Abstract: A systematic exploration was conducted on the geometrical structures, electronic structures and optical properties of a series of compounds A₃PO₄ (A=Li, Na, K, Rb, Cs), made up of P-O coordinated polyhedra with different cations, based on density functional theory. The results show that by changing the substitution of alkali metal atoms, the structural framework can be manipulated, thereby modulating its band gap and optical properties, providing an effective approach for designing materials with excellent comprehensive performance. In investigating the relationship between the geometric structures and band gap properties of these compounds, the calculations of band structure indicates that all five compounds show direct bandgap structure and have wide band gaps of 5.853, 5.153, 4.083, 3.559 and 3.405 eV for A=Li, Na, K, Rb, Cs, respectively. Analysis of the atomic populations indicate that A(A=Li, Na, K, Rb) cation bind with oxygen to form O—A bond exhibiting ionic characteristics. This bonding behavior likely contributes to the gradual decrease in the band gap of A₃PO₄ compounds as the cation atomic number increases. On the other hand, Cs₃PO₄ doesn't form an O—Cs bond with an ionic character, thus leading to a reduction in the band gap. The conduction band of these five compounds is composed of the s and p orbitals of alkali metal atoms as well as the P-3p orbital. The main contributor to the top of the valence band is the O-2p orbital, and the O-2p orbital of O atom also shows strong localization near the Fermi level. The P-3p orbitals bond with the 2p orbitals of O, showing a strong covalent bond of P—O. All five compounds have weak responses to low-energy electromagnetic waves, mainly concentrated in the high-energy region of 5~15 eV.

Key words: phosphate crystal, first-principle, density functional theory, electronic structure, optical property