D3 Correction Research Articles

Adsorption properties of boroxol ring doped zigzag boron nitride nanotube toward NO molecule using DFT

In previous researches it is demonstrated that reactivity and sensitivity of boron nitride nanotubes (BNNTs) toward gas molecules can be modified by impurity. In this work, oxygen defect for three nitrogen sites was used to study the adsorption of NO molecule through the surface of boroxol ring of oxygen doped BNNT (7,0) with different adsorption patterns, including side-on and end-on. All calculations are performed using the DFT-B3LYP/6-31G[Formula: see text] level of theory, and their electronic energies are corrected by gCP and D3 correction terms. High binding energies indicate that NO molecule undergoes chemical adsorption with large charge transfer from the tube which can significantly change electronic properties of the tube. Density of state (DOS) and partial DOS (PDOS) analyses revealed that adsorption of NO molecule on the boroxol ring position is covalent in nature with significant effect on the electronic properties of tube. The Laplacian of electron density, Lagrangian kinetic energy density, Hamiltonian kinetic energy density and potential energy density at bond critical points between the tube and NO indicate that the interaction between the tube and NO molecule is covalent in nature. Topological analysis of the electron localization function shows that electrons in the new formed bonds are approximately localized, meaning that the nature of adsorption process is chemical covalent. The studied nanotube is a suitable candidate to filter and eliminate NO gas molecule.

The contact of graphene with Ni(111) surface: description by modern dispersive forces approaches

Here we present a density-functional theory (DFT) study on the suitability of modern corrections for the inclusion of dispersion-related terms (DFT-D) in treating the interaction of graphene and metal surfaces, exemplified by the graphene/Ni(111) system. The Perdew–Burke–Ernzerhof exchange–correlation functional is used as basis, on top of which we tested the family of Grimme corrections (D2 and D3, including Becke–Johnson damping and the Andersson approach) as well as different flavors of the approach by Tkatchenko and Scheffler (TS). Two experimentally observed chemisorbed states, top-fcc and bridge-top conformations, were examined, as well as one physisorbed situation, the hcp-fcc state. Geometric, energetic, and electronic properties were compared to sets of experimental data for our model system of graphene/Ni(111), but also for available data of bulk Ni, graphite, and free-standing graphene. Results show that two of the most recent approximations, the fully ab initio TS–MBD, and the semi-empirical Grimme D3 correction are best suited to describe graphene–metal contacts, yet, comparing to earlier studies, the Rev-vdW-DF2 functional is also a good option, whereas optB86-vdW and optB88b-vdW functionals are fairly close to experimental values to be harmlessly used. The present results highlight how different approaches for the approximate treatment of dispersive forces yield different results, and so fine-tuning and testing of the envisioned approach for every specific system are advisable. The present survey clears the path for future accurate and affordable theoretical studies of nanotechnological devices based on graphene–metal contacts.

Ozonolysis mechanism of heterocyclic organic sulfides: A computational study

The reaction mechanism of the ozonation of benzothiophene (BT) and its derivatives was explored by using the density functional theory (DFT) considering the solvation effect in acetonitrile using both the COSMO implicit solvent approach and SMD solvent model with and without D3 corrections. Two pathways are proposed for ozonation of BT. The path through Criegee mechanism was found to be more favorable. Furthermore, we also calculated the ozonation of the derivatives of BT such as dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The reaction mechanisms of DBT and 4,6-DMDBT are different from that of BT. Based on the activation energies, the reactivity of BT and its derivatives to ozone are in the following order: BT>4, 6-DMDBT>DBT.

