Study of the vibrational, dielectric and infrared properties of CdSiP2 via first principles

• Phonon frequencies and their vibrational modes are obtained and analyzed.
• Born effective charges and LO–TO splitting are computed and discussed.
• Dielectric, refractive index and infrared reflectance spectra are simulated.

CdSiP2is a promising nonlinear optical crystal for frequency conversion in the mid-IR spectral range. In this work, the vibrational, dielectric and infrared properties of CdSiP2 are studied by using density functional perturbation calculation. The Born effective charges of the constituent ions, the vibrational modes and the splitting of the longitudinal and transverse optical (LO–TO) frequencies at the Brillouin zone center are calculated and discussed. Its dielectric constant and dielectric spectra are also calculated, which reveals that electrons in CdSiP2 have a larger contribution to the dielectric constant than the lattice. The theoretically obtained birefringence Δn and the simulated infrared reflectance spectra agree well with the available experimental results.