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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

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

3

Quantum Mechanics and physical calculations  

NASA Astrophysics Data System (ADS)

We suggest to realize the computer simulation and calculation by the algebraic structure built on the basis of the logic inherent to processes in physical systems (called physical computing). We suggest a principle for the construction of quantum algorithms of neuroinformatics of quantum neural networks. The role of academician Sahakyan is emphasized in the development of quantum physics in Armenia.

Karayan, H. S.

2014-03-01

4

Theoretical calculations of shallow donor impurity states in GaAs\\/GaAlAs multi-quantum wells with magnetic fields applied parallel to the layers  

Microsoft Academic Search

A method is presented for the calculation of the energy eigenvalues and eigenstates of the electron associated with a shallow donor impurity in a GaAs\\/GaAlAs multi-quantum well structure in the presence of a magnetic field parallel to the layers. Compared to the case of an impurity in a magnetic field directed perpendicular to the layers, the problem is complicated by

P. W. Barmby; J. L. Dunn; C. A. Bates

1995-01-01

5

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

6

Theoretical investigation of photonic quantum wells and defects  

Microsoft Academic Search

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

Yuankai Jiang

2004-01-01

7

Theoretical study on the spin-forbidden predissociation reaction of N2O: Ab initio potential energy surfaces and quantum dynamics calculations  

NASA Astrophysics Data System (ADS)

The spin-forbidden predissociation reaction of the ground state N2O is studied by quantum dynamics calculations. Ab initio calculations are carried out to obtain the potential energy surfaces (PES') of the singlet ground state of N2O and three triplet ones correlating with the asymptote N2+O(3P) and the spin-orbit coupling (SOC) elements among them. The decay rate of individual singlet vibrational state to the 3A' state are estimated by applying Fermi golden rule. For the 1A' state, totally 1692 vibrational eigenstates with the even parity for the total angular momentum J=0 are obtained, and time-dependent wave packet calculations on the triplet PES are performed to obtain the autocorrelation functions whose Fourier transforms provides the decay rates. The resultant decay rates for 887 singlet vibrational states in the energy range 67.3?E?83.7 kcal/mol are analyzed in terms of a random matrix/transition state theory. Incomplete energy randomization of the vibrational energy in the singlet state even near the singlet state dissociation threshold is concluded from the analyses of calculated decay rate distributions.

Nakamura, Hisao; Kato, Shigeki

1999-05-01

8

A theoretical analysis of quantum control landscapes  

NASA Astrophysics Data System (ADS)

A quantum control landscape is a dynamical optimization metric expressed as a function of the control variables. A landscape can be defined for various problems in quantum control, such as the transfer of population between distinct quantum states, the optimization of the expectation value of an observable operator, or the construction of a quantum unitary transformation of a specific form. The first chapter outlines the history of quantum control to the present. The second through fifth chapters develop the foundation for a theoretical analysis of quantum control landscapes, focusing particularly on the critical topology. The enumeration of the critical regions is found in general to scale favorably with the Hilbert space dimension of the system. The dimensionality of the critical regions also has desirable scaling properties, imparting intrinsic robustness to the control solutions that comprise them. The sixth chapter focuses on the local geometry of the landscape. The main result is that the landscape gradient can at any point be expanded in a low-dimensional subspace of the control function space. This provides not only a theoretical rationale for the dimension-reduction for the quantum optimal control problem, but also the basis for a qualitatively new experimental control protocol. In the seventh chapter is presented a generalization of the "toolkit" method of propagating the Schrodinger equation, used for computations in the sixth chapter, but generally applicable to many kinds of numerical computations in quantum control. A summary of findings and open questions are discussed in the eighth chapter.

Hsieh, Michael M.

9

Quantum probabilities: an information-theoretic interpretation  

E-print Network

This Chapter develops a realist information-theoretic interpretation of the nonclassical features of quantum probabilities. On this view, what is fundamental in the transition from classical to quantum physics is the recognition that \\emph{information in the physical sense has new structural features}, just as the transition from classical to relativistic physics rests on the recognition that space-time is structurally different than we thought. Hilbert space, the event space of quantum systems, is interpreted as a kinematic (i.e., pre-dynamic) framework for an indeterministic physics, in the sense that the geometric structure of Hilbert space imposes objective probabilistic or information-theoretic constraints on correlations between events, just as the geometric structure of Minkowski space in special relativity imposes spatio-temporal kinematic constraints on events. The interpretation of quantum probabilities is more subjectivist in spirit than other discussions in this book (e.g., the chapter by Timpson), insofar as the quantum state is interpreted as a credence function---a bookkeeping device for keeping track of probabilities---but it is also objective (or intersubjective), insofar as the credences specified by the quantum state are understood as uniquely determined, via Gleason's theorem, by objective correlational constraints on events in the nonclassical quantum event space defined by the subspace structure of Hilbert space.

Jeffrey Bub

2010-05-14

10

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

11

Field theoretic calculation of scalar turbulence  

E-print Network

The cascade rate of passive scalar and Bachelor's constant in scalar turbulence are calculated using the flux formula. This calculation is done to first order in perturbation series. Batchelor's constant in three dimension is found to be approximately 1.25. In higher dimension, the constant increases as $d^{1/3}$.

Mahendra K. Verma

2002-05-08

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

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

14

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

2012-12-22

15

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

16

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

17

Calculation of Theoretical Isotropic Compton Profile for Many Particle Systems  

Microsoft Academic Search

Theoretical isotropic (spherically symmetric) Compton profiles (ICP) have been calculated for many particle systems' He, Li, Be and B atoms in their ground states. Our calculations were performed using Roothan-Hartree-Fock (RHF) wave function, HF wave function of Thakkar and re-optimized HF wave function of Clementi-Roetti, taking into account the impulse approximation. The theoretical analysis included a decomposition of the various

Ali A. Alzubadi; Khalil H. Albayati

2010-01-01

18

Information-theoretic temporal Bell inequality and quantum computation  

SciTech Connect

An information-theoretic temporal Bell inequality is formulated to contrast classical and quantum computations. Any classical algorithm satisfies the inequality, while quantum ones can violate it. Therefore, the violation of the inequality is an immediate consequence of the quantumness in the computation. Furthermore, this approach suggests a notion of temporal nonlocality in quantum computation.

Morikoshi, Fumiaki [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198 (Japan) and PRESTO, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)

2006-05-15

19

On kaonic hydrogen. Quantum field theoretic and relativistic covariant approach  

E-print Network

We study kaonic hydrogen, the bound K^-p state A_(Kp). Within a quantum field theoretic and relativistic covariant approach we derive the energy level displacement of the ground state of kaonic hydrogen in terms of the amplitude of K^-p scattering for arbitrary relative momenta. The amplitude of low-energy K^-p scattering near threshold is defined by the contributions of three resonances Lambda(1405), Lambda(1800) and Sigma^0(1750) and a smooth elastic background. The amplitudes of inelastic channels of low-energy K^-p scattering fit experimental data on near threshold behaviour of the cross sections and the experimental data by the DEAR Collaboration. We use the soft-pion technique (leading order in Chiral Perturbation Theory) for the calculation of the partial width of the radiative decay of pionic hydrogen A_(pi p) -> n + gamma and the Panofsky ratio. The theoretical prediction for the Panofsky ratio agrees well with experimental data. We apply the soft-kaon technique (leading order in Chiral Perturbation Theory) to the calculation of the partial widths of radiative decays of kaonic hydrogen A_(Kp) -> Lambda^0 + gamma and A_(Kp) -> Sigma^0 + gamma. We show that the contribution of these decays to the width of the energy level of the ground state of kaonic hydrogen is less than 1%.

A. N. Ivanov; M. Cargnelli; M. Faber; J. Marton; N. I. Troitskaya; J. Zmeskal

2003-12-14

20

Theoretical calculation of partition coefficients of dimethoxypyrimidinylsalicylic acids.  

PubMed

Despite their importance as herbicides, dimethoxypyrimidinylsalicylic acids has been poorly characterized from a physical-chemical point of view. This lack of information has prevented the assessment of their impact in the environment once they are released. In this study, environmentally important properties (free energy of solvation, Henry's law constant, octanol/air, and octanol/water partition coefficients) of 39 dimethoxypyrimidinylsalicylic derived compounds are calculated by density functional theory (DFT) methods at B3LYP/6-31G(d,p) level of theory using the Poisson-Boltzmann solvation model. These properties have not been reported previously for this family of compounds, neither experimentally or theoretically. PMID:20162309

Delgado, Eduardo J

2010-08-01

21

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

22

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.

Edgar A. Gomez; J. D. Hernandez-Rivero; Herbert Vinck-Posada

2015-02-01

23

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.

24

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

25

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

26

Limitations on information theoretically secure quantum homomorphic encryption  

E-print Network

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 localisation argument, that deterministic fully homomorphic encryption necessarily incurs exponential overhead if perfect security is required.

Li Yu; Carlos A. Perez-Delgado; Joseph F. Fitzsimons

2014-06-10

27

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

28

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

2012-02-20

29

GENERAL: Theoretical analysis of quantum game in cavity QED  

NASA Astrophysics Data System (ADS)

Recent years, several ways of implementing quantum games in different physical systems have been presented. In this paper, we perform a theoretical analysis of an experimentally feasible way to implement a two player quantum game in cavity quantum electrodynamic(QED). In the scheme, the atoms interact simultaneously with a highly detuned cavity mode with the assistance of a classical field. So the scheme is insensitive to the influence from the cavity decay and the thermal field, and it does not require the cavity to remain in the vacuum state throughout the procedure.

Cao, Shuai; Fang, Mao-Fa; Liu, Jian-Bin; Wang, Xin-Wen; Zheng, Xiao-Juan; Li, Hai

2009-03-01

30

Theoretical and Phenomenological Aspects of Perturbative Quantum Chromodynamics  

Microsoft Academic Search

There are two topics discussed in this thesis. The first, on the renormalization of composite operators, is theoretical in nature while the other, on heavy quark production in deep-inelastic scattering, is phenomenological. The hope is that the study of both topics will lead to a better understanding of Quantum Chromodynamics (QCD). To place these topics in context introductory material is

Brian William Harris

1995-01-01

31

Theoretical method for analyzing quantum dynamics of correlated photons  

SciTech Connect

We present a theoretical method for the efficient analysis of quantum nonlinear dynamics of correlated photons. Since correlated photons can be regarded as a superposition of uncorrelated photons, semiclassical analysis can be applied to this problem. The proposed method is demonstrated for a V-type three-level atom as a nonlinear optical system.

Koshino, Kazuki; Nakatani, Masatoshi [College of Liberal Arts and Sciences, Tokyo Medical and Dental University, 2-8-30 Konodai, Ichikawa 272-0827 (Japan) and PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012 (Japan)

2009-05-15

32

Quantum public-key algorithms to encrypt and authenticate quantum messages with information-theoretic security  

E-print Network

Public-key cryptosystems for quantum messages are considered from two aspects: public-key encryption and public-key authentication. Firstly, we propose a general construction of quantum public-key encryption scheme, and then construct an information-theoretic secure instance. Then, we propose a quantum public-key authentication scheme, which can protect the integrity of quantum messages. This scheme can both encrypt and authenticate quantum messages. It is information-theoretic secure with regard to encryption, and the success probability of tampering decreases exponentially with the security parameter with regard to authentication. Compared with classical public-key cryptosystems, one private-key in our schemes corresponds to an exponential number of public-keys, and every quantum public-key used by the sender is an unknown quantum state to the sender.

Min Liang; Li Yang

2012-05-10

33

Quantum public-key algorithms to encrypt and authenticate quantum messages with information-theoretic security  

E-print Network

Public-key cryptosystems for quantum messages are considered from two aspects: public-key encryption and public-key authentication. Firstly, we propose a general construction of quantum public-key encryption scheme, and then construct an information-theoretic secure instance. Then, we propose a quantum public-key authentication scheme, which can protect the integrity of quantum messages. This scheme can both encrypt and authenticate quantum messages. It is information-theoretic secure with regard to encryption, and the success probability of tampering decreases exponentially with the security parameter with regard to authentication. Compared with classical public-key cryptosystems, one private-key in our schemes corresponds to an exponential number of public-keys, and every quantum public-key used by the sender is an unknown quantum state to the sender.

Liang, Min

2012-01-01

34

Quantum biological channel modeling and capacity calculation.  

PubMed

Quantum mechanics has an important role in photosynthesis, magnetoreception, and evolution. There were many attempts in an effort to explain the structure of genetic code and transfer of information from DNA to protein by using the concepts of quantum mechanics. The existing biological quantum channel models are not sufficiently general to incorporate all relevant contributions responsible for imperfect protein synthesis. Moreover, the problem of determination of quantum biological channel capacity is still an open problem. To solve these problems, we construct the operator-sum representation of biological channel based on codon basekets (basis vectors), and determine the quantum channel model suitable for study of the quantum biological channel capacity and beyond. The transcription process, DNA point mutations, insertions, deletions, and translation are interpreted as the quantum noise processes. The various types of quantum errors are classified into several broad categories: (i) storage errors that occur in DNA itself as it represents an imperfect storage of genetic information, (ii) replication errors introduced during DNA replication process, (iii) transcription errors introduced during DNA to mRNA transcription, and (iv) translation errors introduced during the translation process. By using this model, we determine the biological quantum channel capacity and compare it against corresponding classical biological channel capacity. We demonstrate that the quantum biological channel capacity is higher than the classical one, for a coherent quantum channel model, suggesting that quantum effects have an important role in biological systems. The proposed model is of crucial importance towards future study of quantum DNA error correction, developing quantum mechanical model of aging, developing the quantum mechanical models for tumors/cancer, and study of intracellular dynamics in general. PMID:25371271

Djordjevic, Ivan B

2012-01-01

35

Quantum Chemical Calculations of the Influence of Anchor-Cum-Spacer Groups on Femtosecond Electron  

E-print Network

Quantum Chemical Calculations of the Influence of Anchor-Cum-Spacer Groups on Femtosecond Electron different anchor-cum-spacer groups, have been studied theoretically using density functional theory (DFT injection rate depends strongly on the ability of the anchor-cum-spacer unit that separates the d

Goddard III, William A.

36

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

37

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

38

A charge patching method calculation of a quantum dot/quantum well nanosystem.  

NASA Astrophysics Data System (ADS)

First principles density functional calculations typically involve finding self-consistent solution to the Kohn-Sham equations, scaling with the cube of system size. To study large systems, such as semiconductor nanocrystals, an approximate ab initio potential may be constructed by patching together local charge motifs determined from self-consistent calculations on small prototype systems, and the eigenvalues determined using the folded spectrum method for a few band-edge states. In this talk, I will discuss the recent applications of this method to CdS/CdSe/CdS colloidal quantum dot quantum wells. Results on the effect of core, well, and shell thicknesses on the wavefunction and optical properties will be discussed. We find the conduction band wavefunction to be significantly less confined to the CdSe quantum well layer than predicted by k.p theory, and discuss the implications of this result on the theoretical interpretation of recent time-resolved Faraday rotation experiments. We will also briefly discuss the extensions of this approach to the explicit treatment of surface ligand effects and transition-metal doped nanocrystals.

Schrier, Joshua; Wang, Lin-Wang

2006-03-01

39

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

40

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

41

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

42

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

43

Theoretical investigation of the stability and nonempirical quantum chemical calculation for the B/sub 6/H/sub 6//sup 2 -/ anion and its protonated and lithium derivatives  

SciTech Connect

Calculations were performed using the GAUSSIAN-80 and MONSTER-GAUSS-81 programs with complete optimization of geometry and imposing symmetry restrictions in the average basis 4-31G for the B/sub 6/H/sub 6//sup 2 -/ and B/sub 6/H/sub 7//sup -/ anions. Geometric results of the calculations are compared with data obtained by x-ray diffraction. The possibility of forming substituted derivatives of B/sub 6/H/sub 8/ with lithium as the hydrogen-like atoms was investigated. It was established that both B/sub 6/H/sub 6/Li and B/sub 6/H/sub 6/Li/sub 2/ have an energy minimum with Li-B distances of 2.17 A, which corresponds to the sum of the covalent radii of lithium and boron.

Kuznetsov, I.Yu.; Solntsev, K.A.; Kuznetsov, N.T.

1988-01-01

44

Surface complex structures modelled with quantum chemical calculations: carbonate, phosphate,  

E-print Network

Surface complex structures modelled with quantum chemical calculations: carbonate, phosphate to provide good agree- ment with experimental observations for the oxyanions carbonate, phosphate, sulphate, the interaction of species such as carbon- ate, phosphate, sulphate, arsenate and arsenite with metal oxide

Sparks, Donald L.

45

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.

46

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

47

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

48

A helium discharge with neutral gas flow: Theoretical calculations  

Microsoft Academic Search

This study carries out numerical calculations using the ‘‘theory for rf ionization of noble gases with turbulent flow based on a two-electron group model,’’ which was developed in order to investigate the problem of ionizing a high speed neutral gas by the application of an external rf electric field. The plasma model is described by the electron energy and the

Panayiotis J. Karditsas

1990-01-01

49

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

50

Accurate rotational barrier calculations with diffusion quantum Monte Carlo  

NASA Astrophysics Data System (ADS)

Accurate quantum Monte Carlo, MP2, coupled cluster, and DFT calculations of rotational barriers of several small molecules are presented. With the diffusion quantum Monte Carlo method (DMC) excellent agreement with experimental barriers is obtained except for the gauche-gauche barriers of n-butane and ethylmethylether. It is argued that these two experimental values might be erroneous. Additionally, barriers calculated with the more efficient variational quantum Monte Carlo method (VMC) are presented. The VMC barriers are less accurate than the DMC results, but it is demonstrated that accurate barriers can be obtained with sophisticated Jastrow correlation functions.

Klahm, Sebastian; Lüchow, Arne

2014-04-01

51

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

52

Theoretical calculations on the reaction of ethylene with oxygen  

NASA Astrophysics Data System (ADS)

The triplet potential energy surface for the reaction of ethylene with molecular oxygen in the ground state has been calculated at the QCISD(T, full)/6-311++G(3df,2p)//MP2(full)/6-311G(d,p) level of theory. Four intermediates and 17 transition states are located along the minimum energy reaction path. Six major radical product channels are revealed, namely, C 2H 3 + HO 2, O( 3P) + C 2H 4O, H + C 2H 3O 2, OH + C 2H 3O, OH + CH 3CO, and O( 3P) + CH 3CHO. In view of reaction barrier heights, the dominant channels are predicted to be C 2H 3 + HO 2, O( 3P) + C 2H 4O, H + C 2H 3O 2, and C 2H 4O 2( 3A?). The calculated rate constants for the abstraction reaction path are in good agreement with the available experimental data. The implication of the current results in the initiation of the combustion of ethylene is discussed.

Hua, Hou; Ruscic, Branko; Wang, Baoshan

2005-05-01

53

Detailed discussions and calculations of quantum Regge calculus of Einstein-Cartan theory  

SciTech Connect

This article presents detailed discussions and calculations of the recent paper 'Quantum Regge calculus of Einstein-Cartan theory' in [9]. The Euclidean space-time is discretized by a four-dimensional simplicial complex. We adopt basic tetrad and spin-connection fields to describe the simplicial complex. By introducing diffeomorphism and local Lorentz invariant holonomy fields, we construct a regularized Einstein-Cartan theory for studying the quantum dynamics of the simplicial complex and fermion fields. This regularized Einstein-Cartan action is shown to properly approach to its continuum counterpart in the continuum limit. Based on the local Lorentz invariance, we derive the dynamical equations satisfied by invariant holonomy fields. In the mean-field approximation, we show that the averaged size of 4-simplex, the element of the simplicial complex, is larger than the Planck length. This formulation provides a theoretical framework for analytical calculations and numerical simulations to study the quantum Einstein-Cartan theory.

Xue Shesheng [ICRANeT Piazzale della Repubblica, 10-65122, Pescara (Italy); Department of Physics, University of Rome 'Sapienza', Piazzale A. Moro 5, 00185, Rome (Italy)

2010-09-15

54

Macroscopic Quantum-Type Potentials in Theoretical Systems Biology  

PubMed Central

We review in this paper the use of the theory of scale relativity and fractal space-time as a tool particularly well adapted to the possible development of a future genuine systems theoretical biology. We emphasize in particular the concept of quantum-type potentials, since, in many situations, the effect of the fractality of space—or of the underlying medium—can be reduced to the addition of such a potential energy to the classical equations of motion. Various equivalent representations—geodesic, quantum-like, fluid mechanical, stochastic—of these equations are given, as well as several forms of generalized quantum potentials. Examples of their possible intervention in high critical temperature superconductivity and in turbulence are also described, since some biological processes may be similar in some aspects to these physical phenomena. These potential extra energy contributions could have emerged in biology from the very fractal nature of the medium, or from an evolutive advantage, since they involve spontaneous properties of self-organization, morphogenesis, structuration and multi-scale integration. Finally, some examples of applications of the theory to actual biological-like processes and functions are also provided. PMID:24709901

Nottale, Laurent

2014-01-01

55

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

PubMed Central

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

2012-01-01

56

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

57

Quantum field theoretical description for the reflectivity of graphene  

NASA Astrophysics Data System (ADS)

We derive the polarization tensor of graphene at nonzero temperature in (2 +1 ) -dimensional space-time. The obtained tensor coincides with the previously known result at all Matsubara frequencies, but, in contrast, it admits analytic continuation to the real frequency axis satisfying all physical requirements. Using the obtained representation for the polarization tensor, we develop a 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 the 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.; Klimchitskaya, G. L.; Mostepanenko, V. M.; Petrov, V. M.

2015-02-01

58

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

59

Quantum statistical calculation of cluster abundances in hot dense matter  

E-print Network

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

Gerd Ropke

2014-07-01

60

Review of theoretical calculations of hydrogen storage in carbon-based materials  

Microsoft Academic Search

.   In this paper we review the existing theoretical literature on hydrogen storage in single-walled nanotubes and carbon nanofibers.\\u000a The reported calculations indicate a hydrogen uptake smaller than some of the more optimistic experimental results. Furthermore\\u000a the calculations suggest that a variety of complex chemical processes could accompany hydrogen storage and release.

V. Meregalli; M. Parrinello

2001-01-01

61

Spatially resolved photoluminescence in quantum wells with interface roughness: a theoretical description  

NASA Astrophysics Data System (ADS)

We present a microscopic theoretical description of spatially resolved photoluminescence in GaAs quantum wells with interface roughness. The theory derives the kinetic equations using the excitonic wavefunctions obtained by solving numerically the effective Schrödinger equation for the excitonic centre of mass motion in the presence of disorder. The kinetic equations describe acoustic phonon scattering, radiative decay, and inhomogeneous sample excitation and/or light detection. The influence of disorder, temperature, and spatial resolution on the image formation is analysed with emphasis on the role of different interface textures. In particular, we consider two samples characterized by effective disorder potentials with different correlation lengths. Numerically calculated two-dimensional images agree with images from spatially resolved photoluminescence experiments and put forward the potential of the method for the understanding of near-field light emission from semiconductor quantum structures.

Martino, G.; Pistone, G.; Savasta, S.; Di Stefano, O.; Girlanda, R.

2006-03-01

62

Simulation of Quantum-Mechanical Measurements with Programmable Pocket Calculators.  

ERIC Educational Resources Information Center

Described is a method for the illustration of the statistical nature of measurements in quantum physics by means of simulation with pocket calculators. The application to examples like the double-slit experiment, Mott scattering, and the demonstration of the uncertainty relation is discussed. (Author/HM)

Sauer, G.

1979-01-01

63

On kaonic deuterium. Quantum field theoretic and relativistic covariant approach  

E-print Network

We study kaonic deuterium, the bound K^-d state A_(K d). Within a quantum field theoretic and relativistic covariant approach we derive the energy level displacement of the ground state of kaonic deuterium in terms of the amplitude of K^-d scattering for arbitrary relative momenta. Near threshold our formula reduces to the well-known DGBT formula. The S-wave amplitude of K^-d scattering near threshold is defined by the resonances Lambda(1405), Sigma(1750) and a smooth elastic background, and the inelastic channels K^- d -> NY and K^- d -> NY pion, with Y = Sigma^(+/-), Sigma^0 and Lambda^0, where the final-state interactions play an important role. The Ericson-Weise formula for the S-wave scattering length of K^-d scattering is derived. The total width of the energy level of the ground state of kaonic deuterium is estimated using the theoretical predictions of the partial widths of the two-body decays A_(Kd) -> NY and experimental data on the rates of the NY-pair production in the reactions K^-d -> NY. We obtain Gamma_{1s} = (630 +/-100) eV. For the shift of the energy level of the ground state of kaonic deuterium we predict epsilon_(1s) = (353 +/-60)eV.

A. N. Ivanov; M. Cargnelli; M. Faber; H. Fuhrmann; V. A. Ivanova; J. Marton; N. I. Troitskaya; J. Zmeskal

2006-07-04

64

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

E-print Network

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

Tarasov, Vasily E.

65

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...

66

Quantum Monte Carlo calculations of light nuclei using chiral potentials.  

PubMed

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

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

2014-11-01

67

Electronic state calculations of Si quantum dots: Oxidation effects  

NASA Astrophysics Data System (ADS)

Electronic states for the configuration of a Si dihydride backbonded to oxygen on the H-covered surface of spherical Si35H36 quantum dots (QDs) are calculated self-consistently using the extended Hückel-type nonorthogonal tight-binding method. The proposed backbond oxidation accounts for oxidation-induced redshifts in luminescence-peak energy observed in porous Si. It is found that optical transitions between the band edges in the Si QD backbonded to oxygen are dipole allowed as in the H-covered case. A comparison is made with a calculation for the double-bonded oxygen configuration.

Nishida, Masahiko

2004-04-01

68

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

E-print Network

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

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

2014-10-18

69

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

70

On kaonic hydrogen. Phenomenological quantum field theoretic model revisited  

E-print Network

We argue that due to isospin and U-spin invariance of strong low-energy interactions the S-wave scattering lengths a^0_0 and a^1_0 of bar-KN scattering with isospin I=0 and I = 1 satisfy the low-energy theorem a^0_0 + 3 a^1_0 = 0 valid to leading order in chiral expansion. In the model of strong low-energy bar-KN interactions at threshold (EPJA 21,11 (2004)) we revisit the contribution of the Sigma(1750) resonance, which does not saturate the low-energy theorem a^0_0 + 3 a^1_0 = 0, and replace it by the baryon background with properties of an SU(3) octet. We calculate the S-wave scattering amplitudes of K^-N and K^-d scattering at threshold. We calculate the energy level displacements of the ground states of kaonic hydrogen and kaonic deuterium. The result obtained for kaonic hydrogen agrees well with recent experimental data by the DEAR Collaboration. We analyse the cross sections for elastic and inelastic K^-p scattering for laboratory momenta of the incident K^- meson from the domain 70 MeV/c < p_K < 150 MeV/c. The theoretical results agree with the available experimental data within two standard deviations.

A. N. Ivanov; M. Cargnelli; M. Faber; H. Fuhrmann; V. A. Ivanova; J. Marton; N. I. Troitskaya; J. Zmeskal

2006-07-04

71

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...

72

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

73

Calculating the theoretical project completion time of large networks in polynomial time  

Microsoft Academic Search

One of the most important theoretical problems in project management is to obtain the distribution of the total completion time in PERT networks. For practical and managerial purposes what matters is the criticality of each activity within a PERT network, which can be assessed using a sound approach to calculate the completion time. Critical activities are activities that if delayed

L. F. Copertari; N. P. Archer

2001-01-01

74

Quantum chemistry calculation of resveratrol and related stilbenes  

NASA Astrophysics Data System (ADS)

We report a semiempirical investigation of the first excited states and of the spectroscopic properties of resveratrol, a phytoalexin with well-known antioxidative properties, and of structurally related stilbenes. The analysis of the calculated bond length and charge rearrangements resulting from the photoexcitation and of the corresponding theoretical spectra gives us some insight of how chemical modifications of these molecules could affect the possible physiological properties of resveratrol.

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

2003-01-01

75

Angular distribution of photoelectrons in small molecules: A molecular quantum defect calculation  

NASA Astrophysics Data System (ADS)

The molecular quantum defect orbital (MQDO) method, previously used in the determination of molecular photoionization cross sections, is applied here to calculate the angular distribution of photoelectrons arising from the molecular photoionization. Calculations are performed for the ionization from outer valence orbitals of HF, H2O, NH3, N2O, and H2CO molecules. The results are compared with previous measurements and with theoretical curves found in the literature. Profiles of the angular distribution parameter as a function of photoelectron energy covering a range from the photoionization threshold to 120 eV are presented for the above molecules. The energy dependence of the angular distributions predicted by the MQDO calculations agrees fairly well with predictions from more sophisticated theories and with observed results.

Vega, M. V.; Lavín, C.; Velasco, A. M.

