One-electron Density Research Articles

Symmetry Breaking of Electronic Structure upon the π→π* Excitation in Anthranilic Acid Homodimer

The main purpose of this study is to characterize the nature of the low-energy singlet excited states of the anthranilic acid homodimer (AA2) and their changes (symmetry breaking) caused by deformation of the centrosymmetric, ground state structure of AA2 towards the geometry of the S1 state. We employ both the correlated ab initio methods (approximate Coupled Clusters Singles and Doubles—CC2 and CASSCF/NEVPT2) as well as the DFT/TDDFT calculations with two exchange–correlation functionals, i.e., B3LYP and CAM-B3LYP. The composition of the wavefunctions is investigated using the one-electron transition density matrix and difference density maps. We demonstrate that in the case of AA2, small asymmetric distortions of geometry bring about unproportionally large changes in the excited state wavefunctions. We further provide comprehensive characterization of the AA2 electronic structure, showing that the excitation is nearly completely localized on one of the monomers, which stands in agreement with the experimental evidence. The excitation increases the π-electronic coupling of the substituents and the aromatic ring, but only in the excited monomer, while the changes in the electronic structure of the unexcited monomer are negligible (after geometry relaxation). The increased electronic density strengthens both intra- and intermolecular hydrogen bonds formed by the carbonyl oxygen atom of the excited monomer, making them significantly stronger than in the ground state. Although the overall pattern of changes remains qualitatively consistent across all methods employed, CC2 predicts more pronounced excitation-induced modifications of the electronic structure compared to the more routinely used TDDFT approach. The most important deficiency of the B3LYP functional in the present context is locating two charge-transfer states at erroneously low energies, in close proximity of the S1 and S2 states. The range-corrected CAM-B3LYP exchange–correlation functional gives a considerably improved description of the CT states at the price of overshot excitation energies.

The Aromaticity of Osmapentalenes Derivatives - An Analysis Based on Electron-Delocalization Indices.

A systematic investigation of the aromatic features of the electronic structures of a family of recently synthesized osmapentalene derivatives has been carried by means of indices derived from the calculated one-electron density matrix of the corresponding geometry optimized compounds, and complemented by the analysis of the valence molecular orbitals and the delocalized bonding units emerging from the adaptive natural density partitioning method. The calculated delocalization indices between consecutive atom pairs, and normalized multicenter indices are very suggestive of the aromatic character of the equatorial fused carbon rings (except triangular ones) for all the members of the family. Since the electron-delocalization based indices allow precise quantification of the aromaticity, differences of the aromatic character among the various members have also been highlighted, and have been found to be consistent with the magnetic based criteria indices reported earlier. Finally, the valence molecular orbitals along with the delocalized bonding units of the adaptive natural density partitioning indicate that the aromaticity of these compounds is sustained by either 10 or 14 π electrons, which satisfy the Hückel aromatic electron counting rule.

Exploring Interatomic Electron Transfer and Metal-Ligand Binding Mechanism in Trimethylenemethane Iron Tricarbonyl: Insights from Potentials per Electron and Corresponding Force Density Fields.

This study employs an analysis of the per-electron potentials and the superposition of the electrostatic and kinetic force fields, Fes(r) and Fk(r), and the gradients of the potential energy and one-electron densities to investigate the binding mechanism in trimethylenemethane iron tricarbonyl complex (TMM)Fe(CO)3. Our approach permits the delineation of the "ligand-binding" force field generated by the metal nucleus but partially operating within the ligand atoms. A mechanical rationale for metal-ligand interactions is thus presented: In the corresponding area, the attractive force Fes(r) provides the backdrop against which the homotropic static force (r) and the heterotropic kinetic force Fk(r) exert attractive and repulsive influences, respectively, toward the metal nucleus on a portion of the electrons belonging to the ligand atoms. This area thus represents electron sharing, which emerges as a quantum chemical response against the metal-to-ligand electron transfer. It has been demonstrated that the response is facilitated by the decreased potential energy density in the vicinity of the interatomic surface. Our findings indicate that the polar coordination bonds in (TMM)Fe(CO)3 exhibit notable quantum chemical responses. However, the previously described nonbonded contact also features an unexpectedly pronounced response, despite the absence of a bond path. It can be proposed that the unforeseen response is a consequence of the formation of the 18-electron, closed valence shell, rather than an indication of the establishment of an organometallic chemical bond.

