Engineering topics

Pribram-Jones, A.

Publications and source records attributed to Pribram-Jones, A..

4 records

DOE OSTI2017

First-principles investigation of structural and magnetic disorder in CuNiMnAl and CuNiMnSn Heusler alloys

Two quaternary Heusler alloys, equiatomic CuNiMnAl and CuNiMnSn, are studied using density functional theory to understand their tendency for atomic disorder on the lattice and the magnetic effects of disorder. Disordered structures with antisite defects of atoms of the same and different sublattices are considered, with the level of atomic disorder ranging from 3% to 25%. Formation energies and magnetic moments are calculated relative to the ordered ground state and combined with a simple thermodynamical model to estimate temperature effects. We predict the relative levels of disordering in the two equiatomic alloys with good correlation to experimental x-ray diffraction results. In conclusion, the effect of swaps involving Mn is also discussed.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Exact thermal density functional theory for a model system: Correlation components and accuracy of the zero-temperature exchange-correlation approximation

Thermal density functional theory calculations often use the Mermin-Kohn-Sham scheme, but employ ground-state approximations to the exchange-correlation (XC) free energy. In the simplest solvable nontrivial model, an asymmetric Hubbard dimer, we calculate the exact many-body energies and the exact Mermin-Kohn-Sham functionals for this system and extract the exact XC free energy. For moderate temperatures and weak correlation, we find this approximation to be excellent. Here we extract various exact free-energy correlation components and the exact adiabatic connection formula.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Connection formulas for thermal density functional theory

We show that the adiabatic connection formula of ground-state density functional theory relates the correlation energy to a coupling-constant integral over a purely potential contribution, and is widely used to understand and improve approximations. The corresponding formula for thermal density functional theory is cast as an integral over temperatures instead, ranging upward from the system's physical temperature. We also show how to relate different correlation components to each other, either in terms of temperature or coupling-constant integrations. Lastly, we illustrate our results on the uniform electron gas.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

Exact conditions on the temperature dependence of density functionals

Universal exact conditions guided the construction of most ground-state density functional approximations in use today. Here, we derive the relation between the entropy and Mermin free energy density functionals for thermal density functional theory. Both the entropy and sum of kinetic and electron-electron repulsion functionals are shown to be monotonically increasing with temperature, while the Mermin functional is concave downwards. Analogous relations are found for both exchange and correlation. The importance of these conditions is illustrated in two extremes: the Hubbard dimer and the uniform gas.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