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1

Theoretical Study of the Inverting Mechanism in a Processive Cellobiohydrolase with Quantum Mechanical Calculations  

SciTech Connect

The Hypocrea jecorina Family 6 cellobiohydrolase (Cel6A) is one of most efficient enzymes for cellulose deconstruction to soluble sugars and is thus of significant current interest for the growing biofuels industry. Cel6A is known to hydrolyze b(1,4)-glycosidic linkages in cellulose via an inverting mechanism, but there are still questions that remain regarding the role of water and the catalytic base. Here we study the inverting, single displacement, hydrolytic reaction mechanism in Cel6A using density functional theory (DFT) calculations. The computational model used to follow the reaction is a truncated active site model with several explicit waters based on structural studies of H. jecorina Cel6A. Proposed mechanisms are evaluated with several density functionals. From our calculations, the role of the water in nucleophilic attack on the anomeric carbon, and the roles of several residues in the active site loops are elucidated explicitly for the first time. We also apply quantum mechanical calculations to understand the proton transfer reaction which completes the catalytic cycle.

Kim, S.; Payne, C. M.; Himmel, M. E.; Crowley, M. F.; Paton, R. S.; Beckham, G. T.

2012-01-01

2

Theoretical study of dehydration-carbonation reaction on brucite surface based on ab initio quantum mechanic calculations  

NASA Astrophysics Data System (ADS)

The carbonation of brucite (Mg(OH)2) has been considered as a potential technology for cleaning industrial carbon dioxide waste. The kinetics of the reaction Mg(OH)2 + CO2 -> MgCO3 + H2O have been studied experimentally at 573°C by Bearat at al. [1]. Their experiments suggest that the carbonation of magnesium hydroxide proceeds by the reaction Mg(OH)2 -> MgO + H2O followed by the adsorption of CO2 molecules on the dehydrated brucite surface. Due to the large difference in volumes between Mg(OH)2 and MgO, dehydration causes the formation of dislocations and cracks, allowing water molecules to leave the brucite surface and facilitating the advance of the carbonation front in the bulk solid. The detailed mechanism of this process is however unknown. We used the Car-Parrinello ab initio molecular dynamics method to study the structure and dynamics of the (0001), (1-100) and (11-20) surfaces of brucit and calculated the enthalpy and activation barrier of H2O nucleation and dehydration on different surfaces. The results obtained are in agreement with previous studies of brucite dehydration by Masini and Bernasconi [2]. The reactive Car-Parrinello molecular dynamics method [3] has been applied to investigate the detailed mechanism of the dehydration-carbonation reaction at the (1-100) interface of brucite with the gas phase. Based on the results of our MD simulations and the calculated enthalpy of CO2 adsorption on the dehydrated brucite surfaces we propose a mechanism for the dehydration/carbonation reaction. [1] Bearat H, McKelvy MJ, Chizmeshya AVG, Sharma R, Carpenter RW (2002) J. Amer. Ceram. Soc. 85(4):742 [2] Masini P and Bernasconi M (2001) J. Phys. Cond. Mat. 13: 1-12 [3] Iannuzzi M, Laio A and Parrinello M (2003) Phys. Rev. Lett. (submitted)

Churakov, S. V.; Parrinello, M.

2003-04-01

3

Theoretical modeling of large molecular systems. Advances in the local self consistent field method for mixed quantum mechanics/molecular mechanics calculations.  

PubMed

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 the atom: for an sp(3) carbon atom, we consider the two core 1s electrons and treat that carbon as an atom with three electrons. This results in an LSCF+3 model. Similarly, a nitrogen atom with a lone pair of electrons available for conjugation is treated as an atom with five electrons (LSCF+5). This approach is particularly well suited to splitting peptide bonds and other bonds that include carbon or nitrogen atoms. To embed the induced polarization within the calculation, researchers must use a polarizable force field. However, because the parameters of the usual force fields include an average of the induction effects, researchers typically can obtain satisfactory results without explicitly introducing the polarization. When considering electronic transitions, researchers must take into account the changes in the electronic polarization. One approach is to simulate the electronic cloud of the surroundings by a continuum whose dielectric constant is equal to the square of the refractive index. This Electronic Response of the Surroundings (ERS) methodology allows researchers to model the changes in induced polarization easily. We illustrate this approach by modeling the electronic absorption of tryptophan in human serum albumin (HSA). PMID:23249409

Monari, Antonio; Rivail, Jean-Louis; Assfeld, Xavier

2013-02-19

4

Quantum transport calculations using periodic boundaryconditions  

SciTech Connect

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.

Wang, Lin-Wang

2004-06-15

5

Numerical Object Oriented Quantum Field Theory Calculations  

E-print Network

The qft++ package is a library of C++ classes that facilitate numerical (not algebraic) quantum field theory calculations. Mathematical objects such as matrices, tensors, Dirac spinors, polarization and orbital angular momentum tensors, etc. are represented as C++ objects in qft++. The package permits construction of code which closely resembles quantum field theory expressions, allowing for quick and reliable calculations.

M. Williams

2008-05-19

6

Quantum Monte Carlo Calculations of Light Nuclei  

E-print Network

During the last 15 years, there has been much progress in defining the nuclear Hamiltonian and applying quantum Monte Carlo methods to the calculation of light nuclei. I describe both aspects of this work and some recent results.

Steven C. Pieper

2007-11-09

7

Theoretical comparisons of average normalized gain calculations  

NSDL National Science Digital Library

Since its introduction, the normalized gain or the g-factor has been widely used in assessing students' performance in pre- and post-tests. The average g-factor can be calculated using either the average scores of the class or individual student's scores. In general, these two calculations produce different results. The nature of these two results is explored for several idealized situations. The results suggest that we may be able to utilize the difference between the two results to extract information on how the population may have changed as a result of instruction

Bao, Lei

2009-04-13

8

Bhabha Process at LEP - Theoretical Calculations  

E-print Network

In this contribution we give a short overview of the situation in the precision calculation of the Bhabha process and we present a preliminary numerical result on the second-order sub-leading correction to the small angle Bhabha process.

S. Jadach; M. Melles; B. F. L. Ward; S. A. Yost

1996-07-17

9

Theoretical calculations of proton affinities in phenol  

Microsoft Academic Search

It is shown that a relatively simple MP2(fc)\\/6–31G??\\/\\/HF\\/6–31G? model is capable of providing quantitative description of protonation in phenol. The use of the 6–31G?? basis set in the single-point MP2 calculation is crucial in this respect. The zero-point energy (ZPE) contribution to the proton affinity (PA) is estimated at the HF\\/6–31G? level of approximation. It appears that the contribution of

M. Eckert-Maksi; M. Klessinger; Z. B. Maksi?

1995-01-01

10

Theoretical analysis of perfect quantum state transfer with superconducting qubits  

E-print Network

Superconducting quantum circuits, fabricated with multiple layers, are proposed to implement perfect quantum state transfer between nodes of a hypercube network. For tunable devices such as the phase qubit, each node can transmit quantum information to any other node at a constant rate independent of the distance between qubits. The physical limits of quantum state transfer in this network are theoretically analyzed, including the effects of disorder, decoherence, and higher-order couplings.

Frederick W. Strauch; Carl J. Williams

2007-08-03

11

Algorithmic Information Theoretic Issues in Quantum Mechanics  

E-print Network

.1 The unpublished ideas of Sidney Coleman and Andrew Lesniewski210 6.2 Karl Svozil's invention of Quantum 248 6.6 Peter Gacs' quantum algorithmic entropy . . . . . . . . . . . . . 248 6.7 The algorithmic

12

Quantum Cryptography for Information-Theoretic Security  

NASA Astrophysics Data System (ADS)

This article explains quantum computing and its potential for rendering current encrypted communication via public channels insecure. A review of quantum key distribution is given as a way to ensure secure public-channel communication regardless of the computational power of an adversary, that may possesses a quantum computer. Finally, state-of-the-art quantum key distribution is discussed with an insight into its future.

Sanders, Barry

13

Theoretical calculation of radon emanation fraction  

NASA Astrophysics Data System (ADS)

Emanation fraction of radon atoms created in a granular material was estimated using Monte Carlo method. Two models based on different arrangements of grains were considered: one of them representing simple cubic structure and the other one based on face centered cubic structure. As it was expected, the structure that provided higher density of grain packing (FCCS) gave lower values of radon emanation fraction. Both models showed that the probability of radon embedding in the neighboring grains would approach zero for large values of grain radius. Assuming homogenous distribution of 226Ra within the whole grain volume, radon emanation fraction decreased with increasing grain radius while it showed the opposite behavior in the case of surface distribution of 226Ra. The order of magnitude of radon emanation fraction decreased from 10-2% (for grain radius of few micrometers) to 10-4% (for grain radius larger than few millimeters) when homogenous distribution of 226Ra was considered. If the distribution of 226Ra was assumed only within the surface layer of a grain, emanation increased from less than 1% (obtained for grain size of few micrometers) to almost 25% (for large grain radius). The effect of moisture on the emanation fraction was confirmed by examining the case of water filling the space among the grains. Radon emanation was also considered analytically and the results were compared with Monte Carlo calculations.

Stajic, J. M.; Nikezic, D.

2014-10-01

14

Theoretical calculations of He scattering intensities from MgO  

SciTech Connect

We report close-coupling calculations of the specular intensity of He atoms scattered from the (100) surface of MgO. The atom-surface interactions used in this study were developed within a semiempirical effective-medium theory. We find good agreement between the experimentally determined and theoretically calculated specular scattering intensities. We further identify features in the theoretical spectra that are sensitive to the size of the Fourier components, which can be used to refine further the input potentials.

Schwartz, C.; Karimi, M.; Vidali, G.

1989-05-15

15

Quantum Monte Carlo calculations for light nuclei  

SciTech Connect

Quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A {le} 8 have been made using a realistic Hamiltonian that fits NN scattering data. Results for more than two dozen different (J{sup {pi}}, T) p-shell states, not counting isobaric analogs, have been obtained. The known excitation spectra of all the nuclei are reproduced reasonably well. Density and momentum distributions and various electromagnetic moments and form factors have also been computed. These are the first microscopic calculations that directly produce nuclear shell structure from realistic NN interactions.

Wiringa, R.B. [Argonne National Lab., IL (United States). Physics Div.

1997-10-01

16

Quantum Monte Carlo calculations for light nuclei  

SciTech Connect

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.

Wiringa, R.B.

1998-08-01

17

Quantum Monte Carlo calculations for light nuclei.  

SciTech Connect

Quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A {le} 8 are made using a realistic Hamiltonian that fits NN scattering data. Results for more than 40 different (J{pi}, T) states, plus isobaric analogs, are obtained and the known excitation spectra are reproduced reasonably well. Various density and momentum distributions and electromagnetic form factors and moments have also been computed. These are the first microscopic calculations that directly produce nuclear shell structure from realistic NN interactions.

Wiringa, R. B.

1998-10-23

18

Graph-Theoretic Approach to Quantum Correlations  

E-print Network

Correlations in Bell and noncontextuality inequalities can be expressed as a positive linear combination of probabilities of events. Exclusive events can be represented as adjacent vertices of a graph, so correlations can be associated to a subgraph. We show that the maximum value of the correlations for classical, quantum, and more general theories is the independence number, the Lov\\'asz number, and the fractional packing number of this subgraph, respectively. We also show that, for any graph, there is always a correlation experiment such that the set of quantum probabilities is exactly the Gr\\"otschel-Lov\\'asz-Schrijver theta body. This identifies these combinatorial notions as fundamental physical objects and provides a method for singling out experiments with quantum correlations on demand.

Adan Cabello; Simone Severini; Andreas Winter

2014-01-28

19

A Universal Operator Theoretic Framework for Quantum Fault Tolerance  

E-print Network

In this paper 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, which incorporates as special cases all known...

Gilbert, Gerald; Weinstein, Yaakov S; Aggarwal, Vaneet; Calderbank, A Robert

2007-01-01

20

A Universal Operator Theoretic Framework for Quantum Fault Tolerance.  

NASA Astrophysics Data System (ADS)

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.

Gilbert, Gerald; Calderbank, Robert; Aggarwal, Vaneet; Hamrick, Michael; Weinstein, Yaakov

2008-03-01

21

A Universal Operator Theoretic Framework for Quantum Fault Tolerance  

E-print Network

In this paper 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. This is demonstrated both formally and with an explicit numerical example. The basis for our approach is the Quantum Computer Condition (QCC), an inequality governing the evolution of a quantum computer. We show that 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, which incorporates as special cases all known error correcting protocols, and is itself a special case of the QCC.

Gerald Gilbert; Michael Hamrick; Yaakov S. Weinstein; Vaneet Aggarwal; A. Robert Calderbank

2007-09-02

22

Quantum mechanical calculations to chemical accuracy  

NASA Technical Reports Server (NTRS)

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.

Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

1991-01-01

23

Quantum Monte Carlo Calculations of Light Nuclei  

E-print Network

Variational Monte Carlo and Green's function Monte Carlo are powerful tools for calculations of properties of light nuclei using realistic two-nucleon and three-nucleon potentials. Recently the GFMC method has been extended to multiple states with the same quantum numbers. The combination of the Argonne v_18 two-nucleon and Illinois-2 three-nucleon potentials gives a good prediction of many energies of nuclei up to 12C. A number of other recent results are presented: comparison of binding energies with those obtained by the no-core shell model; the incompatibility of modern nuclear Hamiltonians with a bound tetra-neutron; difficulties in computing RMS radii of very weakly bound nuclei, such as 6He; center-of-mass effects on spectroscopic factors; and the possible use of an artificial external well in calculations of neutron-rich isotopes.

Steven C. Pieper

2004-10-27

24

Quantum Monte Carlo Calculations of Light Nuclei  

E-print Network

Variational Monte Carlo and Green's function Monte Carlo are powerful tools for calculations of properties of light nuclei using realistic two-nucleon and three-nucleon potentials. Recently the GFMC method has been extended to multiple states with the same quantum numbers. The combination of the Argonne v_18 two-nucleon and Illinois-2 three-nucleon potentials gives a good prediction of many energies of nuclei up to 12C. A number of other recent results are presented: comparison of binding energies with those obtained by the no-core shell model; the incompatibility of modern nuclear Hamiltonians with a bound tetra-neutron; difficulties in computing RMS radii of very weakly bound nuclei, such as 6He; center-of-mass effects on spectroscopic factors; and the possible use of an artificial external well in calculations of neutron-rich isotopes.

Pieper, S C

2005-01-01

25

Quantum Public-Key Encryption with Information Theoretic Security  

E-print Network

We propose a definition for the information theoretic security of a quantum public-key encryption scheme, and present bit-oriented and two-bit-oriented encryption schemes satisfying our security definition via the introduction of a new public-key algorithm structure. We extend the scheme to a multi-bitoriented one, and conjecture that it is also information theoretically secure, depending directly on the structure of our new algorithm.

Jiangyou Pan; Li Yang

2010-06-02

26

Quantum Monte Carlo Calculations of Light Nuclei  

NASA Astrophysics Data System (ADS)

Variational Monte Carlo and Green's function Monte Carlo are powerful tools for cal- culations of properties of light nuclei using realistic two-nucleon (NN) and three-nucleon (NNN) potentials. Recently the GFMC method has been extended to multiple states with the same quantum numbers. The combination of the Argonne v18 two-nucleon and Illinois-2 three-nucleon potentials gives a good prediction of many energies of nuclei up to 12C. A number of other recent results are presented: comparison of binding energies with those obtained by the no-core shell model; the incompatibility of modern nuclear Hamiltonians with a bound tetra-neutron; difficulties in computing RMS radii of very weakly bound nuclei, such as 6He; center-of-mass effects on spectroscopic factors; and the possible use of an artificial external well in calculations of neutron-rich isotopes.

Pieper, Steven C.

2005-04-01

27

Theoretical calculation of the structure and spectra of lithium oxides  

Microsoft Academic Search

The structures, properties, and spectra of the diatomic and triatomic lithium oxides LiO, LiOLi, LiLiO, and LiO2 have been computed using self-consistent field theory with large contracted Gaussian basis sets. In particular, equilibrium geometries, vibrational frequencies, electronic excitation energies, ionization potentials, and dipole moments have been calculated and compared with other results, both experimental and theoretical, where available. The existence

Dana T. Grow; Russell M. Pitzer

1977-01-01

28

Quantum Monte Carlo calculations of neutron matter  

NASA Astrophysics Data System (ADS)

Uniform neutron matter is approximated by a cubical box containing a finite number of neutrons, with periodic boundary conditions. We report variational and Green’s function Monte Carlo calculations of the ground state of fourteen neutrons in a periodic box using the Argonne v8' two-nucleon interaction at densities up to one and half times the nuclear matter density. The effects of the finite box size are estimated using variational wave functions together with cluster expansion and chain summation techniques. They are small at subnuclear densities. We discuss the expansion of the energy of low-density neutron gas in powers of its Fermi momentum. This expansion is strongly modified by the large nn scattering length, and does not begin with the Fermi-gas kinetic energy, as assumed in both Skyrme and relativistic mean field theories. The leading term of neutron gas energy is approximately half the Fermi-gas kinetic energy. The quantum Monte Carlo results are also used to calibrate the accuracy of variational calculations employing Fermi hypernetted and single operator chain summation methods to study nucleon matter over a larger density range, with more realistic Hamiltonians including three-nucleon interactions.

Carlson, J.; Morales, J.; Pandharipande, V. R.; Ravenhall, D. G.

2003-08-01

29

Quantum Monte Carlo Calculations of Neutron Matter  

E-print Network

Uniform neutron matter is approximated by a cubic box containing a finite number of neutrons, with periodic boundary conditions. We report variational and Green's function Monte Carlo calculations of the ground state of fourteen neutrons in a periodic box using the Argonne $\\vep $ two-nucleon interaction at densities up to one and half times the nuclear matter density. The effects of the finite box size are estimated using variational wave functions together with cluster expansion and chain summation techniques. They are small at subnuclear densities. We discuss the expansion of the energy of low-density neutron gas in powers of its Fermi momentum. This expansion is strongly modified by the large nn scattering length, and does not begin with the Fermi-gas kinetic energy as assumed in both Skyrme and relativistic mean field theories. The leading term of neutron gas energy is ~ half the Fermi-gas kinetic energy. The quantum Monte Carlo results are also used to calibrate the accuracy of variational calculations employing Fermi hypernetted and single operator chain summation methods to study nucleon matter over a larger density range, with more realistic Hamiltonians including three-nucleon interactions.

J. Carlson; J. Morales Jr; V. R. Pandharipande; D. G. Ravenhall

2003-02-17

30

Quantum Monte Carlo Calculations of Neutron Matter  

E-print Network

Uniform neutron matter is approximated by a cubic box containing a finite number of neutrons, with periodic boundary conditions. We report variational and Green's function Monte Carlo calculations of the ground state of fourteen neutrons in a periodic box using the Argonne $\\vep $ two-nucleon interaction at densities up to one and half times the nuclear matter density. The effects of the finite box size are estimated using variational wave functions together with cluster expansion and chain summation techniques. They are small at subnuclear densities. We discuss the expansion of the energy of low-density neutron gas in powers of its Fermi momentum. This expansion is strongly modified by the large nn scattering length, and does not begin with the Fermi-gas kinetic energy as assumed in both Skyrme and relativistic mean field theories. The leading term of neutron gas energy is ~ half the Fermi-gas kinetic energy. The quantum Monte Carlo results are also used to calibrate the accuracy of variational calculations ...

Carlson, J; Ravenhall, D G

2003-01-01

31

Calculation of the Deflection of Light Ray near the Sun with Quantum-corrected Newton's Gravitation Law  

E-print Network

The deflection of light ray passing near the Sun is calculated with quantum-corrected Newton's gravitation law. The satisfactory result suggests that there may exist other theoretical possibilities besides the theory of relativity.

Zhen Wang

1999-06-16

32

Theoretical calculations of hyperfine coupling constants for muoniated butyl radicals.  

PubMed

The hyperfine coupling constants (HFCCs) of all the butyl radicals that can be produced by muonium (Mu) addition to butene isomers (1- and 2-butene and isobutene) have been calculated, to compare with the experimental results for the muon and proton HFFCs for these radicals reported in paper II (Fleming, D. G.; et al. J. Phys. Chem. A 2011, 10.1021/jp109676b) that follows. The equilibrium geometries and HFCCs of these muoniated butyl radicals as well as their unsubstituted isotopomers were treated at both the spin-unrestricted MP2/EPR-III and B3LYP/EPR-III levels of theory. Comparisons with calculations carried out for the EPR-II basis set have also been made. All calculations were carried out in vacuo at 0 K only. A C-Mu bond elongation scheme that lengthens the equilibrium C-H bond by a factor of 1.076, on the basis of recent quantum calculations of the muon HFCCs of the ethyl radical, has been exploited to determine the vibrationally corrected muon HFCCs. The sensitivity of the results to small variations around this scale factor was also investigated. The computational methodology employed was "benchmarked" in comparisons with the ethyl radical, both with higher level calculations and with experiment. For the ?-HFCCs of interest, compared to B3LYP, the MP2 calculations agree better with higher level theories and with experiment in the case of the eclipsed C-Mu bond and are generally deemed to be more reliable in predicting the equilibrium conformations and muon HFCCs near 0 K, in the absence of environmental effects. In some cases though, the experimental results in paper II demonstrate that environmental effects enhance the muon HFCC in the solid phase, where much better agreement with the experimental muon HFCCs near 0 K is found from B3LYP than from MP2. This seemingly better level of agreement is probably fortuitous, due to error cancellations in the DFT calculations, which appear to mimic these environmental effects. For the staggered proton HFCCs of the butyl radicals exhibiting no environmental effect in paper II, the best agreement with experiment is consistently found from the B3LYP calculations, in agreement also with benchmark calculations carried out for the ethyl radical. PMID:21395223

Chen, Ya Kun; Fleming, Donald G; Wang, Yan Alexander

2011-04-01

33

A quantum-theoretic approach to genetic problems  

Microsoft Academic Search

A quantum-theoretic picture of the transfer of genetic information is described. The advantage of such an approach is that\\u000a a number of genetic effects appear to be explicable on the basis of general microphysical laws, independent of any specific\\u000a model (such as DNA-protein coding) for the transmission of genetic information. It is assumed that the genetic information\\u000a is carried by

Robert Rosen

1960-01-01

34

Quantum calculations of Stark broadening of Li-like ions; T and Z—scaling  

NASA Astrophysics Data System (ADS)

Quantum-mechanical calculations for the electron impact Stark linewidths of the 3s-3p transitions for the lithium-like ions from C IV to Ne VIII are performed in the frame of the impact approximation and for intermediate coupling. Good agreement is obtained with experimental and other theoretical results. Dependence of Stark widths with temperature and charge has been studied.

Elabidi, Haykel; Nessib, Nébil Ben; Sahal-Bréchot, Sylvie

2008-10-01

35

Calorimetric determinations and theoretical calculations of polymorphs of thalidomide  

NASA Astrophysics Data System (ADS)

The analysis of the thermograms of thalidomide obtained for the two reported polymorphs ? and ? by differential scanning calorimetry (DSC) shows some inconsistencies that are discussed in the present work. The conception of a new polymorph form, named ? ?, allowed us to explain the observed thermal behavior more satisfactorily. This new polymorph shows enantiotropy with both ? and ? 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 ? and ?. 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 ? and ?. These results suggested a possible conformation for the newly discovered polymorph ? ?.

Lara-Ochoa, F.; Pérez, G. Espinosa; Mijangos-Santiago, F.

2007-09-01

36

Preliminary theoretical acoustic and rf sounding calculations for MILL RACE  

SciTech Connect

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)

Warshaw, S.I.; Dubois, P.F.

1981-11-02

37

The calculated photon: Visualization of a quantum field Martin Ligarea)  

E-print Network

Teachers. DOI: 10.1119/1.1417531 I. INTRODUCTION The dual wave­particle nature of quantum objects is dis, or where to draw the line between wave-like aspects and particle-like aspects and how to justifyThe calculated photon: Visualization of a quantum field Martin Ligarea) and Ryan Oliveri Department

Ligare, Martin

38

Theoretical analysis of quantum ghost imaging through turbulence  

SciTech Connect

Atmospheric turbulence generally affects the resolution and visibility of an image in long-distance imaging. In a recent quantum ghost imaging experiment [P. B. Dixon et al., Phys. Rev. A 83, 051803 (2011)], it was found that the effect of the turbulence can nevertheless be mitigated under certain conditions. This paper gives a detailed theoretical analysis to the setup and results reported in the experiment. Entangled photons with a finite correlation area and a turbulence model beyond the phase screen approximation are considered.

Chan, Kam Wai Clifford [Rochester Optical Manufacturing Company, 1260 Lyell Avenue, Rochester, New York 14606 (United States); Simon, D. S.; Sergienko, A. V. [Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215 (United States); Hardy, Nicholas D.; Shapiro, Jeffrey H. [Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States); Dixon, P. Ben; Howland, Gregory A.; Howell, John C.; Eberly, Joseph H. [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States); O'Sullivan, Malcolm N.; Rodenburg, Brandon [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Boyd, Robert W. [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States); Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5 (Canada)

2011-10-15

39

Anomalous thermal conduction in one dimension: a quantum calculation.  

PubMed

In this paper, we study the thermal conductivity of an anharmonically coupled chain of atoms. Numerical studies using classical dynamics have shown that the conductivity of a chain with nearest neighbor couplings diverges with chain length L as L(alpha); earlier studies found alpha approximately = 0.4 under a range of conditions, but a recent study on longer chains claims alpha = 1/3. Analytically, this problem has been studied by calculating the relaxation rate gamma(q) of the normal modes of vibration as a function of its wave vector q. Two theoretical studies of classical chains, one using the mode-coupling formulation and the other the Boltzmann equation method, led to gamma(q) proportional to q(5/3), which is consistent with alpha = 0.4. Here we study the problem for a quantum anharmonic chain with quartic anisotropy. We develop a low-temperature expansion for gamma(q) and find that, in the regime Dirac's constant omega(q) < k(B)T, gamma(q) is proportional to q(5/3)T2, where omega(q) is the frequency of the mode. In our analysis, the relaxation arises due to umklapp scattering processes. We further evaluate the thermal conductivity of the chain using the Kubo formula, which enables us to take into account the transport relaxation time through vertex corrections for the current-current correlator. This calculation also yields alpha = 0.4. PMID:17930004

Santhosh, G; Kumar, Deepak

2007-08-01

40

Quantum Monte Carlo Calculations for Minimum Energy Structures  

E-print Network

We present an efficient method to find minimum energy structures using energy estimates from accurate quantum Monte Carlo calculations. This method involves a stochastic process formed from the stochastic energy estimates ...

Grossman, Jeffrey C.

41

Quantum robots and quantum computers.  

National Technical Information Service (NTIS)

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 acti...

P. Benioff

1998-01-01

42

Macroscopic Quantum-Type Potentials in Theoretical Systems Biology  

PubMed Central

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

Nottale, Laurent

2014-01-01

43

Theoretical calculations on the electron absorption spectra of selected Polycyclic Aromatic Hydrocarbons (PAH) and derivatives  

NASA Technical Reports Server (NTRS)

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.

Du, Ping

1993-01-01

44

Local hidden variable theoretic measure of quantumness of mutual information  

NASA Astrophysics Data System (ADS)

Entanglement, a manifestation of quantumness of correlations between the observables of the subsystems of a composite system, and the quantumness of their mutual information are widely studied characteristics of a system of spin-1/2 particles. The concept of quantumness of correlations between the observables of a system is based on incommensurability of the correlations with the predictions of some local hidden variable (LHV) theory. However, the concept of quantumness of mutual information does not invoke the LHV theory explicitly. In this paper, the concept of quantumness of mutual information for a system of two spin-1/2 particles, named A and B, in the state described by the density matrix \\hat{\\rho }^{AB} is formulated by invoking explicitly the LHV theory. To that end, the classical mutual information I(a, b) of the spins is assumed to correspond to the joint probability p(\\epsilon ^A_a;\\epsilon ^B_b) (\\epsilon ^A_a, \\epsilon ^B_b=+/- 1) for the spin A to have the component \\epsilon ^A_a/2 in the direction a and the spin B to have the component \\epsilon ^B_b/2 in the direction b, constructed by invoking the LHV theory. The quantumness of mutual information is then defined as Q_LHV =I_Q(\\hat{\\rho }^AB)-I_LHV where I_Q(\\hat{\\rho }^AB) is the quantum theoretic information content in the state \\hat{\\rho }^AB and the LHV theoretic classical information ILHV is defined in terms of I(a, b) by choosing the directions a, b as follows. The choice of the directions a, b is made by finding the Bloch vectors \\langle \\hat{\\bf S}^A\\rangle and \\langle \\hat{\\bf S}^B\\rangle of the spins A and B where \\hat{\\bf S}^A (\\hat{\\bf S}^B) is the spin vector of spin A (spin B) and \\langle \\hat{P}\\rangle =Tr(\\hat{P}\\hat{\\rho }^{AB}). The directions a and b are taken to be along the Bloch vector of A and B respectively if those Bloch vectors are non-zero. In that case ILHV = I(a, b) and QLHV turns out to be identical with the measurement induced disturbance. If \\langle \\hat{\\bf S}^A\\rangle =\\langle \\hat{\\bf S}^B\\rangle =0, then ILHV is defined to be the maximum of I(a, b) over a and b. The said optimization in this case can be performed analytically exactly and QLHV is then found to be the same as the symmetric discord. If \\langle \\hat{\\bf S}^A\\rangle =0, \\langle \\hat{\\bf S}^B\\rangle \

Puri, R. R.

2014-03-01

45

17O and 33S nuclear magnetic shielding of sulfur trioxides from the experimental measurements and theoretical calculations.  

PubMed

In a recent (17)O NMR spectra of liquid sulfur trioxide, several unexpected peaks appeared with the temperature-dependent integrated peak ratio. In order to interpret NMR spectra and assign peaks to possible molecular structures, the theoretical quantum mechanical density functional theory and Møller-Plesset second-order perturbation theory calculations were performed. It is suggested that in the liquid sulfur trioxide, apart from monomeric SO3, a significant amount of (SO3)3 cyclic trimers should appear. No theoretical data support hypothesis on (SO3)2 dimers formation. PMID:24446425

Makulski, W?odzimierz; Tulewicz, Adam; Le?, Andrzej

2014-03-01

46

Theoretical and experimental studies of (In,Ga)As/GaP quantum dots  

PubMed Central

(In,Ga)As/GaP(001) quantum dots (QDs) are grown by molecular beam epitaxy and studied both theoretically and experimentally. The electronic band structure is simulated using a combination of k·p and tight-binding models. These calculations predict an indirect to direct crossover with the In content and the size of the QDs. The optical properties are then studied in a low-In-content range through photoluminescence and time-resolved photoluminescence experiments. It suggests the proximity of two optical transitions of indirect and direct types. PMID:23176537

2012-01-01

47

MSU-Wind Applications Center: Wind Resource Worksheet Theoretical Power Calculation  

E-print Network

MSU-Wind Applications Center: Wind Resource Worksheet Theoretical Power Calculation Equations: A. = ___________/(________*________)= _________kg/m3 5. Theoretical Power a. Low Setting Theoretical Wind Power i. Power= ½*______*______*______*.59 = _____ (watts) b. High Setting Theoretical Wind Power i. Power= ½*______*______*______*.59 = _____ (watts) #12

Dyer, Bill

48

Theoretical study of transport property in InAsSb quantum well heterostructures  

NASA Astrophysics Data System (ADS)

Theoretical studies of transport properties in InAsSb-based quantum well heterostructures are presented. The concentration of two-dimensional electron gas is calculated self-consistently from our improved Schrödinger-Poisson model by taking into account of nonparabolicity effect and strain effect, and the results are used to obtain the electron mobility. All major scattering mechanisms by acoustic phonon, polar optical phonon, remote ionized impurity, background impurity, interface roughness, and alloy disorder have been included in our calculation. Particularly, dislocation scattering, intrasubband scattering, and intersubband scattering, which are always neglected in heterostructure systems, are considered. The calculated electron mobility is proved to be in good agreement with the experimental data for modulation-doped AlSb/InAsSb quantum well heterostructures. With a view to optimize the transport property, quantum well width, spacer thickness, barrier thickness, and remote doping concentration for AlSb/InAsSb heterostructures are discussed to examine their effect on total electron mobility. Intrinsic electron mobility exceeding 40 000 cm2/Vs is predicted at 300 K for AlSb/InAs0.4Sb0.6 heterostructures which is dominated by a combination of polar optical phonon scattering, remote ionized impurity scattering, and interface roughness scattering.

Zhang, Yuwei; Zhang, Yang; Guan, Min; Cui, Lijie; Wang, Chengyan; Zeng, Yiping

2013-10-01

49

Fast LiH Destruction in Reaction with H: Quantum Calculations and Astrophysical Consequences  

Microsoft Academic Search

We present a quantum-mechanical study of the exothermic 7LiH reaction with H. Accurate reactive probabilities and rate coefficients are obtained by solving the Schrödinger equation for the motion of the three nuclei on a single Born-Oppenheimer potential energy surface and using a coupled-channel hyperspherical coordinate method. Our new rates indeed confirm earlier, qualitative predictions and some previous theoretical calculations, as

S. Bovino; M. Wernli; F. A. Gianturco

2009-01-01

50

Efficient free energy calculations of quantum systems through computer simulations  

NASA Astrophysics Data System (ADS)

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)

Antonelli, Alex; Ramirez, Rafael; Herrero, Carlos; Hernandez, Eduardo

2009-03-01

51

Theoretical and Mathematical Physics, 158(2): 179195 (2009) FRACTIONAL GENERALIZATION OF THE QUANTUM  

E-print Network

in recent studies in physics (see, e.g., [9]­[12] and [13]­[16]). In quantum mechanics, observablesTheoretical and Mathematical Physics, 158(2): 179­195 (2009) FRACTIONAL GENERALIZATION OF THE QUANTUM MARKOVIAN MASTER EQUATION V. E. Tarasov We propose a generalization of the quantum Markovian

Tarasov, Vasily E.

52

Entanglement of Interacting Fermions in Quantum Monte Carlo Calculations  

NASA Astrophysics Data System (ADS)

Given a specific interacting quantum Hamiltonian in a general spatial dimension, can one access its entanglement properties, such as the entanglement entropy corresponding to the ground state wave function? Even though progress has been made in addressing this question for interacting bosons and quantum spins, as yet there exist no corresponding methods for interacting fermions. Here we show that the entanglement structure of interacting fermionic Hamiltonians has a particularly simple form—the interacting reduced density matrix can be written as a sum of operators that describe free fermions. This decomposition allows one to calculate the Renyi entropies for Hamiltonians which can be simulated via determinantal quantum Monte Carlo calculations, while employing the efficient techniques hitherto available only for free fermions. The method presented works for the ground state, as well as for the thermally averaged reduced density matrix.

Grover, Tarun

2013-09-01

53

Quantum Monte Carlo calculations of symmetric nuclear matter  

E-print Network

We present an accurate numerical study of the equation of state of nuclear matter based on realistic nucleon--nucleon interactions by means of Auxiliary Field Diffusion Monte Carlo (AFDMC) calculations. The AFDMC method samples the spin and isospin degrees of freedom allowing for quantum simulations of large nucleonic systems and can provide quantitative understanding of problems in nuclear structure and astrophysics.

Stefano Gandolfi; Francesco Pederiva; Stefano Fantoni; Kevin E. Schmidt

2006-07-12

54

Theoretical Calculations of the Characteristics of Precious Metal Clusters  

NASA Astrophysics Data System (ADS)

It is reported that core/shell type Pd/Pt bimetallic nanoclusters where the inner atoms of a Pd cluster are substituted by Pt atoms have extremely enhanced catalytic activity for cyclooctadiene hydrogenation. In order to discuss the electronic states of core/shell clusters, DFT calculations were carried out for Au13, Pd13, Pt13, Pt/Pd12, Pd/Pt12, Pd/Au12, Pd38, and Pd6/Pt32 clusters. From these calculations, it was found that the charge transfer between the core atoms and the shell atoms played an important role in the modification of the electronic state of the surface atoms.

Okumura, Mitsutaka; Kitagawa, Yasutaka; Kawakami, Takashi; Haruta, Masatake; Yamaguchi, Kizashi

2008-09-01

55

Information-theoretic approach to quantum error correction and reversible measurement  

E-print Network

Quantum operations provide a general description of the state changes allowed by quantum mechanics. The reversal of quantum operations is important for quantum error-correcting codes, teleportation, and reversing quantum measurements. We derive information-theoretic conditions and equivalent algebraic conditions that are necessary and sufficient for a general quantum operation to be reversible. We analyze the thermodynamic cost of error correction and show that error correction can be regarded as a kind of ``Maxwell demon,'' for which there is an entropy cost associated with information obtained from measurements performed during error correction. A prescription for thermodynamically efficient error correction is given.

M. A. Nielsen; Carlton M. Caves; Benjamin Schumacher; Howard Barnum

1997-06-30

56

A theoretical model for calculation of molecular stopping power  

Microsoft Academic Search

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

Y. J. Xu

1984-01-01

57

a Theoretical Model for Calculation of Molecular Stopping Power  

Microsoft Academic Search

A modified local plasma model based on the work of Linhard-Winther, Bethe, Brown, and Walske 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 H(,2) and He gas was calculated for incident proton energy ranging from 100 KeV to 2.5 MeV.

Yuan-Jian Xu

1984-01-01

58

Theoretical study of auger recombination processes in deep quantum wells  

SciTech Connect

The basic processes and mechanisms of Auger recombination of nonequilibrium carriers in a semiconductor heterostructure with deep InAs{sub 0.84}Sb{sub 0.16}/AlSb quantum wells (QWs) are analyzed. It is shown that a zero-threshold Auger recombination process involving two heavy holes predominates in sufficiently narrow QWs, and a resonant process involving two electrons is dominant in wide QWs. The range of QW widths at which the Auger recombination is suppressed in a given structure to the greatest extent (suppression region) is determined. In this case, the threshold process involving two electrons remains the basic nonradiative recombination process, with its probability being several orders of magnitude lower than those for the zero-threshold and resonant mechanisms. In turn, the zero-threshold mechanism involving two electrons is totally impossible in the heterostructure under study because of the large conduction-band offset (which markedly exceeds the energy gap). Also, the range of emission wavelengths that corresponds to the suppression region is estimated. It is shown that the interval calculated belongs to the mid-IR range.

Danilov, L. V., E-mail: danleon84@mail.ru; Zegrya, G. G. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)], E-mail: zegrya@theory.ioffe.ru

2008-05-15

59

Hydrogen in Ag-doped ZnO: theoretical calculations.  

PubMed

Based on density functional theory calculations, we systematically investigate the behaviors of a H atom in Ag-doped ZnO involving the preference sites, diffusion behaviors, the electronic structures, and vibrational properties. We find that a H atom can migrate to the doped Ag to form a Ag-H complex by overcoming energy barriers of 0.3-1.0 eV. The lowest-energy site for H location is the bond center of a Ag-O in the basal plane. Moreover, H can migrate between this site and its equivalent sites with energy cost of less than 0.5 eV. In contrast, dissociation of such a Ag-H complex needs energy of about 1.1-1.3 eV. This implies that the Ag-H complexes can commonly exist in the Ag-doped ZnO, which have a negative effect on the desirable p-type carrier concentrations of Ag-doped ZnO. In addition, based on the frozen phonon calculation, the vibrational properties of ZnO with a Ag-H complex are predicted. Some new vibrational modes associated with the Ag-H complex present in the vibrational spectrum of the system. PMID:19485466

He, H Y; Hu, J; Pan, B C

2009-05-28

60

Theoretical calculation of spectra of dibutyl phthalate and dioctyl phthalate  

NASA Astrophysics Data System (ADS)

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 ?* transition, and the stronger absorption in the E belt of benzene electronic transition from ? to ?*. There are blue shift for DOP end absorption belt from n to ?* transition and red shift for DOP E absorption belt from ? to ?* transition relative to that of DBP. This calculation results are better in accord with the spectral data measured by UNICO ultraviolet and visible spectrophotometer.

Du, Jian-Bin; Tang, Yan-Lin; Long, Zheng-Wen; Hu, Shuang-Hui; Li, Tao

2014-05-01

61

Quantum monte carlo calculations of light nuclei using chiral potentials.  

PubMed

We present the first Green's function Monte Carlo calculations of light nuclei with nuclear interactions derived from chiral effective field theory up to next-to-next-to-leading order. Up to this order, the interactions can be constructed in a local form and are therefore amenable to quantum Monte Carlo calculations. We demonstrate a systematic improvement with each order for the binding energies of A=3 and A=4 systems. We also carry out the first few-body tests to study perturbative expansions of chiral potentials at different orders, finding that higher-order corrections are more perturbative for softer interactions. Our results confirm the necessity of a three-body force for correct reproduction of experimental binding energies and radii, and pave the way for studying few- and many-nucleon systems using quantum Monte Carlo methods with chiral interactions. PMID:25415900

Lynn, J E; Carlson, J; Epelbaum, E; Gandolfi, S; Gezerlis, A; Schwenk, A

2014-11-01

62

Quantum Monte Carlo Calculations of Light Nuclei Using Chiral Potentials  

NASA Astrophysics Data System (ADS)

We present the first Green's function Monte Carlo calculations of light nuclei with nuclear interactions derived from chiral effective field theory up to next-to-next-to-leading order. Up to this order, the interactions can be constructed in a local form and are therefore amenable to quantum Monte Carlo calculations. We demonstrate a systematic improvement with each order for the binding energies of A =3 and A =4 systems. We also carry out the first few-body tests to study perturbative expansions of chiral potentials at different orders, finding that higher-order corrections are more perturbative for softer interactions. Our results confirm the necessity of a three-body force for correct reproduction of experimental binding energies and radii, and pave the way for studying few- and many-nucleon systems using quantum Monte Carlo methods with chiral interactions.

Lynn, J. E.; Carlson, J.; Epelbaum, E.; Gandolfi, S.; Gezerlis, A.; Schwenk, A.

2014-11-01

63

Quantum Monte Carlo calculations of light nuclei using chiral potentials  

E-print Network

We present the first Green's function Monte Carlo calculations of light nuclei with nuclear interactions derived from chiral effective field theory up to next-to-next-to-leading order. Up to this order, the interactions can be constructed in local form and are therefore amenable to quantum Monte Carlo calculations. We demonstrate a systematic improvement with each order for the binding energies of $A=3$ and $A=4$ systems. We also carry out the first few-body tests to study perturbative expansions of chiral potentials at different orders, finding that higher-order corrections are more perturbative for softer interactions. Our results confirm the necessity of a three-body force for correct reproduction of experimental binding energies and radii, and pave the way for studying few- and many-nucleon systems using quantum Monte Carlo methods with chiral interactions.

J. E. Lynn; J. Carlson; E. Epelbaum; S. Gandolfi; A. Gezerlis; A. Schwenk

2014-06-11

64

Quantum Monte Carlo calculations of light nuclei using chiral potentials  

E-print Network

We present the first Green's function Monte Carlo calculations of light nuclei with nuclear interactions derived from chiral effective field theory up to next-to-next-to-leading order. Up to this order, the interactions can be constructed in local form and are therefore amenable to quantum Monte Carlo calculations. We demonstrate a systematic improvement with each order for the binding energies of $A=3$ and $A=4$ systems. We also carry out the first few-body tests to study perturbative expansions of chiral potentials at different orders, finding that higher-order corrections are more perturbative for softer interactions. Our results confirm the necessity of a three-body force for correct reproduction of experimental binding energies and radii, and pave the way for studying few- and many-nucleon systems using quantum Monte Carlo methods with chiral interactions.

