Abstract
We report ab initio calculations of the phonon dispersion relations of the single-layer and bulk dichalcogenides MoS and WS. We explore in detail the behavior of the Raman-active modes and as a function of the number of layers. In agreement with recent Raman spectroscopy measurements [C. Lee et al., ACS Nano 4, 2695 (2010)], we find that the mode increases in frequency with an increasing number of layers while the mode decreases. We explain this decrease by an enhancement of the dielectric screening of the long-range Coulomb interaction between the effective charges with a growing number of layers. This decrease in the long-range part overcompensates for the increase of the short-range interaction due to the weak interlayer interaction.
- Received 28 July 2011
DOI:https://doi.org/10.1103/PhysRevB.84.155413
©2011 American Physical Society