Systematic Errors in Computed Alkane Energies Using B3LYP and Other Popular DFT Functionals

Energies computed by B3LYP and other popular DFT functionals are flawed by systematic errors, which can become considerable for larger mols. These errors, predominately due to inadequacies in assessing longer-range nonbonded attractive effects (dispersion), are illustrated by the isodesmic stabilization energies of n-alkanes (based on methane and ethane, which have no stabilizing 1,3-alkyl group interactions). Newer functionals, designed to describe weak interactions, give somewhat better agreement with expt., but are not fully satisfactory. [on SciFinder (R)]