A concept of strong interaction in a single unit cell is used to predict Co
oper instability in a system with hopping between main-group cations and an
ions. A phase diagram of ferromagnetic ordering is constructed for differen
t degrees of (n(p))p(6)- and (n(s))s(2)-shell filling in main-group element
s. (C) 2001 MAIK "Nauka/Interperiodica".