We present first-principles total-energy density-functional theory electronic structure calculations for the neutral and charge states of an oxygen vacancy in KH2PO4 (KDP). Even though the overall density of states profiles for the defective KDP are quite similar to those of the perfect KDP, the oxygen vacancy in the neutral and +1 charge states induces defect states in the band gap. For the neutral oxygen vacancy, one electron is localized in the O vacancy maintaining the charge that was at that site in the pure crystal, while the neighboring P atom to the vacancy gains about one electron relative to its charge state in pure KDP. For the +1 charge oxygen vacancy, the removal of an electron reduces the occupation of the filled gap states in the neutral case from two to one electron and produces a new empty state in the gap. The new empty gap state is very close to the highest occupied states, leading to a dramatic decrease of the band gap. In sharp contrast, no defect states appear in the energy gap for the +2 charge O vacancy, where the neighboring P atom to the O vacancy almost returns to its perfect-crystal charge state. For the -1 charge oxygen vacancy, the added electron does not localize on any of the atoms near the vacancy; rather it goes into the vacancy to spin-pair with the electron that was there in the neutral vacancy.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Oct 1 2005|
ASJC Scopus subject areas
- Condensed Matter Physics