Assessing the quality of QM/MM approaches to describe vacuo-to-water solvatochromic shifts

Abstract

The performance of different Quantum Mechanics/Molecular Mechanics embedding models to compute vacuo-to-water solvatochromic shifts are investigated. In particular, both non-polarizable and polarizable approaches are analyzed and computed results as compared to reference experimental data. We show that none of the approaches outperforms the others and that errors strongly depend on the nature of the molecular transition. Thus, we prove that the best choice of embedding model highly depends on the molecular system and that the use a specific approach as a black-box can lead to errors and sometimes totally wrong predictions.

Multiple Facets of Modeling Electronic Absorption Spectra of Systems in Solution

“…To conclude this section, we refer interested readers to a recent assessment of the performance of different polarizable embedding approaches, ranging from QM/FQ to QM/ Discrete Reaction Field (QM/DRF) and QM/FQFμ, in the reproduction of solvatochromic shifts of several dyes dissolved in aqueous solution. 54…”

“…Second, the different description of electrostatic interactions given by QM/FQ and QM/FQFμ leads to a diverse value of solvatochromic shifts for the π → π* transition of PNA (see the position of the vertical bars in Figure b). Experiments , suggest that the solvatochromic shift of PNA is 0.99 eV, which is a value better achieved in the case of the QM/FQFμ approach. , …”

“…Experiments 107,108 suggest that the solvatochromic shift of PNA is 0.99 eV, which is a value better achieved in the case of the QM/FQFμ approach. 13,54 Still commenting on PNA, it is well-known that a correct definition of the solvation regime, i.e., how to reliably describe the environment response following the electronic transition, is crucial to compute accurate excitation energies in solution. Specifically, here we focus on the LR and cLR approaches, which have already been extended to both QM/FQ and QM/ FQFμ.…”

“…Once the solute–solvent phase space is explored, the computational sample is prepared ( iii ) by extracting some configurations or representative structures, ensuring no correlation between them. Frequently those snapshots are cut in sphere-shaped droplets and, for absorption spectra, a radius less than 20 Å and just hundreds of them have proven to give excellent results. − Later, ( iv ) QM/FQ calculations of the target property, here electronic absorption spectroscopy, are carried out on the spherical frames obtained at the previous step, at a given QM computational level, which is chosen according to previous studies on similar properties/systems or based on a thorough benchmarking. The two model variants, QM/FQ and QM/FQFμ may be exploited at this step as well as different sets of parameters for water and for nonaqueous solvents.…”

“…Vertical bars mark the position of excitation energies in vacuum and those obtained with ω 0 , i.e., the frozen density approximation . c) PNA vacuo-to-water solvatochromic shifts, Δ E = E solv – E vac , in water computed with QM/EE and different QM/FQ parametrizations. PNA was freely allowed to move during MD simulations.…”