In Part I, theoretical derivations for Variational Monte Carlo
calculations are compared with results from a numerical calculation of
He; both indicate that minimization of the ratio estimate of Evar , denoted
EMC
' provides different optimal variational parameters than does
minimization of the variance of E
MC
• Similar derivations for Diffusion
Monte Carlo calculations provide a theoretical justification for empirical
observations made by other workers.
In Part II, Importance sampling in prolate spheroidal coordinates
allows Monte Carlo calculations to be made of E for the vdW molecule
var
He2' using a simplifying partitioning of the Hamiltonian and both an
HF-SCF and an explicitly correlated wavefunction. Improvements are
suggested which would permit the extension of the computational precision
to the point where an estimate of the interaction energy could be made