Note: This page contains sample records for the topic quantum theoretical calculations from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

A Compression Algorithm for Quantum Field Theoretic Calculations  

NASA Astrophysics Data System (ADS)

In this study, we present a compression algorithm to solve quantum field eigenvalue problems with dramatically reduced memory requirements. We represent light-cone quantized basis states as 2D matrices, in which one index stands for longitudinal momenta and the other represents transverse momenta. These matrices are stored as singular value decompositions, compressed to retain only the nsvd largest contributions. Basic Lanczos iterations are applied to obtain eigenvalues. At each Lanczos iteration, each sector of the Lanczos vector is projected into nsvd longitudinal and transverse vectors using singular value decomposition. The converged smallest real eigenvalues are obtained by these Lanczos iterations. The convergence of the ground state with respect to nsvd is then studied. It shows that our compression algorithm reduces memory cost significantly with little sacrifice in the accuracy of calculations.

Pu, Xiao

2

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

3

Unusual approach to 3-aryl-2-aminopyridines through a radical mechanism: synthesis and theoretical rationale from quantum mechanical calculations.  

PubMed

Tris(trimethylsilyl)silane and azobis(cyclohexanenitrile) promoted the easy intramolecular arylation of aryl bromopyridine carbamates through a radical [1,6] ipso substitution process. These substrates showed a preference for this type of reaction over the alternative [1,7] addition. The results were rationalized by making use of quantum mechanical calculations and computer graphics. PMID:21265527

Camacho-Artacho, Marta; Abet, Valentina; Frutos, Luis M; Gago, Federico; Alvarez-Builla, Julio; Burgos, Carolina

2011-03-01

4

Tools of Theoretical Quantum Optics.  

National Technical Information Service (NTIS)

In the last several years three different theoretical techniques have been used extensively in quantum optical problems, to wit, density matrix, Green's function, and quantum noise operator techniques. However, while many workers use one or the other of t...

K. G. Whitney M. O. Scully

1972-01-01

5

Theoretical analysis of quantum dot infrared photodetectors  

Microsoft Academic Search

Quantum dot infrared photodetectors (QDIPs) have many advantages compared with other types of semiconductor-based photodetectors. Therefore, it is important to evaluate their characteristics theoretically. In this paper our aim is to develop a simple algorithm for this interesting type of photodetector. This algorithm describes a non-trivial evaluation of the most important characteristics. It is used to calculate the dark current,

Mohamed B. El Mashade; M. Ashry; A. Nasr

2003-01-01

6

The assignment of quantum numbers in the theoretical spectra of the H 2 16 O, H 2 17 O, and H 2 18 O molecules calculated by variational methods in the region 0–26000 cm ?1  

Microsoft Academic Search

Quantum numbers have been assigned in the theoretical spectra of three isotopologues of the water molecule: H2\\u000a 16O, H2\\u000a 17O, and H2\\u000a 18O. The spectra were calculated by variational methods in the region 0–26000 cm?1 at a temperature of 296 K. For each molecule, the quantum numbers are assigned to more than 28000 levels. The quantum numbers\\u000a are assigned to

N. F. Zobov; R. I. Ovsyannikov; S. V. Shirin; O. L. Polyansky

2007-01-01

7

Accurate quantum chemical calculations  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

8

Quantum Mechanics and physical calculations  

NASA Astrophysics Data System (ADS)

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

Karayan, H. S.

2014-03-01

9

Quantum Information Theoretical Analysis of Quantum Secret Sharing  

NASA Astrophysics Data System (ADS)

Quantum secret sharing (QSS) schemes are analyzed from an information theoretical perspective centered on the Araki—Lieb inequality. Based on this inequality, mathematical characterizations of QSS schemes and quantum error-correcting codes (QECCs) are given. Furthermore, we present a proof of the relation between QSS schemes and QECCs. This information theoretic description of QSS schemes is used to derive the quantum Singleton bound.

Xiao, He-Ling; Guo, Wang-Mei; Wang, Xiao

2012-11-01

10

Theoretical calculations of silylation reaction of photoresists  

NASA Astrophysics Data System (ADS)

Molecular orbital calculations to predict the activation energy of silylation are performed. The activation energy for polyvinylphenol is predicted to be 19.6 kcal/mol at the MP-2 (the second-order Moller-Plesset perturbation theory) level, and this value is in good agreement with an experimental value of 19.4 kcal/mol. Theoretical values calculated from the Hartree-Fock and nonlocal density functional theories are found to be larger than the experimental value by about 15 kcal/mol and 5 kcal/mol, respectively. Thus, the MP-2 level of calculation is required for a quantitative prediction of the activation energy of silylation. Comparison between the theoretical and experimental values further showed that the rate-determining step of the silylation is the diffusion when pure polyvinylphenol is silylated, whereas it is the reaction when additives are mixed to polyvinylphenol. This result shows that the theoretical calculations become a tool for clarifying the kinetics of silylation, and can be used for designing new materials. The activation energy of silylation for carboxylic acid and alcohol is also predicted, and experiments to silylate polyvinylalcohol are performed. It is shown that the alcohol unit can be silylated with a higher activation energy than that for polyvinylphenol, whereas for carboxylic acid, significant desilylation may occur after the silylation.

Matsuzawa, Nobuyoki N.; Mori, Shigeyasu; Morisawa, Taku; Kaimoto, Yuko; Endo, Masayuki; Ohfuji, Takeshi; Kuhara, Koichi; Sasago, Masaru

1998-06-01

11

Theoretical Calculations of Atomic Data for Spectroscopy  

NASA Technical Reports Server (NTRS)

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

Bautista, Manuel A.

2000-01-01

12

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

13

Getting a theoretical handle on fullerene ions: Quantum chemical calculations on the reactions of C60+, C602+ and C603+ with ammonia  

NASA Astrophysics Data System (ADS)

Hybrid density functional theory calculations at the B3-LYP/6-31G** level of theory are used to explore the interactions between singly, doubly, and triply charged fullerene cations and ammonia. The calculations illuminate (and generally support) several aspects of the previously-reported experimental results for these systems. Primary adduct formation is exothermic but is hindered by an energetically costly localized distortion of the fullerene cage at the site of addition, as the `chosen' carbon atom shifts from strained sp2 to sp3 coordination. The 50-75 kJ mol-1 `deformation energy' is substantially larger than the residual strength of the bond between C60+ and NH3. Although the deformation energy rises with increasing fullerene ion charge state, it does so less steeply than does the electrostatic attraction between C60n+ and NH3, so that the overall bond strength to NH3 is progressively and substantially larger for the di- and tricationic adduct ions. For all charge states, a proton-bound structure is found to be the energetically preferred secondary adduct, but for dicationic and tricationic adducts formation of a secondary adduct is significantly less exothermic than proton transfer. It appears that the failure of C60+ to add measurably to nucleophiles weaker than NH3 arises because such nucleophiles are not able to overcome the required deformation energy to effect bond formation. We find also that, in contrast to a simple electrostatically-driven model of `handle' formation (in which it was proposed that the most strongly bound doubly-derivatized fullerene dications would be those for which the `handles' were most widely separated across the fullerene framework) the lowest-energy double-handled adducts are in fact those for which the remaining resonance stabilization is greatest, with electrostatic considerations apparently taking a back seat on the question of relative stability. Similar considerations appear to apply to the double-handled tricationic adducts.

Petrie, Simon

2006-09-01

14

Theoretical stability analysis of quantum dash distributed Bragg reflector lasers  

NASA Astrophysics Data System (ADS)

A detailed theoretical analysis of stability in a quantum dash distributed Bragg reflector (DBR) laser is presented under the small-signal condition. The influence of p-type doping and inhomogeneous line broadening on the hysteresis width of the quantum dash DBR laser is studied using a rate equation model that includes all of the multidiscrete energy levels in the valence and conduction bands. Our calculations show that a large hysteresis width is obtained by detuning the laser by ~10 meV above the ground state energy and doping the dashes by acceptor concentration NA=3.7×1017 cm-3. Also we find that a large self-pulsation frequency is obtained by detuning the laser by -15 meV from the ground state energy and doping the dashes by NA=2.5×1017 cm-3. The laser hysteresis width can be greatly reduced by doping the dashes with NA>1×1018 cm-3.

Qasaimeh, Omar; Qasaimeh, Hadeel

2009-12-01

15

A quantum theoretical study of polyimides  

NASA Technical Reports Server (NTRS)

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

Burke, Luke A.

1987-01-01

16

Theoretical Calculation of Actinide Nuclear Reaction Data  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

17

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

18

EXPERIMENTAL AND THEORETICAL ASPECTS OF QUANTUM TELEPORTATION  

Microsoft Academic Search

We present a short summary of progress achieved at the Center for Engineering Science Advanced Research (CESAR) of the Oak Ridge National Laboratory (ORNL) in the recently initiated Quantum Teleportation project. The primary objective of this effort is to study the signaling potential of quantum information processing systems based on quantum entanglement. Our initial effort has focused on the development

Lei Zhang; Jacob Barhen; Hua-Kuang Liu

19

Energy levels and quantum states of [Leu]enkephalin conformations based on theoretical and experimental investigations  

NASA Astrophysics Data System (ADS)

This paper describes a theoretical and experimental study of [Leu]enkephalin conformations with respect to the quantum states of the atomic structure of the peptide. Results from vibrational absorption measurements and quantum calculations are used to outline a quantum picture and to assign vibrational modes to the different conformations. The energy landscape of the conformations is reported as a function of a Hamming distance in Ramachandran space. Molecular dynamics simulations reveal a pronounced stability of the so-called single-bend low-energy conformation, which supports the derived quantum picture of this peptide.

Abdali, Salim; Jensen, Morten Ø.; Bohr, Henrik

2003-05-01

20

Quantum Monte Carlo calculations of light nuclei.  

SciTech Connect

Quantum Monte Carlo calculations using realistic two- and three-nucleon interactions are presented for nuclei with up to eight nucleons. We have computed the ground and a few excited states of all such nuclei with Greens function Monte Carlo (GFMC) and all of the experimentally known excited states using variational Monte Carlo (VMC). The GFMC calculations show that for a given Hamiltonian, the VMC calculations of excitation spectra are reliable, but the VMC ground-state energies are significantly above the exact values. We find that the Hamiltonian we are using (which was developed based on {sup 3}H, {sup 4}He, and nuclear matter calculations) underpredicts the binding energy of p-shell nuclei. However our results for excitation spectra are very good and one can see both shell-model and collective spectra resulting from fundamental many-nucleon calculations. Possible improvements in the three-nucleon potential are also be discussed.

Pieper, S. C.

1998-08-25

21

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

22

A theoretical model of multi-agent quantum computing  

NASA Astrophysics Data System (ADS)

The best design for practical quantum computing is one that emulates the multi-agent quantum logic function of natural biological systems. Such systems are theorized to be based upon a quantum gate formed by a nucleic acid Szilard engine (NASE) that converts Shannon entropy of encountered molecules into useful work of nucleic acid geometric reconfiguration. This theoretical mechanism is logically and thermodynamically reversible in this special case because it is literally constructed out of the (nucleic acid) information necessary for its function, thereby allowing the nucleic acid Szilard engine to function reversibly because, since the information by which it functions exists on both sides of the theoretical mechanism simultaneously, there would be no build-up of information within the theoretical mechanism, and therefore no irreversible thermodynamic energy cost would be necessary to erase information inside the mechanism. This symmetry breaking Szilard engine function is associated with emission and/or absorption of entangled photons that can provide quantum synchronization of other nucleic acid segments within and between cells. In this manner nucleic acids can be considered as a natural model of topological quantum computing in which the nonabelian interaction of genes can be represented within quantum knot/braid theory as anyon crosses determined by entropic loss or gain that leads to changes in nucleic acid covalent bond angles. This naturally occurring biological form of topological quantum computing can serve as a model for workable man-made multi-agent quantum computing systems.

Mihelic, F. Matthew

2011-05-01

23

Experimental observation and theoretical calculation of the diamagnetic spectrum of sodium Rydberg states  

NASA Astrophysics Data System (ADS)

We report diamagnetic spectra of sodium atoms observed in a strong magnetic field up to 3 T and compare them with theoretical calculations based on the formulation of an exact quantum-defect theory. We focus on one-photon absorption processes from the ground 3s state to the excited np Rydberg states whose magnetic quantum numbers are determined by the polarization of the laser field. The calculations employ B-spline basis expansion and the complex spatial coordinate rotation technique, and their results agree well with the observed ones when atomic core effects are appropriately taken into account. When graphed against magnetic field, level anticrossings and core-induced interaction of the np states provide clear signatures for studying the effects of quantum defect on the diamagnetic spectra.

Gao, W.; Yang, H. F.; Cheng, H.; Liu, X. J.; Liu, H. P.

2012-07-01

24

Acetylation of rhamnogalacturonan I and homogalacturonan: Theoretical calculations  

Microsoft Academic Search

The possible confirmation of experimental data through theoretical calculations on the exact position of acetyl groups at the galacturonic acid residues in pectin backbones was investigated. With MM3(92) it was calculated that acetyl groups at both O2 and O3 of galacturonic acid in the backbone of rhamnogalacturonan I (RG-I) and homogalacturonan are energetically favourable, where the most important contribution comes

Milou Kouwijzer; Henk Schols; Serge Pérez

1996-01-01

25

Quantum Monte Carlo calculations on positronium compounds  

NASA Astrophysics Data System (ADS)

The stability of compounds containing one or more positrons in addition to electrons and nuclei has been the focus of extensive scientific investigations. Interest in these compounds stems from the important role they play in the process of positron annihilation, which has become a useful technique in material science studies. Knowledge of these compounds comes mostly from calculations which are presently less difficult than laboratory experiments. Owing to the small binding energies of these compounds, quantum chemistry methods beyond the molecular orbital approximation must be used. Among them, the quantum Monte Carlo (QMC) method is most appealing because it is easy to implement, gives exact results within the fixed nodes approximation, and makes good use of existing approximate wavefunctions. Applying QMC to small systems like PsH for binding energy calculation is straightforward. To apply it to systems with heavier atoms, to systems for which the center-of-mass motion needs to be separated, and to calculate annihilation rates, special techniques must be developed. In this project a detailed study and several advancements to the QMC method are carried out. Positronium compounds PsH, Ps2, PsO, and Ps2O are studied with algorithms we developed. Results for PsH and Ps2 agree with the best accepted to date. Results for PsO confirm the stability of this compound, and are in fair agreement with an earlier calculation. Results for Ps2O establish the stability of this compound and give an approximate annihilation rate for the first time. Discussions will include an introduction to QMC methods, an in-depth discussion on the QMC formalism, presentation of new algorithms developed in this study, and procedures and results of QMC calculations on the above mentioned positronium compounds.

Jiang, Nan

26

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

27

A Universal Operator Theoretic Framework for Quantum Fault Tolerance  

NASA Astrophysics Data System (ADS)

We extend standard fault tolerance theory and Kitaev's model for quantum computation so as to enable quantitative determination of design parameters for quantum computers that ensure that the overall computation yields a correct final result with some prescribed probability, as opposed to merely ensuring that the desired final quantum state is obtained. Our extension allows us to explicitly calculate the number of levels of error correction concatenation needed to achieve a correct final result with some prescribed success probability and demonstrate a clear connection between error correction and fault tolerance.

Gilbert, Gerald; Weinstein, Yaakov S.

2009-04-01

28

Theoretical calculation of bending stiffness of alveolar wall.  

PubMed

The bending stiffness of the alveolar wall is theoretically analyzed in this study through analytical modeling. First, the alveolar wall facet and its characteristics were geometrically simplified and then modeled using known physical laws. Bending stiffness is shown to be dependent on alveolar wall thickness, density, Poisson's ratio and speed of the longitudinal wave. The normal bending stiffness of the alveolar wall was further determined. For the adult human, the normal bending stiffness is calculated to be 71.0-414.7 nNm, while for the adult mouse it is 1.9-30.0 nNm. The results of this study can be used as a reference for future pulmonary emphysema and fibrosis studies, as the bending stiffness of alveolar wall will be lower and higher, respectively; than the theoretically determined normal values. PMID:24121628

Jabaraj, D John; Jaafar, Mohamad Suhaimi

2013-12-01

29

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

30

Spectrometric studies and theoretical calculations of some beta-ketonitriles.  

PubMed

The tautomerism of some beta-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 beta-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. PMID:20630795

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

2010-10-01

31

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

32

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

NASA Astrophysics Data System (ADS)

Theoretical computations have been carried out on 4-silaspiro(3,3)heptane (SSH) in order to calculate its molecular structure and conformational energies. The molecule has two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. Energy calculations were carried out for different conformations of SSH. These results allowed the generation of a two-dimensional ring-puckering potential energy surface (PES) of the form V = a(x14 + x24) - b(x12 + x22) + cx12x22, where x1 and x2 are the ring-puckering coordinates for the two rings. The presence of sufficiently high potential energy barriers prevents the molecule from undergoing pseudorotation. The quantum states, wave functions, and predicted spectra resulting from the PESs were calculated.

Ocola, Esther J.; Medders, Cross; Meinander, Niklas; Laane, Jaan

2014-04-01

33

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

PubMed

Theoretical computations have been carried out on 4-silaspiro(3,3)heptane (SSH) in order to calculate its molecular structure and conformational energies. The molecule has two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. Energy calculations were carried out for different conformations of SSH. These results allowed the generation of a two-dimensional ring-puckering potential energy surface (PES) of the form V = a(x1 (4) + x2 (4)) - b(x1 (2) + x2 (2)) + cx1 (2)x2 (2), where x1 and x2 are the ring-puckering coordinates for the two rings. The presence of sufficiently high potential energy barriers prevents the molecule from undergoing pseudorotation. The quantum states, wave functions, and predicted spectra resulting from the PESs were calculated. PMID:24784278

Ocola, Esther J; Medders, Cross; Meinander, Niklas; Laane, Jaan

2014-04-28

34

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

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

Maxwell's demon. (II) A quantum-theoretic exorcism  

NASA Astrophysics Data System (ADS)

In Part II of this two-part paper we prove that Maxwell's demon is unable to accomplish his task of sorting air molecules into swift and slow because in air in a thermodynamic equilibrium state there are no such molecules. The proof is based on the principles of a unified quantum theory of mechanics and thermodynamics. The key idea of the unified theory is that von Neumann's concept of a homogeneous ensemble of identical systems, identically prepared, is valid not only for a density operator ? equal to a projector (every member of the ensemble is assigned the same projector, ?i=| ?i> < ?i|= ?i2, or the same wave function ? i as any other member) but also for a density operator that is not a projector (every member of the ensemble is assigned the same density operator, ?>? 2, as any other member). So, the latter ensemble is not a statistical mixture of projectors. The broadening of the validity of the homogeneous ensemble is consistent with the quantum-theoretic postulates about observables, measurement results, and value of any observable. In the context of the unified theory, among the many novel results is the theorem that each molecule of a system in a thermodynamic equilibrium state has zero value of momentum, that is, each molecule is at a standstill and, therefore, there are no molecules to be sorted as swift and slow. Said differently, if Maxwell were cognizant of quantum theory, he would not have conceived of the idea of the demon. It is noteworthy that the zero value of momentum is not the result of averaging over different momenta of many molecules. Under the specified conditions, it is the quantum-theoretic value of the momentum of any one molecule, and the same result is valid even if the system consists of only one molecule.

Gyftopoulos, Elias P.

2002-05-01

37

Theoretical analysis of quantum ghost imaging through turbulence  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

38

Theoretical characteristics of quantum dot laser through modeling  

Microsoft Academic Search

Gain characteristics of injection lasers based on self-organized quantum dots (QD) were studied for two systems: InGaAs QDs in AlGaAs matrix on GaAs substrate and InAs QDs in an InGaAs matrix on an InP substrate. A ground to excited state transition was observed with increasing threshold gain. The current density of the model gain was calculated for the QD-on-GaAs and

I. I. Mahmoud

2008-01-01

39

Anomalous thermal conduction in one dimension: a quantum calculation.  

PubMed

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

Santhosh, G; Kumar, Deepak

2007-08-01

40

Quantum robots and quantum computers.  

National Technical Information Service (NTIS)

Validation of a presumably universal theory, such as quantum mechanics, requires a quantum mechanical description of systems that carry out theoretical calculations and systems that carry out experiments. The description of quantum computers is under acti...

P. Benioff

1998-01-01

41

Macroscopic quantum-type potentials in theoretical systems biology.  

PubMed

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

Nottale, Laurent

2013-01-01

42

Macroscopic Quantum-Type Potentials in Theoretical Systems Biology  

PubMed Central

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

Nottale, Laurent

2014-01-01

43

Infrared and theoretical calculations in 2-halocycloheptanones conformational analysis  

NASA Astrophysics Data System (ADS)

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

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

44

Infrared and theoretical calculations in 2-halocycloheptanones conformational analysis.  

PubMed

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

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

2012-08-01

45

Accurate rotational barrier calculations with diffusion quantum Monte Carlo  

NASA Astrophysics Data System (ADS)

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

Klahm, Sebastian; Lüchow, Arne

46

QUANTUM CHEMICAL CALCULATIONS IN INDUSTRIAL LIQUID CRYSTAL RESEARCH  

Microsoft Academic Search

In advance to syntheses in the laboratory, it is very useful, to have quick and easy procedures available, allowing the calculation of physical properties of liquid crystal materials without any experimental basis. Using different quantum chemical methods, it is possible to calculate molecular data like electrical dipole moment and polarizability including the anisotropy of these data. By comparison of the

Dietrich Demus; Takashi Inukai

2003-01-01

47

Multiphase Equation of State and Strength Properties of Beryllium from AB INITIO and Quantum Molecular Dynamics Calculations  

Microsoft Academic Search

In the framework of density functional theory, static properties and phonon spectra of beryllium have been calculated under high compression (for pressures up to 4 Mbar) for two solid phases: hexagonal compact (hcp) and body-centered cubic (bcc). The melting curve and some isotherms in the liquid phase have been calculated using quantum molecular dynamics. The coupling of these theoretical data

G. Robert; A. Sollier; Ph. Legrand

2007-01-01

48

Multiphase equation of state and strength properties of beryllium from ab initio and quantum molecular dynamics calculations  

Microsoft Academic Search

In the framework of density functional theory, static properties and phonons spectra of beryllium have been calculated under high compression (for pressures up to four Mbar) for two solids phases : hexagonal compact (hcp) and body-centred cubic (bcc). The melting curve and some isotherms in the liquid phase are calculated using quantum molecular dynamic. The coupling of these theoretical data

Gregory Robert; Arnaud Sollier

2007-01-01

49

Quantum Monte Carlo calculations on positronium compounds  

Microsoft Academic Search

The stability of compounds containing one or more positrons in addition to electrons and nuclei has been the focus of extensive scientific investigations. Interest in these compounds stems from the important role they play in the process of positron annihilation, which has become a useful technique in material science studies. Knowledge of these compounds comes mostly from calculations which are

Nan Jiang

1999-01-01

50

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

51

Calculation of the external quantum efficiency of light emitting diodes with different chip designs  

Microsoft Academic Search

External quantum efficiency of GaN light emitting diode (LED) with SiO2-coated grating patterned substrate and\\/or surface-textured structure were calculated theoretically. Our results show that the enhancement of the reflectance coefficient was obtained by a factor of about 30% in LED chip with SiO2-coated grating patterned substrate, compared to conventional LED chip. The grating parameters such as height and width should

T. V. Cuong; H. S. Cheong; C.-H. Hong

2004-01-01

52

Advanced Quantum Mechanical Calculation of the Beta Decay Probabilities  

SciTech Connect

Advanced theoretical schemes for calculating atomic chemical environment effect on the {beta} decay characteristics are developed. As method of calculation of the relativistic atomic fields and electron wave functions, the gauge invariant Dirac-Fock type and Dirac-Kohn-Sham approaches are used. The numerical results for atomic chemical environment effect on the {beta} decay of the sulfur and plutonium are presented.

Malinovskaya, Svetlana V.; Dubrovskaya, Yu.V.; Vitavetskaya, L.A. [Dept.Quantum Optics and Nucl.Physics, Odessa University, P.O.Box 24a, Odessa-9, 65009 (Ukraine)

2005-10-26

53

Theoretical Quantum-Information Properties of Nuclei and Trapped Bose Gases  

NASA Astrophysics Data System (ADS)

We will study fermionic systems like atomic nuclei and bosonic systems like the correlated atoms in a trap from an information-theoretical point of view. The Shannon and Onicescu information measures are calculated for the above systems by comparing the correlated and uncorrelated cases as functions of the strength of the short range correlations. One-body and two-body density and momentum distributions are employed. Thus, the effect of short-range correlations on the information content is evaluated. The magnitude of distinguishability between the correlated and uncorrelated densities is also discussed employing suitable measures for the distance of states i.e. the well known Kullback-Leibler relative entropy and the recently proposed Jensen-Shannon divergence entropy. We will see that the same information-theoretical properties hold for quantum many-body systems obeying Bose-Einstein and Fermi-Dirac (statistics).

Moustakidis, Ch. C.; Chatzisavvas, K. Ch.; Panos, C. P.

54

Quantum Theoretical Study of Palladium and Silver Clusters  

NASA Astrophysics Data System (ADS)

We continue our interest on the chemisorption of different atomic and molecular species on small clusters of metallic elements, by examining the interactions of H, O and F atoms with Pdn and Agn clusters (n = 2 thru 12). Transition-metal clusters can be useful for the study of quantum size effects and for formation of metallic states, and are ideal candidates for catalytic processes. Hybrid ab initio methods of quantum chemistry (particularly the DFT-B3LYP model) are used to derive optimal geometries for the clusters of interest. We compare calculated binding energies, bond-lengths, ionization potentials, electron affinities and HOMO-LUMO gaps for the clusters of the two different metals. Of particular interest are the comparisons of binding strengths at the three important types of sites: edge (E) sites, hollow sites (H) site and on-top (T) sites. Effects of crystal symmetries corresponding to the bulk structures for the two metals will also be investigated. The implications for the molecular dissociation of the H2 and O2 species will be considered.

Hira, Ajit; Salazar, Justin; Pacheco, Jose

2013-03-01

55

Theoretical Study of the Quantum Conductance of Carbon Nanotube Structures  

NASA Astrophysics Data System (ADS)

We present a first-principles study of the quantum conductance of various carbon nanotube structures. First, the structural deformation and electrical conductance of crossed carbon nanotube junctions are studied. The structures are determined by constrained minimization of total energy, and the linear-response conductance is calculated using the Landauer-Büttiker formula. We show that the reason one sees a sizable intertube conductance is because of the structural deformation resulting from a contact force at the junction. In addition, the intertube conductance is very sensitive to external applied force, and hence the crossed junctions are potentially useful as nanoscale electro-mechanical devices. Second, the electronic structure and quantum conductance of nano-peapods, single walled carbon nanotubes with C_60 buckyballs in the interior, are studied. The energetics of buckyball motion is clarified within an ab initio pseudopotential density functional approach with a linear combination of atomic orbitals. Hybridization of C_60 states and nanotube states in the presence of potassium dopants leads to molecular level shifts until the C_60 LUMO level is pinned at the Fermi level. Consequently, resonant scattering together with controlled dopant concentration may produce interesting I-V characteristics. Third, we present tight-binding calculations on the effects of disorder on the conductance of the carbon nanotubes. Backscattering by long-range disorder is suppressed in metallic (n,n) tubes, but not in doped or gated semiconducting tubes. These results explain the distinctly different mean free paths of different kind of nanotubes as observed in Coulomb blockade measurements. The carbon nanotubes in various structures thus show unique and interesting electronic and transport properties, leading to new physical phenomena and making potential use in device application very promising.

Yoon, Young-Gui

2001-03-01

56

Automated quantum conductance calculations using maximally-localised Wannier functions  

Microsoft Academic Search

A robust, user-friendly, and automated method to determine quantum conductance in quasi-one-dimensional systems is presented. The scheme relies upon an initial density-functional theory calculation in a specific geometry after which the ground-state eigenfunctions are transformed to a maximally-localised Wannier function (MLWF) basis. In this basis, our novel algorithms manipulate and partition the Hamiltonian for the calculation of coherent electronic transport

Matthew Shelley; Nicolas Poilvert; Arash A. Mostofi; Nicola Marzari

2011-01-01

57

Simulation of Quantum-Mechanical Measurements with Programmable Pocket Calculators.  

ERIC Educational Resources Information Center

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

Sauer, G.

1979-01-01

58

Quantum Monte Carlo calculation of entanglement Rényi entropies for generic quantum systems  

NASA Astrophysics Data System (ADS)

We present a general scheme for the calculation of the Rényi entropy of a subsystem in quantum many-body models that can be efficiently simulated via quantum Monte Carlo. When the simulation is performed at very low temperature, the above approach delivers the entanglement Rényi entropy of the subsystem, and it allows us to explore the crossover to the thermal Rényi entropy as the temperature is increased. We implement this scheme explicitly within the stochastic series expansion as well as within path-integral Monte Carlo, and apply it to quantum spin and quantum rotor models. In the case of quantum spins, we show that relevant models in two dimensions with reduced symmetry (XX model or hard-core bosons, transverse-field Ising model at the quantum critical point) exhibit an area law for the scaling of the entanglement entropy.

Humeniuk, Stephan; Roscilde, Tommaso

2012-12-01

59

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

NASA Astrophysics Data System (ADS)

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

Sasanpour, Pezhman; Mohammadpour, Raheleh

2014-05-01

60

Potential theoretic methods for far field sound radiation calculations  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

61

Transmission resonance Raman spectroscopy: experimental results versus theoretical model calculations.  

