  Semilocal and dispersion-corrected density-functional calculations have been
performed to study the crystal structure, equation of state, and electronic
structure of metal tellurohalides with chemical formula MeTeI where Me=Bi, Au,
or Pd. A comparative investigation of the results of these calculations is
conducted which reveals the role of van der Waals attraction. It is shown that
the prediction of crystal structure of metal tellurohalides is systematically
improved thanks to the inclusion of van der Waals dispersion. It is found for
BiTeI and AuTeI that the energy versus volume curve is anomalously flat in the
vicinity of equilibrium volume and the calculated equation of state has an
excessively steep slope in the low-pressure region; these are also fixed in the
dispersion-corrected calculations. Analysis based on the computation of the
volume and axial compressibilities shows that predicting the anisotropy of
BiTeI via the semilocal calculations yields an unrealistic result, whereas the
results of dispersion-corrected calculations agree with the experimental
compressibility data. Our calculations render that BiTeI (AuTeI) is a narrow
band gap semiconductor with Rashba-type spin splitting at the band edges (with
an indirect band gap) while PdTeI is a metal with relatively low density of
states at the Fermi level. The band gaps of BiTeI and AuTeI obtained via
semilocal (dispersion-corrected) calculations are found to be greater (smaller)
than the respective experimental values, which is against (in line with) the
expected trend. Similarly, the Rashba parameters of BiTeI are bracketed by the
respective values obtained via semilocal and dispersion-corrected calculations.
Excellent agreement with the experimental Rashba parameters is obtained via
interpolation of the calculated (semilocal and dispersion-corrected) values.
