Potential energy surface

About: Potential energy surface is a research topic. Over the lifetime, 11674 publications have been published within this topic receiving 307691 citations.

Variational transition state theory calculations for an atom--radical reaction with no saddle point: O+OH

Abstract: We have extended the general polyatomic canonical variational theory formalism of Isaacson and one of the authors to improved canonical and microcanonical variational theory. We have calculated the rate constants for the reaction in the title over the temperature range 200–2500 K using all three variational theories and the Melius–Blint ab initio potential energy surface. The results are compared to canonical variational calculations based on the reaction‐path interpolation scheme of Quack and Troe, to the trajectory calculations of Miller, and to experiment. We find that the microcanonical variational transition states have a strong energy dependence and the generalized free energy of activation curves have two maxima. Quantization effects appear to be important at the lower temperatures, and recrossing effects may be important at higher temperatures.

A neural network potential-energy surface for the water dimer based on environment-dependent atomic energies and charges.

Abstract: Understanding the unique properties of water still represents a significant challenge for theory and experiment. Computer simulations by molecular dynamics require a reliable description of the atomic interactions, and in recent decades countless water potentials have been reported in the literature. Still, most of these potentials contain significant approximations, for instance a frozen internal structure of the individual water monomers. Artificial neural networks (NNs) offer a promising way for the construction of very accurate potential-energy surfaces taking all degrees of freedom explicitly into account. These potentials are based on electronic structure calculations for representative configurations, which are then interpolated to a continuous energy surface that can be evaluated many orders of magnitude faster. We present a full-dimensional NN potential for the water dimer as a first step towards the construction of a NN potential for liquid water. This many-body potential is based on environment-dependent atomic energy contributions, and long-range electrostatic interactions are incorporated employing environment-dependent atomic charges. We show that the potential and derived properties like vibrational frequencies are in excellent agreement with the underlying reference density-functional theory calculations.

A reactant-coordinate-based time-dependent wave packet method for triatomic state-to-state reaction dynamics: application to the H + O2 reaction.

Abstract: A new time-dependent wavepacket method is developed to study the A + BC -> AB + C, AC + B reaction at the state-to-state level. The method only requires propagation of the wavepacket in reactant Jacobi coordinates by extracting S-matrix information on a dividing surface right before the absorption potential in the product region. It has particular advantages for reactions with deep wells and long-range attractive interactions in the product channels in which the wavepacket in the product channels can only be absorbed sufficiently far away from the interaction potential. Demonstration made on the benchmark H + H-2 reaction shows that the method is rather efficient in dealing with a direct reaction at high collision energy. The method is applied to study the very challenging H + O-2 (v(0) = 0, j(0) = 0, 1) reaction, with state-to-state differential cross sections obtained for the first time for collision energies up to 1.1 eV. The calculations not only show the power and accuracy of the new approach in dealing with complex-forming reactions but also shed light on the dynamics of the H + O-2 reaction.

Development of transferable interaction models for water. I. Prominent features of the water dimer potential energy surface

Abstract: We present an analysis of the morphology of the water dimer potential energy surface (PES) obtained from ab initio electronic structure calculations and perform a quantitative comparison with the results from various water potentials. In order to characterize the morphology of the PES we have obtained minimum energy paths (MEPs) as a function of the intermolecular O–O separation by performing constrained optimizations under various symmetries (Cs, Ci, C2, and C2v). These constitute a primitive map of the dimer PES and aid in providing an account for some of its salient features such as the energetic stabilization of “doubly hydrogen-bonded” configurations for R(O–O)<2.66 A. Among the various interaction potentials that are examined, it is found that the family of anisotropic site potential (ASP) models agrees better with the ab initio results in reproducing the geometries along the symmetry-constrained MEPs. It is demonstrated that the models that produce closest agreement with the morphology of the ab initio PES, tend to better reproduce the experimental data for the second virial coefficients. We finally comment on the functional forms of simple water models and discuss how effects such as charge overlap can be incorporated into such models.

Potential energy surface of the H+3 ground state in the neighborhood of the minimum with microhartree accuracy and vibrational frequencies derived from it

Abstract: The potential energy surface (PES) of the H+3 ground state is computed by means of the single and double excitation configuration interaction with an explicit linear r12 term in the wave function (CISD‐R12) developed recently by the present authors, with a nearly saturated basis set. The points of the PES suggested by Meyer, Botschwina, and Burton (MBB) were chosen and the fitting procedure of the same authors was followed. The present PES has both on an absolute and a relative scale (i.e., relative to the minimum) an error of a few microhartrees (μEh) in the relevant region, an accuracy that has never before been achieved in a quantum chemical calculation for a triatomic molecule. From the fit the vibrational term values for the fundamental bands and some overtones of H+3, H2D+, HD+2, and D+3 were computed by means of the TRIATOM package of Tennyson and Miller. The computed frequencies are in better agreement with experiment (maximum error ∼0.5 cm−1) than those of all previous ab initio calculations (wit...