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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

Quantum Chemical Calculations  

NASA Technical Reports Server (NTRS)

The current methods of quantum chemical calculations will be reviewed. The accent will be on the accuracy that can be achieved with these methods. The basis set requirements and computer resources for the various methods will be discussed. The utility of the methods will be illustrated with some examples, which include the calculation of accurate bond energies for SiF$_n$ and SiF$_n^+$ and the modeling of chemical data storage.

Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)

1997-01-01

3

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

4

Accurate quantum chemical calculations  

NASA Technical Reports Server (NTRS)

An important goal of quantum chemical calculations is to provide an understanding of chemical bonding and molecular electronic structure. A second goal, the prediction of energy differences to chemical accuracy, has been much harder to attain. First, the computational resources required to achieve such accuracy are very large, and second, it is not straightforward to demonstrate that an apparently accurate result, in terms of agreement with experiment, does not result from a cancellation of errors. Recent advances in electronic structure methodology, coupled with the power of vector supercomputers, have made it possible to solve a number of electronic structure problems exactly using the full configuration interaction (FCI) method within a subspace of the complete Hilbert space. These exact results can be used to benchmark approximate techniques that are applicable to a wider range of chemical and physical problems. The methodology of many-electron quantum chemistry is reviewed. Methods are considered in detail for performing FCI calculations. The application of FCI methods to several three-electron problems in molecular physics are discussed. A number of benchmark applications of FCI wave functions are described. Atomic basis sets and the development of improved methods for handling very large basis sets are discussed: these are then applied to a number of chemical and spectroscopic problems; to transition metals; and to problems involving potential energy surfaces. Although the experiences described give considerable grounds for optimism about the general ability to perform accurate calculations, there are several problems that have proved less tractable, at least with current computer resources, and these and possible solutions are discussed.

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

1989-01-01

5

Theoretical Calculations of Atomic Data for Spectroscopy  

E-print Network

Several different approximations and techniques have been developed for the calculation of atomic structure, ionization, and excitation of atoms and ions. These techniques have been used to compute large amounts of spectroscopic data of various levels of accuracy. This paper presents a review of these theoretical methods to help non-experts in atomic physics to better understand the qualities and limitations of various data sources and assess how reliable are spectral models based on those data.

Manuel A. Bautista

2000-06-20

6

Theoretical Calculations of Atomic Data for Spectroscopy  

NASA Technical Reports Server (NTRS)

Several different approximations and techniques have been developed for the calculation of atomic structure, ionization, and excitation of atoms and ions. These techniques have been used to compute large amounts of spectroscopic data of various levels of accuracy. This paper presents a review of these theoretical methods to help non-experts in atomic physics to better understand the qualities and limitations of various data sources and assess how reliable are spectral models based on those data.

Bautista, Manuel A.

2000-01-01

7

Energy calculations of quantum dot  

NASA Astrophysics Data System (ADS)

We calculated the total energy of a semiconductor quantum dot formed in gate and etching defined devices. A 3D Poisson equation is solved self-consistently to obtain the electron density and potential profile. The total energies of electrons in the quantum dots with two different sizes are calculated with three different approximations by using the density and potential obtained from self-consistent procedure. In our calculation we used a recently developed energy functional called “orbital-free energy functional”, Thomas-Fermi approximation and standard local-density approximation within density functional theory. The comparison of these methods reveals the efficacy of the used newly developed orbital-free energy functional which facilitates the calculation of Hartree integral for treatment of electron-electron interaction.

Bilgeç Akyüz, G.; Akgüngör, K.; ?akiro?lu, S.; Siddiki, A.; Sökmen, ?.

2011-06-01

8

Hybrid quantum teleportation: A theoretical model  

NASA Astrophysics Data System (ADS)

Hybrid quantum teleportation - continuous-variable teleportation of qubits - is a promising approach for deterministically teleporting photonic qubits. We propose how to implement it with current technology. Our theoretical model shows that faithful qubit transfer can be achieved for this teleportation by choosing an optimal gain for the teleporter's classical channel.

Takeda, Shuntaro; Mizuta, Takahiro; Fuwa, Maria; Yoshikawa, Jun-ichi; Yonezawa, Hidehiro; Furusawa, Akira

2014-12-01

9

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

10

Quantum turbulence: Theoretical and numerical problems  

NASA Astrophysics Data System (ADS)

The term “quantum turbulence” (QT) unifies the wide class of phenomena where the chaotic set of one dimensional quantized vortex filaments (vortex tangles) appear in quantum fluids and greatly influence various physical features. Quantum turbulence displays itself differently depending on the physical situation, and ranges from quasi-classical turbulence in flowing fluids to a near equilibrium set of loops in phase transition. The statistical configurations of the vortex tangles are certainly different in, say, the cases of counterflowing helium and a rotating bulk, but in all the physical situations very similar theoretical and numerical problems arise. Furthermore, quite similar situations appear in other fields of physics, where a chaotic set of one dimensional topological defects, such as cosmic strings, or linear defects in solids, or lines of darkness in nonlinear light fields, appear in the system. There is an interpenetration of ideas and methods between these scientific topics which are far apart in other respects. The main purpose of this review is to bring together some of the most commonly discussed results on quantum turbulence, focusing on analytic and numerical studies. We set out a series of results on the general theory of quantum turbulence which aim to describe the properties of the chaotic vortex configuration, starting from vortex dynamics. In addition we insert a series of particular questions which are important both for the whole theory and for the various applications. We complete the article with a discussion of the hot topic, which is undoubtedly mainstream in this field, and which deals with the quasi-classical properties of quantum turbulence. We discuss this problem from the point of view of the theoretical results stated in the previous sections. We also included section, which is devoted to the experimental and numerical suggestions based on the discussed theoretical models.

Nemirovskii, Sergey K.

2013-03-01

11

Information Theoretic Axioms for Quantum Theory  

E-print Network

In this paper we derive the complex Hilbert space formalism of quantum theory from four simple information theoretic axioms. It is shown that quantum theory is the only non classical probabilistic theory satisfying the following axioms: distinguishability, conservation, reversibility, composition. The new results of this reconstruction compared to other reconstructions by other authors are: (i) we get rid of axiom "subspace" in favor of axiom conservation eliminating mathematical requirements contained in previous axiomatics; (ii) we are able to classify all the probabilistic theories that are consistent requiring (a) only the first two axioms (b) only the first three axioms; this could be useful in experimental tests of quantum theory since it gives the possibility to understand whether or not other mathematical models could be consistent with such tests; (iii) we provide a connection between two different approaches to quantum foundations, quantum logic and the one based on information theoretic primitives showing that any theory satisfying the first two axioms given above either is classical or is a theory in which physical systems are described by a projective geometry.

Marco Zaopo

2012-05-10

12

Theoretical Calculation of Actinide Nuclear Reaction Data  

NASA Astrophysics Data System (ADS)

All cross sections, angular distributions, energy spectra of neutron, proton, deuteron, triton, helium and alpha-particle emission, as well as the prompt fission neutron spectra for n+232Th, 233,234,236,238U, 237Np, 239,240,241,242Pu and 241,242,243Am reactions are consistently calculated and analyzed at incident neutron energies from 0.01 to 200 MeV. Calculated results are compared with recent experimental data and other evaluated data from ENDF/B-VII and JENDL-3.

Han, Y.; Xu, Y.; Liang, H.; Guo, H.; Cai, C.; Shen, Q.

2014-04-01

13

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

2009-05-07

14

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

15

Photophysical study and theoretical calculations of an ionic liquid crystal bearing oxadiazole  

NASA Astrophysics Data System (ADS)

We report a detailed photophysical study of 1-dodecyl-4-[5-(4-dodecyloxyphenyl)-1,3,4-oxadiazole-2-yl]pyridinium bromide (454Do), a cationic amphiphile that behaves as a fluorescent liquid crystal. Excitation and emission spectra of the probe in different environments result in significant changes in quantum yields which are correlated with changes in lifetimes and theoretical calculations.

Pedro, Jorge A.; Mora, José R.; Westphal, Eduard; Gallardo, Hugo; Fiedler, Haidi D.; Nome, Faruk

2012-05-01

16

Calculations of theoretical strength: State of the art and history  

Microsoft Academic Search

Current state and historical evolution of theoretical strength calculations is presented as a brief overview completed by a database of selected theoretical and experimental results. Principles of a sophisticated analysis of mechanical stability of crystals are elucidated by means of a schematic example. Stability conditions and Jacobian matrixes are presented for selected crystalline symmetries and deformation paths. The importance of

J. Pokluda; M. ?erný; P. Šandera; M. Šob

2004-01-01

17

Theoretical investigation of photonic quantum wells and defects  

NASA Astrophysics Data System (ADS)

In this dissertation, band gaps of photonic crystal slabs are calculated and single and multiple photonic quantum well systems are theoretically investigated. A comprehensive study of defects in the photonic crystal is also presented in the dissertation. The major milestones and current developments in the photonic crystal research are briefly outlined in the introduction. Four theoretical approaches most commonly applied in the photonic crystal studies are reviewed. They are the plane wave expansion method, finite difference time domain method, transfer matrix method and modal expansion with R-matrix propagation algorithm. A comparison of these theoretical methods is discussed and the R-matrix formalism is implemented in the present work. The modal expansion with R-matrix propagation algorithm is applied to calculate the band gap for two-dimensional photonic crystal slabs and the results are compared with experimental measurements and with other numerical calculations. Excellent agreement with experiments is found and the R-matrix formalism proves to be more advantageous than other approaches. These advantages include its stability, efficiency and the fact that it can deal with finite photonic crystal slabs. The effect of the finite photonic slab on the band gap is also discussed. It is demonstrated that the band gap for a photonic slab structure can be controlled by the dielectric contrast, filling factor, filling geometry, lattice structure and polarization of the electric field. A photonic quantum well structure is proposed and investigated by the R-matrix algorithm. The band gap of photonic materials with periodic spatial modulation of the refractive index greater than unity can actually be regarded as a potential barrier for photons. Similar to the semiconductor quantum well systems, a photonic quantum well can be constructed by sandwiching a uniform medium between two photonic barriers due to the photonic band gap mismatch. The transmission and reflection coefficients of light through the photonic quantum well are calculated and the resonance tunneling through photonic quantum well structures is observed by varying either the well width or the frequency of incident light. Resonance peaks are found within the band gap region, indicating the existence of photon virtual states in the well. This is the first study of such heterostructure of photonic crystals with a potential of practical applications. The predictions of resonance tunneling in this dissertation are confirmed by experiments with excellent agreement. (Abstract shortened by UMI.)

Jiang, Yuankai

18

A quantum theoretical study of polyimides  

NASA Technical Reports Server (NTRS)

One of the most important contributions of theoretical chemistry is the correct prediction of properties of materials before any costly experimental work begins. This is especially true in the field of electrically conducting polymers. Development of the Valence Effective Hamiltonian (VEH) technique for the calculation of the band structure of polymers was initiated. The necessary VEH potentials were developed for the sulfur and oxygen atoms within the particular molecular environments and the explanation explored for the success of this approximate method in predicting the optical properties of conducting polymers.

Burke, Luke A.

1987-01-01

19

Sheaf-theoretic representation of quantum measure algebras  

SciTech Connect

We construct a sheaf-theoretic representation of quantum probabilistic structures, in terms of covering systems of Boolean measure algebras. These systems coordinatize quantum states by means of Boolean coefficients, interpreted as Boolean localization measures. The representation is based on the existence of a pair of adjoint functors between the category of presheaves of Boolean measure algebras and the category of quantum measure algebras. The sheaf-theoretic semantic transition of quantum structures shifts their physical significance from the orthoposet axiomatization at the level of events, to the sheaf-theoretic gluing conditions at the level of Boolean localization systems.

Zafiris, Elias [University of Athens, Institute of Mathematics, Panepistimiopolis, 15784 Athens (Greece)

2006-09-15

20

Sheaf-theoretic representation of quantum measure algebras  

Microsoft Academic Search

We construct a sheaf-theoretic representation of quantum probabilistic structures, in terms of covering systems of Boolean measure algebras. These systems coordinatize quantum states by means of Boolean coefficients, interpreted as Boolean localization measures. The representation is based on the existence of a pair of adjoint functors between the category of presheaves of Boolean measure algebras and the category of quantum

Elias Zafiris; Elias

2006-01-01

21

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

2008-12-12

22

Quantum chemical calculations of KTN solid solutions  

Microsoft Academic Search

The results of semi-empirical calculations for perovskite KNbxTa1?xO3 (KTN) solid solutions are presented for x = 0.04, 0.11, 0.89, and 0.96. Quantum chemical method of the Intermediate Neglect of the Differential Overlap (INDO) was combined with 135- and 320-atom supercells. Analysis of the optimised atomic and electronic structure has clearly demonstrated that several nearest Nb atoms substituting for Ta in

R. I Eglitis; E. A Kotomin; G Borstel

1998-01-01

23

Game-theoretic discussion of quantum state estimation and cloning  

E-print Network

We present a game-theoretic perspective on the problems of quantum state estimation and quantum cloning. This enables us to show why the focus on universal machines and the different measures of success, as employed in previous works, are in fact legitimite.

Chiu Fan Lee; Neil F. Johnson

2002-07-24

24

Green's functions technique for calculating the emission spectrum in a quantum dot-cavity system  

E-print Network

We introduce the Green's functions technique as an alternative theory to the quantum regression theorem formalism for calculating the two-time correlation functions in open quantum systems. In particular, we investigate the potential of this theoretical approach by its application to compute the emission spectrum of a dissipative system composed by a single quantum dot inside of a semiconductor cavity. We also describe a simple algorithm based on the Green's functions technique for calculating the emission spectrum of the quantum dot as well as of the cavity which can easily be implemented in any numerical linear algebra package. We find that the Green's functions technique demonstrates a better accuracy and efficiency in the calculation of the emission spectrum and it allows to overcome the inherent theoretical difficulties associated to the direct application of the quantum regression theorem approach.

Gomez, Edgar A; Vinck-Posada, Herbert

2015-01-01

25

Information Theoretical Analysis of Quantum Optimal Control  

E-print Network

We study the relations between classical information and the feasibility of accurate manipulation of quantum system dynamics. We show that if an efficient classical representation of the dynamics exists, optimal control ...

Montangero, S.

26

A Game Theoretic Approach to Quantum Information  

E-print Network

This work is an application of game theory to quantum information. In a state estimate, we are given observations distributed according to an unknown distribution $P_{\\theta}$ (associated with award $Q$), which Nature chooses at random from the set $\\{P_{\\theta}: \\theta \\in \\Theta \\}$ according to a known prior distribution $\\mu$ on $\\Theta$, we produce an estimate $M$ for the unknown distribution $P_{\\theta}$, and in the end, we will suffer a relative entropy cost $\\mathcal{R}(P;M)$, measuring the quality of this estimate, therefore the whole utility is taken as $P \\cdot Q -\\mathcal{R}(P; M)$. In an introduction to strategic game, a sufficient condition for minimax theorem is obtained; An estimate is explored in the frame of game theory, and in the view of convex conjugate, we reach one new approach to quantum relative entropy, correspondingly quantum mutual entropy, and quantum channel capacity, which are more general, in the sense, without Radon-Nikodym (RN) derivatives. Also the monotonicity of quantum relative entropy and the additivity of quantum channel capacity are investigated.

Xianhua Dai; V. P. Belavkin

2007-12-28

27

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

28

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

29

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

30

Limitations on information-theoretically-secure quantum homomorphic encryption  

NASA Astrophysics Data System (ADS)

Homomorphic encryption is a form of encryption which allows computation to be carried out on the encrypted data without the need for decryption. The success of quantum approaches to related tasks in a delegated computation setting has raised the question of whether quantum mechanics may be used to achieve information-theoretically-secure fully homomorphic encryption. Here we show, via an information localization argument, that deterministic fully homomorphic encryption necessarily incurs exponential overhead if perfect security is required.

Yu, Li; Pérez-Delgado, Carlos A.; Fitzsimons, Joseph F.

2014-11-01

31

Quantum Monte Carlo Calculations Applied to Magnetic Molecules  

SciTech Connect

We have calculated the equilibrium thermodynamic properties of Heisenberg spin systems using a quantum Monte Carlo (QMC) method. We have used some of these systems as models to describe recently synthesized magnetic molecules, and-upon comparing the results of these calculations with experimental data-have obtained accurate estimates for the basic parameters of these models. We have also performed calculations for other systems that are of more general interest, being relevant both for existing experimental data and for future experiments. Utilizing the concept of importance sampling, these calculations can be carried out in an arbitrarily large quantum Hilbert space, while still avoiding any approximations that would introduce systematic errors. The only errors are statistical in nature, and as such, their magnitudes are accurately estimated during the course of a simulation. Frustrated spin systems present a major challenge to the QMC method, nevertheless, in many instances progress can be made. In this chapter, the field of magnetic molecules is introduced, paying particular attention to the characteristics that distinguish magnetic molecules from other systems that are studied in condensed matter physics. We briefly outline the typical path by which we learn about magnetic molecules, which requires a close relationship between experiments and theoretical calculations. The typical experiments are introduced here, while the theoretical methods are discussed in the next chapter. Each of these theoretical methods has a considerable limitation, also described in Chapter 2, which together serve to motivate the present work. As is shown throughout the later chapters, the present QMC method is often able to provide useful information where other methods fail. In Chapter 3, the use of Monte Carlo methods in statistical physics is reviewed, building up the fundamental ideas that are necessary in order to understand the method that has been used in this work. With these ideas in hand, we then provide a detailed explanation of the current QMC method in Chapter 4. The remainder of the thesis is devoted to presenting specific results: Chapters 5 and 6 contain articles in which this method has been used to answer general questions that are relevant to broad classes of systems. Then, in Chapter 7, we provide an analysis of four different species of magnetic molecules that have recently been synthesized and studied. In all cases, comparisons between QMC calculations and experimental data allow us to distinguish a viable microscopic model and make predictions for future experiments. In Chapter 8, the infamous ''negative sign problem'' is described in detail, and we clearly indicate the limitations on QMC that are imposed by this obstacle. Finally, Chapter 9 contains a summary of the present work and the expected directions for future research.

Larry Engelhardt

2006-08-09

32

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

33

Ewald mesh method for quantum mechanical calculations  

PubMed Central

The Fourier transform Coulomb (FTC) method has been shown to be effective for the fast and accurate calculation of long-range Coulomb interactions between diffuse (low-energy cutoff) densities in quantum mechanical (QM) systems. In this work, we split the potential of a compact (high-energy cutoff) density into short-range and long-range components, similarly to how point charges are handled in the Ewald mesh methods in molecular mechanics simulations. With this linear scaling QM Ewald mesh method, the long-range potential of compact densities can be represented on the same grid as the diffuse densities that are treated by the FTC method. The new method is accurate and significantly reduces the amount of computational time on short-range interactions, especially when it is compared to the continuous fast multipole method. PMID:22443753

Chang, Chun-Min; Shao, Yihan; Kong, Jing

2012-01-01

34

Infrared and theoretical calculations in 2-halocycloheptanones conformational analysis.  

PubMed

2-Halocycloheptanones (Halo=F, Cl, Br and I) were synthesized and their conformational analysis was performed through infrared spectroscopy data. The corresponding conformers geometries and energies were obtained by theoretical calculations at B3LYP/aug-cc-pVDZ level of theory in the isolated state and in solution. It was observed, by both approaches, that the conformational preferences were very sensitive to the solvent polarity, since its increase led to an increase in the population of the more polar conformer. An analysis of these conformational equilibria showed they suffer also the influence of stereoelectronic effects, like hyperconjugation and steric effects. These results were interpreted using natural bond orbital (NBO) analysis, which indicated that the electronic delocalization to the orbital ?*(C=O) is directly involved in the stability increase of conformers I and II. The relative effect of the period of the halogen can also be noted, with changes in the conformational preferences and in the energies involved in the interactions of NBO. PMID:22534556

Rozada, Thiago C; Gauze, Gisele F; Favaro, Denize C; Rittner, Roberto; Basso, Ernani A

2012-08-01

35

Infrared and theoretical calculations in 2-halocycloheptanones conformational analysis  

NASA Astrophysics Data System (ADS)

2-Halocycloheptanones (Halo = F, Cl, Br and I) were synthesized and their conformational analysis was performed through infrared spectroscopy data. The corresponding conformers geometries and energies were obtained by theoretical calculations at B3LYP/aug-cc-pVDZ level of theory in the isolated state and in solution. It was observed, by both approaches, that the conformational preferences were very sensitive to the solvent polarity, since its increase led to an increase in the population of the more polar conformer. An analysis of these conformational equilibria showed they suffer also the influence of stereoelectronic effects, like hyperconjugation and steric effects. These results were interpreted using natural bond orbital (NBO) analysis, which indicated that the electronic delocalization to the orbital ?*Cdbnd O is directly involved in the stability increase of conformers I and II. The relative effect of the period of the halogen can also be noted, with changes in the conformational preferences and in the energies involved in the interactions of NBO.

Rozada, Thiago C.; Gauze, Gisele F.; Favaro, Denize C.; Rittner, Roberto; Basso, Ernani A.

36

Surface Segregation Energies of BCC Binaries from Ab Initio and Quantum Approximate Calculations  

NASA Technical Reports Server (NTRS)

We compare dilute-limit segregation energies for selected BCC transition metal binaries computed using ab initio and quantum approximate energy method. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent parameterization. Quantum approximate segregation energies are computed with and without atomistic relaxation. The ab initio calculations are performed without relaxation for the most part, but predicted relaxations from quantum approximate calculations are used in selected cases to compute approximate relaxed ab initio segregation energies. Results are discussed within the context of segregation models driven by strain and bond-breaking effects. We compare our results with other quantum approximate and ab initio theoretical work, and available experimental results.

Good, Brian S.

2003-01-01

37

Electron impact broadening of spectral lines in Be-like ions: quantum calculations  

NASA Astrophysics Data System (ADS)

We present in this paper quantum mechanical calculations for the electron impact Stark linewidths of the 2s3s-2s3p transitions for the four beryllium-like ions from N IV to Ne VII. Calculations are made in the frame of the impact approximation and intermediate coupling, taking into account fine-structure effects. A comparison between our calculations, experimental and other theoretical results, shows a good agreement. This is the first time that such a good agreement is found between quantum and experimental linewidths of highly charged ions.

Elabidi, Haykel; Ben Nessib, Nébil; Cornille, Marguerite; Dubau, Jacques; Sahal-Bréchot, Sylvie

2008-01-01

38

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

39

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

40

Theoretical analysis of quantum ghost imaging through turbulence  

Microsoft Academic Search

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 , Phys. Rev. APLRAAN1050-294710.1103\\/PhysRevA.83.051803 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

Kam Wai Clifford Chan; D. S. Simon; A. V. Sergienko; Nicholas D. Hardy; Jeffrey H. Shapiro; P. Ben Dixon; Gregory A. Howland; John C. Howell; Joseph H. Eberly; Malcolm N. O'Sullivan; Brandon Rodenburg; Robert W. Boyd

2011-01-01

41

Information-theoretic aspects of quantum inseparability of mixed states  

E-print Network

Information-theoretic aspects of quantum inseparability of mixed states are investigated in terms of the $\\alpha$-entropy inequalities and teleportation fidelity. Inseparability of mixed states is defined and a complete characterization of the inseparable $2\\times2$ systems with maximally disordered subsystems is presented within the Hilbert-Schmidt space formalism. A connection between teleportation and negative conditional $\\alpha$-entropy is also emphasized.

Ryszard Horodecki; Michal Horodecki

1996-07-08

42

Information–theoretic implications of quantum causal structures  

NASA Astrophysics Data System (ADS)

It is a relatively new insight of classical statistics that empirical data can contain information about causation rather than mere correlation. First algorithms have been proposed that are capable of testing whether a presumed causal relationship is compatible with an observed distribution. However, no systematic method is known for treating such problems in a way that generalizes to quantum systems. Here, we describe a general algorithm for computing information–theoretic constraints on the correlations that can arise from a given causal structure, where we allow for quantum systems as well as classical random variables. The general technique is applied to two relevant cases: first, we show that the principle of information causality appears naturally in our framework and go on to generalize and strengthen it. Second, we derive bounds on the correlations that can occur in a networked architecture, where a set of few-body quantum systems is distributed among some parties.

Chaves, Rafael; Majenz, Christian; Gross, David

2015-01-01

43

Information-theoretic implications of quantum causal structures.  

PubMed

It is a relatively new insight of classical statistics that empirical data can contain information about causation rather than mere correlation. First algorithms have been proposed that are capable of testing whether a presumed causal relationship is compatible with an observed distribution. However, no systematic method is known for treating such problems in a way that generalizes to quantum systems. Here, we describe a general algorithm for computing information-theoretic constraints on the correlations that can arise from a given causal structure, where we allow for quantum systems as well as classical random variables. The general technique is applied to two relevant cases: first, we show that the principle of information causality appears naturally in our framework and go on to generalize and strengthen it. Second, we derive bounds on the correlations that can occur in a networked architecture, where a set of few-body quantum systems is distributed among some parties. PMID:25562600

Chaves, Rafael; Majenz, Christian; Gross, David

2015-01-01

44

New Theoretical Approach to Quantum Size Effects of Interactive Electron-hole in Spherical Semiconductor Quantum Dots  

E-print Network

Semiconductor Quantum Dots B. Billaud and M. Picco Laboratoire de Physique Th´eorique et Hautes Energies (LPTHE semiconductor quantum dots is put to question. A sharper theoretical approach is suggested based on a new pseudo on their dimensionality, these structures are called quantum dots (0D), quantum wires (1D) or quantum wells (2D

Paris-Sud XI, Université de

45

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

46

Theoretical calculations and vibrational potential energy surface of 4-silaspiro(3,3)heptane  

SciTech Connect

Theoretical computations have been carried out on 4-silaspiro(3,3)heptane (SSH) in order to calculate its molecular structure and conformational energies. The molecule has two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. Energy calculations were carried out for different conformations of SSH. These results allowed the generation of a two-dimensional ring-puckering potential energy surface (PES) of the form V = a(x{sub 1}{sup 4} + x{sub 2}{sup 4}) – b(x{sub 1}{sup 2} + x{sub 2}{sup 2}) + cx{sub 1}{sup 2}x{sub 2}{sup 2}, where x{sub 1} and x{sub 2} are the ring-puckering coordinates for the two rings. The presence of sufficiently high potential energy barriers prevents the molecule from undergoing pseudorotation. The quantum states, wave functions, and predicted spectra resulting from the PESs were calculated.

Ocola, Esther J.; Medders, Cross; Laane, Jaan, E-mail: laane@mail.chem.tamu.edu [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States)] [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States); Meinander, Niklas [Department of Military Technology, Finnish National Defence University, P.O. Box 7, 00861 Helsinki (Finland)] [Department of Military Technology, Finnish National Defence University, P.O. Box 7, 00861 Helsinki (Finland)

2014-04-28

47

Metal Vapors in Gas Tungsten Arcs: Part II. Theoretical Calculations of Transport Properties  

E-print Network

( ( Metal Vapors in Gas Tungsten Arcs: Part II. Theoretical Calculations of Transport Properties G. J. DUNN and T. W. EAGAR Theoretical calculations of gas tungsten arc transport properties have, the effects of vapors emitted by the tungsten electrode may have a great effect on arc properties

Eagar, Thomas W.

48

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.

49

Molecular conformational stability and Spectroscopic analysis of Parared with experimental techniques and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The complete vibrational assignment and analysis of the fundamental modes of Parared 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 from the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of Parared have been computed using B3LYP quantum chemical calculations. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.

Srinivasaraghavan, R.; Thamaraikannan, S.; Seshadri, S.; Gnanasambandan, T.

2015-02-01

50

Molecular conformational stability and Spectroscopic analysis of Parared with experimental techniques and quantum chemical calculations.  

PubMed

The complete vibrational assignment and analysis of the fundamental modes of Parared 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 from the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of Parared have been computed using B3LYP quantum chemical calculations. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated. PMID:25305611

Srinivasaraghavan, R; Thamaraikannan, S; Seshadri, S; Gnanasambandan, T

2015-02-25

51

Information-Theoretic Implications of Quantum Causal Structures  

E-print Network

The correlations that can be observed between a set of variables depend on the causal structure underpinning them. Causal structures can be modeled using directed acyclic graphs, where nodes represent variables and edges denote functional dependencies. In this work, we describe a general algorithm for computing information-theoretic constraints on the correlations that can arise from a given interaction pattern, where we allow for classical as well as quantum variables. We apply the general technique to two relevant cases: First, we show that the principle of information causality appears naturally in our framework and go on to generalize and strengthen it. Second, we derive bounds on the correlations that can occur in a networked architecture, where a set of few-body quantum systems is distributed among a larger number of parties.

Rafael Chaves; Christian Majenz; David Gross

2014-07-14

52

Theoretical analysis of quantum ghost imaging through turbulence  

NASA Astrophysics Data System (ADS)

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 , Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.83.051803 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; Simon, D. S.; Sergienko, A. V.; Hardy, Nicholas D.; Shapiro, Jeffrey H.; Dixon, P. Ben; Howland, Gregory A.; Howell, John C.; Eberly, Joseph H.; O'Sullivan, Malcolm N.; Rodenburg, Brandon; Boyd, Robert W.

2011-10-01

53

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

54

Searching for the critical point of QCD: Theoretical benchmark calculations  

SciTech Connect

We present a comprehensive study of event-by-event multiplicity fluctuations in nucleon-nucleon and nucleus-nucleus interactions from the BNL Alternating Gradient Synchrotron/GSI Facility for Antiproton and Ion Research to BNL Relativistic Heavy Ion Collider energies within the ultrarelativistic quantum molecular dynamics transport approach. The scaled variances of negative, positive, and all charged hadrons are analyzed. The scaled variance in central Pb+Pb collisions increases with energy and behaves similar to inelastic p+p interactions. We find a nontrivial dependence of multiplicity fluctuations on the rapidity and transverse-momentum interval used for the analysis and on the centrality selection procedure. Quantitative predictions for the NA49 experiment are given, taking into account the acceptance of the detector and the selection procedure of central events.

Lungwitz, Benjamin; Bleicher, Marcus [Institut fuer Kernphysik, Johann Wolfgang Goethe Universitaet, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main (Germany)

2007-10-15

55

Potential theoretic methods for far field sound radiation calculations  

NASA Technical Reports Server (NTRS)

In the area of computational acoustics, procedures which accurately predict the far-field sound radiation are much sought after. A systematic development of such procedures are found in a sequence of papers by Atassi. The method presented here is an alternate approach to predicting far field sound based on simple layer potential theoretic methods. The main advantages of this method are: it requires only a simple free space Green's function, it can accommodate arbitrary shapes of Kirchoff surfaces, and is readily extendable to three-dimensional problems. Moreover, the procedure presented here, though tested for unsteady lifting airfoil problems, can easily be adapted to other areas of interest, such as jet noise radiation problems. Results are presented for lifting airfoil problems and comparisons are made with the results reported by Atassi. Direct comparisons are also made for the flat plate case.

Hariharan, S. I.; Stenger, Edward J.; Scott, J. R.

1995-01-01

56

Theoretical calculation of scattering efficiency of isotropic and anisotropic scattering particles employed in nanostructured solar cells  

NASA Astrophysics Data System (ADS)

Light scattering design in dye and quantum dot sensitized solar cells is one of the main concerns in enhancing their light harvesting efficiency, and also in improving their power conversion efficiency. Herein, we present a theoretical analysis to calculate the dependence of the light scattering efficiency in dye solar cells that have employed scattering agents with various sizes and morphologies incorporated in nanostructured photoanodes with different designs. Various isotropic and anisotropic nanostructures, including filled and hollow spheres, spherical voids, nanowires and hollow fibres in a size range of 100 nm to 900 nm, have been considered as scattering centres. The scattering materials are included in the photoanode of dye solar cells, either on top of the mesoporous layer or embedded in an active medium, and the scattering cross section has been calculated accordingly. The results indicate that employing hollow isotropic and anisotropic structures with thin wall thicknesses as a separate layer on top of the active meso-porous film may result in better scattering efficiency in the ultraviolet (UV) and visible wavelength range; however, a submicron filled sphere works better in near infrared (NIR) wavelength range. Incorporating anisotropic hollow fibres in the meso-porous photoelectrode will result in enhanced optical scattering features. The proposed model can provide a useful general framework for optimization of the photoanode of dye solar cells, employing various novel types of sensitizers.

Sasanpour, Pezhman; Mohammadpour, Raheleh

2014-05-01

57

Relativistic quantum mechanical calculations of electron-impact broadening for spectral lines in Be-like ions  

NASA Astrophysics Data System (ADS)

Aims: We present relativistic quantum mechanical calculations of electron-impact broadening of the singlet and triplet transition 2s3s ? 2s3p in four Be-like ions from N IV to Ne VII. Methods: In our theoretical calculations, the K-matrix and related symmetry information determined by the colliding systems are generated by the DARC codes. Results: A careful comparison between our calculations and experimental results shows good agreement. Our calculated widths of spectral lines also agree with earlier theoretical results. Our investigations provide new methods of calculating electron-impact broadening parameters for plasma diagnostics.

Duan, B.; Bari, M. A.; Wu, Z. Q.; Jun, Y.; Li, Y. M.; Wang, J. G.

2012-11-01

58

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

59

Monte-carlo calculations for some problems of quantum mechanics  

SciTech Connect

The Monte-Carlo technique for the calculations of functional integral in two one-dimensional quantum-mechanical problems had been applied. The energies of the bound states in some potential wells were obtained using this method. Also some peculiarities in the calculation of the kinetic energy in the ground state had been studied.

Novoselov, A. A., E-mail: novoselov@goa.bog.msu.ru; Pavlovsky, O. V.; Ulybyshev, M. V. [Moscow State University (Russian Federation)

2012-09-15

60

Macroscopic quantum-type potentials in theoretical systems biology.  

PubMed

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

2013-01-01

61

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

62

Continuum variational and diffusion quantum Monte Carlo calculations.  

PubMed

This topical review describes the methodology of continuum variational and diffusion quantum Monte Carlo calculations. These stochastic methods are based on many-body wavefunctions and are capable of achieving very high accuracy. The algorithms are intrinsically parallel and well suited to implementation on petascale computers, and the computational cost scales as a polynomial in the number of particles. A guide to the systems and topics which have been investigated using these methods is given. The bulk of the article is devoted to an overview of the basic quantum Monte Carlo methods, the forms and optimization of wavefunctions, performing calculations under periodic boundary conditions, using pseudopotentials, excited-state calculations, sources of calculational inaccuracy, and calculating energy differences and forces. PMID:21386247

Needs, R J; Towler, M D; Drummond, N D; López Ríos, P

2010-01-20

63

Quantum field theoretical description for the reflectivity of graphene  

E-print Network

We derive the polarization tensor of graphene at nonzero temperature in (2+1)-dimensional space-time. The obtained tensor coincides with the previously known one at all Matsubara frequencies, but, in contrast to it, admits analytic continuation to the real frequency axis satisfying all physical requirements. Using the obtained representation for the polarization tensor, we develope quantum field theoretical description for the reflectivity of graphene. The analytic asymptotic expressions for the reflection coefficients and reflectivities at low and high frequencies are derived for both independent polarizations of the electromagnetic field. The dependencies of reflectivities on the frequency and angle of incidence are investigated. Numerical computations using the exact expressions for the polarization tensor are performed and application regions for the analytic asymptotic results are determined.

Bordag, M; Mostepanenko, V M; Petrov, V M

2015-01-01

64

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

65

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

66

Studies on free energy calculations. II. A theoretical approach to molecular solvation  

E-print Network

Studies on free energy calculations. II. A theoretical approach to molecular solvation Haluk Resat methods of performing the thermodynamic integration in solvation free energy calculations are also at the particle creation limit in obtaining quantitatively reliable results for the solvation free energies. I

Mezei, Mihaly

67

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.

68

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

69

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

70

Theoretical Study of Electronic States and Spin Operation in Coupled Quantum Dots  

NASA Astrophysics Data System (ADS)

We theoretically study the electronic states and spin operation in coupled quantum dots, based on the calculations of many-body wavefunctions. We adopt a tight-binding model on a square lattice with a smooth tunnel barrier around its center. Taking into account the electron-electron interaction by the exact diagonalization method, we evaluate the spin coupling J between two electron spins, as a function of magnetic field perpendicular to the quantum dots, and show a transition from antiferromagnetic coupling (J > 0) to ferromagnetic coupling (J < 0). The coupling J is not seriously influenced by the size difference between the dots if the energy levels are tuned to match each other using the gate voltage. Next, we simulate SWAP gate operation by calculating the time development of two electron spins. A nonadiabatic change of the tunnel barrier between the quantum dots may cause operation errors, due to the contribution from high energy states. The complete exchange of the spin states could be also blocked by the spin-orbit interaction.

Goto, D.; Eto, M.

2008-10-01

71

Fidelity: A quantum information-theoretic approach to problems in condensed matter physics and quantum chaos  

NASA Astrophysics Data System (ADS)

In this dissertation, we address several problems in condensed matter physics, statistical mechanics, and quantum chaos from the perspective of the quantum information-theoretic notion of state distinguishability, as measured though evaluation of the appropriate fidelity measure. We find that the fidelity susceptibility, a measure for the response of the fidelity to infinitesimal changes of the Hamiltonian parameters, serves as a useful tool for studying the effects of disorder on quantum phase transitions. We study in detail the phase diagram of the well-known one-dimensional random quantum XY chain. Through an analysis of the fidelity susceptibility's finite-size scaling and statistics for this model, we find that the fidelity approach reflects large variation between average and typical behavior, may detect the presence of Griffiths phases, and indicates the modifications to the phase diagram due to disorder. For this same model, though without disorder, we evaluate the dynamics following a sudden Hamiltonian quench using the Loschmidt echo, a form of the fidelity that compares the initial state with the time-evolved state. Through a central limit theorem-type argument we find that the long-time statistics of the Loschmidt echo takes one of two universal forms, even at finite temperature, depending on the system's proximity to the quantum critical lines. Finally, for a canonical model exhibiting quantum chaos, the hydrogen atom in a uniform external magnetic field, we evaluate the operator fidelity susceptibility (OFS) between unitary operators generating the dynamics. We find that the part of the OFS which corresponds to the variation of the Hamiltonian eigenvectors serves to indicate the transition from the regular perturbative and n-mixing regimes to the quantum chaotic regime.

