Although such noncovalent interaction of halogen (X) and aromatic π systems has recently been extensively studied, their contribute to their X-π interactions. Herein, we calculated the different density functional theories (DFT) to find more reliable methods for X-π interactions based on deviations from them with respect to CCSD(T) values on the halogen-benzene(Bz) model. -arts quantum computing tools to study the nature of the X-π interactions for applying the Most DFT methods show clear deviations from the CCSD(T)/CBS binding energies, especially in the case of strongly halogen-bonded X2-Bz where the electrostatic influence is more important, while the deviations are relatively small for CX4-Bz where the dispersion is more important than electrostatic.
This is evidenced by the performance of the dispersion-corrected hybrid functional, PBE0-D3, and the double-dispersion-corrected hybrid functional, B2GP-PLYP-D3, which include the most accurate exchange term compensated by the Hartree-Fock and MP2 methods. This benchmark study of various DFT methods and research on X-π systems should help to understand the nature of X-π interactions in biological systems and halogen-intercalated graphene systems and to design supramolecules using the halogen and aromatic ring.
List of tables
Introduction
The research of two-dimensional chemistry originated and fascinated in materials chemistry due to its controllable physical and chemical properties with functionality,1 non-covalent adsorption2,3 and intercalation in the bilayer of graphene.4-6 While intermolecular interactions between The electronic Negative halogen compounds and nucleophilic molecules have received attention in the various research fields because the halogen bond plays an important role in many ways. In particular, the interactions between the halogen atom (X) and the π complex are common in the ligand-protein complexes on it plays a crucial role in stabilizing them7-9 and in the halogen-adsorbed carbon compounds such as graphite (or graphene).10, 11 All the above examples are influenced by the X-π interaction as a major driving force. So it may be counterintuitive that the halogen has attraction for other electronically negative groups (Figure 1.1). In this sense, halogen bonding could be interpreted as most components of electrostatic interactions with weak dispersion, polarization and induced effect.
Although the electrostatic interaction largely contributes to the halogen bond, the geometry of the halogen complex can be determined by exchange repulsion and electrostatics.16 In addition, the halogen bond interactions have also been treated as intrinsic dispersion, yet the electrostatic contributions are dominant.17 Therefore, More correctly is to say that halogen bonds of the halogen-π (X-π) type do not only drive the electrostatic interaction. In addition, recent advances in halogen bonding research have noted inaccuracies of DFT methods for calculating their intermolecular binding energies, resulting from the delocalization error of approximate functionals, which could lead to an overestimation of halogen bonding.23.
Computational Details
- Simulation models
- Computational methods
Cor can show the relationship between bond energy and the number of aromatic rings. We search for the lowest conformers of After pre-screening tasks, we obtained a large number of possible conformations, but we only chose some meaningful geometry sets for X2-Bz and CX4-Bz, as shown in the previous Figure 2.1.1 and Figure 2.1.2.
All the structures are confirmed by the vibrational frequency calculation by checking their number of imaginary frequencies. In the case of more extended π-systems, the number of possible conformations of X2/CX4. The final conformer sets were used as the starting geometries for the calculations using the other xc functions.
The following xc density functionals were used in the study: B97-D3, PBE33-D3, BLYP34-D3, BP8635-D3, PBE036-D3, B3LYP37-D3, M06-2X,38 B2GP-PLYP39-D3, PBE-TS and PBE0- TS, where D3 stands for the Grimme dispersion correction scheme D3, and TS stands for the Tkatchenko-Scheffler dispersion correction scheme. -tier3 indicates tier2/tier3. All calculations used in our research were done using Turbomole,41 Gaussian09,42 Molpro,43 Orca,44 the Fritz Haber Institute for Ab Initio Molecular Simulation (FHI-AIMS)45 and the Vienna Ab-initio Simulation Package (VASP). ).46,47 Bz and Cor super cells 30 Å × 30 Å × 30 Å were used for the periodic calculation of small molecules, and 3x3 and 4x4 unit cells with a vacuum layer of 20 Å in the z-direction were used for the Gr plates. All VASP calculations were performed with a kinetic energy cutoff of 500 eV for the plane wave (PW) basis set, projected augmented wave (PAW) pseudopotentials48,49 and a 5x5x1 k-point Monkhorst-Pack grid were used except for the PBE0 calculation, which uses 3x3x1 k-points.
The electrostatic potential maps (EPM) of X2, CX4 and Bz are performed to aid in the understanding of the nature of halogen bonding, σ-hole and distribution of π-electrons. The former term means the contribution of electrostatic potentials of the nucleus in position r, and the latter means the contribution of electrostatic potentials of the electrons in position r. The EPM diagrams of the system should be a useful tool for describing the electronically positive and negative region.
