Fully Polarizable QM/Fluctuating Charge Approach to Two-Photon Absorption of Aqueous Solutions

Abstract

We present the extension of the quantum/classical polarizable fluctuating charge model to the calculation of single residues of quadratic response functions, as required for the computational modeling of two-photon absorption cross-sections. By virtue of a variational formulation of the quantum/classical polarizable coupling, we are able to 1 arXiv:1903.11408v3 [physics.comp-ph] 3 Jun 2019 exploit an atomic orbital-based quasienergy formalism to derive the additional coupling terms in the response equations. Our formalism can be extended to the calculation of arbitrary order response functions and their residues. The approach has been applied to the challenging problem of one-and two-photon spectra of rhodamine 6G (R6G) in aqueous solution. Solvent effects on one-and two-photon spectra of R6G in aqueous solution have been analyzed by considering three different approaches, from a continuum (QM/PCM) to two QM/MM models (non-polarizable QM/TIP3P and polarizable QM/FQ). Both QM/TIP3P and QM/FQ simulated OPA and TPA spectra show that the inclusion of discrete water solvent molecules is essential to increase the agreement between theory and experiment. QM/FQ has been shown to give the best agreement with experiments.

Combining multilevel Hartree–Fock and multilevel coupled cluster approaches with molecular mechanics: a study of electronic excitations in solutions

“…Finally, we note that the three layer approach that we have developed can also be applied to any QM/classical approach, as for instance the polarizable continuum model (PCM), 20,120 due to its theoretical similarity with the QM/FQ approach. 121…”

Calculation of Linear and Non-linear Electric Response Properties of Systems in Aqueous Solution: A Polarizable Quantum/Classical Approach with Quantum Repulsion Effects

“…42,46,50,51 We have shown how the model can have tremendous success in describing a wide array of spectroscopic properties of molecules in water, a highly polar solvent that can form hydrogen bonds with the solute. The properties we have studied include Raman spectroscopy and Raman optical activity, 51,53 electronic and vibrational absorption and circular dichroism, 53−56 two-photon absorption, 57 optical rotation, 58,59 and electronic paramagnetic resonance. 60 The model describes electrostatic interactions through its fluctuating charges and dipoles that dynamically respond to changes in the solute's electronic density and has recently been extended to the treatment of non-electrostatic dispersion and repulsion effects.…”

e T 1.0: An open source electronic structure program with emphasis on coupled cluster and multilevel methods

“…The environment is described in terms of an infinite, homogeneous, continuum dielectric that mutually polarizes with the QM part, as in QM/FQ. 64 In the QM/PCM and QM/FQ implementations, additional terms are only added to the Fock matrix. Additional terms at the coupled cluster level can also be considered.…”