Self-interaction-corrected band structure calculations for intracavity electrons in electro-sodalite

The zeolite sodalite is a crystalline compound consisting of cages. The win dows connecting the cages are large enough to allow small molecules to be a bsorbed. The material studied here, called sodium electro-sodalite (SES), i s prepared by absorbing one Na atom in each cage. Because of the large elec tric fields inside the cages, each alkali atom is ionized and the donated e lectron is shared among several ions. A noninteracting electron model, used in earlier work, calculated the absorption spectrum and the temperature de pendence of the Al and Si NMR shifts and found good agreement with experime nt. The model predicted that the material is a metal. However, recently pub lished low-temperature magnetic susceptibility measurements show that the g round electronic state is antiferromagnetic. This is incompatible with a no ninteracting electron model. In this paper we study the electronic properti es of this material by using various levels of spin-density functional (loc al density approximation, local spin-density approximation, generalized gra dient spin-density approximation, and self-interaction corrected generalize d gradient spin-density approximation) and unrestricted Hartree-Fock calcul ations. While all calculations show SES to be a narrow band material, only the unrestricted Hartree-Fock (UHF) and self-interaction corrected (SIC) de nsity functional calculations lead to an autoferromagnetic ground state. Th e resulting Wannier functions are used to calculate the exchange constant f or the antiferromagnetic Heisenberg spin-Hamiltonian. The Neel temperature predicted by UHF is 47 K while the self-interaction-corrected generalized g radient spin-density approximation gives a Neel temperature of 42 K. (C) 19 98 American Institute of Physics. [S0021-9606(98)01946-1].