Conformation of six fentanyls revisited

Conformation of fentanyl and its five derivatives was studied at the B3LYP/6-31G∗∗ level. Two stereoisomers for α-methyl-β-hydroxy fentanyl and four for the ohmefentanyl were taken into account. Conformation in the gas phase and water, simulated using the IEF-PCM and SMD implicit models of solvents, was independently optimized using 27 starting structures resulted from rotations about the most important three torsion angles. The role of the Grimme’s D3 correction for the dispersion forces was additionally considered for each medium. The correction appeared to influence more the gas phase than water dissolved structures. Moreover, the correction influences more the conformations of N-phenylpropionamide group than those of the modified phenylethyl substituent. In water solution simulated by the IEF-PCM and SMD solvation models, the conformers connected to the phenylethyl moiety, are substantially different only for the two derivatives, for which indications coming from different computational variants are the most vague. However, for the conformers connected to the N-phenylpropionamide group, the IEF-PCM model favors the t conformation for three derivatives while SMD prefers sum of the g+ and g− conformations for the other three derivatives. For the ohmefentanyl stereoisomers, irrespectively, the solvation or presence of the D3 correction, all the methods concordingly predict the N-phenylpropionamide group conformation twisted by either −120° or to 120°.

Adsorption of carbon monoxide on boroxol-ring-doped zigzag boron nitride nanotube: Electronic study via DFT

Previous works have already demonstrated that reactivity and sensitivity of boron nitride nanotubes (BNNTs) toward gas molecules can be modified by impurity. In this work, three nitrogen atoms of BNNT \( (7,0)\) are replaced with oxygen to study the adsorption of CO molecule through the surface of boroxol ring with different adsorption patterns, including side-on and end-on. All calculations have been done using the DFT-B3LYP/6-31G * level of theory, and their electronic energies are corrected by gCP and D3 correction terms. The calculated binding energies are large, which indicates that CO molecule undergoes chemical adsorption. NBO results showed that the charge transfer occurs from the tube to the gas molecule, which can slightly change the electronic properties of the tube. Density of state (DOS) and partial DOS (PDOS) analysis revealed that adsorption of CO molecule on the boroxol ring position is covalent in nature. The Laplacian of electron density, Lagrangian kinetic energy density, Hamiltonian kinetic energy density, and potential energy density at bond critical points between the tube and CO indicate that the interaction between the tube and CO molecule is covalent in nature. Topological analysis of the electron localization function shows that electrons in the new formed bonds are approximately localized, meaning that the nature of the adsorption process is chemical covalent.

First-Principles Study of the Structural, Electronic, Dynamic, and Mechanical Properties of HOPG and Diamond: Influence of Exchange–Correlation Functionals and Dispersion Interactions

Various properties of two polymorphs of carbon, highly oriented pyrolytic graphite (HOPG) and diamond, were investigated at the ab initio level using different Hamiltonians with all-electron Gaussian-type functions (GTF) and projector augmented wave (PAW) basis sets. Their equilibrium lattice parameters, cohesive and interlayer interaction energies, band structures, vibrational frequencies, and elastic constants were evaluated. The calculations were performed at the Hartree–Fock, density functional theory (DFT), and hybrid (B3LYP and PBE0) levels. As regards DFT, the local density and generalized gradient (PBE and PBEsol) approximations were used. For GTF, the influence of the basis set superposition error (BSSE) was assessed. Since these approaches do not take dispersion interactions correctly into account, two different versions of Grimme’s dispersion correction, D2 and D3, were evaluated. The D2 and D3 corrections were reparameterized in order to reproduce the experimental structure of HOPG. For the properties depending on the description of the covalent bonds, such as the cohesive energy, C11 and C12, the dispersion corrections have a negligible influence. The best agreement is found for B3LYP-GTF-D3, PBE providing close results. For the properties depending on the description of the interaction between different layers, such as the interlayer interaction energies, C33, and C44, using the dispersion corrections improves the results. In general, D3 performs better than D2. PBE overall provides better results than the other functionals. As regards the basis sets, PAW describes the vibrational frequencies better than GTF due to the BSSE, whereas GTF provides a better description of the bandwidths and interband separations, elastic constants, and thermodynamical data. On the basis of the overall results, PBE-GTF-D3 appears to be a good compromise for an accurate description of the properties of graphite.

