Z-transition state calculations of energy changes and electrostatic potentials in isoelectronic atoms and molecules

A Z-transition state (ZTS) method based on nonintegral nuclear charges is tested numerically for calculating isoelectronic energy differences and electrostatic potentials. A self-interaction-corrected local spin density functional approximation is used for atoms, and an ab initio SCF-MO procedure with a modified STO-5G basis set for molecules. It is shown that the ZTS method permits accurate isoelectronic energy differences to be obtained through a single computation at an intermediate nuclear charge. The electrostatic potentials are found to vary nearly linearly with nuclear charge over small intervals.