Efficient method for the quantum Monte Carlo evaluation of the static density response function of a many-electron system

In a recent letter we introduced Hellmann-Feynman operator sampling in diffusion Monte Carlo calculations. Here we derive, by evaluating the second derivative of the total energy, an efficient method for the calculation of the static density-response function of a many-electron system. Our analysis of the effect of the nodes suggests that correlation is described correctly and we find that nodal issues can be dealt with.