative imaginary potential method. Infinite-order sudden approximation and the coupled state approximation have been used to simplify the angular coupling dynamics. Rate coefficients are obtained from the reactive cross sections by further integration over Boltzmann distribution of velocities. The results from the present calculations suggest that, at low redshifts (z), LiH{sup +} should be amenable to observation as imprinted on the cosmic background radiation, in contrast with its neutral counterpart. At higher z, the ionic species may disappear through both depletion reaction and three-body break-up processes.
Spin-glass behavior of Sn0.9Fe3.1N: An experimental and quantum-theoretical study
NASA Astrophysics Data System (ADS)
Scholz, Tanja; Dronskowski, Richard
2016-05-01
Based on comprehensive experimental and quantum-theoretical investigations, we identify Sn0.9Fe3.1N as a canonical spin glass and the first ternary iron nitride with a frustrated spin ground state. Sn0.9Fe3.1N is the end member of the solid solution SnxFe4-xN (0 < x ≤ 0.9) derived from ferromagnetic γ'-Fe4N. Within the solid solution, the gradual incorporation of tin is accompanied by a drastic weakening of the ferromagnetic interactions. To explore the dilution of the ferromagnetic coupling, the highly tin-substituted Sn0.9Fe3.1N has been magnetically reinvestigated. DC magnetometry reveals diverging susceptibilities for FC and ZFC measurements at low temperatures and an unsaturated hysteretic loop even at high magnetic fields. The temperature dependence of the real component of the AC susceptibility at different frequencies proves the spin-glass transition with the characteristic parameters Tg = 12.83(6) K, τ* = 10-11.8(2) s, zv = 5.6(1) and ΔTm/(Tm ṡ Δlgω) = 0.015. The time-dependent response of the magnetic spins to the external field has been studied by extracting the distribution function of relaxation times g(τ, T) up to Tg from the complex plane of AC susceptibilities. The weakening of the ferromagnetic coupling by substituting tin into γ'-Fe4N is explained by the Stoner criterion on the basis of electronic structure calculations and a quantum-theoretical bonding analysis.
NASA Astrophysics Data System (ADS)
Baer, Michael; Niedner, Gereon; Toennies, J. Peter
1988-06-01
A 3-D quantum mechanical close coupling study for the system H(+) +H2 is communicated. The quantum calculations, caried out in the finite order swiden approximation, show a better fit to previous experiments than the classical trajectory surface hopping (TSH) calculations, and provide direct evidence for the usefulness of a quantum treatment in predicting charge transfer (CT) processes. The total differential cross sections (summed over all final vibrational states) for the CT processes were calculated, in good agreement with experimental results. It is shown that a quantum mechanical treatment of both the inelastic and the charge transfer nonadiabatic processes is feasible and provides a superior description of the experiments compared to the TSH treatment. This demonstrates the importance of quantum effects in ion-molecule charge transfer.
NASA Astrophysics Data System (ADS)
Khan, A.; Yoshimura, B.; Freericks, J. K.
2015-10-01
One of the challenges with quantum simulation in ion traps is that the effective spin-spin exchange couplings are not uniform across the lattice. This can be particularly important in Penning-trap realizations where the presence of an ellipsoidal boundary at the edge of the trap leads to dislocations in the crystal. By adding an additional anharmonic potential to better control interion spacing, and a triangular-shaped rotating wall potential to reduce the appearance of dislocations, one can achieve better uniformity of the ionic positions. In this work, we calculate the axial phonon frequencies and the spin-spin interactions driven by a spin-dependent optical dipole force, and discuss what effects the more uniform ion spacing have on the spin simulation properties of Penning-trap quantum simulators. Indeed, we find that the spin-spin interactions behave more like a power law for a wide range of parameters.
NASA Astrophysics Data System (ADS)
Shilova, S. V.; Romanova, K. A.; Galyametdinov, Yu. G.; Tret'yakova, A. Ya.; Barabanov, V. P.
2016-06-01
The complexing of protonated chitosan with dodecyl sulfate ions in water solutions is studied using IR spectroscopy data and quantum-chemical calculations. It is established that the electrostatic interaction between the protonated amino groups of chitosan and dodecyl sulfate ions is apparent in the IR spectrum as a band at 833 cm-1. The need to consider the effect the solvent has on the formation of hydrogen-bound ion pairs [CTS+ ṡ C12H25O 3 - ] is shown via a quantum-chemical simulation of the equilibrium geometry and the energy characteristics of complexing and hydration.
Nanowire terahertz quantum cascade lasers
Grange, Thomas
2014-10-06
Quantum cascade lasers made of nanowire axial heterostructures are proposed. The dissipative quantum dynamics of their carriers is theoretically investigated using non-equilibrium Green functions. Their transport and gain properties are calculated for varying nanowire thickness, from the classical-wire regime to the quantum-wire regime. Our calculation shows that the lateral quantum confinement provided by the nanowires allows an increase of the maximum operation temperature and a strong reduction of the current density threshold compared to conventional terahertz quantum cascade lasers.
NASA Technical Reports Server (NTRS)
Sun, Yan; Yu, Chin-Hui; Kouri, Donald J.; Schwenke, David W.; Halvick, Philippe
1989-01-01
A new formalism of the generalized Newton variational principle for the calculation of quantum mechanical state-to-state reaction probabilities is presented. The reformulation involves solving directly for the transition matrix rather than the reactance mtrix so that calculations may be carried out for individual columns of the transition matrix without obtaining solutions for all possible initial channels. The convergence of calculations with real and complex boundary conditions are compared for H + H2 - H2 + H, O + H2 - OH + H, and O + HD - OH + D and OD + H.
Cortés-Arriagada, Diego; Villegas-Escobar, Nery; Miranda-Rojas, Sebastián; Toro-Labbé, Alejandro
2017-02-08
The interaction of formaldehyde (H2CO) onto Fe-doped graphene (FeG) was studied in detail from density functional theory calculations and electronic structure analyses. Our aim was to obtain insights into the adsorption, desorption and sensing properties of FeG towards H2CO, a hazardous organic compound. The adsorption of H2CO was shown to be energetically stable onto FeG, with adsorption energies of up to 1.45 eV and favored in different conformations. This interaction was determined to be mostly electrostatic in nature, where the oxygen plays an important role in this contribution; besides, our quantum molecular dynamics results showed the high stability of the FeG-H2CO interaction at ambient temperature (300 K). All the interactions were determined to be accompanied by an increase in the HOMO-LUMO energy gap with respect to the isolated adsorbent, indicating that FeG is highly sensitive to H2CO with respect to pristine graphene. Finally, it was found that external electric fields of 0.04-0.05 a.u. were able to induce the pollutant desorption from the adsorbent, allowing the adsorbent reactivation for repetitive applications. These results indicate that FeG could be a promising candidate for adsorption/sensing platforms of H2CO.
NASA Astrophysics Data System (ADS)
Yu, Shujun; Wang, Xiangxue; Zhang, Rui; Yang, Tongtong; Ai, Yuejie; Wen, Tao; Huang, Wei; Hayat, Tasawar; Alsaedi, Ahmed; Wang, Xiangke
2017-01-01
Although graphene oxide (GO) has been used in multidisciplinary areas due to its excellent physicochemical properties, its environmental behavior and fate are still largely unclear. In this study, batch experiments, spectroscopy analysis and theoretical calculations were addressed to promote a more comprehensive understanding toward the coagulation behavior of GO onto TiO2 under various environmental conditions (pH, co-existing ions, temperature, etc.). The results indicated that neutral pH was beneficial to the removal of GO due to the electrostatic interaction. The presence of cations accelerated GO coagulation significantly owing to the influence of electrical double layer compression. On the contrary, the presence of anions improved the stability of GO primarily because of electrostatic repulsion and steric hindrance. Results of XRD, FTIR and XPS analysis indicated that the coagulation of GO on TiO2 was mainly dominated by electrostatic interactions and hydrogen bonds, which were further evidenced by DFT calculations. The high binding energy further indicated the stability of GO + TiO2 system, suggesting that TiO2 can be used as an effective coagulant for the efficient elimination and coagulation of GO from aqueous solutions. These findings might likely lead to a better understanding of the migration and transformation of carbon nanomaterials in the natural environment.
