High Temperature Expansion for Frustrated and Unfrustrated S=1/2 Spin Chains

Abstract

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 coefficients and dispersion data yields very good agreement already in low order of the expansion which makes this approach very promising for the application to other problems, for instance in higher dimensions.Comment: 13 pages, 8 figures, to appear in Eur. Phys. J. B, minor corrections, correction of a[5] in table A.1.a, discussion of the region of validity added, coefficients available electronically: http://www.thp.uni-koeln.de/~g