Recent angle-resolved photoemission spectroscopy measurements of single-layer $1H-{\mathrm{TaS}}_2$ grown on Au(111) suggest strong electron doping from the substrate. In addition, scanning tunneling microscopy/spectroscopy measurements on this system show suppression of the charge-density-wave (CDW) instability that occurs in bulk $2H-{\mathrm{TaS}}_2$. We present results from ab initio density functional theory calculations of free-standing single-layer $1H-{\mathrm{TaS}}_2$ to explore the effects of doping on the CDW. In the harmonic approximation, we find that a lattice instability along the $\mathrm{\Gamma }M$ line occurs in the undoped monolayer, consistent with the bulk $3\times 3$ CDW ordering vector. Electron doping removes the CDW instability, in agreement with the experimental findings. The doping and momentum dependences of both the electron-phonon coupling and of the bare phonon energy (unscreened by metallic electrons) determine the stability of lattice vibrations. Electron doping also causes an expansion of the lattice, so strain is a secondary but also relevant effect.

• Received 27 February 2017

DOI:https://doi.org/10.1103/PhysRevB.95.235121