title: Weak intermolecular interactions calculated with diffusion Monte Carlo.
abstract: The performance of fixed node diffusion Monte Carlo (FNDMC) for weakly interacting molecules is investigated. The effect of Gaussian basis sets on the asymptotic description of the molecular orbitals which is crucial for a successful importance sampling is analyzed for the example of the hydrogen atom. We find that accurate reference binding energies of the water, the ammonia, and the T-shaped as well as the parallel-displaced benzene dimer are correctly reproduced by FNDMC. The binding energies for the benzene dimers are -3.00(0.38) and -3.58(0.38) kcal/mol, respectively. The description of the methane dimer which has the smallest binding energy and a quite large intermolecular distance requires a more flexible basis set of diffuse quadruple-zeta quality in order to prevent sampling errors.
authors.affiliation: Theoretische Organische Chemie, Organisch-Chemisches-Institut der Universität Münster, D-48149 Münster, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Diedrich
authors.forename: Arne
authors.initials: A
authors.lastname: Lüchow
authors.forename: Stefan
authors.initials: S
authors.lastname: Grimme