Density functional theory has been gaining popularity for studying the radical scavenging activity of antioxidants. However, only a few studies investigate the importance of calculation methods on the radical-scavenging reactions. In this study, we examined the significance of (i) the long-range correction on the coulombic interaction and (ii) the London dispersion correction to the hydroperoxyl radical-scavenging reaction of trans-resveratrol and gnetin C. We employed B3LYP, CAM-B3LYP, M06-2X exchange-correlation functionals and B3LYP with the D3 version of Grimme’s dispersion in the calculations. The results showed that long-range correction on the coulombic interaction had a significant effect on the increase of reaction and activation energies. The increase was in line with the change of hydroperoxyl radical’s orientation in the transition state structure. Meanwhile, the London dispersion correction only had a minor effect on the transition state structure, reaction energy and activation energy. Overall, long-range correction on the coulombic interaction had a significant impact on the radical-scavenging reaction.

Hydrogen atom transfer is one important reaction in biological system, in industry, and in atmosphere. The reaction is preluded by hydrogen bond dissociation. To gain a comprehensive understanding on the reaction, it is necessary to investigate how the current computational methods model hydrogen bond dissociation. As a starting point, we utilized density functional theory-based calculations to identify the effect of dispersion and long-range corrections on O-H and C-H dissociations in non-phenyl and phenyl groups. We employed five different methods, namely B3LYP, CAM-B3LYP (with long-range correction), M06-2X, and B3LYP and CAM-B3LYP with the D3 version of Grimme's dispersion. The results showed that for the case of O-H dissociation in two member of phenyl groups, namely phenol and catechol, the dispersion correction's effect was negligible, but the long-range correction's effect was significant. The significant effect was shown by the increasing of energy barrier and the shortening of O-H interatomic distance in the transition state. Therefore, we suggest one should consider the long-range correction in modeling hydrogen bond dissociation in phenolic compounds, namely phenol and catechol.

We report a density-functional coupled with vibrational calculation on justifying the isomerization pathway of cyclopropene to propyne. The idea is to present the pathway in energy level diagram which the transition state is ensured by tracking a particular mode that supports the cyclic bond breaking and triple bond formation to occur. This mode decreases along the pathway and disappears at the transition state. To verify the designed pathway, the activation energy of the isomerization is used to find the rate constant with respect to experimental data at 500 K and 700 K by using transition state theory (TST). At those temperatures, TST predicts the rate constant at the same order of magnitude with the experimental result. It shows that the trend between calculation and experimental data is qualitatively in a good agreement, which implies that the designed pathway is justified. Furthermore, this study can be used as a guide if one needs to construct an isomerization pathway.