Calculation of energies of excited states using <scp>MNDO</scp>

Abstract

Abstract The energies of the lowest singlet ( S 1 ) and triplet ( T 1 ) states of 28 molecules have been calculated by the “half‐electron” ( MNDO ‐ HE ) and spin‐unrestricted ( UMNDO ) versions of MNDO . While most of the calculated values are too negative, because of overestimation of the correlation energy in MNDO ‐ HE and UMNDO , the errors are systematic and depend in an understandable way on the nature of the molecular orbitals ( MO S) involved. When appropriate corrections are applied, the calculated energies agree with experiment almost as well as they do for ground states. This justifies the use of MNDO ‐ HE or UMNDO for studies of excited state processes.