The atomic and electronic structures of irradiation-induced interstitial halide atoms (H centers) in crystals were calculated by using 16-atom super-cells and the first-principles full-potential linear muffin-tin orbital method. The vibrational properties of the H centers were studied for the 2 known orientations of the molecular axis of the H center in alkali halide crystals: along (110) and (111). Only in the former case (which was known to be energetically more favorable in KCl) was the local vibrational frequency close to that which was experimentally observed by means of Raman spectroscopy. A strong coupling was found between the stretching molecular mode of the H center, and the breathing motion of its 6 nearest K+ cations. This was predicted to lead to another local mode at around 257/cm.

A.Svane, E.A.Kotomin, N.E.Christensen: Physical Review B, 1996, 53[1], 24-7