A Variational Method in Wannier Representation for an Electron Weakly Bound to an Isoelectronic Impurity

The problem of a single electron bound to an isoelectronic impurity (solved in k ‐space by Koster and Slater) is reconsidered in lattice space. An analytically tractable variational method for the ground state is developed and compared with the numerically evaluated solution in k ‐space. For GaP:N taking into account the real band structure of the lowest conduction band the variational method yields a sufficient agreement with the k ‐space eigenwert equation. The variational approach developed in the lattice space allows a straightforward generalization to the binding of an exciton (considered in I) which takes into account the electron‐hole correlation, crucially in the region of weak binding (e.g. GaP:N).