Electronic structure beyond the generalized gradient approximation for Ni2MnGa

Abstract

The stability of the nonmodulated martensitic phase, the austenitic Fermi surface and the phonon dispersion relations for ferromagnetic Ni2MnGa are studied using density functional theory. Exchange-correlation effects are considered with various degrees of precision, starting from the simplest local spin density approximation (LSDA), then adding corrections within the generalized gradient approximation (GGA) and finally, including the meta-GGA corrections within the strongly constrained and appropriately normed (SCAN). We discuss a simple procedure to reduce a possible overestimation of magnetization and underestimation of nesting vector in SCAN by parametrically decreasing self-interaction corrections.

Localization versus delocalization of d-states within the $$\hbox {Ni}_{{2}}$$MnGa Heusler alloy

“…2 a), the use of meta-GGA SCAN +U could result in a better agreement with the experiments. Anyway, SCAN already approaches higher magnetic moments than GGA 47 , 55 , 57 and correctly predicts higher magnetization of austenite over martensite phase in agreement with our results. Therefore, smaller values of the parameter U would be necessary in the meta-GGA + U approach, which is consistent with the metallic nature of the constituent elements.…”

“…An increase in the magnetization calculated by HSE03 was expected due to stronger electron localization and pronounced exchange splitting, as observed in bulk metallic systems 35,36 . Calculations using meta-GGA exchange-correlation functional also predict higher magnetization than GGA 47,55 (see also Supplementary Information SI Figs. 1, 2).…”

“…Note that the total magnetization of the austenite at 0 K is smaller than the one of the martensite when we use uncorrected GGA or U correction on Mn. Contrarily meta-GGA SCAN 47,[55][56][57] , HSE03 and U on Ni all predict the austenite phase to have larger µ tot at zero Kelvin (emphasized by arrows in Fig. 2c and SI Fig.…”

Experimental Observations versus First‐Principles Calculations for Ni–Mn–Ga Ferromagnetic Shape Memory Alloys: A Review

“…[145,146] Pioneering calculations for off-stoichiometric compositions were performed by Enkovaara et al, [125] who showed that stability of NM martensite with respect to austenite is stronger in Mn-rich alloys than in stoichiometric alloy. The increased stability of NM martensite was also observed for Nirich alloys by Zayak et al [95] and other authors. [62,147] The validity of this approach for predicting T M was also confirmed for alloys with Fe and Co, [145,146] Al, [97] Pt, [61] Cu, [148] Zn, [124,149] Ti, [150] B, [122] and CoþCu.…”

“…[89,[91][92][93] Advanced approximations of the exchange-correlation energy, including dependence on the kinetic energy density, [94] were shown to modify the nesting properties of the austenitic Fermi surface. [95] This, nevertheless, results in an underestimation of the magnitude of the nesting vector but more accurate predictions of the c=a ratio for the NM phase. [90] Valuable results were obtained for the 10M modulated phase under the assumption of smooth harmonic modulations.…”