The performance of the isotropic spherical atom model (SAM) can be significantly enhanced through combination with anisotropic three-body dispersion interactions to give the new PFD-3B density functional, which reduces the mean absolute deviation relative to CCSD(T)/CBS benchmark energies from 0.78 kcal/mol to 0.20 kcal/mol for the S22 test set. Comparison with the extended S22 x 5 test set in the figure indicates that this accuracy is maintained through large variations in geometry. The performance of the PFD-3B functional over the S22 x 5 test set is superior to any of the functionals previously applied to this set. Over the S22 set of examples the MAD from the CCSD(T)/CBS values for Re, De, and ωe, are 0.032 Å, 0.20 kcal/mol, and 6 cm-1 respectively. Over a comparable set of 20 examples containing second and third row atoms, the MAD from the CCSD(T)/CBS values for Re, De, and ωe, are 0.041 Å, 0.09 kcal/mol, and 3 cm-1 respectively. If used to optimize the geometry of the 42 examples, on average the PFD-3B functional introduces an error of only 0.04 kcal/mol in CCSD(T) single point energies. This small error combines with the reported analytical first and second derivatives to make the PFD-3B functional an attractive model for geometry optimization and zero point energy calculations.

Three body dispersion corrections to the spherical atom model: PFD-3B density functional

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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