  Recent experiments have found that monolayer 1H-TaS2 grown on Au(111) lacks
the charge density wave (CDW) instability exhibited by bulk 2H-TaS2.
Additionally, angle-resolved photoemission spectroscopy measurements suggest
that the monolayer becomes strongly electron doped by the substrate. While
density functional theory (DFT) calculations have shown that electron doping
can suppress the CDW instability in monolayer 1H-TaS2, it has been suggested
that the actual charge transfer from the substrate may be much smaller than the
apparent doping deduced from photoemission data. We present DFT calculations of
monolayer 1H-TaS2 on Au(111) to explore substrate effects beyond doping. We
find that the CDW instability is suppressed primarily by strong S-Au
interactions rather than by doping. The S-Au interaction results in a
structural distortion of the TaS2 monolayer characterized by both lateral and
out-of-plane atomic displacements and a 7 x 7 periodicity dictated by the
commensurate interface with Au. Simulated STM images of this 7 x 7 distorted
structure are consistent with experimental STM images. In contrast, we find a
robust 3 x 3 CDW phase in monolayer 1H-TaS2 on a graphene substrate with which
there is minimal interaction.