Plain Capping for Improved Accuracy of Approximate One- and Two-Electron Densities at Two-Particle Coalescence Points.

The values of the one-electron and intracule densities at two-particle coalescence points that enter the expressions for relativistic corrections to energies of Coulombic systems cannot be efficiently computed with sufficient accuracy from approximate wave functions expressed in terms of cuspless basis functions such as the explicitly correlated Gaussians. A new approach to alleviation of this problem, called plain capping, is proposed. Unlike those offered by the previously published formalisms, such as the expectation value identities and integral transforms, the accuracy improvements effected by the plain capping are attained with negligible computational effort and minimum programming. In the case of the on-top two-electron densities, whose accurate computation is particularly costly, the plain capping constitutes the only viable means of error reduction available at present.

Ultrafast x-ray scattering and electronic coherence at avoided crossings: complete isotropic signals

Nonadiabatic transitions at conical intersections and avoided crossings play a pivotal role in shaping the outcomes of photochemical reactions. Using the photodissociation of LiF as a model, this theoretical study explores the application of gas phase nonresonant ultrafast x-ray scattering to map nonadiabatic transitions at an avoided crossing, utilizing the part of the scattering signal that probes electronic coherence directly. The presented scattering signals are rotationally averaged and calculated from two- rather than one-electron (transition) densities, which inherently accounts for all possible electronic transitions driven by the x-ray photon. This approach provides quantitative predictions of the experimental signals, thereby facilitating future experimental endeavors to observe nonadiabatic effects and coherent electron dynamics with ultrafast x-ray scattering.

Excitonic Configuration Interaction: Going Beyond the Frenkel Exciton Model.

We present the excitonic configuration interaction (ECI) method─a fragment-based analogue of the CI method for electronic structure calculations of multichromophoric systems. It can also be viewed as a generalization of the exciton approach, with the following properties: (i) It constructs the effective Hamiltonian exclusively from monomer calculations. (ii) It employs the strong orthogonality assumption and is exact within McWeeny's group function theory, thus requiring only one-electron density matrices of the monomer states. (iii) It is agnostic of the monomer electronic structure method, allowing us to use/combine different methods. (iv) It includes an embedding point charge scheme (called excitonic Hartree-Fock, EHF) to improve the accuracy of the monomer states, but such that the effective full-system Hamiltonian is not explicitly dependent on the embedding. (v) It is systematically improvable, by expanding the set of monomer states and by including configurations where two or more monomers are excited (defining the ECIS, ECISD, etc., methods). The performance of ECI is assessed by computing the absorption spectrum of two exemplary multichromophoric systems, using CIS as the monomer electronic structure method. The accuracy of ECI significantly depends on the chosen embedding charges and the ECI expansion. The most accurate assessed combinations─ECIS or ECISD with EHF embedding─yield spectra that agree qualitatively and quantitatively with full-system direct calculations, with deviations of the excitation energies below 0.1 eV. We also show that ECISD based on CIS monomer calculations can predict states where two monomers are excited simultaneously (e.g., triplet-triplet double-local excitations) that are inaccessible in a full-system CIS calculation.

