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A new nine-dimensional potential energy surface (PES) for methane has beengenerated using state-of-the-art \textit{ab initio} theory. The PES is based onexplicitly correlated coupled cluster calculations with extrapolation to thecomplete basis set limit and incorporates a range of higher-level additiveenergy corrections. These include: core-valence electron correlation,higher-order coupled cluster terms beyond perturbative triples, scalarrelativistic effects and the diagonal Born-Oppenheimer correction.Sub-wavenumber accuracy is achieved for the majority of experimentally knownvibrational 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 agreementwith previous values despite pure rotational energies displaying minorsystematic errors as $J$ (rotational excitation) increases. It is shown thatthese errors can be significantly reduced by adjusting the equilibriumgeometry. The PES represents the most accurate \textit{ab initio} surface todate and will serve as a good starting point for empirical refinement.

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