2012-06-01

76

Quantum Calculations including Hyperfine Structure in Photoassociation Spectra  

NASA Astrophysics Data System (ADS)

We present a quantum formulation of photoassociation spectroscopy that fully treats all rotational and spin degrees of freedom for the ground state collision, the optical excitation, and the final photoassociative bound state.(C.J. Williams, E. Tiesinga, and P.S. Julienne, Phys. Rev. A (submitted).) When the calculated lineshapes and intensity patterns are compared with experimental data it is possible to extract ground state scattering lengths and excited state atomic lifetimes. Here we present calculations relevant to the recent extraction of a precise Na(3P) atomic lifetime (?(P_3/2) = 16.230(16)ns).(K.M. Jones, P.S. Julienne, P.D. Lett, W.D. Phillips, E. Tiesinga, and C.J. Williams, Phys. Rev. Lett. (submitted).) These results along with additional calculations are used to extract the Na2 X^1?_g^+ and a^3?_u^+ scattering lengths.

Tiesinga, Eite; Williams, Carl; Julienne, Paul

1996-05-01

77

An experimental and theoretical mechanistic study of biexciton quantum yield enhancement in single quantum dots near gold nanoparticles.  

PubMed

In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs of appropriate sizes were chosen so that the plasmon resonance overlaps with the absorption and emission of the QDs. We observed that in the regime of a low excitation power, the photon antibunching and blinking properties of single QDs were modified significantly when the QDs were on the Au@SiO2 substrates compared to those on glass. Most significantly, second-order photon intensity correlation data show that the presence of plasmons increases the ratio of the biexciton quantum yield over the exciton quantum yield (QYBX/QYX). An electrodynamics model was developed to quantify the effect of plasmons on the lifetime, quantum yield, and emission intensity of the biexcitons for the QDs. Good agreement was obtained between the experimentally measured and calculated changes in QYBX/QYX due to Au@SiO2 NPs, showing the validity of the developed model. The theoretical studies also indicated that the relative position of the QDs to the Au NPs and the orientation of the electric field are important factors that regulate the emission properties of the excitons and biexcitons of QDs. The study suggests that the multiexciton emission efficiency in QD systems can be manipulated by employing properly designed plasmonic structures. PMID:25806486

Dey, Swayandipta; Zhou, Yadong; Tian, Xiangdong; Jenkins, Julie A; Chen, Ou; Zou, Shengli; Zhao, Jing

2015-04-01

78

Calculation of the partition function using quantum genetic algorithms  

NASA Astrophysics Data System (ADS)

We present a new method based on genetic algorithms which permits to determine efficiently the partition function and the excitation spectrum of few-body quantum systems. In our approach, we use a variational formulation for the partition function Z of the system as a functional of its eigenfunctions. Z is obtained by applying the procedure of survival of the fittest, starting from initial random population. During the evolution the best representative converges to a set of eigenfunctions for a given Hamiltonian, while the partition function attains its global extremum (maximum) for a given temperature. We calculate the spectrum and the partition function in the case of few interacting particles in one-dimensional infinite potential well. We investigate formation of the Wigner crystal and study its melting induced by termal and quantum fluctuations.

Grigorenko, I.; Garcia, M. E.

2002-10-01

79

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

80

The Nature of Infinity in Quantum Field Calculations  

NASA Astrophysics Data System (ADS)

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

Kriske, Richard

2011-06-01

81

Quantum Monte Carlo calculated potential energy curve for the helium dimer.  

PubMed

We report on the results of both the diffusion quantum Monte Carlo (DMC) and reptation quantum Monte Carlo (RMC) methods on the potential energy curve of the helium dimer. We show that it is possible to obtain a highly accurate description of the helium dimer. An improved stochastic reconfiguration technique is employed to optimize the many-body wave function, which is the starting point for highly accurate simulations based on the DMC and RMC methods. We find that the results of these methods are in excellent agreement with the best theoretical results at short range, especially the recently developed RMC method, yield particularly accurate results with reduced statistical error, which gives very excellent agreement across the whole potential curve. For the equilibrium internuclear distance of 5.6 bohrs, the calculated total energy with RMC method is -5.807 483 599+/-0.000 000 016 hartree and the corresponding well depth is -11.003+/-0.005 K. PMID:20515092

Wu, Xuebin; Hu, Xianru; Dai, Yunchuan; Du, Chenlei; Chu, Shibin; Hu, Leibo; Deng, Jianbo; Feng, Yuanping

2010-05-28

82

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

83

Theoretical methods for the calculation of Bragg curves and 3D distributions of proton beams  

NASA Astrophysics Data System (ADS)

The well-known Bragg-Kleeman rule RCSDA = A ? E has become a pioneer work in radiation physics of charged particles and is still a useful tool to estimate the range RCSDA of approximately monoenergetic protons with initial energy E0 in a homogeneous medium. The rule is based on the continuous-slowing-down-approximation (CSDA). It results from a generalized (nonrelativistic) Langevin equation and a modification of the phenomenological friction term. The complete integration of this equation provides information about the residual energy E(z) and dE(z)/dz at each position z(0 ? z ? RCSDA). A relativistic extension of the generalized Langevin equation yields the formula RCSDA = A ? (E0 + E/2M ? c2)p. The initial energy of therapeutic protons satisfies E0 ? 2M ? c2(M ? c2 = 938.276 MeV), which enables us to consider the relativistic contributions as correction terms. Besides this phenomenological starting-point, a complete integration of the Bethe-Bloch equation (BBE) is developed, which also provides the determination of RCSDA, E(z) and dE(z)/dz and uses only those parameters given by the BBE itself (i.e., without further empirical parameters like modification of friction). The results obtained in the context of the aforementioned methods are compared with Monte-Carlo calculations (GEANT4); this Monte-Carlo code is also used with regard to further topics such as lateral scatter, nuclear interactions, and buildup effects. In the framework of the CSDA, the energy transfer from protons to environmental atomic electrons does not account for local fluctuations. Based on statistical quantum mechanics, an analysis of the Gaussian convolution and the Landau-Vavilov distribution function is carried out to describe these fluctuations. The Landau tail is derived as Hermite polynomial corrections of a Gaussian convolution. It is experimentally confirmed that proton Bragg curves with E0 ? 120 MeV show a buildup, which increases with the proton energy. This buildup is explained by a theoretical analysis of impinging proton beamlets. In order to obtain a complete dose calculation model for proton treatment planning, some further aspects have to be accounted for: the decrease of the fluence of the primary protons due to nuclear interactions, the transport of released secondary protons, the dose contribution of heavy recoil nuclei, the inclusion of lateral scatter of the primary and secondary protons based on Molière's multiple-scatter theory, and the scatter contributions of collimators. This study also presents some results which go beyond proton dose calculation models; namely, the application of the relativistic generalization of the Bragg-Kleeman rule to electrons and, in an appendix, a method to determine inelastic cross-sections of therapeutic protons in media of therapeutic interest.

Ulmer, W.; Matsinos, E.

2010-12-01

84

Importance of parametrizing constraints in quantum-mechanical variational calculations  

NASA Technical Reports Server (NTRS)

In variational calculations of quantum mechanics, constraints are sometimes imposed explicitly on the wave function. These constraints, which are deduced by physical arguments, are often not uniquely defined. In this work, the advantage of parametrizing constraints and letting the variational principle determine the best possible constraint for the problem is pointed out. Examples are carried out to show the surprising effectiveness of the variational method if constraints are parameterized. It is also shown that misleading results may be obtained if a constraint is not parameterized.

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

1992-01-01

85

Pseudotime Schrödinger equation with absorbing potential for quantum scattering calculations.  

PubMed

The Schrödinger equation (Hpsi) (r) = [E+u(E)W(r)]psi(r) with an energy-dependent complex absorbing potential -u(E)W(r), associated with a scattering system, can be reduced for a special choice of u(E) to a harmonic inversion problem of a discrete pseudotime correlation function y(t) = phi(T)U(t)phi. An efficient formula for Green's function matrix elements is also derived. Since the exact propagation up to time 2t can be done with only approximately t real matrix-vector products, this gives an unprecedently efficient scheme for accurate calculations of quantum spectra for possibly very large systems. PMID:11384413

Neumaier, A; Mandelshtam, V A

2001-05-28

86

Variational calculation of polarization of quantum-well photoluminescence  

Microsoft Academic Search

We calculate for the first time the circular polarization of GaAs\\/Ga1-xAlxAs quantum-well photoluminescence taking into account the true nonparabolic valence-band structure. Versus the excitation energy, we find high positive polarization for the transition n=1 heavy-hole-to-conduction-band transition and negative polarization at the onset of n=1 light-hole-to-conduction-band transition in qualitative agreement with experiments. We also study the GayIn1-yAs\\/InP system and predict no

A. Twardowski; C. Hermann

1987-01-01

87

Biological Applications of Hybrid Quantum Mechanics/Molecular Mechanics Calculation  

PubMed Central

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 tRNALeu, 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

88

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

89

PFI-ZEKE SPECTROSCOPY AND THEORETICAL CALCULATIONS OF TRANSITION METAL-AROMATIC HYDROCARBON COMPLEXES  

Microsoft Academic Search

Transition metal-aromatic hydrocarbon complexes were generated in a supersonic jet and studied by zero electron kinetic energy (ZEKE) photoelectron spectroscopy and theoretical calculations. The target metal complexes were identified using time-of-flight mass spectrometry, and their ionization thresholds were located via photoionization efficiency spectroscopy. ZEKE spectroscopy was used to measure the ionization energies and vibrational frequencies of the metal complexes. Their

Bradford Raymond Sohnlein

2007-01-01

90

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

91

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

Microsoft Academic Search

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

Claudio Garola; Luigi Solombrino

1996-01-01

92

The actual content of quantum theoretical kinematics and mechanics  

NASA Technical Reports Server (NTRS)

First, exact definitions are supplied for the terms: position, velocity, energy, etc. (of the electron, for instance), such that they are valid also in quantum mechanics. Canonically conjugated variables are determined simultaneously only with a characteristic uncertainty. This uncertainty is the intrinsic reason for the occurrence of statistical relations in quantum mechanics. Mathematical formulation is made possible by the Dirac-Jordan theory. Beginning from the basic principles thus obtained, macroscopic processes are understood from the viewpoint of quantum mechanics. Several imaginary experiments are discussed to elucidate the theory.

Heisenberg, W.

1983-01-01

93

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

94

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

PubMed

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

Lundahl, Gunnel

2007-01-01

95

Local Hidden Variable Theoretic Measure of Quantumness of Mutual Information  

E-print Network

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, by invoking explicitly the local hidden variable theory, a measure of quantumness of mutual information, $Q_{LHV}$, for a system of two spin-1/2 particles is proposed. It is based on finding the difference between the quantum and classical mutual informations in which the classical mutual information corresponds to the joint probability of the eigenvalues of the spins each along a specified direction. The proposed measure circumvents the need of optimization when the Bloch vector of each spin is non-zero; the optimization is needed but can be performed analytically exactly when the Bloch vector of each spin vanishes and is simplified when the Bloch vector of only one of the spins is zero. In essence, the proposed measure is identical with the measurement induced disturbance when the Bloch vector of each of the spins is non-zero. However, whereas the measurement induced disturbance is non-unique when the Bloch vector of one or both the spins is zero, the proposed measure even then determines the quantumness of mutual information unambiguously. The $Q_{LHV}$ is identical with the symmetric discord if the Bloch vector of each spin vanishes. It is same as the quantum discord if the Bloch vector of only one spin is zero and if the state in question possesses certain additional properties.

R. R. Puri

2014-09-30

96

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

97

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

NASA Technical Reports Server (NTRS)

Models and spectra of sunspots were studied, because they are important to energy balance and variability discussions. Sunspot observations in the ultraviolet region 140 to 168 nn was obtained by the NRL High Resolution Telescope and Spectrograph. Extensive photometric observations of sunspot umbrae and prenumbrae in 10 chanels covering the wavelength region 387 to 3800 nm were made. Cool star opacities and model atmospheres were computed. The Sun is the first testcase, both to check the opacity calculations against the observed solar spectrum, and to check the purely theoretical model calculation against the observed solar energy distribution. Line lists were finally completed for all the molecules that are important in computing statistical opacities for energy balance and for radiative rate calculations in the Sun (except perhaps for sunspots). Because many of these bands are incompletely analyzed in the laboratory, the energy levels are not well enough known to predict wavelengths accurately for spectrum synthesis and for detailed comparison with the observations.

Avrett, E. H.

1984-01-01

98

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

99

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

100

Single vs. Cumulative Grain Size Distribution: Effects on Theoretical Reflectance Calculations  

NASA Astrophysics Data System (ADS)

We are developing a new approach to quantitative spectral characterization of remotely sensed objects. The work is an iterative and integrated theoretical and laboratory investigation. We are relating the spectral signature of the two types of carbonaceous chondrites (CV and CM) with their chemistry, mineralogy, and grain size distribution. In the future, the laboratory and theoretical portions of the study will be related to remote observations of asteroid surfaces. Radiative theory is being used to model the laboratory reflectance spectra of members of each of the two classes of carbonaceous chondrites (the theoretical mixtures will be generated using the known chemistry, mineralogy, optical constants and grain size distributions which have been previously determined) and verify the goodness of fit of the theoretical models to the laboratory spectra of meteorites. In using theoretical modeling assumptions about the physical and chemical properties of materials must be made. For the wavelength range we intend to consider (0.2-5 micrometers), we have previously obtained reasonable results using optical constants derived from reflectance spectra. That is, using a powdered sample in a narrow grain size range we invert a Hapke-based theoretical reflectance calculation to obtain an absorption coefficient. The primary disadvantage to this method is that it requires an assumption regarding the behavior of the index of refraction. However, as the index typically does not vary strongly in this wavelength interval, this is a reasonable assumption. Assumptions about the grain size of the materials being modelled are also important considerations when using Hapke-based theoretical modeling techniques. Commonly a single grain size range is deemed appropriate for a specific calculation and from that range an average grain size is estimated for the material. However, as most materials, including planetary regoliths and meteorites, are not composed of single mineralogies or single particle grain sizes we have investigated the disadvantages of making assumptions about a single grain size to represent the entire grain size distribution. For this preliminary study we selected pyroxene separates that were ground into narrow size intervals and for which an average grain size for each interval had been determined by Scanning Electron Microscope. Using a Hapke-based theoretical model we calculated the absorption coefficient. Then using a cumulative power-law distribution we calculated an absorption coefficient of the mixture. The average grain size of the cumulative distribution was determined to be 51.8 micrometers. This compound absorption coefficient was then used to compute a reflectance spectra of the pyroxene with a grain size of 52 micrometers. This spectrum was compared with the theoretical spectrum of the pyroxene in which the size distribution was a single size interval with an average grain size of 52 micrometers. Differences in the strengths of the resulting 2 micrometers absorption feature were nearly 7%, although no change was observed in the 1 micrometer absorption feature. Thus, suggesting that using a single grain size value to determine the absorption coefficient of a poly-grain size material needs to be reevaluated. Deriving the absorption coefficient based on a cumulative power-law distribution rather than a single average grain size is necessary, especially in multi-component mixtures where each mineral component, whether it is in the matrix or appears as an inclusion or chondrule, will likely have a unique grain size distribution. When modelling surfaces or materials with several mineralogic materials present, the failure to consider a cumulative size distribution will effect the estimates of mineral abundances.

King, T. V. V.; Calvin, W. M.

1995-09-01

101

Can category-theoretic semantics resolve the problem of the interpretation of the quantum state vector?  

E-print Network

Do correctness and completeness of quantum mechanics jointly imply that quantum state vectors are necessarily in one-to-one correspondence with elements of the physical reality? In terms of category theory, such a correspondence would stand for an isomorphism, so the problem of the status of the quantum state vector could be turned into the question of whether state vectors are necessarily isomorphic to elements of the reality. As it is argued in the present paper, in order to tackle this question, one needs to complement the category-theoretic approach to quantum mechanics with the computational-complexity-theoretic considerations. Based on such considerations, it is demonstrated in the paper that the hypothesis of the isomorphism existing between state vectors and elements of the reality is expected to be unsuitable for a generic quantum system.

Arkady Bolotin

2015-02-25

102

Fragment quantum mechanical calculation of proteins and its applications.  

PubMed

Conspectus The desire to study molecular systems that are much larger than what the current state-of-the-art ab initio or density functional theory methods could handle has naturally led to the development of novel approximate methods, including semiempirical approaches, reduced-scaling methods, and fragmentation methods. The major computational limitation of ab initio methods is the scaling problem, because the cost of ab initio calculation scales nth power or worse with system size. In the past decade, the fragmentation approach based on chemical locality has opened a new door for developing linear-scaling quantum mechanical (QM) methods for large systems and for applications to large molecular systems such as biomolecules. The fragmentation approach is highly attractive from a computational standpoint. First, the ab initio calculation of individual fragments can be conducted almost independently, which makes it suitable for massively parallel computations. Second, the electron properties, such as density and energy, are typically combined in a linear fashion to reproduce those for the entire molecular system, which makes the overall computation scale linearly with the size of the system. In this Account, two fragmentation methods and their applications to macromolecules are described. They are the electrostatically embedded generalized molecular fractionation with conjugate caps (EE-GMFCC) method and the automated fragmentation quantum mechanics/molecular mechanics (AF-QM/MM) approach. The EE-GMFCC method is developed from the MFCC approach, which was initially used to obtain accurate protein-ligand QM interaction energies. The main idea of the MFCC approach is that a pair of conjugate caps (concaps) is inserted at the location where the subsystem is divided by cutting the chemical bond. In addition, the pair of concaps is fused to form molecular species such that the overcounted effect from added concaps can be properly removed. By introducing the electrostatic embedding field in each fragment calculation and two-body interaction energy correction on top of the MFCC approach, the EE-GMFCC method is capable of accurately reproducing the QM molecular properties (such as the dipole moment, electron density, and electrostatic potential), the total energy, and the electrostatic solvation energy from full system calculations for proteins. On the other hand, the AF-QM/MM method was used for the efficient QM calculation of protein nuclear magnetic resonance (NMR) parameters, including the chemical shift, chemical shift anisotropy tensor, and spin-spin coupling constant. In the AF-QM/MM approach, each amino acid and all the residues in its vicinity are automatically assigned as the QM region through a distance cutoff for each residue-centric QM/MM calculation. Local chemical properties of the central residue can be obtained from individual QM/MM calculations. The AF-QM/MM approach precisely reproduces the NMR chemical shifts of proteins in the gas phase from full system QM calculations. Furthermore, via the incorporation of implicit and explicit solvent models, the protein NMR chemical shifts calculated by the AF-QM/MM method are in excellent agreement with experimental values. The applications of the AF-QM/MM method may also be extended to more general biological systems such as DNA/RNA and protein-ligand complexes. PMID:24851673

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

2014-09-16

103

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

104

Theoretical modeling of dark current and photo-response for quantum well and quantum dot infrared detectors  

Microsoft Academic Search

Dark currents (due to direct tunneling process) and photo-response for both quantum well (QW) and quantum dot (QD) systems are calculated. A stabilization method (SM) is used to study the dynamic behavior and photo-response of an electron in an isolated QW, coupled QW or QD (with conical shape) under uniform electric field. A stabilization graph is obtained by plotting the

David M.-T. Kuo; Angbo Fang; Y. C. Chang

2001-01-01

105

Consistency of field-theoretical and kinetic calculations of viscous transport coefficients for a relativistic fluid  

NASA Astrophysics Data System (ADS)

We investigate the ratios ?? ? ? /?? and ?? ? ? /??, i.e., the ratios of shear, ?, and bulk, ?, viscosities to the relaxation times ??, ?? of the shear stress tensor and bulk viscous pressure, respectively, in the framework of causal relativistic dissipative fluid dynamics. These viscous transport coefficients are computed both in a field-theoretical and a kinetic approach based on the Boltzmann equation. Our results differ from those of the traditional Boltzmann calculation by Israel and Stewart. The new expressions for the viscous transport coefficients agree with the results obtained in the field-theoretical approach when the contributions from pair annihilation and creation (PAC) are neglected. The latter induce non-negligible corrections to the viscous transport coefficients.

Denicol, Gabriel S.; Huang, Xu-Guang; Koide, Tomoi; Rischke, Dirk H.

2012-02-01

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

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

SciTech Connect

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

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

2008-04-15

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

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

110

A quantum theoretical approach to information processing in neural networks  

Microsoft Academic Search

A reinterpretation of experimental data on learning was used to formulate a law on data acquisition similar to the Hamiltonian of a mechanical system. A matrix of costs in decision making specifies values attributable to a barrier that opposed to hypothesis formation about decision making. The interpretation of the encoding costs as frequencies of oscillatory phenomena leads to a quantum

Jose´ Barahona da Fonseca; Isabel Barahona da Fonseca; Carmen Paz Suarez AraujoJ; Jose´ Simões da Fonseca

2000-01-01

111

Epithermal effects in muon-catalyzed [ital dt] fusion: Comparison of experimental data with theoretical calculations  

SciTech Connect

Epithermal effects in muonic molecular formation were observed during experiments in a low-density deuterium-tritium gas target carried out at the Paul Scherrer Institute. The high molecular formation rate of epithermal'' (not yet thermalized) muonic tritium atoms was reflected by a strong fast component in the fusion neutron time spectra followed by a smaller steady-state'' component where molecular formation occurs mostly from thermalized ( cold'') [ital t][mu] atoms. Further experimental evidence for high epithermal [ital dt][mu] molecular formation rates has been derived from measurements in triple H-D-T mixtures. First, theoretical calculations predicted strong resonances at high [ital t][mu] kinetic energies and showed qualitative agreement with the observed experimental data, but yielded molecular formation rates that differed substantially from the observed values. At present, refined calculations are being carried out which may improve the agreement with experiment. Further experiments are being planned to clarify open questions.

Jeitler, M.; Breunlich, W.H.; Cargnelli, M.; Kammel, P.; Marton, J.; Naegele, N.; Pawlek, P.; Scrinzi, A.; Werner, J.; Zmeskal, J. (Institut fuer Mittelenerglephysik, Austrian Academy of Sciences, A-1090 Wien (Austria)); Bossy, H.; Daniel, H.; Hartmann, F.J.; Schmidt, G.; von Egidy, T. (Physik Department, Technical University of Munich, D-85747 Garching (Germany)); Petitjean, C. (Paul Scherrer Institute, CH-5232 Villigen (Switzerland)); Bistirlich, J.; Crowe, K.M.; Justice, M.; Kurck, J. (University of California and Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States)); Sherman, R.H. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Neumann, W. (Eidgenoessische Technische Hochschule, CH-8049 Zuerich (Switzerland)); Faifman, M.P. (RRC Kurchatov Institute, Moscow 123182 (Russian Federation))

1995-04-01

112

Double Exponential Relativity Theory Coupled Theoretically with Quantum Theory?  

SciTech Connect

Here the problem of special relativity is analyzed into the context of a new theoretical formulation: the Double Exponential Theory of Special Relativity with respect to which the current Special or Restricted Theory of Relativity (STR) turns to be a particular case only.

Montero Garcia, Jose de la Luz [Institute for Scientific and Technological Information (IDICT), National Capitol, Havana (Cuba); Novoa Blanco, Jesus Francisco

2007-04-28

113

Theoretical calculations of magnetic order and anisotropy energies in molecular magnets  

SciTech Connect

We present theoretical electronic structure calculations on the nature of electronic states and the magnetic coupling in the Mn{sub 12}O{sub 12} free cluster and the Mn{sub 12}O{sub 12}(RCOO){sub 16}(H{sub 2}O){sub 4} molecular magnetic crystal. The calculations have been performed with the all-electron full-potential NRLMOL code. We find that the free Mn{sub 12}O{sub 12} cluster relaxes to an antiferromagnetic cluster with no net moment. However, when coordinated by sixteen HCOO ligands and four H{sub 2}O groups, as it is in the molecular crystal, we find that the ferrimagnetic ordering and geometrical and magnetic structure observed in the experiments is restored. Local Mn moments for the free and ligandated molecular magnets are presented and compared to experiment. We identify the occupied and unoccupied electronic states that are most responsible for the formation of the large anisotropy barrier and use a recently developed full-space and full-potential method for calculating the spin-orbit coupling interaction and anisotropy energies. Our calculated second-order anisotropy energy is in excellent agreement with experiment. (c) 2000 American Institute of Physics.

Pederson, M. R. [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States)] [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States); Porezag, D. V. [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States)] [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States); Kortus, J. [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States)] [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States); Khanna, S. N. [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000 (United States)] [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000 (United States)

2000-05-01

114

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

115

Investigation on the Gas-Phase Decomposition of Trichlorfon by GC-MS and Theoretical Calculation  

PubMed Central

The gas phase pyrolysis of trichlorfon was investigated by the on-line gas chromatography – mass spectrometry (GC-MS) pyrolysis and theoretical calculations. Two reaction channels were proposed in the pyrolytic reaction, by analyzing the detected pyrolytic products in the total ion chromatography, including 2,2,2-trichloroacetaldehyde, dimethyl phosphite, and dichlorvos. Theoretical calculations showed that there is an intramolecular hydrogen bond between the hydroxyl group and the phosphate O atom in trichlorfon, through which the hydroxyl H atom can be easily transferred to phosphate O atom to trigger two pyrolytic channels. In path-a, migration of H atom results in direct decomposition of trichlorfon to give 2,2,2-trichloroacetaldehyde and dimethyl phosphite in one step. In path-b, migration of H atom in trichlorfon is combined with formation of the O-P bond to give an intermediate, followed by HCl elimination to afford dichlorvos. Path-a is kinetically more favorable than path-b, which is consistent with the GC-MS results. PMID:25856549

Jiang, Kezhi; Zhang, Ningwen; Zhang, Hu; Wang, Jianmei; Qian, Mingrong

2015-01-01

116

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

NASA Astrophysics Data System (ADS)

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

Bai, Yihui; Du, Jinyan; Weng, Xuexiang

117

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

118

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

119

Number-Theoretic Nature of Communication in Quantum Spin Systems  

NASA Astrophysics Data System (ADS)

The last decade has witnessed substantial interest in protocols for transferring information on networks of quantum mechanical objects. A variety of control methods and network topologies have been proposed, on the basis that transfer with perfect fidelity—i.e., deterministic and without information loss—is impossible through unmodulated spin chains with more than a few particles. Solving the original problem formulated by Bose [Phys. Rev. Lett. 91, 207901 (2003)], we determine the exact number of qubits in unmodulated chains (with an XY Hamiltonian) that permit transfer with a fidelity arbitrarily close to 1, a phenomenon called pretty good state transfer. We prove that this happens if and only if the number of nodes is n=p-1, 2p-1, where p is a prime, or n=2m-1. The result highlights the potential of quantum spin system dynamics for reinterpreting questions about the arithmetic structure of integers and, in this case, primality.

Godsil, Chris; Kirkland, Stephen; Severini, Simone; Smith, Jamie

2012-08-01

120

A quantum theoretical approach to information processing in neural networks  

NASA Astrophysics Data System (ADS)

A reinterpretation of experimental data on learning was used to formulate a law on data acquisition similar to the Hamiltonian of a mechanical system. A matrix of costs in decision making specifies values attributable to a barrier that opposed to hypothesis formation about decision making. The interpretation of the encoding costs as frequencies of oscillatory phenomena leads to a quantum paradigm based in the models of photoelectric effect as well as of a particle against a potential barrier. Cognitive processes are envisaged as complex phenomena represented by structures linked by valence bounds. This metaphor is used to find some prerequisites to certain types of conscious experience as well as to find an explanation for some pathological distortions of cognitive operations as they are represented in the context of the isolobal model. Those quantum phenomena are understood as representing an analogue programming for specific special purpose computations. The formation of complex chemical structures within the context of isolobal theory is understood as an analog quantum paradigm for complex cognitive computations.

Barahona da Fonseca, José; Barahona da Fonseca, Isabel; Suarez Araujo, Carmen Paz; Simões da Fonseca, José

2000-05-01

121

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

122

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

123

The information-theoretical entropy of some quantum oscillators  

NASA Astrophysics Data System (ADS)

The Wehrl entropy or the "classical" entropy associated with a quantum system is the entropy of the probability distribution in phase space, corresponding to the Husimi Q-function in terms of coherent states. In the present paper, we shall focus our attention on the examination of the Wehrl entropy for both the pure and the mixed (thermal) states of the pseudoharmonic oscillator (PHO). The choice of the PHO is interesting because this oscillator is an intermediate between the ideal one-dimensional harmonic oscillator (HO-1D) and the more practical anharmonicone.

Popov, D.; Pop, N.; Popov, M.; imon, S.

2014-11-01

124

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

125

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

NASA Astrophysics Data System (ADS)

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

Chen, Xin

2014-04-01

126

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

127

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

E-print Network

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

Reid, Scott A.

