NEW DONOR STATE OF S-SYMMETRY

The influence of the short-range potential and the electron-phonon coupling on the donor spectrum is discussed. It is shown that the attractive short-range potential leads to a formation of a single additional state of s symmetry and with energy lying below a weakly perturbed hydrogen-like spectrum, which includes the 1s level. The new state can be called the 0s state. With decreasing short-range attraction, the energy of this state increases crossing over the hydrogen-like levels and, for weak short-range potential, the 0s state disappears. If the electron-phonon coupling is sufficiently strong, the donor hydrogen-like spectrum is perturbed only in a very narrow region of the level crossing.