First principles lattice dynamics calculations of Ag⁺ doped KX (X = Cl, Br and I)

Phonon states of Ag doped potassium halides, KX:Ag⁺ (X = Cl, Br and I), are computed by a first principles lattice dynamic method using 64-atoms supercells. Results are compared to experimental data in literature. Phonon density of states of host KC1 and KI crystals satisfactorily agree to the experimental inelastic neutron scattering data. Experimental frequencies of the impurity-induced infra-red (IR) and Raman active modes in the low frequency region are reasonably well reproduced because the vibrations are localized within the first nearest neighbour anions of the Ag⁺-ion. On the other hand, limitations of present calculations to reproduce the high frequency impurity-induced modes are pointed out. They are less localized to the Ag ⁺-ion.