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1

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

SciTech Connect

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

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

2012-01-01

2

Theoretical calculations of spin dynamics and quantum effects in rare earth SMMs  

NASA Astrophysics Data System (ADS)

Rare-earth single-molecular magnets constitute a hot emerging topic in molecular magnetism. It also constitutes a promising field to study and eventually remedy the processes that lead to decoherence. In fact, experiments show some success in the design of rare-earth spin qubits with long coherence times. Furthermore, these long-lived quantum states of rare-earth SMMs can in principle be manipulated for quantum information processing. In particular, a simple quantum error correction protocol might be realizable using ElectroNuclear DOuble Resonance. Going further on this path will require a detailed knowledge of the wave function of the low-energy multiplet, and an understanding of how it can be tailored by chemical means. An inexpensive point-charge model has been presented recently that is able to reproduce the main features of the Crystal Field Hamiltonian of both lanthanoids (such as Dysprosium, Holmium, Terbium) and actinoids such as Uranium.

Gaita-Ariño, Alejandro

2013-03-01

3

Topics in theoretical and computational nanoscience: From controlling light at the nanoscale to calculating quantum effects with classical electrodynamics  

NASA Astrophysics Data System (ADS)

Interest in structures with nanometer-length features has significantly increased as experimental techniques for their fabrication have become possible. The study of phenomena in this area is termed nanoscience, and is a research focus of chemists, pure and applied physicists, electrical engineers, and others. The reason for such focus is the wide range of novel effects that exist at this scale, both of fundamental and practical interest, which often arise from the interaction between metallic nanostructures and light, and range from large electromagnetic field enhancements to extraordinary optical transmission of light through arrays of subwavelength holes. For the theoretician and computational scientist, this area has been, and continues to be rich with interesting problems to explore and phenomena to explain. For the most part, the phenomena can be explained using classical electrodynamics. However, recent experimental techniques allow individual nanostructures to be studied, questioning the accuracy of such methods at this most detailed level. Moreover, for structures with dimensions of just a few nanometers, the applicability of such methods at all needs to be questioned. Even if a system contains many hundreds of atoms or more so that a continuum level of description is adequate, the optical (and other) properties can be difficult to correctly calculate due to the importance of quantum effects. Thus, the theoretician is in trouble, and the accurate descriptions of such structures remain largely unknown. This dissertation is aimed at addressing some of the most fundamental and outstanding questions in nanoscience from a theoretical and computational perspective, specifically: (i) At the single nanoparticle level, how well do experiment and classical electrodynamics agree? (ii) What is the detailed relationship between optical response and nanoparticle morphology, composition, and environment? (iii) Does an optimal nanostructure exist for generating large electromagnetic field enhancements, and is there a fundamental limit to this? (iv) Can nanostructures be used to control light, such as confining it, or causing fundamentally different scattering phenomena to interact, such as electromagnetic surface modes and diffraction effects? (v) Is it possible to calculate quantum effects using classical electrodynamics, and if so, how do they affect optical properties?

McMahon, Jeffrey Michael

4

Calculations in Quantum Chromodynamics  

NASA Astrophysics Data System (ADS)

I analyze two problems which extend the predictive ability of Quantum Chromodynamics. I study composite operators in lattice gauge theory that reduce to operators of the form (')(psi) (GAMMA) DDDD . . . (psi) in the continuum limit; such operators arise in perturbative analyses of quantum chromodynamics. Using our results and the data of a numerical simulation one could normalize exclusive processes and predict moments of deep inelastic scattering structure functions. To initiate the program we construct and renormalize lattice operators to the one-loop level. We are encouraged that the hadronic matrix elements of the simpler operators are within reach of numerical simulations. I also calculate a corrected photon spectrum in the endpoint region, z (--->) 1, for direct photon decay of the upsilon by summing the leading logarithms of (1 -z) to all orders in perturbation theory. This effect causes the cross section to level out at (DBLTURN)z = .8, removing the sharp peak in the tree level prediction, but does not cause the cross section to turn over.

Photiadis, Douglas Marc

5

Theoretical framework for quantum networks  

NASA Astrophysics Data System (ADS)

We present a framework to treat quantum networks and all possible transformations thereof, including as special cases all possible manipulations of quantum states, measurements, and channels, such as, e.g., cloning, discrimination, estimation, and tomography. Our framework is based on the concepts of quantum comb—which describes all transformations achievable by a given quantum network—and link product—the operation of connecting two quantum networks. Quantum networks are treated both from a constructive point of view—based on connections of elementary circuits—and from an axiomatic one—based on a hierarchy of admissible quantum maps. In the axiomatic context a fundamental property is shown, which we call universality of quantum memory channels: any admissible transformation of quantum networks can be realized by a suitable sequence of memory channels. The open problem whether this property fails for some nonquantum theory, e.g., for no-signaling boxes, is posed.

Chiribella, Giulio; D'Ariano, Giacomo Mauro; Perinotti, Paolo

2009-08-01

6

Theoretical Calculations of H2O Linewidths and Pressure Shifts: Comparison of Anderson Theory with Quantum Many-Body Theory for N2 and Air Broadened Lines.  

National Technical Information Service (NTIS)

The purpose of this paper is to make specific comparisons of two theoretical methods with available experimental measurements of H2O widths and shifts for the case of N2 (or air) broadening. The earliest calculations of H2O-n2 half widths were carried out...

R. W. Davies B. A. Oli

1977-01-01

7

Theoretical studies of quantum dynamics  

Microsoft Academic Search

Quantum mechanical methods have been developed for the study of dynamical processes in polyatomic systems and condensed matter. First, we developed an exact scheme for wavefunction propagation with a few degrees of freedom based on time-dependent discrete variable representations (TD-DVR) of the evolution operator. The TD-DVR evolves under appropriate reference Hamiltonians and leads to an efficient scheme for studying intramolecular

Eunji Sim

1997-01-01

8

Theoretical Calculations of Atomic Data for Spectroscopy  

NASA Astrophysics Data System (ADS)

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.

2000-10-01

9

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

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

Domain theoretic structures in quantum information theory  

NASA Astrophysics Data System (ADS)

In this thesis, we continue the study of domain theoretic structures in quantum information theory initiated by Keye Martin and Bob Coecke in 2002. The first part of the thesis is focused on exploring the domain theoretic properties of qubit channels. We discover that the Scott continuous qubit channels are exactly those that are unital or constant. We then prove that the unital qubit channels form a continuous dcpo, and identify various measurements on them. We show that Holevo capacity is a measurement on unital qubit channels, and discover the natural measurement in this setting. We find that qubit channels also form a continuous dcpo, but capacity fails to be a measurement. In the second part we focus on the study of exact dcpos, a domain theoretic structure, closely related to continuous dcpos, possessed by quantum states. Exact dcpos admit a topology, called the exact topology, and we show that the exact topology has an order theoretic characterization similar to the characterization of the Scott topology on continuous dcpos. We then explore the connection between exact and continuous dcpos; first, by identifying an important set of points, called the split points, that distinguishes between exact and continuous structures; second, by exploring a continuous completion of exact dcpos, and showing that we can recover the exact topology from the Scott topology of the completion.

Feng, Johnny

12

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

13

Sheaf-theoretic representation of quantum measure algebras  

SciTech Connect

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

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

2006-09-15

14

Quantum Cryptography for Information-Theoretic Security  

NASA Astrophysics Data System (ADS)

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

Sanders, Barry

15

Theoretical calculations of proton affinities in phenol  

NASA Astrophysics Data System (ADS)

It is shown that a relatively simple MP2(fc)/6-31G ??//HF/6-31G ? model is capable of providing quantitative description of protonation in phenol. The use of the 6-31G ?? basis set in the single-point MP2 calculation is crucial in this respect. The zero-point energy (ZPE) contribution to the proton affinity (PA) is estimated at the HF/6-31G ? level of approximation. It appears that the contribution of the ZPE energy to relative ?PA proton affinities is negligible. The simple additivity rule for calculating empirical ZP energies works relatively well for the protonated species too. The energetically most favourable site of the proton attack is para to the OH substitution in accordance with the experimental finding. Performance of the MP2(fc)6-31G ??+ZPE(HF/6-31G ?) model in reproducing protonation at the oxygen atom is tested in some medium size alcohols and ethers. The calculated PA values are in good agreement with the measured data.

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

1995-01-01

16

Theoretical principles of inflationary quantum metrology  

Microsoft Academic Search

A hypothetical foundation is presented for future metrology in the form of a simple alternative to superstring and quantum-gravitation\\u000a theories: a phase-tree model, which agrees with ideas of combining quantum fields and cosmological inflation.

A. F. Kotyuk; A. V. Khromov

2008-01-01

17

Quantum Monte Carlo calculations for light nuclei.  

SciTech Connect

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

Wiringa, R. B.

1998-10-23

18

Quantum Monte Carlo calculations for light nuclei  

SciTech Connect

Quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A {le} 8 are made using a realistic Hamiltonian that fits NN scattering data. Results for more than 30 different (j{sup {prime}}, T) states, plus isobaric analogs, are obtained and the known excitation spectra are reproduced reasonably well. Various density and momentum distributions and electromagnetic form factors and moments have also been computed. These are the first microscopic calculations that directly produce nuclear shell structure from realistic NN interactions.

Wiringa, R.B.

1998-08-01

19

Quantum Monte Carlo calculations for light nuclei  

SciTech Connect

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

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

1997-10-01

20

Reconciling motor performance indicators from theoretical calculations and laboratory tests  

Microsoft Academic Search

Quite often because of the complexity in the design of large industrial motors, the theoretical motor parameter calculations do not match actual results from laboratory tests. Thus, it becomes important to predict the amount of discrepancy between the two methods to develop confidence in the motor parameter calculations. This paper discusses the development of multiple artificial neural networks (ANNs) designed

Himanshu Hirlekar; Badrul H. Chowdhury; S. Ruffing

2010-01-01

21

Theoretical calculation of dielectronic recombination cross sections for hydrogenlike helium  

SciTech Connect

We have developed a simplified relativistic configuration-interaction method to calculate the dielectronic recombination cross sections and rates. In this method, the infinite resonant doubly excited states can be treated conveniently in the frame of quantum defect theory. As a stringent test, we calculated the dielectronic recombination cross sections for hydrogenlike helium. The results for the {ital KLL} and {ital KLM} resonances are in good agreement with the experimental measurement.

Wang, J.; Qu, Y.; Li, J. [Institute of Physics, P.O. Box 603, Chinese Academy of Sciences, Beijing 100080 (China)

1995-11-01

22

Theoretical study of quantum computation with nonlinear optics  

NASA Astrophysics Data System (ADS)

Quantum computing has been of intense interest over the last 10 years because of its promising ability to do high-speed factoring and its potential for the efficient simulation of quantum dynamics. It could be implemented in many different ways using optical techniques. A better understanding of the advantages and disadvantages of these approaches would allow the experimental groups working in this area to optimize their choice of experiment and to concentrate on the approaches that are most likely to succeed. In this thesis, we are interested in quantum logic gates based on nonlinear optical approaches and mainly focus on one of the approaches----quantum Zeno gates. We theoretically analyze two-photon absorption, which is essential to perform quantum Zeno gates for coherent light and for frequency-entangled light. We also analyze and compare quantum Zeno gates with nonlinear phase gates, which is another promising optical implementation for quantum logic. The results of our theoretical analysis will be useful for future experimental work in quantum computation.

You, Hao

23

Theoretical Analysis of Quantum Noise in Ghost Imaging  

Microsoft Academic Search

Ghost imaging is a method to image nonlocally an object by transmitting pairs of entangled photons through the object and a reference optical system respectively. We present a theoretical analysis of the quantum noise in this imaging technique. The dependence of the noise on the properties of the apertures in the imaging system are discussed and demonstrated with a numerical

Jing Cheng; Shen-Sheng Han

2005-01-01

24

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

25

Theoretical Calculation of Stability for NASA Stage 57 Stator  

NASA Astrophysics Data System (ADS)

The stability of 595 operational points, belonging to 25 different experimental arrangements of the NASA stage 57, is studied by means of a theoretical calculation based on a theorem recently presented in the scientific literature. This large number of tests is used for checking the results of the theory for a wide variation of the operational and the design parameters. This study completes a previous one by adding the calculations for the stator. Both rotor and stator results are related with the stage stability. While only seven test points appear as potentially unstable due to the rotor, nine test points do due to the stator.

Benavides, Efrén M.; Juste, Gregorio L.

2011-09-01

26

Quantum Monte Carlo calculations applied to magnetic molecules  

NASA Astrophysics Data System (ADS)

In this dissertation, we have implemented a quantum Monte Carlo (QMC) algorithm, and have used it to perform calculations for a variety of finite Heisenberg spin systems. A detailed description of the QMC method has been provided, which is followed by applications of the method to various systems. These applications begin with a detailed analysis of the (calculated) equilibrium magnetization and magnetic susceptibility for a number of Heisenberg Hamiltonians. In particular, we have studied the dependence of these quantities on intrinsic spin s, and have quantified the approach to the classical (s ? infinity) limit. These results are not specific to a particular physical system, but are potentially applicable to many systems. We have also analyzed four recently synthesized species of magnetic molecules, each of which is theoretically challenging to the methods that are normally used for such analyses. Using the QMC method, we have distinguished the microscopic (exchange) parameters that describe the interactions in each of these magnetic molecules, and, based upon these parameters, we have made predictions for future experiments. The well-known "negative sign problem" (NSP) can be problematic for QMC calculations. However, for some systems, our analysis was able to proceed despite the NSP. For other systems, this is not the cases, so we have clearly indicated when the NSP is, and is not, insurmountable for these types of calculations.

Engelhardt, Larry Paul

27

Theoretical Analysis of Quantum Noise in Ghost Imaging  

NASA Astrophysics Data System (ADS)

Ghost imaging is a method to image nonlocally an object by transmitting pairs of entangled photons through the object and a reference optical system respectively. We present a theoretical analysis of the quantum noise in this imaging technique. The dependence of the noise on the properties of the apertures in the imaging system are discussed and demonstrated with a numerical example. For a given source, the resolution and the signal-to-noise ratio cannot be improved simultaneously.

Cheng, Jing; Han, Shen-Sheng

2005-07-01

28

Theoretical analysis of quantum ghost imaging through turbulence  

Microsoft Academic Search

Atmospheric turbulence generally affects the resolution and visibility of an image in long-distance imaging. In a recent quantum ghost imaging experiment [P. B. Dixon , Phys. Rev. APLRAAN1050-294710.1103\\/PhysRevA.83.051803 83, 051803 (2011)], it was found that the effect of the turbulence can nevertheless be mitigated under certain conditions. This paper gives a detailed theoretical analysis to the setup and results reported

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

2011-01-01

29

Theoretical investigation of the quantum noise in ghost imaging  

Microsoft Academic Search

Ghost imaging is a method to nonlocally image an object by transmitting pairs\\u000aof entangled photons through the object and a reference optical system\\u000arespectively. We present a theoretical analysis of the quantum noise in this\\u000aimaging technique. The dependence of the noise on the properties of the\\u000aapertures in the imaging system are discussed and demonstrated with a numerical

Jing Cheng; Shensheng Han

2004-01-01

30

New approaches for quantum chemical calculations on very large molecules  

SciTech Connect

This is the final report for a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Ab initio quantum chemistry has proven to be a valuable tool for understanding the electronic structure of small molecules containing 5--50 atoms. Calculations on larger systems have been prohibitive because of the forbidding scaling properties of the methods used. In the simplest traditional many-body method, second-order perturbation theory, the work scales as the fifth power of N, where N is proportional to the number of electrons in the system. New methods for the many-body problem, which scale as the third power of N and are well suited to utilize parallel computation, have been studied. The combination of these two developments enable the treatment of molecules in the range of 50--500 atoms with first principles methods. The ability to treat molecules containing 50--500 atoms with quantum chemistry techniques would open new vistas for theoretical chemistry. Large organic molecules of pharmaceutical interest and novel species such as fullerenes would be amenable to study. Inorganic complexes containing transition metals and actinides could be treated using realistic ligands. Important problems such as the chemistry at active sites in enzymes and the photochemistry involved in photosynthesis of chlorophyll could be studied. Catalytic reactions of hydrocarbons on zeolites and other supports of interest to the petrochemical and chemical industries could be examined.

Martin, R.L.; Russo, T.V.; Hay, P.J.

1996-04-01

31

Theoretical calculation of proton mobility for collective surface proton transport.  

PubMed

We present a theoretical study of surface proton mobility at a minimally hydrated array of protogenic surface groups. At dense packing, the array assembles into a 2D bicomponent lattice that is formed by sulfonate anions, which are only allowed to fluctuate about fixed equilibrium positions, and mobile hydronium ions. Proton transport on the lattice proceeds by collective translocations of hydronium ions. This type of motion is described within the framework of soliton theory. Our main objective in this article is to establish the relation between microscopic surface structure and effective proton mobility. To this end, we present an approach to calculate microscopic interaction parameters that determine hydronium ion motion. The developed formalism enables us to theoretically derive an expression for soliton mobility at a given surface structure and compare it with experimentally measured mobilities. PMID:23848749

Golovnev, Anatoly; Eikerling, Michael

2013-06-14

32

Theoretical calculation of proton mobility for collective surface proton transport  

NASA Astrophysics Data System (ADS)

We present a theoretical study of surface proton mobility at a minimally hydrated array of protogenic surface groups. At dense packing, the array assembles into a 2D bicomponent lattice that is formed by sulfonate anions, which are only allowed to fluctuate about fixed equilibrium positions, and mobile hydronium ions. Proton transport on the lattice proceeds by collective translocations of hydronium ions. This type of motion is described within the framework of soliton theory. Our main objective in this article is to establish the relation between microscopic surface structure and effective proton mobility. To this end, we present an approach to calculate microscopic interaction parameters that determine hydronium ion motion. The developed formalism enables us to theoretically derive an expression for soliton mobility at a given surface structure and compare it with experimentally measured mobilities.

Golovnev, Anatoly; Eikerling, Michael

2013-06-01

33

Spectrometric studies and theoretical calculations of some ?-ketonitriles  

NASA Astrophysics Data System (ADS)

The tautomerism of some ?-ketonitriles is investigated by the analysis of their mass spectra and theoretical calculations performed at the MP2/6-31G(d,p) level. The mass spectra of some ?-ketonitriles can provide valuable information regarding the keto-enol and nitrile-ketenimine equilibria taking place in the gas phase. The predictive value of this methodology is supported by the influence of the nature and size of substituents on tautomeric equilibria and the rather good correlation existing between the abundance ratios of selected fragments. Results show that the tautomeric equilibria of these bifunctional compounds can be evaluated by mass spectrometry.

Ruiz, Danila; Giussi, Juan; Albesa, Alberto; Schiavoni, Mercedes; Furlong, Jorge; Allegretti, Patricia

2010-10-01

34

Quantum Method for Fault Tolerance Calculations in Quantum-dot Cellular Automata Clocked Devices  

Microsoft Academic Search

A full basis quantum method is used for the study of the joint influence of temperature and positional defects on quasi-adiabatically clocked Quantum-dot Cellular Automata (QCA) devices. The full quantum statistical calculation is done diachronically at the level of a clocking zone in the locking phase, while the charge distribution of the other clocking zones is considered as external conditions.

Ioan Sturzu

2005-01-01

35

Absorbing-like boundaries for quantum field theoretical grid simulations  

NASA Astrophysics Data System (ADS)

We introduce a computational method that permits us to increase the interaction time for quantum mechanical and quantum field theoretical simulations of multi-particle states on a finite space–time grid. In contrast to the usual approach where the unwanted portion of the wave function close to the grid boundaries is absorbed by a potential with a negative imaginary part, this method is unitary and therefore conserves the norm of the state. This technique is based on assigning particles close to the boundary a larger effective mass (or slower speed of light) such that the particles slow down and cannot re-enter the interaction zone. The method can therefore be applied to multi-particle states for which imaginary potential methods fail.

Norris, S.; Vikartofsky, A.; Wagner, R. E.; Su, Q.; Grobe, R.

2013-11-01

36

Theoretical analysis of quantum ghost imaging through turbulence  

SciTech Connect

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

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

2011-10-15

37

Quantum-chemical Calculations in the Study of Antitumour Compounds  

NASA Astrophysics Data System (ADS)

The results of quantum-chemical calculations on antitumour preparations concerning the mechanism of their action at the electronic and molecular levels and structure-activity correlations are discussed in this review. Preparations whose action involves alkylating and free-radial mechanisms, complex-forming agents, and antimetabolites are considered. Modern quantum-chemical methods for calculations on biologically active substances are described. The bibliography includes 106 references.

Luzhkov, V. B.; Bogdanov, G. N.

1986-01-01

38

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

39

A calculation of the theoretical significance of matched bullets.  

PubMed

The comparison and identification of bullets from the striations that appear on their surfaces, after they have been fired from a gun, have been practiced since the 1920s. Although the significance of the correspondences of these impression marks has been empirically justified, there is a conspicuous absence of any theoretical foundation for the likelihood. What is presented here is the derivation of the formulae for calculating the probability for the correspondence of the impression marks on a subject bullet to a random distribution of a similar number of impression marks on a suspect bullet of the same type. The approach to the calculation entails subdividing the impression marks into a series of individual lines having widths equal to the separation distance at which a misalignment of striations between the two bullets cannot be distinguished. This distance depends upon the resolution limit imposed by the microscope as well as by the visual acuity of the examiner. A calculation of the probabilities for finding pairs and triplets of consecutively matching lines on nonmatching bullets, by an examiner with normal perception using a microscope at 40x magnification, produces values that agree well with the empirical probabilities determined by Biasotti in the 1950s and when determined for larger consecutive sequences suggest that they are extremely unlikely to occur. The formulae can be used to determine the probabilities for the random occurrence of any sequence of striae and provide a straightforward way to quantitatively justify the significance of a specific match between any two bullets. PMID:18547357

Howitt, David; Tulleners, Fred; Cebra, Karen; Chen, Shiahn

2008-07-01

40

Operator Calculations in Loop Quantum Gravity  

NASA Astrophysics Data System (ADS)

In canonical quantum gravity we express various geometrical and physical quantities as non-local operators based on loops. The action of these operators leads to expressions which are evaluated with the aid of a specific loop calculus. The loop calculus is closely related to the recoupling theory of colored knots and links with trivalent vertices. We introduce the basic ingredients of the loop calculus and present few examples.

Borissov, R.

1997-08-01

41

Theoretical Calculation of Surface Properties of Silver and Aluminum Nanoparticles  

NASA Astrophysics Data System (ADS)

Determining the surface properties of nanoscale systems is extremely difficult. Due to their relatively simple structures, metallic nanoparticles are frequently used as test objects to study the physics of nanosystems. However, the existing literature often contains conflicting and contradictory data pertaining to the surface energy and surface stress of metallic nanoparticles. Application of Tolman's liquid droplet model to the values of surface energy and stress of these nanoparticles opened up new problems. Even the applicability of the liquid droplet model to metallic nanoparticles is doubted. This thesis addresses these inconsistencies by explicitly determining the surface stress and surface energy of Ag and Al nanoparticles from rigorous calculations based on a combination of ab initio and empirical principles. We employ ab initio density functional theory combined with the pseudopotential formalism to calculate the surface properties of Ag and Al nanoparticles containing up to several hundred atoms. For larger nanoparticles, containing up to ˜ 10,000 atoms, we use an empirical embedded atom method based on density functional theory. The results of our calculations show that both Ag and Al nanoparticles conform to Tolman's liquid droplet model. We found that, based on the material, the Tolman's length can be either positive or negative. In previous models, it has been assumed that the Tolman's length has a functional dependence only on the size of nanoparticle. We found that in addition to the size dependence, Tolman's length has also a functional dependence on the ratio of surface stress and surface energy. This result allows us to construct a more accurate theoretical model for Tolman's length of metallic nanoparticles.

Medasani, Bharat

42

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

43

Quantum mechanical cluster calculations of critical scintillationprocesses  

SciTech Connect

This paper describes the use of commercial quantum chemistrycodes to simu-late several critical scintillation processes. The crystalis modeled as a cluster of typically 50 atoms embedded in an array oftypically 5,000 point charges designed to reproduce the electrostaticfield of the infinite crystal. The Schrodinger equation is solved for theground, ionized, and excited states of the system to determine the energyand electron wavefunction. Computational methods for the followingcritical processes are described: (1) the formation and diffusion ofrelaxed holes, (2) the formation of excitons, (3) the trapping ofelectrons and holes by activator atoms, (4) the excitation of activatoratoms, and (5) thermal quenching. Examples include hole diffusion in CsI,the exciton in CsI, the excited state of CsI:Tl, the energy barrier forthe diffusion of relaxed holes in CaF2 and PbF2, and prompt hole trappingby activator atoms in CaF2:Eu and CdS:Te leading to an ultra-fast (<50ps) scintillation risetime.

Derenzo, Stephen E.; Klintenberg, Mattias K.; Weber, Marvin J.

2000-02-22

44

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

45

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

NASA Astrophysics Data System (ADS)

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 (B3g-2) and the anion (Au-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

1993-04-01

46

Binding energy calculation of excitonic trions in spherical quantum dots with the quantum adiabatic theorem  

Microsoft Academic Search

The stability of the charged excitons X+ and X? as a function of the spherical quantum dot radius R and also as a function of the effective mass ratio ? is studied with a formulation of the Hartree–Fock approximation using a calculation method which is based on the quantum adiabatic theorem. Our results indicate that the binding energies of X+

S. Baskoutas; A. F. Terzis

2005-01-01

47

Spin-unrestricted calculations in quantum chemistry  

SciTech Connect

The unrestricted complete active space self-consistent field (UCASSCF) function is defined, and a proof that a UCASSCF eigenfunction of the spin operator S[sup 2] is a CASSCF function is given. The spin-contamination for an unrestricted Hartree-Fock (UHF) function is evaluated by using Araki angle operators, and the UHF function is then projected on the restricted open-shell Hartree-Fock (ROHF) space. The present analysis has deep consequences since it implies that the only non-spin-contaminated UHF functions are the ROHF functions. This is illustrated in a calculation of the spin density of He[sub 2][sup +]. 1 fig.

Cassam-Chenaie, P.; Chandler, G.S. (Univ. of Western Australia, Nedlands (Australia))

1993-01-01

48

ZnO controllable sized quantum dots produced by polyol method: An experimental and theoretical study  

Microsoft Academic Search

Zinc oxide quantum dots were prepared in diethyleneglycol using zinc acetate as a precursor compound and the particle size of the dried powders was determined using the X-ray diffraction method (XRD). It was found that quantum dot size ranges from 4 to 9 nm and is influenced by the initial zinc acetate concentration and the centrifugation speed. Theoretical predictions concerning quantum

Nikolaos Bouropoulos; Ioannis Tsiaoussis; Panagiotis Poulopoulos; Panayotis Roditis; Sotirios Baskoutas

2008-01-01

49

Entanglement of Interacting Fermions in Quantum Monte Carlo Calculations  

NASA Astrophysics Data System (ADS)

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

Grover, Tarun

2013-09-01

50

Entanglement of interacting fermions in quantum monte carlo calculations.  

PubMed

Given a specific interacting quantum Hamiltonian in a general spatial dimension, can one access its entanglement properties, such as the entanglement entropy corresponding to the ground state wave function? Even though progress has been made in addressing this question for interacting bosons and quantum spins, as yet there exist no corresponding methods for interacting fermions. Here we show that the entanglement structure of interacting fermionic Hamiltonians has a particularly simple form-the interacting reduced density matrix can be written as a sum of operators that describe free fermions. This decomposition allows one to calculate the Renyi entropies for Hamiltonians which can be simulated via determinantal quantum Monte Carlo calculations, while employing the efficient techniques hitherto available only for free fermions. The method presented works for the ground state, as well as for the thermally averaged reduced density matrix. PMID:24116750

Grover, Tarun

2013-09-24

51

Quantum Statistical Calculations for Thermal Effect in Quantum-Dot Cellular Automata (QCA)1  

Microsoft Academic Search

A theoretical study of thermal effect in QCA is presented. Quantum statistical analysis for average polarization of each cell is done. A computational model has been developed to find all the possible configurations of polarizations in an array of cells. All cells are in one of the two possible eigenstates corresponding to the total Hamiltonian. Here, only the locked states

Mahfuza Khatun; Ioan Sturzu; Jonathan Kanuchok; Douglas Tougaw

2003-01-01

52

Quantum Monte Carlo calculations of BiFeO3  

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

53

Wavelength dependence of nitrate radical quantum yield from peroxyacetyl nitrate photolysis: experimental and theoretical studies.  

PubMed

The photolysis wavelength dependence of the nitrate radical quantum yield for peroxyacetyl nitrate (CH(3)C(O)OONO(2), PAN) is investigated. The wavelength range used in this work is between 289 and 312 nm, which mimics the overlap of the solar flux available in the atmosphere and PAN's absorption cross section. We find the nitrate radical quantum yield from PAN photolysis to be essentially invariant; Phi(NO3)(PAN) = 0.30 +/- 0.07 (+/-2sigma) in this region. The excited states involved in PAN photolysis are also investigated using ab initio calculations. In addition to PAN, calculations on peroxy nitric acid (HOONO(2), PNA) are performed to examine general photochemical properties of the -OONO(2) chromophore. Equation of motion coupled cluster calculations (EOM-CCSD) are used to examine excited state energy gradients for the internal coordinates, oscillator strengths, and transition energies for the n --> pi* transitions responsible for the photolysis of both PNA and PAN. We find in both molecules, photodissociation of both O-O and O-N bonds occurs via excitation to predissociative electronic excited states and subsequent redistribution of that energy as opposed to directly dissociative excitations. Comparison and contrast between experimental and theoretical studies of HOONO(2) and PAN photochemistry from this and other work provide unique insight on the photochemistry of these species in the atmosphere. PMID:17958340

Flowers, Bradley A; Stanton, John F; Simpson, William R

2007-10-24

54

Quantum Method for Fault Tolerance Calculations in Quantum-dot Cellular Automata Clocked Devices  

NASA Astrophysics Data System (ADS)

A full basis quantum method is used for the study of the joint influence of temperature and positional defects on quasi-adiabatically clocked Quantum-dot Cellular Automata (QCA) devices. The full quantum statistical calculation is done diachronically at the level of a clocking zone in the locking phase, while the charge distribution of the other clocking zones is considered as external conditions. A full basis quantum method requires numerical calculations with large sparse matrices. Therefore, usage of some approximation techniques is needed for larger clocking zones. Using an approximation method results for thermal effect and fabrication defect properties will be shown for a wire and a shift register. The work has been supported by the Indiana 21^st Century Research and Technology Fund (#04-492)

Sturzu, Ioan

2005-03-01

55

Exact quantum dynamics calculations using a symmetrized Gaussian basis  

NASA Astrophysics Data System (ADS)

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

Halverson, Thomas; Poirier, Bill

2012-10-01

56

Quantum state determination: estimates for information gain and some exact calculations  

NASA Astrophysics Data System (ADS)

It is known that mutually unbiased bases (MUBs), whenever they exist, are optimal in an information theoretic sense for the determination of the unknown state of a quantum ensemble. Such bases may not exist for most dimensions. The present paper deals with information gain in some generalizations and approximations of MUBs. We give estimates of the information loss (relative to MUBs) in these suboptimal choice of bases. For some generalization of MUBs we give exact calculations for the information gain. It is calculated directly in terms of transition probabilities among the measurement bases. We also give the formal solutions for the problem of quantum state tomography in these casesSome of the results in this paper was reported in the proceedings of EQIS 2005. A large part of this work was done at CQCT, Macquarie University, Sydney..

Patra, M. K.

2007-08-01

57

Quantum Monte Carlo calculations of BiFeO3  

Microsoft Academic Search

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

Lucas K. Wagner; David Sulock; Lubos Mitas

2007-01-01

58

Theoretical Calculation of the N_2 Broadened Half-Widths of H_2O  

NASA Astrophysics Data System (ADS)

For many applications, in addition to accurate spectral line frequencies and intensities one needs accurate Lorentzian parameters (half-widths, pressure shifts, and their temperature dependencies). Because of the importance of H_2O in the Earth's atmosphere, extensive compilations of these data are available in the HITRAN database. Recently, ab initio calculations have been carried out and databases containing tens of millions of line frequencies and intensities are available. Obviously, it is not possible to measure their Lorentzian parameters, and one must rely on theoretical calculations. For many years researchers have used the Robert-Bonamy (RB) formalism; however, we recently discovered a subtle error was made in their original derivation, and this modification is not negligible for certain systems. In this theory the internal motions are treated quantum mechanically, while the translational motion is treated classically. In order to achieve the desired accuracy, one needs to use a realistic interaction potential, and a realistic trajectory model for the translational motion. Because of the large number of potential matrix elements appearing in the standard application of the RB theory, one is forced to introduce cut-offs that may limit the accuracy attainable. To obviate the necessity of low-order cut-offs and achieve results for half-widths to the accuracy of the interaction potential, we recently reformulated the theory using the coordinate representation. In the present paper, we present results to study the effects of using different experimental half-width data to obtain the parameters in several models for the interaction potential, and the effects of different trajectory models for treating the relative motion. From our detailed analysis, we are able to draw several conclusions that should help theorists to make choices in order to achieve realistic theoretical half-widths and to assess their accuracy. Q. Ma, R. H. Tipping, and C. Boulet, J. Chem. Phys. 124, 014109 (2006).

Tipping, R. H.; Ma, Q.

2010-06-01

59

Theoretical Calculations for Transfer-Excitation and Transfer-Ionization  

NASA Astrophysics Data System (ADS)

Theoretical fully differential cross sections (FDCS) will be compared with experimental results for transfer-excitation and transfer-ionization occurring in proton-helium collisions. In the experiments, the incident proton captures one electron from a helium atom, and the remaining electron is left either in an excited bound state of the helium ion, or is ejected into the continuum as a free particle. The transfer-excitation experiments have been performed in Rolla, MO and the transfer-ionization experiments have been performed in Frankfurt, Germany. The theoretical approach we use is a full four-body approach, taking each particle into account. This results in a nine dimensional integral to evaluate the T-matrix. For transfer-excitation, the incident projectile and the outgoing hydrogen atom are treated as Hartree-Fock distorted waves, and a Hylleraas wavefunction is used for the initial state helium atom. In the final state, bound hydrogenic wavefunctions are used for the hydrogen atom and the residual ion. In the case of transfer-ionization, the ejected electron is treated as a Hartree-Fock distorted wave instead of a bound hydrogenic.

Harris, A. L.; Peacher, J. L.; Schulz, M.; Madison, D. H.

2007-06-01

60

Quantum-Theoretical Methods and Studies Relating to Properties of Materials.  

National Technical Information Service (NTIS)

This research concerned the development of new ab initio nonempirical quantum-theoretical methods and computational techniques for studying molecular properties related to those of advanced materials. Extensive computations were performed to demonstrate t...

C. S. Ewig

1989-01-01

61

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

62

A novel quantum physics course for physics teachers: theoretical background  

Microsoft Academic Search

The aim of this cooperation project between Universities of Joensuu and Helsinki is to study the learning and teaching of quantum physics and to develop a new research-based quantum physics course for physics teachers. This way the new instructional models are hopefully spreading also to the lower educational levels. As physics educators have stated, physics is not considered very attractive

Mervi Asikainen; Pekka E. Hirvonen; Matti Heikkinen; Ville Nivalainen

63

A Quantum Theoretical Explanation for Probability Judgment Errors  

Microsoft Academic Search

A quantum probability model is introduced and used to explain human probability judgment errors including the conjunction and disjunction fallacies, averaging effects, unpacking effects, and order effects on inference. On the one hand, quantum theory is similar to other categorization and memory models of cognition in that it relies on vector spaces defined by features and similarities between vectors to

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

2011-01-01

64

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

65

a Theoretical Model for Calculation of Molecular Stopping Power  

Microsoft Academic Search

A modified local plasma model based on the work of Linhard-Winther, Bethe, Brown, and Walske is established. The Gordon-Kim's molecular charged density model is employed to obtain a formula to evaluate the stopping power of many useful molecular systems. The stopping power of H(,2) and He gas was calculated for incident proton energy ranging from 100 KeV to 2.5 MeV.

Yuan-Jian Xu

1984-01-01

66

A theoretical model for calculation of molecular stopping power  

Microsoft Academic Search

A modified local plasma model is established. The Gordon-Kim's molecular charged density model is employed to obtain a formula to evaluate the stopping power of many useful molecular systems. The stopping power of H2 and He gas was calculated for incident proton energy ranging from 100 keV to 2.5 MeV. The stopping power of O2, N2, and water vapor was

Y. J. Xu

1984-01-01

67

Quantum mechanical resonance calculations using an energy selected basis in hyperspherical coordinates  

NASA Astrophysics Data System (ADS)

Scattering resonances play a key role in many chemical processes, including unimolecular and bimolecular reactions and photodissociation. A significant theoretical emphasis over the past several decades has been placed on accurate resonance calculations for polyatomic systems. In spite of such efforts, a quantum treatment of molecular systems which exhibit a high density of states and strong coordinate coupling near dissociation remains a formidable task. The research described herein employs improved quantum mechanical methods to calculate a representation of nuclear motion, both bound and unbound, which is used subsequently to calculate accurate resonance energies and lifetimes for two triatomic systems: the neon trimer and ozone. Specifically, theory and results are given regarding the construction of an optimal, L2 eigenbasis using techniques such as the discrete variable representation, the energy selected basis (ESB) method, and iterative diagonalization methods. A new energy selection method is also developed and implemented for the neon trimer. Subsequent resonance calculations are described which make use of the artificial boundary inhomogeneity (ABI) method, adapted to work with the above mentioned ESB and hyperspherical coordinates. The ABI method is used to calculate a set of linearly independent wavefunctions (LIWs) at a given energy for the representation of the scattering wavefunction. Resonance parameters are obtained by imposing scattering boundary conditions on a linear combination of LIWs and solving for the S-matrix, S, its energy derivative, dS/dE, and the Smith lifetime matrix, Q. When available, comparisons are made with previously reported calculations.

Montgomery, Jason

68

Symmetry in auxiliary-field quantum Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

We show how symmetry properties can be used to greatly increase the accuracy and efficiency in auxiliary-field quantum Monte Carlo (AFQMC) calculations of electronic systems. With the Hubbard model as an example, we study symmetry preservation in two aspects of ground-state AFQMC calculations, the Hubbard-Stratonovich transformation and the form of the trial wave function. It is shown that significant improvement over state-of-the-art calculations can be achieved. In unconstrained calculations, the implementation of symmetry often leads to shorter convergence time and much smaller statistical errors and thereby a substantial reduction of the sign problem. Moreover, certain excited states become possible to calculate which are otherwise beyond reach. In calculations with constraints, the use of symmetry can reduce the systematic error from the constraint. It also allows release-constraint calculations, leading to essentially exact results in many cases. Detailed comparisons are made with exact diagonalization results. Accurate ground-state energies are then presented for larger system sizes in the two-dimensional repulsive Hubbard model.

