A DIFFUSION MONTE-CARLO ALGORITHM WITH VERY SMALL TIME-STEP ERRORS

We propose modifications to the simple diffusion Monte Carlo algorithm that greatly reduce the time-step error. The improved algorithm has a time-step error smaller by a factor of 70 to 300 in the energy of Be, Li2 and Ne. For other observables the improvement is yet larger. The effective time step possible with the improved algorithm is typically a factor of a few hundred larger than the time step used in domain Gre en function Monte Carlo. We also present an optimized 109 parameter tr ial wave function for Be which, used in combination with our algorithm , yields an exceedingly accurate ground state energy. A simple solutio n to the population control bias in diffusion Monte Carlo is also disc ussed.