Ab initio studies for ethyl halides and improvements of integral evaluation procedures

Abstract

In chapter I, integral evaluation procedures are improved. New recurrence relation is derived from the recurrence relation of Obara and Saika. The new recurrence relation is quite useful especially for high angular momentum cases. In order to conduct the recursion optimally, the tree search problem occurring during the application of recurrence relation is considered. A systematic way of performing tree search is shown. By applying the result of tree searching to newly derived recursion relation, we obtain significant reductions of the floating point operations (FLOPS) counts in $K^4$ region. The resulting FLOPS counts in $K^4$ region are comparable up to [dd/dd] angular momentum cases to the LRL1 method of LRL, currently the method requiring least FLOPS for [dd/dd] and higher angular momentum basis functions. For [ff/ff], [gg/gg], [hh/hh] and [ii/ii] cases, the required FLOPS are 24\%, 40\%, 51\% and 59\%, respectively, less than the LRL1 method in $K^4$ region. These are the best FLOPS counts available in the literature for high angular momentum cases. The works for $K^0$ step are also reduced by including tree search. By eliminating redundant work, it is possible to achieve 13\%, 25\%, 38\% and 44\%, savings in FLOPS and 21\%, 34\%, 46\% and 53\%, reductions in memory requiremints for (ff/ff), (gg/gg), (hh/hh) and (ii/ii) cases, respectively. The combination of the new recurrence relation and the results of tree searching should lead to more efficient codes of integral evaluations for higher angular momentum cases than any other existing codes. In chapter II, The internal rotation barriers for $C_2H_5X$ where X = F, Cl, Br and I are considered. 6-$31G^*$ and 6-$311^{**}$ basis sets were used for RHF and MP2 calculations. In order to find the source of discrepancy between calculated and experimental values, correlation and zero-point vibration energy effects were considered. Geometries were optomized for both staggered and eclipsed conformers at given level u...