Modeling solvation effects in real-space and real-time within Density Functional Approaches

TL;DR

This paper introduces a real-space and real-time methodology for modeling solvation effects within Density Functional Theory, using boundary elements and Gaussian regularization to improve accuracy in electronic and optical property simulations.

Contribution

It develops a novel approach combining boundary elements and Gaussian functions to incorporate solvation effects in real-space (TD)DFT calculations, implemented in the Octopus code.

Findings

Accurately computes solvation free energies for organic molecules in water.

Predicts solvatochromic shifts consistent with experimental data.

Demonstrates the method's effectiveness in real-space and real-time simulations.

Abstract

The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the Van der Waals solute surface. In a real-space representation this potential may exhibit a Coulomb singularity at grid points that are close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the Octopus code and present results for the electrostatic contribution to the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water.