Study of the orbital hardness and the Kohn‐Sham radius on single monoatomic anions

Within the Kohn‐Sham framework and for a series of single charged monatomic anions, the orbital hardness is calculated as a change in the frontier eigenvalue, which is equivalent to integrate the local hardness function obtained through the derivative of the KS effective potential respect to the occupation number. The local hardness function is composed by the sum of two terms with opposite sign that describe the electrostatic and exchange‐correlation interactions. Moreover, it is found that, at the KS radii, the last term vanishes with the result that the orbital hardness of the anion is a measure of the electrostatic potential exerted by the frontier density at the KS radii. A further derivation leads to establish a direct relationship between hardness and the inverse of the KS radii. The polarizability of the anion is also examined by computing it from the volume of a sphere having the KS radii. These results show that anions from the halide group are hard and little polarizable, whereas anions from the alkali group are soft and highly polarizable. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011