A5021439072- Advanced Chemical Physics Studies
- Spectroscopy and Quantum Chemical Studies
- Quantum, superfluid, helium dynamics
- Mass Spectrometry Techniques and Applications
- Spectroscopy and Laser Applications
- Geological and Geochemical Analysis
- Geology and Paleoclimatology Research
- Nonlinear Photonic Systems
- Molecular Spectroscopy and Structure
- Water Systems and Optimization
- Atomic and Molecular Physics
- Atmospheric Ozone and Climate
- Advanced Physical and Chemical Molecular Interactions
- Quantum chaos and dynamical systems
- Nonlinear Dynamics and Pattern Formation
- Groundwater flow and contamination studies
- Molecular Junctions and Nanostructures
- Machine Learning in Materials Science
- Advanced NMR Techniques and Applications
- Free Radicals and Antioxidants
- Atmospheric chemistry and aerosols
- Crystallography and molecular interactions
- Photochemistry and Electron Transfer Studies
- Water resources management and optimization
- Fluid Dynamics and Turbulent Flows
Commonwealth Scientific and Industrial Research Organisation
2024
Gridpoint solutions (United Kingdom)
2023
Australian National University
2009-2019
Iowa State University
2009
National University
2009
Ames National Laboratory
2009
University of Oxford
2003
National University of Singapore
2002
University of Wisconsin–Milwaukee
1999
Southern Methodist University
1973-1984
A moving interpolation technique which provides an accurate representation of potential energy surfaces for polyatomic molecules is presented. The method uses the ab initio energy, gradient, and second derivatives calculated at dynamically important configurations. interpolant its converges to exact value with increasing number data. procedure given finding optimum configurations calculations are performed. demonstrated by application six-dimensional surface a diatomic plus reaction.
An analytical method is proposed by which the effects of flow nonuniformity and variable dispersion coefficients can be evaluated for problems involving longitudinal in porous media. A boundary layer approximation used to develop general solutions one‐dimensional convective‐dispersion equation steady flow. Several examples are considered using method, effect on discussed. Comparisons solution with numerical exact indicate that will yield accurate results many applications.
A scheme is introduced for generating a hierarchy of molecular fragmentations by which the total electronic energy can be approximated from energies fragments. Higher levels in produce fragments larger size and approximate more reliably. correction to account nonbonded interactions also presented. The accuracy approach tested number examples, shown essentially independent level ab initio theory employed. computational cost increases linearly with molecule.
We present a method for expressing potential energy surface (PES) polyatomic molecules as an interpolation of local Taylor expansions in internal coordinates. This approach extends and replaces earlier which was only directly applicable to no more than four atoms. In general, the are derived from ab initio quantum calculations. Here, methodology is evaluated by comparison with analytic reactions H+CH4⇌H2+CH3. Approximately 1000–1300 data points required accurate 12-dimensional describes both...
A recently proposed scheme for interpolating and iteratively improving molecular potential energy surfaces [Ischtwan Collins, J. Chem. Phys. 100, 8080 (1994)] is evaluated by comparison with an analytic surface the OH+H2→H2O+H reaction. An improvement in procedure constructing suggested implemented. The most efficient means of converging determined. It found that probability reaction, example, may be accurately calculated using order 200–400 data points to define surface.
A modified form of Shepard interpolation ab initio molecular potential energy surfaces is presented. This approach yields significant improvement in accuracy over previous related schemes. Here each Taylor expansion used the formula assigned a confidence volume which controls relative weight to that expansion. The parameters determining this are derived automatically from simple Bayesian analysis data. As iterative scheme expands data set, volumes also iteratively refined. for nine reactions...
A full quantum dynamical study of the reactions a hydrogen atom with water, on an accurate ab initio potential energy surface, is reported. The theoretical results are compared available experimental data for exchange and abstraction in H + D2O H2O. Clear agreement between theory experiment revealed thermal rate coefficients effects vibrational excitation reactants. excellent integral cross sections reaction unprecedented beyond atom-diatom reactions. However, larger than values by more...
For more than forty years, approximate solutions for the classical pipe network analysis problem have been obtained by direct solution of nonlinear stationary point conditions. We propose a revolutionary new approach involving optimization techniques solving this well-known engineering problem. It is shown that may be described mathematically in terms convex cost flow Three mathematical programming algorithms coded and are computationally compared with code using traditional Newton-Raphson...
A systematic method for approximating the ab initio electronic energy of molecules from energies molecular fragments is tested on a large sample typical organic structures. The detailed methods, including some additional refinements rings and long range interactions, are described. accuracy computational efficiency hierarchy methods reported.