Lynn, J E; Epelbaum, E; Gandolfi, S; Gezerlis, A; Schwenk, A

2014-01-01

65

Quantum statistical calculation of cluster abundances in hot dense matter  

E-print Network

The cluster abundances are calculated from a quantum statistical approach taking into account in-medium corrections. For arbitrary cluster size the self-energy and Pauli blocking shifts are considered. Exploratory calculations are performed for symmetric matter at temperature $T=5$ MeV and baryon density $\\varrho=0.0156$ fm$^{-3}$ to be compared with the solar element distribution. It is shown that the abundances of weakly bound nuclei with mass number $4

Gerd Ropke

2014-07-01

66

A Quantum Theoretical Explanation for Probability Judgment Errors  

ERIC Educational Resources Information Center

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…

Busemeyer, Jerome R.; Pothos, Emmanuel M.; Franco, Riccardo; Trueblood, Jennifer S.

2011-01-01

67

Theoretical study of polarization tracking in satellite quantum key distribution  

Microsoft Academic Search

The BB84 and B92 protocols based on polarization coding are usually used in free-space quantum key distribution. Polarization tracking technique is one of the key techniques in the satellite quantum key distribution. Because the photon polarization state will be changed as a result of the satellite movement, both the transmitter and receiver need to have the ability to track the

Jing Ma; Guangyu Zhang; Yiwen Rong; Liying Tan

2005-01-01

68

Quantum-mechanical DFT calculation supported Raman spectroscopic study of some amino acids in bovine insulin.  

PubMed

In this article Quantum mechanical (QM) calculations by Density Functional Theory (DFT) have been performed of all amino acids present in bovine insulin. Simulated Raman spectra of those amino acids are compared with their experimental spectra and the major bands are assigned. The results are in good agreement with experiment. We have also verified the DFT results with Quantum mechanical molecular mechanics (QM/MM) results for some amino acids. QM/MM results are very similar with the DFT results. Although the theoretical calculation of individual amino acids are feasible, but the calculated Raman spectrum of whole protein molecule is difficult or even quite impossible task, since it relies on lengthy and costly quantum-chemical computation. However, we have tried to simulate the Raman spectrum of whole protein by adding the proportionate contribution of the Raman spectra of each amino acid present in this protein. In DFT calculations, only the contributions of disulphide bonds between cysteines are included but the contribution of the peptide and hydrogen bonds have not been considered. We have recorded the Raman spectra of bovine insulin using micro-Raman set up. The experimental spectrum is found to be very similar with the resultant simulated Raman spectrum with some exceptions. PMID:24747859

Tah, Bidisha; Pal, Prabir; Roy, Sourav; Dutta, Debodyuti; Mishra, Sabyashachi; Ghosh, Manash; Talapatra, G B

2014-08-14

69

The heat of formation of the uranyl dication: theoretical evaluation based on relativistic density functional calculations.  

PubMed

By using a set of model reactions, we estimated the heat of formation of gaseous UO2(2+) from quantum-chemical reaction enthalpies and experimental heats of formation of reference species. For this purpose, we performed relativistic density functional calculations for the molecules UO2(2+), UO2, UF6, and UF5. We used two gradient-corrected exchange-correlation functionals (revised Perdew-Burke-Ernzerhof (PBEN) and Becke-Perdew (BP)) and we accounted for spin-orbit interaction in a self-consistent fashion. Indeed, spin-orbit interaction notably affects the energies of the model reactions, especially if compounds of U(IV) are involved. Our resulting theoretical estimates for delta fH(o)0 (UO2(2+)), 365+/-10 kcal mol(-1) (PBEN) and 370+/-12 kcal mol(-1) (BP), are in quantitative agreement with a recent experimental result, 364+/-15 kcal mol(-1). Agreement between the results of the two different exchange-correlation functionals PBEN and BP supports the reliability of our approach. The procedure applied offers a general means to derive unknown enthalpies of formation of actinide species based on the available well-established data for other compounds of the element in question. PMID:16331710

Moskaleva, Lyudmila V; Matveev, Alexei V; Krüger, Sven; Rösch, Notker

2005-12-23

70

Theoretical prediction of improved figure-of-merit in Si/Ge quantum dot superlattices  

NASA Astrophysics Data System (ADS)

A detailed theoretical model for thermoelectric transport perpendicular to the multilayers of a Si-Ge heterostructure is presented. The electronic structure of a three-dimensional superlattice, consisting of a regular array of Ge quantum dots in each layer, capped by Si layers, is calculated using an atomistic tight-binding approach. The Seebeck coefficient, the electric conductivity and the contribution of the electrons to the thermal conductivity for n-doped samples are worked out within Boltzmann transport theory. Using experimental literature data for the lattice thermal conductivity, we determine the temperature dependence of the figure of merit ZT. A nonlinear increase of ZT with temperature is found, with ZT > 2 at T = 1000 K in highly doped samples. Moreover, we find an enhanced thermoelectric power factor already at room temperature and below, which is due to highly mobile electrons in strain-induced conductive channels.

Fiedler, Gregor; Kratzer, Peter

2013-12-01

71

Theoretical approach to ground states of the ?=2/3 bilayer fractional quantum Hall systems  

NASA Astrophysics Data System (ADS)

The ground states and phase diagrams of the ?=2/3 bilayer fractional quantum Hall systems at the layer balanced point are investigated theoretically by finite size exact-diagonalization calculations and an exactly solvable model. The degeneracy of the ground states occurs depending on the difference between intralayer and interlayer Coulomb energies, when interlayer tunneling energy (?SAS) gets close to zero. The transitions between the spin-polarized and spin-unpolarized phases are mainly determined by the competition between the Zeeman energy (?Z) and the electron Coulomb energy. The phase diagrams in ?SAS-?Z planes are given for the first time. We also compare the numerical results with the experimental data and acquire a good agreement.

Zheng, Yangdong; Sawada, Anju; Ezawa, Zyun F.

2013-02-01

72

CS294-4: Fourier Transforms and Theoretical Computer Science Spring 1999 Lecture 11: Quantum Algorithms  

E-print Network

CS294-4: Fourier Transforms and Theoretical Computer Science Spring 1999 Lecture 11: Quantum of the major quantum algorithms. We will discuss the next algorithms: #15; Computation of Fourier Transform #15 Computation of Fourier Transform We consider two kinds of Fourier Transforms: #15; Fourier Transform over ZZ N

Vazirani, Umesh

73

The theoretical apparatus of semantic realism: A new language for classical and quantum physics  

Microsoft Academic Search

The standard interpretation of quantum physics (QP) and some recent generalizations of this theory rest on the adoption of a rerificationist theory of truth and meaning, while most proposals for modifying and interpreting QP in a realistic way attribute an ontological status to theoretical physical entities (ontological realism). Both terms of this dichotomy are criticizable, and many quantum paradoxes can

Claudio Garola; Luigi Solombrino

1996-01-01

74

Reconciling field-theoretical and semiclassical approaches to quantum 2D antiferromagnets  

Microsoft Academic Search

We show that, starting from the field-theoretical expression for the correlation length ? of the 2D quantum Heisenberg antiferromagnet corrected for cut-off effects and our knowledge of the classical thermodynamics of the model, the observed temperature dependence of ? can be reproduced. We find also that the cut-off effects contains the same pure-quantum renormalizations of the pure-quantum self-consistent harmonic approximation

Bernard B. Beard; Alessandro Cuccoli; Ruggero Vaia; Paola Verrucchi

2004-01-01

75

A theoretical study of blue phosphorene nanoribbons based on first-principles calculations  

NASA Astrophysics Data System (ADS)

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.

Xie, Jiafeng; Si, M. S.; Yang, D. Z.; Zhang, Z. Y.; Xue, D. S.

2014-08-01

76

Generalized information theoretic measure to discern the quantumness of correlations  

E-print Network

A novel measure, quantumness of correlations is introduced here for bipartite states, by incorporating the required measurement scheme crucial in defining any such quantity. Quantumness coincides with the previously proposed measures in special cases and it vanishes for separable states - a feature not captured by the measures proposed earlier. It is found that an optimal generalized measurement on one of the parts leaves the overall state in its closest separable form, which shares the same marginal for the other part, implying that quantumness is non-zero for all entangled bipartite states and it serves as an upper bound to the relative entropy of entanglement.

A. R. Usha Devi; A. K. Rajagopal

2007-07-15

77

Theoretical study of polarization tracking in satellite quantum key distribution  

E-print Network

The BB84 and B92 protocols based on polarization coding are usually used in free-space quantum key distribution. Polarization tracking technique is one of the key techniques in the satellite quantum key distribution. Because the photon polarization state will be changed as a result of the satellite movement, both the transmitter and receiver need to have the ability to track the polarization orientation variation to accomplish the quantum cryptography protocols. In this paper, the polarization tracking principles are analyzed based on Faraday effect and the half-wave plate. The transforms of six photon polarization states in three conjugative bases are given and the quantum key coding principles based on the polarization tracking are analyzed for the BB84 and B92 protocols.

Jing Ma; Guangyu Zhang; Yiwen Rong; Liying Tan

2005-04-11

78

Theoretical analysis of quantum ghost imaging through turbulence  

E-print Network

Atmospheric turbulence generally affects the resolution and visibility of an image in long-distance imaging. In a recent quantum ghost imaging experiment [P. B. Dixon et al. Phys. Rev. A 83 051803 (2011)], it was found ...

Chan, Kam Wai Clifford

79

Quantum chemistry calculation of resveratrol and related stilbenes  

NASA Astrophysics Data System (ADS)

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.

Del Nero, J.; de Melo, C. P.

2003-01-01

80

The Nature of Infinity in Quantum Field Calculations  

NASA Astrophysics Data System (ADS)

In many textbooks on Quantum Field Theory it has been noted that an infinity is taken a circle and the flux is calculated from the A field in that manner. There are of course many such examples of this sort of calculation using infinity as a circle. This author would like to point out that if the three dimensions of space are curved and the one dimension of time is not, in say a four space, infinity is the horizon, which is not a circle but rather a sphere; as long as space-time is curved uniformly, smoothly and has positive curvature. This author believes the math may be in error, since maps of the CMBR seem to indicate a ``Swiss-Cheese'' type of topology, wherein the Sphere at infinity (the Horizon of the Universe), has holes in it that can readily be seen. This author believes that these irregularities most certainly have a calculable effect on QED, QCD and Quantum Field Theory.

Kriske, Richard

2011-06-01

81

Theoretical investigations on molecular structure, vibrational spectra, HOMO, LUMO, NBO analysis and hyperpolarizability calculations of thiophene-2-carbohydrazide  

NASA Astrophysics Data System (ADS)

The Fourier-Transform infrared and Fourier-Transform Raman spectra of thiophene-2-carbohydrazide (TCH) was recorded in the region 4000-400 cm-1 and 3500-100 cm-1. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of TCH were carried out by DFT (B3LYP) method with 6-311++G(d,p) as basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. Stability of the molecule arising from hyper conjugative interaction and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV spectrum was measured in different solvent. The energy and oscillator strength are calculated by Time Dependant Density Functional Theory (TD-DFT) results. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. The complete assignments were performed on the basis of the potential energy distribution (PED) of vibrational modes, calculated with scaled quantum mechanics (SQM) method. Finally the theoretical FT-IR, FT-Raman, and UV spectra of the title molecule have also been constructed.

Balachandran, V.; Janaki, A.; Nataraj, A.

2014-01-01

82

Calculation of low-lying energy levels in quantum mechanics  

E-print Network

This paper proposes a very simple perturbative technique to calculate the low-lying eigenvalues and eigenstates of a parity-symmetric quantum-mechanical potential. The technique is to solve the time-independent Schroedinger eigenvalue problem as a perturbation series in which the perturbation parameter is the energy itself. Unlike nearly all perturbation series for physical problems, for the ground state this perturbation expansion is convergent and, even though the ground-state energy is in general not small compared with 1, the perturbative results are numerically accurate. The perturbation series is divergent for higher energy levels but can be easily evaluated by using methods such as Pade summation.

Carl M. Bender; Hugh F. Jones

2014-02-05

83

Importance of parametrizing constraints in quantum-mechanical variational calculations  

NASA Technical Reports Server (NTRS)

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.

Chung, Kwong T.; Bhatia, A. K.

1992-01-01

84

Ambiguity in quantum-theoretical descriptions of experiments  

E-print Network

This paper contributes to a burgeoning area of investigation, the ambiguity inherent in mathematics and the implications for physics of this ambiguity. To display the mathematical form of equations of quantum theory used to describe experiments, we make explicit the knobs by which the devices of an experiment are arranged and adjusted. A quantum description comes in two parts: (1) a statement of results of an experiment, expressed by probabilities of detections as functions of knob settings, and (2) an explanation of how we think these results come about, expressed by linear operators, also as functions of knob settings. Because quantum mechanics separates the two parts of any description, it is known that between the statements of results and the explanations lurks a logical gap: given any statement of results one has a choice of explanations. Here we work out some consequences of this openness to choice. We show how quantum theory as mathematical language in which to describe experiments necessarily involves multiple descriptions: multiple explanations of a given result, as well as multiple statements of results and multiple arrangement of knobs. Appreciating these multiplicities resolves what otherwise is a confusion in the concept of invariance. Implications of multiplicity of description for the security of quantum key distribution are noted.

John M. Myers; F. Hadi Madjid

2014-09-19

85

Biological applications of hybrid quantum mechanics/molecular mechanics calculation.  

PubMed

Since in most cases biological macromolecular systems including solvent water molecules are remarkably large, the computational costs of performing ab initio calculations for the entire structures are prohibitive. Accordingly, QM calculations that are jointed with MM calculations are crucial to evaluate the long-range electrostatic interactions, which significantly affect the electronic structures of biological macromolecules. A UNIX-shell-based interface program connecting the quantum mechanics (QMs) and molecular mechanics (MMs) calculation engines, GAMESS and AMBER, was developed in our lab. The system was applied to a metalloenzyme, azurin, and PU.1-DNA complex; thereby, the significance of the environmental effects on the electronic structures of the site of interest was elucidated. Subsequently, hybrid QM/MM molecular dynamics (MD) simulation using the calculation system was employed for investigation of mechanisms of hydrolysis (editing reaction) in leucyl-tRNA synthetase complexed with the misaminoacylated tRNA(Leu), and a novel mechanism of the enzymatic reaction was revealed. Thus, our interface program can play a critical role as a powerful tool for state-of-the-art sophisticated hybrid ab initio QM/MM MD simulations of large systems, such as biological macromolecules. PMID:22536015

Kang, Jiyoung; Hagiwara, Yohsuke; Tateno, Masaru

2012-01-01

86

Crystal structure and theoretical calculations of Julocrotine, a natural product with antileishmanial activity  

NASA Astrophysics Data System (ADS)

Julocrotine, N-(2,6-dioxo-1-phenethyl-piperidin-3-yl)-2-methyl-butyramide, is a potent antiproliferative agent against the promastigote and amastigote forms of Leishmania amazonensis (L.). In this work, the crystal structure of Julocrotine was solved by X-ray diffraction, and its geometrical parameters were compared with theoretical calculations at the B3LYP and HF level of theory. IR and NMR spectra also have been obtained and compared with theoretical calculations. IR absorptions calculated with the B3LYP level of theory employed together with the 6-311G+(d,p) basis set, are close to those observed experimentally. Theoretical NMR calculations show little deviation from experimental results. The results show that the theory is in accordance with the experimental data.0

Moreira, Rafael Y. O.; Brasil, Davi S. B.; Alves, Cláudio N.; Guilhon, Giselle M. S. P.; Santos, Lourivaldo S.; Arruda, Mara S. P.; Müller, Adolfo H.; Barbosa, Patrícia S.; Abreu, Alcicley S.; Silva, Edilene O.; Rumjanek, Victor M.; Souza, Jaime, Jr.; da Silva, Albérico B. F.; Santos, Regina H. De A.

87

Open Quantum Dynamics Calculations with the Hierarchy Equations of Motion on Parallel Computers.  

PubMed

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. PMID:23105920

Strümpfer, Johan; Schulten, Klaus

2012-08-14

88

Photoluminescence spectroscopy of trions in quantum dots: A theoretical description  

NASA Astrophysics Data System (ADS)

We present a full configuration-interaction study of the spontaneous recombination of neutral and singly charged excitons (trions) in semiconductor quantum dots from weak- to strong-coupling regimes. We find that the enhancement of the recombination rate of neutral excitons with increasing dot size is suppressed for negative trions and even reversed for positive trions. Our findings agree with recent comprehensive photoluminescence experiments in self-assembled quantum dots [P. Dalgarno , Phys. Rev. B 77, 245311 (2008)] and confirm the major role played by correlations in the valence band. The effect of the temperature on the photoluminescence spectrum and that of the ratio between the electron and hole wave-function length scales are also described.

Climente, Juan I.; Bertoni, Andrea; Goldoni, Guido

2008-10-01

89

Multiconfigurational nuclear-electronic orbital approach: Incorporation of nuclear quantum effects in electronic structure calculations  

E-print Network

Multiconfigurational nuclear-electronic orbital approach: Incorporation of nuclear quantum effects are that nuclear quantum effects are incorporated during the electronic structure calculation, the Born basis functions. They also enable the location and characterization of geometry stationary points

Hammes-Schiffer, Sharon

90

Structure and vibrational spectrum of 2-methylallyl radical. Nonempirical quantum chemical calculation  

SciTech Connect

In the study of the role of allyl type radicals in the pyrolysis of hydrocarbons it is of interest to investigate the conditions of formation, structure, and reactivity of 2-methylallyl radical (C/sub 4/H/sub 7//sup ./). The authors performed theoretical assignment of the bands, which were observed in the lattice spectra of the pyrolysis products, to the vibrations of the C/sub 4/H/sub 7//sup ./ radical by means of calculation of the frequencies and shapes of the normal vibrations. Since the necessary geometrical parameters and force coefficients of C/sub 4/H/sub 7//sup ./ are not known, they determined them by means of nonempirical quantum chemical calculation. The quantum chemical calculation of C/sub 4/H/sub 7//sup ./ was performed by means of the unrestricted Hartree-Fock method using STO-4G (geometry optimization taking into account the characteristics of calculation of radicals in minimal bases and calculation of the force coefficients by means of numerical differentiation) and 4-31G bases (electron density distribution) by means of GAUSSIAN-70 program. For comparison of the energy and electron density distribution they performed calculations also for the 2-methylallyl cation C/sub 4/H/sub 7//sup ./. From the calculation of the difference of the total energies of C/sub 4/H/sub 7//sup ./ and C/sub 4/H/sub 7//sup ./ in the 4-31G basis was 7.4 eV, which is comparable to the ionization energy of the 2-methylallyl radical, 7.95 eV.

Avakyan, V.G.; Volkova, V.V.; Gusel'nikov, L.E.; Ziegler, U.; Zimmermann, G.; Ondurshka, B.; Nametkin, N.S.

1987-04-01

91

Calculated quantum yield of photosynthesis of phytoplankton in the Marine Light-Mixed Layers (59 deg N, 21 deg W)  

NASA Technical Reports Server (NTRS)

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.

Carder, K. L.; Lee, Z. P.; Marra, John; Steward, R. G.; Perry, M. J.

1995-01-01

92

Quantum chemical calculations, vibrational studies, HOMO-LUMO and NBO/NLMO analysis of 2-bromo-5-nitrothiazole  

NASA Astrophysics Data System (ADS)

The complete vibrational assignment and analysis of the fundamental modes of 2-bromo-5-nitrothiazole (BNT) was carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the ab initio HF and DFT-B3LYP gradient calculations employing 6-311++G(d,p) basis set. Thermodynamic properties like entropy, heat capacity and zero point energy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of BNT have been computed using B3LYP quantum chemical calculation.

Gobinath, E.; Xavier, R. John

2013-03-01

93

Constant chemical potential approach for quantum chemical calculations in electrocatalysis.  

PubMed

In order to simulate electrochemical reactions in the framework of quantum chemical methods, density functional theory, methods can be devised that explicitly include the electrochemical potential. In this work we discuss a Grand Canonical approach in the framework of density functional theory in which fractional numbers of electrons are used to represent an open system in contact with an electrode at a given electrochemical potential. The computational shortcomings and the additional effort in such calculations are discussed. An ansatz for a SCF procedure is presented, which can be applied routinely and only marginally increases the computational effort of standard constant electron number approaches. In combination with the common implicit solvent models this scheme can become a powerful tool, especially for the investigation of omnipresent non-faradaic effects in electrochemistry. PMID:24991504

Schneider, Wolfgang B; Auer, Alexander A

2014-01-01

94

Exact Quantum Dynamics Calculations Using Phase Space Wavelets  

NASA Astrophysics Data System (ADS)

In a series of earlier papers, the authors introduced the first exact quantum dynamics method that defeats the exponential scaling of CPU effort with system dimensionality. The method used a ``weylet'' basis set (orthogonalized Weyl-Heisenberg wavelets), combined with a phase space truncation scheme first proposed by M. Davis and E. Heller. Here, we use a related, but much simpler, wavelet basis consisting of momentum-symmetrized phase space Gaussians. Despite being non-orthogonal, symmetrized Gaussians exhibit collective locality, allowing for effective phase space truncation and the defeat of exponential scaling. A ``universal'' and remarkably simple code has been written, which is dimensionally independent, and which also exploits massively parallel algorithms. The codes have been used to calculate the vibrational spectra of several molecules of varying dimensionality.

Halverson, Thomas; Poirier, Bill

2013-06-01

95

Fragment quantum mechanical calculation of proteins and its applications.  

PubMed

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 embedding field in each fragment calculation and two-body interaction energy correction on top of the MFCC approach, the EE-GMFCC method is capable of accurately reproducing the QM molecular properties (such as the dipole moment, electron density, and electrostatic potential), the total energy, and the electrostatic solvation energy from full system calculations for proteins. On the other hand, the AF-QM/MM method was used for the efficient QM calculation of protein nuclear magnetic resonance (NMR) parameters, including the chemical shift, chemical shift anisotropy tensor, and spin-spin coupling constant. In the AF-QM/MM approach, each amino acid and all the residues in its vicinity are automatically assigned as the QM region through a distance cutoff for each residue-centric QM/MM calculation. Local chemical properties of the central residue can be obtained from individual QM/MM calculations. The AF-QM/MM approach precisely reproduces the NMR chemical shifts of proteins in the gas phase from full system QM calculations. Furthermore, via the incorporation of implicit and explicit solvent models, the protein NMR chemical shifts calculated by the AF-QM/MM method are in excellent agreement with experimental values. The applications of the AF-QM/MM method may also be extended to more general biological systems such as DNA/RNA and protein-ligand complexes. PMID:24851673

He, Xiao; Zhu, Tong; Wang, Xianwei; Liu, Jinfeng; Zhang, John Z H

2014-09-16

96

Information-theoretic treatment of tripartite systems and quantum channels  

NASA Astrophysics Data System (ADS)

A Holevo measure is used to discuss how much information about a given positive operator valued measure (POVM) on system a is present in another system b, and how this influences the presence or absence of information about a different POVM on a in a third system c. The main goal is to extend information theorems for mutually unbiased bases or general bases to arbitrary POVMs, and especially to generalize “all-or-nothing” theorems about information located in tripartite systems to the case of partial information, in the form of quantitative inequalities. Some of the inequalities can be viewed as entropic uncertainty relations that apply in the presence of quantum side information, as in recent work by Berta [Nature PhysicsRMPHAT1745-247310.1038/nphys1734 6, 659 (2010)]. All of the results also apply to quantum channels: For example, if E accurately transmits certain POVMs, the complementary channel F will necessarily be noisy for certain other POVMs. While the inequalities are valid for mixed states of tripartite systems, restricting to pure states leads to the basis invariance of the difference between the information about a contained in b and c.

Coles, Patrick J.; Yu, Li; Gheorghiu, Vlad; Griffiths, Robert B.

2011-06-01

97

Theoretical Calculations for Predicted States of Heavy Quarkonium via Non-Relativistic Frame Work  

E-print Network

In this paper, we calculate the mass spectra of heavy quarkonium by using matrix Numerov's method to make the predictions of F and G states for further experiments. The method gives a very reasonable result which is in a good agreement with other methods and with recently published theoretical data. From the yielded wave functions we calculate the root mean square radius r_ms and \\b{eta} coefficients of heavy quarkonium

A. M. Yasser; T. A. Nahool; G. S. Hassan

2014-10-18

98

Theoretical Calculations for Predicted States of Heavy Quarkonium via Non-Relativistic Frame Work  

E-print Network

In this paper, we calculate the mass spectra of heavy quarkonium by using matrix Numerov's method to make the predictions of F and G states for further experiments. The method gives a very reasonable result which is in a good agreement with other methods and with recently published theoretical data. From the yielded wave functions we calculate the root mean square radius r_ms and \\b{eta} coefficients of heavy quarkonium

Yasser, A M; Hassan, G S

2014-01-01

99

Quantum Monte Carlo calculations of NiO  

NASA Astrophysics Data System (ADS)

We describe variational and diffusion quantum Monte Carlo (VMC and DMC) calculations [1] of NiO using a 1024-electron simulation cell. We have used a smooth, norm-conserving, Dirac-Fock pseudopotential [2] in our work. Our trial wave functions were of Slater-Jastrow form, containing orbitals generated in Gaussian-basis UHF periodic calculations. Jastrow factor is optimized using variance minimization with optimized cutoff lengths using the same scheme as our previous work. [4] We apply the lattice regulated scheme [5] to evaluate non-local pseudopotentials in DMC and find the scheme improves the smoothness of the energy-volume curve. [1] CASINO ver.2.1 User Manual, University of Cambridge (2007). [2] J.R. Trail et.al., J. Chem. Phys. 122, 014112 (2005). [3] CRYSTAL98 User's Manual, University of Torino (1998). [4] Ryo Maezono et.al., Phys. Rev. Lett., 98, 025701 (2007). [5] Michele Casula, Phys. Rev. B 74, 161102R (2006).

Maezono, Ryo; Towler, Mike D.; Needs, Richard. J.

2008-03-01

100

Invariant-theoretic method for calculating Clebsch-Gordan coefficients for space groups  

SciTech Connect

A new invariant-theoretic method to directly calculate Clebsch-Gordan coefficients for space and point groups representations is proposed. The method is exemplified with the space groups O{sub h}{sup 5} and D{sub 6h}{sup 1}. 34 refs.

Aizenberg, A.Ya.; Gufan, Yu.M. [North Caucasus Research Center, Rostov-na-Donu (Russian Federation)

1995-03-01

101

Time Asymmetry in Quantum Physics - I. Theoretical Conclusion from Resonance and Decay-Phenomenology  

E-print Network

It is explained how the unification of resonance and decay phenomena into a consistent mathematical theory leads to quantum mechanical time-asymmetry. This provides the theoretical basis for a subsequent paper II in which the interpretation and experimental demonstration of this time-asymmetry is discussed.

A. Bohm; H. Kaldass; S. Komy

2007-03-18

102

REVIEW: Experimental and theoretical challenges for the trapped electron quantum computer  

Microsoft Academic Search

We discuss quantum information processing with trapped electrons. After recalling the operation principle of planar Penning traps, we sketch the experimental conditions to load, cool and detect single electrons. Here we present a detailed investigation of a scalable scheme including feasibility studies and the analysis of all important elements, relevant for the experimental stage. On the theoretical side, we discuss

IRENE MARZOLI; PAOLO TOMBESI; GIACOMO CIARAMICOLI; G. Werth; P. Bushev; S. Stahl; F. Schmidt-Kaler; M. Hellwig; C. Henkel; G. Marx; I. Jex; E. Stachowska; G. Szawiola; A. Walaszyk

2009-01-01

103

Black Hole State Counting in Loop Quantum Gravity: A Number-Theoretical Approach  

Microsoft Academic Search

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

Iván Agulló; J. Fernando Barbero G; Jacobo Díaz-Polo; Enrique Fernández-Borja; Eduardo J. S. Villaseñor

2008-01-01

104

Theoretical and Experimental Investigation of Quantum Dot Passively Mode Locked Lasers for  

E-print Network

Theoretical and Experimental Investigation of Quantum Dot Passively Mode Locked Lasers for Telecomm lasers. The motivation behind this endeavour was the fundamental need, of many scientific areas, for high power, ultra-short and time stabilized optical pulses, generated directly from highly integrated laser

Kouroupetroglou, Georgios

105

Theoretical quantum chemical study of protonated - deuteronated PAHs: Interstellar implications  

NASA Astrophysics Data System (ADS)

Diffuse Interstellar Bands (DIBs) are optical absorption features on the interstellar extinction curve. Ultra-high resolution spectroscopic observations suggest that at least some of these features are due to large molecules. Observational results also reveal that the strengths of the DIBs are not strongly correlated with each other, implying that there must be several carriers. Considering the wide range of interstellar species and the cost and duration of experimental work that is involved to determine the carriers of DIBs, Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT) calculations offer opportunities to investigate which molecules are suitable for laboratory studies. The widespread presence of Polycyclic Aromatic Hydrocarbons (PAHs) in astrophysical environments is known from observations of the Unidentified Infrared (UIR) emission bands. Since PAHs are stable enough to be present under interstellar conditions, they are good candidates to be the carriers of the DIBs. We report DFT and TDDFT calculations to predict electronic transitions of neutral as well as protonated-deuteronated PAHs with various sites of protonation and deuteronation. The PAH molecules considered for calculation include pyrene, perylene, coronene and heptacene. Compared to their neutral forms, these charged isoelectronic forms of PAHs are predicted to have active transitions in the visible region, which means they are suitable candidates as carriers for some of the DIBs.

Buragohain, Mridusmita; Pathak, Amit; Hammonds, Mark; Sarre, Peter J.

2013-06-01

106

Quantum Monte Carlo calculations of the one-body density matrix and excitation energies of silicon  

E-print Network

for realistic systems are the variational quantum Monte Carlo1,2 VMC and diffusion quantum Monte Carlo2,3 DMCQuantum Monte Carlo calculations of the one-body density matrix and excitation energies of silicon, Madingley Road, Cambridge CB3 0HE, United Kingdom Received 8 October 1997 Quantum Monte Carlo QMC techniques

Kent, Paul

107

Accurate Calculations of Rotationally Inelastic Scattering Cross Sections Using Mixed Quantum/Classical Theory  

E-print Network

of rotationally inelastic scattering of molecules, we propose to use the mixed quantum/classical theory, MQCT. The idea of such mixed quantum/classical theory (MQCT) is not entirely new, but it has never been fullyAccurate Calculations of Rotationally Inelastic Scattering Cross Sections Using Mixed Quantum/Classical

Reid, Scott A.

108

Fundamental High-Pressure Calibration from All-Electron Quantum Monte Carlo Calculations  

NASA Astrophysics Data System (ADS)

We develop an all-electron quantum Monte Carlo (QMC) method for solids that does not rely on pseudopotentials, and use it to construct a primary ultra-high-pressure calibration based on the equation of state of cubic boron nitride. We compute the static contribution to the free energy with the QMC method and obtain the phonon contribution from density functional theory, yielding a high-accuracy calibration up to 900 GPa usable directly in experiment. We compute the anharmonic Raman frequency shift with QMC simulations as a function of pressure and temperature, allowing optical pressure calibration. In contrast to present experimental approaches, small systematic errors in the theoretical EOS do not increase with pressure, and no extrapolation is needed. This all-electron method is applicable to first-row solids, providing a new reference for ab initio calculations of solids and benchmarks for pseudopotential accuracy.

Esler, K. P.; Cohen, R. E.; Militzer, B.; Kim, Jeongnim; Needs, R. J.; Towler, M. D.

2010-05-01

109

Fundamental high-pressure calibration from all-electron quantum Monte Carlo calculations.  

PubMed

We develop an all-electron quantum Monte Carlo (QMC) method for solids that does not rely on pseudopotentials, and use it to construct a primary ultra-high-pressure calibration based on the equation of state of cubic boron nitride. We compute the static contribution to the free energy with the QMC method and obtain the phonon contribution from density functional theory, yielding a high-accuracy calibration up to 900 GPa usable directly in experiment. We compute the anharmonic Raman frequency shift with QMC simulations as a function of pressure and temperature, allowing optical pressure calibration. In contrast to present experimental approaches, small systematic errors in the theoretical EOS do not increase with pressure, and no extrapolation is needed. This all-electron method is applicable to first-row solids, providing a new reference for ab initio calculations of solids and benchmarks for pseudopotential accuracy. PMID:20482190

Esler, K P; Cohen, R E; Militzer, B; Kim, Jeongnim; Needs, R J; Towler, M D

2010-05-01

110

Full-dimensional quantum calculations of the vibrational states of H5(+).  

PubMed

Full-dimensional quantum calculations of the vibrational states of H5(+) have been performed on the accurate potential energy surface developed by Xie et al. [J. Chem. Phys. 122, 224307 (2005)]. The zero point energies of H5(+), H4D(+), D4H(+), and D5(+) and their ground-state geometries are presented and compared with earlier theoretical results. The first 10 low-lying excited states of H5(+) are assigned to the fundamental, overtone, and combination of the H2-H3(+) stretch, the shared proton hopping and the out-of-plane torsion. The ground-state torsional tunneling splitting, the fundamental of the photon hopping mode and the first overtone of the torsion mode are 87.3 cm(-1), 354.4 cm(-1), and 444.0 cm(-1), respectively. All of these values agree well with the diffusion Monte Carlo and multi-configuration time-dependent Hartree results where available. PMID:23556725

Song, Hongwei; Lee, Soo-Ying; Yang, Minghui; Lu, Yunpeng

2013-03-28

111

Quantum calculations of correlated electron-ion collisions in a strong laser field  

E-print Network

Quantum calculations of correlated electron-ion collisions in a strong laser field G. Rascol, H September 2006; published online 31 October 2006 The energy spectrum and angular distribution of electrons for small impact parameters. The energy distribution has been calculated quantum-mechanically by a method

Kull, Hans-Jörg

112

Theoretical Calculation of Photoabsorption of Various Polymers in an Extreme Ultraviolet Region  

Microsoft Academic Search

We have calculated the linear absorption coefficients of various resist polymers using the mass absorption coefficients at 13 nm and the density obtained from the graph-theoretical treatment derived by Bicerano. The values indicate that the transmittance at 13 nm of conventional resists used in 193-nm, 248-nm and 365-nm lithography is about 30% when the thickness is 3000 Å and 60

Nobuyuki N. Matsuzawa; Hiroaki Oizumi; Shigeyasu Mori; Shigeo Irie; Shigeru Shirayone; Ei Yano; Shinji Okazaki; Akihiko Ishitani; David A. Dixon

1999-01-01

113

A Mathematical Solution to the Theoretical Band Gap Underestimation: Predictive Calculations of Properties of Semiconductors  

Microsoft Academic Search

Most density functional theory (DFT) calculations find band gaps that are 30-50 percent smaller than the experimental ones, as illustrated in this presentation that recalls some popular explanations of this band gap problem, i.e., self-interaction effects and derivative discontinuities of the exchange correlation energy. A survey of the increasingly numerous approaches aimed at resolving the theoretical underestimation follows these explanations.

Diola Bagayoko

2008-01-01

114

A formula for calculating theoretical photoelectron fluxes resulting from the He/+/ 304 A solar spectral line  

NASA Technical Reports Server (NTRS)

A simplified method for the evaluation of theoretical photoelectron fluxes in the upper atmosphere resulting from the solar radiation at 304 A is presented. The calculation is based on considerations of primary and cascade (secondary) photoelectron production in the two-stream model, where photoelectron transport is described by two electron streams, one moving up and one moving down, and of loss rates due to collisions with neutral gases and thermal electrons. The calculation is illustrated for the case of photoelectrons at an energy of 24.5 eV, and it is noted that the 24.5-eV photoelectron flux may be used to monitor variations in the solar 304 A flux. Theoretical calculations based on various ionization and excitation cross sections of Banks et al. (1974) are shown to be in generally good agreement with AE-E measurements taken between 200 and 235 km, however the use of more recent, larger cross sections leads to photoelectron values a factor of two smaller than observations but in agreement with previous calculations. It is concluded that a final resolution of the photoelectron problem may depend on a reevaluation of the inelastic electron collision cross sections.

Richards, P. G.; Torr, D. G.

1981-01-01

115

Quantum chemical calculations of vibrational spectra of para-ethylbenzenesulfonic acid  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations of vibrational spectra of para-ethylbenzenesulfonic acid have been conducted by means of a non-empirical SCF MO LCAO method with the use of the 6-31G( d) basis set. Calculated IR and Raman frequencies are assigned to vibrations of specific atomic groups. It is shown that para-ethylbenzenesulfonic acid can serve as a reasonable quantum chemical model in calculations of vibrational spectra for polystyrene sulfonic resins of various degrees of hydration.

Zelenkovskii, V. M.; Bezyazychnaya, T. V.; Soldatov, V. S.

2010-05-01

116

Advanced Quantum Mechanical Calculation of Superheavy Ions: Energy Levels, Radiation and Finite Nuclear Size Effects  

NASA Astrophysics Data System (ADS)

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.

Glushkov, Alexander V.; Gurnitskaya, E. P.; Loboda, A. V.

2005-10-01

117

Raman and infrared spectra and theoretical calculations of dipicolinic acid, dinicotinic acid, and their dianions  

NASA Astrophysics Data System (ADS)

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.

McCann, Kathleen; Laane, Jaan

2008-11-01

118

Evaluation of steam sterilization processes: comparing calculations using temperature data and biointegrator reduction data and calculation of theoretical temperature difference.  

PubMed

When calculating of the physical F121.1 degrees c-value by the equation F121.1 degrees C = t x 10(T-121.1/z the temperature (T), in combination with the z-value, influences the F121.1 degrees c-value exponentially. Because the z-value for spores of Geobacillus stearothermophilus often varies between 6 and 9, the biological F-value (F(Bio) will not always correspond to the F0-value based on temperature records from the sterilization process calculated with a z-value of 10, even if the calibration of both of them are correct. Consequently an error in calibration of thermocouples and difference in z-values influences the F121.1 degrees c-values logarithmically. The paper describes how results from measurements with different z-values can be compared. The first part describes the mathematics of a calculation program, which makes it easily possible to compare F0-values based on temperature records with the F(BIO)-value based on analysis of bioindicators such as glycerin-water-suspension sensors. For biological measurements, a suitable bioindicator with a high D121-value can be used (such a bioindicator can be manufactured as described in the article "A Method of Increasing Test Range and Accuracy of Bioindicators-Geobacillus stearothermophilus Spores"). By the mathematics and calculations described in this macro program it is possible to calculate for every position the theoretical temperature difference (deltaT(th)) needed to explain the difference in results between the thermocouple and the biointegrator. Since the temperature difference is a linear function and constant all over the process this value is an indication of the magnitude of an error. A graph and table from these calculations gives a picture of the run. The second part deals with product characteristics, the sterilization processes, loading patterns. Appropriate safety margins have to be chosen in the development phase of a sterilization process to achieve acceptable safety limits. Case studies are discussed and experiences are shared. PMID:17390699

Lundahl, Gunnel

2007-01-01

119

Theoretical Analysis About Quantum Noise Squeezing of Optical Fields From an Intracavity Frequency-Doubled Laser  

NASA Technical Reports Server (NTRS)

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.

Zhang, Kuanshou; Xie, Changde; Peng, Kunchi

1996-01-01

120

Octacoordinate metal carbonyls of lanthanum and cerium: experimental observation and theoretical calculation.  

PubMed

The octacoordinate metal carbonyls La(CO)8(+) and Ce(CO)8(+) were observed in laser vaporization of La and Ce in pure CO gas. The peak intensities in the mass spectra, the infrared photodissociation spectra, and the theoretical calculations indicate that all CO ligands in these two complexes are bonded with the central metal atoms. The CO stretching frequencies in La(CO)8(+) and Ce(CO)8(+) are determined to be 2110 and 2108 cm(-1), respectively. Theoretical studies indicate that the most stable structures for La(CO)8(+) and Ce(CO)8(+) are an Oh geometry at its triplet state and a slightly distorted Oh geometry at its quartet state, respectively. These two complexes represent new octacoordinate metal carbonyls after previously determined U(CO)8(+) and Y(CO)8(+). PMID:25203282

Xie, Hua; Wang, Jie; Qin, Zhengbo; Shi, Lei; Tang, Zichao; Xing, Xiaopeng

2014-10-01

121

A simple theoretical approach to calculate the electrical conductivity of nonideal copper plasma  

SciTech Connect

A simple theoretical approach to calculate the electrical conductivity of partially ionized nonideal copper plasma is introduced. The densities of plasma species are calculated, to machine accuracy, including electronic excitation and allowing for high ionization states up to the atomic number of the element. Depression of ionization energies is taken into account using an interpolation formula that is valid over a wide range of densities. The formula yields the results of the Debye-Hueckel and the ion-sphere models at the limiting boundaries of low and high densities, respectively. The nonideal Coulomb logarithm is represented by an analytic wide-range formula supplemented by a specially tailored cutoff parameter. Effects of excluding excited and high ionization states on the calculation of ionization equilibrium and electrical conductivity of copper are investigated and assessed. Computational results of the electrical conductivity are compared with results from other theoretical models and available experimental measurements and showed reasonable agreement. A discussion about the choice of the ion-sphere radius is included and concerns about thermodynamic inconsistency when using the modified nonideal Saha equations are discussed and cleared.

Zaghloul, Mofreh R. [Department of Physics, College of Sciences, United Arab Emirates University, P.O.B. 17551, Al-Ain (United Arab Emirates)

2008-04-15

122

Guanidinium perchlorate ferroelectric crystal. Study of vibrational properties based on experimental measurements and theoretical calculations.  

PubMed

The infrared and Raman spectra of guanidinium perchlorate were measured at room temperature. The spectra are discussed with the framework of literature X-ray structure in relation to internal hydrogen bond network. For complete vibrational analysis the theoretical calculation of both infrared and Raman spectra in DFT approach were performed. The clear-cut assignment of observed bands was made on the basis of PED analysis. On the basis of theoretical studies the electrostatic charges and energies of HOMO and LUMO orbitals were obtained. Additionally the first order hyperpolarizability of investigated molecule was calculated. The obtained results are in good agreement with literature data, but according to performed calculation the specific damping of ? hyperpolarizability in unit cell (comparable with isolated molecule) is observed. To explain in detail phase transitions phenomena (at ca. 452 and 454K) described in literature the temperature dependent infrared powder spectra were recorded. The temperature dependencies of bands position and intensities for titled crystal in the range 11-480K are analyzed. PMID:23851177

Drozd, M; Dudzic, D

2013-11-01

123

Vinylphosphine-borane: synthesis, gas phase infrared spectroscopy, and quantum chemical vibrational calculations.  

