Periodic density functional plane wave calculations of triplet exciton in NaCl

We performed calculations of the triplet excited state of NaCl using a periodic model and starting from the perfect lattice configuration. The Density Functional Theory and a plane wave basis set were used to calculate supercells of up to 144 atoms. No minimum of the total energy was found along an adiabatic curve corresponding to the displacement of one Cl atom along the [110] axis and adiabatic relaxation of surrounding ions. The electron density in calculated configurations corresponds to the off-centre STE model and F-H pair. We suggest that the existence of a local energy minimum is not a necessary condition for exciton self-trapping in NaCl and that it could have a dynamic nature starting from precursor states due to lattice fluctuations.