PubMed

A laser spectroscopic technique is described that combines transmission and resonance-enhanced Raman inelastic scattering together with low laser power (< 30 mW) and good spatial resolution (< 200 ?m) as operational features. The monitoring of the transmitted inelastic scattering provides an increased signal-to-noise ratio because the low fluorescence background and, on the other hand, the resonant character of the laser excitation, leads to enhanced analytical sensitivity. The spectroscopic technique was applied to investigate the carotenoid content (specifically the ?-carotene concentration) of distinct samples that included fruits, reaching a detection limit of the order of hundreds of picograms in solid samples, which is below the level needed for typical food control analysis. Additional features of the present development are direct sampling, noninvasive character, and fast analysis that is not time consuming. From a theoretical point of view, a model for the Raman signal dependence on the sample thickness is also presented. Essentially, the model considers the sample to be homogeneous and describes the underlying physics using only three parameters: the Raman cross-section, the laser-radiation attenuation cross-section, and the Raman signal attenuation cross-section. The model was applied successfully to describe the sample-size dependence of the Raman signal in both ?-carotene standards and carrot roots. The present technique could be useful for direct, fast, and nondestructive investigations in food quality control and analytical or physiological studies of animal and human tissues. PMID:23031699

Gonzálvez, Alicia G; González Ureña, Ángel

2012-10-01

62

Theoretical study of auger recombination processes in deep quantum wells  

SciTech Connect

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

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

2008-05-15

63

Theoretical calculation of spectra of dibutyl phthalate and dioctyl phthalate  

NASA Astrophysics Data System (ADS)

Dibutyl phthalate DBP and dioctyl phthalate DOP are the main components of the plasticizers. In order to investigate their molecular structure, chemical bond and spectrum, the geometrical parameters of the ground state and infrared (IR) spectrum are calculated using the density functional theory B3LYP method at the level of 6-311++G( d, p). On this basis, the first twenty-six excited states and the UV-Vis absorption spectra of DBP and DOP are studied using the time-dependent density functional theory (TDDFT) in the same fundamental group and compared with the ultraviolet absorption peak of the molecules measured with UNICO UV-Vis spectrophotometer. The two kinds of molecular spectra are then classified and compared with that in reference. The results show that the strong absorption of IR spectra of DOP and DBP are produced by C-H bending in-plane vibration and C=O telescopic vibration producing. The most absorption of UV-Vis absorption spectra appears in the end absorption belt from n to ?* transition, and the stronger absorption in the E belt of benzene electronic transition from ? to ?*. There are blue shift for DOP end absorption belt from n to ?* transition and red shift for DOP E absorption belt from ? to ?* transition relative to that of DBP. This calculation results are better in accord with the spectral data measured by UNICO ultraviolet and visible spectrophotometer.

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

2014-05-01

64

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

65

Quantum efficiency of the MCP detector: Monte Carlo calculation  

Microsoft Academic Search

A prototype scanning-slit X-ray imaging system with microchannel plate (MCP) detector has recently been developed and tested for potential applications in medical imaging. For this purpose, the quantum efficiency of the MCP needs to be calculated and verified experimentally for polychromatic X-ray beams. X-ray detection in the MCP is a cascade of several processes including the absorption of the photon

Polad M. Shikhaliev; Justin L. Ducote; Tong Xu; Sabee Molloi

2005-01-01

66

Four coordinate tin complexes: synthesis, characterization, thermodynamic and theoretical calculations.  

PubMed

In this work, two new Sn(IV) complexes, [SnL(x)]Cl2 where (L(x))(2-) is the deprotonated form of 5-A-salabza-H2=N,N'-bis(salicylidene)-2-aminobenzylamine and A=5-OMe, 5-H, 5-NO2, 5-Br, were synthesized and fully characterized by UV-Vis, FT-IR, (1)H NMR, (13)C NMR, (119)Sn NMR spectroscopies, mass spectrometry and elemental analysis. The thermodynamic formation constants of the complexes were determined spectrophotometrically at 25 °C in acetonitrile. The trend of formation constants of the complexes are as: 5-OMe>5-H>5-NO2>5-Br and Ph2SnCl2>Me2SnCl2>n-Bu2SnCl2. DFT/B3LYP molecular orbital calculations were carried out for the 5-H substituent isomer, [SnL(2)](2+), in an attempt to explain the structure of complexes. The optimized resulting geometries, vibrational frequencies and the NMR resonances of the complexes are discussed. PMID:23988534

Mohammadikish, Maryam

2014-01-01

67

Quantum calculations of Coulomb reorientation for sub-barrier fusion.  

PubMed

Classical mechanics and time dependent Hartree-Fock (TDHF) calculations of heavy ions collisions are performed to study the rotation of a deformed nucleus in the Coulomb field of its partner. This reorientation is shown to be independent of the charges and relative energy of the partners. It only depends upon the deformations and inertias. TDHF calculations predict an increase by 30% of the induced rotation due to quantum effects while the nuclear contribution seems negligible. This reorientation modifies strongly the fusion cross section around the barrier for light deformed nuclei on heavy collision partners. For such nuclei a hindrance of the sub-barrier fusion is predicted. PMID:15447400

Simenel, C; Chomaz, Ph; de France, G

2004-09-01

68

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

69

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

70

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

71

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

PubMed

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

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

2014-08-14

72

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

73

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

NASA Astrophysics Data System (ADS)

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

Fiedler, Gregor; Kratzer, Peter

2013-12-01

74

Theoretical study of spin relaxation in a carbon nanotube quantum dot  

NASA Astrophysics Data System (ADS)

Carbon nanotubes offer an attractive environment for coherent spin manipulation due to the small population of nuclear spins and weak spin-orbit interaction. While a couple of specific spin relaxation mechanisms have been investigated theoretically[1][2], there is still no comprehensive study of spin lifetimes in carbon nanotubes. In the present study we calculate the spin decay rate for electrons in gate-defined quantum dots on carbon nanotubes due to the spin-orbit and electron-phonon interactions. More specifically, we explore effects of magnetic field strength and orientation, tube diameter and chirality, and confinement. [1] Y. G. Semenov, K. W. Kim, G. J. Iafrate, Phys. Rev. B 75, 045429 (2007) [2] K. M. Borysenko, Y. G. Semenov, K. W. Kim, J. M. Zavada, arXiv 0710.3382 (2007)

Bezanson, Brian; Hu, Xuedong

2008-03-01

75

Theoretical modeling of dark current in quantum dot infrared photodetectors using nonequilibrium Green's functions  

Microsoft Academic Search

A theoretical model describing electron dynamics in quantum dot (QD) infrared photodetectors (QDIPs) is presented. The model is based on the nonequilibrium Green's functions formalism which provides a general framework to study electron transport in a nonequilibrium quantum system and in the presence of interactions. A self-consistent solution of the charge density and the average potential energy through the device

M. A. Naser; M. J. Deen; D. A. Thompson

2008-01-01

76

Theoretical modeling of dark current in quantum dot infrared photodetectors using nonequilibrium Green’s functions  

Microsoft Academic Search

A theoretical model describing electron dynamics in quantum dot (QD) infrared photodetectors (QDIPs) is presented. The model is based on the nonequilibrium Green’s functions formalism which provides a general framework to study electron transport in a nonequilibrium quantum system and in the presence of interactions. A self-consistent solution of the charge density and the average potential energy through the device

M. A. Naser; M. J. Deen; D. A. Thompson

2008-01-01

77

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

78

Theoretical prediction of the vibrational spectrum, geometry, and scaled quantum mechanical force field for phenylacetylene  

SciTech Connect

The optimized geometry and the complete harmonic force field of phenylacetylene have been determined by ab initio Hartree-Fock calculations, using a 4-21 Gaussian basis set. Systematic errors in the bond lengths, characteristic at this level of theory, were corrected by empirical offset values. Only at the ipso position does the equilibrium geometry obtained in this way differ significantly from the experimental one (MW; r{sub g}). A detailed analysis suggests that while the experimental ipso CCC angle may be correct, the ipso CC distance should be reconsidered. The force field was evaluated at the above geometry as a reference. To remove systematic deficiencies, the final scaled quantum mechanical (SQM) force field was obtained by applying scale factors optimized previously for benzene and acetylene. All force constants that occur both in phenylacetylene and in the isoelectronic molecule benzonitrile are very nearly the same. Frequencies calculated from the SQM force field of phenylacetylene confirm, with only a few exceptions, the published experimental assignments for all four isotopomers investigated. When the C-H (and C-D) stretching frequencies, perturbed by anharmonicity, are not considered, the average deviation between the observed and calculated frequencies is below 10 cm{sup {minus}1}. Theoretical dipole moment derivatives are discussed, and infrared intensities are presented. Quartic centrifugal distortion constants, calculated also from the SQM force field, agree well with the results of an incomplete experimental study.

Csaszar, A.G.; Fogarasi, G. (Eoetvoes Lorand Univ., Budapest (Hungary)); Boggs, J.E. (Univ. of Texas, Austin (USA))

1989-11-02

79

Quantum calculations of H2--H2 collisions: from ultracold to thermal energies  

NASA Astrophysics Data System (ADS)

We present quantum dynamics of rotational and vibrational energy transfer in collisions between two para-H2 molecules over a wide range of energies spanning the ultracold limit to thermal energies. The calculations were carried out using a quantum scattering code [1] that solves the time-independent Schrödinger equation in its full-dimensionality without any angular momentum decoupling approximations. The sensitivity of the results to details of the interaction potential as well as the initial vibrational and rotational quantum numbers of the H2 molecules is explored. Cross sections and rate coefficients for elastic and inelastic collisions from our calculations are compared with available experimental and theoretical results [2,3].References: [1] R. V. Krems, TwoBC - quantum scattering program, University of British Columbia, Vancouver, Canada (2006); [2] G. Qu'em'ener, N. Balakrishnan, and R. V. Krems, Phys. Rev. A 77, 030704(R) (2008); [3] G. Qu'em'ener and N. Balakrishnan, arXiv:0812.3866 (accepted in J. Chem. Phys.).

Quéméner, Goulven; Krems, Roman; Naduvalath, Balakrishnan

2009-05-01

80

Q-branch linewidths of N2 perturbed by H2: Experiments and quantum calculations from an ab initio potential  

NASA Astrophysics Data System (ADS)

In this work the authors present an experimental and theoretical study about the Q-branch lines' broadening coefficients of N2 perturbed by H2. Experimental values for these parameters have been obtained at 440 and 580 K, and quantum calculations have been performed using a new ab initio potential energy surface, obtained by quantum chemistry methods. The results of these calculations are compared to experimental data obtained previously at 77 and 298 K [L. Gomez et al., Mol. Phys. 104, 1869 (2006)] and to the present measurements. A satisfactory agreement is obtained for the whole range of temperatures used in the experiments.

Gómez, Laura; Martínez, Raúl Z.; Bermejo, Dionisio; Thibault, Franck; Joubert, Pierre; Bussery-Honvault, Béatrice; Bonamy, Jeanine

2007-05-01

81

A theoretical structure calculation of MWIR HgCdTe e-APD  

NASA Astrophysics Data System (ADS)

A theoretical calculation result of Hg1-xCdxTe (x=0.3) avalanche photodiodes (APDs) based on PIN structure is obtained in the paper, which has a ratio of ionization factor k=0.06. The energy dispersion factor and the threshold energy are acquired according to the parameters of material. And the gain, as well as the breakdown voltage, is obtained. The composition, thickness, doping level is calculated theoretically to get an optimized APD device.

Gu, Ren-Jie; Shen, Chuan; Chen, Lu

2011-06-01

82

Variational calculations on the energy levels of graphene quantum antidots  

NASA Astrophysics Data System (ADS)

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

Kandemir, B. S.; Omer, G.

2013-07-01

83

Quantum chemistry calculation of resveratrol and related stilbenes  

NASA Astrophysics Data System (ADS)

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

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

2003-01-01

84

Vibrational spectroscopic studies of Isoleucine by quantum chemical calculations.  

PubMed

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

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

2014-04-24

85

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

86

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

87

Theoretical study of molecular quantum dot cellular automata  

Microsoft Academic Search

Molecular quantum-dot cellular automata (QCA) is an alternative paradigm for molecular electronics. Each single molecule acts as a QCA cell and binary information is encoded in the configuration of charge among redox-active molecular sites. Coulomb interaction between neighboring molecules provides information transport from one molecule to another, so the heat dissipation is low because no current through molecular circuits is

Yuhui Lu; C. S. Lent

2004-01-01

88

Maxwell's demon. (II) A quantum-theoretic exorcism  

Microsoft Academic Search

In Part II of this two-part paper we prove that Maxwell's demon is unable to accomplish his task of sorting air molecules into swift and slow because in air in a thermodynamic equilibrium state there are no such molecules. The proof is based on the principles of a unified quantum theory of mechanics and thermodynamics.The key idea of the unified

Elias P. Gyftopoulos

2002-01-01

89

Quantum Monte Carlo calculations of A <= 10 nuclei  

NASA Astrophysics Data System (ADS)

We report the latest quantum Monte Carlo calculations of light nuclei up to A=10. These variational and Green's function Monte Carlo calculations use the realistic Argonne v18 two-nucleon potential, with or without any of several three-nucleon potentials, including the new Illinois models. The GFMC method converges on the lowest state of any given spin and parity, J^?, with binding energies that are accurate to about 1--2%. Our best model, AV18/IL2 reproduces the energies of 27 narrow states in 3 <= A <= 10 nuclei with an rms error of 600 keV. Many additional levels have been studied, including a number of second states of given J^?. We also show a number of applications, including density distributions, intrinsic shapes, and electroweak reactions. We also present a study of a set of simpler potential models to see how nuclear spectra evolve as the nuclear force is made increasingly realistic.

Pieper, Steven C.; Wiringa, R. B.

2002-10-01

90

Automated quantum conductance calculations using maximally-localised Wannier functions  

NASA Astrophysics Data System (ADS)

A robust, user-friendly, and automated method to determine quantum conductance in quasi-one-dimensional systems is presented. The scheme relies upon an initial density-functional theory calculation in a specific geometry after which the ground-state eigenfunctions are transformed to a maximally-localised Wannier function (MLWF) basis. In this basis, our novel algorithms manipulate and partition the Hamiltonian for the calculation of coherent electronic transport properties within the Landauer-Buttiker formalism. Furthermore, we describe how short-ranged Hamiltonians in the MLWF basis can be combined to build model Hamiltonians of large (>10,000 atom) disordered systems without loss of accuracy. These automated algorithms have been implemented in the Wannier90 code (Mostofi et al., 2008) [1], which is interfaced to a number of electronic structure codes such as Quantum-ESPRESSO, AbInit, Wien2k, SIESTA and FLEUR. We apply our methods to an Al atomic chain with a Na defect, an axially heterostructured Si/Ge nanowire and to a spin-polarised defect on a zigzag graphene nanoribbon.

Shelley, Matthew; Poilvert, Nicolas; Mostofi, Arash A.; Marzari, Nicola

2011-10-01

91

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

92

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

NASA Astrophysics Data System (ADS)

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.; von Winckel, G.; Stintz, A.; Krishna, S.

2004-10-01

93

Number-Theoretic Nature of Communication in Quantum Spin Systems  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

94

Field theoretical quantities in the fractional quantum Hall effect  

Microsoft Academic Search

This thesis studies two models of the fractional quantum Hall effect (FQHE), the bosonic (Chern-Simons-Landau-Ginzburg) description and the fermionic (composite fermion gauge theory) description. The bosonic theory attempts to describe the FQHE states at filling fractions nu={1\\/ 2n+1} while the fermionic theory attempts to describe the states at nu={p\\/ 2np±1} and the metallic states in between. Within the bosonic theory,

Stephanie Hythe Curnoe

1997-01-01

95

Double Exponential Relativity Theory Coupled Theoretically with Quantum Theory?  

NASA Astrophysics Data System (ADS)

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 García, José De La Luz; Novoa Blanco, Jesús Francisco

2007-04-01

96

[Theoretical calculation and experimental study of membrane thickness of alginate-(poly-L-lysine)-alginate microcapsules].  

PubMed

Alginate-(Poly-L-Lysine)-Alginate(APA) microcapsules were prepared by Electrostatic Droplet Generator(EDG) technique and the thickness of microcapsule membrane, which was composed by polyelectrolyte complex, were studied in this paper. The theoretical formula was given for the measurement of membrane thickness of APA microcapsules by element analysis of membrane and calculation. The membrane thickness was 7-10 microns by theoretical calculation. On the other hand, the thickness of membrane was measured by SEM and optical microscopy and the results were 7 microns and 12 microns, respectively. The results showed that theoretical calculation is in good accordance with experimental determoination of mermbrane thickness and the membrane thickness of APA microcapsule is about 7-10 microns. The optical microscopy is an easy way to measure membrane thickness. PMID:12561369

Sun, Duoxian; Chen, Yiqing; Yang, Jun; Su, Jing; Sun, Anthony M

2002-12-01

97

Theoretical model of optical fiber secure communication system with chaotic multiple-quantum-well lasers  

Microsoft Academic Search

Chaotic synchronization of injected multiple-quantum-well lasers of optical fiber system and a theoretical model of optical\\u000a fiber chaotic secure communication system are presented by coupling a chaotic multiple-quantum-well laser synchronization\\u000a system and a fiber channel. A new chaotic encoding method of chaos phase shift keying On\\/Off is proposed for optical fiber\\u000a secure communications. Chaotic synchronization is achieved numerically in long-haul

Sen-Lin Yan

2007-01-01

98

Quantum mechanical and information theoretic view on classical glass transitions  

NASA Astrophysics Data System (ADS)

Using the mapping of the Fokker-Planck description of classical stochastic dynamics onto a quantum Hamiltonian, we argue that a dynamical glass transition in the former must have a precise definition in terms of a quantum phase transition in the latter. At the dynamical level, the transition corresponds to a collapse of the excitation spectrum at a critical point. At the static level, the transition affects the ground-state wave function: while in some cases it could be picked up by the expectation value of a local operator, in others the order may be nonlocal and impossible to be determined with any local probe. Here we instead propose to use concepts from quantum information theory that are not centered around local order parameters, such as fidelity and entanglement measures. We show that for systems derived from the mapping of classical stochastic dynamics, singularities in the fidelity susceptibility translate directly into singularities in the heat capacity of the classical system. In classical glassy systems with an extensive number of metastable states, we find that the prefactor of the area law term in the entanglement entropy jumps across the transition. We also discuss how entanglement measures can be used to detect a growing correlation length that diverges at the transition. Finally, we illustrate how static order can be hidden in systems with a macroscopically large number of degenerate equilibrium states by constructing a three-dimensional lattice gauge model with only short-range interactions but with a finite temperature continuous phase transition into a massively degenerate phase.

Castelnovo, Claudio; Chamon, Claudio; Sherrington, David

2010-05-01

99

Quantum and conversion efficiency calculation of AlGaAs\\/GaAs multiple quantum well solar cells  

Microsoft Academic Search

The quantum well solar cell (QWSC) is a novel device that has been proposed by Barnham and co-workers at Imperial College London. In this work, the quantum efficiency for AlGaAs\\/GaAs QWSC has been calculated and compared with available data from the group at Imperial College London. Quantum efficiency calculations will be presented and compared with experimental data for several AlGaAs\\/GaAs

J. C. Rimada; L. Hernandez; J. P. Connolly; K. W. J. Barnham

2005-01-01

100

Crystal structures, optical properties and theoretical calculation of novel two-photon polymerization initiators  

Microsoft Academic Search

Three novel A–?–D–?–A type compounds 3,6-bis[2-(4-pyridyl)ethenyl]-9-ethylcarbazole (1), 3,6-bis[2-(2-pyridyl)ethenyl]-9-ethylcarbazole (2), 3,6-bis[2-(4-pyridyl)ethenyl]-9-ethylpyridylcarbazole (3) were conveniently synthesized by Pd-catalyzed Heck coupling methodology and characterized by single crystal X-ray diffraction determination. One-photon fluorescence, one-photon fluorescence quantum yields, one-photon fluorescence lifetime, and two-photon fluorescence have been investigated. The calculated two-photon absorption cross-sections for the three initiators by quantum chemical method are as high as 947,

Hong-Ping Zhou; Dong-Mei Li; Ju-Zhou Zhang; Yong-Min Zhu; Jie-Ying Wu; Zhang-Jun Hu; Jia-Xiang Yang; Gui-Bao Xu; Yu-Peng Tian; Yi Xie; Xu-Tang Tao; Min-Hua Jiang; Li-Min Tao; Ya-Hui Guo; Chuan-Kui Wang

2006-01-01

101

The absolute configuration of (+)-oxopropaline D by theoretical calculation of specific rotation and asymmetric synthesis.  

PubMed

The specific optical rotations of (R)-oxopropaline D calculated by two ab initio MO methods were +52+/-31 degrees and +61+/-29 degrees, respectively, and (+)-oxopropaline D (3) was presumed to have an R-configuration. On the basis of this theoretical result, the reaction of 1-litio-beta-carboline with (R)-glyceraldehyde acetonide followed by oxidation with MnO(2) gave (R)-oxopropaline D acetonide (4a), which was consistent with the previously synthesized (+)-oxopropaline D acetonide (4) in all respects. From the results of theoretical calculations and the experimental synthesis, we determined that natural (+)-oxopropaline D (3) has an R-configuration. PMID:12520122

Kuwada, Takeshi; Fukui, Miyako; Hata, Toshiyuki; Choshi, Tominari; Nobuhiro, Junko; Ono, Yukio; Hibino, Satoshi

2003-01-01

102

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

NASA Technical Reports Server (NTRS)

The quantum yield of photosynthesis (mol C/mol photons) was calculated at six depths for the waters of the Marine Light-Mixed Layer (MLML) cruise of May 1991. As there were photosynthetically available radiation (PAR) but no spectral irradiance measurements for the primary production incubations, three ways are presented here for the calculation of the absorbed photons (AP) by phytoplankton for the purpose of calculating phi. The first is based on a simple, nonspectral model; the second is based on a nonlinear regression using measured PAR values with depth; and the third is derived through remote sensing measurements. We show that the results of phi calculated using the nonlinear regreesion method and those using remote sensing are in good agreement with each other, and are consistent with the reported values of other studies. In deep waters, however, the simple nonspectral model may cause quantum yield values much higher than theoretically possible.

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

1995-01-01

103

Theoretical calculation and vibrational spectral analysis of L-arginine trifluoroacetate  

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

104

Pseudopotential Calculation of the Excited States of Semiconductor Quantum Dots  

NASA Astrophysics Data System (ADS)

We present the results of our pseudopotential calculations of up to 10 single-exciton states in free standing InP, InAs and CdSe quantum dots with diameters ranging from 10 to 50ÅIn the first step we solve for ?20-40 single particle hole and electron states using a screened atomic pseudopotential Hamiltonian[1], solved within a plane wave basis using the Folded Spectrum Method[2]. In the second step, we calculate the electron-hole Coulomb energy[3] and the dipole transition probability for each of the ?1000 possible single particle excitations. We present a comparison of the size scaling of the peaks in absorption and emission spectra obtained in our calculations with those from recent experiments and those of the effective mass based, k.p method. We also compare pseudopotential and k.p predictions of the character of the initial and final single particle states associated with each of these emission peaks. [1] J. Kim, A.J. Williamson, L.W. Wang, S.H-. Wei and A. Zunger, submitted to Phys. Rev. B [2] L. W. Wang and A. Zunger, J. Chem. Phys. 100, 2394 (1994). [3] A. Franceschetti and A. Zunger, Phys. Rev. Lett. 78, 915 (1997). *Supported under BES/OER/DMS contract No. DE---AC36---83CH10093

Williamson, Andrew; Wang, Lin-Wang; Fu, Hiauxiang; Zunger, Alex

1998-03-01

105

Constant chemical potential approach for quantum chemical calculations in electrocatalysis  

PubMed Central

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

Schneider, Wolfgang B

2014-01-01

106

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

107

Large Scale Electronic Structure Calculations using Quantum Chemistry Methods  

NASA Astrophysics Data System (ADS)

This talk will address our recent efforts in developing fast, linear scaling electronic structure methods for large scale applications. Of special importance is our fast multipole method( M. C. Strain, G. E. Scuseria, and M. J. Frisch, Science 271), 51 (1996). (FMM) for achieving linear scaling for the quantum Coulomb problem (GvFMM), the traditional bottleneck in quantum chemistry calculations based on Gaussian orbitals. Fast quadratures(R. E. Stratmann, G. E. Scuseria, and M. J. Frisch, Chem. Phys. Lett. 257), 213 (1996). combined with methods that avoid the Hamiltonian diagonalization( J. M. Millam and G. E. Scuseria, J. Chem. Phys. 106), 5569 (1997) have resulted in density functional theory (DFT) programs that can be applied to systems containing many hundreds of atoms and ---depending on computational resources or level of theory-- to many thousands of atoms.( A. D. Daniels, J. M. Millam and G. E. Scuseria, J. Chem. Phys. 107), 425 (1997). Three solutions for the diagonalization bottleneck will be analyzed and compared: a conjugate gradient density matrix search (CGDMS), a Hamiltonian polynomial expansion of the density matrix, and a pseudo-diagonalization method. Besides DFT, our near-field exchange method( J. C. Burant, G. E. Scuseria, and M. J. Frisch, J. Chem. Phys. 105), 8969 (1996). for linear scaling Hartree-Fock calculations will be discussed. Based on these improved capabilities, we have also developed programs to obtain vibrational frequencies (via analytic energy second derivatives) and excitation energies (through time-dependent DFT) of large molecules like porphyn or C_70. Our GvFMM has been extended to periodic systems( K. N. Kudin and G. E. Scuseria, Chem. Phys. Lett., in press.) and progress towards a Gaussian-based DFT and HF program for polymers and solids will be reported. Last, we will discuss our progress on a Laplace-transformed \\cal O(N^2) second-order pertubation theory (MP2) method.

Scuseria, Gustavo E.

1998-03-01

108

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

109

157-nm Resist Material Design for Improvement of Its Transparency Using Highly Precise Theoretical Calculation  

Microsoft Academic Search

Vacuum ultraviolet (VUV) absorption spectra of resist materials for 157 nm lithography were calculated theoretically by the symmetry adapted cluster configuration interaction (SAC-CI) method. In this study, we investigated the excited states of several alkanes and fluorinated alkanes in the VUV region, and found that most of the transitions of the evaluated alkanes are Rydberg-like transitions. Furthermore, we found a

Tamio Yamazaki; Toshiro Itani

2003-01-01

110

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

111

A theoretical calculation model for the acidification capacity of natural waters  

Microsoft Academic Search

The acidification capacity model is mainly used for the classification and the regional partitioning of the acidification sensitivity of natural waters. The theoretical calculation system of the acidification capacity from the conventional monitoring items, such as alkalinity, chemical oxygen demand and pH value, is established by simulating the acidification process of natural waters. In this study, the contributions of the

Jinhui Li; Hongxiao Tang

1998-01-01

112

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

113

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

NASA Astrophysics Data System (ADS)

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

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

114

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

PubMed

The geometries involved in the conformational equilibria of 2,2-dichloro-N-cyclohexyl-N-methyl-acetamide (DCCMA) and 2-chloro-N,N-dicyclohexylacetamide (CDCA) were investigated. Theoretical calculations at the B3LYP/cc-pVDZ level of theory showed that gauche forms (ClCCO) are the most stable and the predominant conformers in isolated phase. Both compounds had the conformational behavior in solvents of different polarities estimated from theoretical calculations with the PCM (Polarizable Continuum Model), at the same level of theory, using infrared data from deconvolution of the carbonyl absorption bands and (13)C NMR spectra. Their IR spectra showed two carbonyl absorptions and that the conformer with the highest dipole moment had its population increased when the most polar solvents were used, in accordance with the theoretical calculation in solution. (1)JCH coupling constants were obtained from their NMR spectra, and revealed that there was population variation of conformers with solvent exchange. Experimental data (NMR and IR) as well as calculations including the solvent effects followed the same trend. PMID:24727174

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

2014-08-14

115

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

116

Benchmark Quantum Monte Carlo Calculations of Optical gaps of carbon Nanotubes  

NASA Astrophysics Data System (ADS)

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

Reboredo, Fernando; Kent, Paul

2007-03-01

117

Quantum Monte Carlo Calculations of Excitations in Hydrogenated Germanium Clusters  

NASA Astrophysics Data System (ADS)

Quantum Monte Carlo (QMC) calculations are presented for energies of ground and excited states of Ge atom and hydrogen passivated closed-shell molecules and clusters: GeH4, Ge2H6, Ge5H12, Ge10H16 and Ge29H36. We compare the results for excitations with previous QMC and time-dependant Density Functional Theory (TD- DFT) done for the corresponding Silicon clusters [1,2]; in particular; we find that preliminary results for lowest excitation enregy of Ge29H36 5.08[29]eV is lower than the gap 5.4eV reported for Si[2]. Core-valence partitioning for Ge is implemented by replacing the core-states with a Hartree-Fock pseudopotential plus a Core Polarization Potential (CPP)[3]. Core-valence correlation treated by the CPP is shown to be essential for accurate atomic energies and significant for the molecules, but smaller in the clusters. [1] Porter et. al., PRB 64, 035320 (2001). [2] Williamson et. al., PRL 89, 196803 (2002). [3] Shirley and Martin, PRB 47, 15413 (1993)

Vincent, Jordan; Kim, Jeongnim; Martin, Richard

2006-03-01

118

Self-assembled quantum dots: A theoretical study of the exciton in single and vertically coupled type-II quantum dots  

NASA Astrophysics Data System (ADS)

In recent years, quantum dots (QD's) have attracted considerable interest because they can be regarded as ideal model systems for quasi-zero-dimensional systems. They are therefore often called artificial atoms. Two such artificial atoms can be placed above each other, resulting in vertically coupled quantum dots or artificial molecules. The possibility to discover new physics in these zero-dimensional systems together with possible applications in opto-electronics has led to many experimental and theoretical results. The so-called self-assembled quantum dots, as studied in my thesis, form spontaneously when growing two semiconductor materials with a substantially different lattice parameter on top of each other. In such self-assembled quantum dots, it is possible to create an exciton (i.e. a bound electron-hole pair), which will be trapped due to the different band structure of the two materials. One can distinguish between two types of dots: type-I, where both the electron and the hole are confined inside the dot, and type-II, where one of the particles is located in the barrier material. In my thesis, I studied theoretically the behaviour of one exciton in a type-II quantum dot, where the electron is sitting inside the dot and the hole is located in the barrier under the influence of an externally applied magnetic field. The quantum dot was modeled by a disk of finite radius R and thickness d. In the first part of the thesis, the exciton properties were examined in the absence of strain effects. For the study of a single disk, we found a different behaviour for a disk-like system (d << 2R) and for a pillar-like system (d >> 2 R), where the latter exhibits angular momentum transitions for the hole with increasing magnetic field. These transitions follow from the fact that the hole is located at the radial boundary of the disk for a pillar-like system, and is pushed against the barrier when the magnetic field is applied. When studying a system of vertically coupled disk, we found that this system exhibits a similar behaviour as the single pillar-like system. The second part of the thesis is dedicated to the study of the exciton in quantum disk in the presence of strain fields. These strain fields are important, as the cause the formation of the self-assembled dots. They also have an appreciable influence on the band structure and it is therefore necessary to take them into account. The strain was calculated using the isotropic elasticity model. (Abstract shortened by UMI.)

