Ab-Initio simulation of heme using GGA+U: a step toward accurate spin state energetics

DAMIAN SCHERLIS, MATTEO COCOCCIONI, NICOLA MARZARI

Los Angeles, USA

Congreso; 2005 Meeting of the American Physical Society; 2005

American Physical Society

Enzymatic sites containing transition metals areamong the most relevant biophysical systems currently studiedusing first-principles quantum mechanical approaches. In his context, however,the application of ab-initio methods is severely limitedas a consequence of the inability of conventional electronicstructure methods - as Hartree-Fock or Density Functional Theory (DFT) - to provide, in many cases, a qualitativelycorrect description of the spin-state energetics of the metal center. This is a key issue in the simulation of transition metal active sites, whereas function and spin state are intimately related.In this work we apply the LDA+U methodto compute the low lying states of ligated and unligated iron hemecomplexes, as well as other iron and manganese compounds.This technique, in which the U term is obtained in a fully ab-initiofashion using linear response theory, was originally introducedto correct for DFT-GGA inacuracies in strongly correlatedmaterials in the solid state. In this presentation we showthis methodology is extremely useful for the treatment of organometalliccompounds, in particular the heme system, where DFT functionals predict the wrong spin energetics. Calculations of ligand exchange thermodynamics, spin transitions, and dynamical properties,point to LDA+U as an appealing tool to overcome the limitations entailed by the use of DFT in the description of bioinorganic complexes.