Jacobson, Noah Tobias

2011-12-01

72

Quantum Monte Carlo calculations of BiFeO3  

NASA Astrophysics Data System (ADS)

Multiferroic Bismuth Ferrite (BiFeO3) exhibits both ferroelectricity and antiferromagnetism, possibly enabling a connection between the two effects in the same material. While its antiferromagnetic character is relatively well-understood, experimental measurements of the spontaneous polarization vary significantly over two orders of magnitude, from 0.06 C/m^2 to 1.50 C/m^2. We cary out accurate quantum Monte Carlo calculations to estimate the cohesion energy and the ferroelectric distortion well depth. We discuss the mechanisms proposed to understand the variations of polarization experimental data in the light of our quantum Monte Carlo results.

Wagner, Lucas K.; Sulock, David; Mitas, Lubos

2007-03-01

73

Exact quantum dynamics calculations using a symmetrized Gaussian basis  

NASA Astrophysics Data System (ADS)

In a series of earlier articles, a new method was introduced for performing exact quantum dynamics calculations. The method uses a ``weylet'' basis set (orthogonalized Weyl-Heisenberg wavelets), combined with phase space truncation, to defeat the exponential scaling of CPU effort with system dimensionality that has long plagued such calculations. Here, we present results obtained using a basis of momentum-symmetrized Gaussians. Despite being non-orthogonal, symmetrized Gaussians do exhibit collectively locality, allowing for effective phase space truncation. Application to both isotropic uncoupled harmonic oscillators and coupled anharmonic oscillators are discussed. Results for uncoupled systems up to 15 dimensions are compared with previous weylet calculations and found to be essentially just as efficient. A ``universal'' code has been written, which is dimensionally independent, and which also exploits massively parallel algorithms. Using the new codes, calculations up to 27 dimensions have been achieved. Lastly, symmetrized Gaussian calculations for coupled anharmonic oscillators are analyzed, and compared to first order degenerate perturbation theory.

Halverson, Thomas; Poirier, Bill

2012-10-01

74

Theoretical calculation and vibrational spectral analysis of L-arginine trifluoroacetate  

NASA Astrophysics Data System (ADS)

Fourier transform infrared and Raman spectra of the nonlinear optical crystal, L-arginine trifluoroacetate ( L-arginine·CF 3COOH, abbreviated as LATF) have been calculated by the first-principles calculation and investigated in experiment. The calculated results are slightly different from those experimental values because of the distinction resulted from the intermolecular hydrogen bonds. The role of this type of intermolecular interaction on the crystal vibrational spectra and nonlinear optical properties has been discussed. The absorption-edge on the IR side has been estimated by the theoretical approach on basis of the calculated infrared spectrum, which will be meaningful for further research on NLO crystal.

Sun, Z. H.; Zhang, L.; Xu, D.; Wang, X. Q.; Liu, X. J.; Zhang, G. H.

2008-11-01

75

Determination of absolute configuration of natural products: theoretical calculation of electronic circular dichroism as a tool  

Technology Transfer Automated Retrieval System (TEKTRAN)

Determination of absolute configuration (AC) is one of the most challenging features in the structure elucidation of chiral natural products, especially those with complex structures. With revolutionary advancements in the area of quantum chemical calculations of chiroptical spectroscopy over the pa...

76

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

77

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

78

Quantum Monte Carlo calculations of BiFeO3  

Microsoft Academic Search

Multiferroic Bismuth Ferrite (BiFeO3) exhibits both ferroelectricity and antiferromagnetism, possibly enabling a connection between the two effects in the same material. While its antiferromagnetic character is relatively well-understood, experimental measurements of the spontaneous polarization vary significantly over two orders of magnitude, from 0.06 C\\/m^2 to 1.50 C\\/m^2. We cary out accurate quantum Monte Carlo calculations to estimate the cohesion energy

Lucas K. Wagner; David Sulock; Lubos Mitas

2007-01-01

79

Microcomputer Calculation of Theoretical Pre-Exponential Factors for Bimolecular Reactions.  

ERIC Educational Resources Information Center

Described is the application of microcomputers to predict reaction rates based on theoretical atomic and molecular properties taught in undergraduate physical chemistry. Listed is the BASIC program which computes the partition functions for any specific bimolecular reactants. These functions are then used to calculate the pre-exponential factor of…

Venugopalan, Mundiyath

1991-01-01

80

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

81

Theoretical Calculation of Electronic Circular Dichroism of a Hexahydroxydiphenoyl-Containing Flavanone Glycoside  

Technology Transfer Automated Retrieval System (TEKTRAN)

Time-dependent density functional theory (TDDFT) was employed for theoretical calculation of electronic circular dichroism (ECD) of a hexahydroxydiphenoyl (HHDP)-containing flavanone glycoside, mattucinol-7-O-[4'',6''-O-(aS)-hexahydroxydiphenoyl]-ß-d-glucopyranoside (2). It identified the roles of t...

82

Cavity ring-down spectroscopy and theoretical calculations of the S1,,1  

E-print Network

was prepared with a pulsed discharge slit nozzle and detected by cavity ring-down spectroscopy. A numberCavity ring-down spectroscopy and theoretical calculations of the S1,,1 B3u...]S0,,1 Ag of the trapped species with the solid lattice. This shortcoming was overcome by the application of cavity ring

83

Vibrational spectroscopic studies of Isoleucine by quantum chemical calculations.  

PubMed

In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of Isoleucine (2-Amino-3-methylpentanoic acid). The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments, thermodynamics properties, NBO analyses, NMR chemical shifts and ultraviolet-visible spectral interpretation of Isoleucine have been studied by performing MP2 and DFT/cc-pVDZ level of theory. The FTIR, FT-Raman spectra were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. The UV-visible absorption spectra of the compound were recorded in the range of 200-800 nm. Computational calculations at MP2 and B3LYP level with basis set of cc-pVDZ is employed in complete assignments of Isoleucine molecule on the basis of the potential energy distribution (PED) of the vibrational modes, calculated using VEDA-4 program. The calculated wavenumbers are compared with the experimental values. The difference between the observed and calculated wavenumber values of most of the fundamentals is very small. (13)C and (1)H nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method and compared with experimental results. The formation of hydrogen bond was investigated in terms of the charge density by the NBO calculations. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands were carried out. Besides, molecular electrostatic potential (MEP) were investigated using theoretical calculations. PMID:24508874

Moorthi, P P; Gunasekaran, S; Ramkumaar, G R

2014-04-24

84

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

85

QUANTUM CALCULATIONS: Quantum computer based on activated dielectric nanoparticles selectively interacting with short optical pulses  

NASA Astrophysics Data System (ADS)

The operation principle of a quantum computer is proposed based on a system of dielectric nanoparticles activated with two-level atoms — cubits, in which electric dipole transitions are excited by short intense optical pulses. It is proved that the logical operation (logical operator) CNOT (controlled NOT) is performed by means of time-dependent transfer of quantum information over `long' (of the order of 104 nm) distances between spherical nanoparticles owing to the delayed interaction between them in the optical radiation field. It is shown that one-cubit and two-cubit logical operators required for quantum calculations can be realised by selectively exciting dielectric particles with short optical pulses.

Gadomskii, Oleg N.; Kharitonov, Yu Ya

2004-03-01

86

Rotational isomerism of some chloroacetamides: Theoretical and experimental studies through calculations, infrared and NMR  

NASA Astrophysics Data System (ADS)

The geometries involved in the conformational equilibria of 2,2-dichloro-N-cyclohexyl-N-methyl-acetamide (DCCMA) and 2-chloro-N,N-dicyclohexylacetamide (CDCA) were investigated. Theoretical calculations at the B3LYP/cc-pVDZ level of theory showed that gauche forms (Clsbnd Csbnd Cdbnd O) are the most stable and the predominant conformers in isolated phase. Both compounds had the conformational behavior in solvents of different polarities estimated from theoretical calculations with the PCM (Polarizable Continuum Model), at the same level of theory, using infrared data from deconvolution of the carbonyl absorption bands and 13C NMR spectra. Their IR spectra showed two carbonyl absorptions and that the conformer with the highest dipole moment had its population increased when the most polar solvents were used, in accordance with the theoretical calculation in solution. 1JCH coupling constants were obtained from their NMR spectra, and revealed that there was population variation of conformers with solvent exchange. Experimental data (NMR and IR) as well as calculations including the solvent effects followed the same trend.

Santos, Marcela F.; Braga, Carolyne B.; Rozada, Thiago C.; Basso, Ernani A.; Fiorin, Barbara C.

2014-08-01

87

Variational calculations on the energy levels of graphene quantum antidots  

NASA Astrophysics Data System (ADS)

Within the Dirac-Weyl description of the graphene, the ground and low-lying excited state energies of a graphene quantum antidot subjected to a uniform static magnetic field is calculated by employing a variational scheme. The procedure is based on the choice of exact solutions of the Dirac-Weyl equation corresponding to massless fermions under the homogeneous magnetic field as basis sets for the trial wave functions. It is found that, for parabolic graphene antidots, the valley splitting occurs due to the introduction of spatial confinement, and it increases as the confinement strength increases. Furthermore, it is also investigated that, in such dot structures, switching an antidot potential on enhances this splitting. Therefore, we investigated that it is possible to control valley splitting by geometrical parameters of a graphene quantum antidot and/or by the strength of external magnetic field.

Kandemir, B. S.; Omer, G.

2013-07-01

88

Delay time calculation for dual-wavelength quantum cascade lasers  

SciTech Connect

In this paper, we calculate the turn-on delay (t{sub th}) and buildup (?t) times of a midinfrared quantum cascade laser operating simultaneously on two laser lines having a common upper level. The approach is based on the four-level rate equations model describing the variation of the electron number in the states and the photon number present within the cavity. We obtain simple analytical formulae for the turn-on delay and buildup times that determine the delay times and numerically apply our results to both the single and bimode states of a quantum cascade laser, in addition the effects of current injection on t{sub th} and ?t are explored.

Hamadou, A., E-mail: abd-hamado@yahoo.fr [Département des Sciences et Techniques, Faculté des Sciences et de la Technologie, Université de Bordj Bou Arreridj 34000 (Algeria); Laboratoire d’étude des surfaces et interfaces des matériaux solides (LESIMS), Sétif 19000 (Algeria); Lamari, S. [Laboratoire d’étude des surfaces et interfaces des matériaux solides (LESIMS), Sétif 19000 (Algeria); Département de Physique, Faculté des Sciences, Université Sétif 1, 19000 (Algeria); Thobel, J.-L. [Institut d'Electronique, de Microélectronique et de Nanotechnologie (IEMN), UMR 8520, Université Lille1, Avenue Poincaré, BP 60069, 59652 Villeneuve d'Ascq Cédex (France)

2013-11-28

89

Automatic generation of active coordinates for quantum dynamics calculations: Application to the dynamics of benzene photochemistry  

SciTech Connect

A new practical method to generate a subspace of active coordinates for quantum dynamics calculations is presented. These reduced coordinates are obtained as the normal modes of an analytical quadratic representation of the energy difference between excited and ground states within the complete active space self-consistent field method. At the Franck-Condon point, the largest negative eigenvalues of this Hessian correspond to the photoactive modes: those that reduce the energy difference and lead to the conical intersection; eigenvalues close to 0 correspond to bath modes, while modes with large positive eigenvalues are photoinactive vibrations, which increase the energy difference. The efficacy of quantum dynamics run in the subspace of the photoactive modes is illustrated with the photochemistry of benzene, where theoretical simulations are designed to assist optimal control experiments.

Lasorne, Benjamin; Sicilia, Fabrizio; Bearpark, Michael J.; Robb, Michael A. [Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ (United Kingdom); Worth, Graham A. [School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Blancafort, Lluis [Institut de Quimica Computacional and Departament de Quimica, Universitat de Girona, E-17071 Girona (Spain)

2008-03-28

90

Synthesis, structure, theoretical calculations and biological activity of sulfonate active ester new derivatives  

NASA Astrophysics Data System (ADS)

A series of naphthyl and tolyl sulfonate ester were synthesized and characterized by H NMR. X-ray single crystal diffraction experiments established the molecular structure of three new sulfonate esters derivatives, and spectral data agree with these in solution. The observed hydrogen bonding is discussed on the basis of crystal structural analyses and DFT/MP2 geometry optimization quantum calculations. Antimicrobial activities were screened for selected compounds against three human cancer cell lines and Mosquito Culex pipiens larvae.

Ghazzali, Mohamed; Khattab, Sherine A. N.; Elnakady, Yasser A.; Al-Mekhlafi, Fahd A.; Al-Farhan, Khalid; El-Faham, Ayman

2013-08-01

91

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

92

Quantum-mechanical calculations on molecular substructures involved in nanosystems.  

PubMed

In this review article, four ideas are discussed: (a) aromaticity of fullerenes patched with flowers of 6-and 8-membered rings, optimized at the HF and DFT levels of theory, in terms of HOMA and NICS criteria; (b) polybenzene networks, from construction to energetic and vibrational spectra computations; (c) quantum-mechanical calculations on the repeat units of various P-type crystal networks and (d) construction and stability evaluation, at DFTB level of theory, of some exotic allotropes of diamond D5, involved in hyper-graphenes. The overall conclusion was that several of the yet hypothetical molecular nanostructures herein described are serious candidates to the status of real molecules. PMID:25264833

Szefler, Beata; Diudea, Mircea V

2014-01-01

93

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

94

Theoretical calculation of the low-lying electronic states of the molecule BN  

NASA Astrophysics Data System (ADS)

The potential energy curves have been investigated for the 42 singlet, triplet, and quintet lowest electronic states in the ?(±)2s+1 representation below 95,000 cm-1 of the molecule BN via CASSCF and MRCI (singly and doubly excitation with Davidson correction) calculations. Eighteen electronic states have been investigated in the present work for the first time. The harmonic frequency ?e, the internuclear distance Re, the rotational constants Be, the electronic energy with respect to the ground state Te, and the static dipole moment have been calculated. A very good agreement has been noticed by comparing the present results with those reported in the literature, theoretically as well as experimentally.

Mahmoud, Salman; Bechelany, Mikhael; Miele, Philippe; Korek, Mahmoud

2015-01-01

95

Photoacoustic experimental studies on an AR coated laser window and some related theoretical calculations  

Microsoft Academic Search

Experimental photoacoustic spectroscopy (PAS) amplitude and phase results on an AR coated ZnSe laser window were obtained at 10.6 micrometers as a function of chopping frequency. The PAS phase angle varied by 20 deg between 1000 Hz and 50 Hz; 7 deg between 1000 Hz and 100 Hz. Theoretical calculations related to the situation were performed using the Bennett-Forman and

N. C. Fernelius

1980-01-01

96

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

97

Quantum electrodynamic calculation of quantum beats in a spontaneously radiating three level system  

Microsoft Academic Search

The coherence properties of a spontaneously radiating three-level atomic system are investigated in a first principle calculation that utilizes either coherent or incoherent preparation. Quantum beat phenomena are explained for the first time in a manner that reveals the statistical nature of the preparative step as well as a possible radiative correction to the beat frequency.

A. Schenzle; Richard G. Brewer

1975-01-01

98

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

99

Theoretical simulation of carrier capture and relaxation rates in quantum-dot semiconductor optical amplifiers  

NASA Astrophysics Data System (ADS)

Based on Auger scattering mechanism, carrier-carrier scattering dynamics between the two-dimensional carrier reservoir (also called wetting layer, i.e., WL) and the confined quantum dot ground and first excited state in quantum-dot semiconductor optical amplifiers (QD-SOAs) are investigated theoretically in this paper. The scattering rates for independent electron and hole densities are calculated. The results show an ultra-fast carrier capture (relaxation) rate up to 1 ps-1, and there is a complex dependence of the Coulomb scattering rates on the WL electron and hole densities. In addition, due to the different effective mass and the level distribution, the scattering rates for electron and hole are very different. Finally, in order to provide a direction to control (increase or decrease) the input current in realistic QD-SOA systems, a simple method is proposed to determine the trends of the carrier recovery rates with the WL carrier densities in the vicinity of the steady-state.

Wu, Yunhu; Zhang, Guoping; Guo, Ling; Li, Xiaoming; Qi, Guoqun

2014-06-01

100

Theoretical simulation of carrier capture and relaxation rates in quantum-dot semiconductor optical amplifiers  

SciTech Connect

Based on Auger scattering mechanism, carrier-carrier scattering dynamics between the two-dimensional carrier reservoir (also called wetting layer, i.e., WL) and the confined quantum dot ground and first excited state in quantum-dot semiconductor optical amplifiers (QD-SOAs) are investigated theoretically in this paper. The scattering rates for independent electron and hole densities are calculated. The results show an ultra-fast carrier capture (relaxation) rate up to 1 ps{sup ?1}, and there is a complex dependence of the Coulomb scattering rates on the WL electron and hole densities. In addition, due to the different effective mass and the level distribution, the scattering rates for electron and hole are very different. Finally, in order to provide a direction to control (increase or decrease) the input current in realistic QD-SOA systems, a simple method is proposed to determine the trends of the carrier recovery rates with the WL carrier densities in the vicinity of the steady-state.

Wu, Yunhu [College of Physical Science and Technology, Central China Normal University, Wuhan 430079 (China); Department of Physics, Kashi Normal College, Kashi 844006 (China); Zhang, Guoping, E-mail: gpzhang@phy.ccnu.edu.cn [College of Physical Science and Technology, Central China Normal University, Wuhan 430079 (China); Guo, Ling; Qi, Guoqun [Department of Physics, Kashi Normal College, Kashi 844006 (China); Li, Xiaoming [Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China)

2014-06-14

101

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

102

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

103

A combined study based on experimental analyses and theoretical calculations on properties of poly (lactic acid) under annealing treatment  

NASA Astrophysics Data System (ADS)

In this paper, the significance of annealing, in two different atmospheres (air and vacuum), on the surface characteristics of poly (lactic acid) (PLA) films was investigated. X-ray diffraction (XRD) measurements correlated to atomic force microscopy (AFM) observations of the cast PLA films show that thermal treatment under air atmosphere is responsible for a significant increase of crystallinity with the increase of temperature. However, band gap energy of the title compound is slightly affected by annealing at different temperatures. As for the untreated PLA, the molecular geometry was optimized using density functional theory (DFT/B3LYP) method with 6-31g (d) basis set in ground state. From the optimized geometry, HOMO and LUMO energies and quantum chemical parameters were performed at B3LYP/6-31g (d). The theoretical results, applied to simulated optical spectra of the compound, were compared to the observed ones. On the basis of theoretical vibrational analyses, the thermodynamic properties were calculated at different temperatures, revealing the correlation between internal energy (U), enthalpy (H), entropy (S), Free energy (G) and temperatures.

Loued, W.; Wéry, J.; Dorlando, A.; Alimi, K.

2015-02-01

104

A modular method for the efficient calculation of ballistic transport through quantum billiards  

E-print Network

a numerical method which allows to efficiently calculate quantum transport through phase-coherent scattering the quantum scattering problem of a large class of systems very efficiently. We will illustrate]. However, even for two-dimensional quantum dots ("quantum billiards") the numerical solution of the Schr

Florian, Libisch

105

Theoretical calculation and experimental study of acousto-optically Q-switched CO2 laser.  

PubMed

Using resonator inserted with acousto-optically modulator, the experiments of the compacted CO(2) laser were performed with Q-switch. According to various factors that influenced the output of laser, the theoretical calculation of its main parameters was conducted by Q-switched pulsed laser rate equations. Based on the results, the technical route and approach were presented for optimization design of this laser. The measured peak power of this laser device was more than 4000W and pulsed width was 180ns which agreed well with the theoretical calculation. The range of repetition frequency could adjust from 1 Hz to 100 kHz. The theoretical analyzes and experimental results showed that the acoustic traveling time of ultrasonic field could not influence the pulse width of laser so that it did not require inserting optical lens in the cavity to reduce the diameter of beam. The acoustic traveling time only extended the establishingtime of laser pulse. The optimum working frequency of laser is about 1 kHz, which it matched with the radiation life time (1 ms) of CO(2) molecular upper energy level. When the frequency is above 1 kHz, the pulse width of laser increased with the frequency. The full band of wavelength tuning between 9.2 microm and 10.8 microm was obtained by grating selection one by one which the measured spectrum lines were over 30 in the condition of Q-switch. PMID:20588363

Xie, Jijang; Guo, Ruhai; Li, Dianjun; Zhang, Chuansheng; Yang, Guilong; Geng, Yumin

2010-06-01

106

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

107

Correlation of Calculated Excited-state Energies and Experimental Quantum Yields of Luminescent Tb(III) ?-diketonates  

SciTech Connect

Theoretical calculations employing time dependent density functional theory (TDDFT) are used to characterize the excited states of Tb(III) ?-diketonate complexes. Calculated results are compared directly with experimental results that together show a correlation between relative quantum yields and the excited-state energies that depend on the electronic properties of the p,p’- substituent group associated with the coordinating N-donor neutral ligand. It is found that changes in the electron donating nature of the neutral ligand structure leads to shifts in the lowest triplet energy level of the complex that consequently changes the relative quantum yield. Thus providing critical direction for the synthesis of high quantum yield terbium complexes.

De Silva, Channa R.; Li, Jun; Zheng, Zhiping; Corrales, Louis R.

2008-05-22

108

Theoretical calculation of the melting curve of Cu-Zr binary alloys  

NASA Astrophysics Data System (ADS)

Helmholtz free energies of the dominant binary crystalline solids found in the Cu-Zr system at high temperatures close to the melting curve are calculated. Our theoretical approach combines fundamental measure density functional theory (applied to the hard-sphere reference system) and a perturbative approach to include the attractive interactions. The studied crystalline solids are Cu(fcc), Cu51Zr14 (? ), CuZr(B2), CuZr2(C11b), Zr(hcp), and Zr(bcc). The calculated Helmholtz free energies of crystalline solids are in good agreement with results from molecular-dynamics (MD) simulations. Using the same perturbation approach, the liquid phase free energies are calculated as a function of composition and temperature, from which the melting curve of the entire composition range of this system can be obtained. Phase diagrams are determined in this way for two leading embedded atom method potentials, and the results are compared with experimental data. Theoretical melting temperatures are compared both with experimental values and with values obtained directly from MD simulations at several compositions.

Gunawardana, K. G. S. H.; Wilson, S. R.; Mendelev, M. I.; Song, Xueyu

2014-11-01

109

Theoretical calculation of the melting curve of Cu-Zr binary alloys.  

PubMed

Helmholtz free energies of the dominant binary crystalline solids found in the Cu-Zr system at high temperatures close to the melting curve are calculated. Our theoretical approach combines fundamental measure density functional theory (applied to the hard-sphere reference system) and a perturbative approach to include the attractive interactions. The studied crystalline solids are Cu(fcc), Cu_{51}Zr_{14}(?), CuZr(B2), CuZr_{2}(C11b), Zr(hcp), and Zr(bcc). The calculated Helmholtz free energies of crystalline solids are in good agreement with results from molecular-dynamics (MD) simulations. Using the same perturbation approach, the liquid phase free energies are calculated as a function of composition and temperature, from which the melting curve of the entire composition range of this system can be obtained. Phase diagrams are determined in this way for two leading embedded atom method potentials, and the results are compared with experimental data. Theoretical melting temperatures are compared both with experimental values and with values obtained directly from MD simulations at several compositions. PMID:25493799

Gunawardana, K G S H; Wilson, S R; Mendelev, M I; Song, Xueyu

2014-11-01

110

A practical approach to the theoretical models to calculate NO parameters of the respiratory system.  

PubMed

Expired nitric oxide (NO) is used as a biomarker in different respiratory diseases. The recommended flow rate of 50 mL s?¹ (F(E)NO?.??) does not reveal from where in the lung NO production originated. Theoretical models of NO transfer from the respiratory system, linear or nonlinear approaches, have therefore been developed and applied. These models can estimate NO from distal lung (alveolar NO) and airways (bronchial flux). The aim of this study was to show the limitation in exhaled flow rate for the theoretical models of NO production in the respiratory system, linear and nonlinear models. Subjects (n = 32) exhaled at eight different flow rates between 10-350 mL s?¹ for the theoretical protocols. Additional subjects (n = 32) exhaled at tree flow rates (20, 100 and 350 mL s?¹) for the clinical protocol. When alveolar NO is calculated using high flow rates with the linear model, correction for axial back diffusion becomes negligible, -0.04 ppb and bronchial flux enhanced by 1.27. With Högman and Meriläinen algorithm (nonlinear model) the corrections factors can be understood to be embedded, and the flow rates to be used are ?20, 100 and ?350 mL s?¹. Applying these flow rates in a clinical setting any F(E)NO can be calculated necessitating fewer exhalations. Hence, measured F(E)NO?.?? 12.9 (7.2-18.7) ppb and calculated 12.9 (6.8-18.7) ppb. In conclusion, the only possibility to avoid inconsistencies between research groups is to use the measured NO values as such in modelling, and apply tight quality control to accuracies in both NO concentration and exhaled flow measurements. PMID:24565997

Högman, M; Thornadtsson, A; Hedenstierna, G; Meriläinen, P

2014-03-01

111

Molecular structures of benzoic acid and 2-hydroxybenzoic acid, obtained by gas-phase electron diffraction and theoretical calculations.  

PubMed

The structures of benzoic acid (C6H5COOH) and 2-hydroxybenzoic acid (C6H4OHCOOH) have been determined in the gas phase by electron diffraction using results from quantum chemical calculations to inform restraints used on the structural parameters. Theoretical methods (HF and MP2/6-311+G(d,p)) predict two conformers for benzoic acid, one which is 25.0 kJ mol(-1) (MP2) lower in energy than the other. In the low-energy form, the carboxyl group is coplanar with the phenyl ring and the O-H group eclipses the C=O bond. Theoretical calculations (HF and MP2/6-311+G(d,p)) carried out for 2-hydroxybenzoic acid gave evidence for seven stable conformers but one low-energy form (11.7 kJ mol(-1) lower in energy (MP2)) which again has the carboxyl group coplanar with the phenyl ring, the O-H of the carboxyl group eclipsing the C=O bond and the C=O of the carboxyl group oriented toward the O-H group of the phenyl ring. The effects of internal hydrogen bonding in 2-hydroxybenzoic acid can be clearly observed by comparison of pertinent structural parameters between the two compounds. These differences for 2-hydroxybenzoic acid include a shorter exocyclic C-C bond, a lengthening of the ring C-C bond between the substituents, and a shortening of the carboxylic single C-O bond. PMID:16836466

Aarset, Kirsten; Page, Elizabeth M; Rice, David A

2006-07-20

112

Some theoretical results on semiconductor spherical quantum dots B. Billaud a,b , T.T. Truong #,b  

E-print Network

Some theoretical results on semiconductor spherical quantum dots B. Billaud a,b , T.­T. Truong #,b approximation model to describe quantum e#ects in nanometric semiconductor Quantum Dots (QDs). This allows of visible light. Key words: spherical quantum dot, semiconductor, Stark e#ect, Lamb shift, Purcell e

113

Modeling Concept Combinations in a Quantum-theoretic Framework  

E-print Network

We present modeling for conceptual combinations which uses the mathematical formalism of quantum theory. Our model faithfully describes a large amount of experimental data collected by different scholars on concept conjunctions and disjunctions. Furthermore, our approach sheds a new light on long standing drawbacks connected with vagueness, or fuzziness, of concepts, and puts forward a completely novel possible solution to the 'combination problem' in concept theory. Additionally, we introduce an explanation for the occurrence of quantum structures in the mechanisms and dynamics of concepts and, more generally, in cognitive and decision processes, according to which human thought is a well structured superposition of a 'logical thought' and a 'conceptual thought', and the latter usually prevails over the former, at variance with some widespread beliefs

Diederik Aerts; Sandro Sozzo

2014-01-15

114

Shock wave induced decomposition of RDX: quantum chemistry calculations.  

PubMed

Quantum chemical calculations on single molecules were performed to provide insight into the decomposition mechanism of shocked RDX. These calculations complement time-resolved spectroscopy measurements on shock wave compressed RDX crystals (previous paper, this issue). It is proposed that unimolecular decomposition is the primary pathway for RDX decomposition in its early stages and at stresses lower than approximately 10 GPa. This decomposition leads to the generation of broadband emission from 350 to 850 nm. Chemiluminescence from (2)B1 and (2)B2 excited states of NO2 radicals is associated with a major portion of the experimentally observed emission spectrum (>400 nm). The remaining portion (<400 nm) of the emission spectrum primarily results from excited HONO intermediates. It is proposed that for stresses higher than 10 GPa, bimolecular reactions between radical decomposition products and unreacted RDX molecules become the dominant pathway. This radical assisted homolysis pathway is cyclic and leads to the acceleration of decomposition, with increased production of low energy NO2 radicals. These radicals produce emission that is stronger in the long wavelength portion of the spectrum. Finally, a comprehensive chemical decomposition mechanism is put forward that is consistent with the experimental observations of shock-induced emission in RDX crystals. PMID:18642890

Miao, Maosheng; Dreger, Zbigniew A; Patterson, James E; Gupta, Yogendra M

2008-08-14

115

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

116

Comment on ``Laboratory measurements and theoretical calculations of O2 A-band electric quadrupole transitions''  

NASA Astrophysics Data System (ADS)

D. A. Long [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.80.042513 80, 042513 (2009)] recently reported accurate measurements on the ultraweak electric quadrupole (E2) transitions in the O2 A band. They also presented elegant theoretical calculation of the line intensities based on Hund's case (b) formulation. However, their theoretical elucidation fails to relate to a highly relevant previous work by Balasubramanian and Narayanan [Acta Phys. Hung 74, 341 (1994)] in which closed-form expressions for the E2 branch line strengths for the eight possible rotational branches of the b1?g+-X3?g- transition, in intermediate coupling, are derived. The complete equivalence of the two methods is proven through direct calculation. A second point of concern is that the magnetic dipole (M1) transition moment M1 = 0.0687 ?B deduced by Long from the previously measured transition intensities is ˜2.7 times the ab initio value of 0.0255 ?B computed by Minaev [Chem. Phys.CMPHC20301-010410.1016/0301-0104(96)00126-7 208, 299 (1996)]. Since the latter reproduces closely the measured Einstein's spontaneous emission coefficient of the A band, this large discrepancy is intriguing.

Balasubramanian, T. K.; Mishra, A. P.

2011-11-01

117

Synthesis, characterization, optical properties and theoretical calculations of 6-fluoro coumarin.  

PubMed

6-Fluoro coumarin is synthesized and characterized by (1)H NMR and (13)C NMR. The optical properties of the title compound are investigated by UV-vis absorption and fluorescence emission spectra, the results show the title compound can absorb UV-vis light at 319, 269 and 215nm, moreover it exhibits blue-purple fluorescence emission at 416nm. Theoretical studies on molecular structure, infrared spectra (IR), nuclear magnetic resonance ((1)H NMR, (13)C NMR) chemical shifts, UV-vis absorption and fluorescence emission of the synthesized compound have been worked out. Most chemical calculations were performed by density functional theory (DFT) method at the B3LYP/6-311G(d,p) level (NMR at B3LYP/Aug-CC-Pvdz level) using Gaussian 09 program. The compared results reveal that the scaled theoretical vibrational frequencies are in good accordance with the observed spectra; computational chemical shifts are consistent with the experimental values in most parts, except for some minor deviations; the UV-vis absorption calculated matches the experimental one very well, and the fluorescence emission spectrum is in good agreement with the experimental one when the solute-solvent hydrogen-bonding interaction is considered. These good coincidences prove that the computational methods selected can be used to predict these properties of other similar materials where it is difficult to arrive at experimental results. PMID:24568846

Bai, Yihui; Du, Jinyan; Weng, Xuexiang

2014-05-21

118

Vibrational Spectra, Theoretical Calculations, and Two-Dimensional Potential Energy Surface for the Ring-Puckering Vibrations of 2,4,7-Trioxa[3.3.0]octane.  

PubMed

2,4,7-Trioxa[3.3.0]octane (247TOO) is an unusual bicyclic molecule which can exist in four different conformational forms which are determined by the directions of the two ring- puckering motions. The vibrational assignments of 247TOO have been made based on its infrared and Raman spectra and theoretical density functional theory (DFT) calculations. The two ring-puckering motions (in-phase and out-of-phase) were observed in the Raman spectra of the liquid at 249 and 205 cm(-1) and these values correspond well to the DFT values of 247 and 198 cm(-1). Ab initio calculations were utilized to calculate the structures and conformational energies for the four energy minima and the barriers to interconversion and the data was utilized to generate a two-dimensional potential energy surface (PES) for the two ring-puckering motions. The resulting quantum state energies for this PES were then calculated in order to better understand the patterns that are produced when the PES has four energy minima at different energy values. The wave functions corresponding to the different quantum states were also calculated. The NMR spectrum of 247TOO showed the presence of the two lowest energy conformations, consistent with the results of the ab initio calculations. PMID:25514365

Chun, Hye Jin; Meinander, Niklas; Villarreal, John R; Laane, Jaan

2015-01-15

119

Experimentation and Theoretic Calculation of a BODIPY Sensor Based on Photoinduced Electron Transfer for Ions Detection  

NASA Astrophysics Data System (ADS)

A boron-dipyrromethene (BODIPY)-based fluorescence probe with a N,N'-(pyridine-2, 6-diylbis(methylene))-dianiline substituent (1) has been prepared by condensation of 2,6-pyridinedicarboxaldehyde with 8-(4-amino)-4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene and reduction by NaBH4. The sensing properties of compound 1 toward various metal ions are investigated via fluorometric titration in methanol, which show highly selective fluorescent turn-on response in the presence of Hg2+ over the other metal ions, such as Li+, Na+, K+, Ca2+, Mg2+, Pb2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ag+, and Mn2+. Computational approach has been carried out to investigate the mechanism why compound 1 provides different fluorescent signal for Hg2+ and other ions. Theoretic calculations of the energy levels show that the quenching of the bright green fluorescence of boradiazaindacene fluorophore is due to the reductive photoinduced electron transfer (PET) from the aniline subunit to the excited state of BODIPY fluorophore. In metal complexes, the frontier molecular orbital energy levels changes greatly. Binding Zn2+ or Cd2+ ion leads to significant decreasing of both the HOMO and LUMO energy levels of the receptor, thus inhibit the reductive PET process, whereas an oxidative PET from the excited state fluorophore to the receptor occurs, vice versa, which also quenches the fluorescence. However, for 1-Hg2+ complex, both the reductive and oxidative PETs are prohibited; therefore, strong fluorescence emission from the fluorophore can be observed experimentally. The agreement of the experimental results and theoretic calculations suggests that our calculation method can be applicable as guidance for the design of new chemosensors for other metal ions.

Lu, Hua; Zhang, Shushu; Liu, Hanzhuang; Wang, Yanwei; Shen, Zhen; Liu, Chungen; You, Xiaozeng

2009-12-01

120

Thermochemical properties and contribution groups for ketene dimers and related structures from theoretical calculations.  

PubMed

This research's main goals were to analyze ketene dimers' relative stability and expand group additivity value (GAV) methodology for estimating the thermochemical properties of high-weight ketene polymers (up to tetramers). The CBS-Q multilevel procedure and statistical thermodynamics were used for calculating the thermochemical properties of 20 cyclic structures, such as diketenes, cyclobutane-1,3-diones, cyclobut-2-enones and pyran-4-ones, as well as 57 acyclic base compounds organized into five groups. According to theoretical heat of formation predictions, diketene was found to be thermodynamically favored over cyclobutane-1,3-dione and its enol-tautomeric form (3-hydroxycyclobut-2-enone). This result did not agree with old combustion experiments. 3-Hydroxycyclobut-2-enone was found to be the least stable dimer and its reported experimental detection in solution may have been due to solvent effects. Substituted diketenes had lower stability than substituted cyclobutane-1,3-diones with an increased number of methyl substituents, suggesting that cyclobutane-1,3-dione type dimers are the major products because of thermodynamic control of alkylketene dimerization. Missing GAVs for the ketene dimers and related structures were calculated through linear regression on the 57 acyclic base compounds. Corrections for non next neighbor interactions (such as gauche, eclipses, and internal hydrogen bond) were needed for obtaining a highly accurate and precise regression model. To the best of our knowledge, the hydrogen bond correction for GAV methodology is the first reported in the literature; this correction was correlated to MP2/6-31Gdagger and HF/6-31Gdagger derived geometries to facilitate its application. GAVs assessed by the linear regression model were able to reproduce acyclic compounds' theoretical thermochemical properties and experimental heat of formation for acetylacetone. Ring formation and substituent position corrections were calculated by consecutively replacing the GAVs regarding the 20 cyclic structures' thermochemical properties. PMID:19572711

Morales, Giovanni; Martínez, Ramiro

2009-07-30

121

Benchmark Quantum Monte Carlo Calculations of Optical gaps of carbon Nanotubes  

NASA Astrophysics Data System (ADS)

Optical properties of single wall carbon nanotubes SWCNT have attracted considerable experimental and theoretical attention because they are strongly dependent on the details of the atomic structure (chiral vector). In these systems electronic correlations have been shown to play a dominant role both theoretically [1] and experimentally [2] as electron-electron interactions are increased in low dimensions. In this talk we present ongoing calculations of the optical gaps and quasi-particle energies of SWCNT with an alternative ab-initio technique: Diffusion Quantum Monte Carlo (DMC). We take advantage of a novel algorithm based on non-orthogonal localized orbitals that allows almost linear scaling calculations for ˜1000 electrons. DMC is a complementary technique to methods based on the GW approximation and the Bethe-Salpeter equation avoiding strong approximations. While the full absorption spectra cannot be obtained with DMC, we provide accurate benchmark values for the quasiparticle energy gaps and exciton binding energies. Research sponsored by the Division of Materials Sciences and Engineering, U. S. DOE, under Contract DE-AC05-00OR22725 with UT-Battelle, LLC. and by the Division of Scientific User Facilities, U. S. DOE. This work used resources of the NCCS at ORNL. [1] C. S. Spataru, PRL 92, 077402 (2004). [2] Z. Wang PRL 96, 047403 (2006)

Reboredo, Fernando; Kent, Paul

2007-03-01

122

The rigorous stochastic matrix multiplication scheme for the calculations of reduced equilibrium density matrices of open multilevel quantum systems  

SciTech Connect

Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.

