A DMRG study of the q-symmetric Heisenberg chain

The spin one-half Heisenberg chain with $U_q[SU(2)]$ symmetry is studied via density-matrix renormalization. Ground-state energy and $q$-symmetric correlation functions are calculated for the non-hermitian case $q=\exp(i\pi/(r+1))$ with integer $r$. This gives bulk and surface exponents for (para)fermionic correlations in the related Ising and Potts models. The case of real $q$ corresponding to a diffusion problem is treated analytically.