128

Quantum Chemical Calculations of Sulfate Adsorption at the Al-and  

E-print Network

Quantum Chemical Calculations of Sulfate Adsorption at the Al- and Fe-(Hydr)oxide-H2O Interfaces, The Pennsylvania State University, University Park, Pennsylvania 16802 Quantum chemical calculations were performed-(hydr)oxides. Sulfate adsorption is influenced, to a varying extent, by pH, ionic strength, hydration state, and mineral

Sparks, Donald L.

129

On the Theoretical Calculation of the Stability Line of an Axial-flow Compressor Stage  

NASA Astrophysics Data System (ADS)

Recently, an analytical model to calculate the stability of an axial-flow compressor rotor has been presented in the scientific literature. The range of validity of that theoretical characterization was supported by several lemmas and theorems. One of the main results was the definition of a dimensionless coefficient for determining the location of the stability line in the rotor map. In this work the mathematical structure of that solution is studied. As a result of this detailed study, a new stability theorem and a new stability coefficient are obtained. This stability coefficient is an improvement of the previous one since it is physically and mathematically well defined in all the operational points of the compressor map. As a consequence, the new model is able to capture the stall inception for rotors and stators as well as the full characteristic curve (pressure rise versus mass flow rate) including rotating stall and possibly reverse flow. It is proved, as a consequence of the restriction imposed by the Stability Theorem, that each local component (rotor or stator) has its own instability point and its own post-stall characteristic curve. This theoretical criterion for predicting the averaged characteristic curve is in good accord with the experimental data. The stability coefficient is also verified for a compressor stage. Finally, the model is shown to provide an adequate quantitative and qualitative description of the averaged stall line giving a physical explanation of the mechanism involved in the instable region of the compressor map.

Benavides, Efrén M.

2011-12-01

130

On pionic hydrogen. Quantum field theoretic, relativistic covariant and model-independent approach  

E-print Network

We consider pionic hydrogen A_(pi p), the bound pi^- p state. Within the quantum field theoretic and relativistic covariant approach we calculate the shift and width of the energy level of the ground state of pionic hydrogen caused by strong low-energy interactions treated perturbatively. The generalization of the Deser-Goldberger-Baumann-Thirring (DGBT) formulas (Phys. Rev. 96, 774 (1954)) is given. The generalized DGBT formulas for the energy level displacement of the ground state of pionic hydrogen contain the non-perturbative and model-independent correction about 1%, caused by the relativistic covariant smearing of the wave function of the ground state around origin. This non-perturbative correction is very important for the precise extraction of the S-wave scattering lengths of pion-nucleon scattering from the experimental data on the energy level displacements in pionic hydrogen by the PSI Collaboration. In addition the shift of the energy level of the ground state of pionic hydrogen is improved by the second order correction of strong low-energy interactions which is about 0.1%. This testifies the applicability of the perturbative treatment of strong low-energy interactions to the analysis of pionic hydrogen. We show that the width of the energy level of the ground state of pionic hydrogen is valid to all order of perturbation theory in strong low-energy interactions.

A. N. Ivanov; M. Faber; A. Hirtl; J. Marton; N. I. Troitskaya

2003-11-20

131

Hyperon puzzle: hints from quantum monte carlo calculations.  

PubMed

The onset of hyperons in the core of neutron stars and the consequent softening of the equation of state have been questioned for a long time. Controversial theoretical predictions and recent astrophysical observations of neutron stars are the grounds for the so-called hyperon puzzle. We calculate the equation of state and the neutron star mass-radius relation of an infinite systems of neutrons and ? particles by using the auxiliary field diffusion Monte Carlo algorithm. We find that the three-body hyperon-nucleon interaction plays a fundamental role in the softening of the equation of state and for the consequent reduction of the predicted maximum mass. We have considered two different models of three-body force that successfully describe the binding energy of medium mass hypernuclei. Our results indicate that they give dramatically different results on the maximum mass of neutron stars, not necessarily incompatible with the recent observation of very massive neutron stars. We conclude that stronger constraints on the hyperon-neutron force are necessary in order to properly assess the role of hyperons in neutron stars. PMID:25793808

Lonardoni, Diego; Lovato, Alessandro; Gandolfi, Stefano; Pederiva, Francesco

2015-03-01

132

Hyperon Puzzle: Hints from Quantum Monte Carlo Calculations  

NASA Astrophysics Data System (ADS)

The onset of hyperons in the core of neutron stars and the consequent softening of the equation of state have been questioned for a long time. Controversial theoretical predictions and recent astrophysical observations of neutron stars are the grounds for the so-called hyperon puzzle. We calculate the equation of state and the neutron star mass-radius relation of an infinite systems of neutrons and ? particles by using the auxiliary field diffusion Monte Carlo algorithm. We find that the three-body hyperon-nucleon interaction plays a fundamental role in the softening of the equation of state and for the consequent reduction of the predicted maximum mass. We have considered two different models of three-body force that successfully describe the binding energy of medium mass hypernuclei. Our results indicate that they give dramatically different results on the maximum mass of neutron stars, not necessarily incompatible with the recent observation of very massive neutron stars. We conclude that stronger constraints on the hyperon-neutron force are necessary in order to properly assess the role of hyperons in neutron stars.

Lonardoni, Diego; Lovato, Alessandro; Gandolfi, Stefano; Pederiva, Francesco

2015-03-01

133

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

134

Theoretical calculating the thermodynamic properties of solid sorbents for CO{sub 2} capture applications  

SciTech Connect

Since current technologies for capturing CO{sub 2} to fight global climate change are still too energy intensive, there is a critical need for development of new materials that can capture CO{sub 2} reversibly with acceptable energy costs. Accordingly, solid sorbents have been proposed to be used for CO{sub 2} capture applications through a reversible chemical transformation. By combining thermodynamic database mining with first principles density functional theory and phonon lattice dynamics calculations, a theoretical screening methodology to identify the most promising CO{sub 2} sorbent candidates from the vast array of possible solid materials has been proposed and validated. The calculated thermodynamic properties of different classes of solid materials versus temperature and pressure changes were further used to evaluate the equilibrium properties for the CO{sub 2} adsorption/desorption cycles. According to the requirements imposed by the pre- and post- combustion technologies and based on our calculated thermodynamic properties for the CO{sub 2} capture reactions by the solids of interest, we were able to screen only those solid materials for which lower capture energy costs are expected at the desired pressure and temperature conditions. Only those selected CO{sub 2} sorbent candidates were further considered for experimental validations. The ab initio thermodynamic technique has the advantage of identifying thermodynamic properties of CO{sub 2} capture reactions without any experimental input beyond crystallographic structural information of the solid phases involved. Such methodology not only can be used to search for good candidates from existing database of solid materials, but also can provide some guidelines for synthesis new materials. In this presentation, we first introduce our screening methodology and the results on a testing set of solids with known thermodynamic properties to validate our methodology. Then, by applying our computational method to several different kinds of solid systems, we demonstrate that our methodology can predict the useful information to help developing CO{sub 2} capture Technologies.

Duan, Yuhua

2012-11-02

135

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

136

Theoretical calculations of nonlinear refraction and absorption coefficients of doped graphene  

NASA Astrophysics Data System (ADS)

In this study, we present the first theoretical predictions concerning the nonlinear refractive and absorptive properties of the doped graphene in which the Fermi energy {{E}F} of charge carriers (noninteracting massless Dirac fermions) is controlled by an external gate voltage. We base our study on the original perturbation theory technique developed by Genkin and Mednis (1968 Sov. Phys. JETP 27 609) for calculating the nonlinear-optical (NLO) response coefficients of bulk crystalline semiconductors with partially filled bands. Using a simple tight-binding model for the ?-electron energy bands of graphene, we obtain analytic expressions for the nonlinear refractive index {{n}2}(? ) and the nonlinear absorption coefficient {{? }2}(? ) of the doped graphene at photon energies above twice the value of the Fermi energy (\\hbar ? \\gt 2{{E}F}). We show that in this spectral region, both the nonlinear refraction ant the nonlinear absorption are determined predominantly by the combined processes which simultaneously involve intraband and interband motion of ?-electrons. Our calculations indicate that extremely large negative values of n2 (of the order of -{{10}-6} cm2 W?1) can be achieved in the graphene at a relatively low doping level (of about 1012 cm?2) provided that the excitation frequency slightly exceeds the threshold frequency corresponding to the onset of interband transitions. With a further increase of the radiation frequency, the {{n}2}(? ) becomes positive and begins to decrease in its absolute magnitude. The peculiar frequency dispersion of n2 and a negative sign of the {{? }2} (absorption bleaching), as predicted by our theory, suggest that the doped graphene is a prospective NLO material to be used in practical optical switching applications.

Margulis, Vl A.; Muryumin, E. E.; Gaiduk, E. A.

2014-12-01

137

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

138

Molecular structure and nicotinic activity of arecoline. A gas electron diffraction study combined with theoretical calculations  

NASA Astrophysics Data System (ADS)

The molecular structure of arecoline (methyl 1,2,5,6-tetrahydro-1-methylnicotinate, ? has been determined by gas electron diffraction. Diffraction patterns were taken at about 370 K. Structural constraints for the data analysis were obtained from MP2/6-31G** calculations. Vibrational mean amplitudes and shrinkage corrections were calculated from the force constants obtained from the gas-phase vibrational frequencies and the B3LYP/6-31G** calculations. The electron diffraction data were well reproduced by assuming the mixture of four conformers. The determined structural parameters ( rg (Å) and ? (°)) for the main conformer with 3 ? in parentheses are as follows: < rg(N-C ring)>=1.456(4); rg(N-C methyl)=1.451 (d.p.); rg(C dbnd6 C)=1.339(9); < rg(C-C)>=1.512(3); rg(O-C methyl)=1.434(5); rg(C(O)-O)=1.355 (d.p.); rg(C dbnd6 O)=1.209(4); the out-of-plane angle of the methyl group=50.3(23); ?C ringN ringC ring=112.8(30); ?N ringC ringC ring(H 2)=110.5(16); =118.4(5); ?C dbnd6 CC(O)=116.8(7); ?CC dbnd6 O=127.6(9); ?CC-O=109.8(8), where the angle brackets denote averaged values and d.p. denotes dependent parameters. Fixing the abundances of the minor conformers, Ax-s- cis and Ax-s- trans, at the theoretical values (13% in total), those of the Eq-s- cis and Eq-s- trans conformers were determined to be 46(16) and 41(16)%, respectively. Here Ax and Eq denote the axial and equatorial directions of the N-CH 3 bond and s- cis and s- trans show the orientation of the methoxycarbonyl group expressed by the configuration of the C dbnd6 O and C dbnd6 C bonds. The N⋯O carbonyl distances of the Eq-s- cis and Ax-s- cis conformers are 4.832(13) and 4.874(16) Å, respectively. They are close to the N⋯N distance of the most abundant conformer of nicotine, 4.885(6) Å, suggesting that the Eq-s- cis and Ax-s- cis conformers have nicotinic activity.

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

2005-01-01

139

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

140

Theoretical investigation of carrier capture and escape processes in cylindrical quantum dots  

NASA Astrophysics Data System (ADS)

In order to optimize the design of various optoelectronic devices utilizing quantum dots (QD), we must better understand the properties of carrier capture and escape times in these systems. Some of the properties of cylindrical quantum dots were studied. The wavefunctions and eigenenergies of a cylindrical quantum dot were approximated by a product of solutions of an infinite cylinder and a quantum well. It was assumed that the majority of transitions are caused by absorption/emission of polar optical phonons, and Fermi's golden rule was applied to calculate the transition rates to and from the QD. We have restricted our calculations to one-phonon (first order) processes only. We determined the carrier capture and escape times as a function of the size of the QD and carrier density. We have shown that the smallest capture times are achieved if the QD has only one quantum level. A short capture time is also achieved for a low carrier density. Similarly, the capture time has the smallest value when the QD has only one quantum level. The dependence of the carrier escape time for a fixed dot dimension shows a minimum as a function of carrier density. For small QDs, the capture and escape times are approximately independent of carrier density.

Miloszewski, Jacek M.; Wartak, Marek S.; Wallace, Steven G.; Fafard, Simon

2013-10-01

141

Excitons bound to isoelectronic Te traps in ZnSe quantum wells: A theoretical study  

Microsoft Academic Search

A theoretical study is made of excitons and holes bound to a single tellurium (Te) impurity in bulk ZnSe and centered in ZnSe-Zn1-xMnxSe strained quantum wells. We use an effective-bond-orbital model for the holes in order to account for the complicated valence-band structure, and the spherical effective-mass approximation to describe the electron. The mutual Coulomb interaction is included, and solutions

G. T. Einevoll; D. S. Citrin; Yia-Chung Chang

1991-01-01

142

Assembling gas-phase reaction mechanisms for high temperature inorganic systems based on quantum chemistry calculations  

E-print Network

Assembling gas-phase reaction mechanisms for high temperature inorganic systems based on quantum chemistry calculations and reaction rate theories Mark T. Swihart* Department of Chemical Engineering quantum chemistry and reaction rate theories. In addition, for both of these cases there is a database

Swihart, Mark T.

143

Path-integral virial estimator for reaction rate calculation basedon the quantum instanton aproximation  

Microsoft Academic Search

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

Sandy Yang; Takeshi Yamamoto; William H. Miller

2005-01-01

144

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

145

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

146

Converged quantum calculations of HO2 bound states and resonances for J=6 and 10.  

PubMed

Bound and resonance states of HO(2) are calculated quantum mechanically using both the Lanczos homogeneous filter diagonalization method and the real Chebyshev filter diagonalization method for nonzero total angular momentum J=6 and 10, using a parallel computing strategy. For bound states, agreement between the two methods is quite satisfactory; for resonances, while the energies are in good agreement, the widths are in general agreement. The quantum nonzero-J specific unimolecular dissociation rates for HO(2) are also calculated. PMID:15267970

Zhang, Hong; Smith, Sean C

2004-05-22

147

Converged quantum calculations of HO2 bound states and resonances for J=6 and 10  

NASA Astrophysics Data System (ADS)

Bound and resonance states of HO2 are calculated quantum mechanically using both the Lanczos homogeneous filter diagonalization method and the real Chebyshev filter diagonalization method for nonzero total angular momentum J=6 and 10, using a parallel computing strategy. For bound states, agreement between the two methods is quite satisfactory; for resonances, while the energies are in good agreement, the widths are in general agreement. The quantum nonzero-J specific unimolecular dissociation rates for HO2 are also calculated.

Zhang, Hong; Smith, Sean C.

2004-05-01

148

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

Microsoft Academic Search

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

Sandy Yang; Takeshi Yamamoto; William H. Miller

2006-01-01

149

Quantum complex rotation and uniform semiclassical calculations of complex energy eigenvalues  

Microsoft Academic Search

Quantum and semiclassical calculations of complex energy eigenvalues have been carried out for an exponential potential of the form V0r2 exp(?r) and Lennard-Jones (12,6) potential. A straightforward method, based on the complex coordinate rotation technique, is described for the quantum calculation of complex eigenenergies. For singular potentials, the method involves an inward and outward integration of the radial Schro¨dinger equation,

J. N. L. Connor; A. D. Smith

1983-01-01

150

Quantum complex rotation and uniform semiclassical calculations of complex energy eigenvalues  

Microsoft Academic Search

Quantum and semiclassical calculations of complex energy eigenvalues have been carried out for an exponential potential of the form Vâr² exp(-r) and Lennard-Jones (12,6) potential. A straightforward method, based on the complex coordinate rotation technique, is described for the quantum calculation of complex eigenenergies. For singular potentials, the method involves an inward and outward integration of the radial Schroedinger equation,

J. N. L. Connor; A. D. Smith

1983-01-01

151

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

152

Molecular structure analysis and spectroscopic characterization of carbimazole with experimental (FT-IR, FT-Raman and UV-Vis) techniques and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The complete vibrational assignment and analysis of the fundamental modes of carbimazole (CBZ) was carried out using the experimental FTIR, FT-Raman and UV-Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of CBZ have been computed using B3LYP quantum chemical calculation. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.

Gnanasambandan, T.; Gunasekaran, S.; Seshadri, S.

2013-11-01

153

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

154

Theoretical calculation are based on the DFT with GGA implemented in the VASP code, with the PAW  

E-print Network

Theoretical calculation are based on the DFT with GGA implemented in the VASP code, with the PAW, and the Gamma point approximation for Brillouin zone sampling and it's spin non-polarized A cage structure with the experimental PES. Once again, the relativistic effect of the heavy gold element is responsible to the stability

Gong, Xingao

155

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

E-print Network

Diode laser spectroscopic measurements and theoretical calculations of line parameters of nitrogen region are measured by using a tunable diode laser spectrometer. Water vapor is kept at its saturated. in the presence of perturbers like oxygen, nitrogen, air, argon etc [11-13]. 3 #12;FTIR and diode laser

Gamache, Robert R.

156

Wavelets in curvilinear coordinate quantum calculations: H2+ electronic states  

NASA Astrophysics Data System (ADS)

Multiscale wavelets are used to solve the quantum eigenvalue equations for the hydrogen molecular ion H2+ in the Born-Oppenheimer approximation. Normally restricted to Cartesian systems, "wavelets on the interval" (a normal wavelet family augmented by special edge functions) have recently been applied to such boundary value problems as the hydrogen atom in spherical polar coordinates [J. Mackey, J. L. Kinsey, and B. R. Johnson, J. Comp. Phys. 168, 356 (2001)]. These methods are extended here to ground and excited electronic states of the simplest molecule, for which the electronic Hamiltonian is separable in confocal elliptic coordinates. The set of curvilinear coordinate quantum systems for which wavelet bases have been applied is thus enlarged.

Maloney, A.; Kinsey, James L.; Johnson, Bruce R.

2002-08-01

157

Conformational analysis and study of anomeric effect on 2-alkoxytetrahydropyrans by molecular mechanics (MM2) and theoretical 3JHH calculation  

NASA Astrophysics Data System (ADS)

Molecular mechanics calculations have been carried out for conformers of the 2-alkoxytetrahydropyran derivatives (compounds 1-12) with the alkoxy group in the axial and equatorial conformations. According to the numerical results obtained, the anomeric effects can be predicted as well as the geometry tendencies of the different conformers studied. Thus, the coupling constants 2-3, are calculated theoretically, giving results consistent with the experimental data. Comparisons are made using different effective dielectric constants, and carrying out calculations with different versions of MM2.

Florido Navio, Pilar; Molina Molina, José

1990-05-01

158

Quantum chemical calculations for polymers and organic compounds  

NASA Technical Reports Server (NTRS)

The relativistic effects of the orbiting electrons on a model compound were calculated. The computational method used was based on 'Modified Neglect of Differential Overlap' (MNDO). The compound tetracyanoplatinate was used since empirical measurement and calculations along "classical" lines had yielded many known properties. The purpose was to show that for large molecules relativity effects could not be ignored and that these effects could be calculated and yield data in closer agreement to empirical measurements. Both the energy band structure and molecular orbitals are depicted.

Lopez, J.; Yang, C.

1982-01-01

159

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

160

Analytic and numerical calculations of quantum synchrotron spectra from relativistic electron distributions  

NASA Technical Reports Server (NTRS)

Calculations are performed numerically and analytically of synchrotron spectra for thermal and power-law electron distributions using the single-particle synchrotron power spectrum derived from quantum electrodynamics. It is found that the photon energy at which quantum effects appear is proportional to temperature and independent of field strength for thermal spectra; quantum effects introduce an exponential roll-off away from the classical spectra. For power law spectra, the photon energy at which quantum effects appear is inversely proportional to the magnetic field strength; quantum effects produce a steeper power law than is found classically. The results are compared with spectra derived from the classical power spectrum with an energy cutoff ensuring conservation of energy. It is found that an energy cutoff is generally an inadequate approximation of quantum effects for low photon energies and for thermal spectra, but gives reasonable results for high-energy emission from power-law electron distributions.

Brainerd, J. J.; Petrosian, V.

1987-01-01

161

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

162

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.

163

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.

164

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

165

Quantum noise in the mirror-field system: A field theoretic approach  

SciTech Connect

We revisit the quantum noise problem in the mirror-field system by a field-theoretic approach. Here a perfectly reflecting mirror is illuminated by a single-mode coherent state of the massless scalar field. The associated radiation pressure is described by a surface integral of the stress-tensor of the field. The read-out field is measured by a monopole detector, from which the effective distance between the detector and mirror can be obtained. In the slow-motion limit of the mirror, this field-theoretic approach allows to identify various sources of quantum noise that all in all leads to uncertainty of the read-out measurement. In addition to well-known sources from shot noise and radiation pressure fluctuations, a new source of noise is found from field fluctuations modified by the mirror's displacement. Correlation between different sources of noise can be established in the read-out measurement as the consequence of interference between the incident field and the field reflected off the mirror. In the case of negative correlation, we found that the uncertainty can be lowered than the value predicted by the standard quantum limit. Since the particle-number approach is often used in quantum optics, we compared results obtained by both approaches and examine its validity. We also derive a Langevin equation that describes the stochastic dynamics of the mirror. The underlying fluctuation-dissipation relation is briefly mentioned. Finally we discuss the backreaction induced by the radiation pressure. It will alter the mean displacement of the mirror, but we argue this backreaction can be ignored for a slowly moving mirror. - Highlights: Black-Right-Pointing-Pointer The quantum noise problem in the mirror-field system is re-visited by a field-theoretic approach. Black-Right-Pointing-Pointer Other than the shot noise and radiation pressure noise, we show there are new sources of noise and correlation between them. Black-Right-Pointing-Pointer The noise correlations can be used to suppress the overall quantum noise on the mirror. Black-Right-Pointing-Pointer The equation of motion of the mirror is derived and the backreaction of the radiation field is discussed.

Hsiang, Jen-Tsung, E-mail: cosmology@gmail.com [Department of Physics, National Dong-Hwa University, Hua-lien, Taiwan, ROC (China)] [Department of Physics, National Dong-Hwa University, Hua-lien, Taiwan, ROC (China); Wu, Tai-Hung [Department of Physics, National Dong-Hwa University, Hua-lien, Taiwan, ROC (China)] [Department of Physics, National Dong-Hwa University, Hua-lien, Taiwan, ROC (China); Lee, Da-Shin, E-mail: dslee@mail.ndhu.edu.tw [Department of Physics, National Dong-Hwa University, Hua-lien, Taiwan, ROC (China)] [Department of Physics, National Dong-Hwa University, Hua-lien, Taiwan, ROC (China); King, Sun-Kun [Institutes of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan, ROC (China)] [Institutes of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan, ROC (China); Wu, Chun-Hsien [Department of Physics, Soochow University, Taipei, Taiwan, ROC (China)] [Department of Physics, Soochow University, Taipei, Taiwan, ROC (China)

2013-02-15

166

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

SciTech Connect

Oxidation state is a powerful concept that is widely used in chemistry and materials physics, although the concept itself is arguably ill-defined quantum mechanically. In this work, we present impartial comparison of four, well-recognized theoretical approaches based on Lowdin atomic orbital projection, Bader decomposition, maximally localized Wannier function, and occupation matrix diagonalization, for assessing how well transition metal oxidation states can be characterized. Here, we study a representative molecular complex, tris(bipyridine)ruthenium. We also consider the influence of water solvation through first-principles molecular dynamics as well as the improved electronic structure description for strongly correlated d-electrons by including Hubbard correction in density functional theory calculations.

Reeves, Kyle G. [Department of Chemistry, University of North Carolina at Chapel Hill, North Carolina 27599-3290 (United States); Kanai, Yosuke, E-mail: ykanai@unc.edu [Department of Chemistry, University of North Carolina at Chapel Hill, North Carolina 27599-3290 (United States); Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, California, 94550 (United States)

2014-07-14

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

A Theoretical Model of Pyramidal InAs/inP Quantum Dots  

NASA Astrophysics Data System (ADS)

A quantum dot is an atomic-like system consisting of a semiconductor nanoparticle surrounded by an insulator. When an electron in the valence band of the semiconductor becomes excited, the electron-hole pair that is created (called an exiton) acts much like a hydrogen atom. Investigations have demonstrated the potential application of quantum dots for optical switching and optical memory. A model of a truncated pyramidal InAs quantum dot in an InP matrix will be presented and described. The model uses a single band envelope theory that accurately describes the truncated pyramidal shape of the dot. The matrix representation of the Hamiltonian is calculated in a basis consisting of kinetic energy eigenfunctions that vanish on the surface of a cube containing the dot. The eigenvalues of this matrix are the energy levels. These results will then be compared with photoluminescence measurements of energy levels conducted at the Microelectronics-Photonics Center at the University of Arkansas - Fayetteville

Alford, Brian

2002-03-01

169

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

170

A discussion of theoretical ionization equilibrium calculations based on solar flare X-ray spectra  

NASA Technical Reports Server (NTRS)

Several sets of ionization equilibrium calculations exist for use in interpreting X-ray and EUV spectra of astrophysical plasmas. In particular, the calculations of Jordan (1969, 1970), Jacobs et al. (1977, 1978) and Summers (1974) are well known. The temperatures of maximum fractional abundance calculated by Summers for the more highly ionized and heavier elements such as iron are about a factor of two higher than the temperatures calculated by Jordan and Jacobs et al. By the use of recently obtained X-ray spectra of solar flares, it is shown that the temperatures calculated by Summers (1974) for iron are incorrect. The temperatures calculated by Jordan or Jacobs et al. should be used until further improvements become available.

Feldman, U.; Doschek, G. A.; Cowan, R. D.

1981-01-01

171

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

NASA Technical Reports Server (NTRS)

The Cassini Imaging Science System (ISS) has been returning images of Titan, along with other Saturnian satellites. Images taken through the 938 nm methane window see down to Titan's surface. One of the purposes of the Cassini mission is to investigate possible fluid cycling on Titan. Lemniscate features shown recently and radar evidence of surface flow prompted us to consider theoretically the creation by methane fluid flow of streamlined forms on Titan. This follows work by other groups in theoretical consideration of fluid motion on Titan's surface.

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

2005-01-01

172

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

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

Equation of State of Al Based on Quantum Molecular Dynamics Calculations  

NASA Astrophysics Data System (ADS)

In this work, we present quantum molecular dynamics calculations of the shock Hugoniots of solid and porous samples as well as release isentropes and values of isentropic sound velocity behind the shock front for aluminum. We use the VASP code with an ultrasoft pseudopotential and GGA exchange-correlation functional. Up to 108 particles have been used in calculations. For the Hugoniots of Al we solve the Hugoniot equation numerically. To calculate release isentropes, we use Zel'dovich's approach and integrate an ordinary differential equation for the temperature thus restoring all thermodynamic parameters. Isentropic sound velocity is calculated by differentiation along isentropes. The results of our calculations are in good agreement with experimental data. Thus, quantum molecular dynamics results can be effectively used for verification or calibration of semiempirical equations of state under conditions of lack of experimental information at high energy densities.

Minakov, Dmitry V.; Levashov, Pavel R.; Khishchenko, Konstantin V.

2011-06-01

176

QLib - A Matlab Package for Quantum Information Theory Calculations with Applications  

E-print Network

Developing intuition about quantum information theory problems is difficult, as is verifying or ruling-out of hypothesis. We present a Matlab package intended to provide the QIT community with a new and powerful tool-set for quantum information theory calculations. The package covers most of the "QI textbook" and includes novel parametrization of quantum objects and a robust optimization mechanism. New ways of re-examining well-known results is demonstrated. QLib is designed to be further developed and enhanced by the community and is available for download at www.qlib.info

Shai Machnes

2007-08-03

177

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

178

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

179

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

180

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

2014-07-10

181

Quantum dynamics study of the Cl+D2 reaction: Time-dependent wave packet calculations  

NASA Astrophysics Data System (ADS)

The quantum dynamics of the Cl+D2 reaction has been studied by means of time-dependent quantum wave packet calculations on the G3 and BW2 potential energy surfaces. Initial state-specific total reaction probabilities and integral cross sections are calculated, and the thermal rate constant is obtained. On the G3 surface, the effect of the reagent's rotational excitation on the reactivity is negative, while on the BW2 surface, the rotation of reagent has positive effect on the reactivity. Comparison of the thermal rate constants on the G3 and BW2 surfaces with experimental measurement is shown.

Yang, Ben-Hui; Tang, Bi-Yu; Yin, Hong-Ming; Han, Ke-Li; Zhang, John Z. H.

2000-11-01

182

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

183

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

184

Scaled Quantum Mechanical scale factors for vibrational calculations using alternate polarized and augmented basis sets with the B3LYP density functional calculation model.  

