Nanotubes with diameters in the magnitude of 10 nm can be treated by quantum chemical methods, made possible by utilization of line group symmetries. The methodology presented here is applied for magnesium dichloride nanotubes. The structural preferences Of MgCl2 nanotubes are strongly dependent on the tube diameter. The rolled layer of a crystalline sheet becomes favorable above a diameter of 3.4 nm, below which alternative stable coordination modes dominate. Application of the methodology for other nanotubular compounds, including multiwalled nanotubes, is expected to be straightforward.