Gauge effects in local hybrid functionals evaluated for weak interactions and the GMTKN30 test set

ABSTRACTThe so-called ‘gauge problem’, due to the non-uniqueness of exchange-energy densities, is a fundamental challenge for density functionals depending on these energy densities, such as local hybrid functionals. We have recently demonstrated how gauge effects influence the potential-energy curves of the argon dimer, and other quantities depending on ‘non-physical’ Pauli repulsions introduced by incompatible gauges of (semi-)local and exact-exchange energy densities . Introduction of suitable calibration functions depending only on semi-local quantities allowed to correct for these deficiencies and suggested ways to obtain more accurate local hybrid functionals beyond the local spin density approximation (LSDA) exchange-energy density. Here we extend the study of the gauge problem by comparing a number of uncalibrated and calibrated local hybrids for (1) the potential-energy curves of further noble-gas dimers and (2) for the entire GMTKN30 test set and its individual subsets. We find that DFT-D3 dispersion corrections fitted to be compatible with uncalibrated local hybrids have to correct not only for missing London dispersion but also for gauge artefacts that make weak interactions too repulsive. This burden is taken away when using properly calibrated local hybrids, which perform much better for dispersion-sensitive quantities already without D3 corrections, and which require only the physically relevant dispersion to be corrected for. The present results suggest directions for further improvement of calibration functions for local hybrids.

Successful application of the DBLOC method to the hydroxylation of camphor by cytochrome p450.

The activation barrier for the hydroxylation of camphor by cytochrome P450 was computed using a mixed quantum mechanics/molecular mechanics (QM/MM) model of the full protein-ligand system and a fully QM calculation using a cluster model of the active site at the B3LYP/LACVP*/LACV3P** level of theory, which consisted of B3LYP/LACV3P** single point energies computed at B3LYP/LACVP* optimized geometries. From the QM/MM calculation, a barrier height of 17.5 kcal/mol was obtained, while the experimental value was known to be less than or equal to 10 kcal/mol. This process was repeated using the D3 correction for hybrid DFT in order to investigate whether the inadequate treatment of dispersion interaction was responsible for the overestimation of the barrier. While the D3 correction does reduce the computed barrier to 13.3 kcal/mol, it was still in disagreement with experiment. After application of a series of transition metal optimized localized orbital corrections (DBLOC) and without any refitting of parameters, the barrier was further reduced to 10.0 kcal/mol, which was consistent with the experimental results. The DBLOC method to CH bond activation in methane monooxygenase (MMO) was also applied, as a second, independent test. The barrier in MMO was known, by experiment, to be 15.4 kcal/mol. After application of the DBLOC corrections to the MMO barrier compute by B3LYP, in a previous study, and accounting for dispersion with Grimme's D3 method, the unsigned deviation from experiment was improved from 3.2 to 2.3 kcal/mol. These results suggested that the combination of dispersion plus localized orbital corrections could yield significant quantitative improvements in modeling the catalytic chemistry of transition-metal containing enzymes, within the limitations of the statistical errors of the model, which appear to be on the order of approximately 2 kcal/mole.

Unraveling the performance of dispersion-corrected functionals for the accurate description of weakly bound natural polyphenols.

Long-range non-covalent interactions play a key role in the chemistry of natural polyphenols. We have previously proposed a description of supramolecular polyphenol complexes by the B3P86 density functional coupled with some corrections for dispersion. We couple here the B3P86 functional with the D3 correction for dispersion, assessing systematically the accuracy of the new B3P86-D3 model using for that the well-known S66, HB23, NCCE31, and S12L datasets for non-covalent interactions. Furthermore, the association energies of these complexes were carefully compared to those obtained by other dispersion-corrected functionals, such as B(3)LYP-D3, BP86-D3 or B3P86-NL. Finally, this set of models were also applied to a database composed of seven non-covalent polyphenol complexes of the most interest. Graphical abstract Weakly bound natural polyphenolsᅟ.

