The elastic properties and electronic structure of tetragonal Potassium dihydrogen phosphate (KDP) under polishing pressures were investigated using the plane-wave pseudopotential method based on density functional theory. The results show that the calculated lattice constant, elastic constants and bandgap agreed well with the results of the experiments and the other calculations at ambient pressure. The elastic constants and the elastic moduli of KDP increase with increasing pressure, but Vickers hardness of KDP decreases. KDP crystal changes from brittleness to ductility beyond the pressure of 3 GPa. The anisotropy of KDP increases and the ratio of [Formula: see text]/[Formula: see text] increases with the increase of pressure. When the pressure reaches 4.5 GPa, the tetragonal KDP will undergo structural phase transition. As pressure increases, the bandgap between and O-2[Formula: see text] and P-3[Formula: see text] states increases. The interatomic distances were shortened under external pressure, and the interaction between K[Formula: see text] and the neighboring H2PO[Formula: see text] was enhanced, which leads to the increase of elastic mechanical properties.

中文翻译：

---

第一性原理抛光压力下四方KDP晶体的弹性和电子结构

采用基于密度泛函理论的平面波赝势方法研究了四方磷酸二氢钾（KDP）在抛光压力下的弹性和电子结构。结果表明，计算得到的晶格常数、弹性常数和带隙与实验结果和环境压力下的其他计算结果吻合良好。KDP的弹性常数和弹性模量随着压力的增加而增加，但KDP的维氏硬度降低。KDP 晶体在超过 3 GPa 的压力下从脆性转变为延展性。随着压力的增加，KDP的各向异性增加，[公式：见正文]/[公式：见正文]的比值增加。当压力达到 4.5 GPa 时，四方 KDP 将发生结构相变。随着压力的增加，和 O-2[公式：见文本] 和 P-3[公式：见文本] 状态之间的带隙增加。外力作用下，原子间距离缩短，K[公式：见正文]与相邻的H相互作用2PO[公式：见正文]增强，导致弹性力学性能增加。