Yu, Shujun; Wang, Xiangxue; Zhang, Rui; Yang, Tongtong; Ai, Yuejie; Wen, Tao; Huang, Wei; Hayat, Tasawar; Alsaedi, Ahmed; Wang, Xiangke
2017-01-03
Although graphene oxide (GO) has been used in multidisciplinary areas due to its excellent physicochemical properties, its environmental behavior and fate are still largely unclear. In this study, batch experiments, spectroscopy analysis and theoretical calculations were addressed to promote a more comprehensive understanding toward the coagulation behavior of GO onto TiO2 under various environmental conditions (pH, co-existing ions, temperature, etc.). The results indicated that neutral pH was beneficial to the removal of GO due to the electrostatic interaction. The presence of cations accelerated GO coagulation significantly owing to the influence of electrical double layer compression. On the contrary, the presence of anions improved the stability of GO primarily because of electrostatic repulsion and steric hindrance. Results of XRD, FTIR and XPS analysis indicated that the coagulation of GO on TiO2 was mainly dominated by electrostatic interactions and hydrogen bonds, which were further evidenced by DFT calculations. The high binding energy further indicated the stability of GO + TiO2 system, suggesting that TiO2 can be used as an effective coagulant for the efficient elimination and coagulation of GO from aqueous solutions. These findings might likely lead to a better understanding of the migration and transformation of carbon nanomaterials in the natural environment.
Park, Hanwool
2016-01-01
Abstract Microalgae have long been considered as one of most promising feedstocks with better characteristics for biofuels production over conventional energy crops. There have been a wide range of estimations on the feasibility of microalgal biofuels based on various productivity assumptions and data from different scales. The theoretical maximum algal biofuel productivity, however, can be calculated by the amount of solar irradiance and photosynthetic efficiency (PE), assuming other conditions are within the optimal range. Using the actual surface solar irradiance data around the world and PE of algal culture systems, maximum algal biomass and biofuel productivities were calculated, and feasibility of algal biofuel were assessed with the estimation. The results revealed that biofuel production would not easily meet the economic break‐even point and may not be sustainable at a large‐scale with the current algal biotechnology. Substantial reductions in the production cost, improvements in lipid productivity, recycling of resources, and utilization of non‐conventional resources will be necessary for feasible mass production of algal biofuel. Among the emerging technologies, cultivation of microalgae in the ocean shows great potentials to meet the resource requirements and economic feasibility in algal biofuel production by utilizing various marine resources. PMID:27782372
Park, Hanwool; Lee, Choul-Gyun
2016-11-01
Microalgae have long been considered as one of most promising feedstocks with better characteristics for biofuels production over conventional energy crops. There have been a wide range of estimations on the feasibility of microalgal biofuels based on various productivity assumptions and data from different scales. The theoretical maximum algal biofuel productivity, however, can be calculated by the amount of solar irradiance and photosynthetic efficiency (PE), assuming other conditions are within the optimal range. Using the actual surface solar irradiance data around the world and PE of algal culture systems, maximum algal biomass and biofuel productivities were calculated, and feasibility of algal biofuel were assessed with the estimation. The results revealed that biofuel production would not easily meet the economic break-even point and may not be sustainable at a large-scale with the current algal biotechnology. Substantial reductions in the production cost, improvements in lipid productivity, recycling of resources, and utilization of non-conventional resources will be necessary for feasible mass production of algal biofuel. Among the emerging technologies, cultivation of microalgae in the ocean shows great potentials to meet the resource requirements and economic feasibility in algal biofuel production by utilizing various marine resources.
Yu, Shujun; Wang, Xiangxue; Zhang, Rui; Yang, Tongtong; Ai, Yuejie; Wen, Tao; Huang, Wei; Hayat, Tasawar; Alsaedi, Ahmed; Wang, Xiangke
2017-01-01
Although graphene oxide (GO) has been used in multidisciplinary areas due to its excellent physicochemical properties, its environmental behavior and fate are still largely unclear. In this study, batch experiments, spectroscopy analysis and theoretical calculations were addressed to promote a more comprehensive understanding toward the coagulation behavior of GO onto TiO2 under various environmental conditions (pH, co-existing ions, temperature, etc.). The results indicated that neutral pH was beneficial to the removal of GO due to the electrostatic interaction. The presence of cations accelerated GO coagulation significantly owing to the influence of electrical double layer compression. On the contrary, the presence of anions improved the stability of GO primarily because of electrostatic repulsion and steric hindrance. Results of XRD, FTIR and XPS analysis indicated that the coagulation of GO on TiO2 was mainly dominated by electrostatic interactions and hydrogen bonds, which were further evidenced by DFT calculations. The high binding energy further indicated the stability of GO + TiO2 system, suggesting that TiO2 can be used as an effective coagulant for the efficient elimination and coagulation of GO from aqueous solutions. These findings might likely lead to a better understanding of the migration and transformation of carbon nanomaterials in the natural environment. PMID:28045053
Hendry, Robin Findlay
2003-05-01
The emergence of quantum chemistry in the early twentieth century was an international as well as an interdisciplinary affair, involving dialogue between physicists and chemists in Germany, the United States, and Britain. Historians of science have recently documented both the causes and effects of this internationalism and interdisciplinarity. Chemists and physicists involved in the development of quantum chemistry in its first few decades tended to argue for opposing views on acceptable standards of explanation in their field, although the debate did not divide along disciplinary lines. The purpose of this paper is to investigate these different positions, through the methodological reflections of John Clarke Slater, Linus Pauling, and Charles Coulson. Slater tended to argue for quantum-mechanical rigor and the application of fundamental principles as the values guiding models of molecular bonding. Although they were on different sides of the debate between the valence-bond and molecular-orbital approaches, Pauling and Coulson both emphasized the recovery of traditional chemical explanations and systematic explanatory power within chemistry.
A theoretical study of perovskite CsXCl3 (X=Pb, Cd) within first principles calculations
NASA Astrophysics Data System (ADS)
Ilyas, Bahaa M.; Elias, Badal H.
2017-04-01
The structural, elastic, electronic, optical acoustic and thermodynamic properties of the cubic perovskite CsPbCl3 and CsCdCl3 unit cell, were studied using an ultra-soft pseudopotential plane wave, the Trouiller-Martins-Functional was utilized to perform these calculations. The study was implemented within both the Local Density Approximation (LDA) and the Generalized Gradient Approximation (GGA). the Generalized Gradient Approximation (GGA) scheme proposed by van Leeuwen-Baerends which is the same as the Perdew-Wang 92 functional have been carried out to preform our calculations. As for the Local Density Approximation (LDA) the Teter-Pade parametrization (4/93) was implemented which is the same as Perdew-Wang that in its turn reproduces the Ceperley-Alder-Functional. The computed GGA/LDA-lattice parameter for both CsCdCl3 and CsPbCl3 is in an exquisite agreement with the experimental and theoretical results. The energy band structure shows that CsCdCl3 is Γ-R indirect band gap insulator, while CsPbCl3 is an insulator with a direct band gap Γ-Γ separating the valence bands from the conduction bands, which shows metallic nature after pressure 30 GPa. A hybridization exists between Pb-p states and Cl-p states for CsPbCl3, and Cd-p states and Cs-p states for the CsCdCl3 in the valence bonding region. Optimization of both cell shape (geometry) volume were investigated as pressure of 0-20 GPa and 0-40 GPa for the CsCdCl3 and CsPbCl3 respectively. The Pressure dependence of cubic perovskite elastic constants, Young modulus, bulk and shear moduli, Lame's constants, elastic anisotropy factor, elastic wave velocities, phonon dispersion, Debye temperature and the density of states of CsXCl3 (X=Pb, Cd) were theoretically calculated and compared with the other available theoretical results. The above elastic constants reveal the fact that both compounds are stable and show nature of ductility. For the optical properties, both the static refractive index and dielectric
Aragó, Juan; Ponce Ortiz, Rocío; Nieto-Ortega, Belén; Hernández, Víctor; Casado, Juan; Facchetti, Antonio; Marks, Tobin J; Viruela, Pedro M; Ortí, Enrique; López Navarrete, Juan T
2012-01-16
This work investigates the evolution of the molecular, vibrational, and optical properties within a family of carbonyl-functionalized quaterthiophenes: 5,5'''-diheptanoyl-2,2':5',2'':5'',2'''-quaterthiophene (1), 5,5'''-diperfluorohexylcarbonyl-2,2':5',2'':5'',2'''-quaterthiophene (2), and 2,7-[bis(5-perfluorohexylcarbonylthien-2-yl)]-4H-cyclopenta[2,1-b:3,4-b']-dithiophene-4-one (3). The analysis is performed by Raman and UV/Vis absorption/excitation/fluorescence spectroscopy in combination with density functional calculations. Theoretical calculations show that substitution with carbonyl groups and perfluorohexyl chains induces progressive quinoidization of the π-conjugated backbone in comparison to the carbonyl-free compound 5,5'''-dimethyl-2,2':5',2'':5'',2'''-quaterthiophene (DM-4T) used as reference. Raman spectra are dominated by a strong Raman line which mainly corresponds to a combination of C-C/C=C stretching vibrations spreading over the whole thiophene core. This band undergoes a remarkable downshift as a consequence of the structural changes induced by the electron-withdrawing groups on the π-conjugated backbone. The band splitting on incorporation of a central carbonyl bridge evidences the formation of two structural domains in the molecule. The excitation and fluorescence spectra recorded at low temperature show well-resolved vibronic structures associated with the most intense collective C-C/C=C stretching mode. Optical absorption and fluorescence bands exhibit remarkable bathochromic dispersion on carbonyl functionalization, indicative of extension of π conjugation. TDDFT calculations enable a detailed description of the trends observed in the absorption spectra. Resonance Raman spectra reflect the structural changes predicted for the S(0)→S(1) electronic transition and evidence the cross-conjugated character that the central carbonyl group confers on 3.
