Diffusion Monte Carlo using domains in configuration space

The sampling of the configuration space in diffusion Monte Carlo is done using walkers moving randomly. In a previous work on the Hubbard model [R. Assaraf, P. Azaria, M. Caffarel, and P. Lecheminant, Phys. Rev. B 60, 2299 (1999).], it was shown that the probability for a walker to stay a certain amount of time in the same state obeys a Poisson law and that the on-state dynamics can be integrated out exactly, leading to an effective dynamics connecting only different states. Here, we extend this idea to the general case of a walker trapped within domains of arbitrary shape and size. The equations of the resulting effective stochastic dynamics are derived. The larger the average (trapping) time spent by the walker within the domains, the greater the reduction in statistical fluctuations. A numerical application to the Hubbard model is presented. Although this work presents the method for (discrete) finite linear spaces, it can be generalized without fundamental difficulties to continuous configuration spaces.