  The conventional technique for solving the equations of quantum chemistry (of
solid state) is extended unconventionally to the structures possessing certain
symmetries. This proposal concerns changing the way for selection of occupied
orbitals, allowing, in turn, to release the unoccupied electronic states
located lower than the ground state Fermi level of a specific system. Such
states can be treated as 'spectral holes'. Application of this technique, in
particular, when calculating the electronic structure of the HTSC-compound
$YBa_2Cu_3O_{7-x}$ (0<x<1) results in the following. The spectral holes of high
spatial localization are found. These 'spatial spectral holes' are located,
mainly at the $P_y$-orbitals of the apex oxygens. These orbitals overlap and
form linear chains which are parallel to the known Cu(1)-O chains, disappearing
when x is closed to 1. One can suppose that the linear chains of the
overlapping hole states form a 'superconducting channel'. Some other parameters
closely related to the critical characteristics of HTSC-materials are also
calculated. The calculations show that 'the superconducting channel' is broken
when the oxygen chain atoms O(1) are removed (x>0). One could easily connect
the obtained results to the high-temperature superconductivity of Little's
linear chains, as well as Ginzburg's two-dimensional layers and even to
BCS-model.