NASA Astrophysics Data System (ADS)
Dattani, Nikesh S.
2013-12-01
This MATLAB program calculates the dynamics of the reduced density matrix of an open quantum system modeled either by the Feynman-Vernon model or the Caldeira-Leggett model. The user gives the program a Hamiltonian matrix that describes the open quantum system as if it were in isolation, a matrix of the same size that describes how that system couples to its environment, and a spectral distribution function and temperature describing the environment’s influence on it, in addition to the open quantum system’s initial density matrix and a grid of times. With this, the program returns the reduced density matrix of the open quantum system at all moments specified by that grid of times (or just the last moment specified by the grid of times if the user makes this choice). This overall calculation can be divided into two stages: the setup of the Feynman integral, and the actual calculation of the Feynman integral for time propagation of the density matrix. When this program calculates this propagation on a multi-core CPU, it is this propagation that is usually the rate-limiting step of the calculation, but when it is calculated on a GPU, the propagation is calculated so quickly that the setup of the Feynman integral can actually become the rate-limiting step. The overhead of transferring information from the CPU to the GPU and back seems to have a negligible effect on the overall runtime of the program. When the required information cannot fit on the GPU, the user can choose to run the entire program on a CPU. Catalogue identifier: AEPX_v1_0. Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPX_v1_0.html. Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland. Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html. No. of lines in distributed program, including test data, etc.: 703. No. of bytes in distributed program, including test data, etc.: 11026. Distribution format: tar.gz. Programming
Ferenczy, György G
2013-04-05
Mixed quantum mechanics/quantum mechanics (QM/QM) and quantum mechanics/molecular mechanics (QM/MM) methods make computations feasible for extended chemical systems by separating them into subsystems that are treated at different level of sophistication. In many applications, the subsystems are covalently bound and the use of frozen localized orbitals at the boundary is a possible way to separate the subsystems and to ensure a sensible description of the electronic structure near to the boundary. A complication in these methods is that orthogonality between optimized and frozen orbitals has to be warranted and this is usually achieved by an explicit orthogonalization of the basis set to the frozen orbitals. An alternative to this approach is proposed by calculating the wave-function from the Huzinaga equation that guaranties orthogonality to the frozen orbitals without basis set orthogonalization. The theoretical background and the practical aspects of the application of the Huzinaga equation in mixed methods are discussed. Forces have been derived to perform geometry optimization with wave-functions from the Huzinaga equation. Various properties have been calculated by applying the Huzinaga equation for the central QM subsystem, representing the environment by point charges and using frozen strictly localized orbitals to connect the subsystems. It is shown that a two to three bond separation of the chemical or physical event from the frozen bonds allows a very good reproduction (typically around 1 kcal/mol) of standard Hartree-Fock-Roothaan results. The proposed scheme provides an appropriate framework for mixed QM/QM and QM/MM methods.
Mariappan Balasekaran, Samundeeswari; Todorova, Tanya K.; Pham, Chien Thang; Hartmann, Thomas; Abram, Ulrich; Sattelberger, Alfred P.; Poineau, Frederic
2016-06-06
A simple method for the high-yield preparation of (NH_{4})_{2}[Re_{2}F_{8}]· 2H_{2}O has been developed that involves the reaction of (n-Bu_{4}N)2[Re_{2}Cl_{8}] with molten ammonium bifluoride (NH_{4}HF_{2}). Using this method, the new salt [NH_{4}]_{2}[Re_{2}F_{8}]·2H_{2}O was prepared in ~90% yield. The product was characterized in solution by ultraviolet-visible light (UV-vis) and ^{19}F nuclear magnetic resonance (19F NMR) spectroscopies and in the solid-state by elemental analysis, powder X-ray diffraction (XRD), and infrared (IR) spectroscopy. Multiconfigurational CASSCF/CASPT2 quantum chemical calculations were performed to investigate the molecular and electronic structure, as well as the electronic absorption spectrum of the [Re_{2}F_{8}] ^{2-} anion. The metal-metal bonding in the Re_{2} ^{6+} unit was quantified in terms of effective bond order (EBO) and compared to that of its [Re_{2}Cl_{8}] ^{2-} and [Re_{2}Br_{8}] ^{2-} analogues.
Quantum Monte Carlo calculations of three and six-quark states
NASA Astrophysics Data System (ADS)
Paris, Mark Wayne
2001-06-01
Quantum Monte Carlo techniques are applied to quark descriptions of single baryon and nuclear systems using a non-relativistic constituent quark model Hamiltonian. The assumed interaction includes a three-body term arising due to flux-tube confinement, and two-body interactions arising from one-gluon and one-pion exchange. It is strongly dependent on the spin and isospin of the quarks. We solve for single baryon S and P-wave spectra by solving the Schrödinger equation variationally for the ground state of three interacting light-flavored valence quarks. The variational Monte Carlo method is then used to find the ground state of six quarks confined to a cavity of diameter Rc. The variational wave function is written as a product of three-quark nucleon states with correlations between quarks in different nucleons. We study the role of quark exchange effects by allowing flux-tube configuration mixing. An accurate six-body variational wave function is obtained. It has only ~13% rms fluctuation in the total energy and yields a standard deviation of <=.1% small enough to be useful in discerning nuclear interaction effects from the large rest mass of the two nucleons. Results are presented for three values of the cavity diameter, R c = 2, 4, and 6 fm. They indicate that the flux-tube model Hamiltonian with gluon and pion exchange requires revisions in order to obtain agreement with the energies estimated from realistic two- nucleon interactions. We calculate the two-quark density, spin, isospin, and color distribution functions and show how they may be used to study and adjust the model Hamiltonian.
Doitomi, Kazuki; Kamachi, Takashi; Toraya, Tetsuo; Yoshizawa, Kazunari
2012-11-13
Inactivation of diol dehydratase during the glycerol dehydration reaction is studied on the basis of quantum mechanical/molecular mechanical calculations. Glycerol is not a chiral compound but contains a prochiral carbon atom. Once it is bound to the active site, the enzyme adopts two binding conformations. One is predominantly responsible for the product-forming reaction (G(R) conformation), and the other primarily contributes to inactivation (G(S) conformation). Reactant radical is converted into a product and byproduct in the product-forming reaction and inactivation, respectively. The OH group migrates from C2 to C1 in the product-forming reaction, whereas the transfer of a hydrogen from the 3-OH group of glycerol to C1 takes place during the inactivation. The activation barrier of the hydrogen transfer does not depend on the substrate-binding conformation. On the other hand, the activation barrier of OH group migration is sensitive to conformation and is 4.5 kcal/mol lower in the G(R) conformation than in the G(S) conformation. In the OH group migration, Glu170 plays a critical role in stabilizing the reactant radical in the G(S) conformation. Moreover, the hydrogen bonding interaction between Ser301 and the 3-OH group of glycerol lowers the activation barrier in G(R)-TS2. As a result, the difference in energy between the hydrogen transfer and the OH group migration is reduced in the G(S) conformation, which shows that the inactivation is favored in the G(S) conformation.
Nam, Kwangho
2013-08-13
The implementation and performance of the atom-centered density matrix propagation (ADMP) [J. Chem. Phys. 2001, 114, 9758] and the curvy-steps (CURV) methods [J. Chem. Phys. 2004, 121, 1152] are described. These methods solve the electronic Schrödinger equation approximately by propagating the electronic degrees of freedom using the extended Lagrangian molecular dynamics (ELMD) simulation approach. The ADMP and CURV methods are implemented and parallelized to accelerate semiempirical quantum mechanical (QM) methods (such as the MNDO, AM1, PM3, MNDO/d, and AM1/d methods). Test calculations show that both the ADMP and the CURV methods are 2∼4 times faster than the Born-Oppenheimer molecular dynamics (BOMD) method and conserve the total energy well. The accuracy of the ADMP and CURV simulations is comparable to the BOMD simulations. The parallel implementation accelerates the MD simulation by up to 28 fold for the ADMP method and 25 fold for the CURV method, respectively, relative to the speed of the single core BOMD. In addition, a multiple time scale (MTS) approach is introduced to further speed up the semiempirical QM and QM/MM ELMD simulations. Since a larger integration time step is used for the propagation of the nuclear coordinates than that for the electronic degrees of freedom, the MTS approach allows the ELMD simulation to be carried out with a time step that is larger than the time step accessible by the original ADMP and CURV methods. It renders MD simulation to be carried out about 20 times faster than the BOMD simulation, and yields results that are comparable to the single time scale simulation results. The use of the methods introduced in the present work provides an efficient way to extend the length of the QM and QM/MM molecular dynamics simulations beyond the length accessible by BOMD simulation.
