Quantum Chemistry Study On Cooperative Effect Of Hydrogen Bonds In Single Cage Water Cluster

The water molecules in single cage cluster interact with each other through a hydrogen bond network.There are numerous isomers in the water clusters due to the different orientation of hydrogen bonds,but only four types of hydrogen bonds 1221,1212,2121 and 2112 in single cage cluster,if considering the different type of donor and acceptor to to one water molecule pair.In view of the influence of the neighboring and next-neighbor water molecules on the central water molecule pair and the mirror symmetry,the central water molecule pair can be divided into five categories and 74 sub-grouped hydrogen bonds.In this paper,a large number of 512,51262 and 435663 single cage water cluster isomers were constructed to study the hydrogen bond network in the water cluster.The bond energies of 74 sub-grouped hydrogen bonds was obtained by iteration method,and the stability of 51268 single cage water clusters was predicted using the energies'average value of sub-grouped hydrogen bonds.The results show that the number of 1221 hydrogen bonds in single cage cluster increases with the number of water molecules increasing.The average value of the hydrogen bond network energy and the average value of the single hydrogen bond energy in the same cage water clusters become stronger with the increase of the number of 1221 hydrogen bonds.The number of 1212 hydrogen bonds is equal to the number of 2121 hydrogen bonds,and the sum of the number of 1221 hydrogen bonds and 1212 hydrogen bonds is always equal to 1/3 of the total number of hydrogen bonds or 1/2 of the total number of water molecules.Using six-digit coding method of sub-grouped hydrogen bond proposed by us,74 sub-grouped hydrogen bonds in water clusters were analyzed.When the three-digit value of the donor fragment or the acceptor fragment is the same,there is poor cooperative effect between the water molecules in the environment and the central water molecule pair.And the cooperative effect will become much poorer when the six digits are the same.On the other hand,if three donor fragment digits are different,and three acceptor fragment digits are also different,there will be strong cooperative effect between the water molecules in the environment and the central water molecule pair.Therefore,whether the three digits of the donor fragment or the acceptor fragment are the same is a necessary condition for judging the strong or weak cooperative effect.