Shi, Hao; Zhang, Shiwei

2013-09-01

69

Fault Tolerance Calculations for Quantum-dot Cellular Automata devices  

NASA Astrophysics Data System (ADS)

A numerical study of the joint influence of temperature and positional defects on Quantum-dot Cellular Automata (QCA) operation will be presented. The statistical model that has been introduced, simulates the random distribution of positional defects of the dots within cells, and of cells within arrays. We have studied specific clocked and non-clocked QCA devices using both a full basis quantum statistical method and Inter-cellular Hartree Approximation for different temperatures. Parameters such as success rate and breakdown displacement factor were defined and calculated numerically. Results show the thermal dependence of breakdown displacement factor of the QCA devices. The breakdown displacement factor decreases with the temperature. The work has been supported by the Indiana 21^st Century Research and Technology Fund (# 04-492)

Khatun, Mahfuza

2005-03-01

70

TOPICAL REVIEW: Recent advances in jointed quantum mechanics and molecular mechanics calculations of biological macromolecules: schemes and applications coupled to ab initio calculations  

NASA Astrophysics Data System (ADS)

We review the recent research on the functional mechanisms of biological macromolecules using theoretical methodologies coupled to ab initio quantum mechanical (QM) treatments of reaction centers in proteins and nucleic acids. Since in most cases such biological molecules are large, the computational costs of performing ab initio calculations for the entire structures are prohibitive. Instead, simulations that are jointed with molecular mechanics (MM) calculations are crucial to evaluate the long-range electrostatic interactions, which significantly affect the electronic structures of biological macromolecules. Thus, we focus our attention on the methodologies/schemes and applications of jointed QM/MM calculations, and discuss the critical issues to be elucidated in biological macromolecular systems.

Hagiwara, Yohsuke; Tateno, Masaru

2010-10-01

71

A quantum theoretical explanation for probability judgment errors.  

PubMed

A quantum probability model is introduced and used to explain human probability judgment errors including the conjunction and disjunction fallacies, averaging effects, unpacking effects, and order effects on inference. On the one hand, quantum theory is similar to other categorization and memory models of cognition in that it relies on vector spaces defined by features and similarities between vectors to determine probability judgments. On the other hand, quantum probability theory is a generalization of Bayesian probability theory because it is based on a set of (von Neumann) axioms that relax some of the classic (Kolmogorov) axioms. The quantum model is compared and contrasted with other competing explanations for these judgment errors, including the anchoring and adjustment model for probability judgments. In the quantum model, a new fundamental concept in cognition is advanced--the compatibility versus incompatibility of questions and the effect this can have on the sequential order of judgments. We conclude that quantum information-processing principles provide a viable and promising new way to understand human judgment and reasoning. PMID:21480739

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

2011-04-01

72

Quantum Monte Carlo calculated potential energy curve for the helium dimer  

NASA Astrophysics Data System (ADS)

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.

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

2010-05-01

73

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

SciTech Connect

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

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

2008-03-28

74

Spectroscopic investigations, quantum chemical calculations, HOMO-LUMO and NBO/NLMO analysis of 4-pyridinecarbohydrazide  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman spectra of 4-pyridinecarbohydrazide have been recorded. The complete vibrational assignment and analysis of the fundamental modes was carried out using the experimental 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 6-311++G(d,p) basis set. The 1H and 13C NMR chemical shifts have been simulated. Thermodynamic properties have been calculated at different temperatures. 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.

Gobinath, E.; John Xavier, R.

2013-11-01

75

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

PubMed

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

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

2005-12-23

76

Self-consistent calculations of optical properties of type I and type II quantum heterostructures  

NASA Astrophysics Data System (ADS)

In this Thesis the self-consistent computational methods are applied to the study of the optical properties of semiconductor nanostructures with one- and two-dimensional quantum confinements. At first, the self-consistent Schrodinger-Poisson system of equations is applied to the cylindrical core-shell structure with type II band alignment without direct Coulomb interaction between carriers. The electron and hole states and confining potential are obtained from a numerical solution of this system. The photoluminescence kinetics is theoretically analyzed, with the nanostructure size dispersion taken into account. The results are applied to the radiative recombination in the system of ZnTe/ZnSe stacked quantum dots. A good agreement with both continuous wave and time-resolved experimental observations is found. It is shown that size distribution results in the photoluminescence decay that has essentially non-exponential behavior even at the tail of the decay where the carrier lifetime is almost the same due to slowly changing overlap of the electron and hole wavefunctions. Also, a model situation applicable to colloidal core-shell nanowires is investigated and discussed. With respect to the excitons in type I quantum wells, a new computationally efficient and flexible approach of calculating the characteristics of excitons, based on a self-consistent variational treatment of the electron-hole Coulomb interaction, is developed. In this approach, a system of self-consistent equations describing the motion of an electron-hole pair is derived. The motion in the growth direction of the quantum well is separated from the in-plane motion, but each of them occurs in modified potentials found self-consistently. This approach is applied to a shallow quantum well with the delta-potential profile, for which analytical expressions for the exciton binding energy and the ground state eigenfunctions are obtained, and to the quantum well with the square potential profile with several different well and barrier materials. The numerical results yield lower exciton binding energies in comparison to standard variational calculations, while the iterative scheme used to calculate the energies and respective wavefunctions is stable, rapidly convergent and requires reduced computational effort. Thus, the method can be an important computational tool in computing exciton characteristics in quantum wells exceeding currently existing approaches in accuracy and efficiency. The method can also be naturally generalized for quantum wires and dots.

Shuvayev, Vladimir A.

77

Nuclear-magnetic-resonance quantum calculations of the Jones polynomial  

SciTech Connect

The repertoire of problems theoretically solvable by a quantum computer recently expanded to include the approximate evaluation of knot invariants, specifically the Jones polynomial. The experimental implementation of this evaluation, however, involves many known experimental challenges. Here we present experimental results for a small-scale approximate evaluation of the Jones polynomial by nuclear magnetic resonance (NMR); in addition, we show how to escape from the limitations of NMR approaches that employ pseudopure states. Specifically, we use two spin-1/2 nuclei of natural abundance chloroform and apply a sequence of unitary transforms representing the trefoil knot, the figure-eight knot, and the Borromean rings. After measuring the nuclear spin state of the molecule in each case, we are able to estimate the value of the Jones polynomial for each of the knots.

Marx, Raimund; Spoerl, Andreas; Pomplun, Nikolas; Schulte-Herbrueggen, Thomas; Glaser, Steffen J. [Department of Chemistry, Technische Universitaet Muenchen, Lichtenbergstr. 4, D-85747 Garching (Germany); Fahmy, Amr [Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115 (United States); Kauffman, Louis [University of Illinois at Chicago, 851 S. Morgan Street, Chicago, Illinois 60607-7045 (United States); Lomonaco, Samuel [University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250 (United States); Myers, John M. [Cruft Laboratory, Harvard University, 19 Oxford Street, Cambridge, Massachusetts 02138 (United States)

2010-03-15

78

Theoretical discussion for quantum computation in biological systems  

NASA Astrophysics Data System (ADS)

Analysis of the brain as a physical system, that has the capacity of generating a display of every day observed experiences and contains some knowledge of the physical reality which stimulates those experiences, suggests the brain executes a self-measurement process described by quantum theory. Assuming physical reality is a universe of interacting self-measurement loops, we present a model of space as a field of cells executing such self-measurement activities. Empty space is the observable associated with the measurement of this field when the mass and charge density defining the material aspect of the cells satisfy the least action principle. Content is the observable associated with the measurement of the quantum wave function ? interpreted as mass-charge displacements. The illusion of space and its content incorporated into cognitive biological systems is evidence of self-measurement activity that can be associated with quantum operations.

Baer, Wolfgang

2010-04-01

79

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.

Kang, Jiyoung; Hagiwara, Yohsuke; Tateno, Masaru

2012-01-01

80

Controlling phosphorescence color and quantum yields in cationic iridium complexes: a combined experimental and theoretical study.  

PubMed

We report a combined experimental and theoretical study on cationic Ir(III) complexes for OLED applications and describe a strategy to tune the phosphorescence wavelength and to enhance the emission quantum yields for this class of compounds. This is achieved by modulating the electronic structure and the excited states of the complexes by selective ligand functionalization. In particular, we report the synthesis, electrochemical characterization, and photophysical properties of a new cationic Ir(III) complex, [Ir(2,4-difluorophenylpyridine)2(4,4'-dimethylamino-2,2'-bipyridine)](PF(6)) (N969), and compare the results with those reported for the analogous [Ir(2-phenylpyridine)2(4,4'-dimethylamino-2,2'-bipyridine)](PF(6)) (N926) and for the prototype [Ir(2-phenylpyridine)2(4,4'-tert-butyl-2,2'-bipyridine)](PF(6)) complex, hereafter labeled N925. The three complexes allow us to explore the (C/\\N) and (N/\\N) ligand functionalization: considering N925 as a reference, we investigate in N926 the effect of electron-releasing substituents on the bipyridine ligand, while in N969, we investigate the combined effect of electron-releasing substituents on the bipyridine ligand and the effect of electron-withdrawing substituents on the phenylpyridine ligands. For N969 we obtain blue-green emission at 463 nm with unprecedented high quantum yield of 85% in acetonitrile solution at room temperature. To gain insight into the factors responsible for the emission color change and the different quantum yields, we perform DFT and TDDFT calculations on the ground and excited states of the three complexes, characterizing the excited-state geometries and including solvation effects on the calculation of the excited states. This computational procedure allows us to provide a detailed assignment of the excited states involved in the absorption and emission processes and to rationalize the factors determining the efficiency of radiative and nonradiative deactivation pathways in the investigated complexes. This work represents an example of electronic structure-driven tuning of the excited-state properties, thus opening the way to a combined theoretical and experimental strategy for the design of new iridium(III) phosphors with specific target characteristics. PMID:17583337

De Angelis, Filippo; Fantacci, Simona; Evans, Nicholas; Klein, Cedric; Zakeeruddin, Shaik M; Moser, Jacques-E; Kalyanasundaram, Kuppuswamy; Bolink, Henk J; Grätzel, M; Nazeeruddin, Mohammed K

2007-06-21

81

Information-theoretic measure of uncertainty due to quantum and thermal fluctuations  

NASA Astrophysics Data System (ADS)

We study an information-theoretic measure of uncertainty for quantum systems. It is the Shannon information I of the phase-space probability distribution , where ||z> are coherent states and ? is the density matrix. As shown by Lieb I>=1, and this bound represents a strengthened version of the uncertainty principle. For a harmonic oscillator in a thermal state, I coincides with von Neumann entropy, -Tr(?ln?), in the high-temperature regime, but unlike entropy, it is nonzero (and equal to the Lieb bound) at zero temperature. It therefore supplies a nontrivial measure of uncertainty due to both quantum and thermal fluctuations. We study I as a function of time for a class of nonequilibrium quantum systems consisting of a distinguished system coupled to a heat bath. We derive an evolution equation for I. For the harmonic oscillator, in the Fokker-Planck regime, we show that I increases monotonically, if the width of the coherent states is chosen to be the same as the width of the harmonic oscillator ground state. For other choices of the width, and for more general Hamiltonians, I settles down to a monotonic increase in the long run, but may suffer an initial decrease for certain initial states that undergo ``reassembly'' (the opposite of quantum spreading). Our main result is to prove, for linear systems, that I at each moment of time has a lower bound Imint, over all possible initial states. This bound is a generalization of the uncertainty principle to include thermal fluctuations in nonequilibrium systems, and represents the least amount of uncertainty the system must suffer after evolution in the presence of an environment for time t. Imint is an envelope, equal for each time t, to the time evolution of I for a certain initial state, which we calculate to be a nonminimal Gaussian. Imint coincides with the Lieb bound in the absence of an environment, and is related to von Neumann entropy in the long-time limit. The form of Imint indicates that the thermal fluctuations become comparable with the quantum fluctuations on a time scale equal to the decoherence time scale, in agreement with earlier work of Hu and Zhang. Our results are also related to those of Zurek, Habib, and Paz, who looked for the set of initial states generating the least amount of von Neumann entropy after a fixed period of nonunitary evolution.

Anderson, Arlen; Halliwell, Jonathan J.

1993-09-01

82

Theoretical Physics Student Seminar 2008-2009 Alternative Theories of Gravity: Loop Quantum Gravity and Loop Quantum Cosmology  

Microsoft Academic Search

Quantizing gravity and unifying it with the other fundamental inter- actions has been the focus of theoretical physics research in the last cou- ple of decades. Among dierent attempts, numerous theories have been suggested, some representing a more conservative approach, while others introduce new underlying fundamental theories, which reduce to known physics in certain limits. Loop Quantum Gravity (LQG) represents

Marcin Dukalski

2009-01-01

83

Theoretical modeling and experimental characterization of InAs/InGaAs quantum dots in a well detector  

SciTech Connect

Theoretical modeling and experimental characterization of InGaAs/GaAs quantum dots-in-a-well (DWELL) intersubband heterostructures, grown by molecular beam epitaxy are reported. In this heterostructure, the self-assembled dots are confined to the top half of a 110 A InGaAs well which in turn is placed in a GaAs matrix. Using transmission electron microscopy, the quantum dots are found to be pyramidal in shape with a base dimension of 110 A and height of 65 A. The band structure for the above mentioned DWELL heterostructure was theoretically modeled using a Bessel function expansion of the wave function. The energy levels of the three lowest states of the conduction band of the quantum dot are calculated as a function of the electric field. Intersubband n-i-n detectors were fabricated using a ten layer DWELL heterostructure. The spectral response of the detector is measured at a temperature between 30 and 50 K and compared with the prediction of our theoretical model.

Amtout, A.; Raghavan, S.; Rotella, P.; Winckel, G. von; Stintz, A.; Krishna, S. [Center of High Technology Materials, Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87106 (United States)

2004-10-01

84

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; Simo~Es da Fonseca, José

2000-05-01

85

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

NASA Astrophysics Data System (ADS)

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

Gobinath, E.; Xavier, R. John

2013-03-01

86

Theoretical Study of Operational Limits of High-Speed Quantum Dot Lasers.  

National Technical Information Service (NTIS)

A comprehensive theory of the modulation response of quantum dot (QD) lasers is developed. The factors limiting the modulation bandwidth are identified and the highest possible bandwidth is calculated. The highest bandwidth increases directly with overlap...

L. V. Asryan

2012-01-01

87

Charged vs. Neutral particle creation in expanding Universes: A Quantum Field Theoretic Treatment  

Microsoft Academic Search

A complete quantum field theoretic study of charged and neutral particle creation in a rapidly\\/adiabatically expanding Friedman-Robertson-Walker metric for an O(4) scalar field theory with quartic interactions (admitting a phase transition) is given. Quantization is carried out by inclusion of quantum fluctuations. We show that the quantized Hamiltonian admits an su(1,1) invariance. The squeezing transformation diagonalizes the Hamiltonian and shows

B. Bambah; C. Mukku

2003-01-01

88

InAsSb\\/InP quantum dots for midwave infrared emitters: A theoretical study  

Microsoft Academic Search

A theoretical study of the electronic properties of InAsSb quantum dots (QDs) deposited on InP substrate is presented. Unstrained bulk materials present a direct gap between 0.1 and 0.35 eV suitable for mid-infrared emitters (2-5 mum). However, strain and quantum-confinement effects may limit the extension of the emission spectrum of these nanostructures towards the higher wavelengths. Various associations of materials

C. Cornet; F. Doré; A. Ballestar; J. Even; N. Bertru; A. Le Corre; S. Loualiche

2005-01-01

89

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

90

On the efficient calculation of the quantum properties (dipolar moments) of the molecular heteroatomic (nitrogen) polycyclic aromatic hydrocarbons  

Microsoft Academic Search

In this work, we have developed an efficient (very fast) theoretical methodology able to calculate the quantum properties\\u000a of any molecular heteroatomic PAH. If all the heteroatoms are Nitrogens, we can obtain these results directly from its chemical\\u000a formula. We have obtained and analyzed the electric dipolar moment of 43 small Nitrogen PAHs (NPAHs). We have obtained the\\u000a atomic spin

José Ramón Álvarez-Collado

2011-01-01

91

AM and FM quantum noise in semiconductor lasers-part II: comparison of theoretical and experimental results for AlGaAs lasers  

SciTech Connect

Four different theoretical formulations for AM and FM quantum noise properties in semiconductor lasers are compared with each other for AlGaAs lasers. These formulations are based on van der Pol, Fokker-Planck, rate, and photon density matrix equations. Experimental results with AM noise spectra, FM noise spectra, and spectral linewidths for four different types of AlGaAs lasers are also delineated and compared with the theoretical predictions. The spontaneous emission coefficient ..beta.. and population inversion parameter which are basic parameters for determining the quantum noise properties of semiconductor lasers, were calculated by the density of states with Kane function interpolated to Halperin-Lax bandtail and the Stern's improved matrix element. Experimental AM and FM quantum noise properties show good agreement with the theoretical predictions derived through use of estimated ..beta.. and /eta/ /SUB sp/ values.

Yamamoto, Y.; Mukai, T.; Saito, S.

1983-01-01

92

Theoretical characteristics of 1.55 ?m InN based quantum dot laser  

NASA Astrophysics Data System (ADS)

The theoretical characteristics of photon emission at 1.55 ?m wavelength are presented considering single layer of indium nitride (InN) quantum dots in the active region. The transparency threshold has been obtained at photon energy of 0.8016 eV and at zero normalized applied transition energy, respectively. The modal gain of about 12.5 cm-1 is obtained at the threshold current density of 51 Acm-2. The external differential quantum efficiency of 65% has been achieved for the cavity length of 640 ?m. The proposed structure with acceptable enhanced results will create a way to fabricate InN based quantum dot laser.

Hossain, Md. Mottaleb; Al-Humayun, Md. Abdullah; Bhuiyan, Ashraful Ghani

2013-09-01

93

Information-theoretic treatment of tripartite systems and quantum channels  

SciTech Connect

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

Coles, Patrick J.; Yu Li; Gheorghiu, Vlad; Griffiths, Robert B. [Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)

2011-06-15

94

Quantum-chemistry calculations of hydrogen adsorption in MOF-5.  

PubMed

High concentrations of molecular hydrogen adsorption on MOF-5 were evaluated at the semiempirical PM6 (periodic and cluster) and ab initio MP2 (cluster) theoretical levels. From the semiempirical calculations, an uptake of 3.9% weight on the inorganic building unit of MOF-5 was estimated, in good agreement with a recent accurate estimation of 4.5-5.2%. Although PM6 allows a correct estimation of the maximum uptake, the adsorption energy was overestimated and hence ab initio calculations, including a correlation treatment at the MP2 level as well as corrections for basis set superposition error, were performed with full optimisation, including the 6-31G basis set, which rendered an adsorption energy (per hydrogen molecule) of -0.14 kcal mol(-1). The crucial role of the quality of the basis set, as well as the importance of simulating high hydrogen loading (resembling experimental measurements), are remarked. Single point calculations (using the 6-31G geometry) with improved basis sets 6-31G(d,p) and 6-31++G(d,p) yielded adsorption energies of -0.33 and -0.57 kcal mol(-1), the latter in reasonable agreement with a recent experimental estimation of -1.0 kcal mol(-1). The role of the intermolecular hydrogen interactions is highlighted in this study, since many previous computational studies were performed at low hydrogen loadings, far from the experimental uptake conditions. PMID:19812846

Gomez, Diego A; Combariza, Aldo F; Sastre, German

2009-08-17

95

Theoretical Calculations on ?-DECAY Half-Lives by the Density-Dependent Cluster Model  

NASA Astrophysics Data System (ADS)

The theoretical calculations of ?-decay half-lives for three kinds of ?-emitters (even-even, even-odd, odd-odd nuclei) are systematically reviewed within the framework of the density-dependent cluster model (DDCM). The half-lives of three typical ?-emitters (8Be, 212Po, and 270Ds) are discussed in detail. The good agreement between experimental and theoretical results shows that DDCM is applicable in the whole mass table from very light nuclei to heavy and superheavy ones.

Ren, Zhongzhou; Xu, Chang

96

Quantum Calculations of the O + OH ? H + O2 Reaction  

NASA Astrophysics Data System (ADS)

The hydroxyl radical is a key trace species in the earth's atmosphere. It plays an important role in the chemical composition and energy balance of the earth's atmosphere and serves as a major atmospheric cleanser as it oxidizes most atmospheric species. Because it is a catalytic destroyer of ozone its abundance is closely linked to the abundance of ozone in the upper stratosphere. The O+OH?H+O2 reaction is an important process linked to the abundance of OH in the earth's stratosphere and mesosphere and it is also a key reaction in oxygen chemistry in the interstellar medium. We present here quantum mechanical calculations of rate coefficients for the O+OH reaction at temperatures of interest in the earth's atmosphere and astrophysical environments [1,2]. Two different representations of the electronic ground state potential energy surface of the HO2 system is employed in the calculations and the sensitivity of the rate coefficients to the details of the interaction potential is explored. Our calculations show that the rate coefficient remains largely constant in the astrophysically relevant temperature range of 10 -- 39 K [1], in agreement with the conclusions of a recent experimental study of the O+OH reaction [3]. Implications of our findings to oxygen chemistry in the interstellar medium are discussed. [1] G. Quemener, N. Balakrishnan, and B. K. Kendrick, J. Chem. Phys. 129, 224309 (2008). [2] G. Quemener, N. Balakrishnan, and B. K. Kendrick, Phys. Rev. A 79, 022703 (2009). [3] Carty et al., J. Phys. Chem. A 110, 3101 (2006). This work is supported by NSF grant No. ATM-0635715.

Naduvalath, B.; Quemener, G.; Kendrick, B. K.

2009-12-01

97

Information-theoretic measure of uncertainty due to quantum and thermal fluctuations  

Microsoft Academic Search

We study an information-theoretic measure of uncertainty for quantum systems. It is the Shannon information I of the phase-space probability distribution , where ||z> are coherent states and rho is the density matrix. As shown by Lieb I>=1, and this bound represents a strengthened version of the uncertainty principle. For a harmonic oscillator in a thermal state, I coincides with

Arlen Anderson; Jonathan J. Halliwell

1993-01-01

98

Three-dimensionality of space and the quantum bit: an information-theoretic approach  

NASA Astrophysics Data System (ADS)

It is sometimes pointed out as a curiosity that the state space of quantum two-level systems, i.e. the qubit, and actual physical space are both three-dimensional and Euclidean. In this talk, I report on joint work with Lluis Masanes [1], where we attempt an information-theoretic analysis of this relationship, by proving a particular mathematical result: suppose that physics takes place in d spatial dimensions, and that some events happen probabilistically (not assuming quantum theory in any way). Furthermore, suppose there are systems that behave in some sense as ``units of direction information,'' interacting continuously and reversibly in time. We prove that this uniquely determines spatial dimension d=3 and quantum theory on two qubits (that is, the complex Hilbert space formalism and unitary time evolution). Moreover, we prove that it allows observers to infer local spatial geometry from probability measurements. This applies and generalizes results obtained earlier with further collaborators [2,3]. [4pt] [1] M. P. Mueller and Ll. Masanes, Three-dimensionality of space and the quantum bit: how to derive both from information-theoretic postulates, arXiv:1206.0630[0pt] [2] G. de la Torre, Ll. Masanes, A. J. Short, and M. P. Mueller, Deriving quantum theory from its local structure and reversibility, Phys. Rev. Lett. 109, 090403 (2012)[0pt] [3] Ll. Masanes, M. P. Mueller, D. Perez-Garcia, and R. Augusiak, Entangling dynamics beyond quantum theory, arXiv:1111.4060

Mueller, Markus

2013-03-01

99

Theoretical XUV spectra from carbon-like cobalt ions by relativistic configuration interaction calculation  

NASA Astrophysics Data System (ADS)

Allowed ?n = 0 transitions of highly ionized metal atoms, which may appear in the solar spectra as well as in spectra from the high-temperature tokamak plasmas, lie in the extreme vacuum UV (XUV) region, 100Å <= ? <= 200Å. Here we report our theoretical calculation of the ?n = 0 transitions of C-like cobalt ions; it is in good agreement with the experimental measurement. Such theoretical calculations of the transition wave lengths and their oscillator strengths should be very helpful to identify the XUV spectra.

Zou, Yu; Li, Jiaming

1990-05-01

100

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

NASA Astrophysics Data System (ADS)

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

Good, Brian

2004-03-01

101

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

SciTech Connect

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

Esler, K. P. [Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C. 20015 (United States); NCSA, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Cohen, R. E. [Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C. 20015 (United States); Militzer, B. [Department of Earth and Planetary Science and of Astronomy, University of California Berkeley, Berkeley, California 94720 (United States); Kim, Jeongnim [NCSA, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Needs, R. J.; Towler, M. D. [TCM Group, Cavendish Laboratory, Cambridge CB3 0HE (United Kingdom)

2010-05-07

102

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

PubMed

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

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

2010-05-05

103

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

104

Quantum Monte Carlo calculations for point defects in semiconductors  

NASA Astrophysics Data System (ADS)

Point defects in silicon have been studied extensively for many years. Nevertheless the mechanism for self diffusion in Si is still debated. Direct experimental measurements of the selfdiffusion in silicon are complicated by the lack of suitable isotopes. Formation energies are either obtained from theory or indirectly through the analysis of dopant and metal diffusion experiments. Density functional calculations predict formation energies ranging from 3 to 5 eV depending on the approximations used for the exchange-correlation functional [1]. Analysis of dopant and metal diffusion experiments result in similar broad range of diffusion activation energies of 4.95 [2], 4.68 [3], 2.4 eV [4]. Assuming a migration energy barrier of 0.1-0.3 eV [5], the resulting experimental interstitial formation energies range from 2.1 - 4.9 eV. To answer the question of the formation energy of Si interstitials we resort to a many-body description of the wave functions using quantum Monte Carlo (QMC) techniques. Previous QMC calculations resulted in formation energies for the interstitials of around 5 eV [1,6]. We present a careful analysis of all the controlled and uncontrolled approximations that affect the defect formation energies in variational and diffusion Monte Carlo calculations. We find that more accurate trial wave functions for QMC using improved Jastrow expansions and most importantly a backflow transformation for the electron coordinates significantly improve the wave functions. Using zero-variance extrapolation, we predict interstitial formation energies in good agreement with hybrid DFT functionals [1] and recent GW calculations [7]. [4pt] [1] E. R. Batista, J. Heyd, R. G. Hennig, B. P. Uberuaga, R. L. Martin, G. E. Scuseria, C. J. Umrigar, and J. W. Wilkins. Phys. Rev. B 74, 121102(R) (2006).[0pt] [2] H. Bracht, E. E. Haller, and R. Clark-Phelps, Phys. Rev. Lett. 81, 393 (1998). [0pt] [3] A. Ural, P. B. Griffin, and J. D. Plummer, Phys. Rev. Lett. 83, 3454 (1999). [0pt] [4] R. Vaidyanathan, M. Y. L. Jung, and E. G. Seebauer, Phys. Rev. B 75, 195209 (2007). [0pt] [5] P. G. Coleman and C. P. Burrows, Phys. Rev. Lett. 98, 265502 (2007). [0pt] [6] W. K. Leung, R. J. Needs, G. Rajagopal, S. Itoh, and S. Ihara, Phys. Rev. Lett. 83, 2351 (1999). [0pt] [7] P. Rinke, A. Janotti, M. Scheffler, and C. G. Van de Walle, Phys. Rev. Lett. 102, 026402 (2009).

Hennig, Richard

2010-03-01

105

Quantum chemistry by quantum Monte Carlo: beyond ground-state energy calculations  

SciTech Connect

We present recent advances with the quantum Monte Carlo (QMC) method in its application to molecular systems. The QMC method is a procedure for solving the Schroedinger equation statistically, by the simulation of an appropriate random process. The formal similarity of the Schroedinger equation with a diffusion equation allows one to calculate quantum mechanical expectation values as Monte Carlo averages over an ensemble of random walks. We have previously obtained highly accurate correlation energies for a number of molecules, as well as the singlet-triplet splitting in methylene and the barrier height for the H + H/sub 2/ exchange reaction. Recently we have begun a program of extending the QMC approach to the calculation of analytic derivatives of the energy. A brief description of the approach is presented here, together with some preliminary results. In addition, we are now computing expectation values of properties other than the energy. We summarize how standard QMC must be modified, and present some results for H/sub 2/ and N/sub 2/. Finally, we describe preliminary work toward the goal of obtaining accurate molecular excited states through QMC. 24 refs., 5 tabs.

Reynolds, P.J.; Barnett, R.N.; Hammond, B.L.; Grimes, R.; Lester, W.A. Jr.

1985-08-01

106

Quantum critical scaling in beta-YbAlB4 and theoretical implications  

NASA Astrophysics Data System (ADS)

Emergent phenomena in quantum materials are subject of intense experimental and theoretical research at present. A wonderful example thereof are the sister phases of YbAlB4 - a newly discovered heavy fermion material [1]. While one phase (?-YbAlB4) is a heavy Fermi liquid, its sibling ?-YbAlB4 is quantum critical, supporting an unconventional superconductivity with a tiny transition temperature of ˜80 mK. Latest experiments [2] uncover the quantum critical T/B-scaling in ?-YbAlB4 and prove that superconductivity emerges from a strange metal governed by an extremely fragile quantum criticality, which apparently occurs at zero field, without any external tuning. Here, we will present a theoretical perspective on the quantum critical scaling in ?-YbAlB4 and will show that the critical exponents can be derived from the nodal structure of the hybridization matrix between Yb f-band and the conduction electrons. It follows that the free energy at low temperatures can be written in a scaling form F[(kBT)^2 + (g?BB)^2]^3/4, which predicts the divergent Sommerfeld coefficient ? and quasi-particle effective mass as B->0: ?˜m^*/m B-1/2. This is indeed observed in the experiment [1,2], which places a tiny upper bound on the critical magnetic field Bc<0.2 mT. We will discuss theoritical implications of this fragile intrinsic quantum criticality in ?-YbAlB4 and discuss the possibility of a quantum critical phase, rather than a quantum critical point, in this material. [1] S. Nakatsuji et al., Nature Physics 4, 603 (2008). [2] Y. Matsumoto, S. Nakatsuji, K. Kuga, Y. Karaki, Y. Shimura, T. Sakakibara, A. H. Nevidomskyy, and P. Coleman, Science 331, 316 (2011).

Nevidomskyy, Andriy

2012-02-01

107

Theoretical calculation of electronic stopping power of water vapor by proton impact.  

PubMed

The energy loss of proton beams in water vapor is analyzed with a full quantum-mechanical treatment, the distorted-wave model. This model takes into account distortion effects due to the long-range Coulomb potential. Projectile energies from 10 keV up to 1 MeV are considered. Mean stopping power and equilibrium charge-state fractions are calculated and compared with experimental data. The validity of Bragg's additivity rule is investigated. PMID:7480652

Olivera, G H; Martínez, A E; Rivarola, R D; Fainstein, P D

1995-11-01

108

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...

109

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

SciTech Connect

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

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

1995-03-01

110

Theoretical calculation of SSNTD response for radon measurements and optimum diffusion chambers dimensions  

Microsoft Academic Search

The response of some SSNTDs was calculated theoretically taking into consideration the major parameters that affect them. These parameters are related to the behavior of alpha emitters, the detectors types and the used diffusion chambers. The obtained results showed that the response of the filtered CR-39 detector is about 5 times higher than that of the LR-115 detector and more

M. Mansy; M. A. Sharaf; H. M. Eissa; S. U. El-Kamees; M. Abo-Elmagd

2006-01-01

111

Efficiency and power loss in d. c. chopper circuits. [Theoretical calculation  

SciTech Connect

The object of this paper was to investigate the efficiency and source of power losses of various classes of dc chopper circuits. The study involved a theoretical calculation of the power losses, supported by a considerable amount of practical work on full power-rated traction motor test bed. 3 refs.

Beck, M.O.

1981-01-01

112

Numerical and theoretical study of Bernstein modes in a magnetized quantum plasma  

SciTech Connect

A numerical and theoretical study is presented for the propagation of electron Bernstein modes in a magnetized quantum plasma. The dispersion relation for electrostatic waves is derived, using a semiclassical Vlasov model for Fermi-Dirac distributed electrons. The dispersion relation is checked numerically with direct Vlasov simulations, where the wave energy is concentrated to the Bernstein modes as well as to the zero-frequency convective mode. Dispersion relations in the long wavelength limit are derived, including the upper hybrid dispersion relation for a degenerate quantum plasma.

Eliasson, Bengt; Shukla, Padma K. [Department of Physics, Umea ring University, SE-901 87 Umea ring , Sweden and Institut fuer Theoretische Physik IV, Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2008-10-15

113

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

114

Information-Theoretic Equilibration: The Appearance of Irreversibility under Complex Quantum Dynamics  

NASA Astrophysics Data System (ADS)

The question of how irreversibility can emerge as a generic phenomenon when the underlying mechanical theory is reversible has been a long-standing fundamental problem for both classical and quantum mechanics. We describe a mechanism for the appearance of irreversibility that applies to coherent, isolated systems in a pure quantum state. This equilibration mechanism requires only an assumption of sufficiently complex internal dynamics and natural information-theoretic constraints arising from the infeasibility of collecting an astronomical amount of measurement data. Remarkably, we are able to prove that irreversibility can be understood as typical without assuming decoherence or restricting to coarse-grained observables, and hence occurs under distinct conditions and time scales from those implied by the usual decoherence point of view. We illustrate the effect numerically in several model systems and prove that the effect is typical under the standard random-matrix conjecture for complex quantum systems.

Ududec, Cozmin; Wiebe, Nathan; Emerson, Joseph

2013-08-01

115

Approximate Quantum Mechanical Calculation of Reactive Scattering Cross Sections - The Fixed Angle Reactor Model (FARM)  

NASA Astrophysics Data System (ADS)

An approximate three-dimensional quantum mechanical method for the calculation of atom-diatom reactive scattering cross sections and rate constants is described. The method is known as the Fixed Angle Reactor Model (FARM). Its key features are that it uses information from both classical trajectory and simplified quantum mechanical calculations to compute vibrational state-to-state reactive scattering cross sections. The classical trajectory calculations are used to estimate the degree to which torques acting during the approach of the collision partners are able to successfully reorient them into the most favorable geometry for subsequent reaction. This information is then used, together with fixed angle quantum reactive scattering calculations to approximate a full three-dimensional quantum reactive scattering calculation. Test results are presented for the reactions: H + H2(? = 0) ? H2(?' = 0) + H and D + H2(? = 1) ? HD + H and comparison is made with other methods.

Balint-Kurti, G. G.; de Haar, B. M. D. D. Jansen op

1988-01-01

116

Efficient calculation of unbiased expectation values in diffusion quantum Monte Carlo  

NASA Astrophysics Data System (ADS)

Despite the proven utility of quantum Monte Carlo methods in addressing the quantum many-body problem, many important observables are difficult to calculate due to the presence of large, and sometimes divergent, statistical errors. The present state of the art allows the construction of renormalized estimators which result in finite variances, but which invariably include some systematic bias. We present a simple method for calculating unbiased expectation values of local operators in the diffusion quantum Monte Carlo method which is applicable to both bare and renormalized estimators, allowing the accurate calculation of important properties such as forces.

Per, Manolo C.; Snook, Ian K.; Russo, Salvy P.

2012-11-01

117

Nuclear radii calculations in various theoretical approaches for nucleus-nucleus interactions  

SciTech Connect

The information about sizes and nuclear density distributions in unstable (radioactive) nuclei is usually extracted from the data on interaction of radioactive nuclear beams with a nuclear target. We show that in the case of nucleus-nucleus collisions the values of the parameters depend somewhat strongly on the considered theoretical approach and on the assumption about the parametrization of the nuclear density distribution. The obtained values of root-mean-square radii (R{sub rms}) for stable nuclei with atomic weights A=12-40 vary by approximately 0.1 fm when calculated in the optical approximation, in the rigid target approximation, and using the exact expression of the Glauber theory. We present several examples of R{sub rms} radii calculations using these three theoretical approaches and compare these results with the data obtained from electron-nucleus scattering.

Merino, C.; Novikov, I. S.; Shabelski, Yu. [Departamento de Fisica de Particulas, Facultade de Fisica, and Instituto Galego de Fisica de Altas Enerxias (IFGAE), Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Galiza (Spain); Department of Physics and Astronomy, Western Kentucky University, Bowling Green, Kentucky 42101-1077 (United States); Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg 188350 (Russian Federation)

2009-12-15

118

Nuclear radii calculations in various theoretical approaches for nucleus-nucleus interactions  

NASA Astrophysics Data System (ADS)

The information about sizes and nuclear density distributions in unstable (radioactive) nuclei is usually extracted from the data on interaction of radioactive nuclear beams with a nuclear target. We show that in the case of nucleus-nucleus collisions the values of the parameters depend somewhat strongly on the considered theoretical approach and on the assumption about the parametrization of the nuclear density distribution. The obtained values of root-mean-square radii (Rrms) for stable nuclei with atomic weights A=12-40 vary by approximately 0.1 fm when calculated in the optical approximation, in the rigid target approximation, and using the exact expression of the Glauber theory. We present several examples of Rrms radii calculations using these three theoretical approaches and compare these results with the data obtained from electron-nucleus scattering.

Merino, C.; Novikov, I. S.; Shabelski, Yu.

2009-12-01

119

Application of the theoretical reference ionosphere model for calculating HF-radiowave propagation characteristics  

NASA Astrophysics Data System (ADS)

We study the possibilities of the Theoretical Ionosphere Model (TIM) developed at the Institute of Solar-Terrestrial Physics, Siberian Branch, Russian Academy of Sciences, for calculating the HF-radiowave propagation characteristics. The results of simulation based on the TIM are compared with calculations based on the IRI model and data from experimental observations. Analysis of the results of calculations for the maximum usable frequency (MUF) have shown that with the same input data (coordinates of the receipt and transmission points, the route length, date, and time), the differences in the calculated MUFs (using two different models supplying radio routes with ionospheric information) amount to ˜1% in the daytime and reach 10% at night.

Kotovich, G. V.; Grozov, V. P.; Kim, A. G.; Oinats, A. V.; Romanova, E. B.; Tashchilin, A. V.

2010-08-01

120

The theoretical calculation of p+232Th reaction for energies up to 250 MeV  

NASA Astrophysics Data System (ADS)

All reaction cross sections, energy spectra and double differential cross sections of neutron, proton, deuteron, triton, and alpha-particle emission for p+232Th reaction are consistent calculated and analyzed with the optical model, the intranuclear cascade model, the unified Hauser-Feshbach theory and the exciton model which included the improved Iwamoto-Harada model, the fission model and the distorted wave Born approximation theory in the energy range of Ep?250MeV. Theoretical calculations are compared with existing experimental data.

