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\subsection{\texorpdfstring{Transition Metal Dichalcogenides (MX2)}{Transition Metal Dichalcogenides MX2}}
\label{sec:transition_metal_dichalcogenides_mx2}


\href{https://en.wikipedia.org/wiki/Transition_metal_dichalcogneide_monolayers}{Transition metal
dichalcogneides (MX2)} are another 2D layered materials similar to
graphene. We investigate the physical properties of various
MX\textsubscript{2}, where M is a transition metal atom in group 4 (Ti, Zr,
Hf), 5 (V, Nb, Ta), or 6 (Cr, Mo, W) elements; and X is a chalcogen
atom, either S or Se.

\subsubsection{\texorpdfstring{Single-layer MX\$\_2\$}{Singlelayer MX_2}}
\label{sec:singlelayer_mx_2}


We investigate the structural, electronic properties of MX$_2$. 
(M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) (X=S, Se) and their phase 
transition. We calculate the relative stability of two phase 
structures (octahedral-T and trigonal-H) determined by considering 
relative positions of X. We find interesting phase existence for 
the each group in the periodic table. The stable phase structure 
of IV-group (Ti, Zr, Hf) is octahedral, while VI-group (Cr, Mo, W) 
is trigonal, and V-group (V, Nb, Ta) is possible two phase structures. 
Two phase structures of MX$_2$ have a same total energy at the same 
lattice constant near the each most stable lattice constant. 
From these results, we also study activation energy barriers 
at the various lattice constants such as from stable T phase to H phase, 
same total energy, and from stable H to T. Interestingly 
we find that the activation energy barrier is small at the small and 
large lattice constants for the stable lattice constants. 
It means that the phase transition occurs by compressive and tensile strains. 



\subsubsection{\texorpdfstring{Stacking Configurations of MX\$\_2\$}{Stacking Configurations of MX_2}}
\label{sec:stacking_configurations_of_mx_2}


We investigate the effect of the interlayer interaction on the structural and electronic properties of layered MX\textsubscript{2}(M=Ti, Zr, Hf, Cr, Mo, W) structures with van der Waals interaction. We calculate the relative stability of various layer-layer stacking configurations determined by considering relative positions and orientations between neighboring layers. It is found that an intriguing coupling effect between stacking and electronic structure. Some stacking configuration with a lager inter-layer distance exhibit larger electronic band gap than the other structures.


$\leftarrow$ \href{http://nanophys.khu.ac.kr/doku.php?id=lab:research\%23li_adsorption_on_transition_metal_dichalcogenides}{Li adsorption on transition metal dichalcogendies}

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