NASA Astrophysics Data System (ADS)
Dimitriou, K. I.; Mercouris, Th.; Constantoudis, V.; Komninos, Y.; Nicolaides, C. A.
2006-05-01
The multiphoton vibrational excitation and dissociation of Morse molecules have been computed nonperturbatively using Hamilton's and Schrφdinger's time-dependent equations, for a range of laser pulse parameters. The time-dependent Schrφdinger equation is solved by the state-specific expansion approach [e.g.,1]. For its solution, emphasis has been given on the inclusion of the continuous spectrum, whose contribution to the multiphoton probabilities for resonance excitation to a number of excited discrete states as well as to dissociation has been examined as a function of laser intensity, frequency and pulse duration. An analysis of possible quantal-classical correspondences for this system is being carried out. We note that distinct features exist from previous classical calculations [2]. For example, the dependence on the laser frequency gives rise to an asymmetry around the red-shifted frequency corresponding to the maximum probability. [1] Th. Mercouris, I. D. Petsalakis and C. A. Nicolaides, J. Phys. B 27, L519 (1994). [2] V. Constantoudis and C. A. Nicolaides, Phys. Rev. E 64, 562112 (2001). ^1This work was supported by the program 'Pythagoras' which is co - funded by the European Social Fund (75%) and Natl. Resources (25%). ^2Physics Department, National Technical University, Athens, Greece.^3Theoretical and Physical Chemistry Institute, Hellenic Research Foundation, Athens, Greece.
NASA Technical Reports Server (NTRS)
Predoi-Cross, A.; Hambrook, Kyle; Brawley-Tremblay, Marco; Bouanich, J. P.; Smith, Mary Ann H.
2006-01-01
In this paper, we report measured Lorentz N2-broadening and N2-induced pressure-shift coefficients of CH3D in the v2 fundamental band using a multispectrum fitting technique. These measurements were made by analyzing 11 laboratory absorption spectra recorded at 0.0056 cm(exp -1) resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 10.2 and 25 cm. The total sample pressures ranged from 0.98 to 402.25 Torr with CH3D volume mixing ratios of 0.01 in nitrogen. We have been able to determine the N2 pressure- broadening coefficients of 368 v2 transitions with quantum numbers as high as J"= 20 and K = 16, where K" = K' equivalent to K (for a parallel band). The measured N2-broadening coefficients range from 0.0248 to 0.0742 cm(exp -1) atm(exp -1) at 296 K. All the measured pressure-shifts are negative. The reported N2-induced pressure-shift coefficients vary from about 0.0003 to 0.0094 cm(exp -1) atm(exp -1). We have examined the dependence of the measured broadening and shift parameters on the J", and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = -J", J", and J" + 1 in the (sup Q)P-, (sup Q)Q-, and (sup Q)R-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.7%. The N2-broadening and pressureshift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom atom Lennard-Jones potential. The theoretical results of the broadening coefficients are in good overall agreement with the experimental data (8.7%). The N2-pressure shifts whose vibrational contribution is derived from parameters fitted in the (sup Q)Q-branch of self-induced shifts of CH3D, are also in
Minami, Takuya; Nakano, Masayoshi
2015-01-22
Electromagnetically induced transparency (EIT), which is known as an efficient control method of optical absorption property, is investigated using the polarizability spectra and population dynamics obtained by solving the quantum Liouville equation. In order to clarify the intermolecular interaction effect on EIT, we examine several molecular aggregate models composed of three-state monomers with the dipole-dipole coupling. On the basis of the present results, we discuss the applicability of EIT in molecular aggregate systems to a new type of optical switch.
Parker, James K; Payne, Walter A; Cody, Regina J; Nesbitt, Fred L; Stief, Louis J; Klippenstein, Stephen J; Harding, Lawrence B
2007-02-15
The rate coefficient has been measured under pseudo-first-order conditions for the Cl+CH3 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 CH3 were generated rapidly and simultaneously by reaction of F with HCl and CH4, respectively. Fluorine atoms were produced by microwave discharge in an approximately 1% mixture of F2 in He. The decay of CH3 was monitored under pseudo-first-order conditions with the Cl-atom concentration in large excess over the CH3 concentration ([Cl]0/[CH3]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 8.4x10(-12) at P=0.30 Torr He to 1.8x10(-11) at P=2.00 Torr He, both in units of cm3 molecule-1 s-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 k2=6.0x10(-11) cm3 molecule-1 s-1, independent of temperature in the range from 200 to 300 K.
NASA Astrophysics Data System (ADS)
Seto, Keita; Nagatomo, Hideo; Koga, James; Mima, Kunioki
In the near future, the intensity of the ultra-short pulse laser will reach to 1022 W/cm2. When an electron is irradiated by this laser, the electron's behavior is relativistic with significant bremsstrahlung. This radiation from the electron is regarded as the energy loss of electron. Therefore, the electron's motion changes because of the kinetic energy changing. This radiation effect on the charged particle is the self-interaction, called the “radiation reaction” or the “radiation damping”. For this reason, the radiation reaction appears in laser electron interactions with an ultra-short pulse laser whose intensity becomes larger than 1022 W/cm2. In the classical theory, it is described by the Lorentz-Abraham-Dirac (LAD) equation. But, this equation has a mathematical difficulty, which we call the “run-away”. Therefore, there are many methods for avoiding this problem. However, Dirac's viewpoint is brilliant, based on the idea of quantum electrodynamics. We propose a new equation of motion in the quantum theory with radiation reaction in this paper.
Predicted phototoxicities of carbon nano-material by quantum mechanical calculations.
The basis of this research is obtaining the best quantum mechanical structure of carbon nanomaterials and is fundamental in determining their other properties. Therefore, their predictive phototoxicity is directly related to the materials’ structure. The results of this project w...
NASA Astrophysics Data System (ADS)
Silvi, Pietro; Calarco, Tommaso; Morigi, Giovanna; Montangero, Simone
2014-03-01
Ions of the same charge inside confining potentials can form crystalline structures which can be controlled by means of the ion density and of the external trap parameters. In particular, a linear chain of trapped ions exhibits a transition to a zigzag equilibrium configuration, which is controlled by the strength of the transverse confinement. Studying this phase transition in the quantum regime is a challenging problem, even when employing numerical methods to simulate microscopically quantum many-body systems. Here we present a compact analytical treatment to map the original long-range problem into a short-range quantum field theory on a lattice. We provide a complete numerical architecture, based on the density matrix renormalization group, to address the effective quantum ϕ4 model. This technique is instrumental in giving a complete characterization of the phase diagram, as well as pinpointing the universality class of the criticality.
NASA Astrophysics Data System (ADS)
Korlyukov, Alexander A.; Antipin, Mikhail Yu
2012-02-01
The review generalizes the results of structural studies of crystals of organic and organometallic compounds by modern quantum chemical calculations within the framework of the density functional theory reported in the last decade. Features of the software for such calculations are discussed. Examples of the use of quantum chemical calculations for the studies of the electronic structure, spectroscopic and other physicochemical properties of molecular crystals are presented. The bibliography includes 223 references.
NASA Technical Reports Server (NTRS)
Jaffe, Richard; Han, Jie; Yoon, Do; Langhoff, Stephen R. (Technical Monitor)
1997-01-01
The so-called oxygen gauche effect in poly(oxyethylene) (POE) and its model molecules such as 1,2-dimethoxyethane (DME) and diglyme (CH3OC2H4OC2H4OCH3) is manifested in the preference for gauche C-C bond conformations over trans. This has also been observed for poly(ethylene terephthalate) (PET). Our previous quantum chemistry calculations demonstrated that the large C-C gauche population in DME is due, in part, to a low-lying tg +/- g+ conformer that exhibits a substantial 1,5 CH ... O attraction. New calculations will be described that demonstrate the accuracy of the original quantum chemistry calculations. In addition, an extension of this work to model molecules for PET will be presented. It is seen that the C-C gauche preference is much stronger in 1,2 diacetoxyethane than in DME. In addition, there exist low-lying tg +/- g+/- and g+/-g+/-g+/- conformers that exhibit 1,5 CH ... O attractions involving the carbonyl oxygens. It is expected that the -O-C-C-O- torsional properties will be quite different in these two polymers. The quantum chemistry results are used to parameterize rotational isomeric states models (RIS) and force fields for molecular dynamics simulations of these polymers.
