APPLICABILITY OF SIZE-CONSISTENT SELF-CONSISTENT CONFIGURATION-INTERACTION TO EXCITED-STATES

The size-consistent self-consistent configuration interaction (SC)(CI) -C-2 method is applied to the calculation of excitation energies, This method diagonalizes a dressed SDCI matrix built for the ground state but it is shown that the extra eigenvalues are not phony solutions but represent the excited roots of the system. Numerical tests are encour aging, The method is further improved by using the (SC)(2)MRCI scheme where the desired excited determinant is added to the ground state det erminant as a generator of the CI space. Excellent results are obtaine d with this method for single and double replacement excitations in CH 2.