A Highly Correlated, Multireference Study of the Lowest Lying Singlet and Triplet States of the Four Thiophene Diradicals.

ABSTRACT: The energies and geometries of the lowest lying singlet and triplet states of the four diradicals formed by removing two H atoms from thiophene have been characterized. We utilized the highly correlated, multireference methods configuration interaction with single and double excitations with and without the Pople correction for size-extensivity (MR-CISD+Q and MR-CISD) and averaged quadratic coupled cluster theory (MR-AQCC). CAS (8,7) and CAS (10,8) active spaces involving σ, σ*, π, and π* orbitals were employed along with the cc-pVDZ and cc-pVTZ basis sets. The larger active space included the two electrons in the nonbonding sp² hybrid orbital on sulfur. We find that all didehydro isomers exist as planar, stable ground state singlets. The singlet-triplet (S-T) adiabatic gaps ran

SUBMITTER: Pandian J 

PROVIDER: S-EPMC11756580 | biostudies-literature | 2025 Jan

REPOSITORIES: biostudies-literature