Alloys play an important role in our society, such as the nickel and cobalt-based superalloys used in jet engines. A very interesting type of alloy is the high-entropy alloy (HEA) formed by five or more elements with all elements having large fractions. By properly selecting the elements and adjusting their fractions, HEA may outperform conventional alloys. Accurate modeling will help us design high-performance HEAs by, for instance, predicting their structures and mechanical properties at different elemental compositions, temperatures, and pressures.

However, simulating HEAs usually requires large simulation boxes. Large-scale Kohn-Sham density functional theory (KS-DFT) simulations of metallic systems are very challenging, due to the steep computational scaling with system sizes. Orbital-free DFT (OF-DFT) is a promising method for simulating large-scale metallic systems. OF-DFT is highly accurate for simulating main group metals, but its performance on transition metals is very poor, mainly due to the following two obstacles:

1. Most kinetic energy density functionals are not able to treat the localized d electrons in transition metals.

2. Lack of accurate local pseudopotentials for transition metals.

Obstacle #1 was resolved by Huang and Carter by introducing an electron density decomposition technique.[1] In 2021 summer, we overcame Obstacle #2 by developing a new method to generate high-quality local pseudopotentials that give accurate predictions to metals and alloys.[2] A stringent test is the alloy formation energies, which are crucial for predicting properties such as phase diagrams. In the right table, excellent results on nickel and nickel-aluminum alloy are shown. The local pseudopotential results are compared against the projector augmented wave (PAW) method (the benchmark). Based on these new developments, we are in the progress of developing a new orbital-free program for large-scale, accurate alloy simulations. 

All local pseudopotentials can be download here.

[1] Huang and Carter, Phys. Rev. B 85, 045126 (2012)

[2] Chi and Huang, J. Chem. Theory Comput. (2024) in press