  The valence band offsets (VBO) for the \b{eta}-type A3B6 layered compounds
depending on the thickness of the crystals have been investigated from the
first principles, based on the density functional theory. To simulate the
structure of a given thickness the periodic slab model was used. Two adjacent
crystal slabs consisting of several layers were separated by a vacuum region of
two-layer width. It is shown that at the crystal thickness more than 12 layers,
photothreshold practically becomes independent on the thickness of the crystal.
