Periodic Hartree−Fock Study of LixTiS2, 0 ≤ x ≤ 1: The Structural, Elastic, and Electronic Effects of Lithium Intercalation in TiS2

Abstract

The structural and electronic properties of the intercalation compound LixTiS2, x = 1/4, 3/4, and 1, are investigated at the ab initio, all-electron, periodic Hartree−Fock level, using an extended basis set and a posteriori density functional correlation corrections to the total energy. Calculated lattice parameters, bulk moduli, linear moduli, cohesive energy, elastic constants, band structure, density of states, and Mulliken populations are reported. This study indicates that the following physical changes in LixTiS2 are induced by intercalation. (1) The crystal expands uniaxially in the c⃗ direction. (2) The S−Ti−S layers expand negligibly (<0.01 Å) in the c⃗ direction at x = 1/4, but a large (0.16 Å) layer expansion occurs at x = 1. (3) The elastic properties change negligibly at x = 1/4, but the interlayer stiffness c33 increases by a factor of ∼4 at x = 1. (4) Lithium charge is donated to the S(3p) and Ti(3d) orbitals. At least 75% of this charge is acquired by sulfur atoms. (5) At x = 1/4, the donated charge is localized over the lithium near-neighbor S(3p) and Ti(3d) orbitals. (6) Charge transfer to a Ti(3d)-based conduction band yields metallic properties.