Results and Discussion
- Binding energies of the X 2 /CX 4 -Bz
- Benchmark study for X-π interaction
- Nature of X-π interaction in large π system
The ability of the different density functionals was evaluated with the calculation of binding energies of the X2/CX4-Bz complexes. The binding energies for Cl2/Br2-Bz and CCl4/CBr4-Bz calculated by various DFT methods collected and tabulated and the deviations with respect to the CCSD(T)/CBS values are Table 3.2.5. The PBE-TS/tier2 binding energies are in reasonable agreement with the CCSD(T)/CBS values; The S1 bond energy differs by ∼2.3/4.3 kJ/mol for Cl2/Br2-Bz.
Slightly more accurate binding energies are obtained with the larger basis set (namely, the PBE-TS/tier3 energies are close to the CCSD(T)/CBS values within ∼1 kJ/mol for almost all the conformers of Cl2/Br2-Bz except for the Br2-Bz (S1) conformer giving the deviation of ~3 kJ/mol). Considering only the CX4-Bz complexes, the binding energies obtained at the GGA-D3 level are in line with the CCSD(T)/CBS values without serious overestimation, unlike the X2-Bz ( S1 ) complexes. The binding energies obtained at the PBE-TS/tier2 and tier3 levels are very close to the CCSD(T)/CBS values.
In general, PBE-TS/tier2 or tier3 binding energies are reliable (although the S1 Br2-Bz conformer shows strong halogen bond character). For most density functionals, the errors in the binding energies are huge for the X2-Bz (S1) conformers, which involve a strong halogen bond, while they are small for the X2-Bz (S2, S3) and CX4-Bz (S1, S2) conformers. ECCSD(T)/CBS) of various DFT binding energies (based on CBS* for Gaussian basis sets, level 3 for TS dispersion correction or 500 eV cutoff for PW) from CCSD(T)/CBS binding energies.
However, in the case of an S3 conformer, the binding energies are smaller than other conformers due to the lack of dispersion interaction. For other basis set and dispersion corrected methods, the binding energies show good agreement with the PBE0-D3/CBS. The relationship between the dispersion contribution and binding energies is well revealed in the CX4-Cor case.
All cases of X2-Gr show that the S2 conformer has larger binding energies than the S1 conformer around ~3kJ/mol. Overall, the bond energies are not proportional to the number of aromatic rings because the halogen bond, kind of electrostatic interaction, is weaker when the π system is extended.
- Conclusion
- Reference
The S1 will be favored in a small π-system because of the halogen bonding, but it does not have the advantage in a greatly extended system because they cannot be significant halogen bonding. The atom-top position (S1) is favored over ring-center top position (S2) due to the position of conjugated π electrons in Gr shell. We performed first principles calculations of the X2/CX4-π systems, X =Cl and Br, where π stands for Bz, Cor and Gr.
For the first step, we have evaluated a number of DFT methods by comparing with CCSD(T)/CBS values for the X2-Bz and CX4-Bz complexes (X = Cl, Br) and then the relative dispersion interaction trend and the Contributions of of the electrostatic interaction on the overall binding energy of the X2/CX4-π complexes were evaluated based on the PBE0 functional and the EPM scope by analyzing the nature of the X-π interaction. The results of the comparison study showed that B2GP-PLYP-D3, PBE0-TS and PBE0-D3/CBS give good results in terms of overall performance reflected in MAD/RMSD, followed by M06-2X/CBS and PBE -TS. For large systems, one would be inclined to use small basis sets such as aVDZ, but most calculation methods using aVDZ give seriously overestimated binding energies even with BSSE correction.
In particular, the GGA-D3 binding energies based on aVDZ are strongly overestimated and the overestimation of binding energies is large for the S1 conformers that represented a strong halogen bonding complex. Although the overestimation is somewhat reduced by using larger basis sets, the description of systems with strong halogen bonding still remains unsatisfactory. The unsatisfactory description of halogen bonding is probably caused by the delocalization error arising from the less accurate exchange of density functionals leading to a large overestimation of the electrostatic interaction.
Finally, we have confirmed the presence of the σ-hole and reasonable binding trends of the X2/CX4-Bz models by modern quantum computing tools. The binding energies of X2/CX4-Gr are not larger than we expected because they cannot be significant halogen bonds to the electronically neutral graphene surface. Full basis set limit of ab initio binding energies and geometrical parameters for various typical types of complexes.
