Structural, elastic, and vibrational properties of layered titanium dichalcogenides: A van der Waals density functional study

Using the van der Waals density functionals (vdW-DFs), we present results of a density functional theory (DFT) study on the structure of layered titanium dichalcogenides TiX2 (X = S, Se, or Te). By accounting for non-local component in long-ranged electron correlation effects, the vdW-DFs lead to more accurate predictions of the structural parameters relative to conventional DFT. In particular, the vdW-optB86b functional [J. Klimes et al., Phys. Rev. B83, 195131 (2011)] gives the most agreement with experimental measurements for the lattice constant involving the vdW interactions. Based on the relaxed structure, the calculated elastic constants and vibrational frequencies are compared to experimental work and overall good agreement is obtained. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770293]