Vibrational, thermodynamic and acoustic properties of AgAlS2 crystal

First-principles calculations of vibrational properties of AgAlS2 crystal have been performed for the first time. The phonon dispersion and phonon density of states were calculated. Phonon dispersion curves disclose dynamical stability of the system. The group-theoretical classification of vibrational modes has been done and classification according to selection rules of modes active in infrared and Raman spectra has been performed. Raman and infrared spectra of AgAlS2 were calculated within the DFPT method. The LO-TO splitting of the infrared modes are reported. The effective Born charges for constituent atoms of the crystal were calculated and analyzed. Thermodynamic functions such as enthalpy, entropy, free energy and heat capacity at constant volume are obtained. The propagation velocities of longitudinal and transverse acoustic waves in the crystal were calculated for the (100) and (001) directions. The anisotropy coefficients are calculated and anisotropy of the propagation speed of acoustic waves in AgAlS2 crystal is analyzed.