The molecular structures of the model systems were based on the parallel-stranded quadruplex of d(G4) stabilized by three potassium ions with ID 1KF1 47 in the protein data bank (PDB). The full sequence of this DNA strand is included in our simulation (largest model system) and reads AGGGTTAGGGTTAGGGTTAGGG, where the guanine nucleotides forming the three layers of the G-quadruplex are written in italic.