A numerical Poisson solver with improved radial solutions for a self-consistent locally scaled self-interaction correction method

The universal applicability of density functional approximations is limited by self-interaction error made by these functionals. Recently, a novel one-electron self-interaction-correction (SIC) method that uses an iso-orbital indicator to apply the SIC at each point in space by scaling the exchange-correlation and Coulomb energy densities was proposed. The locally scaled SIC (LSIC) method is exact for the one-electron densities, and unlike the well-known Perdew–Zunger SIC (PZSIC) method recovers the uniform electron gas limit of the uncorrected density functional approximation, and reduces to PZSIC method as a special case when isoorbital indicator is set to the unity. Here, we present a numerical scheme that we have adopted to evaluate the Coulomb potential of the electron density scaled by the iso-orbital indicator required for the self-consistent LSIC calculations. After analyzing the behavior of the finite difference method (FDM) and the green function solution to the radial part of the Poisson equation, we adopt a hybrid approach that uses the FDM for the Coulomb potential due to the monopole and the GF for all higher-order terms. The performance of the resultant hybrid method is assessed using a variety of systems. The results show improved accuracy than earlier numerical schemes. We also find that, even with a generic set of radial grid parameters, accurate energy differences can be obtained using a numerical Coulomb solver in standard density functional studies.

SPAHM(a,b): Encoding the Density Information from Guess Hamiltonian in Quantum Machine Learning Representations.

Recently, we introduced a class of molecular representations for kernel-based regression methods─the spectrum of approximated Hamiltonian matrices (SPAHM)─that takes advantage of lightweight one-electron Hamiltonians traditionally used as a self-consistent field initial guess. The original SPAHM variant is built from occupied-orbital energies (i.e., eigenvalues) and naturally contains all of the information about nuclear charges, atomic positions, and symmetry requirements. Its advantages were demonstrated on data sets featuring a wide variation of charge and spin, for which traditional structure-based representations commonly fail. SPAHM(a,b), as introduced here, expand the eigenvalue SPAHM into local and transferable representations. They rely upon one-electron density matrices to build fingerprints from atomic and bond density overlap contributions inspired from preceding state-of-the-art representations. The performance and efficiency of SPAHM(a,b) is assessed on the predictions for data sets of prototypical organic molecules (QM7) of different charges and azoheteroarene dyes in an excited state. Overall, both SPAHM(a) and SPAHM(b) outperform state-of-the-art representations on difficult prediction tasks such as the atomic properties of charged open-shell species and of π-conjugated systems.

Contrasting the excited state properties of different conformers of trans- and cis-2,2'-bipyridine oligomers in the gas phase.

In this article, we present conformation-dependent photophysical and excited state properties of trans- and cis- BPY oligomers. Oligomers up to tetramers for three conformers, namely, o-, m-, and p-, are constructed and optimized at the B3LYP-D3/def2-SVPD level. The photophysical and excited state properties are interpreted in terms of UV and CD spectra at the RI-ADC(2)/def2-TZVPD level. The UV spectra of oligomers of the m-conformer show high-intensity and red-shifted UV bands compared to o- and p-oligomers. The CD spectra of p-oligomers show intense CD bands compared to o- and p-oligomers in the case of trans-structures. In contrast, oligomers of each conformer of cis-structures show high-intensity CD bands. The excited states of (BPY)2 and (BPY)4 are also characterized by analysis of one-electron transition density matrix considering three descriptors: ωCT, dexc, and PRNTO. The ωCT values of dimers are in the range of 0.06-0.32, which indicates the excited states are mainly LE states, whereas, for (BPY)4, the ωCT values range from 0.17 to 0.53, indicating the possibility of partial CT in the excited states. These observations are also explained using the NTOs and e-h correlation plots.

Excited state properties of an A-D-A non-fullerene electron acceptor: a LC-TD-DFTB study.

