To test the chemical stability of each monolayer, formation energy is calculated using the above mentioned relation in Section 2. The calculated formation energy of CrS 2 , CrSe 2 and CrSSe monolayers are -1.7, -1.4 and -1.5 eV/atom, respectively. These computed values fairly agree with the available theoretical and experimental data. To test the dynamical stability of all monolayers, we have calculated phonon dispersion (Fig. ) along with the Γ-K-M-Γ highsymmetry directions. The phonon dispersion bands depict the three acoustic and six optical bands due to the presence of bands from one Cr atom and two X (S or Se) atoms in the unit cell. The highest acoustic modes for the monolayers are in the order of CrS 2 > CrSSe > CrSe 2 . In addition, the lowfrequency gap between acoustic and optical modes in all the monolayers suggests the possibility of frequent scattering events . The frequency and phonon dispersion bands of all three monolayers are not quite different from each other. The presence of real frequencies in all three monolayers demonstrates good dynamical stability.