Assessment of Contemporary Theoretical Methods for Bond Dissociation Enthalpies

Abstract

The density functional theory (DFT) is the most popular method for evaluating bond dissociation enthalpies (BDEs) of most molecules. Thus, we are committed to looking for alternative methods that can balance the computational cost and higher precision to the best for large systems. The performance of DFT, double-hybrid DFT, and high-level composite methods are examined. The tested sets contain monocyclic and polycyclic aromatic molecules, branched hydrocarbons, small inorganic molecules, etc. The results show that the mPW2PLYP and G4MP2 methods achieve reasonable agreement with the benchmark values for most tested molecules, and the mean absolute deviations are 2.43 and 1.96 kcal/mol after excluding the BDEs of branched hydrocarbons. We recommend the G4MP2 is the most appropriate method for small systems (atoms number≤20); the double-hybrid DFT methods are advised for large aromatic molecules in medium size (20≤atoms number≤50), and the double-hybrid DFT methods with empirical dispersion correction are recommended for long-chain and branched hydrocarbons in the same size scope; the DFT methods are advised to apply for large systems (atoms number≥50), and the M06-2X and B3P86 methods are also favorable. Moreover, the differences of optimized geometry of different methods are discussed and the effects of basis sets for various methods are investigated.

Bond Energies of Enamines

“…Since theoretical approaches have been found to give a precise prediction of thermodynamics properties in solution, , we explored theoretical methods to predict the properties of enamines using Gaussian 09 . As Truhlar et al’s M06-2X hybrid functional was shown to provide accurate predictions of thermodynamic properties of organic molecules, geometry optimizations and frequency computations were performed at the M06-2X/6-311G­(d,p) level of theory.…”