). This relationship indicates that the higher bond strength of T-O than that of Ti-S and Ti-Se, significantly affects the stiffness of the materials. Due to the smaller ν values of Ti 2 CO 2 , Ti 2 CS 2 , and Ti 2 CSO than that of Ti 2 CSSe, the resistance produced against strain by those three monolayers are higher than that from Ti 2 CSSe.