INFINITESIMAL DIFFERENTIAL DIFFUSION QUANTUM MONTE-CARLO STUDY OF CUH SPECTROSCOPIC CONSTANTS

We show how to extend the formalism of infinitesimal differential diffusion quantum Monte Carlo to the case, of higher derivatives of the ground-state energy of a molecule with respect to the molecular geometry for a large-Z molecule. We propose a new all-electron approach based on the idea of using different simulation time-scales for different shells of the constituent atoms, viz., a substantially smaller time-step for innermost shells, and relatively large time-steps for the valence electrons. We avoid the approximations inherent in pseudopotential methods while at the same time, when used in conjunction with variational Monte Carlo, the sampling is done on a firm theoretical basis. We use CuH as an example, obtaining properties with an accuracy on par with those from SDCI, despite our using a crude single-determinant wave function with only two adjustable parameters.