Calculation of Linear and Non-linear Electric Response Properties of Systems in Aqueous Solution: A Polarizable Quantum/Classical Approach with Quantum Repulsion Effects

Abstract

We present a computational study of polarizabilities and hyperpolarizabilities of organic molecules in aqueous solutions, focusing on solute–water interactions and the way they affect a molecule’s linear and non-linear electric response properties. We employ a polarizable quantum mechanics/molecular mechanics (QM/MM) computational model that treats the solute at the QM level while the solvent is treated classically using a force field that includes polarizable charges and dipoles, which dynamically respond to the solute’s quantum-mechanical electron density. Quantum confinement effects are also treated by means of a recently implemented method that endows solvent molecules with a parametric electron density, which exerts Pauli repulsion forces upon the solute. By applying the method to a set of aromatic molecules in solution we show that, for both polarizabilities and first hyperpolarizabilities, observed solution values are the result of a delicate balance between electrostatics, hydrogen-bonding, and non-electrostatic solute solvent interactions.

The Negative Solvatochromism of Reichardt‘s Dye B30 – A Complementary Study

“…Quantum chemical calculations performed to understand this finding must take into account not only chemical interactions between solute and solvent, but also the polarizing effect of light on matter. Often the solvent is only taken into account as a dielectric continuum while a fully quantum‐mechanical treatment would be necessary, which is computationally costly [53–56] …”

“…Often the solvent is only taken into account as a dielectric continuum while a fully quantum-mechanical treatment would be necessary, which is computationally costly. [53][54][55][56] The polarity of B30 is concentration dependent, as 13 C NMR experiments show. [20] With increasing the solute (B30) concentration, the polarity of the dye decreases according to the modern view.…”

Linear response properties of solvated systems: a computational study

“…Also, the quality of long-range electrostatics and polarization effects can be increased by including an additional source of polarization in the FQ force field in terms of fluctuating dipoles (FQFm) to account for anisotropic interactions. [123][124][125] Finally, the protocol can be extended to the treatment of higher-order properties, such as first hyperpolarizabilities (b).…”

Multiple Facets of Modeling Electronic Absorption Spectra of Systems in Solution

“…Depending on the coupling between the QM and MM portions, different approaches can be formulated, ranging from the electrostatic embedding, in which the MM part polarizes the QM part, but not viceversa, to polarizable embedding (PE), where mutual solute–solvent polarization effects are recovered; ,, clearly, PE gives the most physically consistent picture of the solvation phenomenon. Among the PE approaches that have been developed so far, in this Perspective the focus is on QM/Fluctuating Charges (FQ) and QM/Fluctuating Charges and Fluctuating Dipoles (FQFμ), which have been developed and extended to calculate spectroscopic and response properties of molecules in solution. − …”