Doubly differential cross sections for inclusive single-electron emission i
n 3.6 MeV/amu AU(53+) + Ar collisions are calculated in the continuum disto
rted wave with eikonal initial-state approximation. Previously observed str
uctures in the low-energy continuum are traced back to a known deficiency o
f the Hartree-Fock-Slater target potential that has been used in the work [
R. Moshammer et al., Phys. Rev. Lett. 83, 4721 (1999)]. The structures do n
ot occur, if the argon atom is described in terms of the optimized potentia
l method, in which the electronic exchange interaction is treated exactly.