The stacking structure of COF-1 and other 2D COFs is not eclipsed as assumed from early low-resolution powder X-ray diffraction data (PXRD), 1 but between two layers there is a small shift of about 1.6 Å along one of the high-symmetry directions. This stacking is denoted as AA' and shown in Figure . These apparently small shifts can impose significant changes in the electronic properties. In realistic COFs, there is no pronounced interaction between second next layers, yielding to a stochastic sequence of small shifts, which result in non-periodic structures normal to the COF plane. Accommodating a statistical stacking model is computationally too expensive for AIMD simulations. We employed thus COF-1 models with AA' stacking for the static calculations and as starting structures for the AIMD simulations. However, we tried to take the statistical stacking model somewhat into account by repeating the unit cell shown in Figure (c) 2-3 times via a supercell approach, which is described in detail in Section 4.1. In the supercell model, symmetry is not enforced normal to the plane of the layers during the AIMD simulation, allowing as much independent stacking shifts as the selected supercell can afford. In a 1 × 1 × 2 supercell, layers 1 and 1' will not remain aligned on top of each other during the AIMD simulation, see Figure for labels.