ACCURATE CI EXPANSION IN A SPLINE BASIS OF THE HELIUM GROUND-STATE WAVE-FUNCTION

Careful study of radial spline basis-set convergence on the angular limits of the He 1s(2) state has been performed. Improvement of algorithm allows reaching the full CI limit in a large radial (79 spline functions) and angular (l(max) = 80) expansion. A variational energy of -2.903724299061 au, with an error of 7.8 x 10(-8) au is obtained, improving by over two orders of magnitude the previous available limit. Accurate angular momentum limits (1 X 10(-8) au) are obtained up to l = 25. Analysis of the behavior of two-particle radial wave functions reveals a sharply peaked behavior which allows effective truncation of the two-electron radial basis for high angular momentum values. A reasonable estimate of computational resources required indicate that an accuracy below 1 x 10(-8) an is presently feasible and about 1 x 10(-9) au possible in the near future. (C) 1995 John Wiley and Sons, Inc.