Density functional theory study of nitrogen atoms and molecules interacting with Fe(111) surfaces

Abstract

We present Density functional theory (DFT) calculations for the investigation of the structural relaxation of Fe(111), as well as for the study of the interaction of nitrogen atoms and molecules with this surface.We perform spin polarized DFT calculations using VASP (Vienna Ab-initio Simulation Package) code. We use the supercell approach and up to 19 slab layers for the relaxation of the Fe(111) surface. We find acontraction of the first two interlayer distances with a relative value ofD12¼-7:8% and D23¼-21:7% with respect to the bulk reference. The third interlayer distance is however expanded with a relativechange of D34¼9:7%. Early experimental studies of the surface relaxation using Low Energy ElectronDiffraction (LEED) and Medium Energy Ion Scattering (MEIS) showed contradictory results, even on therelaxation general trend. Our current theoretical results support the LEED conclusions and are consistentqualitatively with other recent theoretical calculations. In addition, we study the interaction energy ofnitrogen atoms and molecules on the Fe(111) surface. The nitrogen atoms are adsorbed in the hollow siteof the unit cell, with an adsorption energy consistent with the one found in previous studies. In addition,we find the three molecularly adsorbed states that are observed experimentally. Two of them correspondto the adsorbed molecule oriented normal to the surface and a third one corresponds to the moleculeadsorbed parallel to the surface. We conclude that our results are accurate enough to be used to builda full six-dimensional potential energy surface for the N2 system.