Carvalho, Nathália F; Pliego, Josefredo R
2016-09-16
Fluorinated organic molecules are playing an increased role in the area of pharmaceuticals and agrochemicals. This fact demands the development of efficient catalytic fluorination processes. In this paper, we have designed a new crown ether with four hydroxyl groups strategically positioned. The catalytic activity of this basic scaffold was investigated with high levels of electronic structure theory, such as the ONIOM approach combining MP4 and MP2 methods. On the basis of the calculations, this new structure is able to solubilize potassium fluoride in toluene solution much more efficiently than 18-crown-6 (18C6). In addition, the strong interaction of the new catalyst with the SN2 transition state leads to a very important catalytic effect, with a predicted free energy barrier of 23.3 kcal mol(-1) for potassium fluoride plus ethyl bromide reaction model. Compared with experimental data and previous theoretical studies, this new catalyst is 10(4) times more efficient than 18C6 for nucleophilic fluorination of alkyl halides. The catalysis is predicted to be selective, leading to 97% of fluorination and only 3% of elimination. Catalytic fluorination of the aromatic ring has also been investigated, and although the catalyst is less efficient in this case, our analysis has indicated further development of this strategy can lead to more efficient catalysis.
Quantum confined Stark effect in Gaussian quantum wells: A tight-binding study
Ramírez-Morales, A.; Martínez-Orozco, J. C.; Rodríguez-Vargas, I.
2014-05-15
The main characteristics of the quantum confined Stark effect (QCSE) are studied theoretically in quantum wells of Gaussian profile. The semi-empirical tight-binding model and the Green function formalism are applied in the numerical calculations. A comparison of the QCSE in quantum wells with different kinds of confining potential is presented.
Hagiwara, Yohsuke; Ohno, Kazuki; Orita, Masaya; Koga, Ryota; Endo, Toshio; Akiyama, Yutaka; Sekijima, Masakazu
2013-09-01
The growing power of central processing units (CPU) has made it possible to use quantum mechanical (QM) calculations for in silico drug discovery. However, limited CPU power makes large-scale in silico screening such as virtual screening with QM calculations a challenge. Recently, general-purpose computing on graphics processing units (GPGPU) has offered an alternative, because of its significantly accelerated computational time over CPU. Here, we review a GPGPU-based supercomputer, TSUBAME2.0, and its promise for next generation in silico drug discovery, in high-density (HD) silico drug discovery.
NASA Astrophysics Data System (ADS)
Tan, I.-Hsing
1992-01-01
With the success of the optoelectronic devices based on the two-dimensional (2D) quantum well, it is a natural trend to continue to reduce system's dimensionality to 1D and 0D systems. However, extrinsic fabrication defects such as process-induced damage and pattern non-uniformity and intrinsic defects such as a slower hot carrier cooling rate can render the luminescence of the wires and dots extremely poor. In this dissertation, I will show that strain modulation and low-damage dry/wet etching techniques allow one to obtain high luminescence strain-induced quantum wires (SIQWs) and dots (SIQDs) with lateral dimensions less than 100 nm. The reduction of the fabrication-induced defects has allowed us to examine the intrinsic optical properties of the SIQWs and SIQDs through the photoluminescence (PL), PL excitation (PLE), and PL decay spectroscopy. Using epitaxial InGaAs layer as a stressor, we have achieved a ~20 meV of strain modulation and a ~7 meV of subband spacing in the SIQW structures having a lateral dimension of 75 nm and have observed an increase of FL decay time in the SIQD structures. The energy shifts, subband spacing, and increased PL decay time observed in the SIQWs and SIQDs can be well interpreted by our theoretical model, based on solving both the elasticity equation as well as the Luttinger-Kohn four-band Hamiltonian including strain.
Ishida, Toyokazu; Fedorov, Dmitri G; Kitaura, Kazuo
2006-01-26
To elucidate the catalytic power of enzymes, we analyzed the reaction profile of Claisen rearrangement of Bacillus subtilis chorismate mutase (BsCM) by all electron quantum chemical calculations using the fragment molecular orbital (FMO) method. To the best of our knowledge, this is the first report of ab initio-based quantum chemical calculations of the entire enzyme system, where we provide a detailed analysis of the catalytic factors that accomplish transition-state stabilization (TSS). FMO calculations deliver an ab initio-level estimate of the intermolecular interaction between the substrate and the amino acid residues of the enzyme. To clarify the catalytic role of Arg90, we calculated the reaction profile of the wild-type BsCM as well as Lys90 and Cit90 mutant BsCMs. Structural refinement and the reaction path determination were performed at the ab initio QM/MM level, and FMO calculations were applied to the QM/MM refined structures. Comparison between three types of reactions established two collective catalytic factors in the BsCM reaction: (1) the hydrogen bonds connecting the Glu78-Arg90-substrate cooperatively control the stability of TS relative to the ES complex and (2) the positive charge on Arg90 polarizes the substrate in the TS region to gain more electrostatic stabilization.
Theoretical framework for thin film superfluid optomechanics: towards the quantum regime
NASA Astrophysics Data System (ADS)
Baker, Christopher G.; Harris, Glen I.; McAuslan, David L.; Sachkou, Yauhen; He, Xin; Bowen, Warwick P.
2016-12-01
Excitations in superfluid helium represent attractive mechanical degrees of freedom for cavity optomechanics schemes. Here we numerically and analytically investigate the properties of optomechanical resonators formed by thin films of superfluid 4He covering micrometer-scale whispering gallery mode cavities. We predict that through proper optimization of the interaction between film and optical field, large optomechanical coupling rates {g}0> 2π × 100 {kHz} and single photon cooperativities {C}0> 10 are achievable. Our analytical model reveals the unconventional behaviour of these thin films, such as thicker and heavier films exhibiting smaller effective mass and larger zero point motion. The optomechanical system outlined here provides access to unusual regimes such as {g}0> {{{Ω }}}M and opens the prospect of laser cooling a liquid into its quantum ground state.
Quantum Monte Carlo Calculation for the Equation of State of MgSiO3 perovskite at high pressures
NASA Astrophysics Data System (ADS)
Lin, Yangzheng; Cohen, R. E.; Driver, Kevin P.; Militzer, Burkhard; Shulenburger, Luke; Kim, Jeongnim
2014-03-01
Magnesium silicate (MgSiO3) is among the most abundant minerals in the Earth's mantle. Its phase behavior under high pressure has important implications for the physical properties of deep Earth and the core-mantle boundary. A number of experiments and density functional theory calculations have studied perovskite and its transition to the post-perovskite phase. Here, we present our initial work on the equation of state of perovskite at pressures up to 200 GPa using quantum Monte Carlo (QMC), a benchmark ab initio method. Our QMC calculations optimize electron correlation by using a Slater-Jastrow type wave function with a single determinant comprised of single-particle orbitals extracted from fully converged DFT calculations. The equation of state obtained from QMC calculations agrees with experimental data. E-mail: rcohen@carnegiescience.edu; This work is supported by NSF.
NASA Astrophysics Data System (ADS)
Yasuda, H.; Kubis, T.; Hosako, I.; Hirakawa, K.
2012-04-01
We theoretically investigated GaN-based resonant phonon terahertz-quantum cascade laser (QCL) structures for possible high-temperature operation by using the non-equilibrium Green's function method. It was found that the GaN-based THz-QCL structures do not necessarily have a gain sufficient for lasing, even though the thermal backfilling and the thermally activated phonon scattering are effectively suppressed. The main reason for this is the broadening of the subband levels caused by a very strong interaction between electrons and longitudinal optical (LO) phonons in GaN.
NASA Astrophysics Data System (ADS)
Varfolomeev, Mikhail A.; Klimovitskii, Alexander E.; Abaidullina, Dilyara I.; Madzhidov, Timur I.; Solomonov, Boris N.
2012-06-01
Experimental study of hydrogen bond cooperativity in hetero-complexes in the gas phase was carried out by IR-spectroscopy method. Stretching vibration frequencies of Osbnd H groups in phenol and catechol molecules as well as of their complexes with nitriles and ethers were determined in the gas phase using a specially designed cell. Osbnd H groups experimental frequency shifts in the complexes of catechol induced by the formation of intermolecular hydrogen bonds are significantly higher than in the complexes of phenol due to the hydrogen bond cooperativity. It was shown that the cooperativity factors of hydrogen bonds in the complexes of catechol with nitriles and ethers in the gas phase are approximately the same. Quantum chemical calculations of the studied systems have been performed using density functional theory (DFT) methods. It was shown, that theoretically obtained cooperativity factors of hydrogen bonds in the complexes of catechol with proton acceptors are in good agreement with experimental values. Cooperative effects lead to a strengthening of intermolecular hydrogen bonds in the complexes of catechol on about 30%, despite the significant difference in the proton acceptor ability of the bases. The analysis within quantum theory of atoms in molecules was carried out for the explanation of this fact.
