Intra- and intermolecular dispersion

As reported recently on this blog, dispersion energy corrections play an important role in computational chemistry, in particular with density functional theory.

We have applied our SSB-D functional to a number of systems where weak interactions are important. In particular, we have studied the six isomers of water-hexamer systems, dimers of noble gases, twelve isomers of C12H12 hydrocarbons, Grimme’s difficult systems (branching energy of octane, dimerization of anthracene) and the stacking of adenine dimers. For all of these systems, accurate reference data at the CCSD(T) level are available, either from the literature or calculated by ourselves. We also studied these interactions with other popular current density functionals (B3LYP, B3LYP-D, BLYP, BLYP-D, PBE, PBE-D, PBEsol, PBEsol-D, OPBE, M05-2X, B3PW91, B3PW91-D, B2PLYP, B2PLYP-D, B97-D), but found that indeed the inclusion of Grimme's dispersion correction improves the results. However, it does not correct all shortcomings of the different density functionals, which leads to sizeable differences compared to ab initio CCSD(T) and experimental reference data. The only exception is shown to be our recently presented SSB-D functional that works well for all systems studied. The paper describing this work has just been published in the Journal of Computational Chemistry.


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