Benchmark Calculations of Three-Body Intermolecular Interactions and the Performance of Low-Cost Electronic Structure Methods.

Many-body noncovalent interactions are increasingly important in large and/or condensed-phase systems, but the current understanding of how well various models predict these interactions is limited. Here, benchmark complete-basis set coupled cluster singles, doubles, and perturbative triples (CCSD(T)) calculations have been performed to generate a new test set for three-body intermolecular interactions. This "3B-69" benchmark set includes three-body interaction energies for 69 total trimer structures, consisting of three structures from each of 23 different molecular crystals. By including structures that exhibit a variety of intermolecular interactions and packing arrangements, this set provides a stringent test for the ability of electronic structure methods to describe the correct physics involved in the interactions. Both MP2.5 (the average of second- and third-order Møller-Plesset perturbation theory) and spin-component-scaled CCSD for noncovalent interactions (SCS-MI-CCSD) perform well. MP2 handles the polarization aspects reasonably well, but it omits three-body dispersion. In contrast, many widely used density functionals corrected with three-body D3 dispersion correction perform comparatively poorly. The primary difficulty stems from the treatment of exchange and polarization in the functionals rather than from the dispersion correction, though the three-body dispersion may also be moderately underestimated by the D3 correction.

Dispersion Corrections Improve the Accuracy of Both Noncovalent and Covalent Interactions Energies Predicted by a Density-Functional Theory Approximation.

The use of pairwise dispersion corrections together with dispersion-correcting potentials (DCPs) offers a computationally low-cost approach to improving the performance of a density-functional theory based method with respect to the prediction of important chemical properties. In this work, we develop DCPs for the C, H, N, and O atoms for use with the BLYP generalized gradient approximation functional coupled with "D3" pairwise dispersion corrections and 6-31+G(2d,2p) basis sets. The combined approach, referred to as BLYP-D3-DCP, offers generally improved performance over both unadorned BLYP and BLYP with D3 corrections with respect to the prediction of noncovalent binding energies (BEs) and covalent bond dissociation enthalpies (BDEs). Predicted barrier heights for a set of pericyclic and Diels-Alder reactions are improved in some instances, as are organic bond separation reaction energies and radical stabilization energies. It is also shown that the BLYP-D3-DCP approach outperforms B3LYP-D3 in the prediction of many chemical properties, in particular noncovalent BEs and BDEs, suggesting that the addition of D3 and DCP corrections, which have negligible computational cost, to simple density functionals like BLYP may elevate their performance to that of more complex functionals such as B3LYP.

Accurate Diels-Alder reaction energies from efficient density functional calculations.

We assess the performance of the semilocal PBE functional; its global hybrid variants; the highly parametrized empirical M06-2X and M08-SO; the range separated rCAM-B3LYP and MCY3; the atom-pairwise or nonlocal dispersion corrected semilocal PBE and TPSS; the dispersion corrected range-separated ωB97X-D; the dispersion corrected double hybrids such as PWPB95-D3; the direct random phase approximation, dRPA, with Hartree-Fock, Perdew-Burke-Ernzerhof, and Perdew-Burke-Ernzerhof hybrid reference orbitals and the RPAX2 method based on a Perdew-Burke-Ernzerhof exchange reference orbitals for the Diels-Alder, DARC; and self-interaction error sensitive, SIE11, reaction energy test sets with large, augmented correlation consistent valence basis sets. The dRPA energies for the DARC test set are extrapolated to the complete basis set limit. CCSD(T)/CBS energies were used as a reference. The standard global hybrid functionals show general improvements over the typical endothermic energy error of semilocal functionals, but despite the increased accuracy the precision of the methods increases only slightly, and thus all reaction energies are simply shifted into the exothermic direction. Dispersion corrections give mixed results for the DARC test set. Vydrov-Van Voorhis 10 correction to the reaction energies gives superior quality results compared to the too-small D3 correction. Functionals parametrized for energies of noncovalent interactions like M08-SO give reasonable results without any dispersion correction. The dRPA method that seamlessly and theoretically correctly includes noncovalent interaction energies gives excellent results with properly chosen reference orbitals. As the results for the SIE11 test set and H2(+) dissociation show that the dRPA methods suffer from delocalization error, good reaction energies for the DARC test set from a given method do not prove that the method is free from delocalization error. The RPAX2 method shows good performance for the DARC, the SIE11 test sets, and for the H2(+) and H2 potential energy curves showing no one-electron self-interaction error and reduced static correlation errors at the same time. We also suggest simplified DARC6 and SIE9 test sets for future benchmarking.

