Completed coarsegrained model for Pu hydriding that has quantum accuracy (Progress Summary)
Abstract
Our team has developed a highly computationally efficient coarsegrained model for PuH _{2} formation, based on highlevel quantum mechanical calculations. KohnSham Density Functional Theory (DFT) is a quantum mechanical approach that can be highly accurate for modeling condensed phases, including reactive materials that are subject to the breaking and forming of chemical bonds. DFT calculations, though, are extremely computationally intensive, and are generally limited to exceedingly small system sizes and time scales. This is particularly true for felectron solids such as plutonium, where the high computational effort due to electron correlations and minimizing to specific electronic spinstates (e.g., antiferromagnetic vs. ferromagnetic) limits standard calculations to systems of tens of atoms and precludes the determination of timedependent properties (e.g., chemical kinetic data). In this regard, we have created a simplified Pu + H _{2}/PuH _{2} equilibrium model based on a small number of interaction energies determined from DFT calculations. We have determined that PuH bond energetics in the bulk are largely defined by nearestneighbor interactions, only. In other words, a hydrogen atom in a dPu tetrahedral interstitial site will only experience perturbations to its HPu bonded interactions when there is an additional hydrogen ion in a directly adjacent adsorption site. Thismore »
 Authors:

 Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
 Publication Date:
 Research Org.:
 Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
 Sponsoring Org.:
 USDOE
 OSTI Identifier:
 1527288
 Report Number(s):
 LLNLTR778385
972390
 DOE Contract Number:
 AC5207NA27344
 Resource Type:
 Technical Report
 Country of Publication:
 United States
 Language:
 English
 Subject:
 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE
Citation Formats
Goldman, Nir, and Mullen, Ryan. Completed coarsegrained model for Pu hydriding that has quantum accuracy (Progress Summary). United States: N. p., 2019.
Web. doi:10.2172/1527288.
Goldman, Nir, & Mullen, Ryan. Completed coarsegrained model for Pu hydriding that has quantum accuracy (Progress Summary). United States. doi:10.2172/1527288.
Goldman, Nir, and Mullen, Ryan. Mon .
"Completed coarsegrained model for Pu hydriding that has quantum accuracy (Progress Summary)". United States. doi:10.2172/1527288. https://www.osti.gov/servlets/purl/1527288.
@article{osti_1527288,
title = {Completed coarsegrained model for Pu hydriding that has quantum accuracy (Progress Summary)},
author = {Goldman, Nir and Mullen, Ryan},
abstractNote = {Our team has developed a highly computationally efficient coarsegrained model for PuH2 formation, based on highlevel quantum mechanical calculations. KohnSham Density Functional Theory (DFT) is a quantum mechanical approach that can be highly accurate for modeling condensed phases, including reactive materials that are subject to the breaking and forming of chemical bonds. DFT calculations, though, are extremely computationally intensive, and are generally limited to exceedingly small system sizes and time scales. This is particularly true for felectron solids such as plutonium, where the high computational effort due to electron correlations and minimizing to specific electronic spinstates (e.g., antiferromagnetic vs. ferromagnetic) limits standard calculations to systems of tens of atoms and precludes the determination of timedependent properties (e.g., chemical kinetic data). In this regard, we have created a simplified Pu + H2/PuH2 equilibrium model based on a small number of interaction energies determined from DFT calculations. We have determined that PuH bond energetics in the bulk are largely defined by nearestneighbor interactions, only. In other words, a hydrogen atom in a dPu tetrahedral interstitial site will only experience perturbations to its HPu bonded interactions when there is an additional hydrogen ion in a directly adjacent adsorption site. This is due to the strong electronic screening from the Pu atoms, which essentially limits the spatial extent of how hydrogen ions interact with each other within the Pu lattice. As a result, we are able to pretabulate all essential PuH interaction energies and model PuH2 formation via a Monte Carlo simulation approach. This allows us to greatly expand the spatial and time scales of our calculations while maintaining most of the accuracy of quantum methods. Our model can thus be extended to system sizes if 100,000 atoms or greater and can be used to model hydride equilibrium processes, all of which are computationally cost prohibitive with any standard quantum code. We have used our approach to compute a twodimensional free energy heat map and temperature dependence at subatmospheric pressures for PuH2 formation. Our results compare well to the limited available experimental data, in particular for the enthalpy of formation (DH). Our goal is to extend these results to compute nucleation parameters such as the critical nucleus size and nucleation growth rates for continuum models.},
doi = {10.2172/1527288},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {6}
}