Janssens, Karen

119

Theoretical study on Curcumin: A comparison of calculated spectroscopic properties with NMR, UV vis and IR experimental data  

NASA Astrophysics Data System (ADS)

The main target of this study is a high-level computational analysis of Curcumin, employing DFT approach with two different sets of basis functions (B3LYP/6-31G ? and B3LYP/6-311G ??). Accurate quantum mechanical studies, both in vacuum and in methanol medium, are carried out with the aim to analyze the conformational equilibria, to find the most stable equilibrium structure and to define the nature of the molecular orbitals, fundamental to explain Curcumin binding characteristic. Our theoretical calculations, performed at B3LYP/6-31G ? and B3LYP/6-311G ?? levels both in vacuum and in methanol medium, confirm that the keto-enolic forms are more stable than the di-keto one, whose extremely low population suggests that this structure should not influence Curcumin properties. Keto-enolic form C results the most stable, independently on calculation level and solvent (methanol) effect. HOMO and LUMO molecular orbitals are calculated for all the structures with the two sets of basis with very similar results. MEPs show that the negative charge is localized on the oxygen atoms, which, in the keto-enolic forms, point in the same direction enabling metal coordination. NMR, UV-vis and FT-IR experimental data are employed in the comparison with electronic and conformational properties of Curcumin resulting from theoretical calculations. The two different calculation levels (B3LYP/6-31G ? and B3LYP/6-311G ??) give very similar results. Good linear correlations between the experimental 1H and 13C NMR chemical shifts ( ?exp), in methanol- d4 (MeOD) and DMSO- d6 (DMSO), and calculated magnetic isotropic shielding tensors ( ?calc) are found ( ?exp = a · ?calc + b). A good prediction of UV-vis experimental maximum absorption ( ?max) on the basis of conformer populations is obtained. A linear relation with a good correlation coefficient is observed plotting the FT-IR experimental wavenumbers vs . the calculated ones, allowing to predict FT-IR spectra.

Benassi, Rois; Ferrari, Erika; Lazzari, Sandra; Spagnolo, Ferdinando; Saladini, Monica

2008-12-01

120

Interaction effects on topological phase transitions via numerically exact quantum Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

We theoretically study topological phase transitions in four generalized versions of the Kane-Mele-Hubbard model with up to 2×182 sites. All models are free of the fermion-sign problem allowing numerically exact quantum Monte Carlo (QMC) calculations to be performed to extremely low temperatures. We numerically compute the Z2 invariant and spin Chern number C? directly from the zero-frequency single-particle Green's functions, and study the topological phase transitions driven by the tight-binding parameters at different on-site interaction strengths. The Z2 invariant and spin Chern number, which are complementary to each another, characterize the topological phases and identify the critical points of topological phase transitions. Although the numerically determined phase boundaries are nearly identical for different system sizes, we find strong system-size dependence of the spin Chern number, where quantized values are only expected upon approaching the thermodynamic limit. For the Hubbard models we considered, the QMC results show that correlation effects lead to shifts in the phase boundaries relative to those in the noninteracting limit, without any spontaneously symmetry breaking. The interaction-induced shift is nonperturbative in the interactions and cannot be captured within a "simple" self-consistent calculation either, such as Hartree-Fock. Furthermore, our QMC calculations suggest that quantum fluctuations from interactions stabilize topological phases in systems where the one-body terms preserve the D3 symmetry of the lattice, and destabilize topological phases when the one-body terms break the D3 symmetry.

Hung, Hsiang-Hsuan; Chua, Victor; Wang, Lei; Fiete, Gregory A.

2014-06-01

121

Quantum phase transitions in a strongly entangled spin-orbital chain: A field-theoretical approach  

Microsoft Academic Search

Motivated by recent experiments on quasi-one-dimensional vanadium oxides, we study quantum phase transitions in a one-dimensional spin-orbital model describing a Haldane chain and a classical Ising chain locally coupled by the relativistic spin-orbit interaction. By employing a field-theoretical approach, we analyze the topology of the ground-state phase diagram and identify the nature of the phase transitions. In the strong coupling

Alexander Nersesyan; Gia-Wei Chern; Natalia B. Perkins

2011-01-01

122

Determination of Absolute Configuration of Natural Products: Theoretical Calculation of Electronic Circular Dichroism as a Tool  

PubMed Central

Determination of absolute configuration (AC) is one of the most challenging features in the structure elucidation of chiral natural products, especially those with complex structures. With revolutionary advancements in the area of quantum chemical calculations of chiroptical spectroscopy over the past decade, the time dependent density functional theory (TDDFT) calculation of electronic circular dichroism (ECD) spectra has emerged as a very promising tool. The principle is simply based on the comparison of the calculated and experimental ECD spectra: the more closely they match, the more reliable conclusion for the AC assignment can be drawn. This review attempts to use several examples representing monomeric flavonoids, rotationally restricted biflavonoids, complex hexahydroxydiphenoyl-containing flavonoids, conformationally flexible and restrained sesquiterpenoids, cembrane-africanene terpenoids, dihydropyranocoumarins, alkaloids, and dihydroxanthones to illustrate the applicability of this approach in determining the AC of structurally diverse natural products. The findings clearly indicate that the TDDFT calculation of ECD spectra can quantify the contribution of individual conformers and the interaction of multiple chromophores, making it possible to determine the AC of complex chiral molecules. The calculated electronic transitions and molecular orbitals provide new insight into the interpretation of ECD spectra at the molecular level.

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

2013-01-01

123

Theoretical calculation of product contents: battery and cathode ray tube examples.  

PubMed

Most product environmental assessments are based on manufacturer-supplied data on the material content of the product. This paper explores the potential for the material content of key components to be estimated with theoretical calculations. Two examples, the amount of cadmium in a nickel-cadmium battery and the amount of lead in a TV or computer CRT monitor, are developed. Both an upper and a lower limit on the amount of cadmium in a nickel-cadmium battery are calculated on the basis of the battery's chemical reaction. The amount of lead shielding needed in a TV or CRT computer monitor is estimated on the basis of the potential difference through which electrons are accelerated and the absorption length of photons in lead. Such calculations can be used as benchmarks in product environmental assessments, providing validation of manufacturer-supplied data and providing insight into the composition and design of products. PMID:12775079

Thomas, Valerie M

2003-05-01

124

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

NASA Technical Reports Server (NTRS)

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

Avrett, E. H.

1984-01-01

125

Gold(III) six-membered N^C^N pincer complexes: synthesis, structure, reactivity and theoretical calculations.  

PubMed

The first six-membered gold(III) N^C^N pincer complex was obtained in good yield, under very mild conditions, by transmetalation of [Hg(?C-N^C^N)Cl] (N^CH^N = 1,3-bis(pyridin-2-ylmethyl)benzene, HL(1)) with Na[AuCl(4)]. The X-ray crystal structure of [Au(N^C^N)Cl][PF(6)] showed that the fused six-membered metallacycles each exist in a strongly puckered boat conformation. As shown by the (1)H NMR spectra in various solvents, the same structure is also retained in solution: no inversion of the six-membered metallacycles is observed in DMSO up to 95 °C. This correlates well with a reaction barrier of 17.5 kcal/mole, as determined by quantum chemical calculations. The reactivity of the present pincer complex is compared to that of the analogous 1,3-bis(2-pyridyl)benzene, HL(2), derivative, which has five-membered fused metallacycles. Sharp differences are found in the reactions with phosphines, such as PPh(3) and dppe (1,2-bis-diphenylphosphino-ethane), and with silver salts. Theoretical calculations were carried out on the two pincer complexes in order to try to understand these differences, and we found that the gold-chlorine bond is significantly stronger in the case of the complex containing five-membered metallacyclic rings. PMID:20886134

Alesso, Giuseppe; Cinellu, Maria Agostina; Stoccoro, Sergio; Zucca, Antonio; Minghetti, Giovanni; Manassero, Carlo; Rizzato, Silvia; Swang, Ole; Ghosh, Manik Kumer

2010-11-14

126

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

NASA Astrophysics Data System (ADS)

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

Aly, Abou El-Maaty M.; Nasr, A.

2014-03-01

127

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

NASA Astrophysics Data System (ADS)

Advanced quantum approach to calculation of spectra for superheavy ions with an account of relativistic, correlation, nuclear, radiative effects is developed and based on the gauge invariant quantum electrodynamics (QED) perturbation theory (PT). The Lamb shift polarization part is calculated in the Ueling approximation, self-energy part is defined within a new non-PT procedure of Ivanov-Ivanova. Calculation results for energy levels, hyperfine structure parameters of some heavy elements ions are presented.

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

2005-10-01

128

Quantitative analysis of nanometer anatase-rutile mixtures via experimentation and theoretical calculation.  

PubMed

In this paper, we developed a method based on X-ray diffractometry for determining the weight ratio of nanometer anatase to rutile or their relative amounts in TiO2 polymorphs, and corresponding formulas for such determination were put forward. The very key constant K in these formulas has been specially evaluated by experimentalizing nanometer polymorphs of titanium dioxide. Furthermore, a theoretical value of K was obtained through detailed theoretical calculation based on X-ray powder diffraction theory. The K value concluded from experimentation coincides well with that yielded from theoretical calculation, thus the validity and reliability of the experimental K value has been further confirmed. This coincidence may also suggest the applicability of X-ray powder diffraction theory to nanometer crystals. With this method, the relative amounts of nanometer anatase and rutile in their mixtures or the weight ratio of nanometer anatase to rutile in any a mixture can be easily determined only upon a XRD test. PMID:23447946

Guo, Li; Zhou, Zhiqiang; Jia, Peiyun; Ye, Feng

2012-12-01

129

Quantum Computing in Condensed Matter Systems.  

National Technical Information Service (NTIS)

Specific theoretical calculations of Hamiltonians corresponding to several quantum logic gates, including the NOT gate, quantum signal splitting, and quantum copying, were obtained and prepared for publication. Directions for future work have been identif...

V. Privman

1997-01-01

130

Theoretical prediction of high pressure phase transition in ScC and YC: Ab initio calculations  

NASA Astrophysics Data System (ADS)

The structural stability of ScC and YC has been analyzed under hydrostatic compression employing the first-principles calculations using the plane-wave pseudopotential method. The comparison of theoretically calculated enthalpies of rocksalt type (B1), primitive orthorhombic (Pmmn), and CsCl type (B2) structures as a function of pressure suggests that the B1 structure transforms to Pmmn phase instead of transforming to B2 phase that predicted by Soni et al. [J. Phys. Chem. Solids 72, 810 (2011)]. The pressure for B1 to Pmmn transition predicted for ScC and YC are ~80 GPa and ~30 GPa, respectively. To further substantiate the outcomes of our static lattice calculations, we have performed lattice dynamic calculations also. Our lattice dynamic calculations correctly demonstrate that the B1 phase is dynamically stable structure at ambient condition. Further, for both the carbides, we find that the Pmmn structure becomes dynamically stable around the transition pressure whereas the B2 structure remains unstable, supporting the B1 to Pmmn phase transition predicted by our static lattice calculations.

Sahoo, B. D.; Joshi, K. D.; Gupta, Satish C.

2013-08-01

131

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

NASA Technical Reports Server (NTRS)

The dependence of the quantum fluctuation of the output fundamental and second-harmonic waves upon cavity configuration has been numerically calculated for the intracavity frequency-doubled laser. The results might provide a direct reference for the design of squeezing system through the second-harmonic-generation.

Zhang, Kuanshou; Xie, Changde; Peng, Kunchi

1996-01-01

132

Multi-million atom electronic structure calculations for quantum dots  

Microsoft Academic Search

Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In

Muhammad Usman

2010-01-01

133

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

134

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

135

Theoretical examination of quantum coherence in a photosynthetic system at physiological temperature  

PubMed Central

The observation of long-lived electronic coherence in a photosynthetic pigment–protein complex, the Fenna–Matthews–Olson (FMO) complex, is suggestive that quantum coherence might play a significant role in achieving the remarkable efficiency of photosynthetic electronic energy transfer (EET), although the data were acquired at cryogenic temperature [Engel GS, et al. (2007) Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems. Nature 446:782–786]. In this paper, the spatial and temporal dynamics of EET through the FMO complex at physiological temperature are investigated theoretically. The numerical results reveal that quantum wave-like motion persists for several hundred femtoseconds even at physiological temperature, and suggest that the FMO complex may work as a rectifier for unidirectional energy flow from the peripheral light-harvesting antenna to the reaction center complex by taking advantage of quantum coherence and the energy landscape of pigments tuned by the protein scaffold. A potential role of quantum coherence is to overcome local energetic traps and aid efficient trapping of electronic energy by the pigments facing the reaction center complex.

Ishizaki, Akihito; Fleming, Graham R.

2009-01-01

136

Vibrational spectra, theoretical calculations, and structure of 4-silaspiro(3,3)heptane  

NASA Astrophysics Data System (ADS)

Theoretical computations have been carried out for 4-silaspiro(3,3)heptane (SSH) in order to calculate its structure and vibrational spectra. SSH was found to have two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. The puckering and tilting reduce the D2d symmetry to C2. Nonetheless, the vibrational assignments can be done quite well on the basis of D2d symmetry. This is confirmed by the fact that all but the lowest E vibrations show insignificant splitting into A and B modes of C2 symmetry. However, the observed splittings of the lowest frequency modes do confirm the lower conformational symmetry. The calculated infrared and Raman spectra were compared to the experimental spectra collected for the vapor, liquid, and solid states, and the agreement is excellent.

Ocola, Esther J.; Medders, Cross; Cooke, Joel M.; Laane, Jaan

2014-09-01

137

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

PubMed

The FT-IR and FT-Raman spectra of 4-chloro-2-nitroanisole were recorded and analyzed. The vibrational wavenumbers were examined theoretically with the aid of the GAUSSIAN 09 package of programs using the B3LYP/6-311G(d,p) and 6-311++G(d,p) levels of theory. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied molecule. The first hyperpolarizability, NBO, HOMO-LUMO, NMR, UV, infrared intensities and Raman intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non-linear optics. The geometrical parameters of the title compound are in good agreement with the values of similar structures. PMID:24915766

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

2014-10-15

138

Vibrational spectra, theoretical calculations, and structure of 4-silaspiro(3,3)heptane.  

PubMed

Theoretical computations have been carried out for 4-silaspiro(3,3)heptane (SSH) in order to calculate its structure and vibrational spectra. SSH was found to have two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. The puckering and tilting reduce the D2d symmetry to C2. Nonetheless, the vibrational assignments can be done quite well on the basis of D2d symmetry. This is confirmed by the fact that all but the lowest E vibrations show insignificant splitting into A and B modes of C2 symmetry. However, the observed splittings of the lowest frequency modes do confirm the lower conformational symmetry. The calculated infrared and Raman spectra were compared to the experimental spectra collected for the vapor, liquid, and solid states, and the agreement is excellent. PMID:24810025

Ocola, Esther J; Medders, Cross; Cooke, Joel M; Laane, Jaan

2014-09-15

139

Photophysical properties of structurally and electronically modified flavin derivatives determined by spectroscopy and theoretical calculations.  

PubMed

Four different riboflavin (RF) derivatives, two electronically modified compounds (1- and 5-deazariboflavin, 1DRF and 5DRF) and two sterically modified compounds (7,8-didemethyl- and 8-isopropylriboflavin, DMRF and iprRF), were subjected to a combination of time-resolved measurements (absorption and fluorescence) and high-level quantum chemical investigations. Both alkyl-modified flavins showed similar fluorescence properties as the parent compound, yet 5DRF had a larger quantum yield of fluorescence (PhiF = 0.52) than RF (PhiF = 0.27). Interestingly, 1DRF did not show fluorescence at all under these steady state conditions. The triplet quantum yield was different for the modified flavins such that no triplet formation was found for 1DRF, whereas the other compounds all formed triplet states (PhiTR for 5DRF of 0.64 and 0.50 and 0.23 for iprRF and DMRF, respectively). The triplet states of the two alkyl-modified flavins decayed with similar time constants as the parent compound, whereas a shorter lifetime was measured for 5DRF (tauTR = 15 micros, compared to tauTR = 29 micros for RF). In the calculations, the flavin derivatives were modeled as lumiflavins, that is, without the ribityl chain. We conclude that for aqueous solutions of DMRF, iprRF, and 5DRF intersystem crossing (ISC) takes place from the S1 1(pipi*) to the T2 3(pipi*) state by a vibronic spin-orbit coupling mechanism, a process common to most flavins, whereas ISC is slow in excited 1DRF due to the absence of a close-by triplet state. PMID:19639947

Salzmann, Susanne; Martinez-Junza, Víctor; Zorn, Björn; Braslavsky, Silvia E; Mansurova, Madina; Marian, Christel M; Gärtner, Wolfgang

2009-08-20

140

A theoretical study of third-harmonic generation in semi-parabolic plus semi-inverse squared quantum wells  

NASA Astrophysics Data System (ADS)

A theoretical study of third-harmonic generation is performed by using the compact-density-matrix method. An electron is confined in semi-parabolic potential plus semi-inverse squared potential quantum wells. Our calculations show that the absolute value, the imaginary part and the real part of third-harmonic generation coefficients are greatly influenced by the parabolic confinement frequency and the characteristic parameter of the inverse squared potential. The relationship between the absolute value and the imaginary part as well as the relationship between the absolute value and the real part is discussed. It is found that the resonant peaks of the absolute value originate from the imaginary part and are not related to the real part.

Zhai, Wangjian; Hassanbadi, Hassan; Lu, Liangliang; Liu, Guanghui

2014-05-01

141

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

SciTech Connect

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

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

2013-02-15

142

Role of an information-theoretic measure of quantum correlation in a dynamical phase transition of entanglement  

Microsoft Academic Search

The nearest-neighbor entanglement of the evolved state of an asymmetric quantum XY spin chain, in a transverse time-dependent field, exhibits criticalities (dynamical phase transitions) as the initial field parameter is varied at a given fixed time. After a discussion of the dynamical phase transition, we investigate the extent to which the role of an information-theoretic quantum correlation measure, called quantum

Himadri Shekhar Dhar; Rupamanjari Ghosh; Ujjwal Sen

2010-01-01

143

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

144

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

NASA Astrophysics Data System (ADS)

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

Bai, Yihui; Du, Jinyan; Weng, Xuexiang

145

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

PubMed

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

Bai, Yihui; Du, Jinyan; Weng, Xuexiang

2014-05-21

146

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

NASA Technical Reports Server (NTRS)

With different choices of the cut-offs used in theoretical calculations, we have carried out extensive numerical calculations of the N2-broadend Lorentzian half-widths of the H2O lines using the modified Robert-Bonamy formalism. Based on these results, we are able to thoroughly check for convergence. We find that, with the low-order cut-offs commonly used in the literature, one is able to obtain converged values only for lines with large half-widths. Conversely, for lines with small half-widths, much higher cut-offs are necessary to guarantee convergence. We also analyse the uncertainties associated with calculated half-widths, and these are correlated as above. In general, the smaller the half-widths, the poorer the convergence and the larger the uncertainty associated with them. For convenience, one can divide all H2O lines into three categories, large, intermediate, and small, according to their half-width values. One can use this division to judge whether the calculated half-widths are converged or not, based on the cut-offs used, and also to estimate how large their uncertainties are. We conclude that with the current Robert- Bonamy formalism, for lines in category lone can achieve the accuracy requirement set by HITRAN, whereas for lines in category 3, it 'is impossible to meet this goal.

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

2010-01-01

147

Theoretical calculations, far-infrared spectra and the potential energy surfaces of four cyclic silanes  

NASA Astrophysics Data System (ADS)

Theoretical computations have been carried out to calculate the potential energy functions for the out-of-plane vibrations of four cyclic silanes, and the results were compared to experimental functions determined from far-infrared data. The experimental and computed ring-puckering potential functions for 1-silacyclopent-3-ene, which are in excellent agreement, are quartic in nature with tiny barriers to planarity. Similarly, the calculated and experimental potential functions for 1,3-disilacyclopent-3-ene are nearly identical. For silacyclopentane and 1,3-disilacyclopentane the calculations predict ring-twisitng barriers of 2493 cm-1 (vs. 2110 cm-1 observed) and 1395 cm-1, respectively. The conformational energies for the bent forms were calculated to be 1467 cm-1 (vs. 1509 cm-1 observed) for the former and 878 cm-1 for the latter relative to the energy of the twist minima. One-dimensional hindered pseudorotational potential energy functions were found to work well for predicting the observed far-infrared spectra for the bending (pseudorotational) vibration.

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

2014-03-01

148

The implementation of ab initio quantum chemistry calculations on transputers  

Microsoft Academic Search

The RHF and geometry optimization sections of the ab initio quantum chemistry code, GAMESS, have been optimized for a network of parallel microprocessors, Inmos T800-20 transputers, using both indirect and direct SCF techniques. The results indicate great scope for implementation of such codes on small parallel computer systems, very high efficiencies having been achieved, particularly in the cases of direct

M. D. Cooper; I. H. Hillier

1991-01-01

149

A perspective on quantum mechanics calculations in ADMET predictions.  

PubMed

Understanding the molecular basis of drug action has been an important objective for pharmaceutical scientists. With the increasing speed of computers and the implementation of quantum chemistry methodologies, pharmacodynamic and pharmacokinetic problems have become more computationally tractable. Historically the former has been the focus of drug design, but within the last two decades efforts to understand the latter have increased. It takes about fifteen years and over $1 billion dollars for a drug to go from laboratory hit, through lead optimization, to final approval by the U.S. Food and Drug Administration. While the costs have increased substantially, the overall clinical success rate for a compound to emerge from clinical trials is approximately 10%. Most of the attrition rate can be traced to ADMET (absorption, distribution, metabolism, excretion, and toxicity) problems, which is a powerful impetus to study these issues at an earlier stage in drug discovery. Quantum mechanics offers pharmaceutical scientists the opportunity to investigate pharmacokinetic problems at the molecular level prior to laboratory preparation and testing. This review will provide a perspective on the use of quantum mechanics or a combination of quantum mechanics coupled with other classical methods in the pharmacokinetic phase of drug discovery. A brief overview of the essential features of theory will be discussed, and a few carefully selected examples will be given to highlight the computational methods. PMID:23675934

Bowen, J Phillip; Güner, Osman F

2013-01-01

150

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

NASA Technical Reports Server (NTRS)

Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.

Kahn, L. R.

1982-01-01

151

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

SciTech Connect

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

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

2003-01-01

152

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

153

A Calculation of Cosmological Scale from Quantum Coherence  

SciTech Connect

We use general arguments to examine the energy scales for which a quantum coherent description of gravitating quantum energy units is necessary. The cosmological dark energy density is expected to decouple from the Friedman-Lemaitre energy density when the Friedman-Robertson-Walker scale expansion becomes sub-luminal at R = c, at which time the usual microscopic interactions of relativistic quantum mechanics (QED, QCD, etc) open new degrees of freedom. We assume that these microscopic interactions cannot signal with superluminal exchanges, only superluminal quantum correlations. The expected gravitational vacuum energy density at that scale would be expected to freeze out due to the loss of gravitational coherence. We define the vacuum energy which generates this cosmological constant to be that of a zero temperature Bose condensate at this gravitational de-coherence scale. We presume a universality throughout the universe in the available degrees of freedom determined by fundamental constants during its evolution. Examining the reverse evolution of the universe from the present, long before reaching Planck scale dynamics one expects major modifications from the de-coherent thermal equations of state, suggesting that the pre-coherent phase has global coherence properties. Since the arguments presented involve primarily counting of degrees of freedom, we expect the statistical equilibrium states of causally disconnected regions of space to be independently identical. Thus, there is no horizon problem associated with the lack of causal influences between spatially separated regions in this approach. The scale of the amplitude of fluctuations produced during de-coherence of cosmological vacuum energy are found to evolve to values consistent with those observed in cosmic microwave background radiation and galactic clustering.

Lindesay, J

2004-07-23

154

The theoretical tensile strength of fcc crystals predicted from shear strength calculations.  

PubMed

This work presents a simple way of estimating uniaxial tensile strength on the basis of theoretical shear strength calculations, taking into account its dependence on a superimposed normal stress. The presented procedure enables us to avoid complicated and time-consuming analyses of elastic stability of crystals under tensile loading. The atomistic simulations of coupled shear and tensile deformations in cubic crystals are performed using first principles computational code based on pseudo-potentials and the plane wave basis set. Six fcc crystals are subjected to shear deformations in convenient slip systems and a special relaxation procedure controls the stress tensor. The obtained dependence of the ideal shear strength on the normal tensile stress seems to be almost linearly decreasing for all investigated crystals. Taking these results into account, the uniaxial tensile strength values in three crystallographic directions were evaluated by assuming a collapse of the weakest shear system. Calculated strengths for [Formula: see text] and [Formula: see text] loading were found to be mostly lower than previously calculated stresses related to tensile instability but rather close to those obtained by means of the shear instability analysis. On the other hand, the strengths for [Formula: see text] loading almost match the stresses related to tensile instability. PMID:21825337

Cerný, M; Pokluda, J

2009-04-01

155

Theoretical study of UV spectra of diazaphenanthrenesulfonamides calculated by AM1 and DFT B3-LYP methods  

NASA Astrophysics Data System (ADS)

Two diazaphenanthrenesulfonamides have been synthesized. For calculation of experimental and theoretical UV values of these compounds the AM1 CI method has been used; their geometry optimisation was made with AM1 CI and DFT B-3 LYP methods.

Dondela, Barbara; Chrzastek, Lidia

2007-08-01

156

Theoretical study of UV spectra of diazaphenanthrenesulfonamides calculated by AM1 and DFT B3-LYP methods  

Microsoft Academic Search

Two diazaphenanthrenesulfonamides have been synthesized. For calculation of experimental and theoretical UV values of these compounds the AM1 CI method has been used; their geometry optimisation was made with AM1 CI and DFT B-3 LYP methods.

Barbara Dondela; Lidia Chrzastek

2007-01-01

157

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

158

Quantum Calculations of Coulomb Reorientation for Sub-Barrier Fusion  

Microsoft Academic Search

Classical mechanics and time dependent Hartree-Fock (TDHF) calculations of heavy ions collisions are performed to study the rotation of a deformed nucleus in the Coulomb field of its partner. This reorientation is shown to be independent of the charges and relative energy of the partners. It only depends upon the deformations and inertias. TDHF calculations predict an increase by 30%

Cedric Simenel; Philippe Chomaz; G. de France

2004-01-01

159

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

NASA Astrophysics Data System (ADS)

We have measured dielectronic recombination (DR) for Fe12 + forming Fe11 + using the heavy ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Using our results, we have calculated a plasma rate coefficient from these data that can be used for modeling astrophysical and laboratory plasmas. For the low temperatures characteristic of photoionized plasmas, the experimentally derived rate coefficient is orders of magnitude larger than the previously recommended atomic data. The existing atomic data were also about 40% smaller than our measurements at temperatures relevant for collisionally ionized plasmas. Recent state-of-the-art theory has difficulty reproducing the detailed energy dependence of the DR spectrum. However, for the Maxwellian plasma rate coefficient, recent theoretical results agree with our measurements to within about 30% for both photoionized and collisionally ionized plasmas.

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

2014-06-01

160

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

161

Ligand recognition by chloroperoxidase using molecular interaction fields and quantum chemistry calculations  

Microsoft Academic Search

We recently reported that chloroperoxidase (CPO) from Caldariomyces fumago showed atypical kinetic behavior for the oxidation of 4,6 dimethyl dibenzothiophene (DMDBT). In this work, we undertake the theoretical study of DMDBT docking into CPO's active site, in order to clarify its binding capacity and affinity using molecular interaction fields and quantum mechanical procedure. The results revealed that CPO has two

J. C.-Basurto; J. Aburto; J. T.-Ferrara; E. Torres

2007-01-01

162

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

163

The multiconfiguration time-dependent Hartree-Fock method for quantum chemical calculations  

Microsoft Academic Search

We apply the multiconfiguration time-dependent Hartree-Fock method to electronic structure calculations and show that quantum chemical information can be obtained with this explicitly time-dependent approach. Different equations of motion are discussed, as well as the numerical cost. The two-electron integrals are calculated using a natural potential expansion, of which we describe the convergence behavior in detail.

M. Nest; T. Klamroth; P. Saalfrank

2005-01-01

164

Linear scaling calculation of an n-type GaAs quantum dot.  

PubMed

A linear scale method for calculating electronic properties of large and complex systems is introduced within a local density approximation. The method is based on the Chebyshev polynomial expansion and the time-dependent method, which is tested on the calculation of the electronic structure of a model n-type GaAs quantum dot. PMID:17930374

Nomura, Shintaro; Iitaka, Toshiaki

2007-09-01

165

Self-Interaction-Free Density Functional Theoretical Study of the Electronic Structure of Quantum Dots  

NASA Astrophysics Data System (ADS)

We present a study of the electronic structure of both spherical and vertical quantum dots by means of the DFT with optimized effective potential (OEP) and self-interaction-correction (SIC)[1]. The method eliminates the spurious self-interaction energy in the conventional DFT and the the highest occupied orbital energy of the N-electron quantum dots provides a direct measure of the electron affinity. We apply the theory to the study of the capacitive energy of N-electron quantum dots for N up to 70 [2]. The results show the instructive shell and subshell structure pattern and the electron filling pattern follows closely the Hund's rule. The calculated capacitive energy spectrum is in good agreement with recent experimental results, providing physical insights regarding the origin of electron shells and the role of electron-electron interaction in quantum dots [2]. [1] X.M. Tong and S.I. Chu, Phys. Rev. A55 (1997) 3406. [2] T.F. Jiang, X.M. Tong, and S.I. Chu, Phys. Rev. B63 (2001) 045317.