Varfolomeev, Mikhail A; Klimovitskii, Alexander E; Abaidullina, Dilyara I; Madzhidov, Timur I; Solomonov, Boris N
2012-06-01
Experimental study of hydrogen bond cooperativity in hetero-complexes in the gas phase was carried out by IR-spectroscopy method. Stretching vibration frequencies of O-H groups in phenol and catechol molecules as well as of their complexes with nitriles and ethers were determined in the gas phase using a specially designed cell. O-H groups experimental frequency shifts in the complexes of catechol induced by the formation of intermolecular hydrogen bonds are significantly higher than in the complexes of phenol due to the hydrogen bond cooperativity. It was shown that the cooperativity factors of hydrogen bonds in the complexes of catechol with nitriles and ethers in the gas phase are approximately the same. Quantum chemical calculations of the studied systems have been performed using density functional theory (DFT) methods. It was shown, that theoretically obtained cooperativity factors of hydrogen bonds in the complexes of catechol with proton acceptors are in good agreement with experimental values. Cooperative effects lead to a strengthening of intermolecular hydrogen bonds in the complexes of catechol on about 30%, despite the significant difference in the proton acceptor ability of the bases. The analysis within quantum theory of atoms in molecules was carried out for the explanation of this fact.
Quantum Mechanical Calculations of Charge Effects on gating the KcsA channel
Kariev, Alisher M.; Znamenskiy, Vasiliy S.; Green, Michael E.
2007-02-06
The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. A series of ab initio (density functional) calculations were carried out on side chains of a set of amino acids, plus water, from the (intracellular) gating region of the KcsA K+ channel. Their atomic coordinates, except hydrogen, are known from X-ray structures [D.A. Doyle, J.M. Cabral, R.A. Pfuetzner, A. Kuo, J.M. Gulbis, S.L. Cohen, B.T. Chait, R. MacKinnon, The structure of the potassium channel: molecular basis of K+ conduction and selectivity, Science 280 (1998) 69–77; R. MacKinnon, S.L. Cohen, A. Kuo, A. Lee, B.T. Chait, Structural conservation in prokaryotic and eukaryotic potassium channels, Science 280 (1998) 106–109; Y. Jiang, A. Lee, J. Chen, M. Cadene, B.T. Chait, R. MacKinnon, The open pore conformation of potassium channels. Nature 417 (2001) 523–526], as are the coordinates of some water oxygen atoms. The 1k4c structure is used for the starting coordinates. Quantum mechanical optimization, in spite of the starting configuration, places the atoms in positions much closer to the 1j95, more tightly closed, configuration. This state shows four water molecules forming a “basket” under the Q119 side chains, blocking the channel. When a hydrated K+ approaches this “basket”, the optimized system shows a strong set of hydrogen bonds with the K+ at defined positions, preventing further approach of the K+ to the basket. This optimized structure with hydrated K+ added shows an ice-like 12 molecule nanocrystal of water. If the water molecules exchange, unless they do it as a group, the channel will remain blocked. The “basket” itself appears to be very stable, although it is possible that the K+ with its hydrating water molecules may be more mobile, capable
Image Analysis Using Quantum Entropy Scale Space and Diffusion Concepts
2009-11-01
theoretical physics concerned were quantum field theory and quantum statistical mechanics. The PI gave two lectures at the graduate level on Feynman ...sums has been shown important in various areas of theoretical physics , including in support of Feynman diagram calculations. Even more recently, it...quantum and semi-classical entropies of modeled physical systems was also performed. The feasibility of applying forms of generalized quantum search to
NASA Astrophysics Data System (ADS)
Chen, L.; Woon, D. E.
2009-06-01
Complex organic molecules, including amino acid precursors, have been observed in young stellar objects. Both laboratory and theoretical studies have shown that ice chemistry can play an important role in low-temperature synthetic pathways, with water serving as a catalyst that can significantly enhance reaction rates by lowering barriers or eliminating them altogether. Reactions between carbonyl species and ammonia are particularly promising, as shown in previous studies of the formaldehyde-ammonia reaction. In this study, we explore the reactions of ammonia with two larger carbonyl species, acetaldehyde and acetone, embedded in a water ice cluster. To examine the explicit impact of the water, we gradually increase the size of the cluster from 4H_2O to 12H_2O. Cluster calculations were performed at the MP2/{6-31}+G^{**} or B3LYP/{6-31}+G^{**} level. In order to account for the electrostatic contribution from bulk ice, the Polarizable Continuum Model (PCM) and Isodensity Surface Polarized Continuum Model (IPCM) were used to model reaction field solvation effects. For both acetaldehyde and acetone, the reactant is a charge transfer complex (a partial charge-transfer complex in small clusters and full proton-transfer complex in larger clusters). Rearrangement to amino-hydroxylated products can occur by surmounting a small reaction barrier. Stereo-selectivity is observed in the case of acetaldehyde. P. Ehrenfreund and S. B. Charnley, Ann. Rev. Astron. Astrophys. 38, 427 (2000). W. A. Schutte, L. J. Allamandola, and S. A. Sandford, Science 259, 1143 (1993) W. A. Schutte, L. J. Allamandola, and S. A. Sandford, Icarus 104, 118 (1993) D. E. Woon, Icarus 142, 550 (1999) S. P. Walch, C. W. Bauschicher, Jr., A. Ricca and E. L. O. Bakes, Chem. Phys. Lett, 333, 6 (2001)
Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang
2014-05-07
We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.
Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang
2014-05-07
We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.
He, Fu-yuan; Deng, Kai-wen; Huang, Sheng; Liu, Wen-long; Shi, Ji-lian
2013-09-01
The paper aims to elucidate and establish a new mathematic model: the total quantum statistical moment standard similarity (TQSMSS) on the base of the original total quantum statistical moment model and to illustrate the application of the model to medical theoretical research. The model was established combined with the statistical moment principle and the normal distribution probability density function properties, then validated and illustrated by the pharmacokinetics of three ingredients in Buyanghuanwu decoction and of three data analytical method for them, and by analysis of chromatographic fingerprint for various extracts with different solubility parameter solvents dissolving the Buyanghanwu-decoction extract. The established model consists of four mainly parameters: (1) total quantum statistical moment similarity as ST, an overlapped area by two normal distribution probability density curves in conversion of the two TQSM parameters; (2) total variability as DT, a confidence limit of standard normal accumulation probability which is equal to the absolute difference value between the two normal accumulation probabilities within integration of their curve nodical; (3) total variable probability as 1-Ss, standard normal distribution probability within interval of D(T); (4) total variable probability (1-beta)alpha and (5) stable confident probability beta(1-alpha): the correct probability to make positive and negative conclusions under confident coefficient alpha. With the model, we had analyzed the TQSMS similarities of pharmacokinetics of three ingredients in Buyanghuanwu decoction and of three data analytical methods for them were at range of 0.3852-0.9875 that illuminated different pharmacokinetic behaviors of each other; and the TQSMS similarities (ST) of chromatographic fingerprint for various extracts with different solubility parameter solvents dissolving Buyanghuanwu-decoction-extract were at range of 0.6842-0.999 2 that showed different constituents
Sawant, Amit; Antonuk, Larry E; El-Mohri, Youcef; Zhao, Qihua; Wang, Yi; Li, Yixin; Du, Hong; Perna, Louis
2006-04-01
Modern-day radiotherapy relies on highly sophisticated forms of image guidance in order to implement increasingly conformal treatment plans and achieve precise dose delivery. One of the most important goals of such image guidance is to delineate the clinical target volume from surrounding normal tissue during patient setup and dose delivery, thereby avoiding dependence on surrogates such as bony landmarks. In order to achieve this goal, it is necessary to integrate highly efficient imaging technology, capable of resolving soft-tissue contrast at very low doses, within the treatment setup. In this paper we report on the development of one such modality, which comprises a nonoptimized, prototype electronic portal imaging device (EPID) based on a 40 mm thick, segmented crystalline CsI(Tl) detector incorporated into an indirect-detection active matrix flat panel imager (AMFPI). The segmented detector consists of a matrix of 160 x 160 optically isolated, crystalline CsI(Tl) elements spaced at 1016 microm pitch. The detector was coupled to an indirect detection-based active matrix array having a pixel pitch of 508 microm, with each detector element registered to 2 x 2 array pixels. The performance of the prototype imager was evaluated under very low-dose radiotherapy conditions and compared to that of a conventional megavoltage AMFPI based on a Lanex Fast-B phosphor screen. Detailed quantitative measurements were performed in order to determine the x-ray sensitivity, modulation transfer function, noise power spectrum, and detective quantum efficiency (DQE). In addition, images of a contrast-detail phantom and an anthropomorphic head phantom were also acquired. The prototype imager exhibited approximately 22 times higher zero-frequency DQE (approximately 22%) compared to that of the conventional AMFPI (approximately 1%). The measured zero-frequency DQE was found to be lower than theoretical upper limits (approximately 27%) calculated from Monte Carlo simulations, which
Matsumoto, Takafumi; Teki, Yoshio
2012-08-07
The population transfer to the spin-sublevels of the unique quartet (S = 3/2) high-spin state of the strongly exchange-coupled (SC) radical-triplet pair (for example, an Acceptor-Donor-Radical triad (A-D-R)) via a doublet-quartet quantum-mixed (QM) state is theoretically investigated by a stochastic Liouville equation. In this work, we have treated the loss of the quantum coherence (de-coherence) due to the de-phasing during the population transfer and neglected the effect of other de-coherence mechanisms. The dependences on the magnitude of the exchange coupling or the fine-structure parameter of the QM state are investigated. The dependence on the velocity of the population transfer (by the electron transfer or the energy-transfer) from the QM state to the SC quartet state is also clarified. It is revealed that the de-coherence during the population transfer mainly originates from the fine-structure term of the QM state in the doublet-triplet exchange coupled systems. This de-coherence leads to the unique dynamic electron polarization (DEP) on the high-field spin sublevels of the SC state, which is similar to the unique DEP pattern of the photo-excited triplet states of the reaction centers of photosystems I and II. The magnetic field dependence of the population transfer leading to the populations of the spin-sublevels of the SC states is also calculated. The possibility of the control of energy transport, spin transport and information technology by using the QM state is discussed based on these results. The knowledge obtained in this work is useful in the spin dynamics of any doublet-triplet exchange coupled systems.
