Conformational Dependence of Isotropic Polarizabilities

We perform a statistical and energetic analysis of atomic polarizabilities obtained with the LoProp approach for all atoms in the avidin tetramer for 70 snapshots from molecular dynamics simulations with seven different biotin analogues, and from the crystal structure of the photosynthetic reaction center (in total 560 698 individual polarizabilities). Dynamic effects give a variation of the polarizabilities of 0.09 Å(3) on average. Atoms at different positions in the sequence show a variation of 0.14 Å(3) on average, caused by the conformational dependence of the polarizabilities. This variation gives errors of 2 and 1 kJ/mol for relative conformational and ligand-binding induction energies. Averaged elementwise or atom-type polarizabilities give larger errors, e.g., 9 and 7 kJ/mol, respectively, for the relative conformational energies. Therefore, we recommend that polarizabilities should be assigned atomwise (i.e., individual polarizabilities for each atom in all residues), in the same way as for charges. We provide such a set of extensively averaged polarizabilities (xAvPol) for all atoms in avidin and the photosynthetic reaction center, applicable at the B3LYP/aug-cc-pVTZ level, which is converged with respect to the basis-set limit.