N.I.Kashirina, V.D.Lakhno, V.V.Sychyov
Investigation of electron correlations effect on energy spectrum of two-electron systems in crystals with strong electron-phonon coupling //Semiconductor Physics, Quantum Electronics & Optoelectronics, 2002, v.5, №3, p.235-242

      The influence of electron correlations (direct dependence of electronic wave function on distance between electrons) on energy spectra of two-electron systems (D, F′, F2-centers and bipolarons) in polar crystals with strong electron-phonon interaction is investigated. Bipolaron is chosen as the simplest model of two-electron system in the crystal. Bipolaron energy is calculated for various distances between the centers of polarization wells of two polarons with accounting the electron correlations. A singlet bipolaron is stable at rather high energy of ion binding ηηm ≈ 0.143 (η = ε / ε0. The unique energy minimum corresponds to a one-center bipolaron (an analog of a helium atom). The bipolaron binding energy constitutes up to 25.8% of a double polaron energy at η → 0. A triplet bipolaron (an analog of orthohelium) is energetically disadvantageous. The one center configuration of a triplet bipolaron corresponds to a maximum on the distance dependence of the total energy JBp(R). The exchange interaction between polarons has antiferromagnetic character. A prediction is made about a possibility of the Wigner crystallization of a polaron gas, which occurs with antiferromagnetic ordering in the polaron system. The examples of energy calculations with accounting the electron correlations of exchanged-coupled pairs, D and F′-centers in polar crystals are also given.