  The gas of the interacted electrons is usually described within Kohn-Sham
approximation by the set of Poisson and Schr\"{o}dinger equations with an
effective potential for the single-particle wave functions. The solution of
these equations should give the self-consistent electron density distribution
and Coulomb potential those can only be obtained using many-step iteration
procedure. The well known difficulty in this task is that the wave functions
obtained after every iteration step give the distribution of electron density
which is not corresponded to the boundary conditions for the Coulomb potential.
As a result, either it is impossible to obtain the solution for the next
iteration step or some parameters of the system are to be changed, for example,
the density of the positive charge. The last way is disagreed with the
Euler-Lagrange variational derivation of the self-consistent equations. We
propose new converging iterative scheme for solving Kohn-Sham and Poisson
equations, where we do not need to modify parameters of the system. This
procedure was tested for two tasks:
  1. Semi-infinite electron gas bounded by infinite potential barrier. This
model allows to simulate the behavior of the electron density near a
semiconductor-insulator interface. The quantum corrections to the capacity of
the barrier structure are calculated.
  2. Semi-infinite electron gas which is bounded by self-consistent potential
barrier within the famous Lang-Kohn jellium model of the metal surface. The new
converging calculations give the results which are different from the
non-selfconsistent ones obtained by Lang and Kohn and have the better agreement
with the experimental data.
