Overcoming systematic DFT errors for hydrocarbon reaction energies

Abstract

Despite the widespread use and numerous successful applications of density functional theory, descriptions of hydrocarbon reaction energies remain problematic. Illustrative examples include large underestimation of energies associated with alkane bond separation reactions and poor general description of intramolecular dispersion in hydrocarbons (e.g., B3LYP, MAD = 14.1 kcal mol-1). More recent, but not readily availably functionals, along with efficient posteriori corrections, not only show considerable improvement in the energy description of hydrocarbons but also help identify the sources of error in traditional DFT. Interactions in branched alkanes and compact hydrocarbons are adequately mimicked by systems compressed below their typical van der Waals distances. At these distances, standard DFT exchange functionals are overly repulsive for non-bonded density overlaps, and significant improvement is offered by the long-range corrected exchange functionals (e.g., LC-BLYP0.33, MAD = 5.5 kcal mol-1). For those systems, the neglect of long-range dispersion is found to be a critical shortcoming, as well as ''overlap dispersion'', for which non-negligible amounts are captured by the correlation functional. Accounting for the missing dispersion interactions is of key importance. Accordingly, most noteworthy improvements over standard functionals are obtained by using non-local van der Waals density functionals (e.g., LC-S-VV09, MAD = 3.6 kcal mol-1 , rPW86-VV09, MAD = 5.8 kcal mol-1), a dispersion corrected double hybrid (B2PLYP-D, MAD = 2.5 kcal mol-1), or by the addition of an atom pairwise densitydependent dispersion correction to a standard functional (e.g., PBE-dDXDM, MAD = 0.8 kcal mol-1). To a lesser extent, the reduction of the delocalization error (e.g., MCY3, MAD = 6.3 kcal mol-1) or careful parameter fitting (e.g., M06-2X, MAD = 5.6 kcal mol-1) also lowers the errors.

An accurate benchmark description of the interactions between carbon dioxide and polyheterocyclic aromatic compounds containing nitrogen

“…As argued in our recent work on interactions between CO 2 and pristine carbon nanotubes, 41 there are likely two reasons for this deterioration: overestimation of exchange by standard GGA functionals 88,89 and inadequacy of the damping functions used in the -D3 dispersion correction. The first of these issues can be alleviated by improving on the asymptotic behavior of the exchange functional by increasing the fraction of exact exchange at long range.…”

Applications and validations of the Minnesota density functionals

“…Some recent validations [77][78][79][80][81][82] have shown that M06-2X has much improved performance for main-group organic chemistry as compared to B3LYP. A key reason for this improved performance is the improved treatment of medium-range correlation energy, which includes overlap dispersion interactions, that is, dispersion-like attractive interactions at geometries where orbital overlap (and hence exchange repulsion) of the interacting subsystems cannot be neglected [82].…”

Double-hybrid density functionals: merging wavefunction and density approaches to get the best of both worlds

“…These and similar examples have recently attracted a lot of attention in the theoretical community [126][127][128][129][130][131][132][133][134][135][136] although, from the very beginning, the DH forms were announced as the way to go in the future [137,138]; more discussion can be found in the series of last annual reviews highlighting achievements in computational organic chemistry [139][140][141].…”