Strategies for improving the efficiency of quantum Monte Carlo calculations

We describe a number of strategies for minimizing and calculating accurately the statistical uncertainty in quantum Monte Carlo calculations. We investigate the impact of the sampling algorithm on the efficiency of the variational Monte Carlo method. Our finding that a relative time-step ratio of 1:4 is optimal in DMC is in agreement with the result of [J. Vrbik and S.M.Rothstein, Intern. J. Quantum Chem. 29, 461-468 (1986)]. Finally, we discuss the removal of serial correlation from data sets by reblocking, setting out criteria for the choice of block length and quantifying the effects of the uncertainty in the estimated correlation length.