PubMed

Both experimental and theoretical investigations are reported on the infrared spectrum of vinylphosphine-borane (CH(2)=CHPH(2) x BH(3)), a donor-acceptor complex. The gas phase infrared spectra (3500-600 cm(-1)) have been recorded at 0.5 cm(-1) resolution. This first primary alpha,beta-unsaturated phosphine-borane synthesized up to now is kinetically very unstable in the gas phase and decomposes rapidly into two fragments: the free vinylphosphine CH(2)=CHPH(2) and the monoborane BH(3) which dimerizes to form the more stable diborane B(2)H(6). Spectra of free CH(2)=CHPH(2) and B(2)H(6) compounds were also recorded to assign some vibration modes of the complex in very dense spectral regions. The analysis was completed by carrying out quantum mechanical calculations by density functional theory method at the B3LYP/6-31+G(**) level. Anharmonic frequencies and infrared intensities of the two predicted gauche and syn conformers of the vinylphosphine-borane complex were calculated in the 3500-100 cm(-1) region with the use of a variational approach, implemented in the P_ANHAR_V1.2 code. Because of the relatively weak interaction between the vinylphosphine and the monoborane, the vibrations of the complex can easily be subdivided into modes localized in the CH(2)=CHPH(2) and BH(3) moieties and into "intermolecular" modes. Localized modes are unambiguously correlated with the modes of the isolated monomers. Therefore, they are described in terms of the monomer vibrations, and the complexation shifts are defined as Delta nu = nu(complex) - nu(monomer) to make the effect of the complexation precise on each localized mode. In this objective, anharmonic frequencies and infrared intensities of the BH(3) monomer and the stable gauche and syn conformers of the free vinylphosphine were obtained at the same level of theory. In the gas phase, only the syn form of the complex was observed and assigned. All theoretically predicted frequencies and complexation shifts in magnitude and direction are in good agreement with experiment. By infrared spectroscopy assisted by quantum chemical calculations, the consequences of the complexation of an alpha,beta-unsaturated phosphine by borane on the physicochemical properties of the formed 12-atom complex have been efficiently evaluated. PMID:19071917

Khater, Brahim; Guillemin, Jean-Claude; Benidar, Abdessamad; Bégué, Didier; Pouchan, Claude

2008-12-14

124

The calculated photon: Visualization of a quantum field Martin Ligare a) and Ryan Oliveri  

E-print Network

Teachers. #DOI: 10.1119/1.1417531# I. INTRODUCTION The dual wave--particle nature of quantum objects is dis, or where to draw the line between wave­like aspects and particle­like aspects and how to justifyThe calculated photon: Visualization of a quantum field Martin Ligare a) and Ryan Oliveri

Ligare, Martin

125

Theoretical and experimental calculations, Mulliken charges and thermodynamic properties of 4-chloro-2-nitroanisole  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman spectra of 4-chloro-2-nitroanisole were recorded and analyzed. The vibrational wavenumbers were examined theoretically with the aid of the GAUSSIAN 09 package of programs using the B3LYP/6-311G(d,p) and 6-311++G(d,p) levels of theory. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied molecule. The first hyperpolarizability, NBO, HOMO-LUMO, NMR, UV, infrared intensities and Raman intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non-linear optics. The geometrical parameters of the title compound are in good agreement with the values of similar structures.

Arunagiri, C.; Arivazhagan, M.; Subashini, A.; Maruthaiveeran, N.

2014-10-01

126

Fast LiH destruction in reaction with H: quantum calculations and astrophysical consequences  

E-print Network

We present a quantum-mechanical study of the exothermic 7LiH reaction with H. Accurate reactive probabilities and rate coefficients are obtained by solving the Schrodinger equation for the motion of the three nuclei on a single Born-Oppenheimer potential energy surface (PES) and using a coupled-channel hyperspherical coordinate method. Our new rates indeed confirm earlier, qualitative predictions and some previous theoretical calculations, as discussed in the main text. In the astrophysical domain we find that the depletion process largely dominates for redshift (z) between 400 and 100, a range significant for early Universe models. This new result from first-principle calculations leads us to definitively surmise that LiH should be already destroyed when the survival processes become important. Because of this very rapid depletion reaction, the fractional abundance of LiH is found to be drastically reduced, so that it should be very difficult to manage to observe it as an imprinted species in the cosmic back...

Bovino, S; Gianturco, F A; 10.1088/0004-637X/699/1/383

2009-01-01

127

A perspective on quantum mechanics calculations in ADMET predictions.  

PubMed

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. PMID:23675934

Bowen, J Phillip; Güner, Osman F

2013-01-01

128

Benchmark all-electron ab initio quantum Monte Carlo calculations for small molecules  

Microsoft Academic Search

We study the efficiency, precision and accuracy of all-electron variational and diffusion quantum Monte Carlo calculations using Slater basis sets. Starting from wave functions generated by Hartree–Fock and density functional theory, we describe an algorithm to enforce the electron-nucleus cusp condition by linear projection. For the 55 molecules in the G2 set, the diffusion quantum Monte Carlo calculations recovers an

Norbert Nemec; Michael D. Towler; R. J. Needs

2010-01-01

129

Benchmark all-electron ab initio quantum Monte Carlo calculations for small molecules  

Microsoft Academic Search

We study the efficiency, precision and accuracy of all-electron variational and diffusion quantum Monte Carlo calculations using Slater basis sets. Starting from wave functions generated by Hartree-Fock and density functional theory, we describe an algorithm to enforce the electron-nucleus cusp condition by linear projection. For the 55 molecules in the G2 set, the diffusion quantum Monte Carlo calculations recovers an

Norbert Nemec; Michael D. Towler; R. J. Needs

2010-01-01

130

Quantum chemical calculation of the equilibrium structures of small metal atom clusters  

NASA Technical Reports Server (NTRS)

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.

Kahn, L. R.

1982-01-01

131

Theoretical calculation (DFT), Raman and surface-enhanced Raman scattering (SERS) study of ponceau 4R  

NASA Astrophysics Data System (ADS)

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 ?g/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.

Xie, Yunfei; Li, Yan; Sun, Yingying; Wang, Heya; Qian, He; Yao, Weirong

2012-10-01

132

Uncertainties Associated with Theoretically Calculated N2-Broadened Half-Widths of H2O Lines  

NASA Technical Reports Server (NTRS)

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.

Ma, Q.; Tipping, R. H.; Gamache, R. R.

2010-01-01

133

Molecular structure of 1,3-dimethoxybenzene as studied by gas-phase electron diffraction and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The molecular structure and conformational properties of 1,3-dimethoxybenzene (1,3-DMB) have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 methods with 6-31G(d,p) and cc-pVTZ basis sets). The differences between geometrical parameters were constrained at values calculated at B3LYP/cc-pVTZ and MP2/cc-pVTZ levels. Quantum chemical calculations predict three stable planar conformers for 1,3-DMB: syn-anti ( Cs symmetry), anti-anti ( C2v symmetry), and syn-syn ( C2v symmetry) with abundances of about 65%, 20%, and 15%, respectively ( syn and anti describe the orientation of the O-CH 3 bonds relative to the C1-C2 and C2-C3 bonds, respectively). The GED analysis results in a mixture of 46(19)% syn-anti, 31(15)% anti-anti, and 23% syn-syn conformers, close to the contributions predicted by theoretical calculations. The experimental structural parameters agree well with results of B3LYP/cc-pVTZ and MP2/cc-pVTZ calculations.

Dorofeeva, Olga V.; Shishkov, Igor F.; Rykov, Anatoliy N.; Vilkov, Lev V.; Oberhammer, Heinz

2010-08-01

134

Absorption of solar radiation by stratocumulus clouds: Aircraft measurements and theoretical calculations  

SciTech Connect

Aircraft observations of shortwave radiative properties of stratocumulus clouds were carried out over the western North Pacific Ocean during January 1991. Two aircraft were equipped with a pair of pyranometers and near-infrared pyranometers. Downward and upward shortwave fluxes above and below the cloud were synchronously measured by two aircraft. The cloud radiative properties, especially the absorptance obtained from measurements, were compared with those calculated. Aircraft measurements and Monte Carlo calculations showed that spatial inhomgeneities of clouds cause horizontal radiative convergence and divergence, and that vertical radiative convergence-that is, absorptance with a usual definition-apparently becomes extremely large or negative. The apparent absorptance could be corrected by a method that evaluates the true absorption from the difference between the apparent visible and near-infrared absorptions. The corrected absorptance agreed well with the theoretical absorptance calculated with plane-parallel cloud models. It is also inferred that the anomalous absorption pointed out by aircraft observations in previous studies does not exist. 12 refs., 7 figs., 1 tab.

Hayasaka, T.; Kikuchi, N.; Tanaka, M. [Tohoku Univ., Sendai (Japan)] [Tohoku Univ., Sendai (Japan)

1995-05-01

135

Quantum Robots and Quantum Computers  

E-print Network

Validation of a presumably universal theory, such as quantum mechanics, requires a quantum mechanical description of systems that carry out theoretical calculations and 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 environments. Some properties of these systems are discussed. A specific model based on the literature descriptions of quantum Turing machines is presented.

Paul Benioff

1997-06-04

136

Quantum robots and quantum computers  

SciTech Connect

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.

Benioff, P.

1998-07-01

137

Electron-Ion Recombination of Fe12 + Forming Fe11 +: Laboratory Measurements and Theoretical Calculations  

NASA Astrophysics Data System (ADS)

We have measured dielectronic recombination (DR) for Fe12 + forming Fe11 + 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.

Hahn, M.; Badnell, N. R.; Grieser, M.; Krantz, C.; Lestinsky, M.; Müller, A.; Novotný, O.; Repnow, R.; Schippers, S.; Wolf, A.; Savin, D. W.

2014-06-01

138

Quantum chemical calculations for polymers and organic compounds  

NASA Technical Reports Server (NTRS)

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.

Lopez, J.; Yang, C.

1982-01-01

139

Quantum Monte Carlo: Direct calculation of corrections to trial wave functions and their energies  

E-print Network

ARTICLES Quantum Monte Carlo: Direct calculation of corrections to trial wave functions, Pennsylvania 16802 Received 4 January 2000; accepted 10 March 2000 We report an improved Monte Carlo method Monte Carlo QMC method for the direct calculation of corrections to trial wave functions.1­3 We report

Anderson, James B.

140

Nano, Quantum, and Statistical Mechanics and Thermodynamics: Data and Property Calculation Websites  

NSDL National Science Digital Library

This collection of links provides access to web sites associated with nano, quantum, and statistical mechanics and thermodynamics. The links are arranged by type: data sites, calculation/program download sites, organizations involved with data compilation and property calculation, and bibliographies.

141

Accurate quantum Monte Carlo calculations for hydrogen fluoride and the fluorine atom  

E-print Network

Accurate quantum Monte Carlo calculations for hydrogen fluoride and the fluorine atom Arne Lu state energies of the fluorine atom and the hydrogen fluoride molecule have been carried out using both fluoride, the calculation of the dissociation energy and other energy differences with a chemical accuracy

Anderson, James B.

142

Molecular Design Using Quantum Chemical Calculations for Property Estimation  

E-print Network

. In both examples, a genetic algorithm is applied to generate and screen candidate molecules. The molecular (calculations from first principles) obtain molecular properties from the most fundamental level of molecular

Maranas, Costas

143

Quantum field theoretic properties of Lorentz-violating operators of nonrenormalizable dimension in the fermion sector  

NASA Astrophysics Data System (ADS)

In the current paper the properties of a quantum field theory based on certain sets of Lorentz-violating coefficients in the nonminimal fermion sector of the Standard Model extension are analyzed. In particular, three families of coefficients are considered, where two of them are C P T even and the third is C P T odd. As a first step the modified fermion dispersion relations are obtained. Then the positive- and negative-energy solutions of the modified Dirac equation and the fermion propagator are derived. These are used to demonstrate the validity of the optical theorem at tree level, which provides a cross-check for the results obtained. Furthermore unitarity is examined and seems to be valid for the first set of C P T -even coefficients. However for the remaining sets certain issues with unitarity are found. The article demonstrates that the adapted quantum field theoretical methods at tree level work for the nonminimal, Lorentz-violating framework considered. Besides, the quantum field theory based on the first family of C P T -even coefficients is most likely well behaved at lowest order perturbation theory. The results are important for future phenomenological investigations carried out in the context of field theory, e.g., the computation of decay rates and cross sections at tree level.

Schreck, M.

2014-10-01

144

Accurate quantum calculations of the reaction rates for H\\/D+CH4  

Microsoft Academic Search

In previous work [T. Wu, H. J. Werner, and U. Manthe, Science 306, 2227 (2004)], accurate quantum reaction rate calculations of the rate constant for the H+CH4-->CH3+H2 reaction have been presented. Both the electronic structure calculations and the nuclear dynamics calculations are converged with respect to the basis sets employed. In this paper, the authors apply the same methodology to

Rob van Harrevelt; Gunnar Nyman; Uwe Manthe

2007-01-01

145

Self-consistent approach for calculations of exciton binding energy in quantum wells  

Microsoft Academic Search

We introduce a computationally efficient approach to calculating characteristics of excitons in quantum wells. In this approach we derive a system of self-consistent equations describing the motion of an electron–hole pair. The motion in the growth direction of the quantum well in this approach is separated from the in-plane motion, but each of them occurs in modified potentials found self-consistently.

I. V. Ponomarev; L. I. Deych; V. A. Shuvayev; A. A. Lisyansky

2005-01-01

146

Quantum Monte Carlo calculations of neutron-alpha scattering  

E-print Network

We describe a new method to treat low-energy scattering problems in few-nucleon systems, and we apply it to the five-body case of neutron-alpha scattering. The method allows precise calculations of low-lying resonances and their widths. We find that a good three-nucleon interaction is crucial to obtain an accurate description of neutron-alpha scattering.

Kenneth M. Nollett; Steven C. Pieper; R. B. Wiringa; J. Carlson; G. M. Hale

2006-12-09

147

Energetic factors determining the binding of type I inhibitors to c-Met kinase: experimental studies and quantum mechanical calculations  

PubMed Central

Aim: To decipher the molecular interactions between c-Met and its type I inhibitors and to facilitate the design of novel c-Met inhibitors. Methods: Based on the prototype model inhibitor 1, four ligands with subtle differences in the fused aromatic rings were synthesized. Quantum chemistry was employed to calculate the binding free energy for each ligand. Symmetry-adapted perturbation theory (SAPT) was used to decompose the binding energy into several fundamental forces to elucidate the determinant factors. Results: Binding free energies calculated from quantum chemistry were correlated well with experimental data. SAPT calculations showed that the predominant driving force for binding was derived from a sandwich ?–? interaction with Tyr-1230. Arg-1208 was the differentiating factor, interacting with the 6-position of the fused aromatic ring system through the backbone carbonyl with a force pattern similar to hydrogen bonding. Therefore, a hydrogen atom must be attached at the 6-position, and changing the carbon atom to nitrogen caused unfavorable electrostatic interactions. Conclusion: The theoretical studies have elucidated the determinant factors involved in the binding of type I inhibitors to c-Met. PMID:24056705

Yu, Zhe; Ma, Yu-chi; Ai, Jing; Chen, Dan-qi; Zhao, Dong-mei; Wang, Xin; Chen, Yue-lei; Geng, Mei-yu; Xiong, Bing; Cheng, Mao-sheng; Shen, Jing-kang

2013-01-01

148

Calculating work in adiabatic two-level quantum Markovian master equations: A characteristic function method  

NASA Astrophysics Data System (ADS)

We present a characteristic function method to calculate the probability density functions of the inclusive work in adiabatic two-level quantum Markovian master equations. These systems are steered by some slowly varying parameters and the dissipations may depend on time. Our theory is based on the interpretation of the quantum jump for the master equations. In addition to the calculation, we also find that the fluctuation properties of the work can be described by the symmetry of the characteristic functions, which is exactly the same as in the case of isolated systems. A periodically driven two-level model is used to demonstrate the method.

Liu, Fei

2014-09-01

149

Renyi entanglement entropy of interacting fermions calculated using the continuous-time quantum Monte Carlo method.  

PubMed

We present a new algorithm for calculating the Renyi entanglement entropy of interacting fermions using the continuous-time quantum Monte Carlo method. The algorithm only samples the interaction correction of the entanglement entropy, which by design ensures the efficient calculation of weakly interacting systems. Combined with Monte Carlo reweighting, the algorithm also performs well for systems with strong interactions. We demonstrate the potential of this method by studying the quantum entanglement signatures of the charge-density-wave transition of interacting fermions on a square lattice. PMID:25259962

Wang, Lei; Troyer, Matthias

2014-09-12

150

Spectroscopic data for the LiH molecule from pseudopotential quantum Monte Carlo calculations  

E-print Network

Quantum Monte Carlo and quantum chemistry techniques are used to investigate pseudopotential models of the lithium hydride (LiH) molecule. Interatomic potentials are calculated and tested by comparing with the experimental spectroscopic constants and well depth. Two recently-developed pseudopotentials are tested, and the effects of introducing a Li core polarization potential are investigated. The calculations are sufficiently accurate to isolate the errors from the pseudopotentials and core polarization potential. Core-valence correlation and core relaxation are found to be important in determining the interatomic potential.

Trail, J R

2009-01-01

151

Postseismic viscoelastic surface deformation and stress. Part 1: Theoretical considerations, displacement and strain calculations  

NASA Technical Reports Server (NTRS)

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.

Cohen, S. C.

1979-01-01

152

Theoretical and experimental investigation on tandem Theoretical and experimental investigation on tandem modulator configurations for Frequency Coded Quantum Key Distribution systems  

Microsoft Academic Search

We have theoretically and experimentally address the possible tandem electro-optical modulator configurations that can be employed to implement Frequency Coded Quantum Key Distribution systems (FC-QKD). A closed and general formulation of the end to end field propagation in a dispersion compensated FC-QKD optical fiber system under the low modulation index regime is presented which accounts for all the possible tandem

J. Mora; A. Ruiz-Alba; W. Amaya; V. Garcia-Munoz; J. Capmany

2009-01-01

153

Quantum Humor: The Playful Side of Physics at Bohr's Institute for Theoretical Physics  

NASA Astrophysics Data System (ADS)

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.

Halpern, Paul

2012-09-01

154

Information-theoretic security proof for quantum-key-distribution protocols  

SciTech Connect

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.

Renner, Renato [Computer Science Department, ETH Zuerich, CH-8092 Zurich (Switzerland); Gisin, Nicolas; Kraus, Barbara [Group of Applied Physics, University of Geneva, CH-1211 Geneva 4 (Switzerland)

2005-07-15

155

Quantum Monte Carlo calculations of the dimerization energy of borane.  

PubMed

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. PMID:21913771

Fracchia, Francesco; Bressanini, Dario; Morosi, Gabriele

2011-09-01

156

Quantum Monte Carlo calculations of the dimerization energy of borane  

NASA Astrophysics Data System (ADS)

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 BH3, B2H6, BH3CO, CO, and BH2+ allowed us to predict the borane dimerization energy, both via the direct process and indirect processes such as the dissociation of BH3CO. Our De = -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 BH3CO gives -34.5(2) kcal/mol. Overall, our values suggest a slightly less De than the most recent W4 estimate De = -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.

Fracchia, Francesco; Bressanini, Dario; Morosi, Gabriele

2011-09-01

157

Hartree-Fock calculations of a finite inhomogeneous quantum wire  

NASA Astrophysics Data System (ADS)

We use the Hartree-Fock method to study an interacting one-dimensional electron system on a finite wire, partially depleted at the center by a smooth potential barrier. A uniform 1T Zeeman field is applied throughout the system. We find that with the increase in the potential barrier, the low density electrons under it go from a nonmagnetic state to an antiferromagnetic state and then to a state with a well-localized spin-aligned region isolated by two antiferromagnetic regions from the high density leads. At this final stage, in response to a continuously increasing barrier potential, the system undergoes a series of abrupt density changes, corresponding to the successive expulsion of a single electron from the spin-aligned region under the barrier. Motivated by the recent momentum-resolved tunneling experiments in a parallel wire geometry, we also compute the momentum-resolved tunneling matrix elements. Our calculations suggest that the eigenstates being expelled are spatially localized, consistent with the experimental observations. However, additional mechanisms are needed to account for the experimentally observed large spectral weight near k=0 in the tunneling matrix elements.

Qian, Jiang; Halperin, Bertrand I.

2008-02-01

158

Elucidating the interaction of H2O2 with polar amino acids - Quantum chemical calculations  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations have been carried out to investigate the interaction motifs of H2O2 with polar amino acid residues. Binding energies obtained from gas phase and continuum solvent phase calculations range between 2 and 30 kcal/mol. H2O2 interacts with the side chain of polar amino acids chiefly through the formation of hydrogen bonds. The sbnd CH group in side chains of a few residues provides additional stabilization to H2O2.

Karmakar, Tarak; Balasubramanian, Sundaram

2014-10-01

159

Quantum-chemical calculations of electronic-absorption spectra of aromatic amino acids in aqueous solution  

NASA Astrophysics Data System (ADS)

Quantum-chemical methods are used to calculate electronic-absorption spectra, dipole moments, and atomic-charge distributions of aromatic amino acids in aqueous solutions at various concentrations. The electronic-absorption spectra are analyzed and compared with the spectra that are calculated for gas phase. The bathochromic shift of the spectral position is shown for the long-wavelength absorption peak of the singlet-singlet transition for aqueous solutions of amino acids.

Migovich, M. I.; Kel'man, V. A.

2014-08-01

160

Thermochemistry and accurate quantum reaction rate calculations for H2\\/HD\\/D2 + CH3  

Microsoft Academic Search

Accurate quantum-mechanical results for thermodynamic data, cumulative reaction probabilities (for J = 0), thermal rate constants, and kinetic isotope effects for the three isotopic reactions H-2 + CH3 -> CH4 + H, HD + CH3 -> CH4 + D, and D-2 + CH3 -> CH3D + D are presented. The calculations are performed using flux correlation functions and the multiconfigurational

Gunnar Nyman; Rob van Harrevelt; Uwe Manthe

2007-01-01

161

Characterization of azobenzene chromophores for reversible optical data storage: molecular quantum calculations  

Microsoft Academic Search

Azobenzene chromophores are promising as molecularly engineered materials for reversible optical data storage based on molecular reorientation. In this paper, the optical properties of several different azobenzene chromophores are studied using molecular quantum calculations. Special emphasis is put on molecular anisotropy since a high degree of anisotropy is essential for the storage performance. The trans isomers are all found to

Thomas G. Pedersen; Per M. Johansen; Henrik C. Pedersen

2000-01-01

162

Multi-Jastrow trial wavefunctions for electronic structure calculations with quantum Monte Carlo  

Microsoft Academic Search

A new type of electronic trial wavefunction suitable for quantum Monte Carlo calculations of molecular systems is presented. In contrast with the standard Jastrow–Slater form built with a unique global Jastrow term, it is proposed to introduce individual Jastrow factors attached to molecular orbitals. Such a form is expected to be more physical since it allows to describe differently the

Michel Caffarel

2010-01-01

163

Multi-Jastrow trial wavefunctions for electronic structure calculations with quantum Monte Carlo  

Microsoft Academic Search

A new type of electronic trial wavefunction suitable for quantum Monte Carlo calculations of molecular systems is presented. In contrast with the standard Jastrow-Slater form built with a unique global Jastrow term, it is proposed to introduce individual Jastrow factors attached to molecular orbitals. Such a form is expected to be more physical since it allows to describe differently the

Thomas Bouabça; Benoît Braïda; Michel Caffarel

2010-01-01

164

On the Bayesian approach to calculating time correlation functions in quantum systems; reaction dynamics  

E-print Network

On the Bayesian approach to calculating time correlation functions in quantum systems; reaction eciently by stochastic simulation methods. The simulation data are then used to obtain the values is the Hamiltonian of the system, and b 1=kT is the inverse temperature, and Z is the canonical parti- tion function

Berne, Bruce J.

165

Quantum Monte Carlo calculations of the dissociation energy of the water dimer  

Microsoft Academic Search

We report diffusion quantum Monte Carlo (DMC) calculations of the equilibrium dissociation energy De of the water dimer. The dissociation energy measured experimentally, D0, can be estimated from De by adding a correction for vibrational effects. Using the measured dissociation energy and the modern value of the vibrational energy Mas et al., [J. Chem. Phys. 113, 6687 (2000)] leads to

N. A. Benedek; I. K. Snook; M. D. Towler; R. J. Needs

2006-01-01

166

Vibrational spectroscopic studies (FT-IR, FT-Raman, SERS) and quantum chemical calculations on cyclobenzaprinium salicylate.  

PubMed

FT-IR, FT-Raman and surface enhanced Raman scattering spectra of cyclobenzaprinium salicylate were recorded and analyzed. The vibrational wavenumbers were examined theoretically using the Gaussian09 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution calculations. The downshift of the OH stretching frequency is due to strong hydrogen bonded system present in the title compound as given by XRD results. The presence of CH3, CH2 and CO2 modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface which affects the orientation and metal molecule interaction. The presence of phenyl ring modes in the SERS spectrum indicates a tilted orientation with respect to the metal surface. The geometrical parameters of the title compound are in agreement with XRD results. A computation of the first hyperpolarizability indicates that the compound may be a good candidate as a NLO material. PMID:24200648

Mary, Y Shyma; Jojo, P J; Van Alsenoy, Christian; Kaur, Manpreet; Siddegowda, M S; Yathirajan, H S; Nogueira, Helena I S; Cruz, Sandra M A

2014-01-01

167

Theoretical oxidation state analysis of Ru-(bpy)3: Influence of water solvation and Hubbard correction in first-principles calculations  

NASA Astrophysics Data System (ADS)

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.

Reeves, Kyle G.; Kanai, Yosuke

2014-07-01

168

Quantum mechanical calculation of spectral statistics of a modified Kepler problem  

NASA Astrophysics Data System (ADS)

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.

Ma, Tao; Serota, R. A.

2012-03-01

169

Structural determination of carvone, a component of spearmint, by means of gas electron diffraction augmented by theoretical calculations  

Microsoft Academic Search

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

Toru Egawa; Yukari Kachi; Tsuguhide Takeshima; Hiroshi Takeuchi; Shigehiro Konaka

2003-01-01

170

The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot q  

E-print Network

spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We calculations. Published by Elsevier Inc. Keywords: Computational nano-technology; Electronic structure nano-science is to predict electronic properties and their changes due to quantum confinement effects

Dongarra, Jack

171

Search for a reliable nucleic acid force field using neutron inelastic scattering and quantum mechanical calculations: Bases, nucleosides and nucleotides  

SciTech Connect

Neutron inelastic scattering (NIS), IR and Raman spectra of the RNA constituents: bases, nucleosides and nucleotides have been analyzed. The complementary aspects of these different experimental techniques makes them especially powerful for assigning the vibrational modes of the molecules of interest. Geometry optimization and harmonic force field calculations of these molecules have been undertaken by quantum mechanical calculations at several theoretical levels: Hartree-Fock (HF), Moller-plesset second-order perturbation (MP2) and Density Functional Theory (DFT). In all cases, it has been shown that HF calculations lead to insufficient results for assigning accurately the intramolecular vibrational modes. In the case of the nucleic bases, these discrepancies could be satisfactorily removed by introducing the correlation effects at MP2 level. However, the application of the MP2 procedure to the large size molecules such as nucleosides and nucleotides is absolutely impossible, taking into account the prohibitive computational time needed. On the basis of our results, the calculations at DFT levels using B3LYP exchange and correlation functional appear to be a cost-effective alternative in obtaining a reliable force field for the whole set of nucleic acid constituents.

Leulliot, Nicolas; Ghomi, Mahmoud [Laboratoire de Physicochimie Biomoleculaire et Cellulaire, UPRESA 7033, Universite P. and M. Curie, Case Courrier 138, 75252 Paris Cedex 05 (France); Jobic, Herve [Institut de Recherche sur la Catalyse, 2 avenue A. Einstein, 69626 Villeurbanne (France)

1999-06-15

172

Ab initio no core calculations of light nuclei and preludes to Hamiltonian quantum field theory  

SciTech Connect

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.

Vary, J.P.; Maris, P.; /Iowa State U.; Shirokov, A.M.; /Iowa State U. /SINP, Moscow; Honkanen, H.; li, J.; /Iowa State U.; Brodsky, S.J.; /SLAC; Harindranath, A.; /Saha Inst.; Teramond, G.F.de; /Costa Rica U.

2009-08-03

173

Ab initio no core calculations of light nuclei and preludes to Hamiltonian quantum field theory  

SciTech Connect

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.

Vary, J. P.; Maris, P.; Honkanen, H.; Li, J. [Department of Physics and Astronomy, Iowa State University, Ames, Iowa, 50011 (United States); Shirokov, A. M. [Department of Physics and Astronomy, Iowa State University, Ames, Iowa, 50011 (United States); Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 (Russian Federation); Brodsky, S. J. [SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California (United States); Harindranath, A. [Theory Group, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata, 700064 (India); Teramond, G. F. de [Universidad de Costa Rica, San Jose (Costa Rica)

2009-12-17

174

Revisiting the calculation of condensed Fukui functions using the quantum theory of atoms in molecules  

NASA Astrophysics Data System (ADS)

The analysis of previously reported shortcomings of the condensed Fukui functions obtained making use of the quantum theory of atoms in molecules indicates these drawbacks are due to the inadequacy of the definition employed to compute them and not to the partitioning. A new procedure, which respects the mathematical definition and solves these problems, is presented for the calculation of condensed Fukui functions for atomic basins defined according to the quantum theory of atoms in molecules. It is tested in a set of 18molecules, which includes the most controversial reported cases.

Otero, Nicolás; Mandado, Marcos; Mosquera, Ricardo A.

2007-06-01

175

Recombination of W18+ ions with electrons: Absolute rate coefficients from a storage-ring experiment and from theoretical calculations  

E-print Network

We present new experimentally measured and theoretically calculated rate coefficients for the electron-ion recombination of W$^{18+}$([Kr] $4d^{10}$ $4f^{10}$) forming W$^{17+}$. At low electron-ion collision energies, the merged-beam rate coefficient is dominated by strong, mutually overlapping, recombination resonances. In the temperature range where the fractional abundance of W$^{18+}$ is expected to peak in a fusion plasma, the experimentally derived Maxwellian recombination rate coefficient is 5 to 10 times larger than that which is currently recommended for plasma modeling. The complexity of the atomic structure of the open-$4f$-system under study makes the theoretical calculations extremely demanding. Nevertheless, the results of new Breit-Wigner partitioned dielectronic recombination calculations agree reasonably well with the experimental findings. This also gives confidence in the ability of the theory to generate sufficiently accurate atomic data for the plasma modeling of other complex ions.

Spruck, K; Krantz, C; Novotný, O; Becker, A; Bernhardt, D; Grieser, M; Hahn, M; Repnow, R; Savin, D W; Wolf, A; Müller, A; Schippers, S

2014-01-01

176

Recombination of W18+ ions with electrons: Absolute rate coefficients from a storage-ring experiment and from theoretical calculations  

NASA Astrophysics Data System (ADS)

We present experimentally measured and theoretically calculated rate coefficients for the electron-ion recombination of W18+([Kr ]4d104f10) forming W17+. At low electron-ion collision energies, the merged-beam rate coefficient is dominated by strong, mutually overlapping recombination resonances. In the temperature range where the fractional abundance of W18+ is expected to peak in a fusion plasma, the experimentally derived Maxwellian recombination rate coefficient is 5 to 10 times larger than that which is currently recommended for plasma modeling. The complexity of the atomic structure of the open-4f system under study makes the theoretical calculations extremely demanding. Nevertheless, the results of the present Breit-Wigner partitioned dielectronic recombination calculations agree reasonably well with the experimental findings. This also gives confidence in the ability of the theory to generate sufficiently accurate atomic data for the plasma modeling of other complex ions.

Spruck, K.; Badnell, N. R.; Krantz, C.; Novotný, O.; Becker, A.; Bernhardt, D.; Grieser, M.; Hahn, M.; Repnow, R.; Savin, D. W.; Wolf, A.; Müller, A.; Schippers, S.

2014-09-01

177

Efficient first-principles calculation of the quantum kinetic energy and momentum distribution of nuclei  

E-print Network

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 ...

Ceriotti, Michele

2014-01-01

178

Quantum dynamics calculations using symmetrized, orthogonal Weyl-Heisenberg wavelets with a phase space truncation scheme. III. Representations and calculations  

NASA Astrophysics Data System (ADS)

In a previous paper [J. Theo. Comput. Chem. 2, 65 (2003)], one of the authors (B.P.) presented a method for solving the multidimensional Schrödinger equation, using modified Wilson-Daubechies wavelets, and a simple phase space truncation scheme. Unprecedented numerical efficiency was achieved, enabling a ten-dimensional calculation of nearly 600 eigenvalues to be performed using direct matrix diagonalization techniques. In a second paper [J. Chem. Phys. 121, 1690 (2004)], and in this paper, we extend and elaborate upon the previous work in several important ways. The second paper focuses on construction and optimization of the wavelength functions, from theoretical and numerical viewpoints, and also examines their localization. This paper deals with their use in representations and eigenproblem calculations, which are extended to 15-dimensional systems. Even higher dimensionalities are possible using more sophisticated linear algebra techniques. This approach is ideally suited to rovibrational spectroscopy applications, but can be used in any context where differential equations are involved.

Poirier, Bill; Salam, A.

2004-07-01

179

Quantum Matching Theory (with new complexity-theoretic, combinatorial and topical insights on the nature of the quantum entanglement)  

SciTech Connect

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.

Gurvits, L. (Leonid)

2002-01-01

180

A generalized any particle propagator theory: Assessment of nuclear quantum effects on electron propagator calculations  

NASA Astrophysics Data System (ADS)

In this work we propose an extended propagator theory for electrons and other types of quantum particles. This new approach has been implemented in the LOWDIN package and applied to sample calculations of atomic and small molecular systems to determine its accuracy and performance. As a first application of the method we have studied the nuclear quantum effects on electron ionization energies. We have observed that ionization energies of atoms are similar to those obtained with the electron propagator approach. However, for molecular systems containing hydrogen atoms there are improvements in the quality of the results with the inclusion of nuclear quantum effects. An energy term analysis has allowed us to conclude that nuclear quantum effects are important for zero order energies whereas propagator results correct the electron and electron-nuclear correlation terms. Results presented for a series of n-alkanes have revealed the potential of this method for the accurate calculation of ionization energies of a wide variety of molecular systems containing hydrogen nuclei. The proposed methodology will also be applicable to exotic molecular systems containing positrons or muons.

Romero, Jonathan; Posada, Edwin; Flores-Moreno, Roberto; Reyes, Andrés

2012-08-01

181

Theoretical Calculations on Sediment Transport on Titan, and the Possible Production of Streamlined Forms  

NASA Technical Reports Server (NTRS)

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.

Burr, D. M.; Emery, J. P.; Lorenz, R. D.

2005-01-01

182

Single crystal structure, spectroscopic (FT-IR, FT-Raman, 1H NMR, 13C NMR) studies, physico-chemical properties and theoretical calculations of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene.  

PubMed

In this paper, we will report a combined experimental and theoretical investigation of the molecular structure and spectroscopic parameteres (FT-IR, FT-Raman, (1)H NMR, (13)C NMR) of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene, CNT. The optimized geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were obtained at the B3LYP/6-311++G(d,p) level of theory and thermodynamic functions were calculated at the same level. A detailed interpretation of the Infrared, Raman and NMR spectra of the compound was reported as well. Analysis of experimental NMR chemical shifts was supported by quantum chemical calculations and HOSE code fragment based prediction tool (ACD/NMR). The theoretical results showed an excellent agreement with the experimental values. The physico-chemical properties (such as logP, hydrophobicity, …) were also calculated using three commercially available programs. PMID:22343079

Fereyduni, E; Rofouei, M K; Kamaee, M; Ramalingam, S; Sharifkhani, S M

2012-05-01

183

Single crystal structure, spectroscopic (FT-IR, FT-Raman, 1H NMR, 13C NMR) studies, physico-chemical properties and theoretical calculations of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene  

NASA Astrophysics Data System (ADS)

In this paper, we will report a combined experimental and theoretical investigation of the molecular structure and spectroscopic parameteres (FT-IR, FT-Raman, 1H NMR, 13C NMR) of 1-(4-chlorophenyl)-3-(4-nitrophenyl)triazene, CNT. The optimized geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were obtained at the B3LYP/6-311++G(d,p) level of theory and thermodynamic functions were calculated at the same level. A detailed interpretation of the Infrared, Raman and NMR spectra of the compound was reported as well. Analysis of experimental NMR chemical shifts was supported by quantum chemical calculations and HOSE code fragment based prediction tool (ACD/NMR). The theoretical results showed an excellent agreement with the experimental values. The physico-chemical properties (such as log P, hydrophobicity, …) were also calculated using three commercially available programs.

Fereyduni, E.; Rofouei, M. K.; Kamaee, M.; Ramalingam, S.; Sharifkhani, S. M.

2012-05-01

184

Helium trimer calculations with a public quantum three-body code  

SciTech Connect

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.

Kolganova, E. A. [Joint Institute for Nuclear Research (Russian Federation); Roudnev, V.; Cavagnero, M. [University of Kentucky, Department of Physics and Astronomy (United States)

2012-10-15

185

Conformational stability of allylbenzene: A combined study by dispersed fluorescence spectroscopy and quantum chemistry calculation  

Microsoft Academic Search

Two conformational isomers of allylbenzene are identified in a supersonic free jet expansion by use of laser-induced fluorescence excitation and dispersed fluorescence spectroscopy. With the aid of the predictions of ab initio quantum chemistry calculations at the MP2 level for a series of extended basis sets [6-311+G(d,p), 6-311++G(d,p), and cc-pVTZ], the major species of the electronic spectrum is shown to

Sujit Sankar Panja; Tapas Chakraborty

2003-01-01

186

Quantum vs classical calculation of nonlinear spectra-reduced dynamics and intramolecular entropy  

Microsoft Academic Search

A non-Markovian reduced equation of motion (REM) is derived for a generating function P(a,t;a?) which allows the calculation of two-time correlation functions in nonlinear systems. The form of the REM is identical for classical and quantum systems and it depends on an entropy function ln g(a), a velocity kernel W(a,a?), and a non-Markovian kernel K(a,a?,t), a being the expectation value

Shaul Mukamel

1983-01-01

187

Quantum Monte Carlo calculations of the dissociation energy of the water dimer  

Microsoft Academic Search

We report diffusion quantum Monte Carlo (DMC) calculations of the equilibrium dissociation energy De of the water dimer. The dissociation energy measured experimentally, D0, can be estimated from De by adding a correction for vibrational effects. Using the measured dissociation energy and the modern value of the vibrational energy Mas &etal;, [J. Chem. Phys. 113, 6687 (2000)] leads to De=5.00±0.7

N. A. Benedek; I. K. Snook; M. D. Towler; R. J. Needs

2006-01-01

188

Thermal boundary resistance predictions from molecular dynamics simulations and theoretical calculations  

E-print Network

for thermoelectric energy conversion applications.4,5 The most commonly applied theoretical models for pre- dicting.10. i, 63.22. m, 65.40. b I. INTRODUCTION A. Background The scattering of thermal energy carriers i thermal boundary resistance are the acoustic mis- match model AMM and the diffuse mismatch model DMM .1

McGaughey, Alan

189

Quantum calculations of the carrier mobility: Methodology, Matthiessen's rule, and comparison with semi-classical approaches  

NASA Astrophysics Data System (ADS)

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 ?M associated with a given elastic scattering mechanism "M," taking phonons (PH) as a reference (?M-1=?PH+M-1-?PH-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.

Niquet, Yann-Michel; Nguyen, Viet-Hung; Triozon, François; Duchemin, Ivan; Nier, Olivier; Rideau, Denis

2014-02-01

190

Quantum-chemical calculations on a novel reaction mechanism of CNN with NO  

NASA Astrophysics Data System (ADS)

Quantum-chemical calculations of the possible interaction between CNN and NO have been performed at the CCSD(T)/aug-cc-PVTZ//B3LYP/6-31++G(d,p) level of theory. Fourteen conformers corresponding to local minima of potential energy and sixteen transition structures are located, and various possible reaction paths are probed. Products P3 - NCO + N 2 - and P4 - N 2O + CN - were the two leading channels with slight energy barriers as compared to the reactants CNN + NO. Employing the Fukui functions and HSAB theory, we are able to rationalize the calculated outcomes.

Chen, Hui-Lung; Li, Han-Jung; Ho, Jia-Jen

2007-07-01

191

Quantum information with Gaussian states  

E-print Network

Quantum optical Gaussian states are a type of important robust quantum states which are manipulatable by the existing technologies. So far, most of the important quantum information experiments are done with such states, including bright Gaussian light and weak Gaussian light. Extending the existing results of quantum information with discrete quantum states to the case of continuous variable quantum states is an interesting theoretical job. The quantum Gaussian states play a central role in such a case. We review the properties and applications of Gaussian states in quantum information with emphasis on the fundamental concepts, the calculation techniques and the effects of imperfections of the real-life experimental setups. Topics here include the elementary properties of Gaussian states and relevant quantum information device, entanglement-based quantum tasks such as quantum teleportation, quantum cryptography with weak and strong Gaussian states and the quantum channel capacity, mathematical theory of quantum entanglement and state estimation for Gaussian states.

X. -B. Wang; T. Hiroshima; A. Tomita; M. Hayashi

2008-01-30

192

Calculations of Bose-Einstein correlations from Relativistic Quantum Molecular Dynamics  

SciTech Connect

Bose-Einstein correlation functions which are in good agreement with pion data can be calculated from an event generator. Here pion and (preliminary) kaon data from CERN experiment NA44 are compared to the calculations. The dynamics of 200 GeV/nucleon {sup 32}S + Pb collisions are calculated, without correlations due to interference patterns of a many-body wavefunction for identical particles, using the Relativistic Quantum Molecular Dynamics model (RQMD). The model is used to generate the phase-space coordinates of the emitted hadrons at the time they suffer their last strong interaction (freeze-out). Using the freeze-out position and momentum of pairs of randomly selected identical particles, a two-particle symmetrized wave-function is calculated and used to add two-body correlations. Details of the technique have been described previously. The method is similar to that used in the Spacer program.

Sullivan, J.P.; Berenguer, M.; Fields, D.E.; Jacak, B.V.; Sarabura, M.; Simon-Gillo, J.; Sorge, H.; van Hecke, H. [Los Alamos National Lab., NM (United States); Pratt, S. [Michigan State Univ., East Lansing, MI (United States)

1993-10-01

193

On the calculation rule of probability of relativistic free particle in quantum mechanics  

E-print Network

As is well known, in quantum mechanics, the calculation rule of the probability that an eigen-value a_n is observed when the physical quantity A is measured for a state described by the state vector |> is P(a_n)= . However, in Ref.[1], based on strict logical reasoning and mathematical calculation, it has been pointed out, replacing , one should use a new rule to calculate P(a_n) for particle satisfying the Dirac equation. In this paper, we first state some results given by Ref.[1]. And then, we present a proof for the new calculation rule of probability according to Dirac sea of negative energy particles, hole theory and the principle "the vacuum is not observable". Finally, we discuss simply the case of particle satisfying the Klein-Gordon equation.

T. Mei

2008-08-05

194

On the group-theoretic structure of a class of quantum dialogue protocols  

NASA Astrophysics Data System (ADS)

A sufficient condition for implementation of the quantum dialogue protocol is obtained and it is shown that the set of unitary operators used for the purpose must form a group under multiplication. A generalized protocol of quantum dialogue is obtained using the sufficient condition. Further, several examples of possible groups of unitary operators and quantum states that may be used for implementation of quantum dialogue are systematically generated. As examples, it is shown that GHZ state, GHZ-like state, W state, 4 and 5-qubit Cluster states, ? state, Brown state, Q4 state and Q5 state can be used to implement quantum dialogue protocol. It is also shown that if a quantum system is found to be suitable for quantum dialogue then that can provide solution of the socialist millionaire problem too.

