Abstract
The combination of density functional theory (DFT) with a multiconfigurational wave function is an efficient way to include dynamical correlation in calculations with multiconfiguration self-consistent field wave functions. These methods can potentially be employed to elucidate reaction mechanisms in bio-inorganic chemistry, where many other methods become either too computationally expensive or too inaccurate. In this paper, a complete active space (CAS) short-range DFT (CAS-srDFT) hybrid was employed to investigate a bio-inorganic system, namely H2 binding to the active site of [NiFe] hydrogenase. This system was previously investigated with coupled-cluster (CC) and multiconfigurational methods in the form of cumulant-approximated second-order perturbation theory, based on the density matrix renormalization group (DMRG). We find that it is more favorable for H2 to bind to Ni than to Fe, in agreement with previous CC and DMRG calculations. The accuracy of CAS-srDFT is comparable to both CC and DMRG, despite much smaller active spaces were employed than in the corresponding DMRG calculations. This enhanced efficiency at the smaller active spaces shows that CAS-srDFT can become a useful method for bio-inorganic chemistry.
Highlights
Another serious problem is that all complete active space (CAS) methods, even with very large active spaces, neglect a major part of the dynamical correlation
To recover the missing dynamical correlation, perturbation theory is normally employed after a complete active space selfconsistent field (CASSCF) or density matrix renormalization group (DMRG)–self-consistent field (SCF) calculation, as done in CASPT216,21–24 or NEVPT2.20,25,26 the perturbation correction comes with additional computational cost
We have compared the results of CAS–srPBE with previously published CCSD(T) and cumulant approximated DMRG–CASPT2 calculations for the two binding modes of H2 to the active site of [NiFe] hydrogenase.[58]
Summary
Another serious problem is that all CAS methods, even with very large active spaces, neglect a major part of the dynamical correlation. An efficient method to recover the dynamical correlation in multiconfigurational methods is to merge DFT with a multiconfigurational wave function, thereby capitalizing on the efficient treatment of semi-local dynamical electron correlation within DFT methods. Has the advantage that the multiconfigurational wave function can include static correlation.[27,28,29,30,31] In this paper, we explore the multiconfigurational short-range DFT (MC–srDFT) method. We study the method’s dependence on the size of the active space and the employed basis set
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