We present some recent developments in hybrid quantum/classical methodology for first-principles photochemistry simulations of large multichromophoric complexes. The first key tool utilized is an ab initio exciton model (AIEM) that uses on-the-fly ab initio computations on chromophore monomers to parametrize a Frenkel-Davydov-type exciton model that is mappable to a Pauli-sparse qubit Hamiltonian with one or more qubits per monomer. The second key tool involved is the multistate, contracted variational quantum eigensolver" (MC-VQE), a new extension of VQE that enables the even-handed quantum circuit treatment of ground-, excited-, and transition-property observables. MC-VQE+AIEM shows promise for the accurate treatment of absorption spectra and other photochemical observables for systems with several thousand atoms using only a few dozen qubits and relatively short quantum circuits. We numerically demonstrate the potential accuracy of the method for the classically-simulated MC-VQE+AIEM computation of the absorption spectrum of the B850 ring of LHII, discuss the extension of the method to the efficient computation of the analytical nuclear gradient (needed for dynamics simulations), and the consider prospects for deployment of the method on near-term quantum circuit hardware.

Hybrid quantum/classical algorithms for photochemistry

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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