WAVE-FUNCTION OPTIMIZATION WITH A FIXED SAMPLE IN QUANTUM MONTE-CARLO

The optimization of trial functions consisting of a product of a single determinant and simple correlation functions is studied. The method involves minimizing the variance of the local energy over a finite number of points (sample). The role of optimization parameters, e.g., sample characteristics, initial trial function parameters, and reference energy, is examined for H 2, Li2, and H2O. The extent to which cusp conditions are satisfied is also discussed. The resulting variational Monte Carlo energies <ψT|H|ψT> recover 46%-95% of the correlation energy for the simple trial function forms studied. When used as importance functions for quantum Monte Carlo calculations, these optimized trial functions recover 90%-100% of the correlation energy. Time-step bias of the computed quantum Monte Carlo energies is found to be small. © 1990 American Institute of Physics.