Reply to the Comment on: Quantum Monte Carlo study of the dipole moment of CO [J. Chem. Phys. 110, 11700 (1999)]

Abstract

In our previous publication we have mistakenly claimed that the applicability of the Hellmann-Feynman theorem in fixed-node quantum Monte Carlo calculations is not subject to the manner how the nodal boundary depends on an external parameter. This statement is not correct in general, except where the Hellmann-Feynman force is calculated for a nodal boundary which coincides with that of the unconstrained exact eigenfunction. We point out the error in our arguments and present an explicit expression for the correction term which supplements the Hellmann-Feynman force. This term can be interpreted as the linear response of the energy with respect to variations of the the nodal region.