T-1U HUBBARD-MODEL FOR FERROMAGNETIC AND OPTICAL-PROPERTIES OF POTASSIUM-DOPED ZEOLITE

Both the ferromagnetic and optical properties of potassium-doped zeolite are studied from a unified point of view, by using a T-1u Hubbard model for electrons donated from potassium to the alpha-cage of zeolite. Within the mean-field theory, it is shown that the ferromagnetic state occurs even in the half-filled case, in contrast to the literal non-degenerate Hubbard model, wherein the ground state is widely believed only to become an antiferromagnetic insulator or a paramagnetic metal. This new property is due to the interplay of Coulombic interactions with off-diagonal hybridization between T-1u orbitals. The absorption spectrum of the optical transition from a low lying A(1g), level to this T-1u band is also calculated in good agreement with experimental results.