Validation of Exchange−Correlation Functionals for Spin States of Iron Complexes

Abstract

Spin state energies of iron complexes are important for biochemical applications such as the catalytic cycle of cytochrome P450. Due to the size of these systems and the presence of iron, accurate computational results can be obtained only with density functional theory (DFT). Validation of exchange−correlation (xc) DFT functionals for predicting the correct spin ground state of iron complexes is a rather unexplored area. In this contribution we report a systematic study on the performance of several xc functionals for seven iron complexes that are experimentally found to have either a low, intermediate, or high spin ground state. Standard xc functionals like LDA, BLYP, and PBE are found to disfavor high spin states, whereas hybrid and some meta-GGA functionals do provide the correct spin ground state for all molecules. Recently improved pure DFT functionals such as Handy's optimized exchange (OPTX) also perform well. The origin for the apparent performance of the DFT functionals has been addressed and seems to be related to the inclusion of fourth-order terms (s 4) of the dimensionless (or reduced) density gradient s in the exchange functional.

Computational Insight into the Mechanism of Alkane Hydroxylation by Non-heme Fe(PyTACN) Iron Complexes. Effects of the Substrate and Solvent

“…Previous validation studies have shown the validity of the OPBE functional for the spin-state splittings of iron complexes. [51][52][53][54] The comparison between UB3LYP and UOPBE spin ground states indicates that same qualitative pictures are obtained with the two functionals. The same conclusion was drawn by de Visser et al when comparing the spin state splittings obtained using the UB3LYP, UBLYP, UB3PW91, and TPSS functionals.…”

Titanium as a Potential Addition for High-Capacity Hydrogen Storage Medium

“…Equilibrium structures were optimized using analytical gradient techniques, with geometries and energies calculated at the OLYP [15,16] level of theory. Our choice for the functional is motivated by its superior performance for the relative energies of different spin states of various transition-metal complexes in the gas phase, in particular when high-spin states are involved [17][18][19]. Interactions between H 2 molecules and the C 6 H 6 -Ti complexes were analyzed using the molecular fragment method that is a standard tool in energy decomposition methods for interactions between molecules, as detailed in Reference [11].…”

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