title: Low-Scaling Quantum Chemistry Approach to Excited-State Properties via an ab Initio Exciton Model: Application to Excitation Energy Transfer in a Self-Assembled Nanotube.
abstract: We introduce a charge-embedding scheme for an excited-state quantum chemistry method aimed at weakly interacting molecular aggregates. The Hamiltonian matrix for the aggregate is constructed in a basis of direct products of configuration-state functions for the monomers, and diagonalization of this matrix affords excitation energies within ∼0.2 eV of the corresponding supersystem calculation. Both the basis states and the coupling matrix elements can be computed in a distributed way, resulting in an algorithm whose time-to-solution is independent of the number of chromophores, and we report calculations on systems with almost 55 000 basis functions using fewer than 450 processors. In a semiconducting organic nanotube, we find evidence of ultrafast, coherent dynamics followed by energy localization driven by static disorder. Truncation of the model system has a qualitative effect on the energy-transfer dynamics, demonstrating the importance of simulating an extended portion of the nanotube, which is not feasible using traditional quantum chemistry.
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Adrian F
authors.initials: AF
authors.lastname: Morrison
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: John M
authors.initials: JM
authors.lastname: Herbert
keywords: Förster exchange; exciton transport; fragment-based quantum chemistry