Quadratic scaling path integral molecular dynamics for fictitious identical particles and its application to fermion systems

Abstract

Recently, fictitious identical particles have provided a promising way to overcome the fermion sign problem and have been used in path integral Monte Carlo (PIMC) to accurately simulate warm dense matter with up to 1000 electrons (T. Dornheim et al., arXiv:2311.08098 (2023)). The inclusion of fictitious identical particles in path integral molecular dynamics (PIMD) can provide another way to simulate fermion systems. In a recent paper (J. Chem. Phys. 159, 154107 (2023)), Feldman and Hirshberg improved the recursive formula for PIMD of N identical bosons, significantly reducing the computational complexity from $O(PN^3)$ to $O(N^2+PN)$. In this paper, we extend this latest recursive formula for bosons to PIMD of fictitious identical particles to improve the efficiency of simulating fermion systems. We also provide the virial estimator for calculating energy by using the recursive technique. As an example, we use the quadratic scaling PIMD for fictitious identical particles to study the simulation of hundreds of fermions in a two-dimensional periodic potential, in the hope of providing a simulation tool for two-dimensional Fermi-Hubbard model and other strongly correlated fermion systems, such as the simulation of ultracold fermionic gases in optical lattices.