Understanding charge transfer processes is essential to estimate the performance of organic photovoltaic technologies. Although experimental production is on the rise, predictability strongly relies on theoretical modeling, which is limited to the size of semiconductors. As a computationally favorable approach, we benchmarked the long-range corrected (LC) time-dependent (TD) formulation of the semi-empirical density functional-based tight-binding method (DFTB) for three polycyclic aromatic hydrocarbons (PAHs) and studied the DTP-IC-4Ph molecule, a PAH-based non-fullerene electron acceptor (NFA) with an A-D-A backbone structure. After a thorough investigation into the long-range parameter (ω) tuning for naphthalene, anthracene and pyrene, the excitation energies, oscillator strengths and Natural Transition Orbitals (NTOs) were compared with the standard ωB97X-D/6-31G(d,p) level of theory and the ADC2/6-31G(d,p) multiconfigurational method. We estimated mobility-related properties of the NFA and considered 1000 thermally accessible configurations to qualitatively reproduce the experimental absorption profile and investigate the energetic disorder. Finally, we conducted a fragment-based analysis using the one-electron transition density matrix (1TDM) to determine the character of the excited states and investigate the effect of side chains on exciton formation. Our results are sensitive to the level of theory and highly dependent on the long-range parameter but suggest that the presence of alkyl chains promotes a higher average charge delocalization and allows for additional hopping mechanisms, favoring the charge transfer dynamics.

Evaluation of Coulomb integrals with various energy operators to estimate the correlation energy in electronic structure calculations for molecules

Using energy operators RC1-nRD1-m, RC1-nr12-m, and r12-nr13-m with small (n, m) values is fundamental in electronic structure calculations. Analytical integrations of the cases (n, m) = (1, 0) and (0, 1) are based on the Laplace transformation with the integrand exp(-a2t2), the other cases are based on the Laplace transformation with the integrand exp(-a2t) and the two-dimensional version of the Boys function. These analytic expressions, with Gaussian function integrands, are useful for manipulation with higher moments of interelectronic distances, for example, in correlation calculations. The equations derived help to evaluate the one-, two-, and three-electron Coulomb integrals, òρ(1)RC1-nRD1-mdr1, òρ(1)ρ(2)RC1-nr12-mdr1dr2, and òρ(1)ρ(2)ρ(3)r12-nr13-mdr1dr2dr3, wherein ρ(i) is the one-electron density describing the electron clouds in molecules, solids, or any media or ensemble of materials. Analytical solutions to integrals are more useful than numeric solutions; however, the former is not available in many cases. We evaluate these integrals numerically, even more so, the òf(ρ(1))dr1 to òf(ρ(1),ρ(2),ρ(3))dr1dr2dr3 with the analytical function f. For this task, the commonly used density functional theory numerical integration scheme has been elaborated to 6 and 9 dimensions via Descartes product. More importantly, this numerical integration scheme works not only for Gaussian type but also for Slaterian types. Analogy is commented on in terms of the powerful empirical correction between quantum potential energy correction and the empirically corrected Newton’s universal law of gravity in the explanation of dark matter and energy, as well as its relation to Hartree-Fock and Kohn-Sham formalisms.

Elucidating the conformational change and electronic absorption spectrum of p-dimethylamino-cinnamaldehyde merocyanine across different solvent polarities.

We present a theoretical study on the structural and electronic properties of the p-dimethylamino-cinnamaldehyde (DMACA) merocyanine molecule in solvents of different polarities by combining the free energy gradient and the average solvent electrostatic configuration methods via an iterative procedure based on the sequential quantum mechanics/molecular mechanics hybrid methodology. Studying such a system in solution is a crucial step for understanding the solvent effects on its properties, which can have implications in fields such as optoelectronics and biophysics. We found that the DMACA molecule presents different geometries in nonpolar and polar solvents, changing from a polyene-like structure with a pyramidal dimethylamino group (in gas phase or nonpolar solvents) to a cyanine-like structure with a planar dimethylamino group in water due to the stabilizing effect of hydrogen bonds between DMACA and water. The molecular absorption spectrum showed a significant change, increasing solvent polarity with a large shift of the lower energy band, while the other two low lying bands did not shift significantly. The study accurately described the solvatochromic shift of the lowest-energy band and analyzed the structure of the excited states in terms of the one-electron transition density matrix, which showed that the dominant excited state (associated with the first lower energy band) is characterized by a local excitation on the benzene ring with charge transfer character to the carbon conjugated segment.

