QUANTUM MAGNETISM OF CUGEO3

The magnetic properties of CuGeO{sub 3}are shown to be well described by the one-dimensional Heisenberg {ital S}={ital cf};1;2 model with competing antiferromagnetic interactions. Provided that the competing exchange is moderately large but smaller than the critical value required to produce a gap in the excitation spectrum without lattice dimerization, the model agrees with a variety of experimental properties. It is argued that competing exchange interactions are a general feature of organic charge transfer compounds, and that they increase the temperature at which a spin-Peierls transition takes place.