A theoretical study of domain walls in uniaxial displacive ferrodistortive systems is presented. We start from a generalized Langevin equation motion for the movements ions, which includes dissipative terms and external fields, addition to anharmonic strain-force terms. obtain large- small-amplitude solutions corresponding usual soft-mode phonons, respectively. show that apart translation are absolutely stable our fields they reach unique terminal velocity. The linear dependence velocity on...
Crossed molecular beam experiments and accurate quantum scattering calculations have been carried out for the polyatomic H + CD 4 → HD 3 reaction. Unprecedented agreement has achieved between theory on energy dependence of integral cross section in a wide collision region that first rises then falls considerably as increases far over reaction barrier this simple hydrogen abstraction Detailed theoretical analysis shows at energies above incoming H-atom moves so quickly heavier D-atom cannot...
ConspectusChemistry, particularly organic chemistry, is mostly concerned with functional groups: amines, amides, alcohols, ketones, and so forth. This because the reactivity of molecules can be categorized in terms reactions these groups, by influence other adjacent groups molecule. These simple truths ought to reflected electronic structure energy molecules, as determined structure. However, sophisticated ab initio quantum calculations molecular usually do not make apparent. In recent...
A new version of systematic molecular fragmentation is presented which provides a hierarchy estimates for the energy, and other properties, large molecules with computation time that scales linearly size molecule. This method combined an algorithm ensures evaluation fragment compositions efficient very molecules. The illustrated using protein structures derived from NMR spectroscopy.
K. C. Thompson and M. A. Collins, J. Chem. Soc., Faraday Trans., 1997, 93, 871 DOI: 10.1039/A606038B
Accurate global ab initio surfaces are presented for the title reactions and competing exchange processes. The calculations were based on quadratic configuration interaction treatment with all single double excitations perturbative account triple together a 6-311++G(3df,2pd) basis, multi-reference method Davidson correction procedure an aug-cc-pVTZ unrestricted coupled-cluster aug-cc-pVQZ basis. interpolations of data energies, energy gradients, second derivatives at configurations scattered...
In this paper we evaluate the use of higher order derivatives in construction an interpolated potential energy surface for OH+H2→H2O+H reaction. The involves interpolating between local Taylor expansions about a set known data points. We examine first, second, third, and fourth interpolation scheme. convergence various surfaces is evaluated terms probability conclude that first (and by implication zeroth expansions) are not suitable constructing reactive systems. also it inefficient to...
A method for constructing diabatic potential energy matrices by interpolation of ab initio quantum chemistry data is described and tested. This approach applicable to any number interacting electronic states, relies on a formalism computational procedure that are more general than those presented previously the case two states. The tested against an analytic model three states NH(3) (+).
The hydrodynamic stability (to both stationary and oscillatory convection) of binary, Boussinesq fluids in Bénard geometry, with the Soret Dufour effects included is studied. A variational principle for Rayleigh number Rcr at onset convection found; complete exact solutions are also given. Apart from trivial multiplicative factors, depends only on a single dimensionless parameter ψ which transport thermodynamic coefficients. For ψ⩾0 (’’normal’’ effect) system becomes stable if heated below...
The accuracy of the systematic fragment approach to estimation molecular electronic energies is enhanced by a significantly improved treatment nonbonded interactions between fragments. Distributed electrostatic interactions, pairwise dispersion and many-body induction are evaluated from ab initio calculations small complete reported for large sample typical neutral organic molecules.
A new full-dimensional potential energy surface for the title reaction has been constructed using modified Shepard interpolation scheme. Energies and derivatives were calculated UCCSD(T) method with aug-cc-pVTZ 6-311++G(3df,2pd) basis sets, respectively. total number of 30,000 data points selected from a huge molecular configurations sampled by trajectory method. Quantum dynamical calculations showed that is well converged collision up to 2.5 eV. Total probabilities integral cross sections...
Seawater intrusion beneath a semipervious layer in two‐layer coastal aquifer system is described. Freshwater can occur the aquitard because of head losses induced by upward flow through layer. A steady state Dupuit model formulated to predict piezometric variation landward and above intruding seawater. Exact solutions are given for variation, but numerical solution necessary zone The mathematical compared experimental results Hele‐Shaw study Long Island, New York. analysis provides...
Two electronic structure methods, the fragment molecular orbital (FMO) and systematic fragmentation (SMF) that are based on fragmenting a large system into smaller, more computationally tractable components (fragments), presented compared with fully ab initio results for predicted binding energies of water clusters. It is demonstrated that, even when explicit three-body effects included (especially necessary clusters due to their complex hydrogen-bonded networks) both methods present viable,...