Theoretical and experimental investigation of crown/ammonium complexes in solution.

The Gibbs energies of association ΔGsolT between primary alkyl ammonium ions and crown ethers in solution are measured and calculated. Measurements are performed by isothermal titration calorimetry and revealed a strong solvent-dependent ion pair effect. Calculations are performed with density functional theory including Grimme's dispersion correction D3(BJ). The translational, rotational, and vibrational contributions to the Gibbs energy of association ΔGsolT are taken into account by a rigid-rotor-harmonic-oscillator approximation with a free-rotor approximation for low lying vibrational modes. Solvation effects δGseT are taken into account by applying the continuum solvation model COSMO-RS. Our study aims at finding a suitable theoretical method for the evaluation of the host guest interaction in crown/ammonium complexes as well as the observed ion pair effects. A good agreement of theory and experiment is only achieved, when solvation and the effects of the counterions are explicitly taken into account.

Non-parametrized functionals with empirical dispersion corrections: A happy match?

The performances of two parametrized functionals (namely B3LYP and B2PYLP) have been compared with those of two non-parametrized functionals (PBE0 and PBE0-DH) on a relatively large benchmark set when three different types of dispersion corrections are applied [namely the D2, D3 and D3(BJ) models]. Globally, the MAD computed using non-parametrized functionals decreases when adding dispersion terms although the accuracy not necessarily increases with the complexity of the model of dispersion correction used. In particular, the D2 correction is found to improve the performances of both PBE0 and PBE0-DH, while no systematic improvement is observed going from D2 to D3 or D3(BJ) corrections. Indeed when including dispersion, the number of sets for which PBE0-DH is the best performing functional decreases at the benefit of B2PLYP. Overall, our results clearly show that inclusion of dispersion corrections is more beneficial to parametrized double-hybrid functionals than to non-parametrized ones. The same conclusions globally hold for the corresponding global hybrids, showing that the marriage between non-parametrized functionals and empirical corrections may be a difficult deal.

Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of E[tbnd]UX3 (E = N, P, CH; X = H, F, Cl)

Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [EUX3] at DFT, DFT-D3, DFT-D3(BJ) and DFT-dDSc levels using different density functionals BP86, BLYP, PBE, revPBE, PW91, TPSS and M06-L. The stretching frequency of UN bond in [NUF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate UN vibrational frequencies follows the order BLYP>revPBE>BP86>PW91>TPSS>PBE>M06-L. The BLYP functional gives accurate value of the UE bond distances. The uranium atom in the studied compounds [EUX3] is positively charged. Upon going from [EUF3] to [EUCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan–Jug bond order for UE bonds ranges from 2.90 to 3.29. The UE bond dissociation energies vary with different density functionals as M06-L<TPSS<BLYP<revPBE<BP86<PBE≈PW91. The orbital interactions ΔEorb, in all studied compounds [EUX3] are larger than the electrostatic interaction ΔEelstat, which means the UN bonds in these compound have greater degree of covalent character (in the range 63.8–77.2%). The UE σ-bonding interaction is the dominant bonding interaction in the nitride and methylidyne complexes while it is weaker in [PUX3]. The dispersion energy contributions to the total bond dissociation energies are rather small. Compared to the Grimme’s D3(BJ) corrections, the Corminboeuf’s dispersion corrections are larger with metaGGA functionals (TPSS, M06-L) while smaller with GGA functionals.

