  We demonstrate that the charge distributions in Hubbard-model representations
of transition metal oxide heterojucntions can be described by a Thomas-Fermi
theory in which the energy is approximated as the sum of the electrostatic
energy and the uniform three-dimensional Hubbard model energy per site at the
local density equals to a constant. When charged atomic layers in the oxides
are approximated as two-dimensional sheets with uniform charge density, the
electrostatic energy is simply evaluated. We find that this Thomas-Fermi theory
can reproduce results obtained from full Hartree-Fock theory for various
different heterostructures. We also show explicitly how Thomas-Fermi theory can
be used to estimate some key properties qualitatively.
