A PROCEDURE TO OBTAIN AN ACCURATE APPROXIMATION TO A FULL CI WAVE-FUNCTION

Based on Jacobi elementary rotations, a simple, elegant procedure to o btain approximate CI wavefunctions is discussed. Essentially, a sequen ce of (2 x 2) matrices is built-up, and the eigenvector attached to th e lowest eigenvalue is used to construct a stepwise set of coefficient s, which become a very good approximation to the exact CI result. Full CI calculations could easily be reached in this way. An example forme d by some atoms of the He isoelectronic sequence is provided in order to test the flexibility and accuracy of the procedure. A Fortran 90 co de is available.