As we discussed above, the individual S-H…S HB energies and respective dimers energies are seen to fall between 2.08 to 3.88 kcal mol -1 and 1.67 to 3.02 kcal mol -1 , respectively. These individual S-H…S HB energies are seen extremely smaller than the O-H…O HB energies (0.40 to 11.60 kcal mol -1 ), present in the pure water clusters, reported by Ahirwar et al. The O-H…O HB energies in the dimer also seen to be moderately larger (1.50 to 5.40 kcal mol -1 ) than the respective S-H…S HB energies (1.67 to 3.02 kcal mol -1 ) in the dimer. These small energies in the H 2 S clusters are due to the smaller cooperativity contribution. On the other hand, the strong O-H…O HBs strength observed due to the strong cooperative networking effect of other HBs. The calculated values of cooperativity contribution towards the individual S-H…S HB in pure (H 2 S) n clusters fall in the range between -0.10 to 0.90 kcal mol -1 . This cooperativity contribution towards S-H…S HB is relatively very small as compared to the O-H…O HB (-1.10 to 6.90 kcal mol -1 ) in water. This weak cooperativity contribution could be one of the possible reasons for the formation of extremely weak HB in the (H 2 S) n clusters.