Su, Xinwu; Liang, Haiying; Han, Yinlu; Cai, Chonghai; Shen, Qingbiao

2010-09-01

121

Simulations of X-Ray Photoelectron Diffraction Experiment from Theoretical Calculations  

Microsoft Academic Search

In this paper, we demonstrate the simulation of XPD experiments through theoretical calculations. We present examples, e.g. oxygen-induced Cu(210) surface and oxygenated diamond surface, to illustrate how to obtain the optimized XPD experimental parameters by MSCD simulations for distinguishing two different models. Our results suggest that for the adsorbate-induced reconstructions on metal or semiconductor surfaces, XPD from adsorbate is more

Jin-Cheng Zheng; Hui-Qiong Wang; C. H. A. Huan; A. T. S. Wee

2001-01-01

122

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

Microsoft Academic Search

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

N. C. Fernelius

1980-01-01

123

Interactions between indazole derivative and magnesium cations – NMR investigations and theoretical calculations  

NASA Astrophysics Data System (ADS)

The paper describes a new NMR approach for the determination of interaction sites between a heterocyclic ligand, like indazole, and magnesium ions. The method is based on the comparison of chemical shifts of indazole derivative before and after complexation with magnesium salt and is supported by DFT (B3LYP/6-31G(d,p) level of theory, solvent model PCM, IGLO-II basis set) theoretical calculations.

Kujawski, Jacek; Doskocz, Marek; Popielarska, Hanna; Myka, Anna; Drabi?ska, Beata; Kruk, Joanna; Bernard, Marek K.

2013-09-01

124

Conformational analysis of cis-2-halocyclohexanols; solvent effects by NMR and theoretical calculations.  

PubMed

Conformational problems often involve very small energy differences, even low as 0.5 kcal mol(-1). This accuracy can be achieved by theoretical methods in the gas phase with the appropriate accounting of electron correlation. The solution behavior, on the other hand, comprises a much greater challenge. In this study, we conduct and analysis for cis-2-fluoro-, cis-2-chloro-, and cis-2-bromocyclohexanol using low temperature NMR experiments and theoretical calculations (DFT, perturbation theory, and classical molecular dynamics simulations). In the experimental part, the conformers' populations were measured at 193 K in CD(2)Cl(2), acetone-d(6), and methanol-d(4) solutions; the preferred conformer has the hydroxyl group in the equatorial and the halogen in the axial position (ea), and its population stays at about 60-70%, no matter the solvent or the halogen. Theoretical calculations, on the other hand, put the ae conformer at a lower energy in the gas phase (MP2/6-311++G(3df,2p)). Moreover, the theoretical calculations predict a markedly increase in the conformational energy on going from fluorine to bromine, which is not observed experimentally. The solvation models IEF-PCM and C-PCM were tested with two different approaches for defining the atomic radii used to build the molecular cavity, from which it was found that only with explicit consideration of hydrogens can the conformational preference be properly described. Molecular dynamic simulations in combination with ab initio calculations showed that the ea conformer is slightly favored by hydrogen bonding. PMID:21121596

Basso, Ernani A; Abiko, Layara A; Gauze, Gisele F; Pontes, Rodrigo M

2010-12-01

125

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

Microsoft Academic Search

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

Diola Bagayoko

2008-01-01

126

Dissociation energy of the water dimer from quantum Monte Carlo calculations  

Microsoft Academic Search

We report a study of the electronic dissociation energy of the water dimer using quantum Monte Carlo techniques. We have performed variational quantum Monte Carlo and diffusion quantum Monte Carlo (DMC) calculations of the electronic ground state of the water monomer and dimer using all-electron and pseudopotential approaches. We have used Slater-Jastrow trial wave functions with B3LYP type single-particle orbitals,

I. G. Gurtubay; R. J. Needs

2007-01-01

127

Fault tolerance calculations for clocked quantum-dot cellular automata devices  

Microsoft Academic Search

We present a numerical study of fault tolerance properties in quantum-dot cellular automata (QCA) devices. A full-basis quantum method is used for calculations of the Hamiltonian, and a statistical model has been introduced to simulate the influence of position defects of the dots within cells on the logical output. Combined effects of temperature and cell defects on a shift register

M. Khatun; T. Barclay; I. Sturzu; P. D. Tougaw

2005-01-01

128

Quantum mechanical methods for calculating proton tunneling splittings and proton-coupled electron transfer vibronic couplings  

Microsoft Academic Search

Development of quantum mechanical methods for the calculation of proton tunneling splittings and proton-coupled electron transfer vibronic couplings is presented in this thesis. The fundamental physical principles underlying proton transfer in the electronically adiabatic and nonadiabatic limits are illustrated by applying the quantum mechanical methods we developed to chemical systems exemplary of the electronically adiabatic and nonadiabatic proton-tunneling regimes. Overall,

Jonathan H. Skone

2008-01-01

129

Quantum mechanical potential surfaces and calculations on minerals and molecular clusters  

Microsoft Academic Search

Recently, ab-initio quantum mechanical potential surfaces calculated for silicate hydroxyacid molecules were used to extract covalent potentials for use in mineral physics calculations (Lasaga and Gibbs 1987). The calculations showed that these potentials are capable of generating the structure and physical properties of silicate minerals. In this paper we explore in more detail the suitability of various covalent potentials in

Antonio C. Lasaga; G. V. Gibbs

1988-01-01

130

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

131

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

132

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

133

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

134

Investigation of attractive and repulsive interactions associated with ketones in supercritical CO2, based on Raman spectroscopy and theoretical calculations.  

PubMed

Carbonyl compounds are solutes that are highly soluble in supercritical CO2 (scCO2). Their solubility governs the efficiency of chemical reactions, and is significantly increased by changing a chromophore. To effectively use scCO2 as solvent, it is crucial to understand the high solubility of carbonyl compounds, the solvation structure, and the solute-solvent intermolecular interactions. We report Raman spectroscopic data, for three prototypical ketones dissolved in scCO2, and four theoretical analyses. The vibrational Raman spectra of the C=O stretching modes of ketones (acetone, acetophenone, and benzophenone) were measured in scCO2 along the reduced temperature Tr = T?Tc = 1.02 isotherm as a function of the reduced density ?r = ???c in the range 0.05-1.5. The peak frequencies of the C=O stretching modes shifted toward lower energies as the fluid density increased. The density dependence was analyzed by using perturbed hard-sphere theory, and the shift was decomposed into attractive and repulsive energy components. The attractive energy between the ketones and CO2 was up to nine times higher than the repulsive energy, and its magnitude increased in the following order: acetone < acetophenone < benzophenone. The Mulliken charges of the three solutes and CO2 molecules obtained by using quantum chemistry calculations described the order of the magnitude of the attractive energy and optimized the relative configuration between each solute and CO2. According to theoretical calculations for the dispersion energy, the dipole-induced-dipole interaction energy, and the frequency shift due to their interactions, the experimentally determined attractive energy differences in the three solutes were attributed to the dispersion energies that depended on a chromophore attached to the carbonyl groups. It was found that the major intermolecular interaction with the attractive shift varied from dipole-induced dipole to dispersion depending on the chromophore in the ketones in scCO2. As the common conclusion for the Raman spectral measurements and the four theoretical calculations, solute polarizability, modified by the chromophore, was at the core of the solute-solvent interactions of the ketones in scCO2. PMID:23927272

Kajiya, Daisuke; Saitow, Ken-ichi

2013-08-01

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 investigations of open-shell systems: 1. Spectral simulation of the 2s(2)p(2) (2)D <- 2s(2)2p (2)P(o) valence transition in the boron diargon cluster, and 2. Quantum Monte Carlo calculations of boron in solid molecular hydrogen  

NASA Astrophysics Data System (ADS)

This dissertation is concerned in part with the construction of accurate pairwise potentials, based on reliable ab initio potential energy surfaces (PES's), which are fully anisotropic in the sense that multiple PES's are accessible to systems with orientational electronic properties. We have carried out several investigations of B (2s 22p 2Po) with spherical ligands: (1)an investigation of the electronic spectrum of the BAr2 complex and (2)two related studies of the equilibrium properties and spectral simulation of B embedded in solid pH 2. Our investigations suggest that it cannot be assumed that nuclear motion in an open-shell system occurs on a single PES. The 2s2p2 2 D <-- 2s22p 2Po valence transition in the BAr 2 cluster is investigated. The electronic transition within BAr 2 is modeled theoretically; the excited potential energy surfaces of the five-fold degenerate B(2s2p2 2D) state within the ternary complex are computed using a pairwise-additive model. A collaborative path integral molecular dynamics investigation of the equilibrium properties of boron trapped in solid para-hydrogen (pH2) and a path integral Monte Carlo spectral simulation. Using fully anisotropic pair potentials, coupling of the electronic and nuclear degrees of freedom is observed, and is found to be an essential feature in understanding the behavior and determining the energy of the impure solid, especially in highly anisotropic matrices. We employ the variational Monte Carlo method to further study the behavior of ground state B embedded in solid pH2. When a boron atom exists in a substitutional site in a lattice, the anisotropic distortion of the local lattice plays a minimal role in the energetics. However, when a nearest neighbor vacancy is present along with the boron impurity, two phenomena are found to influence the behavior of the impure quantum solid: (1)orientation of the 2p orbital to minimize the energy of the impurity and (2)distortion of the local lattice structure to promote an energetically favorable nuclear configuration. This research was supported by the Joint Program for Atomic, Molecular and Optical Science sponsored by the University of Maryland at College Park and the National Insititute of Standards and Technology, and by the U.S. Air Force Office of Scientific Research. (Abstract shortened by UMI.)

Krumrine, Jennifer Rebecca

137

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

NASA Astrophysics Data System (ADS)

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

Drozd, M.; Dudzic, D.

2013-11-01

138

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

139

[Contrasts in the FLASH sequences in the study of musculoskeletal tumors: phantom study and theoretical calculations].  

PubMed

The contrast between samples simulating musculoskeletal neoplasms and muscle or bone marrow achieved with FLASH sequences, was analysed in phantom studies and was compared with theoretically calculated contrast with and without correction for flip angle distribution over the slice profile. The contrast was correlated closer with the flip angle than with TR or TE. For delineation of the tumour from muscle, only a FLASH sequence with a large flip angle following intravenous administration of Gd-DTPA can be recommended, if a tumour shows a clear Gd-DTPA uptake. With all FLASH sequences analysed, no sufficient contrast between "tumour" without Gd-DTPA uptake and muscle was obtained. Maximal contrast between "tumour" and bone marrow was achieved with small flip angles; and an additional peak was noted with large flip angles and short TR. Experimentally measured T2*-dependent contrasts were nearly identical with theoretically calculated contrasts without correction of flip angle distribution. For calculation of T1-dependent contrasts, correction of the flip angle distribution over the slice profile was of high value. PMID:1852035

Erlemann, R; Stöber, U; Drews, C; Böcker, D; Peters, P E

1991-05-01

140

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

141

The structures and properties of Si/SiO2 core/shell quantum dots studied by density-functional tight-binding calculations  

NASA Astrophysics Data System (ADS)

Si/SiO2 core/shell quantum dots (QDs) have been shown with wavelength-tunable photoluminescence in addition to their inert, nontoxic, abundant, low-cost, biocompatible advantages. Due to their big size, here, we apply density-functional tight-binding (DFTB) method to perform calculations to study their structures and properties. We systematically investigate the effects of surface passivation, thickness of SiO2 shell, and Si/O ratio on the structures and properties of Si/SiO2 core/shell quantum dots. We find that hydroxyl passivated Si/SiO2 core/shell quantum dots are able to stabilize the quantum dots compared with hydrogen passivated Si/SiO2 core/shell quantum dots. By using DFTB method, we are able to study Si/SiO2 core/shell quantum dots of big size (3 nm) and we find that, in Si/SiO2 core/shell quantum dots, there are competing effects between quantum confinement (blueshift) and oxidation (redshift) with the decrease of the size of Si core. The transition point is when Si/SiO2 ratio is around 1:1. The effect of the thickness of SiO2 on energy gap is not as significant as the effect of the size of the Si core. Our study provides theoretical basis for designing Si quantum dots with tunable photoluminescence.

Dong, Huilong; Hou, Tingjun; Sun, Xiaotian; Li, Youyong; Lee, Shuit-Tong

2013-09-01

142

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

NASA Astrophysics Data System (ADS)

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.

Hsiang, Jen-Tsung; Wu, Tai-Hung; Lee, Da-Shin; King, Sun-Kun; Wu, Chun-Hsien

2013-02-01

143

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

144

Quantum Monte Carlo calculation of reduced density matrices  

NASA Astrophysics Data System (ADS)

Quantum Monte Carlo(QMC) methods offer an efficient way to approximate the interacting ground state and some excited states of realistic model Hamiltonians based on the fundamental Coulomb interaction between electrons and nuclei. Many highly accurate results have been obtained using this method; however, it is often a challenge to extract the important correlations that the QMC wave function contains. I will describe some new results using the reduced density matrices(RDM's) to understand the electron correlation in the many-body wave function. The RDM's have both informative usage for describing correlation and pragmatic uses in further improving the variational wave function.

Wagner, Lucas

2012-02-01

145

Reaction cross-section calculations using new experimental and theoretical level structure data for deformed nuclei  

SciTech Connect

A technique for modeling quasiparticle excitation energies and rotational parameters in odd-odd deformed nuclei has been used to construct sets of discrete states with energy 0 to 1.5 MeV in /sup 176/Lu and /sup 236/Np. These data were used as part of the input for calculation of isomer production cross-section ratios in the /sup 175/Lu(n,..gamma..)/sup 176/Lu and /sup 237/Np(n,2n)/sup 236/Np reactions. In order to achieve agreement with experiment, it has been found necessary to include in the modeled set many rotational bands (35 to 95), which are comprised of hundreds of levels with their gamma-ray branching ratios. It is essential that enough bands be included to produce a representative selection of K quantum numbers in the de-excitation cascade. 20 refs., 3 figs., 3 tabs.

Hoff, R.W.; Gardner, D.G.; Gardner, M.A.

1984-10-05

146

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

147

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

148

Theoretical calculation of electronic circular dichroism of a hexahydroxydiphenoyl-containing flavanone glycoside.  

PubMed

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]-beta-d-glucopyranoside (2). It identified the roles of the (2S)-flavanone and (aS)-HHDP moieties in generating the ECD spectrum of 2 and provided theoretical evidence for the empirical ECD rules applicable to monomeric flavanones and HHDP-containing compounds. The experimentally observed high-amplitude positive Cotton effect (CE) around 240 nm in 2 is derived from the (aS)-HHDP chromophore, while the low-amplitude negative CE in the 260-300 nm region is contributed by both the (aS)-HHDP and (2S)-flavanone moieties. The "linker" glucosyl moiety has little effect on the overall ECD. It appears that the respective chromophores in 2 contribute additively to the overall ECD, and the empirical rules are applicable for configurational assignment. However, if an (aR)-HHDP chromophore is present, as shown in mattucinol-7-O-[4'',6''-O-(aR)-hexahydroxydiphenoyl]-beta-d-glucopyranoside (3), the dominant role of the (aR)-HHDP and interaction between the (aR)-HHDP and (2S)-flavanone moieties in its overall ECD may be confusing when applying the empirical rules to experimental ECD interpretation. Thus, theoretical calculation of the ECD that quantifies the contributions and interactions of different chromophores is essential for the assignment of the absolute configuration of such molecules. PMID:19099470

Ding, Yuanqing; Li, Xing-Cong; Ferreira, Daneel

2009-03-27

149

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

NASA Astrophysics Data System (ADS)

Most density functional theory (DFT) calculations find band gaps that are 30-50 percent smaller than the experimental ones, as illustrated in this presentation that recalls some popular explanations of this band gap problem, i.e., self-interaction effects and derivative discontinuities of the exchange correlation energy. A survey of the increasingly numerous approaches aimed at resolving the theoretical underestimation follows these explanations. These approaches include the Green function and screened Coulomb approximation (GWA), time dependent density functional theory (TDDFT), the exact exchange and screened exchange methods, and the use of local density approximation (LDA) potentials plus additional potentials located at atomic sites. Using the Rayleigh theorem, we describe a basis set and variational effect inherently associated with calculations that employ a linear combination of atomic orbitals (LCAO) in a variational approach of the Rayleigh-Ritz type. This description concomitantly shows a source of large underestimation errors in calculated band gaps, i.e., an often dramatic lowering of some unoccupied energies on account of the Rayleigh theorem as opposed to the Hamiltonian. We present the Bagayoko, Zhao, and Williams (BZW) method [Phys. Rev. B 60, 1563 (1999); PRB 74, 245214 (2006); and PRB 76, 037101 (2007)] that follows from the description of the aforementioned effect and that leads (a) to DFT and LDA calculated band gaps of semiconductors in agreement with experiment and (b) theoretical predictions of band gaps that are confirmed by experiment. Unlike most calculations, BZW computations solve, self-consistently, a system of two coupled equations. DFT-BZW calculated effective masses and optical properties (dielectric functions) also agree with measurements. We illustrate ten years of success of the BZW method with its results for GaN, C, Si, 3C-SIC, 4H-SiC, ZnO, AlAs, Ge, ZnSe, w-InN, InAs, and AlN. We conclude with a request to revisit beliefs relative to actual limitations of DFT and of schemes purporting to correct it or to go beyond it.

Bagayoko, Diola

2008-03-01

150

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

151

Quantum conductance of In nanowires on Si(1 1 1) from first principles calculations  

NASA Astrophysics Data System (ADS)

The quantum conductance of the paradigmatic quasi-one-dimensional In/Si(1 1 1) surface system is calculated for 4 × 1, 4 × 2 and 8 × 2 surface reconstructions. In agreement with experiment, we find the recently suggested formation of hexagons within the In nanowires [C. Gonzalez, F. Flores, J. Ortega, Phys. Rev. Lett. 96 (2006) 136101] to drastically modify the electron transport along the In chains. In contrast, the formation of trimers barely changes the quantum conductance.

Wippermann, S.; Schmidt, W. G.; Calzolari, A.; Nardelli, M. Buongiorno; Stekolnikov, A. A.; Seino, K.; Bechstedt, F.

2007-09-01

152

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

Microsoft Academic Search

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

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

2010-01-01

153

Calculation of the number of theoretical and actual plates in rectification columns by means of the enthalpy diagram  

Microsoft Academic Search

This paper makes a comparison between the results of calculations made from I-t-x and y-x diagrams. The physicoehemical constants taken from the handbook literature were used to calculate the number of theoretical plates for a number of mixtures (Table i). Two methods were used in the calculation: the familiar method of plotting the enthalpy diagram and calculating the number of

V. A. Ivanov; A. N. Planovskii; V. I. Astakhov

1966-01-01

154

Summary of Ebw Theoretical Calculations in the Tj-Ii Stellarator  

NASA Astrophysics Data System (ADS)

An overview of the main Electron Bernstein Waves (EBW) theoretical results obtained in the TJ-II stellarator is presented. Firstly, former studies helping us to determine the best excitation scheme are discussed. Next, we describe the procedure used to find the optimum launching position and direction of the injected power, as well as the ray tracing optimization method that was developed to find the optimum launched beam. The 2D full-wave simulations that were performed in order to check the beam ray tracing optimization results are also presented. Final topics are devoted to the comparison between relativistic and non-relativistic ray tracing calculations and to the preliminary transport simulations performed with the ASTRA system. Plans for future work are briefly outlined. [Spanish MCyT project ENE2004-06957/FTN].

Cappa, A.; Castejon, F.; Lopez-Bruna, D.; Fernandez, A.; Tereshchenko, M.; Holzhauer, E.; Kohn, A.; Palov, S. S.

2009-04-01

155

Theoretical and practical aspects of chemical functionalization of carbon nanofibers (CNFs): DFT calculations and adsorption study.  

PubMed

The nitric acid-functionalized commercial carbon nanofibers (CNFs) were comprehensively studied by instrumental (XRD, BET, SEM, TGA) and theoretical (DFT calculations) methods. The detailed surface study revealed the variation in the characteristics of functionalized CNFs, such as a decreased (up to 34%) surface area and impacted structural, electronic and chemical properties. The effects of functional groups were studied by comparison with pristine nanofibers. The results showed that the C-C bond lengths of the modified CNFs varied significantly. Chemical functionalization altered the frontier orbitals of the pristine material, and therefore altered the nature of their interactions with other substances. Moreover, the pristine and modified CNFs were tested for the removal of phenol from aqueous solutions. It was observed that surface modification tuned the adsorption capacity of carbon nanofibers (up to 0.35 mmol g(-1)), whereas original fibers did not demonstrate any adsorption capacity of phenol. PMID:22209137

Rokhina, Ekaterina V; Lahtinen, Manu; Makarova, Katerina; Jegatheesan, Veeriah; Virkutyte, Jurate

2011-12-14

156

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, Efrn M.

2011-12-01

157

Stabilisation of a laser by the calculated quantum transition frequency  

SciTech Connect

A method is proposed to stabilise the frequency of a He-Ne laser with an intracavity nonlinear absorption cell by the calculated frequency of the 7{yields}6 transition of F{sub 2}{sup (2)}P(7){nu}{sub 3} in methane. The long-term frequency stability and reproducibility are measured for a He-Ne/CH{sub 4} laser with a telescopic cavity. (control of laser radiation parameters)

Bagaev, S N; Lugovoy, A A [Institute of Laser Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk (Russian Federation); Dmitriev, A K [Novosibirsk State Technical University, Novosibirsk (Russian Federation)

2008-01-31

158

Linearized Tensor Renormalization Group Algorithm for the Calculation of Thermodynamic Properties of Quantum Lattice Models  

NASA Astrophysics Data System (ADS)

A linearized tensor renormalization group algorithm is developed to calculate the thermodynamic properties of low-dimensional quantum lattice models. This new approach employs the infinite time-evolving block decimation technique, and allows for treating directly the transfer-matrix tensor network that makes it more scalable. To illustrate the performance, the thermodynamic quantities of the quantum XY spin chain as well as the Heisenberg antiferromagnet on a honeycomb lattice are calculated by the linearized tensor renormalization group method, showing the pronounced precision and high efficiency.

Li, Wei; Ran, Shi-Ju; Gong, Shou-Shu; Zhao, Yang; Xi, Bin; Ye, Fei; Su, Gang

2011-03-01

159

Linearized tensor renormalization group algorithm for the calculation of thermodynamic properties of quantum lattice models.  

PubMed

A linearized tensor renormalization group algorithm is developed to calculate the thermodynamic properties of low-dimensional quantum lattice models. This new approach employs the infinite time-evolving block decimation technique, and allows for treating directly the transfer-matrix tensor network that makes it more scalable. To illustrate the performance, the thermodynamic quantities of the quantum XY spin chain as well as the Heisenberg antiferromagnet on a honeycomb lattice are calculated by the linearized tensor renormalization group method, showing the pronounced precision and high efficiency. PMID:21517348

Li, Wei; Ran, Shi-Ju; Gong, Shou-Shu; Zhao, Yang; Xi, Bin; Ye, Fei; Su, Gang

2011-03-22

160

Infrared and NMR spectra, tautomerism, vibrational assignment, normal coordinate analysis, and quantum mechanical calculations of 4-amino-5-pyrimidinecarbonitrile  

NASA Astrophysics Data System (ADS)

The infrared (4000-200 cm-1) spectrum for 4-amino-5-pyrimidinecarbonitrile (APC, C5H4N4) was acquired in the solid phase. In addition, the 1H and 13C NMR spectra of APC were obtained in DMSO-d6 along with its mass spectrum. Initially, six isomers were hypothesized and then investigated by means of DFT/B3LYP and MP2(full) quantum mechanical calculations using a 6-31G(d) basis set. Moreover, the 1H and 13C NMR chemical shifts were predicted using a GIAO approximation at the 6-311+G(d,p) basis set and the B3LYP method with (and without) solvent effects using PCM method. The correlation coefficients showed good agreement between the experimental/theoretical chemical shift values of amino tautomers (1 and 2) rather than the eliminated imino tautomers (3-6), in agreement with the current quantum mechanical calculations. Structures 3-6 are less stable than the amino tautomers (1 and 2) by about 5206-8673 cm-1 (62.3-103.7 kJ/mol). The MP2(full)/6-31G(d) computational results favor the amino structure 1 with a pyramidal NH2 moiety and calculated real vibrational frequencies, however; structure 2 is considered a transition state owing to the calculated imaginary frequency. It is worth mentioning that, the calculated structural parameters suggest a strong conjugation between the amino nitrogen and pyrimidine ring. Aided by frequency calculations, normal coordinate analysis, force constants and potential energy distributions (PEDs), a complete vibrational assignment for the observed bands is proposed herein. Finally, NH2 internal rotation barriers for the stable non-planar isomer (1) were carried out using MP2(full)/6-31G(d) optimized structural parameters. Our results are discussed herein and compared to structural parameters for similar molecules whenever appropriate.

Afifi, Mahmoud S.; Farag, Rabei S.; Shaaban, Ibrahim A.; Wilson, Lee D.; Zoghaib, Wajdi M.; Mohamed, Tarek A.

161

Synthesis and theoretical calculations of 5-aminosalicylic acid derivatives as potential analgesic agents.  

PubMed

5-Aminosalicylic acid is one of the drugs most commonly used for inflammatory bowel disease treatment, although its use is limited due to side effects. The aim of this work was to synthesize four 5-ASA derivatives (1-4) and analyze their pharmacological effects. The compound structures were elucidated by spectral (IR and 1H and 13C-NMR) analysis, and their analgesic effects and lethal doses 50 (LD50) were evaluated in the mouse model. In addition, their Log Ps and affinities for both cyclooxygenase enzymes (COX I and COX II) were evaluated through theoretical calculations. All compounds showed analgesic activities from 0.1 mg/Kg to 16 mg/Kg in the mouse model. The imides showed more affinity by COX enzymes and their Log Ps were the highest. The docking calculations showed that all compounds have good affinities for COX I and COX II ( identical with 1 microM), making pi-pi, van der Waals interactions and hydrogen bonds. The toxicities of all compounds were low, judging by the LD50. Finally, the docking analysis show that the compounds act on COX enzymes and their analgesic effects could be mediated in part by the inhibition of these enzymes. PMID:18220969

José, Correa-Basurto; Rosales-Hernández, M C; Eduardo, Ramírez-San Juan; Abigail, Badillo; Carlo, Z Gómez-Castro; Fabila-Castillo, L H; José, Trujillo-Ferrara

2008-01-01

162

Excited state calculations in solids by auxiliary-field quantum Monte Carlo  

NASA Astrophysics Data System (ADS)

We present an approach for ab initio many-body calculations of excited states in solids. Using auxiliary-field quantum Monte Carlo, we introduce an orthogonalization constraint with virtual orbitals to prevent collapse of the stochastic Slater determinants in the imaginary-time propagation. Trial wave functions from density-functional calculations are used for the constraints. Detailed band structures can be calculated. Results for standard semiconductors are in good agreement with experiments; comparisons are also made with GW calculations and the connections and differences are discussed. For the challenging ZnO wurtzite structure, we obtain a fundamental band gap of 3.26(16) eV, consistent with experiments.

Ma, Fengjie; Zhang, Shiwei; Krakauer, Henry

2013-09-01

163

The polarization response in InAs quantum dots: theoretical correlation between composition and electronic properties.  

PubMed

III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed in an effort to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two-layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows us to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response. PMID:22469563

Usman, Muhammad; Tasco, Vittorianna; Todaro, Maria Teresa; De Giorgi, Milena; O'Reilly, Eoin P; Klimeck, Gerhard; Passaseo, Adriana

2012-04-02

164

Semiclassical and quantum field theoretic bounds for traversable Lorentzian stringy wormholes  

SciTech Connect

A lower bound on the size of a Lorentzian wormhole can be obtained by semiclassically introducing the Planck cutoff on the magnitude of tidal forces (Horowitz-Ross constraint). Also, an upper bound is provided by the quantum field theoretic constraint in the form of the Ford-Roman Quantum Inequality for massless minimally coupled scalar fields. To date, however, exact static solutions belonging to this scalar field theory have not been worked out to verify these bounds. To fill this gap, we examine the wormhole features of two examples from the Einstein frame description of the vacuum low energy string theory in four dimensions which is the same as the minimally coupled scalar field theory. Analyses in this paper support the conclusion of Ford and Roman that wormholes in this theory can have sizes that are indeed only a few order of magnitudes larger than the Planck scale. It is shown that the two types of bounds are also compatible. In the process, we point out a 'wormhole' analog of naked black holes.

Nandi, Kamal Kanti [Department of Mathematics, University of North Bengal, Darjeeling (W.B.) 734 430 (India); Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100080 (China); Zhang Yuanzhong [CCAST (World Laboratory), P.O. Box 8730, Beijing 100080 (China); Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100080 (China); Kumar, K.B. Vijaya [Department of Physics, University of Mangalore, Mangalore 574 199 (India)

2004-09-15

165

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

Microsoft Academic Search

As is well known, in quantum mechanics, the calculation rule of the probability that an eigen-value a_n is observed when the physical quantity A is measured for a state described by the state vector |> is P(a_n)= . However, in Ref.[1], based on strict logical reasoning and mathematical calculation, it has been pointed out, replacing , one should use a

T. Mei

2008-01-01

166

Exact six-dimensional quantum calculations of the rovibrational levels of (HCl)2  

Microsoft Academic Search

Results of comprehensive full-dimensional (6D) quantum calculations of the rovibrational levels of (HCl)2, for total angular momentum J=0,1 are presented. The calculations employed two 6D potential energy surfaces (PES)—the ab initio PES of Bunker and co-workers, and the semiempirical PES of Elrod and Saykally. This 6D study provides the first rigorous, approximation-free description of the bound state properties of (HCl)2,

Yanhui Qiu; Zlatko Bacic

1997-01-01

167

Thermal boundary resistance predictions from molecular dynamics simulations and theoretical calculations  

NASA Astrophysics Data System (ADS)

The accuracies of two theoretical expressions for thermal boundary resistance are assessed by comparing their predictions to independent predictions from molecular dynamics (MD) simulations. In one expression (RE) , the phonon distributions are assumed to follow the equilibrium, Bose-Einstein distribution, while in the other expression (RNE) , the phonons are assumed to have nonequilibrium, but bulk-like distributions. The phonon properties are obtained using lattice dynamics-based methods, which assume that the phonon interface scattering is specular and elastic. We consider (i) a symmetrically strained Si/Ge interface, and (ii) a series of interfaces between Si and “heavy-Si,” which differs from Si only in mass. All of the interfaces are perfect, justifying the assumption of specular scattering. The MD-predicted Si/Ge thermal boundary resistance is temperature independent and equal to 3.1×10-9m2-K/W below a temperature of ˜500K , indicating that the phonon scattering is elastic, as required for the validity of the theoretical calculations. At higher-temperatures, the MD-predicted Si/Ge thermal boundary resistance decreases with increasing temperature, a trend we attribute to inelastic scattering. For the Si/Ge interface and the Si/heavy-Si interfaces with mass ratios greater than two, RE is in good agreement with the corresponding MD-predicted values at temperatures where the interface scattering is elastic. When applied to a system containing no interface, RE is erroneously nonzero due to the assumption of equilibrium phonon distributions on either side of the interface. While RNE is zero for a system containing no interface, it is 40%-60% less than the corresponding MD-predicted values for the Si/Ge interface and the Si/heavy-Si interfaces at temperatures where the interface scattering is elastic. This inaccuracy is attributed to the assumption of bulk-like phonon distributions on either side of the interface.

Landry, E. S.; McGaughey, A. J. H.

2009-10-01

168

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

Microsoft Academic Search

Graphics Processing Units (GPUs) are having a transformational effect on numerical lattice quantum chromo- dynamics (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

Ronald Babich; Michael A. Clark; Bálint Joó

2010-01-01

169

Iterative path integral calculation of quantum correlation functions for dissipative systems  

Microsoft Academic Search

An iterative path integral procedure is developed for calculating equilibrium two-time correlation functions of quantum dissipative systems. Its numerical feasibility is demonstrated by studying the position–position correlation function of two-level systems at various temperatures. It is also shown that canonical partition functions are also amenable to an iterative treatment.

Jiushu Shao; Nancy Makri

2001-01-01

170

A perturbation theory for calculating strain distributions in heterogeneous and anisotropic quantum dot structures  

Microsoft Academic Search

By introducing a homogenous comparison material, a perturbation theory based on Green's function is proposed to calculate the strain distribution inside and outside an arbitrarily shaped and anisotropic quantum dot (QD) embedded in an alien infinite medium. This theory removes the limitations of the previous analytical methods which are based upon the assumption that the QD is isotropic and has

J. Wang; H. J. Chu

2006-01-01

171

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

172

LETTER TO THE EDITOR: Mn2+ impurities in fluoroperovskites: a test for theoretical calculations  

NASA Astrophysics Data System (ADS)

The equilibrium impurity-ligand distance, Re, in six fluoroperovskites of the AMF3 series (A: K, Rb, Cs; M: Mg, Zn, Cd, Ca) doped with Mn2+ has been explored through density functional calculations for MnF6A8M616+ clusters where the effects of the electrostatic potential due to the rest of the lattice are included. The Re-values obtained coincide, within the experimental uncertainties, with those derived from the analysis of the experimental isotropic superhyperfine constant, As, and the 10Dq-parameter and also with available extended x-ray absorption fine-structure results. This important result is shown to be practically independent of the quality of the basis set employed. From the analysis of recent electron paramagnetic resonance data for AlF3:Mn2+ it is concluded that, for this system, Reicons/Journals/Common/approx" ALT="approx" ALIGN="TOP"/>197 pm which is 7% smaller than the average distance for pure compounds involving MnF64- complexes. The latter figure is shown to be consistent with the substitution of Mn2+ for a trivalent cation in AlF3:Mn2+. The present theoretical scheme has also been applied to Tl+ impurities in NaI. First results indicate an outwards relaxation of ligands which is equal to, at least, 5% and thus is much higher than the figure (1%) calculated by Aguado et al (Aguado A, Ayuela A, Lopez J M and Alonso J A 1998 Phys. Rev. B 58 11 964).

Barriuso, M. T.; Aramburu, J. A.; Moreno, M.

1999-12-01

173

[Calculation method of absolute quantum yields in photocatalytic slurry reactor based on cylindrical light].  

PubMed

Heterogeneous photocatalysis in slurry reactors have the particular characteristic that the catalyst particles not only absorb but also scatter photons so the radiation scattering can not be neglected. However, it is very difficult in mathematics to obtain the rigorous solution of the radiative transfer equation. Consequently present methods, in which the apparent quantum yields can be calculated by employing the incident radiation intensity, always underestimate quantum yields calculations. In this paper, a method is developed to produce absolute values of photocatalytic quantum yields in slurry reactor based on cylindrical UV light source. In a typical laboratory reactor (diameter equal to 5.6 cm and length equal to 10 cm) the values for the photocatalytic degradation of phenol are reported under precisely defined conditions. The true value of the local volumetric rate of photon absorption (LVRPA) can be obtained. It was shown that apparent quantum yields differ from true quantum yields 7.08% and that for the same geometric arrangement, vanishing fraction accounts for 1.1% of the incident radiation. The method can be used to compare reactivity of different catalysts or, for a given catalyst, reactivity with different model compounds and as a principle to design a reactor. PMID:15859439

Shen, Xun-wei; Yuan, Chun-wei

2005-01-01

174

Quantum effects in ab-initio calculations of rate constants for chemical reactions occuring in the condensed phase  

Microsoft Academic Search

An overview of recent advances in the development of methods designed to calculate rate constants for chemical reactions obeying mass action kinetic equations in condensed phases is presented. A general framework addressing mixed quantum-classical systems is elaborated that enables quantum features such as tunneling effects, zero-point vibrations, dynamic quantum coherence, and non-adiabatic effects to be calculated. An efficient Monte Carlo

Jeremy Schofield

2006-01-01

175

Dielectronic Recombination (via N=2-->N'=2 Core Excitations) and Radiative Recombination of Fe XX: Laboratory Measurements and Theoretical Calculations  

Microsoft Academic Search

We have measured the resonance strengths and energies for dielectronic recombination (DR) of Fe XX forming Fe XIX via N=2-->N'=2 (DeltaN=0) core excitations. We have also calculated the DR resonance strengths and energies using the AUTOSTRUCTURE, Hebrew University Lawrence Livermore Atomic Code (HULLAC), Multiconfiguration Dirac-Fock (MCDF), and R-matrix methods, four different state-of-the-art theoretical techniques. On average the theoretical resonance strengths

D. W. Savin; E. Behar; S. M. Kahn; G. Gwinner; A. A. Saghiri; M. Schmitt; M. Grieser; R. Repnow; D. Schwalm; A. Wolf; T. Bartsch; A. Müller; S. Schippers; N. R. Badnell; M. H. Chen; T. W. Gorczyca

2002-01-01

176

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

177

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

178

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

179

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

SciTech Connect

Classical matching theory can be defined in terms of matrices with nonnegative entries. The notion of Positive operator, central in Quantum Theory, is a natural generalization of matrices with non-negative entries. Based on this point of view, we introduce a definition of perfect Quantum (operator) matching. We show that the new notion inherits many 'classical' properties, but not all of them. This new notion goes somewhere beyound matroids. For separable bipartite quantum states this new notion coinsides with the full rank property of the intersection of two corresponding geometric matroids. In the classical situation, permanents are naturally associated with perfects matchings. We introduce an analog of permanents for positive operators, called Quantum Permanent and show how this generalization of the permanent is related to the Quantum Entanglement. Besides many other things, Quantum Permanents provide new rational inequalities necessary for the separability of bipartite quantum states. Using Quantum Permanents, we give deterministic poly-time algorithm to solve Hidden Matroids Intersection Problem and indicate some 'classical' complexity difficulties associated with the Quantum Entanglement. Finally, we prove that the weak membership problem for the convex set of separable bipartite density matrices is NP-HARD.

Gurvits, L. (Leonid)

2002-01-01

180

Theoretical investigation of intersubband transition energies and oscillator strength in CdS/SiO2 quantum dots  

NASA Astrophysics Data System (ADS)

Recent rapid advances in atomic-scale crystal growth and nanofabrication techniques have enabled researchers to realise various kinds of three-dimensional (3D) electron confinement in semiconductors. This paper presents a numerical simulation for quantum-dot-based electronic devices. The electronic structures calculations of a CdS/SiO2 quantum dot have been have been performed based on the resolution of the three-dimensional time-independent Schrödinger equation in the effective mass theory (EMT) and the band parabolicity approximation. The influence of the strain and dot separation on the formation of coupled quantum dot levels has been discussed. The oscillator strengths for intersubband electronic transitions have been also calculated. Besides, it is found that the subband energies and intersubband optical absorption are rather sensitive to the applied electric field. This gives a further parameter in various device applications based on the intersubband transitions. We hope that the present results may make a contribution to experimental studies of CdS/SiO2 quantum dot based structures which can be produced by inexpensive means. Our calculations provide good guidance for the selection of dot parameters to obtain absorption in quantum dot infrared photodetectors and a better understanding of the intersubband transition phenomena in quantum dot.