Chen, Xin, E-mail: xin.chen.nj@gmail.com [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)] [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2014-04-21

123

Theoretical calculations for structural, elastic, and thermodynamic properties of RuN2 under high pressure  

NASA Astrophysics Data System (ADS)

The structural and elastic properties of RuN2 were investigated through the first-principles calculation using generalized gradient approximation (GGA) and local density approximation (LDA) within the plane-wave pseudopotential density functional theory. The obtained equilibrium structure and mechanical properties are in excellent agreement with other theoretical results. Then we compared the elastic modulus of RuN2 with several other isomorphic noble metal nitrides. Results show that RuN2 can nearly rival with OsN2 and IrN2, which indicate RuN2 is a potentially ultra-incompressible and hard material. By the elastic stability criteria, it is predicted that RuN2 is stable in our calculations (0-100 GPa). The calculated B/G ratios indicate that RuN2 possesses brittle nature at 0 GPa and when the pressure increases to 13.4 GPa (for LDA) or 20.8 GPa (for GGA), it begins to prone to ductility. Through the quasi-harmonic Debye model, we also investigated the thermodynamic properties of RuN2.

Dong, Bing; Zhou, Xiao-Lin; Liu, Ke; Chang, Jing

2014-08-01

124

Vibrational spectra and density functional theoretical calculations on the anti-neurodegenerative drug: Orphenadrine hydrochloride  

NASA Astrophysics Data System (ADS)

Vibrational spectral analysis and quantum chemical computations based on density functional theory have been performed on the anti-neuro-degenerative drug Orphenadrine hydrochloride. The geometry, intermolecular hydrogen bond, and harmonic vibrational frequencies of the title molecule have been investigated with the help of B3LYP method. The calculated molecular geometry has been compared with the experimental data. The various intramolecular interactions have been exposed by natural bond orbital analysis. The distribution of Mulliken atomic charges and bending of natural hybrid orbitals also reflect the presence of intramolecular hydrogen bonding. The analysis of the electron density of HOMO and LUMO gives an idea of the delocalization and low value of energy gap indicates electron transport in the molecule and thereby bioactivity. Effective docking of the drug molecule with NMDA receptor subunit 3A also enhances its bioactive nature.

Edwin, Bismi; Hubert Joe, I.

2012-11-01

125

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

126

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

127

A quantum Monte Carlo calculation of the ground state energy of the hydrogen molecule  

E-print Network

A quantum Monte Carlo calculation of the ground state energy of the hydrogen molecule Carol A of the hydrogen molecule using the quantum Monte Carlo (QMC) method of solving the Schrodinger equation, without protons). Two different methods were employed: the diffusion quantum Monte Carlo (DQMC) method

Anderson, James B.

128

Predicting heats of formation of energetic materials using quantum mechanical calculations  

Microsoft Academic Search

Quantum mechanical calculations are used to predict gas, liquid, and solid heats of formation of energetic molecules. A simple atom-equivalent method converts quantum mechanical energies of molecules and their atomic constituents to gas-phase heats of formation of energetic materials. Functional relationships between heats of vaporization and sublimation and properties associated with quantum mechanically determined electrostatic potentials of isolated molecules are

BETSY M. RICE; SHARMILA V. PAI; Jennifer Hare

1999-01-01

129

Europium doped zinc sulfide: a correlation between experimental and theoretical calculations.  

PubMed

This paper presents the correlation among electronic and optical property effects induced by the addition of different concentrations of europium (Eu3+) in zinc sulfide (ZnS) by microwave-assisted solvothermal (MAS) method. A shift of the photoluminescence (PL) emission was observed with the increase of Eu3+. The periodic DFT calculations with the B3LYP hybrid functional were performed using the CRYSTAL computer code. The UV-vis spectra and theoretical results indicate a decrease in behavior of the energy gap as a function of dopant concentration. Therefore, new localized states are generated in the forbidden band gap region, the new states increase the probability of less energy transitions which may be responsible for a red shift in the PL bands spectrum. PMID:25081607

Ferrer, Mateus M; de Santana, Yuri V B; Raubach, Cristiane W; La Porta, Felipe A; Gouveia, Amanda F; Longo, Elson; Sambrano, Julio R

2014-08-01

130

Heats of Segregation of BCC Binaries from ab Initio and Quantum Approximate Calculations  

NASA Technical Reports Server (NTRS)

We compare dilute-limit heats of segregation for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent LMTO-based parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation, while the ab initio calculations are performed without relaxation. Results are discussed within the context of a segregation model driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.

Good, Brian S.

2004-01-01

131

Conformational preferences for some 5-substituted 2-acetylthiophenes through infrared spectroscopy and theoretical calculations  

NASA Astrophysics Data System (ADS)

The s- cis- trans isomerisms of some derivatives of thiophene (2-acetyl, AT; 2-acetyl-5-bromo, ABT and 2-acetyl-5-chloro, ACT) were analyzed, using data from deconvolution of their carbonyl absorption bands in two solvents (CCl 4 and CHCl 3). These infrared data showed that the O,S- cis conformer largely predominates in the studied solvents and that the same occurs in the gas phase, as observed from theoretical calculations. The latter results were obtained using B3LYP/6-311++G(3df,3p) and MP2/6-311++G(3df,3p) levels of theory, with zero-point energy correction. Moreover, the use of the IEFPCM (Integral Equation Formalism Polarizable Continuum Model) to take into account the solvent effects, using the same levels of theory, confirmed the results observed from infrared data. Low temperature 13C NMR spectra in CS 2/CD 2Cl 2 (-90 °C) and in acetone- d6 (-80 °C) did not show pairs of signals for each carbon, due to the known low energy barrier (˜8 kcal mol -1) for the cis- trans interconversion. Data from NBO calculations show that the n??S-C5* and n??C2-C3* interactions occur only in the O,S -cis isomer and can explain its conformational preference.

Rittner, Roberto; Ducati, Lucas C.; Tormena, Cláudio F.; Fiorin, Barbara C.; Braga, Carolyne B.

2011-09-01

132

Conformational preferences for some 5-substituted 2-acetylthiophenes through infrared spectroscopy and theoretical calculations.  

PubMed

The s-cis-trans isomerisms of some derivatives of thiophene (2-acetyl, AT; 2-acetyl-5-bromo, ABT and 2-acetyl-5-chloro, ACT) were analyzed, using data from deconvolution of their carbonyl absorption bands in two solvents (CCl4 and CHCl3). These infrared data showed that the O,S-cis conformer largely predominates in the studied solvents and that the same occurs in the gas phase, as observed from theoretical calculations. The latter results were obtained using B3LYP/6-311++G(3df,3p) and MP2/6-311++G(3df,3p) levels of theory, with zero-point energy correction. Moreover, the use of the IEFPCM (Integral Equation Formalism Polarizable Continuum Model) to take into account the solvent effects, using the same levels of theory, confirmed the results observed from infrared data. Low temperature 13C NMR spectra in CS2/CD2Cl2 (-90 °C) and in acetone-d6 (-80°C) did not show pairs of signals for each carbon, due to the known low energy barrier (?8 kcal mol(-1)) for the cis-trans interconversion. Data from NBO calculations show that the nO(2)??S-C5* and nO(2)??C2-C3* interactions occur only in the O,S-cis isomer and can explain its conformational preference. PMID:21620762

Rittner, Roberto; Ducati, Lucas C; Tormena, Cláudio F; Fiorin, Barbara C; Braga, Carolyne B

2011-09-01

133

[Chloro(difluoro)acetyl]phosphoramidic acid dichloride ClF 2CC(O)NHP(O)Cl 2, synthesis, vibrational and NMR spectra and theoretical calculations  

NASA Astrophysics Data System (ADS)

The synthesis of a new carbacylamidophosphate compound, [chloro(difluoro)acetyl]phosphoramidic acid dichloride (ClF 2CC(O)NHP(O)Cl 2), is reported along with its FTIR, Raman and mass spectra. The theoretical vibrational spectra were used to perform a tentative assignment of the observed bands. Quantum chemical calculations were realized with ab initio and density functional theory (DFT) methods using different levels of approximation. The title compound was analyzed as a dimer with C i symmetry (C dbnd O double bond in anti position with respect to the P dbnd O double bond). The simulation of the potential energy surface was performed varying the dihedral angles ?(Cl sbnd C sbnd C sbnd N) and ?(C sbnd C sbnd N sbnd P) using HF and B3LYP methods. The harmonic vibrations obtained by all theoretical methods are in good agreement with the experimental results. 1H, 13C and 31P NMR are also reported.

Iriarte, Ana G.; Erben, Mauricio F.; Gholivand, Khodayar; Jios, Jorge L.; Ulic, Sonia E.; Della Védova, Carlos O.

2008-08-01

134

Nitrogen-broadened lineshapes in the oxygen A-band: Experimental results and theoretical calculations  

NASA Astrophysics Data System (ADS)

We report measurements for N 2-broadening, pressure-shift and line mixing coefficients for 55 oxygen transitions in the A-band retrieved using a multispectrum fitting technique. Nineteen laboratory absorption spectra were recorded at 0.02 cm -1 resolution using a multi-pass absorption cell with path length of 1636.9 cm and the IFS 120 Fourier transform spectrometer located at Justus-Liebig-University in Giessen, Germany. The total sample pressures ranged from 8.8 to 3004.5 Torr with oxygen volume mixing ratios in nitrogen ranging between 0.057 and 0.62. An Exponential Power Gap (EPG) scaling law was used to calculate the N 2-broadening and N 2-line mixing coefficients. The line broadening and shift coefficients for the A-band of oxygen self-perturbed and perturbed by N 2 are modeled using semiclassical calculations based on the Robert-Bonamy formalism and two intermolecular potentials. These potentials involve electrostatic contributions including the hexadecapole moment of the molecules and (a) a simple dispersion contribution with one adjustable parameter to fit the broadening coefficients or (b) the atom-atom Lennard-Jones model without such adjustable parameters. The first potential leads to very weak broadening coefficients for high J transitions whereas the second potential gives much more improved results at medium and large J values, in reasonable agreement with the experimental data. For the line shifts which mainly arise in our calculation from the electronic state dependence of the isotropic potential, their general trends with increasing J values can be well predicted, especially from the first potential. From the theoretical results, we have derived air-broadening and air-induced shift coefficients with an agreement comparable to that obtained for O 2-O 2 and O 2-N 2.

Predoi-Cross, Adriana; Holladay, Christopher; Heung, Henry; Bouanich, Jean-Pierre; Mellau, Georg Ch.; Keller, Reimund; Hurtmans, Daniel R.

2008-09-01

135

A pedagogical introduction to quantum integrability, with a view towards theoretical high-energy physics  

E-print Network

These are lecture notes of an introduction to quantum integrability given at the Tenth Modave Summer School in Mathematical Physics, 2014, aimed at PhD candidates and junior researchers in theoretical physics. We introduce spin chains and discuss the coordinate Bethe Ansatz (CBA) for a representative example: the Heisenberg XXZ model. The focus lies on the structure of the CBA and on its main results, deferring a detailed treatment of the CBA for the general $M$-particle sector of the XXZ model to an appendix. Subsequently the transfer-matrix method is discussed for the six-vertex model, uncovering a relation between that model and the XXZ spin chain. Equipped with this background the quantum inverse-scattering method (QISM) and algebraic Bethe Ansatz (ABA) are treated. We emphasize the use of graphical notation for algebraic quantities as well as computations. Finally we turn to quantum integrability in the context of theoretical high-energy physics. We discuss factorized scattering in two-dimensional QFT, and conclude with a qualitative introduction to one current research topic relating quantum integrability to theoretical high-energy physics: the Bethe/gauge correspondence.

J. Lamers

2015-01-27

136

Supercomputer requirements for theoretical chemistry  

SciTech Connect

Many problems important to the theoretical chemist would, if implemented in their full complexity, strain the capabilities of today's most powerful computers. Several such problems are now being implemented on the CRAY-1 computer at Los Alamos. Examples of these problems are taken from the fields of molecular electronic structure calculations, quantum reactive scattering calculations, and quantum optics. 12 figures.

Walker, R.B.; Hay, P.J.; Galbraith, H.W.

1980-01-01

137

Feeding biomechanics and theoretical calculations of bite force in bull sharks (Carcharhinus leucas) during ontogeny.  

PubMed

Evaluations of bite force, either measured directly or calculated theoretically, have been used to investigate the maximum feeding performance of a wide variety of vertebrates. However, bite force studies of fishes have focused primarily on small species due to the intractable nature of large apex predators. More massive muscles can generate higher forces and many of these fishes attain immense sizes; it is unclear how much of their biting performance is driven purely by dramatic ontogenetic increases in body size versus size-specific selection for enhanced feeding performance. In this study, we investigated biting performance and feeding biomechanics of immature and mature individuals from an ontogenetic series of an apex predator, the bull shark, Carcharhinus leucas (73-285cm total length). Theoretical bite force ranged from 36 to 2128N at the most anterior bite point, and 170 to 5914N at the most posterior bite point over the ontogenetic series. Scaling patterns differed among the two age groups investigated; immature bull shark bite force scaled with positive allometry, whereas adult bite force scaled isometrically. When the bite force of C. leucas was compared to those of 12 other cartilaginous fishes, bull sharks presented the highest mass-specific bite force, greater than that of the white shark or the great hammerhead shark. A phylogenetic independent contrast analysis of anatomical and dietary variables as determinants of bite force in these 13 species indicated that the evolution of large adult bite forces in cartilaginous fishes is linked predominantly to the evolution of large body size. Multiple regressions based on mass-specific standardized contrasts suggest that the evolution of high bite forces in Chondrichthyes is further correlated with hypertrophication of the jaw adductors, increased leverage for anterior biting, and widening of the head. Lastly, we discuss the ecological significance of positive allometry in bite force as a possible "performance gain" early in the life history of C. leucas. PMID:23040789

Habegger, Maria L; Motta, Philip J; Huber, Daniel R; Dean, Mason N

2012-12-01

138

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

139

A new experimental and theoretical investigation on the structures of aminoethyl phosphonic acid in aqueous medium based on the vibrational spectra and DFT calculations  

NASA Astrophysics Data System (ADS)

A new study on the structural and vibrational properties of the aminoethylphosphonic acid was performed in aqueous solution phase by using the self-consistent reaction field (SCRF) method. We have studied and characterized it by infrared and Raman spectroscopies in solid and aqueous solution phases. The Density Functional Theory (DFT) method with Pople's basis set show that three stable zwitterions for the title molecule have been theoretically determined in aqueous solution and that probably they are present in it medium. Here, the solvent effects were studied by means of the self-consistent reaction field (SCRF) method with the polarized continuum model (PCM). The harmonic vibrational frequencies for the optimized geometries of the three zwitterions were calculated at the B3LYP/6-31G? level of the theory. A complete assignment of the IR and Raman spectra of the compound in aqueous solution was performed combining the DFT calculations with Pulay's Scaled Quantum Mechanics Force Field (SQMFF) methodology in order to fit the theoretical frequency values to the experimental ones. Moreover, Natural Bond Orbital (NBO) and topological properties calculations were performed to analyze the energies and geometrical parameters of its three zwitterions in aqueous medium as well as the magnitude of the intramolecular interactions. The bond orders, atomic charges, solvation energies, dipole moments, molecular electrostatic potentials and force constants parameters calculated for zwitterions in aqueous solution, may be used to gain chemical and vibrational insights into related compounds.

Roldán, María L.; Ledesma, Ana E.; Raschi, Ana B.; Castillo, María V.; Romano, Elida; Brandán, Silvia A.

2013-06-01

140

Heats of Segregation of BCC Binaries from Ab Initio and Quantum Approximate Calculations  

NASA Technical Reports Server (NTRS)

We compare dilute-limit segregation energies for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation. Results are discussed within the context of segregation models driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.

Good, Brian S.

2003-01-01

141

Quantum field theoretic descriptions of topological phases in two and three dimensions  

NASA Astrophysics Data System (ADS)

Topological phases of matter are purely quantum mechanical and have no classical analogue. Most phases in nature can be classified and studied classically through the concept of symmetry breaking and its theoretical description, Landau-Ginzburg field theory. In contrast to the general wisdom of Landau-Ginzburg field theory, the topological phases share the same symmetry as a trivial insulator and still are different phases. Having gapped spectrum in bulk, they support a metallic edge excition robust against symmetry-respecting perturbation or an emergent fractional excitation in bulk. Following after fractional quantum Hall fluids, many topologically orderd phases, such as spin liquids and topological insulators, have been found and studied. Spin liquids are disordered phases of frustrated antiferromagnets and do not freeze and order even at the lowest temperature. They support an electrically neutral spin-1/2 excitation, which does not exist in a microscopic scale, with emergent dynamical gauge field in bulk and do not have an adiabatic path to a trivial paramagnet phase. The topological insulators are time-reversal symmetric band insulators which cannot evolve smoothly into a trivial insulator with the symmetry, and they have been intensely studied theoretically and experimetally for the last decade. Though the topological insulators are inherently non-interacting systems, they have exotic gapless edge and surface states which demonstrate many interesting quantum phenomena such as fractionalization, axionic electromagnetism, and half quantum Hall effect. In this thesis, we study various quantum phenomena of the topological phases, mainly of the topological insulator and its close relatives in which the physics of spin liquids has been merged into. As they are intrinsically quantum many-body states, the quantum field theory is an invaluable tool to explore the venue of the phases and will be used thorougly in this work. (Abstract shortened by UMI.).

Cheng, Zhenzhou

142

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

143

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

NASA Astrophysics Data System (ADS)

Both experimental and theoretical investigations are reported on the infrared spectrum of vinylphosphine-borane (CH2=CHPH2?BH3), 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 ?,?-unsaturated phosphine-borane synthesized up to now is kinetically very unstable in the gas phase and decomposes rapidly into two fragments: the free vinylphosphine CH2=CHPH2 and the monoborane BH3 which dimerizes to form the more stable diborane B2H6. Spectra of free CH2=CHPH2 and B2H6 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 CH2=CHPH2 and BH3 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 ??=?complex-?monomer to make the effect of the complexation precise on each localized mode. In this objective, anharmonic frequencies and infrared intensities of the BH3 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 ?,?-unsaturated phosphine by borane on the physicochemical properties of the formed 12-atom complex have been efficiently evaluated.

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

2008-12-01

144

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

145

Quantum Circuit for Calculating Mean Values Via Grover-like Algorithm  

E-print Network

In this paper, we give a quantum circuit for calculating the mean value of a function $A(x^n)\\in \\mathbb{C}$, where $x^n\\in \\{0,1\\}^n$. Known classical algorithms for calculating the mean value of a structureless function $A(x^n)$ take ${\\cal O}(2^n)$ steps. Our quantum algorithm is based on a Grover-like algorithm and it takes ${\\cal O}(\\sqrt{2^n})$ steps. Our algorithm differs significantly from previously proposed quantum algorithms for calculating the mean value of a function via Grover's algorithm.

Robert R. Tucci

2014-03-31

146

A theoretical analysis of the optical absorption properties in one-dimensional InAs/GaAs quantum dot superlattices  

SciTech Connect

We present theoretical investigations of miniband structures and optical properties of InAs/GaAs one-dimensional quantum dot superlattices (1D-QDSLs). The calculation is based on the multi-band k·p theory, including the conduction and valence band mixing effects, the strain effect, and the piezoelectric effect; all three effects have periodic boundary conditions. We find that both the electronic and optical properties of the 1D-QDSLs show unique states which are different from those of well known single quantum dots (QDs) or quantum wires. We predict that the optical absorption spectra of the 1D-QDSLs strongly depend on the inter-dot spacing because of the inter-dot carrier coupling and changing strain states, which strongly influence the conduction and valence band potentials. The inter-miniband transitions form the absorption bands. Those absorption bands can be tuned from almost continuous (closely stacked QD case) to spike-like shape (almost isolated QD case) by changing the inter-dot spacing. The polarization of the lowest absorption peak for the 1D-QDSLs changes from being parallel to the stacking direction to being perpendicular to the stacking direction as the inter-dot spacing increases. In the case of closely stacked QDs, in-plane anisotropy, especially [110] and [11{sup ¯}0] directions also depend on the inter-dot spacing. Our findings and predictions will provide an additional degree of freedom for the design of QD-based optoelectronic devices.

Kotani, Teruhisa, E-mail: kotani.teruhisa@sharp.co.jp [Advanced Technology Research Laboratories, Sharp Corporation, 2613-1 Ichinomoto-cho, Tenri, Nara 632-8567 (Japan); Institute for Nanoelectronics, Technische Universität München, Arcisstr. 21, 80333 Munich (Germany); Birner, Stefan [Institute for Nanoelectronics, Technische Universität München, Arcisstr. 21, 80333 Munich (Germany); Walter Schottky Institute, Technische Universität München, Am Coulombwall 4, 85748 Garching (Germany); Lugli, Paolo [Institute for Nanoelectronics, Technische Universität München, Arcisstr. 21, 80333 Munich (Germany); Hamaguchi, Chihiro [Advanced Technology Research Laboratories, Sharp Corporation, 2613-1 Ichinomoto-cho, Tenri, Nara 632-8567 (Japan)

2014-04-14

147

Theoretical performance of solar cell based on mini-bands quantum dots  

SciTech Connect

The tremendous amount of research in solar energy is directed toward intermediate band solar cell for its advantages compared with the conventional solar cell. The latter has lower efficiency because the photons have lower energy than the bandgap energy and cannot excite mobile carriers from the valence band to the conduction band. On the other hand, if mini intermediate band is introduced between the valence and conduction bands, then the smaller energy photons can be used to promote charge carriers transfer to the conduction band and thereby the total current increases while maintaining a large open circuit voltage. In this article, the influence of the new band on the power conversion efficiency for structure of quantum dots intermediate band solar cell is theoretically investigated and studied. The time-independent Schrödinger equation is used to determine the optimum width and location of the intermediate band. Accordingly, achievement of a maximum efficiency by changing the width of quantum dots and barrier distances is studied. Theoretical determination of the power conversion efficiency under the two different ranges of QD width is presented. From the obtained results, the maximum power conversion efficiency is about 70.42%. It is carried out for simple cubic quantum dot crystal under fully concentrated light. It is strongly dependent on the width of quantum dots and barrier distances.

Aly, Abou El-Maaty M., E-mail: drabouelmaaty@hotmail.com, E-mail: ashraf.nasr@gmail.com [Power Electronics and Energy Conversion Department, ERI, NRCB (Egypt); College of Computer, Qassim University, P.O.B. 6688, Buryadah 51453 (Saudi Arabia); Nasr, A., E-mail: drabouelmaaty@hotmail.com, E-mail: ashraf.nasr@gmail.com [Radiation Engineering Department, NCRRT, Atomic Energy Authority (Egypt); College of Computer, Qassim University, P.O.B. 6688, Buryadah 51453 (Saudi Arabia)

2014-03-21

148

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

149

Exact quantum Monte Carlo calculations of the potential energy surface for the reaction H+H,-+H,+H  

E-print Network

Exact quantum Monte Carlo calculations of the potential energy surface for the reaction H" quantum Monte Carlo calculations of the potential energy surface for the reaction H+H2-+H2+H. The method of r0.2 kcal/mol. INTRODUCTION In a previous paper' we reported quantum Monte Carlo calculations

Anderson, James B.

150

Experimental and theoretical studies of band gap alignment in GaAs1-xBix/GaAs quantum wells  

NASA Astrophysics Data System (ADS)

Band gap alignment in GaAs1-xBix/GaAs quantum wells (QWs) was studied experimentally by photoreflectance (PR) and theoretically, ab initio, within the density functional theory in which the supercell based calculations are combined with the alchemical mixing approximation applied to a single atom in a supercell. In PR spectra, the optical transitions related to the excited states in the QW (i.e., the transition between the second heavy-hole and the second electron subband) were clearly observed in addition to the ground state QW transition and the GaAs barrier transition. This observation is clear experimental evidence that this is a type I QW with a deep quantum confinement in the conduction and valence bands. From the comparison of PR data with calculations of optical transitions in GaAs1-xBix/GaAs QW performed for various band gap alignments, the best agreement between experimental data and theoretical calculations has been found for the valence band offset of 52 ± 5%. A very similar valence band offset was obtained from ab initio calculations. These calculations show that the incorporation of Bi atoms into GaAs host modifies both the conduction and the valence band. For GaAs1-xBix with 0 < x < 0.074, the conduction band shifts lineary at a rate of ˜33 meV per % Bi, which only slightly decreases with Bi concentration. Whereas the valance band shift is clearly non-linear. Reducing initially at a rate of ˜51 meV per % Bi for low concentrations of Bi and then at a significantly reduced rate of ˜20 meV per % Bi near the end of the studied composition range. The overall reduction rate of the band gap is parabolic and the reduction rates change from ˜84 to ˜53 meV per % Bi for lower and higher Bi concentrations, respectively. The calculated shifts of valence and conduction bands give the variation of valence (conduction) band offset between GaAs1-xBix and GaAs in the range of ˜60%-40% (˜40%-60%), which is in good agreement with our conclusion derived from PR measurements.

Kudrawiec, R.; Kopaczek, J.; Polak, M. P.; Scharoch, P.; Gladysiewicz, M.; Misiewicz, J.; Richards, R. D.; Bastiman, F.; David, J. P. R.

2014-12-01

151

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

152

Acidity of mesoporous MoO(x)/ZrO2 and WO(x)/ZrO2 materials: a combined solid-state NMR and theoretical calculation study.  

PubMed

The acidity of mesoporous MoO(x)/ZrO2 and WO(x)/ZrO2 materials was studied in detail by multinuclear solid-state NMR techniques as well as DFT quantum chemical calculations. The 1H MAS NMR experiments clearly revealed the presence of two different types of strong Brønsted acid sites on both MoO(x)/ZrO2 and WO(x)/ZrO2 mesoporous materials, which were able to prontonate adsorbed pyrine-d5 (resulting in 1H NMR signals at chemical shifts in the range 16-19 ppm) as well as adsorbed trimethylphosphine (giving rise to 31P NMR signal at ca. 0 ppm). The 13C NMR of adsorbed 2-(13)C-acetone indicated that the average Brønsted acid strength of the two mesoporous materials was stronger than that of zeolite HZSM-5 but still weaker than that of 100% H2SO4, which was in good agreement with theoretical predictions. The quantum chemical calculations revealed the detailed structures of the two distinct types of Brønsted acid sites formed on the mesoporous MoO(x)/ZrO2 and WO(x)/ZrO2. The existence of both monomer and oligomer Mo (or W) species containing a Mo-OH-Zr (or W-OH-Zr) bridging OH group was confirmed with the former having an acid strength close to zeolite HZSM-5, with the latter having an acid strength similar to sulfated zirconia. On the basis of our NMR experimental and theoretical calculation results, a possible mechanism was proposed for the formation of acid sites on these mesoporous materials. PMID:16771312

Xu, Jun; Zheng, Anmin; Yang, Jun; Su, Yongchao; Wang, Jiqing; Zeng, Danlin; Zhang, Mingjin; Ye, Chaohui; Deng, Feng

2006-06-01

153

A pedagogical introduction to quantum integrability, with a view towards theoretical high-energy physics  

E-print Network

These are lecture notes of an introduction to quantum integrability given at the Tenth Modave Summer School in Mathematical Physics, 2014, aimed at PhD candidates and junior researchers in theoretical physics. We introduce spin chains and discuss the coordinate Bethe Ansatz (CBA) for a representative example: the Heisenberg XXZ model. The focus lies on the structure of the CBA and on its main results, deferring a detailed treatment of the CBA for the general $M$-particle sector of the XXZ model to an appendix. Subsequently the transfer-matrix method is discussed for the six-vertex model, uncovering a relation between that model and the XXZ spin chain. Equipped with this background the quantum inverse-scattering method (QISM) and algebraic Bethe Ansatz (ABA) are treated. We emphasize the use of graphical notation for algebraic quantities as well as computations. Finally we turn to quantum integrability in the context of theoretical high-energy physics. We discuss factorized scattering in two-dimensional QFT, a...

Lamers, J

2015-01-01

154

On the interaction between supercritical CO2 and epoxides combining infrared absorption spectroscopy and quantum chemistry calculations.  

PubMed

The nature and strength of the interactions occurring between epoxides and CO(2) have been investigated by combining infrared spectroscopy with quantum chemistry calculations. A series of infrared absorption experiments on four model epoxide molecules highly diluted in supercritical CO(2) have been performed at constant temperature T = 40 °C for various CO(2) pressures varying from 1 to 30 MPa. Then, we carried out a theoretical analysis based on quantum chemistry calculations using Density Functional Theory (B3PW91 and CAM-B3LYP) and ab initio (MP2) computational methods. A very good agreement between experimental and calculated vibrational frequency shifts of the epoxide ring vibrations group was obtained using the CAM-B3LYP functional, hence validating the calculated optimized geometries of the epoxide-CO(2) complexes. Whatever the epoxide considered, CO(2) is found to be on average above the oxygen atom of the epoxy ring and interacts with the carbon atom of CO(2) through a Lewis acid-Lewis base type of interaction. The substituents on the epoxide ring are found to influence the stability of the epoxide-CO(2) complexes mainly because of the partial charge on the oxygen atom that is sensitive to the nature of the substituent. PMID:21465049

Foltran, Stéphanie; Méreau, Raphaël; Tassaing, Thierry

2011-05-28

155

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

156

Molecular structure of cotinine studied by gas electron diffraction combined with theoretical calculations  

NASA Astrophysics Data System (ADS)

The molecular structure of cotinine (( S)-1-methyl-5-(3-pyridinyl)-2-pyrrolidinone), the major metabolite of nicotine, has been determined at about 182 °C by gas electron diffraction combined with MP2 and DFT calculations. The diffraction data are consistent with the existence of the (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers, where ax and eq indicate the configuration of the pyrrolidinone ring by means of the position (axial and equatorial) of the pyridine ring, and sc, sp and ap distinguish the isomers arising from the internal rotation around the bond connecting the two rings. The (CH 3)NCCC(N) dihedral angles, ?, of the (ax, sc) and (eq, sp) conformers were determined independently to be 158(12)° and 129(13)°, respectively, where the numbers in parentheses are three times the standard errors, 3 ?. According to the MP2 calculations, the corresponding dihedral angles for the (ax, ap) and (eq, ap) conformers were assumed to differ by 180° from their syn counterparts. The ratios x(ax, sc)/ x(ax, ap) and x(eq, sp)/ x(eq, ap) were taken from the theoretically estimated free energy differences, ? G, where x is the abundance of the conformer. The resultant abundances of (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers are 34(6)%, 21% (d.p.), 28% (d.p.), and 17% (d.p.), respectively, where d.p. represents dependent parameters. The determined structural parameters ( rg (Å) and ? ? (°)) of the most abundant conformer, (ax, sc), are as follows: r(N sbnd C) pyrrol = 1.463(5); r(N sbnd C methyl) = 1.457(?); r(N sbnd C( dbnd O)) = 1.384(12); r(C dbnd O) = 1.219(5); < r(C sbnd C) pyrrol> = 1.541(3); r(C pyrrolsbnd C pyrid) = 1.521(?); < r(C sbnd C) pyrid> = 1.396(2); < r(C sbnd N) pyrid> = 1.343(?); ?(CNC) pyrrol = 113.9(11); ?CCC pyrrol(-C pyrid) = 103.6(?); ?NCO = 124.1(13); ?NC pyrrolC pyrid = 113.1(12); ?C pyrrolC pyrrolC pyrid = 113.3(?); ?(CNC) pyrid = 117.1(2); = 124.4(?); ?C methylNC( dbnd O) = ?C methylNC(-C pyrid) = 122.8(d.p.); ?NC( dbnd O)C = 107.1(d.p.); ?NC pyrrol(-C pyrid)C pyrrol = 103.0(d.p.) and ?CCC( dbnd O) = 105.2(d.p.), where ? in the parentheses means that the parameter is bound to the preceding one and < > denote average values. The puckering angle, ?, of the pyrrolidinone ring is 26(3)°. The N⋯N distances of the (ax, sc) and (eq, sp) conformers, which are 4.844(5) and 4.740(5) Å, respectively, are close to that of the most stable conformer of nicotine, 4.885(6) Å and the corresponding one of arecoline, 4.832(13) Å. It is concluded that the weak nicotinic activity of cotinine cannot be ascribed to such a small difference in the N⋯N distances.

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

2007-09-01

157

Time-dependent wave packet quantum scattering and quasi-classical trajectory calculations of the H + FCl(v=0,j=0) ? HF + Cl/HCl + F reaction.  

PubMed

The dynamics of the title reaction are investigated using both time-dependent wave packet quantum scattering and quasi-classical trajectory (QCT) methods on adiabatic ground 1(2)A' potential energy surface (PES). Compared with the quantum results of reaction probabilities of H + FCl(J=0) ? HF + Cl/HCl + F, the QCT method is proven feasible and further employed to produce integral cross sections and rate constants. Significant resonance structures are observed in the reaction probabilities using the quantum method; however, there are some undulations in the calculated QCT integral cross sections for both product channels. A comparison between the quantum mechanical coupled-channel (CC) calculation and centrifugal sudden approximation calculation reveals the very important role of Coriolis coupling effects in the quantum calculation. Comparisons between the calculated thermal rate constants for both reactions and the previous theoretical and experimental results have been done. HCl product formation is favored over the HF product in the reactive system. Finally, the HF products are found to be mainly forward scattering, and the HCl products are mainly backward scattering. PMID:24125031

Zhao, Juan; Miao, Xiangyang; Luo, Yi

2013-11-14

158

Theoretical calculation of the OH vibrational overtone spectra of 1-n alkane diols (n = 2-4): origin of disappearing hydrogen-bonded OH peak.  

PubMed

In this theoretical study, we simulated the vibrational overtone spectrum of ethylene glycol (EG), 1-3 propanediol (PD), and 1-4 butanediol (BD). Using the local mode model along with the potential energy curve and dipole moment function calculated by B3LYP/6-31+G(d,p) and QCISD/6-311++G(3df,3pd), we obtained the theoretical peak position and integrated absorption coefficient. Furthermore, the vibrational spectra was simulated using a Voigt function using homogeneous and inhomogenous width obtained from quantum chemical calculation methods. Previously, Howard and Kjaergaard recorded the second and third overtone photoacoustic spectra of the three aforementioned alkane diols in the gas phase and observed that the intramolecular hydrogen bonded OH peak becomes difficult to observe as the intramolecular hydrogen bonding strength increased, that is, as the chain length was increased. In this paper we show that the disappearance of the hydrogen-bonded OH peak for the OH stretching overtone excitation for BD is partly due to the increase in homogeneous width due to the increase in the hydrogen bond strength and partly due to the decrease in the relative population of the intramolecular hydrogen-bonded conformers as the chain length is increased. This latter feature is a consequence of the unfavorable strained geometry needed to form the intramolecular hydrogen bond in longer alkane chains. PMID:21568300

Cheng, Yu-Lung; Chen, Hui-Yi; Takahashi, Kaito

2011-06-01

159

Quantum mechanical method of fragment's angular and energy distribution calculation for binary and ternary fission  

SciTech Connect

In the framework of quantum-mechanical fission theory, the method of calculation for partial fission width amplitudes and asymptotic behavior of the fissile nucleus wave function with strong channel coupling taken into account has been suggested. The method allows one to solve the calculation problem of angular and energy distribution countation for binary and ternary fission.

Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru; Titova, L. V.; Pen'kov, N. V. [Voronezh State University (Russian Federation)

2006-08-15

160

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.

161

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.

162

Quantum Monte Carlo Calculations of the Energy of the Relativistic Homogeneous Electron Gas  

NASA Astrophysics Data System (ADS)

The ground state energy of the unpolarized homogeneous electron gas at zero temperature is calculated within the density range rs = 0.1-10, incorporating relativistic effects via first-order perturbation theory. Accurate nonrelativistic wave functions and variational and diffusion quantum Monte Carlo techniques are used to calculate the required expectation values.

Kenny, S. D.; Rajagopal, G.; Needs, R. J.; Leung, W.-K.; Godfrey, M. J.; Williamson, A. J.; Foulkes, W. M. C.

1996-08-01

163

Theoretical study of polarization insensitivity of carrier-induced refractive index change of multiple quantum well.  

PubMed

Characteristics of polarization insensitivity of carrier-induced refractive index change of 1.55 ?m tensile-strained multiple quantum well (MQW) are theoretically investigated. A comprehensive MQW model is proposed to effectively extend the application range of previous models. The model considers the temperature variation as well as the nonuniform distribution of injected carrier in MQW. Tensile-strained MQW is expected to achieve polarization insensitivity of carrier-induced refractive index change over a wide wavelength range as temperature varies from 0°C to 40°C, while the magnitude of refractive index change keeps a large value (more than 3 × 10-3). And that the polarization insensitivity of refractive index change can maintain for a wide range of carrier concentration. Multiple quantum well with different material and structure parameters is anticipated to have the similar polarization insensitivity of refractive index change, which shows the design flexibility. PMID:25607157

Miao, Qingyuan; Zhou, Qunjie; Cui, Jun; He, Ping-An; Huang, Dexiu

2014-12-29

164

Quantum-field-theoretical approach to phase-space techniques: Generalizing the positive-P representation  

SciTech Connect

We present an introduction to phase-space techniques (PST) based on a quantum-field-theoretical (QFT) approach. In addition to bridging the gap between PST and QFT, our approach results in a number of generalizations of the PST. First, for problems where the usual PST do not result in a genuine Fokker-Planck equation (even after phase-space doubling) and hence fail to produce a stochastic differential equation (SDE), we show how the system in question may be approximated via stochastic difference equations (S{delta}E). Second, we show that introducing sources into the SDE's (or S{delta}E's) generalizes them to a full quantum nonlinear stochastic response problem (thus generalizing Kubo's linear reaction theory to a quantum nonlinear stochastic response theory). Third, we establish general relations linking quantum response properties of the system in question to averages of operator products ordered in a way different from time normal. This extends PST to a much wider assemblage of operator products than are usually considered in phase-space approaches. In all cases, our approach yields a very simple and straightforward way of deriving stochastic equations in phase space.

Plimak, L.I. [Fachbereich Physik, Universitaet Kaiserslautern, D-67663 Kaiserslautern (Germany); Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand); Fleischhauer, M. [Fachbereich Physik, Universitaet Kaiserslautern, D-67663 Kaiserslautern (Germany); Olsen, M.K. [Instituto de Fisica da Universidade Federal Fluminense, Boa Viagem Cep.: 24210-340, Niteroi-RJ (Brazil); Collett, M.J. [Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand)

2003-01-01

165

Theoretical and experimental insights into the surface chemistry of semiconductor quantum dots.  

