Quasi-atom local chemistry that governs α-Mn structure

As opposed to the conventional free-electron-based theories of metals, a simple chemical theory, based on electrons occupying the quantum orbitals as the interstitial quasi-atoms (ISQs), has been successful to characterize the structure and stability of both high-symmetry (fcc, bcc, or hcp) and complex metals and metallic super hydrides [1,2]. Manganese (Mn) adopts a unique α (space group #217) structure under ambient conditions and up to high pressures of 165 GPa. The structural stability, phase transitions, and related phenomena in solids are typically driven by either magnetic or electronic properties. For a long time, the stability of α-Mn at high pressures has been attributed to the competing tendencies of its half-filled Mn-d band to maximize both the magnetic moment and bond strength. However, our calculations reveal that the magnetic moment of α-Mn becomes negligible above 55 GPa. In this study, we applied the quasi-atom theory to α-Mn. Electron localization function (ELF) and crystal orbital Hamiltonian population (COHP) analyses indicate that chemical interactions at the ISQ sites play a crucial role to stabilize the α-Mn structure.

[1] Y. Sun et. al, Proc. Natl. Acad. Sci. U.S.A. 120, e2218405120 (2023).

[2] Y. Sun and M. Miao, Chem 9, 443 (2023).