Density functional theory study of structural and thermodynamical stabilities of ferromagnetic MnX (X = P, As, Sb, Bi) compounds
Abstract
Density functional theory (DFT) calculations for deriving enthalpies of formation [ image ]H for ferromagnetic MnX (X [ image ] P, As, Sb, Bi) compounds were made for the two competing structures, hexagonal [ image ] and orthorhombic [ image ]. Standard calculations were performed by using pseudopotentials with the generalized-gradient-approximation (PBE) as exchange-correlation functional. Enhanced exchange-correlation interactions were included by making use of a so-called DFT[ image ]U approach which requires [ image ] as a parameter. Application of PBE potentials for all compounds and elementary phases (all-PBE) resulted in negative values of [ image ]H for MnP and MnAs in both structures whereby the result for MnP [ image ] agrees very well with experiment. For MnSb and MnBi the all-PBE calculation gives a positive nonbonding [ image ]H disagreeing with experiment. To overcome this discrepancy for MnSb and MnBi a DFT[ image ]U ansatz was employed for all compounds and elemental Mn. The values for [ image ] ranging between 0.7 for MnBi and 1.4 eV for MnAs were determined by fitting the DFT results to measured data of [ image ]H. As a reference for pure Mn the [ image ]-Mn phase was taken with [ image ] eV by which choice the experimental volume is fitted. Atomic volumes and ionicities were derived applying Bader's concept resulting in ionicities of Mn less than [ image ].
- Publication:
-
Journal of Physics Condensed Matter
- Pub Date:
- February 2019
- DOI:
- 10.1088/1361-648X/aaf2db
- Bibcode:
- 2019JPCM...31e4001P
- Keywords:
-
- magnetic Mn-pnictides;
- structure;
- phase stability;
- DFT