Correlation Energy of Double-electron System Obtained by Using B-spline Basic Sets∗

Electron correlation has wide applications in various domains of physics. In the past decade, a variety of methods have been proposed to obtain accurate eigenvalues and eigenfunctions of the ground states. These variational methods can be divided into two categories according to whether their trial basis functions depend explicitly on the inter-electron separation r12 or not. The methods employing trial functions that depend explicitly on the r12 are known as correlated basis set (CB) method. The other types of methods are those with trial functions that do not depend explicitly on r12, a typical example of which is the configuration-interaction (CI) method. In recent years, the CI method has been greatly used in calculations of manyelectron atomic and molecular systems. But given the slow radial and angular convergence of CI, the usual CI method is unable to obtain highly accurate results. For