Electron spectrum and optical constants of ferroelectrics with hydrogen bonds

The electron energy spectrum of the KDP-type crystals in the ferroelectric phase is calculated using the tight-binding approximation. We proceed from the basis of Bloch functions taking into account the 3s and 3p orbitals of the phosphorus, 2p orbitals of the oxygen and 1s orbitals of the hydrogen....
Ausführliche Beschreibung

The electron energy spectrum of the KDP-type crystals in the ferroelectric phase is calculated using the tight-binding approximation. We proceed from the basis of Bloch functions taking into account the 3s and 3p orbitals of the phosphorus, 2p orbitals of the oxygen and 1s orbitals of the hydrogen. In the case of the high-symmetry points q of Brillouin zone we have constructed the basis of symmetrized combinations of Bloch functions which correspond to the irreducible representations of the q wave vector group. The dependence of electron spectrum on wave vector q along the main directions of Brillouin zone is investigated. The obtained double degeneration of the electron spectrum at the Brillouin zone edge is connected with the invariance of Schrodinger equation with respect to the inversion of time. The joint electron density was calculated. Its frequency dependence is investigated. The matrix elements of electric dipole moment on the basis of Bloch-type wave functions are calculated. Real and imaginary parts of the dielectric permeability for different polarizations of light are determined. The refraction index and extinction coefficient are obtained. Ausführliche Beschreibung