A highly accurate {\it ab initio} potential energy surface for methane

Abstract

A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art \textit{ab initio} theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include: core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of ${}^{12}$CH${}_4$ reproduced with a root-mean-square error of $0.70$cm${}^{-1}$. The computed \textit{ab initio} equilibrium C{--}H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as $J$ (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the equilibrium geometry. The PES represents the most accurate \textit{ab initio} surface to date and will serve as a good starting point for empirical refinement.

References in corpus (2)

• The spectrum of hot methane in astronomical objects using a comprehensive computed line list
• Methane and Ammonia in the near-infrared spectra of late T dwarfs

Cited by in corpus (3)

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