Electronic and magnetic structure of Fe_{3}S_{4} : GGA+U investigation
Abstract
The electronic and magnetic behavior of the iron sulphide mineral greigite (Fe_{3}S_{4}) is studied using ab initio densityfunctional theory in the generalized gradient approximation (GGA) with the onsite Hubbard U_{eff} parameter ( GGA+U ). The effect of the Hubbard correction is investigated and is found to be a necessary requirement for the accurate description of both the unit cell structure and the magnetic moment. A ferrimagnetic normalspinel structure is found when U_{eff}=0eV , while for all values of U_{eff}>0eV an inverse spinel structure is predicted, in agreement with experiment. For low values of U_{eff} (0<U_{eff}<4eV) the predicted electronic structure corresponds to that of a semimetal, with semimetallicity arising from electron hopping between ferric and ferrous Fe on octahedral sites. For values of U_{eff}≥4eV the S atoms are found to oxidize the ferrous octahedral sites Fe to the ferric state. To determine whether GGA+U predicts a stable monoclinic form of greigite arising from a Verweytype lowtemperature transition, analogous to that seen in magnetite, a monoclinic form of greigite is postulated. It is found that such a phase is stable, with an electronic bandgap opening up for values of U_{eff}≥2eV , but is energetically unfavorable when compared with the spinel phase for all U_{eff} values tested. It is argued that an accurate description of all the properties of greigite requires a U_{eff} value of approximately 1 eV.
 Publication:

Physical Review B
 Pub Date:
 May 2009
 DOI:
 10.1103/PhysRevB.79.195126
 Bibcode:
 2009PhRvB..79s5126D
 Keywords:

 71.20.b;
 71.15.Mb;
 71.27.+a;
 71.28.+d;
 Electron density of states and band structure of crystalline solids;
 Density functional theory local density approximation gradient and other corrections;
 Strongly correlated electron systems;
 heavy fermions;
 Narrowband systems;
 intermediatevalence solids