Jiang, T. F.; Tong, X. M.; Chu, Shih-I.

2001-05-01

166

Vibrationally resolved photoelectron imaging of Cu2H- and AgCuH- and theoretical calculations.  

PubMed

Vibrationally resolved photoelectron spectra have been obtained for Cu(2)H(-) and AgCuH(-) using photoelectron imaging at 355 nm. Two transition bands X and A are observed for each spectrum. The X bands in both spectra show the vibration progressions of the Cu-H stretching mode and the broad peaks of these progressions indicate significant structural changes from Cu(2)H(-) and AgCuH(-) to their neutral ground states. The A bands in the spectra of Cu(2)H(-) and CuAgH(-) show stretching progressions of Cu-Cu and Ag-Cu, respectively. The contours of these two progressions are pretty narrow, indicating relatively small structural changes from Cu(2)H(-) and AgCuH(-) to their neutral excited states. Calculations based on density functional theory indicate that the ground states of Cu(2)H(-) and AgCuH(-) and the first excited states of their neutrals are linear, whereas their neutral ground states are bent. The photoelectron detachment energies and vibrational frequencies from these calculations are in good agreement with the experimental observations. Especially, the theoretical predication of linear structures for the anions and the neutral excited states are supported by the spectral features of A bands, in which the bending modes are inactive. Comparisons among the vertical detachment energies of Cu(2)H(-), AgCuH(-), and their analogs help to elucidate electronic characteristics of coinage metal elements and hydrogen in small clusters. PMID:23388039

Xie, Hua; Li, Xiaoyi; Zhao, Lijuan; Liu, Zhiling; Qin, Zhengbo; Wu, Xia; Tang, Zichao; Xing, Xiaopeng

2013-02-28

167

Theoretical Calculation of the N_2 Broadened Half-Widths of H_2O  

NASA Astrophysics Data System (ADS)

The water molecule is the most important Greenhouse gas and thus plays a pivotal role in atmospheric spectra. In addition to accurate intensities and frequencies, one also needs accurate self and foreign half-widths and shifts, and their temperature dependence. Over the years, a large number of theoretical calculations have been carried out by Gamache and his collaborators. They used the complex Robert-Bonamy theory with a sophisticated interaction potential. The drawback of this method is that one has to carry out the calculations to a high-order perturbation in order to obtain converged results. However, by using the coordinate representation one is able to obviate the perturbation expansion and obtain results corresponding to a high cut-off order. We present comparisons for the H_2O-N_2 system for a few lines using the same interaction potential for a comparison between the methods. We conclude that for lines having a large half-width, the convergence is rapid but, on the other hand, for lines with relatively small half-widths the convergence is very slow. I. E. Gordon et al., J.Q.S.R.T. 108, 389 (2007) and references therein. Q. Ma, R. H. Tipping, and C. Boulet, J. Chem. Phys. 124, 014109 (2006).

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

2009-06-01

168

Torsional path integral Monte Carlo method for calculating the absolute quantum free energy of large molecules  

NASA Astrophysics Data System (ADS)

A new technique for evaluating the absolute free energy of large molecules is presented. Quantum-mechanical contributions to the intramolecular torsions are included via the torsional path integral Monte Carlo (TPIMC) technique. Importance sampling schemes based on uncoupled free rotors and harmonic oscillators facilitate the use of the TPIMC technique for the direct evaluation of quantum partition functions. Absolute free energies are calculated for the molecules ethane, n-butane, n-octane, and enkephalin, and quantum contributions are found to be significant. Comparison of the TPIMC technique with the harmonic oscillator approximation and a variational technique is performed for the ethane molecule. For all molecules, the quantum contributions to free energy are found to be significant but slightly smaller than the quantum contributions to internal energy.

Miller, Thomas F.; Clary, David C.

2003-07-01

169

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

170

Symmetry-projected wave functions in quantum Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

171

Quantum Observables Algebras and Abstract Differential Geometry: The Topos-Theoretic Dynamics of Diagrams of Commutative Algebraic Localizations  

NASA Astrophysics Data System (ADS)

We construct a sheaf-theoretic representation of quantum observables algebras over a base category equipped with a Grothendieck topology, consisting of epimorphic families of commutative observables algebras, playing the role of local arithmetics in measurement situations. This construction makes possible the adaptation of the methodology of Abstract Differential Geometry (ADG), à la Mallios, in a topos-theoretic environment, and hence, the extension of the “mechanism of differentials” in the quantum regime. The process of gluing information, within diagrams of commutative algebraic localizations, generates dynamics, involving the transition from the classical to the quantum regime, formulated cohomologically in terms of a functorial quantum connection, and subsequently, detected via the associated curvature of that connection.

Zafiris, Elias

2007-02-01

172

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

NASA Astrophysics Data System (ADS)

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

Gladysiewicz, M.; Kudrawiec, R.; Wartak, M. S.

2014-01-01

173

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

Microsoft Academic Search

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

A. Amtout; S. Raghavan; P. Rotella; G. von Winckel; A. Stintz; S. Krishna

2004-01-01

174

Theoretical Study of Unipolar Intersubband Impact Ionization in Quantum Dot Based Photodetectors  

NASA Astrophysics Data System (ADS)

In this paper, we study the intersubband impact ionization through conduction band states of quantum dot (QD) layers of an infrared photodetector. For this purpose, a photogenerated electron moving in high field active region of a p-i-n diode is assumed which can excite an electron from ground state of a QD by carrier-carrier scattering. The generated electron can escape the QD by tunneling and contribute in photocurrent giving avalanche gain to photodetector. The ionization rate and responsivity of detector are calculated from an analytical approach of intersubband transition rate equations. Results show increased responsivity in the order of several A/W.

Yusefli, Amir; Zavvari, Mahdi; Abedi, Kambiz

2013-11-01

175

A Calculable Field-Theoretic 'Landscape': Vacuum Structure, Phase Transitions, and Infrared Fixed Points  

SciTech Connect

Motivated by recent discussions of the string-theory landscape, we propose field-theoretic realizations of models with large numbers of vacua. These models contain multiple U(1) gauge groups, and can be interpreted as deconstructed versions of higher-dimensional gauge theory models with fluxes in the compact space. We find that the vacuum structure of these models is very rich, defined by parameter-space regions with different classes of stable vacua separated by boundaries. This allows us to explicitly calculate physical quantities such as the supersymmetry-breaking scale, the presence or absence of R-symmetries, and probabilities of stable versus unstable vacua. Furthermore, we find that this landscape picture evolves with energy, allowing vacua to undergo phase transitions as they cross the boundaries between different regions in the landscape. Surprisingly, we show that this landscape flow approaches an infrared fixed point, suggesting that it may not be necessary to determine all of the parameters of the ultraviolet theory in order to deduce relevant features of the low-energy phenomenology.

Dienes, Keith R. [Department of Physics, University of Arizona, Tucson, AZ 85721 (United States); Dudas, Emilian [Centre de Physique Theorique, Ecole Polytechnique, F-91128, Palaiseau Cedex (France); LPT, Bat. 210, Univ. Paris-Sud, F-91405, Orsay Cedex (France); Gherghetta, Tony [School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)

2005-12-02

176

Quantum transport calculation of the small-signal response of a resonant tunneling diode  

NASA Astrophysics Data System (ADS)

The linear and lowest-order nonlinear response of a quantum well resonant tunneling diode is evaluated using quantum transport theory. The calculations show that the negative conductance persists up to about 5 THz, although parasitic circuit elements will limit the maximum oscillation frequency to a much lower value. The nonlinear response (rectification) remains significant to frequencies near 10 THz and shows a resonant peak near 4 THz. These calculations support the interpretation of the experimental data of Sollner et al. (1983) showing that rectification at 2.5 THz was observed in their devices.

Frensley, William R.

1987-08-01

177

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.

178

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

NASA Astrophysics Data System (ADS)

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

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

2005-01-01

179

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

180

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

PubMed

The path integral formulation has been combined with several methods to determine free energies of quantum many-body systems, such as adiabatic switching and reversible scaling. These techniques are alternatives to the standard thermodynamic integration method. A quantum Einstein crystal is used as a model to demonstrate the accuracy and reliability of these free energy methods in quantum simulations. Our main interest focuses on the calculation of the melting temperature of Ne at ambient pressure, taking into account quantum effects in the atomic dynamics. The free energy of the solid was calculated by considering a quantum Einstein crystal as reference state, while for the liquid, the reference state was defined by the classical limit of the fluid. Our findings indicate that, while quantum effects in the melting temperature of this system are small, they still amount to about 6% of the melting temperature, and are therefore not negligible. The particle density as well as the melting enthalpy and entropy of the solid and liquid phases at coexistence is compared to results obtained in the classical limit and also to available experimental data. PMID:18715054

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

2008-08-14

181

Calculating thermodynamics properties of quantum systems by a non-Markovian Monte Carlo procedure.  

PubMed

We present a history-dependent Monte Carlo scheme for the efficient calculation of the free energy of quantum systems inspired by Wang-Landau and metadynamics. In the two-dimensional quantum Ising model, chosen here for illustration, the accuracy of free energy, critical temperature, and specific heat is demonstrated as a function of simulation time and successfully compared with the best available approaches. The approach is based on a path integral formulation of the quantum problem and can be applied without modifications to quantum Hamiltonians of any level of complexity. The combination of high accuracy and performance with a much broader applicability is a major advance with respect to other available methods. PMID:19658767

Crespo, Yanier; Laio, Alessandro; Santoro, Giuseppe E; Tosatti, Erio

2009-07-01

182

The extent of disorder and properties of silicate glasses, melts and layer-silicates: Spectroscopic analysis and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

Silicate glasses and melts have long been studied not only because of their geologic relevance to natural magmas but also because of their technological applications to the glass industry. The inherent aspect of silicate glasses and melts are extent of disorder among framework units and the distribution of internal structural variables. This dissertation is for a systematic exploration of the extent of disorder in silicate glasses, melts and layer-silicates using NMR spectroscopy and analysis both by theoretical prediction based on statistical thermodynamics and by quantum chemical calculations. The objective of the dissertation includes exploration of the consequences of the degree of disorder of the system on physical properties of interest to geologists and material scientists. The degree of randomness in framework in silicate glasses including borosilicate and aluminosilicates was quantified using the models introducing order parameters such as the degree of Al avoidance and the degree of inter-mixing. The model in conjunction with input from high-resolution NMR and quantum chemical calculations was used to calculate the configurational thermodynamic properties in these glasses. We presented general framework for understanding the extent of short-range order in framework silicates, demonstrating that a more complete description of the macroscopic thermodynamic properties of silicates can be derived from information on the degree of framework disorder and provides another strong link between structures of melts and properties. Bond angle and length distributions, one aspect of topological disorder in this system, were also quantified using these methods. 17O MQ (multiple quantum) MAS NMR at high fields were applied to better understand reactivity of oxygen sites in layer silicates which are one of the most dominant constituents of the Earth's surfaces. Several basal and apical oxygen sites in model clay minerals were resolved, providing improved prospects for atomic scale understanding on the geochemical processes such as weathering.

Lee, Sung Keun

183

On kaonic deuterium. Quantum field-theoretic and relativistic covariant approach  

NASA Astrophysics Data System (ADS)

We study kaonic deuterium, the bound K- d state AK d. Within a quantum field-theoretic and relativistic covariant approach we derive the energy level displacement of the ground state of kaonic deuterium in terms of the amplitude of K- d scattering for arbitrary relative momenta. Near threshold our formula reduces to the well-known DGBT formula. The S-wave amplitude of K- d scattering near threshold is defined by the resonances ?(1405), ?(1750) and a smooth elastic background, and the inelastic channels K- d ? NY and K- d ? NY?, where Y = ?±,?{0} and ?{0}, where the final-state interactions play an important role. The Ericson-Weise formula for the S-wave scattering length of K- d scattering is derived. The total width of the energy level of the ground state of kaonic deuterium is estimated using the theoretical predictions of the partial widths of the two-body decays AKd ? NY and experimental data on the rates of the NY pair production in the reactions K- d ? NY. We obtain ?{1s} = (630±100)eV. For the shift of the energy level of the ground state of kaonic deuterium we predict ?{1s} = (325±60)eV.

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

2005-01-01

184

Investigation of the ICT state of DPA-DSB using spectroscopic experiments and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The excited states of a symmetric D- ?-D structure two-photon excited fluorescence material 1,4-di (4'- N, N-diphenylaminostyryl) benzene (DPA-DSB) have been investigated by spectroscopic experiments and quantum chemical calculations. The solvent polarity dependent fluorescence properties indicate that upon photoexcitation, a radiative intramolecular charge-transfer (ICT) state is formed resulting from the ICT process. The molecular structure does not have large change during the ICT process, which is confirmed by the quantum chemical calculations performed by G AUSSIAN 03 software. The planar structure of the fluorescent ICT state results in the high fluorescence quantum yield which is important in the two-photon excited fluorescence application.

He, Xing; Wang, Yang; Liu, Weilong; Yang, Zhenling; Du, Xin; Liu, Yuqiang; Yang, Yanqiang

2011-01-01

185

Non-perturbative calculation of correlators in 2D quantum gravity.  

National Technical Information Service (NTIS)

The 'fifth-time' action provides a truly non-perturbative definition of 2D-quantum gravity. We show that it can be used for numerical calculation of correlators. We compare with the results obtained by defining 2D-gravity by contour rotation in the functi...

J. Ambjoern J. Greensite

1990-01-01

186

Effective potentials and multiconfiguration wave functions in quantum Monte Carlo calculations  

Microsoft Academic Search

Using relativistic effective potentials to eliminate the electron density in the core region we have computed quantum Monte Carlo (QMC) atomic energies for Be which accurately reproduce the experimental values in the range from the ground state to the first ionization energy. These calculations required only a few hours on a MicroVAX computer to obtain statistical errors smaller than a

P. A. Christiansen

1988-01-01

187

Second-Order Calculations of the Single-Quantum Annihilation Cross Sections in Various Atomic Shells.  

National Technical Information Service (NTIS)

A general method for calculating the cross sections for single-quantum annihilation (SQA) of positrons in various atomic shells, valid to second order in the alpha-Z expansion (one order beyond the leading term), is presented with the help of the modified...

A. Davidz D. S. Moroi R. F. Kess

1969-01-01

188

Potential and Current Distributions Calculated Across a Quantum Hall Effect Sample at Low and High Currents.  

National Technical Information Service (NTIS)

The potential and current distributions are calculated across the width of a quantum Hall effect sample for applied currents between 0 microA and 225 microA. For the first time, both a confining potential and a current- induced charge-redistribution poten...

C. F. Lavine M. E. Cage

1995-01-01

189

Stereoelectronic effects in silicon, phosphorus, and sulfur molecules. Quantum-chemical calculations and qualitative orbital models  

NASA Astrophysics Data System (ADS)

The results of non-empirical quantum-chemical calculations for silicon, phosphorus, and sulfur compounds of different structure are discussed. Qualitative orbital models, which establish a relation between the distribution of electrons and molecular structure and properties, are analysed. A general definition of stereoelectronic effects is presented. The bibliography includes 176 references.

Korkin, A. A.

1992-05-01

190

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

191

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

NASA Astrophysics Data System (ADS)

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.

2010-12-01

192

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

PubMed

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

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

2014-02-24

193

Acceleration of Monte Carlo modeling of light transport in turbid media; an approach based on hybrid, theoretical and numerical, calculations  

Microsoft Academic Search

A novel method to accelerate Monte Carlo (MC) simulations of photon migration in turbid media is presented. It is specifically suited for transillumination studies in slab geometries including some deep inhomogeneity. Propagation up to the inhomogeneity, at a given depth S1, is replaced by theoretical calculations using well established models. Then, photon propagation is continued inside the complete slab using

Héctor O. Di Rocco; Daniela I. Iriarte; Juan A. Pomarico; Héctor F. Ranea-Sandoval

2009-01-01

194

Theoretical calculations of excited rovibrational levels of HD. Term values and transition probabilities of VUV electronic bands  

Microsoft Academic Search

In this paper, we derive the theoretical properties of rovibrational levels belonging to excited B, C, B', and D electronic states of HD. We compute the eigenvalues and eigenfunctions of the nuclear coupled Schroedinger equations using ab initio electronic molecular properties available in the literature. Transition wavenumbers and spontaneous emission probabilities are calculated for all transitions belonging to B-X, C-X,

H. Abgrall; E. Roueff

2006-01-01

195

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

Microsoft Academic Search

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

Sergei N. Yurchenko; Walter Thiel; Per Jensen

2007-01-01

196

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

PubMed

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

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

2014-04-14

197

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

198

Toward three-dimensional quantum state-resolved collision dynamics at the gas-liquid interface: theoretical investigation of incident angle.  

PubMed

Quantum state-resolved energy transfer dynamics at the gas-liquid interface are explored through a comparison of classical molecular dynamics (MD) simulations and previously reported experimental studies (Perkins, B. G.; et al. J. Phys. Chem. A 2008, 112, 9234). Theoretically, large scale MD trajectory calculations have been performed for collisions of CO(2) with a model fluorinated self-assembled monolayer surface (F-SAMs), based on an explicit atom-atom interaction potential obtained from earlier theoretical studies (Martinez-Nunez, E.; et al. J. Phys. Chem. C 2007, 111, 354). Initial conditions for the simulations match those in the experimental studies where high-energy jet-cooled CO(2) molecules (E(inc) = 10.6(8) kcal/mol, approximately 10 cm(-1)) are scattered from a 300 K perfluorinated liquid surface (PFPE) from a range of incident angles (theta(inc) = 0-60 degrees ). Nascent CO(2) rotational distributions prove to be remarkably well characterized by a simple two-temperature trapping-desorption (TD) and impulsive scattering (IS) model with nearly quantitative agreement between experimental and theoretical column integrated densities. Furthermore, three-dimensional (3D) quantum state resolved flux maps for glancing incident angles (theta(inc) approximately 60 degrees ) reveal broad, lobular distributions peaking strongly in the forward subspecular direction as cos(n)(theta(scat) - theta') with n approximately 5.6(1.2) and theta' approximately 49(2) degrees . PMID:19334697

Perkins, Bradford G; Nesbitt, David J

2009-04-23

199

Quantum mechanical calculation of spectral statistics of a modified Kepler problem  

NASA Astrophysics Data System (ADS)

For a modified Kepler problem, we reexamine jumps in the saturation spectral rigidity and large oscillations of the level number variance with near zero minima. Earlier discrepancy between the periodic orbit theory and numerical calculation is cleared by a quantum mechanical calculation. A new class of radial periodic orbits is included establishing a complete correspondence between the periodic orbit theory and the quantum mechanical approach. We show that the diagonal approximation for the level density in the periodic orbit theory already gives a good fit with the numerical calculation. Even greater accuracy is achieved by considering coherent interference between the classical periodic orbits term and the Balian-Bloch term. This procedure produces improved results for the hard-wall rectangular billiards as well.

Ma, Tao; Serota, R. A.

2012-03-01

200

Molecular structures of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid, obtained by gas-phase electron diffraction and theoretical calculations.  

PubMed

The structures of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid have been determined by gas-phase electron diffraction using results from quantum chemical calculations to inform the choice of restraints applied to some of the structural parameters. The results from the study presented here demonstrate that resonance hybrids are not as helpful in rationalizing the structures of 2-, 3-, and 4-hydroxybenzoic acids as are models based upon electrostatic effects. PMID:18798606

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

2008-10-01

201

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

202

Quantum monte carlo calculations of neutron matter with nonlocal chiral interactions.  

PubMed

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

Roggero, Alessandro; Mukherjee, Abhishek; Pederiva, Francesco

2014-06-01

203

Quantum Monte Carlo Calculations of Neutron Matter with Nonlocal Chiral Interactions  

NASA Astrophysics Data System (ADS)

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

Roggero, Alessandro; Mukherjee, Abhishek; Pederiva, Francesco

2014-06-01

204

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

205

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

206

On the calculation of energy eigenstates of electrons in a spherical quantum dot  

NASA Astrophysics Data System (ADS)

The fundamental problem in the investigation of the properties of a quantum dot is the calculation of the energy eigen values of its confined charge carriers and evaluation of their corresponding wave functions. The quantum dots may be approximated as spheres whose surfaces constitute infinite potential barriers for carriers. Consequently, the motion of electrons and holes (which are confined inside the dot) can be analyzed by effective mass approximation applied to noninteracting particles. An attempt has been made here to solve the Schrödinger's equation for particles inside the infinite spherical potential well to determine their allowed energy eigen values and eigen functions.

Purohit, Pranati; Roy, Dilip K.; Pati, Shankar P.

2012-10-01

207

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

NASA Astrophysics Data System (ADS)

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

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

2007-09-01

208

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

PubMed

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

Ceriotti, Michele; Manolopoulos, David E

2012-09-01

209

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

210

Theoretical investigation of intersubband transition energies and oscillator strength in CdS/SiO 2 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/SiO 2 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/SiO 2 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

211

Accuracy of the theoretical calculation of the Soret coefficient for water-ethanol mixtures in comparison with experimental data  

NASA Astrophysics Data System (ADS)

The Soret coefficient of water-ethanol mixtures at one atmosphere and temperatures ranging from 20°C to 40°C has been studied in detail. Comparisons between the experimental data and predictions of existing theoretical models showed satisfactory agreement only for certain conditions. In order to properly model the behavior of water in the mixture, the thermodynamic properties of water-ethanol mixtures were calculated using the Cubic Plus Association (CPA) equation of state. Compared to the theoretical models of Haase, Kempers, Dougherty and Drickamer, the Firoozabadi model was found to perform much better in predicting the thermal diusion phenomena for water-alcohol mixtures.

Jiang, Charles Guobing; Saghir, M. Ziad; Derawi, Samer; Kawaji, Masahiro

2005-11-01

212

Shock Hugoniot calculations of polymers using quantum mechanics and molecular dynamics  

NASA Astrophysics Data System (ADS)

Using quantum mechanics (QM) and classical force-field based molecular dynamics (FF), we have calculated the principle shock Hugoniot curves for numerous amorphous polymers including poly[methyl methacrylate] (PMMA), poly[styrene], polycarbonate, as well as both the amorphous and crystalline forms of poly[ethylene]. In the FF calculations, we considered a non-reactive force field (i.e., polymer consistent FF). The QM calculations were performed with density functional theory (DFT) using dispersion corrected atom centered pseudopotentials. Overall, results obtained by DFT show much better agreement with available experimental data than classical force fields. In particular, DFT calculated Hugoniot curves for PMMA up to 74 GPa are in very good agreement with experimental data, where a preliminary study of chain fracture and association was also performed. Structure analysis calculations of the radius of gyration and carbon-carbon radial distribution function were also carried out to elucidate contraction of the polymer chains with increasing pressure.

Chantawansri, Tanya L.; Sirk, Timothy W.; Byrd, Edward F. C.; Andzelm, Jan W.; Rice, Betsy M.

2012-11-01

213

{ital Ab initio} quantum chemical calculation of electron transfer matrix elements for large molecules  

SciTech Connect

Using a diabatic state formalism and pseudospectral numerical methods, we have developed an efficient {ital ab initio} quantum chemical approach to the calculation of electron transfer matrix elements for large molecules. The theory is developed at the Hartree{endash}Fock level and validated by comparison with results in the literature for small systems. As an example of the power of the method, we calculate the electronic coupling between two bacteriochlorophyll molecules in various intermolecular geometries. Only a single self-consistent field (SCF) calculation on each of the monomers is needed to generate coupling matrix elements for all of the molecular pairs. The largest calculations performed, utilizing 1778 basis functions, required {approximately}14h on an IBM 390 workstation. This is considerably less cpu time than would be necessitated with a supermolecule adiabatic state calculation and a conventional electronic structure code. {copyright} {ital 1997 American Institute of Physics.}

Zhang, L.Y.; Friesner, R.A. [Department of Chemistry, Columbia University, New York, New York 10027 (United States)] [Department of Chemistry, Columbia University, New York, New York 10027 (United States); Murphy, R.B. [Schroedinger, Inc., Portland, Oregon 97204 (United States)] [Schroedinger, Inc., Portland, Oregon 97204 (United States)

1997-07-01

214

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

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

215

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

216

Calculation of quantum-limit cyclotron-resonance linewidths in Ge and Si by the isolation-projection technique  

NASA Astrophysics Data System (ADS)

On the basis of the line-shape theory introduced by the isolation-projection technique, we calculate the cyclotron-resonance half-linewidths for intravalley-deformation-potential scattering in the quantum limit. For comparison of the theoretical values with the experimental data, the effective deformation-potential constant (E1) is chosen as the fitting parameter, as in the works of Bagguley, Flaxen, and Stradling [Phys. Lett. 1, 111 (1962)], Stradling and Zhukov [Proc. Phys. Soc. 87, 263 (1966)], Ito, Kawamura, and Fukai [Phys. Lett. 13, 26 (1964)], and Murase, Enjouji, and Otsuka [J. Phys. Soc. Jpn. 29, 1248 (1970)]. In the best fitting, we obtain E1=12.7 eV for Ge and E1=7.90 eV for Si, which are similar to the values obtained by the other authors. In the quantum limit, the half-linewidths in Ge and Si are in good agreement with the experimental data of Kobori, Ohyama, and Otsuka [J. Phys. Soc. Jpn. 59, 2141 (1990)], except for the extremely low-temperature region.

Cho, Yong Jai; Choi, Sang Don

1994-05-01

217

Molecular structure of chloro-dodecafluorosubphthalocyanato boron(III) by gas-phase electron diffraction and quantum chemical calculations.  

PubMed

The molecular structure of the chloro-dodecafluorosubphthalocyaninato boron(III) (F-SubPc) was determined with use of Gas Electron Diffraction (GED) and high-level quantum chemical calculations. The present results show that the F-SubPc molecule has a cone-shaped configuration, isoindole units are not planar, and the pyrrole ring has an envelope conformation. The structure parameters in the gas phase are determined. Some structural details can be observed such as the dihedral angle about the bond connecting the pyrrole ring and the benzene ring being ca. 174 degrees . High-level theoretical calculations with several extended basis sets for this molecule have been carried out. The calculations are in very good agreement with experimental methods: X-ray and GED. Nevertheless, some disagreements particularly related to the B-Cl bond distance found in GED are discussed. Vibrational frequencies were computed obtaining eight values below 100 cm-1 and three bending potentials were examined. They suggest that this molecule is very flexible. PMID:17447746

Samdal, S; Volden, H V; Ferro, V R; García de la Vega, J M; Gonzalez-Rodríguez, D; Torres, T

2007-05-24

218

Theoretical Calculation of Inrush Currents in Three and Five-Legged Core Transformers  

Microsoft Academic Search

In this paper, a theoretical study of the three-phase transformer behavior in the presence of a sag is presented by considering that the fault clearing is produced simultaneously in all phases. Analytical expressions of the magnetic flux and the inrush current after voltage recovery are obtained, and the results presented in the literature are analytically justified. The influence of depth,

Luis Sainz; Felipe Corcoles; Joaquín Pedra; Luis Guasch

2007-01-01

219

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

220

Variational calculation on ground-state energy of bound polarons in parabolic quantum wires  

Microsoft Academic Search

Within the framework of Feynman path-integral variational theory, we calculate the ground-state energy of a polaron in parabolic quantum wires in the presence of a Coulomb potential. It is shown that the polaronic correction to the ground-state energy is more sensitive to the electron-phonon coupling constant than the Coulomb binding parameter and it increases monotonically with decreasing effective wire radius.

Zhuang-bing Wang; Fu-li Wu; Qing-hu Chen; Zheng-kuan Jiao

2001-01-01

221

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

PubMed Central

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

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

2011-01-01

222

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

223

Quantum-chemical calculations on the electronic circular dichroism of (-)-dibromophakellin and (-)-dibromophakell-statin.  

PubMed

The CD spectra of the pyrrole-imidazole alkaloids, (-)-dibromophakellin and (-)-dibromophakellstatin, have been calculated employing the quantum-chemical time-dependent density functional theory. Comparison of calculated and measured spectra showed that this well-established method is also a useful tool to elucidate the absolute stereochemistry of this class of compounds. The computational results have further been used to analyze the spectra measured in methanol and to explain the remarkable red shift of one CD band when trifluoroethanol is used as a solvent instead of methanol. PMID:17487888

Atodiresei, Iuliana; Zöllinger, Michael; Lindel, Thomas; Fleischhauer, Jörg; Raabe, Gerhard

2007-07-01

224

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

NASA Technical Reports Server (NTRS)

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

Mccluney, W. R.

1974-01-01

225

Theoretical calculations of emission of wolframite and scheelite-type tungstate crystals  

SciTech Connect

Tungstate crystals AWO{sub 4} (A = Zn,Cd,Pb) are well-known scintillation materials for various applications in science and technology. In recent years the optical properties of these crystals were intensively studied experimentally and theoretically. However, the origin of luminescence in lead, cadmium and zinc tungstates is still the subject of discussion. According to generally accepted view, the centers of luminescence in AWO{sub 4} crystals are in some or other way related to the tungstate anionic groups. We developed a cluster approach in theoretical investigation of the electronic structure of AWO{sub 4} tungstate crystals based on the configuration interaction (CI) computation in which the lattice vibrations were taken into account.

Nikolaenko, T.; Hizhnyi, Y.; Nedilko, S. [Faculty of Physics, Kyiv National Taras Shevchenko University, 2, block 1, Acad. Hlushkova ave., 03680, Kyiv (Ukraine)

2009-01-21

226

Theoretical calculations of emission of wolframite and scheelite-type tungstate crystals  

NASA Astrophysics Data System (ADS)

Tungstate crystals AWO4 (A = Zn,Cd,Pb) are well-known scintillation materials for various applications in science and technology. In recent years the optical properties of these crystals were intensively studied experimentally and theoretically. However, the origin of luminescence in lead, cadmium and zinc tungstates is still the subject of discussion. According to generally accepted view, the centers of luminescence in AWO4 crystals are in some or other way related to the tungstate anionic groups. We developed a cluster approach in theoretical investigation of the electronic structure of AWO4 tungstate crystals based on the configuration interaction (CI) computation in which the lattice vibrations were taken into account [1-3].

