Band structure and UV optical spectra of TGS crystals in the range of 4–10 eV

Theoretical and experimental studies of the band energy structure and optical spectra for triglycine sulphate crystal (TGS), (NH2CH2COOH)3·H2SO4, in the ferroelectric phase have been performed for the first time. First principal DFT calculations of the band structure, density of states and dielectric functions spectra ε′(E  ) and ε″(E)ε″(E) of TGS crystal have been done using the computer package Cambridge Serial Total Energy Package (CASTEP) code. Experimental spectral dispersions of the complex reflection ratio ρ(E) have been measured using the synchrotron radiation at BESSY synchrotron source in the spectral range of 4–10 eV and the pseudo-dielectric functions 〈ε〉=〈ε′〉+i〈ε″〉〈ε〉=〈ε′〉+i〈ε″〉 were evaluated. Experimental data and theoretically calculated dielectric functions have demonstrated a good agreement. The band energy dispersion of valence and conducting bands have been analyzed and were used to identify the dielectric functions peculiarities.