Benchmark DFT Approach for Dissociation Energies of Chemically Important Bonds

Abstract

A very fascinating aspect in quantum chemical research is to acquire accurate and costeffective method for the calculation of electronic as well as structural properties. The benchmarking is a famous approach where theoretical results from low-level calculations are compared with accurate high-level quantum chemical methods or experimental results. The current study focuses on performance evaluation of density functional theory methods for accurate measurement of bond dissociation energies. Bond dissociation energy (BDE) measurement has got noteworthy attention due to its importance in all areas of chemistry. Keeping in view the importance of bond dissociation energy (BDE), the current study is focused on the exploration of accurate and low cost DFT method for bond dissociation energy calculations of different chemically important bonds. The selected bonds include C−X (X = Cl and Br), C−Sn, C−CN, C−Mg and M−O2 bonds. Various functionals of DFT classes with a variety of basis sets are implemented for the calculation of BDE. The accuracy of a method is examined through different statistical tests including root mean square deviation (RMSD), standard deviation (SD), Pearson’s correlation (R) and mean absolute error (MAE). Theoretical results are compared with the already reported experimental BDE values of respective bonds. The method which has less deviation and error with a reasonable Pearson’s correlation is considered as the method of interest. For the BDE measurement of carbon halogen (C−X where X = Cl and Br) bond, 33 different density functionals (DFs) with four basis sets are used for sixteen halogen containing compounds. Two basis sets (6-31G(d) and 6-311G(d)) are selected from Pople basis sets and other two are selected from Dunning basis sets (aug-cc-pVDZ and aug-cc-pVTZ). Among all selected DFs, ꞷB97X-D shows the best performance with least deviations (RMSD, SD), error (MAE) and a significant Pearson's correlation (R) when compared with experimental data. Secondly, nineteen DFs from eight different DFT classes with four basis sets are selected for BDE calculation of the C−Sn bond of ten organotin compounds. Two basis sets containing pseudopotential basis sets (LANL2DZ and SDD) and other are selected from Karlsruhe basis sets (def2-SVP and xi def2-TZVP). In this benchmark approach, BLYP-D3 functional of dispersion corrected GGA class with SDD basis set is observed as the best method for homolytic BDE calculation of C−Sn bond. Thirdly, for twelve organo-nitrile compounds thirty-one DFs with eight basis sets including Pople, Dunning and Karlsruhe basis sets are used. Thus, 6-31G(d), 6-31G(d,p), 6-311G(d,p), 6-31+G(d) and 6-311++G(d,p) basis sets are selected from Pople basis sets, aug-cc-pVDZ and aug-cc-pVTZ basis sets are selected from Dunning basis sets and def2-SVP basis set is selected from Karlsruhe basis sets. Overall, CAM-B3LYP functional of range separated hybrid GGA class with Pople’s 6- 311G(d,p) basis set provides the most accurate results for the BDE measurement of C−CN bond of nitrile compounds. Fourthly, twenty-nine DFs from thirteen DFT classes with four basis sets (Pople’s 6-31G(d) and 6-311G(d), Dunning’s aug-ccpVDZ and Karlsruhe’s def2-SVP basis sets) are implemented for BDE measurement of C−Mg bond of fifteen Grignard reagents. TPSS of meta-GGA class with 6-31G(d) basis set gave the accurate results. Finally, for BDE measurements of M−O2 bond in five metal complexes with dioxygen, fourteen DFs are chosen from seven DFT classes with two series of mixed basis sets. A combination of pseudopotential and Pople basis sets (LANL2DZ & 6-31G(d) and SDD & 6-31+G(d)) are used as a series of mixed basis sets. M06 functional with SDD & 6-31+G(d) gave outstanding results due to low deviations, error and the best R between experimental and theoretical data.