Abdi-Ben Nasrallah, S.; Bouazra, A.; Poncet, A.; Said, M.

2010-11-01

181

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

PubMed

In this work we propose an extended propagator theory for electrons and other types of quantum particles. This new approach has been implemented in the LOWDIN package and applied to sample calculations of atomic and small molecular systems to determine its accuracy and performance. As a first application of the method we have studied the nuclear quantum effects on electron ionization energies. We have observed that ionization energies of atoms are similar to those obtained with the electron propagator approach. However, for molecular systems containing hydrogen atoms there are improvements in the quality of the results with the inclusion of nuclear quantum effects. An energy term analysis has allowed us to conclude that nuclear quantum effects are important for zero order energies whereas propagator results correct the electron and electron-nuclear correlation terms. Results presented for a series of n-alkanes have revealed the potential of this method for the accurate calculation of ionization energies of a wide variety of molecular systems containing hydrogen nuclei. The proposed methodology will also be applicable to exotic molecular systems containing positrons or muons. PMID:22920101

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

2012-08-21

182

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

PubMed

In a previous paper [J. Theo. Comput. Chem. 2, 65 (2003)], one of the authors (B.P.) presented a method for solving the multidimensional Schrodinger equation, using modified Wilson-Daubechies wavelets, and a simple phase space truncation scheme. Unprecedented numerical efficiency was achieved, enabling a ten-dimensional calculation of nearly 600 eigenvalues to be performed using direct matrix diagonalization techniques. In a second paper [J. Chem. Phys. 121, 1690 (2004)], and in this paper, we extend and elaborate upon the previous work in several important ways. The second paper focuses on construction and optimization of the wavelength functions, from theoretical and numerical viewpoints, and also examines their localization. This paper deals with their use in representations and eigenproblem calculations, which are extended to 15-dimensional systems. Even higher dimensionalities are possible using more sophisticated linear algebra techniques. This approach is ideally suited to rovibrational spectroscopy applications, but can be used in any context where differential equations are involved. PMID:15260721

Poirier, Bill; Salam, A

2004-07-22

183

Photophysical properties of dipeptides containing substituted 3-(quinoxalin-6-yl) alanine. Spectroscopic studies and theoretical calculations.  

PubMed

The photophysical properties of excited states of two hybrid dipeptides [N-(3-(2,3-diphenylquinoxaline-6-ylo)alanylo) glycine], Pe-DPhQ, and [N-(3-(2,3 (pirydine-2-ylo) quinoxaline-6-ylo)alanylo) glycine], Pe-DPiQ, have been investigated by a combined solution-state study (absorption, emission) and quantum-mechanical (ab initio, DFT) calculations. The RHF and DFT B3LYP/6-31G (d,p) computations of the ground-state isomers of Pe-DPiQ dipeptide (open, half-closed, and closed) indicate that the most stable is the "open"-type structure with approximately equal (-44.43 degrees , -43.05 degrees ) dihedral angles describing rotation of the aromatic side rings with respect to the quinoxaline framework. This agrees with the literature findings that synthetic peptides are mostly unfolded. The experiments show that emission of Pe-DPiQ dipeptide is strongly temperature dependent, and at ambient and elevated temperatures the fluorescence is prevailing while the phosphorescence dominated emission spectra are observed at 77 K. On the basis of the decay curves that in the broad temperature range (rt-77 K) are biexponential (2 and 9 ns), it was concluded that at least its two major excited-state conformations may interconvert on the nanosecond time scale. The third component, of a small amplitude (10%) and a long time constant (25 ns), appears only in a new fluorescence band (570 nm) that grows up with the temperature increase. Analysis of the CIS/6-31G(d,p) results of the excited-state isomers of Pe-DPiQ supports the interpretation of experimental emission spectra and enables one to assign two excited-state conformations, demonstrating a tendency to keep one of their two side rings coplanar relative to the central quinoxaline plane, as Pe-DPiQ-I* (41.9 degrees , 6.3 degrees ) and Pe-DPiQ-II* (40.1 degrees , 4.5 degrees ) isomers contributing to the room temperature (403 nm) and 363 K (570 nm) fluorescence bands, respectively. The calculations also explain the electronic character of the corresponding S(1)<-->S(0) transitions and show that the state ordering of Pe-DPiQ resembles that of other diazines where the first singlet is of the npi* character while the S(2) and T(1) are the pipi* states. The reason for a strong phosphorescence is assigned to an effective spin-orbit coupling of appropriate singlet and triplet states that leads to ISC transitions and in result to population of the T(1) state and a phosphorescence from the T(1) state. From the present study, it was concluded that incorporation of quinoxaline moiety into the model peptides does not change the useful spectroscopic properties of the fluorophore and allows one to design its new analogues with improved activity and specificity. PMID:20712385

Wi?niewski, ?; Deperasi?ska, I; Staszewska, A; Stefanowicza, P; Berski, S; Lipkowski, P; Szewczuka, Z; Szemik-Hojniak, A

2010-09-01

184

Bosonic helium droplets with cationic impurities: Onset of electrostriction and snowball effects from quantum calculations  

SciTech Connect

Variational Monte Carlo and diffusion Monte Carlo calculations have been carried out for cations such as Li{sup +}, Na{sup +}, and K{sup +} as dopants of small helium clusters over a range of cluster sizes up to about 12 solvent atoms. The interaction has been modeled through a sum-of-potential picture that disregards higher order effects beyond atom-atom and atom-ion contributions. The latter were obtained from highly correlated ab initio calculations over a broad range of interatomic distances. This study focuses on two of the most striking features of the microsolvation in a quantum solvent of a cationic dopant: electrostriction and snowball effects. They are discussed here in detail and in relation with the nanoscopic properties of the interaction forces at play within a fully quantum picture of the cluster features.

Coccia, E.; Bodo, E.; Marinetti, F.; Gianturco, F. A.; Yildrim, E.; Yurtsever, M.; Yurtsever, E. [Department of Chemistry, University of Rome 'La Sapienza' and CNISM, Piazzale A. Moro 5, 00185 Rome (Italy); Chemistry Department, Istanbul Technical University, 80626 Maslak, Istanbul (Turkey); Chemistry Department, Koc University, Istanbul 34450 (Turkey)

2007-03-28

185

Quantum Matching Theory (with new complexity theoretic, combinatorial and topological insights on the nature of the Quantum Entanglement)  

Microsoft Academic Search

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 nonnegative entries. Based on this point of view, we introduce a definition of perfect Quantum (operator) matching . We show that the new notion inherits many \\

Leonid Gurvits

2002-01-01

186

Helium trimer calculations with a public quantum three-body code  

SciTech Connect

We present an illustration of using a quantumthree-body code being prepared for public release. The code is based on iterative solving of the three-dimensional Faddeev equations. The code is easy to use and allows users to perform highly-accurate calculations of quantum three-body systems. The previously known results for He{sub 3} ground state are well reproduced by the code.

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

2012-10-15

187

Transfer matrix approach to quantum conductivity calculations in single-wall carbon nanotubes  

Microsoft Academic Search

We present an efficient transfer matrix formalism for obtaining the quantum conductivity of single-wall carbon nanotubes (SWCN's) based on a nonorthogonal tight-binding scheme. The formalism is used to calculate conductivity in the presence of topological defects and H adsorbates. I-V characteristics show large oscillatory behavior as a function of the number of H adatoms for both (10,0) and (5,5) SWCN's.

Antonis N. Andriotis; Madhu Menon; Deepak Srivastava

2002-01-01

188

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

189

Calculation of Host-Guest Binding Affinities Using a Quantum-Mechanical Energy Model  

PubMed Central

The prediction of protein-ligand binding affinities is of central interest in computer-aided drug discovery, but it is still difficult to achieve a high degree of accuracy. Recent studies suggesting that available force fields may be a key source of error motivate the present study, which reports the first mining minima (M2) binding affinity calculations based on a quantum mechanical energy model, rather than an empirical force field. We apply a semi-empirical quantum-mechanical energy function, PM6-DH+, coupled with the COSMO solvation model, to 29 host-guest systems with a wide range of measured binding affinities. After correction for a systematic error, which appears to derive from the treatment of polar solvation, the computed absolute binding affinities agree well with experimental measurements, with a mean error 1.6 kcal/mol and a correlation coefficient of 0.91. These calculations also delineate the contributions of various energy components, including solute energy, configurational entropy, and solvation free energy, to the binding free energies of these host-guest complexes. Comparison with our previous calculations, which used empirical force fields, point to significant differences in both the energetic and entropic components of the binding free energy. The present study demonstrates successful combination of a quantum mechanical Hamiltonian with the M2 affinity method.

Muddana, Hari S.; Gilson, Michael K.

2012-01-01

190

Theoretical study of optical properties in deep ultraviolet Al-rich AlGaN/AIN quantum wells  

NASA Astrophysics Data System (ADS)

Optical properties of deep ultraviolet Al-rich AlGaN/AlN quantum wells (QWs) were theoretically investigated by using the multiband effective-mass theory. The theoretical PL transition wavelength is found to agree well with the experimental result. The internal field in AlGaN/AlN QW structures with lower Al contents is much larger than that in QW structures with higher Al contents. The intensity of the spontaneous emission spectra is shown to be improved with increasing Al content because the optical matrix elements are largely enhanced due to the reduced internal field.

Park, S. H.

2009-03-01

191

On Quantum Statistical Inference, II  

Microsoft Academic Search

Interest in problems of statistical inference connected to measurements of quantum systems has recently increased substantially, in step with dramatic new developments in experimental techniques for studying small quantum systems. Furthermore, theoretical developments in the theory of quantum measurements have brought the basic mathematical framework for the probability calculations much closer to that of classical probability theory. The present paper

O. E. Barndorff-Nielsen; R. D. Gill; P. E. Jupp

2003-01-01

192

Collective excitations in quantum Hall liquid crystals: Single-mode approximation calculations  

SciTech Connect

A variety of recent experiments probing the low-temperature transport properties of quantum Hall systems have suggested an interpretation in terms of liquid crystalline mesophases dubbed quantum Hall liquid crystals. The single mode approximation (SMA) has been a useful tool for the determination of the excitation spectra of various systems such as phonons in {sup 4}He and in the fractional quantum Hall effect. In this paper we calculate (via the SMA) the spectrum of collective excitations in a quantum Hall liquid crystal by considering nematic, tetratic, and hexatic generalizations of Laughlin's trial wave function having twofold, fourfold, and sixfold broken rotational symmetry, respectively. In the limit of zero wave vector q the dispersion of these modes is singular, with a gap that is dependent on the direction along which q=0 is approached for nematic and tetratic liquid crystalline states, but remains regular in the hexatic state, as permitted by the fourth order wave-vector dependence of the (projected) oscillator strength and static structure factor.

Lapilli, Cintia M.; Wexler, Carlos [Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, Missouri 65211 (United States)

2006-02-15

193

A theoretical study of an integrated quantum-well resonant tunneling oscillator initiated by an IMPATT diode  

Microsoft Academic Search

A novel initiation scheme, utilizing the new pulsed IMPATT to generate millimeter-wave oscillations in a series-integrated quantum-well resonant tunneling diode (RTD), is proposed and theoretically investigated for the first time. To facilitate transient analysis, a generalized impedance is defined and adopted in this work. The detailed investigation of a two-RTD oscillator is carried out at 100 GHz. The maximum oscillator

Cheng Chih Yang; Dee-Son Pan

1995-01-01

194

Using experimental studies and theoretical calculations to analyze the molecular mechanism of coumarin, p-hydroxybenzoic acid, and cinnamic acid  

NASA Astrophysics Data System (ADS)

Three natural products, Coumarin (1), p-hydroxybenzoic acid (2), trans-cinnamic acid (3) were isolated from the natural plant of indigenous cinnamon and the structures including relative stereochemistry were elucidated on the basis of spectroscopic data and theoretical calculations. Their sterochemical structures were determined by NMR spectroscopy, mass spectroscopy, and X-ray crystallography. The p-hydroxybenzoic acid complex with water is reported to show the existence of two hydrogen bonds. The two hydrogen bonds are formed in the water molecule of two hydrogen-accepting oxygen of carbonyl group of the p-hydroxybenzoic acid. The intermolecular interaction two hydrogen bond of the model system of the water-p-hydroxybenzoic acid was investigated. An experimental study and a theoretical analysis using the B3LYP/6-31G* method in the GAUSSIAN-03 package program were conducted on the three natural products. The theoretical results are supplemented by experimental data. Optimal geometric structures of three compounds were also determined. The calculated molecular mechanics compared quite well with those obtained from the experimental data. The ionization potentials, highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy, energy gaps, heat of formation, atomization energies, and vibration frequencies of the compounds were also calculated. The results of the calculations show that three natural products are stable molecules with high reactive and various other physical properties. The study also provided an explicit understanding of the sterochemical structure and thermodynamic properties of the three natural products.

Hsieh, Tiane-Jye; Su, Chia-Ching; Chen, Chung-Yi; Liou, Chyong-Huey; Lu, Li-Hwa

2005-05-01

195

Strategy for Time Dependent Quantum Mechanical Calculations Using a Gaussian Wave Packet Representation of the Wave Function.  

National Technical Information Service (NTIS)

We develop methodology for performing time dependent quantum mechanical calculations by representing the wave function as a sum of Gaussian wave packets (GWP), each characterized by a set of parameters such as width, position, momentum and phase. The prob...

B. Jackson H. Metiu R. Heather S. I. Sawada

1985-01-01

196

Stretched DNA investigated using molecular-dynamics and quantum-mechanical calculations.  

PubMed

We combined atomistic molecular-dynamics simulations with quantum-mechanical calculations to investigate the sequence dependence of the stretching behavior of duplex DNA. Our combined quantum-mechanical/molecular-mechanical approach demonstrates that molecular-mechanical force fields are able to describe both the backbone and base-base interactions within the highly distorted nucleic acid structures produced by stretching the DNA from the 5' ends, which include conformations containing disassociated basepairs, just as well as these force fields describe relaxed DNA conformations. The molecular-dynamics simulations indicate that the force-induced melting pathway is sequence-dependent and is influenced by the availability of noncanonical hydrogen-bond interactions that can assist the disassociation of the DNA basepairs. The biological implications of these results are discussed. PMID:20074515

Rezác, Jan; Hobza, Pavel; Harris, Sarah A

2010-01-01

197

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

PubMed

An interface between the APMO code and the electronic structure package MOLPRO is presented. The any particle molecular orbital APMO code [Gonza?lez et al., Int. J. Quantum Chem. 108, 1742 (2008)] implements the model where electrons and light nuclei are treated simultaneously at Hartree-Fock or second-order Mo?ller-Plesset levels of theory. The APMO-MOLPRO interface allows to include high-level electronic correlation as implemented in the MOLPRO package and to describe nuclear quantum effects at Hartree-Fock level of theory with the APMO code. Different model systems illustrate the implementation: (4)He2 dimer as a protype of a weakly bound van der Waals system; isotopomers of [He-H-He](+) molecule as an example of a hydrogen bonded system; and molecular hydrogen to compare with very accurate non-Born-Oppenheimer calculations. The possible improvements and future developments are outlined. PMID:23676035

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

2013-05-14

198

Fault tolerance calculations for clocked quantum-dot cellular automata devices  

NASA Astrophysics Data System (ADS)

We present a numerical study of fault tolerance properties in quantum-dot cellular automata (QCA) devices. A full-basis quantum method is used for calculations of the Hamiltonian, and a statistical model has been introduced to simulate the influence of position defects of the dots within cells on the logical output. Combined effects of temperature and cell defects on a shift register have been studied. Uniform and normal distributions have been used for the cell defect simulations. Normal distribution simulations produce realistic results compared to the uniform distribution. In order to show the operational limit of a device, parameters such as ``displacement factor'' and ``success rate'' are introduced. Results show that the fault tolerance of a QCA device is strongly dependent on temperature as well as on the cell defects. The robustness of a shift register is also dependent on the size of the device.

Khatun, M.; Barclay, T.; Sturzu, I.; Tougaw, P. D.

2005-11-01

199

Dynamical structure functions from quantum Monte Carlo calculations of a proper integral transform  

NASA Astrophysics Data System (ADS)

An ab initio method for determining the dynamical structure function of an interacting many-body quantum system has been devised by combining a generalized integral transform method with quantum Monte Carlo (QMC) methods. A kernel has been found that (i) lets the transform be calculable with QMC methods and (ii) is a representation of the ? function, allowing an inversion of the transform with a much higher predictive power than the inverse Laplace transform. As a first application, the excitation spectrum of bulk atomic 4He has been computed, both in the low and intermediate momentum ranges. The peculiar form of the kernel allows us to predict, without using any model, both positions and widths of the collective excitations in the maxon-roton region, as well as the existence of the second collective peak. A prediction of the dispersion of the single-particle modes described by the incoherent part is also presented.

Roggero, Alessandro; Pederiva, Francesco; Orlandini, Giuseppina

2013-09-01

200

Augmented solar energy collection using different types of planar reflective surfaces - Theoretical calculations and experimental results  

Microsoft Academic Search

The paper reports theoretical and experimental studies of the use of different types of flat reflective surfaces to increase the collection of solar energy by flat collectors. Specular, diffuse, and combination specular\\/diffuse reflective surfaces are discussed. The reflectivity properties of a given surface are measured as a function of incident and reflected angles, and on the basis of these measurements

D. P. Grimmer; K. G. Zinn; K. C. Herr; B. E. Wood

1978-01-01

201

Theoretical calculations of thermophysical properties of single-wall carbon nanotube bundles  

Microsoft Academic Search

Carbon nanotube bundles are promising thermal interfacial materials due to their excellent thermal and mechanical characteristics. In this study, the phonon dispersion relations and density of states of the single-wall carbon nanotube bundles are calculated by using the force constant model. The calculation results show that the inter-tube interaction leads to a significant frequency raise of the low frequency modes.

Ting-Ting Miao; Meng-Xuan Song; Wei-Gang Ma; Xing Zhang

2011-01-01

202

COMPLEX CALCULATORS IN THE CLASSROOM: THEORETICAL AND PRACTICAL REFLECTIONS ON TEACHING PRECALCULUS  

Microsoft Academic Search

University and older school students following scientific courses now use complex calculators with graphical, numerical and symbolic capabilities. In this context, the design of lessons for 11th grade pre-calculus students was a stimulating challenge. In the design of lessons, emphasising the role of mediation of calculators and the devel- opment of schemes of use in an 'instrumental genesis' was productive.

JEAN-BAPTISTE LAGRANGE

1999-01-01

203

Comparison of different theoretical models for flash temperature calculation under fretting conditions  

Microsoft Academic Search

The wear and friction properties of tribological interfaces depend significantly on the contact temperature, and its determination is therefore important for each tribological application. Temperature calculation methods available in the literature use quite different physical, dynamic and geometrical assumptions. Furthermore, the assumptions necessary for temperature calculations also include various interfacial properties, which are usually unknown due to many difficulties in

Mitjan Kalin; Jože Vižintin

2001-01-01

204

A theoretical model for molecules interacting with intense laser pulses: The Floquet-based quantum-classical Liouville equation  

NASA Astrophysics Data System (ADS)

The Floquet-based quantum-classical Liouville equation (F-QCLE) is presented as a novel theoretical model for the interaction of molecules with intense laser pulses. This equation efficiently combines the following two approaches: First, a small but spectroscopically relevant part of the molecule is treated quantum-mechanically while the remaining degrees of freedom are modeled by means of classical molecular dynamics. The corresponding nonadiabatic dynamics is given by the quantum-classical Liouville equation which is a first-order approximation to the partial Wigner transform of full quantum dynamics. Second, the dynamics of the quantum subsystem is described in terms of instantaneous Floquet states thus eliminating highly oscillatory terms from the equations of motion. The resulting F-QCLE is shown to have a well defined adiabatic limit: For infinitely heavy classical particles and for infinitely slow modulation the dynamics adiabatically follows the Floquet quasi-energy surfaces for a strictly time-periodic field. Otherwise, nonadiabtic effects arise both from the motion of the classical particles and from the modulation of the field which is assumed to be much slower than the carrier frequency. A numerical scheme to solve the F-QCLE is based on a Trotter splitting of the time evolution. The simplest implementation can be realized by an ensemble of trajectories stochastically hopping between different Floquet surfaces. As a first application we demonstrate the excellent agreement of quantum-classical and fully quantum-mechanical dynamics for a two-state model of photodissociation of molecular fluorine. In summary, due to the favorable scaling of the numerical effort the F-QCLE provides an efficient tool for the simulation of medium to large molecules interacting with intense fields beyond the perturbative regime.

Horenko, Illia; Schmidt, Burkhard; Schütte, Christof

2001-10-01

205

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.

206

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

NASA Astrophysics Data System (ADS)

The hydrogen-bonded structures of pyrrole-solvent (H2O,CH3OH,C2H5OH) 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-H2O, pyrrole-CH3OH, and pyrrole-C2H5OH, 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 ?-type (NH...O) hydrogen-bonded structures had 7.6-9.0 kJ/mol larger binding energies than the ?-type structures (OH...? electron cloud of pyrrole), and that the vibrational frequencies of the ?-type structures are consistent with the observed spectra. In addition to the 1:1 clusters, the NH or OH stretching vibrations of pyrrole-CH3OH binary clusters were observed at 3432 and 3549 cm-1. Among three optimized structures of the pyrrole-(CH3OH)2, the ?-? bridge pyrrole-(CH3OH)2 provided a reasonable agreement between the observed and calculated vibrational frequencies. For the pyrrole-H2O 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-H2O cluster, which has a closed cyclic hydrogen-bonded structure.

Matsumoto, Yoshiteru; Honma, Kenji

2009-02-01

207

Theoretical calculations of 95 Mo-NMR chemical shifts for compounds [MoO 4? n S n ] 2?  

Microsoft Academic Search

Summary Theoretical calculation of95Mo-NMR chemical shifts for [MoO4-nSn]2- (n=0-4) compounds is reported here for the first time on the basis of Fenske-Hall method and Sum-Over-State (SOS) perturbation theory. A systematic decrease in shielding of95Mo nuclei with increase of number of sulfur in [MoO4-nSn]2-, which is observed experimentally, can be reasonably explained by our calculation. A good linear relationship between chemical

Sun Yue-ming; Zhu Long-geng; You Xiao-zeng; Jiang Yuang-sheng

1992-01-01

208

Molecular modeling study of dihydrofolate reductase inhibitors. Molecular dynamics simulations, quantum mechanical calculations, and experimental corroboration.  

PubMed

A molecular modeling study on dihydrofolate reductase (DHFR) inhibitors was carried out. By combining molecular dynamics simulations with semiempirical (PM6), ab initio, and density functional theory (DFT) calculations, a simple and generally applicable procedure to evaluate the binding energies of DHFR inhibitors interacting with the human enzyme is reported here, providing a clear picture of the binding interactions of these ligands from both structural and energetic viewpoints. A reduced model for the binding pocket was used. This approach allows us to perform more accurate quantum mechanical calculations as well as to obtain a detailed electronic analysis using the quantum theory of atoms in molecules (QTAIM) technique. Thus, molecular aspects of the binding interactions between inhibitors and the DHFR are discussed in detail. A significant correlation between binding energies obtained from DFT calculations and experimental IC?? values was obtained, predicting with an acceptable qualitative accuracy the potential inhibitor effect of nonsynthesized compounds. Such correlation was experimentally corroborated synthesizing and testing two new inhibitors reported in this paper. PMID:23834278

Tosso, Rodrigo D; Andujar, Sebastian A; Gutierrez, Lucas; Angelina, Emilio; Rodríguez, Ricaurte; Nogueras, Manuel; Baldoni, Héctor; Suvire, Fernando D; Cobo, Justo; Enriz, Ricardo D

2013-07-24

209

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

PubMed

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

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

2006-02-28

210

Comparison of experimental and theoretical GaInP quantum well gain spectra  

SciTech Connect

A microscopic analysis of experimental GaInP quantum well gain spectra is presented for a wide range of excitation. A consistent treatment of carrier collision effects, at the level of quantum kinetic theory in the Markovian limit, is found to be necessary for agreement with experiment. {copyright} {ital 1997 American Institute of Physics.}

Chow, W.W. [Sandia National Laboratories, Albuquerque, New Mexico 85718-0601 (United States); Smowton, P.M.; Blood, P. [Department of Physics and Astronomy, University of Wales, Cardiff, Cardiff CF2 3YB (United Kingdom); Girndt, A.; Jahnke, F.; Koch, S.W. [Department of Physics and Material Sciences Center, Philipps University, Renthof 5, 35032 Marburg (Germany)

1997-07-01

211

Theoretical Analysis for Calculation of the Through Thickness Effective Constants for Orthotropic Thick Filament Wound Tubes  

Microsoft Academic Search

This paper presents a method for determining the theoretical values for all the elastic constants needed for three-dimensional stresses of angle-ply laminates and filament wound tube from the properties of unidirectional fiber reinforced epoxy resin. The layers were arranged symmetrically about the mid-surface of the laminate. The stress in the longitudinal axis is assumed to be constant throughout the thickness

Abdalla F. Hamed; M. H. Megat; S. M. Sapuan; B. B. Sahari

2008-01-01

212

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

SciTech Connect

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

DeVries, P.L.

1984-01-01

213

Indecomposable Set-Theoretical Solutions to the Quantum Yang–Baxter Equation on a Set with a Prime Number of Elements  

Microsoft Academic Search

In this paper we show that all indecomposable nondegenerate set-theoretical\\u000asolutions to the Quantum Yang-Baxter equation on a set of prime order are\\u000aaffine, which allows us to give a complete and very simple classification of\\u000asuch solutions. This result is a natural application of the general theory of\\u000aset-theoretical solutions to the quantum Yang-Baxter equation. It is also a

Pavel Etingof; Alexander Soloviev; Robert Guralnick

2001-01-01

214

MFP (Magnetic Field Package): A Flexible System of Computer Programs for Theoretical Magnetic Field Calculations.  

National Technical Information Service (NTIS)

The report contains a description of three separate computer routines which are used to calculate various parameters utilized in the analysis of data transmitted from probes flown on research rockets and satellites. The majority of the parameters calculat...

A. Abelowitz R. E. McInerney

1973-01-01

215

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

216

Quantum methyl rotations in zeolitic imidazolate framework-8: Inelastic neutron scattering and first-principles calculations  

NASA Astrophysics Data System (ADS)

Zeolitic imidazolate framework-8 (ZIF8), which consists of ZnN4 clusters linked by 2-methylimidazole [H2C3N2-(CH3)], is a newly discovered framework compound with interesting hydrogen-adsorption properties. The presence of a single type of methyl group in its crystal structure renders ZIF8 an ideal system for studying quantum methyl rotations. Combining inelastic neutron scattering measurements and first-principles calculations, we studied the quantum rotational tunneling and phonons associated with the ZIF8 methyl groups. The rotational tunnel splitting is an extremely sensitive probe of the local potential. The measured tunnel splitting (˜345 ?eV at 1.4 K) indicated a nearly free quantum rotor (i.e., a very low methyl rotational barrier), which is unusual for the solid state. With guest molecules adsorbed inside the framework, the rotational barrier was found to change significantly. Hydrogen adsorption decreased the barrier at low loading, yet increased it at higher loading. Methane adsorption nearly doubled the rotational barrier. These results provided clues for understanding the nature of the ZIF-guest molecule interactions.

Rush, J. J.; Zhou, W.; Wu, H.; Udovic, T. J.; Yildirim, T.

2007-03-01

217

Single and dual cation sites in zeolites: theoretical calculations and FTIR spectroscopic studies on CO adsorption on K-FER.  

PubMed

Interaction of CO with K-FER zeolite was investigated by a combination of variable-temperature IR spectroscopy and computational study. Calculations were performed using omega(CO)/r(CO) correlation method in combination with a periodic density functional theory model. On the basis of agreement between experimental and calculated results, the following carbonyl complexes were identified: (i) mono- and dicarbonyl C-down complexes on single K(+) sites characterized by IR absorption bands at 2163 and 2161 cm(-1), respectively; (ii) complexes formed by CO bridging two K(+) ions separated by about 7-8 A (dual sites) characterized by a band at 2148 cm(-1); and (iii) isocarbonyl (O-down) complexes characterized by a band at 2116 cm(-1). The bridged carbonyl complexes on dual K(+) sites are about 5 kJ/mol more stable than monodentate (monocarbonyl) CO complexes. The C-O stretching frequency of monocarbonyl species in K-FER depends on K(+) location in the zeolite, and not on K(+) coordination to the framework. A combination of theoretical calculations using a periodic density functional model and experimental results showed formation of two types of monocarbonyls. The most abundant type appears at 2163 cm(-1), and the less abundant one at 2172 cm(-1). These experimentally determined wavenumber values coincide, within +/-2 cm(-1), with those derived from theoretical calculations. PMID:17091999

Garrone, E; Bulánek, R; Frolich, K; Otero Aréan, C; Rodríguez Delgado, M; Palomino, G Turnes; Nachtigallová, D; Nachtigall, P

2006-11-16

218

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

USGS Publications Warehouse

In order to standardize methods and facilitate rapid calculation and archival of stream-metabolism variables, the Stream Metabolism Program was developed to calculate gross primary production, net ecosystem production, respiration, and selected other variables from continuous measurements of dissolved-oxygen concentration, water temperature, and other user-supplied information. Methods for calculating metabolism from continuous measurements of dissolved-oxygen concentration and water temperature are fairly well known, but a standard set of procedures and computation software for all aspects of the calculations were not available previously. The Stream Metabolism Program addresses this deficiency with a stand-alone executable computer program written in Visual Basic.NET?, which runs in the Microsoft Windows? environment. All equations and assumptions used in the development of the software are documented in this report. Detailed guidance on application of the software is presented, along with a summary of the data required to use the software. Data from either a single station or paired (upstream, downstream) stations can be used with the software to calculate metabolism variables.

Bales, Jerad D.; Nardi, Mark R.

2007-01-01

219

Theoretical study on the excited-state intramolecular proton transfer in the aromatic schiff base salicylidene methylamine: an electronic structure and quantum dynamical approach.  

PubMed

The proton-transfer dynamics in the aromatic Schiff base salicylidene methylamine has been theoretically analyzed in the ground and first singlet (pi,pi) excited electronic states by density functional theory calculations and quantum wave-packet dynamics. The potential energies obtained through electronic calculations that use the time-dependent density functional theory formalism, which predict a barrierless excited-state intramolecular proton transfer, are fitted to a reduced three-dimensional potential energy surface. The time evolution in this surface is solved by means of the multiconfiguration time-dependent Hartree algorithm applied to solve the time-dependent Schrödinger equation. It is shown that the excited-state proton transfer occurs within 11 fs for hydrogen and 25 fs for deuterium, so that a large kinetic isotope effect is predicted. These results are compared to those of the only previous theoretical work published on this system [Zgierski, M. Z.; Grabowska, A. J. Chem. Phys. 2000, 113, 7845], reporting a configuration interaction singles barrier of 1.6 kcal mol(-1) and time reactions of 30 and 115 fs for the hydrogen and deuterium transfers, respectively, evaluated with the semiclassical instanton approach. PMID:16599431

Ortiz-Sanchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel; Lluch, José M

2006-04-13

220

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

221

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

NASA Astrophysics Data System (ADS)

In previous work [T. Wu, H. J. Werner, and U. Manthe, Science 306, 2227 (2004)], accurate quantum reaction rate calculations of the rate constant for the H+CH4-->CH3+H2 reaction have been presented. Both the electronic structure calculations and the nuclear dynamics calculations are converged with respect to the basis sets employed. In this paper, the authors apply the same methodology to an isotopic variant of this reaction: D+CH4-->CH3+HD. Accurate rate constants are presented for temperatures between 250 and 400 K. For temperatures between 400 and 800 K, they use a harmonic extrapolation to obtain approximate rate constants for H/D+CH4. The calculations suggest that the experimentally reported rate constants for D+CH4 are about a factor of 10-20 too high. For H+CH4, more accurate experiments are available and agreement is much better: the difference is less than a factor of 2.6. The kinetic isotope effect for the H/D+CH4 reactions is studied and compared with experiment and transition state theory (TST) calculations. Harmonic TST was found to provide a good description of the kinetic isotope effect.

van Harrevelt, Rob; Nyman, Gunnar; Manthe, Uwe

2007-02-01

222

Theoretical calculations of the total and ionization cross sections for electron impact on some simple biomolecules  

SciTech Connect

In this paper we report total cross sections (TCS), Q{sub T}, total elastic cross sections, Q{sub el}, and total ionization cross section, Q{sub ion} for electron impact on water, formaldehyde, formic acid, and the formyl radical from circa 15 eV to 2 KeV. The results are compared where possible, with previous theoretical and experimental results and, in general, are found to be in good agreement. The total and elastic cross sections for HCHO, HCOOH, and CHO radical are reported.

Vinodkumar, Minaxi [V. P. and R. P. T. P. Science College, Vallabh Vidyanagar-388120 (India); Joshipura, K. N. [Department of Physics, Sardar Patel University, Vallabh Vidyanagar-388120 (India); Limbachiya, Chetan [P. S. Science College, Kadi--382 715 (India); Mason, Nigel [Department of Physics and Astronomy, Open University, Milton Keynes, MK7 6AA (United Kingdom)

2006-08-15

223

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

224

Quantum-mechanical calculation of the intensity distribution in resonance Raman spectra of cytosine  

NASA Astrophysics Data System (ADS)

A quantum-mechanical calculation of the relative intensities of lines in resonance Raman (RR) spectra of cytosine excited by laser radiation at 266, 218, and 200 nm was performed in different approximations of the vibronic theory. Both the Herzberg-Teller effect and the contribution from electronic states located close to the resonance state are shown to play a significant role in determining the relative intensities of lines. A satisfactory agreement between the calculated results and experimental data is obtained. The specific features of the intensity distribution in the RR spectra of cytosine are compared with those in the spectra of the previously studied thymine and uracil, which have a similar structure and also belong to the simplest nucleic acid bases.

Burova, T. G.; Ten, G. N.; Kucherova, V. V.

2004-07-01

225

Trial wave functions for the calculation of vibrational states of molecules using quantum Monte Carlo  

NASA Astrophysics Data System (ADS)

In this article we test three kinds of trial wave functions for the calculation of vibrational excited states of molecules using quantum Monte Carlo. We begin our study with the basis set originally used by Bernu and co-workers and further modified by Acioli and Soares Neto. The second set tested was the simplified Morse oscillator-like with harmonic coupling (SMOL-HC) proposed by Brown et al. to study the vibrational spectra of C3. Finally we proposed a third basis set, based on the previous two. This basis set keeps the anharmonicity of the SMOL-HC basis but with well conditioned Hamiltonian and overlap matrices. The calculations were performed in the H2, H3+, and H2O molecules. The results indicate that the basis sets proposed in this work yield more accurate results with a smaller number of basis functions.

da Silva, Washington B.; Acioli, Paulo H.

2001-06-01

226

Theoretical Calculation for the Ionization of Molecules by Short Strong Laser Pulses  

SciTech Connect

We have developed several calculation methods for the ionization of atoms and molecules by strong and ultrashort laser pulses, based on the numerical solution of the time dependent Schroedinger equation (TDSE) in the momentum space. We have performed calculations within the strong field approximation (Volkov) and using iterative and direct methods for solving the TDSE. The investigated molecules are H{sub 2}{sup +} and H{sub 2}O. In case of the ionization of diatomic molecules the interference effects in the ejected electron spectra due to the coherent addition of the waves associated to the electrons ejected from the vicinity of different nuclei were also analysed.

Nagy, L.; Borbely, S. [Faculty of Physics, Babes-Bolyai University, str. Kogalniceanu 1, RO-400084 Cluj-Napoca (Romania)

2011-10-03

227

Theoretical calculations on dipyridamole structure allow to explain experimental properties associated to electrochemical oxidation and protonation  

NASA Astrophysics Data System (ADS)

PM3 calculations of charge distributions for dipyridamole (DIP) in the neutral, single- and double-ionized states allowed to estimate the first and second ionization potentials. Results are compared with electrochemical oxidation, a sequential two-step process. Single ionization produces a cation radical, the electron being removed from the nitrogen atoms in the substituent positions 2,4,6,8 with participation of the carbons in the pyrimido-pyrimidine ring. Protonation of one of the nitrogens is allowed energetically while a second protonation is forbidden due to the high energy required. Our calculations allow to explain some interesting experimental results related to electrochemical oxidation and protonation of the drug.

Alves, C. N.; Castilho, M.; Mazo, L. H.; Tabak, M.; da Silva, A. B. F.

2001-11-01

228

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

229

Structure of neutral molecules and monoanions of selected oxopurines in aqueous solutions as studied by NMR spectroscopy and theoretical calculations.  

PubMed

A methodology enabling investigation of a multicomponent tautomeric and acid-base equilibria by (13)C NMR spectroscopy supported by theoretical calculations has been proposed. The effectiveness of this method has been illustrated in a study of 2-oxopurine, 6-oxopurine (hypoxanthine), 8-oxopurine, and 2,6-dioxopurine (xanthine) in neutral and alkaline aqueous solutions. For each compound a series of (13)C NMR spectra were recorded at pH ranges in which neutral molecules, monoanions and/or dianions occurred in dynamic equilibrium. The carbon chemical shifts for these three forms of the investigated compounds were retrieved from the analysis of pH-dependence of the measured, dynamically averaged values of these parameters. The structures of several stable tautomers of the neutral and monoanionic oxopurine forms were predicted from theoretical calculations and nuclear magnetic shielding constants for (13)C nuclei in these tautomers were calculated. At both calculation steps (molecular geometry optimization and calculation of NMR parameters) the PBE1PBE/6-311++G(2d,p) level of theory was used. The populations of the most stable tautomers were determined from the experimental data analysis exploiting the fact that they were population-weighted averages of the chemical shifts of particular tautomers. It has been shown that only the oxo forms of the investigated oxopurines are present in aqueous solutions and that the determined populations in most cases remain in a qualitative agreement with the calculated free energies of the appropriate tautomers. The obtained results are in general agreement with other literature reports on oxopurine tautomerism and confirm importance of the hydration phenomena for the investigated systems. The data analysis has shown that the best compliance between theory and experiment is obtained when the hydration phenomenon is modeled by discrete hydration augmented by PCM (polarizable continuum solvation model). PMID:21338162

Dybiec, Katarzyna; Molchanov, Sergey; Gryff-Keller, Adam

2011-02-22

230

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

SciTech Connect

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

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

2011-03-21

231

Theoretical calculation of low-lying states of NaAr and NaXe  

NASA Astrophysics Data System (ADS)

Potential curves as well as dipole moments and linking transition moments are calculated for the ground X 2 Sigma + and low lying excited A 2 Pi, B 2 Sigma +, C 2 Sigma +, (4) 2 Sigma +, (2) 2 Pi and (1) 2 Delta states of NaAr and NaXe. Calculations are performed using a self-consistent field plus configuration-interaction procedure with the core electrons replaced by an ab initio effective core potential. The potential curves obtained are found to be considerably less repulsive than the semiempirical curves of Pascale and Vandeplanque (1974) and to agree well with existing experimental data, although the binding energies of those states having potential minima due to van der Waals interactions are underestimated. Emission bands are also calculated for the X 2 Sigma + - C 2 Sigma + excimer transitions of NaAr and NaXe using the calculated transition moments and potential curves, and shown to agree well with experiment on the short-wavelength side of the maximum.

