A multireference coupled-cluster study of electronic excitations in furan and pyrrole.
A multireference (MR), general-model-space (GMS), state-universal (SU), coupled-cluster (CC) method that considers singly (S) and doubly (D) excited cluster amplitudes relative to the reference configurations spanning the model space (GMS SU CCSD) is employed to investigate a number of low-lying excited states of two five-membered, six pi -electron aromatic ring molecules, namely, furan and pyrrole. An extended basis set that includes diffuse functions and molecule-centered Rydberg functions is employed. Computed vertical excitation energies are compared with experimental values as well as with other theoretical results, namely, those obtained by the equation-of-motion (EOM) CCSD method or, equivalently, the symmetry adapted cluster configuration interaction (SAC-CI) method, by the MR CI method, by MR perturbation theory, and by other methods whenever available. For excited states dominated by single-excitations the GMS SU CCSD energies represent an improvement relative to the most closely related EOM CCSD results by about 0.1 eV.
Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
Xiangzhu
X
Li
Josef
J
Paldus
D003198:Computer Simulation; D004583:Electrons; D005663:Furans / Q000737:chemistry*; D011758:Pyrroles / Q000737:chemistry*; D011789:Quantum Theory
D005663:Furans; D011758:Pyrroles; C039281:furan