) of the monolayer. The strain is applied from -2% to 2% for each direction with an increment of 1%. For each iteration of strain, the atomic positions of the system is fully relaxed. Further, the result is fitted to the strain energy, = 1 2 + 2 2 + 3 . Here, 1 , 2 and 3 are three constants that are obtained during the fitting process. Further, due to the isotropy in the honeycomb symmetry, 1 is equal to 2 . The three-dimensisonal surface fit (Fig. ) shows the distribution of strain energy with respect to the different mode of applied strain. The strain energy profile of monolayers is in the order of CrSe 2 >CrSSe > CrS 2 , which predicts the relative mechanical strength. The preceding expression is also obtained from elasticity matrix in terms of elastic stiffness constants 11 and 12 by employing 11 = 2 1 ∕ 0 and 12 = 3 ∕ 0 . For hexagonal symmetry, 11 and 12 are only two significant independent elastic stiffness coefficients . Another calculated elastic constant, C 66 is (C 11 -C 12 )/2. The in-plane stiffness (C) and Poisson's ratio( ) are represented by 11 × [1 -( 12 ∕ C 11 ) 2 ] and 12 ∕ 11 , respectively. In 2D materials, the bulk modulus which gives a measure of the material's resilience to an external biaxial strain is calculated in terms of layer modulus ( ) with the expression, = (C 11 +C 22 +2C 12 )/4. In addition, using these second-order elastic constants C , the shear modulus, K=C/2(1-), is calculated. The shear modulus estimates the resistance of a material to the shear strain. Further, the in-plane stiffness and Poisson's ratio are used to test the mechanical anisotropy. They are functions of the direction angles , which can be represented as : the same trend (Table ). Interestingly, the stiffest monolayer CrS 2 (110.42 N/m) has the in-plane stiffness value closer to it's prototype MoS 2 (120.6 N/m ) but it is very much lower than that of graphene (370.1 N/m ).