  A computational approach combining dispersion-corrected density functional
theory (DFT) and classical molecular dynamics is employed to characterize the
geometrical and thermo-mechanical properties of a recently proposed 2D
transition metal dihalide NiCl$_2$. The characterization is performed using a
classical interatomic force field whose parameters are determined and verified
through the comparison with the results of DFT calculations. The developed
force field is used to study the mechanical response, thermal stability, and
melting of a NiCl$_2$ monolayer on the atomistic level of detail. The 2D
NiCl$_2$ sheet is found to be thermally stable at temperatures below its
melting point of ~695 K. At higher temperatures, several subsequent structural
transformations of NiCl$_2$ are observed, namely a transition into a porous 2D
sheet and a 1D nanowire. The computational methodology presented through the
case study of NiCl$_2$ can also be utilized to characterize other novel 2D
materials, including recently synthesized NiO$_2$, NiS$_2$, and NiSe$_2$.
