ATOMIC ORDERING IN CUGEO3 DURING THE SPIN-PEIERLS TRANSITION - CALCULATION OF CU-63 NQR FREQUENCIES

The X-alpha discrete variation (X-alpha-DV) method is used to calculat e the electronic structures of the clusters modeling the spin-Peierls transition in CuGeO3. The Cu-63 NQR frequencies of two centers that fa ll within the simulated supercell are calculated It is shown that the nature of the forbidden gap and the Cu-63 NQR spectral parameters depe nd on the motion of copper atoms in the chains. Some assumptions are m ade to explain the fact that dimerization in chains of Cu atoms is exp erimentally unobservable.