title: Active-space completely-renormalized equation-of-motion coupled-cluster formalism: Excited-state studies of green fluorescent protein, free-base porphyrin, and oligoporphyrin dimer.
abstract: The completely renormalized equation-of-motion coupled-cluster approach with singles, doubles, and noniterative triples [CR-EOMCCSD(T)] has proven to be a reliable tool in describing vertical excitation energies in small and medium size molecules. In order to reduce the high numerical cost of the genuine CR-EOMCCSD(T) method and make noniterative CR-EOMCCSD(T) approaches applicable to large molecular systems, two active-space variants of this formalism [the CR-EOMCCSd(t)-II and CR-EOMCCSd(t)-III methods], based on two different choices of the subspace of triply excited configurations employed to construct noniterative correction, are introduced. In calculations for green fluorescent protein (GFP) and free-base porphyrin, where the CR-EOMCCSD(T) results are available, we show good agreement between the active-space CR-EOMCCSD(T) (variant II) and full CR-EOMCCSD(T) excitation energies. For the oligoporphyrin dimer (P(2)TA) active-space CR-EOMCCSD(T) results provide reasonable agreement with experimentally inferred data. For all systems considered we demonstrated that the active-space CR-EOMCCSD(T) corrections lower the EOMCCSD (iterative equation-of-motion coupled-cluster method with singles and doubles) excitation energies by 0.2 and 0.3 eV, which leads to a better agreement with experiment. We also discuss the quality of basis sets used and compare EOMCC excitation energies with excitation energies obtained with other methods. In particular, we demonstrate that for GFP and FBP Sadlej's TZP and cc-pVTZ basis sets lead to a similar quality of the EOMCC results. The performance of the CR-EOMCCSD(T) implementation is discussed from the point of view of timings of iterative parts and scalability of the most expensive, N(7), part of the calculation. In the latter case the scalability across 34 008 processors is reported.
authors.affiliation: William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA. karol.kowalski@pnl.gov
authors.forename: Karol
authors.initials: K
authors.lastname: Kowalski
authors.forename: Sriram
authors.initials: S
authors.lastname: Krishnamoorthy
authors.forename: Oreste
authors.initials: O
authors.lastname: Villa
authors.forename: Jeff R
authors.initials: JR
authors.lastname: Hammond
authors.forename: Niranjan
authors.initials: N
authors.lastname: Govind
mesh_terms: D000465:Algorithms; D019281:Dimerization; D049452:Green Fluorescent Proteins / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D011166:Porphyrins; D049452:Green Fluorescent Proteins