Optimization of Spin-Unrestricted Density Functional Theory for Redox Properties of Rubredoxin Redox Site Analogues
Systematic studies of the accuracy of density functional theory (DFT) methods, especially the recently developed hybrid generalized gradient approximation (GGA) functionals, for structural and energetic properties of iron-sulfur redox sites are essential before these methods can be used to answer important biological questions about these systems. Here, the geometries, electronic structures, and reduction potentials of redox site analogs of the iron-sulfur protein rubredoxin are investigated using DFT (B3LYP, B97gga1 and BHandH), the Moller-Plesset perturbation theory series (MP2, MP3, MP4SDQ), and coupled cluster (CCSD, CCSD(T)) methods. For the geometries of [Fe(SCH3)4]2-/1- and [Fe(SCH3)3]1-/0, the DFT optimizations give reasonable values and the inclusion of a core electron basis substantially reduces the errors in the calculated geometries. However, for the vertical detachment energy (VDE) and adiabatic detachment energy (ADE) of [Fe(SCH3)4]1- and [Fe(SCH3)3]1-, the B3LYP functional gives the most accurately computed ADE and VDE using DFT, which are comparable with those at the CCSD level of theory. When diffuse functions are added to the sulfur basis set, they have little effect on the geometry optimization but significantly improve the calculated VDE and ADE, which is important for the anionic reduced sites. When multiple polarization functions are added to the sulfur basis set, they lead to a slightly better description of the geometry by giving more angular flexibility but underestimate ADE and VDE, most likely due to overestimating the stabilizing energy of the oxidized sites. Overall, the B3LYP calculations with the more flexible full-core basis sets give a reasonable description both of the geometry and of the ADE and VDE. Thus, improving the basis sets seems to be an efficient and convenient way to obtain reliable reduction potentials of the high-spin iron-sulfur redox sites.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 963586
- Report Number(s):
- PNNL-SA-36522; KC0301020; TRN: US200918%%401
- Journal Information:
- Journal of Chemical Theory and Computation, 5(5):1361-1368, Vol. 5, Issue 5
- Country of Publication:
- United States
- Language:
- English
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