A polarizable three-layer frozen density embedding/molecular mechanics approach.

Tommaso Giovannini,Chiara Cappelli,Franco Egidi,Piero Lafiosca,Sara Angelico

doi:10.1063/5.0045574

Abstract

We present a novel multilayer polarizable embedding approach in which the system is divided into three portions, two of which are treated using density functional theory and their interaction is based on frozen density embedding (FDE) theory, and both also mutually interact with a polarizable classical layer described using an atomistic model based on fluctuating charges (FQ). The efficacy of the model is demonstrated by extending the formalism to linear response properties and applying it to the simulation of the excitation energies of organic molecules in aqueous solution, where the solute and the first solvation shell are treated using FDE, while the rest of the solvent is modeled using FQ charges.

Highlights

The correct treatment of ever larger and more complex systems at an amenable computational cost has for long been at the forefront of quantum chemistry research
We have presented a three-layer computational model in which the chemical system is divided into a central moiety treated quantum mechanically, while its close-range environment is modeled through the Frozen Density Embedding theory, and long-range interactions are included via the polarizable Quantum Mechanics (QM)/Molecular Mechanics (MM) model based on fluctuating charges (QM/frozen density embedding (FDE)/FQ)
This approach aims to overcome the main limitation of the quantum/classical QM/FQ description that is based solely on electrostatic interactions by including a middle layer that is described quantum mechanically and retains a description of non-electrostatic interactions

Summary

Introduction

The correct treatment of ever larger and more complex systems at an amenable computational cost has for long been at the forefront of quantum chemistry research. Among the most well-known methods within this class are atomistic approaches based on a Quantum Mechanics (QM)/Molecular Mechanics (MM) paradigm.. Among the most well-known methods within this class are atomistic approaches based on a Quantum Mechanics (QM)/Molecular Mechanics (MM) paradigm.5,6 For the latter model, the mutual polarization between the target (QM portion) and the environment (MM portion) may be of particular importance for the modeling of the properties of a molecular system, since in a much simpler electrostatic embedding scheme, the environmental response to a probing electromagnetic field could not be accurately taken into account.. Ad hoc methods to include non-electrostatic interactions within QM/MM methods have been proposed, but another possibility is to resort to QM/QM embedding methodologies to treat close-range interactions between the system and its environment

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