Molecular dynamics study of perchloric acid using the extended Madrid-2019 force field

TL;DR

This study uses the extended Madrid-2019 force field to model perchloric acid solutions, accurately predicting densities, structural features, and transport properties across various concentrations and temperatures.

Contribution

It applies and validates the extended Madrid-2019 force field for perchloric acid, providing detailed thermodynamic, structural, and transport property predictions.

Findings

Experimental densities are predicted accurately up to 10 m.

Predicted viscosities agree with experimental data below 4 m.

The model effectively predicts the temperature of maximum density (TMD).

Abstract

Perchloric acid (HClO$_4$) is widely used to prepare perchlorate salts with applications in propellants, industry, environmental chemistry, and biology. In this work, we used the intermolecular parameters from the extended Madrid-2019 force field for the perchlorate anion (ClO$_4^-$) and the oxonium cation (H$_3$O$^+$) together with TIP4P/2005 water to model perchloric acid solutions. The force field uses scaled charges of $\pm0.85e$ for monovalent ions and has been widely applied for aqueous ionic systems. We used the model to predict thermodynamic properties [densities and temperatures of maximum in density (TMD)], structural features (ion-water correlations: ion-hydrogen and ion-oxygen), and transport properties (self-diffusion coefficients and viscosity) of perchloric acid solutions at several concentrations. Experimental densities are predicted in excellent agreement up to 10 $m$. We also performed molecular simulations over a wide range of temperatures in order to determine the TMD of perchloric acid at different molalities. Predicted viscosities at 298.15 K and 1 bar are in good agreement with experimental data for concentrations below 4 $m$. Results are discussed in terms of model strengths and limitations.