Thermodynamic properties of the dimerized and frustrated S=1/2 chain - art. no. 024428

By high-temperature series expansion, exact diagonalization, and temperatur e density-matrix renormalization the magnetic susceptibility chi (T) and th e specific heat C(T) of dimerized and frustrated S= 1/2 chains are computed . All three methods yield reliable results, in particular, for not too smal l temperatures or not too small gaps. The series-expansion results are prov ided in the form of polynomials allowing very fast and convenient fits in d ata analysis using algebraic programs. We discuss the difficulty to extract more than two coupling constants from the temperature dependence of chi (T ).