S <sub> 2 </ Sub> O On Vibrational Spectra Calculation And Double Contraction Of The Ci Method Applications

This paper consists of two parts: one is to construct local potential energy surface for the disulfur monoxide (S2O) and then to perform vibration analysis; the other is to discuss applications of the doubly contracted CI method.In Chapter 1, the theoretical backgrounds for this work are given, including some most popular and well developed post HF methods for calculating the energks of data points, construction of potential energy surface (PES) and the theoretical basis of vibration spectroscopy. Because MRCISD is the most widely used tool in investigating the chemical processes, the realization and characteristics of MRCI method as well as its some approximation methods are illustrated as the main subjects.S2O is an important kind of molecules. It has been realized that S2O exists since 1933, recently it was approved that S2O exists in the atmospheres of various planetary bodies. The highly reactive disulfur monoxide (S2O) system has suffered a long history of mistaken identity and muddled spectral interpretation. Much of this confusion arose from erroneous determination of chemical stoichiometry, with a measured S:O ration of 1:1 leading to several proposed geometrical structures. In the thesis, the energy calculations of geometry points in the vicinity of a stationary point were carried out at MRCISD and MRPT2 level. Further, the data points selected were fitted to a polynomial force filed by using SURVIB and the calculations for the interaction of vibration configuration were employed by use of the POLYMODE.In Chapter 2, the analysis of normal vibration modes and vibration energy levels for S2O of the ground state and the excited state were performed. These results are in good accord with experimental vibration spectra. The mean square root of the deviation between calculation and available experimental vibration spectra for the ground state and the excited state are 38.52cm-1 and 6.44cm-1, respectively.In Chapter 3,we introduce the doubly contracted CI method and applications. A new CI algorithm is presented. Some examples are tested by the double contraction, the length of formula tape and disk storage will be drastically decreased and the time required for a CI calculation will be drastically saved.