Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 12 of 12

Full-Text Articles in Physics

Ab Initio Study Of Formazan And 3-Nitroformazan, G. Buemi, F. Zuccarello, P. Venuvanalingam, M. Ramalingam, Salai Ammal May 2015

Ab Initio Study Of Formazan And 3-Nitroformazan, G. Buemi, F. Zuccarello, P. Venuvanalingam, M. Ramalingam, Salai Ammal

Salai C. Ammal

Formazan and 3-nitroformazan have been investigated at abinitio level (MP2/6-31G** and B3LYP/6-31G**) in all their possible conformations, for studying the various possibilities of intramolecular hydrogen bonding formation. The trans-syn-s-cis (TSSC), known also asyellowform, has been found to be the most stable conformer (at least in the gas phase) in both compounds. This particular structure is strongly stabilized by a N–H···N hydrogen bridge, which gives rise to a hexatomic chelate ring, with the possibility of a proton transfer process.This closely resembles that of malondialdehyde, previously studied, in the evolution of the potential energy shape but with ...


Dynamic Path Bifurcation For The Beckmann Reaction: Observation And Implication, H. Yamataka, M. Sato, H. Hasegawa, Salai Ammal May 2015

Dynamic Path Bifurcation For The Beckmann Reaction: Observation And Implication, H. Yamataka, M. Sato, H. Hasegawa, Salai Ammal

Salai C. Ammal

The reaction of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles instead of amides when the cations have reasonable stability. The reactions of oxime derivatives of 1-substituted-phenyl-2-propanones and 3-substituted-phenyl-2-butanones in aqueous solvents gave both rearrangement and fragmentation products, the ratio of which was dependent on substituents. Transition state (TS) optimizations and intrinsic reaction coordinate (IRC) calculations for the reaction of 1-phenyl-2-propanone oximes showed that there is a single TS for each substituted compound. The IRC path from the TS either led to a rearrangement product or a fragmentation product depending on the substituent ...


Ab Initio And Dft Investigations Of Lithium/Hydrogen Bonded Complexes Of Trimethylamine, Dimethyl Ether And Dimethyl Sulfide, Salai Ammal, P. Venuvanalingam May 2015

Ab Initio And Dft Investigations Of Lithium/Hydrogen Bonded Complexes Of Trimethylamine, Dimethyl Ether And Dimethyl Sulfide, Salai Ammal, P. Venuvanalingam

Salai C. Ammal

Ab initio and DFT computations have been carried out on LiF and HF complexes of a set of n-donors viz. trimethylamine, dimethyl ether and dimethyl sulfide with a 6-31++G(d,p) basis set. The effect of correlation has been included with MP2, MP4 and DFT calculations. NBO analyses of the wavefunctions have been performed to examine the intermolecular interaction at the orbital level. Calculations reveal that these donors form strong n→σ* complexes and computed binding energies of the (CH3)2O···HF complex agree very well with the experimental binding energies from IR spectroscopy. LiF forms stronger ...


Dynamical Signature Of The Mott-Hubbard Transition In Ni(S,Se)(2), Yevgeniya Zastavker, Anke Husmann, Deborah Jin, Thomas Rosenbaum, X Yao, J Honig Jun 2012

Dynamical Signature Of The Mott-Hubbard Transition In Ni(S,Se)(2), Yevgeniya Zastavker, Anke Husmann, Deborah Jin, Thomas Rosenbaum, X Yao, J Honig

Yevgeniya V. Zastavker

The transition metal chalcogenide Ni(S,Se)2 is one of the few highly correlated, Mott-Hubbard systems without a strong first-order structural distortion that normally cuts off the critical behavior at the metal-insulator transition. The zero-temperature (T) transition was tuned with pressure, and significant deviations were found near the quantum critical point from the usual T1/2 behavior of the conductivity characteristic of electron-electron interactions in the presence of disorder. The transport data for pressure and temperature below 1 kelvin could be collapsed onto a universal scaling curve.


Qsats: Mpi-Driven Quantum Simulations Of Atomic Solids At Zero Temperature, R. Hinde Dec 2010

Qsats: Mpi-Driven Quantum Simulations Of Atomic Solids At Zero Temperature, R. Hinde

Robert Hinde

We describe QSATS, a parallel code for performing variational path integral simulations of the quantum mechanical ground state of monatomic solids. QSATS is designed to treat Boltzmann quantum solids, in which individual atoms are permanently associated with distinguishable crystal lattice sites and undergo large-amplitude zero-point motions around these sites. We demonstrate the capabilities of QSATS by using it to compute the total energy and potential energy of hexagonal close packed solid 4He at the density 4.61421 x 10-3 a0-3.