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

1981-07-01

232

Theoretical attenuation of sound in a lined duct: some computer calculations  

Microsoft Academic Search

When the Newton-Raphson method for complex roots is used, numerical solutions of both the Morse and Scott equations for attenuation in a lined duct can readily be obtained. The method of calculation and some comparative results using both theories are presented in this note.

D. R. A. Christie

1971-01-01

233

Theoretical model for calculating pulling loads for pipes in horizontal directional drilling  

Microsoft Academic Search

The paper presents a model for calculating installation loads imposed on pipes during the pulling operation in horizontal directional drilling. The model is implemented into a numerical program PipeForce 2005. The analysis includes pulling load contributions from directional changes, fluidic drag, solid friction and pipe’s weight. The emphasis in this paper is on details related to directional changes during the

Elisabeth Cheng; Maria Anna Polak

2007-01-01

234

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

SciTech Connect

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

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

2005-05-24

235

Evaluation and theoretical calculation of the neutron reaction data for natural tin.  

National Technical Information Service (NTIS)

The evaluation of the neutron reaction cross section for natural tin measured by experiments have been completed. The interaction reaction data of the neutron with tin have been calculated by using the optical model (OPM), Hauser-Feshbach theory with widt...

L. Yao Y. Jin

1993-01-01

236

The simple theoretical analysis of quantum well wires superlattice (QWSL) of communication technology  

NASA Astrophysics Data System (ADS)

I study the dimension-dependent (such as quantum well (QWs), quantum well wires (QWWs) and quantum dots (QDs)) transport in different nano-structures and the derivation of the expressions of many important transport coefficients are based on the temperature dependent electron concentration in nonlinear optical and optoelectronic nanostructure materials. The results for the corresponding emission and the electron statistics in the constituent materials have also been obtained. The thickness and the doping dependences of the field emission from all the aforementioned cases have been studied for the purpose of relative comparison, taking GaxAsyP1-y and AlAs lattice matched to InP quantum wire superlattice (QWSL) as an example.

Singha Roy, Subhamoy

2013-05-01

237

A two-step method of calculation of the electronic structure of molecules with heavy atoms: Theoretical aspect  

SciTech Connect

An approach for a space-separated calculation of the wave function in the valence and core regions of a molecule is proposed. As the first step, the calculation of the orbitals (or two-component spinors in the relativistic case) in the valence region by the effective core potential (ECP) method is preformed. Then, it is followed by a restoration of orbitals (four component spinors) expanded on spherical harmonics in the core regions of heavy atoms. Theoretical questions of the variational calculation on the molecular orbitals are considered in some core region limited by a sphere. Inclusion from the electronic cloud outside this region is reduced by the necessity of taking into account the orthonormality and boundary conditions together with an effective external field in respect to the selected core region. This method may be used for calculation of matrix elements of operators that are singular near nuclei (P,T-odd interactions, hyperfine structure, etc.). A substantial computational saving can be reached because the method enables, by the most optimal way, to combine the advantages of two well-developed approaches: molecular ECP calculations in the Gaussian basis set and one-center numerical atomic calculations with an external field. It is especially important when the relativistic effects are taken into account. 27 refs.

Titov, A.V. [Petersburg Nuclear Physics Institute (Russian Federation)

1996-02-05

238

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

239

Molecular-Beam Scattering Experiments and Theoretical Calculations Probing Charge Transfer in Weakly Bound Complexes of Water  

NASA Astrophysics Data System (ADS)

We describe and analyze in depth a series of molecular beam scattering experiments, first reported by Aquilanti et al. ( Angew. Chemie Int. Ed. 2005, 44, 2356. ), proving that a measurable bond stabilization component beyond the van-der-Waals forces is present in the prototypal hydrophobic interaction of water with the noble gases (Ng). The experimental integral cross-section data, exhibiting a fully resolved "glory" interference pattern in the velocity dependence, are here quantitatively analyzed and characterized employing a recently proposed model potential. The stabilization component of the water-Ng bond has recently been attributed, through very accurate theoretical calculations and an unambiguous, model-free analysis of the electron density displacement, to a net electron transfer taking place from Ng to H2O. We review the theoretical analysis and discuss additional computational results, comparing them to experiment, that clarify the effect of charge transfer on the interaction energies.

Roncaratti, L. F.; Belpassi, L.; Cappelletti, D.; Pirani, F.; Tarantelli, F.

2009-08-01

240

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

PubMed Central

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

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

2012-01-01

241

Theoretical calculation of fully differential cross sections for electron-impact ionization of hydrogen molecules  

NASA Astrophysics Data System (ADS)

We have recently proposed the orientation averaged molecular orbital (OAMO) approximation for calculating fully differential cross sections (FDCS) for electron-impact ionization of molecules averaged over all molecular orientations. Orientation averaged FDCS were calculated for electron-impact ionization of nitrogen molecules using the distorted wave impulse approximation (DWIA) and the molecular three-body distorted wave (M3DW) approximation. In this paper, we use the same methods to examine the FDCS for ionization of hydrogen molecules. It is found that the DWIA yields reasonable results for high-energy incident electrons. While the DWIA breaks down for low-energy electrons, the M3DW gives reasonable results down to incident-electron energies around 35 eV.

Gao, Junfang; Madison, D. H.; Peacher, J. L.

2006-03-01

242

A theoretical method to determine atomic pseudopotentials for electronic structure calculations of molecules and solids  

Microsoft Academic Search

The characteristic features of model potentials, effective potentials and pseudopotentials are carefully investigated. Then we justify our choice to work only with hermitian pseudopotential operators, and we develop a general non-empirical method to determine atomic pseudopotentials. In view of their numerical use for molecular calculations, these pseudopotentials are cast into semi-local forms, and their parameters are obtained by a least-squares

Philippe Durand; Jean-Claude Barthelat

1975-01-01

243

Dielectronic Recombination of Fe XIX Forming Fe XVIII: Laboratory Measurements and Theoretical Calculations  

Microsoft Academic Search

We have measured resonance strengths and energies for dielectronic recombination (DR) of Fe XIX forming Fe XVIII via N=2-->N'=2 and N=2-->N'=3 core excitations. All measurements were carried out using the heavy-ion Test Storage Ring at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We have also calculated these resonance strengths and energies using two independent, state-of-the-art techniques: the

D. W. Savin; S. M. Kahn; J. Linkemann; A. A. Saghiri; M. Schmitt; M. Grieser; R. Repnow; D. Schwalm; A. Wolf; T. Bartsch; A. Müller; S. Schippers; M. H. Chen; N. R. Badnell; T. W. Gorczyca; O. Zatsarinny

2002-01-01

244

Theoretical calculation of the solar diurnal variation of the cosmic ray intensity  

Microsoft Academic Search

Summary  By formulating an expression for the anisotropy of the primary cosmic ray intensity, the expected solar diurnal variation\\u000a of the intensity of the nucleonic component of the cosmic radiation at sea level is calculated at various geomagnetic latitudes\\u000a and longitudes for the following cases: (a) the anisotropy is produced outside the terrestrial magnetic field (extra-terrestrial origin), and (b) the anisotropy

K. Nagashima; V. R. Potnis; M. A. Pomerantz

1961-01-01

245

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

Microsoft Academic Search

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

J-Philippe Leininger; Christian Minot; François Lorant

2008-01-01

246

Magnetism and magnetic phase diagram of Gd2O2SO4 II. Theoretical calculations  

NASA Astrophysics Data System (ADS)

The experimental data of the quasi-two-dimensional Heisenberg antiferromagnet Gd2O2SO4 are discussed in a two-sublattices mean-field approximation. It turns out that the measured orthorhombic anisotropy is consistent with the calculated dipole interactions. Deviations from the mean-field approximation can be understood as effects of field-dependent anisotropy, short-range ordering and spin waves. Present address: Asea Brown Boveri, Corporate Research, CH-5405 Baden, Switzerland.

Paul, W.

1990-06-01

247

Theoretical study of the dissociation of HF + in the B 2Sigma + state by quantum-mechanical methods  

Microsoft Academic Search

The dissociative pathway of the HF+ molecular ion, initially in its B 2?+ electronic state, is studied by a full quantum-mechanical technique. The vibronic time-dependent wave function is expanded on the twelve lowest 2?+ electronic states computed by a limited configuration-interaction calculation. The nuclear functions are projected on a monodimensional grid and the time-evolution operator is represented by its (1,1)

Ivo Cacelli

1992-01-01

248

Theoretical calculations of electron densities in zinc chalcogenides and in zinc fluoride  

NASA Astrophysics Data System (ADS)

Self-consistent, non-relativistic Hartree-Fock calculations on a finite cluster of atoms with zinc at the center have been performed on the zinc blende compounds ZnTe, ZnSe, ZnS, on ZnO (wurtzite structure), ZnO (NaCl structure), and on ZnF2 (rutile-type structure) to obtain changes in s electron density ??(0) at the67Zn nucleus. We solved the eigenvalue problem of the dynamic matrix to calculate the second-order Doppler shift S SOD using appropriate force constant models and determined the isomer shift S from the measured center shift for each compound. Our calculations clearly show the importance of the covalency of the Zn-ligand bond for the origin of S and fully corroborate the experimental linear correlations between decreasing S values and increasing electronegativity of the ligands. The most important contribution to ??(0) comes from the Zn(4s) electrons, with a smaller but significant contribution from the Zn(3s) electrons. For the change of the mean-square nuclear charge radius for the Mössbauer transition in67Zn, we obtain ?< r 2>=+(13.9±1.4) × 10-3 fm2.

Mitchell, D. W.; Das, T. P.; Potzel, W.; Köfferlein, M.; Karzel, H.; Schiessl, W.; Steiner, M.; Kalvius, G. M.

1994-12-01

249

Complexities in diluted magnetic semiconductors-a theoretical perspective from ab-initio electronic structure calculations  

NASA Astrophysics Data System (ADS)

Diluted magnetic semiconductors (DMS), the essential materials for semiconductor spintronics, show a variety of complex properties, e.g., defect-mediated (ferro/antiferro)magnetic interactions and the disorder leading to magnetic percolation effects. Using the ab-initio Korringa-Kohn-Rostoker-Coherent-Potential-Approximation, the magnetic pair exchange parameters of a Heisenberg model have been calculated for Mn doped ZnO and half-Heusler NiTiSn hosts followed by the calculation of transition temperatures using Monte-Carlo simulations. Zinc vacancies and nitrogen substituting oxygen atoms lead to ferromagnetic interactions in Mn doped ZNO while in a defect free case, the interaction between Mn atoms is antiferromagnetic. The calculated critical temperatures are low (˜35 K) due to the short-ranged exchange interactions and low defect concentration. In the other case, Mn doped NiTiSn shows a high critical temperature (˜300 K) for 22 % Mn concentration. Below 3% Mn, there is no magnetic long range order as the magnetic percolation is not established. The results are in good agreement with experiments.

Sanyal, Biplab; Iusan, Diana; Eriksson, Olle

2007-03-01

250

Total losses analysis and calculations for PbSe/PbSrSe multiple quantum well structures  

NASA Astrophysics Data System (ADS)

In order for laser oscillation to occur, the modal gain at the lasing photon energy must equal the total losses. In this work, we analyze and calculate the total losses due to the free carrier absorption, optical waveguide scattering and the laser cavity end losses for PbSe/Pb0.934Sr0.066 Se quantum well laser structures. The small confinement factor value causes the free carrier absorption loss to be negligible. The calculated scattering loss values showed a decreasing order for the MQW, MMQW and SCH-SQW structures, for a surface roughness amplitude of 10nm. Increasing the surface roughness amplitude increases these scattering losses even further. However, the calculated cavity loss calculations showed that its values are in an increasing order for the MQW (or MMQW) and SCH-SQW structures. These cavity losses are lowest for uncoated cavity ends. Coating these ends with a quarter wavelength BaF2 layer increases the total cavity loss. In addition, coating the cavity ends with alternating quarter wavelength layers of BaF2 and CaF2 also results in an increase in the cavity loss. The increase in cavity loss due to coating is caused by the decrease in the mirrors' reflectivity values. These results show that coating with fluoride layers can best be utilized in applications where high transitivity values are needed.

Khodr, M.

2010-08-01

251

The reaction mechanism of allene oxide synthase: Interplay of theoretical QM/MM calculations and experimental investigations.  

PubMed

A combined theoretical and experimental study highlights the reaction mechanism of allene oxide synthase (AOS) and its possible link to hydroperoxide lyase (HPL) pathway. A previously published study (Lee et al., Nature 455 (2008) 363) has shown that the F137 residue is of central importance in differentiating between the AOS and HPL pathways after initial identical steps. In the experimental part of this study, we show that wild-type AOS from Arabidopsis or rice in fact produces both AOS and HPL products in a ratio of about 80:15, something that was found only in trace amounts before. Theoretical calculations successfully map the whole AOS pathway with 13(S)-hydroperoxy linolenic and linoleic acid as substrates. Subsequent calculations investigated the effects of in silico F137L mutation at the suggested diverging point of the two pathways. The results show that QM/MM calculations can reasonably reproduce three out of four experimentally available cases, and confirm that the pathways are energetically very close to each other, thus making a switch from one path to other plausible under different circumstances. PMID:20654573

Cho, Kyung-Bin; Lai, Wenzhen; Hamberg, Mats; Raman, C S; Shaik, Sason

2010-07-21

252

Well-defined insulating band for electronic transport through a laterally coupled double-quantum-dot chain: Nonequilibrium Green's function calculations  

Microsoft Academic Search

By means of the nonequilibrium Green function technique, electronic transport through a multiple-quantum-dot system is theoretically studied. In this system, a one-dimensional quantum dot chain between two contacts forms a main channel for the electronic tunneling. Each quantum dot in the chain couples laterally to a dangling quantum dot. Whenever the energy of the incident electron is aligned with the

Weijiang Gong; Yisong Zheng; Yu Liu; Tianquan Lü

2006-01-01

253

Calculated effects of interface grading in GaAs--Ga1-xAlxAs quantum wells  

Microsoft Academic Search

Effects of interface grading on energy levels of electrons in GaAs-Ga1-xAlxAs quantum wells have been estimated using both a tight-binding formalism and an effective-mass Hamiltonian of the BenDaniel-Duke form. Graded interfaces a few atomic layers thich have only a small effect on energy levels in both schemes. Self-consistent calculations for electrons in a relatively wide (40 nm) quantum well show

Frank Stern; Joel N. Schulman

1985-01-01

254

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

255

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

PubMed

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

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

2012-11-12

256

A Potential-Theoretic Method for Far-Field Sound Radiation Calculations  

NASA Astrophysics Data System (ADS)

The far-field acoustic radiation due to the interaction of upstream, unsteady vortical disturbances with an airfoil in subsonic, compressible flow is calculated using potential theory. A Kirchhoff surface is placed in the near field surrounding the airfoil and the pressure on this surface is calculated from the unsteady flow field, obtained using a second-order finite-difference code. The governing equation is reduced to the Helmholtz equation in the frequency domain and the solution is written in terms of an integral over the Kirchhoff surface involving the free-space Green's function and an unknown single-layer density function. The single-layer density is then determined from the boundary condition on the Kirchhoff surface. This method is presented as an alternative to classical Kirchhoff methods. It has the advantage of being able to accommodate arbitrarily shaped Kirchhoff surfaces and is also readily extendable to three-dimensional problems. Numerical results are presented for thin, symmetric, and loaded airfoils. Thin-airfoil results are compared to the analytical solution, and thick-airfoil results are checked for numerical convergence and compared to results obtained from a time-domain Euler solver.

Hariharan, S. I.; Scott, J. R.; Kreider, K. L.

2000-10-01

257

Molecular structure of caffeine as determined by gas electron diffraction aided by theoretical calculations  

NASA Astrophysics Data System (ADS)

The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G?? basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters (rg and ??) of caffeine are as follows: = 1.382(3) Å; r(CC) = 1.382(?) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; = 1.459(13) Å; = 1.206(5) Å; = 1.085(11) Å; ?N1C2N3 = 116.5(11)°; ?N3C4C5 = 121. 5(13)°; ?C4C5C6 = 122.9(10)°; ?C4C5N7 = 104.7(14)°; ?N9 C4=C5 = 111.6(10)°; = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3?) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one.

Egawa, Toru; Kamiya, Akemi; Takeuchi, Hiroshi; Konaka, Shigehiro

2006-12-01

258

Theoretical calculations for neutrino-induced charged current reactions in sup 12 C and recent experimental results  

SciTech Connect

Theoretical calculations are presented for the reaction {nu}{sub {ital e}}+{sup 12}C{r arrow}{sup 12}N{sub g.s.} +{ital e}{sup {minus}} for {ital E}{sub {nu}} from threshold to 135 MeV, for the reaction {nu}{sub {mu}}+{sup 12}C{r arrow}{sup 12}N{sub g.s.} +{mu}{sup {minus}}, and the corresponding antineutrino reaction for {ital E}{sub {nu}} from threshold to 160 MeV. Use is made of updated form factors based on more recent data for {ital e}{sup {minus}}+{sup 12}C{r arrow}{sup 12}C{sup *}+{ital e}{prime} {minus} and {gamma}+{sup 12}C{r arrow}{sup 12}C{sup *}. The recent neutrino reaction experiments are discussed in light of these calculations.

Mintz, S.L. (Physics Department, Florida International University, Miami, Florida 33199 (USA)); Pourkaviani, M. (Physics Department, University of Miami, Coral Gables, Florida 33124 Florida International University, Miami, Florida 33199 (USA))

1989-12-01

259

A new theoretical method for calculating the radiative association cross section of a triatomic molecule: application to N2-H-.  

PubMed

We present a new theoretical method to treat the atom-diatom radiative association within a time independent approach. This method is an adaptation of the driven equations method developed for photodissociation. The bound state energies and wave functions of the molecule are calculated exactly and used to propagate the overlap with the initial scattering wave function. In the second part of this paper, this approach is applied to the radiative association of the N2H(-) anion. The main features of the radiative association cross sections are analysed and the magnitude of the calculated rate coefficient at 10 K is used to discuss the existence of the N2H(-) in the interstellar medium which could be used as a tracer of both N2 and H(-). PMID:23868402

Stoecklin, T; Lique, F; Hochlaf, M

2013-07-18

260

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

PubMed Central

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

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

2012-01-01

261

Quantum Darwinism Requires an Extra-Theoretical Assumption of Encoding Redundancy  

NASA Astrophysics Data System (ADS)

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

Fields, Chris

2010-10-01

262

Phenylazoindole dyes--part I: the syntheses, characterizations, crystal structures, quantum chemical calculations and antimicrobial properties.  

PubMed

In this study, the synthesis of four new phenylazo indole dyes (dye 1-4) were carried out by diazotization of 4-aminoacetophenone and coupling with various 2- and 1,2-disubstituted indole derivatives. The dyes were characterized by UV-vis, FT-IR, (1)H NMR, HRMS and X-ray single crystal diffraction methods. Azo-hydrazone tautomeric bahavior of the dyes in different solvents (DMSO, methanol, acetic acid and chloroform) was investigated by using (1)H NMR and UV-vis results. The experimental results were compared with the corresponding calculated values. The results of experimental data and theoretical calculations showed that the azo tautomer is more stable than hydrazone tautomer. In addition to this, the antimicrobial activity of the dyes was also evaluated. PMID:23735210

Sefero?lu, Zeynel; Yalç?n, Ergin; Babür, Banu; Sefero?lu, Nurgül; Hökelek, Tuncer; Y?lmaz, Ebru; ?ahin, Ertan

2013-05-14

263

Phenylazoindole dyes - Part I: The syntheses, characterizations, crystal structures, quantum chemical calculations and antimicrobial properties  

NASA Astrophysics Data System (ADS)

In this study, the synthesis of four new phenylazo indole dyes (dye 1-4) were carried out by diazotization of 4-aminoacetophenone and coupling with various 2- and 1,2-disubstituted indole derivatives. The dyes were characterized by UV-vis, FT-IR, 1H NMR, HRMS and X-ray single crystal diffraction methods. Azo-hydrazone tautomeric bahavior of the dyes in different solvents (DMSO, methanol, acetic acid and chloroform) was investigated by using 1H NMR and UV-vis results. The experimental results were compared with the corresponding calculated values. The results of experimental data and theoretical calculations showed that the azo tautomer is more stable than hydrazone tautomer. In addition to this, the antimicrobial activity of the dyes was also evaluated.

Sefero?lu, Zeynel; Yalç?n, Ergin; Babür, Banu; Sefero?lu, Nurgül; Hökelek, Tuncer; Y?lmaz, Ebru; ?ahin, Ertan

2013-09-01

264

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

SciTech Connect

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

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

2008-01-24

265

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

266

Characterization of covalent linkages in organically functionalized MCM-41 mesoporous materials by solid-state NMR and theoretical calculations.  

PubMed

The covalent linkages formed during functionalization of MCM-41 mesoporous molecular sieves with five chloroalkylsilanes ((EtO)3Si(CH2Cl), (MeO)3Si(CH2CH2CH2Cl), Cl3Si(CH2CH2CH3), Cl2Si(CH3)(CH2Cl) and Cl2Si(CH3)2) have been investigated using high-resolution solid-state NMR spectroscopy and DFT calculations. Structural information was obtained from 1H-13C and 1H-29Si heteronuclear (HETCOR) NMR spectra, in which high resolution in the 1H dimension was obtained by using fast MAS. The 1H-13C HETCOR results provided the assignments of 1H and 13C resonances associated with the surface functional groups. Sensitivity-enhanced 1H-29Si HETCOR spectra, acquired using Carr-Purcell-Meiboom-Gill refocusing during data acquisition, revealed the identity of 29Si sites (Qn, Tn, and Dn) and the location of functional groups relative to these sites. Optimal geometries of local environments representing the Qn, Tn and Dn resonances were calculated using molecular mechanics and ab initio methods. Subsequently, DFT calculations of 29Si, 13C, and 1H chemical shifts were performed using Gaussian 03 at the B3LYP/6-311++G(2d,2p) level. The theoretical calculations are in excellent accord with the experimental chemical shifts. This work illustrates that state-of-the-art spectroscopic and theoretical tools can be used jointly to refine the complex structures of inorganic-organic hybrid materials. PMID:17388623

Wiench, Jerzy W; Avadhut, Yamini S; Maity, Niladri; Bhaduri, Sumit; Lahiri, Goutam Kumar; Pruski, Marek; Ganapathy, Subramanian

2007-03-28

267

Auxiliary-field quantum Monte Carlo calculations of molecular systems with a Gaussian basis  

SciTech Connect

We extend the recently introduced phaseless auxiliary-field quantum Monte Carlo (QMC) approach to any single-particle basis and apply it to molecular systems with Gaussian basis sets. QMC methods in general scale favorably with the system size as a low power. A QMC approach with auxiliary fields, in principle, allows an exact solution of the Schroedinger equation in the chosen basis. However, the well-known sign/phase problem causes the statistical noise to increase exponentially. The phaseless method controls this problem by constraining the paths in the auxiliary-field path integrals with an approximate phase condition that depends on a trial wave function. In the present calculations, the trial wave function is a single Slater determinant from a Hartree-Fock calculation. The calculated all-electron total energies show typical systematic errors of no more than a few millihartrees compared to exact results. At equilibrium geometries in the molecules we studied, this accuracy is roughly comparable to that of coupled cluster with single and double excitations and with noniterative triples [CCSD(T)]. For stretched bonds in H{sub 2}O, our method exhibits a better overall accuracy and a more uniform behavior than CCSD(T)

Al-Saidi, W.A.; Zhang Shiwei; Krakauer, Henry [Department of Physics, College of William and Mary, Williamsburg, Virginia 23187-8795 (United States)

2006-06-14

268

Improved estimators for quantum Monte Carlo calculation of spherically averaged intracule densities  

NASA Astrophysics Data System (ADS)

System-averaged pair densities or ``intracule densities'' are important for qualitative and quantitative descriptions of electron correlation [1] In quantum Monte Carlo (QMC) simulations, spherically averaged intracule densities are usually calculated by means of the traditional histogram technique (i.e., by counting the number of times two electrons are found at a certain distance) that is very noisy at short electron-electron distances. We will show how previously-used improved estimators for the on-top pair density [2,3] can be generalized to the case of non-vanishing electron-electron distances, as an application of the ``zero-variance'' procedure [4]. The obtained estimators lead to noise several orders of magnitude smaller than the histogram technique, allowing unprecedented fast and accurate calculations of intracule densities in QMC. Illustrative calculations on simple atomic systems will be given. [1] J. M. Mercero, E. Valderrama and J. M. Ugalde, in ``NATO-ASI Series in Metal-Ligand Interaction in Molecular-, Nano-, Micro, and Macro-systems in Complex Environments'', Ed.: N. Russo, D. R. Salahub and M. Witko, Kluwer Academic Publishres, Dordrecht (2003). [2] P. Langfelder, S. M. Rothstein and J. Vrbik, J. Chem. Phys. 107, 8525 (1997). [3] A. Sarsa, F. J. G'alvez and E. Buend'ia, J. Chem. Phys. 109, 7075 (1998). [4] R. Assaraf and M. Caffarel, Phys. Rev. Lett. 83, 4682 (1999).

Toulouse, Julien; Assaraf, Roland; Umrigar, Cyrus

2006-03-01

269

Silicon Oxysulfide, OSiS: Rotational Spectrum, Quantum-Chemical Calculations, and Equilibrium Structure  

NASA Astrophysics Data System (ADS)

Silicon oxysulfide, OSiS, and seven of its minor isotopic species have been characterized for the first time in the gas phase at high spectral resolution by means of Fourier transform microwave spectroscopy. The equilibrium structure of OSiS has been determined from the experimental data using calculated vibration-rotation interaction constants. The structural parameters (rO-Si = 1.5064 Angstrom and rSi-S = 1.9133 Angstrom) are in very good agreement with values from high-level quantum chemical calculations using coupled-cluster techniques together with sophisticated additivity and extrapolation schemes. The bond distances in OSiS are very short in comparison with those in SiO and SiS. This unexpected finding is explained by the partial charges calculated for OSiS via a natural population analysis. The results suggest that electrostatic effects rather than multiple bonding are the key factors in determining bonding in this triatomic molecule. The data presented provide the spectroscopic information needed for radio astronomical searches for OSiS.

Thorwirth, S.; Mück, L. A.; Gauss, J.; Tamassia, F.; Lattanzi, V.; McCarthy, M. C.

2011-05-01

270

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

271

The parent anion of the RGD tripeptide: Photoelectron spectroscopy and quantum chemistry calculations  

NASA Astrophysics Data System (ADS)

The gas-phase conformation of the intact (parent) unprotected RGD- peptide anion has been investigated using a combination of anion photoelectron spectroscopy and quantum chemistry calculations of its low-energy stable structures. The experimentally observed RGD- species correspond to a conformation in which the guanidinium group is protonated, the C-terminus is neutral, the aspartic acid carboxyl is deprotonated, and the anion's excess electron orbital is localized on the protonated guanidinium. This structure is reminiscent of the RGD loop, which is the peptide motif recognized by trans-membrane integrins. The parent RGD- radical anion was generated using a unique infrared desorption-photoemission-helium jet ion source, whose ability to produce radical anions of peptides may also have analytical mass spectrometric implications.

Li, Xiang; Wang, Haopeng; Bowen, Kit H.; Grégoire, G.; Lecomte, F.; Schermann, Jean-Pierre; Desfrançois, Charles

2009-06-01

272

Quantum dynamical calculations of ultracold collisions induced by nonlinearly chirped light  

NASA Astrophysics Data System (ADS)

We describe quantum dynamical calculations of ultracold 85Rb trap-loss collisions induced by pulses of light whose frequency is chirped on the nanosecond time scale. The chirped light excites the ground-state collisional wave function to the long-range attractive potential and escape from the trap is modeled by an absorbing boundary at short range. Both positive and negative chirps are considered and various chirp shapes and detunings are examined. For positive chirps, the loss rates are rather independent of the chirp shape. Negative chirps, on the other hand, show a dependence on chirp shape for detunings where collisional flux can be coherently returned to the ground state. These trends are consistent with the results of a recent experiment.

Carini, J. L.; Pechkis, J. A.; Rogers, C. E., III; Gould, P. L.; Kallush, S.; Kosloff, R.

2012-01-01

273

Ammonia adsorption on Keggin-type heteropolyacid catalysts explored by density functional quantum chemistry calculations  

SciTech Connect

Density functional quantum chemical calculations have been used to compare the acid strengths of phosphotungstic and phosphomolybdic acids by computing the adsorption energy of ammonia on model clusters of each heteropolyacid. The adsorption of ammonia on a phosphotungstic acid cluster was stronger than the adsorption on a phosphomolybdic acid cluster. The predicted adsorption energies were near {minus}150 and {minus}106 kJ mol{sup {minus}1} for phosphotungstic and phosphomolybdic acid, respectively. This compares well with the experimental heats of ammonia sorption determined from microcalorimetry. An analysis of different adsorption modes of ammonia on phosphotungstic acid showed that bidentate adsorption of ammonia on the heteropolyacid clusters aided in proton transfer and yielded stronger adsorption energies than did a monodentate adsorption mode. In addition, the authors report the computed adsorption energies of pyridine on a heteropolyacid cluster.

Bardin, B.B.; Davis, R.J.; Neurock, M.

2000-04-20

274

Electronic properties of amino acid side chains: quantum mechanics calculation of substituent effects  

PubMed Central

Background Electronic properties of amino acid side chains such as inductive and field effects have not been characterized in any detail. Quantum mechanics (QM) calculations and fundamental equations that account for substituent effects may provide insight into these important properties. PM3 analysis of electron distribution and polarizability was used to derive quantitative scales that describe steric factors, inductive effects, resonance effects, and field effects of amino acid side chains. Results These studies revealed that: (1) different semiempirical QM methods yield similar results for the electronic effects of side chain groups, (2) polarizability, which reflects molecular deformability, represents steric factors in electronic terms, and (3) inductive effects contribute to the propensity of an amino acid for ?-helices. Conclusion The data provide initial characterization of the substituent effects of amino acid side chains and suggest that these properties affect electron density along the peptide backbone.

Dwyer, Donard S

2005-01-01

275

Temperature influence on a molecular switching under electric field: quantum transport ab initio calculation  

NASA Astrophysics Data System (ADS)

A molecular transistor based on torsion-angle conformation change driven by gate electric field is designed and studied using ab initio calculations. This transistor consists of a SH-C6H2F(CH3)C6H2(CH3)F-SH molecule sandwiched between two Au(111) electrodes, where the interaction between the molecular dipole and a gate voltage induced electric field will cause the molecule to twist along its c-axis. This twist changes the quantum conductivity of the molecule. The effect of thermal fluctuation on the molecular conformation is studied, so is the ability of the transistor to shut off its current. The advantages and challenges of using such molecular conformation change as a mechanism for transistor gating are discussed

Vergniory, Maia; Grandino-Roldan, Jose; García-Lekue, Aran; Wang, Lin-Wang

2011-03-01

276

Ab initio calculations for quantum transport through atomic bridges by the recursion transfer-matrix method  

NASA Astrophysics Data System (ADS)

We present an efficient self-consistent method for the quantum transport of atomic-scale electronic conductors bridged between two metallic electrodes. It is based on density-functional theory using the recursion-transfer-matrix method with separable norm-conserving nonlocal pseudopotentials. We performed calculations with this method on the electric conductance of Al atomic wires with several kinds of substitutional atoms connecting to one of the electrodes. We found that a local mixing of atoms at the contact significantly affects the transport properties. The conductance is strongly dependent on the bonding nature of the atom at the contact and does not change much as a length of the atomic wire increases. The bias drop in the wire is influenced by the local polarization of the atom at the contact.

Hirose, Kenji; Kobayashi, Nobuhiko; Tsukada, Masaru

2004-06-01

277

Decades of Theoretical Work on Protonated Hydrates  

Microsoft Academic Search

Theoretical studies on protonated hydrates (PH) are illustrative of the progress realized in theoretical chemistry over several decades. The evolution of such studies is presented. The main methods used (quantum chemistry, Monte Carlo or Molecular Dynamics calculations…) and the problems encountered are briefly recalled. Some of the results obtained are commented.

E. Kochanski; R. Kelterbaum; S. Klein; M. M. Rohmer; A. Rahmouni

1997-01-01

278

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

SciTech Connect

D. A. Long et al.[Phys. Rev. A 80, 042513 (2009)] recently reported accurate measurements on the ultraweak electric quadrupole (E2) transitions in the O{sub 2} A band. They also presented elegant theoretical calculation of the line intensities based on Hund's case (b) formulation. However, their theoretical elucidation fails to relate to a highly relevant previous work by Balasubramanian and Narayanan [Acta Phys. Hung 74, 341 (1994)] in which closed-form expressions for the E2 branch line strengths for the eight possible rotational branches of the b{sup 1}{Sigma}{sub g}{sup +}-X{sup 3}{Sigma}{sub g}{sup -} transition, in intermediate coupling, are derived. The complete equivalence of the two methods is proven through direct calculation. A second point of concern is that the magnetic dipole (M1) transition moment M{sub 1} = 0.0687 {mu}{sub B} deduced by Long et al. from the previously measured transition intensities is {approx}2.7 times the ab initio value of 0.0255 {mu}{sub B} computed by Minaev et al.[Chem. Phys. 208, 299 (1996)]. Since the latter reproduces closely the measured Einstein's spontaneous emission coefficient of the A band, this large discrepancy is intriguing.

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

2011-11-15

279

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

Microsoft Academic Search

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

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

2008-01-01

280

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

281

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

2013-09-13

282

Measurements and calculations of spontaneous emission of tensile and compressively strained multiple quantum-wells structures  

NASA Astrophysics Data System (ADS)

The characterization of material and structural properties is essential in the development of high-performance optoelectronics devices. The gain and spontaneous emission of semiconductor emitters are intrinsically related, and knowing one determines the other. In this paper, we report on a comparison between the measured and calculated spontaneous emission spectra of complex semiconductor structures that were developed in our laboratory. Transversely emitted spontaneous emission spectra over a wide range of carrier densities have been obtained for GRIN-SCH-MQW InxGa1-xAsyP1-y structures consisting of three tensile and three compressive wells. Information from these measurements and materials parameters were used to estimate carrier density for each well and subsequently used in the calculation of the emission spectra. The theoretical results were obtained by calculating the spontaneous emission rate for each well independently and then by summing over the six wells. We first calculate the band structure from a 6x6 Luttinger-Kohn Hamiltonian and find the spontaneous emission rate using the carrier density obtained from experimental measurements. A comparison between the Markovian (Lorentzian) and non-Markovian (Gaussian) line shape functions is established, considering the bandgap renormalization. We show that the Gaussian broadening function gives better agreement with the experimental data.

Matei, Rodica; Mercure, Philippe; Champagne, Alain; Lestrade, Michel; Maciejko, Romain; Kashyap, Raman

2005-09-01

283

Crystalline ice as a cryoprotectant: theoretical calculation of cooling speed in capillary tubes.  

PubMed

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

Yakovlev, S; Downing, K H

2011-04-28

284

Measurements and theoretical calculations of self-broadening and self-shift coefficients in the ?2 band of CH3D  

NASA Astrophysics Data System (ADS)

In this paper, we report measured Lorentz self-broadening and self-induced pressure-shift coefficients of 12CH3D in the ?2 fundamental band (?0 ? 2200 cm-1). The multispectrum fitting technique allowed us to analyze simultaneously seven self-broadened absorption spectra. All spectra were recorded at the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory (NSO) on Kitt Peak, AZ with an unapodized resolution of 0.0056 cm-1. Low-pressure (0.98-2.95 Torr) as well as high-pressure (17.5-303 Torr) spectra of 12C-enriched CH3D were recorded at room temperature to determine the pressure-broadening coefficients of 408 ?2 transitions with quantum numbers as high as J? = 21 and K = 18, where K? = K? ? K (for a parallel band). The measured self-broadening coefficients range from 0.0349 to 0.0896 cm-1 atm-1 at 296 K. All the measured pressure-shifts are negative. The reported pressure-induced self-shift coefficients vary from about -0.004 to -0.008 cm-1 atm-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 QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 3.6%. A semiclassical theory based upon the Robert-Bonamy formalism of interacting linear molecules has been used to calculate these self-broadening and self-induced pressure-shift coefficients. In addition to the electrostatic interactions involving the octopole and hexadecapole moments of CH3D, the intermolecular potential includes also an atom-atom Lennard-Jones model. For low K (K ? 3) with |m| ? 8 the theoretical results of the broadening coefficients are in overall good agreement (3.0%) with the experimental data. For transitions with K approaching |m|, they are generally significantly underestimated (8.8%). The theoretical self-induced pressure shifts, whose vibrational contribution is derived from results in the QQ-branch, are generally smaller in magnitude than the experimental data in the QP-, and QR-branches (15.2%).

Predoi-Cross, Adriana; Hambrook, Kyle; Brawley-Tremblay, Marco; Bouanich, Jean-Pierre; Malathy Devi, V.; Benner, D. Chris; Brown, Linda R.

