Potential energy surface for interactions between two hydrogen molecules

Published

September 4, 2008

Author(s)

Allan H. Harvey, Konrad Patkowski, Wojciech Cencek, Piotr Jankowski, Krzysztof Szalewicz, Giovanni Garberoglio

Abstract

Nonrelativistic clamped-nuclei energies of interaction between two ground-state hydrogen molecules with intramolecular distances fixed at their average value in the lowest rovibrational state have been computed. The calculations applied the supermolecular coupled-cluster method with single, double, and noniterative triple excitations [CCSD(T)] and very large orbital basis sets - up to augmented quintuple-zeta size supplemented with bond functions. The same basis sets were used in symmetry-adapted perturbation theory (SAPT) calculations performed mainly for larger separations to provide an independent check of the supermolecular approach. The contributions beyond CCSD(T) were computed using the full configuration interaction (FCI) method and basis sets up to augmented triple-zeta plus midbond size. All the calculations were followed by extrapolations to complete basis set limits. For two representative points, calculations were also performed using basis sets with the cardinal number increased by one or two. For the same two points, we have also solved the Schrödinger equation directly using four-electron explicitly-correlated Gaussian (ECG)functions. These additional calculations allowed us to estimate the accuracy of the interaction energies used to fit the potential to be about 0.1 K or 0.2% at the minimum of the potential well. This accuracy is about an order of magnitude better than achieved by earlier potentials for this system. The computed points were fitted by an analytic four-dimensional potential function. The uncertainties of the fit relative to the ab initio energies are almost always smaller than the estimated uncertainty of the latter energies. The fit was applied to compute the second virial coefficient using an exact quantum approach. The achieved agreement with experiment is substantially better than in any previous work.

Citation

Journal of Chemical Physics

Volume

129

Pub Type

Journals

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Keywords

computational chemistry, hydrogen, potential energy surface, second virial coefficient

Citation

Harvey, A. , Patkowski, K. , Cencek, W. , Jankowski, P. , Szalewicz, K. and Garberoglio, G. (2008), Potential energy surface for interactions between two hydrogen molecules, Journal of Chemical Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=832305 (Accessed December 26, 2024)