COMPLETE SOLUTION OF THE XXZ-MODEL ON FINITE RINGS - THERMODYNAMICAL PROPERTIES

The thermodynamical properties of the XXZ-model are studied by means o f a complete diagonalization of the XXZ-Hamiltonian on rings with N = 4,6,.... 16 sites. Based on a finite size analysis we are able to extr act the 'universal' term in the free energy as it is predicted by conf ormal invariance. We also study the finite site scaling properties of the density of states in a properly chosen scaling variable for the ex citation energies. The thermal averages of the modulus of the momentum and of the reflection parity appear to be independent of the temperat ure in the thermodynamical limit.