SINGLE-EXCITATIONS-ADAPTED MOLECULAR-ORBITALS FOR A SIMPLIFIED DESCRIPTION OF ELECTRONIC EXCITED-STATES

An orbital transformation that minimizes the sum of the squares of the off-diagonal Hamiltonian elements between the singly excited configurations is described. The resulting single-excitations-adapted molecular orbitals (SEAMOS) are found to be very suitable for the description of electronic excited states. The test calculations on the singlet and triplet excited states of the N2, CO, and H2CO molecules are presented.