Accurate Modeling of Organic Molecular Crystals by Dispersion-Corrected Density Functional Tight Binding (DFTB).

The ambitious goal of organic crystal structure prediction challenges theoretical methods regarding their accuracy and efficiency. Dispersion-corrected density functional theory (DFT-D) in principle is applicable, but the computational demands, for example, to compute a huge number of polymorphs, are too high. Here, we demonstrate that this task can be carried out by a dispersion-corrected density functional tight binding (DFTB) method. The semiempirical Hamiltonian with the D3 correction can accurately and efficiently model both solid- and gas-phase inter- and intramolecular interactions at a speed up of 2 orders of magnitude compared to DFT-D. The mean absolute deviations for interaction (lattice) energies for various databases are typically 2-3 kcal/mol (10-20%), that is, only about two times larger than those for DFT-D. For zero-point phonon energies, small deviations of <0.5 kcal/mol compared to DFT-D are obtained.

DFT-D3 Study of Some Molecular Crystals

We investigate the performance of the dispersion correction D3 with and without an explicit three-body dispersion term for the energetic and structural properties of rare gas and molecular crystals. Therefore, the two- and three-body gradient of the dispersion energy is implemented in the periodic plane-wave program VASP. It is combined with different density functionals at the level of the general gradient approximation (GGA) and hybrid functionals. Cohesive energies and lattice parameters for the rare gas crystals Ar, Kr, and Xe and a set of 23 molecular crystals are calculated and compared to experimental reference values. In general, all tested methods yield very good results. For the molecular crystals the mean absolute deviation of lattice energies from reference data (about 1–2 kcal/mol) is close to or below their uncertainties. The influence of the three-body Axilrod–Teller–Muto dispersion term on energy and structure is found to be rather small. While on a GGA level cohesive energies become sligh...

Nature of Noncovalent Interactions in Catenane Supramolecular Complexes: Calibrating the MM3 Force Field with ab Initio, DFT, and SAPT Methods

The design and assembly of mechanically interlocked molecules, such as catenanes and rotaxanes, are dictated by various types of noncovalent interactions. In particular, [C-H···O] hydrogen-bonding and π-π stacking interactions in these supramolecular complexes have been identified as important noncovalent interactions. With this in mind, we examined the [3]catenane 2·4PF6 using molecular mechanics (MM3), ab initio methods (HF, MP2), several versions of density functional theory (DFT) (B3LYP, M0X), and the dispersion-corrected method DFT-D3. Symmetry adapted perturbation theory (DFT-SAPT) provides the highest level of theory considered, and we use the DFT-SAPT results both to calibrate the other electronic structure methods, and the empirical potential MM3 force field that is often used to describe larger catenane and rotaxane structures where [C-H···O] hydrogen-bonding and π-π stacking interactions play a role. Our results indicate that the MM3 calculated complexation energies agree qualitatively with the energetic ordering from DFT-SAPT calculations with an aug-cc-pVTZ basis, both for structures dominated by [C-H···O] hydrogen-bonding and π-π stacking interactions. When the DFT-SAPT energies are decomposed into components, we find that electrostatic interactions dominate the [C-H···O] hydrogen-bonding interactions, while dispersion makes a significant contribution to π-π stacking. Another important conclusion is that DFT-D3 based on M06 or M06-2X provides interaction energies that are in near-quantitative agreement with DFT-SAPT. DFT results without the D3 correction have important differences compared to DFT-SAPT, while HF and even MP2 results are in poor agreement with DFT-SAPT.

