What is the true ground state of intermetallic compound Fe3Al?

We discuss recent doubts about the true ground-state (GS) structure of the intermetallic compound Fe₃Al. It seems that it should be the D0₃ structure (observed experimentally), but there are some considerations that, perhaps, D0₃ might be a high-temperature (>400 K) structure and the GS at 0 K might be the L1₂ structure because there might be a high energy barrier between both structures and, when the temperature is lowered, the system is not able to transform into the (perhaps) lower-energy L1₂ structure. To elucidate this problem, we re-interpret our recent extended ab initio electronic structure calculations for Fe₃Al performed with the help of the VASP code and using various exchange-correlation energies within the generalized gradient approximation (GGA). Regrettably, some calculations provide the L1₂ and some of them D0₃ as the GS structure.

To resolve this question, we performed further calculations testing 9 frequently applied metaGGAs, such as TPSS, revTPSS, M06-L, SCAN(-L), rSCAN(-L) and r²SCAN(-L) representing a higher rung of the Jacob's ladder. It turns out that also here some meta-GGAs lead to L1₂ and some others to D0₃ GS structure and, again, we cannot decide.

In this way, the present results represent the very first step on the way to understand the energetics of the Fe₃Al compound and its ground state. We hope they may motivate future theoretical and experimental work in this direction.