BaNi₂As₂ represents a non-magnetic analogue to the iron-pnictide compound BaFe₂As₂. Despite the absence of magnetic order, BaNi₂As₂ exhibits a rich spectrum of structural, electronic and lattice dynamical instabilities, including charge-density waves (CDW) and superconductivity. The CDW at ambient pressure is linked to a soft transverse phonon mode [1,2], and in addition triggers a specific dynamical nematicity of a Raman-active mode [3]. Under hydrostatic pressure, a variety of new structural modifications are observed, which profoundly impact the type of CDW [4]. This suggests that the tetragonal structure of BaNi₂As₂ lies energetically close to a plethora of competing phases.

Here, a detailed density-functional perturbation study of lattice properties and electron-phonon coupling (EPC) for the various structural phases occurring at ambient and high pressure is presented to elucidate the origin of the instabilities. While many of the structural modifications and CDW-type instabilities can be reproduced by DFT, the strength of the EPC attached to the corresponding soft modes varies significantly, which indicates a more complex relationship between EPC, lattice instabilities and superconductivity.

[1] M. Souliou et al., Phys. Rev. Lett. 129, 247602 (2022)

[2] T. Lacmann et al., Phys. Rev. B 112, 054101 (2025)

[3] Y. Yao et al., Nat. Commun. 13, 4535 (2022)