Excitation energies from diffusion Monte Carlo using selected configuration interaction nodes

Anthony Scemama (1) , Anouar Benali (2) , Denis Jacquemin (3) , Michel Caffarel (1) , Pierre-François Loos (1)

1 GMO - Groupe THEO (LCPQ)
2 CIRIMAT - Centre interuniversitaire de recherche et d'ingenierie des matériaux
3 UN - Université de Nantes

Quantum Monte Carlo (QMC) is a stochastic method that has been particularly successful for ground-state electronic structure calculations but mostly unexplored for the computation of excited-state energies. Here, we show that within a Jastrow-free QMC protocol relying on a deterministic and systematic construction of nodal surfaces using selected configuration interaction (sCI) expansions, one is able to obtain accurate excitation energies at the fixed-node diffusion Monte Carlo (FN-DMC) level. This evidences that the fixed-node errors in the ground and excited states obtained with sCI wave functions cancel out to a large extent. Our procedure is tested on two small organic molecules (water and formaldehyde) for which we report all-electron FN-DMC calculations. For both the singlet and triplet manifolds, accurate vertical excitation energies are obtained with relatively compact multi-determinant expansions built with small (typically double-ζ) basis sets. Published by AIP Publishing.

Domaines: Chimie théorique et/ou physique

Anthony Scemama, Anouar Benali, Denis Jacquemin, Michel Caffarel, Pierre-François Loos. Excitation energies from diffusion Monte Carlo using selected configuration interaction nodes. Journal of Chemical Physics, 2018, 149 (3), pp.034108. ⟨10.1063/1.5041327⟩. ⟨hal-01858533⟩