Effective yet reliable computation of hyperfine coupling constants in solution by a QM/MM approach: Interplay between electrostatics and non-electrostatic effects

Abstract

In this paper, we have extended to the calculation of hyperfine coupling constants, the model recently proposed by some of the present authors [Giovannini et al., J. Chem. Theory Comput. 13, 4854–4870 (2017)] to include Pauli repulsion and dispersion effects in Quantum Mechanical/Molecular Mechanics (QM/MM) approaches. The peculiarity of the proposed approach stands in the fact that repulsion/dispersion contributions are explicitly introduced in the QM Hamiltonian. Therefore, such terms not only enter the evaluation of energetic properties but also propagate to molecular properties and spectra. A novel parametrization of the electrostatic fluctuating charge force field has been developed, thus allowing a quantitative reproduction of reference QM interaction energies. Such a parametrization has been then tested against the prediction of EPR parameters of prototypical nitroxide radicals in aqueous solutions.

Molecular spectroscopy of aqueous solutions: a theoretical perspective

“…10a). 47 While these molecules are not especially flexible, the oxygen atom can still move about the molecular plane leading to a pyramidalization of the nitrogen atom. The degree of deviation from the planar structure can be evaluated by measuring the improper dihedral angle d = C a NOC a .…”

Electronic transitions for a fully polarizable QM/MM approach based on fluctuating charges and fluctuating dipoles: Linear and corrected linear response regimes

“…The interaction between the QM and MM portions is usually described in terms of electrostatic forces, although approaches to include non-electrostatic QM/MM interactions have been proposed recently. [32][33][34] In order to fully capure the physics of solute-…”

“…As a consequence, non-electrostatic interactions should reasonably shift QM/FQFµ values towards the experimental data. On the other hand, in light of such considerations, the good performance of QM/FQ for pyridine and pyrimidine might be ascribed to error cancellations between the description of electrostatic effects and the lack of explicit consideration of exchange-repulsion effects [32][33][34]. 5 Summary and ConclusionsIn this work, we have extended the fully polarizable QM/FQFµ approach to the evaluation of excited state energies.…”

Multiscale electrostatic embedding simulations for modeling structure and dynamics of molecules in solution: A tutorial review

“…In fact, since the Pauli repulsion from the electron cloud that would surround the classical atoms is absent, the electronic density is overpolarized at short ranges by an incorrect, purely attractive total potential. This is called the “electron” or “charge spillout problem.” [ 20,37,57,81 ] The effect is particularly pronounced when using plane waves or real‐space grids as basis, in which the electrons are more free to delocalize than in LCAO basis sets. However, for LCAO basis sets that are sufficiently diffuse, the effect can still be observed.…”

“…This tutorial review focuses on electrostatic embedding, currently the most used of the QM/MM models, often directly available to nonexperts. However, much work is being put into advancing the field towards polarizable coupling models, [46][47][48][49][50][51][52][53][54][55][56][57][58][59] and readers are invited to inform themselves further about the differences between the approximations through the aforementioned reviews. In electrostatic embedding, the two subsystems are coupled through an addition to the QM Hamiltonian, such that the effects of the environment is included explicitly and on an atomistic level, while the environment itself is less accurately modeled.…”