Ab Initio Simulations of Exciton Polarons from Path Integral Monte Carlo

We construct a path integral based simulation framework to evaluate exciton binding energies in CsPbBr3 and other semiconducting materials with a full accounting of electronic correlation and electron-phonon coupling. The effective Hamiltonian we employ is parametrized electronically with GW calculations and the charge-phonon interaction elements with density-functional perturbation theory. Assuming the charge-lattice interaction is linear we derive an imaginary time influence functional to capture the renormalization of the exciton by arbitrary phonon modes with arbitrary coupling strength. We evaluate the exciton polaron binding energy using path integral Monte Carlo and study it as a function of temperature. We find that short-ranged interactions from acoustic phonons and long-ranged interactions from longitudinal optical phonons can significantly affect single charge polaron binding, but generally only longitudinal optical phonons appreciably renormalize exciton binding.