Theoretical Study On Multilayer Nitrogen Cages And A Method For Estimating The Relative Stabilities Of Molecules

Four aspects are studied in this thesis: (i) The study on the relationship between the bonding properties and the selected computational level of molecules; (ii) Recommending a new method for estimating the relative stabilities of compounds which have the same atomic group; (iii)Investigating the stabilizing factors of polynitrogen molecules, especially of the"multilayer"nitrogen cages; (iv) Discussing a method for calculating the heats of formation (HOF) based on the density functional theory (DFT).Gaussian 98 A.11 program package is applied for the structural optimization and vibrational frequency calculations. The computational methods applied are G3 theory and G3MP2 theory. For the large molecules, especially for the nitrogen cages, the structural optimization and vibrational frequency calculations are carried out at the level DFT/cc-pVDZ, and the DFT HOFs of these molecules are calculated using the DFT method discussed. Natural Bond Ortibal (NBO) analysis and Atom In Molecules (AIM) analysis have been used to study the bonding properties of these molecules. We have develop a software named"DATA Retrieve"for retrieving the useful information from the huge data produced by the calculations.At first, Gaussian 98 A.11 and AIM2000 (V2.0) are carried out to calculate the geometric structures and bonding properties of the 28 typical compounds at 20 kinds of basis sets. The studies show that the results obtained from AIM analysis and from NBO analysis are more reliable than that of Mulliken population analysis when the calculation results are used to estimate bonding properties of molecules. The results show that the high computational level is necessary for obtaining the stable...