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Polarizable QM/MM multiconfiguration self-consistent field approach with state-specific corrections: Environment effects on cytosine absorption spectrum

We present the formulation and implementation of a polarizable quantum mechanics/molecular mechanics (QM/MM) strategy to describe environment effects in multiconfiguration self-consistent field calculations. The strategy is applied to the calculation of the vertical absorption spectrum of cytosine in water. In our approach, mutual polarization of the solute and the solvent is solved self-consistently at the complete-active-space self-consistent-field (CASSCF) level, and the resulting set of charges and dipoles is used to calculate vertical excitation energies using the complete-active-space second-order perturbative (CASPT2) approach and its multistate (MS-CASPT2) variant. In order to treat multiple excited states, we converge the solvent polarization with respect to the state-averaged density of the solute. In order to obtain the final energies, however, we introduce a state-specific correction, where the solvent polarization is recomputed with the density of each state, and demonstrate that this correction brings the excitation energies closer to the values obtained with state-optimized orbitals. Comparison with PCM and nonpolarizable QM/MM calculations shows the importance of specific solute-solvent interactions and environment polarization in describing experiments. Overall, the calculated excitations for the π → π∗ states in water show good agreement with the experimental spectrum, whereas the n → π∗ appear at energies above 6 eV, approximately 1 eV higher than in the gas phase. Beyond solvents, the new method will allow studying the impact of heterogeneous biological environments in multiple excited states, as well as the treatment of multichromophoric systems where charge transfer and exciton states play important roles

© Journal of Chemical Theory and Computation, 2015, vol. 11, núm. 4, p. 1674-1682

American Chemical Society (ACS)

Author: Li, Quansong
Mennucci, Benedetta
Robb, Michael A.
Blancafort San José, Lluís
Curutchet, Carles
Date: 2015
Abstract: We present the formulation and implementation of a polarizable quantum mechanics/molecular mechanics (QM/MM) strategy to describe environment effects in multiconfiguration self-consistent field calculations. The strategy is applied to the calculation of the vertical absorption spectrum of cytosine in water. In our approach, mutual polarization of the solute and the solvent is solved self-consistently at the complete-active-space self-consistent-field (CASSCF) level, and the resulting set of charges and dipoles is used to calculate vertical excitation energies using the complete-active-space second-order perturbative (CASPT2) approach and its multistate (MS-CASPT2) variant. In order to treat multiple excited states, we converge the solvent polarization with respect to the state-averaged density of the solute. In order to obtain the final energies, however, we introduce a state-specific correction, where the solvent polarization is recomputed with the density of each state, and demonstrate that this correction brings the excitation energies closer to the values obtained with state-optimized orbitals. Comparison with PCM and nonpolarizable QM/MM calculations shows the importance of specific solute-solvent interactions and environment polarization in describing experiments. Overall, the calculated excitations for the π → π∗ states in water show good agreement with the experimental spectrum, whereas the n → π∗ appear at energies above 6 eV, approximately 1 eV higher than in the gas phase. Beyond solvents, the new method will allow studying the impact of heterogeneous biological environments in multiple excited states, as well as the treatment of multichromophoric systems where charge transfer and exciton states play important roles
Format: application/pdf
ISSN: 1549-9618 (versió paper)
1549-9626 (versió electrònica)
Document access: http://hdl.handle.net/10256/11464
Language: eng
Publisher: American Chemical Society (ACS)
Collection: MICINN/PN 2012-2014/CTQ2011-26573
AGAUR/2014-2017/2014SGR1202
Reproducció digital del document publicat a: http://dx.doi.org/10.1021/ct5010388
Articles publicats (D-Q)
Is part of: © Journal of Chemical Theory and Computation, 2015, vol. 11, núm. 4, p. 1674-1682
Rights: Tots els drets reservats
Subject: Quàntums, Teoria dels
Quantum theory
Química de l’estat excitat
Excited state chemistry
Title: Polarizable QM/MM multiconfiguration self-consistent field approach with state-specific corrections: Environment effects on cytosine absorption spectrum
Type: info:eu-repo/semantics/article
Repository: DUGiDocs

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