  The author suggests an approach based on the separation of total energy of
multielectron systems into the semi-classical Coulomb part and the
non-classical additional part. This approach allows on the one hand to simplify
calculations and on the other hand to see very simple and very interesting
relations. These relations were not obvious when using more complex methods.
The most interesting aspect is that on all levels of chemical matter - from
two-electron atoms up to molecules and crystals - we find additional
non-classical electron-electron attraction. The most important practical
consequence is the discovery that under certain conditions additional
electron-electron attraction can exceed usual electron-electron repulsion. It
can result in existence of ordered structures of a new type in a special-way
exited matter