Shukla, Chitra; Kothari, Vivek; Banerjee, Anindita; Pathak, Anirban

2013-02-01

195

A simple theoretical model for calculating and parameterizing the ionospheric photoelectron flux  

NASA Technical Reports Server (NTRS)

A method for calculating the ionospheric photoelectron flux is developed which uses the concept of average electron energy loss to simplify the calculation of the degraded electron spectrum. This method requires only a knowledge of the total inelastic electron impact cross sections and can be used for the calculation of all secondary ion and excited state production rates. The simple calculation reduces the computing time by a factor of 10 and considerably reduces storage requirements. It is found that the ionospheric photoelectron flux in the local equilibrium region is directly proportional to the attenuated solar EUV flux, which is a function only of the total neutral column density, and is independent of the neutral density composition. Thus, it is shown that electron impact cross section can be chosen so that this method may also be used to parameterize the measured ionospheric photoelectron fluxes.

Richards, P. G.; Torr, D. G.

1983-01-01

196

Theoretical calculation of rapid x-ray transients and radius expansion  

SciTech Connect

We present the results of a calculation of a thermonuclear runaway on a 10 km neutron star which produced a precursor, radius expansion, and after the envelope had begun to shrink, a seconds x-ray burst about 2500 second later. Although such an event has not yet been observed, decreasing the initial envelope mass should bring the calculations into better agreement with the observations.

Starrfield, S.; Sparks, W.; Truran, J.; Kenyon, S.

1984-05-26

197

Ternary nitride GaFe(3)N: an experimental and quantum-theoretical study.  

PubMed

The recently published two-step ammonolysis reaction giving access to phase-pure GaFe(3)N has been reinvestigated. Thermochemical calculations show that a high-temperature route is necessary to avoid the formation of the competing GaN phase. Compared to the prior study showing a Vegard-like behavior (that is, a linear correlation between lattice parameter and elemental composition), improved X-ray analysis using Mo K?(1) radiation in combination with density-functional theory calculations reveal a more complicated behavior of the lattice parameter within the entire Ga(x)Fe(4-x)N series. The new finding originates from the magnetic properties, and the change in the magnetic ordering with increasing Ga content from ferromagnetic ?'-Fe(4)N to antiferromagnetically ordered GaFe(3)N, as observed from susceptibility measurements, is reproduced by different theoretical spin-alignment models, that is, a systematic evaluation of several antiferromagnetic spin orientations. Nonetheless, all structural models are based on the favored atomic ordering for GaFe(3)N, explainable by the strong affinity between iron and nitrogen. PMID:20886876

Burghaus, Jens; Wessel, Michael; Houben, Andreas; Dronskowski, Richard

2010-11-01

198

Theoretical comparison of multiple quantum wells and thick-layer designs in InGaN/GaN solar cells  

NASA Astrophysics Data System (ADS)

This theoretical work analyzes the photovoltaic effect in non-polar InGaN/GaN solar cells. Our electronic transport model considers quantum behaviors related to confinement, tunneling, electron-phonon, and electron-photon scatterings. Based on this model, we compare a multiple quantum wells cell with its thick-layer counterpart. We show that the structure of multiple quantum wells is a promising design providing better compromise between photon-absorption and electronic transport. This balance is necessary since these two phenomena are shown to be antagonist in nanostructure based solar cells. In these devices, we also show that phonon absorption increases the short-circuit current, while phonon emission reduces the open-circuit voltage.

Cavassilas, Nicolas; Michelini, Fabienne; Bescond, Marc

2014-08-01

199

Automated Routines for Calculating Whole-Stream Metabolism: Theoretical Background and User's Guide  

USGS Publications Warehouse

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.

Bales, Jerad D.; Nardi, Mark R.

2007-01-01

200

The calculation of theoretical chromospheric models and the interpretation of solar spectra from rockets and spacecraft  

NASA Technical Reports Server (NTRS)

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 non-radiative heating, and for solar activity in general.

Avrett, Eugene H.

1993-01-01

201

The calculation of theoretical chromospheric models and the interpretation of the solar spectrum  

NASA Technical Reports Server (NTRS)

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.

Avrett, Eugene H.

1994-01-01

202

An optimized initialization algorithm to ensure accuracy in quantum Monte Carlo calculations.  

PubMed

Quantum Monte Carlo (QMC) calculations require the generation of random electronic configurations with respect to a desired probability density, usually the square of the magnitude of the wavefunction. In most cases, the Metropolis algorithm is used to generate a sequence of configurations in a Markov chain. This method has an inherent equilibration phase, during which the configurations are not representative of the desired density and must be discarded. If statistics are gathered before the walkers have equilibrated, contamination by nonequilibrated configurations can greatly reduce the accuracy of the results. Because separate Markov chains must be equilibrated for the walkers on each processor, the use of a long equilibration phase has a profoundly detrimental effect on the efficiency of large parallel calculations. The stratified atomic walker initialization (STRAW) shortens the equilibration phase of QMC calculations by generating statistically independent electronic configurations in regions of high probability density. This ensures the accuracy of calculations by avoiding contamination by nonequilibrated configurations. Shortening the length of the equilibration phase also results in significant improvements in the efficiency of parallel calculations, which reduces the total computational run time. For example, using STRAW rather than a standard initialization method in 512 processor calculations reduces the amount of time needed to calculate the energy expectation value of a trial function for a molecule of the energetic material RDX to within 0.01 au by 33%. PMID:18473326

Fisher, Daniel R; Kent, David R; Feldmann, Michael T; Goddard, William A

2008-11-15

203

The three-fold theoretical basis of the Gravity Probe B gyro precession calculation  

E-print Network

The Gravity Probe B (GP-B) experiment is complete and the results are in agreement with the predictions of general relativity (GR) for both the geodetic precession, 6.6 arcsec/yr to about 0.3%, and the Lense-Thirring precession, 39 marcsec to about 19%. This note is concerned with the theoretical basis for the predictions. The predictions depend on three elements of gravity theory, firstly that macroscopic gravity is described by a metric theory such as general relativity, secondly that the Lense-Thirring metric provides an approximate description of the gravitational field of the spinning earth, and thirdly that the spin axis of a gyroscope is parallel displaced in spacetime, which gives its equation of motion. We look at each of these three elements to show how each is solidly based on previous experiments and well-tested theory. The agreement of GP-B with theory strengthens our belief that all three elements are correct and increases our confidence in applying GR to astrophysical phenomena. Conversely, if GP-B had not verified the predictions a major theoretical quandary would have occurred.

Ronald J. Adler

2014-05-21

204

Quantum chemical calculation of the equilibrium structures of small metal atom clusters  

NASA Technical Reports Server (NTRS)

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.

Kahn, L. R.

1981-01-01

205

Theoretical calculations of the thermal rate constants for the gas-phase chemical reactions H + NH  

SciTech Connect

Rate constants for the title reactions are computed by using variational transition-state theory with semiclassical ground-state adiabatic transmission coefficients for the temperature range from 200 to 2,400 K. The rates are computed from selected information about the potential energy surface along the minimum energy path as parameters of the reaction path Hamiltonian. The potential information is obtained from ab initio electronic structure calculations with an empirical bond additivity correction. The accuracy of this semiempirical technique for obtaining the potential information is tested by comparing the results of the underlying ab initio calculations with higher quality multiconfiguration SCF and multireference CI calculations and by using increasingly higher quality ab initio electronic structure calculations before applying the bond additivity correction. For the reactions H + NH{sub 3} {yields} H{sub 2} + NH{sub 2}, H{sub 2} + NH{sub 2} {yields} H + NH{sub 3}, and D + ND{sub 3} {yields} D{sub 2} + ND{sub 2}, the ultimate test is given by comparison with recent experimental results. Although the agreement is good in general, the comparisons of experiment and theory indicate that the computed barrier height is overestimated by about 1 kcal/mol.

Garrett, B.C. (Chemical Dynamics Corp., Marlboro, MD (USA)); Koszykowski, M.L.; Melius, C.F. (Sandia National Lab., Livermore, CA (USA)); Page, M. (Naval Research Lab., Washington, DC (USA))

1990-09-06

206

Theoretical calculation of low-lying states of NaAr and NaXe  

NASA Technical Reports Server (NTRS)

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.

Laskowski, B. C.; Langhoff, S. R.; Stallcop, J. R.

1981-01-01

207

Calculations of band gaps in polyaniline from theoretical studies of oligomers  

SciTech Connect

Geometries and band gaps of polyaniline oligomers up to decamer have been systematically calculated and analyzed using various computational techniques such as molecular mechanics, semiempirical, and ab initio methods. On the basis of fully optimized geometries of neural and charged forms of polyaniline oligomers, excitation energies are calculated at the semiempirical ZINDO (INDO/S) level and extrapolated to the band gap value of the infinite chain. Band gaps are also approximately by extrapolating the HOMO/LUMO difference calculated at the density functional level (B3LYP/6--31G*). The SINDO//AM1 band gaps in the reduced and oxidized form of polyaniline (4.3 and 2.7 eV) are in good agreement with experimental values (3.8 {+-} 2 and 1.8 {+-} 3 eV, respectively). The doped form of polyaniline (two positive charges per four aniline units) has been computed with a spin-unrestricted method (UAM1) and the band gap approximated from an extrapolation of the tetramer and octamer. The calculated band gap of 1.3 eV (UZINDO//UAM1) is in good agreement with experiment (1.5 eV). The influence of ring torsional angle and interchain interaction on the band gap of the polyaniline system are also discussed.

Kwon, O.; McKee, M.L.

2000-03-02

208

FragBuilder: an efficient Python library to setup quantum chemistry calculations on peptides models.  

PubMed

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. PMID:24688855

Christensen, Anders S; Hamelryck, Thomas; Jensen, Jan H

2014-01-01

209

FragBuilder: an efficient Python library to setup quantum chemistry calculations on peptides models  

PubMed Central

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. PMID:24688855

Hamelryck, Thomas; Jensen, Jan H.

2014-01-01

210

Including nuclear quantum effects into highly correlated electronic structure calculations of weakly bound systems  

NASA Astrophysics Data System (ADS)

An interface between the APMO code and the electronic structure package MOLPRO is presented. The any particle molecular orbital APMO code [González et al., Int. J. Quantum Chem. 108, 1742 (2008)] implements the model where electrons and light nuclei are treated simultaneously at Hartree-Fock or second-order Möller-Plesset levels of theory. The APMO-MOLPRO interface allows to include high-level electronic correlation as implemented in the MOLPRO package and to describe nuclear quantum effects at Hartree-Fock level of theory with the APMO code. Different model systems illustrate the implementation: 4He2 dimer as a protype of a weakly bound van der Waals system; isotopomers of [He-H-He]+ molecule as an example of a hydrogen bonded system; and molecular hydrogen to compare with very accurate non-Born-Oppenheimer calculations. The possible improvements and future developments are outlined.

Aguirre, Néstor F.; Villarreal, Pablo; Delgado-Barrio, Gerardo; Posada, Edwin; Reyes, Andrés; Biczysko, Malgorzata; Mitrushchenkov, Alexander O.; de Lara-Castells, María Pilar

2013-05-01

211

Infrared spectra and theoretical calculations of KH and (KH)2 in solid hydrogen.  

PubMed

A matrix isolation IR study of laser-ablated potassium atom reactions with H2 has been performed in solid molecular hydrogen. The KH molecule and (KH)2 cluster were identified by infrared spectra with isotopic substitution (HD and D2) and by comparison to frequencies calculated using density functional theory. In para-hydrogen, the sharp KH absorption suggests dihydrogen complex formation with the ionic KH molecule, which is also characterized by an absorption at 4095 cm(-1). The highly ionic rhombic (KH)2 molecule is formed by dimerization and trapped in solid hydrogen. Calculations at the CCSD(T) level of theory show the increasing ionic character and decreasing stability for the (MH)2 molecule series from Li to Cs. PMID:17958401

Wang, Xuefeng; Andrews, Lester

2007-12-13

212

Theoretical Calculations of Photoabsorption of Several Alicyclic Molecules in the Vacuum Ultraviolet Region  

SciTech Connect

In order to aid in the design of transparent materials for use as photoresists for F2 lithography (157 nm), we have performed time-dependent density functional theory (TD-DFT) calculations of the photoabsorption of molecules in the vacuum ultraviolet region. The application of this TD-DFT method to the prediction of photoabsorption was benchmarked using model molecules such as formaldehyde, and an empirical equation for correcting the calculated transition energy was obtained. The TD-DFT method with the empirical correction equation provides dramatically more accurate results than those obtained with the CIS (single-excitation configuration interaction) method, which we employed in previous studies. We used it to predict the photoabsorption of various molecules such as methanol, t-butylalcohol, acetic acid, methyl acetate, cycloalkane, norbonane, tricyclodecane, tetrahydropyrane, adamantane, maleic anhydride and their fluorinated derivatives.

Matsuzawa, Nobuyuki; Ishitani, Akihiko; Dixon, David A.; Uda, Tsuyoshi

2001-06-13

213

Method and Basis Set Analysis of Oxorhenium(V) Complexes for Theoretical Calculations  

PubMed Central

A variety of method and basis set combinations has been evaluated for monooxorhenium(V) complexes with N, O, P, S, Cl, and Se donor atoms. The geometries and energies obtained are compared to both high-level computations and literature structures. These calculations show that the PBE0 method outperforms the B3LYP method with respect to both structure and energetics. The combination of 6-31G** basis set on the nonmetal atoms and LANL2TZ effective core potential on the rhenium center gives reliable equilibrium structures with minimal computational resources for both model and literature compounds. Single-point energy calculations at the PBE0/LANL2TZ,6-311+G* level of theory are recommended for energetics. PMID:23087847

Demoin, Dustin Wayne; Li, Yawen; Jurisson, Silvia S.; Deakyne, Carol A.

2012-01-01

214

Two theoretical simulations of hydrocarbons thermal cracking: Reactive force field and density functional calculations  

Microsoft Academic Search

The aim of this study was to simulate 1-methylnaphthalene (1-MNa) thermal cracking with the use of a new reactive force field, ReaxFF, and to compare it with experimental results of 1-MNa pyrolysis and density functional calculations. Thermal decomposition of polyaromatic compounds is important to understand the oils thermal cracking in geological reservoirs. Pyrolysis experiments and simulation provided useful information on

J-Philippe Leininger; Christian Minot; François Lorant

2008-01-01

215

Raman and infrared spectra and theoretical calculations of dipicolinic acid, dinicotinic acid, and their dianions  

Microsoft Academic Search

The Raman and infrared spectra of dipicolinic acid (DPA) and dinicotinic acid (DNic) and their salts (CaDPA, Na2DPA, 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

Kathleen McCann; Jaan Laane

2008-01-01

216

Theoretical calculations on the adhesion, stability, electronic structure and bonding of SiC/W interface  

NASA Astrophysics Data System (ADS)

The ?-SiC(1 1 1)/?-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 (?int) were calculated for six different interfacial structures, taking into account both Si- and C-terminations of ?-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 ?int. 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.

Jin, Na; Yang, Yanqing; Luo, Xian; Li, Jian; Huang, Bin; Liu, Shuai; Xiao, Zhiyuan

2014-09-01

217

Quantum mechanical calculation of aqueuous uranium complexes: carbonate, phosphate, organic and biomolecular species  

Microsoft Academic Search

BACKGROUND: Quantum mechanical calculations were performed on a variety of uranium species representing U(VI), U(V), U(IV), U-carbonates, U-phosphates, U-oxalates, U-catecholates, U-phosphodiesters, U-phosphorylated N-acetyl-glucosamine (NAG), and U-2-Keto-3-doxyoctanoate (KDO) with explicit solvation by H2O molecules. These models represent major U species in natural waters and complexes on bacterial surfaces. The model results are compared to observed EXAFS, IR, Raman and NMR spectra.

James D Kubicki; Gary P Halada; Prashant Jha; Brian L Phillips

2009-01-01

218

Benchmarking quantum chemical methods for the calculation of molecular dipole moments and polarizabilities.  

PubMed

The calculation of molecular electric moments, polarizabilities, and electrostatic potentials is a widespread application of quantum chemistry. Although a range of wave function and density functional theory (DFT) methods have been applied in these calculations, combined with a variety of basis sets, there has not been a comprehensive evaluation of how accurate these methods are. To benchmark the accuracy of these methods, the dipole moments and polarizabilities of a set of 46 molecules were calculated using a broad set of quantum chemical methods and basis sets. Wave function methods Hartree-Fock (HF), second-order Møller-Plesset (MP2), and coupled cluster-singles and doubles (CCSD) were evaluated, along with the PBE, TPSS, TPSSh, PBE0, B3LYP, M06, and B2PLYP DFT functionals. The cc-pVDZ, cc-pVTZ, aug-cc-pVDZ, aug-cc-pVTZ, and Sadlej cc-pVTZ basis sets were tested. The aug-cc-pVDZ, Sadlej cc-pVTZ, and aug-cc-pVTZ basis sets all yield results with comparable accuracy, with the aug-cc-pVTZ calculations being the most accurate. CCSD, MP2, or hybrid DFT methods using the aug-cc-pVTZ basis set are all able to predict dipole moments with RMSD errors in the 0.12-0.13 D range and polarizabilities with RMSD errors in the 0.30-0.38 Å(3) range. Calculations using Hartree-Fock theory systematically overestimated dipole moments and underestimate polarizabilities. The pure DFT functionals included in this study (PBE and TPSS) slightly underestimate dipole moments and overestimate polarizability. Polarization anisotropy and implications for charge fitting are discussed. PMID:24796376

Hickey, A Leif; Rowley, Christopher N

2014-05-22

219

The three-fold theoretical basis of the Gravity Probe B gyro precession calculation  

E-print Network

The Gravity Probe B (GP-B) experiment is complete and the results are in agreement with the predictions of general relativity (GR) for both the geodetic precession, 6.6 arcsec/yr to about 0.3%, and the Lense-Thirring precession, 39 marcsec to about 19%. This note is concerned with the theoretical basis for the predictions. The predictions depend on three elements of gravity theory, firstly that macroscopic gravity is described by a metric theory such as general relativity, secondly that the Lense-Thirring metric provides an approximate description of the gravitational field of the spinning earth, and thirdly that the spin axis of a gyroscope is parallel displaced in spacetime, which gives its equation of motion. We look at each of these three elements to show how each is solidly based on previous experiments and well-tested theory. The agreement of GP-B with theory strengthens our belief that all three elements are correct and increases our confidence in applying GR to astrophysical phenomena. Conversely, if ...

Adler, Ronald J

2014-01-01

220

Infrared spectra and theoretical calculations of lithium hydride clusters in solid hydrogen, neon, and argon.  

PubMed

A matrix isolation IR study of laser-ablated lithium atom reactions with H2 has been performed in solid para-hydrogen, normal hydrogen, neon, and argon. The LiH molecule and (LiH)(2,3,4) clusters were identified by IR spectra with isotopic substitution (HD, D(2), and H(2) + D(2)) and comparison to frequencies calculated by density functional theory and the MP2 method. The LiH diatomic molecule is highly polarized and associates additional H(2) to form primary (H(2))(2)LiH chemical complexes surrounded by a physical cage of solid hydrogen where the ortho and para spin states form three different primary complexes and play a role in the identification of the bis-dihydrogen complex and in characterization of the matrix cage. The highly ionic rhombic (LiH)(2) dimer, which is trapped in solid matrices, is calculated to be 22 kcal/mol more stable than the inverse hydrogen bonded linear LiH-LiH dimer, which is not observed here. The cyclic lithium hydride trimer and tetramer clusters were also observed. Although the spontaneous reaction of 2 Li and H(2) to form (LiH)(2) occurs on annealing in solid H(2), the formation of higher clusters requires visible irradiation. We observed the simplest possible chemical reduction of dihydrogen using two lithium valence electrons to form the rhombic (LiH)(2) dimer. PMID:17547379

Wang, Xuefeng; Andrews, Lester

2007-07-12

221

Ab initio quantum chemical calculations of aluminum substitution in zeolite ZSM-5  

SciTech Connect

The authors have performed ab initio quantum mechanical calculations in monomeric clusters modeling the 12 different T sites of zeolite ZSM-5. By comparing the results of calculations that use minimum basis sets with those that employ valence double-[zeta] bases, the authors conclude that minimum basis sets are unreliable for predicting relative replacement energies for the substitution of silicon by aluminum atoms at the T sites of the zeolite. From these calculations, it is also concluded that small differences in the bond lengths and angles can significantly alter the order of the sites with respect to the replacement energies. From calculations using valence double-[zeta] basis sets on T(OH)[sub 4] monomers, it is concluded that in the absence of protons or other ions, the most favorable sites for Al substitution in zeolite ZSM-5 are the T[sub 6], T[sub 12], and T[sub 9] sites, whereas the least favorable site is T[sub 3]. However, the least favorable and most favorable sites only differ by 3.3 kcal/mol. The authors also present a simple empirical model that is capable of reproducing the results of the ab initio calculations. This model gives the replacement energy in terms of the bond lengths and bond angles about each site.

Alvarado-Swaisgood, A.E.; Barr, M.K. (Amoco Research Center, Naperville, IL (United States)); Hay, P.J.; Redondo, A. (Los Alamos National Lab., NM (United States))

1991-11-28

222

Theoretical calculations of the nonlinear dielectric function of inhomogeneous thin films  

SciTech Connect

The optical response of thin dielectric films can be influenced by grain morphology and the presence and distribution of defects. In the limit of random defects and small electric field amplitudes, approximate methods exist to model the real part of the dielectric constant in terms of volume fractions and bulk dielectric constants of the film components. Explicit inclusion of nonlinear polarizabilities and details of the microstructure, such as particle phase, shape, and orientation requires a more exact approach. We have developed a method to self-consistently determine the local internal electric field and polarization in the long wavelength limit for model films with a random distributions of defects of arbitrary phase and orientation. From this we have calculated the real part of the dielectric constant as a function of nonlinear polarizability of the components, and have shown the effect of defect phase and orientation on the dielectric constant of the film. 2 refs., 4 figs.

Risser, S.M.; Ferris, K.F.

1990-08-01

223

Theoretical method for calculating relative joint geometry of assembled robot arms  

NASA Technical Reports Server (NTRS)

Equations are developed to extract the relative joint parameters of an assembled robot arm. Specifically, the Denavit-Hartenberg parameters, which completely characterize the relative joint geometry, are calculated. These parameters are needed to control the hand of the robot arm by resolved rate. As an example, the parameter extraction equations are used with perfect simulated data (no measurement noise) obtained from a mathematical model of a six-degree-of-freedom robot arm. For an actual application, measurement data needed to estimate the relative joint parameters can be generated by moving a robot arm to different positions, measuring the location of the hand (or other extension) in base coordinates, and recording the corresponding joint angles.

Barker, L. K.; Moore, M. C.

1983-01-01

224

Calculation of stress intensity factors in an isotropic multicracked plate. Part 1: Theoretical development  

NASA Technical Reports Server (NTRS)

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.

Binienda, W. K.; Arnold, S. M.; Tan, H. Q.

1992-01-01

225

Calculating the entanglement spectrum in quantum Monte Carlo with application to ab initio Hamiltonians  

NASA Astrophysics Data System (ADS)

Several algorithms have been proposed to calculate the spatial entanglement spectrum from high order Rényi entropies and maximum entropy techniques. We present an alternative approach for computing the entanglement spectrum with quantum Monte Carlo for both continuum and lattice Hamiltonians. This method provides direct access to the matrix elements of the spatially reduced density matrix and we determine an estimator that can be used in variational Monte Carlo as well as other Monte Carlo methods. The algorithm is based on using a generalization of the swap operator, which can be extended to calculate a general class of density matrices that can include combinations of spin, space, particle, and even momentum degrees of freedom. We demonstrate the method by applying it to the H2 and N2 molecules and describe how the spatial entanglement spectrum encodes a covalent bond that includes all the many body correlations.

Tubman, Norm M.; Yang, D. ChangMo

2014-08-01

226

Parallelizing the QUDA Library for Multi-GPU Calculations in Lattice Quantum Chromodynamics  

SciTech Connect

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.

Ronald Babich, Michael Clark, Balint Joo

2010-11-01

227

Absorption of laser radiation in a H-He plasma. I - Theoretical calculation of the absorption coefficient  

NASA Technical Reports Server (NTRS)

The theory for calculating the absorption of laser radiation by hydrogen is outlined for the temperatures and pressures of common laboratory plasmas. Nonhydrogenic corrections for determining the absorption by helium are also included. The coefficients for the absorption of He-Ne laser radiation at the wavelengths of 0.633, 1.15, and 3.39 microns in a H plasma is presented for temperatures in the range from 10,000 to 40,000 K and electron number densities in the range from 10 to the 15th power to 10 to the 18th power per cu cm. The total absorption of a H-He plasma calculated from this theory is compared with the measured absorption. The theoretical composition of the H-He absorption is analyzed with respect to the significant absorption processes, inverse bremsstrahlung, photoionization, resonance excitation, and photodetachment.

Stallcop, J. R.

1974-01-01

228

Hybrid theory and calculation of e-N2 scattering. [quantum mechanics - nuclei (nuclear physics)  

NASA Technical Reports Server (NTRS)

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.

Chandra, N.; Temkin, A.

1975-01-01

229

Comment on "Theoretical Model of a Purported Empirical Violation of the Predictions of Quantum Theory"  

E-print Network

to explain a single questionable experiment on paranormal psychic abilities in humans. Version 2.2. 05 NOV 98 their psychic powers to alter the laws of quantum mechanics and thereby modify the outcome of events that have

Dowling, Jonathan P.

230

On the Theoretical Possibility of Quantum Visual Information Transfer to the Human Brain  

E-print Network

The feasibility of wave function collapse in the human brain has been the subject of vigorous scientific debates since the advent of quantum theory. Scientists like Von Neumann, London, Bauer and Wigner (initially) believed that wave function collapse occurs in the brain or is caused by the mind of the observer. It is a legitimate question to ask how human brain can receive subtle external visual quantum information intact when it must pass through very noisy and complex pathways from the eye to the brain? There are several approaches to investigate information processing in the brain, each of which presents a different set of conclusions. Penrose and Hameroff have hypothesized that there is quantum information processing inside the human brain whose material substrate involves microtubules and consciousness is the result of a collective wavefunction collapse occurring in these structures. Conversely, Tegmark stated that owing to thermal decoherence there cannot be any quantum processing in neurons of the brain and processing in the brain must be classical for cognitive processes. However, Rosa and Faber presented an argument for a middle way which shows that none of the previous authors are completely right and despite the presence of decoherence, it is still possible to consider the brain to be a quantum system. Additionally, Thaheld, has concluded that quantum states of photons do collapse in the human eye and there is no possibility for collapse of visual quantum states in the brain and thus there is no possibility for the quantum state reduction in the brain. In this paper we conclude that if we accept the main essence of the above approaches taken together, each of them can provide a different part of a teleportation mechanism.

V. Salari; M. Rahnama; J. A. Tuszynski

2008-08-29

231

Calculation of Double-Quantum-Coherence Two-dimensional Spectra: Distance Measurements and Orientational Correlations  

PubMed Central

The double quantum coherence (DQC) echo signal for two coupled nitroxides separated by distances ?10 Å, is calculated rigorously for the six-pulse sequence. Successive application of six pulses on the initial density matrix, with appropriate inter-pulse time evolution and coherence pathway selection leaves only the coherent pathways of interest. The amplitude of the echo signal following the last ? pulse can be used to obtain a one-dimensional dipolar spectrum (Pake doublet), and the echo envelope can be used to construct the two-dimensional DQC spectrum. The calculations are carried out using the product space spanned by the two electron-spin magnetic quantum numbers m1, m2 and the two nuclear-spin magnetic quantum numbers M1, M2, describing e.g. two coupled nitroxides in bilabeled proteins. The density matrix is subjected to a cascade of unitary transformations taking into account dipolar and electron exchange interactions during each pulse and during the evolution in the absence of a pulse. The unitary transformations use the eigensystem of the effective spin-Hamiltonians obtained by numerical matrix diagonalization. Simulations are carried out for a range of dipolar interactions, D, and microwave magnetic field strength B for both fixed and random orientations of the two 14N (and 15N) nitroxides. Relaxation effects were not included. Several examples of one- and two-dimensional Fourier transforms of the time domain signals vs. dipolar evolution and spin-echo envelope time variables are shown for illustration. Comparisons are made between 1D rigorous simulations and analytical approximations. The rigorous simulations presented here provide insights into DQC ESR spectroscopy, they serve as a standard to evaluate the results of approximate theories, and they can be employed to plan future DQC experiments. PMID:20161423

Misra, Sushil K.; Borbat, Peter P.; Freed, Jack H.

2009-01-01

232

Quantum Mechanical Calculations to Interpret Vibrational and NMR Spectra of Organic Compounds Adsorbed onto Mineral Surfaces  

NASA Astrophysics Data System (ADS)

Vibrational (e.g., ATR FTIR and Raman) and nuclear magnetic resonance (NMR) spectroscopies provide excellent information on the bonding and atomic environment of adsorbed organic compounds. However, interpretation of observed spectra collected for organic compounds adsorbed onto mineral surfaces can be complicated by the lack of comparable analogs of known structure and uncertainties about the mineral surface structure. Quantum mechanical calculations provide a method for testing interpretations of observed spectra because models can be built to mimic predicted structures, and the results are independent of experimental parameters (i.e., no fitting to data is necessary). In this talk, methodologies for modeling vibrational frequencies and NMR chemical shifts of adsorbed organic compounds are discussed. Examples included salicylic acid (as an analog for important binding functional groups in humic acids) adsorbed onto aluminum oxides, organic phosphoryl compounds that represent herbicides and bacterial extracellular polymeric substances (EPS), and ofloxacin (a common agricultural antibiotic). The combination of the ability of quantum mechanical calculations to predict structures, spectroscopic parameters and energetics of adsorption with experimental data on these same properties allows for more definitive construction of surface complex models.

Kubicki, J. D.

2008-12-01

233

Unusual mechanism for H{sub 3}{sup +} formation from ethane as obtained by femtosecond laser pulse ionization and quantum chemical calculations  

SciTech Connect

The formation of H{sub 3}{sup +} from saturated hydrocarbon molecules represents a prototype of a complex chemical process, involving the breaking and the making of chemical bonds. We present a combined theoretical and experimental investigation providing for the first time an understanding of the mechanism of H{sub 3}{sup +} formation at the molecular level. The experimental approach involves femtosecond laser pulse ionization of ethane leading to H{sub 3}{sup +} ions with kinetic energies on the order of 4 to 6.5 eV. The theoretical approach involves high-level quantum chemical calculation of the complete reaction path. The calculations confirm that the process takes place on the potential energy surface of the ethane dication. A surprising result of the theoretical investigation is, that the transition state of the process can be formally regarded as a H{sub 2} molecule attached to a C{sub 2}H{sub 4}{sup 2+} entity but IRC calculations show that it belongs to the reaction channel yielding C{sub 2}H{sub 3}{sup +}+ H{sub 3}{sup +}. Experimentally measured kinetic energies of the correlated H{sub 3}{sup +} and C{sub 2}H{sub 3}{sup +} ions confirm the reaction path suggested by theory.

Kraus, Peter M.; Schwarzer, Martin C.; Schirmel, Nora; Urbasch, Gunter; Frenking, Gernot; Weitzel, Karl-Michael [Fachbereich Chemie, Physikalische Chemie, Philipps-Universitaet Marburg, Hans-Meerwein-Strasse, D-35032 Marburg (Germany)

2011-03-21

234

Infrared spectra and theoretical calculations for Fe, Ru, and Os metal hydrides and dihydrogen complexes.  

PubMed

Laser-ablated iron, ruthenium, and osmium atoms react with hydrogen in excess argon, neon and pure hydrogen to produce the FeH(2) molecule, and the FeH(2)(H(2))(3), RuH(H(2))(4), RuH(2)(H(2))(4), and (H(2))MH complexes (M = Fe, Ru, Os), as identified through infrared spectra with D(2) and HD substitution. DFT frequency calculations support the assignment of absorptions observed experimentally. The FeH(2) molecule has a quintet ground state with a quasi-linear structure, and is repulsive to the addition of one more H(2) ligand: however, with three more H(2) ligands, stable triplet and singlet state FeH(2)(H(2))(3) supercomplexes can be formed. The quintet FeH(2) molecule and FeH(2)(H(2))(3) supercomplex undergo reversible near-ultraviolet photochemical rearrangement in solid neon and hydrogen. The RuH(2) molecule has a bent triplet ground state and forms the stable singlet RuH(2)(H(2))(4) supercomplex, but only the latter is observed in these experiments. In like fashion RuH has a quartet ground state and the doublet RuH(H(2))(4) complex is trapped in solid hydrogen. All three (H(2))MH complexes with lower energy than MH(3) are trapped, and no absorptions are observed for MH(3) molecules. PMID:19099441

Wang, Xuefeng; Andrews, Lester

2009-01-22

235

Sodium hydride clusters in solid hydrogen and neon: infrared spectra and theoretical calculations.  

PubMed

Laser-ablated sodium atom reactions with H2 have been investigated in solid molecular hydrogens and neon. The NaH molecule and (NaH)2,3,4 clusters were identified by IR spectra with isotopic substitution (HD and D2) and comparison to frequencies calculated by density functional theory and the MP2 method. The use of para-hydrogen enriched samples provides evidence for a (H2)nNaH subcomplex surrounded by the solid hydrogen matrix cage. The ionic rhombic (NaH)2 dimer is characterized by strong absorptions at 761.7, 759.1, and 757.0 cm(-1), respectively, in solid neon, para-hydrogen, and normal hydrogen matrices. The cyclic sodium hydride trimer and tetramer clusters are also observed. Although the spontaneous reaction of two Li and H2 to form (LiH)2 occurs on annealing in solid H2, the formation of (NaH)2 requires near uv photoexcitation. PMID:17602543

Wang, Xuefeng; Andrews, Lester

2007-08-01

236

Theoretical calculations on the conformation of cyclopentadienyl coordination in Ru nitrosyl and thionitrosyl complexes  

SciTech Connect

X-ray structural characterization of a series of CpRu(NE)LL` complexes (Cp = cyclopentadieny), C{sub 5}R{sub 5}; L, L` = ligand; E = O, S) reveals systematic trends in the coordination conformation of the cyclopentadienyl ligand. The thionitrosyl complex (C{sub 5}(CH{sub 3}){sub 5})Ru(NS)Cl{sub 2} exhibits a slipped (eta-3,eta-2 Cp ring, with the central C(skeletal)-CH{sub 3} bond of the more tightly bound eta-3 portion eclipsing the Ru-N-S vector. With NO derivatives, ring {open_quotes}slippage{close_quotes} is not significant, but ring orientation is variable depending upon the L and L` ligand set. NMR spectroscopy measurements show that the barriers to changes in ring conformation become very low in solution. For catalytic purposes, it is of interest to fix the Cp geometry with respect to rotation. Ab initio SCF and DFT calculations have been performed, using the NWChem suite of computer codes, developed at Pacific Northwest Laboratory, to explore three questions: By what mechanism does the choice of ligand affect the Cp orientation? What is the barrier to rotation of the Cp? By what mechanism does salvation affect the barriers to Cp rotation?

Burns, R.M.; Hubbard, J.L.; McCullough, E.A. Jr. [Pacific Northwest Lab., Richland, WA (United States)] [and others

1995-12-01

237

Hydration of simple carboxylic acids from infrared spectra of HDO and theoretical calculations.  

PubMed

The hydration of carboxylic acids in dilute aqueous solutions is important for our understanding of their functioning in the biochemical context. Here we apply vibrational spectra of HDO isotopically diluted in H(2)O to study this phenomenon, using the difference spectra method for analysis and interpretation of the results. The spectra of HDO affected by formic, acetic, and propionic acid display characteristic component bands, significantly red-shifted from the bulk HDO band position. The appearance of these component bands is linked with isotopic substitution on the carboxylic acid molecule, which forms a short and strong hydrogen bond with a water molecule. Additionally, a charge separation due to the proton transfer in the neutral form of the complex leading to a contact ion pair formation may be inferred from the affected HDO spectra. Apart from the contraction of the principal acid-water hydrogen bond, it results in other major structural changes in the hydration shell, as revealed by density functional theory (DFT) calculations of optimal geometries of aqueous clusters of the studied acids. PMID:21466173

Smiechowski, Maciej; Goj?o, Emilia; Stangret, Janusz

2011-04-28

238

Theoretical Calculation of the Gas-Sensing Properties of Pt-Decorated Carbon Nanotubes  

PubMed Central

The gas-sensing properties of Pt-decorated carbon nanotubes (CNTs), which provide a foundation for the fabrication of sensors, have been evaluated. In this study, we calculated the gas adsorption of Pt-decorated (8,0) single-wall CNTs (Pt-SWCNTs) with SO2, H2S, and CO using GGA/PW91 method based on density functional theory. The adsorption energies and the changes in geometric and electronic structures after absorption were comprehensively analyzed to estimate the responses of Pt-SWCNTs. Results indicated that Pt-SWCNTs can respond to the three gases. The electrical characteristics of Pt-SWCNTs show different changes after adsorption. Pt-SWCNTs donate electrons and increase the number of hole carriers after adsorbing SO2, thereby enhancing its conductivity. When H2S is adsorbed on CNTs, electrons are transferred from H2S to Pt-SWCNTs, converting Pt-SWCNTs from p-type to n-type sensors with improved conductivity. However, Pt-SWCNTs obtain electrons and show decreased conductivity when reacted with CO gas. PMID:24201317

Zhang, Xiaoxing; Dai, Ziqiang; Wei, Li; Liang, Naifeng; Wu, Xiaoqing

2013-01-01

239

Theoretical calculations of phase transitions and optical properties of solid iodine under high pressures  

NASA Astrophysics Data System (ADS)

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.

San, Xiaojiao; Wang, Liancheng; Ma, Yanming; Liu, Zhiming; Cui, Tian; Liu, Bingbing; Zou, Guangtian

2008-04-01

240

Ab initio theoretical calculations of the electronic excitation energies of small water clusters.  

PubMed

A direct ab initio molecular dynamics method has been applied to a water monomer and water clusters (H(2)O)(n) (n = 1-3) to elucidate the effects of zero-point energy (ZPE) vibration on the absorption spectra of water clusters. Static ab initio calculations without ZPE showed that the first electronic transitions of (H(2)O)(n), (1)B(1)?(1)A(1), are blue-shifted as a function of cluster size (n): 7.38 eV (n = 1), 7.58 eV (n = 2) and 8.01 eV (n = 3). The inclusion of the ZPE vibration strongly affects the excitation energies of a water dimer, and a long red-tail appears in the range of 6.42-6.90 eV due to the structural flexibility of a water dimer. The ultraviolet photodissociation of water clusters and water ice surfaces is relevant to these results. PMID:22005972

Tachikawa, Hiroto; Yabushita, Akihiro; Kawasaki, Masahiro

2011-12-14

241

Crystalline Ice as a Cryoprotectant: Theoretical Calculation of Cooling Speed in Capillary Tubes  

PubMed Central

It is generally assumed that vitrification of both cells and the surrounding medium provides the best preservation of ultrastructure of biological material for study by electron microscopy. At the same time it is known that the cell cytoplasm may provide substantial cryoprotection for internal cell structure even when the medium crystallizes. Thus vitrification of the medium is not essential for good structural preservation. In contrast, a high cooling rate is an essential factor for good cryopreservation because it limits phase separation and movement of cellular components during freezing, thus preserving the native-like state. Here we present calculations of freezing rates that incorporate the effect of medium crystallization, using finite difference methods. We demonstrate that crystallization of the medium in capillary tubes may increase the cooling rate of suspended cells by a factor of 25-300 depending on the distance from the center. We conclude that crystallization of the medium, for example due to low cryoprotectant content, may actually improve cryopreservation of some samples in a near native state. PMID:21534954

Yakovlev, Sergey; Downing, Kenneth H.

2014-01-01

242

Microwave spectrum, molecular structure, dipole moment, and theoretical calculation of cyclopentanone oxime  

NASA Astrophysics Data System (ADS)

The microwave spectra of cyclopentanone oxime (C 5H 8dbnd NOH) and its deuterated species (C 5H 8dbnd NOD) were observed in the frequency region from 9 to 40 GHz. Only a-type R-branch transitions were assigned in the vibrational ground and excited states. The rotational constants of normal species were determined to be A = 5870.80(33), B = 1917.021(8), and C = 1526.784(8) MHz in the vibrational ground state, and A = 5870.16(43), B = 1842.707(9), and C = 1479.401(9) MHz for deuterated species. The dipole moments were determined as ?a = 0.80(10), ?b = 0.20(10), and ?c = 0.40(10) D. The ring-puckering vibrational states were observed up to v = 6. The vibrational mode was nearly harmonic. The fundamental frequency of the ring-puckering mode was found to be 70(20) cm -1. The molecular structure of cyclopentanone oxime was determined to be a twisted configuration by comparing the observed and calculated rotational constants, planar moment of inertia, Pcc, and rs coordinates of the hydroxyl hydrogen atom. On the molecular geometry, the bond angle, ?C 2C 1N 6 ( Fig. 1), is larger than ?C 5C 1N 6 by ca. 6°, because of the steric repulsion between the methylene group of C 2 atom and hydroxyl group.

Murakami, Arata; Fujimaki, Keizo; Inoue, Shigeki; Kuze, Nobuhiko; Sakaizumi, Takeshi; Kolandaivel, Ponmalai G.; Ohashi, Osamu

2005-04-01

243

A theoretical calculation of microlensing signatures caused by free-floating planets towards the Galactic bulge  

E-print Network

Free-floating planets are recently drawing a special interest of the scientific community. Gravitational microlensing is up to now the exclusive method for the investigation of free-floating planets, including their spatial distribution function and mass function. In this work, we examine the possibility that the future Euclid space-based observatory may allow to discover a substantial number of microlensing events caused by free-floating planets. Based on latest results about the free-floating planet mass function in the mass range $[10^{-5}, 10^{-2}]M_{\\odot}$, we calculate the optical depth towards the Galactic bulge as well as the expected microlensing rate and find that Euclid may be able to detect hundreds to thousands of these events per month. Making use of a synthetic population, we also investigate the possibility of detecting parallax effect in simulated microlensing events due to free-floating planets and find a significant efficiency for the parallax detection that turns out to be around 30%.

Hamolli, L; Nucita, A A

2014-01-01

244

Studies on the interaction between 9-fluorenylmethyl chloroformate and Fe3+ and Cu2+ ions: Spectroscopic and theoretical calculation approach  

NASA Astrophysics Data System (ADS)

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.

Gu, Zhenyan; Lei, Wu; Shi, Wenyan; Hao, Qingli; Si, Weimeng; Xia, Xifeng; Wang, Fengxiang

2014-11-01

245

Comment on ''Laboratory measurements and theoretical calculations of O{sub 2} A-band electric quadrupole transitions''  

SciTech Connect

D. A. Long et al.[Phys. Rev. A 80, 042513 (2009)] recently reported accurate measurements on the ultraweak electric quadrupole (E2) transitions in the O{sub 2} 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 b{sup 1}{Sigma}{sub g}{sup +}-X{sup 3}{Sigma}{sub g}{sup -} 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 M{sub 1} = 0.0687 {mu}{sub B} deduced by Long et al. from the previously measured transition intensities is {approx}2.7 times the ab initio value of 0.0255 {mu}{sub B} computed by Minaev et al.[Chem. Phys. 208, 299 (1996)]. Since the latter reproduces closely the measured Einstein's spontaneous emission coefficient of the A band, this large discrepancy is intriguing.

