Structural phase stability and elastic properties of lanthanum monochalcogenides at high pressure

Ab initio calculations have been performed on the structural, elastic and high pressure properties of cubic inter-metallic LaS, LaSe and LaTe compounds. The Kohn-Sham equations were solved by applying the full-potential (linear) augmented plane wave method plus local orbitals (FP-(L)APW+lo) as implanted in the WIEN2K package. In this approach, the generalized gradient approximation (GGA) and the local density approximations (LDA) are used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus and its pressure derivative. The pressure transition at which these compounds undergo structural phase transition from NaCl-type (B1) to CsCl-type (B2) structure are calculated and compared with previous calculations and available experimental data. The elastic constants at room conditions and under pressure in both B1 and B2 phases are also calculated.