title: Benchmarking two-photon absorption cross sections: performance of CC2 and CAM-B3LYP.
abstract: We investigate the performance of CC2 and TDDFT/CAM-B3LYP for the calculation of two-photon absorption (TPA) strengths and cross sections and contrast our results to a recent coupled cluster equation-of-motion (EOM-EE-CCSD) benchmark study [K. D. Nanda and A. I. Krylov, J. Chem. Phys., 2015, 142, 064118]. In particular, we investigate whether CC2 TPA strengths are significantly overestimated compared to higher-level coupled-cluster calculations for fluorescent protein chromophores. Our conclusion is that CC2 TPA strengths are only slightly overestimated compared to the reference EOM-EE-CCSD results and that previously published overestimated cross sections are a result of inconsistencies in the conversion of the TPA strengths to macroscopic units. TDDFT/CAM-B3LYP TPA strengths, on the other hand, are found to be 1.5 to 3 times smaller than the coupled-cluster reference for the molecular systems considered. The unsatisfactory performance of TDDFT/CAM-B3LYP can be linked to an underestimation of excited-state dipole moments predicted by TDDFT/CAM-B3LYP.
authors.affiliation: Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø-The Arctic University of Norway, N-9037 Tromsø, Norway. maarten.beerepoot@uit.no.
authors.forename: Maarten T P
authors.initials: MT
authors.lastname: Beerepoot
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Friese
authors.forename: Nanna H
authors.initials: NH
authors.lastname: List
authors.forename: Jacob
authors.initials: J
authors.lastname: Kongsted
authors.forename: Kenneth
authors.initials: K
authors.lastname: Ruud