where M is the mass of Ti ). Therefore, we used those minimum energy sites of each surface as the initial and final locations of the ions to calculate the energy barrier. Thus, E diff of a Li/Mg ion is almost equal on both surfaces of Ti 2 CSSe monolayer. E diff found for Li on O-surface of Ti 2 CSO is around 0.34 eV and that on S-surface is 0.18 eV. Mg shows exceptionally higher E diff (0.71 eV) as a result of bivalency of Mg ions. Ti 2 CSSe monolayer also evidences that Mg has a higher barrier by exhibiting 0.47 eV maximum E diff which is twice the value found for Li-ions on the same monolayer. E diff of Ti 2 CSSeMg 0.0625 is approximately equal to that of Ti 2 CS 2 Mg 0.0625 . It is reported that a single Mg ion adsorbed 4 × 4 supercells of Ti 2 SO 2 , and Ti 3 CO 2 monolayers show E diff greater than 0.6 eV, which is higher than that of Ti 2 CSSeMg 0.0625 .