Balasubramanian, T. K.; Mishra, A. P. [Atomic and Molecular Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India)

2011-11-15

246

Studies on the interaction between 9-fluorenylmethyl chloroformate and Fe3+ and Cu2+ ions: spectroscopic and theoretical calculation approach.  

PubMed

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. PMID:24887497

Gu, Zhenyan; Lei, Wu; Shi, Wenyan; Hao, Qingli; Si, Weimeng; Xia, Xifeng; Wang, Fengxiang

2014-11-11

247

A combined quantum-classical dynamics method for calculating thermal rate constants of chemical reactions in solution  

E-print Network

-flux correlation function for calculating the thermal rate constants of chemical reactions in solutionA combined quantum-classical dynamics method for calculating thermal rate constants of chemical reactions in solution Thanh N. Truong,") J. Andrew McCammon, and Donald J. Kouri Department of Chemistry

Truong, Thanh N.

248

Comparing quantum-chemical calculation methods for structural investigation of zeolite crystal structures by solid-state NMR spectroscopy.  

PubMed

Combining quantum-chemical calculations and ultrahigh-field NMR measurements of (29)Si chemical shielding (CS) tensors has provided a powerful approach for probing the fine details of zeolite crystal structures. In previous work, the quantum-chemical calculations have been performed on 'molecular fragments' extracted from the zeolite crystal structure using Hartree-Fock methods (as implemented in Gaussian). Using recently acquired ultrahigh-field (29) Si NMR data for the pure silica zeolite ITQ-4, we report the results of calculations using recently developed quantum-chemical calculation methods for periodic crystalline solids (as implemented in CAmbridge Serial Total Energy Package (CASTEP) and compare these calculations to those calculated with Gaussian. Furthermore, in the context of NMR crystallography of zeolites, we report the completion of the NMR crystallography of the zeolite ITQ-4, which was previously solved from NMR data. We compare three options for the 'refinement' of zeolite crystal structures from 'NMR-solved' structures: (i) a simple target-distance based geometry optimization, (ii) refinement of atomic coordinates in which the differences between experimental and calculated (29)Si CS tensors are minimized, and (iii) refinement of atomic coordinates to minimize the total energy of the lattice using CASTEP quantum-chemical calculations. All three refinement approaches give structures that are in remarkably good agreement with the single-crystal X-ray diffraction structure of ITQ-4. PMID:20623826

Brouwer, Darren H; Moudrakovski, Igor L; Darton, Richard J; Morris, Russell E

2010-12-01

249

Electron-Ion Recombination of Fe XII Forming Fe XI: Laboratory Measurements and Theoretical Calculations  

NASA Astrophysics Data System (ADS)

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 ? 3p and 3p ? 3d core excitations. At higher energies, we observe contributions from 3 ? N' and 2 ? 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 103-107 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.

Novotný, O.; Badnell, N. R.; Bernhardt, D.; Grieser, M.; Hahn, M.; Krantz, C.; Lestinsky, M.; Müller, A.; Repnow, R.; Schippers, S.; Wolf, A.; Savin, D. W.

2012-07-01

250

Quantum physics and computers  

Microsoft Academic Search

Recent theoretical results confirm that quantum theory provides the possibility of new ways of performing efficient calculations. The most striking example is the factoring problem. It has recently been shown that computers that exploit quantum features could factor large composite integers. This task is believed to be out of reach of classical computers as soon as the number of digits

Adriano Barenco

1996-01-01

251

Theoretical Limits of Photovoltaics Efficiency and Possible Improvements by Intuitive Approaches Learned from Photosynthesis and Quantum Coherence  

E-print Network

In this review, we present and discussed the main trends in photovoltaics with emphasize on the conversion efficiency limits. The theoretical limits of various photovoltaics device concepts are presented and analyzed using a flexible detailed balance model where more discussion emphasize is toward the losses. Also, few lessons from nature and other fields to improve the conversion efficiency in photovoltaics are presented and discussed as well. From photosynthesis, the perfect exciton transport in photosynthetic complexes can be utilized for PVs. Also, we present some lessons learned from other fields like recombination suppression by quantum coherence. For example, the coupling in photosynthetic reaction centers is used to suppress recombination in photocells.

Fahhad H Alharbi; Sabre Kais

2014-02-09

252

Pentafluoroethyliminosulfur difluoride, CF 3CF 2N dbnd SF 2: Vibrational spectra and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The vibrational spectra of pentafluoroethyliminosulfur difluoride, CF 3CF 2N dbnd SF 2, were recorded in the gas phase with IR spectroscopy and in the liquid state with Raman spectroscopy. Quantum chemical calculations at the B3LYP (6-311+G(d) and 6-311+G(2df) basis sets) and MP2 levels of theory (6-31+G(d) and 6-311G(d) basis sets) were performed. According to all calculations the lowest energy conformer possesses C1 symmetry with syn orientation of the SF 2 group relative to the C sbnd N bond and near- trans orientation of the CF 3 group relative to the N dbnd S bond ( syn- trans). Calculations predict the hypothetical presence of a second stable conformer with anti-orientation of the SF 2 group ( anti- trans) which, however, possesses considerably higher energy and is therefore not observed in the analysis of the experimental spectra. The vibrational spectra were assigned for a single conformer in agreement with these calculations.

Robles, Norma L.; Cutin, Edgardo H.; Mews, Rüdiger; Della Védova, Carlos O.

2010-08-01

253

Quantum scattering calculations of energy transfer and dissociation of HCO in collisions with Ar  

SciTech Connect

We report a quantum scattering calculation of energy transfer and collision-induced dissociation of HCO in collisions with Ar. The HCO rotation is treated in the infinite order sudden approximation, and the HCO vibrations are treated by the coupled-channel method. Sixty {ital L}{sup 2} HCO vibrational wave functions are included in the coupled-channel basis, of which 15 correspond to bound HCO states for zero HCO angular momentum, and the remainder represent a discretized continuum, which includes ten resonances. A simple ``sum-of-pairs`` potential is used to describe the Ar--HCO interaction, and the HCO intramolecular potential is the previous Legendre polynomial fit to {ital ab} {ital initio} calculations. Vibrational state-specific and state-to-state cross sections, averaged over the orientation of Ar relative to the CO-bond axis, are calculated over a range of translational energies. Collision-induced dissociation cross sections to form H+CO from all HCO bound states are presented, and decomposed into components corresponding to dissociation via HCO resonances and dissociation via no``nresonance states. The energy transfer from selected initial states is also calculated as a function of initial relative translational energy. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Pan, B.; Bowman, J.M. [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)] [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)

1995-12-08

254

Converged five-dimensional quantum calculations for OH+CO-->H+CO2  

NASA Astrophysics Data System (ADS)

We perform five-dimensional quantum wave packet calculations of initial-state-resolved reaction probabilities for the reaction OH+CO?H+CO2, with OH and CO initially in the rovibrational ground state, and total angular momentum J=0. In essence, the dynamics are treated exactly for all molecular degrees of freedom except the CO reactant bond, for which a vibrational-averaging approximation is adopted. Comparison of reaction probabilities to those obtained in an earlier, similar study [D. H. Zhang and J. Z. H. Zhang, J. Chem. Phys. 103, 6512 (1995)] show that the previously obtained results were not well converged, primarily because too few rotational basis functions were used in the calculations. The resonances found in the current study are also more abundant and narrower than in the earlier study. Reaction probabilities from calculations on an updated potential energy surface (PES) [K. S. Bradley and G. C. Schatz, J. Chem. Phys. 106, 8464 (1997)] do not differ significantly from those for the PES used in the rest of the calculations [K. Kudla, G. Schatz, and A. Wagner, J. Chem. Phys. 95, 1635 (1991)], though there is a severe effect on resonance structure.

McCormack, Drew A.; Kroes, Geert-Jan

2002-03-01

255

Analytical calculation of the quantum 1/f coherence parameter for HFETs  

NASA Astrophysics Data System (ADS)

The ratio s of the coherent magnetic energy term and the incoherent mechanical kinetic energy terms of the drift motion in the hamiltonian of a current carrying system is calculated for the special cases of a HFET or FET. This ratio defines the resulting quantum 1/f noise from the coherent and conventional quantum 1/f effects. In this case of FETs and HFETs of much larger width w>>LDS>t, the kinetic energy Ek of average motion with drift velocity vd per unit length in the direction of the drain-source distance LDS in the channel of thickness t, is still given by Nmvd 2/2, but the magnetic energy Em per unit length in the direction of LDS is roughly proportional with the first power of w only, instead of w2, and can be approximated by Em = ?[ln(w/2LDS)]LDS[nevS/c]2/w. Here S=wt is the cross section though which current flows this indicates field-decoherence along the large device width w. This yields a coherence ratio of s ? Em/Ek ~ ?nrotLDSln(w/2LDS), which shows that only an effective width w=weff about equal to LDS should be used in the calculation of s in this special case; larger widths are subject to de-coherence. This favors lower, mainly conventional, quantum 1/f noise in these devices, in spite of the large values of w. It also explains for the first time why the huge widths are possible with impunity, i.e., without causing the much larger coherent quantum 1/f noise to appear. For non-uniform current distribution across t, and for piezoelectric coupling, improved forms are derived for s. Specifically, the coherence parameter, called s' for the piezo case, is given by s' = (gN'h/m*vs)( vs/u)3F(u/vs)t/12w, where F(u/vs) = (2/3)(u/vs) for small drift velocity u, much smaller than the sound velocity vs in the semiconductor. Here N'=nwt.

Handel, Peter H.; Sherif, Taher S.

2010-03-01

256

Magnetic coupling constants of self-assembled Cu(II) [3×3] grids: alternative spin model from theoretical calculations.  

PubMed

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. PMID:24965865

Calzado, Carmen J; Ben Amor, Nadia; Maynau, Daniel

2014-07-14

257

An improved fragment-based quantum mechanical method for calculation of electrostatic solvation energy of proteins  

NASA Astrophysics Data System (ADS)

An efficient approach that combines the electrostatically embedded generalized molecular fractionation with conjugate caps (EE-GMFCC) method with conductor-like polarizable continuum model (CPCM), termed EE-GMFCC-CPCM, is developed for ab initio calculation of the electrostatic solvation energy of proteins. Compared with the previous MFCC-CPCM study [Y. Mei, C. G. Ji, and J. Z. H. Zhang, J. Chem. Phys. 125, 094906 (2006)], quantum mechanical (QM) calculation is applied to deal with short-range non-neighboring interactions replacing the classical treatment. Numerical studies are carried out for proteins up to 3837 atoms at the HF/6-31G* level. As compared to standard full system CPCM calculations, EE-GMFCC-CPCM shows clear improvement over the MFCC-CPCM method for both the total electrostatic solvation energy and its components (the polarized solute-solvent reaction field energy and wavefunction distortion energy of the solute). For large proteins with 1000-4000 atoms, where the standard full system ab initio CPCM calculations are not affordable, the EE-GMFCC-CPCM gives larger relative wavefunction distortion energies and weaker relative electrostatic solvation energies for proteins, as compared to the corresponding energies calculated by the Divide-and-Conquer Poisson-Boltzmann (D&C-PB) method. Notwithstanding, a high correlation between EE-GMFCC-CPCM and D&C-PB is observed. This study demonstrates that the linear-scaling EE-GMFCC-CPCM approach is an accurate and also efficient method for the calculation of electrostatic solvation energy of proteins.

Jia, Xiangyu; Wang, Xianwei; Liu, Jinfeng; Zhang, John Z. H.; Mei, Ye; He, Xiao

2013-12-01

258

Fundamental Principles of Theoretical Physics and Concepts of Quantum Protectorate and Emergence  

E-print Network

A concise survey of the advanced unifying ideas of modern physics, namely, spontaneous symmetry breaking, quasiaverages, quantum protectorate and emergence was presented. The interrelation of the concepts of symmetry breaking, quasiaverages and quantum protectorate was analyzed in the context of quantum theory and statistical physics. The main aim of this analysis was to demonstrate the connection and interrelation of these conceptual advances of the many-body physics and to try to show explicitly that those concepts, though different in details, have a certain common features. Some problems in the field of statistical physics of complex materials and systems e.g. foundation of the microscopic theory of magnetism and superconductivity were pointed in relation to these ideas.

A. L. Kuzemsky

2012-03-14

259

Monte-Carlo calculation of the lateral Casimir forces between rectangular gratings within the formalism of lattice quantum field theory  

E-print Network

We propose a new Monte-Carlo method for calculation of the Casimir forces. Our method is based on the formalism of noncompact lattice quantum electrodynamics. This approach has been tested in the simplest case of two ideal conducting planes. After this the method has been applied to the calculation of the lateral Casimir forces between two ideal conducting rectangular gratings. We compare our calculations with the results of PFA and "Optimal" PFA methods.

Oleg Pavlovsky; Maxim Ulybyshev

2011-05-03

260

One pot synthesis of biologically active pregnane derivatives, their single crystal structures, spectroscopic characterization and theoretical calculations  

NASA Astrophysics Data System (ADS)

One pot allylic oxidation of 3?-acetoxypregna-5,16-diene-20-one (2) and nucleophilic addition at C-16 position of 3?-hydroxypregna-5,16-diene-20-one (3) yielded 3?-acetoxypregna-5,16-diene-7,20-dione (4) and 3?-hydroxy-16?-(5'-hydroxypentyloxy)-pregn-5-ene-20-one (5) respectively in high yield. A detailed theoretical study supported by X-ray analysis of compounds 4 and 5 has been carried out. Conformational analysis of compounds 4 and 5 was done with the help of crystal structure, which crystallize out in orthorhombic form having P212121 space group. Structural characterization of compounds 4 and 5 was done with the aid of 1H, 13C NMR, IR, UV, ESI-MS and ESI-HRMS. The molecular geometries and vibrational frequencies for compounds 4 and 5 in the ground state were calculated using the Density functional theory (DFT) with 6-31G(d,p) basis set and compared with experimental data. 1H and 13C nuclear magnetic resonance magnetic shifts of 4 and 5 were calculated using GIAO method and compared with the experimental data. UV-Vis spectra of both the compounds were recorded and electronic properties such as HOMO-LUMO energies were calculated by time dependent TD-DFT approach. The compounds were screened for their anti-hyperlipidemic and anti-oxidant activity.

Sethi, Arun; Bhatia, Akriti; Bhatia, Gitika; Shrivastava, Atul; Prakash, Rohit

2013-11-01

261

Theoretical calculations of X-ray absorption spectra of a copper mixed ligand complex using computer code FEFF9  

NASA Astrophysics Data System (ADS)

The terms X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) refer, respectively, to the structure in the X-ray absorption spectrum at low and high energies relative to the absorption edge. Routine analysis of EXAFS experiments generally makes use of simplified models and several many-body parameters, e.g. mean free paths, many-body amplitude factors, and Debye-Waller factors, as incorporated in EXAFS analysis software packages like IFEFFIT which includes Artemis. Similar considerations apply to XANES, where the agreement between theory and experiment is often less satisfactory. The recently available computer code FEFF9 uses the real-space Green's function (RSGF) approach to calculate dielectric response over a broad spectrum including the dominant low-energy region. This code includes improved treatments of many-body effects such as inelastic losses, core-hole effects, vibrational amplitudes, and the extension to full spectrum calculations of optical constants including solid state effects. In the present work, using FEFF9, we have calculated the X-ray absorption spectrum at the K-edge of copper in a complex, viz., aqua (diethylenetriamine) (isonicotinato) copper(II), the crystal structure of which is unknown. The theoretical spectrum has been compared with the experimental spectrum, recorded by us at the XAFS beamline 11.1 at ELETTRA synchrotron source, Italy, in both XANES and EXAFS regions.

Gaur, A.; Shrivastava, B. D.

2014-09-01

262

Quantum-Chemical Calculations of Carbon-Isotope Fractionation in CO2(g), Aqueous Carbonate Species, and Carbonate Minerals  

SciTech Connect

Quantum chemical calculations on large supermolecular carbonate-water and carbonate mineral clusters are used to predict equilibrium constants for 13,12C-isotope-exchange reactions between CO2(g), aqueous carbonate species, and the common carbonate minerals. For the aqueous species, we evaluate the influence of the size and conformational variability of the solvation shell, the exchange-correlation functional, and the basis set. The choice of exchange-correlation functional (PBE vs B3LYP), the basis set (6-31G* vs aug-cc-pVDZ), and solvation shell size (first shell only vs first shell and a partial second shell) each produce changes of ~5-10 per mil in the reduced partition function ratio. Conformational variability gives rise to a standard error of ~0.5 per mil using ~10 solute-solvent conformations. The best results are obtained with the B3LYP/ aug-cc-pVDZ combination, but because the improvements in the basis set and exchange correlation functional drive the reduced partition function ratios in opposite directions, reasonably good results are also obtained with the PBE/6-31G* combination. To construct molecular clusters representative of mineral environments, a new method is introduced on the basis of conservation of Pauling bond strength. Using these clusters as models for minerals, calculations of mineral-gas and mineral-aqueous carbon-isotope fractionation factors, are in good agreement with experimental measurements. Carbon-isotope fractionation factors for gas, aqueous, and mineral phases are thus integrated into a single theoretical/computational framework.

Rustad, James R.; Nelmes, Sierra L.; Jackson, Virgil E.; Dixon, David A.

2008-01-24

263

Fluorescent substituted amidines of benzanthrone: Synthesis, spectroscopy and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

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.

Gonta, Svetlana; Utinans, Maris; Kirilov, Georgii; Belyakov, Sergey; Ivanova, Irena; Fleisher, Mendel; Savenkov, Valerij; Kirilova, Elena

2013-01-01

264

Connections Between Quantum Mechanics and Polymer Physics - Two Examples of Ab Initio Calculations on Polymer Systems  

NASA Astrophysics Data System (ADS)

Ever since the realization of IR and Raman spectroscopy, scientists have been using vibrational spectroscopy as a standard analytical tool for routine sample identification. Today, both molecular species and polymers can be conveniently studied by these spectroscopic techniques based upon characteristic molecular vibrations. However, the interpretation of these complicated vibrations, especially for new materials, is rarely straight forward. Isotope substitution, normal mode and symmetry analysis have been the most widely applied techniques to aid spectral interpretation but they all pose serious limitations on the complexity of the system one can study. This is especially true for polymers. In this work, the possibility of using ab initio calculations to identify spectroscopic features of quasi-polymeric molecular systems has been explored. These calculations not only provide the band frequencies, but also band intensities, polarization and symmetry species which can be compared to experimental data and results from other analysis. Polysilaethylene (PSE), a polymeric ceramic precursor; and polydimethylsiloxane (PDMS), a polymer of great importance in biomedical applications have been studied. The success in describing complicated vibrations of polymeric systems with quantum mechanics in these examples implies that it is possible to simplify the lengthy task of band assignment with ab initio calculations in the future.

Tsao, Mei-Wei; Rabolt, John F.; Pfeifer, Karl-Heinz

1998-03-01

265

Calculation of solvation free energy from quantum mechanical charge density and continuum dielectric theory.  

PubMed

We have combined ultrasoft pseudopotential density functional theory utilizing plane wave basis with a Poisson-Boltzmann/solvent-accessible surface area (PB/SA) model to calculate the solvation free energy of small neutral organic compounds in water. The solute charge density obtained from density functional theory was directly used in solving the Poisson-Boltzmann equation to obtain the reaction field. The polarized electronic wave function of the solute in the solvent was solved by including the reaction field in the density functional Hamiltonian. The quantum mechanical and Poisson-Boltzmann equations were solved self-consistently until the charge density and reaction field converged. Using the solute charge density directly instead of a point-charge representation permitted asymmetric distortion and spreading out of the electron cloud. Because the electron density could leave the van der Waals surface to penetrate into the high-dielectric solvent, the reaction field generated by this density was generally smaller than that obtained by using the point-charge representation. In applying this model to calculate the solvation free energy of 31 small neutral organic molecules spanning a range of 25 kcal/mol, we obtained a root-mean-square error of only 1.3 kcal/mol if we allowed one adjustable parameter to shift the calculated solvation free energy. PMID:16599457

Wang, Mingliang; Wong, Chung F

2006-04-13

266

Calculation of metamorphic two-dimensional quantum energy system: Application to wetting layer states in InAs/InGaAs metamorphic quantum dot nanostructures  

SciTech Connect

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.

Seravalli, L.; Trevisi, G.; Frigeri, P. [IMEM-CNR Institute, Parco Area delle Scienze, 37/A 43100 Parma (Italy)

2013-11-14

267

Theoretical aspects of photon emission from a single quantum dot nanocavity system  

Microsoft Academic Search

In this work, we investigate the aspects of photon emitted from a single quantum dot exciton, strongly coupled to a planar nanocavity, from which the exact spectrum is derived. By using the rigorous medium-dependent theory of fully quantized cavity-QED formulas, the exact spectrum is reduced to two separate forms, in terms of the leaky cavity mode emission and the radiation

Guangcun Shan; Wei Huang; Miao Zhang

2010-01-01

268

Atomistic Pseudopotential Calculations of Thickness-Fluctuation GaAs Quantum Dots  

SciTech Connect

We calculate the electronic and optical properties of thickness-fluctuation quantum dots of different sizes and elongations using an atomistic empirical pseudopotential approach and configuration interaction. The carriers are confined by a monolayer fluctuation in the thickness of a GaAs/Al{sub 0.3}Ga{sub 0.7}As quantum well with a nominal thickness between 10 and 20 monolayers. For 10 monolayer thickness, we find several confined electron and hole levels of dominant heavy-hole character penetrating deep into the barrier (out of plane) and far beyond the physical dimension of the monolayer step (in-plane). The spatial extent of the states is strongly affected by the random-alloy fluctuations of the barrier, pushing the states toward Ga-rich regions of the interface. The similarity in the spatial extent of the electron and hole states leads to strong oscillator strength and a rich optical spectrum. The exciton as well as biexciton and trions (positive and negative) all show several lines in absorption despite the very shallow confinement potential given in these structures. The effects of correlations is drastic on the optical spectrum with the creation of highly correlated states that deviate strongly from the uncorrelated results.

Luo, J. W.; Bester, G.; Zunger, A.

2009-03-01

269

Quantum mechanical calculations related to ionization and charge transfer in DNA  

NASA Astrophysics Data System (ADS)

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.

Cauët, E.; Valiev, M.; Weare, J. H.; Liévin, J.

2012-07-01

270

Accurate experimental and theoretical comparisons between superconductor-insulator-superconductor mixers showing weak and strong quantum effects  

NASA Technical Reports Server (NTRS)

A systematic study of the gain and noise in superconductor-insulator-superconductor mixers employing Ta based, Nb based, and Pb-alloy based tunnel junctions was made. These junctions displayed both weak and strong quantum effects at a signal frequency of 33 GHz. The effects of energy gap sharpness and subgap current were investigated and are quantitatively related to mixer performance. Detailed comparisons are made of the mixing results with the predictions of a three-port model approximation to the Tucker theory. Mixer performance was measured with a novel test apparatus which is accurate enough to allow for the first quantitative tests of theoretical noise predictions. It is found that the three-port model of the Tucker theory underestimates the mixer noise temperature by a factor of about 2 for all of the mixers. In addition, predicted values of available mixer gain are in reasonable agreement with experiment when quantum effects are weak. However, as quantum effects become strong, the predicted available gain diverges to infinity, which is in sharp contrast to the experimental results. Predictions of coupled gain do not always show such divergences.

Mcgrath, W. R.; Richards, P. L.; Face, D. W.; Prober, D. E.; Lloyd, F. L.

1988-01-01

271

Quantum Monte Carlo calculations of magnetic moments and M1 transitions in $A \\le 9$ nuclei  

E-print Network

We present Quantum Monte Carlo calculations of magnetic moments and M1 transitions in $A\\le 9$ nuclei which take into account contributions of two-body electromagnetic currents. The Hamiltonian utilized to generate the nuclear wave functions includes the realistic Argonne-{\\it v}$_{18}$ two-nucleon and the Illinois-7 three-nucleon interactions. The nuclear two-body electromagnetic currents are derived from a pionful chiral effective field theory including up to one-loop corrections. These currents involve unknown Low Energy Constants which have been fixed so as to reproduce a number of experimental data for the two- and three-nucleon systems, such as $np$ phase shifts and deuteron, triton, and $^3$He magnetic moments. This preliminary study shows that two-body contributions provide significant corrections which are crucial to bring the theory in agreement with the experimental data in both magnetic moments and M1 transitions.

S. Pastore; Steven C. Pieper; R. Schiavilla; R. B. Wiringa

2012-08-29

272

Quantum Monte Carlo calculations of magnetic moments and M1 transitions in $A \\le 9$ nuclei  

E-print Network

We present Quantum Monte Carlo calculations of magnetic moments and M1 transitions in $A\\le 9$ nuclei which take into account contributions of two-body electromagnetic currents. The Hamiltonian utilized to generate the nuclear wave functions includes the realistic Argonne-{\\it v}$_{18}$ two-nucleon and the Illinois-7 three-nucleon interactions. The nuclear two-body electromagnetic currents are derived from a pionful chiral effective field theory including up to one-loop corrections. These currents involve unknown Low Energy Constants which have been fixed so as to reproduce a number of experimental data for the two- and three-nucleon systems, such as $np$ phase shifts and deuteron, triton, and $^3$He magnetic moments. This preliminary study shows that two-body contributions provide significant corrections which are crucial to bring the theory in agreement with the experimental data in both magnetic moments and M1 transitions.

Pastore, S; Schiavilla, R; Wiringa, R B

2012-01-01

273

Characterization of azobenzene chromophores for reversible optical data storage: molecular quantum calculations  

NASA Astrophysics Data System (ADS)

Azobenzene chromophores are promising as molecularly engineered materials for reversible optical data storage based on molecular reorientation. In this paper, the optical properties of several different azobenzene chromophores are studied using molecular quantum calculations. Special emphasis is put on molecular anisotropy since a high degree of anisotropy is essential for the storage performance. The trans isomers are all found to be practically one-dimensional whereas the anisotropy of the cis isomers is highly dependent on substituents. Molecular reorientation of chromophores in liquid-crystalline polymers is simulated in order to study the influence of lacking cis anisotropy. It is demonstrated that photoinduced birefringence is significantly reduced in materials characterized by a low degree of cis anisotropy.

Pedersen, Thomas G.; Johansen, Per M.; Pedersen, Henrik C.

2000-07-01

274

Constraining the nuclear energy density functional with quantum Monte Carlo calculations  

E-print Network

We study the problem of an impurity in fully polarized (spin-up) low density neutron matter with the help of an accurate quantum Monte Carlo method in conjunction with a realistic nucleon-nucleon interaction derived from chiral effective field theory at next-to-next-to-leading-order. Our calculations show that the behavior of the proton spin-down impurity is very similar to that of a polaron in a fully polarized unitary Fermi gas. We show that our results can be used to put tight constraints on the time-odd parts of the energy density functional, independent of the time-even parts, in the density regime relevant to neutron-rich nuclei and compact astrophysical objects such as neutron stars and supernovae.

Alessandro Roggero; Abhishek Mukherjee; Francesco Pederiva

2014-06-06

275

Constraining the nuclear energy density functional with quantum Monte Carlo calculations  

E-print Network

We study the problem of an impurity in fully polarized (spin-up) low density neutron matter with the help of an accurate quantum Monte Carlo method in conjunction with a realistic nucleon-nucleon interaction derived from chiral effective field theory at next-to-next-to-leading-order. Our calculations show that the behavior of the proton spin-down impurity is very similar to that of a polaron in a fully polarized unitary Fermi gas. We show that our results can be used to put tight constraints on the time-odd parts of the energy density functional, independent of the time-even parts, in the density regime relevant to neutron-rich nuclei and compact astrophysical objects such as neutron stars and supernovae.

Roggero, Alessandro; Pederiva, Francesco

2014-01-01

276

Free-Radical-Induced DNA Damage as Approached by Quantum-Mechanical and Monte Carlo Calculations  

NASA Astrophysics Data System (ADS)

The free-radical chemistry of DNA and its model systems has been widely studied by experimentalists as well as theoreticians. In the present paper, the important contributions of theory to a better understanding of this complex matter has been reviewed by an experimentalist with an emphasis on the following topics: modeling of DNA damage induced by ionizing radiation, pattern of -OH attack on DNA, ionization potentials and electron affinities of the nucleobases (reduction potentials), hole and electron transfer through DNA, tautomerization and isomerization reactions of DNA radicals, regioselectivity of -OH attack on the nucleobases, selectivity of free-radical attack at the sugar moiety, reactions of alkyl radicals, assignment of transients by quantum-chemical calculations of their electronic transitions, reduction potentials of DNA radicals, and DNA stability and repair. Some pending questions that may be tackled by theoreticians are addressed.

von Sonntag, Clemens

277

Quantum-mechanical calculation of carrier distribution in MOS accumulation and strong inversion layers  

SciTech Connect

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.

Lee, Chien-Wei; Hwu, Jenn-Gwo [Graduate Institute of Electronics Engineering/ Department of Electrical Engineering, National Taiwan University, Taipei, 10617, Taiwan (China)] [Graduate Institute of Electronics Engineering/ Department of Electrical Engineering, National Taiwan University, Taipei, 10617, Taiwan (China)

2013-10-15

278

Electronic structure calculations of PbS quantum rods and tubes  

NASA Astrophysics Data System (ADS)

We study absorption spectra, optical and HOMO-LUMO gaps, and the density of states for PbS quantum rods (QRs) and tubes (QTs). We find some similarities and also differences in QR and QT properties. For both QRs and QTs, the optical and HOMO-LUMO gaps reach the plateaus for small lengths. We find that tubes are as stable as rods. The optical spectra exhibit a peak that can be due to the electron-hole interaction or be a prototype of an Se-Sh transition in the effective mass approximation. We also calculate the density of states by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The TDDFT density of states function is shifted towards the red side by 0.5 eV indicating the strong e-h interaction.

Pimachev, Artem; Dahnovsky, Yuri

2014-01-01

279

Finite-Temperature Pairing Gap of a Unitary Fermi Gas by Quantum Monte Carlo Calculations  

SciTech Connect

We calculate the one-body temperature Green's (Matsubara) function of the unitary Fermi gas via quantum Monte Carlo, and extract the spectral weight function A(p,omega) using the methods of maximum entropy and singular value decomposition. From A(p,omega) we determine the quasiparticle spectrum, which can be accurately parametrized by three functions of temperature: an effective mass m*, a mean-field potential U, and a gap DELTA. Below the critical temperature T{sub c}=0.15epsilon{sub F} the results for m*, U, and DELTA can be accurately reproduced using an independent quasiparticle model. We find evidence of a pseudogap in the fermionic excitation spectrum for temperatures up to T*{approx_equal}0.20{epsilon}{sub F}>T{sub c}.

Magierski, Piotr; Wlazlowski, Gabriel [Faculty of Physics, Warsaw University of Technology, ulica Koszykowa 75, 00-662 Warsaw (Poland); Bulgac, Aurel; Drut, Joaquin E. [Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States)

2009-11-20

280

Actinometric measurements and theoretical calculations of j/O3/, the rate of photolysis of ozone to O/1D/  

NASA Technical Reports Server (NTRS)

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.

Dickerson, R. R.; Stedman, D. H.; Chameides, W. L.; Crutzen, P. J.; Fishman, J.

1979-01-01

281

Quantum-Mechanical Calculation of Ionization-Potential Lowering in Dense Plasmas  

NASA Astrophysics Data System (ADS)

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.

Son, Sang-Kil; Thiele, Robert; Jurek, Zoltan; Ziaja, Beata; Santra, Robin

2014-07-01

282

Spectroscopic analysis of 3-Bromodiphenylamine with experimental techniques and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 3500-100 cm-1 and 4000-400 cm-1, respectively, for 3-Bromodiphenylamine (3BDPA). Theoretical calculations were performed by using Density Functional Theory (DFT) method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The calculated wavenumbers were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (?0) and related properties (?, ? and ??) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization were analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the ?* and ?* anti-bonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. Molecular electrostatic potential (MEP) and HOMO-LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures and the results reveals the heat capacity (C), and entropy (S) increases with rise in temperature.

Sudharsan, A.; Seshadri, S.; Gnanasambandan, T.; Saravanan, R. R.

2014-10-01

283

Some foundational aspects of quantum computers and quantum robots.  

SciTech Connect

This paper addresses foundational issues related to quantum computing. The need for a universally valid theory such as quantum mechanics to describe to some extent its own validation is noted. This includes quantum mechanical descriptions of systems that do theoretical calculations (i.e. quantum computers) and systems that perform experiments. Quantum robots interacting with an environment are a small first step in this direction. Quantum robots are described here as mobile quantum systems with on-board quantum computers that interact with environments. Included are discussions on the carrying out of tasks and the division of tasks into computation and action phases. Specific models based on quantum Turing machines are described. Differences and similarities between quantum robots plus environments and quantum computers are discussed.

Benioff, P.; Physics

1998-01-01

284

Structural determination of carvone, a component of spearmint, by means of gas electron diffraction augmented by theoretical calculations  

NASA Astrophysics Data System (ADS)

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 ? ?) of the most abundant conformer of carvone are as follows: < r(C-C)>=1.520(3) Å; < r(C?C)>=1.360(5) Å; r(C?O)=1.225(5) Å; < r(C-H)>=1.104(4)Å; =121.1(5)°; =110.4(5)°; ?C-CO-C=117.1(14)°; =111.1(13)°. Angle brackets denote average values and parenthesized values are the estimated limits of error (3 ?) referring to the last significant digit.

Egawa, Toru; Kachi, Yukari; Takeshima, Tsuguhide; Takeuchi, Hiroshi; Konaka, Shigehiro

2003-10-01

285

Electronic structure calculation of single and coupled self-assembled quantum dots  

NASA Astrophysics Data System (ADS)

There are two main contributions of this thesis. First, from the theoretical point of view, we find that different treatments of the nanostructure-barrier interface in the framework of multiband effective-mass theory, result in the existence of non-physical solutions for the hole energy levels of a nanostructure. Our proposed improvement is an approach based on the envelope-function theory for nanostructures developed by Burt and Foreman. In structures with a large difference of the structural parameters between the constituent materials, such as InAs/GaAs quantum nanostructures, the conventional multiband models lead to non-physical solutions. Second, we investigate underlying physics of the theoretically less investigated QD systems. Variation of electronic and optical properties of InAs/GaAs QDs and QDM grown on [11k] substrates, where k=1,2,3 were analyzed and we found that: (i) The QD size in the growth direction determines the degree of influence of the substrate orientation: the flatter the dots, the larger the difference from the reference [001] case. (ii) The small variation of inter-dot distance in eight QD molecule qualitatively changes the transition energy dependence on the substrate orientation. (iii) Size of the QD in the growth direction determines the influence of the (In,Ga)As capping layer on the optical properties of [11k] grown InAs QDs, where k=1,2,3. Next, two cases of type II QDs where hole is localized outside the dot, were discussed: InP/InGaP QDs and QDMs in an external magnetic field, and InAs QDs capped with Ga(As,Sb). Competition between confinement, quantum mechanical coupling, and strain influence the exciton diamagnetic shift in single QD and double and triple QDM is investigated in details. Available experimental data were successfully described by one of the optically active exciton states of the lowest lying exciton quartet. Finally, the electronic and optical properties of unstrained GaAs self-assembled QDs with precisely known sizes and shape, placed in an external magnetic field are investigated. For magnetic fields applied both, in growth direction and perpendicular to it (B?50T), we found good agreement between our predicted exciton diamagnetic shift and recent experimental magneto-photoluminescence data.

Mlinar, Vladan

286

Quantum Calculations on Salt Bridges with Water: Potentials, Structure, and Properties  

SciTech Connect

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 potentials are used in Molecular Dynamics simulations.

Liao, Sing; Green, Michael E.

2011-01-01

287

A quantum-information-theoretic approach to the signalling time of cryptochromes in Arabidopsis thaliana  

E-print Network

An important problem in the magnetoreception of birds is the identification of a host molecule for a magnetically sensitive chemical reaction known as the radical-pair mechanism. Current experiments and theory suggest cryptochrome (a class of receptor molecules) as a viable candidate. Cryptochrome functions as a signalling molecule, triggering further chemical reactions that lead to a neural signal when it attains a certain population in a particular state. Here we characterise cryptochrome response times by proposing a simple model to describe its radical-pair reaction. A key element of the reaction is the quantum coherent oscillations between singlet and triplet spin states of the radicals. While this is essential for enabling the magnetic sensing of cryptochrome, coherent state transitions can also increase the speed of certain processes. By using the well-known formalism of Kraus maps from quantum information theory we study the influence of decoherence on how quickly cryptochrome can signal. In particular we describe the radical-pair reaction as a quantum random walk with a variable dephasing parameter for the singlet-triplet oscillations. This allows us to study the state transitions of the radical pair subject to different levels of decoherence. We find that for realistic system parameters (transition rates) obtained from the literature, dephasing induces a change in cryptochrome signalling times of only a few percent. We thus argue that the process is essentially robust to dephasing. This change is seen to occur over only a small window of dephasing noise strengths. Artificial system parameters are also explored.

A. Chia; A. Gorecka; P. Kurzynski; T. Paterek; D. Kaszlikowski

2014-09-16

288

Quantum-mechanical calculations of the dynamic polarizability of atoms and molecules  

SciTech Connect

Two variants of nonstationary perturbation theory are commonly used in the quantum-mechanical calculations of the dynamic polarizability of atomic and molecular systems within the one-electron approximation. These are the nonstationary bound Hartree-Fock perturbation theory and nonstationary variational perturbation theory combined with the method of superposition of singly excited configurations. In order to obtain stable results for dynamic polarizability for small as opposed to polyatomic molecules in nonempirical calculations atomic orbital basis sets containing several tens of Gaussian functions are required. The spectral decomposition method in this case requires requires a vast amount of computer time. In this paper the authors have developed an iterative method of solution for the two perturbation theory variants in which the transformation of integrals has to be performed only for two indices and consequently results in a reduction of computer time required. In addition, they have successfully used basis sets containing more than forty Gaussian orbitals in their simulation of the dynamic polarizability of small molecules.

Kukanov, M.A.; Malykhanov, Yu.B.

1986-07-01

289

Modeling catalytic mechanism of nitrile hydratase by semi-empirical quantum mechanical calculation.  

PubMed

Nitrile hydratase (NHase) is an important industrial enzyme capable of converting nitriles to corresponding amides. Utilizing the method of semi-empirical quantum mechanical (QM) calculation by TRITON, the bioconversion process of acrylonitrile to acrylamide catalyzed by NHase was successfully performed on a computer. Crystal structure of a Co-type NHase from Pseudonocardia thermophila JCM 3095 (PDB code 1IRE) was selected as the target for acrylonitrile autodock. In silico calculations were performed on the NHase-acrylonitrile complex to simulate the enzyme catalysis mechanism by quantitatively comparing energy changes of each reaction pathway. Simulation results showed that active site activation is the first step of NHase catalysis, in which the Co2+ coordinated to a water molecule forms a Co-OH complex mediated by the oxidized alpha-CEA113. Then the oxygen atom in the Co-OH attacks the C atom in the -CN triple bond of acrylonitrile, forming a precursor of acrylamide. Consequently, proton rearrangement happens transforming the precursor into the final product of acrylamide, under the assistance of the hydrogen atom in the -OH group of alpha-SER112. Gibbs energy changes of three steps corresponding to the active center activation, nucleophilic attack and proton rearrangement are around -31, 23 and -12 kcal/mol, respectively. PMID:18945629

Yu, Huimin; Liu, Jie; Shen, Zhongyao

2008-11-01

290

Efficiency enhancement calculations of state-of-the-art solar cells by luminescent layers with spectral shifting, quantum cutting, and quantum tripling function  

NASA Astrophysics Data System (ADS)

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%.

ten Kate, O. M.; de Jong, M.; Hintzen, H. T.; van der Kolk, E.

2013-08-01

291

A quantum field theoretical approach to the P vs. NP problem via the sign of the fermionic Quantum Monte Carlo  

E-print Network

I present here a new method that allows the introduction of a discrete auxiliary symmetry in a theory in such a way that the eigenvalue spectrum of the fermion functional determinant is made up of complex conjugated pairs. The method implies a particular way of introducing and integrating over auxiliary fields related to a set of artificial shift symmetries. Gauge-fixing the artificial continuous shift symmetries in the direct and dual sectors leads to the implementation of direct and dual BRST-type global symmetries and of a symplectic structure over the field space (as prescribed by the Batalin-Vilkovisky method). A procedure similar to Kahler polarization in geometric quantization guarantees the possibility to choose a Kahler structure over the field space. This structure is generated by a special way of performing gauge fixing over the direct and dual sectors. The desired discrete symmetry appears to be induced by the Hodge-* operator. The particular extension of the field space presented here makes the operators of the de-Rham cohomology manifest. These become symmetries in the extended theory. This method implies the identification of the (anti)-BRST and dual-(anti)-BRST operators with the exterior derivative and its dual in the context of the complex de-Rham cohomology. The novelty of this method relies on the fact that the field structure is doubled two times in order to make use of a supplemental symmetry prescribed by algebraic geometry. This leads to a generalization of Kramers theorem that avoids the Quantum Monte Carlo phase sign problem without any apparent increase in complexity.

Andrei T. Patrascu

2014-03-09

292

Nanowire terahertz quantum cascade lasers  

NASA Astrophysics Data System (ADS)

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.

Grange, Thomas

2014-10-01

293

A quantum-information-theoretic approach to the signalling time of cryptochromes in Arabidopsis thaliana  

E-print Network

An important problem in the magnetoreception of birds is the identification of a host molecule for a magnetically sensitive chemical reaction known as the radical-pair mechanism. Current experiments and theory suggest cryptochrome (a class of receptor molecules) as a viable candidate. Cryptochrome functions as a signalling molecule, triggering further chemical reactions that lead to a neural signal when it attains a certain population in a particular state. Here we characterise cryptochrome response times by proposing a simple model to describe its radical-pair reaction. A key element of the reaction is the quantum coherent oscillations between singlet and triplet spin states of the radicals. While this is essential for enabling the magnetic sensing of cryptochrome, coherent state transitions can also increase the speed of certain processes. By using the well-known formalism of Kraus maps from quantum information theory we study the influence of decoherence on how quickly cryptochrome can signal. In particular we describe the radical-pair reaction as a quantum random walk with a variable dephasing parameter for the singlet-triplet oscillations. This allows us to study the state transitions of the radical pair subject to different levels of decoherence. We find that for realistic system parameters (transition rates) obtained from the literature, dephasing induces a change in cryptochrome signalling times of only a few percent. We thus argue that the process is essentially robust to dephasing. This change is seen to occur over only a small window of dephasing noise strengths. Artificial (i.e. unrealistic) system parameters are also explored.

A. Chia; A. Gorecka; P. Kurzynski; T. Paterek; D. Kaszlikowski

2014-09-16

294

Quantifying desorption of saturated hydrocarbons from silicon with quantum calculations and scanning tunneling microscopy.  