Nikolaenko, T.; Hizhnyi, Y.; Nedilko, S.

2009-01-01

227

Theoretical calculation of excitonic binding energies and optical absorption spectra for Armchair graphene nanoribbons  

NASA Astrophysics Data System (ADS)

In this paper the excitons of armchair graphene nanoribbons with layers of different width and thickness have been investigated. In this investigation, the band structure and energy gap of armchair graphene nanoribbons have been calculated using a tight-binding model including edge deformation effects (all edge atoms have been passivated with hydrogen atoms). Also, by calculating the conductance in armchair graphene nanoribbons (A-GNRs) optical absorption of armchair graphene nanoribbon in the single-electron approximation has been obtained. Finally, the binding energy of excitons in armchair graphene nanoribbons has been calculated using the Wannier model, Hartree-Fock approximation and the Bethe-Salpeter equation.

Mohammadzadeh, L.; Asgari, A.; Shojaei, S.; Ahmadi, E.

2011-11-01

228

Theoretical calculations for using positive electrode compression to increase lead-acid battery life  

NASA Astrophysics Data System (ADS)

Investigators have confirmed that applying a small amount of mechanical pressure, approximately 1 bar (10 5 Pa), to the face of the positive electrode can dramatically increase the life of deep cycled, lead acid batteries. In this paper, we calculate the pressures required to stabilize the active material in the positive electrode based on the "Agglomerate of Spheres" model. The calculations agree closely with the experimental observations. In addition to these calculations, we also provide another possible interpretation of the "Agglomerate of Spheres" model and give an improved estimate for the surface tension of lead dioxide, an important physical quantity for the model.

Edwards, Dean B.; Schmitz, Claus

229

Theoretical calculation of collisions between ultra-cold Cesium atoms in a magnetic field  

Microsoft Academic Search

We present the results of a theoretical study investigating the collisional properties of ultra-cold ground state Cesium atoms in a magnetic field. Since the accuracy of existing ^1Sigmag and ^3Sigmau potentials for the ground state Cs2 dimer are not sufficient to provide reliable scattering data at ultra-cold temperatures, we adopt a procedure whereby the potentials are adjusted to reproduce the

Paul Leo; Eite Tiesinga; Paul Julienne

1998-01-01

230

Theoretical calculation of the excited states of the KCs molecule including the spin-orbit interaction.  

PubMed

For the molecule KCs the potential energy has been calculated for the 72 lowest molecular states Omega. Using an ab initio method the calculation is based on nonempirical pseudopotentials within the range of 5.0a0-34.0a0 of the internuclear distance R. Gaussian basis sets have been used for both atoms and spin-orbit effects have been taken into account through a semiempirical spin-orbit pseudopotential added to the electrostatic Hamiltonian. The spectroscopic constants for 60 states have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance R. The components of the spin-orbit splitting for (1,2,5,6) 3Pi and (1) 3delta have been identified. The comparison of the present results with those available in the literature shows a very good agreement, while the other results, to the best of our knowledge, are given here for the first time. PMID:16526859

Korek, M; Moghrabi, Y A; Allouche, A R

2006-03-01

231

Theoretical calculations of pressure broadening coefficients for H2O perturbed by hydrogen or helium gas  

NASA Technical Reports Server (NTRS)

Halfwidths were calculated for H2O with H2 as a broadening gas and were estimated for He as the broadening species. The calculations used the model of Robert and Bonamy with parabolic trajectories and all relevant terms in the interaction potential. The calculations investigated the dependence of the halfwidth on the order of the atom-atom expansion, the rotational states, and the temperature in the range 200 to 400K. Finally, calculations were performed for many transitions of interest in the 5 micrometer window region of the spectrum. The resulting data will be supplied to Dr. R. Freedman for extracting accurate water mixing ratios from the analysis of the thermal channels for the Net Flux experiment on the Galileo probe.

Gamache, Robert R.; Pollack, James B.

1995-01-01

232

Theoretical calculation of shakeup intensities using Xa--SW wave functions  

SciTech Connect

The ground and 1s core hole state molecular wave functions of CH/sub 4/, NH/sub 3/, H/sub 2/O, and HF obtained from Xa--SW calculations using the touching spheres (TS) and overlapping spheres (OS) approximations are used to calculate the intensity of shakeup satellites observed in their ls core level photoelectron spectra. The sudden approximation was assumed in the calculation. In case of TS Xa--SW wave functions, the one electron overlap integral inside the intersphere was calculated via Green's theorem. For OS Xa--SW wave functions, the integration over the awkwardly shaped intersphere region was circumvented by distributing the intersphere charge into the atomic spheres according to the charge partition scheme suggested by Case and Karplus. Our results show that there are no significant differences between the shakeup energies calculated from the TS and OS approximations. However, shakeup intensities calculated from TS Xa--SW wave functions are more reliable and in better numerical agreement with experiment.

Tse, J.S.; Loubriel, G.

1981-05-01

233

A Comparison of Two Topos-Theoretic Approaches to Quantum Theory  

NASA Astrophysics Data System (ADS)

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

Wolters, Sander A. M.

2013-01-01

234

Calculation of density functional theory (DFT) vibrational parameters of nucleotides for use in theoretical optical calculations: Herein applied to circular dichroism (CD) and absorption of polynucleotides  

NASA Astrophysics Data System (ADS)

The Vibrational Circular Dichroism (VCD) of Nucleic Acids is a sensitive function of their conformation. DeVoe's classically derived polarizability theory allows the calculation of polymer absorption and circular dichroism spectra in any frequency range. Following the approach of Tinoco and Cech as modified by Moore and Self, calculations were done in the infrared (IR) region with theoretically derived monomer input parameters. Presented herein are calculated absorption and CD spectra for nucleic acid oligomers and polymers. These calculations improve upon earlier attempts, which utilized frequencies, intensities and normal modes from empirical analysis of the nitrogenous base of the monomers. These more complete input polarizability parameters include all contributions to specific vibrational normal modes for the entire nucleotide structure. They are derived from density functional theory (DFT) vibrational analysis on quasi-nucleotide monomers using the GAUSSIAN '98/'03 program. The normal modes are "integrated" for the first time into single virtual (DeVoe) oscillators by incorporating "fixed partial charges" in the manner of Schellman. The results include the complete set of monomer normal modes. All of these modes may be analyzed, in a manner similar to those demonstrated here (for the 1500-1800 cm-1 region). A model is utilized for the polymer/oligomer monomers which maintains the actual electrostatic charge on the adjacent protonated phosphoryl groups (hydrogen phosphate, a mono-anion). This deters the optimization from "collapsing" into a hydrogen-bonded "ball" and thereby maintains the extended (polymer-like) conformation. As well, the precise C2 "endo" conformation of the sugar ring is maintained in the DNA monomers. The analogous C3 "endo" conformation is also maintained for the RNA monomers, which are constrained by massive "anchors" at the phosphates. The complete IR absorbance spectra (0-4,000 cm-1) are calculated directly in Gaussian. Calculated VCD and Absorbance Spectra for the eight standard Ribonucleic and Deoxy-ribonucleic acid homo-polymers in the nitrogenous base absorbing region 1550-1750 cm-1 are presented. These spectra match measured spectra at least as well as spectra calculated from empirical parameters. These results demonstrate that the purely theoretical calculation, an example given herein, should serve to provide more transferable, universal parameters for the polarizability treatment of the optical properties of oligomers and polymers.

Ferber, Steven Dwight

235

The Calculation of Theoretical Chromospheric Models and the Interpretation of the Solar Spectrum  

NASA Technical Reports Server (NTRS)

Since the early 1970s we have been developing the extensive computer programs needed to construct models of the solar atmosphere and to calculate detailed spectra for use in the interpretation of solar observations. This research involves two major related efforts: work by Avrett and Loeser on the Pandora computer program for non-LTE modeling of the solar atmosphere including a wide range of physical processes, and work by Rurucz on the detailed synthesis of the solar spectrum based on opacity data or over 58 million atomic and molecular lines. our goals are: to determine models of the various features observed on the Sun (sunspots, different components of quiet and active regions, and flares) by means of physically realistic models, and to calculate detailed spectra at all wavelengths that match observations of those features. These two goals are interrelated: discrepancies between calculated and observed spectra are used to determine improvements in the structure of the models, and in the detailed physical processes used in both the model calculations and the spectrum calculations. The atmospheric models obtained in this way provide not only the depth variation of various atmospheric parameters, but also a description of the internal physical processes that are responsible for non-radiative heating, and for solar activity in general.

Avrett, Eugene H.

1998-01-01

236

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

237

Adaptive Clustering of Adatoms Around Ionic Dopants in He Droplets: Quantum Calculations  

NASA Astrophysics Data System (ADS)

The structuring and collocation of individual He atoms as quantum objects around simple atomic and molecular impurities has been the subject of a great number of studies, both experimentally and from the theoretical viewpoint [1,2] since the advent of droplets experiments, where such nanoscopic containers have been exploited to provide a sort of nanocryostat for the analysis of the dopant's spectroscopic behavior [3]. We have carried out computations of potential fields within small clusters which contain a variety of ionic dopants using post-Hartree-Fock, ab initio methods and have further endeavoured to extract from them the corresponding classical and quantum structuring of such impurities within clusters of variable size. For the latter enquiry we have employed both classical optimization methods and Quantum Diffusion Monte Carlo analysis. Results for both atomic (Li^+) and molecular (LiH^+, OH^+, OH^-) ionic dopants will be presented at the meeting. [1] J.P. Toennies and A.F. Vilesov, Angewandte Chemie 43, 2622 (2004). [2] e.g. see: F. Paesani, A. Viel, F.A. Gianturco and K. Whaley, Phys. Rev. Lett. 90, 073401 (2003). [3] J.P. Toennies and A.F. Vilesov, it Ann. Rev. Phys. Chem. bf 49, 1 (1998).

Gianturco, Francesco A.

2006-03-01

238

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

239

Dielectronic recombination of berylliumlike Xe50+ ions: Measurement and theoretical calculations  

NASA Astrophysics Data System (ADS)

Absolute rate coefficients for dielectronic recombination (DR) of Be-like 136Xe50+ have been measured at the heavy-ion storage ring ESR. The experimental results are compared with relativistic distorted-wave calculations employing the multiconfiguration Dirac-Fock method. Based on the DR measurements, multiple intra-L-shell excitation energies were determined.

Bernhardt, D.; Brandau, C.; Kozhuharov, C.; Müller, A.; Schippers, S.; Böhm, S.; Bosch, F.; Harman, Z.; Jacobi, J.; Kieslich, S.; Knopp, H.; Mokler, P. H.; Nolden, F.; Shi, W.; Stachura, Z.; Steck, M.; Stohlker, Th

2014-04-01

240

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

241

Theoretical calculation of low-lying states of NaAr and NaXe  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

242

Laboratory measurements and theoretical calculations of O2 A band electric quadrupole transitions  

NASA Astrophysics Data System (ADS)

Frequency-stabilized cavity ring-down spectroscopy was utilized to measure electric quadrupole transitions within the O162 A band, b?1g+?X?3g-(0,0) . We report quantitative measurements (relative uncertainties in intensity measurements from 4.4% to 11%) of nine ultraweak transitions in the ON , OP , SR , and ST branches with line intensities ranging from 3×10-30 to 2×10-29cmmolec.-1 . A thorough discussion of relevant noise sources and uncertainties in this experiment and other cw-cavity ring-down spectrometers is given. For short-term averaging (t<100s) , we estimate a noise-equivalent absorption of 2.5×10-10cm-1Hz-1/2 . The detection limit was reduced further by co-adding up to 100 spectra to yield a minimum detectable absorption coefficient equal to 1.8×10-11cm-1 , corresponding to a line intensity of ˜2.5×10-31cmmolec.-1 . We discuss calculations of electric quadrupole line positions based on a simultaneous fit of the ground and upper electronic state energies which have uncertainties <3MHz , and we present calculations of electric quadrupole matrix elements and line intensities. The electric quadrupole line intensity calculations and measurements agreed on average to 5%, which is comparable to our average experimental uncertainty. The calculated electric quadrupole band intensity was 1.8(1)×10-27cmmolec.-1 which is equal to only ˜8×10-6 of the magnetic dipole band intensity.

Long, D. A.; Havey, D. K.; Okumura, M.; Pickett, H. M.; Miller, C. E.; Hodges, J. T.

2009-10-01

243

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

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

244

Ultrafast excited state dynamics of the Na3F cluster: Quantum wave packet and classical trajectory calculations compared to experimental results  

NASA Astrophysics Data System (ADS)

Short-time, excited-state dynamics of the lowest isomer of the Na3F cluster is studied theoretically in order to interpret the features of recent time-resolved pump-probe ionization experiments [J. M. L'Hermite, V. Blanchet, A. Le Padellec, B. Lamory, and P. Labastie, Eur. Phys. J. D 28, 361 (2004)]. In the present paper, we propose an identification of the vibrational motion responsible for the oscillations in the ion signal, on the basis of quantum mechanical wave packet propagations and classical trajectory calculations. The good agreement between experiment and theory allows for a clear interpretation of the detected dynamics.

Heitz, M.-C.; Durand, G.; Spiegelman, F.; Meier, C.; Mitri?, R.; Bonac?i?-Koutecký, V.

2004-11-01

245

Free energies of binding from large-scale first-principles quantum mechanical calculations: application to ligand hydration energies.  

PubMed

Schemes of increasing sophistication for obtaining free energies of binding have been developed over the years, where configurational sampling is used to include the all-important entropic contributions to the free energies. However, the quality of the results will also depend on the accuracy with which the intermolecular interactions are computed at each molecular configuration. In this context, the energy change associated with the rearrangement of electrons (electronic polarization and charge transfer) upon binding is a very important effect. Classical molecular mechanics force fields do not take this effect into account explicitly, and polarizable force fields and semiempirical quantum or hybrid quantum-classical (QM/MM) calculations are increasingly employed (at higher computational cost) to compute intermolecular interactions in free-energy schemes. In this work, we investigate the use of large-scale quantum mechanical calculations from first-principles as a way of fully taking into account electronic effects in free-energy calculations. We employ a one-step free-energy perturbation (FEP) scheme from a molecular mechanical (MM) potential to a quantum mechanical (QM) potential as a correction to thermodynamic integration calculations within the MM potential. We use this approach to calculate relative free energies of hydration of small aromatic molecules. Our quantum calculations are performed on multiple configurations from classical molecular dynamics simulations. The quantum energy of each configuration is obtained from density functional theory calculations with a near-complete psinc basis set on over 600 atoms using the ONETEP program. PMID:23841453

Fox, Stephen J; Pittock, Chris; Tautermann, Christofer S; Fox, Thomas; Christ, Clara; Malcolm, N O J; Essex, Jonathan W; Skylaris, Chris-Kriton

2013-08-15

246

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

247

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

248

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

PubMed

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

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

2014-01-01

249

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

NASA Technical Reports Server (NTRS)

The application of ab initio quantum mechanical approaches in the study of metal atom clusters requires simplifying techniques that do not compromise the reliability of the calculations. Various aspects of the implementation of the effective core potential (ECP) technique for the removal of the metal atom core electrons from the calculation were examined. The ECP molecular integral formulae were modified to bring out the shell characteristics as a first step towards fulfilling the increasing need to speed up the computation of the ECP integrals. Work on the relationships among the derivatives of the molecular integrals that extends some of the techniques pioneered by Komornicki for the calculation of the gradients of the electronic energy was completed and a formulation of the ECP approach that quite naturally unifies the various state-of-the-art "shape- and Hamiltonian-consistent" techniques was discovered.

Kahn, L. R.

1981-01-01

250

Porous silicon: theoretical studies  

NASA Astrophysics Data System (ADS)

Porous silicon has attracted considerable scientific interest ever since the recent discovery of visible photoluminescence. We present a review of the theoretical work done on this material. We describe the classical theories and computer simulations of the growth of this brittle, spongy structure. The electronic structure calculations based on first principles local density approximation as well as semi-empirical methodologies are outlined. Phenomenological models for photoluminescence, its broad lineshape, decay and temperature dependence and excitonic effects on optical behavior are reviewed. Rudimentary theories of electroluminescence, transport and quantum efficiency are also described. A unified, consistent theoretical framework appears to be a distant goal. Broad suggestions for further theoretical work are outlined.

John, George C.; Singh, Vijay A.

1995-12-01

251

Quantum-mechanical calculations of magnesium aspartate arginine structure and spectroscopic characteristics  

NASA Astrophysics Data System (ADS)

Theoretical calculations of magnesium aspartate-arginine (Mg[Asp-Arg]) structure and spectroscopic characteristics have been performed in the gas phase with the GAUSSIAN 98 software package using density functional theory (DFT) at the B3PW91 level. The 6-31+G* basis set was selected due to their reasonable quality and size. The comparison with corresponding results for magnesium aspartate-glycine (Mg[Asp-Gly]) is presented. NMR and IR measurements were carried out and obtained experimental 1H and 13C chemical shifts and IR spectra are compared with calculated spectral parameters.

Marcoin, W.; Pasterny, K.; Wrzalik, R.

2005-05-01

252

Quantum-mechanical calculations and spectroscopic characteristics of magnesium glutamate glycine and magnesium glutamate arginine  

NASA Astrophysics Data System (ADS)

Theoretical calculations of magnesium glutamate-glycine ([Mg(glu-gly)]) and magnesium glutamate-arginine ([Mg(glu-arg)]) structures and their spectroscopic characteristics have been performed in the gas phase with the GAUSSIAN 98 software package using density functional theory (DFT) at the B3PW91 level. The 6-31+G* basis set was selected due to their reasonable quality and size. NMR and IR measurements were carried out and obtained experimental 1H and 13C chemical shifts and IR spectra are compared with calculated spectral parameters.

Marcoin, W.; Pasterny, K.; Pasterna, G.; Wrzalik, R.

2006-07-01

253

Field-theoretic calculation of critical exponents for the Lifshitz point  

NASA Astrophysics Data System (ADS)

We use field theory to calculate the critical exponents ?l2, ?l4, ?l2, and ?l4 for the Lifshitz point (LP) with m=2 and m=6. We were motivated by an old controversy on the order ?2 corrections for the exponents of this multicritical point. In a previous paper, we studied the renormalization of the theory that describes the LP and derived expressions for the exponents and scaling relations that hold to all orders in perturbation. In this work we concentrate on the calculation of the Feynman diagrams that are involved in the determination of the exponents and present our results for the exponents to order ?2. The evaluation of these diagrams, due to a free propagator that contains a quartic term in the momentum and is not rotationally invariant, requires special techniques that are presented in detail in the appendixes.

Mergulhão, C., Jr.; Carneiro, C. E. I.

1999-06-01

254

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

SciTech Connect

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

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

2001-06-13

255

Theoretical calculation of absorption intensities of C2H and C2D  

NASA Astrophysics Data System (ADS)

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

Tarroni, Riccardo; Carter, Stuart

2004-01-01

256

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

NASA Technical Reports Server (NTRS)

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

Xu, Y. J.

1984-01-01

257

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

258

Electron correlation effects on the theoretical calculation of nuclear magnetic resonance spin–spin coupling constants  

Microsoft Academic Search

The equation-of-motion coupled cluster singles and doubles (EOM-CCSD) method for general second-order properties is derived providing a quadratic, CI-like approximation and its linked form from coupled cluster (CC) energy derivative theory. The effects of the quadratic contribution, of the atomic basis set employed, and of electron correlation on NMR spin–spin coupling constant calculations using EOM-CCSD methods are investigated for a

S. Ajith Perera; Marcel Nooijen; Rodney J. Bartlett

1996-01-01

259

DFT-based Theoretical Calculation of Nb and W-doped Anatase TiO2  

Microsoft Academic Search

The structure and electronic states in the Nb-doped TiO2 (TNO) and W-doped TiO2 (TWO) in anatase phase were investigated from the first-principle using DFT-based band structure method. In addition to the cases where the dopant substituting a Ti atom, cells containing a dopant (MTi; M = Nb, W) and an oxygen vacancy (VO) were calculated in order to clarify the

Takahiro Suenaga; Hideyuki Kamisaka; Hisao Nakamura; Koichi Yamashita

2010-01-01

260

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

PubMed

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

Huang, Jianhua

2012-07-01

261

Dielectronic recombination of lithiumlike Xe51+ ions: Storage ring experiment and theoretical calculations  

NASA Astrophysics Data System (ADS)

Absolute rate coefficients for dielectronic recombination (DR) of Li-like 136Xe51+ have been measured at the heavy-ion storage ring ESR. The experimental results are compared with relativistic distorted-wave calculations employing the multiconfiguration Dirac-Fock method. Based on the DR measurements the 2s-2p1/2 and 2s-2p3/2 excitation energies in Li-like Xe51+ were determined with a relative accuracy of ~400 ppm.

Bernhardt, D.; Brandau, C.; Harman, Z.; Kozhuharov, C.; Müller, A.; Schippers, S.; Böhm, S.; Bosch, F.; Jacobi, J.; Kieslich, S.; Knopp, H.; Mokler, P. H.; Nolden, F.; Shi, W.; Stachura, Z.; Steck, M.; Stöhlker, Th

2014-04-01

262

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

263

Theoretical studies of cation adsorption on hydroxylated ?-A1 2 O 3 (corundum): electronic structure calculations  

Microsoft Academic Search

The adsorption of alkali metal cations on a hydroxylated corundum surface was investigated using high-level electronic structure\\u000a calculations, with both cluster Hartree–Fock and periodic density-functional theory approaches. The work concentrates on the\\u000a structural aspects of binding sites with threefold oxygen coordination at the basal (0001) surface. It was found that adsorption\\u000a at different sites can give rise to a wide

C. W. Yong; M. C. Warren; I. H. Hillier; D. J. Vaughan

2003-01-01

264

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)] [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)] [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)] [Department of Physics and Material Sciences Center, Philipps University, Renthof 5, 35032 Marburg (Germany)

1997-07-01

265

Theoretical investigations of quantum walks by cold atoms in a double optical lattice  

SciTech Connect

We investigate the feasibility of carrying out quantum walks with cold atoms in a double optical lattice. Monte Carlo simulations of time-of-flight (TOF) detection and absorption imaging were carried out, focusing on a specific experimental implementation. These indicate that absorption imaging would be best suited for detection of quantum walks. With typical experimental parameters a few hundred quantum walk steps will be needed for an unambiguous detection of the quantum walk signature. We show that in special cases, few-step quantum walks can also be detected in our system if one measures the relative population of the atoms in their internal states rather than their displacement in space, that is, measurements are made in the space of the coin operator rather than in that of the displacement operator.

Satapathy, Nandan; Ramachandran, Hema [Raman Research Institute, Sadashivnagar, Bangalore 560 080 (India); Hagman, Henning; Zelan, Martin; Kastberg, Anders [Department of Physics, Umeaa University, SE-90187 Umeaa (Sweden)

2009-07-15

266

Progress in Quantum Monte Carlo Calculations of Light Nuclei with Non-Local Potentials  

NASA Astrophysics Data System (ADS)

Monte Carlo methods often used in nuclear physics, such as auxiliary field diffusion Monte Carlo and Green's function Monte Carlo, have typically relied on phenomenological local real-space potentials containing as few derivatives as possible, such as the Argonne-Urbana family of interactions, to make sampling simple and efficient. Basis set methods such as no-core shell model or coupled-cluster techniques typically use softer non-local potentials because of their more rapid convergence with basis set size. These non-local potentials are typically defined in momentum space and are often based on effective field theory. Comparisons of the results of the two types of methods are complicated by the use of different potentials. I will discuss progress we have made in using such non-local potentials in quantum Monte Carlo calculations of light nuclei. In particular, I will show methods for evaluating the real-space, imaginary-time propagators needed to perform quantum Monte Carlo calculations using such non-local potentials, how to formulate a good trial wave function for such potentials, and how to perform a ``one-step'' Green's function Monte Carlo calculation for such potentials.

Lynn, Joel; Schmidt, Kevin; Carlson, Joe; Gandolfi, Stefano

2013-04-01

267

Quantum Monte Carlo Calculations of Light Nuclei with Non-Local Potentials  

NASA Astrophysics Data System (ADS)

Monte Carlo methods often used in nuclear physics, such as auxiliary field diffusion Monte Carlo and Green's function Monte Carlo, have typically relied on phenomenological local real-space potentials containing as few derivatives as possible, such as the Argonne-Urbana family of interactions, to make sampling simple and efficient. Basis set methods such as no-core shell model or coupled-cluster techniques typically use softer non-local potentials because of their more rapid convergence with basis set size. These non-local potentials are typically defined in momentum space and are often based on effective field theory. Comparisons of the results of the two types of methods are complicated by the use of different potentials. This thesis discusses progress made in using such non-local potentials in quantum Monte Carlo calculations of light nuclei. In particular, it shows methods for evaluating the real-space, imaginary-time propagators needed to perform quantum Monte Carlo calculations using non-local potentials and universality properties of these propagators, how to formulate a good trial wave function for non-local potentials, and how to perform a "one-step" Green's function Monte Carlo calculation for non-local potentials.

Lynn, Joel E.

268

Theoretical study of dynamic electron-spin-polarization via the doublet-quartet quantum-mixed state and time-resolved ESR spectra of the quartet high-spin state.  

PubMed

The mechanism of the unique dynamic electron polarization of the quartet (S = 3/2) high-spin state via a doublet-quartet quantum-mixed state and detail theoretical calculations of the population transfer are reported. By the photo-induced electron transfer, the quantum-mixed charge-separate state is generated in acceptor-donor-radical triad (A-D-R). This mechanism explains well the unique dynamic electron polarization of the quartet state of A-D-R. The generation of the selectively populated quantum-mixed state and its transfer to the strongly coupled pure quartet and doublet states have been treated both by a perturbation approach and by exact numerical calculations. The analytical solutions show that generation of the quantum-mixed states with the selective populations after de-coherence and/or accompanying the (complete) dephasing during the charge-recombination are essential for the unique dynamic electron polarization. Thus, the elimination of the quantum coherence (loss of the quantum information) is the key process for the population transfer from the quantum-mixed state to the quartet state. The generation of high-field polarization on the strongly coupled quartet state by the charge-recombination process can be explained by a polarization transfer from the quantum-mixed charge-separate state. Typical time-resolved ESR patterns of the quantum-mixed state and of the strongly coupled quartet state are simulated based on the generation mechanism of the dynamic electron polarization. The dependence of the spectral pattern of the quartet high-spin state has been clarified for the fine-structure tensor and the exchange interaction of the quantum-mixed state. The spectral pattern of the quartet state is not sensitive towards the fine-structure tensor of the quantum-mixed state, because this tensor contributes only as a perturbation in the population transfer to the spin-sublevels of the quartet state. Based on the stochastic Liouville equation, it is also discussed why the selective population in the quantum-mixed state is generated for the "finite field" spin-sublevels. The numerical calculations of the elimination of the quantum coherence (de-coherence and/or dephasing) are demonstrated. A new possibility of the enhanced intersystem crossing pathway in solution is also proposed. PMID:21321715

Teki, Yoshio; Matsumoto, Takafumi

2011-04-01

269

Quantum mechanical binding free energy calculation for phosphopeptide inhibitors of the Lck SH2 domain.  

PubMed

The accurate and efficient calculation of binding free energies is essential in computational biophysics. We present a linear-scaling quantum mechanical (QM)-based end-point method termed MM/QM-COSMO to calculate binding free energies in biomolecular systems, with an improved description of entropic changes. Molecular dynamics trajectories are re-evaluated using a semiempirical Hamiltonian and a continuum solvent model; translational and rotational entropies are calculated using configurational integrals, and internal entropy is calculated using the harmonic oscillator approximation. As an application, we studied the binding of a series of phosphotyrosine tetrapeptides to the human Lck SH2 domain, a key component in intracellular signal transduction, modulation of which can have therapeutic relevance in the treatment of cancer, osteoporosis, and autoimmune diseases. Calculations with molecular mechanics Poisson-Boltzmann, and generalized Born surface area methods showed large discrepancies with experimental data stemming from the enthalpic component, in agreement with an earlier report. The empirical force field-based solvent interaction energy scoring function yielded improved results, with average unsigned error of 3.6 kcal/mol, and a better ligand ranking. The MM/QM-COSMO method exhibited the best agreement both for absolute (average unsigned error = 0.7 kcal/mol) and relative binding free energy calculations. These results show the feasibility and promise of a full QM-based end-point method with an adequate balance of accuracy and computational efficiency. © 2011 Wiley Periodicals, Inc. J Comput Chem 2011. PMID:21484840

Anisimov, Victor M; Cavasotto, Claudio N

2011-04-11

270

Reduced dimensionality quantum scattering calculations on the Cl+CH4-->HCl+CH3 reaction  

NASA Astrophysics Data System (ADS)

Reduced dimensionality quantum scattering calculations using the Rotating Line Approximation, RLA, are performed on the Cl+CH4-->HCl+CH3 reaction, treating CH4 as a pseudo-diatom QH. A LEPS potential energy surface is used, where the zero-point energy of the modes not explicitly treated in the RLA calculations are included. The calculations are performed using hyperspherical coordinates and the improved log-derivative method of Manolopoulos. Boundary conditions have been applied using a hyperspherical projection method and an approximate method where the boundary conditions are applied directly in the hyperspherical coordinates. It is explicitly shown that the agreement between the methods is good. Scattering resonances are observed and related to the shape of the hyperspherical adiabats. Cumulative and state-to-state reaction probabilities are also presented. Vibrational adiabaticity is found to dominate without being exclusive. For Cl+CH4(v=1)-->HCl(n=1)+CH3 and a translational energy of 0.159 eV, measured differential cross sections give predominantly forward scattering, while for Cl+CH4(v=1)-->HCl(n=0)+CH3 there is predominantly backward and sideways scattering. Our calculated differential cross sections are in agreement with these general observations. Thermal rate constants have been calculated for the temperature range 200-800 K. The calculated rate constants are smaller than the experimental ones by less than 40% over the entire temperature range.

