A new hybrid density functional, APF, avoids the spurious long range attractive or repulsive interactions found in most DFT models. It therefore provides a sound baseline for the addition of an empirical dispersion correction term, developed from a spherical atom model (SAM) based on the interaction of spherical shells of polarizable media. Figure 1. <img src='https://acs-archive-assets2.s3.amazonaws.com/241nm/uploads/71531_acs_poster_graphic.jpg' alt='' /> The AFP-D empirical dispersion model contains 9 adjustable parameters and 2 computed atomic properties (ionization potential and effective atomic polarizability for each element). AFP-D accurately describes the potential energy surfaces of complexes of noble-gas atoms with each other and with various diatomic molecules and of dimers of small hydrocarbons, and it reproduces conformational energies of organic molecules. The accuracy for these weak interactions is comparable to that of CCSD(T)/aug-cc-pVTZ calculations. The geometry of hydrogen bonded complexes is competitive with other models involving DFT and empirical dispersion. Figure 2. Comparison of CCSD(T)/CBS with APF-D potential energy curves for dimers of methane, ethylene, and acetylene

Spherical atom dispersion terms for density functionals

245th National Meeting (2013)

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