We present a simple, robust and efficient method for varying the parameters
in a many-body wave function to optimize the expectation value of the energy.
The effectiveness of the method is demonstrated by optimizing the parameters in
flexible Jastrow factors, that include 3-body electron-electron-nucleus
correlation terms, for the NO2 and decapentaene (C10H12)
molecules. The basic idea is to add terms to the straightforward expression for
the Hessian that are zero when the integrals are performed exactly, but that
cancel much of the statistical fluctuations for a finite Monte Carlo sample.
The method is compared to what is currently the most popular method for
optimizing many-body wave functions, namely minimization of the variance of the
local energy. The most efficient wave function is obtained by optimizing a
linear combination of the energy and the variance.Comment: 4 pages, 4 figures, minor corrections of inexact statements, missing