Ab initio study of the structure, cooperativity, and vibrational properties in the mixed hydrogen-bonded trimers of hydrogen isocyanide and water

摘要

The five trimers of H_2O?HNC?H_2O, H _2O?H_2O?HNC, HNC?H _2O?H_2O, H_2O?HNC?HNC, and HNC?HNC?H_2O have been studied with quantum chemical calculations. Their structures, harmonic vibrational frequencies and interaction energies have been calculated at the B3LYP and MP2 levels with the aug-cc-pVDZ and aug-cc-pVTZ basis sets. The cooperative effect on these properties has also been studied quantitatively. For HNC:(H2O)_2 systems, the cyclic H2O?H2O?HNC trimer is most stable with an interaction energy of -16.01 kcal/mol and a large cooperative energy of -3.25 kcal/mol at the MP2/aug-cc-pVTZ level. For H2O:(HNC) 2 systems, the interaction energy and cooperative energy in the H_2O?HNC?HNC trimer are larger than those in the HNC?HNC?H_2O trimer. The NH stretch frequency has a blue shift for the terminal HNC molecule in the HNC?H_2O? H_2O and HNC?HNC?H_2O trimers and a red shift in other cases. A many-body analysis has also been performed to understand the interaction energies in these hydrogen-bonded clusters.