PubMed

The Scaled Quantum Mechanical (SQM) method of scaling calculated force constants to predict theoretically calculated vibrational frequencies is expanded to include a broad array of polarized and augmented basis sets based on the split valence 6-31G and 6-311G basis sets with the B3LYP density functional. Pulay's original choice of a single polarized 6-31G(d) basis coupled with a B3LYP functional remains the most computationally economical choice for scaled frequency calculations. But it can be improved upon with additional polarization functions and added diffuse functions for complex molecular systems. The new scale factors for the B3LYP density functional and the 6-31G, 6-31G(d), 6-31G(d,p), 6-31G+(d,p), 6-31G++(d,p), 6-311G, 6-311G(d), 6-311G(d,p), 6-311G+(d,p), 6-311G++(d,p), 6-311G(2d,p), 6-311G++(2d,p), 6-311G++(df,p) basis sets are shown. The double d polarized models did not perform as well and the source of the decreased accuracy was investigated. An alternate system of generating internal coordinates that uses the out-of plane wagging coordinate whenever it is possible; makes vibrational assignments via potential energy distributions more meaningful. Automated software to produce SQM scaled vibrational calculations from different molecular orbital packages is presented. PMID:25766474

Legler, C R; Brown, N R; Dunbar, R A; Harness, M D; Nguyen, K; Oyewole, O; Collier, W B

2015-06-15

185

Methacrolein in the IR Atmospheric Window: Mm-Wave and FTIR Spectroscopies Complemented by Quantum Calculations  

NASA Astrophysics Data System (ADS)

Methacrolein, CH_2=C(CH_3)CHO or MAC, is an important atmospheric molecule because it is a major product of the isoprene-OH reaction. Meanwhile the spectroscopic information on MAC is very scarse. On the theoretical side, we have performed quantum calculations at different levels of theory (DFT and ab initio) to model the structure of the two conformers, the large amplitude motion associated with the methyl top, and the anharmonic vibrational structure. On the experimental side, we have at first characterized the millimeter-wave spectrum of MAC in the 150-465 GHz range using the Lille frequency multiplication chain spectrometer. In particular the ground state has been analyzed up to J, K_a = 37, 17 and the first excited states are currently investigated. Secondly, FTIR spectra have been recorded on the AILES beamline of SOLEIL using a long path cell, between 30 and 3500 wn at medium resolution (0.5 wn). A few bands of atmospheric interest have also been recorded at higher resolution (0.001 wn). We will report the details of the vibrational analysis, as well as the molecular parameters derived from the analysis of the high resolution spectrum of the c-type band located around 930 wn. Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged. The experiment on the AILES beam-line of the synchrotron SOLEIL was performed under project number 20130192. M. Suzuki and K. Kozima, J. Molec. Spectrosc. 38 (1971) 314 J. R. Durig, J. Qiu, B. Dehoff and T. S. Little, Spectrochimica Acta 42A (1986) 89

Zakharenko, Olena; Aviles Moreno, Juan-Ramon; Imane, Haykal; Motiyenko, R. A.; Huet, T. R.; Pirali, Olivier

2014-06-01

186

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

NASA Astrophysics Data System (ADS)

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.; Birattari, C.; Bonardi, M. L.; Groppi, F.; Morzenti, S.; Zona, C.

2005-05-01

187

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...

188

Theoretical calculations of dielectronic recombination in crossed electric and magnetic fields  

Microsoft Academic Search

Recently, Robicheaux and Pindzola [Phys. Rev. Lett. 79, 2237 (1997)] reported on model calculations of dielectronic recombination (DR) in the presence of crossed electric and magnetic fields. They showed that the enhancement of the DR by an electric field may be increased further when a magnetic field perpendicular to the electric field is present in the collision region. In this

D. C. Griffin; F. Robicheaux; M. S. Pindzola

1998-01-01

189

Theoretical calculations of dielectronic recombination in crossed electric and magnetic fields  

Microsoft Academic Search

Recently, Robicheaux and Pindzola [Phys. Rev. Lett. {bold 79}, 2237 (1997)] reported on model calculations of dielectronic recombination (DR) in the presence of crossed electric and magnetic fields. They showed that the enhancement of the DR by an electric field may be increased further when a magnetic field perpendicular to the electric field is present in the collision region. In

D. C. Griffin; F. Robicheaux; M. S. Pindzola

1998-01-01

190

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

191

Quantum chemical calculations and experimental studies of third-order nonlinear optical properties of conjugated TTF-quinones  

NASA Astrophysics Data System (ADS)

To investigate microscopic third-order nonlinear optical (NLO) behaviour of two tetrathiafulvalene (TTF) derivatives, TTF-diquinone triad (1) and TTF-monoquinone dyad (2), we have computed both dispersion-free and also dispersion of dipole polarizabilities (?) and third-order hyperpolarizabilities (?) at 532 nm wavelength using time-dependent Hartree-Fock (TDHF) method. The one-photon absorption (OPA) characterizations of the title molecules have been theoretically obtained by means of configuration interaction (CI) method with all doubly occupied molecular orbitals. We have also calculated the dynamic third-order susceptibilities (?(3)) using the TDHF method. Our theoretical results on the maximum OPA wavelengths, third-order susceptibilities and corresponding microscopic NLO responses are in good agreement with the previous experimental observations of the examined TTF-based molecules. The highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO) and the HOMO-LUMO band gaps for 1 and 2 have been evaluated by density functional theory (DFT) quantum mechanical calculations at B3LYP/6-31G(d, p) level.

Karakas, A.; Migalska-Zalas, A.; El Kouari, Y.; Gozutok, A.; Karakaya, M.; Touhtouh, S.

2013-11-01

192

Phenol-benzene complexation dynamics: Quantum chemistry calculation, molecular dynamics simulations, and two dimensional IR spectroscopy  

E-print Network

Phenol-benzene complexation dynamics: Quantum chemistry calculation, molecular dynamics simulations the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/CCl4. Under thermal used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level

Fayer, Michael D.

193

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

E-print Network

Accurate quantum Monte Carlo calculations for hydrogen fluoride and the fluorine atom Arne Lu state energies of the fluorine atom and the hydrogen fluoride molecule have been carried out using both the remaining part of the correlation energy, the nodal error, is of the order of 10 kcal mol 1 for hydrogen

Anderson, James B.

194

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

195

Application of vibrational spectroscopy supported by theoretical calculations in identification of amorphous and crystalline forms of cefuroxime axetil.  

PubMed

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

Talaczy?ska, Alicja; Lewandowska, Kornelia; Jeli?ska, Anna; Garbacki, Piotr; Podborska, Agnieszka; Zalewski, Przemys?aw; Oszczapowicz, Irena; Sikora, Adam; Kozak, Maciej; Cielecka-Piontek, Judyta

2015-01-01

196

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

SciTech Connect

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

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

2001-06-13

197

Theoretical calculation and structural studies for a new nitrogen derivative from nor-lapachol  

NASA Astrophysics Data System (ADS)

Nor-lapachol is a semi-synthetic naphthoquinone obtained by oxidative degradation from natural lapachol. This compound and its derivatives have been investigated for its interesting biological properties. Several naphthoquinone derivatives have been synthesized and characterized using different physicochemical and computational techniques, as such DFT, MM, spectroscopy and X-ray crystallography. Here, the structure of 2-methylamine-3-(2-methyl-1-propenyl-1-yl)-1,4-naphthoquinone was determined by X-ray crystallography and the geometry was optimized using B3LYP functional along with the 6-31G(d) basis set, which was also used in all calculations. The obtained results were compared with the structure determined experimentally, and both structures showed high similarity. Besides, some molecular properties of this compound were also calculated by using DFT as well as Hirschfeld surface.

Santos, Jademilson Celestino dos; de França, José Adonias A.; do Nascimento Aquino, Lucas E.; Pereira, Mariano Alves; Mafud, Ana Carolina; Amorim Camara, Celso; Malta, Valéria R. Santos; Honório, Káthia Maria

2014-02-01

198

Conformational property of carvone as studied by laser-jet spectroscopy and theoretical calculations  

NASA Astrophysics Data System (ADS)

The (1+1) resonance enhanced multiphoton ionization (REMPI) spectrum of carvone was measured in the supersonic free jet. In the low vibrational energy region, transitions arising from the internal rotation of isopropenyl group that causes the conformational variation were observed. With the aid of the MP2 and CIS calculations, the peak positions were assigned and it was found that this compound has three stable conformers in the S 0 electronic state.

Mineyama, Masahiro; Egawa, Toru

2005-01-01

199

Theoretical calculations of ion acceleration in the vicinity of comet Giacobini-Zinner  

NASA Technical Reports Server (NTRS)

Ionization of cometary neutral molecules produces ions which are picked up by the solar wind. The cometary ion pickup process for comet Giacobini-Zinner is studied in two ways: (1) with a test particle method in which trajectories are numerically calculated for several thousand ions whose initial locations were chosen randomly with probability proportional to the neutral density and (2) with a quasi-linear diffusion model. The cometary ion distribution function was calculated with the test particle model at several locations upstream of the bow shock and for several types of magnetic fluctuations (or waves). These waves were allowed to propagate in both directions along the magnetic field at the Alfven speed. Both pitch angle scattering and energy diffusion are evident in the derived ion distributions. The monochromatic waves result in less ion acceleration than turbulent fluctuations with about the same amplitude. The calculated ion distribution functions are in reasonable agreement with the distributions measured in the vicinity of comet Giacobini-Zinner in 1985 by particle detectors on the ICE spacecraft when the ratio of power in sunward propagating Alfven waves to the power in antisunward propagating waves is assumed to lie between about 20% and 50%. However, the quasi-linear diffusion model results agree best with the measured distribution functions when the power ratio is only about 3 percent.

Mckenzie, M. L.; Cravens, T. E.; Ye, G.

1994-01-01

200

Crystal structures and theoretical calculations of two peculiar compounds derived from 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one  

NASA Astrophysics Data System (ADS)

A potassium coordination polymer [K2(PMBP)2(H2O)3]n·2nH2O (1) was prepared by reaction of 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (HPMBP) with potassium hydroxide. The single crystal of the supermolecule C6H11NH3+·PMBP- (2) was then obtained by utilizing cyclohexylamine as the proton acceptor. It is a diketonate salt with an organic base where the PMBP- anions are stabilized by the intermolecular weak interactions (including hydrogen bonding, ?-? stacking interactions and Van der Waals forces), rather than by coordination to a metal centre. Geometrical parameters of the isolated PMBP- anion were optimized through quantum chemistry calculation to simulate the state without any disturbances or interactions. Comparison of geometric parameters of compound 1 with the optimized structure of PMBP- provides an approach to study weak intermolecular interactions in the crystal state. The coordination sites and the proton acceptors of hydrogen bonds predicted by theoretical calculations are consistent to the experimental results.

Yan, Xingchen; Wu, Xiaojing; Xu, Jiakun; Fan, Yuhua; Bi, Caifeng; Zhang, Xia; Zhang, Zhongyu

2014-09-01

201

An efficient synthetic method and theoretical calculations of olmesartan methyl ether: study of biological function of AT1 antagonism.  

PubMed

The dissolution of the antihypertensive AT1 antagonist olmesartan in methanol generates in situ a new highly bioactive methyl ether analogue via SN1 mechanism involving an intramolecular proton transfer from carboxyl to hydroxyl group. Theoretical calculations confirmed the thermodynamic control preference of methyl ether versus the antagonistic product methyl ester. ? facile synthetic method for olmesartan methyl ether from olmesartan or olmesartan medoxomil is also described. Interestingly, the introduction of the methyl group to olmesartan did not alter its pharmacological properties. This observation opens new avenues in the synthesis of novel drugs, since hydroxyl and carboxylate groups have an orthogonal relationship in many drugs. PMID:24875271

Ntountaniotis, Dimitrios; Agelis, George; Resvani, Amalia; Halabalaki, Maria; Liapakis, George; Spyridaki, Katerina; Grdadolnik, Simona Golic; Merzel, Franci; Kostidis, Sarantos; Potamitis, Constantinos; Tselios, Theodore; Matsoukas, John; Skaltsounis, Leandros Alexios; Mavromoustakos, Thomas

2014-01-01

202

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

NASA Astrophysics Data System (ADS)

From the 1930s to the 1950s, a period of pivotal developments in quantum, nuclear, and particle physics, physicists at Niels Bohr's Institute for Theoretical Physics in Copenhagen took time off from their research to write humorous articles, letters, and other works. Best known is the Blegdamsvej Faust, performed in April 1932 at the close of one of the Institute's annual conferences. I also focus on the Journal of Jocular Physics, a humorous tribute to Bohr published on the occasions of his 50th, 60th, and 70th birthdays in 1935, 1945, and 1955. Contributors included Léon Rosenfeld, Victor Weisskopf, George Gamow, Oskar Klein, and Hendrik Casimir. I examine their contributions along with letters and other writings to show that they offer a window into some issues in physics at the time, such as the interpretation of complementarity and the nature of the neutrino, as well as the politics of the period.

Halpern, Paul

2012-09-01

203

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

NASA Technical Reports Server (NTRS)

Solar chromospheric models are described. The models included are based on the observed spectrum, and on the assumption of hydrostatic equilibrium. The calculations depend on realistic solutions of the radiative transfer and statistical equilibrium equations for optically thick lines and continua, and on including the effects of large numbers of lines throughout the spectrum. Although spectroheliograms show that the structure of the chromosphere is highly complex, one-dimensional models of particular features are reasonably successful in matching observed spectra. Such models were applied to the interpretation of chromospheric observations.

Avrett, E. H.

1985-01-01

204

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

205

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

206

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

NASA Technical Reports Server (NTRS)

Calculated results based on two chromospheric flare models F1 and F2 of Machado, et al., (1980) are presented. Two additional models are included: F1*, which has enhanced temperatures relative to the weak-flare model F1 in the upper photosphere and low chromosphere, and F3 which has enhanced temperatures relative to the strong flare model F2 in the upper chromosphere. Each model is specified by means of a given variation of the temperature as a function of column mass. The corresponding variation of particle density and the geometrical height scale are determined by assuming hydrostatic equilibrium. The coupled equations of statistical equilibrium is solved as is radiative transfer for H, H-, He I-II, C I-IV, Si I-II, Mg I-II, Fe, Al, O I-II, Na, and Ca II. The overall absorption and emission of radiation by lines throughout the spectrum is determined by means of a reduced set of opacities sampled from a compilation of over 10 to the 7th power individual lines. That the white flight flare continuum may arise by extreme chromospheric overheating as well as by an enhancement of the minimum temperature region is also shown. The radiative cooling rate calculations for our brightest flare model suggest that chromospheric overheating provides enhanced radiation that could cause significant heating deep in the flare atmosphere.

Avrett, E. H.

1986-01-01

207

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

NASA Astrophysics Data System (ADS)

Calculated results based on two chromospheric flare models F1 and F2 of Machado, et al., (1980) are presented. Two additional models are included: F1*, which has enhanced temperatures relative to the weak-flare model F1 in the upper photosphere and low chromosphere, and F3 which has enhanced temperatures relative to the strong flare model F2 in the upper chromosphere. Each model is specified by means of a given variation of the temperature as a function of column mass. The corresponding variation of particle density and the geometrical height scale are determined by assuming hydrostatic equilibrium. The coupled equations of statistical equilibrium is solved as is radiative transfer for H, H-, He I-II, C I-IV, Si I-II, Mg I-II, Fe, Al, O I-II, Na, and Ca II. The overall absorption and emission of radiation by lines throughout the spectrum is determined by means of a reduced set of opacities sampled from a compilation of over 10 to the 7th power individual lines. That the white flight flare continuum may arise by extreme chromospheric overheating as well as by an enhancement of the minimum temperature region is also shown. The radiative cooling rate calculations for our brightest flare model suggest that chromospheric overheating provides enhanced radiation that could cause significant heating deep in the flare atmosphere.

Avrett, E. H.

1986-02-01

208

Sinc wavepackets : a new form of wave packet for time-dependent quantum mechanical reactive scattering calculations  

Microsoft Academic Search

A new form of wave packet, the sinc wave packet, is defined. The wave packet has some advantages for use in time-dependent quantum mechanical reactive scattering calculations. These advantages consist of the fact that it possesses a reasonable constant amplitude over a range of momenta or energies. Quantum mechanical calculations undertaken using such a wave packet will therefore result in

Marlies Hankel; Gabriel G. Balint-Kurti; Stephen K. Gray

2003-01-01

209

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

210

Field theoretic calculation of renormalized-viscosity, renormalized-resistivity, and energy fluxes of magnetohydrodynamic turbulence  

E-print Network

A self-consistent renormalization (RG) scheme has been applied to nonhelical magnetohydrodynamic turbulence with zero cross helicity. Kolmogorov's 5/3 powerlaw has been shown to be a consistent solution for $d \\ge d_c \\approx 2.2$. For Kolmogorov's solution, both renormalized viscosity and resistivity are positive for the whole range of parameters. Various cascade rate and Kolmogorov's constant for MHD turbulence have been calculated by solving the flux equation to the first order in perturbation series. We find that the magnetic energy cascades forward. The Kolmogorov's constant for $d=3$ does not vary significantly with $r_A$ and is found to be close to the constant for fluid turbulence.

Mahendra K. Verma

2001-09-03

211

Theoretical method for calculating relative joint geometry of assembled robot arms  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

212

[Synthesis, characterization, spectroscopy and theoretical calculation of two novel carbazole derivatives].  

PubMed

Two novel carbazole derivatives, 3-acetyl-9-n-hexylcarbazole (AHCZ) and 3, 6- diacetyl-9-n-hexylcarbazole (DHCZ) were synthesized through Friedel-Crafts reaction. The compounds were characterized by IR spectra, 1H NMR, MS and elemental analysis. UV-visible spectra of AHCZ and DHCZ were measured and compared with those of their precursors, 9-hexylcarbazole(HCZ) and carbazole(CZ). DHCZ and AHCZ exhibited strong absorption band, revealing the extent of pi conjugation in the system. TD-DFT method was performed to analyze the electronic absorption spectra of AHCZ and DHCZ, and the calculated excitation energies and oscillator strengths were compared with the experimental results. PMID:18619321

Yang, Lin; Zhao, Xiang-Hua; Li, Zun-Yun; Deng, Chong-Hai; Shao, Guo-Quan; Wu, Jie-Ying; Tian, Yu-Peng

2008-04-01

213

Band-theoretic calculations of the optical-activity tensor of ?-quartz and trigonal Se  

NASA Astrophysics Data System (ADS)

We present a formalism to compute the optical-activity tensor in the long-wavelength limit neglecting local-field corrections with a nearly first-principles approach. The calculation of optical activity requires perturbation theory in the vector potential in order to describe the rotation of the plane of polarization perpendicular to the direction of propagation. We contrast this approach with perturbation theory in the scalar potential which can be used for the other optical response properties we compute. Band structures are obtained within the Kohn-Sham local-density approximation using standard plane-wave and separable norm-conserving pseudopotential techniques. Self-energy effects necessary to obtain the correct band gap are included by the use of a ``scissors operator.'' In the long-wavelength limit, two components of the optical-activity tensor are computed for both selenium and ?-quartz. For selenium in the low-frequency range, the optical rotatory power along the optic axis is about a factor of 2 too small compared with some of the experimental data. For ?-quartz, the ratio g11/g33 and the frequency dependence of both components obey the phenomenological coupled-oscillator model and are in agreement with experiment. Yet both g11 and g33 (or the optical rotatory power) are about a factor of 5 too small compared with the available experimental data. In addition, the dielectric constants and second-harmonic-generation susceptibilities including local-field corrections are calculated for selenium and ?-quartz in terms of scalar-potential theory. Excellent agreement (discrepancies of a few percent) is obtained with the experiments for these properties.

Zhong, Hua; Levine, Zachary H.; Allan, Douglas C.; Wilkins, John W.

1993-07-01

214

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

215

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

216

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

217

Analysis and calculation of electronic properties and light absorption of defective sulfur-doped silicon and theoretical photoelectric conversion efficiency.  

PubMed

Most material properties can be traced to electronic structures. Black silicon produced from SF6 or sulfur powder via irradiation with femtosecond laser pulses displays decreased infrared absorption after annealing, with almost no corresponding change in visible light absorption. The high-intensity laser pulses destroy the original crystal structure, and the doping element changes the material performance. In this work, the structural and electronic properties of several sulfur-doped silicon systems are investigated using first principle calculations. Depending on the sulfur concentration (level of doping) and the behavior of the sulfur atoms in the silicon lattice, different states or an absence of states are exhibited, compared with the undoped system. Moreover, the visible-infrared light absorption intensities are structure specific. The results of our theoretical calculations show that the conversion efficiency of sulfur-doped silicon solar cells depends on the sulfur concentrations. Additionally, two types of defect configurations exhibit light absorption characteristics that differ from the other configurations. These two structures produce a rapid increase in the theoretical photoelectric conversion efficiency in the range of the specific chemical potential studied. By controlling the positions of the atomic sulfur and the sulfur concentration in the preparation process, an efficient photovoltaic (PV) material may be obtainable. PMID:25798659

Jiang, He; Chen, Changshui

2015-04-23

218

Characterizing attractors using local intrinsic dimensions calculated by singular-value decomposition and information-theoretic criteria  

NASA Astrophysics Data System (ADS)

An algorithm to estimate the average local intrinsic dimension () of an attractor using signal versus noise separation methods based on information-theoretic criteria is explored in this work. Using noisy sample data the is computed from an eigenanalysis of local attractor regions, indicating the local orthogonal directions along which the data are clustered. The algorithm requires the separation of signal eigenvalues, i.e., the dominant eigenvalues, from the noise eigenvalues for which thresholding mechanisms based on two information-theoretic criteria are used. Singular-value decomposition is used to calculate the eigenvalues as well as to determine the rank of the local-phase-space data matrix. The two specific information-theoretic criteria which we consider to separate signal and noise are the Akaike information criterion (AIC) [H. Akaike, IEEE Trans. Auto. Control 19, 716 (1974)] and the minimum description length (MDL) of Rissanen [Automatica 14, 465 (1978)] and Schwarz [Ann. Stat. 6, 461 (1978)]. Several test cases are presented demonstrating the use of the AIC and MDL to calculate . Results are then compared to the correlation dimension as computed by the Grassberger-Procaccia method [Physica D9, 189 (1983)]. The AIC and MDL separation techniques are found to be inappropriate at higher signal-to-noise ratios (SNR), above ~12 dB, and the MDL produces results in good overall agreement with the accepted correlation dimension in the range of SNR between 5 and 12 dB. Two of the primary benefits of the technique are that it will yield reasonable and fairly accurate estimates of the dimension of attractors and that it can probe small length scales on the attractor even for moderate SNR. Other thresholding schemes are being pursued for SNR's above 12 dB.

Hediger, T.; Passamante, A.; Farrell, Mary Eileen

1990-05-01

219

A Comparison of Three Theoretical Methods of Calculating Span Load Distribution on Swept Wings  

NASA Technical Reports Server (NTRS)

Three methods for calculating span load distribution, those developed by V.M Falkner, Wm. Mutterperl, and J. Weissinger, have been applied to five swept wings. The angles of sweep ranged from -45 degrees to +45 degrees. These methods were examined to establish their relative accuracy and case of application. Experimentally determined loadings were used as a basis for judging accuracy. For the convenience of the readers the computing forms and all information requisite to their application are included in appendixes. From the analysis it was found that the Weissinger method would be best suited to an over-all study of the effects of plan form on the span loading and associated characteristics of wings. The method gave good, but not best, accuracy and involved by far the least computing effort. The Falkner method gave the best accuracy but at a considerable expanse in computing effort and hence appeared to be most useful for a detailed study of a specific wing. The Mutterperl method offered no advantages in accuracy of facility over either of the other methods and hence is not recommended for use.

VanDorn, Nicholas H.; DeYoung, John

1947-01-01

220

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

E-print Network

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

Hamolli, L; Nucita, A A

2014-01-01

221

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

PubMed Central

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

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

2013-01-01

222

Field theoretic calculation of energy cascade rates in nonhelical magnetohydrodynamic turbulence  

E-print Network

Energy cascade rates and Kolmogorov's constant for nonhelical steady magnetohydrodynamic turbulence have been calculated by solving the flux equations to the first order in perturbation. For zero cross helicity and space dimension $d=3$, magnetic energy cascades from large length-scales to small length-scales (forward cascade). In addition, there are energy fluxes from large-scale magnetic field to small-scale velocity field, large-scale velocity field to small-scale magnetic field, and large-scale velocity field to large-scale magnetic field. Kolmogorov's constant for magnetohydrodynamics is approximately equal to that for fluid turbulence ($\\approx 1.6$) for Alfv\\'{e}n ratio $0.5 \\le r_A \\le \\infty$. For higher space-dimensions, the energy fluxes are qualitatively similar, and Kolmogorov's constant varies as $d^{1/3}$. For the normalized cross helicity $\\sigma_c \\to 1$, the cascade rates are proportional to $(1-\\sigma_c)/ (1+\\sigma_c)$, and the Kolmogorov's constants vary significantly with $\\sigma_c$.

Mahendra K. Verma

2004-04-25

223

Theoretical calculation of the gas-sensing properties of Pt-decorated carbon nanotubes.  

PubMed

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

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

2013-01-01

224

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

E-print Network

boundary crystal lattice. A quantum dot (QD) is therefore a giant artificial atom which enjoys prospects on their dimensionality, these structures are called quantum dots (0D), quantum wires (1D) or quantum wells (2D structure. In fact, they contain a finite number of elementary charge carriers (from a few to a hundred

Paris-Sud XI, Université de

225

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

226

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

227

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

NASA Astrophysics Data System (ADS)

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

Gaur, A.; Shrivastava, B. D.

2014-09-01

228

Theoretical calculations for structural, elastic, and thermodynamic properties of RuN{sub 2} under high pressure  

SciTech Connect

The structural and elastic properties of RuN{sub 2} were investigated through the first-principles calculation using generalized gradient approximation (GGA) and local density approximation (LDA) within the plane-wave pseudopotential density functional theory. The obtained equilibrium structure and mechanical properties are in excellent agreement with other theoretical results. Then we compared the elastic modulus of RuN{sub 2} with several other isomorphic noble metal nitrides. Results show that RuN{sub 2} can nearly rival with OsN{sub 2} and IrN{sub 2}, which indicate RuN{sub 2} is a potentially ultra-incompressible and hard material. By the elastic stability criteria, it is predicted that RuN{sub 2} is stable in our calculations (0–100?GPa). The calculated B/G ratios indicate that RuN{sub 2} possesses brittle nature at 0?GPa and when the pressure increases to 13.4?GPa (for LDA) or 20.8?GPa (for GGA), it begins to prone to ductility. Through the quasi-harmonic Debye model, we also investigated the thermodynamic properties of RuN{sub 2}.

Dong, Bing; Zhou, Xiao-Lin, E-mail: Zhouxl-wuli@163.com, E-mail: lkworld@126.com; Chang, Jing [College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610101 (China); Liu, Ke, E-mail: Zhouxl-wuli@163.com, E-mail: lkworld@126.com [College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610101 (China); Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China)

2014-08-07

229

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

230

Dynamical basis sets for algebraic variational calculations in quantum-mechanical scattering theory  

NASA Technical Reports Server (NTRS)

New basis sets are proposed for linear algebraic variational calculations of transition amplitudes in quantum-mechanical scattering problems. These basis sets are hybrids of those that yield the Kohn variational principle (KVP) and those that yield the generalized Newton variational principle (GNVP) when substituted in Schlessinger's stationary expression for the T operator. Trial calculations show that efficiencies almost as great as that of the GNVP and much greater than the KVP can be obtained, even for basis sets with the majority of the members independent of energy.

Sun, Yan; Kouri, Donald J.; Truhlar, Donald G.; Schwenke, David W.

1990-01-01

231

Asymptotic Quantum Search and a Quantum Algorithm for Calculation of a Lower Bound of the Probability of Finding a Diophantine Equation That Accepts Integer Solutions  

E-print Network

Several mathematical problems can be modeled as a search in a database. An example is the problem of finding the minimum of a function. Quantum algorithms for solving this problem have been proposed and all of them use the quantum search algorithm as a subroutine and several intermediate measurements are realized. In this work, it is proposed a new quantum algorithm for finding the minimum of a function in which quantum search is not used as a subroutine and only one measurement is needed. This is also named asymptotic quantum search. As an example, we propose a quantum algorithm based on asymptotic quantum search and quantum counting able to calculate a lower bound of the probability of finding a Diophantine equation with integer solution.

R. V. Ramos; J. L. de Oliveira

2008-10-07

232

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

233

A Theoretical Investigation Into Energy Transfer In Photosynthetic Open Quantum Systems  

E-print Network

This thesis looks at the electronic energy transfer in the Fenna-Matthews-Olson complex, in which evidence of long-lived coherence has been observed in 2-dimensional infrared experiments. I use three techniques: the numerically exact Hierarchical Equations of Motion, and the perturbative Redfield and Foerster theories, the latter of which ignores quantum coherence in the transfer. Both of the approximate methods perform very well - and while oscillations in site populations (a hallmark of coherence) are present in the exact transfer dynamics and absent in the dynamics of Foerster theory, the latter gives a reasonable prediction of transfer rates and steady-state populations, despite being incoherent - suggesting that coherence is not vital for the dynamics of transfer. Since Foerster theory is very inexpensive to run and performs so well, I then apply it to calculate the effects of static disorder in bacteriochlorophyll site energies and of a more structured spectral density. Ultimately, the energy transfer i...

