  Fermi and kinetic energy are usually calculated in periodic boundary
conditions model, which is not self-consistent for low-dimensional problems,
where particles are confined. Thus for confined particles the potential box
model was used self-consistently to calculate Fermi and kinetic energies in 3-,
2-, and 1-dimensional cases. This approach is much more logical and
self-consistent. Then the conditions for neglecting dimensions, that is
conditions under which the movement of particles in the box could be considered
as 2- and 1- dimensional, were derived.
