The H <sub> 3 </ Sub> O ~ + (t) Of The Complete Potential Energy Surface Calculation And Hole - Particle Correspondence In Mrcisd

There are two main aspects in the doctoral dissertation, the construction of triplet H3O+ global potential energy surface (PES) and the applications of hole-particle correspondence in MRC1SD calculations.At Chapter 1. the theoretical basis of constructing the PES is presented, including the calculation, fitting and the dynamics study of the PES. On the calculation of data points, the most popular and well-developed post HF methods at present are discussed. Because it is most important to use the multi-reference methods when constructing the PES and investigating the chemical process, the realization and characteristics of MRCISD as well as its some approximations are discussed as the main subjects. Concise evaluation to these approximation methods and how to select the reference space are also discussed. Fitting the data points is the key process in the construction of the PES, and we have presented some basal analytic function form and the general process of fitting, too. At the end of this Chapter, some theories of dynamics calculation is introduced simply.The reaction of H3+ ion and 0 atom provides a pathway for synthesizing H2O in interstellar clouds, thus it has attracted a great deal of experimental and theoretical studies in the past few years. The aim of the Chapter 2 is to construct an accurate global PES of the triplet H3O+ based on the externally contracted multi-reference configuration interaction with single and doubly excitations (EC-MRCISD), which is developed by our research group. We use complete active space (CAS) of HONDO and MELD programs to select the reference space and the computed energies will be fitted as many-body expansion functions suggested by Aguado and Paniagua. By the way. the global PES of H2O+(2B1) is constructed. The results show that the fitted PESs are good. They will be helpful to study the reactions of H2O+(2B1) or triplet H3O+ in detail and accurately. At the same time, the general method of constructing three or four atomic system AP many-body expansion PES is developed.Chapter 3 introduces the applications of hole-particle correspondence in MRCISDcalculations. A new classification of spin adapted MRCISD states using hole-particle correspondence is suggested. The formulas and values of 244 hole loop shapes are derived according as the rule of transform from external space loop shapes to hole loop shapes. Based on the classification and the formulas for the hole loop shapes a new CI algorithm is presented and coded, which is efficient and memory saving indicated from some given examples.At appendix, the codes of calculation and fitting program are mainly presented for four-atomic systems. These fitting program may be applied to any systems including four or less than four atoms. In the code of fitting two-atomic potential energy curves some spectral constants are also calculated.