title: Polarizable Embedded RI-CC2 Method for Two-Photon Absorption Calculations.
abstract: We present a novel polarizable embedded resolution-of-identity coupled cluster singles and approximate doubles (PERI-CC2) method for calculation of two-photon absorption (TPA) spectra of large molecular systems. The method was benchmarked for three types of systems: a water-solvated molecule of formamide, a uracil molecule in aqueous solution, and a set of mutants of the channelrhodopsin (ChR) protein. The first test case shows that the PERI-CC2 method is in excellent agreement with the PE-CC2 method and in good agreement with the PE-CCSD method. The uracil test case indicates that the effects of hydrogen bonding on the TPA of a chromophore with the nearest environment is well-described with the PERI-CC2 method. Finally, the ChR calculation shows that the PERI-CC2 method is well-suited and efficient for calculations on proteins with medium-sized chromophores.
authors.affiliation: Center for Oxygen Microscopy and Imaging, Aarhus University , Langelandsgade 140, 8000 Aarhus, Denmark.
authors.forename: Dalibor
authors.initials: D
authors.lastname: Hršak
authors.affiliation: Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum , Universitätsstraße 150, 44801 Bochum, Germany.
authors.forename: Alireza
authors.initials: A
authors.lastname: Marefat Khah
authors.affiliation: Center for Oxygen Microscopy and Imaging, Aarhus University , Langelandsgade 140, 8000 Aarhus, Denmark.
authors.forename: Ove
authors.initials: O
authors.lastname: Christiansen
authors.affiliation: Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum , Universitätsstraße 150, 44801 Bochum, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Hättig