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Fixed-Node, Importance-Sampling Diffusion Monte Carlo for Vibrational Structure with Accurate and Compact Trial States

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journal contribution
posted on 21.02.2018, 00:00 by Ireneusz W. Bulik, Michael J. Frisch, Patrick H. Vaccaro
We present a new approach to importance sampling in diffusion Monte–Carlo (DMC) simulations of vibrational excited states whereby the trial wave functions for low-energy states are incorporated into the diffusion equations so as to enforce their orthogonality. For the model systems examined here, simple variational wave functions based on the vibrational self-consistent field (VSCF) and the simplest vibrational configuration interaction (VCI) are effective in importance sampling provided that internal coordinates used in the underlying one-particle functions have been variationally optimized. The resulting model yields results comparable in accuracy to the best unguided DMC calculations without requiring an a priori choice of coordinates to specify nodal hyperplanes.