FOHI-D: an iterative Hirshfeld procedure including atomic dipoles.

In this work, a new partitioning method based on the FOHI method (fractional occupation Hirshfeld-I method) will be discussed. The new FOHI-D method uses an iterative scheme in which both the atomic charge and atomic dipole are calculated self-consistently. In order to induce the dipole moment on the atom, an electric field is applied during the atomic SCF calculations. Based on two sets of molecules, the atomic charge and intrinsic atomic dipole moment of hydrogen and chlorine atoms are compared using the iterative Hirshfeld (HI) method, the iterative Stockholder atoms (ISA) method, the FOHI method, and the FOHI-D method. The results obtained are further analyzed as a function of the group electronegativity of Boyd et al. [J. Am. Chem. Soc. 110, 4182 (1988); Boyd et al., J. Am. Chem. Soc. 114, 1652 (1992)] and De Proft et al. [J. Phys. Chem. 97, 1826 (1993)]. The molecular electrostatic potential (ESP) based on the HI, ISA, FOHI, and FOHI-D charges is compared with the ab initio ESP. Finally, the effect of adding HI, ISA, FOHI, and FOHI-D atomic dipoles to the multipole expansion as a function of the precision of the ESP is analyzed.