The Exploration Of The Interactions Between Atoms In The Molecules By Molecular Face Theory And Ab Initio Method

Recently,according to a large number of theoretical methods,many researchers have studied and discussed the interatomic chemical bond and van der Waals interaction in molecules.Two atoms can form a molecule with chemical bond interaction.In order to explore the characters of interaction between atoms,Yang and Zhao proposed and developed the PAEM-MO diagram.Based on PAEM-MO diagram,molecular face theory and ab initio method,we have studied the bonding interactions between atoms in 110 diatomic molecules,C₂,C₂H₂,C₂H₄,C₂H₆,[1.1.1]propellane and C₄N₄P₂S₂H₁₂2 molecules.The contents are as follows:（1）At the B3LYP/6-311++G（3df,3pd）level of theory,the stable structures of N₂,CO,C₂,C₂H₂,C₂H₄,and C₂H₆ molecules were obtained.The Potential Acting on an Electron within a Molecular（PAEM）were calculated at the CISD/6-311++G（d,p）level of theory in the MELD package combined with our own program.The MP2/6-311++G（d,p）method was employed to calculate their bonding molecular orbital（MO）energies(E_BMO).It can be obtained that the strength of N≡N chemical bond is stronger than that of C≡O bond in terms of D_pbb and the single electron potential at the bond center of two atoms(V(r_bc))in these molecules.The bond strength of C≡C is stronger than those of C=C and C-C is the weakest bonds.It can be seen from the molecular face that the electron density of bonding region of N≡N is larger than that of C≡O.The electron density of the C≡C region is larger than that of C=C region.（2）The stable structures of 110 diatomic molecules were obtained at MP2/6-311++G（d,p）level of theory.Their PAEMs and E_BMOs were calculated by the CISD/6-311++G（d,p）method in the MELD package combined with our in-house program.We have proposed AD which is the absolute values of difference between V(r_bc)and E_BMO.The strengths of the interaction between atoms in diatomic molecules were investigated by AD and PAEM-MO diagram.（3）At the MP2/6-311++G（d,p）level of theory,three stable structures of neutral and free radicals of the[1.1.1]propellane can be obtained.The CISD/6-311++G（d,p）method was used to calculate their PAEMs.Moreover,E_BMOs were obtained at the MP2/6-311++G（d,p）level of theory.Bridge bond between C atoms in the neutral[1.1.1]propeller is stronger than that of the alkyl radical structure.Finally,the stable structure of the C₄N₄P₂S₂H₁₂2 molecule was obtained at the B3LYP/6-311++G（d,p）level of theory.PAEMs of the molecule were calculated at the CISD/3-21G level of theory.All the E_BMOMO were obtained by HF/6-311++G（3df,3pd）method.It can be found that there are bonding interactions between S3-S4 and N5-N6 in C₄N₄P₂S₂H₁₂2 molecule from PAEM-MO diagram.Based on the analysis of interatomic interactions between two atoms in a series of molecules,it can be concluded that the strength of interactions between two atoms is related to the barrier of single electron potential,D_pb.In terms of the quantity,AD,we can obtaine the characters of the interactions between two atoms in diatomic molecules.Therefore,it provides theoretical reference for further exploring the characters of interatomic interaction in a molecule.