Effect of Interlayer Interaction on the Structural, Electronic, and Thermal Properties of Layered MS$_2$ (M=W, Mo) Structures

Using density functional theory (DFT) supplemented with van der Waals interaction, we investigate the effect of interlayer interaction on the structural, electroinic, and thermal properties of transition-metal disulfides MS$_2$, such as MoS$_2$ and WS$_2$. We calculate the relative stability of various layer-layer stacking configurations determined by considering relative positions and orientations between neighboring layers. We find that MS$_2$ layers may slide over each other with a small sliding barrier. We explore the effect of layer stacking on the electronic structure, and find an intriguing coupling effect. We also calculate their thermal properties including thermal expansion behavior especially along the direction normal to the plane. Such thermal expansion behavior is considered for our study of Li-intercalation into layered MS$_2$, which may become a fundamental understanding for future development of Li-ion battery. We evaluate thoroughly the diffusion paths and barriers in between layers and compare them with those on the surface. Interestingly we find that the diffusion barrier between layers is ${\sim}100$~meV smaller than that on a single layer, implying layered MS$_2$ may be a good candidate for Li-ion battery electrodes.