PubMed

We present a series of non-stoichiometric cadmium sulfide quantum-dot (QD) models. Using density functional theory (DFT) and semi-empirical molecular orbital (MO) calculations, we explore the ligand binding and exchange chemistry of these models. Their surface morphology allows for these processes to be rationalized on the atomic scale. This is corroborated by ultraviolet-visible (UV-vis), infrared (IR), and inductively coupled plasma-optical emission spectroscopy (ICP-OES). PMID:24266745

Margraf, Johannes T; Ruland, Andrés; Sgobba, Vito; Guldi, Dirk M; Clark, Timothy

2013-12-10

166

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

E-print Network

The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots

Dongarra, Jack

167

Quantum Monte Carlo calculations of the energy-level alignment at hybrid interfaces: Role of many-body effects  

E-print Network

Quantum Monte Carlo calculations of the energy-level alignment at hybrid interfaces: Role of many-level alignment at hybrid interfaces, using quantum Monte Carlo calculations to include many-body effects parameters. Here we present a scheme based on the quantum Monte Carlo QMC method18 to obtain accurate energy-lev

Wu, Zhigang

168

Direct measurement and theoretical calculation of the rate coefficient for Cl + CH3 from T = 202 - 298 K.  

SciTech Connect

The rate coefficient has been measured under pseudo-first-order conditions for the Cl + CH{sub 3} association reaction at T = 202, 250, and 298 K and P = 0.3-2.0 Torr helium using the technique of discharge-flow mass spectrometry with low-energy (12-eV) electron-impact ionization and collision-free sampling. Cl and CH{sub 3} were generated rapidly and simultaneously by reaction of F with HCl and CH{sub 4}, respectively. Fluorine atoms were produced by microwave discharge in an approximately 1% mixture of F{sub 2} in He. The decay of CH{sub 3} was monitored under pseudo-first-order conditions with the Cl-atom concentration in large excess over the CH{sub 3} concentration ([Cl]{sub 0}/[CH{sub 3}]{sub 0} = 9-67). Small corrections were made for both axial and radial diffusion and minor secondary chemistry. The rate coefficient was found to be in the falloff regime over the range of pressures studied. For example, at T = 202 K, the rate coefficient increases from 8.4 x 10{sup -12} at P = 0.30 Torr He to 1.8 x 10{sup -11} at P = 2.00 Torr He, both in units of cm{sup 3} molecule{sup -1} s{sup -1}. A combination of ab initio quantum chemistry, variational transition-state theory, and master-equation simulations was employed in developing a theoretical model for the temperature and pressure dependence of the rate coefficient. Reasonable empirical representations of energy transfer and of the effect of spin-orbit interactions yield a temperature- and pressure-dependent rate coefficient that is in excellent agreement with the present experimental results. The high-pressure limiting rate coefficient from the RRKM calculations is k{sub 2} = 6.0 x 10{sup -11} cm{sup 3} molecule{sup -1} s{sup -1}, independent of temperature in the range from 200 to 300 K.

Payne, Walter A. (NASA/Goddard Space Flight Center, Greenbelt, MD); Harding, Lawrence B. (Argonne National Laboratory, Argonne, IL); Stief, Louis J. (NASA/Goddard Space Flight Center, Greenbelt, MD); Parker, James F. (James Fletcher), 1925-; Klippenstein, Stephen J.; Nesbitt, Fred L. (NASA/Goddard Space Flight Center, Greenbelt, MD); Cody, Regina J. (NASA/Goddard Space Flight Center, Greenbelt, MD)

2004-10-01

169

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

E-print Network

2001 We calculate spatial localization and phase properties of spontaneously emitted photons. Our model is simple yet fully quantized: the emitting atom is a two-level atom located in a one-dimensional multimode, the expectation value of the square of the electric field operator intensity is spatially localized

Ligare, Martin

170

Symmetry-projected wave functions in quantum Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

We consider symmetry-projected Hartree-Fock trial wave functions in constrained-path Monte Carlo (CPMC) calculations. Previous CPMC calculations have mostly employed Hartree-Fock (HF) trial wave functions, restricted or unrestricted. The symmetry-projected HF approach results in a hierarchy of wave functions with increasing quality: the more symmetries that are broken and restored in a self-consistent manner, the higher the quality of the trial wave function. This hierarchy is approximately maintained in CPMC calculations: the accuracy in the energy increases and the statistical variance decreases when further symmetries are broken and restored. Significant improvement is achieved in CPMC with the best symmetry-projected trial wave functions over those from simple HF. We analyze and quantify the behavior using the two-dimensional repulsive Hubbard model as an example. In the sign-problem-free region, where CPMC can be made exact but a constraint is deliberately imposed here, spin-projected wave functions remove the constraint bias. Away from half filling, spatial symmetry restoration in addition to that of the spin leads to highly accurate results from CPMC. Since the computational cost of symmetry-projected HF trial wave functions in CPMC can be made to scale algebraically with system size, this provides a potentially general approach for accurate calculations in many-fermion systems.

Shi, Hao; Jiménez-Hoyos, Carlos A.; Rodríguez-Guzmán, R.; Scuseria, Gustavo E.; Zhang, Shiwei

2014-03-01

171

Relativistic Theoretical Calculation of O III: Radiative Transition Rates and the Bowen Mechanism in Planetary Nebulae  

NASA Astrophysics Data System (ADS)

A full relativistic configuration interaction (RCI) calculation of transition energies and radiative transition rates involved in O III Bowen fluorescence mechanism is presented. The calculated ratios of transition line intensities are in good agreement with the observed ratios. The discrepancies between the RCI calculation and prediction based on LS coupling scheme show that a delicate balance between the electron correlations and the spin-orbital interactions should be important even for the low-Z O III ion.

Tong, Xiaomin; Zou, Yu; Li, Jiaming; Liu, Xiaowei

1994-02-01

172

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

173

Experimental, theoretical calculations of the vibrational spectra and conformational analysis of 2,4-di-tert-butylphenol.  

PubMed

In the present work, we reported a combined experimental and theoretical study on conformational stability, molecular structure and vibrational spectra of 2,4-di-tert-butylphenol (2,4-DTBP). The FT-IR (400-4000cm(-1)) and FT-Raman spectra (50-3500cm(-1)) of 2,4-DTBP were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of 2,4-DTBP in the ground-state have been calculated by using the density functional BLYP/B3LYP methods. The energy calculated by time-dependent density functional theory (TD-DFT) result complements with the experimental findings. The calculated highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies show that charge transfer occurs within the molecule. Finally the calculation results were compared with measured infrared and Raman spectra of the title compound which showed good agreement with observed spectra. PMID:22020168

Kalaichelvan, S; Sundaraganesan, N; Dereli, O; Sayin, U

2012-01-01

174

Probing a cold surface with slow heavy-atom scattering: Experimental results and theoretical calculations  

E-print Network

Probing a cold surface with slow heavy-atom scattering: Experimental results and theoretical manuscript received 20 September 2001; published 2 January 2002 Slow heavy atoms scattering from cold, which is slow and strong, it is typically much more complex.2 In the common case of a light particle

Burke, Kieron

175

Spectroscopic analysis of cinnamic acid using quantum chemical calculations  

NASA Astrophysics Data System (ADS)

In this present study, FT-IR, FT-Raman, 13C NMR and 1H NMR spectra for cinnamic acid have been recorded for the vibrational and spectroscopic analysis. The observed fundamental frequencies (IR and Raman) were assigned according to their distinctiveness region. The computed frequencies and optimized parameters have been calculated by using HF and DFT (B3LYP) methods and the corresponding results are tabulated. On the basis of the comparison between computed and experimental results assignments of the fundamental vibrational modes are examined. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, were performed by HF and DFT methods. The alternation of the vibration pattern of the pedestal molecule related to the substitutions was analyzed. The 13C and 1H NMR spectra have been recorded and the chemical shifts have been calculated using the gauge independent atomic orbital (GIAO) method. The Mulliken charges, UV spectral analysis and HOMO-LUMO analysis of have been calculated and reported. The molecular electrostatic potential (MEP) was constructed.

Vinod, K. S.; Periandy, S.; Govindarajan, M.

2015-02-01

176

Spectroscopic analysis of cinnamic acid using quantum chemical calculations.  

PubMed

In this present study, FT-IR, FT-Raman, (13)C NMR and (1)H NMR spectra for cinnamic acid have been recorded for the vibrational and spectroscopic analysis. The observed fundamental frequencies (IR and Raman) were assigned according to their distinctiveness region. The computed frequencies and optimized parameters have been calculated by using HF and DFT (B3LYP) methods and the corresponding results are tabulated. On the basis of the comparison between computed and experimental results assignments of the fundamental vibrational modes are examined. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, were performed by HF and DFT methods. The alternation of the vibration pattern of the pedestal molecule related to the substitutions was analyzed. The (13)C and (1)H NMR spectra have been recorded and the chemical shifts have been calculated using the gauge independent atomic orbital (GIAO) method. The Mulliken charges, UV spectral analysis and HOMO-LUMO analysis of have been calculated and reported. The molecular electrostatic potential (MEP) was constructed. PMID:25315873

Vinod, K S; Periandy, S; Govindarajan, M

2015-02-01

177

Stretched DNA Investigated Using Molecular-Dynamics and Quantum-Mechanical Calculations  

Microsoft Academic Search

We combined atomistic molecular-dynamics simulations with quantum-mechanical calculations to investigate the sequence dependence of the stretching behavior of duplex DNA. Our combined quantum-mechanical\\/molecular-mechanical approach demonstrates that molecular-mechanical force fields are able to describe both the backbone and base-base interactions within the highly distorted nucleic acid structures produced by stretching the DNA from the 5? ends, which include conformations containing disassociated

Jan ?ezá?; Pavel Hobza; Sarah A. Harris

2010-01-01

178

A comparison between entropies of aromatic compounds from quantum mechanical calculations and experiment  

Microsoft Academic Search

In this work, we perform a set of quantum mechanical and statistical mechanical calculations to generate the entropy of five simple, aromatic compounds—benzene, toluene, p-xylene, m-xylene and o-xylene—in the ideal gas state. We systematically examine how the choice of quantum mechanical level of theory and size of basis set impact the agreement between theory and experiment. Regardless of level of

Mohamad H. Kassaee; David J. Keffer; William V. Steele

2007-01-01

179

Theoretical calculation of medium-energy proton-induced reactions on Al, Zr, and Pb  

SciTech Connect

The intranuclear cascade model of nuclear reactions was used to calculate double differential cross sections for the (p,xn) reaction. The calculations were performed with a generalized version of the code VEGAS, CLUST. Model predictions are compared with recent experimental data. Calculated fast-particle spectral shapes at low angles are reproduced reasonably well for the experimental data. As one possible improvement to the model, the proton reaction cross sections were estimated independently using the prescriptions of Karol, and DeVries and Peng. The systematic trends that emerge from this analysis are discussed. 12 refs., 5 figs.

Ramavataram, S.; Divadeenam, M.; Ward, T.E.

1988-01-01

180

Theoretical studies of optical gain tuning by hydrostatic pressure in GaInNAs/GaAs quantum wells  

SciTech Connect

In order to describe theoretically the tuning of the optical gain by hydrostatic pressure in GaInNAs/GaAs quantum wells (QWs), the optical gain calculations within kp approach were developed and applied for N-containing and N-free QWs. The electronic band structure and the optical gain for GaInNAs/GaAs QW were calculated within the 10-band kp model which takes into account the interaction of electron levels in the QW with the nitrogen resonant level in GaInNAs. It has been shown that this interaction increases with the hydrostatic pressure and as a result the optical gain for GaInNAs/GaAs QW decreases by about 40% and 80% for transverse electric and transverse magnetic modes, respectively, for the hydrostatic pressure change from 0 to 40 kilobars. Such an effect is not observed for N-free QWs where the dispersion of electron and hole energies remains unchanged with the hydrostatic pressure. This is due to the fact that the conduction and valence band potentials in GaInAs/GaAs QW scale linearly with the hydrostatic pressure.

Gladysiewicz, M.; Wartak, M. S. [Institute of Physics, Wroclaw University of Technology, 50-370 Wroclaw, Wybrzeze Wyspianskiego 27 (Poland); Department of Physics and Computer Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5 (Canada); Kudrawiec, R. [Institute of Physics, Wroclaw University of Technology, 50-370 Wroclaw, Wybrzeze Wyspianskiego 27 (Poland)

2014-01-21

181

Ocean color spectrum calculations. [theoretical models relating oceanographic parameters to upwelling radiances  

NASA Technical Reports Server (NTRS)

The development is considered of procedures for measuring a number of subsurface oceanographic parameters using remotely sensed ocean color data. It is proposed that the first step in this effort should be the development of adequate theoretical models relating the desired oceanographic parameters to the upwelling radiances to be observed. A portion of a contributory theoretical model is shown to be described by a modified single scattering approach based upon a simple treatment of multiple scattering. The resulting quasi-single scattering model can be used to predict the upwelling distribution of spectral radiance emerging from the sea. The shape of the radiance spectrum predicted by this model for clear ocean water shows encouraging agreement with measurments made at the edge of the Sargasso Sea off Cape Hatteras.

Mccluney, W. R.

1974-01-01

182

Infrared and Raman spectra and theoretical calculations for benzocyclobutane in its electronic ground state.  

PubMed

The infrared and Raman spectra of vapor-phase and liquid-phase benzocyclobutane (BCB) have been recorded and assigned. The structure of the molecule was calculated using the MP2/cc-pVTZ basis set and the vibrational frequencies and spectral intensities were calculated using the B3LYP/cc-pVTZ level of theory. The agreement between experimental and calculated spectra is excellent. In order to allow comparisons with related molecules, ab initio and DFT calculations were also carried out for indan (IND), tetralin (TET), 1,4-benzodioxan (14BZD), 1,3-benzodioxan (13BZD) and 1,4-dihydronaphthalene (14DHN). The ring-puckering, ring-twisting, and ring-flapping vibrations were of particular interest as these reflect the rigidity of the bicyclic ring system. The infrared spectra of BCB show very nice examples of vapor-phase band types and combination bands. PMID:24507997

Ocola, Esther J; Shin, Hee Won; Laane, Jaan

2015-02-01

183

Infrared and Raman spectra and theoretical calculations for benzocyclobutane in its electronic ground state  

NASA Astrophysics Data System (ADS)

The infrared and Raman spectra of vapor-phase and liquid-phase benzocyclobutane (BCB) have been recorded and assigned. The structure of the molecule was calculated using the MP2/cc-pVTZ basis set and the vibrational frequencies and spectral intensities were calculated using the B3LYP/cc-pVTZ level of theory. The agreement between experimental and calculated spectra is excellent. In order to allow comparisons with related molecules, ab initio and DFT calculations were also carried out for indan (IND), tetralin (TET), 1,4-benzodioxan (14BZD), 1,3-benzodioxan (13BZD) and 1,4-dihydronaphthalene (14DHN). The ring-puckering, ring-twisting, and ring-flapping vibrations were of particular interest as these reflect the rigidity of the bicyclic ring system. The infrared spectra of BCB show very nice examples of vapor-phase band types and combination bands.

Ocola, Esther J.; Shin, Hee Won; Laane, Jaan

2015-02-01

184

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

185

Renyi Entanglement Entropy of Interacting Fermions Calculated Using Continuous-Time Quantum Monte Carlo Method  

E-print Network

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 interaction correction of the entanglement entropy, which by design ensures 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.

Lei Wang; Matthias Troyer

2014-07-02

186

Quantum Circuit for Calculating Mobius-like Transforms Via Grover-like Algorithm  

E-print Network

In this paper, we give quantum circuits for calculating two closely related linear transforms that we refer to jointly as Mobius-like transforms. The first is the Mobius transform of a function $f^{-}(S^-)\\in \\mathbb{C}$, where $S^-\\subset \\{0,1,\\ldots,n-1\\}$. The second is a marginal of a probability distribution $P(y^n)$, where $y^n\\in Bool^n$. Known classical algorithms for calculating these Mobius-like transforms take ${\\cal O}(2^n)$ steps. Our quantum algorithm is based on a Grover-like algorithm and it takes ${\\cal O}(\\sqrt{2^n})$ steps.

Robert R. Tucci

2014-03-27

187

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

188

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

189

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

190

Theoretical X-ray Spectroscopy of Iron Complexes.  

E-print Network

??This thesis discusses both theoretical developments for the calculation of X-ray spectra and applications of quantum-chemical methods to the calculation and interpretation of experimental X-ray… (more)

Atkins, Andrew J.

2013-01-01

191

Theoretical calculation of the energy of formation of LiBH 4  

NASA Astrophysics Data System (ADS)

We report density functional theory calculations on the energy of LiBH 4, relative to solid B and LiH and gaseous H 2. The calculated energy is -71.3 (-76.1) kJ/mol H 2 which can be approximately corrected for zero-point energy to give an enthalpy of -52 (-57) kJ/mol H 2 at the PW91 (LDA) level, smaller than but similar to the experimental value of -68.9 kJ/mol H 2. Calculations on four different LiBH 4 phases indicate that alternative phases are not accessible at low temperatures without applying high pressures. These results indicate that complete decomposition to H 2, B and LiH is not an attractive means of obtaining a reversible hydrogen storage system based on LiBH 4.

Frankcombe, Terry J.; Kroes, Geert-Jan; Züttel, Andreas

2005-03-01

192

Molecular docking, spectroscopic studies and quantum calculations on nootropic drug.  

PubMed

A systematic vibrational spectroscopic assignment and analysis of piracetam [(2-oxo-1-pyrrolidineacetamide)] have been carried out using FT-IR and FT-Raman spectral data. The vibrational analysis was aided by an electronic structure calculation based on the hybrid density functional method B3LYP using a 6-311G++(d,p) basis set. Molecular equilibrium geometries, electronic energies, IR and Raman intensities, and harmonic vibrational frequencies have been computed. The assignments are based on the experimental IR and Raman spectra, and a complete assignment of the observed spectra has been proposed. The UV-visible spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies and the maximum absorption wavelengths ?max were determined by the time-dependent DFT (TD-DFT) method. The geometrical parameters, vibrational frequencies and absorption wavelengths were compared with the experimental data. The complete vibrational assignments are performed on the basis of the potential energy distributions (PED) of the vibrational modes in terms of natural internal coordinates. The simulated FT-IR, FT-Raman, and UV spectra of the title compound have been constructed. Molecular docking studies have been carried out in the active site of piracetam by using Argus Lab. In addition, the potential energy surface, HOMO and LUMO energies, first-order hyperpolarizability and the molecular electrostatic potential have been computed. PMID:24487180

Uma Maheswari, J; Muthu, S; Sundius, Tom

2014-04-01

193

Theoretical investigation of thermostability of incompressible channels in quantum Hall states  

NASA Astrophysics Data System (ADS)

In this work we use self-consistent method considering a two dimensional electron gas system in the integer quantum Hall regime, to calculate the temperature induced decay of incompressible stripes. There are two types of incompressible strips which can form in a Hall bar system by varying the electron density or magnetic field. We observe that the way of collapse of incompressible strips strongly depends on the type of them. With increasing temperature a bulk incompressible strip will decay from the middle and separate into two edge channels by a density ramp, while an incompressible edge channel reduces its size from both sides until vanishes.

Yang, Tao; Benedict, Keith A.

2014-09-01

194

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

195

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

196

Theoretical comparison of advanced methods for calculating nitrous oxide fluxes using non-steady state chambers  

Technology Transfer Automated Retrieval System (TEKTRAN)

Several flux-calculation (FC) schemes are available for determining soil-to-atmosphere emissions of nitrous oxide (N2O) and other trace gases using data from non-steady-state flux chambers. Recently developed methods claim to provide more accuracy in estimating the true pre-deployment flux (f0) comp...

197

Research on theoretical calculation model for dynamic stiffness of air spring with auxiliary chamber  

Microsoft Academic Search

Based on the theory of thermomechanics and fluid dynamics, the dynamic equations of air spring, auxiliary chamber and orifice were established, and then the calculation model for dynamic stiffness of air spring with auxiliary chamber was deduced. The model indicates that the dynamic stiffness of air spring is caused by the air spring effect area variation with air spring deformation,

Zhu Sihong; Wang Jiasheng; Zhang Ying

2008-01-01

198

Comparison between Theoretical Calculation and Experimental Results of Excitation Functions for Production of Relevant Biomedical Radionuclides  

SciTech Connect

The radionuclide production for biomedical applications has been brought up in the years, as a special nuclear application, at INFN LASA Laboratory, particularly in co-operation with the JRC-Ispra of EC. Mainly scientific aspects concerning radiation detection and the relevant instruments, the measurements of excitation functions of the involved nuclear reactions, the requested radiochemistry studies and further applications have been investigated. On the side of the nuclear data evaluations, based on nuclear model calculations and critically selected experimental data, the appropriate competence has been developed at ENEA Division for Advanced Physics Technologies. A series of high specific activity accelerator-produced radionuclides in no-carrier-added (NCA) form, for uses in metabolic radiotherapy and for PET radiodiagnostics, are investigated. In this work, last revised measurements and model calculations are reviewed for excitation functions of natZn(d,X)64Cu, 66Ga reactions, referring to irradiation experiments at K=38 variable energy Cyclotron of JRC-Ispra. Concerning the reaction data for producing 186gRe and 211At/211gPo (including significant emission spectra) and 210At, most recent and critically selected experimental results are considered and discussed in comparison with model calculations paying special care to pre-equilibrium effects estimate and to the appropriate overall parameterization. Model calculations are presented for 226Ra(p,2n)225Ac reaction, according to the working program of the ongoing IAEA CRP on the matter.

Menapace, E. [ENEA, Division for Advanced Physics Technologies, via Don Fiammelli 2, I-40128 Bologna (Italy); Birattari, C.; Bonardi, M.L.; Groppi, F.; Morzenti, S.; Zona, C. [Universita degli Studi di Milano, via F.lli Cervi 201, I-20090 Segrate, Milan (Italy); INFN-Milano, LASA, Radiochemistry Laboratory, via F.lli Cervi 201, I-20090 Segrate, Milan (Italy)

2005-05-24

199

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

200

Application of Vibrational Spectroscopy Supported by Theoretical Calculations in Identification of Amorphous and Crystalline Forms of Cefuroxime Axetil  

PubMed Central

FT-IR and Raman scattering spectra of cefuroxime axetil were proposed for identification studies of its crystalline and amorphous forms. An analysis of experimental spectra was supported by quantum-chemical calculations performed with the use of B3LYP functional and 6-31G(d,p) as a basis set. The geometric structure of a cefuroxime axetil molecule, HOMO and LUMO orbitals, and molecular electrostatic potential were also determined by using DFT (density functional theory). The benefits of applying FT-IR and Raman scattering spectroscopy for characterization of drug subjected to degradation were discussed. PMID:25654137

Lewandowska, Kornelia; Jeli?ska, Anna; Zalewski, Przemys?aw; Oszczapowicz, Irena; Sikora, Adam; Kozak, Maciej

2015-01-01

201

A theoretical model for calculation of molecular stopping power. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

A modified local plasma model is established. The Gordon-Kim's molecular charged density model is employed to obtain a formula to evaluate the stopping power of many useful molecular systems. The stopping power of H2 and He gas was calculated for incident proton energy ranging from 100 keV to 2.5 MeV. The stopping power of O2, N2, and water vapor was also calculated for incident proton energy ranging from 40 keV. to 2.5 MeV. Good agreement with experimental data was obtained. A discussion of molecular effects leading to department from Bragg's rule is presented. The equipartition rule and the effect of nuclear momentum recoiling in stopping power are also discussed.

Xu, Y. J.

1984-01-01

202

Millimeterwave rotational spectrum and theoretical calculations of cis-propionic acid  

NASA Astrophysics Data System (ADS)

The millimeterwave rotational spectra of the cis conformer of propionic acid (C3H6O2) have been investigated in the ground vibrational state in the frequency range of 80.0-100.0 GHz. Many high J and K-1 (Jmax = 50, K-1 = 12) rotational lines have been assigned. A least-squares analysis of the measured and previously reported rotational transition frequencies resulted in the determination of an improved set of rotational and centrifugal distortion (CD) constants of the molecule. Detailed MP2 and DFT calculations were also carried out with various functional and basis sets to evaluate the spectroscopic constants, dipole moment, and various structural parameters of cis-propionic acid and compared with the corresponding experimental values. Potential energy surface has been calculated to identify other probable conformers in this molecule.

Jaman, A. I.; Chakraborty, Shamik; Chakraborty, Rangana

2015-01-01

203

Theoretical calculation of absorption intensities of C2H and C2D  

NASA Astrophysics Data System (ADS)

The theory of dipole-allowed absorption intensities in triatomic molecules is presented for systems with three close-lying electronic states of doublet multiplicity. Its derivation is within the framework of a recently developed variational method [CARTER, S., HANDY, N. C., PUZZARINI, C., TARRONI, R., and PALMIERI, P., 2000, Molec. Phys., 98, 1967]. The method has been applied to the calculation of the infrared absorption spectrum of the C2H radical and its deuterated isotopomer for energies up to 10 000 cm-1 above the ground state, using highly accurate ab initio diabatic potential energy and dipole moment surfaces. The calculated spectra agree very well with those recorded experimentally in a neon matrix [FORNEY, D., JACOX, M. E., and THOMPSON, W. E., 1995, J. molec. Spectrosc., 170, 178] and assignments in the high energy region of the IR spectra are proposed for the first time.

Tarroni, Riccardo; Carter, Stuart

2004-01-01

204

Young’s modulus calculations for cellulose Iß by MM3 and quantum mechanics  

Technology Transfer Automated Retrieval System (TEKTRAN)

Quantum mechanics (QM) and molecular mechanics (MM) calculations were performed to elucidate Young’s moduli for a series of cellulose Iß models. Computations using the second generation empirical force field MM3 with a disaccharide cellulose model, 1,4'-O-dimethyl-ß-cellobioside (DMCB), and an analo...

205

Mechanism of tungsten-dependent acetylene hydratase from quantum chemical calculations  

E-print Network

Mechanism of tungsten-dependent acetylene hydratase from quantum chemical calculations Rong hydratase is a tungsten-dependent enzyme that cata- lyzes the nonredox hydration of acetylene metalloenzyme cluster approach Tungsten is the heaviest metal in biology and plays prominent roles in carbon

Liao, Rongzhen

206

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

Microsoft Academic Search

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

Nicolás Otero; Marcos Mandado; Ricardo A. Mosquera

2007-01-01

207

Theoretical analysis of three methods for calculating thermal insulation of clothing from thermal manikin.  

PubMed

There are three methods for calculating thermal insulation of clothing measured with a thermal manikin, i.e. the global method, the serial method, and the parallel method. Under the condition of homogeneous clothing insulation, these three methods yield the same insulation values. If the local heat flux is uniform over the manikin body, the global and serial methods provide the same insulation value. In most cases, the serial method gives a higher insulation value than the global method. There is a possibility that the insulation value from the serial method is lower than the value from the global method. The serial method always gives higher insulation value than the parallel method. The insulation value from the parallel method is higher or lower than the value from the global method, depending on the relationship between the heat loss distribution and the surface temperatures. Under the circumstance of uniform surface temperature distribution over the manikin body, the global and parallel methods give the same insulation value. If the constant surface temperature mode is used in the manikin test, the parallel method can be used to calculate the thermal insulation of clothing. If the constant heat flux mode is used in the manikin test, the serial method can be used to calculate the thermal insulation of clothing. The global method should be used for calculating thermal insulation of clothing for all manikin control modes, especially for thermal comfort regulation mode. The global method should be chosen by clothing manufacturers for labelling their products. The serial and parallel methods provide more information with respect to the different parts of clothing. PMID:22798547

Huang, Jianhua

2012-07-01

208

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

209

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

210

Theoretical calculation of the longitudinal spherical aberration of rigid and soft contact lenses.  

PubMed

Although previous investigators have attempted to calculate the longitudinal spherical aberration inherent in soft and rigid contact lenses both on and off the eye, the use of inappropriate assumptions on which to base their calculations has left the problem unresolved. In this study, the longitudinal spherical aberration of both soft and rigid contact lenses was calculated surface by surface both in air and on the eye using a two-dimensional, exact ray tracing program. The erroneous assumptions made by previous investigators were avoided by using an elliptical model for the anterior corneal surface and assuming that the posterior surfaces of soft lenses aligned exactly with the anterior corneal surface after flexure onto the eye. The results demonstrated that, with a 6-mm pupil, contact lenses induce significant levels of spherical aberration in the ocular system for soft lenses of back vertex power greater than +3.00 D or -6.00 D and for rigid lenses of powers more positive than -3.00 D. It is suggested that visual disturbance due to induced spherical aberration has not been a major clinical problem in the past because these conditions fall outside those experienced by a large proportion of the contact lens-wearing public. PMID:2342790

Cox, I

1990-04-01

211

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

212

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

E-print Network

A combined quantum-classical dynamics method for calculating thermal rate constants of chemical February 1992) We present a combined quantum-classical-stochastic dynamics method based on the flux to combine classical and quantum dynamics have been pro- posed and have shown some encouraging results

Truong, Thanh N.

213

Correlation of theoretical calculations and experimental measurements of damage around a shaft in salt  

SciTech Connect

Cross-hole ultrasonic measurements were made in the immediate wall of the Air Intake Shaft of the Waste Isolation Pilot Plant facility. These measurements show that compressional wave speed markedly decreases at the shaft wall and then increases with radial distance from the shaft to eventually become that of solid or undamaged salt. This behavior is indicative of deformation damage or microfractures in the salt. These in situ data are compared to both laboratory measurements of wave speed as a function of volume dilatancy and to calculations based on the Multimechanism Deformation Coupled Fracture model, with reasonable agreement.

Munson, D.E.; Holcomb, D.J. [Sandia National Labs., Albuquerque, NM (United States); DeVries, K.L.; Brodsky, N.S. [RE/SPEC, Inc., Rapid City, SD (United States); Chan, K.S. [Southwest Research Inst., San Antonio, TX (United States)

1994-12-31

214

Theoretical calculation of femtosecond time-resolved spectra of initial electron transfer in photosynthetic reaction centers  

SciTech Connect

In this paper, we propose to study the dynamics and spectroscopy of photosynthetic reaction centers (RCs). We shall analyze the experimental femtosecond spectra of Rb. sphaeroides (R-26) which usually consist of contributions from populations and coherences. We shall extract information on vibrational relaxation, electron transfer (ET), and the vibrational modes involved in ET from the analysis of the femtosecond time-resolved spectra with pronounced coherence contributions. Conventional ET theory assumes that vibrational relaxation (VR) is much faster than ET so that the vibrational equilibrium is established before ET takes place. However, the primary ET in RCs occurs in 1-4 ps. This implies that this assumption should be examined. We shall study theoretically the effect of the excitation wavelength; that is, we shall study how the ET in RCs is affected by exciting to different vibronic states of RCs. In the dynamic aspect of primary ET in RCs, these experiments will provide us not only with the mechanism of ET but also with the vibrational relaxation of various modes involved in ET. In this case, it is necessary to know the expressions of single-vibronic level ET rate constants. This will also be presented in this paper. 45 refs., 6 figs., 1 tab.

Lin, S.H.; Alden, R.G.; Hayashi, M.; Suzuki, Satoru; Murchison, H.A. (Arizona State Univ., Tempe, AZ (United States))

1993-12-02

215

New triterpenes from Maytenus robusta: structural elucidation based on NMR experimental data and theoretical calculations.  

PubMed

Leaves of Maytenus robusta (Celastraceae) were subjected to phytochemical investigation mainly directed at the isolation of pentacyclic triterpenes. The compounds friedelin (1), ?-friedelinol (2), 3-oxo-21?-H-hop-22(29)-ene (7), 3,4-seco-friedelan-3,11?-olide (8), 3?-hydroxy-21?-H-hop-22(29)-ene (9), 3,4-seco-21?-H-hop-22(29)-en-3-oic acid (10), 3,4-seco-friedelan-3-oic acid (11), and sitosterol were identified in the hexane extract of M. robusta leaves. Compounds 8 and 9 are described herein for the first time. The structure and stereochemistry of both compounds were experimentally established by IR, HRLC-MS, and 1D (1H, 13C, and DEPT 135) and 2D (HSQC, HMBC and COSY) NMR data and supported by correlations with carbon chemical shifts calculated using the DFT method (BLYP/6-31G* level). Compounds 7 and 10 are also described for the first time, and their chemical structures were established by comparison with NMR data of similar structures described in the literature and correlations with BLYP/6-31G* calculated carbon chemical shifts. Compound 9, a mixture of 11 and sitosterol, and 3?,11?-dihydroxyfriedelane (4) were evaluated by the Ellman’s method and all these compounds showed acethylcholinesterase inhibitory properties. PMID:23147402

Sousa, Grasiely F; Duarte, Lucienir P; Alcântara, Antônio F C; Silva, Grácia D F; Vieira-Filho, Sidney A; Silva, Roqueline R; Oliveira, Djalma M; Takahashi, Jacqueline A

2012-01-01

216

Nuclear magnetic resonance proton dipolar order relaxation in thermotropic liquid crystals: A quantum theoretical approach  

NASA Astrophysics Data System (ADS)

By means of the Jeener-Broekaert nuclear magnetic resonance pulse sequence, the proton spin system of a liquid crystal can be prepared in quasiequilibrium states of high dipolar order, which relax to thermal equilibrium with the molecular environment with a characteristic time (T1D). Previous studies of the Larmor frequency and temperature dependence of T1D in thermotropic liquid crystals, that included field cycling and conventional high-field experiments, showed that the slow hydrodynamic modes dominate the behavior of T1D, even at high Larmor frequencies. This noticeable predominance of the cooperative fluctuations (known as order fluctuations of the director, OFD) could not be explained by standard models based on the spin-lattice relaxation theory in the limit of high temperature (weak order). This fact points out the necessity of investigating the role of the quantum terms neglected in the usual high temperature theory of dipolar order relaxation. In this work, we present a generalization of the proton dipolar order relaxation theory for highly correlated systems, which considers all the spins belonging to correlated domains as an open quantum system interacting with quantum bath. As starting point, we deduce a formulation of the Markovian master equation of relaxation for the statistical spin operator, valid for all temperatures, which is suitable for introducing a dipolar spin temperature in the quantum regime, without further assumptions about the form of the spin-lattice Hamiltonian. In order to reflect the slow dynamics occurring in correlated systems, we lift the usual short-correlation-time assumption by including the average over the motion of the dipolar Hamiltonian together with the Zeeman Hamiltonian into the time evolution operator. In this way, we calculate the time dependence of the spin operators in the interaction picture in a closed form, valid for high magnetic fields, bringing into play the spin-spin interactions within the microscopic time scale. Then, by adopting the spin-temperature density operator to represent the collective state of the spin system, and removing the traditional hypothesis of high temperature, we deduce an expression for the first order quantum contribution to T1D-1, in terms of spectral densities, with coefficients in form of spin traces. The properties that distinguish our result from the high-temperature T1D-1 are as follows. (a) It is exclusively associated to cooperative fluctuations. (b) Because of its quantum character, it relies on both considering the lattice degrees of freedom quantum mechanically and including the spin-spin interactions in the microscopic time scale. With regard to the average dipolar Hamiltonian, only the nonsecular part plays a relevant role. (c) Associated with the structure of the spin operator involved in the quantum contribution, a term arises which is proportional to the number of spins in the correlated molecular domains, showing that the quantum contribution may be of macroscopic size in highly correlated systems. When applied to nematic liquid crystals, the new term exhibits the typical ?-1/2 Larmor frequency dependence through the spectral density of the OFD, in consistence with the experimental results.

Zamar, R. C.; Mensio, O.

2004-12-01

217

Techniques in Analytic Lamb Shift Calculations  

Microsoft Academic Search

Quantum electrodynamics has been the first theory to emerge from the ideas of regularization and renormalization, and the coupling of the fermions to the virtual excitations of the electromagnetic field. Today, bound-state quantum electrodynamics provides us with accurate theoretical predictions for the transition energies relevant to simple atomic systems, and steady theoretical progress relies on advances in calculational techniques, as

Ulrich D. Jentschura

2005-01-01

218

A theoretical study of electronic and optical properties of SiC nanowires and their quantum confinement effects.  

PubMed

We have performed a theoretical study of silicon carbide nanowires (SiCNWs) within the framework of first-principles calculations by incorporating the size effect and hydrogen terminated surface. Specifically, the variation of the energy gap and optical absorption spectra for hydrogen passivated SiCNWs and pristine wires are examined with respect to the wire diameter. All the [001]-orientated SiCNWs derived from the parent zinc-blende (3C) exhibit semiconducting behavior. Our study demonstrates that the saturated 3C-SiCNWs grown along the [001] direction with larger wire sizes are energetically more favorable than the wires with a smaller diameter. Additionally, the energy gaps are reduced with the increment of wire size because of the quantum-confinement effects. The unsaturated SiCNWs possess smaller band gaps than those of saturated ones when the Si- and C-dangling bonds are passivated by hydrogen atoms. Interestingly, the surface terminated by hydrogen atoms substantially alters the onset of absorption as well as the spectrum behavior at upper energies. Moreover, some pronounced fine structures in the absorption peak are conspicuous at the lower energy region of hydrogen saturated SiCNWs as the wire size increases. We find that the distributions of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals are uniform along the wire axis, which reveals that the SiCNWs are exceptional candidates in producing nano-optoelectronic devices. PMID:24535574

Laref, A; Alshammari, Nuyer; Laref, S; Luo, S J

2014-04-14

219

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

220

The potential, limitations, and challenges of divide and conquer quantum electronic structure calculations on energetic materials.  

SciTech Connect

High explosives are an important class of energetic materials used in many weapons applications. Even with modern computers, the simulation of the dynamic chemical reactions and energy release is exceedingly challenging. While the scale of the detonation process may be macroscopic, the dynamic bond breaking responsible for the explosive release of energy is fundamentally quantum mechanical. Thus, any method that does not adequately describe bonding is destined to lack predictive capability on some level. Performing quantum mechanics calculations on systems with more than dozens of atoms is a gargantuan task, and severe approximation schemes must be employed in practical calculations. We have developed and tested a divide and conquer (DnC) scheme to obtain total energies, forces, and harmonic frequencies within semi-empirical quantum mechanics. The method is intended as an approximate but faster solution to the full problem and is possible due to the sparsity of the density matrix in many applications. The resulting total energy calculation scales linearly as the number of subsystems, and the method provides a path-forward to quantum mechanical simulations of millions of atoms.

Tucker, Jon R.; Magyar, Rudolph J.

