  Understanding interlayer and intralayer coupling in two-dimensional layered
materials (2DLMs) has fundamental and technological importance for their
large-scale production, engineering heterostructures, and development of
flexible and transparent electronics. At the same time, the quantification of
weak interlayer interactions in 2DMLs is a challenging task, especially, from
the experimental point of view. Herein, we demonstrate that the use of X-ray
absorption spectroscopy in combination with reverse Monte Carlo (RMC) and ab
initio molecular dynamics (AIMD) simulations can provide useful information on
both interlayer and intralayer coupling in 2DLM 2H$_c$-MoS$_2$. The analysis of
the low-temperature (10-300 K) Mo K-edge extended X-ray absorption fine
structure (EXAFS) using RMC simulations allows for obtaining information on the
means-squared relative displacements $\sigma^2$ for nearest and distant Mo-S
and Mo-Mo atom pairs. This information allowed us further to determine the
strength of the interlayer and intralayer interactions in terms of the
characteristic Einstein frequencies $\omega_E$ and the effective force
constants $\kappa$ for the nearest ten coordination shells around molybdenum.
The studied temperature range was extended up to 1200 K employing AIMD
simulations which were validated at 300 K using the EXAFS data. Both RMC and
AIMD results provide evidence of the reduction of correlation in thermal motion
between distant atoms and suggest strong anisotropy of atom thermal vibrations
within the plane of the layers and in the orthogonal direction.
