Exact quantum Monte Carlo calculations of the potential energy surface for the reaction H+H2→H2+H

Abstract

We report ‘‘exact’’ quantum Monte Carlo calculations of the potential energy surface for the reaction H+H2→H2+H. The method used is free of systematic error. The statistical or sampling error was reduced to ±0.10 kcal/mol for several hundred points distributed across the surface, to ±0.02 kcal/mol for the minimum energy approach of H to H2, to ±0.02 kcal/mol near the saddle point, and to ±0.01 kcal/mol at the saddle point. The upper and lower surfaces in the region of the Jahn–Teller cusp were determined with a statistical error of ±0.2 kcal/mol.