2005-11-01

285

Structural determination of vanillin, isovanillin and ethylvanillin by means of gas electron diffraction and theoretical calculations  

NASA Astrophysics Data System (ADS)

The molecular structures of vanillin (4-hydroxy-3-methoxybenzaldehyde), isovanillin (3-hydroxy-4-methoxybenzaldehyde) and ethylvanillin (3-ethoxy-4-hydroxybenzaldehyde) were determined by means of gas electron diffraction. Among them, vanillin and ethylvanillin have a vanilla odor but isovanillin smells differently. The nozzle temperatures were 125, 173 and 146 °C, for vanillin, isovanillin and ethylvanillin, respectively. The results of MP2 and B3LYP calculations with the 6-31G** basis set were used as supporting information. The MP2 calculations predicted that vanillin and isovanillin have two stable conformers and ethylvanillin has four stable conformers. The electron diffraction data were found to be consistent with these conformational compositions. The determined structural parameters (rg and ??) of vanillin are as follows: =1.397(4) Å; r(C1 Caldehyde)=1.471(?) Å; r(C3 OMe)=1.374(9) Å; r(C4 OH)=1.361(?) Å; r(O CMe)=1.428(?) Å; r(CO)=1.214(8) Å; =1.110(11) Å; r(O H)=0.991(?) Å; ?C6 C1 C2=120.6(2)°; ?C1 C2 C3=118.8(?)°; ?C1 C6 C5=120.1(?)°; ?C2 C1 Caldehyde=122.7(18)°; ?C1 CO=119.4(16)°; ?C4 C3 OMe=112.2(12)°; ?C3 C4 OH=119.1(?)°; ?C3 O C=121.7(29)°. Those of isovanillin are as follows: =1.402(4) Å; r(C1 Caldehyde)=1.479(?) Å; r(C4 OMe)=1.369(9) Å; r(C3 OH)=1.357(?) Å; r(O CMe)=1.422(?) Å; r(CO)=1.221(9) Å; =1.114(14) Å; r(O H)=0.995(?) Å; ?C6 C1 C2=120.2(3)°; ?C1 C2 C3=119.0(?)°; ?C1 C6 C5=119.9(?)°; ?C2 C1 Caldehyde=124.6(25)°; ?C1 CO=121.3(24)°; ?C3 C4 OMe=114.4(12)°; ?C4 C3 OH=121.2(?)°; ?C4 O C=123.8(26)°. Those of ethylvanillin are as follows: =1.397(6) Å; r(C1 Caldehyde)=1.471(?) Å; r(C3 OEt)=1.365(13) Å; r(C4 OH)=1.352(?) Å; r(O CEt)=1.427(?) Å; r(C CEt)=1.494(21) Å; r(CO)=1.206(9) Å; =1.109(10) Å; r(O H)=0.990(?) Å; ?C6 C1 C2=120.2(3)°; ?C1 C2 C3=118.4(?)°; ?C1 C6 C5=119.7(?)°; ?C2 C1 Caldehyde=121.7(21)°; ?C1 CO=128.8(22)°; ?C4 C3 OEt=112.8(14)°; ?C3 C4 OH=119.6(?)°; ?C3 O C=115.1(27)°; ?O C CEt=102.7(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3?) referring to the last significant digit; left arrows in the parentheses mean that these parameters are bound to the preceding one.

Egawa, Toru; Kameyama, Akiyo; Takeuchi, Hiroshi

2006-08-01

286

A comparison between theoretical and experimental state-to-state charge transfer cross sections for H(+) + H2 at 20 eV: Evidence for quantum effects  

NASA Astrophysics Data System (ADS)

A 3-D quantum mechanical close coupling study for the system H(+) +H2 is communicated. The quantum calculations, caried out in the finite order swiden approximation, show a better fit to previous experiments than the classical trajectory surface hopping (TSH) calculations, and provide direct evidence for the usefulness of a quantum treatment in predicting charge transfer (CT) processes. The total differential cross sections (summed over all final vibrational states) for the CT processes were calculated, in good agreement with experimental results. It is shown that a quantum mechanical treatment of both the inelastic and the charge transfer nonadiabatic processes is feasible and provides a superior description of the experiments compared to the TSH treatment. This demonstrates the importance of quantum effects in ion-molecule charge transfer.

Baer, Michael; Niedner, Gereon; Toennies, J. Peter

1988-06-01

287

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.

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

2009-01-01

288

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

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared vibrational echo spectrum as a function of time, which directly displays the formation and dissociation of the complex through the growth of off-diagonal peaks, and the linear absorption spectrum, which displays two hydroxyl stretch peaks, one for the complex and one for the free phenol. The results of the simulations are compared to previously reported experimental data and are found to be in quite reasonable agreement. The electronic structure calculations show that the complex is T shaped. The classical potential used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level of the electronic structure calculations. A variety of other features is extracted from the simulations including the relationship between the structure and the projection of the electric field on the hydroxyl group. The fluctuating electric field is used to determine the hydroxyl stretch frequency-frequency correlation function (FFCF). The simulations are also used to examine the number distribution of benzene and CCl4 molecules in the first solvent shell around the phenol. It is found that the distribution is not that of the solvent mole fraction of benzene. There are substantial probabilities of finding a phenol in either a pure benzene environment or a pure CCl4 environment. A conjecture is made that relates the FFCF to the local number of benzene molecules in phenol's first solvent shell.

Kwac, Kijeong; Lee, Chewook; Jung, Yousung; Han, Jaebeom; Kwak, Kyungwon; Zheng, Junrong; Fayer, M. D.; Cho, Minhaeng

2006-12-01

289

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

PubMed

Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared vibrational echo spectrum as a function of time, which directly displays the formation and dissociation of the complex through the growth of off-diagonal peaks, and the linear absorption spectrum, which displays two hydroxyl stretch peaks, one for the complex and one for the free phenol. The results of the simulations are compared to previously reported experimental data and are found to be in quite reasonable agreement. The electronic structure calculations show that the complex is T shaped. The classical potential used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level of the electronic structure calculations. A variety of other features is extracted from the simulations including the relationship between the structure and the projection of the electric field on the hydroxyl group. The fluctuating electric field is used to determine the hydroxyl stretch frequency-frequency correlation function (FFCF). The simulations are also used to examine the number distribution of benzene and CCl4 molecules in the first solvent shell around the phenol. It is found that the distribution is not that of the solvent mole fraction of benzene. There are substantial probabilities of finding a phenol in either a pure benzene environment or a pure CCl4 environment. A conjecture is made that relates the FFCF to the local number of benzene molecules in phenol's first solvent shell. PMID:17199356

Kwac, Kijeong; Lee, Chewook; Jung, Yousung; Han, Jaebeom; Kwak, Kyungwon; Zheng, Junrong; Fayer, M D; Cho, Minhaeng

2006-12-28

290

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

NASA Astrophysics Data System (ADS)

Solar cells of which the efficiency is not limited by the Shockley-Queisser limit can be obtained by integrating a luminescent spectral conversion layer into the cell structure. We have calculated the maximum efficiency of state-of-the-art c-Si, pc-Si, a-Si, CdTe, GaAs, CIS, CIGS, CGS, GaSb, and Ge solar cells with and without an integrated spectral shifting, quantum cutting, or quantum tripling layer using their measured internal quantum efficiency (IQE) curves. Our detailed balance limit calculations not only take into account light in-coupling efficiency of the direct AM1.5 spectral irradiance but also wavelength dependence of the refractive index and the IQEs of the cells and the angular dependent light in-coupling of the indirect spectral irradiance. An ideal quantum cutting layer enhances all cell efficiencies ranging from a modest 2.9% for c-Si to much larger values of 4.0%, 7.7%, and 11.2% for CIGS, Ge, and GaSb, respectively. A quantum tripling layer also enhances cell efficiencies, but to a lesser extent. These efficiency enhancements are largest for small band gap cells like GaSb (7.5%) and Ge (3.8%). Combining a quantum tripling and a quantum cutting layer would enhance efficiency of these cells by a factor of two. Efficiency enhancement by a simple spectral shifting layer is limited to less than 1% in case the IQE is high for blue and UV lights. However, for CdTe and GaSb solar cells, efficiency enhancements are as high as 4.6% and 3.5%, respectively. A shifting layer based on available red LED phosphors like Sr2Si5N8:Eu will raise CdTe efficiency by 3.0%.

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

2013-08-01

291

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

292

Quantum-statistical line shape calculation for Lyman-? lines in dense H plasmas  

NASA Astrophysics Data System (ADS)

We present results for the Lyman-? line of hydrogen in dense plasmas. Full line profiles are calculated within a quantum-statistical method, based on thermodynamic Green's functions. The contributions of plasma ions and electrons are considered separately. Linear and quadratic Stark effect as well as quadrupole effects are taken into account for ions. The model microfield method is used to include ion dynamics. The focus of this work lies on the contribution to broadening and shift by free electrons beyond the Born approximation. The effect of strong collisions can be identified as ladder-like diagrams of the electron-emitter propagator. In an effective two-particle approximation, the electronic self-energy is given in terms of scattering amplitudes, analogous to Baranger's expressions [Baranger, M 1958 Phys. Rev. 112 855]. We obtained scattering amplitudes from convergent close-coupling calculations including medium effects via Debye screening. Additionally, the electronic coupling between initial and final states is taken care of by a vertex correction. In our examples, the free electron density ranges between 1023 and 1025 m-3 at a plasma temperature of 1 and 2 eV, respectively.

Lorenzen, S.; Wierling, A.; Reinholz, H.; Röpke, G.; Zammit, M. C.; Fursa, D. V.; Bray, I.

2012-12-01

293

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

294

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

PubMed

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). PMID:23248981

Halverson, Thomas; Poirier, Bill

2012-12-14

295

Ionic Polarization and Crystal Lattice Energy of Ionic Crystals: Theoretical Calculations for Applications of Ionic Polarization Energy in All Formulae for Crystal Lattice Energy of Ionic Crystals.  

National Technical Information Service (NTIS)

The concept of effective nuclear charges is used to deduce from the study of electrostatic principles the application of ionic crystals in formulae for the theoretical calculation of ionic polarization energy, and furthermore, their application in formula...

Y. K. Wen J. Shao

1975-01-01

296

A new theoretical method for calculating temperature and water vapor saturation ratio in an expansion cloud chamber  

NASA Astrophysics Data System (ADS)

The expansion cloud chamber is a widely used apparatus for investigating the dynamics of condensational growth of aerosols and clouds. Theoretical calculations of temperature T and water vapor saturation ratio S are necessary for quantitative interpretations of experimental data obtained from the expansion cloud chamber. In this paper, we revisit the thermodynamics associated with the underlying assumptions for calculating the time-dependent temperature T(t) and saturation ratio S(t) in an expansion chamber as a function of experimentally observable parameters. We introduce an intuitive and robust method, the virtual path (VP) method, by which changes in the thermodynamic state of a moist air parcel containing cloud droplets are schematically represented on a thermodynamic diagram. The validity of the VP method is confirmed by comparisons with the differential equation (DE) method, which is a numerical simulation of real physical processes according to the time evolution equations involving T and S. In contrast to the conventional DE method, the governing equations of the VP method do not involve time t, an irrelevant parameter in the framework of classical thermodynamics. The VP method is advantageous compared to the DE method because the former is applicable to the raw experimental data acquired with a finite time resolution, allowing a robust calculation of the T and S values and the errors that are only caused by the measurement errors of the input data.

Moteki, Nobuhiro; Kondo, Yutaka

2013-06-01

297

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

298

Path integral calculation of free energies: Quantum effects on the melting temperature of neon  

Microsoft Academic Search

The path integral formulation has been combined with several methods to determine free energies of quantum many-body systems, such as adiabatic switching and reversible scaling. These techniques are alternatives to the standard thermodynamic integration method. A quantum Einstein crystal is used as a model to demonstrate the accuracy and reliability of these free energy methods in quantum simulations. Our main

R. Ramírez; C. P. Herrero; A. Antonelli; E. R. Hernández

2008-01-01

299

Collective excitations in quantum Hall liquid crystals: Single-mode approximation calculations  

Microsoft Academic Search

A variety of recent experiments probing the low-temperature transport properties of quantum Hall systems have suggested an interpretation in terms of liquid crystalline mesophases dubbed quantum Hall liquid crystals. The single mode approximation (SMA) has been a useful tool for the determination of the excitation spectra of various systems such as phonons in He4 and in the fractional quantum Hall

Cintia M. Lapilli; Carlos Wexler

2006-01-01

300

Collective excitations in quantum Hall liquid crystals: Single-mode approximation calculations  

Microsoft Academic Search

A variety of recent experiments probing the low-temperature transport properties of quantum Hall systems have suggested an interpretation in terms of liquid crystalline mesophases dubbed quantum Hall liquid crystals. The single mode approximation (SMA) has been a useful tool for the determination of the excitation spectra of various systems such as phonons in ⁴He and in the fractional quantum Hall

Cintia M. Lapilli; Carlos Wexler

2006-01-01

301

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

NASA Astrophysics Data System (ADS)

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

Schwerdtfeger, Christine A.; Mazziotti, David A.

2012-12-01

302

On the controversial fitting of susceptibility curves of ferromagnetic Cu(II) cubanes: insights from theoretical calculations.  

PubMed

This paper reports a theoretical analysis of the electronic structure and magnetic properties of a tetranuclear Cu(II) complex, [Cu(4) (HL)(4)], which has a 4+2 cubane-like structure (H(3) L=N,N'-(2-hydroxypropane-1,3-diyl)bis(acetylacetoneimine)). These theoretical calculations indicate a quintet (S=2) ground state; the energy-level distribution of the magnetic states confirm Heisenberg behaviour and correspond to an S(4) spin-spin interaction model. The dominant interaction is the ferromagnetic coupling between the pseudo-dimeric units (J(1) =22.2 cm(-1)), whilst a weak and ferromagnetic interaction is found within the pseudo-dimeric units (J(2) =1.4 cm(-1)). The amplitude and sign of these interactions are consistent with the structure and arrangement of the magnetic Cu 3d orbitals; they accurately simulate the thermal dependence of magnetic susceptibility, but do not agree with the reported J values (J(1) =38.4 cm(-1), J(2) =-18.0 cm(-1)) that result from the experimental fitting. This result is not an isolated case; many other polynuclear systems, in particular 4+2 Cu(II) cubanes, have been reported in which the fitted magnetic terms are not consistent with the geometrical features of the system. In this context, theoretical evaluation can be considered as a valuable tool in the interpretation of the macroscopic behaviour, thus providing clues for a rational and directed design of new materials with specific properties. PMID:23239096

Calzado, Carmen J

2012-12-12

303

Molecular structure of tris(cyclopropylsilyl)amine as determined by gas electron diffraction and quantum-chemical calculations  

Microsoft Academic Search

The molecular structure and conformation of tris(cyclopropylsilyl)amine (TCPSA) has been studied by means of gas-phase electron diffraction at 338K and quantum-chemical calculations. A total of 12 relatively stable conformations of TCPSA molecule were considered. According to the experimental results and the DFT calculations the most stable conformer corresponds to a configuration (according to the Prelog–Klyne notation) of the type (?ac)(?ac)(+ac)-(?ac)(?ac)(+ac),

Yuri V. Vishnevskiy; Maxim A. Abaev; Arkadii A. Ivanov; Lev V. Vilkov; Marwan Dakkouri

2008-01-01

304

Calculations of electronic and optical properties in p-doped AlGaN\\/GaN superlattices and quantum wells  

Microsoft Academic Search

We present the band structure and photoluminescence spectra calculations of h-AlGaN\\/GaN multiple quantum wells and superlattices. The calculations are performed within a self-consistent approach to the k?·p? theory by means of the resolution of a full eight-band Kane Hamiltonian together with Poisson equation for the carriers charge density. Exchange-correlation effects are included within the local density approximation. These are found

S. C. P. Rodrigues; G. M. Sipahi

2002-01-01

305

Electronic structure study by means of x-ray spectroscopy and theoretical calculations of the ``ferric star'' single molecule magnet  

NASA Astrophysics Data System (ADS)

The electronic structure of the single molecule magnet system {M[Fe(L1)2]3}.4CHCl3 [M=Fe,CrL1=CH3N(CH2CH2O)22-] has been studied using x-ray photoelectron spectroscopy, x-ray-absorption spectroscopy, soft-x-ray emission spectroscopy, as well as theoretical density-functional-based methods. There is a good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O,N) exhibit a magnetic polarization yielding effective spin S=5/2 per iron atom, giving a high-spin state molecule with a total S=5 effective spin for the case of M=Fe.

Takács, A. F.; Neumann, M.; Postnikov, A. V.; Kuepper, K.; Scheurer, A.; Sperner, S.; Saalfrank, R. W.; Prince, K. C.

2006-01-01

306

Quantum mechanical calculations on some 4-methyl-5-substituted imidazole derivatives as acidic corrosion inhibitor for zinc  

Microsoft Academic Search

Gas phase quantum chemical calculations for the efficiency of some imidazole derivatives as corrosion inhibitors, along with the relative stability and proton affinity determination were performed by means of the AM1, PM3, MINDO\\/3 and MNDO semi-empirical SCF molecular orbital methods. The agreement with the experimental data was found to be satisfactory.

G. Bereket; C. Ö?retir; A. Yurt

2001-01-01

307

Intramolecular hydrogen bonding in 2-nitromalonaldehyde: Infrared spectrum and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

2-Nitromalonaldehyde (NO2MA), a simple compound to study the intramolecular hydrogen bond, has been synthesized and deuterated at the enolated proton. Molecular structure and vibrational frequencies of NO2MA have been investigated by means of density functional theory (DFT) calculations. The geometrical parameters obtained in the B3LYP level using 6-31G**, 6-311G**, and 6-311++G** basis sets and compared with the corresponding parameters of malonaldehyde (MA). Frequencies calculated at B3LYP level using the 6-311G** and 6-311++G** basis sets are in good agreement with the corresponding experimental results for light and deuterated compounds in CCl4/CS2 solution. The percentage of deviation of the bond lengths and bond angles was used to give a picture of the normal modes, and serves as a basis for the assignment of the wavenumbers. Theoretical calculations show that the hydrogen bond strength of NO2MA is slightly stronger than that of MA, which is in agreement with the spectroscopic results. The observed ?OH/?OD and ?OH/?OD appears at about 2880/2100 and 911/695 cm-1, respectively, are consistent with the calculated geometry and proton chemical shift results. To investigate the effect of NO2 group on the hydrogen bond strength, the charge distributions, steric effects, and electron delocalization in NO2MA and MA were studied by the Natural Bond Orbital (NBO) method for optimized model compounds at B3LYP/6-311++G** level of theory. The results of NBO analysis indicate that the electron-withdrawing effect of NO2 group decreases the hydrogen bond strength, but the steric and resonance effects increase the strength of the bond.

Tayyari, S. F.; Moosavi-Tekyeh, Z.; Zahedi-Tabrizi, M.; Eshghi, H.; Emampour, J. S.; Rahemi, H.; Hassanpour, M.

2006-01-01

308

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

PubMed Central

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

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

2011-01-01

309

Theoretical investigation on polarization control of semipolar-oriented InGaN quantum-well emission using (Al)InGaN alloy substrates  

NASA Astrophysics Data System (ADS)

The polarization properties of InGaN quantum wells on semipolar AlInGaN alloy substrates are calculated numerically using a 6×6.k.p Hamiltonian. It is shown that the polarization direction of quantum-well emission changes, depending on the substrate alloy composition and quantum-well width, and that this polarization switching is caused by the strain anisotropy and quantum confinement effects in the quantum wells. The calculation results indicate that InGaN or AlInGaN alloy substrates can be beneficial in obtaining desirable polarization properties for the formation of cleaved-facet cavity mirrors in laser diodes on semipolar substrates.

Yamaguchi, A. Atsushi

2009-05-01

310

Magnetic cooling through quantum criticality  

NASA Astrophysics Data System (ADS)

We report measurements and theoretical calculations of the magnetocaloric properties of low-dimensional spin-1/2 antiferromagnets close to their magnetic field-induced quantum critical points. We demonstrate that the accumulation of entropy around the quantum critical point, giving rise to a critically enhanced magnetocaloric effect ?B, can be used for realizing a very efficient low-temperature magnetic cooling.

Lang, M.; Wolf, B.; Honecker, A.; Tsui, Y.; Jaiswal-Nagar, D.; Tutsch, U.; Hofmann, G.; Prokofiev, A.; Cong, P. T.; Krüger, N.; Ritter, F.; Assmus, W.

2012-12-01

311

Theoretical ROVibrational Energies (TROVE): A robust numerical approach to the calculation of rovibrational energies for polyatomic molecules  

NASA Astrophysics Data System (ADS)

We present a new computational method with associated computer program TROVE (Theoretical ROVibrational Energies) to perform variational calculations of rovibrational energies for general polyatomic molecules of arbitrary structure in isolated electronic states. The (approximate) nuclear kinetic energy operator is represented as an expansion in terms of internal coordinates. The main feature of the computational scheme is a numerical construction of the kinetic energy operator, which is an integral part of the computation process. Thus the scheme is self-contained, i.e., it requires no analytical pre-derivation of the kinetic energy operator. It is also general, since it can be used in connection with any internal coordinates. The method represents an extension of our model for pyramidal XY3 molecules reported previously [S.N. Yurchenko, M. Carvajal, P. Jensen, H. Lin, J.J. Zheng, W. Thiel, Mol. Phys. 103 (2005) 359]. Non-rigid molecules are treated in the Hougen Bunker Johns approach [J.T. Hougen, P.R. Bunker, J.W.C. Johns, J. Mol. Spectrosc. 34 (1970) 136]. In this case, the variational calculations employ a numerical finite basis representation for the large-amplitude motion using basis functions that are generated by Numerov-Cooley integration of the appropriate one-dimensional Schrödinger equation.

Yurchenko, Sergei N.; Thiel, Walter; Jensen, Per

2007-10-01

312

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

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

313

Reaction path potential for complex systems derived from combined ab initio quantum mechanical and molecular mechanical calculations.  

PubMed

Combined ab initio quantum mechanical and molecular mechanical calculations have been widely used for modeling chemical reactions in complex systems such as enzymes, with most applications being based on the determination of a minimum energy path connecting the reactant through the transition state to the product in the enzyme environment. However, statistical mechanics sampling and reaction dynamics calculations with a combined ab initio quantum mechanical (QM) and molecular mechanical (MM) potential are still not feasible because of the computational costs associated mainly with the ab initio quantum mechanical calculations for the QM subsystem. To address this issue, a reaction path potential energy surface is developed here for statistical mechanics and dynamics simulation of chemical reactions in enzymes and other complex systems. The reaction path potential follows the ideas from the reaction path Hamiltonian of Miller, Handy and Adams for gas phase chemical reactions but is designed specifically for large systems that are described with combined ab initio quantum mechanical and molecular mechanical methods. The reaction path potential is an analytical energy expression of the combined quantum mechanical and molecular mechanical potential energy along the minimum energy path. An expansion around the minimum energy path is made in both the nuclear and the electronic degrees of freedom for the QM subsystem internal energy, while the energy of the subsystem described with MM remains unchanged from that in the combined quantum mechanical and molecular mechanical expression and the electrostatic interaction between the QM and MM subsystems is described as the interaction of the MM charges with the QM charges. The QM charges are polarizable in response to the changes in both the MM and the QM degrees of freedom through a new response kernel developed in the present work. The input data for constructing the reaction path potential are energies, vibrational frequencies, and electron density response properties of the QM subsystem along the minimum energy path, all of which can be obtained from the combined quantum mechanical and molecular mechanical calculations. Once constructed, it costs much less for its evaluation. Thus, the reaction path potential provides a potential energy surface for rigorous statistical mechanics and reaction dynamics calculations of complex systems. As an example, the method is applied to the statistical mechanical calculations for the potential of mean force of the chemical reaction in triosephosphate isomerase. PMID:15260525

Lu, Zhenyu; Yang, Weitao

2004-07-01

314

Molecular dynamics simulation and quantum mechanical calculations on ?-D-N-acetylneuraminic acid.  

PubMed

N-Acetylneuraminic acid is a sugar molecule of biological significance due to its pivotal role in molecular recognition processes. The three dimensional structure and conformation of ?-Neu5Ac in biological environments can be clearly observed by molecular dynamics (MD) simulation and quantum mechanical (QM) calculations. A 10ns MD simulation on ?-Neu5Ac yields two conformational models which are stabilized by water mediated hydrogen bond between O-8/O-9 hydroxyl oxygen and carbonyl of carboxylate group. The average life time of the conformers and the residual time of water which mediates the hydrogen bonding interactions are computed. Based on the amphiprotic nature of water, water mediation of each conformer is divided into two different modes, one donor-one acceptor mode and two donor modes. According to the analysis of simulation trajectories, the preferred mode of water mediation for conformers is the one donor-one acceptor mode. The energy and geometry of the MD derived conformational models of ?-Neu5Ac are optimized using HF/6-31G(?) basis set of Gaussian03. QM calculations also resulted that ?-Neu5Ac is preferentially stabilized by water mediated hydrogen bonding between O-8 hydroxyl and the carboxylate group where the mediation is one donor-one acceptor type. The optimized geometry of ?-Neu5Ac which is in good agreement with the crystal structure of ?-D-N-acetyl-1-O-methylneuraminic acid methyl ester is deposited in the public domain database 3DSDSCAR (http://3dsdscar.org). This optimized structure can be used by biotechnologists, biophysicists and glycobiologists for modelling the sialylglycans and also to design drugs using sialic acid analog inhibitors. PMID:22356929

Priyadarzini, Thanu R K; Subashini, Balakrishnan; Selvin, Jeyasigamani F A; Veluraja, Kasinadar

2012-01-28

315

Quantum Monte Carlo: Applications of the twist-averaged boundary conditions and the calculation of forces  

NASA Astrophysics Data System (ADS)

Quantum Monte Carlo (QMC) method is a powerful simulation tool for studying the properties of physical and chemical systems. The application of QMC to extended systems subjects to finite size effects because the simulation is often done with a small system in a super cell geometry. Periodic boundary condition is commonly used in such a setup which leads to large and fluctuating finite size error. Twist-averaged boundary condition (TABC) averages over all the possible twist angles in the boundary condition and could significantly reduce the finite size effects. In this thesis, we apply TABC to four different physical systems: the three dimensional electron gas (3DEG), the two dimensional electron gas (2DEG), the liquid 3He and the electronic surface. We studied the spin polarization transition of 3DEG with optimized wavefunctions including backflow and three-body correlations. We found electrons spontaneously polarize at low densities. The transition starts at rs = 55 +/- 5. For 2DEG, we calculated the critical magnetic field that polarize the system at higher densities and determined the effective Lande g factor. At the experimental equilibrium density of liquid 3He, we computed the spin polarization energy and found the unpolarized state is stable, in agreement with experiments. We also studied the electronic energy in a slab geometry using both density functional theory within the local density approximation and variational Monte Carlo. In all these systems, we found the finite size effects are much smaller when TABC is used. The extrapolation to the thermodynamic limit also becomes a smooth function. On another topic, we propose a method to calculate electronic forces using path integral Monte Carlo and applied it to study the hydrogen-hydrogen interaction in an electron gas.

Zong, Fenghua

316

Conformational composition of cyclopentadienylphosphine investigated by microwave spectroscopy and quantum chemical calculations.  

PubMed

The properties of cyclopentadienylphosphine have been investigated by means of Stark-modulation microwave spectroscopy and quantum chemical calculations at the MP2/aug-cc-pVTZ, B3LYP/6-311++G(d,p), and G3 levels of theory. Spectra attributable to two rotamers denoted conformers I and II have been assigned. Conformer I has a symmetry plane (Cs symmetry) consisting of the bisectors of the cyclopentadiene ring and of the phosphino group with the lone electron pair of phosphorus pointing toward the carbon ring. In conformer II, the phosphino group is rotated approximately 120 degrees out of this plane. Relative intensity measurements have been made, and it was found that conformer II is more stable than I by 1.3(4) kJ/mol. The preferred conformer represents a borderline case of intramolecular hydrogen bond stabilization. The experimental and MP2/ aug-cc-pVTZ rotational constants differ by several percent, which indicates that the aug-cc-pVTZ basis set is not large enough to be able to predict an accurate structure for the two conformers that are close to the equilibrium geometries. 5-Substituted 1,3-cyclopentadienyl derivatives may undergo circumambulatory rearrangements. However, there is no manifestation of this effect in the microwave spectrum of cyclopentadienylphosphine. PMID:16419990

Møllendal, Harald; Cole, George C; Guillemin, Jean-Claude

2006-01-26

317

A perturbation theory for calculating strain distributions in heterogeneous and anisotropic quantum dot structures  

NASA Astrophysics Data System (ADS)

By introducing a homogenous comparison material, a perturbation theory based on Green's function is proposed to calculate the strain distribution inside and outside an arbitrarily shaped and anisotropic quantum dot (QD) embedded in an alien infinite medium. This theory removes the limitations of the previous analytical methods which are based upon the assumption that the QD is isotropic and has the same elastic properties as the surrounding medium. The numerical results for a truncated pyramidal Ge/Si QD structure demonstrate that the anisotropy of the materials and the difference between the stiffness tensors of the QD and the matrix have a significant influence on the strain field. It is found that the first-order approximate solution obtained by the proposed method can reduce the relative difference of the strain fields induced by the isotropic approximation from 30% to 6%. Moreover, it is shown that the strain fields obtained by the proposed method with the second-order approximate solution are very accurate for the Ge/Si QD structure.

Wang, J.; Chu, H. J.

2006-09-01

318

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

PubMed

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

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

2013-06-05

319

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

NASA Astrophysics Data System (ADS)

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-Sébastien; Jeon, Sangyong

2007-01-01

320

Full dimension Rb2He ground triplet potential energy surface and quantum scattering calculations.  

PubMed

We have developed a three-dimensional potential energy surface for the lowest triplet state of the Rb(2)He complex. A global analytic fit is provided as in the supplementary material [see supplementary material at http://dx.doi.org/10.1063/1.4709433 for the corresponding Fortran code]. This surface is used to perform quantum scattering calculations of (4)He and (3)He colliding with (87)Rb(2) in the partial wave J = 0 at low and ultralow energies. For the heavier helium isotope, the computed vibrational relaxation probabilities show a broad and strong shape resonance for a collisional energy of 0.15 K and a narrow Feshbach resonance at about 17 K for all initial Rb(2) vibrational states studied. The broad resonance corresponds to an efficient relaxation mechanism that does not occur when (3)He is the colliding partner. The Feshbach resonance observed at higher collisional energy is robust with respect to the isotopic substitution. However, its effect on the vibrational relaxation mechanism is faint for both isotopes. PMID:22583230

Guillon, Grégoire; Viel, Alexandra; Launay, Jean-Michel

2012-05-01

321

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

322

LocalSCF method for semiempirical quantum-chemical calculation of ultralarge biomolecules  

NASA Astrophysics Data System (ADS)

A linear-scaling semiempirical method, LocalSCF, has been proposed for the quantum-chemical calculations of ultralarge molecular systems by treating the large-scale molecular task as a variational problem. The method resolves the self-consistent field task through the finite atomic expansion of weakly nonorthogonal localized molecular orbitals. The inverse overlap matrix arising from the nonorthogonality of the localized orbitals is approximated by preserving the first-order perturbation term and applying the second-order correction by means of a penalty function. This allows for the separation of the orbital expansion procedure from the self-consistent field optimization of linear coefficients, thereby maintaining the localized molecular orbital size unchanged during the refinement of linear coefficients. Orbital normalization is preserved analytically by the variation of virtual degrees of freedom, which are orthogonal to the initial orbitals. Optimization of linear coefficients of localized orbitals is performed by a gradient procedure. The computer program running on a commodity personal computer was applied to the GroEL-GroES chaperonin complex containing 119 273 atoms.

Anikin, N. A.; Anisimov, V. M.; Bugaenko, V. L.; Bobrikov, V. V.; Andreyev, A. M.

2004-07-01

323

Calculation of intermolecular interaction strengths in the P beta' phase in lipid bilayers. Implications for theoretical models.  

PubMed Central

The existence of the P beta' phase in certain lipid bilayers is evidence that molecular interactions between lipids are capable of producing unusual large-scale structures at or near biological conditions. The problem of identifying the specific intermolecular interactions responsible for the structures requires construction of theoretical models capable of clear predictions of the observable consequences of postulated intermolecular interactions. To this end we have carried out a twofold modeling effort aimed at understanding the ripple phase. First, we have performed detailed numerical calculations of potential energies of interaction between pairs and triplets of lipid molecules having different chain tilt angles and relative vertical alignments. The calculations support the notion that chain tilting in the gel phase is a result of successive 3-5-A displacements of neighboring molecules perpendicular to the bilayer plane rather than long-range cooperative chain tilting. Secondly, we have used these results as a guide to formulate a new lattice model for lipid bilayer condensed phases. The new model is less complex than our earlier model and it includes interactions which are, based on the energy calculations, more likely to be responsible for the ripple phase. In a certain limit the model maps onto the chiral clock model, a model of much interest in condensed matter theory. In this limit the model exhibits a chain-tilted ordered phase followed by (as temperature increases) a modulated phase followed by a disordered phase. Within this limit we discuss the properties of the model and compare structures of the modulated phase exhibited by the model with experimental data for the P beta' phase in lipid bilayers.

Scott, H L; Pearce, P A

1989-01-01

324

Microwave, infrared, and Raman spectra, structural parameters, vibrational assignments and theoretical calculations of 1,3-disilacyclopentane  

NASA Astrophysics Data System (ADS)

The FT-microwave spectrum of 1,3-disilacyclopentane (c-C3H6Si2H4) has been recorded and 99 transitions for five isotopologues have been assigned for the twist form. The ground state rotational constants were determined from these assignments with following values for A = 4417.6710(7), B = 2887.0548(6), C = 1938.2171(6). From the experimentally reported microwave rotational constants and ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters are reported for the most stable twist form distances (Å) rC?Si = 1.886(2), rSiC?,C?? = 1.888(2), rC?C?? = 1.552(2), and angles (°) ?SiC?Si = 103.9(3), ?C?SiC? = 102.2(3), ?SiC?C?? = 106.4(3), and ?C?SiC?Si = 11.5(3), ?SiC?C??Si = 45.6(3). The conformational stabilities have been predicted from theoretical calculations with basis sets up to aug-cc-pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been made for the observed bands for the twist conformer and the interpretation is utilized by ab initio calculations to predict harmonic force constants, vibrational wavenumbers, infrared intensities, Raman activities and depolarization ratios. The results are discussed and compared to the corresponding properties of some related molecules.

Guirgis, Gamil A.; Klaassen, Joshua J.; Pate, Brooks H.; Seifert, Nathan A.; Darkhalil, Ikhlas D.; Deodhar, Bhushan S.; Wyatt, Justin K.; Dukes, Horace W.; Kruger, Michael; Durig, James R.

2013-10-01

325

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

PubMed

In this work, the FT-IR and FT-Raman spectrum of 1-(chloromethyl)-2-methyl naphthalene (abbreviated as 1-ClM-2MN, C(12)H(11)Cl) have been recorded in the region 3600-10cm(-1). The optimum molecular geometry, normal mode wavenumbers, infrared and Raman intensities, Raman scattering activities, corresponding vibrational assignments, Mullikan atomic charges and thermo-dynamical parameters were investigated with the help of HF and B3LYP (DFT) method using 6-311G(d,p), 6-311++G(d,p) basis sets. Also, the dipole moment, linear polarizabilities, anisotropy, first and second hyperpolarizabilities values were also computed using the same basis set. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. The correlation equations between heat capacities, entropies, enthalpy changes and temperatures were fitted by quadratic formulas. Lower value in the HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. UV-vis spectral analysis of 1-ClM-2MN has been researched by theoretical calculations. In order to understand the electronic transitions of the compound, TD-DFT calculations on electronic absorption spectra in gas phase and solvent (DMSO and chloroform) were performed. The calculated frontier orbital energies, absorption wavelengths (?), oscillator strengths (f) and excitation energies (E) for gas phase and solvent are also illustrated. PMID:22024457

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

2011-10-05

326

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

PubMed

Modern-day radiotherapy relies on highly sophisticated forms of image guidance in order to implement increasingly conformal treatment plans and achieve precise dose delivery. One of the most important goals of such image guidance is to delineate the clinical target volume from surrounding normal tissue during patient setup and dose delivery, thereby avoiding dependence on surrogates such as bony landmarks. In order to achieve this goal, it is necessary to integrate highly efficient imaging technology, capable of resolving soft-tissue contrast at very low doses, within the treatment setup. In this paper we report on the development of one such modality, which comprises a nonoptimized, prototype electronic portal imaging device (EPID) based on a 40 mm thick, segmented crystalline CsI(Tl) detector incorporated into an indirect-detection active matrix flat panel imager (AMFPI). The segmented detector consists of a matrix of 160 x 160 optically isolated, crystalline CsI(Tl) elements spaced at 1016 microm pitch. The detector was coupled to an indirect detection-based active matrix array having a pixel pitch of 508 microm, with each detector element registered to 2 x 2 array pixels. The performance of the prototype imager was evaluated under very low-dose radiotherapy conditions and compared to that of a conventional megavoltage AMFPI based on a Lanex Fast-B phosphor screen. Detailed quantitative measurements were performed in order to determine the x-ray sensitivity, modulation transfer function, noise power spectrum, and detective quantum efficiency (DQE). In addition, images of a contrast-detail phantom and an anthropomorphic head phantom were also acquired. The prototype imager exhibited approximately 22 times higher zero-frequency DQE (approximately 22%) compared to that of the conventional AMFPI (approximately 1%). The measured zero-frequency DQE was found to be lower than theoretical upper limits (approximately 27%) calculated from Monte Carlo simulations, which were based solely on the x-ray energy absorbed in the detector-indicating the presence of optical Swank noise. Moreover, due to the nonoptimized nature of this prototype, the spatial resolution was observed to be significantly lower than theoretical expectations. Nevertheless, due to its high quantum efficiency (approximately 55%), the prototype imager exhibited significantly higher DQE than that of the conventional AMFPI across all spatial frequencies. In addition, the frequency-dependent DQE was observed to be relatively invariant with respect to the amount of incident radiation, indicating x-ray quantum limited behavior. Images of the contrast-detail phantom and the head phantom obtained using the prototype system exhibit good visualization of relatively large, low-contrast features, and appear significantly less noisy compared to similar images from a conventional AMFPI. Finally, Monte Carlo-based theoretical calculations indicate that, with proper optimization, further, significant improvements in the DQE performance of such imagers could be achieved. It is strongly anticipated that the realization of optimized versions of such very high-DQE EPIDs would enable megavoltage projection imaging at very low doses, and tomographic imaging from a "beam's eye view" at clinically acceptable doses. PMID:16696482

Sawant, Amit; Antonuk, Larry E; El-Mohri, Youcef; Zhao, Qihua; Wang, Yi; Li, Yixin; Du, Hong; Perna, Louis

2006-04-01

327

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

SciTech Connect

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

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

2006-04-15

328

Calculation of wave-functions with frozen orbitals in mixed quantum mechanics/molecular mechanics methods. Part I. Application of the Huzinaga equation.  