Wilkins, David M

2015-01-01

234

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.

235

Theoretical studies of quantum amplified isomerizations for imaging systems involving hexamethyl Dewar benzene and related systems.  

PubMed

The ring-opening reactions of the radical cations of hexamethyl Dewar benzene (1) and Dewar benzene have been studied using density functional theory (DFT) and complete active-space self-consistent field (CASSCF) calculations. Compound 1 is known to undergo photoinitiated ring opening by a radical cation chain mechanism, termed "quantum amplified isomerization" (QAI), which is due to the high quantum yield. Why QAI is efficient for 1 but not other reactions is explained computationally. Two radical cation minima of 1 and transition states located near avoided crossings are identified. The state crossings are characterized by conical intersections corresponding to degeneracy between doublet surfaces. Ring opening occurs by formation of the radical cation followed by a decrease in the flap dihedral angle. A rate-limiting Cs transition state leads to a second stable radical cation with an elongated transannular C-C bond and an increased flap dihedral. This structure proceeds through a conrotatory-like pathway of Cs symmetry to give the benzene radical cation. The role of electron transfer was investigated by evaluating oxidation of various systems using adiabatic ionization energies and electron affinities calculated from neutral and cation geometries. Electron-transfer theory was applied to 1 to investigate the limiting effects of back-electron transfer as it is related to the unusual stability of the two radical cations. Expected changes in optical properties between reactants and products of Dewar benzene compounds and other systems known to undergo QAI were characterized by computing frequency-dependent indices of refraction from isotropic polarizabilities. In particular, the reaction of 1 shows greater contrast in index of refraction than that of the Dewar benzene parent system. PMID:16771497

Norton, Joseph E; Olson, Leif P; Houk, K N

2006-06-21

236

Calculator.  

ERIC Educational Resources Information Center

Five activities are presented in this student workbook on using the electronic calculator. Following the directions for using the machine, problems are given on multiplying and dividing, finding percentages, calculating the area of assorted polygons, changing fractions to decimals, and finding squares and square roots. (JH)

Parma City School District, OH.

237

Reactions of ti, zr, and hf atoms with hydrogen sulfide: argon matrix infrared spectra and theoretical calculations.  

PubMed

Laser-ablated Ti, Zr, and Hf atoms have been codeposited at 4 K with hydrogen sulfide in excess argon. The metal atoms insert into the S-H bond of hydrogen sulfide to form the HMSH, H2MS, and H2M(SH)2 molecules (M = Ti, Zr, Hf), which were identified on the basis of the D2S and H2(34)S isotopic substitutions. The observed vibrational frequencies of these species were reproduced by B3LYP functional calculations. The reaction mechanisms have been proposed on the potential energy surface of the studied system to account for the formation of these molecules. We have made a theoretical prediction about the H2MS complexes dehydrogenation, which can provide a novel proposal for generating hydrogen from H2S. PMID:25000436

Wang, Qiang; Zhao, Jie; Wang, Xuefeng

2015-03-19

238

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

239

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

NASA Astrophysics Data System (ADS)

The molecular structure and conformation of carvone, a compound with a minty odor, were investigated by means of gas electron diffraction supported by theoretical calculations. Electron diffraction patterns were recorded by heating the nozzle up to 128 °C to obtain enough scattering intensity. The infrared spectrum was also measured by using an absorption cell with a path length of 10 m. The obtained molecular scattering intensities were analyzed with the aid of theoretical calculations and infrared spectroscopy. It was revealed that the experimental data are well reproduced by assuming that carvone consists of a mixture of three conformers that have the isopropenyl group in the equatorial position and mutually differ in the torsional angle around the single bond connecting the ring and the isopropenyl group. It was also found that the puckering amplitude of the ring of carvone is close to those of menthol and isomenthol, a minty compound and its nonminty isomer. The determined structural parameters ( rg and ? ?) of the most abundant conformer of carvone are as follows: < r(C-C)>=1.520(3) Å; < r(C?C)>=1.360(5) Å; r(C?O)=1.225(5) Å; < r(C-H)>=1.104(4)Å; =121.1(5)°; =110.4(5)°; ?C-CO-C=117.1(14)°; =111.1(13)°. Angle brackets denote average values and parenthesized values are the estimated limits of error (3 ?) referring to the last significant digit.

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

2003-10-01

240

Electrostatic embedding in large-scale first principles quantum mechanical calculations on biomolecules  

NASA Astrophysics Data System (ADS)

Biomolecular simulations with atomistic detail are often required to describe interactions with chemical accuracy for applications such as the calculation of free energies of binding or chemical reactions in enzymes. Force fields are typically used for this task but these rely on extensive parameterisation which in cases can lead to limited accuracy and transferability, for example for ligands with unusual functional groups. These limitations can be overcome with first principles calculations with methods such as density functional theory (DFT) but at a much higher computational cost. The use of electrostatic embedding can significantly reduce this cost by representing a portion of the simulated system in terms of highly localised charge distributions. These classical charge distributions are electrostatically coupled with the quantum system and represent the effect of the environment in which the quantum system is embedded. In this paper we describe and evaluate such an embedding scheme in which the polarisation of the electronic density by the embedding charges occurs self-consistently during the calculation of the density. We have implemented this scheme in a linear-scaling DFT program as our aim is to treat with DFT entire biomolecules (such as proteins) and large portions of the solvent. We test this approach in the calculation of interaction energies of ligands with biomolecules and solvent and investigate under what conditions these can be obtained with the same level of accuracy as when the entire system is described by DFT, for a variety of neutral and charged species.

Fox, Stephen J.; Pittock, Chris; Fox, Thomas; Tautermann, Christofer S.; Malcolm, Noj; Skylaris, Chris-Kriton

2011-12-01

241

From quantum chemistry and the classical theory of polar liquids to continuum approximations in molecular mechanics calculations  

NASA Astrophysics Data System (ADS)

Biological macromolecules and other polymers belong to the class of mesoscopic systems, with characteristic length scale of the order of a nanometer. Although microscopic models would be the preferred choice in theoretical calculations, their use in computer simulations becomes prohibitive for large systems or long simulation times. On the other hand, the use of purely macroscopic models in the mesoscopic domain may introduce artifacts, with effects that are difficult to assess and that may compromise the reliability of the calculations. Here is proposed an approach with the aim of minimizing the empirical nature of continuum approximations of solvent effects within the scope of molecular mechanics (MM) approximations in mesoscopic systems. Using quantum chemical methods, the potential generated by the molecular electron density is first decomposed in a multicenter-multipole expansion around predetermined centers. The monopole and dipole terms of the expansion at each site create electric fields that polarize the surrounding aqueous medium whose dielectric properties can be described by the classical theory of polar liquids. Debye's theory allows a derivation of the dielectric profiles created around isolated point charges and dipoles that can incorporate Onsager reaction field corrections. A superposition of screened Coulomb potentials obtained from this theory makes possible a simple derivation of a formal expression for the total electrostatic energy and the polar component of the solvation energy of the system. A discussion is presented on the physical meaning of the model parameters, their transferability, and their convergence to calculable quantities in the limit of simple systems. The performance of this continuum approximation in computer calculations of amino acids in the context of an atomistic force field is discussed. Applications of a continuum model based on screened Coulomb potentials in multinanosecond simulations of peptides and proteins are briefly reviewed.

Hassan, Sergio A.; Mehler, Ernest L.

242

Quantum calculation of disordered length in fcc single crystals using channelling techniques  

NASA Astrophysics Data System (ADS)

Lattices of face-centred cubic crystals (fcc), due to irradiation processes, may become disordered in stable configurations like the dumb-bell configuration (DBC) or body-centred interstitial (BCI). In this work, a quantum mechanical treatment for the calculation of transmission coefficients of channelled positrons from their bound states in the normal lattice regions into the allowed bound states in the disordered regions is given as a function of the length of the disordered regions. In order to obtain more reliable results, higher anharmonic terms in the planar channelling potential are considered in the calculations by using first-order perturbation theory where new bound states have been found. The calculations were executed in the energy range 10 200 MeV of the incident positron on a copper single crystal in the planar direction (100).

Abu-Assy, M. K.

2006-04-01

243

Calculated surface, image and quantum well states in Ag/Cu(111) system  

NASA Astrophysics Data System (ADS)

The energy spectrum and the probability densities of the surface, the image and the quantum well (QW) states of the Ag/Cu(111) system have been calculated function of the thickness of the silver film. The layer by layer energy spectrum and probability densities of this system are obtained as a solution of the Schrödinger equation using the discrete variable representation (DVR). In this equation we have used an analytical one-dimensional model potential derived from the potential of Chulkov et al. [1]. Our calculated energy spectrum and probability densities of the surface, image and QW states present coverage dependence in agreement with the experiments and other calculations of the surface states.

Bejan, Doina

2013-09-01

244

The complete quantum collapse scenario of 2+1 dust shell: Preliminary Calculations  

E-print Network

If we consider the gravitational collapse of a material object to a black hole, we would expect, for ranges of mass where a black hole would form, the following scenario. A large enough object would collapse classically until an event horizon forms, and to an external observer the object would be lost fom view. However, once the horizon has formed the black hole will begin to emit Hawking radiation and the hole will lose mass and the horizon will shrink. The final state of this process could be either a zero-mass "black hole" with consequent information loss, or some sort of "quantum remnant. A complete investigation of this process would require: 1) A complete and consistent theory of quantum gravity coupled to some kind of field that would provide the Hawking radiation (which could be the gravitational field itself --gravitons); 2) Some kind of definition of a "horizon" in this quantum gravity, and; 3) The calculational tools to achieve a description of the scenario. Lacking these, one may resort to toy models to try to give some sort of preliminary answer. In this paper we will consider the collapse of an infinitesimally thin dust shell in 2+1 gravity, where an exact minisuperspace quantum solution exists, and try to make rough estimates of the collapse-Hawking radiation-remnant formation process.

L. Ortíz; M. P. Ryan Jr

2007-02-24

245

Quantum computing applied to calculations of molecular energies: CH2 benchmark.  

PubMed

Quantum computers are appealing for their ability to solve some tasks much faster than their classical counterparts. It was shown in [Aspuru-Guzik et al., Science 309, 1704 (2005)] that they, if available, would be able to perform the full configuration interaction (FCI) energy calculations with a polynomial scaling. This is in contrast to conventional computers where FCI scales exponentially. We have developed a code for simulation of quantum computers and implemented our version of the quantum FCI algorithm. We provide a detailed description of this algorithm and the results of the assessment of its performance on the four lowest lying electronic states of CH(2) molecule. This molecule was chosen as a benchmark, since its two lowest lying (1)A(1) states exhibit a multireference character at the equilibrium geometry. It has been shown that with a suitably chosen initial state of the quantum register, one is able to achieve the probability amplification regime of the iterative phase estimation algorithm even in this case. PMID:21090853

Veis, Libor; Pittner, Ji?í

2010-11-21

246

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

247

Calculation of the size-quantization levels in strained ZnCdSe\\/ZnSe quantum wells  

Microsoft Academic Search

The ZnSe and CdSe parameters required to calculate levels in ZnCdSe\\/ZnSe quantum wells are determined by fitting to published\\u000a data. The model is shown to be adequate for the example of structures with a collection of quantum wells whose thickness and\\u000a composition were determined by independent methods.

M. V. Maksimov; I. L. Krestnikov; S. V. Ivanov; N. N. Ledentsov; S. V. Sorokin

1997-01-01

248

Calculation of linear and nonlinear optical absorption coefficients of a spherical quantum dot with parabolic potential  

NASA Astrophysics Data System (ADS)

In the effective mass approximation, we calculated the binding energy and wave function for the 1s-, 1p-, 1d- and 1f-states of a spherical quantum dot (QD) with parabolic potential by using a combination of quantum genetic algorithm (QGA) and Hartree-Fock-Roothaan (HFR) method. In addition, we also investigated the linear and the third-order nonlinear optical absorption coefficients as a function of the incident photon energy for the 1s-1p, 1p-1d and 1d-1f transitions. Our results are shown that the existence of impurity has great influence on optical absorption coefficients. Moreover, the optical absorption coefficients are strongly affected by the incident optical intensity, relaxation time, parabolic potential and dot radius.

Yakar, Yusuf; Çak?r, Bekir; Özmen, Ayhan

2010-05-01

249

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

PubMed

We present a powerful Python library to quickly and efficiently generate realistic peptide model structures. The library makes it possible to quickly set up quantum mechanical calculations on model peptide structures. It is possible to manually specify a specific conformation of the peptide. Additionally the library also offers sampling of backbone conformations and side chain rotamer conformations from continuous distributions. The generated peptides can then be geometry optimized by the MMFF94 molecular mechanics force field via convenient functions inside the library. Finally, it is possible to output the resulting structures directly to files in a variety of useful formats, such as XYZ or PDB formats, or directly as input files for a quantum chemistry program. FragBuilder is freely available at https://github.com/jensengroup/fragbuilder/ under the terms of the BSD open source license. PMID:24688855

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

2014-01-01

250

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

PubMed Central

We present a powerful Python library to quickly and efficiently generate realistic peptide model structures. The library makes it possible to quickly set up quantum mechanical calculations on model peptide structures. It is possible to manually specify a specific conformation of the peptide. Additionally the library also offers sampling of backbone conformations and side chain rotamer conformations from continuous distributions. The generated peptides can then be geometry optimized by the MMFF94 molecular mechanics force field via convenient functions inside the library. Finally, it is possible to output the resulting structures directly to files in a variety of useful formats, such as XYZ or PDB formats, or directly as input files for a quantum chemistry program. FragBuilder is freely available at https://github.com/jensengroup/fragbuilder/ under the terms of the BSD open source license. PMID:24688855

Hamelryck, Thomas; Jensen, Jan H.

2014-01-01

251

Toward the quantum chemical calculation of nuclear magnetic resonance chemical shifts of proteins.  

PubMed

Despite the many protein structures solved successfully by nuclear magnetic resonance (NMR) spectroscopy, quality control of NMR structures is still by far not as well established and standardized as in crystallography. Therefore, there is still the need for new, independent, and unbiased evaluation tools to identify problematic parts and in the best case also to give guidelines that how to fix them. We present here, quantum chemical calculations of NMR chemical shifts for many proteins based on our fragment-based quantum chemical method: the adjustable density matrix assembler (ADMA). These results show that (13)C chemical shifts of reasonable accuracy can be obtained that can already provide a powerful measure for the structure validation. (1)H and even more (15)N chemical shifts deviate more strongly from experiment due to the insufficient treatment of solvent effects and conformational averaging. PMID:21557322

Frank, Andrea; Onila, Ionut; Möller, Heiko M; Exner, Thomas E

2011-07-01

252

Calculation of electric field and optical transitions in InGaN/GaN quantum wells  

NASA Astrophysics Data System (ADS)

We present analytical expressions for internal electric field and strain in single and multiple quantum wells, incorporating electromechanical coupling, spontaneous polarization, and periodic boundary conditions. Internal fields are typically 2% lower than the fields calculated using an uncoupled model. We point out two possible interpolation routes to calculate the piezoelectric (PZ) constants eij of an alloy from the PZ constants of the constituent materials and show that, for an In0.2Ga0.8N/GaN quantum well system, the respective internal electric fields differ by 10%. Using an effective-mass model, we explore the effect of the uncertainty in the elastic and PZ constants of GaN on the internal field and optical transitions of InGaN/GaN quantum wells, and find that the range of published values of eij produces an uncertainty of more than +/-20% in the internal field and of more than +/-30% in the blueshift in optical transition energy between zero bias and flatband conditions (when the applied field is equal and opposite to the internal field). Using the PZ constants of Shimada et al. [J. Appl. Phys. 84, 4951 (1998)] in our model gives the best fit to results in the literature for internal field and optical transition energy in InGaN/GaN quantum wells. We find that a well with a smooth In gradient along the growth direction has similar optical properties to a well with constant composition, if the average In content of the two wells is the same.

Christmas, Ursula M. E.; Andreev, A. D.; Faux, D. A.

2005-10-01

253

Path-integral virial estimator for reaction rate calculation basedon the quantum instanton aproximation  

SciTech Connect

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.

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

2005-11-28

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

Electric-field control of magnetism in graphene quantum dots: Ab initio calculations  

PubMed Central

Employing ab initio calculations we predict that the magnetic states of hydrogenated diamond-shaped zigzag graphene quantum dots (GQDs), each exhibiting unique electronic structure, can be selectively tuned with gate voltage, through Stark or hybridization electric-field modulation of the spatial distribution and energy of the spin-polarized molecular orbitals, leading to transitions between these states. Electrical read-out of the GQD magnetic state can be accomplished by exploiting the distinctive electrical properties of the various magnetic configurations. PMID:21765631

Agapito, Luis A.; Kioussis, Nicholas; Kaxiras, Efthimios

2011-01-01

256

Calculation of quantum resonance energies and lifetimes via quasi-minimum residual filter diagonalization  

NASA Astrophysics Data System (ADS)

The quasi-minimum residual (QMR) method of Freund [SIAM J. Sci. Stat. Comput. 13 (1992) 425] is applied to the problem of calculating quantum resonance energies and lifetimes via a filter diagonalization (FD) scheme. Using the HO 2 molecule as a test case, the resulting quasi-minimum residual filter diagonalization (QMRFD) algorithm is shown to be capable of accurately computing complex eigenvalues throughout the spectrum from a single Lanczos subspace. The algorithm is efficient, and requires the storage of only two complex vectors in the primary DVR representation. The quality of the FD results is verified by a comparison with resonance energies and linewidths obtained by fitting the spectral density profile.

Yu, Hua-Gen; Smith, Sean C.

1998-01-01

257

Playing the quantum shuffling game with programmable pocket calculators and microcomputers  

NASA Astrophysics Data System (ADS)

The utilisation of programmable calculators or microcomputers in the classroom for the quantum shuffling game may reinforce the study of statistical physics in unit 9 of the Nuffield advanced physics course since the students are themselves able to work out much more sophisticated applications of the game. Because of the higher speed of computation and the possibilities of graphical representation on the computer screen preference is given to the application of microcomputer games. Copies of the programs described may be obtained from Professor P J Black, Chelsea College Centre for Science Education, Bridges Place, London SW6 4HR or directly from the author at Tulpenweg 3, 6301 Linden, W Germany.

Sauer, G.

1981-03-01

258

A Comparison of Two Topos-Theoretic Approaches to Quantum Theory  

NASA Astrophysics Data System (ADS)

The aim of this paper is to compare the two topos-theoretic approaches to quantum mechanics that may be found in the literature to date. The first approach, which we will call the contravariant approach, was originally proposed by Isham and Butterfield, and was later extended by Döring and Isham. The second approach, which we will call the covariant approach, was developed by Heunen, Landsman and Spitters. Motivated by coarse-graining and the Kochen-Specker theorem, the contravariant approach uses the topos of presheaves on a specific context category, defined as the poset of commutative von Neumann subalgebras of some given von Neumann algebra. In particular, the approach uses the spectral presheaf. The intuitionistic logic of this approach is given by the (complete) Heyting algebra of closed open subobjects of the spectral presheaf. We show that this Heyting algebra is, in a natural way, a locale in the ambient topos, and compare this locale with the internal Gelfand spectrum of the covariant approach. In the covariant approach, a non-commutative C*-algebra (in the topos Set) defines a commutative C*-algebra internal to the topos of covariant functors from the context category to the category of sets. We give an explicit description of the internal Gelfand spectrum of this commutative C*-algebra, from which it follows that the external spectrum is spatial. Using the daseinisation of self-adjoint operators from the contravariant approach, we give a new definition of the daseinisation arrow in the covariant approach and compare it with the original version. States and state-proposition pairing in both approaches are compared. We also investigate the physical interpretation of the covariant approach.

Wolters, Sander A. M.

2013-01-01

259

Quantum Monte Carlo calculations of BiScO3 ferroelectric well-depths  

NASA Astrophysics Data System (ADS)

The perovskite (1-x) BiScO3-x PbTiO3 alloy has been reported as having a large piezoelectric properties. Density functional theory (DFT) using local density approximation (LDA) predicts an extraordinarily large ferroelectric well depths (about 1.2 eV) of the end point compound BiScO3. We perform quantum Monte Carlo calculations on BiScO3 to calculate these well depths. In our QMC method, the two-body terms coming from electron-electron interactions are decoupled using a Hubbard- Stratonovich transformation. The ground state is obtained from projection of an initial trial wave function by random walks in Slater determinant space. To control the sign/phase problem, a trial Slater determinant is used, which in our calculations is taken directly from the DFT calculations. We find in the QMC calculation large finite-size effects in the primitive cell, on the order of a few eV. We study these finite-size effects and explore several schemes to reduce them. R.E. Eitel, et al., Jpn. J. Appl. Phys., Part 1 40,5999 (2001) R.E. Eitel, et al., ibid. 41, 1 (2002) J. 'Iñiquez, D. Vanderbilt, L. Bellaiche, Phys. Rev B 67, 224107 (2003) S. Zhang, H. Krakauer, Phys. Rev. Lett 90, 136401 (2003)

Kwee, Hendra; Krakauer, Henry; Zhang, Shiwei

2006-03-01

260

Construction of environment states in quantum-chemical density-matrix renormalization group calculations.  

PubMed

The application of the quantum-chemical density-matrix renormalization group (DMRG) algorithm is cumbersome for complex electronic structures with many active orbitals. The high computational cost is mainly due to the poor convergence of standard DMRG calculations. A factor which affects the convergence behavior of the calculations is the choice of the start-up procedure. In this start-up step matrix representations of operators have to be calculated in a guessed many-electron basis of the DMRG environment block. Different possibilities for the construction of these basis states exist, and we first compare four procedures to approximate the environment states using Slater determinants explicitly. These start-up procedures are applied to DMRG calculations on a sophisticated test system: the chromium dimer. It is found that the converged energies and the rate of convergence depend significantly on the choice of the start-up procedure. However, since already the most simple start-up procedure, which uses only the Hartree-Fock determinant, is comparatively good, Slater determinants, in general, appear not to be a good choice as approximate environment basis states for convergence acceleration. Based on extensive test calculations it is demonstrated that the computational cost can be significantly reduced if the number of total states m is successively increased. This is done in such a way that the environment states are built up stepwise from system states of previous truncated DMRG sweeps for slowly increasing m values. PMID:16438563

Moritz, Gerrit; Reiher, Markus

2006-01-21

261

Theoretical modeling and calculations of molecular flow through carbon nanotubes and Sigma5 (310)[001] zirconium dioxide grain boundaries  

NASA Astrophysics Data System (ADS)

This thesis will discuss two theoretical studies. The first is molecular flow and separation of molecular mixtures inside carbon nanotubes while the second is an investigation of the structure and stability of 36° Sigma5 (310)[001] ZrO2 grain boundaries. Molecular dynamics simulations with many-body, atomistic, empirical models and geometry optimization with density functional theory were used in this study. For molecular fluids through carbon nanotubes, both one-component and binary systems were investigated at room temperature. Through this work, we systematically studied the mechanisms that control molecular flow inside carbon nanotubes. As a result, complete theoretical diffusive models were established for organic molecules that provide insight into how nanotube membranes may be used in ultrafiltration applications. Several factors are predicted to affect molecular flow over time. In the case of dynamic flow, the size (diameter) of the nanotubes, the molecular density of the molecular fluids, the type of molecules, and the rigidity of the nanotube walls are all shown to be important. In the case of diffusive flow, the size (diameter) of the nanotubes, molecular size and molecular shape are found to be important. Furthermore, the study shows that the type of atomic termination at the nanotube edge can have a significant effect on the diffusion of some molecules but almost no effect on others. Pore-pore correlations in bundles of carbon nanotubes are found to cause the diffusion velocities and coefficients/mobilities to decrease. For binary molecular fluids, the separation trends and diffusion behavior of binary molecular mixtures through carbon nanotubes and bundles were investigated. Molecular structure and the nanotube diameter are predicted to have large effects on the separation and diffusion behavior of the mixtures. The study also shows that the helical structure of the nanotube has no effect on the diffusion behavior of molecular mixtures. Different terminations of the carbon nanotubes also have little effect on the separation trends. In nanotube bundles, the diffusion behavior and coefficients of binary molecular systems are significantly different from the diffusion in individual nanotubes. In the second part of the thesis, density functional theory was employed to investigate the Sigma5 (310)[001] ZrO2 grain boundary. Five pure grain boundary models were constructed based on experimental data for this grain boundary and the model with the lowest energy was identified based on calculated interfacial energies. Then the lowest energy model was relaxed and the structure was compared with experimental Z-contrast image data. The study also included investigation of the stability of Y3+ doped ZrO2 grain boundaries to identify a possible doping pattern. This was accomplished by calculating substitution energies, segregation energies. The calculations indicate that doping along the boundaries will stabilize the grain boundary structure, but that doping the bulk ZrO2 will stabilize the grain boundary structure. Free volume calculations indicate that the grain boundaries are a more active area than the bulk which is why the Y3+ prefers to dope the large free space positions.

Mao, Zugang

2001-07-01

262

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

SciTech Connect

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 [Aix Marseille Univ, CNRS, IM2NP UMR 7334, 13384 Marseille (France)

2014-08-11

263

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

264

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

265

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

266

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

E-print Network

Graphics Processing Units (GPUs) are having a transformational effect on numerical lattice quantum chromodynamics (LQCD) calculations of importance in nuclear and particle physics. The QUDA library provides a package of mixed precision sparse matrix linear solvers for LQCD applications, supporting single GPUs based on NVIDIA's Compute Unified Device Architecture (CUDA). This library, interfaced to the QDP++/Chroma framework for LQCD calculations, is currently in production use on the "9g" cluster at the Jefferson Laboratory, enabling unprecedented price/performance for a range of problems in LQCD. Nevertheless, memory constraints on current GPU devices limit the problem sizes that can be tackled. In this contribution we describe the parallelization of the QUDA library onto multiple GPUs using MPI, including strategies for the overlapping of communication and computation. We report on both weak and strong scaling for up to 32 GPUs interconnected by InfiniBand, on which we sustain in excess of 4 Tflops.

Ronald Babich; Michael A. Clark; Bálint Joó

2010-10-29

267

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

SciTech Connect

Graphics Processing Units (GPUs) are having a transformational effect on numerical lattice quantum chromodynamics (LQCD) calculations of importance in nuclear and particle physics. The QUDA library provides a package of mixed precision sparse matrix linear solvers for LQCD applications, supporting single GPUs based on NVIDIA's Compute Unified Device Architecture (CUDA). This library, interfaced to the QDP++/Chroma framework for LQCD calculations, is currently in production use on the "9g" cluster at the Jefferson Laboratory, enabling unprecedented price/performance for a range of problems in LQCD. Nevertheless, memory constraints on current GPU devices limit the problem sizes that can be tackled. In this contribution we describe the parallelization of the QUDA library onto multiple GPUs using MPI, including strategies for the overlapping of communication and computation. We report on both weak and strong scaling for up to 32 GPUs interconnected by InfiniBand, on which we sustain in excess of 4 Tflops.

Ronald Babich, Michael Clark, Balint Joo

2010-11-01

268

Progesterone and testosterone studies by neutron scattering and nuclear magnetic resonance methods and quantum chemistry calculations  

NASA Astrophysics Data System (ADS)

Inelastic incoherent neutron scattering spectra of progesterone and testosterone measured at 20 and 290 K were compared with the IR spectra measured at 290 K. The Phonon Density of States spectra display well resolved peaks of low frequency internal vibration modes up to 1200 cm -1. The quantum chemistry calculations were performed by semiempirical PM3 method and by the density functional theory method with different basic sets for isolated molecule, as well as for the dimer system of testosterone. The proposed assignment of internal vibrations of normal modes enable us to conclude about the sequence of the onset of the torsion movements of the CH 3 groups. These conclusions were correlated with the results of proton molecular dynamics studies performed by NMR method. The GAUSSIAN program had been used for calculations.

Szyczewski, A.; Ho?derna-Natkaniec, K.; Natkaniec, I.

2004-05-01

269

Experimental and theoretical analysis of the temperature dependence of the two-dimensional electron mobility in a strained Si quantum well  

NASA Astrophysics Data System (ADS)

The temperature dependence of the mobility of the two-dimensional electron gas (2DEG) in a silicon quantum well strained by Si0.7Ge0.3 relaxed buffer layer is determined precisely by a mobility spectrum analysis. The 2DEG mobility is 2780 cm2/V s at room temperature and, upon cooling, increases continuously to reach ?2DEG=7.4×104cm2/Vs at 7 K. A back gate installed on the sample changes the 2DEG concentration n successfully to establish ?2DEG?n1.4 at the constant temperature T =10K, implying that the scattering at such low temperature is limited solely by the remote ionized impurity scattering. Based on this finding, theoretical analysis of the temperature dependence of ?2DEG is performed based on the relaxation time approximation using 2DEG wavefunctions and subband structures determined self-consistently and including three major scatterings; by intravalley acoustic phonons, intervalley g-processes of longitudinal optical (LO) phonons, and remote ionized impurities. The calculation included only three fitting parameters, the shear deformation potential (?u=9.5eV), LO phonon deformation potential for g-process scattering (D0=9.0×108eV/cm), and sheet density of remote ionized impurities that have been determined by quantitative comparison with our experimental results. The temperature dependence of ?2DEG calculated theoretically show excellent agreement with experimentally determined ?2DEG.

