Hwang in [Phys. Rev. E 80, 042103 (2009)] suggested that the two transitions of the six-state clock model on the square lattice are not of the Kosterlitz-Thouless type. Here we show from simulations thatat the upper transition, the helicity modulus does make a discontinuous jump to zero. This gives strong evidence for a Kosterlitz-Thouless transition.
@article{arxiv.1005.4836,
title = {Comment on `Six-state clock model on the square lattice: Fisher zero approach with Wang-Landau sampling'},
author = {Seung Ki Baek and Petter Minnhagen and Beom Jun Kim},
journal= {arXiv preprint arXiv:1005.4836},
year = {2015}
}