The performance of the isotropic spherical atom model (SAM) has been significantly enhanced by including anisotropic three-body dispersion interactions to give the new PFD-3B density functional (abstract 3286870), which reduced 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. 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. Comparison with previous values verified the energies obtained with the new code for the PFD-3B functional (Figure 1). The next step was to compare the analytical first derivatives with numerical derivatives (Figure 2). A similar comparison verified the accuracy of the 9 components of the Cartesian second derivatives. Third and fourth derivatives (and thus anharmonic vibrational spectra) are also available through numerical differentiation of the analytical second derivatives. Perhaps more important, the analytical first and second derivatives make geometry optimization of moderately large molecules practical.

Analytical derivatives of the PFD-3B density functional

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

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.