Heusler compounds (general formula X$_2$YZ ) represent a highly versatile class of materials, exhibiting a rich compositional space and a plethora of exotic properties ideal for shape-memory, magnetocaloric, topological, and spintronic applications.[1,2] Traditionally, the structural stability of these compounds has been attributed to the p-d orbital hybridization between main-group elements and transition metals. However, the recent emergence of "all-d-metal" Heusler alloys—which display distinct mechanical properties—challenges this paradigm, suggesting a stabilization mechanism rooted instead in d-d orbital hybridization.[3]

In this work, we deploy ab initio Density Functional Theory (DFT) coupled with the LOBSTER[4] code and the novel LOPOSTER post-processing tool [5] to quantitatively evaluate these competing stabilization scenarios. By utilizing the integral of the Crystal Orbital Hamilton Population (ICOHP) as a precise descriptor of bond strength, we mapped the cumulative bonding landscapes of Ni$_2$MnGa (a conventional Heusler) and Ni$_2$MnTi (an all-d-metal Heusler). Our interatomic analysis reveals fundamentally distinct bonding topologies: Ni–Ga interactions dictate the structural stability of Ni$_2$MnGa, whereas Mn–Ti bonds are the primary drivers in Ni$_2$MnTi. Most strikingly, our inter-orbital analysis uncovers an overlooked stabilizing force: despite sitting energetically far below the Fermi level, the s orbitals of the Z atom play a surprisingly pivotal role in crystal structure stability. These findings challenge conventional hybridization models and unlock entirely new, atomic-level pathways for engineering the properties of advanced Heusler alloys.

References

[1] C. Lauhoff, A. Reul, D. Langenkämper, P. Krooß, C. Somsen, M.J. Gutmann, B. Pedersen, I.V. Kireeva, Y.I. Chumlyakov, G. Eggeler, W.W. Schmahl, T. Niendorf Acta Mater., 2022, 226, 117623.

[2] L. Wollmann, A.K. Nayak, S.S.P. Parkin, C. Felser Annu Rev. Mater. Res., 2017, 47, 247–270.

[3] Q. Ren, C. Yuan, Z. Du, Q. Zeng, Y. Liu, S. Zhang, Y. Feng, Y. Wang, J. Yang, M. Lyu, B. Wang, X. Zheng, G. Wu, Y. Wang, E. Liu, B. Shen, S. Wang Acta Mater., 2025, 292, 11032.

[4] S. Maintz, V.L. Deringer, A.L. Tchougréeff, R. Dronskowski J. Comput. Chem., 2016, 37, 1030–1035.

[5] Y. Wang, P.C. Müller, D. Hemker, R. Dronskowski J. Comput. Chem., 2025, 46, e70167.

Dr. Yixu Wang