Comment to "Topological insulators and superconductors" by Xiao-Liang Qi and Shou-Cheng Zhang Reviews of Modern Physics 83, 1057 (2011)

The paper reports on the solution in the semi-space corresponding to topological surface state. It was shown that the exponential surface state results from selection of the energy outside the allowed energy range. In the result, the kinetic energy of the state is negative proving that the proposed state is not physically correct solution.