A very high accuracy potential energy surface for H3
An exact quantum Monte Carlo (EQMC) method was used to calculate the potential energy surface (PES) for the ground electronic state of H3 over a grid of about 76000 nuclear geometries. The absolute abinitio statistical or sampling error of the calculation was ±0.01 kcal mol-1 for energies (V) smaller than 3 eV. This PES was fitted by a three-dimensional cubic spline method and the fitting accuracy was determined from a set of 3684 randomly selected nuclear geometries not used in the fitting. For the range V⩽3 eV the rms fitting error was ±0.010 kcal mol-1, and the absolute value of the corresponding maximum error was 0.018 kcal mol-1. This fitted EQMC PES is an order of magnitude more accurate than the best PES previously obtained for this system. Detailed comparisons are made with previous PESs, for the more dynamically important nuclear configurations.