PubMed

Mixed quantum mechanics/quantum mechanics (QM/QM) and quantum mechanics/molecular mechanics (QM/MM) methods make computations feasible for extended chemical systems by separating them into subsystems that are treated at different level of sophistication. In many applications, the subsystems are covalently bound and the use of frozen localized orbitals at the boundary is a possible way to separate the subsystems and to ensure a sensible description of the electronic structure near to the boundary. A complication in these methods is that orthogonality between optimized and frozen orbitals has to be warranted and this is usually achieved by an explicit orthogonalization of the basis set to the frozen orbitals. An alternative to this approach is proposed by calculating the wave-function from the Huzinaga equation that guaranties orthogonality to the frozen orbitals without basis set orthogonalization. The theoretical background and the practical aspects of the application of the Huzinaga equation in mixed methods are discussed. Forces have been derived to perform geometry optimization with wave-functions from the Huzinaga equation. Various properties have been calculated by applying the Huzinaga equation for the central QM subsystem, representing the environment by point charges and using frozen strictly localized orbitals to connect the subsystems. It is shown that a two to three bond separation of the chemical or physical event from the frozen bonds allows a very good reproduction (typically around 1 kcal/mol) of standard Hartree-Fock-Roothaan results. The proposed scheme provides an appropriate framework for mixed QM/QM and QM/MM methods. PMID:23281055

Ferenczy, György G

2012-12-28

329

Accelerating resolution-of-the-identity second-order Møller-Plesset quantum chemistry calculations with graphical processing units.  

PubMed

The modification of a general purpose code for quantum mechanical calculations of molecular properties (Q-Chem) to use a graphical processing unit (GPU) is reported. A 4.3x speedup of the resolution-of-the-identity second-order Møller-Plesset perturbation theory (RI-MP2) execution time is observed in single point energy calculations of linear alkanes. The code modification is accomplished using the compute unified basic linear algebra subprograms (CUBLAS) library for an NVIDIA Quadro FX 5600 graphics card. Furthermore, speedups of other matrix algebra based electronic structure calculations are anticipated as a result of using a similar approach. PMID:18229900

Vogt, Leslie; Olivares-Amaya, Roberto; Kermes, Sean; Shao, Yihan; Amador-Bedolla, Carlos; Aspuru-Guzik, Alan

2008-01-30

330

Measurements and theoretical calculations of N2-broadening and N2-shift coefficients in the ?2 band of CH3D  

NASA Astrophysics Data System (ADS)

In this paper, we report measured Lorentz N2-broadening and N2-induced pressure-shift coefficients of CH3D in the ?2 fundamental band using a multispectrum fitting technique. These measurements were made by analyzing 11 laboratory absorption spectra recorded at 0.0056 cm-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 ?2 transitions with quantum numbers as high as J? = 20 and K = 16, where K? = K? ? K (for a parallel band). The measured N2-broadening coefficients range from 0.0248 to 0.0742 cm-1 atm-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-1 atm-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 QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.7%. The N2-broadening and pressure-shift 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 QQ-branch of self-induced shifts of CH3D, are also in reasonable agreement with the scattered experimental data (20% in most cases).

Predoi-Cross, Adriana; Hambrook, Kyle; Brawley-Tremblay, Marco; Bouanich, Jean-Pierre; Smith, Mary Ann H.

2006-01-01

331

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

PubMed

The rate coefficient has been measured under pseudo-first-order conditions for the Cl+CH3 association reaction at T=202, 250, and 298 K and P=0.3-2.0 Torr helium using the technique of discharge-flow mass spectrometry with low-energy (12-eV) electron-impact ionization and collision-free sampling. Cl and CH3 were generated rapidly and simultaneously by reaction of F with HCl and CH4, respectively. Fluorine atoms were produced by microwave discharge in an approximately 1% mixture of F2 in He. The decay of CH3 was monitored under pseudo-first-order conditions with the Cl-atom concentration in large excess over the CH3 concentration ([Cl]0/[CH3]0=9-67). Small corrections were made for both axial and radial diffusion and minor secondary chemistry. The rate coefficient was found to be in the falloff regime over the range of pressures studied. For example, at T=202 K, the rate coefficient increases from 8.4x10(-12) at P=0.30 Torr He to 1.8x10(-11) at P=2.00 Torr He, both in units of cm3 molecule-1 s-1. A combination of ab initio quantum chemistry, variational transition-state theory, and master-equation simulations was employed in developing a theoretical model for the temperature and pressure dependence of the rate coefficient. Reasonable empirical representations of energy transfer and of the effect of spin-orbit interactions yield a temperature- and pressure-dependent rate coefficient that is in excellent agreement with the present experimental results. The high-pressure limiting rate coefficient from the RRKM calculations is k2=6.0x10(-11) cm3 molecule-1 s-1, independent of temperature in the range from 200 to 300 K. PMID:17253663

Parker, James K; Payne, Walter A; Cody, Regina J; Nesbitt, Fred L; Stief, Louis J; Klippenstein, Stephen J; Harding, Lawrence B

2007-01-25

332

Experimental and theoretical quantum chemical investigations of 8-hydroxy-5-nitroquinoline.  

PubMed

The FT-IR and FT-Raman spectra of 8-hydroxy-5-nitroquinoline have been recorded in the regions 4000-400 and 4000-100 cm(-1), respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The normal coordinate analysis was carried out to confirm the precision of the assignments. The structure of the compound was optimised and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G(**), 6-311++G(**) and cc-pVDZ basis sets. The vibrational frequencies were calculated in all these methods and were compared with the experimental frequencies which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. (1)H and (13)C NMR spectra were recorded and (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-Visible spectrum of the compound was recorded and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The influences of the nitro and hydroxy groups on the skeletal modes and on the proton chemical shifts have been investigated. PMID:22728969

Arjunan, V; Balamourougane, P S; Kalaivani, M; Raj, Arushma; Mohan, S

2012-06-06

333

Vibrational spectra, theoretical calculations, and structures for 1,3-disilacyclopent-4-ene and 1,3-disilacyclopentane and their tetrachloro derivatives  

NASA Astrophysics Data System (ADS)

The infrared and Raman spectra and theoretical calculations for 1,3-disilacyclopent-4-ene and 1,3-disilacyclopentane and their tetrachloro derivatives are reported. The calculated structures for the molecules have been found and the silicon-carbon bond where the carbon atom is olefinic was found to be shortened relative to SiH2CH2 bonds. The agreement between observed and calculated spectra is very good.

Chun, Hye Jin; Colegrove, Lloyd F.; Laane, Jaan

2013-10-01

334

Quantum dynamics calculations on atom-diatom collisions: bosons versus fermions  

NASA Astrophysics Data System (ADS)

We have obtained new potential energy surfaces and carried out full quantum dynamics calculations for spin-polarized Li + Li2 [1] and K + K2 [2] collisions for both bosonic and fermionic isotopes. These are ``reactive'' scattering collisions because they include all possible arrangement channels. They are carried out in hyperspherical coordinates [3], which allow the full boson or fermion symmetry to be imposed. The potential energy surfaces are highly non-additive [4]. Our calculations give very high quenching rates for alkali dimers in excited vibrational states. For the low vibrationally excited states that we can handle at present, we do not see any suppression of inelastic scattering for fermionic atoms, even when the scattering length is large and positive. The low-temperature inelastic rate coefficients are typically above 10-10 cm^3 s-1. We conclude that Pauli blocking occurs only for molecules formed in the highest vibrational state in the potential well. Our results have important implications for experiments aimed at transferring molecules to lower vibrational states. We expect that it will be necessary to transfer them directly to the ground vibrational state for them to be long-lived. Molecules produced in any intermediate vibrational state are likely to be ejected from the trap very quickly. We have also carried out calculations for mixed-isotope collisions involving alkali dimers [5]. For ^7Li colliding with either ^6Li2 or ^6Li^7Li, reactive scattering is possible even when the molecule is in its lowest rovibrational state because of the change in zero-point energy. For ^7Li + ^6Li^7Li, there is only one reactive channel and the reactive scattering rate is suppressed by a factor of 50 compares to the vibrational relaxation rates. [1] M. T. Cvitas et al., PRL 94, 033201 (2005). [2] G. Qu'em'ener et al., PRA 71, 032722 (2005). [3] P. Sold'an et al., PRL 89, 153201 (2002). [4] P. Sold'an et al., PRA. 67, 054702 (2003). [5] M. T. Cvitas et al., PRL 94, 200402 (2005).

Hutson, Jeremy M.

2006-05-01

335

Theoretical Study of Quantum Gel Formation in Superfluid 4 He  

Microsoft Academic Search

Bosonic density functional theory calculations were carried out for neon, argon, and fluorine based systems in superfluid\\u000a 4He with an emphasis on the formation of dimeric species in the liquid. These atomic species display relatively strong binding\\u000a with helium and hence their solvation structures in the liquid exhibit highly localized liquid helium layers around them.\\u000a These solvent layers modify the

Jussi Eloranta

2011-01-01

336

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

PubMed

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

Jamet, Helene; Jourdan, Muriel; Dumy, Pascal

2008-07-23

337

Theoretical and Experimental Studies of the 2 - Grating Coupled Structures for Iii-V Quantum Well Infrared Photodetectors  

Microsoft Academic Search

This research mainly deals with the quantum efficiency enhancement of QWIPs (Quantum Well Infrared Photodetectors) by using the 2-dimensional (2-D) planar metal grating couplers. The motivation is originated from the intersubband selection rule of quantum well, which requires the polarization of incident infrared (IR) radiation to have a component perpendicular to the quantum well layers. The unique features of the

Yeong-Cheng Wang

1994-01-01

338

Quantum communication  

Microsoft Academic Search

Quantum communication, and indeed quantum information in general, has changed the way we think about quantum physics. In 1984 and 1991, the first protocol for quantum cryptography and the first application of quantum non-locality, respectively, attracted interest from a diverse field of researchers in theoretical and experimental physics, mathematics and computer science. Since then we have seen a fundamental shift

Nicolas Gisin; Rob Thew

2007-01-01

339

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

NASA Astrophysics Data System (ADS)

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

Shlyaptseva, Alla; Mancini, Roberto

1998-05-01

340

Theoretical calculations of hydrogen adsorption by SnO2 (110) surface: Effect of doping and calcination  

NASA Astrophysics Data System (ADS)

A pseudopotential plane-wave based density functional theory simulations of the hydrogen adsorption on rutile SnO2 (110) surface is reported. It is found that on doping with trivalent indium, the surface becomes unstable due to the formation of bridging oxygen vacancies. At sufficiently low doping level, the surface stabilizes at an oxygen vacancy to indium ratio of 1:2. Our calculations predict that at a higher doping level of 9 at. %, this ratio becomes larger, and point out a way to synthesize p-type conducting SnO2 thin films. The binding energy of SnO2 (110) surface with adsorbed hydrogen atoms display a maximum at 3-6 at. % of indium doping. This is in good agreement with the experimental results obtained from the SnO2-based hydrogen sensor's sensitivity measurements given by Drake et al. [J. Appl. Phys. 101, 104307 (2007)]. The theoretical modeling explains that the calcinations treatment can critically affect the sensitivity of the hydrogen sensor due to the enhancement of the binding energy between the SnO2 surface and the adsorbed hydrogen atoms.

Inerbaev, Talgat M.; Kawazoe, Yoshiyuki; Seal, Sudipta

2010-05-01

341

Inactivation mechanism of glycerol dehydration by diol dehydratase from combined quantum mechanical/molecular mechanical calculations.  

PubMed

Inactivation of diol dehydratase during the glycerol dehydration reaction is studied on the basis of quantum mechanical/molecular mechanical calculations. Glycerol is not a chiral compound but contains a prochiral carbon atom. Once it is bound to the active site, the enzyme adopts two binding conformations. One is predominantly responsible for the product-forming reaction (G(R) conformation), and the other primarily contributes to inactivation (G(S) conformation). Reactant radical is converted into a product and byproduct in the product-forming reaction and inactivation, respectively. The OH group migrates from C2 to C1 in the product-forming reaction, whereas the transfer of a hydrogen from the 3-OH group of glycerol to C1 takes place during the inactivation. The activation barrier of the hydrogen transfer does not depend on the substrate-binding conformation. On the other hand, the activation barrier of OH group migration is sensitive to conformation and is 4.5 kcal/mol lower in the G(R) conformation than in the G(S) conformation. In the OH group migration, Glu170 plays a critical role in stabilizing the reactant radical in the G(S) conformation. Moreover, the hydrogen bonding interaction between Ser301 and the 3-OH group of glycerol lowers the activation barrier in G(R)-TS2. As a result, the difference in energy between the hydrogen transfer and the OH group migration is reduced in the G(S) conformation, which shows that the inactivation is favored in the G(S) conformation. PMID:23098175

Doitomi, Kazuki; Kamachi, Takashi; Toraya, Tetsuo; Yoshizawa, Kazunari

2012-11-02

342

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

SciTech Connect

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

Dardi, P.S.

1984-11-01

343

Urocanic acid as an efficient hydroxyl radical scavenger: a quantum theoretical study.  

PubMed

The photoisomerization of urocanic acid (UCA)--which is present in human skin epidermis, where it acts as a sunscreen--from its trans isomer to its cis isomer upon exposure to UV-B radiation is known to cause immunosuppression. In recent years, the antioxidant properties of UCA (it acts as a hydroxyl radical scavenger) have also been recognized. In view of this, the mechanisms of stepwise reactions of trans-UCA with up to four hydroxyl radicals were investigated. The molecular geometries of the different species and complexes involved in the reactions (reactant, intermediate and product complexes, as well as transition states) were optimized via density functional theory in the gas phase. Solvation in aqueous media was treated with single point energy calculations using DFT and the polarizable continuum model. Single point energy calculations in the gas phase and aqueous media were also carried out using second-order Møller-Plesset perturbation theory (MP2). The AUG-cc-pVDZ basis set was employed in all calculations. Corrections for basis set superposition error (BSSE) were applied. Vibrational frequency analysis was performed for each optimized structure to ensure the validity of the optimized transition states. It was found that the binding of the first OH? radical to UCA involves a positive energy barrier, while subsequent reactions of OH? radicals are exergonic. Transition states were successfully located, even in those cases where the barrier energies were found to be negative. The cis-trans isomerization barrier energy of UCA and that of the first OH? radical addition to UCA are comparable, meaning that both processes can occur simultaneously. It was found that UCA could serve as an antioxidant in the form of an efficient OH? radical scavenger. PMID:20361345

Tiwari, Saumya; Chand Mishra, Phool

2010-04-02

344

The interaction between atoms of Au and Cu with clean Si(111) surface: a study combining synchrotron radiation grazing incidence X-ray fluorescence analysis and theoretical calculations.  

PubMed

In order to evaluate the interactions between Au/Cu atoms and clean Si(111) surface, we used synchrotron radiation grazing incidence X-ray fluorescence analysis and theoretical calculations. Optimized geometries and energies on different adsorption sites indicate that the binding energies at different adsorption sites are high, suggesting a strong interaction between metal atom and silicon surface. The Au atom showed higher interaction than Cu atom. The theoretical and experimental data showed good agreement. PMID:19592296

de Carvalho, Hudson W P; Batista, Ana P L; Ramalho, Teodorico C; Pérez, Carlos A; Gobbi, Angelo Luiz

2009-06-16

345

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

NASA Astrophysics Data System (ADS)

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

Gavini, Vikram

2013-03-01

346

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

NASA Astrophysics Data System (ADS)

We investigate the interaction of a graphene monolayer with the C(111) diamond surface using ab initio density functional theory. To accommodate the lattice mismatch between graphene and diamond, the overlayer deforms into a wavy structure that binds strongly to the diamond substrate. The detached ridges of the wavy graphene overlayer behave electronically as free-standing polyacetylene chains with delocalized ? electrons, separated by regions containing only sp3 carbon atoms covalently bonded to the (111) diamond surface. We performed quantum transport calculations for different geometries of the system to study how the buckling of the graphene layer and the associated bonding to the diamond substrate affect the transport properties. The system displays high carrier mobility along the ridges and a wide transport gap in the direction normal to the ridges. These intriguing, strongly anisotropic transport properties qualify the hybrid graphene-diamond system as a viable candidate for electronic nanodevices.

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

2013-10-01

347

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

PubMed

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

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

2013-10-04

348

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

PubMed

Experimental study of hydrogen bond cooperativity in hetero-complexes in the gas phase was carried out by IR-spectroscopy method. Stretching vibration frequencies of O-H groups in phenol and catechol molecules as well as of their complexes with nitriles and ethers were determined in the gas phase using a specially designed cell. O-H groups experimental frequency shifts in the complexes of catechol induced by the formation of intermolecular hydrogen bonds are significantly higher than in the complexes of phenol due to the hydrogen bond cooperativity. It was shown that the cooperativity factors of hydrogen bonds in the complexes of catechol with nitriles and ethers in the gas phase are approximately the same. Quantum chemical calculations of the studied systems have been performed using density functional theory (DFT) methods. It was shown, that theoretically obtained cooperativity factors of hydrogen bonds in the complexes of catechol with proton acceptors are in good agreement with experimental values. Cooperative effects lead to a strengthening of intermolecular hydrogen bonds in the complexes of catechol on about 30%, despite the significant difference in the proton acceptor ability of the bases. The analysis within quantum theory of atoms in molecules was carried out for the explanation of this fact. PMID:22366617

Varfolomeev, Mikhail A; Klimovitskii, Alexander E; Abaidullina, Dilyara I; Madzhidov, Timur I; Solomonov, Boris N

2012-02-02

349

Characterization of a Catalytic Ligand Bridging Metal Ions in Phosphodiesterases 4 and 5 by Molecular Dynamics Simulations and Hybrid Quantum Mechanical/Molecular Mechanical Calculations  

PubMed Central

Cyclic nucleotide phosphodiesterases (PDEs) constitute a large superfamily of enzymes regulating concentrations of intracellular second messengers cAMP and cGMP through PDE-catalyzed hydrolysis. Although three-dimensional x-ray crystal structures of PDE4 and PDE5 have been reported, it is uncertain whether a critical, second bridging ligand (BL2) in the active site is H2O or HO? because hydrogen atoms cannot be determined by x-ray diffraction. The identity of BL2 is theoretically determined by performing molecular dynamics simulations and hybrid quantum mechanical/molecular mechanical (QM/MM) calculations, for the first time, on the protein structures resolved by x-ray diffraction. The computational results confirm our previous suggestion, which was based on QM calculations on a simplified active site model, that BL2 in PDE4 should be HO?, rather than H2O, serving as the nucleophile to initialize the catalytic hydrolysis of cAMP. The molecular dynamics simulations and QM/MM calculations on PDE5 demonstrate for the first time that the BL2 in PDE5 should also be HO? rather than H2O as proposed in recently published reports on the x-ray crystal structures, which serves as the nucleophile to initialize the PDE5-catalyzed hydrolysis of cGMP. These fundamental structural insights provide a rational basis for future structure-based drug design targeting PDEs.

Xiong, Ying; Lu, Hai-Ting; Li, Yongjian; Yang, Guang-Fu; Zhan, Chang-Guo

2006-01-01

350

Symmetry of kp Hamiltonian in pyramidal InAs\\/GaAs quantum dots: Application to the calculation of electronic structure  

Microsoft Academic Search

A method for the calculation of the electronic structure of pyramidal self-assembled InAs\\/GaAs quantum dots is presented. The method is based on exploiting the C4 symmetry of the 8-band kp Hamiltonian with the strain taken into account via the continuum mechanical model. The operators representing symmetry group elements were represented in the plane wave basis and the group projectors were

Nenad Vukmirovic; Dragan Indjin; Vladimir D. Jovanovic; Zoran Ikonic; Paul Harrison

351

The structure and conformations of piracetam (2-oxo-1-pyrrolidineacetamide): Gas-phase electron diffraction and quantum chemical calculations  

Microsoft Academic Search

The geometric structure of piracetam was studied by quantum chemical calculations (DFT and ab initio), gas electron diffraction (GED), and FTIR spectroscopy. Two stable mirror symmetric isomers of piracetam were found. The conformation of pyrrolidine ring is an envelope in which the C4 atom deviates from the ring plane, the angle between the planes (C3C4C5) and (C2C3C5) is 154.1°. The

Denis N. Ksenafontov; Natalia F. Moiseeva; Lyudmila V. Khristenko; Nikolai M. Karasev; Igor F. Shishkov; Lev V. Vilkov

2010-01-01

352

Discovery of a nonstoichiometric Zn11MnSe13 magnetic magic quantum dot from ab initio calculations  

Microsoft Academic Search

Ab initio calculations on ZnSe quantum dots (QDs) doped with one Mn atom predict a new nonstoichiometric magnetic magic Zn11MnSe13 structure in contrast to QDs of undoped ZnSe that are stoichiometric and exhibit magic behavior for ZnnSen with n = 13 and 34. Our results suggest that such doping would lead to a high abundance of only one specie (the

Sachin P. Nanavati; Vijayaraghavan Sundararajan; Shailaja Mahamuni; S. V. Ghaisas; Vijay Kumar

2011-01-01

353

GaAs quantum structures: Comparison between direct pseudopotential and single-band truncated-crystal calculations  

SciTech Connect

A single-band approach for semiconductor clusters which accounts for the nonparabolicity of the energy bands was recently used by Rama Krishna and Friesner [M.V. Rama Krishna and R.A. Friesner, Phys. Rev. Lett. {bold 67}, 629 (1991)]. We compare the results of this method (denoted here as single-band truncated-crystal, or SBTC, approximation) with a direct pseudopotential band-structure calculation for free-standing hydrogen-passivated GaAs quantum films, wires, and dots. The direct pseudopotential calculation, which includes coupling between all bands, shows that isolated GaAs quantum films, wires, and dots have an indirect band gap for thicknesses below 16, 28, and at least 30 A (8, 14, and at least 15 ML), respectively; beyond these critical dimensions the transition becomes direct. A comparison of the SBTC approximation with the direct pseudopotential calculation shows that (i) the confinement energy of the valence-band maximum is overestimated by the SBTC method, because the zero-confinement character of this state is neglected; (ii) the confinement energy of the {Gamma}-derived conduction state (direct band gap) is slightly overestimated by the SBTC approximation, mainly because of the assumption of infinite potential barriers at the boundaries; (iii) the confinement energy of the {ital X}-derived conduction state (indirect band gap) is severely underestimated by the SBTC method; (iv) while the SBTC approximation predicts {open_quote}{open_quote}quantum deconfinement{close_quote}{close_quote} (i.e., {ital reduction} of gap as size is reduced) for the direct gap of thin GaAs quantum wires, such effect is not present in the direct pseudopotential calculation. {copyright} {ital 1996 American Institute of Physics.}

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

1996-04-01

354

Quantum Computers and Quantum Control  

NASA Astrophysics Data System (ADS)

Quantum computation is an excercise in quantum control: for a quantum system to compute, its dynamics must be controlled to a high degree of precision. Quantum control, in turn, is an excercise in quantum computation: control can be thought of in terms of how information is represented and processed. This talk reviews recent developments in quantum computation and quantum control with an emphasis on their theoretical and experimental overlap.

Lloyd, Seth

2001-03-01

355

Effect of hydroxyl group position on adsorption behavior and corrosion inhibition of hydroxybenzaldehyde Schiff bases: Electrochemical and quantum calculations  

NASA Astrophysics Data System (ADS)

The corrosion inhibition and adsorption of N,N?-bis(n-hydroxybenzaldehyde)-1,3-propandiimine (n-HBP) Schiff bases has been investigated on steel electrode in 1 M HCl by using electrochemical techniques. The experimental results suggest that the highest inhibition efficiency was obtained for 3-HBP. Polarization curves reveal that all studied inhibitors are mixed type. Density functional theory (DFT) at the B3LYP/6-31G(d,p) and B3LYP/3-21G basis set levels and ab initio calculations using HF/6-31G(d,p) and HF/3-21G methods were performed on three Schiff bases. By studying the effects of hydroxyl groups in ortho-, meta-, para- positions, the best one as inhibitor was found to be meta-position of OH in Schiff base (i.e., 3-HBP). The order of inhibition efficiency obtained was corresponded with the order of most of the calculated quantum chemical parameters. Quantitative structure activity relationship (QSAR) approach has been used and a correlation of the composite index of some of the quantum chemical parameters was performed to characterize the inhibition performance of the Schiff bases studied. The results showed that %IE of the Schiff bases was closely related to some of the quantum chemical parameters but with varying degrees/order. The calculated %IE of the Schiff base studied was found to be close to their experimental corrosion inhibition efficiencies.

Danaee, I.; Ghasemi, O.; Rashed, G. R.; Rashvand Avei, M.; Maddahy, M. H.

2013-03-01

356

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

NASA Astrophysics Data System (ADS)

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

Gusev, A. A.; Hai, L. L.; Vinitsky, S. I.; Chuluunbaatar, O.; Derbov, V. L.; Klombotskaya, A. S.; Dvoyan, K. G.; Sarkisyan, H. A.

2013-08-01

357

Converged quantum dynamics calculations of vibrational energies of CH4 and CH3D using an ab initio potential  

NASA Astrophysics Data System (ADS)

Exact variational calculations of vibrational energies of CH4 and CH3D are carried out using a two-layer Lanczos algorithm based on the ab initio potential energy surface of D. W. Schwenke and H. Partridge, Spectrochim. Acta, Part A 57, 887 (2001). The convergence of the calculated vibrational energies is discussed in detail. In addition, we report all well converged vibrational energy levels up to 6600 cm-1 for CH4, and those up to 5000 cm-1 for CH3D, respectively. These results clearly outperform previous theoretical calculations. And a comparison with experimental results available is also made.

Yu, Hua-Gen

2004-10-01

358

Converged quantum dynamics calculations of vibrational energies of CH4 and CH3D using an ab initio potential.  

PubMed

Exact variational calculations of vibrational energies of CH4 and CH3D are carried out using a two-layer Lanczos algorithm based on the ab initio potential energy surface of D. W. Schwenke and H. Partridge, Spectrochim. Acta, Part A 57, 887 (2001). The convergence of the calculated vibrational energies is discussed in detail. In addition, we report all well converged vibrational energy levels up to 6600 cm(-1) for CH4, and those up to 5000 cm(-1) for CH3D, respectively. These results clearly outperform previous theoretical calculations. And a comparison with experimental results available is also made. PMID:15446929

Yu, Hua-Gen

2004-10-01

359

First-principles theoretical analysis of transition-metal doping of ZnSe quantum dots  

NASA Astrophysics Data System (ADS)

We present a systematic analysis of the underlying mechanism of transition-metal doping in ZnSe nanocrystals, using first-principles density functional theory calculations. Our analysis focuses on the adsorption and surface segregation of Mn dopants on ZnSe nanocrystal surface facets. We find that the chemical potentials of the growth precursor species determine the surface structure and morphology of the nanocrystals. We report binding energies for Mn adsorption onto ZnSe surfaces and find that all the anion-rich surfaces contribute toward dopant adsorption onto ZnSe nanocrystal surface facets. Beyond a critical value of dopant surface coverage, these adsorbed dopants may induce structural transitions in low-Miller-index surface facets, resulting in morphological transitions of the ZnSe nanocrystals. In addition, the dopant binding-energy dependence on the dopant surface concentration explains the doping difficulties during nanocrystal growth. Finally, we report surface segregation energy profiles for Mn dopant segregation on low-Miller-index ZnSe nanocrystal surface facets. We find that, under conditions that render ZnSe(001)-(2 × 1) as the dominant dopable surface of ZnSe nanocrystals, Mn dopants do not have a tendency to segregate on this surface; this guarantees that the dopants remain incorporated into the core regions of the nanocrystal instead of escaping to the surface.

Singh, Tejinder; Mountziaris, T. J.; Maroudas, Dimitrios

2012-07-01

360

Ab Initio Quantum Calculations of Reactions in Astrophysical Ices: Acetaldehyde and Acetone with Ammonia  

NASA Astrophysics Data System (ADS)

Complex organic molecules, including amino acid precursors, have been observed in young stellar objects. Both laboratory and theoretical studies have shown that ice chemistry can play an important role in low-temperature synthetic pathways, with water serving as a catalyst that can significantly enhance reaction rates by lowering barriers or eliminating them altogether. Reactions between carbonyl species and ammonia are particularly promising, as shown in previous studies of the formaldehyde-ammonia reaction. In this study, we explore the reactions of ammonia with two larger carbonyl species, acetaldehyde and acetone, embedded in a water ice cluster. To examine the explicit impact of the water, we gradually increase the size of the cluster from 4H_2O to 12H_2O. Cluster calculations were performed at the MP2/{6-31}+G^{**} or B3LYP/{6-31}+G^{**} level. In order to account for the electrostatic contribution from bulk ice, the Polarizable Continuum Model (PCM) and Isodensity Surface Polarized Continuum Model (IPCM) were used to model reaction field solvation effects. For both acetaldehyde and acetone, the reactant is a charge transfer complex (a partial charge-transfer complex in small clusters and full proton-transfer complex in larger clusters). Rearrangement to amino-hydroxylated products can occur by surmounting a small reaction barrier. Stereo-selectivity is observed in the case of acetaldehyde. P. Ehrenfreund and S. B. Charnley, Ann. Rev. Astron. Astrophys. 38, 427 (2000). W. A. Schutte, L. J. Allamandola, and S. A. Sandford, Science 259, 1143 (1993) W. A. Schutte, L. J. Allamandola, and S. A. Sandford, Icarus 104, 118 (1993) D. E. Woon, Icarus 142, 550 (1999) S. P. Walch, C. W. Bauschicher, Jr., A. Ricca and E. L. O. Bakes, Chem. Phys. Lett, 333, 6 (2001)

Chen, L.; Woon, D. E.

2009-06-01

361

Theoretical study of the vibrational spectra of 2-chloropyridine metal complexes. I. Calculation and analysis of the IR spectrum of 2-chloropyridine  

Microsoft Academic Search

The force field and the electrooptical parameters of 2-chloropyridine were determined by the refinement of the corresponding parameters of the pyridine molecule, for further use in the metal complexes study. During the refinement procedure, the results of semiempirical (MNDO) and ab initio (4-31G*) calculations were taken into account. Approximate normal coordinate analysis was performed on the basis of different theoretical

Meriç Bakiler; I. V. Maslov; Sevim Akyüz

1999-01-01

362

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

PubMed

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

Korth, Martin; Lüchow, Arne; Grimme, Stefan

2008-01-18

363

NMR dipolar constants of motion in liquid crystals: Jeener-Broekaert, double quantum coherence experiments and numerical calculation on a 10-spin cluster.  

PubMed

Two proton quasi-equilibrium states were previously observed in nematic liquid crystals, namely the S and W quasi-invariants. Even though the experimental evidence suggested that they originate in a partition of the spin dipolar energy into a strong and a weak part, respectively, from a theoretical viewpoint, the existence of an appropriate energy scale which allows such energy separation remains to be confirmed and a representation of the quasi-invariants is still to be given. We compare the dipolar NMR signals yielded both by the Jeener-Broekaert (JB) experiment as a function of the preparation time and the free evolution of the double quantum coherence (DQC) spectra excited from the S state, with numerical calculations carried out from first principles under different models for the dipolar quasi-invariants, in a 10-spin cluster which represents the 5CB (4(')-pentyl-4-biphenyl-carbonitrile) molecule. The calculated signals qualitatively agree with the experiments and the DQC spectra as a function of the single-quantum detection time are sensible enough to the different models to allow both to probe the physical nature of the initial dipolar-ordered state and to assign a subset of dipolar interactions to each constant of motion, which are compatible with the experiments. As a criterion for selecting a suitable quasi-equilibrium model of the 5CB molecule, we impose on the time evolution operator consistency with the occurrence of two dipolar quasi-invariants, that is, the calculated spectra must be unaffected by truncation of non-secular terms of the weaker dipolar energy. We find that defining the S quasi-invariant as the subset of the dipolar interactions of each proton with its two nearest neighbours yields a realistic characterization of the dipolar constants of motion in 5CB. We conclude that the proton-spin system of the 5CB molecule admits a partition of the dipolar energy into a bilinear strong and a multiple-spin weak contributions therefore providing two orthogonal constants of motion, which can be prepared and observed by means of the JB experiment. This feature, which implies the existence of two timescales of very different nature in the proton-spin dynamics, is ultimately dictated by the topology of the spin distribution in the dipole network and can be expected in other liquid crystals. Knowledge of the nature of the dipolar quasi-invariants will be useful in studies of dipolar-order relaxation, decoherence and multiple quantum NMR experiments where the initial state is a dipolar-ordered one. PMID:19589661

Segnorile, H H; Bonin, C J; González, C E; Acosta, R H; Zamar, R C

2009-06-21

364

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

SciTech Connect

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

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

1998-01-01

365

Hydrogen adsorbed in a metal organic framework-5: Coupled translation-rotation eigenstates from quantum five-dimensional calculations  

NASA Astrophysics Data System (ADS)

We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (T-R) eigenstates of a H2 molecule adsorbed in metal organic framework-5 (MOF-5), a prototypical nanoporous material, which was treated as rigid. The anisotropic interactions between H2 and MOF-5 were represented by the analytical 5D intermolecular potential energy surface (PES) used previously in the simulations of the thermodynamics of hydrogen sorption in this system [Belof et al., J. Phys. Chem. C 113, 9316 (2009)]. The global and local minima on this 5D PES correspond to all of the known binding sites of H2 in MOF-5, three of which, ?-, ?-, and ?-sites are located on the inorganic cluster node of the framework, while two of them, the ?- and ?-sites, are on the phenylene link. In addition, 2D rotational PESs were calculated ab initio for each of these binding sites, keeping the center of mass of H2 fixed at the respective equilibrium geometries; purely rotational energy levels of H2 on these 2D PESs were computed by means of quantum 2D calculations. On the 5D PES, the three adjacent ?-sites lie just 1.1 meV above the minimum-energy ?-site, and are separated from it by a very low barrier. These features allow extensive wave function delocalization of even the lowest translationally excited T-R eigenstates over the ?- and ?-sites, presenting significant challenges for both the quantum bound-state calculations and the analysis of the results. Detailed comparison is made with the available experimental data.

Matanovi?, Ivana; Belof, Jonathan L.; Space, Brian; Sillar, Kaido; Sauer, Joachim; Eckert, Juergen; Ba?i?, Zlatko

2012-07-01

366

Hydrogen adsorbed in a metal organic framework-5: coupled translation-rotation eigenstates from quantum five-dimensional calculations.  

PubMed

We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (T-R) eigenstates of a H(2) molecule adsorbed in metal organic framework-5 (MOF-5), a prototypical nanoporous material, which was treated as rigid. The anisotropic interactions between H(2) and MOF-5 were represented by the analytical 5D intermolecular potential energy surface (PES) used previously in the simulations of the thermodynamics of hydrogen sorption in this system [Belof et al., J. Phys. Chem. C 113, 9316 (2009)]. The global and local minima on this 5D PES correspond to all of the known binding sites of H(2) in MOF-5, three of which, ?-, ?-, and ?-sites are located on the inorganic cluster node of the framework, while two of them, the ?- and ?-sites, are on the phenylene link. In addition, 2D rotational PESs were calculated ab initio for each of these binding sites, keeping the center of mass of H(2) fixed at the respective equilibrium geometries; purely rotational energy levels of H(2) on these 2D PESs were computed by means of quantum 2D calculations. On the 5D PES, the three adjacent ?-sites lie just 1.1 meV above the minimum-energy ?-site, and are separated from it by a very low barrier. These features allow extensive wave function delocalization of even the lowest translationally excited T-R eigenstates over the ?- and ?-sites, presenting significant challenges for both the quantum bound-state calculations and the analysis of the results. Detailed comparison is made with the available experimental data. PMID:22779674

Matanovi?, Ivana; Belof, Jonathan L; Space, Brian; Sillar, Kaido; Sauer, Joachim; Eckert, Juergen; Ba?i?, Zlatko

2012-07-01

367

Correlations Between XAS and Spectroscopic Ellipsometry Studies and Ab-Initio Quantum Calculations on RPE-MOCVD Deposited Titanium Silicate Alloys  

NASA Astrophysics Data System (ADS)

We report thin film titanium silicate alloys, with a range of compositions between 0 and 100% TiO2, deposited on Si(100) substrates through Remote Plasma Enhanced Metal Organic Chemical Vapor Deposition (RPE-MOCVD). Samples were measured in both their as-deposited condition and after a range of annealing temperatures. The conduction-band electronic structure of these alloys were analyzed though O K1 and Ti L2,3 X-Ray Absorption Spectroscopy (XAS) measurements as well as Spectroscopic Ellipsometry measurements preformed in the 1.5 to 6 and 4.5 to 8.5 eV energy ranges. Results were correlated with previous theoretical and experimental studies as well as new Ab-Initio quantum calculations. Emphasis is placed on correlating spectroscopic data with calculations on 4-fold coordinated tetrahedral as well as 6-fold coordinated rutile and anatase structures to obtain spectroscopic signatures of phase changes and crystallization. Investigations into the effect of bond distortions on the electronic structure will also be presented.

Stoute, Nicholas; Lucovsky, Gerald; Aspnes, David

2008-10-01

368

Quantum confinement and spin-orbit interactions in PbSe and PbTe nanowires: First-principles calculation  

NASA Astrophysics Data System (ADS)

First-principles calculations have been used to investigate the energetic stability and electronic properties of PbSe and PbTe nanowires (NW). The stability of the NWs depends on the NW diameter, while the electronic properties are ruled by three effects: in-plane stoichiometry, quantum confinement, and spin-orbit (SO) interactions. The PbTe NWs present direct band gaps, as it is in the bulk. However the PbSe NWs present indirect or direct band gaps depending on the in-plane stoichiometry. Our results for NWs out of in-plane stoichiometry show that there is an electronic compensation mechanism between quantum confinement effects and SO interactions, resulting in an almost diameter-independent band gap.

Wrasse, E. O.; Baierle, R. J.; Schmidt, T. M.; Fazzio, A.

2011-12-01

369

Calculated effects of interface grading in GaAs--Ga1-xAlxAs quantum wells  

NASA Astrophysics Data System (ADS)

Effects of interface grading on energy levels of electrons in GaAs-Ga1-xAlxAs quantum wells have been estimated using both a tight-binding formalism and an effective-mass Hamiltonian of the BenDaniel-Duke form. Graded interfaces a few atomic layers thich have only a small effect on energy levels in both schemes. Self-consistent calculations for electrons in a relatively wide (40 nm) quantum well show how the lowest levels change from those characteristic of the empty well to those characteristic of two weakly coupled heterojunctions as the electron density is increased. Present address: Hughes Research Laboratories, 3011 Malibu Canyon Road, Malibu, CA 90265, U.S.A.

Stern, Frank; Schulman, Joel N.

370

Hole subband structure and mobility calculations of double p-type d-doped GaAs quantum wells  

NASA Astrophysics Data System (ADS)

We calculate the hole subband structure and the mobility of p-type double -doped (DDD) GaAs quantum wells. The study is performed within the lines of the Thomas-Fermi-Dirac (TFD) approximation, varying the interlayer distance between wells (l) and the impurity density (p2D). We also have analysed the many-body effects. For the mobility calculations we propose a phenomenological formulae, which takes into account the most important scattering mechanism at low temperature (ionised impurities). The study shows that many-body effects are important in the level structure calculations. We have found a maximum mobility at 200 Å for an impurity density of 3.0 × 1012 cm-2.

Rodriguez-Vargas, I.; Gaggero-Sager, L. M.

