ORBITAL RADII AND ENVIRONMENT-INDEPENDENT TRANSFERABLE ATOMIC LENGTH SCALES

The importance of the orbital radii, r(i), obtained from the classical turning point of the valence electron wave function of angular moment um, l, in obtaining interatomic distances for all bonding situations i s demonstrated. Single bond interatomic distances may be expressed in terms of a universal multiplicative constant of a core s orbital radiu s and another universal additive term which is close to the interatomi c distance in the hydrogen molecule. These relationships are obtained from the dependence of the radii of positive or negative singly charge d ionic species, CR(+) and CR(-), on r(i). The shortening of the dista nces in multiple bond systems or in systems involving transition metal d electron elements is described by a simple universal function, F-S, associated with the number of unpaired valence electrons. A principle of maximum mechanical hardness based on minimization of bond distance s is proposed to obtain correct distances in heteropolar MX bonds. The application of these rules to a large number of compounds with ionic, covalent, metallic, and nonbonded interactions yield interatomic dist ances which are within 2% of the observed distances. A brief discussio n is made on the physical significance of the transferable length scal es CR(+) and CR(-) in the context of discrimination of structure based on radius ratio and the requirement of a universal equilibrium chemic al potential for transferability.