Band structure and optical properties of diglycine nitrate crystal

Experimental and theoretical investigations of the electron energy characteristics and optical spectra for diglycine nitrate crystal (DGN), (NH2CH2COOH)2·HNO3, in the paraelectric phase (T=295K) are presented. Spectral dispersion of light reflection R(E) have been measured in the range of 3-22 eV and the optical functions n(E) and k(E) have been calculated using Kramers-Kronig relations. First principal calculations of the electron energy characteristic and optical spectra of DGN crystal have been performed in the frame of density functional theory using CASTEP code (CAmbridge Serial Total Energy Package). Optical transitions forming the low-energy edge of fundamental absorption are associated with the nitrate groups NO3. Peculiarities of the band structure and DOS projected onto glycine and NO3 groups confirm the molecular character of DGN crystal.