Tanaka, Takahisa; Tsuchiya, Go; Hoshi, Yusuke; Sawano, Kentarou; Shiraki, Yasuhiro; Itoh, Kohei M.

2012-04-01

270

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

NASA Astrophysics Data System (ADS)

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

Kubicki, J. D.

2008-12-01

271

A comparative study for quantum transport calculations of nanosized field-effect transistors  

NASA Astrophysics Data System (ADS)

This article presents a comparative study on quantum mechanical frameworks between the widely used local Quasi-Fermi Level (QFL) model and a recently developed top of the barrier splitting (TBS) model. Both models are based on an atomistic quantum mechanical solver using the linear combination of bulk band method (LCBB). The QFL model uses the local Quasi-Fermi Level to represent the local equilibrium and calculate the occupied charge density as well as the current flow along the channel. The TBS model extracts scattering state information from the stationary solution of the system, then calculates the charge density as well as the ballistic and tunneling current. Using these two models, the 10 nm and 22 nm double-gate ultra-thin-body structures are simulated. Comparisons in occupied charge densities, self-consistent potentials as well as the I- V characteristics between these two models are presented. It is found that the QFL model significantly overestimate the subthreshold charge density inside the channel, as well as the current, while it works fine in the ON state of the device. It is also found that the results from both QFL and TBS models tend to coincide with each other as the drain bias approaching zero.

Jiang, Xiang-Wei; Li, Shu-Shen; Wang, Lin-Wang

2012-02-01

272

Theoretical calculations applied to the study of the energetics of reactions of methamphetamine synthesis and to the characterization of reactants, products and by-products  

Microsoft Academic Search

Density Functional Theory (DFT) was used to perform quantum chemical calculations at B3LYP level, with the 6-31G** basis set, as implemented by the Spartan computer program. The entities studied are the reaction of synthesis of MDMA (3,4, methylene dioxymethamphetamine), and a number of analogs of methamphetamine. The analogs have also been geometry-optimized and their infrared vibrational frequencies were calculated.

Danielle Sapse; Elise Champeil; Anne-Marie Sapse

2011-01-01

273

Electronic structure of silicon quantum dots: Calculations of energy-gap redshifts due to oxidation  

NASA Astrophysics Data System (ADS)

Electronic state calculations are performed self-consistently using the extended Hückel-type nonorthogonal tight-binding method for two different oxygen configurations (backbonded and double-bonded oxygen configurations) on the H-covered surface of spherical Si35H36, Si47H60, Si71H84, Si136H120, Si148H120, and Si172H120 quantum dots. The size dependence of the effect of oxygen on the electronic structure of the Si dots is studied. Energy gaps calculated for both oxygen configurations can explain oxidation-induced redshifts in photoluminescence (PL) observed in porous Si. However, the energy gaps calculated for the backbonded oxygen model are around 2.2eV and dipole allowed in all Si dots studied, whereas those for the double-bonded oxygen model are gradually decreased with the increase in size (2.3-1.7eV), and optical transitions are dipole forbidden in the Si dots near 1nm across and dipole allowed in the ones near 2nm in diameter. The results calculated for the backbonded oxygen model coincide well with the experimental fact that the PL-peak energies are fixed at ˜2.1eV when porous Si is exposed to air.

Nishida, Masahiko

2005-07-01

274

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

275

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

SciTech Connect

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

Jia, Xiangyu; Wang, Xianwei; Liu, Jinfeng; Mei, Ye, E-mail: ymei@phy.ecnu.edu.cn, E-mail: xiaohe@phy.ecnu.edu.cn; He, Xiao, E-mail: ymei@phy.ecnu.edu.cn, E-mail: xiaohe@phy.ecnu.edu.cn [State Key Laboratory of Precision Spectroscopy, Department of Physics and Institute of Theoretical and Computational Science, East China Normal University, Shanghai 200062 (China)] [State Key Laboratory of Precision Spectroscopy, Department of Physics and Institute of Theoretical and Computational Science, East China Normal University, Shanghai 200062 (China); Zhang, John Z. H. [State Key Laboratory of Precision Spectroscopy, Department of Physics and Institute of Theoretical and Computational Science, East China Normal University, Shanghai 200062 (China) [State Key Laboratory of Precision Spectroscopy, Department of Physics and Institute of Theoretical and Computational Science, East China Normal University, Shanghai 200062 (China); Joint Research Center for Computational Chemistry at NYU Shanghai, Shanghai 200062 (China)

2013-12-07

276

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

PubMed

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 3500-100cm(-1) and 4000-400cm(-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. PMID:24835947

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

2014-10-15

277

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

278

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

279

All information-theoretically secure key establishing protocols are quantum protocols  

E-print Network

A theorem is proved which states that no classical key generating protocol could ever be provably secure. Consequently, candidates for provably secure protocols must rely on some quantum effect. Theorem relies on the fact that BB84 Quantum key distribution protocol has been proven secure.

Mario Stipcevic

2005-03-26

280

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

281

FragIt: A Tool to Prepare Input Files for Fragment Based Quantum Chemical Calculations  

PubMed Central

Near linear scaling fragment based quantum chemical calculations are becoming increasingly popular for treating large systems with high accuracy and is an active field of research. However, it remains difficult to set up these calculations without expert knowledge. To facilitate the use of such methods, software tools need to be available to support these methods and help to set up reasonable input files which will lower the barrier of entry for usage by non-experts. Previous tools relies on specific annotations in structure files for automatic and successful fragmentation such as residues in PDB files. We present a general fragmentation methodology and accompanying tools called FragIt to help setup these calculations. FragIt uses the SMARTS language to locate chemically appropriate fragments in large structures and is applicable to fragmentation of any molecular system given suitable SMARTS patterns. We present SMARTS patterns of fragmentation for proteins, DNA and polysaccharides, specifically for D-galactopyranose for use in cyclodextrins. FragIt is used to prepare input files for the Fragment Molecular Orbital method in the GAMESS program package, but can be extended to other computational methods easily. PMID:23028546

Steinmann, Casper; Ibsen, Mikael W.; Hansen, Anne S.; Jensen, Jan H.

2012-01-01

282

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

283

Hydrogen-bonded structures of pyrrole-solvent clusters: infrared cavity ringdown spectroscopy and quantum chemical calculations.  

PubMed

The hydrogen-bonded structures of pyrrole-solvent (H(2)O,CH(3)OH,C(2)H(5)OH) binary clusters were studied by the combination of experimental and theoretical techniques. Infrared cavity ringdown spectroscopy was applied to observe the NH and OH stretching vibrations of the clusters. The structures, binding energies, and normal modes of the binary clusters were obtained by quantum chemical calculations of the MP2/6-31+G(d,p) and B3LYP/6-311+G(d,p) levels. For the 1:1 clusters of pyrrole-H(2)O, pyrrole-CH(3)OH, and pyrrole-C(2)H(5)OH, the hydrogen-bonded NH stretching vibrations were observed at 3448, 3414, and 3408 cm(-1), respectively. They were redshifted from the NH stretching vibration of the pyrrole monomer, and the amounts of the redshift were proportional to the proton affinities of the solvent molecules. MP2 level calculations revealed that the sigma-type (NH...O) hydrogen-bonded structures had 7.6-9.0 kJ/mol larger binding energies than the pi-type structures (OH...pi electron cloud of pyrrole), and that the vibrational frequencies of the sigma-type structures are consistent with the observed spectra. In addition to the 1:1 clusters, the NH or OH stretching vibrations of pyrrole-CH(3)OH binary clusters were observed at 3432 and 3549 cm(-1). Among three optimized structures of the pyrrole-(CH(3)OH)(2), the sigma-pi bridge pyrrole-(CH(3)OH)(2) provided a reasonable agreement between the observed and calculated vibrational frequencies. For the pyrrole-H(2)O binary clusters, three new bands were observed at 3414, 3435, and 3541 cm(-1). These bands are consistent with the calculated NH and OH stretching vibrations of the (pyrrole)(2)-H(2)O cluster, which has a closed cyclic hydrogen-bonded structure. PMID:19206977

Matsumoto, Yoshiteru; Honma, Kenji

2009-02-01

284

Insights into the high-pressure behavior of kaolinite from infrared spectroscopy and quantum-mechanical calculations  

NASA Astrophysics Data System (ADS)

The high-pressure behavior of Keokuk kaolinite has been studied to 9.5 GPa by infrared spectroscopy using synchrotron radiation. The kaolinite-I ? kaolinite-II and kaolinite-II ? kaolinite-III transformations have clear spectroscopic expression, with discontinuities coinciding with the transformation pressures bracketed by X-ray diffraction (Welch and Crichton in Am Mineral 95:651-654, 2010). The experimental spectra have been interpreted from band assignments derived from density functional theory for the structures of kaolinite-II and kaolinite-III, using as starting models the ab initio structures reported by Mercier and Le Page (Acta Crystallogr A B64:131-143, 2008, Mater Sci Technol 25:437-442, 2009) and unit-cell parameters from Welch and Crichton (Am Mineral 95:651-654, 2010). The relaxed theoretical structures are very similar to those reported by Mercier and Le Page (Acta Crystallogr A B64:131-143, 2008, Mater Sci Technol 25:437-442, 2009) in their theoretical investigation of kaolinite polytypes at high pressure. The vibrational spectra calculated from the quantum-mechanical analysis allow band assignments of the IR spectra to be made and provide insights into the behavior of different OH environments in the two high-pressure polytypes. The single perpendicular-interlayer OH group of kaolinite-III has a distinctive spectroscopic signature that is diagnostic of this polytype (? = 3,595 cm-1 at 9.5 GPa) and is sensitive to the compression/expansion of the interlayer space. This OH group also has a distinctive signature in the calculated spectra. The spectra collected on decompression are those of kaolinite-III and persist largely unchanged to 4.6 GPa, except for a continuous blue shift of the 3,595 cm-1 band to 3,613 cm-1. Finally, kaolinite-I is recovered at 0.6 GPa, confirming the kaolinite-III ? kaolinite-I transformation previously observed by X-ray diffraction, and the irreversibility of the kaolinite-II ? kaolinite-III transformation. The ambient spectra collected at the start and finish of the experiment are those of kaolinite-I, and start/finish band frequencies agree to within 6 cm-1.

Welch, Mark D.; Montgomery, Wren; Balan, Etienne; Lerch, Philippe

2012-02-01

285

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

286

Research on the chelation between luteolin and Cr(III) ion through infrared spectroscopy, UV-vis spectrum and theoretical calculations  

NASA Astrophysics Data System (ADS)

The chelation between luteolin and Cr(III) ion is studied using the theoretical methods. Many different potential complexes, formed with natural and deprotonated luteolin chelating bare and hydrated Cr(III) ion, respectively, are studied by using Density Functional Theory method. Both total and binding energies are calculated. The results from the studies indicate that Cr(III) ion is affine in forming a complex with luteolin at the 5-hydroxy-4-keto site and that deprotonated luteolin has stronger chelating power than natural luteolin. The reactivity differences between luteolin and luteolin-Cr(III) complexes are observed through comparison of their Conceptual DFT reactivity indices. Apart from the theoretical studies, the experiments are performed to modify the theoretical conclusions. Meanwhile, luteolin-Cr(III) complex has been synthesized, and the chelation site is analyzed using IR spectroscopy and UV/vis spectrum. The experimental results are found to have the same conclusions as those by theoretical studies.

Gao, Li-Guo; Wang, Hua; Song, Xiao-Li; Cao, Wei

2013-02-01

287

Molecular structure, vibrational, electronic and thermal properties of 4-vinylcyclohexene by quantum chemical calculations.  

PubMed

The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100cm(-1). The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated. PMID:25795608

Nagabalasubramanian, P B; Periandy, S; Karabacak, Mehmet; Govindarajan, M

2015-06-15

288

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

289

One-loop calculations in quantum field theory: from Feynman diagrams to unitarity cuts  

SciTech Connect

The success of the experimental program at the Tevatron re-inforced the idea that precision physics at hadron colliders is desirable and, indeed, possible. The Tevatron data strongly suggests that one-loop computations in QCD describe hard scattering well. Extrapolating this observation to the LHC, we conclude that knowledge of many short-distance processes at next-to-leading order may be required to describe the physics of hard scattering. While the field of one-loop computations is quite mature, parton multiplicities in hard LHC events are so high that traditional computational techniques become inefficient. Recently new approaches based on unitarity have been developed for calculating one-loop scattering amplitudes in quantum field theory. These methods are especially suitable for the description of multi-particle processes in QCD and are amenable to numerical implementations. We present a systematic pedagogical description of both conceptual and technical aspects of the new methods.

Ellis, R.Keith; Kunszt, Zoltan; Melnikov, Kirill; Zanderighi, Giulia

2012-09-01

290

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

291

The Submillimeter-Wave Spectrum and Quantum Chemical Calculations of Glyoxylic Acid.  

PubMed

Glyoxylic acid is a possible candidate for interstellar detection. Many transitions of the submillimeter wave spectrum of the ground vibrational state of its most stable conformer have been measured for the first time. These transitions have been used together with microwave transitions measured previously to obtain accurate spectroscopic constants that should facilitate a search for this compound in interstellar space. High-level quantum chemical calculations of the structure, quartic centrifugal distortion constants, inertial defect, and energy difference between the two low-energy conformers of glyoxylic acid have also been made. Accurate predictions of the equilibrium structures of the most stable forms of glyoxylic, as well as of formic acid, are reported. Copyright 2001 Academic Press. PMID:11437557

Bakri, B.; Demaison, J.; Margulès, L.; Møllendal, H.

2001-07-01

292

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

293

QSPR models for various physical properties of carbohydrates based on molecular mechanics and quantum chemical calculations.  

PubMed

Quantitative Structure-Property Relationships (QSPR) have been developed for a series of monosaccharides, including the physical properties of partial molar heat capacity, heat of solution, melting point, heat of fusion, glass-transition temperature, and solid state density. The models were based on molecular descriptors obtained from molecular mechanics and quantum chemical calculations, combined with other types of descriptors. Saccharides exhibit a large degree of conformational flexibility, therefore a methodology for selecting the energetically most favorable conformers has been developed, and was used for the development of the QSPR models. In most cases good correlations were obtained for monosaccharides. For five of the properties predictions were made for disaccharides, and the predicted values for the partial molar heat capacities were in excellent agreement with experimental values. PMID:14698885

Dyekjaer, Jane Dannow; Jónsdóttir, Svava Osk

2004-01-22

294

Electronic structure calculations of PbS quantum rods and tubes  

NASA Astrophysics Data System (ADS)

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

Pimachev, Artem; Dahnovsky, Yuri

2014-01-01

295

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

296

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

SciTech Connect

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

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

2009-11-20

297

Quantum reactive scattering calculations for the H+D2?HD+D reaction  

NASA Astrophysics Data System (ADS)

The results of accurate 3D quantum scattering calculations in symmetrized hyperspherical coordinates are reported for the H+D2(v,j)?HD(v',j')+D reaction at 64 values of total energy in the range 0.5-1.9 eV. Integral and differential cross sections are computed using the Boothroyd-Keogh-Martin-Peterson potential energy surface for all values of total angular momentum J?31. Several transition state resonances survive the sum over J and are observed in many of the fully converged state-to-state integral and differential cross sections. In some cases a series of resonances is observed. The energy spacings between many of the resonances are consistent with the energy spacings between the even or odd bending modes of the quantized transition states of H3.

Kendrick, Brian K.

2001-05-01

298

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

299

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

300

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

301

A quantum-information-theoretic complement to a general-relativistic implementation of a  

E-print Network

theory and, ulti- mately, quantum gravity may play an important role in determining the validity or implementable in the context of a specific physical theory. In the present setting, one such specific theory

Wüthrich, Christian

302

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

303

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

304

An automaton-theoretic approach to the representation theory of quantum algebras  

Microsoft Academic Search

We develop a new approach to the representation theory of quantum algebras supporting a torus action via methods from the theory of finite-state automata and algebraic combinatorics. We show that for a fixed number m, the torus-invariant primitive ideals in m×n quantum matrices can be seen as a regular language in a natural way. Using this description and a semigroup

J. Bell; S. Launois; J. Lutley

2010-01-01

305

An automaton-theoretic approach to the representation theory of quantum algebras  

Microsoft Academic Search

We develop a new approach to the representation theory of quantum algebras supporting a torus action via methods from the theory of finite-state automata and algebraic combinatorics. We show that for a fixed number $m$, the torus-invariant primitive ideals in $m\\\\times n$ quantum matrices can be seen as a regular language in a natural way. Using this description and a

J. Bell; S. Launois; J. Lutley

2009-01-01

306

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

E-print Network

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

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

2010-12-13

307

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

308

Theoretical calculation and prediction of P-glycoprotein-interacting drugs using MolSurf parametrization and PLS statistics  

Microsoft Academic Search

A method for the modelling and prediction of P-glycoprotein-associated ATPase activity using theoretically computed molecular descriptors and multivariate statistics has been investigated using 22 diverse drug-like compounds. The program MolSurf was used to compute theoretical molecular descriptors related to physicochemical properties such as lipophilicity, polarity, polarizability and hydrogen bonding. The multivariate partial least squares projections to latent structures (PLS) method

Thomas Österberg; Ulf Norinder

2000-01-01

309

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

310

The quantum measurement problem and physical reality: a computation theoretic perspective  

E-print Network

Is the universe computable? If yes, is it computationally a polynomial place? In standard quantum mechanics, which permits infinite parallelism and the infinitely precise specification of states, a negative answer to both questions is not ruled out. On the other hand, empirical evidence suggests that NP-complete problems are intractable in the physical world. Likewise, computational problems known to be algorithmically uncomputable do not seem to be computable by any physical means. We suggest that this close correspondence between the efficiency and power of abstract algorithms on the one hand, and physical computers on the other, finds a natural explanation if the universe is assumed to be algorithmic; that is, that physical reality is the product of discrete sub-physical information processing equivalent to the actions of a probabilistic Turing machine. This assumption can be reconciled with the observed exponentiality of quantum systems at microscopic scales, and the consequent possibility of implementing Shor's quantum polynomial time algorithm at that scale, provided the degree of superposition is intrinsically, finitely upper-bounded. If this bound is associated with the quantum-classical divide (the Heisenberg cut), a natural resolution to the quantum measurement problem arises. From this viewpoint, macroscopic classicality is an evidence that the universe is in BPP, and both questions raised above receive affirmative answers. A recently proposed computational model of quantum measurement, which relates the Heisenberg cut to the discreteness of Hilbert space, is briefly discussed. A connection to quantum gravity is noted. Our results are compatible with the philosophy that mathematical truths are independent of the laws of physics.

R. Srikanth

2006-11-07

311

Quantum chemical calculations of bond dissociation energies for COOH scission and electronic structure in some acids  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations are performed to investigate the equilibrium C—COOH bond distances and the bond dissociation energies (BDEs) for 15 acids. These compounds are studied by utilizing the hybrid density functional theory (DFT) (B3LYP, B3PW91, B3P86, PBE1PBE) and the complete basis set (CBS—Q) method in conjunction with the 6-311G** basis as DFT methods have been found to have low basis sets sensitivity for small and medium molecules in our previous work. Comparisons between the computational results and the experimental values reveal that CBS—Q method, which can produce reasonable BDEs for some systems in our previous work, seems unable to predict accurate BDEs here. However, the B3P86 calculated results accord very well with the experimental values, within an average absolute error of 2.3 kcal/mol. Thus, B3P86 method is suitable for computing the reliable BDEs of C—COOH bond for carboxylic acid compounds. In addition, the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of studied compounds are estimated, based on which the relative thermal stabilities of the studied acids are also discussed.

Zeng, Hui; Zhao, Jun; Xiao, Xun

2013-02-01

312

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

313

Progesterone and testosterone studies by neutron-scattering methods and quantum chemistry calculations  

NASA Astrophysics Data System (ADS)

Inelastic incoherent neutron scattering (IINS) and neutron diffraction spectra of progesterone and testosterone were measured simultaneously on the NERA spectrometer at the IBR-2 pulsed reactor in Dubna. Both studied samples do not indicate any phase transition in the temperature range from 20 to 290K. The IINS spectra have been transformed to the phonon density of states (PDS) in the one-phonon scattering approximation. The PDS spectra display well-resolved peaks of low-frequency internal vibration modes up to 600cm-1. The assignment of these modes was proposed taking into account the results of calculations of the structure and dynamics of isolated molecules of the investigated substances. The quantum chemistry calculations were performed by the semi-empirical PM3 method and at the restricted Hartree-Fock level with the 6-31* basis set. The lower internal modes assigned to torsional vibration of the androstane skeleton mix with the lattice vibrations. The intense bands in the PDS spectra in the frequency range from 150 to 300cm-1 are related to librations of structurally inequivalent methyl groups.

Holderna-Natkaniec, K.; Szyczewski, A.; Natkaniec, I.; Khavryutchenko, V. D.; Pawlukojc, A.

314

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

NASA Astrophysics Data System (ADS)

In this work, we calculate the two-dimensional quantum energy system of the In(Ga)As wetting layer that arises in InAs/InGaAs/GaAs metamorphic quantum dot structures. Model calculations were carried on the basis of realistic material parameters taking in consideration their dependence on the strain relaxation of the metamorphic buffer; results of the calculations were validated against available literature data. Model results confirmed previous hypothesis on the extrinsic nature of the disappearance of wetting layer emission in metamorphic structures with high In composition. We also show how, by adjusting InGaAs metamorphic buffer parameters, it could be possible: (i) to spatially separate carriers confined in quantum dots from wetting layer carriers, (ii) to create an hybrid 0D-2D system, by tuning quantum dot and wetting layer levels. These results are interesting not only for the engineering of quantum dot structures but also for other applications of metamorphic structures, as the two design parameters of the metamorphic InGaAs buffer (thickness and composition) provide additional degrees of freedom to control properties of interest.

Seravalli, L.; Trevisi, G.; Frigeri, P.

2013-11-01

315

Quo Vadis Quantum Mechanics?  

Microsoft Academic Search

Quantum mechanics is one of the most successful theoretical structures in all of science. Developed between 1925-26 to explain the optical spectrum of atoms, the theory over the succeeding 80 years has been extended, first to quantum field theories, gauge field theories, and now even string theory. It is used every day by thousands of physicists to calculate physical phenomena

W G Unruh

2006-01-01

316

Quantum physics and computers  

Microsoft Academic Search

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

Adriano Barenco

1996-01-01

317

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

PubMed

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 (2)D, (ii) the two-hole (2)Q, and the (iii) particle-hole (2)G 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)]. 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. PMID:23277924

Schwerdtfeger, Christine A; Mazziotti, David A

2012-12-28

318

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

319

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

320

Microscopic theoretical analysis of optically generated injection currents in semiconductor quantum wells  

NASA Astrophysics Data System (ADS)

A microscopic theory that describes injection currents in GaAs quantum wells is presented. 14 × 14 band k.p theory is used to compute the band structure including anisotropy and spin-orbit interaction. Transient injection currents are obtained via numerical solutions of the semiconductor Bloch equations. Depending on the growth direction of the considered quantum well system and the propagation and polarization directions of the incident light beam, it is possible to generate charge and/or spin photocurrents on ultrashort time scales. The dependence of the photocurrents on the excitation conditions is computed and discussed.

Duc, Huynh Thanh; Förstner, Jens; Meier, Torsten

2010-02-01

321

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

322

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

323

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

324

The Impact of Quantum Theoretical Models of Consciousness on the Study of Education.  

ERIC Educational Resources Information Center

This paper abstracts and discusses the approaches of five educational theorists who have used quantum theory as a model for educational phenomena, sets forth and uses metatheoretical criteria to evaluate the work of these theorists, and states guidelines for further work in this domain. The paper abstracts and discusses the works of the following…

Andris, James F.

325

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

NASA Astrophysics Data System (ADS)

Conventional quantum mechanics with a complex Hilbert space and the Born Rule is derived from five axioms describing experimentally observable properties of probability distributions for the outcome of measurements. Axioms I, II, III are common to quantum mechanics and hidden variable theories. Axiom IV recognizes a phenomenon, first noted by von Neumann (in Mathematical Foundations of Quantum Mechanics, Princeton University Press, Princeton, 1955) and independently by Turing (Teuscher and Hofstadter, Alan Turing: Life and Legacy of a Great Thinker, Springer, Berlin, 2004), in which the increase in entropy resulting from a measurement is reduced by a suitable intermediate measurement. This is shown to be impossible for local hidden variable theories. Axiom IV, together with the first three, almost suffice to deduce the conventional rules but allow some exotic, alternatives such as real or quaternionic quantum mechanics. Axiom V recognizes a property of the distribution of outcomes of random measurements on qubits which holds only in the complex Hilbert space model. It is then shown that the five axioms also imply the conventional rules for any finite dimension.

Fivel, Daniel I.

2012-02-01

326

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

327

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

328

Concepts and Their Dynamics: A Quantum-Theoretic Modeling of Human Thought  

E-print Network

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, i.e. 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 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 paper by analyzing human concepts and their dynamics.

Diederik Aerts; Liane Gabora; Sandro Sozzo

2013-01-05

329

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

330

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

331

Hydrate shell models of acetate ions according to nuclear magnetic relaxation data and quantum-chemical calculations  

NASA Astrophysics Data System (ADS)

Different ion-water clusters for the CH3COO- ion that simulate the structure of its hydrate shells in solution are considered on the basis of the quantum mechanical approach. The possible coordination of water molecules around the ion is studied and the calculation results are compared with the experimental data obtained by nuclear magnetic relaxation.

Vovk, M. A.; Pavlova, M. S.; Chizhik, V. I.; Vorontsova, A. A.

2011-09-01

332

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

333

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

334

Theoretical calculation on ICI reduction using digital coherent superposition of optical OFDM subcarrier pairs in the presence of laser phase noise.  

PubMed

Digital coherent superposition (DCS) of optical OFDM subcarrier pairs with Hermitian symmetry can reduce the inter-carrier-interference (ICI) noise resulted from phase noise. In this paper, we show two different implementations of DCS-OFDM that have the same performance in the presence of laser phase noise. We complete the theoretical calculation on ICI reduction by using the model of pure Wiener phase noise. By Taylor expansion of the ICI, we show that the ICI power is cancelled to the second order by DCS. The fourth order term is further derived out and only decided by the ratio of laser linewidth to OFDM subcarrier symbol rate, which can greatly simplify the system design. Finally, we verify our theoretical calculations in simulations and use the analytical results to predict the system performance. DCS-OFDM is expected to be beneficial to certain optical fiber transmissions. PMID:25607068

Yi, Xingwen; Xu, Bo; Zhang, Jing; Lin, Yun; Qiu, Kun

2014-12-15

335

Quantum mechanical calculation of the collision-induced absorption spectra of N2-N2 with anisotropic interactions  

NASA Astrophysics Data System (ADS)

We present quantum mechanical calculations of the collision-induced absorption spectra of nitrogen molecules, using ab initio dipole moment and potential energy surfaces. Collision-induced spectra are first calculated using the isotropic interaction approximation. Then, we improve upon these results by considering the full anisotropic interaction potential. We also develop the computationally less expensive coupled-states approximation for calculating collision-induced spectra and validate this approximation by comparing the results to numerically exact close-coupling calculations for low energies. Angular localization of the scattering wave functions due to anisotropic interactions affects the line strength at low energies by two orders of magnitude. The effect of anisotropy decreases at higher energy, which validates the isotropic interaction approximation as a high-temperature approximation for calculating collision-induced spectra. Agreement with experimental data is reasonable in the isotropic interaction approximation, and improves when the full anisotropic potential is considered. Calculated absorption coefficients are tabulated for application in atmospheric modeling.

