  We derive an effective low-energy Hamiltonian for potassium loaded zeolite A,
a unique ferromagnet from non-magnetic elements. We perform ab initio density
functional calculations and construct maximally localized Wannier functions for
low-energy states made from potassium s electrons. The resulting Wannier
orbitals, spreading widely in the alminosilicate cage, are found to be the
superatomic s and p orbitals in the confining potential formed by the host
cage. We then make a tight-binding model for these superatomic orbitals and
introduce interaction parameters such as the Hubbard U. After mean-field
calculations for the effective model, we find that ab initio spin density
functional results are well reproduced by choosing appropriate sets of the
interaction parameters. The interaction parameters turn out to be as large as
the band width, $\sim$ 0.5 eV, indicating the importance of electron
correlation, and that the present system is an interesting analog of correlated
multi-orbital transition metal oxides.
