Exploring the impact of semicore level electronic relaxation on polaron dynamics: An adiabaticab initiostudy ofFePO4

In the present work, we study the effects of the electronic relaxation of semicore levels on polaron activation energies and dynamics. Within the framework of adiabatic ab initio theory, we utilize both static transition state theory and molecular dynamics methods for an in-depth study of polaronic hopping in delithiated ${\text{LiFePO}}_{4} ({\text{FePO}}_{4})$. Our results show that electronic relaxation of semicore states is significant in ${\text{FePO}}_{4}$, resulting in a lower activation barrier and kinetics that is one to two orders faster compared to the result of calculations that do not incorporate semicore states. In general, the results suggest that the relaxation of states far below the Fermi energy could dramatically impact the ab initio polaronic barrier estimates for many transition metal oxides and phosphates.