Bond-informed search for ordered configurations in multi-principal element alloys

Abstract

Ordered configurations in multi-principal element alloys (MPEAs) control their local structure and influence a broad range of mechanical and thermodynamic properties. Yet they are notoriously difficult to identify. Locating low-energy ordered candidates requires exploring a configurational space that grows combinatorially with the number of elements, and Monte Carlo searches driven by density-functional theory (DFT) need a new electronic-structure calculation at every trial step. Here we introduce MECx (Minimum Energy Configuration eXplorer), a framework that guides Monte Carlo searches with a surrogate energy model trained on configurations stratified in bond-count space. Applied to ternary, quaternary, and quinary BCC alloys using compact training sets of 100 DFT-labeled configurations, MECx identifies ordered configurations with lower energies than those found by direct DFT-based Monte Carlo within practical computational limits. These configurations exhibit distinct pair-specific ordering, including B2- and B32-like motifs, and undergo progressive disordering as temperature increases. The MPEA-trained models also transfer to selected binary subsystems without retraining. The resulting ordered configurations agree with those obtained by direct DFT-based Monte Carlo and produce experimentally distinguishable superlattice reflections in simulated neutron diffraction patterns.