Figure 1 : Structure of monolayer 1T-MX2.

From: Negative Poisson’s ratio in 1T-type crystalline two-dimensional transition metal dichalcogenides

Figure 1

(a) Crystal structure. The basic X-M1-M2-M3 triangular pyramid unit is marked. The rectangular outline displays the unit cell adopted in our calculation. It contains two MX2 formula units. (b) Local structure of M-centred octahedron. The metal atoms form three one-dimensional chains in the directions of y=x, z=y and z=x in the local reference frame. The M–M interaction is through the t2g-orbital coupling. (c) Schematic configuration of DOS showing the gradual filling of d orbitals from group 4 (d0) to group 10 (d6) 1T-MX2. The horizontal bars denote the corresponding Femi level of the system. t2g and t2g* correspond to the intermetal t2g-bonding and t2g-antibonding states, respectively. (d) Predicted M–X–M bond angles in the relaxed structure of strain-free 1T MX2. Note, in the triangular pyramid as shown in Fig. 1a, M1XM2=M2XM3=M3XM1=MXM.