Atomistic insight into the formation dynamics of charged point defects: A classical molecular dynamics study of F+-centers in NaCl
This paper provides an atomistic exploration of the lattice dissipation mechanisms accompanying the formation of charged point defects through a femtosecond resolved study of F+-center creation in NaCl. Our findings, following from a classical molecular dynamics based investigation of this model system, point to general range of properties that should be present in similar systems. Immediately after the creation of such a charged defect center, its excess energy is imparted amongst the highest energy optical modes with no clear preference based on their degree of localization. This energy is then dissipated through equilibration amongst a bath of lower energy phonon modes. The temporal behavior primarily follows exponential decay trends at all the temperatures and energies explored, with a small degree of competition between phonon population and depopulation amongst lower energy bath modes. Moreover, the dissipation timescale is found to be approximately the same amongst all phonon energies. A temperature-dependent analysis shows the expected decrease in phonon lifetimes with increasing temperature. This is accompanied by similarly more rapid dissipation of thermal energy around the defect center at lower temperatures when the phonon mean free path is increased. An intuitive phenomenological model based on Langevin dynamics is also provided to interpret the atomistically derived phonon decay characteristics in the temporal domain. More broadly, these results are expected to aid the design and experimental investigation of strongly correlated materials where charged defect centers can play an important role in technological applications.
