A systematic approach to vertically excited states of ethylene using configuration interaction and coupled cluster techniques

David Feller; Kirk A Peterson; Ernest R Davidson

doi:10.1063/1.4894482

A systematic approach to vertically excited states of ethylene using configuration interaction and coupled cluster techniques

J Chem Phys. 2014 Sep 14;141(10):104302. doi: 10.1063/1.4894482.

Authors

David Feller¹, Kirk A Peterson¹, Ernest R Davidson²

Affiliations

¹ Department of Chemistry, Washington State University, Pullman, Washington 99164-4630, USA.
² Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA.

PMID: 25217911
DOI: 10.1063/1.4894482

Abstract

A systematic sequence of configuration interaction and coupled cluster calculations were used to describe selected low-lying singlet and triplet vertically excited states of ethylene with the goal of approaching the all electron, full configuration interaction/complete basis set limit. Included among these is the notoriously difficult, mixed valence/Rydberg (1)B(1u) V state. Techniques included complete active space and iterative natural orbital configuration interaction with large reference spaces which led to variational spaces of 1.8 × 10(9) parameters. Care was taken to avoid unintentionally biasing the results due to the widely recognized sensitivity of the V state to the details of the calculation. The lowest vertical and adiabatic ionization potentials to the (2)B(3u) and (2)B3 states were also determined. In addition, the heat of formation of twisted ethylene (3)A1 was obtained from large basis set coupled cluster theory calculations including corrections for core/valence, scalar relativistic and higher order correlation recovery.