High temperature expansion for frustrated and unfrustrated S=1/2 spin chains

A computer aided high temperature expansion of the magnetic susceptibility and the magnetic specific heat is presented and demonstrated for frustrated and unfrustrated spin chains. The results are analytic in nature since the calculations are performed in the integer domain. They are provided in the form of polynomials allowing quick and easy fits. Various representations of the results are discussed. Combining high temperature expansion coeffici ents and dispersion data yields ver!: good agreement already in low order o f the expansion which makes this approach very promising for the applicatio n to other problems, for instance in higher dimensions.