| Popis: |
A comparison is made between different methods of describing superexchange involving paramagnetic cations in non-conducting solids and molecular complexes. A description is given of the methods of Kramers (section 2), Anderson (section 4), Jansen and co-workers (section 3), Hay, Thibeault and Hoffmann (section 5.1), Harcourt (section 5.1) and of Kahn and Briat (section 5.2). To make a numerical comparison, the latter four are applied to a three-center, four-electron system representing a cation-anion-cation unit in an isoceles triangular configuration. Provided that no approximations are made, all methods exhibit the same qualitative behaviour with respect to geometrical variation of the system. For values of the bridging angle around 90°, ferromagnetic coupling is found. In addition, various assumptions and approximations in the methods are discussed and numerically investigated. |
