Application of relativistic SCF(RSCF) calculations using basis set expansions on the systems containing heavy element is important, but difficult. Two areas of particular difficulties are investigated and improvements are suggested. One is basis set selection and the other is the SCF procedure.
RSCF calculation is very time consuming so that the exponent optimization technique like nonrelativistic case is not practical. Various difficulties in many aspects caused by the extremly large basis set size due to small components are discussed. Extended basis sets of I, Br, and At atom are generated through a rational strategy. The quality of these basis sets are partially examined for the numerical stability.
The application of new SCF algorithm, called Direct SCF, on RSCF calculation is useful in several aspects. The four-component RSCF calculation even on medium sized system, requires handling a large integral set. Large integral set is also one of the serious problems in the conventional methods which can be handled by Direct SCF method. And the small magnitudes of density matrices of small component is additional profit in calculation by the Direct RSCF method. General strategy is discussed and the over all procedures are outlined.
무거운 原子를 포함하는 分子에 대한 相對論的 計算은 相對性 效果가 그 분자의 化學的 性質에 影響을 미칠 만큼 충분히 크기 때문에 그 效果를 理解하기 위해 매우 重要하다. 相對性 效果가 原子의 電子軌道 모양에 미치는 影響을 定性的으로 考慮한 相對論的 基本函數條를 구하였다. small component의 基本函數는 kinetic balance 條件으로부터 얻은 다음 overlap이 큰(0.95 이상) 函數雙은 그 중 하나를 除去하여 目的한 基本函數條를 얻는다.
Direct 方法의 相對論的 計算에의 適用에 대하여 살펴보았다. 相對論的 量自力學 計算은 非相對論的 計算보다 훨씬 많은 二電子積分 값들을 다루기 때문에 비교적 큰 分子를 計算할 경우에 그 計算의 限界가 컴퓨터의 記憶容量에 의해서 決定될 수 있다. 그리고 二電子積分값의 Fock matrix에 寄與하는 程度는 Large component와 Small component에서 큰 差異를 보이기 때문에 Direct RSCF가 매우 有用할 것으로 보인다. 多重 Fock matrix를 使用하는 Direct 方法도 提案하였다.
