Revisiting ab-initio excited state forces from many-body Green's function formalism: approximations and benchmark

Abstract: Ab initio techniques for studying the optical and vibrational properties of materials are well-established, but only a few recent studies have focused on the interaction between excitons and atomic vibrations. In this paper, we revisit the excited state forces method, which integrates results from GW/BSE and DFPT calculations to determine the gradient of the excited state energy. We explore its technical aspects, including convergence and the quality of approximations used. We successfully apply this method to investigate self-trapped excitons in LiF. The excited state forces method provides valuable insights into ionic dynamics in the excited state and the microscopic mechanism of exciton self-trapping.