Thermodynamics of frustrated quantum spin chains

We apply the transfer-matrix density matrix renormalization group (DMRG) approach to frustrated quantum spin chains, down to T = 0.025 K in the thermodynamic limit. The incommensurability problem of exact diagonalization and the negative sign problem of quantum Monte Carlo vanish completely. For illustration, we give results for chains with next-nearest-neighbor frustration and for the delta chain, which has been a testbed for many thermodynamic methods. The DMRG approach proves to be an extremely powerful method for the old problem of the thermodynamics of frustrated systems.