Electronic structure of defect of Na substituting for K in KH2PO4 crystals

The electronic structures of defect of Na substituting for K in KH2PO4 (KDP) crystals are studied by first-principles total-energy calculations based on density-functional theory. The calculated formation energy for this defect is about 0.46 eV. No defect states are induced in the energy gap, whereas two extra occupied states are induced in the valence band, which are located at -49 eV and -21.5 eV below the Fermi energy level, respectively.