Nonlinear density response from imaginarytime correlation functions: Ab initio path integral Monte Carlo simulations of the warm dense electron gas
Abstract
The ab initio path integral Monte Carlo (PIMC) approach is one of the most successful methods in quantum manybody theory. A particular strength of this method is its straightforward access to imaginarytime correlation functions (ITCFs). For example, the wellknown densitydensity ITCF F(q, τ) allows one to estimate the linear response of a given system for all wave vectors q from a single simulation of the unperturbed system. Moreover, it constitutes the basis for the reconstruction of the dynamic structure factor S(q, ω)—a key quantity in stateoftheart scattering experiments. In this work, we present analogous relations between the nonlinear density response in the quadratic and cubic order of the perturbation strength and generalized ITCFs measuring correlations between up to four imaginarytime arguments. As a practical demonstration of our new approach, we carry out simulations of the warm dense electron gas and find excellent agreement with previous PIMC results that had been obtained with substantially larger computational effort. In addition, we give a relation between a cubic ITCF and the triple dynamic structure factor S(q_{1}, ω_{1}; q_{2}, ω_{2}), which evokes the enticing possibility to study dynamic threebody effects on an ab initio level.
 Publication:

Journal of Chemical Physics
 Pub Date:
 August 2021
 DOI:
 10.1063/5.0058988
 arXiv:
 arXiv:2106.01619
 Bibcode:
 2021JChPh.155e4110D
 Keywords:

 Condensed Matter  Statistical Mechanics;
 Physics  Computational Physics
 EPrint:
 doi:10.1063/5.0058988