@article{oai:repo.qst.go.jp:00084624,
 author = {Fujita, Takatoshi and Noguchi, Yoshifumi and Takatoshi, Fujita},
 journal = {The Journal of Physical Chemistry A},
 month = {Dec},
 note = {Herein, we present a fragment-based approach for calculating the charged and neutral excited states in molecular systems, based on the many-body Green’s function method within the GW approximation and the Bethe–Salpeter equation (BSE). The implementation relies on the many-body expansion of the total irreducible polarizability on the basis of fragment molecular orbitals. The GW quasi-particle energies in complex molecular environments are obtained by the GW calculation for the target fragment plus induced polarization contributions of the surrounding fragments at the static Coulomb-hole plus screened exchange level. In addition, we develop a large-scale GW/BSE method for calculating the delocalized excited states of molecular aggregates, based on the fragment molecular orbital method and the exciton model. The accuracy of fragment-based GW and GW/BSE methods was evaluated on molecular clusters and molecular crystals. We found that the accuracy of the total irreducible polarizability can be improved systematically by including two-body correction terms, and the fragment-based calculations can reasonably reproduce the results of the corresponding unfragmented calculations with a relative error of less than 100 meV. The proposed approach enables efficient excited-state calculations for large molecular systems with reasonable accuracy.},
 pages = {10580--10592},
 title = {Fragment-Based Excited-State Calculations Using the GW Approximation and the Bethe–Salpeter Equation},
 volume = {125},
 year = {2021}
}