Ab Initio Studies of the Structures, Electronic and Vibrational Properties of Double Phosphates MCdPO₄ (M: Li, Na, Rb, Cs)

Structural, electronic, and vibrational properties of phosphates LiCdPO₄, NaCdPO₄, RbCdPO₄, CsCdPO₄ are studied by density functional theory and Hartree–Fock methods using the CRYSTAL17 code in the LCAO basis set with gradient PBE, PBEsol and hybrid PBE0, PBEsol0 functionals. It is shown that the crystal structures contain infinite zigzag chains consisting of [CdO₆] octahedra and [PO₄] tetrahedra inside which there are alkali metal atoms. By the Gaussian broadening of normal long-wave modes IR absorption and Raman spectra are calculated. Differences in the number of spectral bands, their polarization and intensities are related to different symmetry space groups of the crystals.