PubMed

Electron stimulated desorption of cyclopentene from the Si(100)-(2 x 1) surface is studied experimentally with cryogenic UHV STM and theoretically with transport, electronic structure, and dynamical calculations. Unexpectedly for a saturated hydrocarbon on silicon, desorption is observed at bias magnitudes as low as 2.5 V, albeit the desorption yields are a factor of 500 to 1000 lower than previously reported for unsaturated molecules on silicon. The low threshold voltage for desorption is attributed to hybridization of the molecule with the silicon surface, which results in low-lying ionic resonances within 2-3 eV of the Fermi level. These resonances are long-lived, spatially localized, and displaced in equilibrium with respect to the neutral state. This study highlights the importance of nuclear dynamics in silicon-based molecular electronics and suggests new guidelines for the control of such dynamics. PMID:17155577

Yoder, N L; Guisinger, N P; Hersam, M C; Jorn, R; Kaun, C-C; Seideman, T

2006-11-01

295

Quantum-mechanical calculation of ionization potential lowering in dense plasmas  

E-print Network

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 (XFEL), 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 Kr\\"oll. 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 ...

Son, Sang-Kil; Jurek, Zoltan; Ziaja, Beata; Santra, Robin

2014-01-01

296

Self-healing diffusion quantum Monte Carlo algorithms: Direct reduction of the fermion sign error in electronic structure calculations  

Microsoft Academic Search

We develop a formalism and present an algorithm for optimization of the trial wave function used in fixed-node diffusion quantum Monte Carlo (DMC) methods. The formalism is based on the DMC mixed estimator of the ground-state probability density. We take advantage of a basic property of the walker configuration distribution generated in a DMC calculation, to (i) project out a

F. A. Reboredo; R. Q. Hood; P. R. C. Kent

2009-01-01

297

Quantum-chemical calculations and electron diffraction study of the equilibrium molecular structure of vitamin K3  

NASA Astrophysics Data System (ADS)

The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.

Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.

2014-05-01

298

Measurements and Theoretical Calculations of N2-broadening and N2-shift Coefficients in the v2 band of CH3D  

NASA Technical Reports Server (NTRS)

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 reasonable agreement with the scattered experimental data (20% in most cases).

Predoi-Cross, A.; Hambrook, Kyle; Brawley-Tremblay, Marco; Bouanich, J. P.; Smith, Mary Ann H.

2006-01-01

299

Simple theoretical analysis of the photoemission from quantum confined effective mass superlattices of optoelectronic materials  

PubMed Central

Summary The photoemission from quantum wires and dots of effective mass superlattices of optoelectronic materials was investigated on the basis of newly formulated electron energy spectra, in the presence of external light waves, which controls the transport properties of ultra-small electronic devices under intense radiation. The effect of magnetic quantization on the photoemission from the aforementioned superlattices, together with quantum well superlattices under magnetic quantization, has also been investigated in this regard. It appears, taking HgTe/Hg1? xCdxTe and InxGa1? xAs/InP effective mass superlattices, that the photoemission from these quantized structures is enhanced with increasing photon energy in quantized steps and shows oscillatory dependences with the increasing carrier concentration. In addition, the photoemission decreases with increasing light intensity and wavelength as well as with increasing thickness exhibiting oscillatory spikes. The strong dependence of the photoemission on the light intensity reflects the direct signature of light waves on the carrier energy spectra. The content of this paper finds six different applications in the fields of low dimensional systems in general. PMID:22003442

De, Debashis; Bhattacharya, Sitangshu; Adhikari, S M; Kumar, A; Bose, P K

2011-01-01

300

Interfacial Atmospheric Chemistry: Quantum Chemical Calculations on the Mechanism of Protonation and Oligomerization of Isoprene on Aqueous Surfaces  

NASA Astrophysics Data System (ADS)

It has become increasingly apparent that atmospheric chemistry involves more than gas-phase reactions. Key processes, such as the decay of NO2 in urban plumes and the associated daytime formation of HONO, and the rapid chemistries observed in and over forest canopies at nighttime defy explanation by conventional atmospheric chemistry mechanisms. We have recently reported experimental results on several gas-liquid reactions of atmospheric interest, such as the facile protonation of gaseous isoprene on mildly acidic (pH < 4) water. Although interfacial proton transfers, such as the one involved in the protonation of gaseous isoprene, also participate in cloud and ocean acidification, bioenergetics coupling, 'on-water' catalysis, self-assembly and molecular recognition, little is known about the molecular mechanisms of such reactions. Herein we apply quantum mechanics to investigate how biogenic or anthropogenic olefins may get protonated and undergo oligomerization at the air-water interface by performing model calculations on small water clusters carrying an excess proton as surrogates for the surface of mildly acidic water as sensed by gaseous isoprene (ISO). We find that ISO binds weakly to the surface of water and accepts a proton from H+(H2O)3, leading to ISOH+ via a proton transfer hindered by a ?G1‡ = 5.6 kcal mol-1 kinetic barrier. Subsequently, another ISO attaches loosely to this ensemble, before being attacked by the ISOH+. This process, which represents the first step of the cationic polymerization of ISO, is hindered by a similar ?G2‡ = 5.7 kcal mol-1 barrier. Our theoretical results are consistent with experimental (~ 10-4) uptake coefficients for ISO measured on acidic water.

Mishra, H.; Colussi, A. J.; Enami, S.; Nielsen, R. J.; Hoffmann, M. R.; Goddard, W. A.

2012-12-01

301

NMR and theoretical calculations: a unified view of the cis/trans isomerization of 2-substituted thiazolidines containing peptides.  

PubMed

The cis/trans isomerization of peptides containing the pseudoproline (4R)-thiazolidine-4-carboxylic acid Cys(Psi (R1,R2) pro) is investigated from both an experimental and a theoretical point of view by NMR and DFT calculations. A series of Ac-Cys(Psi(R1,R2) pro)-OCH3 and Ac-Cys(Psi(R1,R2) pro)-NHCH3 peptides were prepared to assess the influence of the substitution at the C2 position as well as of the amide following the thiazolidine residue. For each compound, the cis/trans ratio along with free energy, the puckering of the thiazolidine ring and the free rotational energy barrier are reported and discussed. We observe there is a pronounced effect of the C2 substituents and of the chirality upon the cis/trans ratio with the population of the cis content in the order (2R)-Cys(Psi(CH3,H) pro)<(2S)-Cys(Psi(H,CH3) pro)calculations. It rationalizes the main effects which tailor the cis/trans isomerization. PMID:18646815

Jamet, Helene; Jourdan, Muriel; Dumy, Pascal

2008-08-14

302

Structural conformations, tautomerization and vibrational spectral study of 6-amino-1-methylpurine with density functional theoretical calculations  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman spectra of 6-amino-1-methylpurine (AMP) have been recorded in the region 4000-400 cm-1 and 3500-50 cm-1 respectively. The optimized geometry, frequency and intensity of the vibrational bands of AMP have been obtained by DFT level of theory using B3LYP method with 6-311++G(d,p) basis set. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. Purines, including substituted purines and their tautomers, are the most widely occurring nitrogen-containing heterocyclic in nature. Purines and pyrimidines make up the two groups of nitrogenous bases, including the two groups of nucleotide bases. Two of the four deoxyribonucleotides and two of the four ribonucleotides, the respective building-blocks of DNA and RNA, are purines. The calculated vibrational values are in good agreement when they are compared with IR and Raman experimental data. Amine-imine tautomerism of 6-amino-1-methyl purine is studied in detail. In agreement with experimental results, it was found that imine tautomer is more stable than amine tautomer.

Arivazhagan, M.; Kavitha, R.; Subhasini, V. P.

2014-07-01

303

Theoretical polarization-dependent X-ray spectra of Be-like Fe calculated for different electron beam densities  

NASA Astrophysics Data System (ADS)

We study theoretically the polarization properties of X-ray spectra of Be-like Fe ions excited through resonant capture by an electron beam with different electron densities. Our previous work in this area was related to the study of polarization of dielectronic satellite lines of Fe ions excited by a low-density electron beam. (A.S. Shlyaptseva, R.C. Mancini, P. Neill, P. Beiersdorfer, J.R. Crespo López-Urrutia, and K. Widmann, Phys. Rev. A, 57), 888 (1998) Here we extend our work to the case of higher-density electron beams. As the density of the electron beam increases, new channels of electron capture appear. Thus the atomic and polarization characteristics of the satellite lines change. Moreover, additional X-ray satellite lines will appear. Using the density matrix formalism, we calculate the polarization characteristics and polarization-dependent spectra of dielectronic satellite lines of Be-like Fe produced at different energies and densities of the electron beam. We compare the results of the present work with our previous ones for low-density electron beams. These results are relevant to the identification of X-ray polarization-dependent spectral features and for X-ray line polarization spectroscopy.

Shlyaptseva, Alla; Mancini, Roberto

1998-05-01

304

Studies on the s-cis-trans isomerism for some furan derivatives through IR and NMR spectroscopies and theoretical calculations  

NASA Astrophysics Data System (ADS)

The s-cis-trans isomerism of two furan derivatives [2-acetyl- (AF) and 2-acetyl-5-methylfuran, (AMF)] was analyzed, using data from the deconvolution of their carbonyl absorption band in two solvents (CH2Cl2 and CH3CN). These infrared data showed that the O,O-trans conformers predominate in the less polar solvent (CH2Cl2), but these equilibria change in a more polar solvent (CH3CN) leading to a slight predominance of the O,O-cis conformers, in agreement with the theoretical calculations. The later results were obtained using B3LYP-IEFPCM/6-31++g(3df,3p) level of theory, which taking into account the solvent effects at IEFPCM (Integral Equation Formalism Polarizable Continuum Model). Low temperature 13C NMR spectra in CD2Cl2 (ca. -75 °C) showed pairs of signals for each carbon, due to the known high energy barrier for the cis-trans interconversion leading to a large predominance of the trans isomers, which decreases in acetone-d6. This was confirmed by their 1H NMR spectra at the same temperatures. Moreover, despite the larger hyperconjugative interactions for the O,O-cis isomers, obtained from NBO data, these isomers are destabilized by the their Lewis energy.

Rittner, Roberto; Ducati, Lucas C.; Tormena, Cláudio F.; Cormanich, Rodrigo A.; Fiorin, Barbara C.; Braga, Carolyne B.; Abraham, Raymond J.

2013-02-01

305

Ab initio Quantum Monte Carlo Calculations of Spin Superexchange in Cuprates: The Benchmarking Case of Ca2CuO3  

NASA Astrophysics Data System (ADS)

In view of the continuous theoretical efforts aimed at an accurate microscopic description of the strongly correlated transition metal oxides and related materials, we show that with continuum quantum Monte Carlo (QMC) calculations it is possible to obtain the value of the spin superexchange coupling constant of a copper oxide in a quantitatively excellent agreement with experiment. The variational nature of the QMC total energy allows us to identify the best trial wave function out of the available pool of wave functions, which makes the approach essentially free from adjustable parameters and thus truly ab initio. The present results on magnetic interactions suggest that QMC is capable of accurately describing ground-state properties of strongly correlated materials.

Foyevtsova, Kateryna; Krogel, Jaron T.; Kim, Jeongnim; Kent, P. R. C.; Dagotto, Elbio; Reboredo, Fernando A.

2014-07-01

306

Mechanistic study on the oxidation of anthocyanidin synthase by quantum mechanical calculation.  

PubMed

Anthocyanidin synthase (ANS), a member of the 2-oxoglutarate-dependent dioxygenase family in flavonoid biosynthesis, catalyzes the conversion of leucoanthocyanidins (e.g. 2R,3S,4S-cis-leucocyanidin, LCD) to flav-2-en-3,4-diols, a direct precursor of colored anthocyanidins via flavan-3,3,4-triols. The detailed oxygenation mechanism of 2R,3S,4S-cis-LCD to flav-2-en-3,4-diols was investigated using the density functional theory method. An initial model for the calculation was constructed from a structure obtained by a 100-ps molecular dynamics simulation of Arabidopsis ANS under physiological conditions. This model consisted of an LCD molecule as the substrate together with an iron atom, two histidine residues, an aspartic acid residue, a succinate, and an oxygen atom as ligands of the iron atom. The results of the calculation indicated that both the C-3 and C-4 positions of LCD can be oxidized, although C-4 oxidation is preferable. The C-3 oxidation required several steps to form flavan-3,3,4-triol: 1) formation of Fe(III)-OH and a substrate C-3 radical via hydrogen atom abstraction by Fe(IV)=O, 2) formation of a C-3 ketone and a water molecule, 3) addition of OH(-) into the C-3 position of the ketone, and 4) addition of H(+) to form flavan-3,3,4-triol. On the other hand, C-4 oxidation of 2R,3S,4S-cis-LCD resulted in the direct formation of 2R,3R-trans-dihydroquercetin. These results suggest that the oxidation at C-3 of LCD, a key reaction for coloring in anthocyanin biosynthesis, can be regarded as a "side reaction" from the viewpoint of quantum mechanics of enzymatic reactions. Molecular evolutional implications of ANS and related proteins are discussed in terms of reaction dynamics. PMID:16702218

Nakajima, Jun-ichiro; Sato, Yoshiharu; Hoshino, Tyuji; Yamazaki, Mami; Saito, Kazuki

2006-07-28

307

Interactions of ionic liquids and acetone: thermodynamic properties, quantum-chemical calculations, and NMR analysis.  

PubMed

The interactions between ionic liquids (ILs) and acetone have been studied to obtain a further understanding of the behavior of their mixtures, which generally give place to an exothermic process, mutual miscibility, and negative deviation of Raoult's law. COSMO-RS was used as a suitable computational method to systematically analyze the excess enthalpy of IL-acetone systems (>300), in terms of the intermolecular interactions contributing to the mixture behavior. Spectroscopic and COSMO-RS results indicated that acetone, as a polar compound with strong hydrogen bond acceptor character, in most cases, establishes favorable hydrogen bonding with ILs. This interaction is strengthened by the presence of an acidic cation and an anion with dispersed charge and non-HB acceptor character in the IL. COSMO-RS predictions indicated that gas-liquid and vapor-liquid equilibrium data for IL-acetone systems can be finely tuned by the IL selection, that is, acting on the intermolecular interactions between the molecular and ionic species in the liquid phase. NMR measurements for IL-acetone mixtures at different concentrations were also carried out. Quantum-chemical calculations by using molecular clusters of acetone and IL species were finally performed. These results provided additional evidence of the main role played by hydrogen bonding in the behavior of systems containing ILs and HB acceptor compounds, such as acetone. PMID:23688030

Ruiz, Elia; Ferro, Victor R; Palomar, Jose; Ortega, Juan; Rodriguez, Juan Jose

2013-06-20

308

Schwarzschild radius from Monte Carlo calculation of the Wilson loop in supersymmetric matrix quantum mechanics.  

PubMed

In the string-gauge duality it is important to understand how the space-time geometry is encoded in gauge theory observables. We address this issue in the case of the D0-brane system at finite temperature T. Based on the duality, the temporal Wilson loop W in gauge theory is expected to contain the information of the Schwarzschild radius RSch of the dual black hole geometry as log(W)=RSch/(2pialpha'T). This translates to the power-law behavior log(W)=1.89(T/lambda 1/3)-3/5, where lambda is the 't Hooft coupling constant. We calculate the Wilson loop on the gauge theory side in the strongly coupled regime by performing Monte Carlo simulations of supersymmetric matrix quantum mechanics with 16 supercharges. The results reproduce the expected power-law behavior up to a constant shift, which is explainable as alpha' corrections on the gravity side. Our conclusion also demonstrates manifestly the fuzzball picture of black holes. PMID:19518857

Hanada, Masanori; Miwa, Akitsugu; Nishimura, Jun; Takeuchi, Shingo

2009-05-01

309

Molecular structure, polarizability, hyperpolarizability analysis and spectroscopic characterization of 1-(chloromethyl)-2-methylnaphthalene with experimental (FT-IR and FT-Raman) techniques and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

In this work, the FT-IR and FT-Raman spectrum of 1-(chloromethyl)-2-methyl naphthalene (abbreviated as 1-ClM-2MN, C 12H 11Cl) have been recorded in the region 3600-10 cm -1. The optimum molecular geometry, normal mode wavenumbers, infrared and Raman intensities, Raman scattering activities, corresponding vibrational assignments, Mullikan atomic charges and thermo-dynamical parameters were investigated with the help of HF and B3LYP (DFT) method using 6-311G(d,p), 6-311++G(d,p) basis sets. Also, the dipole moment, linear polarizabilities, anisotropy, first and second hyperpolarizabilities values were also computed using the same basis set. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. The correlation equations between heat capacities, entropies, enthalpy changes and temperatures were fitted by quadratic formulas. Lower value in the HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. UV-vis spectral analysis of 1-ClM-2MN has been researched by theoretical calculations. In order to understand the electronic transitions of the compound, TD-DFT calculations on electronic absorption spectra in gas phase and solvent (DMSO and chloroform) were performed. The calculated frontier orbital energies, absorption wavelengths ( ?), oscillator strengths ( f) and excitation energies ( E) for gas phase and solvent are also illustrated.

Nagabalasubramanian, P. B.; Karabacak, M.; Periandy, S.

2012-01-01

310

Direct calculation of the reactive transition matrix by L-squared quantum mechanical variational methods with complex boundary conditions  

NASA Technical Reports Server (NTRS)

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.

Sun, Yan; Yu, Chin-Hui; Kouri, Donald J.; Schwenke, David W.; Halvick, Philippe

1989-01-01

311

Quantum-classical calculation of the absorption and emission spectral shapes of oligothiophenes at low and room temperature by first-principle calculations.  

PubMed

We report a thorough computational characterization of the low- and room-temperature absorption and emission spectra of a series of oligothiophenes that contain between three and seven thiophene units. Our computational approach is based on time-dependent (TD) density functional calculations with the CAM-B3LYP functional. The effect of vibrations is included without resorting to any empirical parameters either at a fully quantum level or with a hybrid quantum-classical protocol. This latter approach is introduced to describe the relevant broadening effects in absorption at room temperature and is based on the partition of the vibrational modes into two sets: the inter-ring torsions treated at the anharmonic level in a classical way and the remaining modes described at the quantum level. The contribution of the quantum modes to the spectrum is computed by using a harmonic approximation, which accounts for Duschinsky mixing and changes in the vibrational frequencies associated with the electronic transition; a path-integral TD approach is adopted to account for the effect of temperature. The spectra simulated at low temperatures are in very good agreement with their experimental counterparts, which indicates that our calculations can quantitatively reproduce the effect of chain lengthening on the position and the shape of the spectra. Good agreement is also obtained at room temperature, for which we show that the classical description of the broadening, owing to the inter-ring torsions, reproduces the loss of the vibronic structure observed in the experiment and introduces only a slight overestimation of the spectral width. PMID:25110885

Improta, Roberto; Ferrer, Francisco J Avila; Stendardo, Emiliano; Santoro, Fabrizio

2014-10-20

312

FeynDyn: A MATLAB program for fast numerical Feynman integral calculations for open quantum system dynamics on GPUs  

NASA Astrophysics Data System (ADS)

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 language: MATLAB R2012a. Computer: See “Operating system”. Operating system: Any operating system that can run MATLAB R2007a or above. Classification: 4.4. Nature of problem: Calculating the dynamics of the reduced density operator of an open quantum system. Solution method: Numerical Feynman integral. Running time: Depends on the input parameters. See the main text for examples.

Dattani, Nikesh S.

2013-12-01

313

Statistical sampling of semiclassical distributions: Calculating quantum mechanical effects using Metropolis Monte Carlo  

E-print Network

is incorporated with semiclas- sical dynamics. SC-IVR approximates the time-evolution operator as a phase be used to study semiclassical approxi- mations of quantum dynamics. Due to favorable scaling of Monte Carlo with the system size, quantum dynamics of large and complex with many degrees of freedom systems

Sun, Sean

314

Nonperturbative quantum and classical calculations of multiphoton vibrational excitation and dissociation of Morse molecules^1  

NASA Astrophysics Data System (ADS)

The multiphoton vibrational excitation and dissociation of Morse molecules have been computed nonperturbatively using Hamilton's and Schr?dinger's time-dependent equations, for a range of laser pulse parameters. The time-dependent Schr?dinger 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.

Dimitriou, K. I.; Mercouris, Th.; Constantoudis, V.; Komninos, Y.; Nicolaides, C. A.

2006-05-01

315

Seamless bridging of quantum-mechanics with mechanics and electronic structure calculations at macroscopic scales  

NASA Astrophysics Data System (ADS)

Defects play a crucial role in influencing the macroscopic properties of solids---examples include the role of dislocations in plastic deformation, dopants in semiconductor properties, and domain walls in ferroelectric properties. These defects are present in very small concentrations (few parts per million), yet, produce a significant macroscopic effect on the materials behavior through the long-ranged elastic and electrostatic fields they generate. The strength and nature of these fields, as well as other critical aspects of the defect-core are all determined by the electronic structure of the material at the quantum-mechanical length-scale. Hence, there is a wide range of interacting length-scales, from electronic structure to continuum, that need to be resolved to accurately describe defects in materials and their influence on the macroscopic properties of materials. This has remained a significant challenge in multi-scale modeling, and a solution to this problem holds the key for predictive modeling of complex materials systems. In an attempt to address the aforementioned challenge, this talk presents the development of a seamless multi-scale scheme to perform electronic structure calculations at macroscopic scales. The key ideas involved in its development are (i) a real-space variational formulation of electronic structure theories, (ii) a nested finite-element discretization of the formulation, and (iii) a systematic means of adaptive coarse-graining retaining full resolution where necessary, and coarsening elsewhere with no patches, assumptions or structure. This multi-scale scheme has enabled, for the first time, calculations of the electronic structure of multi-million atom systems using orbital-free density-functional theory, thus, paving the way for an accurate electronic structure study of defects in materials. The accuracy of the method and the physical insights it offers into the behavior of defects in materials is highlighted through studies on vacancies and dislocations. Current efforts towards extending this multi-scale method to Kohn-Sham density functional theory will also be presented.

Gavini, Vikram

2013-03-01

316

A Theory of Physical Quantum Computation: The Quantum Computer Condition  

E-print Network

In this paper we present a new unified theoretical framework that describes the full dynamics of quantum computation. Our formulation allows any questions pertaining to the physical behavior of a quantum computer to be framed, and in principle, answered. We refer to the central organizing principle developed in this paper, on which our theoretical structure is based, as the *Quantum Computer Condition* (QCC), a rigorous mathematical statement that connects the irreversible dynamics of the quantum computing machine, with the reversible operations that comprise the quantum computation intended to be carried out by the quantum computing machine. Armed with the QCC, we derive a powerful result that we call the *Encoding No-Go Theorem*. This theorem gives a precise mathematical statement of the conditions under which fault-tolerant quantum computation becomes impossible in the presence of dissipation and/or decoherence. In connection with this theorem, we explicitly calculate a universal critical damping value for...

Gilbert, G; Thayer, F J; Gilbert, Gerald; Hamrick, Michael

2005-01-01

317

Effects of strain and quantum confinement in optically pumped nuclear magnetic resonance in GaAs: Interpretation guided by spin-dependent band structure calculations  

NASA Astrophysics Data System (ADS)

A combined experimental-theoretical study of optically pumped nuclear magnetic resonance (OPNMR) has been performed in a GaAs /A l0.1G a0.9As quantum well film epoxy bonded to a Si substrate with thermally induced biaxial strain. The photon energy dependence of the Ga 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 the electronic structure and differential absorption to spin-up and spin-down states of the electron conduction band using a modified k .p model based on the Pidgeon-Brown model. Comparison of theory with experiment facilitated the assignment of features in the OPNMR energy dependence to specific interband Landau level transitions. The results provide insight into how effects of strain and quantum confinement are manifested in optical nuclear polarization in semiconductors.

Wood, R. M.; Saha, D.; McCarthy, L. A.; Tokarski, J. T.; Sanders, G. D.; Kuhns, P. L.; McGill, S. A.; Reyes, A. P.; Reno, J. L.; Stanton, C. J.; Bowers, C. R.

2014-10-01

318

``Additive'' cooperativity of hydrogen bonds in complexes of catechol with proton acceptors in the gas phase: FTIR spectroscopy and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

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

319

Quantum corrections to the ground state energy of trapped Bose-Einstein condensates: A diffusion Monte Carlo calculation  

Microsoft Academic Search

The diffusion Monte Carlo method is applied to describe a Bose-Einstein condensate at zero temperature in a spherical trap, fully quantum mechanically and nonperturbatively. Our calculations confirm that the exact ground state energy for a sum of two-body interactions depends to a good approximation on only one atomic physics parameter, the s-wave scattering length a, and no other details of

Doerte Blume; Chris H. Greene

2001-01-01

320

Efficiency considerations in the construction of interpolated potential energy surfaces for the calculation of quantum observables by diffusion Monte Carlo  

Microsoft Academic Search

A modified Shepard interpolation scheme is used to construct global potential energy surfaces (PES) in order to calculate quantum observables—vibrationally averaged internal coordinates, fully anharmonic zero-point energies and nuclear radial distribution functions—for a prototypical loosely bound molecular system, the water dimer. The efficiency of PES construction is examined with respect to (a) the method used to sample configurational space, (b)

Deborah L. Crittenden; Keiran C. Thompson; Mary Chebib; Meredith J. T. Jordan

2004-01-01

321

Self-healing diffusion quantum Monte Carlo algorithms: direct reduction of the fermion sign error in electronic structure calculations  

Microsoft Academic Search

We develop a formalism and present an algorithm for optimization of the trial wave-function used in fixed-node diffusion quantum Monte Carlo (DMC) methods. The formalism is based on the DMC mixed estimator of the ground state probability density. We take advantage of a basic property of the walker configuration distribution function generated in a DMC calculation, to i) project-out a

Fernando A Reboredo; Randolph Q. Hood; Paul R Kent

2009-01-01

322

Efficiency considerations in the construction of interpolated potential energy surfaces for the calculation of quantum observables by diffusion Monte Carlo  

Microsoft Academic Search

A modified Shepard interpolation scheme is used to construct global potential energy surfaces (PES) in order to calculate quantum observables-vibrationally averaged internal coordinates, fully anharmonic zero-point energies and nuclear radial distribution functions-for a prototypical loosely bound molecular system, the water dimer. The efficiency of PES construction is examined with respect to (a) the method used to sample configurational space, (b)

Deborah L. Crittenden; Keiran C. Thompson; Mary Chebib; Meredith J. T. Jordan

2004-01-01

323

Effective discrimination of antimalarial potency of artemisinin compounds based on quantum chemical calculations of their reaction mechanism  

Microsoft Academic Search

The reaction mechanism of 12 antimalarial artemisinin compounds with two competitive pathways was studied by means of quantum chemical calculations using the IMOMO(B3LYP\\/6-31(d,p):HF\\/3-21G) method. The oxygen-centered radicals, carbon-centered radicals, and transition states (TS) in both pathways were geometrically optimized. The obtained kinetic and thermodynamic energy profiles show that homolytic C–C cleavage reaction (pathway 2) is energetically more preferable than an

Somsak Tonmunphean; Vudhichai Parasuk; Sirirat Kokpol

2006-01-01

324

Comparison of Oxygen Gauche Effects in Poly(Oxyethylene) and Poly(ethylene terephtylene) Based on Quantum Chemistry Calculations  

NASA Technical Reports Server (NTRS)

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.

Jaffe, Richard; Han, Jie; Yoon, Do; Langhoff, Stephen R. (Technical Monitor)

1997-01-01

325

Analytical and numerical calculations of spectral and optical characteristics of spheroidal quantum dots  

SciTech Connect

In the effective mass approximation for electronic (hole) states of a spheroidal quantum dot with and without external fields the perturbation theory schemes are constructed in the framework of the Kantorovich and adiabatic methods. The eigenvalues and eigenfunctions of the problem, obtained in both analytical and numerical forms, were applied for the analysis of spectral and optical characteristics of spheroidal quantum dots in homogeneous electric fields.

Gusev, A. A., E-mail: gooseff@jinr.ru; Hai, L. L.; Vinitsky, S. I.; Chuluunbaatar, O. [Joint Institute for Nuclear Research (Russian Federation)] [Joint Institute for Nuclear Research (Russian Federation); Derbov, V. L.; Klombotskaya, A. S. [Saratov State University (Russian Federation)] [Saratov State University (Russian Federation); Dvoyan, K. G.; Sarkisyan, H. A. [Russian-Armenian (Slavonic) University (Armenia)] [Russian-Armenian (Slavonic) University (Armenia)

2013-08-15

326

Theoretical investigation of edge reconstruction in the ? =5/2 and 7/3 fractional quantum Hall states  

NASA Astrophysics Data System (ADS)

The edge physics of the ? =5/2 fractional quantum Hall state is of relevance to several recent experiments that use it as a probe to gain insight into the nature of the bulk state. We perform calculations in a semirealistic setup with positive background charge at a distance d, by exact diagonalization both in the full Hilbert space (neglecting Landau level mixing) and in the restricted Pfaffian basis of edge excitations. Our principal finding is that the 5/2 edge is unstable to a reconstruction except for very small d. In addition, the interactions between the electrons in the second Landau level and the lowest Landau level enhance the tendency toward edge reconstruction. We identify the bosonic and fermionic modes of edge excitations and obtain their dispersions by back-calculating from the energy spectra as well as directly from appropriate trial wave functions. We find that the edge reconstruction is driven by an instability in the fermionic sector for setback distances close to the critical ones. We also study the edge of the ? =7/3 state and find that edge reconstruction occurs here more readily than for the ? =1/3 state. Our study indicates that the ? =5/2 and 7/3 edge states are reconstructed for all experimental systems investigated so far and, thus, must be taken into account when analyzing experimental results. We also consider an effective field theory to gain insight into how edge reconstruction might influence various observable quantities.

Zhang, Yuhe; Wu, Ying-Hai; Hutasoit, Jimmy A.; Jain, Jainendra K.

2014-10-01

327

Mixed quantum classical calculation of proton transfer reaction rates: From deep tunneling to over the barrier regimes  

NASA Astrophysics Data System (ADS)

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

2014-05-01

328

Quantum Mechanical Calculations of Charge Effects on gating the KcsA channel  

SciTech Connect

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 of withdrawing from the gate. It is also not surprising that water essentially freezes, or forms a kind of glue, in a nanometer space; this agrees with experimental results on a rather different, but similarly sized (nm dimensions) system [K.B. Jinesh, J.W.M. Frenken, Capillary condensation in atomic scale friction: how water acts like a glue, Phys. Rev. Lett. 96 (2006) 166103/1–4].

Kariev, Alisher M.; Znamenskiy, Vasiliy S.; Green, Michael E.

2007-02-06

329

Self-interaction-free density-functional theoretical study of the electronic structure of spherical and vertical quantum dots  

E-print Network

's rule. We also consider the effect of including the vertical dimension in the quantum dot study. We and vertical quantum dots T. F. Jiang,* Xiao-Min Tong, and Shih-I Chu Department of Chemistry, University and vertical quantum dots by means of the density functional theory DFT with optimized effective potential OEP

Chu, Shih-I

330

Theoretical and numerical calculation of the acoustic radiation force acting on a circular rigid cylinder near a flat wall in a standing wave excitation in an ideal fluid.  

PubMed

The acoustic radiation force acting on a cylinder near a flat wall in a standing wave is calculated by analytical methods and numerical simulations. An exact theoretical solution is presented as well as an approximate solution. The approximate solution is in algebraic form and quite easy to compute. The numerical simulation is based on FVM (Finite Volume Method) on unstructured triangular meshes. The exact theoretical, approximate and numerical solutions are compared with each other and good agreements are obtained. Furthermore, the effects of the flat wall are investigated in detail by the three methods. PMID:21975351

Wang, Jingtao; Dual, Jurg

2012-02-01

331

Toward the exact solution of the electronic Schrödinger equation for noncovalent molecular interactions: worldwide distributed quantum monte carlo calculations.  

PubMed

Quantum Monte Carlo (QMC) calculations on the stacked (st) and Watson/Crick (wc) bound adenine/thymine (A/T) and cytosine/guanine (C/G) DNA base pair complexes were made possible with the first large scale distributed computing project in ab initio quantum chemistry, Quantum Monte Carlo at Home (QMC@HOME). The results for the interaction energies (wc-A/T = 15.7 kcal/mol, wc-C/G = 30.2 kcal/mol, st-A/T = 13.1 kcal/mol, st-C/G = 19.6 kcal/mol) are in very good agreement with the best known coupled-cluster based estimates. The accuracy of these values is further supported by calculations on the S22 benchmark set of noncovalently bound systems, for which we obtain a small mean absolute deviation of 0.68 kcal/mol. Our results support previous claims that the stacking energies are of comparable magnitude to the interactions of the commonly discussed hydrogen-bonded motif. Furthermore, we show that QMC can serve as an advantageous alternative to conventional wave function methods for large noncovalently bound systems. We also investigated in detail all technical parameters of the QMC simulations and recommend a careful optimization procedure of the Jastrow correlation factors in order to obtain numerically stable and reliable results. PMID:18201073

Korth, Martin; Lüchow, Arne; Grimme, Stefan

2008-03-13

332

Protein/Ligand Binding Free Energies Calculated with Quantum Mechanics/Molecular Frauke Gra1ter,, Sonja M. Schwarzl,, Annick Dejaegere,| Stefan Fischer,*, and  

E-print Network

Protein/Ligand Binding Free Energies Calculated with Quantum Mechanics/Molecular Mechanics Frauke of the complexes are predicted (the "docking" problem) as well as in how the free energy is calculated from)solvation during the binding process.3 Typically, binding free energies calculated with these methods have average

Gräter, Frauke

333

{open_quotes}Spectator{close_quotes} modes in resonance-driven reactions: Three-dimensional quantum calculations of HOCO resonances  

SciTech Connect

We have performed three-degree-of-freedom quantum calculations of HOCO resonances by using a complex potential method. The coordinates we consider are the OH internuclear distance, the CO internuclear distance, and the distance between the centers of mass of the OH and CO fragments. The reduced dimensionality potential has been constructed by adding the nonreactive {open_quotes}spectator{close_quotes} CO coordinate to the previous two-degree-of-freedom potential of Schatz and Dyck [G. C. Schatz and J. Dyck, Chem. Phys. Lett. {bold 188}, 11 (1992)] using a Shepard-type interpolation procedure. The positions and lifetimes of more than two hundred resonances are calculated and approximate quantum numbers are assigned. The results are compared with previous two-degree-of-freedom calculations where the CO-stretch mode has not been considered. The appearance of a new group of narrow resonances with a significant CO stretch contribution is reported. The results are tested against the vibrational shifting approximation in which the spectator CO mode is treated adiabatically. The latter is shown to be insufficient for quantitative predictions of resonance positions and widths, however averaged positions and widths are reasonably well described. The rotational shifting approximation is tested by performing the adiabatic rotation calculations of resonances for J=1, K=0 and J=1, K=1 cases, where J is the total angular momentum and K is the body-fixed projection quantum number of a symmetric top. Rotational shifting is shown to work better for K=0 case than for K=1 case. {copyright} {ital 1998 American Institute of Physics.}

Dzegilenko, F.N.; Bowman, J.M. [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)] [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)

1998-01-01

334

How Iron-Containing Proteins Control Dioxygen Chemistry: A Detailed Atomic Level Description Via Accurate Quantum Chemical and Mixed Quantum Mechanics/Molecular Mechanics Calculations.  

SciTech Connect

Over the past several years, rapid advances in computational hardware, quantum chemical methods, and mixed quantum mechanics/molecular mechanics (QM/MM) techniques have made it possible to model accurately the interaction of ligands with metal-containing proteins at an atomic level of detail. In this paper, we describe the application of our computational methodology, based on density functional (DFT) quantum chemical methods, to two diiron-containing proteins that interact with dioxygen: methane monooxygenase (MMO) and hemerythrin (Hr). Although the active sites are structurally related, the biological function differs substantially. MMO is an enzyme found in methanotrophic bacteria and hydroxylates aliphatic C-H bonds, whereas Hr is a carrier protein for dioxygen used by a number of marine invertebrates. Quantitative descriptions of the structures and energetics of key intermediates and transition states involved in the reaction with dioxygen are provided, allowing their mechanisms to be compared and contrasted in detail. An in-depth understanding of how the chemical identity of the first ligand coordination shell, structural features, electrostatic and van der Waals interactions of more distant shells control ligand binding and reactive chemistry is provided, affording a systematic analysis of how iron-containing proteins process dioxygen. Extensive contact with experiment is made in both systems, and a remarkable degree of accuracy and robustness of the calculations is obtained from both a qualitative and quantitative perspective.

Friesner, Richard A.(Columbia University) [Columbia University; Baik, Mu-Hyun (Columbia University) [Columbia University; Gherman, Benjamin F.(Columbia University) [Columbia University; Guallar, Victor (Washington University) [Washington University; Wirstam, Maria E.(1836) [1836; Murphy, Robert B.(Schrodinger Inc) [Schrodinger Inc; Lippard, Stephen J.(Massachusetts Institute of Technology) [Massachusetts Institute of Technology

2003-03-01

335

Diode laser spectroscopic measurements and theoretical calculations of line parameters of nitrogen broadened water vapor overtone transitions in the  

E-print Network

-in amplifier helps to increase the detection efficiency and the signal-to-noise ratio. The collisional. The experimental data are compared with the corresponding theoretical values and the possible causes of deviation, pollution control, differential absorption LIDAR (DIAL) technique. Close monitoring of the global atmosphere

Gamache, Robert R.

336

Possibility of mutation prediction of influenza hemagglutinin by combination of hemadsorption experiment and quantum chemical calculation for antibody binding.  

PubMed

We have performed a quantum-chemical MP2/6-31G* calculation for the hemagglutinin (HA) antigen-antibody system of the H3N2 influenza virus with the fragment molecular orbital method, which provides one of the world's largest ab initio electron-correlated calculations for biomolecular systems. On the basis of the calculated interfragment interaction energies (IFIEs) representing the molecular interactions between the amino acid residues in the antigen-antibody complex, we have identified those residues in the antigenic region E of HA protein that are significantly recognized by the Fab fragment of antibody with strongly attractive interactions. Combining these IFIE results with those of hemadsorption experiments by which the mutation-prohibited sites are specified has enabled us to explain most of the historical mutation data (five of six residues), which would thus provide a promising method for predicting the HA residues that have a high probability of forthcoming mutation. PMID:19323468

Takematsu, Kazutomo; Fukuzawa, Kaori; Omagari, Katsumi; Nakajima, Setsuko; Nakajima, Katsuhisa; Mochizuki, Yuji; Nakano, Tatsuya; Watanabe, Hirofumi; Tanaka, Shigenori

2009-04-16

337

QUANTUM CALCULATION OF INELASTIC CO COLLISIONS WITH H. I. ROTATIONAL QUENCHING OF LOW-LYING ROTATIONAL LEVELS  

SciTech Connect

New quantum scattering calculations for rotational deexcitation transitions of CO induced by H collisions using two CO-H potential energy surfaces (PESs) from Shepler et al. are reported. State-to-state rate coefficients are computed for temperatures ranging from 1 to 3000 K for CO(v = 0, j) deexcitation from j = 1 to 5 to all lower j' levels, with j being the rotational quantum number. Different resonance structures in the cross sections are attributed to the differences in the anisotropy and the long-range van der Waals well depths of the two PESs. These differences affect rate coefficients at low temperatures and give an indication of the uncertainty of the results. Significant discrepancies are found between the current rate coefficients and previous results computed using earlier potentials, while the current results satisfy expected propensity rules. Astrophysical applications to modeling far infrared and submillimeter observations are briefly discussed.

Yang Benhui; Stancil, P. C. [Department of Physics and Astronomy and the Center for Simulational Physics, The University of Georgia, Athens, GA 30602 (United States); Balakrishnan, N. [Department of Chemistry, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States); Forrey, R. C. [Department of Physics, Penn State University, Berks Campus, Reading, PA 19610 (United States); Bowman, J. M. [Department of Chemistry, Emory University, Atlanta, GA 30322 (United States)

2013-07-01

338

Spectral dependencies of the quantum yield of photochemical processes on the surface of nano-\\/microparticulates of wide-band-gap metal oxides. 1: Theoretical approach  

Microsoft Academic Search

In this study, the authors examine theoretically some of the factors that influence the spectral dependencies of the quantum yield, Φ, of photochemical processes on the surface of nano-\\/microparticulates of wide-band-gap metal-oxide photocatalysts. The approach taken is based on solving the steady-state ((dn(t)\\/dt) = 0) continuity equation (eq 7) for a one-dimensional plate with dimensions x = 0 - d

Alexei V. Emeline; N. Serpone; V. K. Ryabchuk

1999-01-01

339

Homogeneous Decomposition Mechanisms of Diethylzinc by Raman Spectroscopy and Quantum Chemical Calculations  

E-print Network

Homogeneous Decomposition Mechanisms of Diethylzinc by Raman Spectroscopy and Quantum Chemical. The homogeneous thermal decomposition of DEZn in N2 carrier was followed in an impinging-jet, up-flow reactor dissociation between zinc and carbon atoms is the dominant homogeneous thermal decomposition pathway

Anderson, Timothy J.

340

Vibrational spectroscopic and quantum chemical calculations of (E)-N-Carbamimidoyl-4-((naphthalen-1-yl-methylene)amino)benzene sulfonamide.  

PubMed

FT-IR and FT-Raman spectra of (E)-N-Carbamimidoyl-4-((naphthalen-1-yl-methylene)amino)benzene sulfonamide were recorded and analyzed. The vibrational wavenumbers were computing at various levels of theory. The data obtained from theoretical calculations are used to assign vibrational bands obtained experimentally. The results indicate that B3LYP method is able to provide satisfactory results for predicting vibrational frequencies and structural parameters. The calculated first hyperpolarizability is comparable with reported values of similar derivatives and is an attractive object for future studies of non-linear optics. The geometrical parameters of the title compound are in agreement with that of similar derivatives. PMID:22153592

Chandran, Asha; Varghese, Hema Tresa; Mary, Y Sheena; Panicker, C Yohannan; Manojkumar, T K; Van Alsenoy, Christian; Rajendran, G

2012-02-15

341

QUANTUM MECHANICAL CALCULATIONS OF CHARGE EFFECTS ON GATING THE KcsA CHANNEL  

PubMed Central

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[1–3], 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 of withdrawing from the gate. It is also not surprising that water essentially freezes, or forms a kind of glue, in a nanometer space; this agrees with experimental results on a rather different, but similarly sized (nm dimensions) system[4] It also agrees qualitatively with simulations on channels[5, 6] and on featureless channel-like systems[7], in that it forms a boundary on water that is not obvious from the liquid state. The idea that a atructure is stable, even if individual molecules exchange, is well known, for example from the hydration shell of ions. We show that when charges are added in the form of protons to the domains (one proton per domain), the optimized structure is open. No stable water hydrogen bonds hold it together; an opening of 11.0 Å appears, measured diagonally between non-neighboring domains as glutamine 119 carbonyl O – O distance. This is comparable to the opening in the MthK potassium channel structure that is generally agreed to be open. The appearance of the opening is in rather good agreement with that found by Perozo and coworkers. In contrast, in the uncharged structure this diagonal distance is 6.5Å, and the water “basket” constricts the uncharged opening still further, with the ice-like structure that couples the K+ ion to the gating region freezing the entrance to the channel. Comparison with our earlier model for voltage gated channels suggests that a similar mechanism may apply in those channels. PMID:17336921

Kariev, Alisher M.; Znamenskiy, Vasiliy S.; Green, Michael E.

