CONSTRAINED SOLUTIONS OF THE EIGENVALUE PROBLEM IN TRUNCATED BASIS-SETS

It is shown that simple orthogonality constraints between some set of known approximate eigenfunctions and another set of functions which ar e to be determined as approximate eigensolutions need to be modified. The proposed modification introduces a measure of the approximate char acter of the known functions and leads to the reduction of the dimensi onality of the eigenvalue problem for other solutions. The discussed m ethod is fully variational and leads directly to a Hermitian eigenvalu e problem. This approach is also independent of the choice of truncate d basis sets for different classes of approximate solutions of the eig envalue problem. (C) 1997 John Wiley & Sons, Inc.