Nyman, Gunnar; Yu, Hua-Gen; Walker, Robert B.

1998-10-01

271

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

NASA Technical Reports Server (NTRS)

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

Avrett, E. H.

1985-01-01

272

Theoretical calculations of base-base interactions in nucleic acids: I. Stacking interactions in free bases.  

PubMed Central

Stacking interactions in free bases were computed on the basis of molecular association. The results of the calculations were compared with the stacking patterns observed in a few single crystals of nucleic acid components as examples. The following are the conclusions: (i) there can be two types of stacking pattern classified as normal and inverted types for any two interacting bases and both can be energetically favourable (ii) in both the types the stacking interaction is a combined effect of the overlap of the interacting bases and relative positions and orientations of the atomic centres of the two bases (iii) crystal symmetry and H-bonding interaction may influence stacking patterns.

Gupta, G; Sasisekharan, V

1978-01-01

273

Theoretical and experimental investigations of the electronic structure for selectively ?-doped strained InxGa1-xAs/GaAs quantum wells  

NASA Astrophysics Data System (ADS)

The electronic structures of Si ?-doped strained InxGa1-xAs/GaAs quantum wells have been studied theoretically and compared with experiments. The emphasis has been on the comparison between well center-, edge-, and barrier-positioned ?-doped layers. The highest achievable single-subband occupation decreases as the ? sheet is moved away from the center to the edge and finally to the barrier, but the electron mobility increases at the same time. Photoluminescence data have been found shifted to lower energies than the predictions of a self-consistent Hartree calculation owing to many-body effects, which have been quantified here using both plasmon-pole and random-phase approximations.

Ke, Mao-Long; Westwood, D.; Williams, R. H.; Godfrey, M. J.

1995-02-01

274

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

SciTech Connect

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

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

1993-12-02

275

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

NASA Astrophysics Data System (ADS)

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

Yu, Hua-Gen; Smith, Sean C.

1998-01-01

276

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

PubMed

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

Garberoglio, Giovanni; Harvey, Allan H

2011-04-01

277

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

PubMed

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

Hickey, A Leif; Rowley, Christopher N

2014-05-22

278

Semiconducting single-walled carbon nanotubes exposed to distilled water and aqueous solution: Electrical measurement and theoretical calculation  

NASA Astrophysics Data System (ADS)

We fabricate and measure a single-walled carbon nanotube transistor having a liquid-gate electrode. The ratio value of Ion/Ioff is as high as 104, indicating the presence of a semiconducting channel. A passivation layer over the source/drain electrode greatly suppresses the liquid-gate leakage by about three orders of magnitude. The channel currents are noticeably distinct between two liquid samples: distilled water and aqueous solution (1×10-4 M NaCl). This biological sensing ability is attributed to the different electrical double-layer capacitances with respect to the bulk part of the channel. The corresponding theoretical calculation is carried out in detail.

Lu, Ming-Pei; Hsiao, Cheng-Yun; Lo, Po-Yuan; Wei, Jeng-Hua; Yang, Yuh-Shyong; Chen, Ming-Jer

2006-01-01

279

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

NASA Technical Reports Server (NTRS)

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

Avrett, E. H.

1986-01-01

280

DFT-based Theoretical Calculation of Nb- and W-doped Anatase TiO2  

NASA Astrophysics Data System (ADS)

The structure and electronic states in the Nb-doped TiO2 (TNO) and W-doped TiO2 (TWO) in anatase phase were investigated from the first-principle using DFT-based band structure method. In addition to the cases where the dopant substituting a Ti atom, cells containing a dopant (MTi; M = Nb, W) and an oxygen vacancy (VO) were calculated in order to clarify the role of the oxygen vacancy in the system. Furthermore, cells containing two dopants and an oxygen vacancy (2MTi--VO), and cells with a dopant and two oxygen vacancies (MTi--2VO) were calculated. Energetically stable structures were found among the sampled 2WTi--VO and WTi--2VO cells, while the corresponding structures in TNO did not show any significant energy stabilization. Impurity states were found in the stable 2WTi--VO and WTi--2VO structures, and an approach of the two WTi atoms was observed in the former. The present results rationalize the lower electronic conductivity of TWO than that of TNO, and suggest possible formation of complex structures consisting of the WTi dopants and the oxygen vacancies.

Suenaga, Takahiro; Kamisaka, Hideyuki; Nakamura, Hisao; Yamashita, Koichi

2010-03-01

281

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

PubMed

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

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

2012-01-01

282

Theoretical studies of cation adsorption on hydroxylated ?-A12O3 (corundum): electronic structure calculations  

NASA Astrophysics Data System (ADS)

The adsorption of alkali metal cations on a hydroxylated corundum surface was investigated using high-level electronic structure calculations, with both cluster Hartree-Fock and periodic density-functional theory approaches. The work concentrates on the structural aspects of binding sites with threefold oxygen coordination at the basal (0001) surface. It was found that adsorption at different sites can give rise to a wide range of adsorption energies, which strongly depends on the freedom of surface hydrogen atoms to adjust their positions. Alkali metal adions from Li+ to Cs+ were studied with the cluster method, periodic plane-wave pseudopotential calculations being carried out for K+ adsorption to validate the cluster results. A site above an octahedral interstice was found to be the least preferred for cation adsorption, despite having the lowest repulsion from surface aluminium atoms. The strongest adsorption was found over an aluminium atom in the second layer, because the hydroxyl groups could reorient towards the neighbouring octahedral interstices, and hence significantly decrease repulsion with the cation. The adsorption energy and the first three interlayer spacings parallel to the basal surface change systematically with ionic size for each adsorption site. Many of these trends extend to adsorption of Ca2+, Co2+ and Pb2+, which were also investigated, although a redistribution of 3d electrons in Co2+ results in strong adsorption even at an unfavourable site. The results suggest that it may be possible not only to predict adsorption behaviour for a wide range of elements, but also to use experimental measurements of interplanar separations to gain information about contaminated surfaces.

Yong, C. W.; Warren, M. C.; Hillier, I. H.; Vaughan, D. J.

283

Combined spectral experiment and theoretical calculation to study the interaction of 1,4-dihydroxyanthraquinone for metal ions in solution  

NASA Astrophysics Data System (ADS)

The interaction between 1,4-dihydroxyanthraquinone (1,4-DHA) and metal ions was studied by UV-Visible and fluorescence spectroscopies in solution. Time-dependent density functional theory calculations confirmed complex structures. The investigation results showed 1,4-DHA can selectively respond some metal ions and can be monitored by UV-Vis, fluorescence spectra and naked-eye. So 1,4-DHA has a potential application in the design of metal ions probe. More, as typical metal ions, Hg2+ and Er3+, their reaction abilities for 1,4-DHA were studied in detailed. Experimental results showed they have better response for 1,4-DHA. And theoretical calculation concluded that Er3+ easily reacts with 1,4-DHA over Hg2+ attributed to the low reaction energy of Er3+-1,4-DHA than Hg2+-1,4-DHA.

Yin, Caixia; Zhang, Jingjing; Huo, Fangjun

2013-11-01

284

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

NASA Technical Reports Server (NTRS)

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

Stallcop, J. R.

1974-01-01

285

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

286

Variational quantum Monte Carlo calculation of the cohesive properties of cubic boron nitride  

SciTech Connect

The cohesive properties of cubic boron nitride are calculated using the variational quantum Monte Carlo approach. The calculated properties are found to be in good agreement with experiment and demonstrate the effectiveness of the variational forms of wave functions previously used in sp-bonded systems involving only one chemical species when applied to solids with more than one type of atom. The formulation of variance minimization for the one-body term in solids without inversion symmetry is presented, and a particularly simple form of one-body term based on a charge-fluctuation picture of electron correlation is shown to obtain excellent results for ground-state energies of B, C, and N atoms, and for the cubic boron nitride solid. {copyright} {ital 1997} {ital The American Physical Society}

Malatesta, A. [Dipartimento di Fisica, Universita di Roma La Sapienza, Piazzale Aldo Moro 2, 00185 Rome (Italy)] [Dipartimento di Fisica, Universita di Roma La Sapienza, Piazzale Aldo Moro 2, 00185 Rome (Italy); Fahy, S. [Physics Department, University College Cork (Ireland)] [Physics Department, University College Cork (Ireland); Bachelet, G.B. [Dipartimento di Fisica and Unita INFM, Universita di Roma La Sapienza, Piazzale Aldo Moro 2, 00185 Rome (Italy)] [Dipartimento di Fisica and Unita INFM, Universita di Roma La Sapienza, Piazzale Aldo Moro 2, 00185 Rome (Italy)

1997-11-01

287

Simple one-body term in variational quantum Monte Carlo calculations for solids and atoms  

NASA Astrophysics Data System (ADS)

We present applications of a particularly simple form of the one-body term in the Jastrow factor used in variational quantum Monte Carlo calculations of electronic many-body energies. This one-body term is calculated in a simple way from Fourier transforms of the mean-field density and the two-body term in the Jastrow factor. The term is compared to the one-body term obtained from a variance minimization approach. Numerical results are presented for energies of valence electrons in B, C, and N atoms, and for diamond and cubic BN solids. ACKNOWLEDGEMENT: This work has been supported by the Human Capital and Mobility Programme of the European Commission through contract CHRX-CT94-0462.

Fahy, Stephen; Malatesta, Antonella; Bachelet, Giovanni

1996-03-01

288

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

289

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

PubMed

Transport properties for collisions of water with hydrogen atoms are computed by means of exact quantum scattering calculations. For this purpose, a potential energy surface (PES) was computed for the interaction of rigid H2O, frozen at its equilibrium geometry, with a hydrogen atom, using a coupled-cluster method that includes all singles and doubles excitations, as well as perturbative contributions of connected triple excitations. To investigate the importance of the anisotropy of the PES on transport properties, calculations were performed with the full potential and with the spherical average of the PES. We also explored the determination of the spherical average of the PES from radial cuts in six directions parallel and perpendicular to the C2 axis of the molecule. Finally, the computed transport properties were compared with those computed with a Lennard-Jones 12-6 potential. PMID:24320328

Dagdigian, Paul J; Alexander, Millard H

2013-11-21

290

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

NASA Astrophysics Data System (ADS)

We study the electronic structure and shell-filling effects of both spherical and vertical quantum dots by means of the density functional theory (DFT) with optimized effective potential (OEP) and self-interaction-correction (SIC) recently developed. The OEP/SIC procedure allows the elimination of the spurious self-interaction energy and the construction of accurate single-particle local potential with proper long-range Coulombic behavior. The OEP/SIC equations are discretized and solved accurately and efficiently by the generalized pseudospectral (GPS) method. The highest occupied orbital energy of N-electron quantum dots provides a direct measure of the electron affinity or chemical potential. We apply the OEP/SIC method to the study of the capacitive energy of N-electron spherical dots for N up to 70. The results show the shell and subshell structure pattern and the electron filling pattern follows closely the Hund's rule. We also consider the effect of including the vertical dimension in the quantum dot study. We perform a detailed study of the shell-filling effect and the angular and radial density distributions of vertical quantum dots. The calculated capacitive energy spectrum is in good agreement with the recent experimental results, providing physical insights regarding the origin of electron shells and the role of electron-electron interaction in quantum dots.

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

2001-01-01

291

Studies on the interaction between 9-fluorenylmethyl chloroformate and Fe(3+) and Cu(2+) ions: Spectroscopic and theoretical calculation approach.  

PubMed

The interaction between 9-fluorenylmethyl chloroformate (FMOC-Cl) and Fe(3+) and Cu(2+) ions was investigated using fluorescence, UV/Vis absorption spectroscopies and theoretical calculation. The optical property of FMOC-Cl was studied in detail in absence and presence of various transition metal ions with particular affinity to Fe(3+) and Cu(2+) ions. With the fluorescence characteristic band centered at 307 and 315nm for FMOC-Cl, the introduction of Fe(3+) or Cu(2+) ions leads to the fluorescence quenching of FMOC-Cl with different shift and intensities of two fluorescent bands. It allows us to differentiate between FMOC-Cl and Fe(3+) and Cu(2+) ions interaction behavior. The study on fluorescent kinetics confirms that the fluorescence quenching of FMOC-Cl with Fe(3+) and Cu(2+) ions is based on the formation of non-fluorescent material, that is, static quenching. Further analyses of bond lengths, Mulliken atomic charges and the frontier orbital compositions for FMOC-Cl and its complexes with Fe(3+) and Cu(2+) ions were carried out. The theoretical calculations prove the fluorescence quenching originates from the formation of coordination bonds between the oxygen atom of the carbonyl group of FMOC-Cl and Fe(3+) and Cu(2+) ions. The commercially available FMOC-Cl can be used as excellent fluorescent probe toward Fe(3+) and Cu(2+) ions with high sensitivity. PMID:24887497

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

2014-11-11

292

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

PubMed

The N-(4-nitrophenyl)-?-alanine in crystalline form directly by the addition of 4-nitroaniline to the acrylic acid in aqueous solution has been obtained. The title ?-alanine derivative crystallizes in the P2(1)/c space group of monoclinic system with four molecules per unit cell. The X-ray geometry of ?-alanine derivative molecule has been compared with those obtained by molecular orbital calculations corresponding to the gas phase. In the crystal the molecules related by an inversion center interact via symmetrically equivalent O-H···O hydrogen bonds with O···O distance of 2.656(2) Å forming a dimeric structure. The dimers of ?-alanine derivative weakly interact via N-H···O hydrogen bonds between the H atom of ?-amine groups and one of O atom of nitro groups. The room temperature powder vibrational (infrared and Raman) measurements are in accordance with the X-ray analysis. In aqueous solution of 4-nitroaniline and acrylic acid, the double CC bond of vinyl group of acrylic acid breaks as result of 4-nitroaniline addition. PMID:20980195

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

2011-08-15

293

Do theoretical calculations really predict nodes in Fe-based superconductors?  

NASA Astrophysics Data System (ADS)

It is well established that calculations based on the LDA band structure and the Hubbard model, with the parameters U˜1.3-1.6 eV, and J˜0.2-0.3 J (a "UJ" model), yield strongly anisotropic, and sometimes nodal gaps. The physical origin of this effect is well understood: the two leading terms in the model are ?Unini and ?' U ninj. The former ensures that the coupling to spin fluctuations proceeds only through the like orbitals, and the latter, not being renormalized by the standard Tolmachev-Morel-Anderson logarithm, tends to equalize the positive and the negative order parameters. Both these features are suspect on a general physics basis: the leading magnetic interaction in itinerant systems is the Hund-rule coupling, which couples every orbital with all the others, and the pnictides, with the order parameter less than 20 meV, should have nearly as strong renormalization of the Coulomb pseudopotential as the conventional superconductors. I will argue that, instead of the UJ model, in pnictides one should use the "I" model, derived from the density functional theory (which is supposed to describe the static susceptibility on the mean field level very accurately). The "I" here is simply the Stoner factor, the second variation of the LSDA magnetic energy. Unfortunately, this approach is very unlikely to produce gap nodes as easily as the UJ model, indicating that one has to look elsewhere for the nodes origin.

Mazin, Igor

2011-03-01

294

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

PubMed Central

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

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

2009-01-01

295

Quantum Monte Carlo and transfer-matrix calculations for one-dimensional easy-plane ferromagnets  

SciTech Connect

We have applied previously used quantum Monte Carlo (QMC) techniques to obtain numerically the thermodynamics of two well-studied quasi-one-dimensional (1D) easy-plane ferromagnetic models, in the presence of an applied magnetic field in the easy plane. The checkerboard decomposition form of the Trotter approximation to the partition function has been used. Internal energy, specific heat, magnetization, and susceptibility have been obtained for model Hamiltonians believed appropriate for spin S-italic = (1/2) ((C/sub 6/H/sub 11/NH/sub 3/)CuBr/sub 3/ (CHAB)) and S-italic = 1 (CsNiF/sub 3/), in temperature and field ranges where classical theories have predicted solitonlike kink excitations. The S-italic = (1/2) QMC calculations are verified and superseded by a numerically exact quantum transfer-matrix (QTM) technique. Results for the temperature dependence of the peak in the specific heat versus field are compared with available experimental results. For the model applicable to CHAB, it is found that there is no value of the easy-plane anisotropy parameter from 4% to 10% for which the QTM calculation can adequately reproduce the experimentally obtained peak height and position. On the other hand, the QMC results for the model assumed for CsNiF/sub 3/ do roughly reproduce the temperature dependence of the experimental peak positions, but not the peak heights. However, statistical errors present in our QMC data are large, and a better method is still needed for computing the quantum statistical mechanics of S-italic = 1 systems.

Wysin, G.M.; Bishop, A.R.

1986-09-01

296

Monte Carlo calculation of the quantum partition function via path integral formulations  

SciTech Connect

Using Bennett's Monte Carlo (MC) method, we calculate the quantum partition functions of path integral formulations. First, from numerically exact results for a harmonic oscillator and a double-well potential, we discuss how fast each approximate partition function converges to the exact value as the number of integral variables involved in the formulation is increased. It turns out that most effective and most suitable for the MC simulation is Takahashi and Imada's path integral fomulation based on a modified Trotter formula in which the original potential is replaced with an effective one. This formulation is well balanced between the following two factors: the effect of zero potential energy is underestimated, resulting in an improper increase in the partition function; and, on the other hand, effective potential restricts the motion of fictitious particles born in the formulation so that the partition function value tends to be smaller. Fictitious particles can be treated as classical ones. We therefore can apply Bennett's MC method to calculating the ratio of two quantum partition functions (of a system under consideration and a reference system). As the number of fictitious particles N is increased, choice of reference system becomes less and less important and multistage sampling becomes dispensable. This, to some extent, compensates for the expense that N is larger than the real particle number. The tunneling mechanism of fictitious particles in the simulation is discussed.

Kono, H.; Takasaka, A.; Lin, S.H.

1988-05-15

297

Structure of acidic haloaluminate melts: Neutron diffraction and quantum chemical calculations  

SciTech Connect

The structure of molten mixtures of (KX){sub {ital y}}(AlX{sub 3}){sub 1{minus}{ital y}} was investigated by neutron diffraction for X=Cl and Br and {ital y}=0.25 and 0.33. These melts, known as acidic haloaluminates, contain different ionic species such as AlX{sup {minus}}{sub 4},Al{sub 2}X{sup {minus}}{sub 7}, Al{sub 3}X{sup {minus}}{sub 10}. The diffraction patterns were similar, although not identical, for the same halide pairs and showed features indicative of short-range and intermediate-range order. Quantum chemical calculations were carried out on AlX{sup {minus}}{sub 4}, Al{sub 2}X{sup {minus}}{sub 7}, and Al{sub 3}X{sup {minus}}{sub 10} to provide information needed to interpret the structural results within the framework of the random packing of structural units model. It is shown that the bent Al--X--Al bridge for Al{sub 2}X{sup {minus}}{sub 7}, obtained from the quantum chemical calculations, is necessary to represent well the structure, and that the values of the bond angles at the central halide atoms are around 110{degree}. Aluminum atoms are found to be tetrahedrally coordinated by the halide atoms, and information on the orientational correlations of neighboring Al{sub 2}X{sup {minus}}{sub 7} is derived.

Blander, M.; Bierwagen, E.; Calkins, K.G.; Curtiss, L.A.; Price, D.L.; Saboungi, M. (Argonne National Laboratory, Argonne, Illinois 60439 (United States))

1992-08-15

298

Ab-Initio Calculations of Electronic Properties and Quantum Transport in U-Shaped Graphene Nanoribbons  

NASA Astrophysics Data System (ADS)

Graphene is a promising candidate as a material used in nano-scale devices because of recent developments in advanced experimental techniques. Motivated by recent successful fabrications of U-shaped graphene channel transistors by using the gallium focused ion beam technology, we have performed ab-initio calculations to investigate the electronic properties and quantum transport in U-shaped graphene nanoribbons. The electronic properties are calculated using a numerical atomic orbital basis set in the framework of the density functional theory. The transport properties are investigated using the non-equilibrium Green's function method. The transmission spectra of U-shaped graphenes are analyzed in order to reveal the quantum transport of the systems. We found that the graphene nanoribbons tend to open a band gap when U-shaped structures are formed in both armchair and zigzag cases. The geometrical structures of U-shaped GNRs had enormous influences on the electron transport around the Fermi energy due to the formation of quasi-bound states at zigzag edges. The obtained results have provided valuable information for designing potential nano-scale devices based on graphenes.

Cuong, Nguyen Tien; Mizuta, Hiroshi; Cong, Bach Thanh; Otsuka, Nobuo; Chi, Dam Hieu

2012-09-01

299

Synthesis, fluorescence properties and theoretical calculations of novel stilbene derivatives based on 1,3,4-oxadiazole bearing anthracene core.  

PubMed

Two novel stilbene derivatives bearing anthracene core based on 1,3,4-oxadiazole were efficiently synthesized and characterized by (1)H-NMR, mass spectrometry and elemental analysis. The optical properties of the title compounds were investigated by UV-vis absorption and fluorescence emission spectra in different solvents. Chemical calculations were performed by density functional theory (DFT) at the (B3LYP)/6-31G* level. The results show the two compounds exhibit strong green fluorescence emission ranged from 489-493 nm, and the fluorescence quantum yield ranged from 0.78-0.92. Their HOMO and LUMO levels are (-5.44 eV, -2.25 eV) and (-5.45 eV, -2.28 eV), respectively. The influence of the solvent on the fluorescence intensities was also discussed. PMID:23666076

Li, Xinwei; Lu, Huixiong; He, Daohang; Luo, Chun; Huang, Jianjun

2013-09-01

300

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: < r(C-C) ring>=1.397(4) Å; r(C 1-C aldehyde)=1.471(?) Å; r(C 3-O Me)=1.374(9) Å; r(C 4-O H)=1.361(?) Å; r(O-C Me)=1.428(?) Å; r(C dbnd6 O)=1.214(8) Å; < r(C-H)>=1.110(11) Å; r(O-H)=0.991(?) Å; ?C 6-C 1-C 2=120.6(2)°; ?C 1-C 2-C 3=118.8(?)°; ?C 1-C 6-C 5=120.1(?)°; ?C 2-C 1-C aldehyde=122.7(18)°; ?C 1-C dbnd6 O=119.4(16)°; ?C 4-C 3-O Me=112.2(12)°; ?C 3-C 4-O H=119.1(?)°; ?C 3-O-C=121.7(29)°. Those of isovanillin are as follows: < r(C-C) ring>=1.402(4) Å; r(C 1-C aldehyde)=1.479(?) Å; r(C 4-O Me)=1.369(9) Å; r(C 3-O H)=1.357(?) Å; r(O-C Me)=1.422(?) Å; r(C dbnd6 O)=1.221(9) Å; < r(C-H)>=1.114(14) Å; r(O-H)=0.995(?) Å; ?C 6-C 1-C 2=120.2(3)°; ?C 1-C 2-C 3=119.0(?)°; ?C 1-C 6-C 5=119.9(?)°; ?C 2-C 1-C aldehyde=124.6(25)°; ?C 1-C dbnd6 O=121.3(24)°; ?C 3-C 4-O Me=114.4(12)°; ?C 4-C 3-O H=121.2(?)°; ?C 4-O-C=123.8(26)°. Those of ethylvanillin are as follows: < r(C-C) ring>=1.397(6) Å; r(C 1-C aldehyde)=1.471(?) Å; r(C 3-O Et)=1.365(13) Å; r(C 4-O H)=1.352(?) Å; r(O-C Et)=1.427(?) Å; r(C-C Et)=1.494(21) Å; r(C dbnd6 O)=1.206(9) Å; < r(C-H)>=1.109(10) Å; r(O-H)=0.990(?) Å; ?C 6-C 1-C 2=120.2(3)°; ?C 1-C 2-C 3=118.4(?)°; ?C 1-C 6-C 5=119.7(?)°; ?C 2-C 1-C aldehyde=121.7(21)°; ?C 1-C dbnd6 O=128.8(22)°; ?C 4-C 3-O Et=112.8(14)°; ?C 3-C 4-O H=119.6(?)°; ?C 3-O-C=115.1(27)°; ?O-C-C Et=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

301

Theoretical Studies of the Influence of Temperature on Photoluminescence Dynamics in GaInNAs/GaAs Quantum Wells  

NASA Astrophysics Data System (ADS)

Dynamics of excitons in GaInNAs/GaAs quantum wells (QWs) is studied theoretically within a model of hopping excitons. In this model the temporal evolution of photoluminescence (PL) is described by the system of rate equations which takes into account hopping of excitons between randomly generated localizing states. In this work we study the influence of temperature on such characteristic features of PL as the decay and rise time of PL signal as well as their spectral dependences. It is clearly shown that our model reproduces experimental data very well.

Baranowski, Micha?; Kudrawiec, Robert; Misiewicz, Jan

2013-08-01

302

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

SciTech Connect

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

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

2012-07-01

303

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

304

Photo-deactivation pathways of a double H-bonded photochromic Schiff base investigated by combined theoretical calculations and experimental time-resolved studies.  

PubMed

The photophysics of N,N'-bis(salicylidene)-p-phenylenediamine (BSP) is analyzed both theoretically and experimentally. The alternative intramolecular proton-transfer reactions lead to three different tautomers. We performed DFT and TDDFT calculations to analyze the topography of the reactions connecting the three tautomers. Deactivation paths through a Conical Intersection (CI) region are also analyzed to explain the low fluorescence quantum yield of the phototautomers. The complex molecular structure of BSP provides a large number of deactivation paths, almost all of them energetically available following the initial photoexcitation. Femtosecond (fs) time-resolved emission studies in solution and flash photolysis experiments (nano to millisecond regime) were performed to get detailed information on the time domain of the full photocycle. The picture that emerges by combining theoretical and experimental results shows a very fast (less than 100 fs) photoinduced single proton transfer process leading to a phototautomer where a single proton has moved. This species may deactivate through a low-energy CI leading in about 20 ps to a rotameric form in the ground state that has a lifetime of several tens of microseconds in solution. This process competes with another deactivation path taking place prior to the proton-transfer reaction which involves a low-energy CI leading to a rotamer of the enol structure. In the flash photolysis studies, the rotamer of the enol structure was directly identified by the positive transient absorption band in the 250-260 nm and its lifetime in n-hexane (10 ms) is almost 3 orders of magnitude longer than the lifetime of the photochrome (around 40 ?s). Our findings do not exclude a double proton transfer reaction in the excited enol form to give a tautomer in less than 100 fs during the first (impulsive) phase of the reaction which reverts back to the photoproducts of the simple proton transfer in 1-3 ps. PMID:21755097

Randino, Carlos; Zió?ek, Marcin; Gelabert, Ricard; Organero, Juan Angel; Gil, Michal; Moreno, Miquel; Lluch, José M; Douhal, Abderrazzak

2011-09-01

305

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

NASA Astrophysics Data System (ADS)

A strong magnetic field applied along the growth direction of a quantum cascade laser (QCL) active region gives rise to a spectrum of discrete energy states, the Landau levels. By combining quantum engineering of a QCL with a static magnetic field, we can selectively inhibit/enhance non-radiative electron relaxation process between the relevant Landau levels of a triple quantum well and realize a tunable surface emitting device. An efficient numerical algorithm implementation is presented of optimization of GaAs/AlGaAs QCL region parameters and calculation of output properties in the magnetic field. Both theoretical analysis and MATLAB implementation are given for LO-phonon and interface roughness scattering mechanisms on the operation of QCL. At elevated temperatures, electrons in the relevant laser states absorb/emit more LO-phonons which results in reduction of the optical gain. The decrease in the optical gain is moderated by the occurrence of interface roughness scattering, which remains unchanged with increasing temperature. Using the calculated scattering rates as input data, rate equations can be solved and population inversion and the optical gain obtained. Incorporation of the interface roughness scattering mechanism into the model did not create new resonant peaks of the optical gain. However, it resulted in shifting the existing peaks positions and overall reduction of the optical gain.

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

2014-03-01

306

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

NASA Astrophysics Data System (ADS)

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

Handel, Peter H.; Sherif, Taher S.

2010-02-01

307

Theoretical study of self-starting gratings in photorefractive multiple-quantum-well structures  

NASA Astrophysics Data System (ADS)

A model of wave mixing is developed for photorefractive multiple-quantum-well structures in quantum-confined Stark effect geometry. This optical model takes into account both absorption and index gratings and is based on the nonlocal character of the optical nonlinearity in the direction of the applied electric field. A coupling gain is defined that depends only on the imaginary part of the relative permittivity grating. It is shown that self-starting gratings can appear when a certain threshold condition on the coupling gain is verified, with this condition being similar to the threshold condition for double phase-conjugate mirror operation in bulk photorefractive materials. The possibility of obtaining with actual devices the relatively high optical nonlinearity necessary to reach the threshold is discussed. Double phase conjugation with multiple-quantum-well structures in a two-zone configuration is envisaged. .

Gosselin, S.; Lovisa, S.; Gravey, P.; Wolffer, N.

1996-10-01

308

Theoretical investigation of a protected quantum bit in a small Josephson junction array with tetrahedral symmetry  

NASA Astrophysics Data System (ADS)

We consider a Josephson junction device which has a symmetry of a tetrahedron; it can be visualized as a tetrahedron that contains two Josephson junctions at each edge. We find the conditions for which the ground state of the system is degenerate or almost degenerate; in this case, the low-energy degrees of freedom can be mapped on a quantum spin 1/2 . We evaluate the effect of the physical perturbations and imperfections on the level splitting in this system and find that they are small for most perturbations. We argue that this system can provide a possible physical implementation of a protected quantum bit with a built-in error correction. We propose a way of manipulating the effective quantum spin by means of electrical potentials and an experimental scheme to read the information that it contains.

Usmanov, R. A.; Ioffe, L. B.

