First-principles total-energy density-functional theory electronic structure calculations were made of the neutral and charge states of H intrinsic (Frenkel pair) and extrinsic (H vacancy or interstitial) point defects. The relaxed atomic structures, the formation energy, the ionization energy and electron and hole affinities for the various defects were calculated. In the case of the Frenkel pair, the additional hole led to a decrease in the O―O bond length between the two O atoms next to the H vacancy, while the effect of the additional electron was small. In the case of the H vacancy, the added hole was trapped and shared by the two O atoms adjacent to the vacancy; thus sharply reducing the O―O bond length and forming a molecular-type polaron. It was found that the positively charged H vacancy, unlike its neutral state, introduced states into the gap. This confirmed that it was a relevant absorbing center. The negatively charged H vacancy led to an increase in the two O atoms close to the H vacancy, and did not introduce states into the gap. The H interstitial did not interact with host atoms in the neutral state. The addition of an electron led to the ejection of a H host atom and to the subsequent formation of a H2 interstitial molecule and a H vacancy. In the positively charged state, the H interstitial bound to its nearest-neighbor O atom to form an hydroxyl bond. The H interstitial, in both the positive and negative charge states, introduced no defect states into the band-gap; unlike its neutral state.

Electronic Structure Calculations of Intrinsic and Extrinsic Hydrogen Point Defects in KH2PO4. C.S.Liu, Q.Zhang, N.Kioussis, S.G.Demos, H.B.Radousky: Physical Review B, 68[22], 224107 (11pp)