2012-02-01

221

A Theoretical Mechanism of Szilard Engine Function in Nucleic Acids and the Implications for Quantum Coherence in Biological Systems  

SciTech Connect

Nucleic acids theoretically possess a Szilard engine function that can convert the energy associated with the Shannon entropy of molecules for which they have coded recognition, into the useful work of geometric reconfiguration of the nucleic acid molecule. This function is logically reversible because its mechanism is literally and physically constructed out of the information necessary to reduce the Shannon entropy of such molecules, which means that this information exists on both sides of the theoretical engine, and because information is retained in the geometric degrees of freedom of the nucleic acid molecule, a quantum gate is formed through which multi-state nucleic acid qubits can interact. Entangled biophotons emitted as a consequence of symmetry breaking nucleic acid Szilard engine (NASE) function can be used to coordinate relative positioning of different nucleic acid locations, both within and between cells, thus providing the potential for quantum coherence of an entire biological system. Theoretical implications of understanding biological systems as such 'quantum adaptive systems' include the potential for multi-agent based quantum computing, and a better understanding of systemic pathologies such as cancer, as being related to a loss of systemic quantum coherence.

Matthew Mihelic, F.

2010-12-22

222

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

223

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

224

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

225

Quantum Monte Carlo calculations of neutron matter with nonlocal chiral interactions.  

PubMed

We present fully nonperturbative quantum Monte Carlo calculations with nonlocal chiral effective field theory (EFT) interactions for the ground-state properties of neutron matter. The equation of state, the nucleon chemical potentials, and the momentum distribution in pure neutron matter up to one and a half times the nuclear saturation density are computed with a newly optimized chiral EFT interaction at next-to-next-to-leading order. This work opens the way to systematic order by order benchmarking of chiral EFT interactions and ab initio prediction of nuclear properties while respecting the symmetries of quantum chromodynamics. PMID:24949752

Roggero, Alessandro; Mukherjee, Abhishek; Pederiva, Francesco

2014-06-01

226

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

227

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

228

Direct Pseudopotential Calculation of Exciton Coulomb and Exchange Energies in Semiconductor Quantum Dots  

SciTech Connect

The effects of electron-hole interaction on the exciton energy of semiconductor quantum dots are calculated using pseudopotential wave functions. A comparison with the widely used, but never tested, effective-mass approximation (EMA) shows that the electron-hole Coulomb energy is significantly ({approximately}40{percent}) overestimated by the EMA, and that the scaling with the dot size R is sublinear in 1/R. The exchange splitting is much smaller than the Coulomb energy, and in the case of CdSe quantum dots shows significant deviations from the 1/R{sup 3} scaling predicted by the EMA. {copyright} {ital 1997} {ital The American Physical Society}

Franceschetti, A.; Zunger, A. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

1997-02-01

229

Quantum Monte Carlo calculations of the dissociation energies of three-electron hemibonded radical cationic dimers.  

PubMed

We report variational and diffusion quantum Monte Carlo (VMC and DMC) calculations of the dissociation energies of the three-electron hemibonded radical cationic dimers of He, NH3, H2O, HF, and Ne. These systems are particularly difficult for standard density-functional methods such as the local-density approximation and the generalized gradient approximation. We have performed both all-electron (AE) and pseudopotential (PP) calculations using Slater-Jastrow wave functions with Hartree-Fock single-particle orbitals. Our results are in good agreement with coupled-cluster CCSD(T) calculations. We have also studied the relative stability of the hemibonded and hydrogen-bonded water radical dimer isomers. Our calculations indicate that the latter isomer is more stable, in agreement with post-Hartree-Fock methods. The excellent agreement between our AE and PP results demonstrates the high quality of the PPs used within our VMC and DMC calculations. PMID:16422594

Gurtubay, I G; Drummond, N D; Towler, M D; Needs, R J

2006-01-14

230

Crystal and molecular structure of N-(4-nitrophenyl)-?-alanine—Its vibrational spectra and theoretical calculations  

NASA Astrophysics Data System (ADS)

The N-(4-nitrophenyl)-?-alanine in crystalline form directly by the addition of 4-nitroaniline to the acrylic acid in aqueous solution has been obtained. The title ?-alanine derivative crystallizes in the P2 1/ c space group of monoclinic system with four molecules per unit cell. The X-ray geometry of ?-alanine derivative molecule has been compared with those obtained by molecular orbital calculations corresponding to the gas phase. In the crystal the molecules related by an inversion center interact via symmetrically equivalent O-H⋯O hydrogen bonds with O⋯O distance of 2.656(2) Å forming a dimeric structure. The dimers of ?-alanine derivative weakly interact via N-H⋯O hydrogen bonds between the H atom of ?-amine groups and one of O atom of nitro groups. The room temperature powder vibrational (infrared and Raman) measurements are in accordance with the X-ray analysis. In aqueous solution of 4-nitroaniline and acrylic acid, the double C dbnd C bond of vinyl group of acrylic acid breaks as result of 4-nitroaniline addition.

Marchewka, M. K.; Drozd, M.; Janczak, J.

2011-08-01

231

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

232

Quantum calculation of protein NMR chemical shifts based on the automated fragmentation method.  

PubMed

The performance of quantum mechanical methods on the calculation of protein NMR chemical shifts is reviewed based on the recently developed automatic fragmentation quantum mechanics/molecular mechanics (AF-QM/MM) approach. By using the Poisson-Boltzmann (PB) model and first solvation water molecules, the influence of solvent effect is also discussed. Benefiting from the fragmentation algorithm, the AF-QM/MM approach is computationally efficient, linear-scaling with a low pre-factor, and thus can be applied to routinely calculate the ab initio NMR chemical shifts for proteins of any size. The results calculated using Density Functional Theory (DFT) show that when the solvent effect is included, this method can accurately reproduce the experimental ¹H NMR chemical shifts, while the ¹³C NMR chemical shifts are less affected by the solvent. However, although the inclusion of solvent effect shows significant improvement for ¹?N chemical shifts, the calculated values still have large deviations from the experimental observations. Our study further demonstrates that AF-QM/MM calculated results accurately reflect the dependence of ¹³C(?) NMR chemical shifts on the secondary structure of proteins, and the calculated ¹H chemical shift can be utilized to discriminate the native structure of proteins from decoys. PMID:25387959

Zhu, Tong; Zhang, John Z H; He, Xiao

2015-01-01

233

ELECTRON-ION RECOMBINATION OF Fe XII FORMING Fe XI: LABORATORY MEASUREMENTS AND THEORETICAL CALCULATIONS  

SciTech Connect

We have measured electron-ion recombination for Fe XII forming Fe XI using a merged-beam configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The measured merged-beam recombination rate coefficient (MBRRC) for collision energies from 0 to 1500 eV is presented. This work uses a new method for determining the absolute MBRRC based on a comparison of the ion beam decay rate with and without the electron beam on. For energies below 75 eV, the spectrum is dominated by dielectronic recombination (DR) resonances associated with 3s {yields} 3p and 3p {yields} 3d core excitations. At higher energies, we observe contributions from 3 {yields} N' and 2 {yields} N' core excitation DR. We compare our experimental results to state-of-the-art multi-configuration Breit-Pauli (MCBP) calculations and find significant differences, both in resonance energies and strengths. We have extracted the DR contributions from the measured MBRRC data and transformed them into a plasma recombination rate coefficient (PRRC) for temperatures in the range of 10{sup 3}-10{sup 7} K. We show that the previously recommended DR data for Fe XII significantly underestimate the PRRC at temperatures relevant for both photoionized plasmas (PPs) and collisionally ionized plasmas (CPs). This is contrasted with our MCBP PRRC results, which agree with the experiment to within 30% at PP temperatures and even better at CP temperatures. We find this agreement despite the disagreement shown by the detailed comparison between our MCBP and experimental MBRRC results. Last, we present a simple parameterized form of the experimentally derived PRRC for easy use in astrophysical modeling codes.

Novotny, O.; Hahn, M.; Lestinsky, M.; Savin, D. W. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Badnell, N. R. [Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Bernhardt, D.; Mueller, A.; Schippers, S. [Institut fuer Atom- und Molekuelphysik, Justus-Liebig-Universitaet Giessen, D-35392 Giessen (Germany); Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A., E-mail: oldrich.novotny@mpi-hd.mpg.de [Max Planck Institute for Nuclear Physics, 69117 Heidelberg (Germany)

2012-07-01

234

Resonance enhanced multiphoton ionization spectroscopy and theoretical calculations of cis- and trans-m-aminostyrene rotamers  

NASA Astrophysics Data System (ADS)

The ab initio and DFT calculations predict that two rotamers, cis and trans m-aminostyrene, are stable for each of the S0, S1 and D0 states. In the one-color resonant two-photon ionization (1C-R2PI) spectra, the band origins of the S1 ? S0 electronic transitions (00 band) of cis and trans m-aminostyrene appear respectively at 30,937 ± 3 and 31,141 ± 3 cm-1. The electronic transition energies (E1's) of both rotamers of m-aminostyrene are lower than that of p-aminostyrene, which is contrary to the prediction according to the previous studies. The redshift of E1's may be related to the mixing character of "1Lb" and "1La" in the S1 states of the two rotamers. The 2C-R2PI spectra give the adiabatic ionization energies of 61,278 ± 15 and 61,495 ± 15 cm-1 for cis and trans rotamers. The observed active modes of rotamers in the S1 states involve mainly the in-plane ring deformation and substituent-sensitive bending vibration. It is derived from the 1C- and 2C-R2PI spectroscopic data that the cis rotamer of m-aminostyrene is more stable than the trans rotamer by 30 ± 30, 234 ± 30 and 247 ± 30 cm-1 for the S0, S1 and D0 states, respectively. This is different from the m-aminophenol and m-aminoanisole that have a more stable trans rotamer.

Dong, Changwu; Zhang, Lijuan; Liu, Sheng; Hu, Lili; Cheng, Min; Du, Yikui; Zhu, Qihe; Zhang, Cunhao

2014-01-01

235

Self-consistent calculations of the type II quantum wells and superlattices  

NASA Astrophysics Data System (ADS)

Type II semiconductor heterostructures attract significant attention for their application as photodetectors and lasers. Such heterostructures are characterized by spatially separated electron and hole confinement. Narrow band gap materials used in these structures require multiband treatment of electrons and holes on the same footing. Furthermore charge separation warrants a self-consistent approach of the resulting electronic structure. We performed such calculations for AlSb/InAs quantum wells and superlattices using a modified eight-band k.p Hamiltonian without spurious states in the envelope function approximation. We studied the dependence of the subband edge positions and subband energy separation on the quantum well thickness under flat-band and self-consistent model with quantum well and superlattice boundary conditions.

Kolokolov, Konstantin; Li, Jianzhong; Ning, Cun-Zheng

2003-03-01

236

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

PubMed

Light nuclei at room temperature and below exhibit a kinetic energy which significantly deviates from the predictions of classical statistical mechanics. This quantum kinetic energy is responsible for a wide variety of isotope effects of interest in fields ranging from chemistry to climatology. It also furnishes the second moment of the nuclear momentum distribution, which contains subtle information about the chemical environment and has recently become accessible to deep inelastic neutron scattering experiments. Here, we show how, by combining imaginary time path integral dynamics with a carefully designed generalized Langevin equation, it is possible to dramatically reduce the expense of computing the quantum kinetic energy. We also introduce a transient anisotropic Gaussian approximation to the nuclear momentum distribution which can be calculated with negligible additional effort. As an example, we evaluate the structural properties, the quantum kinetic energy, and the nuclear momentum distribution for a first-principles simulation of liquid water. PMID:23005275

Ceriotti, Michele; Manolopoulos, David E

2012-09-01

237

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

238

The Protonation Status of Compound II in Myoglobin, Studied by a Combination of Experimental Data and Quantum Chemical Calculations: Quantum Refinement  

PubMed Central

Treatment of met-myoglobin (FeIII) with H2O2 gives rise to ferryl myoglobin, which is closely related to compound II in peroxidases. Experimental studies have given conflicting results for this species. In particular, crystallographic and extended x-ray absorption fine-structure data have shown either a short (?170 pm) or a longer (?190 pm) Fe–O bond, indicating either a double or a single bond. We here present a combined experimental and theoretical investigation of this species. In particular, we use quantum refinement to re-refine a crystal structure with a long bond, using 12 possible states of the active site. The states differ in the formal oxidation state of the iron ion and in the protonation of the oxygen ligand (O2?, OH?, or H2O) and the distal histidine residue (with a proton on N?1, N?2, or on both atoms). Quantum refinement is essentially standard crystallographic refinement, where the molecular-mechanics potential, normally used to supplement the experimental data, is replaced by a quantum chemical calculation. Thereby, we obtain an accurate description of the active site in all the different protonation and oxidation states, and we can determine which of the 12 structures fit the experimental data best by comparing the crystallographic R-factors, electron-density maps, strain energies, and deviation from the ideal structure. The results indicate that FeIII OH? and FeIV OH? fit the experimental data almost equally well. These two states are appreciably better than the standard model of compound II, FeIV O2?. Combined with the available spectroscopic data, this indicates that compound II in myoglobin is protonated and is best described as FeIV OH?. It accepts a hydrogen bond from the distal His, which may be protonated at low pH. PMID:15339813

Nilsson, Kristina; Hersleth, Hans-Petter; Rod, Thomas H.; Andersson, K. Kristoffer; Ryde, Ulf

2004-01-01

239

Direct Pseudopotential Calculation of Exciton Coulomb and Exchange Energies in Semiconductor Quantum Dots  

Microsoft Academic Search

The effects of electron-hole interaction on the exciton energy of semiconductor quantum dots are calculated using pseudopotential wave functions. A comparison with the widely used, but never tested, effective-mass approximation (EMA) shows that the electron-hole Coulomb energy is significantly ( ~40%) overestimated by the EMA, and that the scaling with the dot size R is sublinear in 1\\/R. The exchange

Alberto Franceschetti; Alex Zunger

1997-01-01

240

Quantum Chemical Calculation on the Interaction of Hydrogen Isotopes with Materials for Energy System  

Microsoft Academic Search

A series of our quantum chemical study on the interaction of hydrogen isotopes with defects in Li2O was reported. Three kinds of F-centers and lithium vacancy were considered. Stable positions of -OH in Li2O lattice with defects were calculated and the determined structures were well analyzed from the viewpoint of electron transfer between a proton and defects. In addition to

Satoru Tanaka; Hisashi Tanigawa

2003-01-01

241

Calculation of primordial matter density contrast in the Quantum Big Bang theory of the cosmological constant  

Microsoft Academic Search

In the present paper we calculate the amount of primordial mat- ter density contrast in the recent Quantum Big Bang theory (Arxiv: 0705.4549(gr-qc)(2007)) of the cosmological constant. We obtain (??\\/?)M = 1.75 × 10 5, without the introduction of an adjustable free parameter. Harrison-Zel'dovich k-dependence with A = 64\\/9?2 = 0.72 and n = 1 in |?k|2 = Akn arises

Budh Ram

242

Efficient localized basis set for quantum Monte Carlo calculations on condensed matter  

Microsoft Academic Search

We present an efficient scheme for representing many-body wave functions in quantum Monte Carlo (QMC) calculations. The scheme is based on B splines (blip functions), which consist of localized cubic splines centered on the points of a regular grid. We show that blip functions are unbiased, systematically improvable, and conveniently obtained from any standard plane-wave density functional theory (PW-DFT) code,

D. Alfè; M. J. Gillan

2004-01-01

243

A Theoretical Study of Bulk and Surface Diffusion Processes for Semiconductor Materials Using First Principles Calculations  

NASA Astrophysics Data System (ADS)

Diffusion of point defects on crystalline surfaces and in their bulk is an important and ubiquitous phenomenon affecting film quality, electronic properties and device functionality. A complete understanding of these diffusion processes enables one to predict and then control those processes. Such understanding includes knowledge of the structural, energetic and electronic properties of these native and non-native point defect diffusion processes. Direct experimental observation of the phenomenon is difficult and microscopic theories of diffusion mechanisms and pathways abound. Thus, knowing the nature of diffusion processes, of specific point defects in given materials, has been a challenging task for analytical theory as well as experiment. The recent advances in computing technology have been a catalyst for the rise of a third mode of investigation. The advent of tremendous computing power, breakthroughs in algorithmic development in computational applications of electronic density functional theory now enables direct computation of the diffusion process. This thesis demonstrates such a method applied to several different examples of point defect diffusion on the (001) surface of gallium arsenide (GaAs) and the bulk of cadmium telluride (CdTe) and cadmium sulfide (CdS). All results presented in this work are ab initio, total-energy pseudopotential calculations within the local density approximation to density-functional theory. Single particle wavefunctions were expanded in a plane-wave basis and reciprocal space k-point sampling was achieved by Monkhorst-Pack generated k-point grids. Both surface and bulk computations employed a supercell approach using periodic boundary conditions. Ga adatom adsorption and diffusion processes were studied on two reconstructions of the GaAs(001) surface including the c(4x4) and c(4x4)-heterodimer surface reconstructions. On the GaAs(001)- c(4x4) surface reconstruction, two distinct sets of minima and transition sites were discovered for a Ga adatom relaxing from heights of 3 and 0.5 A from the surface. These two sets show significant differences in the interaction of the Ga adatom with surface As dimers and an electronic signature of the differences in this interaction was identified. The energetic barriers to diffusion were computed between various adsorption sites. Diffusion profiles for native Cd and S, adatom and vacancy, and non-native interstitial adatoms of Te, Cu and Cl were investigated in bulk wurtzite CdS. The interstitial diffusion paths considered in this work were chosen parallel to c-axis as it represents the path encountered by defects diffusing from the CdTe layer. Because of the lattice mismatch between zinc-blende CdTe and hexagonal wurtzite CdS, the c-axis in CdS is normal to the CdTe interface. The global minimum and maximum energy positions in the bulk unit cell vary for different diffusing species. This results in a significant variation, in the bonding configurations and associated strain energies of different extrema positions along the diffusion paths for various defects. The diffusion barriers range from a low of 0.42 eV for an S interstitial to a high of 2.18 eV for a S vacancy. The computed 0.66 eV barrier for a Cu interstitial is in good agreement with experimental values in the range of 0.58 - 0.96 eV reported in the literature. There exists an electronic signature in the local density of states for the s- and d-states of the Cu interstitial at the global maximum and global minimum energy position. The work presented in this thesis is an investigation into diffusion processes for semiconductor bulk and surfaces. The work provides information about these processes at a level of control unavailable experimentally giving an elaborate description into physical and electronic properties associated with diffusion at its most basic level. Not only does this work provide information about GaAs, CdTe and CdS, it is intended to contribute to a foundation of knowledge that can be extended to other systems to expand our overall understanding into the diffusion proc

Roehl, Jason L.

244

Efficiency of free energy calculations of spin lattices by spectral quantum algorithms  

E-print Network

Quantum algorithms are well-suited to calculate estimates of the energy spectra for spin lattice systems. These algorithms are based on the efficient calculation of the discrete Fourier components of the density of states. The efficiency of these algorithms in calculating the free energy per spin of general spin lattices to bounded error is examined. We find that the number of Fourier components required to bound the error in the free energy due to the broadening of the density of states scales polynomially with the number of spins in the lattice. However, the precision with which the Fourier components must be calculated is found to be an exponential function of the system size.

Cyrus P. Master; Fumiko Yamaguchi; Yoshihisa Yamamoto

2002-06-15

245

Quantum reactive scattering calculations of photodetachment spectra of the FHD - anion  

NASA Astrophysics Data System (ADS)

Time-independent quantum reactive scattering calculations have been carried out to simulate the photoelectron spectrum of the FHD - anion using the accurate ab initio potential energy surface of Stark and Werner. Broad peaks which correspond to the direct scattering F+HD hindered-rotor states have been seen in the calculated spectra for both the FHD - and FDH - anions similar to previous FH2 - results. We have also found that the peak associated with the transition-state resonance in the FHD - spectrum but not in the FDH - spectrum. The present computational result predicts that the transition-state resonance can be observed even in low-energy resolution experiments

Takayanagi, Toshiyuki; Wada, Akira

2001-11-01

246

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

SciTech Connect

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 ?{sub M} associated with a given elastic scattering mechanism “M,” taking phonons (PH) as a reference (?{sub M}{sup ?1}=?{sub PH+M}{sup ?1}??{sub PH}{sup ?1}). We argue that this definition makes better sense in a quantum transport framework as it is free from long range interference effects that can appear in purely ballistic calculations. As a matter of fact, these mobilities satisfy Matthiessen's rule for three mechanisms [e.g., surface roughness (SR), remote Coulomb scattering (RCS) and phonons] much better than the usual, single mechanism calculations. We also discuss the problems raised by the long range spatial correlations in the RCS disorder. Finally, we compare semi-classical Kubo-Greenwood (KG) and quantum NEGF calculations. We show that KG and NEGF are in reasonable agreement for phonon and RCS, yet not for SR. We discuss the reasons for these discrepancies.

Niquet, Yann-Michel, E-mail: yniquet@cea.fr; Nguyen, Viet-Hung; Duchemin, Ivan [L-Sim, SP2M, UMR-E CEA/UJF-Grenoble 1, INAC, Grenoble (France); Triozon, François [CEA, LETI-MINATEC, Grenoble (France); Nier, Olivier; Rideau, Denis [ST Microelectronics, Crolles (France)

2014-02-07

247

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

248

Quantum phase space theory for the calculation of v{center_dot}j vector correlations  

SciTech Connect

The quantum state-counting phase space theory commonly used to describe barrierless dissociation is recast in a helicity basis to calculate photofragment v{center_dot}j correlations. Counting pairs of fragment states with specific angular momentum projection numbers on the relative velocity provides a simple connection between angular momentum conservation and the v{center_dot}j correlation, which is not so evident in the conventional basis for phase space state counts. The upper bound on the orbital angular momentum, l, imposed by the centrifugal barrier cannot be included simply in the helicity basis, where l is not a good quantum number. Two approaches for a quantum calculation of the v{center_dot}j correlation are described to address this point. An application to the photodissociation of NCCN is consistent with recent classical phase space calculations of Cline and Klippenstein. The observed vector correlation exceeds the phase space theory prediction. The authors take this as evidence of incomplete mixing of the K states of the linear parent molecule at the transition state, corresponding to an evolution of the body-fixed projection number K into the total helicity of the fragment pair state. The average over a thermal distribution of parent angular momentum in the special case of a linear molecule does not significantly reduce the v{center_dot}j correlation below that computed for total J = 0.

Hall, G.E. [Brookhaven National Lab., Upton, NY (United States). Dept. of Chemistry

1995-07-01

249

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

250

Determination of two structural forms of catalytic bridging ligand in zinc-phosphotriesterase by molecular dynamics simulation and quantum chemical calculation  

SciTech Connect

Although a three-dimensional X-ray crystal structure of zinc-substituted phosphotriesterase was recently reported, it is uncertain whether a critical bridging ligand in the active site is a water molecule or a hydroxide ion. The identity of this bridging ligand is theoretically determined by performing both molecular dynamics simulations and quantum mechanical calculations. All of the results obtained indicate that this critical ligand in the active site of the reported X-ray crystal structure is a hydroxide anion rather than a water molecule and allow us to propose a dynamic ping-pong model in which both kinds of structures might exist.

Zhan, C.G.; Souza, O.N. de; Rittenhhouse, R.; Ornstein, R.L.

1999-08-18

251

Two-dimensional vibrational spectroscopy. I. Theoretical calculation of the nonlinear Raman response function of CHCl3  

NASA Astrophysics Data System (ADS)

The two-dimensional Raman response function of CHCl3 is theoretically considered with interpretations of each peak in terms of the associated vibrational transition pathways. In order to numerically calculate the 2D Raman spectrum, ab initio calculations of necessary quantities, such as the first- and second-order derivatives of the molecular polarizability with respect to vibrational coordinates and cubic potential anharmonic coefficients, were carried out by using the basis set 6-311++G(2df,2pd) at the Hartree-Fock level. Quantitative comparison between the two nonlinear response functions associated with the mechanical and electronic anharmonicities shows that the 2D Raman response from the high-frequency intramolecular vibrational modes of CHCl3 is mainly determined by the mechanical (potential) anharmonicity contributions. On the other hand, it is found that the two distinctive contributions originating from the mechanical and electronic anharmonicities interfere in the low-frequency region of the 2D spectrum. Overall, it is suggested that the high-frequency 2D Raman spectrum could provide a map of the mechanical anharmonic mode couplings. We briefly discuss how the 2D Raman spectrum can be used to elucidate the potential energy hypersurface and in turn to study the intramolecular vibrational energy redistribution process.

Hahn, Sangjoon; Park, Kisam; Cho, Minhaeng

1999-09-01

252

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

253

Variational Monte Carlo calculation of the spin gap in the {nu}=1 quantum Hall liquid  

SciTech Connect

A variational method of calculating the spin 1 excitation energies of the {nu}=1 quantum Hall liquid is presented in detail. We are able to include Landau-level mixing and finite-thickness effects. The many-body wave functions of the states near {nu}=1 filling are taken to be a product of a lowest-Landau-level Laughlin-type wave function and a Jastrow factor. A significant reduction in the calculated spin gap is found due both to Landau-level mixing ({approximately}40{percent} at r{sub s}=1) and to the effect of the finite thickness of the liquid (a further {approximately}30{percent} at r{sub s}=1). We find our calculations to be consistent with recent photoluminescence experiments in {delta}-doped samples. {copyright} {ital 1997} {ital The American Physical Society}

Kralik, B.; Rappe, A.M.; Louie, S.G. [Department of Physics, University of California at Berkeley and Materials Science Division, Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)] [Department of Physics, University of California at Berkeley and Materials Science Division, Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

1997-08-01

254

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

255

Monte Carlo Calculations of the Specific Heat in Quantum Critical Metals  

NASA Astrophysics Data System (ADS)

Quantum critical magnetic metals have unusual low temperature response such as an anomalous temperature dependence of the electronic specific heat (cv˜ T lnT). This dependence originates in the competition between ordering local magnetic moments and the conduction electrons shielding the moments. The Kondo Temperature, TK when moments become shielded depends on the inter-atomic distances. In most systems that have been investigated experimentally quantum criticality is obtained through lattice expansion by chemical substitution, one can expect a distribution of TK reflecting altered local inter-atomic distances. The random removal of these moments leads to the formation of magnetic clusters in quantum critical metals which has indeed been observed in quantum critical CeRu0.5Fe1.5Ge2. We investigate the dependence of the specific heat through the formation through magnetic cluster formation. Once a cluster separates itself from the lattice, it should order and affect the specific heat.. Using a Monte Carlo simulation we calculate the changes in specific heat associated with cluster formation for various Kondo temperature distributions, and we compare our results to those measured in 122-systems like CeRu0.5Fe1.5Ge2.

Gaddy, John; Montfrooij, Wouter; Vojta, Thomas

2009-03-01

256

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

257

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

258

Exploiting the Difference in Probability Calculation between Quantum and Probabilistic Computations  

E-print Network

The main purpose of this paper is to show that we can exploit the difference ($l_1$-norm and $l_2$-norm) in the probability calculation between quantum and probabilistic computations to claim the difference in their space efficiencies. It is shown that there is a finite language $L$ which contains sentences of length up to $O(n^{c+1})$ such that: ($i$) There is a one-way quantum finite automaton (qfa) of $O(n^{c+4})$ states which recognizes $L$. ($ii$) However, if we try to simulate this qfa by a probabilistic finite automaton (pfa) \\textit{using the same algorithm}, then it needs $\\Omega(n^{2c+4})$ states. It should be noted that we do not prove real lower bounds for pfa's but show that if pfa's and qfa's use exactly the same algorithm, then qfa's need much less states.

Masami Amano; Kazuo Iwama; Rudy Raymond

2002-04-15

259

Theoretical issues in quantum computing: Graph isomorphism, PageRank, and Hamiltonian determination  

NASA Astrophysics Data System (ADS)

This thesis explores several theoretical questions pertaining to quantum computing. First we examine several questions regarding multi-particle quantum random walk-based algorithms for the graph isomorphism problem. We find that there exists a non-trivial difference between continuous-time walks of one and two non-interacting particles as compared to non-interacting walks of three or more particles, in that the latter are able to distinguish many strongly regular graphs (SRGs), a class of graphs with many graph pairs that are difficult to distinguish. We demonstrate analytically where this distinguishing power comes from, and we show numerically that three-particle and four-particle non-interacting continuous-time walks can distinguish many pairs of strongly regular graphs. We additionally show that this distinguishing power, while it grows with particle number, is bounded, so that no continuous-time non-interacting walk of fixed particle number can distinguish all strongly regular graphs. We then investigate the relationship between continuous-time and discrete-time walks, in the context of the graph isomorphism problem. While it has been previously demonstrated numerically that discrete-time walks of non-interacting particles can distinguish some SRGs, we demonstrate where this distinguishing power comes from. We also show that while no continuous-time non-interacting walk of fixed particle number can distinguish SRGs, it remains a possibility that such a discrete-time walk could, leaving open the possibility of a non-trivial difference between discrete-time and continuous-time walks. The last piece of our work on graph isomorphism examines limitations on certain kinds of continuous-time walk-based algorithms for distinguishing graphs. We show that a very general class of continuous-time walk algorithms, with a broad class of allowable interactions, cannot distinguish all graphs. We next consider a previously-proposed quantum adiabatic algorithm for computing the PageRank vector, a necessary step in one of Google's search algorithms. It had been previously believed that this algorithm might offer a non-trivial speedup in preparing the PageRank vector. We demonstrate, however, that when this algorithm is tested on graphs that sufficiently resemble the graph of the World Wide Web, there is no appreciable speedup. Lastly, we consider the problem of Hamiltonian determination. We show that in the high temperature limit, the classical signal processing technique of compressed sensing may be used to recover the Hamiltonian for a system of qubits, provided that the Hamiltonian does not possess too many interactions, i.e., it is "sparse". This new procedure allows for the determination of the Hamiltonian with a number of measurements that can be significantly smaller than required by standard techniques.

Rudinger, Kenneth Michael

260

Path-integral virial estimator for reaction-rate calculation based on the quantum instanton approximation.  

PubMed

The quantum instanton approximation is a type of quantum transition-state theory that calculates the chemical reaction rate using the reactive flux correlation function and its low-order derivatives at time zero. Here we present several path-integral estimators for the latter quantities, which characterize the initial decay profile of the flux correlation function. As with the internal energy or heat-capacity calculation, different estimators yield different variances (and therefore different convergence properties) in a Monte Carlo calculation. Here we obtain a virial (-type) estimator by using a coordinate scaling procedure rather than integration by parts, which allows more computational benefits. We also consider two different methods for treating the flux operator, i.e., local-path and global-path approaches, in which the latter achieves a smaller variance at the cost of using second-order potential derivatives. Numerical tests are performed for a one-dimensional Eckart barrier and a model proton transfer reaction in a polar solvent, which illustrates the reduced variance of the virial estimator over the corresponding thermodynamic estimator. PMID:16512703

Yang, Sandy; Yamamoto, Takeshi; Miller, William H

2006-02-28

261

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

262

Path-integral calculation of the third virial coefficient of quantum gases at low temperatures.  

PubMed

We derive path-integral expressions for the second and third virial coefficients of monatomic quantum gases. Unlike previous work that considered only Boltzmann statistics, we include exchange effects (Bose-Einstein or Fermi-Dirac statistics). We use state-of-the-art pair and three-body potentials to calculate the third virial coefficient of (3)He and (4)He in the temperature range 2.6-24.5561 K. We obtain uncertainties smaller than those of the limited experimental data. Inclusion of exchange effects is necessary to obtain accurate results below about 7 K. PMID:21476742

Garberoglio, Giovanni; Harvey, Allan H

2011-04-01

263

Path-integral calculation of the third virial coefficient of quantum gases at low temperatures  

NASA Astrophysics Data System (ADS)

We derive path-integral expressions for the second and third virial coefficients of monatomic quantum gases. Unlike previous work that considered only Boltzmann statistics, we include exchange effects (Bose-Einstein or Fermi-Dirac statistics). We use state-of-the-art pair and three-body potentials to calculate the third virial coefficient of 3He and 4He in the temperature range 2.6–24.5561 K. We obtain uncertainties smaller than those of the limited experimental data. Inclusion of exchange effects is necessary to obtain accurate results below about 7 K.

Garberoglio, Giovanni; Harvey, Allan H.

2011-04-01

264

Quantum calculation of multipole relaxation and transfer cross sections in collisions of Na with Xe  

SciTech Connect

Well-established quantum mechanical methods were used to calculate multipole cross sections in sodium--xenon collisions. The cross sections were opacity analyzed to determine the relative importance of various angular momenta; the relaxation of the alignment was found to be the multipole most dependent upon low angular momenta (e.g., small impact parameter) collisions. While all the cross sections reported are found to be in satisfactory agreement with experiment, the relaxation of occupation of the j = 1/2 state was found to be in excellent agreement with recent experimental results.

DeVries, P.L.

1984-01-01

265

Path-integral calculation of the third virial coefficient of quantum gases at low temperatures  

SciTech Connect

We derive path-integral expressions for the second and third virial coefficients of monatomic quantum gases. Unlike previous work that considered only Boltzmann statistics, we include exchange effects (Bose-Einstein or Fermi-Dirac statistics). We use state-of-the-art pair and three-body potentials to calculate the third virial coefficient of {sup 3}He and {sup 4}He in the temperature range 2.6-24.5561 K. We obtain uncertainties smaller than those of the limited experimental data. Inclusion of exchange effects is necessary to obtain accurate results below about 7 K.

Garberoglio, Giovanni [Interdisciplinary Laboratory for Computational Science (LISC), FBK-CMM and University of Trento, via Sommarive 18, I-38123 Povo (Italy); Harvey, Allan H. [Thermophysical Properties Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)

2011-04-07

266

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

267

Ionic Liquids from Theoretical Investigations  

NASA Astrophysics Data System (ADS)

Theoretical investigations of ionic liquids are reviewed. Three main cate-gories are discussed, i.e., static quantum chemical calculations (electronic structure methods), traditional molecular dynamics simulations and first-principles molecular dynamics simulations. Simple models are reviewed in brief.

Kirchner, Barbara

268

The molecular structure of gaseous 1,4-dioxane: An electron-diffraction reinvestigation aided by theoretical calculations  

NASA Astrophysics Data System (ADS)

The structure of the molecule 1,4-dioxane (DIOX) has some features in common with other ring systems previously studied in this laboratory. In contrast to 1,4-cyclohexanedione, however, which consists both of a twisted boat form of D2 symmetry and a chair form of C2h symmetry, DIOX was reported, in two much earlier studies, to exist only as the chair form. The results of our work are in agreement with the earlier conclusions that gaseous DIOX exists either entirely, or essentially entirely (less than a few percent) in the chair form. Our work is much more extensive than the previous studies, and, aided by high-level theoretical molecular orbital- and normal-coordinate calculations, yielded the following bond distances (rg/Å) and bond angles (??/deg). = 1.104 (4), C-O = 1.420 (2), C-C = 1.514 (4), = 105.4 (55), H-C-H = 108.0 (26), C-C-O = 111.1 (3), C-O-C = 110.9 (10). The “flap” angle - the angle by which the COC plane is tilted up from the plane of the four carbon atoms - is equal to 50.6 (7)°. The structure is discussed and compared with the previous work and with predictions from theory.

Fargher, Mitchell; Hedberg, Lise; Hedberg, Kenneth

2014-08-01

269

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

PubMed

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 (CH(2)Cl(2) and CH(3)CN). These infrared data showed that the O,O-trans conformers predominate in the less polar solvent (CH(2)Cl(2)), but these equilibria change in a more polar solvent (CH(3)CN) 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 (13)CNMR spectra in CD(2)Cl(2) (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-d(6). This was confirmed by their (1)HNMR 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. PMID:23261606

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

2013-02-15

270

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

271

Effect of terrestrial radiation on brightness temperature at lunar nearside: Based on theoretical calculation and data analysis  

NASA Astrophysics Data System (ADS)

Terrestrial radiation is another possible source of heat in lunar thermal environment at its nearside besides the solar illumination. On the basis of Clouds and the Earth's Radiant Energy System (CERES) data products, the effect of terrestrial radiation on the brightness temperature (TBe) of the lunar nearside has been theoretically calculated. It shows that the mafic lunar mare with high TBe is more sensitive to terrestrial radiation than the feldspathic highland with low TBe value. According to the synchronous rotation of the Moon, we extract TBe on lunar nearside using the microwave radiometer data from the first Chinese lunar probe Chang'E-1 (CE-1). Consistently, the average TBe at Mare Serenitatis is about 1.2 K while the highland around the Geber crater (19.4°S, 13.9°E) is relatively small at ?0.4 K. Our results indicate that there is no significant effect of terrestrial radiation on TBe at the lunar nearside. However, to extract TBe accurately, effects of heat flow, rock abundance and subsurface rock fragments which are more significant should be considered in the future work.

Wei, Guangfei; Li, Xiongyao; Wang, Shijie

2015-02-01

272

Exact quantum scattering calculations of transport properties for the H2O-H system.  

PubMed

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 H2O, 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 C2 axis of the molecule. Finally, the computed transport properties were compared with those computed with a Lennard-Jones 12-6 potential. PMID:24320328

Dagdigian, Paul J; Alexander, Millard H

2013-11-21

273

Exact quantum scattering calculations of transport properties for the H2O-H system  

NASA Astrophysics Data System (ADS)

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 H2O, 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 C2 axis of the molecule. Finally, the computed transport properties were compared with those computed with a Lennard-Jones 12-6 potential.

Dagdigian, Paul J.; Alexander, Millard H.

2013-11-01

274

Finite element method-based calculation of the theoretical limit of sensitivity for detecting weak magnetic fields in the human brain using magnetic-resonance imaging  

NASA Astrophysics Data System (ADS)

Detection of weak magnetic fields induced by neuronal electrical activities using magnetic-resonance imaging is a potentially effective method for functional imaging of the brain. In this study, we performed a numerical analysis of the theoretical limit of sensitivity for detecting weak magnetic fields induced in the human brain. The limit of sensitivity was estimated from the intensities of signal and noise in the magnetic-resonance images. The signal intensity was calculated with parameters which are commonly used in measurements of the human brain. The noise due to the head was calculated using the finite element method. The theoretical limit of sensitivity was approximately 10-8T.

