# Deviations from Ideality: Quantum Cluster Equilibrium Theory and the Methanol-Benzene Binary Mixture

## Location

King Building 237

## Document Type

Presentation

## Start Date

4-27-2018 5:30 PM

## End Date

4-27-2018 6:50 PM

## Abstract

The methanol-benzene binary mixture, which has an azeotrope with a 3:2 methanol:benzene molar ratio at 329 K, provides a useful system through which to study the computation of thermodynamic properties of non-ideal mixtures. Methanol-benzene clusters of various molar ratios up to mixed pentamers are described with Density Functional Theory (DFT) to model possible interactions in the binary liquid. Thermodynamic data, cluster populations, and phase transitions are then calculated using Quantum Cluster Equilibrium (QCE) theory in order to evaluate the efficacy of current computational methods in describing deviations from ideality. Vibrational entropy, enthalpy of mixing, Gibbs free energy of mixing, and boiling points are shown to be highly dependent upon the types of normal mode deflections calculated for individual clusters, indicating that vibrational anharmonicity plays an important role in describing thermodynamic behavior. By accounting for the anharmonic characteristics of this non-ideal mixture, azeotropic behavior can be accurately and robustly modeled.

## Keywords:

chemistry, computational chemistry, theoretical chemistry, statistical thermodynamics, applied mathematics, quantum mechanics

## Recommended Citation

Vigilante, Nic, "Deviations from Ideality: Quantum Cluster Equilibrium Theory and the Methanol-Benzene Binary Mixture" (04/27/18). *Senior Symposium*. 78.

https://digitalcommons.oberlin.edu/seniorsymp/2018/presentations/78

## Major

Chemistry; Viola Performance

## Advisor(s)

Manish Mehta, Chemistry and Biochemistry

Kristen Docter, Viola Performance

## Project Mentor(s)

Anne-Marie Kelterer, Institut für Physikalische und Theoretische Chemie, Technische Universität Graz

April 2018

Deviations from Ideality: Quantum Cluster Equilibrium Theory and the Methanol-Benzene Binary Mixture

King Building 237

The methanol-benzene binary mixture, which has an azeotrope with a 3:2 methanol:benzene molar ratio at 329 K, provides a useful system through which to study the computation of thermodynamic properties of non-ideal mixtures. Methanol-benzene clusters of various molar ratios up to mixed pentamers are described with Density Functional Theory (DFT) to model possible interactions in the binary liquid. Thermodynamic data, cluster populations, and phase transitions are then calculated using Quantum Cluster Equilibrium (QCE) theory in order to evaluate the efficacy of current computational methods in describing deviations from ideality. Vibrational entropy, enthalpy of mixing, Gibbs free energy of mixing, and boiling points are shown to be highly dependent upon the types of normal mode deflections calculated for individual clusters, indicating that vibrational anharmonicity plays an important role in describing thermodynamic behavior. By accounting for the anharmonic characteristics of this non-ideal mixture, azeotropic behavior can be accurately and robustly modeled.

## Notes

Session VII, Panel 19 - Physical | Science

Moderator: Dan Stinebring, Francis D. Federighi Professor of Physics