Calculating Bond Capacities by Linear Response Methods

Bond capacities can be considered as atom-atom condensed versions of the density response function. They quantify the ease with which the electron density can be transferred between atoms due to differences in potential and are thus central quantities for modeling charge flow in force fields. We describe an implementation of calculating bond capacities by linear response methods with the minimal basis iterative stockholder definition of atoms in molecules. The calculated bond capacities are moderately sensitive to the level of theory at Hartree-Fock, density functional theory, and multiconfigurational self-consistent field and are insensitive to basis set quality beyond a polarized double-ζ quality. The dependence of bond capacities on chemical structure displays a high degree of transferability and conforms to the concept of functional groups. Bond capacities connect all atom pairs in a molecule; however, the magnitude rapidly diminishes as a function of the number of connecting bonds for the nonconjugated system, while a less rapid decay and oscillating pattern is observed for conjugated systems.