Hybrid quantum mechanical methods (QM/QM) are widely used to assist in the interpretation of molecular spectroscopy. In this work, we investigate improvements to the performance of Our own N-layer Integrated molecular Orbital and molecular Mechanics (ONIOM) hybrid scheme [1], where the molecular system is partitioned into regions treated with different levels of theory, by embedding the core region in a field of point charges generated by the remaining part of the system. It is worth noting that accurate ONIOM calculation of vertical transition energies without electronic embedding have already been reported [2,3]. Our benchmark calculations may improve our understanding of how point charge embedding influences the ONIOM excitation energies, providing a more realistic interaction between the core region and its surrounding. We test different type of point charges, with particular attention to the issue of overpolarization in boundary regions where covalent bonds are severed. The data collected provides information towards the improvement of ONIOM accuracy in modeling the one-electron vertical excited states. [1] K. Morokuma, et al. Chem. Rev., 2015, 115, 5678 [2] M. Caricato, et al. J. Chem. Phys. 2009, 131, 134105 [3] M. Caricato, et al. J. Chem. Phys. 2010, 133, 054104

Modeling excited states of large molecular systems using hybrid QM/QM methods with point charge embedding

251st National Meeting (2016)

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