The shape of the potential energy well of impurities in KCl:Li+ and KF:M+ (M = Li, Na, K)

The shape of the potential well, which is seen by the Li⁺ impurity in KF:Li⁺ and KCl:Li⁺ is calculated, using the polarizable point ion (PPI) model and the simple shell model (SSM), in combination with a number of potentials describing the short range interaction between the ions.For both systems an off-center system is predicted. It is found that the type of short range potential affects the direction along which the absolute potential energy minimum is located. Using the PPI model or the SSM only changes the depth of the minima and their distance from the lattice site but it does not affect the symmetry of the off-center systems.A preliminary calculation of the shape of the potential well in KF:Na⁺ is presented.