BAND-STRUCTURE AND MODEL OF THE PARAELECTRIC STRUCTURE OF THE SN2P2S6CRYSTAL

Since a variety of choices exist in the literature for the symbol of t he space group of crystals of the type Sn2P2S6, hindering the use of a group-theoretic analysis to determine the properties of the band spec trum and phonon spectrum, identified this symbol is identified with th e known coordinates of the atoms of the given crystals. It is shown th at the different arrangements P2(1)/c and P2(1)/n lead to permutations of the points in the Brillouin zone and correspondingly to a change i n the irreducible representations. Calculating the spectra of Sn2P2S6 and Sn2P2Se6 by the method of pseudopotentials fitted to the width of the bandgap confirms the double degeneracy at the X, Y, Z points of th e Brillouin zone, which was not expected for the X point in the arrang ement P2(1)/c. We have detected the previously predicted minimal band complexes in the band spectrum, which are the same as for In4Se3 of th e group D-2h(12). (C) 1997 American Institute of Physics.