Electronic structure and Fermi-surface-related instabilities in 1 T-TaS2 and 1 T-TaSe2

The electronic-energy-band structure and full-Brillouin-zone Fermi surfaces of the layered dichalcogenides, 1 T-TaS2 and 1 T-TaSe2, have been calculated using the Korringa-Kohn-Rostoker method in the muffin-tin approximation. We find that the Fermi surfaces for both systems away from symmetry points and lines have cross sections which are approximately constant along the z direction. Strong nesting features of the Fermi surface are found for a spanning vector parallel to the ΓM direction in reciprocal space with values in good agreement with the charge-density-wave results found by Wilson, Di Salvo, and Mahajan for these compounds.