NASA Astrophysics Data System (ADS)
Bouhali, I.; Bezzaouia, S.; Telmini, M.; Jungen, Ch.
2016-08-01
Variational ab initio R -matrix theory combined with generalized multichannel quantum defect theory is used to calculate singly excited Rydberg states of the hydrohelium molecular ion, HeH+, for Σ,3+1,Π,31,Δ,31,Φ,31, and Γ,31 symmetry. Bound levels are calculated for n values up to n ≈10 , and continuum states up to ≈3 eV above the HeH2 + threshold. The calculations span the range of internuclear distances R from 1 to 5 bohrs. The present work follows a preliminary study on the Δ,31 states of HeH+ [Bouhali, Bezzaouia, Telmini, and Jungen, EPJ Web Conf. 84, 04004 (2015), 10.1051/epjconf/20158404004] which was also based on R -matrix theory. Further—although limited to rather small R values—the present work extends the recent ab initio computations of Jungen and Jungen [Mol. Phys. 113, 2333 (2015), 10.1080/00268976.2015.1040094] to higher excitation energies which are not accessible to standard quantum-chemical methods. Where a comparison with the calculations of Jungen and Jungen and other older results can be made, namely for n ≤5 , very good agreement with previous ab initio results is obtained.
NASA Astrophysics Data System (ADS)
Pimenov, Oleg A.; Belova, Natalya V.; Sliznev, Valery V.
2017-03-01
The molecular structure of tris-2,2,6,6-tetramethyl-heptane-3,5-dione thulium, or Tm(thd)3, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both the DFT(PBE0) calculations and the GED data collected at 400(8) K indicate that the molecules have D3 symmetry with a distorted antiprismatic TmO6 coordination geometry. According to GED refinements the twist angle θ, i.e. the angle of rotation of the upper O3 triangles relative to their position in regular prism is θ = 16.9(2.0)0. This value is close to both the equilibrium value obtained from the DFT calculations and to the thermal average value at the temperature of the GED experiment obtained by integration over the DFT potential energy surface. The bond distances (rh1) in the chelate ring are Tmsbnd O = 2.214(5) Å, Csbnd O = 1.278(4) Å, and Csbnd C = 1.404(3) Å. The DFT calculations yielded structure parameters in close agreement with those found experimentally. As an alternative to conventional Lewis model which was realized in NBO the topological analysis of ρ(r) in the frame of Bader's quantum theory of atoms in molecule (QTAIM) was performed.
NASA Astrophysics Data System (ADS)
Mouhib, Halima
2014-07-01
This tutorial is an introduction for PhD students and researchers who intend to start their future work in the field of microwave spectroscopy to investigate structural and dynamical aspects of isolated molecular systems in the gas phase. Although the presented case studies are related to odorants, i.e., volatile molecules that possess a noticeable scent, the background and applications of the method can be transferred to any other resembling molecular system. In the early days, microwave spectroscopy was mainly related to the structure determination of very small systems such as OCS or ammonia, where the bond lengths could be determined with high accuracy by measuring the different isotopic species of the molecules. Nowadays, the method is far more advanced and is also used to tackle various fundamental molecular problems in different fields such as physical chemistry and molecular physics. Interesting questions that can be investigated concern, e.g., the molecular structure, i.e., the different conformations, not only of the isolated molecule but also of van der Waals complexes with water, noble gases or other molecules. The dynamical and intra- or intermolecular effects can be straightforwardly observed without the influence of the environment as in the condensed phase. This evolution was only achieved by using quantum chemical methods as a complementary tool to elude the necessity of isotopologues for structure determination, which cannot be realized for large systems (>5 atoms). The combination of microwave spectroscopy and quantum chemical calculations is the method of choice when it comes to sampling the conformational space of molecules. This is particularly the case when small energy differences make it difficult to determine the conformers of the lowest energy using computational methods alone. Although quantum chemical calculations are important for the validation of microwave spectra, the focus of the tutorial is set on the experimental part of the
Muresan, Nicoleta; Lu, Connie C; Ghosh, Meenakshi; Peters, Jonas C; Abe, Megumi; Henling, Lawrence M; Weyhermöller, Thomas; Bill, Eckhard; Wieghardt, Karl
2008-06-02
The electronic structure of a family comprising tetrahedral (alpha-diimine)iron dichloride, and tetrahedral bis(alpha-diimine)iron compounds has been investigated by Mossbauer spectroscopy, magnetic susceptibility measurements, and X-ray crystallography. In addition, broken-symmetry density functional theoretical (B3LYP) calculations have been performed. A detailed understanding of the electronic structure of these complexes has been obtained. A paramagnetic (St=2), tetrahedral complex [FeII(4L)2], where (4L)1- represents the diamagnetic monoanion N-tert-butylquinolinylamide, has been synthesized and characterized to serve as a benchmark for a Werner-type complex containing a tetrahedral FeIIN4 geometry and a single high-spin ferrous ion. In contrast to the most commonly used description of the electronic structure of bis(alpha-diimine)iron(0) complexes as low-valent iron(0) species with two neutral alpha-diimine ligands, it is established here that they are, in fact, complexes containing two (alpha-diiminato)1-* pi radical monoanions and a high-spin ferrous ion (in tetrahedral N4 geometry) (SFe=2). Intramolecular antiferromagnetic coupling between the pi radical ligands (Srad=1/2) and the ferrous ion (SFe=2) yields the observed St=1 ground state. The study confirms that alpha-diimines are redox noninnocent ligands with an energetically low-lying antibonding pi* lowest unoccupied molecular orbital which can accept one or two electrons from a transition metal ion. The (alpha-diimine)FeCl2 complexes (St=2) are shown to contain a neutral alpha-diimine ligand, a high spin ferrous ion, and two chloride ligands.
NASA Astrophysics Data System (ADS)
Baulieu, L.; Toppan, Francesco
2016-11-01
We extend to a possibly infinite chain the conformally invariant mechanical system that was introduced earlier as a toy model for understanding the topological Yang-Mills theory. It gives a topological quantum model that has interesting and computable zero modes and topological invariants. It confirms the recent conjecture by several authors that supersymmetric quantum mechanics may provide useful tools for understanding robotic mechanical systems (Vitelli et al.) and condensed matter properties (Kane et al.), where trajectories are allowed or not by the conservation of topological indices. The absences of ground state and mass gaps are special features of such systems.
NASA Astrophysics Data System (ADS)
Wang, Xianwei; Zhang, John Z. H.; He, Xiao
2015-11-01
Recent advance in biophysics has made it possible to directly measure site-specific electric field at internal sites of proteins using molecular probes with C = O or C≡N groups in the context of vibrational Stark effect. These measurements directly probe changes of electric field at specific protein sites due to, e.g., mutation and are very useful in protein design. Computational simulation of the Stark effect based on force fields such as AMBER and OPLS, while providing good insight, shows large errors in comparison to experimental measurement due to inherent difficulties associated with point charge based representation of force fields. In this study, quantum mechanical calculation of protein's internal electrostatic properties and vibrational Stark shifts was carried out by using electrostatically embedded generalized molecular fractionation with conjugate caps method. Quantum calculated change of mutation-induced electric field and vibrational Stark shift is reported at the internal probing site of enzyme human aldose reductase. The quantum result is in much better agreement with experimental data than those predicted by force fields, underscoring the deficiency of traditional point charge models describing intra-protein electrostatic properties.
