In the present work, initial geometries of (H 2 S) n (n = 3 to 8) and (H 2 O) m (H 2 S) n (m + n = 2 to 8) cyclic clusters, were taken from the refs. 40 and 52. We re-optimized these geometries at MP2 level of theory using the aug-cc-pVDZ (referred to as aVDZ, hereafter) basis sets. The vibrational frequency calculations confirmed the local minima nature of all the re-optimized geometries. For the optimized geometries of (H 2 S) n and (H 2 O) m (H 2 S) n (m + n = 2 to 8) cyclic clusters, see Figure . For the Cartesian coordinates of all the geometries, see electronic supporting information (ESI). The single point (SP) energy calculations were performed on these clusters and fragment geometries at the MP2(full) level of theory employing aug-cc-pVTZ (mentioned as aVTZ hereafter) basis sets. All the calculations were performed by using the Gaussian 16 program package. 69 Scheme 1: Fragmentation scheme for the estimation of energy of hydrogen bond HB4 in (H2O)3(H2S)1 (denoted as M). The schematic fragmentation procedure for the estimation of energy of a hydrogen bond HB4 in the cyclic (H 2 O) 3 (H 2 S) 1 tetramer, with three water molecules, indicated as W1, W2 and W3 and a H 2 S molecule as S1, is illustrated in Scheme 1. As seen in Scheme 1, the HB4 consists of an interaction between the S-H bond of S1 and O atom of W1. By removing W1 and S1, respectively, two primary fragments F1 and F2 are generated from the parent cyclic (H 2 O) 3 (H 2 S) 1 tetramer. On virtually putting F1 and F2 fragment geometries together, the geometry of the parent tetramer can be regenerated, except that: (i) the S-H…O hydrogen bond HB4 is missing and (ii) there is a double counting of structural part viz., the dimer W2…W3, common to both primary fragments F1 and F2. This common dimer W2…W3 is the secondary fragment, F3 (cf. Scheme 1). On subtracting the energy of fragment F3 from the sum of energies of fragments F1 and F2, the energy of parent cyclic (H 2 O) 3 (H 2 S) 1 tetramer may be obtained. However, thus-calculated energy of cyclic (H 2 O) 3 (H 2 S) 1 tetramer misses out on the energy of HB4. With this understanding, the energy of HB4 is obtained as . The difference between E HB4 and 𝐸𝐸 𝐻𝐻𝐻𝐻4 𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 is the cooperativity contribution to the HB4, which is 2.17 kcal mol -1 . The individual HB energy (𝐸𝐸 𝐻𝐻𝐻𝐻 𝑀𝑀𝑀𝑀𝑀𝑀 ), dimer energy (𝐸𝐸 𝐻𝐻𝐻𝐻 𝑑𝑑𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 ), and the cooperativity contributions (𝐸𝐸 𝐻𝐻𝐻𝐻 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶. ) in (H 2 S) n ( n = 3 to 8) clusters have been estimated using the aforementioned MTA-based method (cf. Table ). As can be seen from Table , the individual HB energies are seen to fall between 2.08 to 3.88 kcal mol -1 . The respective S-H…S HB energies in the dimers are moderately smaller and fall in the range of 1.67 to 3.02 kcal mol -1 . These calculated values of cooperativity contribution towards the individual S-H…S HB in these clusters fall in the smaller dimer energies are attributed to the loss in cooperativity due to the other HBs in the network. Thus-range between -0.10 to 0.90 kcal mol -1 . The negative value of cooperativity indicates that the HB energy in the dimers is numerically larger in magnitude than the corresponding HB energy in the clusters (anti-cooperativity). This effect is seen to be pronounced in some of these HBs. For instance, consider hydrogen bonds HB1 and HB10 in (H 2 S) 7 cluster. A closer look at HB1 and HB10 suggests that they are involved in the formation of anti-cooperative HBs, wherein, the direction of these two HBs are opposite to each other. Literature suggests that the formation of such an anti-cooperative network of HBs has smaller or negative contributions to the HB cooperativity. For instance, cooperativity contribution towards HB1 is 0.01 kcal mol -1 and that for HB10 is -0.02 kcal mol - that these HBs are relatively strong. These large value of HB energies in cyclic clusters may be due to formation of homodromic (positive cooperativity) cycle with all HBs in same direction. Also, the HB energies in higherorder clusters are, in general, larger. For example, the energies of all the HBs in (H 2 S) 7 and (H 2 S) 8 clusters are in the range of 2.08 to 3.88 kcal mol -1 .