Diffusion, Excitons and Adsorptivity of H and He atoms on KBr (001) M-center Surface: DFT calculations

The energetic properties of M-center diffusion, excitons near M2+, M+,
M, M- and M2- centers and adsorptivity of H and He atoms over defect free and
defect containing surfaces of KBr using Density Functional Theory (DFT)
calculations are discussed. The results clarify that: (i) The calculated barriers
for diffusing M-center in its lowest triplet excited state is similar to those in its
singlet ground state. (ii) Both exciton bands and band gaps depend on the
defect charge. For exciton bands, in the bulk and at the surface, M- and M2-
change the nature of KBr from isolator to semiconductor. (iii) The adsorptivity
of atomic H and He was in the range of chemical adsorption. The M-center
makes H atom more adsorb. (iv) The HOMO and LUMO levels of the substrate
shift to higher energies and band gaps become narrow when M-center is
introduced. This change in the electronic structure causes charge transfer
between adsorbate and substrate levels.