Pressure Shifts of KClF-Center Hyperfine-Interaction Parameters

A joint experimental-theoretical effort combining low-temperature electron-nuclear double-resonance measurements and a pseudopotential calculation was undertakent to determine the main contributing factors to the pressure shifts in the $F$ center hyperfine interaction parameters in KCl. The results indicate that the signs of the pressure shifts beyond shell I are primarily determined by the changes in the indirect overlap contributions to the $F$-electron wave function which result from the requirement of orthogonality of the ion core states at a given site to those on neighboring sites.