A comparison of the structural, electronic, optical and elastic properties of wurtzite, zinc-blende and rock salt TlN: A DFT study

In this article we investigated structural, electronic, elastic, and optical properties of TlN in three phases, using full potential linear augmented plane wave method in the density functional theory frame with WIEN2k code. The calculations have been done in the generalized Perdew-Burke-Ernzerhof generalized gradient approximation, the generalized Wu-Cohen gradient approximation, the generalized Perdew-Burke-Ernzerhof solid gradient approximation, local density approximation, and the modified Becke-Johnson approximations. In spite of the absence of any experimental data for TlN, our results are compared with other results achieved by other different approximations which shows a good agreement with them. The band gap for TlN in wurtzite and zinc-blende are obtained to be 0.07 and 0.09 eV within modified Becke-Johnson-local density approximation+spin-orbit approximation, respectively. The structural properties such as phase transitions, equilibrium lattice parameters, bulk modulus and its first pressure derivative were obtained using an optimization method. Moreover, we calculated quantities such as elastic constants, the Young modulus, shear modulus, the Poisson ratio, and sound velocities for longitudinal and transverse waves, the Debye temperature and the Kleinman parameters in different approximations and we show that TlN is softer than other nitrides of the III-group. The static calculations predicted that wurtzite to rock salt and zinc-blende to rock salt phase transitions occur at 14.7 GPa and 15.8, respectively. The optical properties of TlN in three phases, calculated in generalized gradient approximation and local density approximation and imaginary part of dielectric function show that TlN in wurtzite and zinc-blende phases have semiconductor properties but rock salt phase do not show. As well as, we investigate the influence of the hydrostatic pressure on the elastic parameters and energy band structures for TlN (zinc-blende) within local density approximation.