Theoretical study of mixed hdyrogen-bonded complexes:H_2O…HCM…H_2O and H_2O…HCM…HCM…H_2O

摘要

Mixed hydrogen-bonded clusters H_2O…HCM,H_HCM…H_2O,H_2O…HCM…H_2O,and H_2O…HCM…HCM…H_2O are studied by using ab intitiocalculations.Theoptimized structures and harmonic vibrational freqeuncies are obtained at the DFT/B3LYP and MBPT/MP2 levels with the 6-311++ G(d,p) basis set.To investigate electron correlation effects on the binding energies,single-point calculations are also performed using the CCSD(T) method with the optimized MP2 geometries.The complexation energies are obtained for these systems including correction for basis set superpsition error.In addition,the cooperative effects in the properties of the complexes ae investigated quantitatively.We found a cooperativity contribution of around 10% relative to the totla interaction energy of the HCM…HCN is ca.8 kM/mol stronger in the mixed tetramer than in the corresponding isolated dimer.The effects of higher-order electron correlation are found to be mild,with MP2 giving a well-balanced result.Cooperative effects are predictedeither by MP2 or by B3LYP in hydrogen bond distances and dipole moments of the clusters.In contrast,the B3LYP functional fails to account for the out-of-plane bend angle in H_2O…HCN,which is well-described by the MP2 method.