Pairwise Additive Model For The He-Mgo(100) Interaction, B. Johnson, R. Hinde Dec 2010

Pairwise Additive Model For The He-Mgo(100) Interaction, B. Johnson, R. Hinde

Robert Hinde

We develop a model, based on pairwise additive He-Mg and He-O interactions, for the potential energy of He adsorbates above a rigid MgO(100) surface. The attractive long-range He-Mg and He-O interactions are assumed to have the form C6/r6, with the C6 coefficients determined from atomic data within the context of the Slater-Kirkwood approximation. The repulsive short-range He-Mg and He-O interactions are assumed to have the form Cp/rp, with the exponent p and the Cp coefficients taken as adjustable parameters. We find that for p=9, the Cp coefficients can be ...


Simulating Ch4 Physisorption On Ionic Crystals: Limitations Of An Atomic Partial Charge Model, Philip Stimac, Robert Hinde Dec 2007

Simulating Ch4 Physisorption On Ionic Crystals: Limitations Of An Atomic Partial Charge Model, Philip Stimac, Robert Hinde

Robert Hinde

We use quantum chemical techniques to evaluate the electrostatic and polarization components of the interaction between a rigid CH4 molecule and a lattice of point charges representing the MgO(100) surface. We find that CH4 positioned above Mg adopts an edge-down configuration in which two H atoms are oriented downward towards the MgO(100) surface and point at O ions in the surface layer. The CH4–MgO(100) electrostatic interaction is substantially less favorable (but is still attractive) for the face-down configuration in which three H atoms point downward. Neither configuration is energetically favorable for CH4 molecules positioned above O ...


Three-Body Interactions In Solid Parahydrogen, Robert Hinde Dec 2007

Three-Body Interactions In Solid Parahydrogen, Robert Hinde

Robert Hinde

We use coupled-cluster ab initio methods to evaluate the non-pairwise-additive interactions in clusters of three parahydrogen (pH2) molecules. For acute triangular (pH2)3 geometries that play a prominent role in solid pH2, these interactions lower substantially the trimer’s total interaction energy. Our findings suggest that a widely-used effective pair potential for solid pH2 derives its accuracy from a fortuitous cancellation of errors at small intermolecular distances.


Fpga Acceleration Of A Quantum Monte Carlo Application, Robert Hinde Dec 2007

Fpga Acceleration Of A Quantum Monte Carlo Application, Robert Hinde

Robert Hinde

Quantum Monte Carlo methods enable us to determine the ground-state properties of atomic or molecular clusters. Here, we present a reconfigurable computing architecture using Field Programmable Gate Arrays (FPGAs) to accelerate two computationally intensive kernels of a Quantum Monte Carlo (QMC) application applied to N-body systems. We focus on two key kernels of the QMC application: acceleration of potential energy and wave function calculations. We compare the performance of our application on two reconfigurable platforms. Firstly, we use a dual-processor 2.4 GHz Intel Xeon augmented with two reconfigurable development boards consisting of Xilinx Virtex-II Pro FPGAs. Using this platform ...


Variational Path Integral Simulations Using Discretized Coordinates, Robert Hinde Dec 2005

Variational Path Integral Simulations Using Discretized Coordinates, Robert Hinde

Robert Hinde

We describe a variational path integral simulation algorithm for quantum Monte Carlo studies of many-body systems in which particles are restricted to occupy sites on a regular simple cubic lattice with lattice constant s, and discuss the algorithm’s potential computational benefits. Application of the algorithm to the weakly bound cluster Ne3 shows that accurate coordinate-space observables for this system can be computed using lattice constants as large as s = 0.2 a0.


Dependence Of The H2–H2 Interaction On The Monomer Bond Lengths: Steps Toward An Accurate Ab Initio Estimate, Robert Hinde Dec 2005

Dependence Of The H2–H2 Interaction On The Monomer Bond Lengths: Steps Toward An Accurate Ab Initio Estimate, Robert Hinde

Robert Hinde

We compute the vibrational coupling between two H2 molecules from ab initio quantum chemical calculations of the H2–H2 potential carried out at the full configuration interaction level of theory using the atom-centered aug-cc-pVTZ basis set for hydrogen. We compare the full configuration interaction results with those obtained using two variants of coupled cluster theory and find that a fully iterative treatment of connected triples may be required to estimate the H2–H2 vibrational coupling accurately using coupled cluster theory.


Probing Quantum Solvation With Infrared Spectroscopy: Infrared Activity Induced In Solid Parahydrogen By N2 And Ar Dopants, Robert Hinde Dec 2001

Probing Quantum Solvation With Infrared Spectroscopy: Infrared Activity Induced In Solid Parahydrogen By N2 And Ar Dopants, Robert Hinde

Robert Hinde

We present the first high-resolution study of the infrared (IR) absorption spectra of solid parahydrogen matrices containing low concentrations of N2 or Ar impurities. The spectra reveal dopant-induced absorption features that acquire IR activity through short-range isotropic vibrational transition dipole moments arising from dopant–H2 intermolecular interactions. These dopant-induced features provide new insights into the perturbation of the vibron bands of the H2 matrix by chemical impurities,and thus into the physics of solvation in a quantum solid.