Stability of a two-electron system under pressure confinement: structural and quantum information theoretical analysis

The stability of a two-electron Zee system trapped inside an impenetrable spherical cavity is analyzed using an explicitly correlated multi-exponent Hylleraas-type basis set in the framework of the Ritz variational method. The wave function is considered to be consistent with Dirichlet’s boundary condition. Four different values are considered, where denotes the critical nuclear charge beyond which the system is embedded in a discrete positive energy continuum due to the impenetrable nature of the cavity. The energy contribution due to the total correlation (in the presence of both radial and angular correlation) effect, the radial correlation limit, and the angular correlation limit are also studied in detail. The thermodynamic pressure felt by the two-electron Zee system inside the cavity is estimated, and a formula replicating the behavior between the pressure and volume of the cavity is deduced by a fitting procedure. Different geometrical properties, e.g. radial moments (, , , , ; p = ), angular moments (, ), and related important physical quantities, are determined. The variation of Kirkwood and Buckingham polarizabilities w.r.t. the pressure felt by the two-electron Zee system is analyzed. A one-electron radial density is estimated for each pair of (), which has been employed to generate the electrostatic potential as well as different information theoretical measures like Shannon entropy, Fisher entropy, Rényi entropy, Tsallis entropy, and Onicescu informational energy. The chosen information theoretical measures have been found to be sensitive tools for describing changes in the electronic structure due to spatial confinement. An interesting interplay between the electronic and nuclear contribution to the classical electrostatic potential is observed, leading to a shift in the position of its characteristic minimum due to compression. Wherever possible, a comparison is made in order to ascertain the high accuracy of our numerical results. The procedure of analytic evaluation of the integrals needed to estimate the atomic properties under consideration is discussed in detail.

Phenomenological description of the acidity of the citric acid and its deprotonated species: informational-theoretical study.

In spite of the fact that molecular acidity is a fundamental physicochemical property of molecular systems, the vast majority of theoretical studies have focused attention on monoprotic acids and on the prediction of pKa's. Polyprotic acids, represent a challenge for electronic structure calculations since the multiple acidic sites result in a vast group of species with different conformations and reactivities. In this work, Information-theoretic (IT) concepts of localizability, order and uniformity are applied to the Citric Acid and its deprotonated species through the one-electron density functionals: Shannon entropy (S), Fisher information (I) and Disequilibrium (D), respectively. We pursue the goal of characterizing the acidity of the aforementioned species with the aim to associate the IT concepts to chemical features such as the polarizability of the protonated/deprotonated species, the liability of the acidic sites, atomic electrostatic potentials, covalent bonding. IT analyses looks very promising for future studies on the acidity of specific deprotonation-sites of polyprotic acids. Density functional theory (DFT) calculations were performed with Gaussian 09 program. A sensitivity analysis of the IT-measures was performed for the citric acid and the citrate using B3LYP, B3PW91, BPW91, M05-2X, M06-2X and PBEPBE functionals with the 6-311++g(3df,2p), 6-311++g(d,p), 6.311+g(d,p) and aug-cc-pVDZ basis sets. The rest of the analysis was performed with the M05-2X/6-311+G(d,p) level of theory. Additionally, aqueous media was considered by use of the SMD solvent model. The IT-measures were calculated using a suite of programs developed in our laboratory jointly with the DGRID software package.

