Lattice dynamics of layered ferroelectric semiconductor compound TlGaSe2

Ab initio Lattice Dynamics and Grüneisen Parameters of TlGaSe2

“…Despite the great diversity of experimental data on IR and Raman spectra, calorimetric measurements and thermal expansion for TlGaSe 2 , 3) theoretical calculations of lattice dynamics was just recently published. 4) In the present work the results of calculations of the elastic and compliances tensor, the directional Gru ¨neisen functions and the coefficients of the linear thermal expansion for TlGaSe 2 are presented. The results obtained confirm that both principal coefficients of the linear thermal expansion are positive in the range of temperature above 5 K.…”

“…Optimization data of the unit cell parameters and reduced coordinates of atoms inside the unit cell, as well as calculated phonon spectra, phonon density of states, IR reflection spectra, Raman frequencies and the temperature dependence of heat capacity were published. 4) Calculation of the phonon spectrum of TlGaSe 2 has been performed in the framework of the density perturbation functional theory using the local-density approximation by the same method described. 4) Gru ¨neisen parameters were calculated as follows: first, the phonon spectrum was calculated for a given equilibrium lattice parameters; then full phonon spectrum was calculated for slightly changed lattice parameter a and then same full calculation was performed for slightly changed parameter c. Finally, the thermodynamic functions of heat capacity, entropy and the strain derivatives of entropy were calculated.…”

“…Peculiarities of the phonon dispersion, phonon density of states, heat capacity and calculated IR reflection in the restrahlen range as well as calculated values of Raman frequencies for TlGaSe 2 were published. 4) The elastic tensor components calculated in the present work are given in Table I together with the experimental values from ultrasonic experiments. 6,7) We have calculated the directional Gru ¨neisen functions ( ?…”