title: Introducing QMC/MMpol: Quantum Monte Carlo in Polarizable Force Fields for Excited States.
abstract: We present for the first time a quantum mechanics/molecular mechanics scheme which combines quantum Monte Carlo with the reaction field of classical polarizable dipoles (QMC/MMpol). In our approach, the optimal dipoles are self-consistently generated at the variational Monte Carlo level and then used to include environmental effects in diffusion Monte Carlo. We investigate the performance of this hybrid model in describing the vertical excitation energies of prototypical small molecules solvated in water, namely, methylenecyclopropene and s-trans acrolein. Two polarization regimes are explored where either the dipoles are optimized with respect to the ground-state solute density (polGS) or different sets of dipoles are separately brought to equilibrium with the states involved in the electronic transition (polSS). By comparing with reference supermolecular calculations where both solute and solvent are treated quantum mechanically, we find that the inclusion of the response of the environment to the excitation of the solute leads to superior results than the use of a frozen environment (point charges or polGS), in particular, when the solute-solvent coupling is dominated by electrostatic effects which are well recovered in the polSS condition. QMC/MMpol represents therefore a robust scheme to treat important environmental effects beyond static point charges, combining the accuracy of QMC with the simplicity of a classical approach.
authors.affiliation: MESA+ Institute for Nanotechnology, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Guareschi
authors.affiliation: MESA+ Institute for Nanotechnology, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Habiburrahman
authors.initials: H
authors.lastname: Zulfikri
authors.affiliation: MESA+ Institute for Nanotechnology, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Csaba
authors.initials: C
authors.lastname: Daday
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa , Via Giuseppe Moruzzi 13, 56124 Pisa, Italy.
authors.forename: Franca Maria
authors.initials: FM
authors.lastname: Floris
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa , Via Giuseppe Moruzzi 13, 56124 Pisa, Italy.
authors.forename: Claudio
authors.initials: C
authors.lastname: Amovilli
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa , Via Giuseppe Moruzzi 13, 56124 Pisa, Italy.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Mennucci
authors.affiliation: MESA+ Institute for Nanotechnology, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Claudia
authors.initials: C
authors.lastname: Filippi