Fit of charges due to the electrostatic potential:

$esp_fit fits point charges at the positions of nuclei to electrostatic potential arising from electric charge distribution (for UHF cases also for spin density). For this purpose the ("real") electrostatic potential is calculated at spherical shells of grid points around the atoms. By default, Bragg-Slater radii, $r_{BS}$, are taken as shell radii.

A parametrization very close to that suggested by Kollman (a multiple-shell model with shells of radii ranging from 1.4*$r_{vdW}$ to 2.0*$r_{vdW}$, $r_{vdW}$ is the van-der-Waals radius; U.C. Singh, P.A. Kollman, J. Comput. Chem. 5(2), 129-145 (1984)) is used if the keyword is extended:

$esp_fit kolman