Sampling differences in quantum Monte Carlo: A generalized reweighting method

The estimation of differences using Quantum Monte Carlo enlarges the scope of these methods as it provides information on several quantities of physic al interest. A direct calculation of derivatives by means of uncorrelated d ifferences leads usually to results which are masked by the statistical var iance of the measure. The method we propose relies on general ideas behind correlated sampling and is a kind of generalization of thr reweighting meth od, vastly used in variational Monte Carlo applications. The efficiency and implementation of the method is shown in an explicit calculation of the bi nding energy of one He-3 atom in superfluid He-4 and its kinetic energy. (C ) 1999 Elsevier Science B.V. All rights reserved.