Karman, Tijs; Miliordos, Evangelos; Hunt, Katharine L. C.; Groenenboom, Gerrit C.; van der Avoird, Ad

2015-02-01

336

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

337

The calculation of product quantum state distributions and partial cross-sections in time-dependent molecular collision and photodissociation theory  

Microsoft Academic Search

A new method of analyzing the results of multidimensional time-dependent quantum dynamical wavepacket calculations in terms of the product quantum state distributions is presented. The method requires knowledge only of the time-dependent projection coefficients of the wavepacket onto individual product quantum states along a cut in the exit valley of the photodissociation or reaction process. The squares of the Fourier

Gabriel G. Balint-Kurti; Richard N. Dixon; C. Clay Marston; A. J. Mulholland

1991-01-01

338

Experimental and Theoretical Analysis of Argon Plasma-Enhanced Quantum-Well Intermixing  

Microsoft Academic Search

Plasma-enhanced quantum-well intermixing (QWI) has been developed for tuning the bandgap of InGaAs-InP ma- terial using an inductively coupled plasma system. The applica- tion of inductively coupled plasma enhances the interdiffusion of point defects resulting in a higher degree of intermixing. Based on a semi-empirical model of QW interdiffusion, the bandgap blue-shift with respect to the plasma exposure time and

H. S. Djie; T. Mei; J. Arokiaraj; C. Sookdhis; S. F. Yu; L. K. Ang; X. H. Tang

2004-01-01

339

Leading-order calculation of electric conductivity in hot quantum electrodynamics from diagrammatic methods  

SciTech Connect

Using diagrammatic methods, we show how the Ward identity can be used to constrain the ladder kernel in transport coefficient calculations. More specifically, we use the Ward identity to determine the necessary diagrams that must be resummed using an integral equation. One of our main results is an equation relating the kernel of the integral equation with functional derivatives of the full self-energy; it is similar to what is obtained with two-particle irreducible (2PI) effective action methods. However, since we use the Ward identity as our starting point, gauge invariance is preserved. Using power counting arguments, we also show which self-energies must be included in the resummation at leading order, including 2 to 2 scatterings and 1 to 2 collinear scatterings with the Landau-Pomeranchuk-Migdal effect. We show that our quantum field theory result is equivalent to the one of Arnold, Moore, and Yaffe obtained using effective kinetic theory. In this paper we restrict our discussion to electrical conductivity in hot QED, but our method can in principle be generalized to other transport coefficients and other theories.

Gagnon, Jean-Sebastien; Jeon, Sangyong [Physics Department, McGill University, 3600 University street, Montreal, H3A 2T8 (Canada)

2007-01-15

340

Calculation of band alignments and quantum confinement effects in zero- and one-dimensional pseudomorphic structures  

NASA Astrophysics Data System (ADS)

The strain field distributions and band lineups of zero-dimensional and one-dimensional strained pseudomorphic semiconductor particles inside a three-dimensional matrix of another semiconductor have been studied. The resulting strain in the particle and the matrix leads to band alignments considerably different from that in the conventional two-dimensional (2D) pseudomorphic growth case. The models are first applied to an ideal spherical and cylindrical Si1-xGex particle in a large Si matrix. In contrast to the 2D case, the band alignments for both structures are predicted to be strongly type II, where the conduction-band edge and the valence-band edge of the Si matrix are both significantly lower than those in the Si1-xGex inclusion, respectively. Band lineups and the lowest electron-heavy-hole transition energies of a pseudomorphic V-groove Si1-xGex quantum wire inside a large Si matrix have been calculated numerically for different size structures. The photoluminescence energies of a large Si1-xGex V-groove structure on Si will be lower than those of conventional 2D strained Si1-xGex for similar Ge contents.

Yang, Min; Sturm, J. C.; Prevost, Jean

1997-07-01

341

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

342

Schwarzschild Radius from Monte Carlo Calculation of the Wilson Loop in Supersymmetric Matrix Quantum Mechanics  

SciTech Connect

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 R{sub Sch} of the dual black hole geometry as log=R{sub Sch}/(2{pi}{alpha}{sup '}T). This translates to the power-law behavior log=1.89(T/{lambda}{sup 1/3}){sup -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}{sup '} corrections on the gravity side. Our conclusion also demonstrates manifestly the fuzzball picture of black holes.

Hanada, Masanori [Department of Particle Physics, Weizmann Institute of Science, Rehovot 76100 (Israel); Miwa, Akitsugu [Institute of Physics, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902 (Japan); Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211019 (India); Nishimura, Jun [High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801 (Japan); Department of Particle and Nuclear Physics, School of High Energy Accelerator Science, Graduate University for Advanced Studies (SOKENDAI), Tsukuba 305-0801 (Japan); Takeuchi, Shingo [Department of Particle and Nuclear Physics, School of High Energy Accelerator Science, Graduate University for Advanced Studies (SOKENDAI), Tsukuba 305-0801 (Japan); Asia Pacific Center for Theoretical Physics (APCTP), Pohang, Gyeongbuk 790-784 (Korea, Republic of)

2009-05-08

343

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

344

Theoretical and experimental investigation of the nonlinear dynamical trends of passively mode-locked quantum dot lasers  

NASA Astrophysics Data System (ADS)

In recent years, passively mode-locked quantum dot lasers have shown great promise as compact, efficient and reliable pulsed sources of light for a range of precision and high performance applications, such as high bit-rate optical communications, diverse waveform generation, metrology, and clock distribution in high-performance computing (HPC) processors. For such applications, stable optical pulses with short picosecond pulse durations and multi-gigahertz repetition rates are required. In addition, a low pulse-to-pulse timing jitter is also necessary to prevent errors arising from the ambiguity between neighboring pulses. In order to optimize pulse quality in terms of optical characteristics such as pulse shape and pulse train behavior, as well as RF characteristics such as phase noise and timing jitter, understanding the nonlinear output dynamics of such devices is of critical importance, not only to get a sense of the regimes of operation where device output might be stable or unstable, but also to gain insight into the parameters that influence the output characteristics the most, and how they can be accessed and exploited to optimize design and performance for next generation applications. In this dissertation, theoretical and experimental studies have been combined to investigate the dynamical trends of two-section passively mode-locked quantum dot lasers. On the theoretical side, a novel numerical modeling scheme is presented as a powerful and versatile framework to study the nonlinear dynamics specific to a device, with device-specific parameters extracted over a range of operating conditions. The practical utility of this scheme is then demonstrated, first, in an analytical capability to interpret and explain dynamical trends observed in experiment, and subsequently, as a predictive tool to guide experiment to operate in a desired dynamical regime. Modeling results are compared to experimental findings where possible. Finally, optical feedback from an external reflector is experimentally studied as an additional control mechanism over the output dynamics of the device, and shown to enable invaluable insight into the behavior of the RF and optical spectra of the output. Together, the theoretical and experimental findings of this dissertation are shown to offer a systematic approach to understand, control and exploit the dynamical trends of passively mode-locked two-section quantum dot lasers.

Raghunathan, Ravi

345

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

346

Quantum Chemistry Calculation-Aided Structural Optimization of Combretastatin A-4-like Tubulin Polymerization Inhibitors: Improved Stability and Biological Activity.  

PubMed

A potent combretastatin A-4 (CA-4) like tubulin polymerization inhibitor 22b was found with strong antitumor activity previously. However, it easily undergoes cis-trans isomerization under natural light, and the resulting decrease in activity limits its further applications. In this study, we used quantum chemistry calculations to explore the molecular basis of its instability. Aided by the calculations, two rounds of structural optimization of 22b were conducted. Accelerated quantitative light stability testing confirmed that the stability of these designed compounds was significantly improved as predicted. Among them, compounds 1 and 3b displayed more potent inhibitory activity on tumor cell growth than 22b. In addition, the potent in vivo antitumor activity of compound 1 was confirmed. Quantum chemistry calculations were used in the optimization of stilbene-like molecules, providing new insight into stilbenoid optimization and important implications for the future development of novel CA-4-like tubulin polymerization inhibitors. PMID:25689111

Jiang, Junhang; Zheng, Canhui; Zhu, Kongkai; Liu, Jia; Sun, Nannan; Wang, Chongqing; Jiang, Hualiang; Zhu, Ju; Luo, Cheng; Zhou, Youjun

2015-03-12

347

Line Coupling Effects in the Isotropic Raman Spectra of N2: A Quantum Calculation at Room Temperature  

NASA Technical Reports Server (NTRS)

We present quantum calculations of the relaxation matrix for the Q branch of N2 at room temperature using a recently proposed N2-N2 rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility. This has been done using complementary calculations based on the energy corrected sudden formalism. Agreement of these quantum predictions with experimental data is good, but the main goal of this work is to provide a benchmark relaxation matrix for testing more approximate methods which remain of a great utility for complex molecular systems at room (and higher) temperatures.

Thibault, Franck; Boulet, Christian; Ma, Qiancheng

2014-01-01

348

Quantum chemical calculations of (31)P NMR chemical shifts: scopes and limitations.  

PubMed

The aim of this work is to convince practitioners of (31)P NMR methods to regard simple GIAO quantum chemical calculations as a safe tool in structural analysis of organophosphorus compounds. A comparative analysis of calculated GIAO versus experimental (31)P NMR chemical shifts (CSs) for a wide range of phosphorus containing model compounds was carried out. A variety of combinations (at the HF, DFT (B3LYP and PBE1PBE), and MP2 levels using 6-31G(d), 6-31+G(d), 6-31G(2d), 6-31G(d,p), 6-31+G(d,p), 6-311G(d), 6-311G(2d,2p), 6-311++G(d,p), 6-311++G(2d,2p), and 6-311++G(3df,3pd) basis sets) were tested. On the whole, it is shown that, in contrast to what is claimed in the literature, high level of theory is not needed to obtain rather accurate predictions of (31)P CSs by the GIAO method. The PBE1PBE/6-31G(d)//PBE1PBE/6-31G(d) level can be recommended for express estimation of (31)P CSs. The PBE1PBE/6-31G(2d)//PBE1PBE/6-31G(d) combination can be recommended for routine applications. The PBE1PBE/6-311G(2d,2p)//PBE1PBE/6-31+G(d) level can be proposed to obtain better results at a reasonable cost. Scaling by linear regression parameters significantly improves results. The results obtained using these combinations were demonstrated in (31)P CS calculations for a variety of medium (large) size organic compounds of practical interest. Care has to be taken for compounds that may be involved in exchange between different structural forms (self-associates, associates with solvent, tautomers, and conformers). For phosphorus located near the atoms of third period elements ((CH3)3PS and P(SCH3)3) the impact of relativistic effects may be notable. PMID:25683906

Latypov, Shamil K; Polyancev, Fedor M; Yakhvarov, Dmitry G; Sinyashin, Oleg G

2015-02-25

349

NMR structure determination of proteins supplemented by quantum chemical calculations: Detailed structure of the Ca 2+ sites in the EGF34 fragment of protein S  

Microsoft Academic Search

We present and test two methods to use quantum chemical calculations to improve standard protein structure refinement by molecular dynamics simulations restrained to experimental NMR data. In the first, we replace the molecular mechanics force field (employed in standard refinement to supplement experimental data) for a site of interest by quantum chemical calculations. This way, we obtain an accurate description

Ya-Wen Hsiao; Torbjörn Drakenberg; Ulf Ryde

2005-01-01

350

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

351

Calculation of gain-current characteristics in ZnCdSe-ZnSe quantum well structures including many body effects  

Microsoft Academic Search

The gain-spontaneous recombination characteristics have been calculated for a 40 A? Zn0.8Cd0.2Se-ZnSe quantum well including many body effects. We examine the effect of the inclusion of the Coulomb enhancement on the gain spectra and the gain-current relationship. We show that, in the absence of the Coulomb enhancement, the threshold current density of a 340 ?m 40 A? Zn0.8Cd0.2Se-ZnSe quantum well

P. Rees; F. P. Logue; J. F. Donegan; J. F. Heffernan; C. Jordan; J. Hegarty

1995-01-01

352

A quantum information-theoretic proof of the relation between Horn's problem and the Littlewood-Richardson coefficients  

E-print Network

Horn's problem asks for the conditions on sets of integers mu, nu and lambda that ensure the existence of Hermitian operators A, B and A+B with spectra mu, nu and lambda, respectively. It has been shown that this problem is equivalent to deciding whether the irreducible representation of GL(d) with highest weight lambda is contained in the tensor product of irreducible representations with highest weight mu and nu. In this paper we present a quantum information-theoretic proof of the relation between the two problems that is asymptotic in one direction. This result has previously been obtained by Klyachko using geometric invariant theory. The work presented in this paper does not, however, touch upon the non-asymptotic equivalence between the two problems, a result that rests on the recently proven saturation conjecture for GL(d).

Matthias Christandl

2008-04-10

353

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

E-print Network

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

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

2015-02-05

354

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

355

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

356

Theoretical model calculation of dosimetry cross-sections for cobalt from threshold energy to 50 MeV  

SciTech Connect

Dosimetry cross-sections of the threshold reactions for cobalt have been calculated by the GNASH code in the energy region up to 50 MeV for the application in accelerator-based high energy neutron fields. The dosimetry cross-sections of (n,2n), (n,3n), (n,4n), (n,p), (n, {alpha}), (n,2n {alpha} ) as well as helium accumulation cross-section (n,He) were calculated. The (n,2n {alpha} ) reaction can be a new, promising dosimetry reaction in the region from 30 to 50 MeV.

Iwasaki, S. [Tohoku Univ., Sendai (Japan); Odano, N. [Ship Research Institute, Ibaragi-ken (Japan)

1994-12-31

357

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

358

Calculations of strong coupling between a single quantum dot and a plasmonic nanoresonator  

Microsoft Academic Search

Quantum-mechanical strong coupling between an optical cavity and a single solid-state emitter offers a robust, scalable platform for quantum information processing. Several experiments have demonstrated strong coupling between single quantum dots and dielectric microcavities. Although plasmonic cavities, composed of metal nanostructures, have fast loss rates compared to dielectric cavities, they also have much smaller mode volumes, and therefore stronger dot-cavity

Xiaohua Wu; Jason Montgomery; Stephen Gray; Matthew Pelton

2010-01-01

359

Quantum field theoretic model of metastable resonant spin-singlet state of the np pair  

E-print Network

The np pair in the spin-singlet state is treated as a Cooper np-pair within the extension of the Nambu-Jona-Lasinio model of light nuclei, describing the deuteron as a Cooper np-pair in the spin-triplet state. For the Cooper np-pair in the spin-singlet state we compute the binding energy and express the S-wave scattering length of np scattering in the spin-singlet state in terms of the binding energy. The theoretical value of the S-wave scattering length of np scattering agrees well with the experimental data.

A. N. Ivanov; M. Cargnelli; M. Faber; H. Fuhrmann; V. A. Ivanova; J. Marton; N. I. Troitskaya; J. Zmeskal

2004-07-22

360

Some foundational aspects of quantum computers and quantum robots.  

SciTech Connect

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

Benioff, P.; Physics

1998-01-01

361

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

NASA Astrophysics Data System (ADS)

A new type of electronic trial wavefunction suitable for quantum Monte Carlo calculations of molecular systems is presented. In contrast with the standard Jastrow-Slater form built with a unique global Jastrow term, it is proposed to introduce individual Jastrow factors attached to molecular orbitals. Such a form is expected to be more physical since it allows to describe differently the local electronic correlations associated with various molecular environments (1s-core orbitals, 3d-magnetic orbitals, localized two-center ?-orbitals, delocalized ?-orbitals, atomic lone pairs, etc.). In contrast with the standard form, introducing different Jastrow terms allows us to change the nodal structure of the wavefunction, a point which is important in the context of building better nodes for more accurate fixed-node diffusion Monte Carlo (FN-DMC) calculations. Another important aspect resulting from the use of local Jastrow terms is the possibility of defining and preoptimizing local and transferable correlated units for building complex trial wavefunctions from simple parts. The practical aspects associated with the computation of the intricate derivatives of the multi-Jastrow trial function are presented in detail. Some first illustrative applications for atoms of increasing size (O, S, and Cu) and for the potential energy curve and spectroscopic constants of the FH molecule are presented. In the case of the copper atom, the use of the multi-Jastrow form at the variational Monte Carlo level has allowed us to improve significantly the value of the total ground-state energy (about 75% of the correlation energy with only one determinant and three atomic orbital Jastrow factors). In the case of the FH molecule (fluorine hydride), it has been found that the multi-Jastrow nodes lead to an almost exact FN-DMC value of the dissociation energy [D0=-140.7(4) kcal/mol instead of the estimated nonrelativistic Born-Oppenheimer exact value of -141.1], which is not the case with standard nodes, D0=-138.3(4) kcal/mol.

Bouabça, Thomas; Braïda, Benoît; Caffarel, Michel

2010-07-01

362

Time-dependent quantum dynamics of reactive scattering and the calculation of product quantum state distributions — A study of the collinear F+H 2 ( v =0) ? HF( v ?)+H reaction  

Microsoft Academic Search

Summary A new method for the calculation of partial cross sections in the time-dependent quantum theory of molecular reactive scattering processes is discussed. Preliminary calculations are presented which clearly illustrate the power of the method. They show how all the partial cross sections associated with a single initial quantum state may be computed over a very wide energy range from

C. Clay Marston; Gabriel G. Balint-Kurti; Richard N. Dixon

1991-01-01

363

Theoretical calculation of p Kas of phosphoric (V) acid in the polarisable continuum and cluster-continuum models  

NASA Astrophysics Data System (ADS)

The accuracy of the polarisable continuum model (PCM) and the mixed cluster-continuum model in the prediction of the absolute values of the three consecutive p Kas of phosphoric (V) acid has been checked. PCM calculations at the MP2/6-31+G(d,p) level reproduce the first p Ka with an acceptable error. However, they fail significantly for the next two p Kas and increasing the level of theory to G3B3 compound method does not provide any improvement. On the other hand, cluster-continuum calculations at the same MP2 level adequately predict all three dissociation constants of H 3PO 4. The number of necessary solvating water molecules depends on the polarising power of the anion and increases with the charge of the phosphate group. The obtained results indicate the validity of the cluster-continuum approach for the prediction of reliable p Ka values of polyprotic inorganic acids.

?miechowski, Maciej

2009-04-01

364

First principles calculations of the dark current in quantum well infrared photodetectors  

Microsoft Academic Search

A first principles model of the dark current in quantum well infrared photodetectors has been derived using a quantum mechanical approach. This is based on a combined representation of the field-induced and thermionic emission components of the dark current. It is argued that the contribution of sequential tunnelling to the dark current is affected significantly by the presence of interface

Nkaepe E. I. Etteh; Paul Harrison

2002-01-01

365

Mechanism of Selective Ammoxidation of Propene to Acrylonitrile on Bismuth Molybdates from Quantum Mechanical Calculations  

E-print Network

Mechanism of Selective Ammoxidation of Propene to Acrylonitrile on Bismuth Molybdates from Quantum ammoxidation of propene to acrylonitrile by bismuth molybdates, we report quantum mechanical studies (using stages of this industry, acrylonitrile was produced by propene on simple bismuth and molybdenum oxide

Goddard III, William A.

366

Theoretical calculation of p K as of phosphoric (V) acid in the polarisable continuum and cluster-continuum models  

Microsoft Academic Search

The accuracy of the polarisable continuum model (PCM) and the mixed cluster-continuum model in the prediction of the absolute values of the three consecutive pKas of phosphoric (V) acid has been checked. PCM calculations at the MP2\\/6-31+G(d,p) level reproduce the first pKa with an acceptable error. However, they fail significantly for the next two pKas and increasing the level of

Maciej ?miechowski

2009-01-01

367

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

Microsoft Academic Search

The theory for calculating the absorption of laser radiation by hydrogen is outlined for the temperatures and pressures of common laboratory plasmas. Nonhydrogenic corrections for determining the absorption by helium are also included. The coefficients for the absorption of He-Ne laser radiation at the wavelengths of 0.633, 1.15, and 3.39 ?m in a H plasma is presented for temperatures in

James R. Stallcop

1974-01-01

368

Theoretical comparison of efficiencies of photoluminescence up-conversion mechanisms in semiconductor quantum well structures: Auger recombination versus a two-step two-photon absorption  

NASA Astrophysics Data System (ADS)

In recent experiments, photoluminescence at frequencies far above the excitation laser frequency is observed in semiconductor hetero-structure materials. For example, in GaAs/GaInP_2, photoluminescence at 1.93 eV was observed while the excitation photon energy is 1.54 eV(F.A.J.M. Driessen et al, Appl. Phys. Lett. 67, 2813 (1995); Z.P. Su et al, Solid State Comm. 99, 933 (1996).). There is a controversy about the different mechanisms, Auger recombination versus a two-step two-photon absorption, responsible for the up-conversion. We report here the theoretical results for the up-conversion efficiency calculated for a single quantum well based on both mechanisms. We find that both processes contribute to the up-conversion^1. However, the two-step two-photon absorption mechanism dominates over the Auger process for the parameters common in most experiments, namely, photo-excited carrier densities < 10^17 cm-3 and well width ~ 100ÅP>

Arya, K.; Yu, Peter Y.

1998-03-01

369

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

370

NMR Spectroscopy and Theoretical Calculations in the Conformational Analysis of 1-Methylpyrrolidin-2-one 3-Halo-derivatives.  

PubMed

This study reports the results of ab initio and density functional theory (DFT) electronic structure calculations as well as (3)JHH experimental and calculated coupling constant data obtained in the investigation of the conformational equilibrium of 3-halo-derivatives of 1-methylpyrrolidin-2-one. The five-membered ring assumes an envelope conformation owing to the plane of formation of the O?C-N-R bond, with C4 forming the "envelope lid". When the conformation changes, the "lid" alternates between positions above and below the amide plane. The ?-carbonyl halogen assumes two positions: a pseudo-axial and a pseudo-equatorial. In the gaseous phase, the calculations indicate that the pseudo-axial conformer is more stable and preferable going down the halogen family. Natural bond orbital analysis showed that electronic delocalization is significant only for the iodo derivative. In the other derivatives, the electrostatic repulsion between oxygen and the halogen determines the conformational equilibrium. When the solvated molecule was taken into account, the pseudo-equatorial conformer population increased with the relative permittivity of the solvent. This variation was strong in the fluoro derivative, and the preference was inverted. In the chlorine derivative, the two populations became closer in methanol and acetonitrile. In the bromine and iodine derivatives, the percentage of pseudo-equatorial conformer increased only slightly owing to the dipole moment of the conformation: the pseudo-equatorial conformation has a greater dipole moment and thus is stable in media with high relative permittivity. PMID:25679501

de Melo, Ulisses Zonta; Silva, Raí G M; Yamazaki, Diego A S; Pontes, Rodrigo M; Gauze, Gisele F; Rosa, Fernanda A; Rittner, Roberto; Basso, Ernani A

2015-03-12

371

A multiprecision matrix calculation library and its extension library for a matrix-product-state simulation of quantum computing  

E-print Network

A C++ library, named ZKCM, has been developed for the purpose of multiprecision matrix calculations, which is based on the GNU MP and MPFR libraries. It is especially convenient for writing programs involving tensor-product operations, tracing-out operations, and singular-value decompositions. Its extension library, ZKCM_QC, for simulating quantum computing has been developed using the time-dependent matrix-product-state simulation method. This report gives a brief introduction to the libraries with sample programs.

Akira SaiToh

2011-11-14

372

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

NASA Astrophysics Data System (ADS)

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 differential and integral equations with error independent of the number of dimensions in the problem. Variational Monte Carlo (VMC) applies the variational principle to optimize the wave function used in the Monte Carlo integration of Schrodinger's time-independent equation. Diffusion Monte Carlo (DMC) represents the wave function by electron configurations diffusing stochastically in imaginary time to the ground state. Approximations in VMC and DMC make the problem tractable but introduce error in parameter-controlled and uncontrolled ways. The many-electron wave function consists of single-particle orbitals. The orbitals are combined in a functional form to account for electron exchange and correlation. Plane waves are a convenient basis for the orbitals. However, plane-wave orbitals grow in evaluation cost with basis-set completeness and system size. To speed up the calculation, polynomials approximate the plane-wave sum. Four polynomial methods tested are: Lagrange interpolation, pp-spline interpolation, B-spline interpolation and B-spline approximation. The polynomials all increase speed by an order of the number of particles. B-spline approximation most consistently maintains accuracy in the seven systems tested. However, polynomials increase the memory needed by a factor of two to eight. B-spline approximation with a separate approximation for the Laplacian of the orbitals increases the memory by a factor of four over plane waves. Polynomial-based orbitals enable larger calculations and careful examination of error introduced by approximations in VMC and DMC. In silicon bulk and interstitial defects, tens of variational parameters in the wave function converge the VMC energy. A basis set cutoff ?1000 eV converges the VMC energy to within 10 meV. Controlling the population of electron configurations representing the DMC wave function does not bias the energy above 24 configurations. An imaginary time step for the configurations of 10-2 hartree-1 introduces no error above the 10 meV level. Finite-size correction methods on the 16-atom cell size with difference up to 2 eV error and 1 eV discrepancy between 16- and 64-atom cells indicate finite-size error is still significant. Pseudopotentials constructed with and without scalar relativistic correction agree in DMC energy differences at the 100 meV level, and mean-field calculations with and without pseudopotentials suggest a correction of 50--100 meV. Using the VMC wave function to evaluate the nonlocal portion of the pseudopotential introduces an error on the 1 meV level. DMC energies using orbitals produced with varying mean-field approximations produce a 1 eV range in the defect formation energies while applying a backflow transformation to the electron coordinates reduces Monte Carlo fluctuations. The backflow-transformed average also permits an extrapolation to zero fluctuation. The extrapolated value estimates the formation energy unbiased by the starting wave function to be 4.5--5 eV.

Parker, William David

373

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

374

Electronic and charge-transport properties of 1,1,2,3,4,5-hexaphenysilole (HPS) crystal from theoretical calculations  

NASA Astrophysics Data System (ADS)

The structural, electronic, and charge transport properties of 1,1,2,3,4,5-hexaphenysilole (HPS) crystal are investigated using density functional theory (DFT). The influences of the temperature and pressure variations on the mechanical as well as the charge transport properties of HPS crystal are studied by molecular dynamics simulations combining with DFT calculations. By the analysis of the carrier mobilities and the band structures, we find that the hole may move slightly easier than the electron for the HPS crystal. MD simulation results show that moderately higher pressure and temperature are in favor of better charge transport properties for HPS crystals.

Liu, Yu-Hua; Xie, Yu; Lu, Zhong-Yuan

2010-02-01

375

A theoretical framework for calculations of the structural relaxation time on the basis of the free energy landscape theory  

NASA Astrophysics Data System (ADS)

On the basis of the free energy landscape theory, we develop a framework to calculate the structural relaxation time in supercooled liquids and glasses. By the framework, the relaxation time is obtained by an escaping time from a basin in a given free energy surface. In order to demonstrate its usefulness, we apply the framework to monodisperse hard-sphere glass systems. Then we show that the relaxation time increases drastically with the density. Additionally, we discuss an explicit picture of the cooperatively rearranging region by analyzing the spatial distribution of an activation free energy of one particle.

Ekimoto, Toru; Yoshimori, Akira; Odagaki, Takashi; Yoshidome, Takashi

2013-07-01

376

A Initio Calculations Performed on Carbon Monoxide Adsorption on the IRON(100) Surface and Complementing Theoretical Techniques  

NASA Astrophysics Data System (ADS)

Unrestricted Hartree-Fock calculations were performed on Fe_{x}CO clusters to model the CO(alpha_1), CO(alpha_2), and CO( alpha_3) adsorptions on the Fe(100) surface. Clusters of FeCO(C_{4v}) and a multiplicity of 5, Fe_2 CO(C_{2v}) and a multiplicity of 7, and Fe_2CO(C _{s}) and a multiplicity of 7, were constructed to model, respectively, the adsorption for the on top site, bridging site, and tilted CO structure at the 4-fold site. The CO position was optimized with respect to the Fe bulk distances using gradient techniques and the partial geometry optimization. CO stretching frequencies were calculated for each optimized geometry, and we find no evidence supporting CO adsorption in the bridging site. Using a full basis set the calculated CO stretching frequencies for the FeCO(C_{4v}), Fe_2CO(C_ {2v}), and the Fe_2 CO(C_{s}) clusters are 1992, 1767, and 771 cm^{ -1}, respectively. The CSOV analysis was executed to analyze the major orbital interactions between the CO and Fe_{x} clusters. For both Fe_2CO clusters, the CO pi^* perpendicular to the Fe _2 axis had a more significant contribution involving the pi backdonation from the Fe_2 clusters. Furthermore, the spin minority d electrons are mainly responsible for the pi backdonation. Due to problems with SCF convergence incurred during the Fe_{x}CO studies, we were forced to investigate a number of different techniques to achieve SCF convergence. Therefore, techniques that generate starting guesses of the eigenvectors for the SCF procedure and techniques used to accelerate SCF convergence are reviewed. The standard guesses of H _{core} and charge build -up are examined, and we introduce a new incremental cluster method for generating starting guesses for large clusters. The standard techniques of extrapolation, DIIS, damping, level shifting, restrict, and symmetry blocking are examined, and we also developed the hacker method and partial geometry optimization as new techniques to achieve SCF convergence. Results of the review indicate that the most important element for obtaining SCF convergence is the starting guess. A procedure for performing transition metal cluster calculations is outlined.