2007-01-01

342

Experimental verification of theoretically calculated parameters of Te15(Se100-xBix)85(x = 0,2,4at.%) amorphous semiconductors  

NASA Astrophysics Data System (ADS)

The Se-Te-Bi amorphous semiconductors have been prepared by melt quenching technique. In the present study, we have theoretically calculated the optical energy band gap, glass transition temperature and density of Se-Te-Bi amorphous semiconductors. Experimentally the optical energy band gap has been found from transmission spectra of thin films using Tauc's method, glass transition temperature from Differential Thermal Analysis data and density using Archimedes method.

Kumar, Kameshwar; Thakur, Nagesh

2013-06-01

343

The calculation of polar surface area from first principles: an application of quantum chemical topology to drug design.  

PubMed

The calculation of polar surface areas (PSA) from the electron density using quantum chemical topology (QCT) and a newly developed algorithm to determine isodensity surface areas is described. PSA values were calculated from the atomic partitioning of B3LYP/6-311G* wavefunctions and the results described herein represent the first application of this new algorithm. PSA values were calculated for forty drugs and compared to the topological polar surface area (TPSA) and those calculated by the QikProp program. Oral bioavailabilities predicted from the QCT PSA values for a subset of twenty drugs (the Palm set) were similar to those predicted by the dynamic polar surface area (DPSA) and in general, are in agreement with the observed values. Overall, PSA values obtained from QCT were generally similar to the DPSA, TPSA, and QikProp values, though differences in fragment contributions were found, with nitrogen-bearing functional groups showing the largest variation between methods. Differences between methods showed how the calculation of the PSA is dependent on the method used and, therefore, judicious application of the upper limits used in the prediction of oral bioavailability is warranted. These results also indicate that, because of the differences in the way PSA values are calculated, values from the different methods should not be used interchangeably. PMID:18161739

Bytheway, Ian; Darley, Michael G; Popelier, Paul L A

2008-03-01

344

Use of theoretical efficiencies of protein and fat synthesis to calculate energy requirements for growth in pigs.  

PubMed

From the observation that fasting heat production includes the cost of body protein resynthesis and the evidence that protein resynthesis is included in the regression estimate of protein retention efficiency it is conjectured that the estimate of maintenance from fasting heat production must be conceptually equal to the regression intercept estimate of maintenance plus the cost of body protein resynthesis. Experimental evidence for comparable situations shows an approximate observational equality in agreement with the conjectured conceptual equality. This approximate equality implies that the theoretical (stiochiometric) efficiency of protein synthesis should be used in conjunction with the estimate of maintenance from fasting heat production for the prediction of growth energy requirements. The approximate maintenance equalities suggest furthermore approximate equality of theoretical fat synthesis efficiency and regression fat retention efficiency. This conjecture is also supported by experimental evidence. Some practical nutrition and pig breeding implications of the foregoing conclusions are indicated. PMID:18684340

Roux, Carl Z

2009-03-01

345

Calculating and visualizing the density of states for simple quantum mechanical systems  

E-print Network

We present a graphical approach to understanding the degeneracy, density of states, and cumulative state number for some simple quantum systems. By taking advantage of basic computing operations we define a straightforward procedure for determining the relationship between discrete quantum energy levels and the corresponding density of states and cumulative level number. The density of states for a particle in a rigid box of various shapes and dimensions is examined and graphed. It is seen that the dimension of the box, rather than its shape, is the most important feature. In addition, we look at the density of states for a multi-particle system of identical bosons built on the single-particle spectra of those boxes. A simple model is used to explain how the $N$-particle density of states arises from the single particle system it is based on.

Declan Mulhall; Matthew Moelter

2014-06-27

346

Electron energy level calculations for cylindrical narrow gap semiconductor quantum dot  

Microsoft Academic Search

Three computational techniques are presented for approximation of the ground state energy and wave function of an electron confined by a disk-shaped InAs quantum dot (QD) embedded in GaAs matrix. The problem is treated with the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, and the Ben-Daniel Duke boundary conditions. To solve the three

Yiming Li; Jinn-Liang Liu; O. Voskoboynikov; C. P. Lee; S. M. Sze

2001-01-01

347

Exact quantum scattering calculations of transport properties for the H{sub 2}O–H system  

SciTech Connect

Transport properties for collisions of water with hydrogen atoms are computed by means of exact quantum scattering calculations. For this purpose, a potential energy surface (PES) was computed for the interaction of rigid H{sub 2}O, frozen at its equilibrium geometry, with a hydrogen atom, using a coupled-cluster method that includes all singles and doubles excitations, as well as perturbative contributions of connected triple excitations. To investigate the importance of the anisotropy of the PES on transport properties, calculations were performed with the full potential and with the spherical average of the PES. We also explored the determination of the spherical average of the PES from radial cuts in six directions parallel and perpendicular to the C{sub 2} axis of the molecule. Finally, the computed transport properties were compared with those computed with a Lennard-Jones 12-6 potential.

Dagdigian, Paul J., E-mail: pjdagdigian@jhu.edu [Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685 (United States); Alexander, Millard H., E-mail: mha@umd.edu [Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021 (United States)

2013-11-21

348

Direct calculation of the Entanglement Spectrum in Quantum Monte Carlo with application to \\textit{ab initio} Hamiltonians  

E-print Network

Several algorithms have been proposed to calculate the spatial entanglement spectrum from high order Renyi entropies. In this work we present an alternative approach for computing the entanglement spectrum with quantum Monte Carlo for both continuum and lattice Hamiltonians. This method provides direct access to the matrix elements of the spatially reduced density matrix and we determine an estimator that can be used in variational Monte Carlo as well as other Monte Carlo methods. The algorithm is based on using a generalization of the Swap operator, which can be extended to calculate a general class of density matrices that can include combinations of spin, space, particle and even momentum coordinates. We demonstrate the method by applying it to the Hydrogen and Nitrogen molecules and describe for the first time how the spatial entanglement spectrum encodes a covalent bond that includes all the many body correlations.

Norm M. Tubman; D. ChangMo Yang

2014-02-03

349

Quantum  

Microsoft Academic Search

All unitary representations of the quantum ``az+b'' group are found. It turns out that this quantum group is self dual i.e. all unitary representations are 'numbered' by elements of the same group. Moreover, the formula for all unitary representations involving the quantum exponential function is proven.

Malgorzata Rowicka

2001-01-01

350

Quantum \\  

Microsoft Academic Search

All unitary representations of the quantum ``az+b'' group are found. It turns\\u000aout that this quantum group is self dual i.e. all unitary representations are\\u000a'numbered' by elements of the same group. Moreover, the formula for all unitary\\u000arepresentations involving the quantum exponential function is proven.

Malgorzata Rowicka

2001-01-01

351

Computational investigation of the Jahn-Teller effect in the ground and excited electronic states of the tropyl radical. Part I. Theoretical calculation of spectroscopically observable parameters.  

PubMed

Theoretical calculations are performed for the X2E"2 and A 2E"3 states of the cycloheptatrienyl (tropyl) radical C7H7. An important goal of these calculations is to predict and to guide the analysis of the experimentally observed A 2E"3-X 2E"2 electronic spectrum. Vibrational frequencies of the tropyl radical at the conical intersection and stationary points of its X and A state Jahn-Teller distorted potential energy surfaces are given. Spectroscopically obtainable parameters describing the Jahn-Teller effect are calculated for the X and A electronic states. Additionally, the stabilization energies for the X and A states are computed at the CASSCF(7,7) and EOMEA-CCSD levels of theory using various basis sets. PMID:18315049

Stakhursky, Vadim L; Sioutis, Ilias; Tarczay, György; Miller, Terry A

2008-02-28

352

Studies on the structure of N-phenyl-substituted hexaaza[1(6)]paracyclophane: synthesis, electrochemical properties, and theoretical calculation.  

PubMed

The N-phenyl-substituted hexaaza[1(6)]paracyclophane (3, hexamer) has been synthesized successfully in two steps and the noncoplanar conformation was calculated by gaussian program. The electrochemical properties exhibited lots of interesting results and each overlapping oxidative wave contained two-electron transfer. PMID:22950953

Yang, Te-Fang; Chiu, Kuo Yuan; Cheng, Hsu-Chun; Lee, Yen Wei; Kuo, Ming Yu; Su, Yuhlong Oliver

2012-10-01

353

Four-mode quantum calculations of resonance states in complex-forming bimolecular reactions: Cl-+CH3Br  

NASA Astrophysics Data System (ADS)

The vibrational resonance states of the complexes formed in the nucleophilic bimolecular substitution (SN2) reaction Cl-+CH3Br?ClCH3+Br- were calculated by means of the filter diagonalization method employing a coupled-cluster potential-energy surface and a Hamiltonian that incorporates an optical potential and is formulated in Radau coordinates for the carbon-halogen stretching modes. The four-dimensional model also includes the totally symmetric vibrations of the methyl group (C-H stretch and umbrella bend). The vast majority of bound states and many resonance states up to the first overtone of the symmetric stretching vibration in the exit channel complex have been calculated, analyzed, and assigned four quantum numbers. The resonances are classified into entrance channel, exit channel, and delocalized states. The resonance widths fluctuate over six orders of magnitude. In addition to a majority of Feshbach-type resonances there are also exceedingly long-lived shape resonances, which are associated with the entrance channel and can only decay by tunneling. The state-selective decay of the resonances was studied in detail. The linewidths of the resonances, and thus the coupling to the energetic continuum, increase with excitation in any mode. Due to the strong mixing of the many progressions in the intermolecular stretching modes of the intermediate complexes, this increase as a function of the corresponding quantum numbers is not monotonic, but exhibits pronounced fluctuations.

Schmatz, Stefan

2005-06-01

354

Diagrammatic calculation of energy spectrum of quantum impurity in degenerate Bose-Einstein condensate  

E-print Network

In this paper we considered a quantum particle moving through delute Bose-Einstein condensate at zero temperature. In our formulation the impurity particle interacts with the gas of uncoupled Bogoliubov's excitations. We constructed the perturbation theory for the Green's function of the impurity particle with respect to the impurity-condensate interaction employing the coherent-state path integral approach. The perturbative expansion for the Green's function is resumed into the expansion for its poles with the help of the diagrammatic technique developed in this work. The dispersion relation for the impurity clothed by condensate excitations is obtained and effective mass is evaluated beyond the Golden rule approximation.

Alexey Novikov; Mikhail Ovchinnikov

2008-05-27

355

Step-Scan FTIR spectroscopy and quantum chemical calculations of xanthone in the triplet state  

NASA Astrophysics Data System (ADS)

Step-Scan-FTIR spectroscopy has been used to measure the infrared spectrum of xanthone in the triplet state using chloroform as solvent. Xanthone is an important triplet sensitizer and therefore suitable as model system. Xanthone was excited at 266 nm and its IR triplet spectrum measured in the range 1000-1750 cm-1. The spectrum was analyzed by comparison with DFT/B3LYP/TZVP/COSMO calculations. Further on the results were compared to gas phase IR measurements of triplet xanthone and calculations of isolated xanthone. Mainly based on the calculations we tried to identify the geometry changes from the electronic ground state to the first triplet state.

Buschhaus, L.; Kleinermanns, K.

2014-10-01

356

The assignment of the vibrations of substituted mercaptotetrazoles based on quantum chemical calculations  

NASA Astrophysics Data System (ADS)

We studied four substituted mercaptotetrazoles using IR- and Raman-spectroscopy on the bulk substance and surface enhanced Raman spectroscopy (SERS) on a silver colloid. Semiempirical and ab initio calculations with various basis sets were performed to establish an assignment of the experimentally observed bands to the calculated ones. We found a satisfactory agreement between the calculated and observed frequencies of CH/CC-vibrations in the phenyl ring and encountered problems with the tetrazole ring vibrations. The PM3 hamiltonian failed for the SH group.

Sägmüller, Bernd; Freunscht, Peter; Schneider, Siegfried

1999-05-01

357

Vibrational spectra, structure, and theoretical calculations of 2-chloro- and 3-chloropyridine and 2-bromo- and 3-bromopyridine  

NASA Astrophysics Data System (ADS)

The infrared and Raman spectra of 2-chloropyridine, 3-chloropyridine, 2-bromopyridine, and 3-bromopyridine have been recorded and assigned. Density functional theory calculations (B3LYP with 6-311++G(d,p) basis set) produce excellent agreement with the experimental values. Ab initio calculations (MP2 with the cc-pVTZ basis set) were utilized to compute the molecular structures, which were compared to those of pyridine and the corresponding fluoropyridines. All of the 2-halopyridines show a shortening of the N-C(2) bond resulting from the halogen substitution on the C(2) carbon atom. All of the other ring bond distances for the 2-halopyridines and 3-halopyridines are little different from pyridine itself.

Boopalachandran, Praveenkumar; Sheu, Hong-Li; Laane, Jaan

2012-09-01

358

Theoretical calculations on the influence of the inorganic nitrogen source on parameters for aerobic growth of microorganisms  

Microsoft Academic Search

The amount of ATP required for the formation of microbial cells growing in a minimal medium with various nitrogen sources\\u000a was calculated. In a glucose-mineral salts medium 28.8 g cells can be formed per mole ATP with ammonia and 23.1 for growth\\u000a with nitrate. For growth with molecular nitrogen 11.1; 8.7; 7.1 and 6.0 g cells can be formed per

A. H. Stouthamer

1977-01-01

359

Relative Responses of Noble Gases Using a Pulsed Discharge Helium Photoionization Detector: Theoretical Calculation and Experimental Determination  

Microsoft Academic Search

The relative response factors(RRFs) for noble gas(Ng) were determined on a pulsed discharge helium photoionization detector. Using ab initio method, the atomic orbitals of noble gas were calculated and used to determine the number of ionizable electrons on the basis of the continuous emission of He2. The molar responses of noble gases is well correlated with the number of ionizable

Hai-tao ZHANG; Di WU; Li-xing ZHANG

2008-01-01

360

Many physical properties of a molecule can be calculated as expectation values of a corresponding quantum mechanical operator. The evaluation of other properties can be  

E-print Network

Chapter 20 Many physical properties of a molecule can be calculated as expectation values of a corresponding quantum mechanical operator. The evaluation of other properties can be formulated in terms perturbation. I. Calculations of Properties Other Than the Energy There are, of course, properties other than

Simons, Jack

361

Calculational and experimental investigations of void effect -- A simple theoretical model for space-dependent leakage treatment of heterogeneous assemblies  

SciTech Connect

This method, which takes into account the influence of assembly heterogeneity on neutron leakage, is based on the heterogeneous B[sub 1] formalism, which assumes the existence of a fundamental mode in an infinite and regular lattice of heterogeneous assemblies. A simplified formalism, TIBERE, is presented that allows one to define directional space-dependent leakage coefficients. This method, introduced for two-dimensional x-y geometry in the APOLLO-2 multigroup transport code, uses classical and directional first-flight collision probabilities. One can now define leakage cross sections as additional absorption cross sections that have space and energy dependence, as well as all other cross sections. Hence, one obtains perfectly consistent reaction and leakage rates used in an equivalence procedure, determining cell-homogenized parameters for a whole core calculation. The study of this refined heterogeneous leakage treatment was undertaken because of the insufficiency of the homogeneous leakage model, especially in cases when an assembly contain voided zones or almost voided zones, i.e., zones with a long mean free path, so that the streaming effect may become important. The fission rate comparison between the EPICURE reactor experimental results and the results of the corresponding whole reactor calculations were accomplished, with leakages calculated by the homogeneous and the TIBERE procedures of the APOLLO-2 code.

Benoist, P.; Petrovic, I. (Commissariat a' l'Energie Atomique, Gif-sur-Yvette (France)); Mondot, J. (Commissariat a l'Energie Atomique, Saint Paul lez Durance (France))

1994-12-01

362

A new method of calculation in the Fractional Quantum Hall Effect regime  

NASA Astrophysics Data System (ADS)

The electron-electron and electron-background interaction energies are calculated analytically for systems with up to N = 6 electrons. The method consists of describing the position vectors of electrons using complex coordinates and all the interaction energies with complex notation, whereby simplifications become possible. As is known, in this type of calculation, complicated expressions involving integrals over many variables are encountered and the trick of using complex coordinates greatly facilitates the exact calculation of various quantities. Contrary to previous analytical calculations, using complex coordinates avoids complicated trigonometric functions from appearing in the integrand, simplifying the exact evaluation of the integrals. The method we have used can be straightforwardly extended to larger systems with N > 6 electrons.

Bentalha, Zine el abidine; Moumen, Larabi; Ouahrani, Tarik

2014-07-01

363

Quantum self-consistent calculation of the differential capacitance of a semiconductor film  

SciTech Connect

A fast scheme for calculating the surface differential capacitance of a semiconductor film with an ohmic contact on the rear side is proposed within the self-consistent solution of the Schroedinger and Poisson equations. The method is considered using germanium as an example. Comparison with the results of the phenomenological calculation revealed the specifics of size-quantization effects on the capacitance-voltage characteristic of the film.

Tsurikov, D. E., E-mail: DavydTsurikov@mail.ru; Yafyasov, A. M., E-mail: yafyasov@bk.ru [Saint Petersburg State University, Faculty of Physics (Russian Federation)

2013-09-15

364

Quantum Monte Carlo calculations of spectroscopic overlaps in $A \\leq 7$ nuclei  

E-print Network

We present Green's function Monte Carlo calculations of spectroscopic overlaps for $A \\leq 7$ nuclei. The realistic Argonne v18 two-nucleon and Illinois-7 three-nucleon interactions are used to generate the nuclear states. The overlap matrix elements are extrapolated from mixed estimates between variational Monte Carlo and Green's function Monte Carlo wave functions. The overlap functions are used to obtain spectroscopic factors and asymptotic normalization coefficients, and they can serve as an input for low-energy reaction calculations.

I. Brida; Steven C. Pieper; R. B. Wiringa

2011-06-15

365

Ion-molecule reactions involving HCO$^+$ and N$_2$H$^+$: Isotopologue equilibria from new theoretical calculations and consequences for interstellar isotope fractionation  

E-print Network

$Aims$: We revisit with new augmented accuracy the theoretical dynamics of basic isotope exchange reactions involved in the $^{12}$C/$^{13}$C, $^{16}$O/$^{18}$O, and $^{14}$N/$^{15}$N balance because these reactions have already been studied experimentally in great detail. $Methods$: Electronic structure methods were employed to explore potential energy surfaces, full-dimensional rovibrational calculations to compute rovibrational energy levels that are numerically exact, and chemical network models to estimate the abundance ratios under interstellar conditions. $Results$: New exothermicities, derived for HCO$^+$ reacting with CO, provide rate coefficients markedly different from previous theoretical values in particular at low temperatures, resulting in new abundance ratios relevant for carbon chemistry networks. In concrete terms, we obtain a reduction in the abundance of H$^{12}$C$^{18}$O$^+$ and an increase in the abundance of H$^{13}$C$^{16}$O$^+$ and D$^{13}$C$^{16}$O$^+$. In all studied cases, the reac...

Mladenovi?, Mirjana

2014-01-01

366

Calculation of absorption spectra involving multiple excited states: approximate methods based on the mixed quantum classical Liouville equation.  

PubMed

We investigate the calculation of absorption spectra based on the mixed quantum classical Liouville equation (MQCL) methods. It has been shown previously that, for a single excited state, the averaged classical dynamics approach to calculate the linear and nonlinear spectroscopy can be derived using the MQCL formalism. This work focuses on problems involving multiple coupled excited state surfaces, such as in molecular aggregates and in the cases of coupled electronic states. A new equation of motion to calculate the dipole-dipole correlation functions within the MQCL formalism is first presented. Two approximate methods are then proposed to solve the resulted equations of motion. The first approximation results in a mean field approach, where the nuclear dynamics is governed by averaged forces depending on the instantaneous electronic states. A modification to the mean field approach based on first order moment expansion is also proposed. Numerical examples including calculation of the absorption spectra of Frenkel exciton models of molecular aggregates, and the pyrazine molecule are presented. PMID:24588146

Bai, Shuming; Xie, Weiwei; Zhu, Lili; Shi, Qiang

2014-02-28

367

MATLAB-based program for optimization of quantum cascade laser active region parameters and calculation of output characteristics in magnetic field  

NASA Astrophysics Data System (ADS)

A strong magnetic field applied along the growth direction of a quantum cascade laser (QCL) active region gives rise to a spectrum of discrete energy states, the Landau levels. By combining quantum engineering of a QCL with a static magnetic field, we can selectively inhibit/enhance non-radiative electron relaxation process between the relevant Landau levels of a triple quantum well and realize a tunable surface emitting device. An efficient numerical algorithm implementation is presented of optimization of GaAs/AlGaAs QCL region parameters and calculation of output properties in the magnetic field. Both theoretical analysis and MATLAB implementation are given for LO-phonon and interface roughness scattering mechanisms on the operation of QCL. At elevated temperatures, electrons in the relevant laser states absorb/emit more LO-phonons which results in reduction of the optical gain. The decrease in the optical gain is moderated by the occurrence of interface roughness scattering, which remains unchanged with increasing temperature. Using the calculated scattering rates as input data, rate equations can be solved and population inversion and the optical gain obtained. Incorporation of the interface roughness scattering mechanism into the model did not create new resonant peaks of the optical gain. However, it resulted in shifting the existing peaks positions and overall reduction of the optical gain. Catalogue identifier: AERL_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AERL_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.: 37763 No. of bytes in distributed program, including test data, etc.: 2757956 Distribution format: tar.gz Programming language: MATLAB. Computer: Any capable of running MATLAB version R2010a or higher. Operating system: Any platform supporting MATLAB version R2010a or higher. RAM: Minimum required is 1 GB. Memory usage increases for less intense magnetic fields. Classification: 15. Nature of problem: The nature of the problem is to provide an efficient numerical algorithm implementation for optimization of GaAs/AlGaAs QCL active region parameters and calculation of output properties in the magnetic field. Solution method: The optimization of the QCL laser performance at selected wavelength is performed at entire free-parameters space using simulated annealing algorithm. The scattering rates are calculated in the presence and without magnetic field and used as coefficients in rate equations. The standard MATLAB procedures were used to solve iteratively this system of equations and obtain distribution of electron densities over electronic states. Restrictions: The machine must provide the necessary main memory which decreases roughly quadratically with the increase of the magnetic field intensity. Running time: Optimization time on Intel 3 GHz processor is about 2×104 s. The calculation time of laser output properties for values set automatically in GUI is 5×104 s.

Smiljani?, J.; Žeželj, M.; Milanovi?, V.; Radovanovi?, J.; Stankovi?, I.

2014-03-01

368

Quantum Darwinism  

SciTech Connect

Quantum Darwinism - proliferation, in the environment, of multiple records of selected states of the system (its information-theoretic progeny) - explains how quantum fragility of individual state can lead to classical robustness of their multitude.

Zurek, Wojciech H [Los Alamos National Laboratory

2008-01-01

369

Synthesis and theoretical calculations of carbazole substituted chalcone urea derivatives and studies their polyphenol oxidase enzyme activity.  

PubMed

Synthesis of carbazole substituted chalcone urea derivatives and their polyphenol oxidase enzyme activity effects on the diphenolase activity of banana tyrosinase were evaluated. Tyrosinase has been purified from banana on an affinity gel comprised of Sepharose 4B-L-tyrosine-p-aminobenzoic acid. The results showed that most of the compounds (3,4,5a,5d-h) inhibited and some of them (5c,5i-l) activated the tyrosinase enzyme activity. The molecular calculations were performed using Gaussian software for the synthesized compounds to explain the experimental results. PMID:22803668

Nixha, Arleta Rifati; Arslan, Mustafa; Atalay, Yusuf; Gençer, Nahit; Ergün, Adem; Arslan, Oktay

2013-08-01

370

New Benchmarks from Tokamak Experiments for Theoretical Calculations of the Dielectronic Satellite Spectra of Helium-like Ions  

SciTech Connect

Dielectronic satellite spectra of helium-like argon, recorded with a high-resolution X-ray crystal spectrometer at the National Spherical Torus Experiment, were found to be inconsistent with existing predictions resulting in unacceptable values for the power balance and suggesting the unlikely existence of non-Maxwellian electron energy distributions. These problems were resolved with calculations from a new atomic code. It is now possible to perform reliable electron temperature measurements and to eliminate the uncertainties associated with determinations of non-Maxwellian distributions.

M. Bitter; M.F. Gu; L.A. Vainshtein; P. Beiersdorfer; G. Bertschinger; O. Marchuk; R. Bell; B. LeBlanc; K.W. Hill; D. Johnson; L. Roquemore

2003-08-29

371

Theoretical calculation of reorganization energy for electron self-exchange reaction by constrained density functional theory and constrained equilibrium thermodynamics.  

PubMed

Within the framework of constrained density functional theory (CDFT), the diabatic or charge localized states of electron transfer (ET) have been constructed. Based on the diabatic states, inner reorganization energy ?in has been directly calculated. For solvent reorganization energy ?s, a novel and reasonable nonequilibrium solvation model is established by introducing a constrained equilibrium manipulation, and a new expression of ?s has been formulated. It is found that ?s is actually the cost of maintaining the residual polarization, which equilibrates with the extra electric field. On the basis of diabatic states constructed by CDFT, a numerical algorithm using the new formulations with the dielectric polarizable continuum model (D-PCM) has been implemented. As typical test cases, self-exchange ET reactions between tetracyanoethylene (TCNE) and tetrathiafulvalene (TTF) and their corresponding ionic radicals in acetonitrile are investigated. The calculated reorganization energies ? are 7293 cm(-1) for TCNE/TCNE(-) and 5939 cm(-1) for TTF/TTF(+) reactions, agreeing well with available experimental results of 7250 cm(-1) and 5810 cm(-1), respectively. PMID:23895675

Ren, Hai-Sheng; Ming, Mei-Jun; Ma, Jian-Yi; Li, Xiang-Yuan

2013-08-22

372

Calculation of vertical correlation probability in Ge/Si(001) shallow island quantum dot multilayer systems.  

PubMed

We investigate the behavior of the island vertical pairing probability in multilayer systems of Ge island quantum dots (QDs) in Si(001). By combining a simple kinetic rate model with our previously reported atomistic simulation results on the nature of the stress field from buried shallow Ge islands having {105}-oriented sidewalls, we derive an analytical expression for correlation probability as a function of the parameters characterizing the multi-QD systems. The approach is based upon continuum mechanochemical potential model, which allows one to introduce necessary elements of the kinetics of island formation in a simple way. We compare the model predictions with available experimental data and find that the model provides a satisfactory description of the coupling probability. The correlation probability behavior as a function of capping layer thickness, Ge island size, interisland distance, and Ge adatom diffusion length is investigated within the framework of the developed model. PMID:16771594

Makeev, Maxim A; Madhukar, Anupam

2006-06-01

373

Edge effects on quantum thermal transport in graphene nanoribbons: Tight-binding calculations  

NASA Astrophysics Data System (ADS)

We investigate the quantum thermal transport properties of graphene nanoribbons (GNRs) with natural edges by combining the Naval Research Laboratory tight-binding approach and the phonon nonequilibrium Green’s function method. Thermal transport of GNRs shows substantial dependence on the width due to edge reconstructions. For GNRs with n?12 , where n is the number of atoms along the direction perpendicular to the ribbon axis, the effect of natural edges is negligible and quantized thermal transport is observed. For GNRs with 2

Lan, Jinghua; Wang, Jian-Sheng; Gan, Chee Kwan; Chin, Sai Kong

2009-03-01

374

Vibro-conformational study of F2S(O)NCN: FTIR, pre-resonance Raman effect, force field and theoretical calculations  

NASA Astrophysics Data System (ADS)

The FTIR spectrum for vapour and the Raman spectrum for the liquid of difluorosulphenilimine cyanide (F2S(O)NCN) are presented. CS symmetry is suggested for the main conformer in the liquid phase. Vibrational assignments are made for all but the torsional fundamental mode. The symmetry force constants were calculated using an approximate value for the torsion. The study was complemented by theoretical calculations at various levels of sophistication. According to the ab initio methods (HF/3-21G*, HF/6-31G*, MP2/6-31G*) two stable conformations of the compound exist in the gas phase. The main form possesses CS symmetry (?(OSNC) = 180°, trans), whilst for the less stable rotamer C1 symmetry (?(OSNC) = 4 to 26°, near-cis) is predicted.

Alvarez, R. M. S.; Cutin, E. H.; Mack, H.-G.; Sala, O.; Della Védova, C. O.

1994-12-01

375

Theoretical calculations of the linear, nonlinear elastic constants and the Grüneisen parameters of cubic perovskites (Sr, Ba, Pb)TiO3  

NASA Astrophysics Data System (ADS)

The second-order, third-order and fourth-order elastic constants of SrTiO3, BaTiO3 and PbTiO3 cubic perovskites are calculated by using the first-principles total-energy method combined with the means of homogeneous deformation. The predicted results provide reasonable agreement with the reported experimental data, other theoretical results and Cauchy relations. The curved surfaces of Grüneisen parameters at various acoustic propagation modes are plotted by using predicted results. In addition, the Grüneisen parameters at low temperature limit, high temperature limit and Debye temperature are also calculated. Since nonlinear elastic constants are very difficult to be measured in experiments, the methods and results presented here provide a valuable guidance for experiments and the investigation of anharmonic properties for perovskite materials.

Huang, Wenqi; Yang, Hong; Lu, Guiwu; Gao, Yanan

2013-02-01

376

Quantum confinement effect in armchair graphene nanoribbons: Effect of strain on band gap modulation studied using first-principles calculations  

NASA Astrophysics Data System (ADS)

The quantum confinement effect may play an important role in the gap modulation of armchair graphene nanoribbons (AGNRs) under strain. Using the phase accumulation model, we have investigated the energy-dependent phase shift ?(?) at the ? point of AGNRs under various strains using first-principles calculation. The calculation results show that although the energy dispersion of the phase shift is modified by strain, the phase shift near the Fermi level is close to 0.75?, indicating that strain has little effect near that energy level. We can approximate the energy-dependent phase shift by a constant, ?(?)=0.75?, for AGNRs under various x strains. Due to the structural similarity between AGNRs and zigzag carbon nanotubes (ZCNTs), the electronic properties of AGNRs should be similar to those of ZCNTs. The quantization condition of the wave vector of ZCNTs governed by the periodic boundary condition along the circumference direction is similar to that of AGNRs except that the phase shift is equal to zero, ? (?)=0. Using the zone-folding (ZF) method, we can calculate the band gap of any strained AGNR (ZCNT) from the phase shift ?=0.75? (?=0) and the electronic structure of the strained graphene. The AGNR shows a zigzag behavior of the dependence of the band gap on strain which is very similar to the ZCNT. The zigzag patterns are significantly shifted by different phase shifts. The peak value of the band gap and the period of the pattern decreases as the width of the ribbon increases. For a given AGNR, the peak value and the period of the pattern increase as the strain increases. A flattening of the peaks appears at the strain where the maximum band gap occurs due to large compressive strain. All these observations can be understood easily from our ZF calculations. The agreement between our model and real local-density approximation calculations indicates that our model can provide an efficient and accurate method to estimate the band gap of AGNRs and ZCNTs under strain, and therefore can provide a better understanding of the effect of quantum confinement on the electronic properties of AGNRs.

Loh, Siow Mean; Huang, Yu-Hui; Lin, Ken-Ming; Su, W. S.; Wu, B. R.; Leung, T. C.

2014-07-01

377

Diffusion quantum Monte Carlo calculation of nondifferential properties for atomic groundstates  

Microsoft Academic Search

An algorithm to sample the exact (within the nodal error) ground state distribution to find nondifferential properties of multielectron systems is developed and applied to first-row atoms. Calculated properties are the distribution moments and the electronic density at the nucleus (expected value of the delta operator). For this purpose compact trial functions are developed and optimized, and a new estimator

Peter Langfelder; Stuart M. Rothstein; Jan Vrbik

1998-01-01

378

Diffusion quantum Monte Carlo calculation of nondifferential properties for atomic ground states  

Microsoft Academic Search

An algorithm to sample the exact (within the nodal error) ground state distribution to find nondifferential properties of multielectron systems is developed and applied to first-row atoms. Calculated properties are the distribution moments and the electronic density at the nucleus (expected value of the ? operator). For this purpose compact trial functions are developed and optimized, and a new estimator

Peter Langfelder; Stuart M. Rothstein; Jan Vrbik

1997-01-01

379

Calculation of Planetary Precession from Quantum-corrected Newton's Gravitation Law  

E-print Network

With consideration of quantization of space, we relate Newton's gravitation with the Second Law of thermodynamics. This leads to a correction to its original form, which takes into consideration the role of classical measurement. Our calculation shows this corrected form of gravitation can give explanation for planetary precession.

Zhen Wang

1998-04-29

380

Quantum Communication  

E-print Network

Quantum communication, and indeed quantum information in general, has changed the way we think about quantum physics. In 1984 and 1991, the first protocol for quantum cryptography and the first application of quantum non-locality, respectively, attracted a diverse field of researchers in theoretical and experimental physics, mathematics and computer science. Since then we have seen a fundamental shift in how we understand information when it is encoded in quantum systems. We review the current state of research and future directions in this new field of science with special emphasis on quantum key distribution and quantum networks.

Nicolas Gisin; Rob Thew

2007-03-27

381

Quantum chemical calculations with the inclusion of nonspecific and specific solvation: asymmetric transfer hydrogenation with bifunctional ruthenium catalysts.  

PubMed

Details of the mechanism of asymmetric transfer hydrogenation of ketones catalyzed by two chiral bifunctional ruthenium complexes, (S)-RuH[(R,R)-OCH(Ph)CH(Ph)NH(2)](?(6)-benzene) (Ru-1) or (S)-RuH[(R,R)-p-TsNCH(Ph)CH(Ph)NH(2)](?(6)-mesitylene) (Ru-2), were studied computationally by density functional theory, accounting for the solvation effects by using continuum, discrete, and mixed continuum/discrete solvation models via "solvated supermolecules" approach. In contrast to gas phase quantum chemical calculations, where the reactions were found to proceed via a concerted three-bond asynchronous process through a six-membered pericyclic transition state, incorporation of the implicit and/or explicit solvation into the calculations suggests that the same reactions proceed via two steps in solution: (i) enantio-determining hydride transfer and (ii) proton transfer through the contact ion-pair intermediate, stabilized primarily by ionic hydrogen bonding between the cation and the anion. The calculations suggest that the proton source for neutralizing the chiral RO(-) anion may be either the amine group of the cationic Ru complex or, more likely, a protic solvent molecule. In the latter case, the reaction may not necessarily proceed via the 16e amido complex Ru[(R,R)-XCH(Ph)CH(Ph)NH](?(6)-arene). The origin of enantioselectivity is discussed in terms of the newly formulated mechanism. PMID:23336817

Dub, Pavel A; Ikariya, Takao

2013-02-20

382

An H2/HD Collisional Excitation Database from High-Dimensional Quantum Dynamics Calculations: Benchmarking Interstellar STIS/COS observations  

NASA Astrophysics Data System (ADS)

The detailed understanding of the formation, destruction, and excitation of molecular hydrogen, H2, and its singly-deuterated isotopologue, HD, is crucial for astrophysical models of the postrecombination era, of local and extragalactic interstellar clouds, of circumstellar shells and protoplanetary disks, e.g. nearly every environment where molecular gas is exposed to UV irradiation resulting in a photodissociation region {PDR}. However, the dominant impactors for exciting H2 and HD are para-H2 and ortho-H2. Rate coefficients for these colliders are limited to vibrational levels v<4 for H2 and v=0 for HD. Further, they are based on approximate calculations which treated the colliding H2 as a pseudo-atom. Here we propose to extend our full-dimensional 6D quantum calculations for H2-H2 with v=0-2 up to v=14 and to perform for the first time initial rovibrational calculations for HD-H2. The availability of the proposed rate coefficients will allow for advanced PDR models along site lines observed with STIS and motivate future COS observations. In a number of cases, a large number of absorption features {up to 300} have been observed allowing for detailed model refinement and potentially new PDR physics. The rate coefficients will be distributed to the astrophysical modeling community via standard database formats {e.g., LAMDA, BASECOL, Cloudy}.

Stancil, Phillip

2014-10-01

383

Calculating solution redox free energies with ab initio quantum mechanical/molecular mechanical minimum free energy path method  

SciTech Connect

A quantum mechanical/molecular mechanical minimum free energy path (QM/MM-MFEP) method was developed to calculate the redox free energies of large systems in solution with greatly enhanced efficiency for conformation sampling. The QM/MM-MFEP method describes the thermodynamics of a system on the potential of mean force surface of the solute degrees of freedom. The molecular dynamics (MD) sampling is only carried out with the QM subsystem fixed. It thus avoids 'on-the-fly' QM calculations and thus overcomes the high computational cost in the direct QM/MM MD sampling. In the applications to two metal complexes in aqueous solution, the new QM/MM-MFEP method yielded redox free energies in good agreement with those calculated from the direct QM/MM MD method. Two larger biologically important redox molecules, lumichrome and riboflavin, were further investigated to demonstrate the efficiency of the method. The enhanced efficiency and uncompromised accuracy are especially significant for biochemical systems. The QM/MM-MFEP method thus provides an efficient approach to free energy simulation of complex electron transfer reactions.

Zeng Xiancheng; Hu Hao; Hu Xiangqian; Yang Weitao [Department of Chemistry, Duke University, Durham, North Carolina 27708 (United States)

2009-04-28

384

Studies on vibrational, NMR spectra and quantum chemical calculations of N-Succinopyridine: An organic nonlinear optical material  

NASA Astrophysics Data System (ADS)

Single crystals of N-Succinopyridine (NSP) have been grown from water using solution growth method by isothermal solvent evaporation technique. The solid state Fourier Transform Infrared (FTIR) spectrum of the grown crystal shows a broad absorption extending from 3450 down to 400 cm-1, due to H-bond vibrations and other characteristic vibrations. Fourier Transform Raman (FT-Raman) spectrum of NSP single crystal shows Raman intensities ranging from 3100 to 100 cm-1 due the characteristics vibrations of functional groups present in NSP. The proton and carbon positions of NSP have been described by 1H and 13C NMR spectrum respectively. Ab initio quantum chemical calculations on NSP have been performed by density functional theory (DFT) calculations using B3LYP method with 6-311++G(d,p) basis set. The predicted first hyperpolarizability is found to be 1.29 times greater than that of urea and suggests that the title compound could be an attractive material for nonlinear optical applications. The calculated HOMO-LUMO energies show that charge transfers occur within the molecule and other related molecular properties. Molecular properties such as Mulliken population analysis, thermodynamic functions and perturbation theory energy analysis have also been reported. Electrostatic potential map (ESP) of NSP obtained by electron density isosurface provided the information about the size, shape, charge density distribution and site of chemical reactivity of the title molecule. The molecular stability and bond strength have been investigated through the Natural Bond Orbital (NBO) analysis.

Kannan, V.; Thirupugalmani, K.; Brahadeeswaran, S.

2013-10-01

385

Blue phosphorescent organic light-emitting diodes using an exciplex forming co-host with the external quantum efficiency of theoretical limit.  

PubMed

A high-efficiency blue-emitting organic light-emitting diode (OLED) approaching theoretical efficiency using an exciplex-forming co-host composed of N,N'-dicarbazolyl-3,5-benzene (mCP) and bis-4,6-(3,5-di-3-pyridylphenyl)- 2-methylpyrimidine (B3PYMPM) is fabricated. Iridium(III)bis[(4,6-difluorophenyl)- pyridinato-N,C2']picolinate (FIrpic) is used as the emitter, which turns out to have a preferred horizontal dipole orientation in the emitting layer. The OLED shows a maximum external quantum efficiency of 29.5% (a maximum current efficiency of 62.2 cd A(-1) ), which is in perfect agreement with the theoretical prediction. PMID:24838525

Shin, Hyun; Lee, Sunghun; Kim, Kwon-Hyeon; Moon, Chang-Ki; Yoo, Seung-Jun; Lee, Jeong-Hwan; Kim, Jang-Joo

2014-07-16

386

Peptide Bond Distortions from Planarity: New Insights from Quantum Mechanical Calculations and Peptide/Protein Crystal Structures  

PubMed Central

By combining quantum-mechanical analysis and statistical survey of peptide/protein structure databases we here report a thorough investigation of the conformational dependence of the geometry of peptide bond, the basic element of protein structures. Different peptide model systems have been studied by an integrated quantum mechanical approach, employing DFT, MP2 and CCSD(T) calculations, both in aqueous solution and in the gas phase. Also in absence of inter-residue interactions, small distortions from the planarity are more a rule than an exception, and they are mainly determined by the backbone ? dihedral angle. These indications are fully corroborated by a statistical survey of accurate protein/peptide structures. Orbital analysis shows that orbital interactions between the ? system of C? substituents and the ? system of the amide bond are crucial for the modulation of peptide bond distortions. Our study thus indicates that, although long-range inter-molecular interactions can obviously affect the peptide planarity, their influence is statistically averaged. Therefore, the variability of peptide bond geometry in proteins is remarkably reproduced by extremely simplified systems since local factors are the main driving force of these observed trends. The implications of the present findings for protein structure determination, validation and prediction are also discussed. PMID:21949726

Improta, Roberto; Vitagliano, Luigi; Esposito, Luciana

2011-01-01

387

Molecular dynamics simulation and quantum chemical calculations for the adsorption of some Azo-azomethine derivatives on mild steel  

NASA Astrophysics Data System (ADS)

The adsorption mechanism and inhibition performance of some Azo-azomethine derivatives [2-hydroxyphenylazo-2?,4?-dihydroxy-3?-formylbenzene(Azo-1), 2-carboxyphenylazo-2?,4?-dihydroxy-3?-formylbenzene (Azo-II), 2-hydroxyphenylazo-2?,4?-dihydroxy-3?-{2-hydroxyphenylazomethine}(Azo-I-azomethine I) and 2-carboxyphenylazo-2?,4?-dihydroxy-3?-{2-hydroxyazo methane} (Azo-II-azomethine II) on mild steel at temperatures ranging from 298 K to 333 K have been studied using molecular dynamics (MD) simulation and quantum chemical computational methods. The results obtained revealed that these molecules could effectively adsorb on Fe (0 0 1) surface and the active adsorption sites of these molecules are the nitrogen, oxygen atoms and special negatively charged carbon atoms. All the inhibitors studied had unique corrosion inhibition performance with Azo-II-azomethine II showing the highest inhibition performance at lower temperature ranges from 298 K to 313 K and Azo-II displaying the highest inhibition performance at higher temperature ranges of 323 K and 333 K. Some quantum chemical parameters and the Mulliken charge densities on the optimized structure of inhibitors were calculated using the 6-31?G basis set method to provide further insight into the mechanism of the corrosion inhibition process. The local reactivity was analyzed through the Fukui function and condensed softness indices in order to know the possible sites of nucleophillic and electrophillic attacks.

Shokry, H.

2014-02-01

388

Theoretical and numerical calculations for the time-averaged acoustic force and torque acting on a rigid cylinder of arbitrary size in a low viscosity fluid.  

