A set of atomic polarizability parameters for a new polarizable Gaussian model (pGM)
has been developed with the goal to accurately reproduce the polarizability anisotropy,
taking advantage of its ability to attenuate all short-range electrostatic interactions,
by fitting the ab initio molecular polarizability tensors ( A pq ) calculated at
the B3LYP/aug-cc-pVTZ level. For comparison, we also rederived the parameters for
three Thole models in which the 1–2 (bonded), 1–3 (separated by two bonds) and 1–4
(separated by three bonds) interactions are fully included. The average percent errors
(APEs) of molecular polarizability tensors for 4842 molecules or dimers are 2.98,
3.76, 3.28, and 3.82% for the pGM, Thole linear, Thole exponential, and Thole Amoeba
models, respectively, with atom-type independent, universal screening factors (USF).
The APEs are reduced further to 2.30, 2.69, 2.25, and 2.48% for the four corresponding
polarizable models with atom-type dependent, variable screening factors (VSF). It
is encouraging that the pGM with variable screening factors achieved APEs of 1.83
for 1155 amino acid analogs, dipeptides and tetrapeptides, 1.39 for 28 nucleic acid
bases, 0.708 for 1464 water clusters, and 1.99 for 85 dimers of water and biological
building blocks. Compared to the new set of models, the APEs of the old Thole models
that were fitted to isotropic molecular polarizabilities are 8.7% for the Set A (without
the 1–2 and 1–3 interactions) and 6.3% for the Set D (with the 1–2 and 1–3 interactions)
models, respectively. MPAD, a metric of molecular polarization anisotropy difference
based on the diagonal terms of molecular polarizability tensors was defined and applied
to assess the polarizable models in reproducing the ab initio molecular polarization
anisotropy. The MPADs are 3.71, 4.70, 4.11, and 4.77% for the pGM, Thole linear, Thole
exponential, and Thole Amoeba USF models, respectively. The APEs are reduced further
to 2.85, 3.58, 2.90, and 3.15% for the four corresponding VSF models. Thus, the new
pGM and Thole models notably improve molecular polarization anisotropy. Since pGM
attenuates all short-range electrostatic interactions, its application is expected
to improve stability in charge fitting, energy and force calculations and the accuracy
of multibody polarization.