Two-quartet G-DNA stems used in our computations. From left to right: AA, AS, 3AA+1SS, SA-aabb, SA-abab, SA-aaab and SA-aaaa structures. Each stem consists of four 5′-GG-3′ dinucleotide steps (strands); S and A stand for syn and anti guanines. The notation ‘a’ and ‘b’ is used to distinguish SA stems with different relative 5’-3’ orientation of the adjacent strands around the structure; a is used for strands oriented upward in our Figure while b for strands oriented downward; c.f., the names of the structures with the relative orientation of the arrows showing the 5’-3’ directionality of the strands. White rectangle marks syn and grey anti nucleosides. The channel cation (K+) is not shown. The first six arrangements were considered in the preceding MD simulation study,34 the seventh arrangement has been added in the course of this study.