First-Principles study KDP crystals with defect cluster [MgK + SiP]

[Display omitted] •According to the principle of electrical neutrality, a defect cluster model of [SiP' + MgK•] was constructed.•The defect clusters was corrected using the FNV method with DFT and the PBE-GGA exchange-correlation functional, and the band gap was adjusted using the HSE correction.•Detailed analysis encompasses lattice distortions, electronic structures, and optical properties of defect clusters. In this study, the defect formation energies, lattice distortions, electronic structures and optical properties for the KDP crystal with defect cluster [MgK + SiP] have been obtained by first-principles methods. The accurate defect formation energies have been obtained by corrected with FNV method. The lattice distortion indicate that the appearance of defect clusters causes Si and P atoms to surround magnesium, resulting in a lattice distortion as high as 34.2 %. Furthermore, an silicate structure emerges, possibly leading to a reduction in the crystal damage threshold. The electronic structures reveal that the emergence of new defect states in the band gap of the crystal with [MgK + SiP]’ structure. These defect states cause the bottom of the conduction band to shift downwards, resulting in a decrease in the band gap. This is primarily attributed to the contributions from Mg-3 s and O-2p orbitals. This is self-consistent with the larger distortion around Mg in the lattice distortion. This is also a possible factor contributing to the decrease in the crystal damage threshold. The calculated optical spectra demonstrate that absorption peak values at 3.5 eV, 4.53 eV, 5.54 eV, 5.70 eV, and 5.81 eV, originating from defect clusters [MgK + SiP]. Therefore, it is conjectured that the presence of impurities magnesium and silicon may be one of the reasons for the reduction in the crystal damage threshold.