Electronic Structure of Iron Porphyrin Adsorbed to the Pt(111) Surface

Systematic density functional theory calculations that treat the strong on-site 3d electron electron interactions on iron via a Hubbard U-eff = 3.0 eV and the van der Waals (vdW) interactions between the substrate and adsorbate within the vdW-DF framework are employed to study the adsorption of the iron porphyrin (FeP) molecule to the Pt(111) surface. The more accurate vdW-DF-optPBE and vdW-DF-optB88 functionals found the same binding site to be the most stable and yielded binding energies that were within similar to 20% of each other, whereas the binding energies computed with the vdW-DF-revPBE functional were substantially weaker. This work highlights the importance of vdW interactions for organometallic molecules chemisorbed to transition metal surfaces. The stability of the binding sites was found to depend upon the number of Fe-Pt and C-Pt bonds that were formed. Whereas in the gas phase the most stable spin state of FeP is the intermediate spin S = 1 state, the high spin S = 2 state is preferred for the FeP Pt(111) system on the binding sites considered herein. The spin switch results from the elongation of the Fe-N bonds that occur upon adsorption.