By introducing perturbations of O(τ) type (where τ is the time step used in the simulation) to our diffusion quantum Monte Carlo algorithm we obtain a simulated energy which is reasonably constant over a wide range of τ values. Reliable estimation of the fixed-node energy (τ=0 intercept) results, as extrapolation becomes more robust and a radical change in small τ behavior becomes less likely. We apply our techniques to the problem of estimating the ground-state energy of LiH and H2O.
We report formulas to estimate the relativistic corrections for atoms or molecules (treated as the first order perturbation) by diffusion quantum Monte Carlo (DQMC) simulations. Our formulas involve primarily quantities which are routinely computed in nonrelativistic simulations. Hence our approach entails only minor additional modifications of existing (all electron) DQMC codes. We illustrate our algorithm by estimating various relativistic corrections to the ground state energy of LiH. 3784 J.Since both quantites which appear on the right-hand side of Eq. (4) possess Coulombic singularities, it easily fol-J.
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