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.

Structural studies of the water hexamer.

Abstract: In this paper we report the geometries and properties of 24 structural isomers located on the MP2/6-311++g** potential energy surface of the water hexamer. At least 15 structural patterns are located within 3 kcal/mol of the most stable conformation, leading to a very complex potential energy surface, several isomers having significant contributions. A quadratic correlation between the distance from the proton to the center of the hydrogen bond with the distance between oxygen atoms for all clusters is reported. MP2/6-311++g** and CCSD(T)/aug-cc-pvdz//MP2/6-311++g** predict different stabilization orderings but are in good agreement for binding energies. Compact structures are energetically favored by electronic energies with zero point energy corrections, while noncompact cyclic structures are preferred when temperature and entropy are accounted for.

A dual‐level Shepard interpolation method for generating potential energy surfaces for dynamics calculations

Abstract: We present a new dual‐level approach to representing potential energy surfaces in which a very small number of high‐level electronic structure calculations are combined with a lower‐level global surface, e.g., one defined implicitly by neglect‐of‐diatomic‐differential‐overlap calculations with specific reaction parameters, to generate the potential at any geometry where it may be needed. We interpolate the potential energy surface with a small number of accurate data points (the higher level) that are placed along the reaction path by using information on the global shape of the potential from less accurate calculations (the lower level). We confirm the findings of Ischtwan and Collins on the usefulness of single‐level schemes including Hessians, and we delineate the regime of usefulness of single‐level schemes based on gradients or even single‐point energies. Furthermore we find that dual‐level interpolation can offer cost savings over single‐level schemes, and dual‐level methods employing Hessians, gradients, or even only simple energy evaluations can yield reasonable potential energy surfaces with relatively low cost, with the potentials being more accurate along the reaction path. For all methods considered in this paper the accuracy of the interpolation for our test cases is lower when the potentials at points significantly removed from the reaction path are predicted from data that lie entirely on the reaction path.

Potential energy surface and quasiclassical trajectory studies of the n(2d)+h2 reaction

Abstract: We present dynamical studies of the CN+H{sub 2} reaction based on an empirical potential energy surface that is derived from high quality {ital ab} {ital initio} calculations. The {ital ab} {ital initio} calculations, which use a multireference configuration interaction method with large correlation consistent basis sets, indicate that the linear HHCN barrier is about 4.3 kcal/mol above CN+H{sub 2}, and that there is no reaction path which connects CN+H{sub 2} to the stable intermediate H{sub 2}CN, although there is a path for dissociation of H{sub 2}CN to H+HCN. The empirical surface is written as a sum of two-, three-, and four-body terms, with the two- and three-body terms for HCN based on an accurate global surface that describes both the HCN and HNC force fields. The four-body terms are developed so as to describe the HHCN linear saddle point and the H{sub 2}CN minimum accurately, as well as dissociation of H{sub 2}CN into HCN+H, and the ridge which separates the abstraction and H{sub 2}CN dissociation pathways. Other features of the potential surface, such as the HCNH {ital cis} and {ital trans} minima, and the pathways leading to the formation of HNC+H are also described, though less accurately. Three different choicesmore » for the HHCN saddle point properties are considered. We find that the surface which matches the {ital ab} {ital initio} barrier energy most accurately gives rate constants that are too low. Much better agreement is obtained using a 3.2 kcal/mol barrier. The trajectory results show typical dependence of the CN+H{sub 2} reactive cross sections on initial translational energy and initial vibration/rotation state, with CN behaving as a spectator and H{sub 2} playing an active role in the reaction dynamics. Analysis of the H+HCN products indicates that both the C-H stretch and bend modes are significantly excited, with bend excitation showing strong sensitivity to the saddle point properties and to reagent translational energy.« less

Calculation of thermodynamic properties of small Lennard‐Jones clusters incorporating anharmonicity

Abstract: A method for calculating thermodynamic properties of clusters from knowledge of a sample of minima on the potential energy surface using a harmonic superposition approximation is extended to incorporate anharmonicity using Morse correction terms to the density of states. Anharmonicity parameters are found for different regions of the potential energy surface by fitting to simulation results using the short‐time averaged temperature as an order parameter. The resulting analytical expression for the density of states can be used to calculate many thermodynamic properties in a variety of ensembles, which accurately reproduce simulation results. This method is illustrated for 13‐atom and 55‐atom Lennard‐Jones clusters.