Hatada, Tomohisa; Sekino, Masaki; Ueno, Shoogo

2005-05-01

275

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

276

Efficient quantum calculations of vibrational states of vinylidene in full dimensionality: A scheme with combination of methods  

NASA Astrophysics Data System (ADS)

Full-dimensional quantum calculations of vibrational states of C2H2 and C2D2 are performed in the high-energy region (above 20400cm-1 relative to the acetylene minimum). The theoretical scheme is a combination of several methods. To exploit the full parity and permutation symmetry, the CC-HH diatom-diatom Jacobi coordinates are chosen; phase space optimization in combination with physical considerations is used to obtain an efficient radial discrete variable representation, whereas a basis contraction scheme is applied for angular coordinates. The preconditioned inexact spectral transform method combined with an efficient preconditioner is employed to compute eigenstates within a desired spectral window. The computation is efficient. More definite assignments on vinylidene states than previous studies are acquired using the normal mode projection; in particular, a consistent analysis of the ?1 (symmetric CH stretch) state is provided. The computed vinylidene vibrational energy levels are in general good agreement with experiment, and several vinylidene states are reported for the first time.

Li, Bin; Bian, Wensheng

2008-07-01

277

Use of the Sumudu transform to extract response functions from Quantum Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

We review an ab-initio method for calculating the dynamical structure function of an interacting many-body quantum system. The method consists in coupling a generalized integral transform approach with imaginary time Quantum Monte Carlo calculations. The strength of the method has been tested on the excitation spectrum of bulk atomic 4He. The peculiar form of the kernel as a representation of the delta-function has allowed to minimize the ill-posedness of the integral transform inversion. In fact it has been possible to obtain, at a considerable degree of reliability, both position and width of the collective excitations in the maxon-roton region, as well as the second collective peak. What we stress here is the ability of such a 4-function-like kernel, for which one can control position and width, to maintain in the transformed space the characteristics of the collective structures. The application to the coherent and incoherent density excitation spectrum of liquid 4He is discussed.

Pederiva, Francesco; Roggero, Alessandro; Orlandini, Giuseppina

2014-07-01

278

Halting probability amplitude of quantum Institute for Theoretical Physics, Technische Universat Wien,  

E-print Network

. Therefore, is both: a mathematicians fair coin," and a formalist's nightmare. Here, is generalized is representable by quantum bits qbits. Every qbit is in a coherent superposition of the classical bit basis j0i, 16 ja;bi = ajHALTi+bjGOi ; jaj2 + jbj2 = 1 4 We shall call this quantum bit ja;bi the halting bit

Svozil, Karl

279

Quantum Monte Carlo dynamics: The stationary phase Monte Carlo path integral calculation of finite temperature time correlation functions  

Microsoft Academic Search

We present a numerically exact procedure for the calculation of an important class of finite temperature quantum mechanical time correlation functions. The present approach is based around the stationary phase Monte Carlo (SPMC) method, a general mathematical tool for the calculation of high dimensional averages of oscillatory integrands. In the present context the method makes possible the direct numerical path

J. D. Doll; Thomas L. Beck; David L. Freeman

1988-01-01

280

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

281

Calculation of gain and luminescence spectra of quantum-cascade laser structures taking into account asymmetric emission line broadening  

SciTech Connect

The energy levels, wave functions, and matrix elements of optical dipole transitions are calculated numerically for superlattice quantum-cascade structures. The effect of spectral broadening on the shape of emission spectra is estimated and semiphenomenological asymmetric profiles of emission line broadening are proposed. It is shown that the electroluminescence spectra well agree with the calculated spontaneous recombination spectra. (lasers)

Ushakov, D V; Manak, I S [Belarusian State University, Minsk (Belarus); Kononenko, V K [B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk (Belarus)

2010-05-26

282

Convergence of calculated nuclear magnetic resonance chemical shifts in a protein with respect to quantum mechanical model size  

Microsoft Academic Search

An important aspect of mixed quantum mechanics and molecular mechanics (QM\\/MM) calculation of nuclear magnetic resonance chemical shifts in proteins is the choice of a sufficiently large QM region. This region must be large enough that the electronic structure of the chromophore in the QM\\/MM model is essentially the same as in the complete system. In this work, we calculate

Erin R. Johnson; Gino A. DiLabio

2009-01-01

283

Quantum Monte Carlo dynamics: The stationary phase Monte Carlo path integral calculation of finite temperature time correlation functions  

NASA Astrophysics Data System (ADS)

We present a numerically exact procedure for the calculation of an important class of finite temperature quantum mechanical time correlation functions. The present approach is based around the stationary phase Monte Carlo (SPMC) method, a general mathematical tool for the calculation of high dimensional averages of oscillatory integrands. In the present context the method makes possible the direct numerical path integral calculation of real-time quantum dynamical quantities for times appreciably greater than the thermal time (??). Illustrative applications involving finite temperature anharmonic motion are presented. Issues of importance with respect to future applications are identified and discussed.

Doll, J. D.; Beck, Thomas L.; Freeman, David L.

1988-11-01

284

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

285

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

286

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

E-print Network

is spherical symmetric and can be conveniently solved in terms of spherical harmonics as described in the previous section. The spherical dots have been recently used in the theoretical studies of electrodynamic response32 and hyper- Raman scattering.33 Table I.... Kastner, Phys. Today 46, 24 ~1993!; R.C. Ashoori, Nature ~London! 379, 413 ~1996!. 2 L. Jacak, P. Hawrylak, and A. Wojs, Quantum Dots ~Springer- Verlag, New York, 1989!. 3 R.C. Ashoori et al., Phys. Rev. Lett. 71, 613 ~1993!. 4 A. Lorke, J.P. Kotthaus...

Jiang, T. F.; Tong, Xiao-Min; Chu, Shih-I

2001-01-09

287

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

288

Large-scale atomistic density functional theory calculations of phosphorus-doped silicon quantum bits  

NASA Astrophysics Data System (ADS)

We present density functional theory calculations of phosphorus dopants in bulk silicon and of several properties relating to their use as spin qubits for quantum computation. Rather than a mixed pseudopotential or a Heitler-London approach, we have used an explicit treatment for the phosphorus donor and examined the detailed electronic structure of the system as a function of the isotropic doping fraction, including lattice relaxation due to the presence of the impurity. Doping electron densities (?doped-?bulk) and spin densities (??-??) are examined in order to study the properties of the dopant electron as a function of the isotropic doping fraction. Doping potentials (Vdoped-Vbulk) are also calculated for use in calculations of the scattering cross sections of the phosphorus dopants, which are important in the understanding of electrically detected magnetic resonance experiments. We find that the electron density around the dopant leads to nonspherical features in the doping potentials, such as trigonal lobes in the (001) plane at energy scales of +12 eV near the nucleus and of -700 meV extending away from the dopants. These features are generally neglected in effective mass theory and will affect the coupling between the donor electron and the phosphorus nucleus. Our density functional calculations reveal detail in the densities and potentials of the dopants which are not evident in calculations that do not include explicit treatment of the phosphorus donor atom and relaxation of the crystal lattice. These details can also be used to parametrize tight-binding models for simulation of large-scale devices.

Greenman, Loren; Whitley, Heather D.; Whaley, K. Birgitta

2013-10-01

289

1468 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 41, NO. 12, DECEMBER 2005 Theoretical Investigation of Quantum-Dot Avalanche  

E-print Network

of Quantum-Dot Avalanche Photodiodes for Mid-infrared Applications Sanjay Krishna, Student Member, IEEE, Oh-dot avalanche photodiode (QDAP), is proposed which is expected to have improved signal-to-noise ratio (SNR is coupled with a thin, low-noise GaAs avalanche layer through a tunnel barrier. The avalanche layer provides

Hayat, Majeed M.

290

Theoretical analysis of quantum dynamics in 1D lattices: Wannier-Stark description  

E-print Network

This papers presents a formalism describing the dynamics of a quantum particle in a one-dimensional tilted time-dependent lattice. The description uses the Wannier-Stark states, which are localized in each site of the lattice and provides a simple framework leading to fully-analytical developments. Particular attention is devoted to the case of a time-dependent potential, which results in a rich variety of quantum coherent dynamics is found.

Quentin Thommen; Jean Claude Garreau; Veronique Zehnle

2001-12-19

291

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

292

Reptation Quantum Monte Carlo calculation of charge transfer: The Na-Cl dimer  

NASA Astrophysics Data System (ADS)

The phenomenon of ion pairing in aqueous solutions is of widespread importance in chemistry and physics, and charge transfer between the ions plays a significant role. We examine the performance of quantum Monte Carlo (QMC) calculations for describing the charge transfer behavior in a NaCl dimer. The influence of the fermion nodes is investigated by obtaining the electron density using the reptation Monte Carlo approach. The fermion nodes are given by single-particle orbitals in Slater-Jastrow trial wavefunctions. We consider the single-particle orbitals from Hartree-Fock and density functional theory calculations with several exchange-correlation approximations. Appreciable dependence of the charge transfer on the fixed-node approximation was found although the total energy was found to be rather insensitive. Our work shows that a careful examination of the fixed-node approximation is necessary for quantifying charge transfer in QMC calculations even when other properties such as reaction energetics are insensitive to the approximation.

Yao, Yi; Kanai, Yosuke

2015-01-01

293

Variational calculation of quantum mechanical/molecular mechanical free energy with electronic polarization of solvent  

NASA Astrophysics Data System (ADS)

Quantum mechanical/molecular mechanical (QM/MM) free energy calculation presents a significant challenge due to an excessive number of QM calculations. A useful approach for reducing the computational cost is that based on the mean field approximation to the QM subsystem. Here, we describe such a mean-field QM/MM theory for electronically polarizable systems by starting from the Hartree product ansatz for the total system and invoking a variational principle of free energy. The MM part is then recast to a classical polarizable model by introducing the charge response kernel. Numerical test shows that the potential of mean force (PMF) thus obtained agrees quantitatively with that obtained from a direct QM/MM calculation, indicating the utility of self-consistent mean-field approximation. Next, we apply the obtained method to prototypical reactions in several qualitatively different solvents and make a systematic comparison of polarization effects. The results show that in aqueous solution the PMF does not depend very much on the water models employed, while in nonaqueous solutions the PMF is significantly affected by explicit polarization. For example, the free energy barrier for a phosphoryl dissociation reaction in acetone and cyclohexane is found to increase by more than 10 kcal/mol when switching the solvent model from an empirical to explicitly polarizable one. The reason for this is discussed based on the parametrization of empirical nonpolarizable models.

Nakano, Hiroshi; Yamamoto, Takeshi

2012-04-01

294

Calculation of output characteristics of semiconductor quantum-well lasers with account for both electrons and holes  

NASA Astrophysics Data System (ADS)

Using an extended theoretical model, which includes the rate equations for both electrons and holes, we have studied the output characteristics of semiconductor quantum-well lasers. We have found non-trivial dependences of electron and hole concentrations in the waveguide region of the laser on the capture velocities of both types of carriers from the waveguide region into the quantum well. We have obtained the dependences of the internal differential quantum efficiency and optical output power of the laser on the capture velocities of electrons and holes. An increase in the capture velocities has been shown to result in suppression of parasitic recombination in the waveguide region and therefore in a substantial increase in the quantum efficiency and output power.

Sokolova, Z. N.; Tarasov, I. S.; Asryan, L. V.

2014-09-01

295

Crystal structure, spectroscopic investigations and quantum chemical calculational studies of N-diphenylphosphino-4-methylpiperidine sulfide  

NASA Astrophysics Data System (ADS)

The title molecule, N-diphenylphosphino-4-methylpiperidine sulfide (I), has been synthesized and characterized by elemental analysis, 1H NMR, 31P NMR, IR and X-ray single-crystal determination. The molecular geometry from X-ray determination, vibrational frequencies and gauge, including atomic orbital (GIAO) 1H NMR and 31P NMR chemical shift values of the title compound (I) in the ground state have been calculated using the density functional theory with the 6-31G(d), 6-31G(d,p) and 6-311G(d,p) basis sets. The calculated results show that the optimized geometry can well reproduce the crystal structure, and theoretical vibrational frequencies and chemical shift values show good agreement with experimental values. The predicted nonlinear optical properties of the title compound are greater than those of urea. In addition, DFT calculations of the molecular electrostatic potentials, frontier molecular orbitals of the title compound were carried out at the B3LYP/6-31G(d) level of theory.

Saraço?lu, Hanife; Sariöz, Özlem; Öznergiz, Sena

2014-04-01

296

Far-infrared collision-induced absorption in rare gas mixtures: Quantum and semi-classical calculations  

SciTech Connect

We compare calculations of the translational collision-induced spectra and their integrated intensities of both He–Ar and Ne–Ar collisional complexes, using the quantum mechanical and a semiclassical formalism. Advanced potential energy and induced dipole functions are used for the calculations. The quantum method used is as described previously [L. Frommhold, Collision-induced Absorption in Gases (Cambridge University Press, 1993 and 2006)]. The semiclassical method is based on repeated classical atom-atom scattering calculations to simulate an ensemble average; subsequent Fourier transform then renders the binary absorption coefficient as a function of frequency. The problem of classical calculations is the violation of the principle of detailed balance, which may be introduced only artificially in classical calculations. Nevertheless, it is shown that the use of classical trajectories permits a fairly accurate reproduction of the experimental spectra, comparable to the quantum mechanical results at not too low temperatures and for collisional pairs of not too small reduced mass. Inexpensive classical calculations may thus be promising to compute spectra also of molecular pairs, or even of polyatomic collisional pairs with anisotropic intermolecular interactions, for which the quantum approach is still inefficient or impractical.

Buryak, Ilya [Chemistry Department, Lomonosov Moscow State University, GSP-1, Vorobievy Gory, Moscow 119991 (Russian Federation) [Chemistry Department, Lomonosov Moscow State University, GSP-1, Vorobievy Gory, Moscow 119991 (Russian Federation); Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, 3 Pyzhevsky per., 119017 Moscow (Russian Federation); Frommhold, Lothar [Physics Department, University of Texas at Austin, Austin, Texas 78712-1081 (United States)] [Physics Department, University of Texas at Austin, Austin, Texas 78712-1081 (United States); Vigasin, Andrey A., E-mail: vigasin@ifaran.ru [Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, 3 Pyzhevsky per., 119017 Moscow (Russian Federation)

2014-04-21

297

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

298

Terahertz absorption spectra of oxidized polyethylene and their analysis by quantum chemical calculations  

NASA Astrophysics Data System (ADS)

Low-density polyethylene, either cross-linked or not, was oxidized and its absorption spectra were measured in the terahertz (THz) range and infrared range. The absorption was increased by the oxidation in the whole THz range. In accord with this, infrared absorption due to carbonyl groups appears. Although these results indicate that the increase in absorption is induced by oxidation, its attribution to resonance or relaxation is unclear. To clarify this point, the vibrational frequencies of three-dimensional polyethylene models with and without carbonyl groups were quantum chemically calculated. As a result, it was clarified that optically inactive skeletal vibrations in polyethylene become active upon oxidation. Furthermore, several absorption peaks due to vibrational resonances are induced by oxidation at wavenumbers from 20 to 100 cm-1. If these absorption peaks are broadened and are superimposed on each other, the absorption spectrum observed experimentally can be reproduced. Therefore, the absorption is ascribable to resonance.

Komatsu, Marina; Hosobuchi, Masashi; Xie, Xiaojun; Cheng, Yonghong; Furukawa, Yukio; Mizuno, Maya; Fukunaga, Kaori; Ohki, Yoshimichi

2014-09-01

299

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

300

Electronic structure calculations of PbS quantum rods and tubes  

SciTech Connect

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 S{sub e}–S{sub h} 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, E-mail: yurid@uwyo.edu [Department of Physics and Astronomy/3905, 1000 E. University Avenue, University of Wyoming Laramie, Wyoming 82071 (United States)

2014-01-28

301

Model of the catalytic mechanism of human aldose reductase based on quantum chemical calculations.  

SciTech Connect

Aldose Reductase is an enzyme involved in diabetic complications, thoroughly studied for the purpose of inhibitor development. The structure of an enzyme-inhibitor complex solved at sub-atomic resolution has been used to develop a model for the catalytic mechanism. This model has been refined using a combination of Molecular Dynamics and Quantum calculations. It shows that the proton donation, the subject of previous controversies, is the combined effect of three residues: Lys 77, Tyr 48 and His 110. Lys 77 polarises the Tyr 48 OH group, which donates the proton to His 110, which becomes doubly protonated. His 110 then moves and donates the proton to the substrate. The key information from the sub-atomic resolution structure is the orientation of the ring and the single protonafion of the His 110 in the enzyme-inhibitor complex. This model is in full agreement with all available experimental data.

Cachau, R. C.; Howard, E. H.; Barth, P. B.; Mitschler, A. M.; Chevrier, B. C.; Lamour, V.; Joachimiak, A.; Sanishvili, R.; Van Zandt, M.; Sibley, E.; Moras, D.; Podjarny, A.; UPR de Biologie Structurale; National Cancer Inst.; Univ. Louis Pasteur; Inst. for Diabetes Discovery, Inc.

2000-01-01

302

Quantum three-body calculation of nonresonant triple-{alpha} reaction rate at low temperatures  

SciTech Connect

Triple-{alpha} reaction rate is re-evaluated by directly solving the three-body Schroedinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. An accurate description of the {alpha}-{alpha} nonresonant states significantly quenches the Coulomb barrier between the first two {alpha}-particles and the third {alpha}-particle. Consequently, the{alpha}-{alpha} nonresonant continuum states give a markedly larger contribution at low temperatures than that reported in previous studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find an increase in triple-{alpha} reaction rate by about 20 orders of magnitude around 10{sup 7} K compared with the rate of NACRE.

Ogata, Kazuyuki; Kan, Masataka [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Kamimura, Masayasu [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); RIKEN Nishina Center, Wako 351-0198 (Japan)

2010-08-12

303

Electronically excited states of membrane fluorescent probe 4-dimethylaminochalcone. Results of quantum chemical calculations.  

PubMed

Quantum-chemical calculations of ground and excited states for membrane fluorescent probe 4-dimethylaminochalcone (DMAC) in vacuum were performed. Optimized geometries and dipole moments for lowest-lying singlet and triplet states were obtained. The nature of these electronic transitions and the relaxation path in the excited states were determined; changes in geometry and charge distribution were assessed. It was shown that in vacuum the lowest existed level is of (n, ?*) nature, and the closest to it is the level of (?, ?*) nature; the energy gap between them is narrow. This led to an effective (1)(?, ?*) ?(1)(n, ?*) relaxation. After photoexcitation the molecule undergoes significant transformations, including changes in bond orders, pyramidalization angle of the dimethylamino group, and planarity of the molecule. Its dipole moment rises from 5.5 Debye in the ground state to 17.1 Debye in the (1)(?, ?*) state, and then falls to 2 Debye in the (1)(n, ?*) state. The excited (1)(n, ?*) state is a short living state; it has a high probability of intersystem crossing into the (3)(?, ?*) triplet state. This relaxation path explains the low quantum yield of DMAC fluorescence in non-polar media. It is possible that (3)(?, ?*) is responsible for observed DMAC phosphorescence. PMID:21487602

Romanov, Alexey N; Gularyan, Samvel K; Polyak, Boris M; Sakovich, Ruslan A; Dobretsov, Gennady E; Sarkisov, Oleg M

2011-05-28

304

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

305

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

306

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

PubMed Central

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. Results Agreement between experiment and theory is acceptable in most cases, and the reasons for discrepancies are discussed. Calculated Gibbs free energies are used to constrain which configurations are most likely to be stable under circumneutral pH conditions. Reduction of U(VI) to U(IV) is examined for the U-carbonate and U-catechol complexes. Conclusion Results on the potential energy differences between U(V)- and U(IV)-carbonate complexes suggest that the cause of slower disproportionation in this system is electrostatic repulsion between UO2 [CO3]35- ions that must approach one another to form U(VI) and U(IV) rather than a change in thermodynamic stability. Calculations on U-catechol species are consistent with the observation that UO22+ can oxidize catechol and form quinone-like species. In addition, outer-sphere complexation is predicted to be the most stable for U-catechol interactions based on calculated energies and comparison to 13C NMR spectra. Outer-sphere complexes (i.e., ion pairs bridged by water molecules) are predicted to be comparable in Gibbs free energy to inner-sphere complexes for a model carboxylic acid. Complexation of uranyl to phosphorus-containing groups in extracellular polymeric substances is predicted to favor phosphonate groups, such as that found in phosphorylated NAG, rather than phosphodiesters, such as those in nucleic acids. PMID:19689800

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

2009-01-01

307

On the inclusion of prime factors to calculate the theoretical lower bounds in multiplierless single constant multiplications  

NASA Astrophysics Data System (ADS)

This paper presents an extension to the theoretical lower bounds for the number of adders and for the adder depth in multiplierless single constant multiplications (SCM). It is shown that the number of prime factors of the constants is key information to extend the current lower bounds in certain cases that have not yet been exposed. Additionally, the hidden theoretical lower bound for the number of adders required to preserve the minimum adder depth is revealed.

Troncoso Romero, David E.; Meyer-Baese, Uwe; Dolecek, Gordana Jovanovic

2014-12-01

308

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

309

Quantifying Desorption of Saturated Hydrocarbons from Silicon with Quantum Calculations and Scanning Tunneling Microscopy  

NASA Astrophysics Data System (ADS)

Electron stimulated desorption of cyclopentene from the Si(100)-(2×1) 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.

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

2006-11-01

310

A Modular Method for the Efficient Calculation of Ballistic Transport Through Quantum  

E-print Network

-coherent scattering struc- tures, so-called "quantum billiards". Our approach consists of an exten- sion the quantum scattering problem of a large class of systems very efficiently. We will illustrate]. However, even for two-dimensional quantum dots ("quantum billiards") the numerical solution of the Schr

Rotter, Stefan

311

Derivation of the Rules of Quantum Mechanics from Information-Theoretic Axioms  

E-print Network

Conventional quantum mechanics with a complex Hilbert space and the Born Rule is derived from five axioms describing properties of probability distributions for the outcome of measurements. Axioms I,II,III are common to quantum mechanics and hidden variable theories. Axiom IV recognizes a phenomenon, first noted by Turing and von Neumann, in which the increase in entropy resulting from a measurement is reduced by a suitable intermediate measurement. This is shown to be impossible for local hidden variable theories. Axiom IV, together with the first three, almost suffice to deduce the conventional rules but allow some exotic, alternatives such as real or quaternionic quantum mechanics. Axiom V recognizes a property of the distribution of outcomes of random measurements on qubits which holds only in the complex Hilbert space model. It is then shown that the five axioms also imply the conventional rules for all dimensions.

Daniel I. Fivel

2010-10-26

312

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

313

Quantum Darwinism requires an extra-theoretical assumption of encoding redundancy  

E-print Network

Observers restricted to the observation of pointer states of apparatus cannot conclusively demonstrate that the pointer of an apparatus A registers the state of a system of interest S without perturbing S. Observers cannot, therefore, conclusively demonstrate that the states of a system S are redundantly encoded by pointer states of multiple independent apparatus without destroying the redundancy of encoding. The redundancy of encoding required by quantum Darwinism must, therefore, be assumed from outside the quantum-mechanical formalism and without the possibility of experimental demonstration.

Chris Fields

2010-05-30

314

Quantum Darwinism Requires an Extra-Theoretical Assumption of Encoding Redundancy  

NASA Astrophysics Data System (ADS)

Observers restricted to the observation of pointer states of apparatus cannot conclusively demonstrate that the pointer of an apparatus mathcal{A} registers the state of a system of interest S without perturbing S. Observers cannot, therefore, conclusively demonstrate that the states of a system S are redundantly encoded by pointer states of multiple independent apparatus without destroying the redundancy of encoding. The redundancy of encoding required by quantum Darwinism must, therefore, be assumed from outside the quantum-mechanical formalism and without the possibility of experimental demonstration.

Fields, Chris

2010-10-01

315

Accurate quantum dynamics calculations using symmetrized Gaussians on a doubly dense Von Neumann lattice  

SciTech Connect

In a series of earlier articles [B. Poirier, J. Theor. Comput. Chem. 2, 65 (2003); B. Poirier and A. Salam, J. Chem. Phys. 121, 1690 (2004); and ibid. 121, 1704 (2004)], a new method was introduced for performing exact quantum dynamics calculations. The method uses a 'weylet' basis set (orthogonalized Weyl-Heisenberg wavelets) combined with phase space truncation, to defeat the exponential scaling of CPU effort with system dimensionality-the first method ever able to achieve this long-standing goal. Here, we develop another such method, which uses a much more convenient basis of momentum-symmetrized Gaussians. Despite being non-orthogonal, symmetrized Gaussians are collectively local, allowing for effective phase space truncation. A dimension-independent code for computing energy eigenstates of both coupled and uncoupled systems has been created, exploiting massively parallel algorithms. Results are presented for model isotropic uncoupled harmonic oscillators and coupled anharmonic oscillators up to 27 dimensions. These are compared with the previous weylet calculations (uncoupled harmonic oscillators up to 15 dimensions), and found to be essentially just as efficient. Coupled system results are also compared to corresponding exact results obtained using a harmonic oscillator basis, and also to approximate results obtained using first-order perturbation theory up to the maximum dimensionality for which the latter may be feasibly obtained (four dimensions).

Halverson, Thomas; Poirier, Bill [Department of Chemistry and Biochemistry and Department of Physics, Texas Tech University, P.O. Box 41061, Lubbock, Texas 79409-1061 (United States)

2012-12-14

316

Elucidating electronic transitions from ? orbitals of liquid n- and branched alkanes by far-ultraviolet spectroscopy and quantum chemical calculations.  

PubMed

Attenuated total reflection far-ultraviolet (ATR-FUV) spectra containing Rydberg states of n-alkanes (C(m)H(2m+2); m varies in the range 5-9) and branched alkanes observed in the liquid phase were investigated by quantum chemical calculations with the aim of elucidating electronic transitions from ? orbitals of liquid n- and branched alkanes. New assignments are proposed based on the time-dependent density functional theory (TD-DFT) and symmetry-adapted cluster configuration interaction (SAC-CI) calculations, and the differences in these spectra are analyzed in detail. The FUV spectra of n-alkanes show a broad asymmetric feature near 8.3 eV. The strong band at ?8.3 eV shows a red shift with a significant increase in intensity as the carbon chain length increases, which is attributed to the overlapping transitions from the third (or fourth) highest occupied molecular orbitals HOMO-2 (or HOMO-3) and HOMO-1 to Rydberg 3p(y) by the TD-DFT and SAC-CI calculations. This band was previously assigned to the overlap of two peaks arising from the transition from the HOMO to 3p and from the HOMO-1 to 3s based on their term values. Although the most intense transition, T1, is from HOMO-2 for m = 5 and 6 and HOMO-3 for m varying in the range of 7-9, the shape of Kohn-Sham molecular orbital for T1 is similar among the all-alkanes investigated. The theoretical result also has demonstrated that the red shift originates in both stabilization of the Rydberg 3p(y) and destabilization of the occupied orbitals. The intensity of the shoulder at 7.7 eV drastically increases in the spectra of the branched alkanes, especially for those with quaternary carbon atoms such as 2,2-dimethyl butane. This increase in intensity is caused by a reduction in symmetry in the branched alkanes, which leads the forbidden transitions to Rydberg 3s to allowed transitions. In this way, the present study has provided new insight into the existence of their Rydberg transitions and the shape of the relevant MOs of the transitions. PMID:23140337

Morisawa, Yusuke; Tachibana, Shin; Ehara, Masahiro; Ozaki, Yukihiro

2012-12-01

317

Techniques in Analytic Lamb Shift Calculations  

Microsoft Academic Search

Quantum electrodynamics has been the first theory to emerge from the ideas of\\u000aregularization and renormalization, and the coupling of the fermions to the\\u000avirtual excitations of the electromagnetic field. Today, bound-state quantum\\u000aelectrodynamics provides us with accurate theoretical predictions for the\\u000atransition energies relevant to simple atomic systems, and steady theoretical\\u000aprogress relies on advances in calculational techniques, as

Ulrich D. Jentschura

2005-01-01

318

Quantum-mechanical histories and the uncertainty principle: Information-theoretic inequalities  

Microsoft Academic Search

This paper is generally concerned with understanding how the uncertainty principle arises in formulations of quantum mechanics, such as the decoherent histories approach, whose central goal is the assignment of probabilities to histories. We first consider histories characterized by position or momentum projections at two moments of time. Both exact and approximate (Gaussian) projections are studied. Shannon's information is used

J. J. Halliwell

1993-01-01

319

Proposal of a Communications Theory of Quantum Mechanics. Theoretical Examination of the 'Gyromagnetic Ratio'  

SciTech Connect

Is the 'Two-Slit' experiment best explained by aliasing, first solved by Harry Nyquist (1926)? Does light reflected by an electron rotate through double the angle through which the electron itself rotates? Can a barchart represent the uncertainty principle?A very simple model of quantum mechanics is presented.

Coogan, Anthony

2009-03-09

320

Concepts and their dynamics: a quantum-theoretic modeling of human thought.  

PubMed

We analyze different aspects of our quantum modeling approach of human concepts and, more specifically, focus on the quantum effects of contextuality, interference, entanglement, and emergence, illustrating how each of them makes its appearance in specific situations of the dynamics of human concepts and their combinations. We point out the relation of our approach, which is based on an ontology of a concept as an entity in a state changing under influence of a context, with the main traditional concept theories, that is, prototype theory, exemplar theory, and theory theory. We ponder about the question why quantum theory performs so well in its modeling of human concepts, and we shed light on this question by analyzing the role of complex amplitudes, showing how they allow to describe interference in the statistics of measurement outcomes, while in the traditional theories statistics of outcomes originates in classical probability weights, without the possibility of interference. The relevance of complex numbers, the appearance of entanglement, and the role of Fock space in explaining contextual emergence, all as unique features of the quantum modeling, are explicitly revealed in this article by analyzing human concepts and their dynamics. PMID:24039114

Aerts, Diederik; Gabora, Liane; Sozzo, Sandro

2013-10-01

321

Electronic structure of silicon nitride according to ab initio quantum-chemical calculations and experimental data  

SciTech Connect

Charge transfer {Delta}Q = 0.35e at the Si-N bond in silicon nitride is determined experimentally using photoelectron spectroscopy, and the ionic formula of silicon nitride Si{sub 3}{sup +1.4}N{sub 4}{sup -1.05} is derived. The electronic structure of {alpha}-Si{sub 3}N{sub 4} is studied ab initio using the density functional method. The results of calculations (partial density of states) are compared with experimental data on X-ray emission spectroscopy of amorphous Si{sub 3}N{sub 4}. The electronic structure of the valence band of amorphous Si{sub 3}N{sub 4} is studied using synchrotron radiation at different excitation energies. The electron and hole effective masses m{sub e}{sup *} {approx} m{sub h}{sup *} {approx} 0.5m{sub e} are estimated theoretically. The calculated values correspond to experimental results on injection of electrons and holes into silicon nitride.

Nekrashevich, S. S., E-mail: nss@isp.nsc.ru; Gritsenko, V. A. [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Klauser, R. [Synchrotron Radiation Research Center (China); Gwo, S. [National Tsing-Hua University, Department of Physics (China)

2010-10-15

322

Low-rank spectral expansions of two electron excitations for the acceleration of quantum chemistry calculations  

NASA Astrophysics Data System (ADS)

Treatment of two-electron excitations is a fundamental but computationally expensive part of ab initio calculations of many-electron correlation. In this paper we develop a low-rank spectral expansion of two-electron excitations for accelerated electronic-structure calculations. The spectral expansion differs from previous approaches by relying upon both (i) a sum of three expansions to increase the rank reduction of the tensor and (ii) a factorization of the tensor into geminal (rank-two) tensors rather than orbital (rank-one) tensors. We combine three spectral expansions from the three distinct forms of the two-electron reduced density matrix (2-RDM), (i) the two-particle 2D, (ii) the two-hole 2Q, and the (iii) particle-hole 2G matrices, to produce a single spectral expansion with significantly accelerated convergence. While the resulting expansion is applicable to any quantum-chemistry calculation with two-particle excitation amplitudes, it is employed here in the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], 10.1103/PhysRevLett.101.253002. The low-rank parametric 2-RDM method scales quartically with the basis-set size, but like its full-rank version it can capture multi-reference correlation effects that are difficult to treat efficiently by traditional single-reference wavefunction methods. Applications are made to computing potential energy curves of HF and triplet OH+, equilibrium bond distances and frequencies, the HCN-HNC isomerization, and the energies of hydrocarbon chains. Computed 2-RDMs nearly satisfy necessary N-representability conditions. The low-rank spectral expansion has the potential to expand the applicability of the parametric 2-RDM method as well as other ab initio methods to large-scale molecular systems that are often only treatable by mean-field or density functional theories.

Schwerdtfeger, Christine A.; Mazziotti, David A.

2012-12-01

323

A Calculation of Cosmic Variance in Cosmic Microwave Background Anisotropy  

E-print Network

We present a theoretical calculation of the variance $\\Delta C_l$ of the CMB anisotropy power spectrum $\\langle C_l\\rangle$ caused by gravitational waves based on quantum field theory in an inflationary cosmology.

Kin-Wang Ng; A. D. Speliotopoulos

1995-05-24

324

Effects of Magnetic Ordering on Phonon Spectra in Iron-based Superconductors: First Principle Calculation and Theoretical Analysis  

NASA Astrophysics Data System (ADS)

Recently, inelastic x-ray scattering measurements on single crystals of PrFeAsOy (y˜0.2) have reported that phonons related with Fe-Fe and Fe-As bondings are significantly more softened than those obtained by the first principle calculations [1]. However, it is noted that any previous calculations do not include the magnetic degree of freedom. Therefore, we performed the phonon structure calculations by taking into account the magnetic structure in mother compounds. The magnetic calculations are in better agreement with the observed softening. We show the results and clarify the reason. [3pt] [1] T. Fukuda et al, J. Phys. Soc. Jpn. 77, 103715 (2008).

Nakamura, Hiroki; Machida, Masahiko; Baron, Alfred; Fukuda, Tatsuo; Shamoto, Shinich

2009-03-01

325

Comparison of the results of theoretical calculations with experimental measurements from the Los Alamos free-electron laser oscillator experiment  

SciTech Connect

A comparison between some of the measurements made with a uniform wiggler during the Los Alamos free-electron laser oscillator experiment and the results of one-dimensional pulse propagation calculations using the mathematical model of Colson and Ride will be presented. Small-signal gain data will be discussed. Calculated output power vs. optical resonator length will be compared with data. Time-integrated optical spectral data, which show clear evidence for Raman sidebands, will be compared with calculated spectra as a function of resonator length. The calculated electron energy distribution function, using the measured electron-beam micropulse shape, and the associated extraction efficiency will be compared with measurements.

Goldstein, J.C.; Newnam, B.E.; Warren, R.W.; Sheffield, R.L.

1985-01-01

326

Quantum mechanical method of fragment’s angular and energy distribution calculation for binary and ternary fission  

Microsoft Academic Search

In the framework of quantum-mechanical fission theory, the method of calculation for partial fission width amplitudes and\\u000a asymptotic behavior of the fissile nucleus wave function with strong channel coupling taken into account has been suggested.\\u000a The method allows one to solve the calculation problem of angular and energy distribution countation for binary and ternary\\u000a fission.

S. G. Kadmensky; L. V. Titova; N. V. Pen’kov

2006-01-01

327

Protonation/deprotonation process of Emodin in aqueous solution and pKa determination: UV/Visible spectrophotometric titration and quantum/molecular mechanics calculations  

NASA Astrophysics Data System (ADS)

We combined theoretical and experimental studies to elucidate the important deprotonation process of Emodin in water. We used the UV/Visible spectrophotometric titration curves to obtain its pKa values, pKa1 = 8.0 ± 0.1 and pKa2 = 10.9 ± 0.2. Additionally, we obtained the pKa values of Emodin in the water-methanol mixture (1:3v/v). We give a new interpretation of the experimental data, obtaining apparent pKa1 = 6.2 ± 0.1, pKa2 = 8.3 ± 0.1 and pKa3 > 12.7. Performing quantum mechanics calculations for all possible deprotonation sites and tautomeric isomers of Emodin in vacuum and in water, we identified the sites of the first and second deprotonation. We calculated the standard deprotonation free energy of Emodin in water and the pKa1, using an explicit model of the solvent, with Free Energy Perturbation theory in Monte Carlo simulations obtaining, ?Gaq = 12.1 ± 1.4 kcal/mol and pKa1 = 8.7 ± 0.9. With the polarizable continuum model for the solvent, we obtained ?Gaq = 11.6 ± 1.0 kcal/mol and pKa1 = 8.3 ± 0.7. Both solvent models gave theoretical results in very good agreement with the experimental values.

da Cunha, Antonio R.; Duarte, Evandro L.; Lamy, M. Teresa; Coutinho, Kaline

2014-08-01

328

A stochastic approach to quantum statistics distributions: theoretical derivation and Monte Carlo modelling  

NASA Astrophysics Data System (ADS)

We present a method aimed at a stochastic derivation of the equilibrium distribution of a classical/quantum ideal gas in the framework of the canonical ensemble. The time evolution of these ideal systems is modelled as a series of transitions from one system microstate to another one and thermal equilibrium is reached via a random walk in the single-particle state space. We look at this dynamic process as a Markov chain satisfying the condition of detailed balance and propose a variant of the Monte Carlo Metropolis algorithm able to take into account indistinguishability of identical quantum particles. Simulations performed on different two-dimensional (2D) systems are revealed to be capable of reproducing the correct trends of the distribution functions and other thermodynamic properties. The simulations allow us to show that, away from the thermodynamic limit, a pseudo-Bose-Einstein condensation occurs for a 2D ideal gas of bosons.

Guastella, I.; Bellomonte, L.; Sperandeo-Mineo, R. M.

2009-02-01

329

Ab initio quantum Monte Carlo calculations of spin superexchange in cuprates: the benchmarking case of Ca2CuO3  

SciTech Connect

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 [ORNL] [ORNL; Krogel, Jaron T [ORNL] [ORNL; Kim, Jeongnim [ORNL] [ORNL; Kent, Paul R [ORNL] [ORNL; Dagotto, Elbio R [ORNL] [ORNL; Reboredo, Fernando A [ORNL] [ORNL

2014-01-01

330

Nonadiabatic couplings and gauge-theoretical structure of curved quantum waveguides  

E-print Network

We investigate the quantum mechanics of a single particle constrained to move along an arbitrary smooth reference curve by a confinement that is allowed to vary along the waveguide. The Schr\\"odinger equation is evaluated in the adapted coordinate frame and a transverse mode decomposition is performed, taking into account both curvature and torsion effects and the possibility of a cross-section potential that changes along the curve in an arbitrary way. We discuss the adiabatic structure of the problem, and examine nonadiabatic couplings that arise due to the curved geometry, the varying transverse profile and their interplay. The exact multi-mode matrix Hamiltonian is taken as the natural starting point for few-mode approximations. Such approximate equations are provided, and it is worked out how these recover known results for twisting waveguides and can be applied to other types of waveguide designs. The quantum waveguide Hamiltonian is recast into a form that clearly illustrates how it generalizes the Born-Oppenheimer Hamiltonian encountered in molecular physics. In analogy to the latter, we explore the local gauge structure inherent to the quantum waveguide problem and suggest the usefulness of diabatic states, giving an explicit construction of the adiabatic-to-diabatic basis transformation.