Automatic characterization of drug/amino acid interactions by energy decomposition analysis

The computational study of drug/protein interactions is fundamental to understand the mode of action of drugs and design new ones. In this study, we have developed a python code aimed at characterizing the nature of drug/amino acids interactions in an accurate and automatic way. Specifically, the code is interfaced with different software packages to compute the interaction energy quantum mechanically, and obtain its different contributions, namely, Pauli repulsion, electrostatic and polarisation terms, by an energy decomposition analysis based on one-electron and two-electron deformation densities. The code was tested by investigating the nature of the interaction between the glycine amino acid and 250 drugs. An energy-structure relationship analysis reveals that the strength of the electrostatic and polarisation contributions is related with the presence of small and large size heteroatoms, respectively, in the structure of the drug.

SQMBox: Interfacing a semiempirical integral library to modular ab initio electronic structure enables new semiempirical methods.

Ab initio and semiempirical electronic structure methods are usually implemented in separate software packages or use entirely different code paths. As a result, it can be time-consuming to transfer an established ab initio electronic structure scheme to a semiempirical Hamiltonian. We present an approach to unify ab initio and semiempirical electronic structure code paths based on a separation of the wavefunction ansatz and the needed matrix representations of operators. With this separation, the Hamiltonian can refer to either an ab initio or semiempirical treatment of the resulting integrals. We built a semiempirical integral library and interfaced it to the GPU-accelerated electronic structure code TeraChem. Equivalency between ab initio and semiempirical tight-binding Hamiltonian terms is assigned according to their dependence on the one-electron density matrix. The new library provides semiempirical equivalents of the Hamiltonian matrix and gradient intermediates, corresponding to those provided by the ab initio integral library. This enables the straightforward combination of semiempirical Hamiltonians with the full pre-existing ground and excited state functionality of the ab initio electronic structure code. We demonstrate the capability of this approach by combining the extended tight-binding method GFN1-xTB with both spin-restricted ensemble-referenced Kohn-Sham and complete active space methods. We also present a highly efficient GPU implementation of the semiempirical Mulliken-approximated Fock exchange. The additional computational cost for this term becomes negligible even on consumer-grade GPUs, enabling Mulliken-approximated exchange in tight-binding methods for essentially no additional cost.

Self-consistent implementation of locally scaled self-interaction-correction method.

Recently proposed local self-interaction correction (LSIC) method [Zope et al., J. Chem. Phys. 151, 214108 (2019)] is a one-electron self-interaction-correction (SIC) method that uses an iso-orbital indicator to apply the SIC at each point in space by scaling the exchange-correlation and Coulomb energy densities. The LSIC method is exact for the one-electron densities, also recovers the uniform electron gas limit of the uncorrected density functional approximation, and reduces to the well-known Perdew-Zunger SIC (PZSIC) method as a special case. This article presents the self-consistent implementation of the LSIC method using the ratio of Weizsäcker and Kohn-Sham kinetic energy densities as an iso-orbital indicator. The atomic forces as well as the forces on the Fermi-Löwdin orbitals are also implemented for the LSIC energy functional. Results show that LSIC with the simplest local spin density functional predicts atomization energies of the AE6 dataset better than some of the most widely used generalized-gradient-approximation (GGA) functional [e.g., Perdew-Burke-Ernzerhof (PBE)] and barrier heights of the BH6 database better than some of the most widely used hybrid functionals (e.g., PBE0 and B3LYP). The LSIC method [a mean absolute error (MAE) of 0.008 Å] predicts bond lengths of a small set of molecules better than the PZSIC-LSDA (MAE 0.042 Å) and LSDA (0.011 Å). This work shows that accurate results can be obtained from the simplest density functional by removing the self-interaction-errors using an appropriately designed SIC method.

Spin-state gaps and self-interaction-corrected density functional approximations: Octahedral Fe(II) complexes as case study.