2005-08-01

371

Assessment of theoretical procedures for calculating barrier heights for a diverse set of water-catalyzed proton-transfer reactions.  

PubMed

Accurate electronic barrier heights are obtained for a set of nine proton-transfer tautomerization reactions, which are either (i) uncatalyzed, (ii) catalyzed by one water molecule, or (iii) catalyzed by two water molecules. The barrier heights for reactions (i) and (ii) are obtained by means of the high-level ab initio W2.2 thermochemical protocol, while those for reaction (iii) are obtained using the W1 protocol. These three sets of benchmark barrier heights allow an assessment of the performance of more approximate theoretical procedures for the calculation of barrier heights of uncatalyzed and water-catalyzed reactions. We evaluate initially the performance of the composite G4 procedure and variants thereof (e.g., G4(MP2) and G4(MP2)-6X), as well as that of standard ab initio procedures (e.g., MP2, SCS-MP2, and MP4). We find that the performance of the G4(MP2)-type thermochemical procedures deteriorates with the number of water molecules involved in the catalysis. This behavior is linked to deficiencies in the MP2-based basis-set-correction term in the G4(MP2)-type procedures. This is remedied in the MP4-based G4 procedure, which shows good performance for both the uncatalyzed and the water-catalyzed reactions, with mean absolute deviations (MADs) from the benchmark values lying below the threshold of "chemical accuracy" (arbitrarily defined as 1 kcal mol(-1) ? 4.2 kJ mol(-1)). We also examine the performance of a large number of density functional theory (DFT) and double-hybrid DFT (DHDFT) procedures. We find that, with few exceptions (most notably PW6-B95 and B97-2), the performance of the DFT procedures that give good results for the uncatalyzed reactions deteriorates with the number of water molecules involved in the catalysis. The DHDFT procedures, on the other hand, show excellent performance for both the uncatalyzed and catalyzed reactions. Specifically, almost all of them afford MADs below the "chemical accuracy" threshold, with ROB2-PLYP and B2K-PLYP showing the best overall performance. PMID:22497287

Karton, Amir; O'Reilly, Robert J; Radom, Leo

2012-04-12

372

Comparative theoretical study of the UV/Vis absorption spectra of styrylpyridine compounds using TD-DFT calculations.  

PubMed

This study examined absorption properties of 2-styrylpyridine, trans-2-(m-cyanostyryl)pyridine, trans-2-[3-methyl-(m-cyanostyryl)]pyridine, and trans-4-(m-cyanostyryl)pyridine compounds based on theoretical UV/Vis spectra, with comparisons between time-dependent density functional theory (TD-DFT) using B3LYP, PBE0, and LC-?PBE functionals. Basis sets 6-31G(d), 6-31G(d,p), 6-31+G(d,p), and 6-311+G(d,p) were tested to compare molecular orbital energy values, gap energies, and maxima absorption wavelengths. UV/Vis spectra were calculated from fully optimized geometry in B3LYP/6-311+G(d,p) in gas phase and using the IEFPCM model. B3LYP/6-311+G(d,p) provided the most stable form, a planar structure with parameters close to 2-styrylpyridine X-ray data. Isomeric structures were evaluated by full geometry optimization using the same theory level. Similar energetic values were found: ~4.5 kJ?mol(-1) for 2-styrylpyridine and ~1 kJ?mol(-1) for derivative compound isomers. The 2-styrylpyridine isomeric structure differed at the pyridine group N-atom position; structures considered for the other compounds had the cyano group attached to the phenyl ring m-position equivalent. The energy difference was almost negligible between m-cyano-substituted molecules, but high energy barriers existed for cyano-substituted phenyl ring torsion. TD-DFT appeared to be robust and accurate approach. The B3LYP functional with the 6-31G(d) basis set produced the most reliable ?max values, with mean errors of 0.5 and 12 nm respect to experimental values, in gas and solution, respectively. The present data describes effects on the ?max changes in the UV/Vis absorption spectra of the electron acceptor cyano substituent on the phenyl ring, the electron donor methyl substituent, and the N-atom position on the electron acceptor pyridine ring, causing slight changes respect to the 2-styrylpyridine title compound. PMID:23053012

Castro, Maria Eugenia; Percino, M Judith; Chapela, Victor M; Soriano-Moro, Guillermo; Ceron, Margarita; Melendez, Francisco J

2012-10-11

373

AM and FM quantum noise in semiconductor lasers--Part II: Comparison of theoretical and experimental results for AlGaAs lasers  

Microsoft Academic Search

Four different theoretical formulations for AM and FM quantum noise properties in semiconductor lasers are compared with each other for AlGaAs lasers. These formulations are based on van der Pol, Fokker-Planck, rate, and photon density matrix equations. Experimental results with AM noise spectra, FM noise spectra, and spectral linewidths for four different types of AlGaAs lasers are also delineated and

Y. Yamamoto; S. Saito; T. Mukai

1983-01-01

374

Emission quantum yield of a europium(III) tris-[beta]-diketonate complex bearing a 1,4-diaza-1,3-butadiene: Comparison with theoretical prediction  

NASA Astrophysics Data System (ADS)

The Eu(NTA)3 [middle dot] p-tolyl-DAB complex (DAB = 1,4-diaza-1,3-butadienes of the type RNCHCHNR, R = p-tolyl) is the clearest example reported in the literature until now that provides the experimental validation of the theoretical predictions recently developed for the influence of the intramolecular energy transfer processes involving the ligand-to-metal charge transfer state on the emission quantum yield of Eu3+.

Carlos, L. D.; Fernandes, J. A.; Ferreira, R. A. Sa; Malta, O. L.; Goncalves, I. S.; Ribeiro-Claro, P.

2005-09-01

375

A Theoretical Scheme for Multi-user Quantum Key Distribution with N Einstein-Podolsky-Rosen Pairs on a Passive Optical Network  

Microsoft Academic Search

We propose a theoretical scheme for any-to-any multi-user quantum key distribution on a passive optical network with ordered N Einstein-Podolsky-Rosen pairs. This scheme is safe and more efficient than those with single photons. Its efficiency approaches 100% in the limit that the number of pairs used in the eavesdropping check becomes negligible. It also has high capacity and is convenient

Fu-Guo Deng; Xiao-Shu Liu; Ying-Jun Ma; Li Xiao; Gui-Lu Long

2002-01-01

376

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

Microsoft Academic Search

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

David R. Dion; Joseph O. Hirschfelder

1970-01-01

377

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

378

Quantum dynamics studies of gas-surface reactions and use of complex absorbing potentials in wave-packet calculations  

NASA Astrophysics Data System (ADS)

In this thesis, quantum dynamics studies are conducted on gas-surface reactions and complex absorbing potentials. Through a three-dimensional model, dissociation probabilities for O2 on both (110) and (100) surfaces of copper are calculated for ground state as well as rovibrationally excited oxygen molecules. Specifically, the reason for the difference in calculated dissociation probabilities of oxygen on two surfaces is explained. Then the thermal effect of the surface on the dissociation probability is studied by a one dimensional fluctuating barrier. It is observed that the quantum mechanical tunneling probability exhibits a maximum as a function of the oscillating frequency between the low and the high frequency limits. The physical origin and process underlying this resonantlike phenomenon are proposed. In the second part of this thesis, the complex absorbing potential (CAP) is introduced and studied. Exact numerical calculation shows that use of optimized CAP significantly improves the efficiency of wavefunction absorption over that of negative imaginary potential (NIP) in scattering applications. The CAP is optimized by an efficient time-dependent propagation approach. Application to the prototype inelastic scattering of He + H2 demonstrates the accuracy and efficiency of the channel-dependent CAP for extracting state-to-state scattering information.

Ge, Jiuyuan

1999-11-01

379

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

PubMed

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

Wang, Jingtao; Dual, Jurg

2011-09-16

380

Ketone physics - structure, conformations, and dynamics of methyl isobutyl ketone explored by microwave spectroscopy and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The microwave spectrum of methyl isobutyl ketone was recorded using a molecular beam Fourier transform microwave spectrometer and analyzed to determine the rotational constants A = 4.7517(17) GHz, B = 1.496 115(79) GHz, C = 1.324 364(39) GHz, and centrifugal distortion constants. A-E splittings from 250 MHz up to 1 GHz were observed due to internal rotation of the acetyl methyl group with a potential barrier of 250.3(19) cm-1. 59 A and 57 E species lines were fitted to experimental accuracy. The experimental rotational constants were compared with results from quantum chemical calculations to validate the molecular structure.

Zhao, Yueyue; Stahl, Wolfgang; Nguyen, Ha Vinh Lam

2012-08-01

381

Intramolecular CH?? and CH?O interactions in the conformational stability of benzyl methyl ether studied by matrix-isolation infrared spectroscopy and theoretical calculations  

NASA Astrophysics Data System (ADS)

Contributions of the intramolecular CH?? and CH?O interactions to the molecular conformation of benzyl methyl ether (BME) have been investigated by matrix-isolation infrared (IR) spectroscopy combined with quantum chemical calculations. Comparative investigations have been carried out for propylbenzene. Quantum chemical calculations predict that there are two conformers for BME; for the ET conformer the methyl ether and the phenyl groups lie in the plane of the benzene ring, while for the AG conformer they are out of the plane. Comparison between the observed and calculated spectra for BME reveals that the ET and AG conformers coexist in an Ar matrix. By measuring matrix-isolation IR spectra of BME deposited at different gas temperatures, the enthalpy difference (?H (AG - ET)) between ET and AG conformers was determined to be -1.03 ± 0.06 kJ mol-1. The experimental and calculation results indicate that the AG conformer of BME is stabilized by the intramolecular CH?? and CH?O interactions.

Shin-Ya, Kei; Takahashi, Osamu; Katsumoto, Yukiteru; Ohno, Keiichi

2007-02-01

382

Inclusion of local structure effects in theoretical x-ray resonant scattering amplitudes using ab initio x-ray-absorption spectra calculations  

NASA Astrophysics Data System (ADS)

Improved calculations of Bragg peak intensities near atomic resonance are obtained by including the effect of the local environment around the resonant atoms on the resonant scattering amplitudes ?f=f'+if''. Theoretical absorption cross sections calculated by the ab initio x-ray-absorption code FEFF are used to obtain the imaginary part f'' by extension of the optical theorem to nonforward scattering under the dipole approximation. The real part f' is obtained by a limited range Kramers-Kronig transform of the difference between f'' based on FEFF and existing theoretical calculations of f'' based on an isolated-atom model. The atomic part of ?f calculated by FEFF for the resonant atom embedded in the local potential is assumed to have spherical symmetry; however, no restriction is placed on the spectral features due to multiple scattering of the intermediate-state virtual photoelectron. Bragg peak intensities calculated in the kinematic approximation using the FEFF-based ?f are compared to intensities calculated using the isolated-atom ?f and to experimental data for Cu metal and YBa2Cu3O6.8 at the Cu K absorption edge, and for UO2 at the U MIV absorption edge.

Cross, J. O.; Newville, M.; Rehr, J. J.; Sorensen, L. B.; Bouldin, C. E.; Watson, G.; Gouder, T.; Lander, G. H.; Bell, M. I.

1998-11-01

383

Nuclear quantum effects in calculated NMR shieldings of ethylene; a Feynman path integral – ab initio study  

Microsoft Academic Search

The Feynman path integral Monte-Carlo formalism has been combined with the gauge-including atomic orbital (GIAO) approach to study the absolute magnetic shieldings of C2H4 under consideration of the thermal and quantum degrees of freedom of the nuclei. An ab initio Hamiltonian has been employed for the statistical averaging of NMR parameters. The spatial fluctuations of the atoms around their equilibrium

Michael C Böhm; Joachim Schulte; Rafael Ram??rez

2000-01-01

384

Coulomb-induced emission dynamics and self-consistent calculations of type-II Sb-containing quantum dot systems  

NASA Astrophysics Data System (ADS)

This paper investigates the effects of Coulomb interactions on the emission dynamics of Sb-containing quantum dot (QD) systems under high excitation densities. Two different type-II confinements are studied: confined electrons with unconfined holes using InAs/GaAs QDs capped with a GaAsSb quantum well (type-IIa), and confined holes with unconfined electrons using GaSb/GaAs QDs capped with an InGaAs quantum well (type-IIb). Time-resolved photoluminescence experiments are compared with self-consistent numerical calculations using an 8-band k·p model. In both structures, we observe a significant blueshift of emission and wavelength-dependent radiative lifetimes, but with marked quantitative differences between the two systems: in the type-IIa, the blueshift is 12 meV with a change in lifetime from 1.4 ns to 2.0 ns, and in the type-IIb, the blueshift is 63 meV with lifetime change from 100 ps to 23 ns. We present a comprehensive explanation of all the important features of the experimental data in terms of Coulomb-induced changes to the carrier wave functions and confining potentials, with the separate confinement of the electrons and holes being a crucial factor.

Gradkowski, K.; Ochalski, T. J.; Pavarelli, N.; Liu, H. Y.; Tatebayashi, J.; Williams, D. P.; Mowbray, D. J.; Huyet, G.; Huffaker, D. L.

2012-01-01

385

Quantum Darwinism  

SciTech Connect

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

Zurek, Wojciech H [Los Alamos National Laboratory

2008-01-01

386

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

387

The reaction mechanism of allene oxide synthase: Interplay of theoretical QM\\/MM calculations and experimental investigations  

Microsoft Academic Search

A combined theoretical and experimental study highlights the reaction mechanism of allene oxide synthase (AOS) and its possible link to hydroperoxide lyase (HPL) pathway. A previously published study (Lee et al., Nature 455 (2008) 363) has shown that the F137 residue is of central importance in differentiating between the AOS and HPL pathways after initial identical steps. In the experimental

Kyung-Bin Cho; Wenzhen Lai; Mats Hamberg; C. S. Raman; Sason Shaik

2011-01-01

388

Density functional analysis of key energetics in metal homoepitaxy: Quantum size effects in periodic slab calculations  

Microsoft Academic Search

Adspecies terrace diffusion barriers, pair interaction energies, and formation energies control island nucleation and growth during deposition and postdeposition coarsening in metal homoepitaxial systems. Thus, accurate theoretical determination of such energies is key for predicting behavior or for interpreting experiments. Often energies are obtained from density-functional theory using slab geometries. However, we find surprisingly strong variation in these energies with

Da-Jiang Liu

2010-01-01

389

Efficient Calculation of Electron States in Self-Assembled Quantum Dots: Application to Auger Relaxation  

Microsoft Academic Search

An efficient method for calculation of self-assembled dot states within the effective mass approximation is described and its application to the calculation of Auger relaxation rates is detailed. The method is based on expansion of the dot states in a harmonic oscillator basis whose parameters are optimised to improve the convergence rate. This results in at least an order of

D. Chaney; M. Roy; P. Maksym

390

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

SciTech Connect

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

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

2011-10-18

391

Quantum mechanical calculations of charge effects on gating the KcsA channel.  

PubMed

A series of ab initio (density functional) calculations were carried out on side chains of a set of amino acids, plus water, from the (intracellular) gating region of the KcsA K(+) channel. Their atomic coordinates, except hydrogen, are known from X-ray structures [D.A. Doyle, J.M. Cabral, R.A. Pfuetzner, A. Kuo, J.M. Gulbis, S.L. Cohen, B.T. Chait, R. MacKinnon, The structure of the potassium channel: molecular basis of K(+) conduction and selectivity, Science 280 (1998) 69-77; R. MacKinnon, S.L. Cohen, A. Kuo, A. Lee, B.T. Chait, Structural conservation in prokaryotic and eukaryotic potassium channels, Science 280 (1998) 106-109; Y. Jiang, A. Lee, J. Chen, M. Cadene, B.T. Chait, R. MacKinnon, The open pore conformation of potassium channels. Nature 417 (2001) 523-526], as are the coordinates of some water oxygen atoms. The 1k4c structure is used for the starting coordinates. Quantum mechanical optimization, in spite of the starting configuration, places the atoms in positions much closer to the 1j95, more tightly closed, configuration. This state shows four water molecules forming a "basket" under the Q119 side chains, blocking the channel. When a hydrated K(+) approaches this "basket", the optimized system shows a strong set of hydrogen bonds with the K(+) at defined positions, preventing further approach of the K(+) to the basket. This optimized structure with hydrated K(+) added shows an ice-like 12 molecule nanocrystal of water. If the water molecules exchange, unless they do it as a group, the channel will remain blocked. The "basket" itself appears to be very stable, although it is possible that the K(+) with its hydrating water molecules may be more mobile, capable of withdrawing from the gate. It is also not surprising that water essentially freezes, or forms a kind of glue, in a nanometer space; this agrees with experimental results on a rather different, but similarly sized (nm dimensions) system [K.B. Jinesh, J.W.M. Frenken, Capillary condensation in atomic scale friction: how water acts like a glue, Phys. Rev. Lett. 96 (2006) 166103/1-4]. It also agrees qualitatively with simulations on channels [A. Anishkin, S. Sukharev, Water dynamics and dewetting transitions in the small mechanosensitive channel MscS, Biophys. J. 86 (2004) 2883-2895; O. Beckstein, M.S.P. Sansom, Liquid-vapor oscillations of water in hydrophobic nanopores, Proc. Natl Acad. Sci. U. S. A. 100 (2003) 7063-7068] and on featureless channel-like systems [J. Lu, M.E. Green, Simulation of water in a pore with charges: application to a gating mechanism for ion channels, Prog. Colloid Polym. Sci. 103 (1997) 121-129], in that it forms a boundary on water that is not obvious from the liquid state. The idea that a structure is stable, even if individual molecules exchange, is well known, for example from the hydration shell of ions. We show that when charges are added in the form of protons to the domains (one proton per domain), the optimized structure is open. No stable water hydrogen bonds hold it together; an opening of 11.0 A appears, measured diagonally between non-neighboring domains as glutamine 119 carbonyl O-O distance. This is comparable to the opening in the MthK potassium channel structure that is generally agreed to be open. The appearance of the opening is in rather good agreement with that found by Perozo and coworkers. In contrast, in the uncharged structure this diagonal distance is 6.5 A, and the water "basket" constricts the uncharged opening still further, with the ice-like structure that couples the K(+) ion to the gating region freezing the entrance to the channel. Comparison with our earlier model for voltage gated channels suggests that a similar mechanism may apply in those channels. PMID:17336921

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

2007-02-06

392

First-principles calculations of grain boundary theoretical shear strength using transition state finding to determine generalized gamma surface cross sections  

NASA Astrophysics Data System (ADS)

We present a first-principles calculation of the theoretical shear strength of the Al?3(112bar) tilt boundary. Here we replace the usual ? surface (defined by rigid atomic translations parallel to the boundary) by a ``generalized ? surface'' that includes complex cooperative atomic motions occurring at the grain boundary during shear. Transition-state-finding techniques are well suited for calculations of generalized ?-surface cross sections. The transition states, saddles on the ? surface, occur during grain-boundary sliding and at grain-boundary dislocations.

Hamilton, J. C.; Foiles, S. M.

2002-02-01

393

Quantum calculation of vortices in the inner crust of neutron stars  

SciTech Connect

The self-consistent mean-field quantum mechanical solution of a vortex and a nucleus immersed in a sea of free neutrons, a scenario representative of the inner crust of neutron stars, is presented for the first time. Because of quantal size effects the phase space for vortices inside the nucleus is essentially zero, so that the vortex core opens up and surrounds the nucleus. As a consequence, pinned configurations (in which a vortex becomes anchored to the nucleus) are favored at low and high densities in the inner crust. This result is qualitatively different from that obtained in all previous models, which predict pinning at intermediate densities.

Avogadro, P. [Dipartimento di Fisica, Universita degli Studi di Milano, via Celoria 16, I-20133 Milano (Italy); INFN, Sezione di Milano, via Celoria 16, 20133 I-Milano (Italy); Barranco, F. [Departamento de Fisica Aplicada III, Escuela Superior de Ingenieros, Camino de los Descubrimientos s/n, E-41092 Sevilla (Spain); Broglia, R. A. [Dipartimento di Fisica, Universita degli Studi di Milano, via Celoria 16, I-20133 Milano (Italy); INFN, Sezione di Milano, via Celoria 16, 20133 I-Milano (Italy); The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, DK-2100 Copenhagen (Denmark); Vigezzi, E. [INFN, Sezione di Milano, via Celoria 16, 20133 I-Milano (Italy)

2007-01-15

394

Atomistic linear response voltage drop calculations for quantum transport in materials: The high conductance regime  

NASA Astrophysics Data System (ADS)

A linear response method for computing the voltage drop in the high conductance regime is presented. It is applied to the study of both coherent and incoherent transport in model 1D, 2D, and 3D materials, within the non-equilibrium Green's function formalism. The method is shown to accurately reproduce self-consistent voltage drop results computed from first-principles, including the transition from low dimensional screening oscillations to higher dimensional near classical screening. Overall, the method provides an additional analysis technique in the ``quantum transport toolbox'' that is complementary to self-consistent methods (in the high conductance regime).

Bevan, Kirk H.

2013-09-01

395

Theoretical Physics.  

National Technical Information Service (NTIS)

This report contains the papers delivered at the 14th annual seminar on theoretical physics held at Golden Gate. The following topics were discussed: natural quark field confinement; boson expansions; model calculations for three particles outside a close...

1979-01-01

396

Quantum Chemical Calculation of the Character of Structural Organization and H-Bond Energy in the Benzimidazole Fragment of Fibres of the Armos Type  

Microsoft Academic Search

A quantum chemical calculation of the character of the structure in the benzimidazole fragment of aromatic polyamide fibres of the Armos type is performed. It is shown that the fragments form duplicate H bonds with imidazole rings. The experimental and calculated values of the position of the long-wave band maxima in the UV spectra of model benzimidazole compounds are compared.

I. A. Abbronin; V. A. Rakitina; V. A. Gribanov; M. V. Shablygin

2002-01-01

397

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

Microsoft Academic Search

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

T. Hediger; A. Passamante; Mary Eileen Farrell

1990-01-01

398

Leading order calculation of shear viscosity in hot quantum electrodynamics from diagrammatic methods  

NASA Astrophysics Data System (ADS)

We compute the shear viscosity at leading order in hot quantum electrodynamics. Starting from the Kubo relation for shear viscosity, we use diagrammatic methods to write down the appropriate integral equations for bosonic and fermionic effective vertices. We also show how Ward identities can be used to put constraints on these integral equations. One of our main results is an equation relating the kernels of the integral equations with functional derivatives of the full self-energy; it is similar to what is obtained with two-particle-irreducible effective action methods. However, since we use Ward identities as our starting point, gauge invariance is preserved. Using these constraints obtained from Ward identities and also power counting arguments, we select the necessary diagrams that must be resummed at leading order. This includes all noncollinear (corresponding to 2 to 2 scatterings) and collinear (corresponding to 1+N to 2+N collinear scatterings) rungs responsible for the Landau-Pomeranchuk-Migdal effect. We also show the equivalence between our integral equations obtained from quantum field theory and the linearized Boltzmann equations of Arnold, Moore and Yaffe obtained using effective kinetic theory.

Gagnon, Jean-Sébastien; Jeon, Sangyong

2007-11-01

399

A quantum fluid of metallic hydrogen suggested by first-principles calculations  

Microsoft Academic Search

It is generally assumed that solid hydrogen will transform into a metallic alkali-like crystal at sufficiently high pressure. However, some theoretical models have also suggested that compressed hydrogen may form an unusual two-component (protons and electrons) metallic fluid at low temperature, or possibly even a zero-temperature liquid ground state. The existence of these new states of matter is conditional on

Stanimir A. Bonev; Eric Schwegler; Tadashi Ogitsu; Giulia Galli

2004-01-01

400

Unexpected role of 5OH in DPPH radical-scavenging activity of 4-thiaflavans. Revealed by theoretical calculations  

Microsoft Academic Search

The O–H bond dissociation enthalpies (BDEs) of 4-thiaflavans were calculated by a combined density functional theory method (RO)B3LYP\\/6-311+G(2d,2p)\\/\\/AM1\\/AM1. The calculated BDEs not only gave a reasonable explanation on the DPPH radical-scavenging activity difference of 4-thiaflavans, but also revealed the unexpected role of 5-OH in enhancing the antioxidant activity of A-ring.

Lan-Fen Wang; Hong-Yu Zhang

2004-01-01

401

Three-Dimensional Quantum Calculations on the Ground and Excited State Vibrations of Ethylene.  

National Technical Information Service (NTIS)

Three dimensional potential energy surfaces of the ground and excited states of ethylene were calculated at the MRCEPA (Multi Reference Coupled Electronic Pair Approximation) level. The modes included are the torsion, the CC stretch, and the symmetric sci...

G. C. Groenenboom

1991-01-01

402

Quantum wormholes  

SciTech Connect

This paper presents an application of quantum-mechanical principles to a microscopic variant of the traversable wormholes recently introduced by Morris and Thorne. The analysis, based on the surgical grafting of two Reissner-Nordstroem spacetimes, proceeds by using a minisuperspace model to approximate the geometry of these wormholes. The thin shell'' formalism is applied to this minisuperspace model to extract the effective Lagrangian appropriate to this one-degree-of-freedom system. This effective Lagrangian is then quantized and the wave function for the wormhole is explicitly exhibited. A slightly more general class of wormholes---corresponding to the addition of some dust'' to the wormhole throat---is analyzed by recourse to WKB techniques. In all cases discussed in this paper, the expectation value of the wormhole radius is calculated to be of the order of the Planck length. Accordingly, though these quantum wormholes are of considerable theoretical interest they do not appear to be useful as a means for interstellar travel. The results of this paper may also have a bearing on the question of topological fluctuations in quantum gravity. These calculations serve to suggest that topology-changing effects might in fact be {ital suppressed} by quantum-gravity effects.

Visser, M. (Physics Department, Washington University, St. Louis, Missouri 63130-4899 (US))

1991-01-15

403

Theoretical calculations of the reaction cross-sections for proton-induced reactions on natural copper using ALICE-IPPE code.  

PubMed

A theoretical study of the nuclear-reaction cross sections for proton-induced reactions on (63)Cu and (65)Cu was performed in the proton energy range from threshold values up to 50MeV. The produced nuclei were different isotopes of Zn, Cu, Ni, Co and Mn, some of which have important applications. The reaction cross-section calculations were performed using the ALICE-IPPE code, which depends on the pre-equilibrium compound nucleus model. This code is suitable for the studied energy and isotopic mass ranges. Approximately 14 excitation functions for the different reactions have been constructed from the calculated cross-section values. The excitation function curves for the proton reactions with natural copper targets have been constructed from those for enriched targets using the natural abundance of the copper isotopes. Comparisons between the calculated excitation functions with those previously experimentally measured are given whenever the experimental values were available. Some statistical parameters were introduced to control the quality of the fitting between both the experimental and the theoretical calculated cross-section values. PMID:21996672

Alharbi, A A; Azzam, A

2011-10-01

404

Quantum Calculations of Quenching of Vibrationally Excited OH in Collisions With Atomic Oxygen  

NASA Astrophysics Data System (ADS)

Reaction between atomic hydrogen and ozone is an important source of vibrationally excited OH in the mesosphere. Radiative decay of vibrationally excited OH competes with collisional quenching by atomic and molecular oxygen and to a lesser extent by molecular nitrogen. Here we present the first explicit quantum mechanical investigation of quenching of vibrationally excited OH(v=1) by collisions with atomic oxygen. We explore both non-reactive quenching to OH(v=0) and reactive collisions leading to H+O2. It is found that the branching between reactive and non-reactive channels is strongly influenced by long-range dipole-quadrupole forces in the O+OH channel. The computed results are found to be in close agreement with available experimental results. This work was supported by NSF grant ATM-0635715.

Naduvalath, B.; Juanes-Marcos, J.; Quéméner, G.; Kendrick, B. K.

2011-12-01

405

Self-consistent calculation of the electronic structure and electron-electron interaction in self-assembled InAs-GaAs quantum dot structures  

Microsoft Academic Search

We have performed a detailed self-consistent calculation of the electronic structure and electron-electron interaction energy in pyramidal self-assembled InAs-GaAs quantum dot structures. Our model is general for three-dimensional quantum devices without simplifying assumptions on the shape of the confining potential nor fitting parameters. We have used a continuum model for the strain, from which the position-dependent effective mass and band

L. R. C. Fonseca; J. L. Jimenez; J. P. Leburton; Richard M. Martin

1998-01-01

406

Calculation of the bending area of threading dislocations of InGaAs quantum dots on a GaAs substrate  

NASA Astrophysics Data System (ADS)

An equilibrium approach is used to calculate the strain energy of InGaAs/GaAs quantum dots (QDs) before and after the onset of bending of threading dislocation (TD) into interfacial misfit dislocation (MD). The energy balance method is adopted to predict critical conditions for TD bending. We find that the critical bending area in which the inclination of TD is energetically favorable depends strongly on the QD component. The results provide guidelines for the design of quantum dot dislocation filter.

Zhou, Shuai; Liu, Yumin; Wang, Donglin; Yu, Zhongyuan

2013-11-01

407

Quantum Monte Carlo calculation of the equation of state of neutron matter  

NASA Astrophysics Data System (ADS)

We calculated the equation of state of neutron matter at zero temperature by means of the auxiliary field diffusion Monte Carlo (AFDMC) method combined with a fixed-phase approximation. The calculation of the energy was carried out by simulating up to 114 neutrons in a periodic box. Special attention was given to reducing finite-size effects at the energy evaluation by adding to the interaction the effect due to the truncation of the simulation box, and by performing several simulations using different numbers of neutrons. The finite-size effects due to kinetic energy were also checked by employing the twist-averaged boundary conditions. We considered a realistic nuclear Hamiltonian containing modern two- and three-body interactions of the Argonne and Urbana family. The equation of state can be used to compare and calibrate other many-body calculations and to predict properties of neutron stars.

Gandolfi, S.; Illarionov, A. Yu.; Schmidt, K. E.; Pederiva, F.; Fantoni, S.

2009-05-01

408

Alpha-decay quantum-tunnelling calculations based on a folded Woods-Saxon potential  

NASA Astrophysics Data System (ADS)

Assuming that the ? particle is a structureless point particle with two protons and two neutrons, we construct a mean-field-type cluster potential based on the Woods-Saxon potential with a folding factor which is to satisfy the quantization condition of a quasibound cluster state. The folded Woods-Saxon cluster potential has been successfully applied to the calculations of ?-particle decay in light and superheavy nuclei. The standard values of the Woods-Saxon parameters were used without any adjustment. The calculated ?-decay widths or lifetimes agree generally with experiment. Such a cluster potential leads to a consistent description of single-particle and cluster motions.

Xu, F. R.; Wang, S. M.; Lin, Z. J.; Pei, J. C.

2013-04-01

409

EPR Detection of HNO2- in the Radiolysis of Aqueous Nitrite and Quantum Chemical Calculation of Its Stability and Hyperfine Parameters  

SciTech Connect

Experimental and theoretical evidence is presented to support a prior suggestion [Lymar et al. J. Phys. Chem. A 2002, 106, 7245] that radiolytically generated hydrogen atoms attack at the nitrogen, rather than the oxygen, of nitrite ions in aqueous solution. Time-resolved electron spin resonance detection was used to unambiguously identify the HNO2 ?- radicals formed. At pH 9 the radicals live about 10 ?s, and have quite broad (0.6 G) lines. The observed hyperfine splitting at nitrogen was aN 19.6 G, with each of the three nitrogen lines further split by the small hydrogen coupling, aH 4.5 G. The g factor for the radical is 2.0053. Although this is the first observation of this radical in fluid solution, the ESR parameters are consistent with previous observations in the solid phase. The identity of the radical was also confirmed by quantum chemical calculation of the ESR parameters, including the g factor. It was necessary to take into account vibrational modulation of the computed hyperfine parameters when comparing theory to experiment because of the large-amplitude motion of the hydrogen atom in the pyramidal radical. The yield of HNO2 ?- radicals was estimated at 70% of the available H atoms by a kinetic method. Computed thermodynamic parameters confirm that, in the gas phase, both HNO2 ?- and HONO?- are stable relative to the asymptotes H + NO2- and OH- + NO, with HNO2 ?- 40 kJ mol-1 above HONO?- but protected from rearrangement by a large barrier. In solution, calculations indicate that while HNO2 ?- is still bound with respect to dissociation into H + NO2-, it is now only 3.2 kJ mol-1 above HONO?- which, in turn, lies about 73 kJ mol-1 above OH- + NO, and dissociation is driven by the strong solvation of the hydroxide ion.

Hug, Gordon L.; Camaioni, Donald M.; Carmichael, Ian

2004-08-05

410

Measurement and calculation on some quantities of interaction between (gamma)-ray quantum and plant seeds.  

National Technical Information Service (NTIS)

About 165 samples of crop seeds including 60 kinds of plants have been calculated. The weight percentage constituents of structural elements in nine kinds of main crop seeds such as rice, wheat etc., and three kinds of seedless reproductive plant groups h...

Z. Tao M. Xu

1989-01-01

411

Quantum calculation of the QCA response function for non-zero temperatures  

NASA Astrophysics Data System (ADS)

A full second quantization calculation for QCA arrays has been performed in a matrix form for non-zero temperatures. An analytical result for the response function has been obtained. Comparison has been done to the numerical method Intercellular Hartree approxiamtion results.

Sturzu, Ioan; Khatun, Mahfuza

2004-04-01

412

Quantum calculation of the QCA response function for non-zero temperatures  

Microsoft Academic Search

A full second quantization calculation for QCA arrays has been performed in a matrix form for non-zero temperatures. An analytical result for the response function has been obtained. Comparison has been done to the numerical method Intercellular Hartree approxiamtion results.

Ioan Sturzu; Mahfuza Khatun

2004-01-01

413

CONTROL OF LASER RADIATION PARAMETERS: Stabilisation of a laser by the calculated quantum transition frequency  

NASA Astrophysics Data System (ADS)

A method is proposed to stabilise the frequency of a He—Ne laser with an intracavity nonlinear absorption cell by the calculated frequency of the 7?6 transition of F2(2)P(7)?3 in methane. The long-term frequency stability and reproducibility are measured for a He—Ne/CH4 laser with a telescopic cavity.

Bagaev, S. N.; Dmitriev, A. K.; Lugovoy, A. A.

2008-01-01

414

Quantum Monte Carlo calculation of point defect thermal and optical ionization levels: application to magnesium oxide and zinc oxide  

NASA Astrophysics Data System (ADS)

From electronics to optoelectronics to photovoltaics, point defects influence and dominate the properties of semiconducting materials. Quantitative descriptions of the effect of point defects on electronic, optical, and transport properties are critical to enabling point-defect engineering for materials design. However, accurate prediction of point-defect energetics, thermal ionization energies, and optical transition energies from first principles remains a challenge. We present an approach to calculation of point defect optical and thermal ionization energies based on the highly accurate quantum Monte Carlo methods, and demonstrate it for the oxygen vacancy in the binary ionic compound magnesium oxide and the substitutional nitrogen impurity in zinc oxide. The use of quantum Monte Carlo, an inherently many--body theory that directly treats electron correlation, offers many improvements: it can help overcome the band gap problem in density functional theory and obviate the need for ad-hoc corrections. Our computed optical and thermal ionization energies are in excellent agreement with experimental and/or other high-accuracy results.

Ertekin, Elif; Wagner, Lucas; Grossman, Jeffrey

2013-03-01

415

Studies on vibrational, NMR spectra and quantum chemical calculations of N-Succinopyridine: An organic nonlinear optical material  

NASA Astrophysics Data System (ADS)

Single crystals of N-Succinopyridine (NSP) have been grown from water using solution growth method by isothermal solvent evaporation technique. The solid state Fourier Transform Infrared (FTIR) spectrum of the grown crystal shows a broad absorption extending from 3450 down to 400 cm-1, due to H-bond vibrations and other characteristic vibrations. Fourier Transform Raman (FT-Raman) spectrum of NSP single crystal shows Raman intensities ranging from 3100 to 100 cm-1 due the characteristics vibrations of functional groups present in NSP. The proton and carbon positions of NSP have been described by 1H and 13C NMR spectrum respectively. Ab initio quantum chemical calculations on NSP have been performed by density functional theory (DFT) calculations using B3LYP method with 6-311++G(d,p) basis set. The predicted first hyperpolarizability is found to be 1.29 times greater than that of urea and suggests that the title compound could be an attractive material for nonlinear optical applications. The calculated HOMO-LUMO energies show that charge transfers occur within the molecule and other related molecular properties. Molecular properties such as Mulliken population analysis, thermodynamic functions and perturbation theory energy analysis have also been reported. Electrostatic potential map (ESP) of NSP obtained by electron density isosurface provided the information about the size, shape, charge density distribution and site of chemical reactivity of the title molecule. The molecular stability and bond strength have been investigated through the Natural Bond Orbital (NBO) analysis.

Kannan, V.; Thirupugalmani, K.; Brahadeeswaran, S.

2013-10-01

416

Mixed implicit/explicit solvation models in quantum mechanical calculations of binding enthalpy for protein-ligand complexes  

NASA Astrophysics Data System (ADS)

An approach to quantum mechanical investigation of interactions in protein-ligand complexes has been developed that treats the solvation effect in a mixed scheme combining implicit and explicit solvent models. In this approach, the first solvation shell of the solvent around the solute is modeled with a limited number of hydrogen bonded explicit solvent molecules. The influence of the remaining bulk solvent is treated as a surrounding continuum in the conductor-like screening model (COSMO). The enthalpy term of the binding free energy for the protein-ligand complexes was calculated using the semiempirical PM3 method implemented in the MOPAC package, applied to a trimmed model of the protein-ligand complex constructed with special rules. The dependence of the accuracy of binding enthalpy calculations on size of the trimmed model and number of optimized parameters was evaluated. Testing of the approach was performed for 12 complexes of different ligands with trypsin, thrombin, and ribonuclease with experimentally known binding enthalpies. The root-mean-square deviation (RMSD) of the calculated binding enthalpies from experimental data was found as ?1 kcal/mol over a large range.

Nikitina, E.; Sulimov, V.; Grigoriev, F.; Kondakova, O.; Luschekina, S.

417

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

PubMed Central

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

Zeng, Xiancheng; Hu, Hao; Hu, Xiangqian; Yang, Weitao

2009-01-01

418

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

PubMed

A quantum mechanical/molecular mechanical minimum free energy path (QM/MM-MFEP) method was developed to calculate the redox free energies of large systems in solution with greatly enhanced efficiency for conformation sampling. The QM/MM-MFEP method describes the thermodynamics of a system on the potential of mean force surface of the solute degrees of freedom. The molecular dynamics (MD) sampling is only carried out with the QM subsystem fixed. It thus avoids "on-the-fly" QM calculations and thus overcomes the high computational cost in the direct QM/MM MD sampling. In the applications to two metal complexes in aqueous solution, the new QM/MM-MFEP method yielded redox free energies in good agreement with those calculated from the direct QM/MM MD method. Two larger biologically imp