Corrections to finite-size scaling for quantum chains

Abstract

The authors compute the leading order correction to the energy gap at the critical point for the anisotropic Ising and the Z₃ Potts quantum chains. Periodic, anti-periodic and free boundary conditions are considered. For the Ising case the corrections are independent of the boundary conditions. In the Z₃ case the correction is the same for anti-periodic and free boundary conditions but is ²/₅ smaller for the periodic case. The authors have no explanation for this phenomenon.