2004-06-01

309

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

310

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

SciTech Connect

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

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

2013-12-07

311

Theoretical comparison of quantum Zeno gates and logic gates based on the cross-Kerr nonlinearity  

NASA Astrophysics Data System (ADS)

Quantum logic operations can be implemented using nonlinear phase shifts (the Kerr effect) or the quantum Zeno effect based on strong two-photon absorption. Both approaches utilize three-level atoms, where the upper level is tuned on resonance for the Zeno gates and off-resonance for the nonlinear phase gates. The performance of nonlinear phase gates and Zeno gates are compared under conditions where the parameters of the resonant cavities and three-level atoms are the same in both cases. It is found that the expected performance is comparable for the two approaches despite the fundamental differences between the Zeno and Kerr effects.

You, Hao; Franson, J. D.

2012-12-01

312

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

313

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

ERIC Educational Resources Information Center

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

Andris, James F.

314

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

2013-01-21

315

Quantum mechanical calculations related to ionization and charge transfer in DNA  

NASA Astrophysics Data System (ADS)

Ionization and charge migration in DNA play crucial roles in mechanisms of DNA damage caused by ionizing radiation, oxidizing agents and photo-irradiation. Therefore, an evaluation of the ionization properties of the DNA bases is central to the full interpretation and understanding of the elementary reactive processes that occur at the molecular level during the initial exposure and afterwards. Ab initio quantum mechanical (QM) methods have been successful in providing highly accurate evaluations of key parameters, such as ionization energies (IE) of DNA bases. Hence, in this study, we performed high-level QM calculations to characterize the molecular energy levels and potential energy surfaces, which shed light on ionization and charge migration between DNA bases. In particular, we examined the IEs of guanine, the most easily oxidized base, isolated and embedded in base clusters, and investigated the mechanism of charge migration over two and three stacked guanines. The IE of guanine in the human telomere sequence has also been evaluated. We report a simple molecular orbital analysis to explain how modifications in the base sequence are expected to change the efficiency of the sequence as a hole trap. Finally, the application of a hybrid approach combining quantum mechanics with molecular mechanics brings an interesting discussion as to how the native aqueous DNA environment affects the IE threshold of nucleobases.

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

2012-07-01

316

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

PubMed Central

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

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

2012-01-01

317

Binding of hydrogen on benzene, coronene, and graphene from quantum Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

Quantum Monte Carlo calculations with the diffusion Monte Carlo (DMC) method have been used to compute the binding energy curves of hydrogen on benzene, coronene, and graphene. The DMC results on benzene agree with both Møller-Plessett second order perturbation theory (MP2) and coupled cluster with singles, doubles, and perturbative triples [CCSD(T)] calculations, giving an adsorption energy of ~25 meV. For coronene, DMC agrees well with MP2, giving an adsorption energy of ~40 meV. For physisorbed hydrogen on graphene, DMC predicts a very small adsorption energy of only 5 +/- 5 meV. Density functional theory (DFT) calculations with various exchange-correlation functionals, including van der Waals corrected functionals, predict a wide range of binding energies on all three systems. The present DMC results are a step toward filling the gap in accurate benchmark data on weakly bound systems. These results can help us to understand the performance of current DFT based methods, and may aid in the development of improved approaches.

Ma, Jie; Michaelides, Angelos; Alfè, Dario

2011-04-01

318

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

NASA Astrophysics Data System (ADS)

Several new substituted amidine derivatives of benzanthrone were synthesized by a condensation reaction from 3-aminobenzo[de]anthracen-7-one and appropriate aromatic and aliphatic amides. The obtained derivatives have a bright yellow or orange fluorescence in organic solvents and in solid state. The novel benzanthrone derivatives were characterized by TLC analysis, 1H NMR, IR, MS, UV/vis, and fluorescence spectroscopy. The solvent effect on photophysical behaviors of these dyes was investigated, and the results showed that the Stoke's shift increased, whereas quantum yield decreased with the growth of the solvent polarity. The structure of some dyes was confirmed by the X-ray single crystal structure analysis. AM1, ZINDO/S and ab initio calculations using Gaussian software were carried out to estimate the electron system of structures. The calculations show planar configurations for the aromatic core of these compounds and two possible orientations of amidine substituents. The calculation results correlate well with red-shifted absorption and emission spectra of compounds.

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

2013-01-01

319

The equation of state of diamond from quantum Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

We describe variational and diffusion quantum Monte Carlo (VMC and DMC) calculations that have been performed to evaluate the elastic properties of diamond up to pressures of about 500 GPa. We have used a smooth, norm-conserving, Hartree-Fock carbon pseudopotential in our work. Our trial wave functions were of Slater-Jastrow form, containing orbitals generated in plane-wave DFT-GGA calculations, which were re-expanded in a blip-function basis set. We propose a new scheme for determining the cutoff lengths that occur in our Jastrow factor. Using a 512-electron simulation cell, and fitting a Vinet equation of state to our energy-volume data, we have calculated the equilibrium lattice constant (A, in Angstrom), bulk modulus (B, in GPa), and pressure derivative of the bulk modulus (B') to be (A,B,B')=(3.547, 4.83, 3.43) within VMC and (3.563, 4.52, 3.61) within DMC, as compared with the experimental values of (A,B,B')=(3.567, 4.4-4.5, 3.0-4.0).

Maezono, Ryo; Ma, Andrea; Towler, Mike D.; Drummond, Neil D.; Needs, Richard J.

2006-03-01

320

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

321

Riemannian quantum circuit  

NASA Astrophysics Data System (ADS)

Number theory is an abstract mathematical field that has found a fertile environment for development in theoretical physics. In particular, several physical systems were related to the zeros of the Riemann-zeta function. In this work we present the theory of a unitary matrix related to a finite number of zeros of the Riemann-zeta function. The equivalent quantum circuit and the calculation of the entanglement of a multipartite quantum state produced by the Riemannian quantum circuit are also shown.

Ramos, R. V.; Mendes, F. V.

2014-04-01

322

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

PubMed

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 3500-100cm(-1) and 4000-400cm(-1), respectively, for 3-Bromodiphenylamine (3BDPA). Theoretical calculations were performed by using Density Functional Theory (DFT) method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The calculated wavenumbers were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (?0) and related properties (?, ? and ??) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization were analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the ?(*) and ?(*) anti-bonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. Molecular electrostatic potential (MEP) and HOMO-LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures and the results reveals the heat capacity (C), and entropy (S) increases with rise in temperature. PMID:24835947

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

2014-10-15

323

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

PubMed

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. PMID:19508063

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

2009-06-01

324

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

325

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

SciTech Connect

We derive a statistical physics model of two-dimensional electron gas (2DEG) and propose an accurate approximation method for calculating the quantum-mechanical effects of metal-oxide-semiconductor (MOS) structure in accumulation and strong inversion regions. We use an exponential surface potential approximation in solving the quantization energy levels and derive the function of density of states in 2D to 3D transition region by applying uncertainty principle and Schrödinger equation in k-space. The simulation results show that our approximation method and theory of density of states solve the two major problems of previous researches: the non-negligible error caused by the linear potential approximation and the inconsistency of density of states and carrier distribution in 2D to 3D transition region.

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

2013-10-15

326

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

327

Elastic light scattering by semiconductor quantum dots of arbitrary shape  

Microsoft Academic Search

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

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

2007-01-01

328

Theoretical calculation of the mixing enthalpies of 21 IIIB-IVB, IIIB-VB and IVB-VB binary alloy systems  

NASA Astrophysics Data System (ADS)

The calculation of the formation/mixing enthalpies of binary alloys is an important problem. There have been no systematic theoretical calculations of the mixing enthalpies for group B alloy systems using the famous Miedema theory or from the theoretical methods of first principle. Therefore such calculations for the 21 binary group IIIB-IVB, IIIB-VB and IVB-VB metal alloy systems are performed systematically for the first time using a subregular model. The results show that the agreement between the calculations and experimental data is pretty good and could be accepted from the theoretical or experimental points of view. From the present results and those in other two papers by the authors, it also can be concluded that the subregular model can be used for calculating the mixing enthalpies for all the 36 alloy systems combined with the 9 group B metals of Zn, Cd, Ga, In, Tl, Sn, Pb, Sb and Bi.

Zhang, Bangwei; Liao, Shuzhi; Shu, Xiaolin; Xie, Haowen; Yuan, Xiaojian

2013-06-01

329

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

330

Nuclear Tuning and Detuning of the Electron Spin Resonance in a Quantum Dot: Theoretical Consideration  

NASA Astrophysics Data System (ADS)

We study nuclear spin dynamics in a quantum dot close to the conditions of electron spin resonance. We show that at a small frequency mismatch, the nuclear field detunes the resonance. Remarkably, at larger frequency mismatch, its effect is opposite: The nuclear system is bistable, and in one of the stable states, the field accurately tunes the electron spin splitting to resonance. In this state, the nuclear field fluctuations are strongly suppressed, and nuclear spin relaxation is accelerated.

Danon, Jeroen; Nazarov, Yuli V.

2008-02-01

331

Theoretical calculation of bond dissociation energies and heats of formation for nitromethane and polynitromethanes with density functional theory  

NASA Astrophysics Data System (ADS)

The C bond NO2 bond dissociation energies (BDEs) and the heats of formation (HOFs) of nitromethane and polynitromethanes (dinitromethane, trinitromethane, and tetranitromethane) system in gas phase at 298.15 K were calculated theoretically. Density functional theory (DFT) B3LYP, B3P86, B3PW91, and PBE0 methods in combination with different basis sets were employed. It was found that the C bond NO2 bond BDEs can be improved from B3LYP to B3PW91 to B3P86 or PBE0 functional. Levels of theory employing B3P86 and PBE0 functionals were found to be sufficiently reliable without the presence of diffusion functions. As the number of NO2 groups on the same C atom increases, the PBE0 functional performs better than the B3P86 functional. Regarding the calculated HOFs, all four functionals can yield satisfactory results with deviations of <2 kcal mol-1 from experimental ones for CH2(NO2)2 and CH(NO2)3, when the diffusion functions are not augmented. For the C(NO2)4 molecule, the large basis sets augmented with polarization functions and diffusion functions are required to yield a good result.

Su, Xinfang; Cheng, Xinlu; Liu, Yonggang; Li, Qinghuan

332

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

NASA Astrophysics Data System (ADS)

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

Hahn, Sangjoon; Park, Kisam; Cho, Minhaeng

1999-09-01

333

Determination of lipophilicity of novel potential antituberculotic agents using HPLC on monolithic stationary phase and theoretical calculations.  

PubMed

The HPLC analyses on the monolithic stationary phase were employed for rapid determination of lipophilicity of the two sets of newly synthesized potential antituberculotic agents. The analyses utilized the mixture of methanol and phosphate buffer (pH 7.4) as a mobile phase and a flow rate of 4mL/min. Monolithic stationary phase enabled to significantly reduce the time of analyses, achieve appropriate peak shapes for all tested compounds as well as the separation of positional isomers. Furthermore, the theoretical lipophilic parameters (logP) for all compounds were calculated employing the chemical programs (e.g., ACD/logP, HyperChem, miLogP, AlogP, KOWWIN and COSMOFrag, etc.). The experimental data (logk) and calculated logP values were compared by linear regression analysis. The highest correlation for both series was obtained for KOWWIN and miLogP programs. However, capability of particular chemical software to precisely predict lipophilicity of a compound is structurally dependent. Thus the predictive power of the selected program should be verified using experimental method. The results of this study documented that experimental determination of lipophilicity using HPLC on monolithic stationary phase is practical and reasonable for this purpose. PMID:18272313

Mrkvicková, Z; Kovaríková, P; Balíková, S; Klimes, J

2008-09-29

334

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 XY 3 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

335

A rigorous full-dimensional quantum dynamics calculation of the vibrational energies of H3O2-  

NASA Astrophysics Data System (ADS)

The vibrational energy levels of the H3O2- anion have been calculated using a rigorous quantum dynamics method based on an accurate ab initio potential energy surface. The eigenvalue problem is solved using the two-layer Lanczos iterative diagonalization algorithm in a mixed grid/nondirect product basis set, where the system Hamiltonian is expressed in a set of orthogonal polyspherical coordinates. The lowest 312 vibrational energy levels in each inversion symmetry, together with a comparison of fundamental frequencies with previous quantum dynamics calculations, are reported. Finally, a statistical analysis of nearest level spacing distribution is carried out, revealing a strongly chaotic nature.

Yu, Hua-Gen

2006-11-01

336

Influence of the environment on kinetics and electronic structure of asymmetric azobenzene derivatives — experiment and quantum-chemical calculations  

NASA Astrophysics Data System (ADS)

The kinetics of thermally driven cis- trans isomerisation of asymmetrically substituted azobenzenes dissolved in solvents of various polarities was measured spectrophotometrically. The solvatochromic effect was observed in 4-nitro-4'-aminoazobenzene as well as in 4-nitro-4'methoxyazobenzene. The experiment has been supplemented with quantum-chemical calculations. The solvent effect was taken into account using the quantum-mechanical Langevin dipoles/Monte Carlo (QM/LD/MC) approach. Calculations of first-order hyperpolarizability tensors of investigated molecules have been performed within a sum-over-states (SOS) method. Both methods were implemented in the all-valence method, GRINDOL.

Matczyszyn, K.; Bartkowiak, W.; Leszczynski, J.

2001-05-01

337

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

SciTech Connect

Salt bridges are electrostatic links between acidic and basic amino acids in a protein; quantum calculations are used here to determine the energetics and other properties of one form of these species, in the presence of water molecules. The acidic groups are carboxylic acids (aspartic and glutamic acids); proteins have two bases with pK above physiological pH: one, arginine, with a guanidinium basic group, the other lysine, which is a primary amine. Only arginine is modeled here, by ethyl guanidinium, while propionic acid is used as a model for either carboxylic acid. The salt bridges are accompanied by 0-12 water molecules; for each of the 13 systems, the energy-bond distance relation, natural bond orbitals (NBO), frequency calculations allowing thermodynamic corrections to room temperature, and dielectric constant dependence, were all calculated. The water molecules were found to arrange themselves in hydrogen bonded rings anchored to the oxygens of the salt bridge components. This was not surprising in itself, but it was found that the rings lead to a periodicity in the energy, and to a 'water addition' rule. The latter shows that the initial rings, with four oxygen atoms, become five member rings when an additional water molecule becomes available, with the additional water filling in at the bond with the lowest Wiberg index, as calculated using NBO. The dielectric constant dependence is the expected hyperbola, and the fit of the energy to the inverse dielectric constant is determined. There is an energy periodicity related to ring formation upon addition of water molecules. When 10 water molecules have been added, all spaces near the salt bridge are filled, completing the first hydration shell, and a second shell starts to form. The potentials associated with salt bridges depend on their hydration, and potentials assigned without regard to local hydration are likely to cause errors as large as or larger than kBT, thus suggesting a serious problem if these potentials are used in Molecular Dynamics simulations.

Liao, Sing; Green, Michael E.

2011-01-01

338

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

339

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

NASA Astrophysics Data System (ADS)

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

Raghunathan, Ravi

340

Structure and electric properties of Sn(N) clusters (N = 6-20) from combined electric deflection experiments and quantum theoretical studies.  

PubMed

Electric deflection experiments have been performed on neutral Sn(N) clusters (N = 6-20) at different nozzle temperatures in combination with a systematic search for the global minimum structures and the calculation of the dielectric properties based on density functional theory. For smaller tin clusters (N = 6-11), a good agreement between theory and experiment is found. Taking theoretically predicted moments of inertia and the body fixed dipole moment into account permits a quantitative simulation of the deflected molecular beam profiles. For larger Sn(N) clusters (N = 12-20), distinct differences between theory and experiment are observed; i.e., the predicted dipole moments from the quantum chemical calculations are significantly larger than the experimental values. The investigation of the electric susceptibilities at different nozzle temperatures indicates that this is due to the dynamical nature of the tin clusters, which increases with cluster size. As a result, even at the smallest nozzle temperature of 40 K, the dipole moments of Sn(12-20) are partially quenched. This clearly demonstrates the limits of current electric deflection experiments for structural determination and demonstrates the need for stronger cooling of the clusters in future experiments. PMID:18991425

Schäfer, Sascha; Assadollahzadeh, Behnam; Mehring, Max; Schwerdtfeger, Peter; Schäfer, Rolf

2008-12-01

341

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

342

A regularized and renormalized electrostatic coupling Hamiltonian for hybrid quantum-mechanical-molecular-mechanical calculations  

NASA Astrophysics Data System (ADS)

We describe a regularized and renormalized electrostatic coupling Hamiltonian for hybrid quantum-mechanical (QM)-molecular-mechanical (MM) calculations. To remedy the nonphysical QM/MM Coulomb interaction at short distances arising from a point electrostatic potential (ESP) charge of the MM atom and also to accommodate the effect of polarized MM atom in the coupling Hamiltonian, we propose a partial-wave expansion of the ESP charge and describe the effect of a s-wave expansion, extended over the covalent radius rc, of the MM atom. The resulting potential describes that, at short distances, large scale cancellation of Coulomb interaction arises intrinsically from the localized expansion of the MM point charge and the potential self-consistently reduces to 1/rc at zero distance providing a renormalization to the Coulomb energy near interatomic separations. Employing this renormalized Hamiltonian, we developed an interface between the Car-Parrinello molecular-dynamics program and the classical molecular-dynamics simulation program Groningen machine for chemical simulations. With this hybrid code we performed QM/MM calculations on water dimer, imidazole carbon monoxide (CO) complex, and imidazole-heme-CO complex with CO interacting with another imidazole. The QM/MM results are in excellent agreement with experimental data for the geometry of these complexes and other computational data found in literature.

Biswas, P. K.; Gogonea, V.

2005-10-01

343

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

344

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

NASA Astrophysics Data System (ADS)

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

2012-12-01

345

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

NASA Astrophysics Data System (ADS)

We have studied electronic excitations in solid systems using the phaseless auxiliary-field quantum Monte Carlo (AFQMC) method.ootnotetextS. Zhang and H. Krakauer, Phys. Rev. Lett. 90, 136401 (2003); W. Purwanto, S. Zhang, and H. Krakauer, J. Chem. Phys. 130, 094107 (2009). Trial wave functions for excited states are simply constructed from the corresponding density functional theory (DFT) ground state orbitals by promoting electrons to conduction bands. The post-processing finite size (FS) correction methodootnotetextF. Ma, S. Zhang, and H. Krakauer, Phys. Rev. B 84, 155130 (2011); H. Kwee, S. Zhang, and H. Krakauer, Phys. Rev. Lett. 100, 126404 (2008). is applied to remove the many-body FS effects. By fitting the calculated excitation energies at various crystal momentum values, a many-body electronic band structure is obtained. Our results for prototypical semiconductors such as silicon are compared to those from the GW approximationootnotetextM. Rohlfing, P. Kr"uger, and J. Pollmann, Phys. Rev B. 48, 17791 (1993). and diffusion Monte Carlo calculations.ootnotetextA. J. Williamson, R. Q. Hood, R. J. Needs, and G. Rajagopal, Phys. Rev. B 57, 12140 (1998).

Ma, Fengjie; Zhang, Shiwei; Krakauer, Henry

2012-02-01

346

Classification of Bicovariant Differential Calculi on Quantum Groups (a Representation-Theoretic Approach)  

NASA Astrophysics Data System (ADS)

The restricted dual of a quantized enveloping algebra can be viewed as the algebra of functions on a quantum group. According to Woronowicz, there is a general notion of bicovariant differential calculus on such an algebra. We give a classification theorem of these calculi. The proof uses the notion (due to Reshetikhin and Semenov-Tian-Shansky) of a factorizable quasi-triangular Hopf algebra and relies on results of Joseph and Letzter. On the way, we also give a new formula for Rosso's bilinear form.

Baumann, Pierre; Schmitt, Frédéric

347

Self-consistent phonons in configurationally disordered quantum crystals. II. Group-theoretic considerations  

Microsoft Academic Search

In a foregoing publication a self-consistent phonon theory for configurationally disordered crystals was discussed by W. Biem and the author. In this article some simplifications concerning the coherent potential approximation (CPA) equations and the static relaxations are derived with the help of group-theoretic methods. Besides the familiar reduction of the relevant matrices to block-diagonal form, a very fast Fourier transformation

K. Menn; Justus-Liebig-Universitiit Giessen

1984-01-01

348

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

349

Using molecular dynamics and quantum mechanics calculations to model fluorescence observables  

PubMed Central

We provide a critical examination of two different methods for generating a donor-acceptor electronic coupling trajectory from a molecular dynamics (MD) trajectory and three methods for sampling that coupling trajectory, allowing the modeling of experimental observables directly from the MD simulation. In the first coupling method we perform a single quantum-mechanical (QM) calculation to characterize the excited state behavior, specifically the transition dipole moment, of the fluorescent probe, which is then mapped onto the configuration space sampled by MD. We then utilize these transition dipoles within the ideal dipole approximation (IDA) to determine the electronic coupling between the probes that mediates the transfer of energy. In the second method we perform a QM calculation on each snapshot and use the complete transition densities to calculate the electronic coupling without need for the IDA. The resulting coupling trajectories are then sampled using three methods ranging from an independent sampling of each trajectory point (the Independent Snapshot Method) to a Markov chain treatment that accounts for the dynamics of the coupling in determining effective rates. The results show that the IDA significantly overestimates the energy transfer rate (by a factor of 2.6) during the portions of the trajectory in which the probes are close to each other. Comparison of the sampling methods shows that the Markov chain approach yields more realistic observables at both high and low FRET efficiencies. Differences between the three sampling methods are discussed in terms of the different mechanisms for averaging over structural dynamics in the system. Convergence of the Markov chain method is carefully examined. Together, the methods for estimating coupling and for sampling the coupling provide a mechanism for directly connecting the structural dynamics modeled by MD with fluorescence observables determined through FRET experiments.

Speelman, Amy L.; Munoz-Losa, Aurora; Hinkle, Katie L.; VanBeek, Darren B.; Mennucci, Benedetta; Krueger, Brent P.

2011-01-01

350

Calculator.  

ERIC Educational Resources Information Center

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

Parma City School District, OH.

351

Theoretical Study of Ultra-Relativistic Laser Electron Interaction with Radiation Reaction by Quantum Description  

NASA Astrophysics Data System (ADS)

In the near future, the intensity of the ultra-short pulse laser will reach to 1022 W/cm2. When an electron is irradiated by this laser, the electron's behavior is relativistic with significant bremsstrahlung. This radiation from the electron is regarded as the energy loss of electron. Therefore, the electron's motion changes because of the kinetic energy changing. This radiation effect on the charged particle is the self-interaction, called the “radiation reaction” or the “radiation damping”. For this reason, the radiation reaction appears in laser electron interactions with an ultra-short pulse laser whose intensity becomes larger than 1022 W/cm2. In the classical theory, it is described by the Lorentz-Abraham-Dirac (LAD) equation. But, this equation has a mathematical difficulty, which we call the “run-away”. Therefore, there are many methods for avoiding this problem. However, Dirac's viewpoint is brilliant, based on the idea of quantum electrodynamics. We propose a new equation of motion in the quantum theory with radiation reaction in this paper.

Seto, Keita; Nagatomo, Hideo; Koga, James; Mima, Kunioki

352

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

353

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

2007-02-15

354

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

355

Four-membered rings family in the Si–O extended rocking IR band from quantum chemistry calculations  

Microsoft Academic Search

We calculate the vibrational modes of four-membered rings family in the Si–O extended rocking infrared for vitreous SiO2 materials. In particular these species are obtained in the early stages of the sol–gel process. We have performed high quality\\u000a quantum-mechanical calculations based on cluster models and gradient corrected density functional theory, (GC-DFT). Three\\u000a possible configurations were obtained, a regular planar, a

Elia Monsivais-Gámez; Facundo Ruiz; J. R. Martínez

2007-01-01

356

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

357

Laser cooling of semiconductor quantum wells: Theoretical framework and strategy for deep optical refrigeration by luminescence upconversion  

SciTech Connect

Optical refrigeration has great potential as a viable solution to thermal management for semiconductor devices and microsystems. We have developed a first-principles-based theory that describes the evolution of thermodynamics - i.e., thermokinetics - of a semiconductor quantum well under laser pumping. This thermokinetic theory partitions a well into three subsystems: interacting electron-hole pairs (carriers) within the well, the lattice (thermal phonons), and the ambient (a thermal reservoir). We start from the Boltzmann kinetic equations and derive the equations of motion for carrier density and temperature, and lattice temperature, under the adiabatic approximation. A simplification is possible as a result of ultrafast energy exchange between the carriers and phonons in semiconductors: a single-temperature equation is sufficient for them, whereas the lattice cooling is ultimately driven by the much slower radiative recombination (upconverted luminescence) process. Our theory microscopically incorporates photogeneration and radiative recombination of the interacting electron-hole pairs. We verify that Kubo-Martin-Schwinger relation holds for our treatment, as a necessary condition for consistency in treatment. The current theory supports steady-state solutions and allows studies of cooling strategies and thermodynamics. We show by numerical investigation of an exemplary GaAs quantum well that higher power cools better when the laser is detuned from the band edge between a critical negative value and the ambient thermal energy. We argue for the existence of such a counterintuitive lower bound. Most importantly, we show that there exists an actual detuning, 3 meV above the band edge in the simulated free-carrier case and expected to be pinned at the excitonlike absorption peak owing to Coulomb many-body effects, for optimal laser cooling. Significant improvement in cooling efficacy and theoretical possibility of deep refrigeration are verified with such a fixed optimal actual detuning. In essence, this work provides a consistent microscopic framework and an optimization strategy for achieving net deep cooling of semiconductor quantum wells and related microsystems.

Li Jianzhong [NanoScience Solutions, Inc., Cupertino, California 95014 (United States)

2007-04-15

358

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

PubMed

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

Jamet, Helene; Jourdan, Muriel; Dumy, Pascal

2008-08-14

359

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

360

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

361

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

362

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

NASA Astrophysics Data System (ADS)

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

Fargher, Mitchell; Hedberg, Lise; Hedberg, Kenneth

2014-08-01

363

The infrared spectra and theoretical calculations of frequencies of fac-tricarbonyl octahedral complexes of manganese(I)  

NASA Astrophysics Data System (ADS)

The carbonyl stretching frequencies in the infrared spectra of 38 fac-tricarbonyl octahedral complexes of manganese(I) prepared in this laboratory were determined. These complexes may be grouped into three types: (a) neutral complexes of the structure (CO) 3Mn(P-P)Z where P-P represents depe, dppe, or dppp, and Z represents various anionic functional groups bonded to the manganese; (b) ionic complexes of the structure [(CO) 3Mn(P-P)Z] +BF 4- where Z represents various neutral molecules possessing one phosphorous, nitrogen, or oxygen atom coordinated to the manganese; (c) complexes of the structure (CO) 3Mn(pn)Z where the chelating pn represents 1,1-diphenylphosphino-2,2-dimethylaminoethane, Ph 2PCH 2CH 2NMe 2. All of these complexes show three carbonyl stretching modes (2A'+A''). The effects on the frequencies of these modes induced by both the various Z groups and the various ligands are discussed. Theoretical calculations (B3LYP/6-31G) with optimization of the full molecule make it possible to distinguish between the three stretching modes and to make unambiguous assignments of appropriate symmetry species to each.

Ault, Bruce S.; Becker, Thomas M.; Li, Guang Qing; Orchin, Milton

2004-09-01

364

Quantum field theoretical analysis on unstable behavior of Bose-Einstein condensates in optical lattices  

SciTech Connect

We study the dynamics of Bose-Einstein condensates flowing in optical lattices on the basis of quantum field theory. For such a system, a Bose-Einstein condensate shows an unstable behavior which is called the dynamical instability. The unstable system is characterized by the appearance of modes with complex eigenvalues. Expanding the field operator in terms of excitation modes including complex ones, we attempt to diagonalize the unperturbative Hamiltonian and to find its eigenstates. It turns out that although the unperturbed Hamiltonian is not diagonalizable in the conventional bosonic representation the appropriate choice of physical states leads to a consistent formulation. Then we analyze the dynamics of the system in the regime of the linear response theory. Its numerical results are consistent with those given by the discrete nonlinear Schroedinger equation.

Kobayashi, K. [Department of Materials Science and Engineering, Waseda University, Tokyo 169-8555 (Japan)], E-mail: keita-x@fuji.waseda.jp; Mine, M. [Department of Physics, Waseda University, Tokyo 169-8555 (Japan)], E-mail: mine@aoni.waseda.jp; Okumura, M. [CCSE, Japan Atomic Energy Agency, 6-9-3 Higashi-Ueno, Taito-ku, Tokyo 110-0015 (Japan); CREST (JST), 4-1-8 Honcho, Kawaguti-shi, Saitama 332-0012 (Japan)], E-mail: okumura.masahiko@jaea.go.jp; Yamanaka, Y. [Department of Electronic and Photonic Systems, Waseda University, Tokyo 169-8555 (Japan)], E-mail: yamanaka@waseda.jp

2008-05-15

365

[Establishment of the mathematic model of total quantum statistical moment standard similarity for application to medical theoretical research].  

PubMed

The paper aims to elucidate and establish a new mathematic model: the total quantum statistical moment standard similarity (TQSMSS) on the base of the original total quantum statistical moment model and to illustrate the application of the model to medical theoretical research. The model was established combined with the statistical moment principle and the normal distribution probability density function properties, then validated and illustrated by the pharmacokinetics of three ingredients in Buyanghuanwu decoction and of three data analytical method for them, and by analysis of chromatographic fingerprint for various extracts with different solubility parameter solvents dissolving the Buyanghanwu-decoction extract. The established model consists of four mainly parameters: (1) total quantum statistical moment similarity as ST, an overlapped area by two normal distribution probability density curves in conversion of the two TQSM parameters; (2) total variability as DT, a confidence limit of standard normal accumulation probability which is equal to the absolute difference value between the two normal accumulation probabilities within integration of their curve nodical; (3) total variable probability as 1-Ss, standard normal distribution probability within interval of D(T); (4) total variable probability (1-beta)alpha and (5) stable confident probability beta(1-alpha): the correct probability to make positive and negative conclusions under confident coefficient alpha. With the model, we had analyzed the TQSMS similarities of pharmacokinetics of three ingredients in Buyanghuanwu decoction and of three data analytical methods for them were at range of 0.3852-0.9875 that illuminated different pharmacokinetic behaviors of each other; and the TQSMS similarities (ST) of chromatographic fingerprint for various extracts with different solubility parameter solvents dissolving Buyanghuanwu-decoction-extract were at range of 0.6842-0.999 2 that showed different constituents with various solvent extracts. The TQSMSS can characterize the sample similarity, by which we can quantitate the correct probability with the test of power under to make positive and negative conclusions no matter the samples come from same population under confident coefficient a or not, by which we can realize an analysis at both macroscopic and microcosmic levels, as an important similar analytical method for medical theoretical research. PMID:24358780

He, Fu-yuan; Deng, Kai-wen; Huang, Sheng; Liu, Wen-long; Shi, Ji-lian

2013-09-01

366

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

SciTech Connect

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

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

2014-01-01

367

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

368

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

369

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

370

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

PubMed

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

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

2009-05-01

371

Theoretical study of dynamic electron-spin-polarization via the doublet-quartet quantum-mixed state (II). Population transfer and magnetic field dependence of the spin polarization.  