J. Stockhofe; P. Schmelcher

2014-03-25

331

Comparison between Theoretical Calculations and Oil Film Thickness Measurements Using the Total Capacitance Method for Crankshaft Bearings in a Firing Engine  

Microsoft Academic Search

Comparisons were made between theoretical calculations and experimental measurements for minimum bearing oil film thickness (MBOFT) in main and connecting rod bearings of a typical automotive V6 engine running at 1500 rpm under three load conditions (64, 128, and 192 Nm.). Data for five oils (SAE grades 5W–20, 20W–20, 5W–30, 10W–30, and 20W–50) were obtained for the main bearing and

Rohit S. Paranjpe; Spyros I. Tseregounis; Michael B. Viola

2000-01-01

332

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

333

Path integral calculation of thermal rate constants within the quantum instanton approximation: Application to the HCH4\\H2CH3 hydrogen  

E-print Network

Yamamoto, and William H. Millera) Department of Chemistry and Kenneth S. Pitzer Center for Theoretical and recalibrated version of the Jordan­ Gilbert potential surface. The quantum instanton rate is evaluated using

Miller, William H.

334

Elastic light scattering by semiconductor quantum dots of arbitrary shape  

Microsoft Academic Search

Elastic light scattering by low-dimensional quantum objects without a change in the frequency is theoretically investigated in terms of the quantum perturbation theory. The differential cross section of resonance light scattering from any excitons in any quantum dots is calculated. It is demonstrated that, when the light wavelengths considerably exceed the quantum-dot size, the polarization and angular distribution of the

I. G. Lang; L. I. Korovin; S. T. Pavlov

2007-01-01

335

Carbide reactions and phase equilibria in low alloy Cr-Mo-V steels tempered at 773--993 K. Part 2: Theoretical calculations  

SciTech Connect

The coexistence of carbide phases in thermodynamic equilibrium was studied by means of theoretical calculations and compared with experimental results. The study was carried out for systems corresponding to experimentally used low alloy Cr steel (approx. 2.5 wt%) with different Mo (0.70--1.0 wt%) and V (0.02--0.32 wt%) contents. The carbon content in experimental materials was about 0.1 wt%. Theoretical calculations were realized by the PD-pp software and the modeling of thermodynamic equilibria in the Fe-Cr-Mo-V-C system for the concentration corresponding to the experimental materials based on the Hillert-Staffansson sublattice model was carried out. The equilibrium phase coexistence of carbidic phases with b.c.c. ferrite was calculated in dependence on temperature. It was found that M{sub 23}C{sub 6} carbide is thermodynamically stable for low temperatures (up to 800--850 K) and then gradually replaced by M{sub 7}C{sub 3} for higher temperatures. M{sub 6}C is stable up to 890--950 K and dissolves completely. MC carbide was found to be thermodynamically stable for all temperatures for systems with vanadium content above 0.1 wt%. Good qualitative agreement between the theoretical and experimental results was reached.

Kroupa, A.; Svoboda, M. [Academy of Sciences of Czech Republic, Brno (Czech Republic). Inst. of Physics of Materials; Vyrostkova, A.; Janovec, J. [Slovak Academy of Sciences, Kosice (Slovakia). Inst. of Materials Research

1997-12-19

336

Theoretical calculation of self-broadening coefficients for the ?5 band of methyl chloride at various temperatures  

NASA Astrophysics Data System (ADS)

Self-broadening coefficients of transitions belonging to the ?5 band of methyl chloride have been calculated using a semi-classical model based on the Anderson-Tsao-Curnutte (ATC) theory, including some improvements proposed by Robert and Bonamy. The calculations show the predominance of the dipole-dipole interaction. To better match the experimental measurements performed at room temperature in our previous work, a cut-off of the intermolecular distance has been used. The rotational J and K dependencies of the calculated self-broadening coefficients have been clearly observed and are consistent with our previous measurements.

Barbouchi Ramchani, A.; Jacquemart, D.; Dhib, M.; Aroui, H.

2014-02-01

337

Atomistic and Nanoscale Origins of Macroscopic Properties of Silicate Melts at High-Pressure: Spectroscopy & Quantum Chemical Calculations  

NASA Astrophysics Data System (ADS)

Atomic structure of amorphous oxide melts at high pressure controls their macroscopic properties and geophysical progresses in the Earth's interior. Advances in NMR spectroscopy, x-ray optics, and theoretical analyses enable us to determine the structure of silicate glasses and provides clues to the microscopic origins of melt properties and relevant geochemical processes, such as generation, migration, and dynamics of magmas at high pressures (e.g. Lee et al. Geophy. Res. Letts. 2003, 30, p1845; Lee et al. Phys. Rev. Letts. 2005, 94, p165507; Lee et al. Nature Materials 2005, accepted). Here we report recent progress on pressure-induced structural changes in various amorphous oxide glasses and melt at high pressures using multi-nuclear solid state NMR, and synchrotron X-rays, and quantum simulations. In prototypical amorphous borates, and silicates, as well as complex aluminosilicate glasses and melts, the fractions of highly coordinated framework units (e.g. five coordinated [5,6]Si, [5,6]Al, [4]B) increase with increasing pressure with multiple densification mechanisms. The distribution of these framework cations at high pressure is not completely random but favors formation of oxygen linking dissimilar Si pairs such as [5,6]Si-O-[4]Al. Whereas the general trend in the effect of pressure on the structure is similar in those amorphous oxides, detailed pressure-induced structural changes are largely dependent on the degree of polymerization in the melts, types and fractions of network modifying cations at isobaric conditions. Topological disorder due to Si-O bond length distribution increases with pressure and is also larger for more polymerized amorphous oxides. Na-23 NMR spectra for sodium silicate and aluminosilicate glasses revealed that Na-O distance in the binary sodium silicates increases with pressure but that in the aluminosilicate glasses decreases with pressure. These results demonstrate that the pressure-induced structural changes in the silicate melts at high pressure and the corresponding changes in properties are complex function of composition. Pressure dependence of thermodynamics and transport properties such as diffusivity and viscosity of melts were directly calculated from experimentally measured atomic-scale disorder, and from variation of non-bridging oxygen fraction with pressure from spectroscopic data. These calculation results suggest that non-linear pressure dependence of viscosity of silicate melts stems from both the isobaric NBO fraction and its pressure dependence, yielding improved prospects for understanding the atomistic origins of magmatic processes in Earth's interior.

Lee, S.; Fei, Y.; Cody, G.; Mysen, B.; Mao, H.; Eng, P.

2005-12-01

338

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

339

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

340

Theoretical study on electromagnetically induced transparency in molecular aggregate models using quantum Liouville equation method  

NASA Astrophysics Data System (ADS)

Electromagnetically induced transparency (EIT), which is known as an efficient control method of optical absorption property, is investigated using the polarizability spectra and population dynamics obtained by solving the quantum Liouville equation. In order to clarify the intermolecular interaction effect on EIT, we examine several molecular aggregate models composed of three-state monomers with the dipole-dipole coupling. On the basis of the present results, we discuss the applicability of EIT in molecular aggregate systems to a new type of optical switch.

Minami, Takuya; Nakano, Masayoshi

2015-01-01

341

Elucidating triplet-sensitized photolysis mechanisms of sulfadiazine and metal ions effects by quantum chemical calculations.  

PubMed

Sulfadiazine (SDZ) mainly proceeds triplet-sensitized photolysis with dissolved organic matter (DOM) in the aquatic environment. However, the mechanisms underlying the triplet-sensitized photolysis of SDZ with DOM have not been fully worked out. In this study, we investigated the mechanisms of triplet-sensitized photolysis of SDZ(0) (neutral form) and SDZ(-) (anionic form) with four DOM analogues, i.e., fluorenone (FL), thioxanthone (TX), 2-acetonaphthone (2-AN), and 4-benzoylbenzoic acid (CBBP), and three metal ions (i.e., Mg(2+), Ca(2+), and Zn(2+)) effects using quantum chemical calculations. Results indicated that the triplet-sensitized photolysis mechanism of SDZ(0) with FL, TX, and 2-AN was hydrogen transfer, and with CBBP was electron transfer along with proton transfer (for complex SDZ(0)-CBBP2) and hydrogen transfer (for complex SDZ(0)-CBBP1). The triplet-sensitized photolysis mechanisms of SDZ(-) with FL, TX, and CBBP was electron transfer along with proton transfer, and with 2-AN was hydrogen transfer. The triplet-sensitized photolysis product of both SDZ(0) and SDZ(-) was a sulfur dioxide extrusion product (4-(2-iminopyrimidine-1(2H)-yl)aniline), but the formation routs of the products for SDZ(0) and SDZ(-) were different. In addition, effects of the metal ions on the triplet-sensitized photolysis of SDZ(0) and SDZ(-) were different. The metal ions promoted the triplet-sensitized photolysis of SDZ(0), but inhibited the triplet-sensitized photolysis of SDZ(-). PMID:25496743

Wang, Se; Song, Xuedan; Hao, Ce; Gao, Zhanxian; Chen, Jingwen; Qiu, Jieshan

2015-03-01

342

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

343

Line coupling effects in the isotropic Raman spectra of N{sub 2}: A quantum calculation at room temperature  

SciTech Connect

We present quantum calculations of the relaxation matrix for the Q branch of N{sub 2} at room temperature using a recently proposed N{sub 2}-N{sub 2} rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10?200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility. This has been done using complementary calculations based on the energy corrected sudden formalism. Agreement of these quantum predictions with experimental data is good, but the main goal of this work is to provide a benchmark relaxation matrix for testing more approximate methods which remain of a great utility for complex molecular systems at room (and higher) temperatures.

Thibault, Franck, E-mail: franck.thibault@univ-rennes1.fr [Institut de Physique de Rennes, UMR CNRS 6251, Université de Rennes I, Campus de Beaulieu, Bât. 11B, F-35042 Rennes (France)] [Institut de Physique de Rennes, UMR CNRS 6251, Université de Rennes I, Campus de Beaulieu, Bât. 11B, F-35042 Rennes (France); Boulet, Christian [Institut des Sciences Moléculaires d’Orsay, UMR CNRS 8214, Université Paris-Sud 11, Campus d’Orsay, Bât. 350, F-91405 Orsay (France)] [Institut des Sciences Moléculaires d’Orsay, UMR CNRS 8214, Université Paris-Sud 11, Campus d’Orsay, Bât. 350, F-91405 Orsay (France); Ma, Qiancheng [NASA/Goddard Institute for Space Studies and Department of Applied Physics and Applied Mathematics, Columbia University 2880 Broadway, New York, New York 10025 (United States)] [NASA/Goddard Institute for Space Studies and Department of Applied Physics and Applied Mathematics, Columbia University 2880 Broadway, New York, New York 10025 (United States)

2014-01-28

344

Segmented crystalline scintillators: Empirical and theoretical investigation of a high quantum efficiency EPID based on an initial engineering prototype CsI(Tl) detector  

SciTech Connect

Modern-day radiotherapy relies on highly sophisticated forms of image guidance in order to implement increasingly conformal treatment plans and achieve precise dose delivery. One of the most important goals of such image guidance is to delineate the clinical target volume from surrounding normal tissue during patient setup and dose delivery, thereby avoiding dependence on surrogates such as bony landmarks. In order to achieve this goal, it is necessary to integrate highly efficient imaging technology, capable of resolving soft-tissue contrast at very low doses, within the treatment setup. In this paper we report on the development of one such modality, which comprises a nonoptimized, prototype electronic portal imaging device (EPID) based on a 40 mm thick, segmented crystalline CsI(Tl) detector incorporated into an indirect-detection active matrix flat panel imager (AMFPI). The segmented detector consists of a matrix of 160x160 optically isolated, crystalline CsI(Tl) elements spaced at 1016 {mu}m pitch. The detector was coupled to an indirect detection-based active matrix array having a pixel pitch of 508 {mu}m, with each detector element registered to 2x2 array pixels. The performance of the prototype imager was evaluated under very low-dose radiotherapy conditions and compared to that of a conventional megavoltage AMFPI based on a Lanex Fast-B phosphor screen. Detailed quantitative measurements were performed in order to determine the x-ray sensitivity, modulation transfer function, noise power spectrum, and detective quantum efficiency (DQE). In addition, images of a contrast-detail phantom and an anthropomorphic head phantom were also acquired. The prototype imager exhibited approximately 22 times higher zero-frequency DQE ({approx}22%) compared to that of the conventional AMFPI ({approx}1%). The measured zero-frequency DQE was found to be lower than theoretical upper limits ({approx}27%) calculated from Monte Carlo simulations, which were based solely on the x-ray energy absorbed in the detector--indicating the presence of optical Swank noise. Moreover, due to the nonoptimized nature of this prototype, the spatial resolution was observed to be significantly lower than theoretical expectations. Nevertheless, due to its high quantum efficiency ({approx}55%), the prototype imager exhibited significantly higher DQE than that of the conventional AMFPI across all spatial frequencies. In addition, the frequency-dependent DQE was observed to be relatively invariant with respect to the amount of incident radiation, indicating x-ray quantum limited behavior. Images of the contrast-detail phantom and the head phantom obtained using the prototype system exhibit good visualization of relatively large, low-contrast features, and appear significantly less noisy compared to similar images from a conventional AMFPI. Finally, Monte Carlo-based theoretical calculations indicate that, with proper optimization, further, significant improvements in the DQE performance of such imagers could be achieved. It is strongly anticipated that the realization of optimized versions of such very high-DQE EPIDs would enable megavoltage projection imaging at very low doses, and tomographic imaging from a 'beam's eye view' at clinically acceptable doses.

Sawant, Amit; Antonuk, Larry E.; El-Mohri, Youcef; Zhao Qihua; Wang Yi; Li Yixin; Du Hong; Perna, Louis [Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48103 (United States); Saint Gobain Crystals, Newbury, Ohio 44065 (United States)

2006-04-15

345

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

346

Theoretical investigation of some parameters into the behavior of quantum dot solar cells  

NASA Astrophysics Data System (ADS)

The main goal of this paper is to determine the accurate values of two parameters namely the surface generation—recombination rate and the average total number of electrons density generated in the i-region. These values will enhance the performance of quantum dot solar cells (QDSCs). In order to determine these values, this paper concentrates on the optical generation lifetime, the recombination lifetime, and the effective density state in QDs. Furthermore, these parameters are studied in relation with the average total number of electrons density. The values of the surface generation—recombination rate are found to be negative, which implies that the generation process is dominant in the absorption quantum dot region. Consequently, induced photocurrent density relation with device parameters is determined. The results ensure that QDSCs can have higher response photocurrent and then improve the power conversion efficiency. Moreover, the peak value of the average total number of electrons density is achieved at the UV range and is extended to the visible range, which is adequate for space and ground solar applications.

Nasr, A.; Aly, A.

2014-12-01

347

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

PubMed

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/Hg(1-) (x)Cd(x)Te and In(x)Ga(1-) (x)As/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; Ghatak, K P

2011-01-01

348

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

349

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

2014-05-27

350

Experimental and theoretical investigation of the third-order nonlinearity in CdS quantum dots in a dendrimer matrix  

NASA Astrophysics Data System (ADS)

We have measured the nonlinear optical response of Cadmium Sulfide quantum dots (CdS QD) in a poly(propyleneimine) dendrimer matrix having diaminobutane (DAB) core. Large refractive nonlinear coefficients and low absorption losses were observed at all wavelengths. Dendrimers are nanosize, highly branched, tree like monodisperse macromolecules that emanate from a central core with a branch occurring at each monomer unit. Dendrimers encapsulations convey stability, control of emission wavelengths by QD size. The branching points in the interior of the dendrimers are occupied by tertiary nitrogen to provide numerous nucleation sites to drive formation of QD clusters of small size. The dendrimer-stabilized CdS QDs were stable at room temperature, both in solution and in solid state for several weeks. Thin films were deposited by spin casting from methanol solutions. The resulting samples consisted of a 1mm thick quartz substrate with a 200-400 Å nonlinear optical film on one side. The Z-scan technique was used to characterize the NLO response. A mode-locked YAG laser provided the laser pulses with 30-ps duration at 355 nm, 532 nm and 1064 nm at a 20-Hz repetition rate with energies per pulse ranging from few microjoules to several millijoules. These results indicate relatively large values for the nonlinear response (> 10 -10 esu) at all three wavelengths. Our calculations indicate that quantum dot-organic systems have large optical nonlinearity due to interactions between excitons in the quantum dots and the organic medium. We calculate that an increase of the QD radius to ~4-8 nm will result in a substantial enhancement of the nonlinearity.

Potasek, M. J.; Gao, Y.; Etienne, Michael; Dorsinville, Roger; Bauer, David; Balogh-Nair, Valeria

2006-02-01

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  

NASA Astrophysics Data System (ADS)

Theoretical calculations are performed for the X˜E2?2 and ÃE3?2 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 ÃE3?2-X˜E2?2 electronic spectrum. Vibrational frequencies of the tropyl radical at the conical intersection and stationary points of its X˜ and à state Jahn-Teller distorted potential energy surfaces are given. Spectroscopically obtainable parameters describing the Jahn-Teller effect are calculated for the X˜ and à electronic states. Additionally, the stabilization energies for the X˜ and à states are computed at the CASSCF(7,7) and EOMEA-CCSD levels of theory using various basis sets.

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

2008-02-01

352

Theoretical Calculation of the Power Spectra of the Rolling and Yawing Moments on a Wing in Random Turbulence  

NASA Technical Reports Server (NTRS)

The correlation functions and power spectra of the rolling and yawing moments on an airplane wing due to the three components of continuous random turbulence are calculated. The rolling moments to the longitudinal (horizontal) and normal (vertical) components depend on the spanwise distributions of instantaneous gust intensity, which are taken into account by using the inherent properties of symmetry of isotropic turbulence. The results consist of expressions for correlation functions or spectra of the rolling moment in terms of the point correlation functions of the two components of turbulence. Specific numerical calculations are made for a pair of correlation functions given by simple analytic expressions which fit available experimental data quite well. Calculations are made for four lift distributions. Comparison is made with the results of previous analyses which assumed random turbulence along the flight path and linear variations of gust velocity across the span.

Eggleston, John M; Diederich, Franklin W

1957-01-01

353

Finite-difference calculation of donor energy levels in a spherical quantum dot subject to a magnetic field  

NASA Astrophysics Data System (ADS)

The ground and excited states of a donor impurity at the center of a spherical quantum dot subject to a magnetic field are calculated within the effective-mass approximation. The barriers are infinitely high and the differential equation is solved by combining the finite-difference method with the Richardson extrapolation. The binding and transition energies are more accurate than the available variational values, and excellent agreement is found with the hydrogen atom. The transition energies for a medium-size quantum dot are given.

de Souza, G. V. B.; Bruno-Alfonso, A.

2015-02-01

354

Theoretical study on flueggenines A and B: A comparison of calculated spectroscopic properties with IR, UV and ECD experimental data  

NASA Astrophysics Data System (ADS)

Using DFT at the B3LYP/6-31+G (d) level, DFT-D at the wb97xd/tzvpp level and TD-DFT at the B3LYP/aug-cc-pVDZ level, computational analysis of the first examples of naturally occurring dimeric indolizidine alkaloids, flueggenines A and B, accomplished the simulation and interpretation of their IR, UV and ECD spectra. Compared with the experimental ones, the calculated IR and UV spectra allowed the reinforcement of the carbon skeletons and functional groups. Calculation of the ECD spectra assured the formerly assigned absolute configurations for flueggenines A and B.

Zhou, Chang-Xin; Mo, Jian-Xia; Wang, Xue-Yao; Zhang, Jian; Gan, Li-She

2011-03-01

355

Quantum statistical modified entropic gravity as a theoretical basis for MOND  

NASA Astrophysics Data System (ADS)

Considering the quantum statistics of the degrees of freedom on the holographic screen, it is shown that the ratio of the number of excited bulk degrees of freedom to the number of excited surface degrees of freedom is given by the modified Newtonian dynamics (MOND) interpolating function ?˜. This relationship is shown to hold also in aquadratic Lagrangian theory and in the extension of MOND to de Sitter space. Based on the relationship between the entropy and the number of degrees of freedom on the holographic screen, a simple expression, relating the MOND interpolating function to the ratio of the two-dimensional entropy to Bekenstein-Hawking entropy, is obtained. In terms of this expression MOND can be viewed as a modification of gravity arising due to a bound on the maximum entropy for the holographic screen.

Pazy, Ehoud

2013-04-01

356

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

357

Theoretical calculation of the track mass in the motion of unsprung masses in relation to track dynamic stiffness and damping  

Microsoft Academic Search

In order to calculate the load on the track in the position of a sleeper at the time when an isolated axle of the vehicle passes, it is necessary to determine the mass of the railway track that participates in the movement of the unsprung masses of the vehicle. In this paper, the track is modelled as a vibrating string.

K. Giannakos

2010-01-01

358

Calculation of Auger rates in a quantum well structure and its application to InGaAsP quantum well lasers  

SciTech Connect

We discuss the possible intrinsic limitation on the temperature dependence of threshold current of long wavelength InGaAsP quantum well lasers caused by Auger recombination and intervalence band absorption. A model calculation of the various band-to-band Auger rates are presented. We find that the Auger rates increase with decreasing band gap and also with increasing temperature as in the case of bulk semiconductors. The temperature dependence and the band-gap dependence arises from the energy and momentum conservation (in the direction normal to the well) that the four particle states involved must satisfy. The estimated Auger coefficient is large enough to be important in single quantum well lasers. However, the Auger effect should be much smaller in a multiquantum well laser than for a single quantum well laser. This is because the carrier density at threshold is smaller (by a factor of 3 to 4) for multiquantum well lasers than for single quantum well lasers. The increased intervalence band absorption with increasing temperature in the active layer may not be responsible for increased threshold current of single quantum well lasers.

Dutta, N.K.

1983-03-01

359

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

360

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

361

Feature Article: Thermodynamic properties from ab-initio calculations: New theoretical developments, and applications to various materials systems  

Microsoft Academic Search

The cover picture from the Feature Article [1] depicts the calculated landscape of lowest formation energies for the ternary compound system Ni-Fe-Al. The figure shows for each composition the difference in the formation energy (in meV\\/atom) for the respective homogeneous configuration with lowest energy on the bcc and the fcc parent lattice. The phases on the fcc lattice dominate the

Manfred Fähnle; Ralf Drautz; Frank Lechermann; Reinhard Singer; Alejandro Diaz-Ortiz; Helmut Dosch

2005-01-01

362

X-ray structures of the anticoagulants coumatetralyl and chlorophacinone. Theoretical calculations and SAR investigations on thirteen anticoagulant rodenticides  

NASA Astrophysics Data System (ADS)

Coumatetralyl and chlorophacinone, two substances related to 4-hydroxycoumarin (HC) and to 1,3-indandione (ID), respectively, show activity as anticoagulant rodenticides. In the present study we have investigated the solid-state structures of coumatetralyl and chlorophacinone by means of X-ray single-crystal and powder diffraction, along with thermal analysis. The crystal structures of the two compounds have been used as input geometries for a series of computational chemistry efforts, involving other anticoagulant derivatives as well. Thus, ab initio, semiempirical molecular orbital, molecular mechanics and molecular dynamics/simulated annealing calculations have been performed on thirteen anticoagulant rodenticides. In particular, the annealing calculations have been made to assess the conformational freedom of the compounds under scrutiny. All the generated conformers have been classified into families. The classification has first been made empirically, and then validated by means of a cluster analysis. A number of structural and physico-chemical parameters derived from the calculations has been used in turn for structure-activity relationships (SARs) investigations. In the latter, we have assessed how the selected parameters affect toxicity. The results seem to be consistent with a three-dimensional biophore model, in which higher toxicity is predicted for the more voluminous rodenticides. We suggest that these compounds better fit the active site of the target enzyme vitamin K 2,3-epoxide reductase (KO-reductase).

Dolmella, A.; Gatto, S.; Girardi, E.; Bandoli, G.

1999-12-01

363

Theoretical calculations on the NaS and NaS+ radicals: electronic structure, spectroscopy and spin-orbit couplings  

NASA Astrophysics Data System (ADS)

We used an ab initio methodology for the computation of the potential energy curves of the lowest electronic states of NaS and NaS+ diatomics. Using these highly correlated wavefunctions, we calculated their spin-orbit couplings. The X2? and the A2?+ electronic states of NaS are found to possess deep potential wells. The upper bound electronic states have either shallow potential wells located in the molecular region or potentials of ~1 eV depth located for large NaS distances. For NaS+, our calculations reveal the existence of shallow potentials for all states correlating to the four lowest dissociation limits. Using our potentials, we calculated an accurate set of spectroscopic constants for NaS and NaS+. Most of the data relative to the electronic excited states represent predictions. The spin-orbit induced predissociation of NaS(A2?+ is discussed. Finally, our cationic potentials and the NaS(X2?) potential were used for the prediction of the single ionization spectrum of NaS. Tables S1-S7 are only available in electronic form at www.epj.org

Khadri, F.; Hochlaf, M.

2012-05-01

364

Theoretical study of quantum molecular reaction dynamics and of the effects of intense laser radiation on a diatomic molecule  

SciTech Connect

Within the very broad field of molecular dynamics, we have concentrated on two simple yet important systems. The systems are simple enough so that they are adequately described with a single Born-Oppenheimer potential energy surface and that the dynamics can be calculated accurately. They are important because they give insight into solving more complicated systems. First we discuss H + H/sub 2/ reactive scattering. We present an exact formalism for atom-diatom reactive scattering which avoids the problem of finding a coordinate system appropriate for both reactants and products. We present computational results for collinear H + H/sub 2/ reactive scattering which agree very well with previous calculations. We also present a coupled channel distorted wave Born approximation for atom-diatom reactive scattering which we show is a first order approximation to our exact formalism. We present coupled channel DWBA results for three dimensional H + H/sub 2/ reactive scattering. The second system is an isolated HF molecule in an intense laser field. Using classical trajectories and quantum dynamics, we look at energy absorbed and transition probabilities as a function of the laser pulse time and also averaged over the pulse time. Calculations are performed for both rotating and nonrotating HF. We examine one and two photon absorption about the fundamental frequency, multiphoton absorption, and overtone absorption. 127 references, 31 figures, 12 tables.

Dardi, P.S.

1984-11-01

365

Quantum confined Stark effect in Gaussian quantum wells: A tight-binding study  

SciTech Connect

The main characteristics of the quantum confined Stark effect (QCSE) are studied theoretically in quantum wells of Gaussian profile. The semi-empirical tight-binding model and the Green function formalism are applied in the numerical calculations. A comparison of the QCSE in quantum wells with different kinds of confining potential is presented.

Ramírez-Morales, A.; Martínez-Orozco, J. C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad Esquina Con Paseo La Bufa S/N, 98060 Zacatecas, Zac. (Mexico)

2014-05-15

366

In Vivo Anti-Leukemia, Quantum Chemical Calculations and ADMET Investigations of Some Quaternary and Isothiouronium Surfactants  

PubMed Central

Anti-leukemia screening of previously prepared isothiouronium and quaternary salts was performed, and some salts exhibited promising activity as anticancer agents. Quantum chemical calculations were utilized to explore the electronic structure and stability of these compounds. Computational studies have been carried out at the PM3 semiempirical molecular orbitals level, to establish the HOMO-LUMO, IP and ESP mapping of these compounds. The ADMET properties were also studied to gain a clear view of the potential oral bioavailability of these compounds. The surface properties calculated included critical micelle concentration (CMC), maximum surface excess (?max), minimum surface area (Amin), free energy of micellization (?Gomic) and adsorption (?Goads). PMID:24276171

El-Henawy, Ahmed A.; Khowdiary, Manal M.; Badawi, Abdelfattah B.; Soliman, Hussein M.

2013-01-01

367

New fitting approach of electrostatic potential for stable quantum mechanical calculations using the reference interaction site model  

NASA Astrophysics Data System (ADS)

We proposed a new fitting approach of electrostatic potential (ESP) for stable quantum mechanical (QM) calculations using the reference interaction site model. In this approach, the approximated density matrix is fitted so that the ESP computed from QM calculations can be reproduced. We introduced two conditions: conservation of the number of electrons and positive semi-definite condition of the electron density matrix. This approach was introduced in a linear response approximation of the reference interaction site model self-consistent field explicitly including the spatial electron density distribution. By considering the two conditions, we overcame the instability inherent in a previous approach.

Yokogawa, D.

2013-11-01

368

Theoretical Prediction of Hydrogen-Bond Basicity pKBHX Using Quantum Chemical Topology Descriptors  

PubMed Central

Hydrogen bonding plays an important role in the interaction of biological molecules and their local environment. Hydrogen-bond strengths have been described in terms of basicities by several different scales. The pKBHX scale has been developed with the interests of medicinal chemists in mind. The scale uses equilibrium constants of acid···base complexes to describe basicity and is therefore linked to Gibbs free energy. Site specific data for polyfunctional bases are also available. The pKBHX scale applies to all hydrogen-bond donors (HBDs) where the HBD functional group is either OH, NH, or NH+. It has been found that pKBHX can be described in terms of a descriptor defined by quantum chemical topology, ?E(H), which is the change in atomic energy of the hydrogen atom upon complexation. Essentially the computed energy of the HBD hydrogen atom correlates with a set of 41 HBAs for five common HBDs, water (r2 = 0.96), methanol (r2 = 0.95), 4-fluorophenol (r2 = 0.91), serine (r2 = 0.93), and methylamine (r2 = 0.97). The connection between experiment and computation was strengthened with the finding that there is no relationship between ?E(H) and pKBHX when hydrogen fluoride was used as the HBD. Using the methanol model, pKBHX predictions were made for an external set of bases yielding r2 = 0.90. Furthermore, the basicities of polyfunctional bases correlate with ?E(H), giving r2 = 0.93. This model is promising for the future of computation in fragment-based drug design. Not only has a model been established that links computation to experiment, but the model may also be extrapolated to predict external experimental pKBHX values. PMID:24460383

2014-01-01

369

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

370

Theoretical investigation of the electronic structure and quantum transport in the graphene-C(111) diamond surface system.  

PubMed

We investigate the interaction of a graphene monolayer with the C(111) diamond surface using ab initio density functional theory. To accommodate the lattice mismatch between graphene and diamond, the overlayer deforms into a wavy structure that binds strongly to the diamond substrate. The detached ridges of the wavy graphene overlayer behave electronically as free-standing polyacetylene chains with delocalized ? electrons, separated by regions containing only sp(3) carbon atoms covalently bonded to the (111) diamond surface. We performed quantum transport calculations for different geometries of the system to study how the buckling of the graphene layer and the associated bonding to the diamond substrate affect the transport properties. The system displays high carrier mobility along the ridges and a wide transport gap in the direction normal to the ridges. These intriguing, strongly anisotropic transport properties qualify the hybrid graphene-diamond system as a viable candidate for electronic nanodevices. PMID:24096938

Selli, Daniele; Baburin, Igor; Leoni, Stefano; Zhu, Zhen; Tománek, David; Seifert, Gotthard

2013-10-30

371

A Theoretical Model for Calculating Voltage Sensitivity of Ion Channels and the Application on Kv1.2 Potassium Channel  

PubMed Central

Voltage sensing confers conversion of a change in membrane potential to signaling activities underlying the physiological processes. For an ion channel, voltage sensitivity is usually experimentally measured by fitting electrophysiological data to Boltzmann distributions. In our study, a two-state model of the ion channel and equilibrium statistical mechanics principle were used to test the hypothesis of empirically calculating the overall voltage sensitivity of an ion channel on the basis of its closed and open conformations, and determine the contribution of individual residues to the voltage sensing. We examined the theoretical paradigm by performing experimental measurements with Kv1.2 channel and a series of mutants. The correlation between the calculated values and the experimental values is at respective level, R2 = 0.73. Our report therefore provides in silico prediction of key conformations and has identified additional residues critical for voltage sensing. PMID:22768937

Yang, Huaiyu; Gao, Zhaobing; Li, Ping; Yu, Kunqian; Yu, Ye; Xu, Tian-Le; Li, Min; Jiang, Hualiang

2012-01-01

372

Interaction of curcumin with Al(III) and its complex structures based on experiments and theoretical calculations  

NASA Astrophysics Data System (ADS)

Curcumin has been recognized as a potential natural drug to treat the Alzheimer's disease (AD) by chelating baleful metal ions, scavenging radicals and preventing the amyloid ? (A?) peptides from the aggregation. In this paper, Al(III)-curcumin complexes with Al(III) were synthesized and characterized by liquid-state 1H, 13C and 27Al nuclear magnetic resonance (NMR), mass spectroscopy (MS), ultraviolet spectroscopy (UV) and generalized 2D UV-UV correlation spectroscopy. In addition, the density functional theory (DFT)-based UV and chemical shift calculations were also performed to view insight into the structures and properties of curcumin and its complexes. It was revealed that curcumin could interact strongly with Al(III) ion, and form three types of complexes under different molar ratios of [Al(III)]/[curcumin], which would restrain the interaction of Al(III) with the A? peptide, reducing the toxicity effect of Al(III) on the peptide.

Jiang, Teng; Wang, Long; Zhang, Sui; Sun, Ping-Chuan; Ding, Chuan-Fan; Chu, Yan-Qiu; Zhou, Ping

2011-10-01

373

Interaction of curcumin with Zn(II) and Cu(II) ions based on experiment and theoretical calculation  

NASA Astrophysics Data System (ADS)

Curcumin and its complexes with Zn 2+ and Cu 2+ ions were synthesized and characterized by elemental analysis, mass spectroscopy, IR spectroscopy, UV spectroscopy, solution 1H and solid-state 13C NMR spectroscopy, EPR spectroscopy. In addition, the density functional theory (DFT)-based UV and 13C chemical shift calculations were also performed to view insight into those compound structures and properties. The results show that curcumin easily chelate the metal ions, such as Zn 2+ and Cu 2+, and the Cu(II)-curcumin complex has an ability to scavenge free-radicals. We demonstrated the differences between Zn(II)-curcumin and Cu(II)-curcumin complexes in structure and properties, enhancing the comprehensions about the curcumin roles in the Alzhermer's disease treatment.

Zhao, Xue-Zhou; Jiang, Teng; Wang, Long; Yang, Hao; Zhang, Sui; Zhou, Ping

2010-12-01

374

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

375

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

SciTech Connect

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, E-mail: qshi@iccas.ac.cn [Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190 (China)] [Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190 (China)

2014-05-07

376

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

PubMed

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. PMID:24811623

Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang

2014-05-01

377

Tungsten-dependent formaldehyde ferredoxin oxidoreductase: Reaction mechanism from quantum chemical calculations  

E-print Network

redox reactions, while the latter catalyzes a non-redox hydration of acetylene. In Pyrococcus furiosusTungsten-dependent formaldehyde ferredoxin oxidoreductase: Reaction mechanism from quantum chemical April 2011 Keywords: Tungstoenzyme Formaldehyde oxidoreductase Reaction mechanism Density functional

Liao, Rongzhen

378

Ion-molecule reactions involving HCO+ and N2H+: Isotopologue equilibria from new theoretical calculations and consequences for interstellar isotope fractionation  

NASA Astrophysics Data System (ADS)

Aims: We revisit with new augmented accuracy the theoretical dynamics of basic isotope exchange reactions involved in the 12C/13C, 16O/18O, and 14N/15N 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 H12C18O+ and an increase in the abundance of H13C16O+ and D13C16O+. In all studied cases, the reaction of the ion with a neutral polarizable molecule proceeds through the intermediate proton-bound complex found to be very stable. For the complexes OCH+··· CO, OCH+··· OC, COHOC+, N2··· HCO+, N2H+··· OC, and N2HN2+, we also calculated vibrational frequencies and dissociation energies. Conclusions: The linear proton-bound complexes possess sizeable dipole moments, which may facilitate their detection.

Mladenovi?, M.; Roueff, E.

2014-06-01

379

Numerical Calculation of Electronic Structure for Three-Dimensional Nanoscale Semiconductor Quantum Dots and Rings  

Microsoft Academic Search

In this paper the electronic structure of nanoscale ellipsoid-torus-shaped semiconductor quantum dot and quantum ring is investigated of utilizing a unified model. This three-dimensional model considers the effective one-band Hamiltonian, the position- and energy-dependent effective mass approximation and Landé factor, the finite hard wall confinement potential, and the Ben Daniel-Duke boundary conditions. It is solved numerically without any fitting parameters

Yiming Li

2003-01-01

380

IR and Py-GC/MS spectral simulation of polymer film by quantum chemical and quantum molecular dynamics calculations using the polymer models  

NASA Astrophysics Data System (ADS)

We have simulated IR and pyrolysis gas chromatography mass spectrometry (Py-GCMS) spectra of six polymers (PE, PP, PS, PET, N6, PVDF) with the density-functional theory and quantum molecular dynamics calculations on model oligomers. In the former calculations, experimental harmonic frequencies of the polymers have been assigned from the simulated IR spectra. In the latter QMD calculations on thermal decomposition of polymer models, the approximated mass spectra of six (PE, PP, PS, PET, N6, PVDF) polymers were almost in good accordance with the experimental results in Py-GC/MS, although we adjusted the decomposition temperatures to 2240, 2520, and 2800 K as the average absolute deviation of 8%.

Endo, Kazunaka; Hayashi, Koichiro; Ida, Tomonori; Takemura, Tetsuo

2014-12-01

381

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

382

A systematic theoretical study of the electronic structures of porphyrin dimers: DFT and TD-DFT calculations on diporphyrins linked by ethane, ethene, ethyne, imine, and azo bridges.  

