Ab Initio Potential Energy Values Research Articles

Recommended gas transport properties of argon at low density using ab initio potential

The most important transport properties of argon have been calculated using classical kinetic theory expressions in conjunction with high-quality ab initio potential energy values computed by Patkowski and Szalewicz. Dilute gas transport properties have been calculated for the viscosity, thermal conductivity, self-diffusion coefficient and thermal diffusion factor from 83 to 10,000 K. Comparisons between experimental transport property data and values presently calculated indicate that the present theoretical predictions may be employed as recommended values for this set of transport properties over a wide temperature range.

COMPCHEM: Progress Towards GEMS a Grid Empowered Molecular Simulator and Beyond

Foundations and structure of the building blocks of GEMS, the ab initio molecular simulator designed for implementation on the EGEE computing Grid, are analyzed. The impact of the computational characteristics of the codes composing its blocks (the calculation of the ab initio potential energy values, the integration of the dynamics equations of the nuclear motion, and the statistical averaging of microscopic information to evaluate the relevant observable properties) on their Grid implementation when using rigorous ab initio quantum methods are discussed. The requests prompted by this approach for new computational developments are also examined by considering the present implementation of the simulator that is specialized in atom diatom reactive exchange processes.

MEP–MPE potential energy surface for the Cl + CH4 → HCl + CH3 reaction

AbstractA potential energy functional based on a many‐process expansion minimum energy path approach has been fitted to the ab initio potential energy values of the Cl + CH4 system. The functional form adopted, the parameters of the fitted surface, and the variation of the cone of acceptance as a function of relevant parameters are discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

Dynamics of (H−,H2) collisions: A time-dependent quantum mechanical investigation on a new ab initio potential energy surface

A global analytical potential energy surface for the ground state of H(3)(-) has been constructed by fitting an analytic function to the ab initio potential energy values computed using coupled cluster singles and doubles with perturbative triples [CCSD(T)] method and Dunning's augmented correlation consistent polarized valence triple zeta basis set. Using this potential energy surface, time-dependent quantum mechanical wave packet calculations were carried out to calculate the reaction probabilities (P(R)) for the exchange reaction H(-)+H(2)(v, j)-->H(2)+H(-), for different initial vibrational (v) and rotational (j) states of H(2), for total angular momentum equal to zero. With increase in v, the number of oscillations in the P(R)(E) plot increases and the oscillations become more pronounced. While P(R) increases with increase in rotational excitation from j=0 to 1, it decreases with further increase in j to 2 over a wide range of energies. In addition, rotational excitation quenches the oscillations in P(R)(E) plots.

A LAGROBO Multiproperty Fit to Four-Atom Potential Energy Surfaces: The OH + HCl Case Study

The four-atom LAGROBO functional form has been used to fit the ab initio potential energy values of the OH + HCl → C+ + H2O reaction. A multiproperty analysis of the fitted surfaces based on the value of the rate coefficients and on the fraction of energy disposed into product vibration has prompted the development of a more general and flexible functional. Using the improved LAGROBO functional, it has been possible to play with the height of the barrier and with the depth of the entrance channel well to significantly reduce the difference between calculated and measured properties of the OH (OD) + HCl reactions.

Bound and Quasibound States of He2H+ and He2D+

Bound and quasibound states of He 2 H + and He 2 D + in three dimensions have been computed by use of a time-dependent quantum-mechanical wave packet approach for total angular momentum J=0. Seven bound states were found for He 2 H + and 14 for He 2 D + , as compared to five for both systems by Lee and Secrest (J. Chem. Phys. 1986, 85, 6565). The potential energy surface needed for the dynamical calculation has been computed by carrying out an ab initio calculation with coupled cluster single and double excitations with perturbative triple excitations [CCSD(T)] employing d-aug-cc-PVTZ basis set. A many-body expansion function proposed by Aguado et al. (Comput. Phys. Commun. 1998, 108, 259) was fitted to the ab initio potential energy values and the resulting fit has a root-mean-square deviation of 10.8 meV (0.25 kcal/mol).

The largest angle generalization of the rotating bond order potential: The H+H2 and N+N2 reactions

A generalization of the rotating bond order model potential is discussed. The new functional representation is used for fitting the ab initio potential energy values of the H+H2 system and the main features of a LEPS potential energy surface for the N+N2 system. For H+H2 we analyze the accuracy obtained when fitting the ab initio potential energy values using different functional representations. For N+N2 we examine the deviation of some dynamic and kinetic properties calculated on the new model potential from those obtained from the original LEPS.

Competing mechanisms and products’ properties for the Be+HF reaction

Reactive properties of the Be+HF reaction have been investigated theoretically using a new fit of the ab initio potential energy values. The dependency of the reactive dynamics upon both the partition of the initial energy among the various diatomic degrees of freedom and the features of the potential energy surface is analyzed by discussing the structure of detailed products’ properties and the evolution of the reactive cross section with collision energy. Dynamical properties of competing reaction paths are also investigated by carrying out a detailed examination of selected trajectory plots.