CALCULATED STRUCTURAL-PROPERTIES OF CRSI2, MOSI2, AND WSI2

The linear augmented-plane-wave method has been applied to calculate the valence-electron contribution to the total energy of the hexagonal (C40) and tetragonal (C11b) phases of the group-VI transition-metal dislicides CrSi2, MoSi2, and WSi2 in the local-density approximation (LDA). In agreement with experiment, the results show that the tetragonal C11b phase is the lower-energy structure for both MoSi2 and WSi2 (by 0.11 and 0.22 eV/formula unit, respectively). However, the LDA fails to replicate the observed switch to the stable hexagonal C40 phase in CrSi2, leaving a reduced but positive C40-C11b structural-energy difference of 0.05 eV/formula unit. The calculated lattice parameters for the observed stable phases are in excellent agreement (approximately 0.01-0.03 angstrom) with measured values. Somewhat large discrepancies (approximately 0.1-0.3 angstrom) are found for the c lattice parameters of the metastable hexagonal MoSi2 and WSi2 compounds.