Pseudoatoms in diatomic molecules: restricted radial functions

Molecular charge-density functions for several diatomic molecules of first-row atoms have been analyzed by the least-squares method with pseudoatoms that have restricted radial functions. Multipole expansions up to quadrupoles on the two centers with single exponential radial functions provide qualitative descriptions of the molecular charge densities. They do not provide accurate values of molecular electrostatic properties, however. Extension to octupoles and hexadecapoles does not improve the representation of physical properties. Variations of the valence exponents proved to be the most critical parameters for goodness of fit as well as for retrieval of physical properties. For the selected examples in this work it appears that the valence exponent is more sensitive to the atom type than to the bonding environment; the exception is the hydrogen pseudoatom.