Exchange Integral in Rare-Earth Metals

Calculations of $4f-6s$ electron exchange integrals have been made in order to determine the sign of the exchange integral and the dependence of the integral upon interatomic distance. The exchange integral is found to be positive in sign, and insensitive to changes of interatomic distance. By contrast, the magnetic interactions in rare-earth metals are quite sensitive to changes of interatomic distances in the crystal; it is concluded that this sensitivity is not attributable to variations of the exchange integral.