Accurate prediction of a spin-state energy difference is crucial for understanding the spin crossover phenomena and is very challenging for density functional approximations, especially for local and semi-local approximations due to delocalization errors. Here, we investigate the effect of the self-interaction error removal from the local spin density approximation (LSDA) and Perdew-Burke-Ernzerhof generalized gradient approximation on the spin-state gaps of Fe(II) complexes with various ligands using recently developed locally scaled self-interaction correction (LSIC) by Zope et al. [J. Chem. Phys. 151, 214108 (2019)]. The LSIC method is exact for one-electron density, recovers the uniform electron gas limit of the underlying functional, and approaches the well-known Perdew-Zunger self-interaction correction (PZSIC) as a particular case when the scaling factor is set to unity. Our results, when compared with reference diffusion Monte Carlo results, show that the PZSIC method significantly overestimates spin-state gaps favoring low spin states for all ligands and does not improve upon density functional approximations. The perturbative LSIC-LSDA using PZSIC densities significantly improves the gaps with a mean absolute error of 0.51eV but slightly overcorrects for the stronger CO ligands. The quasi-self-consistent LSIC-LSDA, such as coupled-cluster single double and perturbative triple [CCSD(T)], gives a correct signof spin-state gaps for all ligands with a mean absolute error of 0.56eV, comparable to that of CCSD(T) (0.49eV).

Theoretical insight on model linear oligomers and their ring-fused analogs used in organic electronics

Theoretical systematic study compares chemical and electronic structure of six series of linear aromatic oligomers and their ring-fused analogues with various chain length of 5- and 6-membered rings. Chemical structure was described by structural HOMED and one-electron density topology EL aromaticity descriptors. The calculations demonstrated that the diradical electronic ground-state system is energetically preferred for larger six-membered acenes where the electronic structure can be separated into two linear polyene chains. The influence of intermolecular interaction on the aromaticity perturbation in crystals was also analyzed for 20 available X-ray structures. The aromaticity of central ring is lowered for longer molecules in solids. Next, the primary effect of aromatic chain elongation on frontier orbital energies and vertical excitation energies was predicted. The calculated data were correlated with experimental ones and polymer limits on investigated properties were estimated. Quantitative criteria of aromaticity were explored for various linear organic molecules with increasing chain lengths to extrapolate electronic properties at the polymer limit. • Systematic DFT study of linear oligomers and ring-fused analogues. • The aromaticity indices are evaluated. • The structural conditions for diradical system are determined. • Electrochemical band gaps and optical transitions are calculated. • Polymer limits on investigated properties are estimated.

A Theoretical Study of the C-X Bond Cleavage Mediated by Cob(II)Aloxime.

The C-X bond cleavage in different methyl halides (CH3X; X = Cl, Br, I) mediated by 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(II) (CoIICbx) was theoretically investigated in the present work. An SN2-like mechanism was considered to simulate the chemical process where the cobalt atom acts as the nucleophile and the halogen as the leaving group. The reaction path was computed by means of the intrinsic reaction coordinate method and analyzed in detail through the reaction force formalism, the quantum theory of atoms in molecules (QTAIM), and the calculation of one-electron density derived quantities, such as the source function (SF) and the spin density. A thorough comparison of the results with those obtained in the same reaction occurring in presence of 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(I) (CoICbx) was conducted to reveal the main differences between the two cases. The reactions mediated by CoIICbx were observed to be endothermic and possess higher activation energies in contrast to the reactions where the CoICbx complex is present. The latter was supported by the reaction force results, which suggest a relationship between the activation energy and the ionization potentials of the different nucleophiles present in the cleavage reaction. Moreover, the SF results indicates that the lower axial ligand (i.e., 5,6-dimethylbenzimidazole) exclusively participates on the first stage of the reaction mediated by the CoIICbx complex, while for the CoICbx case, it appears to have an important role along the whole process. Finally, the QTAIM charge analysis indicates that oxidation of the cobalt atom occurs in both cases; at the same time, it suggests the formation of an uncommon two-center one-electron bond in the CoIICbx case. The latter was confirmed by means of electron localization calculations, which resulted in a larger electron count at the Co-C interatomic region for the CoICbx case upon comparison with its CoIICbx counterpart.