Torsional barriers of substituted biphenyls calculated using density functional theory: a benchmarking study

The barriers of torsional isomerization of 13 substituted biphenyls, ranging from 7.4 to 44 kcal mol(-1), were calculated using 9 density functionals (the BP86 and B97D GGAs, the meta-GGA TPSS, hybrids B3LYP, PBE0, ωB97XD, BMK and M06-2X, as well as the double-hybrid B2PLYP), some combined with D and D3 corrections for dispersive interactions, and results were compared with experimental data. As attractive dispersive interactions between substituents had a significant impact on the geometries and stabilities of the ground and transition states of the torsional isomerization pathways, the B3LYP-D, B97-D and TPSS-D3 functionals were identified as the most promising methods, and were used to determine the torsional barriers of 33 other substituted biphenyls with known Gibbs energies of activation (6.0 to 45 kcal mol(-1)). Throughout the 46-member ensemble, results were very accurate relative to experimental values (mean deviation between -0.38 and 0.24 kcal mol(-1)), and narrow distributions of errors were obtained (root-mean-square deviations between 0.14 and 0.16 kcal mol(-1); mean absolute deviations ranging from 0.61 to 0.75 kcal mol(-1)), as long as (1) large triple-ζ basis sets were used, (2) all conformations were screened at these levels of theory, (3) electronic energies were corrected with zero-point energies and entropic contributions, and (4) solvation effects were taken into account for biphenyl derivatives bearing charged ortho-substituents. With its simple procedures, this study is intended as a benchmark for future determinations of torsional barriers of various biphenyl derivatives.

The Cobalt-Methyl Bond Dissociation in Methylcobalamin: New Benchmark Analysis Based on Density Functional Theory and Completely Renormalized Coupled-Cluster Calculations.

The Co-CMe bond dissociation in methylcobalamin (MeCbl), modeled by the Im-[Co(III)corrin]-Me(+) system consisting of 58 atoms, is examined using the coupled-cluster (CC), density-functional theory (DFT), complete-active-space self-consistent-field (CASSCF), and CASSCF-based second-order perturbation theory (CASPT2) approaches. The multilevel variant of the local cluster-in-molecule framework, employing the completely renormalized (CR) CC method with singles, doubles, and noniterative triples, termed CR-CC(2,3), to describe higher-order electron correlation effects in the region where the Co-CMe bond breaking takes place, and the canonical CC approach with singles and doubles (CCSD) to capture the remaining correlation effects, abbreviated as CR-CC(2,3)/CCSD, is used to obtain the benchmark potential energy curve characterizing the Co-CMe dissociation in the MeCbl cofactor. The Co-CMe bond dissociation energy (BDE) resulting from the CR-CC(2,3)/CCSD calculations for the Im-[Co(III)corrin]-Me(+) system using the 6-31G* basis set, corrected for the zero-point energies (ZPEs) and the effect of replacing the 6-31G* basis by 6-311++G**, is about 38 kcal/mol, in excellent agreement with the experimental values characterizing MeCbl of 37 ± 3 and 36 ± 4 kcal/mol. Of all DFT functionals examined, the best dissociation energies and the most accurate description of the Co-CMe bond breaking in the Im-[Co(III)corrin]-Me(+) system are provided by B97-D and BP86 corrected for dispersion using the D3 correction of Grimme et al., which give 35 and 40 kcal/mol, respectively, when the 6-311++G** basis set is employed and when the results are corrected for ZPEs and basis set superposition error. None of the other DFT approaches examined provide results that fall into the experimental range of the Co-CMe dissociation energies in MeCbl of 32-40 kcal/mol. The hybrid DFT functionals with a substantial amount of the Hartree-Fock (HF) exchange, such as B3LYP, considerably underestimate the calculated dissociation energies, with the magnitude of the error being proportional to the percentage of the HF exchange in the functional. It is argued that the overstabilization of diradical structures that emerge as the Co-CMe bond is broken and, to some extent, the neglect of dispersion interactions at shorter Co-CMe distances, postulated in previous studies, are the main factors that explain the substantial underestimation of the Co-CMe BDE by B3LYP and other hybrid functionals. Our calculations suggest that CASSCF and CASPT2 may have difficulties with providing a reliable description of the Co-CMe bond breaking in MeCbl, since using adequate active spaces is prohibitively expensive.