PubMed

Theoretical calculations of the geometries, electronic structures and electronic absorption spectra of a series of covalently-linked porphyrin dimers are reported. The diporphyrins comprise 5,10,15-triphenylporphyrinatozinc(II) (ZnTriPP) units linked through the meso carbons by two-atom bridges, namely 1,2-ethanediyl (1), trans-1,2-ethenediyl (2), ethynediyl (3), 1,2-iminomethenediyl (4), and transdiazenediyl (5). The structures were optimised in toluene solvent by Density Functional Theory (DFT), using the integral equation formalism variant of the polarizable continuum model. The calculations were performed using the B3LYP functional and the 6-31G(d,p) basis set. The complete molecules were modelled, with no substitution of smaller groups on the periphery. In parallel, the compounds 2–5 were prepared by known or novel synthetic routes, to enable comparisons of experimental electronic absorption spectra with those calculated using time dependent-DFT at the same level of theory. As the ethane dimer 1 is not yet synthetically accessible, the model monomer meso-2-phenylethylZnTriPP was used for comparisons with the theoretical predictions. The results form a self-consistent set, enabling for the first time legitimate comparisons of the electronic structures of the series, especially regarding the degree to which the porphyrin p-systems interact by conjugation across the bridges. The theoretical calculations of the electronic transitions match the observed spectra in toluene to a remarkable degree, especially with respect to the peak maximum of the Q band, which represents to a large degree the energy of the HOMO–LUMO transition. The imine 4 is intrinsically polar due to the asymmetric bridge, and the HOMO is located almost exclusively on the ZnTriPP unit attached to the nitrogen of the imine, and the LUMO on the C-attached ring. Thus the Q-band transition is mapped as a comprehensive charge-transfer from the former ring to the latter. This may have consequences for the non-linear optical properties of the system. The azoporphyrin 5 exhibits the largest splittings between the interacting MOs via the conjugated bridge, vindicating a prediction by Anderson and co-workers in 2002, and confirmed experimentally by our synthesis of 5. The collected results also indicate that this level of theory is more thanadequate as a model with which to handle these large delocalised molecules. PMID:24097279

Rintoul, Llew; Harper, Shannon R; Arnold, Dennis P

2013-11-21

383

Feature Article: Thermodynamic properties from ab-initio calculations: New theoretical developments, and applications to various materials systems  

NASA Astrophysics Data System (ADS)

The cover picture from the Feature Article [1] depicts the calculated landscape of lowest formation energies for the ternary compound system Ni-Fe-Al. The figure shows for each composition the difference in the formation energy (in meV/atom) for the respective homogeneous configuration with lowest energy on the bcc and the fcc parent lattice. The phases on the fcc lattice dominate the Ni- and Al-rich regions of the Gibbs triangle.The first author Manfred Fähnle is Professor at the University of Stuttgart and member of the theory group of the department of Prof. Schütz at the Max-Planck-Institut für Metallforschung in Stuttgart. In 1980 he was awarded with the Otto-Hahn medal of the Max-Planck Society and in 1985 he received the Academy Award for Physics of the University of Göttingen. His present research interests are the static and dynamic properties of bulk and nanostructured magnetic systems, as well as the ab-initio statistical mechanics of alloys.

Fähnle, Manfred; Drautz, Ralf; Lechermann, Frank; Singer, Reinhard; Diaz-Ortiz, Alejandro; Dosch, Helmut

2005-05-01

384

Versatile phosphate phosphors ABPO(4) in white light-emitting diodes: collocated characteristic analysis and theoretical calculations.  

PubMed

The orthophosphate host family, A(I)B(II)PO(4) (A(I) = monovalent cation, B(II) = divalent cation), has recently been made available as phosphors that combine with near-UV lighting chips for use in solid-state white light-emitting diodes (LEDs). This study elucidates the crystalline structure and lattice parameters of the products via a solid-state reaction, using powder X-ray diffraction (XRD) and GSAS refinement. The versatility of the phosphor host A(I)B(II)PO(4) is established by examining isovalent substitutions of four cations in the structure-Li or K for A(I), Sr or Ba for B(II)-and three doped activators, RE = Eu(2+), Tb(3+), and Sm(3+). The luminescence properties, decay time, and Commission Internationale de l'Eclairage (CIE) chromaticity index are determined for various concentrations of these activators and metal constituents of the host. The thermal stabilities of all of these compounds are determined for the first time from the crystal structure and the coordination environment of the rare-earth metal. The morphology, composition, and particle size were measured in detail. Finally, density functional calculations were performed using the generalized gradient approximation plus an on-site Coulombic interaction correction (GGA+U) scheme to investigate the electronic structures of the KSrPO(4) system. A concise model was proposed to explain the luminescence mechanism. PMID:20155924

Lin, Chun Che; Xiao, Zhi Ren; Guo, Guang-Yu; Chan, Ting-Shan; Liu, Ru-Shi

2010-03-10

385

Theoretical hardness calculated from crystallo-chemical data for MoS2 and WS2 crystals and nanostructures.  

PubMed

The calculation of the hardness of Mo and W disulfides using a crystallo-chemical model provides a unique opportunity to obtain separate quantitative information on the maximum hardness H(max) governed by strong intra-layer covalent bonds acting within the (0001) plane versus the minimum hardness H(min) governed by weak inter-layer van der Waals bonds acting along the c-axis of the hexagonal lattice. The penetration hardness derived from fundamental crystallo-chemical data (confirmed by experimental determinations) proved to be far lower in MS(2) (M = Mo, W) than in graphite and hexagonal BN, both for H(max) (H(graph)/H(MoS2) = 3.85; H(graph)/H(WS2) = 3.60; H(hBN)/H(MoS2) = 2.54; H(hBN)/H(WS2) = 2.37) as well as for H(min) (H(graph)/H(MoS2) = 6.22; H(graph)/H(WS2) = 5.87; H(hBN)/H(MoS2) = 4.72; H(hBN)/H(WS2) = 4.46). However, the gap between H(max) and H(min) is considerably larger in MS(2) (M = Mo,W), as indicated by H(max)/H(min) being 279 in 2H-MoS(2), 282 in 2H-WS(2), 173 in graphite and 150 in hBN. The gap was found to be even larger in MS(2) (M = Mo, W) nanostructures. These findings help to explain the excellent properties of MS(2) (M = Mo, W) as solid lubricants in high tech fields, either as bulk 2H crystals (inter-layer shear and peeling off lubricating mechanisms), or especially as onion-like fullerene nanoparticles (rolling/sliding mechanisms). PMID:22992795

Petrescu, M I

2012-10-01

386

ELECTRON-IMPACT EXCITATION OF Cr II: A THEORETICAL CALCULATION OF EFFECTIVE COLLISION STRENGTHS FOR OPTICALLY ALLOWED TRANSITIONS  

SciTech Connect

In this paper, we present electron-impact excitation collision strengths and Maxwellian averaged effective collision strengths for the complicated iron-peak ion Cr II. We consider specifically the allowed lines for transitions from the 3d {sup 5} and 3d {sup 4}4s even parity configuration states to the 3d {sup 4}4p odd parity configuration levels. The parallel suite of R-Matrix packages, RMATRX II, which have recently been extended to allow for the inclusion of relativistic effects, were used to compute the collision cross sections. A total of 108 LS{pi}/280 J{pi} levels from the basis configurations 3d {sup 5}, 3d {sup 4}4s, and 3d {sup 4}4p were included in the wavefunction representation of the target including all doublet, quartet, and sextet terms. Configuration interaction and correlation effects were carefully considered by the inclusion of seven more configurations and a pseudo-corrector 4d-bar type orbital. The 10 configurations incorporated into the Cr II model thus listed are 3d {sup 5}, 3d {sup 4}4s, 3d {sup 4}4p, 3d {sup 3}4s {sup 2}, 3d {sup 3}4p {sup 2}, 3d {sup 3}4s4p, 3d{sup 4}4d-bar, 3d{sup 3}4s4d-bar, 3d{sup 3}4p4d-bar, and 3d{sup 3}4d-bar{sup 2}, constituting the largest Cr II target model considered to date in a scattering calculation. The Maxwellian averaged effective collision strengths are computed for a wide range of electron temperatures 2000-100,000 K which are astrophysically significant. Care has been taken to ensure that the partial wave contributions to the collision strengths for these allowed lines have converged with 'top-up' from the Burgess-Tully sum rule incorporated. Comparisons are made with the results of Bautista et al. and significant differences are found for some of the optically allowed lines considered.

Wasson, I. R.; Ramsbottom, C. A.; Scott, M. P., E-mail: iwasson01@qub.ac.uk [Department of Applied Mathematics and Theoretical Physics, Queen's University, Belfast (United Kingdom)

2011-10-01

387

Calculations of time-dependent observables in non-Hermitian quantum mechanics: The problem and a possible solution  

E-print Network

The solutions of the time independent Schrodinger equation for non-Hermitian (NH) Hamiltonians have been extensively studied and calculated in many different fields of physics by using L^2 methods that originally have been developed for the calculations of bound states. The existing non-Hermitian formalism breaks down when dealing with wavepackets(WP). An open question is how time dependent expectation values can be calculated when the Hamiltonian is NH ? Using the F-product formalism, which was recently proposed, [J. Phys. Chem., 107, 7181 (2003)] we calculate the time dependent expectation values of different observable quantities for a simple well known study test case model Hamiltonian. We carry out a comparison between these results with those obtained from conventional(i.e., Hermitian) quantum mechanics (QM) calculations. The remarkable agreement between these results emphasizes the fact that in the NH-QM, unlike standard QM, there is no need to split the entire space into two regions; i.e., the interaction region and its surrounding. Our results open a door for a type of WP propagation calculations within the NH-QM formalism that until now were impossible.

Ido Gilary; Avner Fleischer; Nimrod Moiseyev

2005-07-26

388

Coupling coefficient calculation for GaSb-based quantum well distributed feedback lasers with laterally coupled gratings  

NASA Astrophysics Data System (ADS)

We calculated the coupling coefficient of different types of laterally coupled distributed feedback (LC-DFB) structures with coupled-wave theory and the two-dimensional semivectorial finite difference method. Effects neglected in previous studies such as other partial waves, the ohmic contact and metal contact layers are taken into account in this calculation. The LC-DFB structure with metal gratings is especially studied due to its advantage over index-coupled structures. The dependence of coupling coefficient on structure parameters is theoretically calculated such as grating order, ridge width, thickness of the residual cladding layer, grating depth and lateral proximity of gratings to the ridge waveguide. A complex-coupled GaSb-based 2 µm LC-DFB structure is optimized to achieve a high coupling coefficient of 14.5 cm-1.

Wang, Y. B.; Xu, Y.; Zhang, Y.; Song, G. F.; Chen, L. H.

2012-12-01

389

Measuring the absolute disintegration rate of a radioactive gas with a moveable endplate discharge counter (MEP) and theoretical calculation of wall effect  

SciTech Connect

A precision built moveable endplate Geiger-Mueller counter was used to measure the absolute disintegration rate of a beta-emitting radioactive gas. A Geiger-Mueller counter used for measuring gaseous radioactivity has <100% counting efficiency owing to two factors: (1) ''end effect,'' due to decreased and distorted fields at the ends where wire-insulator joints are placed, and (2) ''wall effect,'' due to non-ionization by beta particles emitted near to and heading into the wall. The end effect was evaluated by making one end of the counter movable and measuring counting rates at a number of endplate positions. Much of the wall effect was calculated theoretically, based on known data for primary ionization of electrons as a function of energy and gas composition. Corrections were then made for the ''shakeoff'' effect in beta decay and for backscattering of electrons from the counter wall. Measurements and calculations were made for a sample of /sup 85/Kr (beta energy, 0.67 MeV). The wall effect calculation is readily extendable to other beta energies.

Jaffey, A.H.; Gray, J.; Bentley, W.C.; Lerner, J.L.

1987-09-01

390

Novel polycarboxylated EDTA-type cyclodextrins as ligands for lanthanide binding: study of their luminescence, relaxivity properties of Gd(iii) complexes, and PM3 theoretical calculations.  

PubMed

Novel -type cyclodextrin (CD) derivatives, , and , bearing 6, 7 and 8 bis(carboxymethyl)amino (iminodiacetic acid) groups, respectively, were prepared, and their complexation with Eu(iii), Tb(iii) and Gd(iii) ions was studied. Luminescence titrations and mass spectrometry showed formation of multimetal complexes ( 2 to 3, mainly 3 and exactly 4 metal ions), whereas luminescence lifetime measurements revealed the presence of exchangeable water molecules. Semiempirical quantum mechanical calculations, performed by the PM3 method and assessed by DFT calculations on model ligands, indicated efficient multi-metal complexation, in agreement with the experiment. The structures showed coordination of the metal ions in the outer primary side of the CDs via 4 carboxylate O atoms, 2 N atoms and a glucopyranose O atom per metal ion. Coordination of water molecules was also predicted, in accordance with experimental results. Calculated bond lengths and angles were in agreement with literature experimental values of lanthanide complexes. Calculated energies showed that complex stability decreases in the order > > . (1)H NMR molecular relaxivity measurements for the Gd(iii) complexes of , or in water afforded values 4 to 10 times higher than the relaxivity of a commercial contrast agent at 12 MHz, and 6 to 20 times higher at 100 MHz. Solutions of and Gd(iii) complexes in human blood plasma displayed relaxivity values at 100 MHz 7 and 12 times, respectively, higher than the commercial agent. MTT tests of the Gd(iii) complexes using human skin fibroblasts did not show toxicity. Attempts to supramolecularly sensitize the luminescence of the lanthanide complexes using various aromatic CD guests were ineffective, evidently due to large guest-metal distances and inefficient inclusion. The described lanthanide complexes, could be useful as contrast agents in MRI. PMID:20449498

Maffeo, Davide; Lampropoulou, Maria; Fardis, Michael; Lazarou, Yannis G; Mavridis, Irene M; Mavridou, Despoina A I; Urso, Elena; Pratsinis, Harris; Kletsas, Dimitris; Yannakopoulou, Konstantina

2010-04-21

391

Vibrational spectra of berberine and their interpretation by means of DFT quantum-mechanical calculations  

E-print Network

Experimental vibrational spectra (Raman and infrared absorption) of berberine are obtained at room temperature. The vibrational spectra of berberine are calculated by the DFT method at the B3LYP/6-311++G(d,p) level. Based on the correlation between experimental and calculated data, the vibrational spectrum is interpreted in the frequency range of 800-1700 cm-1 in detail. The experimental and calculated spectra of intramolecular vibrations are found to correlate closely

Bashmakova, N; Zhurakivsky, R; Hovorun, D; Yashchuk, V

2011-01-01

392

Quantum Mechanical Model of Three-Body Rearrangement Scattering. II. Calculations for a Resonance Energy  

Microsoft Academic Search

In a companion paper, Robinson shows that the basis set which Hulburt and Hirschfelder used to obtain the transmission and reflection coefficients for a quantum mechanical model of reactive scattering of three atoms in a line was incomplete for a set of resonance energies. In the present paper, using Robinson's complete basis set, agreement is obtained with Tang, Kleinman, and

David R. Dion; Joseph O. Hirschfelder

1970-01-01

393

Structural properties and enthalpy of formation of magnesium hydride from quantum Monte Carlo calculations  

E-print Network

Structural properties and enthalpy of formation of magnesium hydride from quantum Monte Carlo-volume equation of state, the cohesive energy, and the enthalpy of formation from magnesium bulk and hydrogen gasV and agrees perfectly with the experimental value of 1.51 eV. The enthalpy of formation of MgH2 from Mg bulk

Alfè, Dario

394

Monte Carlo Calculations of the Specific Heat in Quantum Critical Metals  

Microsoft Academic Search

Quantum critical magnetic metals have unusual low temperature response such as an anomalous temperature dependence of the electronic specific heat (cv˜ T lnT). This dependence originates in the competition between ordering local magnetic moments and the conduction electrons shielding the moments. The Kondo Temperature, TK when moments become shielded depends on the inter-atomic distances. In most systems that have been

John Gaddy; Wouter Montfrooij; Thomas Vojta

2009-01-01

395

Heteroleptic diimine copper (I) complexes with large extinction coefficients: synthesis, quantum chemistry calculations and physico-  

E-print Network

1 Heteroleptic diimine copper (I) complexes with large extinction coefficients: synthesis, quantum. . Abstract Using the HETPHEN approach, five new heteroleptic copper(I) complexes composed of a push-pull 4 complexes experimentally demonstrate that large light harvesting properties with bis-diimine copper

Paris-Sud XI, Université de

396

A critical evaluation of the s-cis-trans isomerism of 2-acetylpyrrole and its N-methyl derivative through infrared and NMR spectroscopies and theoretical calculations  

NASA Astrophysics Data System (ADS)

Literature data are controversial regarding the conformational equilibria of 2-acetylpyrrole (AP) and its N-methyl derivative (AMP). Now, a detailed study through infrared spectroscopy and theoretical calculations has shown that previous data were erroneously interpreted, since only a N,O-cis conformer is present in solution and that it is the stable conformer in the isolated state (?Etrans-cis = 5.05 kcal mol-1, for AP; ?Etrans-cis = 7.14 kcal mol-1, for AMP). Carbonyl and Nsbnd H absorption data in different solvents, supported by theoretical results taking into account the solvent effects [at IEFPCM-B3LYP/6-311++G(3df,3p) level of theory] clearly demonstrated that only the N,O-cis conformer is present in solution. However, a doublet was observed for AP, in CCl4, which can be attributed to this conformer and the lowest wavenumber component to the cis dimer form, stabilized through intermolecular hydrogen bonds (NH⋯Odbnd C). The overall preference for the N,O-cis conformer, in AP and AMP, as interpreted by the NBO analysis, indicated that the hyperconjugative effect is the main contribution to stabilize this rotamer, overcoming the possible steric repulsion. 13C NMR experiments at low temperature in two different solvents (CS2/CDCl2 and acetone-d6) confirmed the occurrence of a single conformer since no separated signals were observed.

Ducati, Lucas C.; Braga, Carolyne B.; Rittner, Roberto; Tormena, Cláudio F.

2013-12-01

397

Quantum chemical and theoretical kinetics study of the O(3P) + C2H2 reaction: a multistate process.  

PubMed

The potential energy surfaces of the two lowest-lying triplet electronic surfaces 3A'' and 3A' for the O(3P) + C2H2 reaction were theoretically reinvestigated, using various quantum chemical methods including CCSD(T), QCISD, CBS-QCI/APNO, CBS-QB3, G2M(CC,MP2), DFT-B3LYP and CASSCF. An efficient reaction pathway on the electronically excited 3A' surface resulting in H(2S) + HCCO(A2A') was newly identified and is predicted to play an important role at higher temperatures. The primary product distribution for the multistate multiwell reaction was then determined by RRKM statistical rate theory and weak-collision master equation analysis using the exact stochastic simulation method. Allowing for nonstatistical behavior of the internal rotation mode of the initial 3A'' adducts, our computed primary-product distributions agree well with the available experimental results, i.e., ca. 80% H(2S) + HCCO(X2A'' + A2A') and 20% CH2(X3B1) + CO(X1sigma+) independent of temperature and pressure over the wide 300-2000 K and 0-10 atm ranges. The thermal rate coefficient k(O + C2H2) at 200-2000 K was computed using multistate transition state theory: k(T) = 6.14 x 10(-15)T (1.28) exp(-1244 K/T) cm3 molecule(-1) s(-1); this expression, obtained after reducing the CBS-QCI/APNO ab initio entrance barriers by 0.5 kcal/mol, quasi-perfectly matches the experimental k(T) data over the entire 200-2000 K range, spanning 3 orders of magnitude. PMID:16722685

Nguyen, Thanh Lam; Vereecken, Luc; Peeters, Jozef

2006-06-01

398

Excitonic optical nonlinearity and exciton dynamics in semiconductor quantum dots  

Microsoft Academic Search

Two salient features of the excitonic state in semiconductor quantum dots are theoretically clarified. One is the enhanced excitonic optical nonlinearity arising from the state filling of discrete levels due to the quantum size effect. The calculated third-order nonlinear susceptibility explains successfully the recent experimental results. The other feature is the exciton dynamics in semiconductor quantum dots. A comprehensive interpretation

T. Takagahara

1987-01-01

399

Theoretical optimization of multi-layer InAs/GaAs quantum dots subject to post-growth thermal annealing for tailoring the photoluminescence emission beyond 1.3 ?m  

NASA Astrophysics Data System (ADS)

In this paper, we present theoretical analysis and computation for tuning the ground state (GS) photoluminescence (PL) emission of InAs/GaAs quantum dots (QDs) at telecommunication window of 1.3-1.55 ?m by optimizing its height and base dimensions through quantum mechanical concepts. For this purpose, numerical modelling is carried out to calculate the quantized energy states of finite dimensional QDs so as to obtain the GS PL emission at or beyond 1.3 ?m. Here, we also explored strain field altering the QD size distribution in multilayer heterostructure along with the changes in the PL spectra, simulation on post growth thermal annealing process which blueshifts the operating wavelength away from the vicinity of 1.3 ?m and improvement of optical properties by varying the thickness of GaAs spacing. The results are discussed in detail which will serve as an important information tool for device scientist fabricating high quality semiconductor quantum structures with reduced defects at telecommunication wavelengths.

Ghosh, K.; Naresh, Y.; Srichakradhar Reddy, N.

2012-07-01

400

Structure of molecular tweezer complexes in the solid state: NMR experiments, X-ray investigations, and quantum chemical calculations.  

PubMed

The structure of supramolecular complexes formed by a naphthalene-spaced tweezer molecule as host and 1,4-dicyanobenzene (DCNB), 1,2,4,5-tetracyanobenzene (TCNB), and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as aromatic, electron-deficient guests is investigated by solid-state NMR and X-ray diffraction measurements. Quantum chemical calculations using linear scaling methods are applied to predict and to assign the 1H NMR chemical shifts of the complexes. By combining experiment and theory, insights into intra- and intermolecular effects influencing the proton chemical shifts of the host-guest system are provided in the solid state. PMID:17263413

Schaller, Torsten; Büchele, Uta P; Klärner, Frank-Gerrit; Bläser, Dieter; Boese, Roland; Brown, Steven P; Spiess, Hans Wolfgang; Koziol, Felix; Kussmann, Jörg; Ochsenfeld, Christian

2007-02-01

401

Monte Carlo calculations of transport parameters of one-dimensional hot electrons in quantum-well wires  

NASA Astrophysics Data System (ADS)

Monte Carlo calculations of hot-electron drift velocity, average energy, and diffusion coefficient are reported for the one-dimensional electron gas in a GaAs quantum-well wire of square cross section with side length L. Electron scattering by acoustic and longitudinal polar optic phonons is included. The transport parameters are found to rise more rapidly with electric field for L=160 Å than for L=40 Å, particularly at a lower ambient temperature. Einstein's relationship is shown to underestimate the hot-electron diffusivity for r=160 Å.

Chattopadhyay, D.; Bhattacharyya, A.

1988-04-01

402

Variational calculations of subbands in a quantum well with uniform electric field - Gram-Schmidt orthogonalization approach  

NASA Technical Reports Server (NTRS)

Variational calculations of subband eigenstates in an infinite quantum well with an applied electric field using Gram-Schmidt orthogonalized trial wave functions are presented. The results agree very well with the exact numerical solutions even up to 1200 kV/cm. It is also shown that, for increasing electric fields, the energy of the ground state decreases, while that of higher subband states increases slightly up to 1000 kV/cm and then decreases for a well size of 100 A.

Ahn, Doyeol; Chuang, S. L.

1986-01-01

403

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

404

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

405

Trifluoroacetylsulfenyl trifluoroacetate, CF(3)C(O)-S-O-C(O)CF(3), a novel compound with a symmetrically substituted S-O bond: synthesis, spectroscopic characterization, and quantum chemical calculations.  

PubMed

The new compound trifluoroacetylsulfenyl trifluoroacetate, CF(3)C(O)SOC(O)CF(3), which possesses two identical carbonyl substituents attached to the S-O bond, has been synthesized. The IR and UV spectra of the gas phase as well as the (13)C NMR spectrum of the solution in CDCl(3) were recorded and assigned. Quantum chemical calculations were performed with the ab initio methods HF and MP2 and the density functional approach B3LYP. The 6-31G basis set was chosen in all calculations. The molecule possesses a skew structure, and according to all computational methods, the syn-syn structure (C=O bonds of both C(O)CF(3) groups synperiplanar to S-O bond) represents the most stable conformer. In agreement with the quantum chemical calculations, the presence of small amounts (< or =5%) of a second conformer (anti-syn) cannot be excluded on the basis of the IR spectrum. The calculated values for the torsional angle around the S-O bond (delta(C-S-O-C)) of the syn-syn form are smaller than 80 degrees (72-78 degrees). Comparison with theoretical results for the corresponding disulfide CF(3)C(O)SSC(O)CF(3) and peroxide CF(3)C(O)OOC(O)CF(3) indicates that the structural properties of sulfenyl compounds are more similar to those of disulfides than to those of peroxides. PMID:12401074

Ulic, S E; Della Védova, C O; Hermann, A; Mack, H-G; Oberhammer, H

2002-11-01

406

Development and Numerical Analysis of "Black-box" Counterpropagating Wave Algorithm for Exact Quantum Scattering Calculations  

E-print Network

In a recent series of papers [J. Chem. Phys. 121 4501 (2004), J. Chem. Phys. 124 034115 (2006), J. Chem. Phys. 124 034116 (2006)] a bipolar counter-propagating wave decomposition, Psi = Psi+ + Psi-, was presented for stationary bound states Psi of the one-dimensional Shrodinger equation, such that the components Psi+- approach their semiclassical WKB analogs in the large action limit. The corresponding bipolar quantum trajectories are classical-like and well-behaved, even when Psi has many nodes, or is wildly oscillatory. In this paper, the earlier results are used to construct a universal ``black-box'' algorithm, numerically robust, stable and efficient, for computing accurate scattering quantities of any quantum dynamical system in one degree of freedom.

Bill Poirier

2008-03-03

407

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

408

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

409

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

410

Speeding Up and Quantifying Approximation Error in Continuum Quantum Monte Carlo Solid-State Calculations  

Microsoft Academic Search

Quantum theory has successfully explained the mechanics of much of the microscopic world. However, Schrodinger's equations are difficult to solve for many-particle systems. Mean-field theories such as Hartree-Fock and density functional theory account for much of the total energy of electronic systems but fail on the crucial correlation energy that predicts solid cohesion and material properties. Monte Carlo methods solve

William David Parker

2010-01-01

411

Collisional transfer of roto-vibrational energy from quantum calculations: The He-HF system  

Microsoft Academic Search

Summary  The problem of simultaneous vibrational and rotational excitations of HF molecules in collision with helium has been approached\\u000a via a quantum-mechanical treatment of the full dynamics and by employing a very accurate potential-energy surface suggested\\u000a earlier in the literature. The complicated coupling of rotational and vibrational channels has been partly simplified by taking\\u000a advantage of their different time scales, thus

F. A. Gianturco; U. T. Lamanna; G. Petrella

1984-01-01

412

Finite lattice calculation of the quantum mechanical n-vector model  

Microsoft Academic Search

The truncated quantum mechanical n-vector model in one dimension is studied by means of the phenomenological renormalisation group (PRG) and the block renormalisation group (BRG) for general values of n. Particular emphasis is put on the extrapolation of the finite size results using the finite size scaling hypothesis. Accurate estimates of the critical properties can be made for 0

M. Kolb; R. Jullien; P. Pfeuty

1982-01-01

413

Structural forms of green fluorescent protein by quantum mechanics\\/molecular mechanics calculations  

Microsoft Academic Search

The molecular modeling of structural forms of the green fluorescent protein (GFP) with the Ser65Thr single-site mutation was\\u000a performed by the quantum mechanics\\/molecular mechanics (QM\\/MM) method. Two model systems were constructed based on the crystallographic\\u000a structure from the Protein Data Bank (PDB entry code 1EMA.) The model systems differ in the initial protonation state of the\\u000a side chain of the

B. L. Grigorenko; I. V. Polyakov; A. P. Savitskii; A. V. Nemukhina

2010-01-01

414

Advanced Calculations and Visualization of Enzymatic Reactions with the Combined Quantum Classical Molecular Dynamics Code  

Microsoft Academic Search

The parallel version of the Quantum Classical Molecular Dynamics code is presented. The execution time scales almost linearly\\u000a with the number of processors. The measured overhead of the parallelization paradigm is extremely small which ensures the\\u000a high efficiency of the presented method. Tools based on the Advanced Visualization System (AVS) framework were developed for\\u000a visualization and analysis of the QCMD

Piotr Bala; Pawel Grochowski; Krzysztof Nowifiski; Terry W. Clark; Bogdan Lesyng; James Andrew Mccammon

1998-01-01

415

Optimal representation of the bath response function & fast calculation of influence functional coefficients in open quantum systems with BATHFIT 1  

E-print Network

Today's most popular techniques for accurately calculating the dynamics of the reduced density operator in an open quantum system, either require, or gain great computational benefits, from representing the bath response function a(t) in the form a(t)={\\Sigma}_k^K p_k e^{O_k t} . For some of these techniques, the number of terms in the series K plays the lead role in the computational cost of the calculation, and is therefore often a limiting factor in simulating open quantum system dynamics. We present an open source MATLAB program called BATHFIT 1, whose input is any spectral distribution functions J(w) or bath response function, and whose output attempts to be the set of parameters {p_k,w_k}_k=1^K such that for a given value of K, the series {\\Sigma}_k^k p_k e^{O_k t} is as close as possible to a(t). This should allow the user to represent a(t) as accurately as possible with as few parameters as possible. The program executes non-linear least squares fitting, and for a very wide variety of spectral distribution functions, competent starting parameters are used for these fits. For most forms of J(w), these starting parameters, and the exact a(t) corresponding to the given J(w), are calculated using the recent Pade decomposition technique - therefore this program can also be used to merely implement the Pade decomposition for these spectral distribution functions; and it can also be used just to efficiently and accurately calculate a(t) for any given J(w) . The program also gives the J(w) corresponding to a given a(t), which may allow one to assess the quality (in the w-domain) of a representation of a(t) being used. Finally, the program can calculate the discretized influence functional coefficients for any J(w), and this is computed very efficiently for most forms of J(w) by implementing the recent technique published in [Quantum Physics Letters (2012) 1 (1) pg. 35].

Nikesh S. Dattani; David M. Wilkins; Felix A. Pollock

2012-05-27

416

Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S{sub 1}(?,?{sup *}) electronic state  

SciTech Connect

The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S{sub 1}(?,?{sup *}) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S{sub 0} and S{sub 1}(?,?{sup *}) electronic states. In each case the decreased ? bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S{sub 0} and S{sub 1}(?,?{sup *}) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S{sub 1}(?,?{sup *}) excited state.

Shin, Hee Won; Ocola, Esther J.; Laane, Jaan, E-mail: laane@mail.chem.tamu.edu [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States)] [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States); Kim, Sunghwan [National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Department of Health and Human Services, 8600 Rockville Pike, Bethesda, Maryland 20894 (United States)] [National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Department of Health and Human Services, 8600 Rockville Pike, Bethesda, Maryland 20894 (United States)

2014-01-21

417

Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S1(?,?*) electronic state  

PubMed Central

The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(?,?*) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(?,?*) electronic states. In each case the decreased ? bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(?,?*) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(?,?*) excited state. PMID:25669377

Shin, Hee Won; Ocola, Esther J.; Kim, Sunghwan; Laane, Jaan

2014-01-01

418

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

NASA Technical Reports Server (NTRS)

A decomposition of the molecular energy is presented that is motivated by the atom superposition and electron delocalization physical model of chemical binding. The energy appears in physically transparent form consisting of a classical electrostatic interaction, a zero order two electron exchange interaction, a relaxation energy, and the atomic energies. Detailed formulae are derived in zero and first order of approximation. The formulation extends beyond first order to any chosen level of approximation leading, in principle, to the exact energy. The structure of this energy decomposition lends itself to the fullest utilization of the solutions to the atomic sub problems to simplify the calculation of the molecular energy. If nonlinear relaxation effects remain minor, the molecular energy calculation requires at most the calculation of two center, two electron integrals. This scheme thus affords the prospects of substantially reducing the computational effort required for the calculation of molecular energies.

Kahn, L. R.

1981-01-01

419

BAND STRUCTURE CALCULATION FOR QUANTUM DOT SOLAR CELLS USING K.P Som N. Dahal  

E-print Network

solar concentration for AM 1.5 spectrum. 1. INTRODUCTION Intermediate band solar cells (IBSCs) have been) as calculated by detailed balance modeling, at maximum solar concentration for blackbody radiation are EG=1.95e

Honsberg, Christiana

420

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

421

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

422

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

423

Furan derivatives of substituted phenylthiourea: spectral studies, semi-empirical quantum-chemical calculations and X-ray structure analyses  

NASA Astrophysics Data System (ADS)

Fifty new derivatives of 1-(furan-2-carbonyl)- and 1-(furan-3-carbonyl)-3-phenyl substituted thiourea have been synthesised and identified. Intramolecular hydrogen bonds were investigated in detail, using IR spectroscopy. The three-level Fermi resonance effect in the IR spectra was analysed after deconvolution and band separation. Semi-empirical quantum-chemical calculations (AM1 and PM3) support the results of the IR spectroscopic studies. X-ray single crystal diffraction analyses of four selected compounds, namely 1-(furan-3-carbonyl)-3-(2-trifluoromethyl-phenyl)-thiourea ( 1e), 1-(2-methyl-furan-3-carbonyl)-3-(2-trifluoromethyl-phenyl)-thiourea ( 2e), 1-(2,6-dichloro-phenyl)-3-(2-methyl-furan-3-carbonyl)-thiourea ( 2n) and 1-(4-methoxyphenyl)-3-(3-methyl-2-furan-carbonyl)-thiourea ( 3e), corroborated the molecular and crystal structure of these compounds. Relatively strong intramolecular hydrogen bonds of the N-H⋯O dbnd6 C type as well as intermolecular two-centred and bifurcated three-centred hydrogen bonds were observed, confirming the results of the IR spectral study and the semi-empirical quantum-chemical calculations. A variety of intermolecular interactions, yielding the supramolecular architectures in the four crystalline compounds, are discussed in detail.

Hritzová, Ol'ga; ?ernák, Juraj; Šafa?, Peter; Fr?hlichová, Zdenka; Cs?regh, Ingeborg

2005-05-01

424

Characterizing Surface Acidic Sites in Mesoporous-Silica-Supported Tungsten Oxide Catalysts Using Solid State NMR and Quantum Chemistry Calculations  

SciTech Connect

The acidic sites in dispersed tungsten oxide supported on SBA-15 mesoporous silica were investigated using a combination of pyridine titration, both fast-, and slow-MAS {sup 15}N NMR, static {sup 2}H NMR, and quantum chemistry calculations. It is found that the bridged acidic -OH groups in surface adsorbed tungsten dimers (i.e., W-OH-W) are the Broensted acid sites. The unusually strong acidity of these Broensted acid sites is confirmed by quantum chemistry calculations. In contrast, terminal W-OH sites are very stable and only weakly acidic as are terminal Si-OH sites. Furthermore, molecular interactions between pyridine molecules and the dimer Broensted and terminal W-OH sites for dispersed tungsten oxide species is strong. This results in restricted molecular motion for the interacting pyridine molecules even at room temperature, i.e., a reorientation mainly about the molecular 2-fold axis. This restricted reorientation makes it possible to estimate the relative ratio of the Broensted (tungsten dimer) to the weakly acidic terminal W-OH sites in the catalyst using the slow-MAS {sup 1}H-{sup 15}N CP PASS method.

Hu, Jian Z.; Kwak, Ja Hun; Wang, Yong; Hu, Mary Y.; Turcu, Romulus VF; Peden, Charles HF

2011-10-18

425

Multiple Environment Single System Quantum Mechanical/Molecular Mechanical (MESS-QM/MM) Calculations. 1. Estimation of Polarization Energies.  

PubMed

In combined quantum mechanical/molecular mechanical (QM/MM) free energy calculations, it is often advantageous to have a frozen geometry for the quantum mechanical (QM) region. For such multiple-environment single-system (MESS) cases, two schemes are proposed here for estimating the polarization energy: the first scheme, termed MESS-E, involves a Roothaan step extrapolation of the self-consistent field (SCF) energy; whereas the other scheme, termed MESS-H, employs a Newton-Raphson correction using an approximate inverse electronic Hessian of the QM region (which is constructed only once). Both schemes are extremely efficient, because the expensive Fock updates and SCF iterations in standard QM/MM calculations are completely avoided at each configuration. They produce reasonably accurate QM/MM polarization energies: MESS-E can predict the polarization energy within 0.25 kcal/mol in terms of the mean signed error for two of our test cases, solvated methanol and solvated ?-alanine, using the M06-2X or ?B97X-D functionals; MESS-H can reproduce the polarization energy within 0.2 kcal/mol for these two cases and for the oxyluciferin-luciferase complex, if the approximate inverse electronic Hessians are constructed with sufficient accuracy. PMID:25321186

Sodt, Alexander J; Mei, Ye; König, Gerhard; Tao, Peng; Steele, Ryan P; Brooks, Bernard R; Shao, Yihan

2014-10-30

426

Direct calculations of vibrational absorption and circular dichroism spectra of alanine dipeptide analog in water: Quantum mechanical\\/molecular mechanical molecular dynamics simulations  

Microsoft Academic Search

The vibrational absorption (IR) and vibrational circular dichroism (VCD) spectra of alanine dipeptide analog in water are directly calculated by Fourier transforming the time correlation functions of the electric and magnetic dipole moments, which are calculated using the dynamic partial charges and trajectory of the peptide generated from the quantum mechanical\\/molecular mechanical molecular dynamics simulations. The alanine dipeptide analog is

Seongeun Yang; Minhaeng Cho

2009-01-01

427

Theoretical studies of dissociative recombination  

NASA Technical Reports Server (NTRS)

The calculation of dissociative recombination rates and cross sections over a wide temperature range by theoretical quantum chemical techniques is described. Model calculations on electron capture by diatomic ions are reported which illustrate the dependence of the rates and cross sections on electron energy, electron temperature, and vibrational temperature for three model crossings of neutral and ionic potential curves. It is shown that cross sections for recombination to the lowest vibrational level of the ion can vary by several orders of magnitude depending upon the position of the neutral and ionic potential curve crossing within the turning points of the v = 1 vibrational level. A new approach for calculating electron capture widths is reported. Ab initio calculations are described for recombination of O2(+) leading to excited O atoms.

Guberman, S. L.

1985-01-01

428

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

SciTech Connect

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.

Bai, Shuming; Xie, Weiwei; Zhu, Lili; Shi, Qiang, E-mail: qshi@iccas.ac.cn [Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190 (China)] [Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190 (China)

2014-02-28