PubMed

In this paper, theoretical calculations as well as numerical simulations are performed for the time-averaged acoustic force and torque on a rigid cylinder of arbitrary size in a fluid with low viscosity, i.e., the acoustic boundary layer is thin compared to the cylinder radius. An exact analytical solution and its approximation are proposed in the form of an infinite series including Bessel functions. These solutions can be evaluated easily by a mathematical software package such as mathematica and matlab. Three types of incident waves, plane traveling wave, plane standing wave, and dual orthogonal standing waves, are investigated in detail. It is found that for a small particle, the viscous effects for an incident standing wave may be neglected but those for an incident traveling wave are notable. A nonzero viscous torque is experienced by the rigid cylinder when subjected to dual orthogonal standing waves with a phase shift even when the cylinder is located at equilibrium positions without imposed acoustic forces. Furthermore, numerical simulations are carried out based on the FVM algorithm to verify the proposed theoretical formulas. The theoretical results and the numerical ones agree with each other very well in all the cases considered. PMID:21682376

Wang, Jingtao; Dual, Jurg

2011-06-01

389

Estimation of the thermodynamic properties of functional groups and biomolecules using quantum chemical/statistical thermodynamic calculations  

NASA Astrophysics Data System (ADS)

The scarcity and sustainability of energy sources have always been a concern while seeking for alternative fuels. Biofuels have drawn the attention of various researchers due to their abundancy and renewability. Understanding the physical and chemical properties of these molecules is essential to determining their potential as alternative fuels or fuel additives. In this work, the properties of these molecules are predicted through methods developed from quantum mechanics and statistical mechanics theories. The heats of formations are calculated with the Gaussian program and combined with the Benson group contribution method to predict the Benson parameters of unknown functional groups in a molecule. The methods developed are used to expand the Benson database and improve the practicability of the group contribution method. The heats of formations are also used to predict and correlate heat capacities across a range of temperatures and energy densities in this study.

Chai, Weisin

390

Toward Accurate Reaction Energetics for Molecular Line Growth at Surface: Quantum Monte Carlo and Density Functional Theory Calculations  

SciTech Connect

We revisit the molecular line growth mechanism of styrene on the hydrogenated Si(001) 2x1 surface. In particular, we investigate the energetics of the radical chain reaction mechanism by means of diffusion quantum Monte Carlo (QMC) and density functional theory (DFT) calculations. For the exchange correlation (XC) functional we use the non-empirical generalized-gradient approximation (GGA) and meta-GGA. We find that the QMC result also predicts the intra dimer-row growth of the molecular line over the inter dimer-row growth, supporting the conclusion based on DFT results. However, the absolute magnitudes of the adsorption and reaction energies, and the heights of the energy barriers differ considerably between the QMC and DFT with the GGA/meta-GGA XC functionals.

Kanai, Y; Takeuchi, N

2009-10-14

391

Quantum Computation  

E-print Network

In the last few years, theoretical study of quantum systems serving as computational devices has achieved tremendous progress. We now have strong theoretical evidence that quantum computers, if built, might be used as a dramatically powerful computational tool. This review is about to tell the story of theoretical quantum computation. I left out the developing topic of experimental realizations of the model, and neglected other closely related topics which are quantum information and quantum communication. As a result of narrowing the scope of this paper, I hope it has gained the benefit of being an almost self contained introduction to the exciting field of quantum computation. The review begins with background on theoretical computer science, Turing machines and Boolean circuits. In light of these models, I define quantum computers, and discuss the issue of universal quantum gates. Quantum algorithms, including Shor's factorization algorithm and Grover's algorithm for searching databases, are explained. I will devote much attention to understanding what the origins of the quantum computational power are, and what the limits of this power are. Finally, I describe the recent theoretical results which show that quantum computers maintain their complexity power even in the presence of noise, inaccuracies and finite precision. I tried to put all results in their context, asking what the implications to other issues in computer science and physics are. In the end of this review I make these connections explicit, discussing the possible implications of quantum computation on fundamental physical questions, such as the transition from quantum to classical physics.

Dorit Aharonov

1998-12-15

392

Rotamers and isotopomers of 3-chloro-5-fluoroanisole studied by resonant two-photon ionization spectroscopy and theoretical calculations  

NASA Astrophysics Data System (ADS)

The ab initio and density functional theory (DFT) calculations reveal that two rotamers, denoted by cis and trans 3-chloro-5-fluoroanisole (3C5FA), are stable for each of the S0, S1, and D0 states. In the one-color resonant two-photon ionization (R2PI) spectra, the band origins of the S1 ? S0 electronic transition (00 bands) of cis35Cl-3C5FA and cis37Cl-3C5FA are both located at 36,468 ± 3 cm-1, while the 00 bands of trans35Cl-3C5FA and trans37Cl-3C5FA are found to be 36,351 ± 3 and 36,354 ± 3 cm-1. The two rotamers display very similar vibrational frequencies in the S1 state, and the observed active modes mainly involve the in-plane ring deformation vibrations. By the two-color R2PI spectroscopy, the adiabatic ionization energies (IEs) of both isotopomers of 3C5FA are determined to be 69,720 ± 15 cm-1 for the cis rotamer and 69,636 ± 15 cm-1 for the trans rotamer. The substitution, conformation, and isotope effects on the properties of 3C5FA, including the molecular structures, vibrational frequencies, and electronic transition and ionization energies, were also discussed in detail.

Zhang, Lijuan; Yu, Dan; Dong, Changwu; Cheng, Min; Hu, Lili; Zhou, Zhimin; Du, Yikui; Zhu, Qihe; Zhang, Cunhao

2013-03-01

393

Synthesis, spectroscopic characterization and theoretical calculations of ClF2CC(O)NPCl3 ([chloro(difluor)acetyl]phosphorimidic trichloride).  

PubMed

The synthesis of [chloro(difluor)acetyl]phosphorimidic trichloride (ClF2CC(O)NPCl3), together with a tentative assignment of the vibrational, NMR and mass spectra, are reported. Quantum chemical calculations (MP2 and B3LYP methods with 6-311+G(d) and 6-311+G(2df,p) basis sets) predict three stable conformers in the gas phase (syn, gauche and anti, defined according to the rotation around both the ClCCN and the CCNP dihedral angles). However, only a single C1 symmetry conformer is observed in the liquid phase, possessing the CO double bond in synperiplanar orientation with respect to the PN double bond, and the ClC bond distorted from the plane defined by the CC(O)NP entity. A Natural Bond Orbital (NBO) analysis was carried out for the title compound and related molecules in order to provide an explanation about the electronic properties. PMID:24177880

Iriarte, Ana G; Cutin, Edgardo H; Argüello, Gustavo A

2014-01-01

394

Quantum calculation of cold-atom diffraction using periodic magnetic fields  

NASA Astrophysics Data System (ADS)

When cold atoms approach a periodically magnetized surface, they are scattered by the effective repulsive potential U(x,y)=?BmFgB(x,y) . If the period a of the magnetized surface is larger than the de Broglie wavelength ? of the atoms, the atoms are diffracted. We have developed a method for calculating the location and intensity of the diffraction peaks using formal scattering theory. We solve the exact two-dimensional Schrödinger equation with the finite element method and calculate the scattering amplitude f(?) using the integral formula; a plot of ?f(?)?2 provides a visualization of the diffraction pattern. By varying the experimental parameters within a realistic range, we predict the optimal conditions for observing atom diffraction.

Hung, Yin; Schuller, Bradley; Giblin, John; Shertzer, Janine

2006-06-01

395

Torsional energy levels of CH3OH(+)/CH3OD(+)/CD3OD(+) studied by zero-kinetic energy photoelectron spectroscopy and theoretical calculations.  

PubMed

The torsional energy levels of CH3OH(+), CH3OD(+), and CD3OD(+) have been determined for the first time using one-photon zero kinetic energy photoelectron spectroscopy. The adiabatic ionization energies for CH3OH, CH3OD, and CD3OD are determined as 10.8396, 10.8455, and 10.8732 eV with uncertainties of 0.0005 eV, respectively. Theoretical calculations have also been performed to obtain the torsional energy levels for the three isotopologues using a one-dimensional model with approximate zero-point energy corrections of the torsional potential energy curves. The calculated values are in good agreement with the experimental data. The barrier height of the torsional potential energy without zero-point energy correction was calculated as 157 cm(-1), which is about half of that of the neutral (340 cm(-1)). The calculations showed that the cation has eclipsed conformation at the energy minimum and staggered one at the saddle point, which is the opposite of what is observed in the neutral molecule. The fundamental C-O stretch vibrational energy level for CD3OD(+) has also been determined. The energy levels for the combinational excitation of the torsional vibration and the fundamental C-O stretch vibration indicate a strong torsion-vibration coupling. PMID:25318721

Dai, Zuyang; Gao, Shuming; Wang, Jia; Mo, Yuxiang

2014-10-14

396

Institute of Photonics and Quantum Sciences @ Heriot-Watt University Our research interests are wide ranging from theoretical studies into quantum physics,  

E-print Network

: These are prestigious and competitive awards that are intended to attract outstanding students from around the world- 1 - Institute of Photonics and Quantum Sciences @ Heriot-Watt University Our research interests support, which is restricted to home students only. We typically have around 10 such studentships awarded

Greenaway, Alan

397

Calculation of the electron two-slit experiment using a quantum mechanical variational principle  

E-print Network

A nonlocal relativistic variational principle (VP) has recently been proposed as an alternative to the Dirac wave equation of standard quantum mechanics. We apply that principle to the electron two-slit experiment. The detection system is modelled as a screen made of atoms, any one of which can be excited by the incident electron, but we avoid restricting the detection mechanism further. The VP is shown to predict that, at the time the electron reaches the screen, its wavefunction will be localized to the neighborhood of a single atom, resulting in a position-type measurement. In an ensemble of such experiments ("identically prepared" except that the initial phase of the wavefunction--the hidden variable in the VP formulation--is sampled over the expected uniform distribution), the distribution of measured positions will reproduce the interference pattern predicted by the Dirac equation. We also demonstrate that with a detection system designed fundamentally to detect the electron's transverse wavelength rather than its position, the VP predicts that one such mode will be detected, that is, a wavelength measurement will result. Finally, it is shown that these results are unchanged in the "delayed choice" variant of the experiment.

Alan K. Harrison

2012-08-02

398

Calculation of the electron two slit experiment using a quantum mechanical variational principle  

SciTech Connect

A nonlocal relativistic variational principle (VP) has recently been proposed as an alternative to the Dirac wave equation of standard quantum mechanics. We apply that principle to the electron two-slit experiment. The detection system is modelled as a screen made of atoms, any one of which can be excited by the incident electron, but we avoid restricting the detection mechanism further. The VP is shown to predict that, at the time the electron reaches the screen, its wavefunction will be localized to the neighborhood of a single atom, resulting in a position-type measurement. In an ensemble of such experiments ('identically prepared' except that the initial phase of the wavefunction - the hidden variable in the VP formulation - is sampled over the expected uniform distribution), the distribution of measured positions will reproduce the interference pattern predicted by the Dirac equation. We also demonstrate that with a detection system designed fundamentally to detect the electron's transverse wavelength rather than its position, the VP predicts that one such mode will be detected, that is, a wavelength measurement will result. Finally, it is shown that these results are unchanged in the 'delayed choice' variant of the experiment.

Harrison, Alan K. [Los Alamos National Laboratory

2012-04-17

399

Quantum chemical and conventional TST calculations of rate constants for the OH + alkane reaction  

NASA Astrophysics Data System (ADS)

Reactions of OH with methane, ethane, propane, i-butane, and n-butane have been modeled using ab initio (MP2) and hybrid DFT (BHandHLYP) methods, and the 6-311G(d,p) basis set. Furthermore, single-point calculations at the CCSD(T) level were carried out at the optimized geometries. The rate constants have been calculated using the conventional transition-state theory (CTST). Arrhenius equations are proposed in the temperature range of 250-650 K. Hindered Internal Rotation partition functions calculations were explicitly carried out and included in the total partition functions. These corrections showed to be relevant in the determination of the pre-exponential parameters, although not so important as in the NO 3 + alkane reactions [G. Bravo-Pérez, J.R. Alvarez-Idaboy, A. Cruz-Torres, M.E. Ruíz, J. Phys. Chem. A 106 (2002) 4645]. The explicit participation of the tunnel effect has been taken into account. The calculated rate coefficients provide a very good agreement with the experimental data. The best agreement for the overall alkane + OH reactions seemed to occur when the BHandHLYP geometries and partition functions are used. For propane and i-butane, in addition to the respective secondary and tertiary H-abstraction channels, the primary one has been considered. These pathways are confirmed to be significant in spite of the large differences in activation energies between primary and secondary or primary and tertiary channels, respectively of propane and i-butane reactions and should not be disregarded.

Bravo-Pérez, Graciela; Alvarez-Idaboy, J. Raúl; Jiménez, Annia Galano; Cruz-Torres, Armando

2005-04-01

400

Symmetry constraints and variational principles in diffusion quantum Monte Carlo calculations of excited-state energies  

Microsoft Academic Search

Fixed-node diffusion Monte Carlo (DMC) is a stochastic algorithm for finding\\u000athe lowest energy many-fermion wave function with the same nodal surface as a\\u000achosen trial function. It has proved itself among the most accurate methods\\u000aavailable for calculating many-electron ground states, and is one of the few\\u000aapproaches that can be applied to systems large enough to act as

W. M. C. Foulkes; Randolph Q. Hoodand; R. J. Needs

1999-01-01

401

Symmetry constraints and variational principles in diffusion quantum Monte Carlo calculations of excited-state energies  

Microsoft Academic Search

Fixed-node diffusion Monte Carlo (DMC) is a stochastic algorithm for finding the lowest energy many-fermion wave function with the same nodal surface as a chosen trial function. It has proved itself among the most accurate methods available for calculating many-electron ground states, and is one of the few approaches that can be applied to systems large enough to act as

W. M. C. Foulkes; Randolph Q. Hood; R. J. Needs

1999-01-01

402

Theoretical Calculations and Simulations of Interaction of X-Rays with High-Z Nanomoities for Use in Cancer Radiotherapy  

NASA Astrophysics Data System (ADS)

When used with X-ray radiotherapy, heavy elements (high atomic number Z or HZ) such as gold(Au) and platinum(Pt) have the potential to greatly sensitize and enhance the damage to tumor tissues. While HZ radiosensitization has been shown to be higly effective in reducing tumor sizes, much work still needs to be done to determine the ideal X-ray energy/energy spectrum. The likelihood of photoelectric absorption of X-rays that result in the production of cell-killing Auger electrons relative to the photon scatter in an HZ sensitized tumor has to be determined for treatments using X-rays from various sources and energies to assess their efficacy. In this report, we present computations that outline the dependence of photoelectric absorption on X-ray energy. The relative X-ray absorption by a radiosensitized tumor was calculated to contrast the efficacy of different X-ray sources in Auger electron production at different tumor depths. Enhanced photoabsorption of low-energy X-rays from broadband sources in the keV range is shown to be much higher than from those in the MeV range. In addition, with the use of the Monte Carlo code package Geant4, we present the total X-ray energy deposited into a radiosensitized tumor located at different depths in a phantom. The enhancement in radiation dose deposition will also be analysed at the microscopic cellular level to determine the HZ radiosensitizer concentration required. Potential use of monochromatic X-rays for more precise HZ radiosensitization will also be described.

Lim, Sara N.; Pradhan, Anil K.; Nahar, Sultana N.

2013-06-01

403

Screening nitrogen-rich bases and oxygen-rich acids by theoretical calculations for forming highly stable salts.  

PubMed

Nitrogen-rich heterocyclic bases and oxygen-rich acids react to produce energetic salts with potential application in the field of composite explosives and propellants. In this study, 12 salts formed by the reaction of the bases 4-amino-1,2,4-trizole (A), 1-amino-1,2,4-trizole (B), and 5-aminotetrazole (C), upon reaction with the acids HNO3 (I), HN(NO2 )2 (II), HClO4 (III), and HC(NO2 )3 (IV), are studied using DFT calculations at the B97-D/6-311++G** level of theory. For the reactions with the same base, those of HClO4 are the most exothermic and spontaneous, and the most negative ?r Gm in the formation reaction also corresponds to the highest decomposition temperature of the resulting salt. The ability of anions and cations to form hydrogen bonds decreases in the order NO3 (-) >N(NO2 )2 (-) >ClO4 (-) >C(NO2 )3 (-) , and C(+) >B(+) >A(+) . In particular, those different cation abilities are mainly due to their different conformations and charge distributions. For the salts with the same anion, the larger total hydrogen-bond energy (EH,tot ) leads to a higher melting point. The order of cations and anions on charge transfer (q), second-order perturbation energy (E2 ), and binding energy (Eb ) are the same to that of EH,tot , so larger q leads to larger E2 , Eb , and EH,tot . All salts have similar frontier orbitals distributions, and their HOMO and LUMO are derived from the anion and the cation, respectively. The molecular orbital shapes are kept as the ions form a salt. To produce energetic salts, 5-aminotetrazole and HClO4 are the preferred base and acid, respectively. PMID:24782247

Zhang, Xueli; Gong, Xuedong

2014-08-01

404

Comparison Of Quantum Mechanical And Classical Trajectory Calculations Of Cross Sections For Ion-Atom Impact Ionization of Negative - And Positive -Ions For Heavy Ion Fusion Applications  

SciTech Connect

Stripping cross sections in nitrogen have been calculated using the classical trajectory approximation and the Born approximation of quantum mechanics for the outer shell electrons of 3.2GeV I{sup -} and Cs{sup +} ions. A large difference in cross section, up to a factor of six, calculated in quantum mechanics and classical mechanics, has been obtained. Because at such high velocities the Born approximation is well validated, the classical trajectory approach fails to correctly predict the stripping cross sections at high energies for electron orbitals with low ionization potential.

Igor D. Kaganovich; Edward A. Startsev; Ronald C. Davidson

2003-05-15

405

Quantum mechanical calculation of 23 Na NMR shieldings in silicates and aluminosilicates  

Microsoft Academic Search

To assist in the assignment and interpretation of 23Na NMR spectra in silicate and aluminosilicate minerals and glasses we have calculated the 23Na NMR shieldings and the electric field gradients (EFG) at the Na for a number of Na-containing species. Included are Na(OH2)\\u000a n\\u000a \\u000a +, n?=?1, 2, 4, 5, 6 and 8, and Na+ complexes with SiH3OH, SiH3ONa and O(SiH3)2.

J. A. Tossell

1999-01-01

406

Quantum Monte Carlo calculations of electroweak transition matrix elements in A = 6,7 nuclei  

E-print Network

Green's function Monte Carlo calculations of magnetic dipole, electric quadrupole, Fermi, and Gamow-Teller transition matrix elements are reported for A=6,7 nuclei. The matrix elements are extrapolated from mixed estimates that bracket the relevant electroweak operator between variational Monte Carlo and GFMC propagated wave functions. Because they are off-diagonal terms, two mixed estimates are required for each transition, with a VMC initial (final) state paired with a GFMC final (initial) state. The realistic Argonne v18 two-nucleon and Illinois-2 three-nucleon interactions are used to generate the nuclear states. In most cases we find good agreement with experimental data.

Muslema Pervin; Steven C. Pieper; R. B. Wiringa

2007-10-05

407

Quantum mechanical calculations for the misincorporation of nucleotides opposite mutagenic 3,N4-ethenocytosine.  

PubMed

The ubiquitous nature and persistence of exocyclic DNA adducts suggest their involvement as initiators of carcinogenesis. We have investigated the misincorporation properties of the exocyclic DNA adduct, 3,N(4)-ethenocytosine, using DFT and DFT-D methods. Computational investigations have been carried out by using the B3LYP, M062X, and wB97XD methods with the 6-31+G* basis set to determine the hydrogen bonding strengths, binding energy, and physical parameters. The single point energy calculations have been carried out at MP2/6-311++G** on corresponding optimized geometries. The energies were compared among the 3,N(4)-ethenocytosine adduct with DNA bases to find the most stable conformer. The solvent phase calculations have also been carried out using the CPCM model. The computed reaction enthalpy values provide computational insights to the earlier experimental observation in in vitro, E.coli, and mammalian cells of a high level of substitution mutation in which C ? A transversion results from ?C-T pairing [?C-T3 and ?C-T4] in the adduct containing DNA sequence. PMID:22889303

Srinivasadesikan, Venkatesan; Sahu, Prabhat K; Lee, Shyi-Long

2012-09-13

408

Vibrational spectra, DFT quantum chemical calculations and conformational analysis of P-iodoanisole.  

PubMed

The solid phase FT-IR and FT-Raman spectra of P-iodoanisole (P-IA) have been recorded in the regions 400-4000 and 50-4000 cm(-1), respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by ab initio (HF) and density functional theory (B3LYP) methods with LanL2DZ as basis set. The potential energy surface scan for the selected dihedral angle of P-IA has been performed to identify stable conformer. The optimized structure parameters and vibrational wavenumbers of stable conformer have been predicted by density functional B3LYP method with LanL2DZ (with effective core potential representations of electrons near the nuclei for post-third row atoms) basis set. The nucleophilic and electrophilic sites obtained from the molecular electrostatic potential (MEP) surface were calculated. The temperature dependence of thermodynamic properties has been analyzed. Several thermodynamic parameters have been calculated using B3LYP with LanL2DZ basis set. PMID:23727676

Arivazhagan, M; Anitha Rexalin, D; Geethapriya, J

2013-09-01

409

Structural properties and enthalpy of formation of magnesium hydride from quantum Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

We have used diffusion Monte Carlo (DMC) calculations to study the structural properties of magnesium hydride (MgH2) , including the pressure-volume equation of state, the cohesive energy, and the enthalpy of formation from magnesium bulk and hydrogen gas. The calculations employ pseudopotentials and B-spline basis sets to expand the single particle orbitals used to construct the trial wave functions. Extensive tests on system size, time step, and other sources of errors, performed on periodically repeated systems of up to 1050 atoms, show that all these errors together can be reduced to below 10meV/f.u. . We find excellent agreement with the experiments for the equilibrium volume of both the Mg and the MgH2 crystals. The cohesive energy of the Mg crystal is found to be 1.51(1)eV and agrees perfectly with the experimental value of 1.51eV . The enthalpy of formation of MgH2 from Mg bulk and H2 gas is found to be 0.85±0.01eV/f.u. , or 82±1kJ/mole , which is off the experimental one of 76.1±1kJ/mole only by 6kJ/mole . This shows that DMC can almost achieve chemical accuracy (1kcal/mole) on this system. Density functional theory errors are shown to be much larger and depend strongly on the functional employed.

Pozzo, M.; Alfè, D.

2008-03-01

410

Hydrogen-bond effect, spectroscopic and molecular structure investigation of sulfamethazine Schiff-base: Experimental and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

Comprehensive theoretical and experimental structural studies on N-(4,6-dimethyl-pyrimidin-2-yl)-4-[(2-hydroxy-benzylidene)-amino]benzenesulfonamide (SMS) have been carried out by elemental analysis, FT IR, 1H NMR, UV-Vis. and MS. Optimized molecular structure and harmonic vibrational frequencies have been investigated by DFT/B3LYP and HF methods combined with 6-31G(d) basis set. Stability of the molecule arises from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed using natural bond orbital (NBO) analysis. Electronic structures were discussed by TD-DFT method and the descriptions of frontier molecular orbitals and the relocation of the electron density were determined. 1H NMR chemical shifts were computed by Gauge-invariant atomic orbital (GIAO) method in both gas and DMSO media, using the polarizable continuum model (PCM). Structure-activity relationship has been used to correlate biological activity with some appropriate quantum descriptors such as EHOMO, ELUMO, energy gap, dipole moment (?), global hardness (?), softness (S), electrophilicity index (?), molecular polarizability (?), Mulliken electronegativity (?), Mulliken charge (Qi) and molecular electrostatic potential (MEP).

Mansour, Ahmed M.; Abdel Ghani, Nour T.

2013-05-01

411

Towards Quantum Chemistry on a Quantum Computer  

E-print Network

The fundamental problem faced in quantum chemistry is the calculation of molecular properties, which are of practical importance in fields ranging from materials science to biochemistry. Within chemical precision, the total energy of a molecule as well as most other properties, can be calculated by solving the Schrodinger equation. However, the computational resources required to obtain exact solutions on a conventional computer generally increase exponentially with the number of atoms involved. This renders such calculations intractable for all but the smallest of systems. Recently, an efficient algorithm has been proposed enabling a quantum computer to overcome this problem by achieving only a polynomial resource scaling with system size. Such a tool would therefore provide an extremely powerful tool for new science and technology. Here we present a photonic implementation for the smallest problem: obtaining the energies of H2, the hydrogen molecule in a minimal basis. We perform a key algorithmic step - the iterative phase estimation algorithm - in full, achieving a high level of precision and robustness to error. We implement other algorithmic steps with assistance from a classical computer and explain how this non-scalable approach could be avoided. Finally, we provide new theoretical results which lay the foundations for the next generation of simulation experiments using quantum computers. We have made early experimental progress towards the long-term goal of exploiting quantum information to speed up quantum chemistry calculations.

Benjamin P. Lanyon; James D. Whitfield; Geoff G. Gillet; Michael E. Goggin; Marcelo P. Almeida; Ivan Kassal; Jacob D. Biamonte; Masoud Mohseni; Ben J. Powell; Marco Barbieri; Alán Aspuru-Guzik; Andrew G. White

2009-05-06

412

Path-integral Mayer-sampling calculations of the quantum Boltzmann contribution to virial coefficients of helium-4  

NASA Astrophysics Data System (ADS)

We present Mayer-sampling Monte Carlo calculations of the quantum Boltzmann contribution to the virial coefficients Bn, as defined by path integrals, for n = 2 to 4 and for temperatures from 2.6 K to 1000 K, using state-of-the-art ab initio potentials for interactions within pairs and triplets of helium-4 atoms. Effects of exchange are not included. The vapor-liquid critical temperature of the resulting fourth-order virial equation of state is 5.033(16) K, a value only 3% less than the critical temperature of helium-4: 5.19 K. We describe an approach for parsing the Boltzmann contribution into components that reduce the number of Mayer-sampling Monte Carlo steps required for components with large per-step time requirements. We estimate that in this manner the calculation of the Boltzmann contribution to B3 at 2.6 K is completed at least 100 times faster than the previously reported approach.

Shaul, Katherine R. S.; Schultz, Andrew J.; Kofke, David A.

2012-11-01

413

Nuclei-selected NMR shielding calculations: a sublinear-scaling quantum-chemical method.  

PubMed

An ab initio method for the direct calculation of NMR shieldings for selected nuclei at the Hartree-Fock and density-functional theory level is presented. Our method shows a computational effort scaling only sublinearly with molecular size, as it is motivated by the physical consideration that the chemical shielding is dominated by its local environment. The key feature of our method is to avoid the conventionally performed calculation of all NMR shieldings but instead to solve directly for specific nuclear shieldings. This has important implications not only for the study of large molecules, but also for the simulation of solvent effects and molecular dynamics, since often just a few shieldings are of interest. Our theory relies on two major aspects both necessary to provide a sublinear scaling behavior: First, an alternative expression for the shielding tensor is derived, which involves the response density matrix with respect to the nuclear magnetic moment instead of the response to the external magnetic field. Second, as unphysical long-range contributions occur within the description of distributed gauge origin methods that do not influence the final expectation value, we present a screening procedure to truncate the B-field dependent basis set, which is crucial in order to ensure an early onset of the sublinear scaling. The screening is in line with the r(-2) distance decay of Biot-Savarts law for induced magnetic fields. Our present truncation relies on the introduced concept of "individual gauge shielding contributions" applied to a reformulated shielding tensor, the latter consisting of gauge-invariant terms. The presented method is generally applicable and shows typical speed-ups of about one order of magnitude; moreover, due to the reduced scaling behavior of O(1) as compared to O(N), the wins become larger with increasing system size. We illustrate the validity of our method for several test systems, including ring-current dominated systems and biomolecules with more than 1000 atoms. PMID:21341823

Beer, Matthias; Kussmann, Jörg; Ochsenfeld, Christian

2011-02-21

414

Dual-wavelength mode-locked quantum-dot laser, via ground and excited state transitions: experimental and theoretical investigation.  

PubMed

We report a dual-wavelength passive mode locking regime where picosecond pulses are generated from both ground (lambda = 1263 nm) and excited state transitions (lambda = 1180 nm), in a GaAs-based monolithic two-section quantum-dot laser. Moreover, these results are reproduced by numerical simulations which provide a better insight on the dual-wavelength mode-locked operation. PMID:20588412

Cataluna, Maria Ana; Nikitichev, Daniil I; Mikroulis, Spiros; Simos, Hercules; Simos, Christos; Mesaritakis, Charis; Syvridis, Dimitris; Krestnikov, Igor; Livshits, Daniil; Rafailov, Edik U

2010-06-01

415

A reduced dimensionality quantum calculation of the reaction of H{sub 2} with diamond (111) surface  

SciTech Connect

We present a reduced dimensionality quantum dynamics study of the hydrogen abstraction reaction on a semirigid (111) diamond surface, C{sub d}+H{sub 2}(v,j,m){yields}C{sub d}H+H. A nine-dimensional potential energy surface is developed by combining a London-Eyring-Polanyi-Sato potential based on ab initio data with nonbonded and surface interactions. Four reactive degrees of freedom are treated explicitly using a recently developed wave packet approach in a real L{sup 2} basis, and the total reaction probabilities for initial states v=0-1, j=0-11, and m=0-4 are calculated over a large total energy range. The remaining five degrees of freedom are treated using energy-shift approximations, and the full cumulative reaction probability is obtained and from it the full thermal rate constant. Comparison with conventional transition state theory indicates that at 300 K tunneling accounts for 90% of the rate constant and remains significant even at high temperatures. Dynamical corrections to transition state theory become important above 1000 K. At 1200 K the tunneling and dynamical corrections nearly cancel each other and the transition state theory rate constant agrees very well with quantum rate constant. The coupling of surface and reactive modes has only a minor, less then 15%, effect on the rate constants, provided that the energetics for the relaxed surface are incorporated into the potential. The thermal rate for H abstraction from diamond, obtained from detailed balance, is in good agreement with experimental data. Under typical chemical vapor deposition conditions the thermal rate for H abstraction by diamond active sites is found to be 100 slower than the rate of competitive reaction, H addition to diamond active sites. (c) 2000 American Institute of Physics.

Skokov, Sergei [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)] [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States); Bowman, Joel M. [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)] [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)

2000-07-08

416

Threshold current calculations and optical cavity optimization for PbSe/PbSrSe multiple quantum well structures  

NASA Astrophysics Data System (ADS)

Threshold current is a key parameter in the design and proper operation of quantum well lasers. In this publication, threshold current analysis and calculations are done on four PbSe/Pb0.934Sr0.066 Se quantum well laser structures: SQW, SCH-SQW, MQW, and MMQW. The current work is a continuation to previous publications where energy levels, modal gain, optical confinement, and total losses were published for these four structures assuming the energy bands are non-parabolic. The threshold current as a function of total losses, cavity length, and cavity end mirror reflectivity was obtained for these structures. It is shown that the threshold current decreases with a decrease in the cavity length and then increases at a critical cavity length. The effects of non-parabolicity on the threshold current values are more obvious for short cavities and decreases with an increase in cavity. Whether the SQW or the MQW is the better structure depends on the loss level. At low loss, the SQW laser is always better because of its lower current density where only one QW has to be inverted. At high loss, the MQW is always better because the phenomena of gain saturation can be avoided by increasing the number of QW's although the injected current to achieve this maximum gain also increases. Owing to this gain saturation effect, there exists an optimum number of QW's for minimizing the threshold current for a given total loss. At this typical value, the effects of non-parabolicity on the threshold current values can be neglected without loss of accuracy. However, there is a 20% shift in the output lasing energy that cannot be neglected.

Khodr, M.

2011-10-01

417

Atomic scale calculations for strain distribution and electronic structure of InAs pyramidal quantum dots on (100) GaAs  

Microsoft Academic Search

The theoretical investigations for the strain distribution and electronic structure of InAs pyramidal quantum dots (QDs) have been performed using the Keating potential and the sp3s* tight-binding method. The 161-, 1222-, and 4047-atom QDs on GaAs with no cap layers are studied. The strain energy is largest at the QD base layer and decreases rapidly with increasing distance from the

T. Saito; J. N. Schulman; Y. Arakawa

1998-01-01

418

Interaction analysis of HIV-1 antibody 2G12 and Man9GlcNAc2 ligand: Theoretical calculations by fragment molecular orbital and MD methods  

NASA Astrophysics Data System (ADS)

In HIV-1 infection, human antibody 2G12 is capable of recognizing the high-mannose glycans on the HIV-1 surface glycoprotein, gp120. To investigate the ligand binding mechanisms of antibody 2G12 with glycans aiming for the contribution to the medications, we carried out classical molecular dynamics (MD) simulations and ab initio fragment molecular orbital (FMO) calculations on the antibody 2G12 complex with its high-mannose ligand. We found that Mannose D1 of the ligand had the largest binding affinity with the antibody, which was well consistent with experimental reports. Furthermore, significant roles of Mannose 4 and 4? in the ligand binding were theoretically indicated.

Koyama, Yuka; Ueno-Noto, Kaori; Takano, Keiko

2013-07-01

419

New efficient approach to calculations of exciton resonance position and width for quantum-confined Stark effect in shallow quantum wells  

Microsoft Academic Search

We develop a new computationally efficient approach to the quantum-confined Stark effect in shallow quantum wells that provides a deeper physical insight, significantly reduces required computational resources, and yields some analytical results for the case of shallow quantum wells. The approach is based on a combination of the self-consistent field approach and the complex-coordinate exterior-scaling procedure that allows one to

I. V. Ponomarev; Lev Deych; Alexander Lisyansky

2004-01-01

420

Low temperature rate constants for the N + CN ? N2 + C reaction: two-dimensional quantum capture calculations on an accurate potential energy surface.  

PubMed

The title reaction is thought to be responsible for the production of molecular nitrogen in interstellar clouds. In this work, we report quantum capture calculations on a new two-dimensional potential energy surface determined by interpolating high-level ab initio data. The low-temperature rate constant calculated using a capture model is quite large and has a positive temperature dependence, in agreement with a recent experiment. The origin of the aforementioned behaviors of the rate constant is analyzed. PMID:22864388

Ma, Jianyi; Guo, Hua; Dawes, Richard

2012-09-21

421

Envelope Function Approximation (EFA) Bandstructure Calculations for III-V Non-square Stepped Alloy Quantum Wells Incorporating Ultra-narrow (˜5Å) Epitaxial Layers  

NASA Astrophysics Data System (ADS)

We describe Envelope Function Approximation (EFA) bandstructure calculations based on a 4-band electron (EL), heavy-hole (HH), light-hole (LH) and split-off hole (SO) effective mass Hamiltonian, with Burt-Foreman hermitianisation, which can handle III-V quantum well structures that incorporate ultra-narrow epi-layers. The model takes into account the coupling of EL, HH, LH and SO bands and is suitable for describing quantum wells tuned to the 1.0 - 1.55 ?m window exploited by optical fibre communication devices. We have used the multi-band solver to calculate the bandstructure of an illustrative InGaAsSb-AlGaSb non-square quantum well that incorporates 6Å potential “spikes” in its well region. Calculations based on the Burt-Foreman hermitianised Hamiltonian and those based on a Hamiltonian with standard “symmetrised” hermitianisation are presented and compared. When coupling to the conduction band is excluded from the calculation, the latter formulation leads to anomalous electron-like curvature of the dispersion curves for our spiked non-square quantum well structure.

Kaduki, K. A.; Batty, W.

2000-02-01

422

PREFACE: Proceedings of the First International Workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) (Nagoya, Japan, 2-4 July 2008) Proceedings of the First International Workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) (Nagoya, Japan, 2-4 July 2008)  

NASA Astrophysics Data System (ADS)

Both electron energy loss near edge structure (ELNES) spectroscopy and x-ray absorption near edge structure (XANES) spectroscopy provide information on the local structural and chemical environments of selected elements of interest. Recent technological progress in scanning transmission electron microscopy has enabled ELNES measurements with atomic column spatial resolution. Very dilute concentrations (nanograms per milliliter or ppb level) of dopants can be observed using third-generation synchrotron facilities when x-ray fluorescence is measured with highly efficient detectors. With such technical developments, ELNES and XANES have become established as essential tools in a large number of fields of natural science, including condensed matter physics, chemistry, mineralogy and materials science. In addition to these developments in experimental methodology, notable progress in reproducing spectra using theoretical methods has recently been made. Using first-principles methods, one can analyze and interpret spectra without reference to experiment. This is quite important since we are often interested in the analysis of exotic materials or specific atoms located at lattice discontinuities such as surfaces and interfaces, where appropriate experimental data are difficult to obtain. Using the structures predicted by reliable first-principles calculations, one can calculate theoretical ELNES and XANES spectra without too much difficulty even in such cases. Despite the fact that ELNES and XANES probe the same phenomenon—essentially the electric dipole transition from a core orbital to an unoccupied band—there have not been many opportunities for researchers in the two areas to meet and discuss. Theoretical calculations of ELNES spectra have been mainly confined to the electron microscopy community. On the other hand, the theory of XANES has been developed principally by researchers in the x-ray community. Publications describing the methods have been written more-or-less independently by the two communities. The three-day workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) was planned to help remedy this situation. It aimed to demonstrate capability of state-of-the-art theoretical techniques to explain and predict ELNES and XANES spectra, and to allow deep discussion between scientists in the two communities. It also provided an excellent opportunity to introduce experimentalists to the computational techniques available. Invited talks and poster presentations by leading scientists were given on the first day, which was followed by tutorial sessions for five computer programs on the second and third days. Excellent lectures were given by Peter Blaha (Vienna, Austria) on the WIEN2k code, Chris J Pickard (St Andrews, UK) on the CASTEP code, John J Rehr (Seattle, USA) on the FEFF8 code, Frank de Groot (Utrecht, The Netherlands) on the CTM4XAS code, and Hidekazu Ikeno (Kyoto, Japan) on the first-principles CI-multiplet code. Thanks to the enthusiastic participation of more than 100 scientists from around the world, the workshop was a complete success. The aim of this special issue in Journal of Physics: Condensed Matter is to share with the readers the most up-to-date knowledge presented at the workshop. We believe this will prove useful as a reference for researchers in many different fields, as well as an overview of the current status and future directions of theoretical calculations for ELNES and XANES. TEX2008 was a satellite meeting of the First International Symposium on Advanced Microscopy and Theoretical Calculations (AMTC1) (Nagoya, Japan, 29-30 June 2008), which was held in commemoration of the establishment of the Nanostuctures Research Laboratory (NSRL) at the Japan Fine Ceramics Center (JFCC) and as a daughter event of EXPO 2005, Aichi, Japan. A Grant-in-Aid for Scientific Research on Priority Areas 'Nano Materials Science for Atomic-Scale Modification' from the Ministry of Education, Culture, Sports and Technology (MEXT) and support from the Chubu Economic Federation for the workshop are grate

Tanaka, Isao; Mizoguchi, Teruyasu; Yamamoto, Tomoyuki

2009-03-01

423

Studies on adsorption of mono- and multi-chromophoric hemicyanine dyes on silver nanoparticles by surface-enhanced resonance raman and theoretical calculations  

NASA Astrophysics Data System (ADS)

Structural and vibrational properties of mono- and multichromophoric hemicyanine (HC) dyes in solution and adsorbed on silver-coated films have been investigated using optical absorption and resonance Raman scattering techniques, with interpretations aided by theoretical calculations. This is the first report on the Raman spectroscopic studies of multichromophoric HC derivatives. The structure of the monomer, N-propyl-4-(p-N,N-dimethylamino styryl)pyridinium bromide (HC3), and its charged and neutral silver complexes (HC3-Ag) in the ground electronic (S0) state were optimized using density functional calculations with the B3LYP method using the 6-31G* and LANL2DZ basis sets. The ground state structure of N-hexyl-4-(p-N,N-dimethylamino styryl)pyridinium bromide (HC6) and multichromophoric HC dyes were computed using the HF/6-31G* method. The negligible shift or broadening observed in the electronic absorption and resonance Raman spectra in solution with increasing size of the HC chromophore suggests that the excitations are localized within individual monomer units in bis and tetra chromophores. However, in the tris chromophore, considerable redshift and broadening were observed, indicating a significant electronic interaction between the nonbonded electrons of the N atom and the aromatic ?-system that is supported by the calculated excitation energies using the time-dependent density functional theory method. The effect of HC dye concentration on the electronic absorption spectra of the silver-coated film showed significant broadening, which was attributed to the formation of H- and J-aggregates in addition to the formation of a metal-molecule complex. A considerable redshift along various vibrations observed in the surface-enhanced resonance Raman scattering (SERRS) spectra of the HC derivatives indicates that adsorption on the silver surface leads to a considerable interaction of the electron rich moiety of HC derivatives with the silver surface. The enhancement of various in-plane and out-of-plane vibrations, along with slight broadening and redshifts observed in the SERRS spectra, suggests that binding of the HC dyes to the silver surface occurs through the aromatic ?-system attached to the electron rich dimethylamino group, with the ring lying almost parallel to the silver surface. Theoretical results have further indicated adsorption via chemisorption for the charged HC3-Ag complexes and by physisorption for the neutral HC3-Ag complexes.

Biswas, Nandita; Thomas, Susy; Kapoor, Sudhir; Mishra, Amaresh; Wategaonkar, Sanjay; Mukherjee, Tulsi

2008-11-01

424

Improved constrained optimization method for reaction-path determination in the generalized hybrid orbital quantum mechanical/molecular mechanical calculations  

NASA Astrophysics Data System (ADS)

The nudged elastic band (NEB) and string methods are widely used to obtain the reaction path of chemical reactions and phase transitions. In these methods, however, it is difficult to define an accurate Lagrangian to generate the conservative forces. On the other hand, the constrained optimization with locally updated planes (CO-LUP) scheme defines target function properly and suitable for micro-iteration optimizations in quantum mechanical/molecular mechanical (QM/MM) systems, which uses the efficient second order QM optimization. However, the method does have problems of inaccurate estimation of reactions and inappropriate accumulation of images around the energy minimum. We introduce three modifications into the CO-LUP scheme to overcome these problems: (1) An improved tangent estimation of the reaction path, which is used in the NEB method, (2) redistribution of images using an energy-weighted interpolation before updating local tangents, and (3) reduction of the number of constraints, in particular translation/rotation constraints, for improved convergence. First, we test the method on the isomerization of alanine dipeptide without QM/MM calculation, showing that the method is comparable to the string method both in accuracy and efficiency. Next, we apply the method for defining the reaction paths of the rearrangement reaction catalyzed by chorismate mutase (CM) and of the phosphoryl transfer reaction catalyzed by cAMP-dependent protein kinase (PKA) using generalized hybrid orbital QM/MM calculations. The reaction energy barrier of CM is in high agreement with the experimental value. The path of PKA reveals that the enzyme reaction is associative and there is a late transfer of the substrate proton to Asp 166, which is in agreement with the recently published result using the NEB method.

Jung, Jaewoon; Re, Suyong; Sugita, Yuji; Ten-no, Seiichiro

2013-01-01

425

A Theory of Physical Quantum Computation: The Quantum Computer Condition  

E-print Network

In this paper we present a new unified theoretical framework that describes the full dynamics of quantum computation. Our formulation allows any questions pertaining to the physical behavior of a quantum computer to be framed, and in principle, answered. We refer to the central organizing principle developed in this paper, on which our theoretical structure is based, as the *Quantum Computer Condition* (QCC), a rigorous mathematical statement that connects the irreversible dynamics of the quantum computing machine, with the reversible operations that comprise the quantum computation intended to be carried out by the quantum computing machine. Armed with the QCC, we derive a powerful result that we call the *Encoding No-Go Theorem*. This theorem gives a precise mathematical statement of the conditions under which fault-tolerant