PubMed

The population transfer to the spin-sublevels of the unique quartet (S = 3/2) high-spin state of the strongly exchange-coupled (SC) radical-triplet pair (for example, an Acceptor-Donor-Radical triad (A-D-R)) via a doublet-quartet quantum-mixed (QM) state is theoretically investigated by a stochastic Liouville equation. In this work, we have treated the loss of the quantum coherence (de-coherence) due to the de-phasing during the population transfer and neglected the effect of other de-coherence mechanisms. The dependences on the magnitude of the exchange coupling or the fine-structure parameter of the QM state are investigated. The dependence on the velocity of the population transfer (by the electron transfer or the energy-transfer) from the QM state to the SC quartet state is also clarified. It is revealed that the de-coherence during the population transfer mainly originates from the fine-structure term of the QM state in the doublet-triplet exchange coupled systems. This de-coherence leads to the unique dynamic electron polarization (DEP) on the high-field spin sublevels of the SC state, which is similar to the unique DEP pattern of the photo-excited triplet states of the reaction centers of photosystems I and II. The magnetic field dependence of the population transfer leading to the populations of the spin-sublevels of the SC states is also calculated. The possibility of the control of energy transport, spin transport and information technology by using the QM state is discussed based on these results. The knowledge obtained in this work is useful in the spin dynamics of any doublet-triplet exchange coupled systems. PMID:22717738

Matsumoto, Takafumi; Teki, Yoshio

2012-08-01

372

Line coupling effects in the isotropic Raman spectra of N2: A quantum calculation at room temperature  

NASA Astrophysics Data System (ADS)

We present quantum calculations of the relaxation matrix for the Q branch of N2 at room temperature using a recently proposed N2-N2 rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10 200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility. This has been done using complementary calculations based on the energy corrected sudden formalism. Agreement of these quantum predictions with experimental data is good, but the main goal of this work is to provide a benchmark relaxation matrix for testing more approximate methods which remain of a great utility for complex molecular systems at room (and higher) temperatures.

Thibault, Franck; Boulet, Christian; Ma, Qiancheng

2014-01-01

373

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

NASA Astrophysics Data System (ADS)

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

Hatada, Tomohisa; Sekino, Masaki; Ueno, Shoogo

2005-05-01

374

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

375

Theoretical foundation for real-time prostate localization using an inductively coupled transmitter and a superconducting quantum interference device (SQUID) magnetometer system.  

PubMed

Real-time, 3D localization of the prostate for intensity-modulated radiotherapy can be accomplished with passively charged radio frequency transmitters and superconducting quantum interference device (SQUID) magnetometers. The overall system design consists of an external dipole antenna as a power source for charging a microchip implant transmitter and SQUID magnetometers for signal detection. An external dipole antenna charges an on-chip capacitor through inductive coupling in the near field region through a small implant inductor. The charge and discharge sequence between the external antenna and the implant circuit can be defined by half duplex, full duplex, or sequential operations. The resulting implant discharge current creates an alternating magnetic field through the inductor. The field is detected by the surrounding magnetometers, and the location of the implant transmitter can be calculated. Problems associated with this system design are interrelated with the signal strength at the detectors, detector sensitivity, and charge time of the implant capacitor. The physical parameters required for optimizing the system for real-time applications are the operating frequency, implant inductance and capacitance, the external dipole current and loop radius, the detector distance, and mutual inductance. Consequently, the sequential operating mode is the best choice for real-time localization for constraints requiring positioning within 1 s due to the mutual inductance and detector sensitivity. We present the theoretical foundation for designing a real-time, 3D prostate localization system including the associated physical parameters and demonstrate the feasibility and physical limitations for such a system. PMID:15738919

McGary, John E

2004-01-01

376

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

PubMed Central

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

2014-01-01

377

Theoretical prediction of hydrogen-bond basicity pKBHX using quantum chemical topology descriptors.  

PubMed

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

Green, Anthony J; Popelier, Paul L A

2014-02-24

378

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

Microsoft Academic Search

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

Nkaepe E. I. Etteh; Paul Harrison

2002-01-01

379

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

NASA Astrophysics Data System (ADS)

The multiphoton vibrational excitation and dissociation of Morse molecules have been computed nonperturbatively using Hamilton's and Schr?dinger's time-dependent equations, for a range of laser pulse parameters. The time-dependent Schr?dinger equation is solved by the state-specific expansion approach [e.g.,1]. For its solution, emphasis has been given on the inclusion of the continuous spectrum, whose contribution to the multiphoton probabilities for resonance excitation to a number of excited discrete states as well as to dissociation has been examined as a function of laser intensity, frequency and pulse duration. An analysis of possible quantal-classical correspondences for this system is being carried out. We note that distinct features exist from previous classical calculations [2]. For example, the dependence on the laser frequency gives rise to an asymmetry around the red-shifted frequency corresponding to the maximum probability. [1] Th. Mercouris, I. D. Petsalakis and C. A. Nicolaides, J. Phys. B 27, L519 (1994). [2] V. Constantoudis and C. A. Nicolaides, Phys. Rev. E 64, 562112 (2001). ^1This work was supported by the program 'Pythagoras' which is co - funded by the European Social Fund (75%) and Natl. Resources (25%). ^2Physics Department, National Technical University, Athens, Greece.^3Theoretical and Physical Chemistry Institute, Hellenic Research Foundation, Athens, Greece.

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

2006-05-01

380

Hydrogen bonding in the gas-phase: the molecular structures of 2-hydroxybenzamide (C7H7NO2) and 2-methoxybenzamide (C8H9NO2), obtained by gas-phase electron diffraction and theoretical calculations.  

PubMed

The structures of 2-hydroxybenzamide (C7H7NO2) and 2-methoxybenzamide (C8H9NO2) 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 four stable conformers for both 2-hydroxybenzamide and 2-methoxybenzamide. For both compounds, evidence for intramolecular hydrogen bonding is presented. In 2-hydroxybenzamide, the observed hydrogen bonded fragment is between the hydroxyl and carbonyl groups, while in 2-methoxybenzamide, the hydrogen bonded fragment is between one of the hydrogen atoms of the amide group and the methoxy oxygen atom. PMID:23485214

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

2013-04-11

381

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

382

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

383

Microscopic study of relaxation oscillations in quantum-dot VCSELs  

Microsoft Academic Search

We propose a theoretical model to investigate the switch-on dynamics of electrically pumped quantum dot vertical-cavity surface-emitting lasers. The model is based on the self-consistently combined quantum dot-wetting layer Maxwell–Bloch equations incorporating microscopically calculated Coulomb and phonon-assisted scattering processes between the quantum dot and the quantum dot-embedding wetting layer states. Our approach allows the calculation of the time delay before

Jeong Eun Kim; Matthias-Rene Dachner; Alexander Wilms; Marten Richter; Ermin Malic

2011-01-01

384

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

PubMed Central

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

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

2013-01-01

385

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

SciTech Connect

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

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

2013-08-15

386

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

387

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

PubMed

We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula. PMID:24811623

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

2014-05-01

388

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

NASA Astrophysics Data System (ADS)

We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.

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

2014-05-01

389

Quantum Mechanical Calculations of Charge Effects on gating the KcsA channel  

SciTech Connect

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. A series of ab initio (density functional) calculations were carried out on side chains of a set of amino acids, plus water, from the (intracellular) gating region of the KcsA K+ channel. Their atomic coordinates, except hydrogen, are known from X-ray structures [D.A. Doyle, J.M. Cabral, R.A. Pfuetzner, A. Kuo, J.M. Gulbis, S.L. Cohen, B.T. Chait, R. MacKinnon, The structure of the potassium channel: molecular basis of K+ conduction and selectivity, Science 280 (1998) 69–77; R. MacKinnon, S.L. Cohen, A. Kuo, A. Lee, B.T. Chait, Structural conservation in prokaryotic and eukaryotic potassium channels, Science 280 (1998) 106–109; Y. Jiang, A. Lee, J. Chen, M. Cadene, B.T. Chait, R. MacKinnon, The open pore conformation of potassium channels. Nature 417 (2001) 523–526], as are the coordinates of some water oxygen atoms. The 1k4c structure is used for the starting coordinates. Quantum mechanical optimization, in spite of the starting configuration, places the atoms in positions much closer to the 1j95, more tightly closed, configuration. This state shows four water molecules forming a “basket” under the Q119 side chains, blocking the channel. When a hydrated K+ approaches this “basket”, the optimized system shows a strong set of hydrogen bonds with the K+ at defined positions, preventing further approach of the K+ to the basket. This optimized structure with hydrated K+ added shows an ice-like 12 molecule nanocrystal of water. If the water molecules exchange, unless they do it as a group, the channel will remain blocked. The “basket” itself appears to be very stable, although it is possible that the K+ with its hydrating water molecules may be more mobile, capable of withdrawing from the gate. It is also not surprising that water essentially freezes, or forms a kind of glue, in a nanometer space; this agrees with experimental results on a rather different, but similarly sized (nm dimensions) system [K.B. Jinesh, J.W.M. Frenken, Capillary condensation in atomic scale friction: how water acts like a glue, Phys. Rev. Lett. 96 (2006) 166103/1–4].

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

2007-02-06

390

Theoretical calculation of the low lying electronic states of the molecular ion RbH(+) with spin-orbit effects.  

PubMed

The potential energy has been calculated for the 42 lowest electronic states of symmetries Omega=12,32,52, for the molecular ion RbH(+). Using an ab initio method, the calculation is based on nonempirical pseudopotentials and parametrized [script-l]-dependent polarization potentials. Gaussian basis sets have been used for both atoms, and spin-orbit effects have been taken into account. The spectroscopic constants for 19 electronic states have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance r. The permanent dipole moment and the transition dipole moments have been calculated for the considered Omega states. Through the canonical functions approach the eigenvalue E(v), the abscissas of the corresponding turning points (r(min) and r(max)) and the rotational constants B(v) have been calculated. The comparison of the present results with those available in literature shows a very good agreement. PMID:19045861

Korek, M; Hammoud, S; Allouche, A R; Harb, T

2008-11-28

391

Quantum calculations of vibrational energies of H3O2(-) and H5O2(+) with new ab initio potentials  

NASA Astrophysics Data System (ADS)

We have performed quantum mechanical studies of the vibrations of H3O2(-) and H5O2(+) in full dimensionality and with sufficient accuracy to resolve important features of the measured spectra. The computational procedure starts with extensive electronic structure calculations (several 10K configurations) at the CCSD(T) level of theory with augmented VTZ basis set using MOLPRO 2002. Then a global fit to the potential energy surface is constructed, based on a functional form that respects the spatial and permutational symmetries of the system. This PES fit is employed in a "Reaction Path Hamiltonian" MULTIMODE [1] calculation to obtain the vibrational spectrum. We provide comparisons with experimental data [2]. [1] MULTIMODE: A code to calculate rovibrational energies of polyatomic molecules, J. M. Bowman, S. Carter, and X.-C. Huang, Int. Rev. Phys. Chem. 22, 533 (2003). [2] Quantum calculations of vibrational energies of H3O2(-) with a new ab initio potential reveal large tunneling splittings. Manuscript in preparation, Dec 2003.

Huang, Xinchuan; Braams, Bastiaan J.; Carter, Stuart; Bowman, Joel M.

2004-03-01

392

Numerical calculation of the electronic structure for three-dimensional quantum dots  

NASA Astrophysics Data System (ADS)

In some recent papers Li, Voskoboynikov, Lee, Sze and Tretyak suggested an iterative scheme for computing the electronic states of quantum dots and quantum rings taking into account an electron effective mass which depends on the position and electron energy level. In this paper we prove that this method converges globally and linearly in an alternating way, i.e. yielding lower and upper bounds of a predetermined energy level in turn. Moreover, taking advantage of the Rayleigh functional of the governing nonlinear eigenproblem, we propose a variant which converges even quadratically thereby reducing the computational cost substantially. Two examples of finite element models of quantum dots of different shapes demonstrate the efficiency of the method.

Voss, Heinrich

2006-03-01

393

Revisiting the nitrosyl complex of myoglobin by high-field pulse EPR spectroscopy and quantum mechanical calculations.  

PubMed

The binding of NO to reduced myoglobin in solution results in the formation of two paramagnetic nitrosyl myoglobin (MbNO) complexes: one with a rhombic g-factor and the other with an axial one, referred to as the R- and A-forms. In spite of past extensive studies of MbNO by crystallography, spectroscopy and quantum chemical calculations it is still not clear what factors determine the appearance of the two forms. In this work we applied a combination of state of the art quantum chemical calculations and high field pulsed EPR spectroscopy (W-band, 3.4 T/95 GHz) to further characterize the two forms. Specifically, we have used (1)H and (2)H electron-nuclear double resonance (ENDOR) spectroscopy to identify and characterize the H-bond to the NO, and hyperfine sub-level correlation (HYSCORE) spectroscopy to determine the hyperfine and quadrupole interactions of the Fe(ii) coordinated (14)N of the proximal histidine (14)N(His93). The calculations employed quantum mechanics (QM), particularly density functional theory (DFT) methods in combination with molecular mechanics (MM) force-field to model the protein environment. Through QM/MM calculations of the EPR parameters we have explored their dependence on several geometrical factors of the Fe-NO bond and found those that reproduce the best experimental results. The spread of the W-band EPR spectrum of MbNO due to the g-anisotropy is large and there is a significant part of the spectrum where the R-form is the sole contributor. This allowed us to resolve some new characteristics of the R-form: (i) a NO-H hydrogen bond has been detected and characterized and through QM/MM calculations has been unambiguously assigned to (epsilon2)H(His64). (ii) The complete hyperfine and quadrupole interactions of (14)N(His93) have been determined and correlated with structural parameters again using QM/MM calculations. The agreement between the experimental results and calculations varied between excellent and good, depending on the EPR parameter in question. As for the more elusive A-form, the results only suggest that it does have a (14)N(His93) ligand with a hyperfine comparable to that of the R-form and it has less hydrogen bonding interaction with His(64). The calculations also established the orientation of the principal g-values, finding that they are closely related to the orientation of the NO bond. This information is essential for deriving structural information from the experimental orientation selective HYSCORE and ENDOR data. PMID:20490401

Radoul, Marina; Sundararajan, Mahesh; Potapov, Alexey; Riplinger, Christoph; Neese, Frank; Goldfarb, Daniella

2010-07-14

394

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

SciTech Connect

The solutions of the time-independent Schroedinger equation for non-Hermitian (NH) Hamiltonians have been extensively studied and calculated in many different fields of physics by using L{sup 2} methods that originally have been developed for the calculations of bound states. The existing non-Hermitian formalism breaks down when dealing with wave packets (WPs). An open question is how time-dependent expectation values can be calculated when the Hamiltonian is NH? Using the F-product formalism that was recently proposed by Moiseyev and Lein [J. Phys. Chem. 107, 7181 (2003)] we calculate the time-dependent expectation values of different observable quantities for a simple well-known study test case model Hamiltonian. We carry out a comparison between these results and those obtained from conventional (i.e., Hermitian) quantum mechanics (QM) calculations. The remarkable agreement between these results emphasizes the fact that in NH QM, unlike standard QM, there is no need to split the entire space into two regions, i.e., the interaction region and its surrounding. Our results open a door for a type of WP propagation calculations within the NH QM formalism that until now were impossible. In particular our work is relevant to the many different fields in physics and chemistry where complex absorbing potentials are introduced in order to reduce the propagation calculations to a restricted region in space where the artificial reflections from the edge of the numerical grid or box are avoided.

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

2005-07-15

395

Synthesis, characterization, and theoretical calculations of mononuclear copper(II) benzoate complex with 2-propylimidazole, [Cu(PIM) 2(PhCOO) 2  

NASA Astrophysics Data System (ADS)

A mononuclear copper(II) complex, [Cu(PIM) 2(PhCOO) 2] ( 1) [where PIM = 2-propylimidazole] has been synthesized and characterized by elemental analysis, IR, UV-Vis, TGA, and single crystal X-ray diffraction. The structural analysis indicated that Cu(II) atom in the complex is six-coordinated in a distorted octahedral geometry by two N atoms from two 2-propylimidazole and four O atoms from two benzoate ligands. In addition, based on crystal structural data, quantum chemistry calculation in DFT/B3LYP level has been used to reoptimize and explore the electronic structure of the compound 1; time-dependent DFT (TD-DFT) calculations have also been performed in order to elucidate its spectroscopic properties. All parameters from the calculations are in well accordance with our experimental result.

Peng, Xian; Cui, Guang-hua; Li, De-jie; Liu, Tong-fei

2010-04-01

396

Formation of NV centers in diamond: A theoretical study based on calculated transitions and migration of nitrogen and vacancy related defects  

NASA Astrophysics Data System (ADS)

Formation and excitation energies as well charge transition levels are determined for the substitutional nitrogen (Ns), the vacancy (V), and related point defects (NV, NVH, N2,N2V, and V2) by screened nonlocal hybrid density functional supercell plane wave calculations in bulk diamond. In addition, the activation energy for V and NV diffusion is calculated. We find good agreement between theory and experiment for the previously well-established data and predict missing ones. Based on the calculated properties of these defects, the formation of the negatively charged NV center is studied, because it is a prominent candidate for application in quantum information processing and for nanosensors. Our results indicate that NV defects are predominantly created directly by irradiation, while simultaneously produced vacancies will form V2 pairs during postirradiation annealing. Divacancies may pin the Fermi level, making the NV defects neutral.

Deák, Peter; Aradi, Bálint; Kaviani, Moloud; Frauenheim, Thomas; Gali, Adam

2014-02-01

397

Group-velocity slowdown in quantum-dots and quantum-dot molecules  

NASA Astrophysics Data System (ADS)

We investigate theoretically the slowdown of optical pulses due to quantum-coherence effects in InGaAs-based quantum dots and quantum dot molecules. Simple models for the electronic structure of quantum dots and, in particular, quantum-dot molecules are described and calibrated using numerical simulations. It is shown how these models can be used to design optimized quantum-dot molecules for quantum coherence applications. The wave functions and energies obtained from the optimizations are used as input for a microscopic calculation of the quantum-dot material dynamics including carrier scattering and polarization dephasing. The achievable group velocity slowdown in quantum-coherence V schemes consisting of quantum-dot molecule states is shown to be substantially higher than what is achievable from similar transitions in typical InGaAs-based single quantum dots.

Michael, Stephan; Chow, Weng W.; Schneider, Hans Christian

2014-03-01

398

Theoretical analysis of the magnetization and of the paramagnetic and diamagnetic magneto-optical effects in Pr-substituted yttrium iron garnets using quantum theory  

NASA Astrophysics Data System (ADS)

By using quantum theory, the magneto-optical (Faraday rotation, Faraday ellipticity) properties at photon energies below 6 eV and the magnetic properties of the Pr3+ ion in the Y3Fe5O12 garnet are analyzed in the 50-300 K temperature range. The strong enhancement of the Faraday rotation induced by the Pr presence originates mainly from the intraionic electrical dipole transitions between the split 4f2 and 4f5d levels. It is shown that the most important factor is the Pr-Fe superexchange interaction: if there is no Zeeman effect, no magneto-optical (MO) effects exist. The ``paramagnetic'' and ``diamagnetic'' contributions to the MO properties are discussed in detail: if only the Zeeman effect on the ground state is taken into account, the paramagnetic term which is strongly temperature dependent is obtained; on the contrary, if only the Zeeman effect on the excited configuration is considered, the diamagnetic contribution which is temperature insensitive is present. The observed MO properties result from these two components but are mainly determined by the paramagnetic one; the MO resonance frequencies are related to the energies of the multiplets of the ground term and of the excited configuration and to the crystal-field splitting of all these multiplets. Using this approach, the theoretically calculated results of both Pr magnetization and MO effects are in good agreement with experimental data. It is shown that the simultaneous treatment of the magnetic and MO phenomena is a powerful tool to prove the correctness of the approach and of the so-determined parameters. Finally, it is demonstrated that the mixing of the different multiplets of the ground term has a great influence on both magnetic and MO properties.

Yang, Jiehui; Xu, You; Zhang, Fang; Guillot, Maurice

1997-11-01

399

Signal transmission through molecular quantum-dot cellular automata: a theoretical study on Creutz-Taube complexes for molecular computing.  

PubMed

Signal transmission through Creutz-Taube complexes [(NH(3))(5)Ru-BL-Ru(NH(3))(5)](5+)(BL = pyrazine (py), 4,4'-bipyridine (bpy)), which are simplified models of the molecular quantum-dot cellular automata (molecular QCA), is discussed both statically and dynamically with a view to designing useful molecular QCA. In the static treatment, the difference between stationary states before and after the switch of the input to the molecular QCA is discussed. In the dynamic treatment, time-evolution of electronic structure after the moment of the switch is simulated, and a simple method for the simulation is also proposed. Geometric and electronic structures are obtained by density functional theory (UB3LYP) and Hartree-Fock (UHF) calculations, and discussions are based on the Mulliken charge. It is found that signal amplitude (A) is strongly dependent on the position and charge of the input to the molecular QCA, but signal period (T) is almost independent of them. These results are explained from molecular orbitals and orbital energies, and a set of large A (large overlap between orbitals) and small T (large energy gap) generally leads to a prompt signal transmission. PMID:19240923

Tokunaga, Ken

2009-03-14

400

Studies on adsorption of mono- and multi-chromophoric hemicyanine dyes on silver nanoparticles by surface-enhanced resonance raman and theoretical calculations  

Microsoft Academic Search

Structural and vibrational properties of mono- and multichromophoric hemicyanine (HC) dyes in solution and adsorbed on silver-coated films have been investigated using optical absorption and resonance Raman scattering techniques, with interpretations aided by theoretical calculations. This is the first report on the Raman spectroscopic studies of multichromophoric HC derivatives. The structure of the monomer, N-propyl-4-(p-N,N-dimethylamino styryl)pyridinium bromide (HC3), and its

Nandita Biswas; Susy Thomas; Sudhir Kapoor; Amaresh Mishra; Sanjay Wategaonkar; Tulsi Mukherjee

2008-01-01

401

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

NASA Astrophysics Data System (ADS)

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

Kumar, Kameshwar; Thakur, Nagesh

2013-06-01

402

Theoretical prediction of the binding of a positron to a formaldehyde molecule using a first-principles calculation  

NASA Astrophysics Data System (ADS)

The vertical positron affinity (PA) value at the equilibrium position of a formaldehyde molecule is predicted as +25(3) meV with the highly accurate quantum Monte Carlo method. Applying anharmonic vibrational analysis, we have found that the vibrational excitation of the C = O stretching mode drastically enhances the PA value, due to the increment of the molecular dipole moment along this mode. Our predictions of the vibrational averaged PA values at the fundamental and overtone states are 31 and 36 meV, respectively, which strongly supports the conclusion that a positron can bind to formaldehyde.

Yamada, Yurika; Kita, Yukiumi; Tachikawa, Masanori

2014-06-01

403

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

404

Quantum chemical calculation on the potential energy surface of H 2CO 3 and its implication for martian chemistry  

Microsoft Academic Search

A detailed theoretical study of the potential energy surface of H2CO3 is explored at the CCSD(T)\\/\\/B3LYP\\/aug-cc-pVTZ level. On the potential energy surface, 12 isomers of H2CO3 are located. Their molecular properties such as geometries, vibrational frequencies, rotational constants, dipole moments, gas-phase acidities, and relative energies are calculated. Various reaction pathways and decomposition products have also been discussed. Among these products,

Yu-Jong Wu; C. Y. Robert Wu; Mao-Chang Liang

2011-01-01

405

Theoretical SIS mixer research  

NASA Astrophysics Data System (ADS)

Theoretical research has been conducted to elucidate the basic physics behind the properties of superconductor-insulator-superconductor (SIS) tunnel junction receiving devices. The properties of SIS mixers using nonideal junctions and finite LO power, were determined by analytic expansion of the equations of the quantum theory of mixing, and also by computer simulations of SIS receivers over the entire range of experimental parameters. The result is a new coherent and intuitive picture of SIS mixer behavior. Many of the outstanding mysteries and questions about SIS receivers are resolved, and this contributes greatly to the design and interpretation of SIS mixer experiments. Other calculations show how to achieve sub-quantum noise temperatures in the phase sensitive SIS mixer, an important step towards realization of ultra-low-noise detectors. A simplified model casts doubt on the superlative experimental results reported for the RF-series dc-parallel biased array SIS mixer.

Feldman, Marc J.

1993-06-01

406

Theoretical Revision and Experimental Comparison of Quantum Yield for Transmission-Mode GaAlAs/GaAs Photocathodes  

NASA Astrophysics Data System (ADS)

The quantum yield formula for uniform-doping GaAlAs/GaAs transmission-mode photocathodes is revised by taking into account the light absorption in the window layer. By using the revised quantum yield formula, the domestic and ITT's experimental quantum yield curves are fitted and the fitted curves match well with the experimental curves. In addition, the fit results show that the integral sensitivity and quantum yield of domestic image intensifier tube has achieved 2130?A/lm and 45%, nearly reaching ITT's third generation level in 2002, whereas the discrepancy in cathode performance is mainly embodied in the electron diffusion length and back interface recombination velocity.

Shi, Feng; Zhang, Yi-Jun; Cheng, Hong-Chang; Zhao, Jing; Xiong, Ya-Juan; Chang, Ben-Kang

2011-04-01

407

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

NASA Astrophysics Data System (ADS)

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

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

2003-08-01

408

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

Microsoft Academic Search

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

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

1993-01-01

409

Charge transfer in systems of conjugated bonds in cyanobiphenyl molecules: Quantum-chemical calculations of the structure and vibrational spectra  

Microsoft Academic Search

Quantum-chemical calculations of the IR absorption spectra and geometric and electronic structure of cyanobiphenyl molecules\\u000a \\u000a (I) were performed for various angles between benzene ring planes by the B3LYP\\/6-31+G** method. It was shown that the stablest\\u000a conformation of I (X=OCH3, OC3H7) should be the twist conformation with ?= 37°, which was in agreement with the gas-phase experimental data. Rotation of benzene

A. N. Isaev; P. P. Shorygin

2009-01-01

410

Calculation of space localized properties in correlated quantum Monte Carlo methods with reweighting: the nonlocality of statistical uncertainties.  

PubMed

We study the efficiency of quantum Monte Carlo (QMC) methods in computing space localized ground state properties (properties which do not depend on distant degrees of freedom) as a function of the system size N. We prove that for the commonly used correlated sampling with reweighting method, the statistical fluctuations ?2(N) do not obey the locality property. ?2(N) grow at least linearly with N and with a slope that is related to the fluctuations of the reweighting factors. We provide numerical illustrations of these tendencies in the form of QMC calculations on linear chains of hydrogen atoms. PMID:24730964

Assaraf, Roland; Domin, Dominik

2014-03-01

411

The hyperfine structure in the rotational spectra of bromofluoromethane: Lamb-dip technique and quantum-chemical calculations  

Microsoft Academic Search

The hyperfine structure in the rotational spectra of six isotopic species of bromofluoromethane, namely CH2 BrF, CH2 BrF, CDHBrF, CDHBrF, CD2 BrF and CD2 BrF, has been investigated using the Lamb-dip technique in the submillimeter-wave frequency range. Measurements and assignment procedures were supported by high-level quantum-chemical calculations of the hyperfine parameters at the coupled-cluster level. For all species, the accuracy

Gabriele Cazzoli; Cristina Puzzarini; Stella Stopkowicz; Jurgen Gauss

2008-01-01

412

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

NASA Technical Reports Server (NTRS)

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

Ahn, Doyeol; Chuang, S. L.

1986-01-01

413

Computer simulation for calculating the second-order correlation function of classical and quantum light  

NASA Astrophysics Data System (ADS)

We propose an undergraduate numerical project for simulating the results of the second-order correlation function as obtained by an intensity interference experiment for two kinds of light, namely bunched light with Gaussian or Lorentzian power density spectrum and antibunched light obtained from single-photon sources. While the algorithm for bunched light was based on a previous publication, the one for antibunched light was developed by master students attending a Quantum Optics course at our University.

Facão, M.; Lopes, A.; Silva, A. L.; Silva, P.

2011-07-01

414

Introduction to Theoretical Modelling  

NASA Astrophysics Data System (ADS)

We briefly overview commonly encountered theoretical notions arising in the modelling of quantum gases, intended to provide a unified background to the `language' and diverse theoretical models presented elsewhere in this book, and aimed particularly at researchers from outside the quantum gases community.

Davis, Matthew J.; Gardiner, Simon A.; Hanna, Thomas M.; Nygaard, Nicolai; Proukakis, Nick P.; Szyma?ska, Marzena H.

2013-02-01

415

Experimental Ft-Ir Dispersive Raman and Theoretical DFT Calculations on Cu(ii) Chloride Complex of P-Toluidine  

NASA Astrophysics Data System (ADS)

In this study Cu(p-tol)2Cl2 (p-tol: p-toluidine) is prepared and characterized by elemental analysis, FT-IR, FT-FIR, and dispersive Raman spectral analysis. The molecular geometry and vibrational modes of p-