Natural population analysis. Considered better than Mulliken populations for assigning atomic charges; results are fairly independent of the basis set. Theory based upon chemical concepts of bonds, lone pairs, etc.
(Natural Population Analysis) A method for determining atomic charge distributions in a molecule. Based on creating atomic natural orbitals from the molecular orbitals, by finding eigenfunctions of atomic sub-blocks of the molecular density matrix, based on chemical concepts of bonds, lone pairs, etc. Fairly independent of basis set.