Theoretical Investigation On The Interaction In M⁺(H₂O)_1-4(M=Cu, Ag, Au)

At the beginning of the last century, the concept of the hydrogen bond was put forward. But since the 90's of the last century, with the development of the computer technology and quantum chemistry scientists have paid more attention to explore the property of the hydrogen bond. With the progress of investigation of the hydrogen bond the interactions between metal ion and H₂O have become one focus field recently. Therefore this paper chooses the cluster M⁺(H₂O)_1-4 which is made of H₂O and M⁺(M=Cu, Ag, Au) as object of the research.Second-order M(?)ller-Plesset Perturbation Theory (MP2) and Single and Double Excitation Coupled–Cluster Theory with perturbative Triples (CCSD(T)) are the research method. In the calculations the basis set used for O and H is a double zeta basis with two polarization functions and two diffuse functions, 6-311++G**. For M⁺(M=Cu, Ag, Au) Relativistic Effective Core Potentials (RECPs) is used, the corresponding basis set is (8s7p6d)/[6s5p3d] with f and g function, (8s7p6d3f2g)/ [6s5p3d3f2g].We optimize the structure of M⁺(H₂O)_1-4(M=Cu, Ag, Au) at Second-order M?ller-Plesset Perturbation Theory(MP2) level. The interaction energies and thermodynamic quantities of M⁺(H₂O)_1-4(M=Cu, Ag, Au) are determined, using CCSD(T) method. And then we analyze the Nature Bond Orbital of O L M+and research the potential energy function of M⁺(HO₂)_1-2.The main conclusion:1) The structures obtained at MP2 level for Cu⁺(H₂O)_1-4, Ag⁺(H₂O)_1-4 Au⁺(H₂O)_1-4 are 1+0C_2v/2+0C₂/3+0C₁/2+2C₂, 1+0C_2v/2+0C₂/2+1C₁/3+1C₁, 1+0C_s/ 2+0C₂/2+1C₁/2+2C₂, respectively. And with the structures which have been optimized at Second-order M(?)ller-Plesset Perturbation Theory(MP2) level we could obtain the data according with experiment using CCSD(T) method.2) After the analysis of the Nature Bond Orbital of O…M⁺we observe that in M⁺(H₂O)_1-4(M=Cu, Au) the bond of O L M+in the first-hydration-shell become strong as the number of H₂O increases. In Ag⁺(H₂O)₂ the bond of O…Ag⁺ is the most stable, In Ag⁺(H₂O)4 as the formation of the hydrogen bond the bond of O…Ag⁺ is stronger than in Ag⁺(H₂O)₃. 3) Through the analysis of NBO of the hydrogen bonds we observe that the formation of the hydrogen bonds could make O…M⁺ more stable. The stronger the bond of O…M⁺becomes, the stronger the hydrogen bond whose donor is H₂O including O in O…M⁺ becomes. The hydrogen bond in Au⁺(H₂O)_3-4 is stronger than that in Cu⁺(H₂O)_3-4 and Ag⁺(H₂O)₄.4) The term of C⁶/R⁶ 6reflecting Van der Waals interactions and the term of C R reflecting coulomb interactions are added to the Morse-Type function, which could reflect the variation of potential energy of M⁺(H₂O)_1-2 (M=Cu, Ag, Au) varying with the length of O…M⁺accurately. We calculate the secondly-order force constant according with the data that have been reported, and predict the third-order force constant and fourth-order force constant.