Wang, Xianwei; Zhang, John Z. H.; He, Xiao
2015-11-14
Recent advance in biophysics has made it possible to directly measure site-specific electric field at internal sites of proteins using molecular probes with C = O or C≡N groups in the context of vibrational Stark effect. These measurements directly probe changes of electric field at specific protein sites due to, e.g., mutation and are very useful in protein design. Computational simulation of the Stark effect based on force fields such as AMBER and OPLS, while providing good insight, shows large errors in comparison to experimental measurement due to inherent difficulties associated with point charge based representation of force fields. In this study, quantum mechanical calculation of protein’s internal electrostatic properties and vibrational Stark shifts was carried out by using electrostatically embedded generalized molecular fractionation with conjugate caps method. Quantum calculated change of mutation-induced electric field and vibrational Stark shift is reported at the internal probing site of enzyme human aldose reductase. The quantum result is in much better agreement with experimental data than those predicted by force fields, underscoring the deficiency of traditional point charge models describing intra-protein electrostatic properties.
Theoretical Prediction of Hydrogen-Bond Basicity pKBHX Using Quantum Chemical Topology Descriptors
2014-01-01
Hydrogen bonding plays an important role in the interaction of biological molecules and their local environment. Hydrogen-bond strengths have been described in terms of basicities by several different scales. The pKBHX scale has been developed with the interests of medicinal chemists in mind. The scale uses equilibrium constants of acid···base complexes to describe basicity and is therefore linked to Gibbs free energy. Site specific data for polyfunctional bases are also available. The pKBHX scale applies to all hydrogen-bond donors (HBDs) where the HBD functional group is either OH, NH, or NH+. It has been found that pKBHX can be described in terms of a descriptor defined by quantum chemical topology, ΔE(H), which is the change in atomic energy of the hydrogen atom upon complexation. Essentially the computed energy of the HBD hydrogen atom correlates with a set of 41 HBAs for five common HBDs, water (r2 = 0.96), methanol (r2 = 0.95), 4-fluorophenol (r2 = 0.91), serine (r2 = 0.93), and methylamine (r2 = 0.97). The connection between experiment and computation was strengthened with the finding that there is no relationship between ΔE(H) and pKBHX when hydrogen fluoride was used as the HBD. Using the methanol model, pKBHX predictions were made for an external set of bases yielding r2 = 0.90. Furthermore, the basicities of polyfunctional bases correlate with ΔE(H), giving r2 = 0.93. This model is promising for the future of computation in fragment-based drug design. Not only has a model been established that links computation to experiment, but the model may also be extrapolated to predict external experimental pKBHX values. PMID:24460383
Theoretical prediction of hydrogen-bond basicity pKBHX using quantum chemical topology descriptors.
Green, Anthony J; Popelier, Paul L A
2014-02-24
Hydrogen bonding plays an important role in the interaction of biological molecules and their local environment. Hydrogen-bond strengths have been described in terms of basicities by several different scales. The pKBHX scale has been developed with the interests of medicinal chemists in mind. The scale uses equilibrium constants of acid···base complexes to describe basicity and is therefore linked to Gibbs free energy. Site specific data for polyfunctional bases are also available. The pKBHX scale applies to all hydrogen-bond donors (HBDs) where the HBD functional group is either OH, NH, or NH+. It has been found that pKBHX can be described in terms of a descriptor defined by quantum chemical topology, ΔE(H), which is the change in atomic energy of the hydrogen atom upon complexation. Essentially the computed energy of the HBD hydrogen atom correlates with a set of 41 HBAs for five common HBDs, water (r2=0.96), methanol (r2=0.95), 4-fluorophenol (r2=0.91), serine (r2=0.93), and methylamine (r2=0.97). The connection between experiment and computation was strengthened with the finding that there is no relationship between ΔE(H) and pKBHX when hydrogen fluoride was used as the HBD. Using the methanol model, pKBHX predictions were made for an external set of bases yielding r2=0.90. Furthermore, the basicities of polyfunctional bases correlate with ΔE(H), giving r2=0.93. This model is promising for the future of computation in fragment-based drug design. Not only has a model been established that links computation to experiment, but the model may also be extrapolated to predict external experimental pKBHX values.
Dardi, P.S.
1984-11-01
Within the very broad field of molecular dynamics, we have concentrated on two simple yet important systems. The systems are simple enough so that they are adequately described with a single Born-Oppenheimer potential energy surface and that the dynamics can be calculated accurately. They are important because they give insight into solving more complicated systems. First we discuss H + H/sub 2/ reactive scattering. We present an exact formalism for atom-diatom reactive scattering which avoids the problem of finding a coordinate system appropriate for both reactants and products. We present computational results for collinear H + H/sub 2/ reactive scattering which agree very well with previous calculations. We also present a coupled channel distorted wave Born approximation for atom-diatom reactive scattering which we show is a first order approximation to our exact formalism. We present coupled channel DWBA results for three dimensional H + H/sub 2/ reactive scattering. The second system is an isolated HF molecule in an intense laser field. Using classical trajectories and quantum dynamics, we look at energy absorbed and transition probabilities as a function of the laser pulse time and also averaged over the pulse time. Calculations are performed for both rotating and nonrotating HF. We examine one and two photon absorption about the fundamental frequency, multiphoton absorption, and overtone absorption. 127 references, 31 figures, 12 tables.
NASA Astrophysics Data System (ADS)
Antipas, Georgios S. E.; Germenis, Anastasios
2015-02-01
A combination of atomic correlation statistics and quantum chemical calculations are shown to predict biological function. In the present study, various antigenic peptide-Major Histocompatibility Complex (pMHC) ligands with near-identical stereochemistries, in complexation with the same T cell receptor (TCR), were found to consistently induce distinctly different quantum chemical behavior, directly dependent on the peptide’s electron spin density and intrinsically expressed by the protonation state of the peptide’s N-terminus. Furthermore, the cumulative coordination difference of any variant in respect to the native peptide was found to accurately reflect peptide biological function and immerges as the physical observable which is directly related to the immunological end-effect of pMHC-TCR interaction.
Selli, Daniele; Baburin, Igor; Leoni, Stefano; Zhu, Zhen; Tománek, David; Seifert, Gotthard
2013-10-30
We investigate the interaction of a graphene monolayer with the C(111) diamond surface using ab initio density functional theory. To accommodate the lattice mismatch between graphene and diamond, the overlayer deforms into a wavy structure that binds strongly to the diamond substrate. The detached ridges of the wavy graphene overlayer behave electronically as free-standing polyacetylene chains with delocalized π electrons, separated by regions containing only sp(3) carbon atoms covalently bonded to the (111) diamond surface. We performed quantum transport calculations for different geometries of the system to study how the buckling of the graphene layer and the associated bonding to the diamond substrate affect the transport properties. The system displays high carrier mobility along the ridges and a wide transport gap in the direction normal to the ridges. These intriguing, strongly anisotropic transport properties qualify the hybrid graphene-diamond system as a viable candidate for electronic nanodevices.
McGary, John E
2004-01-01
Real-time, 3D localization of the prostate for intensity-modulated radiotherapy can be accomplished with passively charged radio frequency transmitters and superconducting quantum interference device (SQUID) magnetometers. The overall system design consists of an external dipole antenna as a power source for charging a microchip implant transmitter and SQUID magnetometers for signal detection. An external dipole antenna charges an on-chip capacitor through inductive coupling in the near field region through a small implant inductor. The charge and discharge sequence between the external antenna and the implant circuit can be defined by half duplex, full duplex, or sequential operations. The resulting implant discharge current creates an alternating magnetic field through the inductor. The field is detected by the surrounding magnetometers, and the location of the implant transmitter can be calculated. Problems associated with this system design are interrelated with the signal strength at the detectors, detector sensitivity, and charge time of the implant capacitor. The physical parameters required for optimizing the system for real-time applications are the operating frequency, implant inductance and capacitance, the external dipole current and loop radius, the detector distance, and mutual inductance. Consequently, the sequential operating mode is the best choice for real-time localization for constraints requiring positioning within 1 s due to the mutual inductance and detector sensitivity. We present the theoretical foundation for designing a real-time, 3D prostate localization system including the associated physical parameters and demonstrate the feasibility and physical limitations for such a system.