11/10/2023
By Faranak Hatami

The Kennedy College of Sciences, Department of Physics and Applied Physics, invites you to attend a Master's thesis defense by Faranak Hatami on "Status of Classical Molecular Dynamics Force Fields for Liquid Tri-n-butyl Phosphate with and without Polarization."

Date: Monday, Nov. 20, 2023
Time: 11 a.m - noon.
Location: Olney 108A

Candidate Name: Faranak Hatami

Advisor: Dr. Valmor F. de Almeida, Associate Professor, Chemical Engineering, Nuclear Engineering

Committee Members:
Dr. Erin Rachel Bertelsen, Assistant Professor, Physics & Applied Physics
Dr. Ofer Cohen, Associate Professor, Physics


Abstract:
Over a decade has passed since the first comparative study of classical force fields for liquid tri-n-butyl phosphate (TBP) was published. In view of advances in open-source computing tools, availability of force fields, and renewed interest in domestic uranium processing and production in US, an up-to-date study of the performance of current force fields for TBP is overdue. We present a comprehensive investigation of key properties of TBP using molecular dynamics simulations using ten compositions of force field models with and without polarization effects; some models used here for the first time for TBP. The microscopic structure, transport properties (diffusion coefficient and dynamic viscosity), and thermodynamic properties (mass density, heat of vaporization, dipole moment, and coefficient of thermal expansion), are thoroughly investigated. Dynamic viscosity and diffusion coefficient are calculated by equilibrium molecular dynamics simulations using the Green-Kubo formalism, and alternatively, by non-equilibrium simulations using the SLLOD method. This study reports on the best force fields currently available as judged by the aforementioned properties predictions in comparison to experimental data. In this study, it turns out that models utilizing varying combinations of charges and Lennard-Jones parameters exhibit differing levels of effectiveness when it comes to reproducing thermodynamic and transport properties. Incorporating polarization into several force field models, especially Optimized Potential for Liquid Simulation (OPLS) models, enhanced agreement with experimental values. The most effective model for viscosity and diffusion coefficient was OPLS2005 with polarization. We hope this study will guide researchers and users in the field of applications of TBP to chemical and physical processes, in particular to the nuclear fuel cycle.