Multi-root configuration interaction calculations

Abstract It is argued that it is not necessary for the two-electron molecular orbital integrals and configuration interaction expansion coefficients to be stored in the computer as accurately as they are in present configuration interaction calculations, so these numbers may be kept in the computer's central memory, even for large basis set calculations. A calculation on H 2 O with 37 root functions plus all single and double replacements with 41 basis functions (52210 spin configurations) is performed.