Meehan, Timothy Erickson

1992-01-01

377

Calculation of calorific values of coals from ultimate analyses: theoretical basis and geochemical implications. Final report. Part 8  

SciTech Connect

The various formulae for calculating calorific values for coals from ultimate analyses depend essentially on a propositon due to Dulong, that the heat of combustion of an organic compound is nearly equal to the heats of combustion of the elements in it, multiplied by their percentage content in the compound in question. This proposition assumes that the enthalpy of decomposition is negligible compared with the heat of combustion. The various published formulae, such as that due to Mott and Spooner, include empirical adjustments to allow for the fact that the enthalpy of formation or decomposition of no organic compound is zero (except rarely by chance). A new equation is proposed, which excludes empirical correction terms but includes a term explicitly related to the enthalpy of decomposition. As expected from the behavior of known compounds, this enthalpy varies with rank, but it also varies at the same level of rank with the geological history of the sample: rank is not the only source of variance in coal properties. The new equation is at least as effective in predicting calorific values for a set of 992 coals as equivalent equations derived for 6 subsets of the coals. On the whole, the distributions of differences between observed and calculated calorific values are skewed to only a small extent. About 86% of the differences lie between -300 and +300 Btu/lb (+- 700 kJ/kg). 10 references, 7 figures, 4 tables.

Given, P.H.; Weldon, D.; Zoeller, J.H.

1984-03-01

378

Substituent effects on zinc phthalocyanine derivatives: a theoretical calculation and screening of sensitizer candidates for dye-sensitized solar cells.  

PubMed

A series of unsymmetrical phthalocyanine sensitizer candidates with different donor and acceptor substituents, namely ZnPcBPh, ZnPcBOPh, ZnPcBtBu, ZnPcBN(Ph)?, ZnPcBNHPh, ZnPcBNH?, ZnPcBNHCH? and ZnPcBN(CH?)?, were designed and calculated using density functional theory (DFT) and time-dependent DFT calculations. The molecular orbital energy levels, the molecular orbital spatial distributions and the electronic absorption spectra of the ZnPcB series molecules were compared with those of TT7 and TT8 to reveal the substituent effects of different donor and acceptor groups on the phthalocyanine compounds and select good sesitizer candidates. The results show that some of these compounds have considerably smaller orbital energy gaps, red-shifted absorption bands and better charge-separated states, causing them to absorb photons in the lower energy region. Several new absorption bands emerge in the 400-600 nm region, which makes it possible for them to become panchromatic sensitizers. This characteristic is superior to the phthalocyanine sensitizers reported previously, including the current record holder, PcS6. The sensitizer candidates screened in the current work are very promising for providing good performance and might even challenge the photon-to-electricity conversion efficiency record of 4.6% for phthalocyanine sensitizers. PMID:23085158

Yang, Linlin; Guo, Lianshun; Chen, Qianqian; Sun, Huafei; Yan, Hui; Zeng, Qinghua; Zhang, Xianxi; Pan, Xu; Dai, Songyuan

2012-09-01

379

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

380

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

381

PCM/TD-DFT analysis of 1-bromo-2,3-dichlorobenzene - A combined study of experimental (FT-IR and FT-Raman) and theoretical calculations  

NASA Astrophysics Data System (ADS)

This study represents an integral approach towards understanding the electronic and structural aspects of 1-bromo-2,3-dichlorobenzene (BDCB). The experimental spectral bands were structurally assigned with the theoretical calculation, and the thermodynamic properties of the studied compound were obtained from the theoretically calculated frequencies. The relationship between the structure and absorption spectrum and effects of solvents have been discussed. It turns that the hybrid PBE1PBE functional with 6-311+G(d,p) basis provide reliable ?max when solvent effects are included in the model. The NBO analysis reveals that the studied compound presents a structural characteristic of electron-transfer within the compound. The frontier molecular orbitals (HOMO-LUMO) are responsible for the electron polarization and electron-transfer properties. The reactivity sites are identified by mapping the electron density into electrostatic potential surface (MESP). Besides, 13C and 1H have been calculated using the gauge-invariant atomic orbital (GIAO) method. The thermodynamic properties at different temperatures were calculated, revealing the correlations between standard heat capacity, standard entropy, standard enthalpy changes and temperatures. Furthermore, the studied compound can be used as a good nonlinear optical material due to the higher value of first hyper polarizability (5.7 times greater than that of urea (0.37289 × 10-30 esu)). Finally, it is worth to mentioning that solvent induces a considerable red shift of the absorption maximum going from the gas phase, and a slight blue shift of the transition S0 ? S1 going from less polar to more polar solvents.

Arivazhagan, M.; Muniappan, P.; Meenakshi, R.; Rajavel, G.

2013-03-01

382

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

E-print Network

Tungsten-dependent formaldehyde ferredoxin oxidoreductase: Reaction mechanism from quantum chemical theory Enzyme catalysis Formaldehyde ferredoxin oxidoreductase from Pyrococcus furiosus is a tungsten the formaldehyde substrate binds directly to the tungsten ion. WVI =O then performs a nucleophilic attack

Liao, Rongzhen

383

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

384

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

385

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

386

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

387

Molecular structure and conformational preferences of methylthiodichlorophosphite, Cl 2PSCH 3, as studied by gas electron diffraction and quantum-chemical calculations  

NASA Astrophysics Data System (ADS)

Free Cl 2PSCH 3 molecule has been studied by gas electron diffraction (ED), B3PW91/6-311+G ? (DFT) and MP2/AUG-cc-PVTZ quantum-chemical calculations. Structure optimizations of Cl 2PSMe molecule by both theoretical methods (DFT/MP2) indicate that the most stable conformer is an anti conformer of Cs symmetry, while the energy of a gauche conformer is about 1.3/1.6 kcal mol -1 higher. Each conformer is characterized by dihedral angle ?(CSP lp) where lp denotes the direction of the electron lone pair on the P atom; assumed to lay in the plane passing through P-S bond and bisector of the ClPCl bond angle. The calculated standard free energies at 298.15 K indicate that the mole fractions in the gas phase at this temperature are: ?( anti) = 65/79%, ?( gauche) = 35/21%. Experimental ED data agree well with joint presence of both conformers in the ratio ?( anti) = 68(12)% and ?( gauche) = 32(12)%. Natural Bond Orbital (NBO) analysis suggests that the relative stabilities of the two conformers as well as the differences between bond distances, valence angles and different NBO descriptors may be determined by anomeric effects. The most important of which is ? lpS ? ?PCl?, that is delocalizations of ? lone pair of the S atom into antibonding orbital of P-Cl bond.

Belyakov, A. V.; Khramov, A. N.; Naumov, V. A.

2010-08-01

388

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

SciTech Connect

The solutions of the time-independent Schroedinger equation for non-Hermitian (NH) Hamiltonians have been extensively studied and calculated in many different fields of physics by using L{sup 2} methods that originally have been developed for the calculations of bound states. The existing non-Hermitian formalism breaks down when dealing with wave packets (WPs). An open question is how time-dependent expectation values can be calculated when the Hamiltonian is NH? Using the F-product formalism that was recently proposed by Moiseyev and Lein [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 and those obtained from conventional (i.e., Hermitian) quantum mechanics (QM) calculations. The remarkable agreement between these results emphasizes the fact that in 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. In particular our work is relevant to the many different fields in physics and chemistry where complex absorbing potentials are introduced in order to reduce the propagation calculations to a restricted region in space where the artificial reflections from the edge of the numerical grid or box are avoided.

Gilary, Ido; Fleischer, Avner; Moiseyev, Nimrod [Department of Chemistry and Minerva Center for Nonlinear Physics of Complex Systems, Technion-Israel Institute of Technology, Haifa 32000 (Israel)

2005-07-15

389

Torsional energy levels of CH3OH+/CH3OD+/CD3OD+ studied by zero-kinetic energy photoelectron spectroscopy and theoretical calculations  

NASA Astrophysics Data System (ADS)

The torsional energy levels of CH3OH+, CH3OD+, and CD3OD+ have been determined for the first time using one-photon zero kinetic energy photoelectron spectroscopy. The adiabatic ionization energies for CH3OH, CH3OD, and CD3OD are determined as 10.8396, 10.8455, and 10.8732 eV with uncertainties of 0.0005 eV, respectively. Theoretical calculations have also been performed to obtain the torsional energy levels for the three isotopologues using a one-dimensional model with approximate zero-point energy corrections of the torsional potential energy curves. The calculated values are in good agreement with the experimental data. The barrier height of the torsional potential energy without zero-point energy correction was calculated as 157 cm-1, which is about half of that of the neutral (340 cm-1). The calculations showed that the cation has eclipsed conformation at the energy minimum and staggered one at the saddle point, which is the opposite of what is observed in the neutral molecule. The fundamental C-O stretch vibrational energy level for CD3OD+ has also been determined. The energy levels for the combinational excitation of the torsional vibration and the fundamental C-O stretch vibration indicate a strong torsion-vibration coupling.

Dai, Zuyang; Gao, Shuming; Wang, Jia; Mo, Yuxiang

2014-10-01

390

Torsional energy levels of CH?OH?/CH?OD?/CD?OD? studied by zero-kinetic energy photoelectron spectroscopy and theoretical calculations.  

PubMed

The torsional energy levels of CH3OH(+), CH3OD(+), and CD3OD(+) have been determined for the first time using one-photon zero kinetic energy photoelectron spectroscopy. The adiabatic ionization energies for CH3OH, CH3OD, and CD3OD are determined as 10.8396, 10.8455, and 10.8732 eV with uncertainties of 0.0005 eV, respectively. Theoretical calculations have also been performed to obtain the torsional energy levels for the three isotopologues using a one-dimensional model with approximate zero-point energy corrections of the torsional potential energy curves. The calculated values are in good agreement with the experimental data. The barrier height of the torsional potential energy without zero-point energy correction was calculated as 157 cm(-1), which is about half of that of the neutral (340 cm(-1)). The calculations showed that the cation has eclipsed conformation at the energy minimum and staggered one at the saddle point, which is the opposite of what is observed in the neutral molecule. The fundamental C-O stretch vibrational energy level for CD3OD(+) has also been determined. The energy levels for the combinational excitation of the torsional vibration and the fundamental C-O stretch vibration indicate a strong torsion-vibration coupling. PMID:25318721

Dai, Zuyang; Gao, Shuming; Wang, Jia; Mo, Yuxiang

2014-10-14

391

Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation  

NASA Astrophysics Data System (ADS)

The excited state intramolecular charge transfer process in donor-chromophore-acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO-LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

Jana, Sankar; Dalapati, Sasanka; Ghosh, Shalini; Kar, Samiran; Guchhait, Nikhil

2011-07-01

392

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

393

Towards Reference Viscosities of Carbon Monoxide and Nitrogen at Low Density Using Measurements between 290K and 680K as well as Theoretically Calculated Viscosities  

NASA Astrophysics Data System (ADS)

An all-quartz oscillating-disk viscometer of very high precision was used to determine the temperature dependence of the viscosities of carbon monoxide and nitrogen at low densities. The measurements were based on a single calibration at room temperature with a value theoretically calculated on the basis of an accurate ab initio pair potential for helium and the kinetic theory of dilute monatomic gases. The uncertainty of the experimental data is conservatively estimated to be ±0.15% at room temperature increasing to ±0.20% at the highest temperature of 682 K. The new data are compared with values recommended by the National Institute of Standards and Technology in the framework of its Standard Reference Data Program REFPROP as well as with experimental data from the literature. Whereas the REFPROP values for nitrogen can be considered as reference values, the new experimental data for carbon monoxide are up to 2% higher than the REFPROP values and should be taken into consideration for a new correlation. The temperature dependence of the viscosities calculated theoretically using ab initio intermolecular potential energy hypersurfaces for carbon monoxide and nitrogen and the kinetic theory of dilute molecular gases should be used for extrapolating the viscosity correlations of both gases to low and high temperatures. In addition, the viscosity ratio of carbon monoxide to nitrogen is investigated with the purpose to establish an improved correlation for carbon monoxide.

Vogel, Eckhard

2012-05-01

394

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

E-print Network

. Rotter, B. Weingartner, F. Libisch, F. Aigner, J. Feist, and J. Burgd¨orfer Institute for Theoretical Physics, Vienna University of Technology, A-1040 Vienna, Austria stefan.rotter@tuwien.ac.at Abstract. We

Rotter, Stefan

395

Fluoro-substitution effects in deoxyfluoro-D-glucose derivatives: random conformational search and quantum chemical calculation.  

PubMed

The effect of substitution by the fluorine atom at different positions of D-glucose was investigated by quantum chemical calculation of the low-energy conformers. These were obtained through the Random conformational search method. The geometries of conformers were optimized at the RHF/6-31(d) level, then reoptimization and vibrational analysis were performed at the B3LYP/6-31+G(d) level. Single-point energies were calculated at the B3LYP/6-311++G(2d,2p) level. The free energies of solvation in water were calculated utilizing the AM1-SM5.4 solvation model. For all substitution positions, the ring conformation does not change much, and the pyranoid 4C1 conformers are dominant, while variations in the substitution site result in different effects in the network of hydrogen bonds, anomeric effect, the solvation free energy, and the ratio of alpha- and beta-anomers. PMID:16839523

Zhou, Jin-Ming; Zhou, Jun-Hong; Zhang, Hua-Bei; Dong, Xi-Cheng; Chen, Min-Bo

2006-09-25

396

Theoretical Calculations and Simulations of Interaction of X-Rays with High-Z Nanomoities for Use in Cancer Radiotherapy  

NASA Astrophysics Data System (ADS)

When used with X-ray radiotherapy, heavy elements (high atomic number Z or HZ) such as gold(Au) and platinum(Pt) have the potential to greatly sensitize and enhance the damage to tumor tissues. While HZ radiosensitization has been shown to be higly effective in reducing tumor sizes, much work still needs to be done to determine the ideal X-ray energy/energy spectrum. The likelihood of photoelectric absorption of X-rays that result in the production of cell-killing Auger electrons relative to the photon scatter in an HZ sensitized tumor has to be determined for treatments using X-rays from various sources and energies to assess their efficacy. In this report, we present computations that outline the dependence of photoelectric absorption on X-ray energy. The relative X-ray absorption by a radiosensitized tumor was calculated to contrast the efficacy of different X-ray sources in Auger electron production at different tumor depths. Enhanced photoabsorption of low-energy X-rays from broadband sources in the keV range is shown to be much higher than from those in the MeV range. In addition, with the use of the Monte Carlo code package Geant4, we present the total X-ray energy deposited into a radiosensitized tumor located at different depths in a phantom. The enhancement in radiation dose deposition will also be analysed at the microscopic cellular level to determine the HZ radiosensitizer concentration required. Potential use of monochromatic X-rays for more precise HZ radiosensitization will also be described.

Lim, Sara N.; Pradhan, Anil K.; Nahar, Sultana N.

2013-06-01

397

Theoretical studies of the effect of strain on the performance of strained quantum well lasers based on GaAs and InP technology  

SciTech Connect

This paper discusses the use of strain to improve the performance of quantum well laser structures. The deformation potential theory is used to study the effect of strain produced by the addition of excess indium on the conduction band and valence band properties. Full-band mixing effects are retained in the calculations. Using a numerical technique developed to study laser parameters in arbitrary quantum well structures, the authors study the effect of strain on the threshold current density and polarization dependence. Dramatic improvements are found due to the strain-induced bandstructure changes. Optimization results are presented which show that single quantum well structures have the best performance.

Loehr, J.P.; Singh, J. (Michigan Univ., Ann Arbor, MI (United States). Dept. of Electrical Engineering and Computer Science)

1991-03-01

398

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

399

Computationally efficient quantum-mechanical technique to calculate the direct tunneling gate current in metal-oxide-semiconductor structures  

NASA Astrophysics Data System (ADS)

We propose a computationally efficient, accurate and numerically stable quantum-mechanical technique to calculate the direct tunneling (DT) gate current in metal-oxide-semiconductor (MOS) structures. Knowledge of the imaginary part ? of the complex eigenenergy of the quasi-bound inversion layer states is required to estimate the lifetimes of these states. Exploiting the numerically obtained exponential dependence of ? on the thickness of the gate-dielectric layer even in the sub-1-nm-thickness regime, we have simplified the determination of ? in devices where it is too small to be calculated directly. It is also shown that the MOS electrostatics, calculated self-consistently with open boundary conditions, is independent of the dielectric layer thickness provided that the other parameters remain unchanged. Utilizing these findings, a computationally efficient and numerically stable method is developed for calculating the tunneling current-gate voltage characteristics. The validity of the proposed model is demonstrated by comparing simulation results with experimental data. Sample calculations for MOS transistors with high-K gate-dielectric materials are also presented. This model is particularly suitable for DT current calculation in devices with thicker gate dielectrics and in device or process characterization from the tunneling current measurement.

Hakim, M. M. A.; Haque, A.

2003-08-01

400

A comparative study of quantum transport properties of silver and copper nanowires using first principles calculations  

NASA Astrophysics Data System (ADS)

The electronic structure and transport properties of silver (Ag) and copper (Cu) nanowires of diameters up to 1.7 nm are investigated using first principles density functional theory and the Landauer formalism in conjunction with a supercell approach. A direct comparison of the ballistic conductances, quantum capacitances, and kinetic inductances indicates that Ag and Cu nanowires show very similar performances. Compared to the electrostatic capacitance, the quantum capacitance is found to have a negligible effect on the total capacitance of the nanowire interconnect. In contrast, the overall inductance has a dominant contribution from the kinetic inductance over the magnetic inductance.

Kharche, Neerav; Manjari, Swati R.; Zhou, Yu; Geer, Robert E.; Nayak, Saroj K.

2011-03-01

401

Quantum chemical calculations predict biological function: The case of T cell receptor interaction with a peptide/MHC class I  

NASA Astrophysics Data System (ADS)

A combination of atomic correlation statistics and quantum chemical calculations are shown to predict biological function. In the present study, various antigenic peptide-Major Histocompatibility Complex (pMHC) ligands with near-identical stereochemistries, in complexation with the same T cell receptor (TCR), were found to consistently induce distinctly different quantum chemical behavior, directly dependent on the peptide’s electron spin density and intrinsically expressed by the protonation state of the peptide’s N-terminus. Furthermore, the cumulative coordination difference of any variant in respect to the native peptide was found to accurately reflect peptide biological function and immerges as the physical observable which is directly related to the immunological end-effect of pMHC-TCR interaction.

Antipas, Georgios S. E.; Germenis, Anastasios

2015-02-01

402

DFT analysis of P-nitrobenzotrifluoride--a combined study of experimental (FT-IR and FT-Raman) and theoretical calculations.  

PubMed

In this, a combined experimental and theoretical study on molecular structure and vibrational analysis of P-nitrobenzotrifluoride (PNBTF) is reported. The Fourier transform infrared and FT-Raman was recorded in the solid phase. The molecular geometry and vibrational frequencies of PNBTF in the ground state have been calculated by using density functional method (B3LYP) with 6-311++G(d,p) as basis set. Comparison of the observed fundamental vibrational frequencies with calculated results by density functional methods indicates that B3LYP/6-311++G(d,p) is superior to other methods for molecular vibrational problems. The bioactivity of the compound is analyzed by the HOMO-LUMO analysis. The reactivity sites are identified by mapping of electron density into electrostatic potential surface (MEP). Besides, (13)C and (1)H nuclear magnetic resonance (NMR) chemical shifts are calculated by using the gauge-invariant atomic orbital (GIAO) method. Furthermore, the compound can be used as a good nonlinear optical material due to the higher value of first hyperpolarizability. Solventation effect of NMR spectra by CPCM model of P-nitrobenzotrifluoride has been analyzed. PMID:24366159

Arivazhagan, M; Rexalin, D Anitha; Ilango, G

2014-01-01

403

Studies on the Conformational Landscape of Tert-Butyl Acetate Using Microwave Spectroscopy and Quantum Chemical Calculations  

NASA Astrophysics Data System (ADS)

The tert-Butyl acetate molecule was studied using a combination of quantum chemical calculations and molecular beam Fourier transform microwave spectroscopy in the 9 to 14 GHz range. Due to its rather rigid frame, the molecule possesses only two different conformers: one of Cs and one of C1 symmetry. According to ab initio calculations, the Cs conformer is 46 kJ/mol lower in energy and is the one observed in the supersonic jet. We report on the structure and dynamics of the most abundant conformer of tert-butyl acetate, with accurate rotational and centrifugal distortion constants. Additionally, the barrier to internal rotation of the acetyl methyl group was determined. Splittings due to the internal rotation of the methyl group of up to 1.3 GHz were observed in the spectrum. Using the programs XIAM and BELGI-Cs, we determine the barrier height to be about 113 cm-1 and compare the molecular parameters obtained from these two codes. Additionally, the experimental rotational constants were used to validate numerous quantum chemical calculations. This study is part of a larger project which aims at determining the lowest energy conformers of organic esters and ketones which are of interest for flavor or perfume synthetic applications Project partly supported by the PHC PROCOPE 25059YB.

Zhao, YueYue; Mouhib, Halima; Li, Guohua; Stahl, Wolfgang; Kleiner, Isabelle

2014-06-01

404

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 gas, performed on periodically repeated systems of up to 1050 atoms, show that all these errors together can

Alfè, Dario

405

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

406

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

E-print Network

trajectory space. A histogram of phases is collect from importance sampling. Techniques of Metropolis Monte in classical simulations such as importance sampling, biased sampling based on Monte Carlo MC techniques can Carlo with the system size, quantum dynamics of large and complex with many degrees of freedom systems

Sun, Sean

407

ccsd00001050, Quantum calculations of Coulomb reorientation for sub-barrier fusion  

E-print Network

the nuclear contribution seems negligible. This reorientation modi#12;es strongly the fusion cross-barrier fusion C. Simenel a;b) , Ph. Chomaz a) and G. de France a) a) GANIL, BP 55027, F-14076 Caen Cedex 5 of the sub-barrier fusion is predicted. Tunneling, the slow "quantum leak" through a classi- cal barrier

408

Interaction analysis of HIV-1 antibody 2G12 and Man9GlcNAc2 ligand: Theoretical calculations by fragment molecular orbital and MD methods  

NASA Astrophysics Data System (ADS)

In HIV-1 infection, human antibody 2G12 is capable of recognizing the high-mannose glycans on the HIV-1 surface glycoprotein, gp120. To investigate the ligand binding mechanisms of antibody 2G12 with glycans aiming for the contribution to the medications, we carried out classical molecular dynamics (MD) simulations and ab initio fragment molecular orbital (FMO) calculations on the antibody 2G12 complex with its high-mannose ligand. We found that Mannose D1 of the ligand had the largest binding affinity with the antibody, which was well consistent with experimental reports. Furthermore, significant roles of Mannose 4 and 4? in the ligand binding were theoretically indicated.

Koyama, Yuka; Ueno-Noto, Kaori; Takano, Keiko

2013-07-01

409

Improved Ligand Field Theoretical Calculations of R-Line Thermal Broadenings of MgO:Cr3+ and MgO:V2+  

NASA Astrophysics Data System (ADS)

With the values of parameters obtained from improved ligand-field theory, by taking into account all the irreducible representations and their components in EPI as well as all the levels and the admixtures of basic wavefunctions within d3 electronic configuration, the R-line thermal broadenings (TB) of both MgO:Cr3+ and MgO:V2+ have microscopic-theoretically been calculated. The results are in very good agreement with the experimental data. It is found that the R-line TB of MgO:Cr3+ or MgO:V2+ comes from the first-order term of EPI. The elastic Raman scattering of acoustic phonons plays a dominant role in R-line TB of MgO:Cr3+ or MgO:V2+.

Zhang, Zheng-Jie; Ma, Dong-Ping

2008-11-01

410

Effect of oxidation on the electronic structure of a Si29 quantum dot: Calculations of redshifts in energy gap  

NASA Astrophysics Data System (ADS)

We calculate the electronic structure of the H-covered Si29 quantum dot (~1 nm across) for four different oxygen configurations self-consistently using the extended Hückel-type nonorthogonal tight-binding method. The redshift in energy gap can occur in all oxygen configurations studied, but the size of the redshift depends on the oxygen configuration and also on the oxidation level. The energy-gap redshifts calculated for both backbonded and double-bonded oxygen configurations are large enough to explain the ones observed in the photoluminescence (PL) spectra from porous Si. For bridge-bonded and inserted oxygen configurations, the calculated redshifts are too small to explain the observed ones. The lifetimes calculated for the double-bonded oxygen configuration are around 2 ?s independent of oxidation level and photon energy. In contrary, for the backbonded oxygen configuration the calculated lifetime increases with an increasing level of oxidation and with decreasing photon energy (from several to a hundred micro seconds), being on the same order of magnitude as lifetimes measured for PL in porous Si.

Nishida, Masahiko

2006-03-01

411

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

412

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

413

Calculated room-temperature threshold current densities for the visible II-VI ZnCdSe\\/ZnSe quantum-well diode lasers  

Microsoft Academic Search

Room-temperature threshold current densities for the visible II-VI ZnCdSe\\/ZnSe semiconductor quantum-well diode lasers have been calculated using a simple model for the quantum-well gain and spontaneous radiative recombination rate. These results are compared with those for the infrared III-V GaAs\\/GaAlAs quantum-well lasers, calculated using the same model. By tailoring the epitaxial structure for optimum optical confinement, CW room-temperature operation of

R. L. Aggarwal; J. J. Zayhowski; B. Lax

1993-01-01

414

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

415

An evolutionary algorithm to calculate the ground state of a quantum system  

NASA Astrophysics Data System (ADS)

We present a new method based on evolutionary algorithms which permits to determine efficiently the ground state of the time-independent Schrödinger equation for arbitrary external potentials. The approach relies on the variational principle. The ground-state wave function of a given Hamiltonian is found by using the procedure of survival of the fittest, starting from a population of wave functions. To perform the search for the fittest wave function we have extended a genetic algorithm to treat quantum mechanical problems. We present results for different one dimensional external potentials and compare them with analytical solutions and with other numerical methods. Our approach yields very good convergence in all cases. Potential applications of the quantum genetic algorithm presented here to more dimensions and many-body problems are discussed.

Grigorenko, I.; Garcia, M. E.

2000-09-01

416

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

417

Quantum calculations of multistructure cross-sections for the Ca(4s5p, 3P2 ?) He collisional process  

NASA Astrophysics Data System (ADS)

Transitions between the magnetic sublevels of the Ca atom in the 4s5p Rydberg state induced by collision with He(1S) are studied by the quantum close-coupled method. Multistructure cross-sections, of both conventional and coherence types, are calculated for the spin-changing transition 3P2 ? 1P1. Scattering calculations are based on a model Ca-He interaction as well as an ab initio approach and are related to the conditions of the recent three-vector correlation experiment of Smith, Ch. J., Driessen, J. P. J., Eno, L., and Leone, S. R., 1992, J. chem. Phys., 96, 8212, in which the alignment selected 3P ? 1P cross-sections were determined. Fairly good qualitative agreement has been found for the relative values of the cross-sections considered.

Paul-Kwiek, Ewa; Orlikowski, Tadeusz

418

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

419

Theoretical studies of the effect of strain on the performance of strained quantum well lasers based on GaAs and InP technology  

Microsoft Academic Search

A discussion is presented of the use of strain to improve the performance of quantum well laser structures. The deformation potential theory is used to study the effect of strain produced by the addition of excess indium on the conduction band and valence band properties. Full-band mixing effects are retained in the calculations. Using a numerical technique developed to study

John P. Loehr; Jasprit Singh

1991-01-01

420

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

421

Deducing the molecular properties of zwitterionic, protonated, deprotonated, and double-deprotonated forms of L-cysteine from vibrational spectroscopy (IR, Raman, VCD) and quantum chemical calculations.  

PubMed

The behavior of L-cysteine (C3H7NO2S, (2R)-2-amino-3-sulfanylpropanoic acid) in water at different pH values was analyzed both experimentally and theoretically. The behavior was studied at pH values of 5.21 (at this pH, L-cysteine is a zwitterionic species), 1.00 (protonated species), 8.84 (monodeprotonated species), and 13.00 (dideprotonated species). We carried out a vibrational study using nonchiroptical (IR-Raman) and chiroptical (VCD) techniques complemented by quantum chemical calculations. We adopted a dual strategy, as follows. (i) The hybrid density functionals B3LYP and M062X and the ab initio MP2 method were employed, with the same 6-311++G (d,p) basis set, in order to characterize the relative energies and structures of an extensive set of conformers of L-cysteine. The presence of water was included by utilizing the IEF-PCM implicit solvation model. (ii) The vibrational analysis was made using a chirality-sensitive using a chirality-sensitive technique (VCD) and chirality-insensitive techniques (IR, including MIR and FIR, and Raman), especially in aqueous solution. The results obtained theoretically and experimentally were compared in order to deduce the most stable structures at each pH. Moreover, for the first time, the monodeprotonated anion of L-cysteine was detected in aqueous solution by means of IR, Raman and vibrational circular dichroism (VCD). Finally, analysis of the low-frequency region using the IR and Raman techniques was shown to be a very important way to understanding the conformational preference of the zwitterionic species. PMID:24916344

Quesada-Moreno, María Mar; Avilés-Moreno, Juan Ramón; Márquez-García, A A; López-González, Juan Jesús

2014-06-01

422

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

423

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