First principles study of Li-Si crystalline phases: Charge transfer, electronic structure, and lattice vibrations

The crystalline Li-Si phases: LiSi, Li12S12, Li7Si3, Li13Si4, Li15Si4, Li21Si5, and Li22Si5 are studied using density functional theory. Charge transfer is evaluated using the Atoms in Molecules method (Bader charge analysis), showing that the Li atoms donate approximately 0.73 electrons to Si atoms in all crystalline Li-Si phases. The electronic structures of the Li-Si phases are studied using both total and projected densities of states. Results confirm the understanding of Li-Si structures as Zintl-like phases. Phonon density of states are calculated for all structures and thermodynamic properties are calculated in the context of the harmonic approximation. Phonon contributions to the free energy of formation cause a loss of stability with increasing temperature which is more pronounced in the LiSi and Li15Si4 phases compared to their neighboring phases. (C) 2010 Elsevier B.V. All rights reserved.