Twist angle and buckle displacement distributions as a function of ion type. (a) Twist angle distribution of step 1 (black), 2 (red) and 3 (green) in quadruplex models PQ (left), AQ-1 (middle) and AQ-2 (right) in DNA form with K+ (top) and Na+ (bottom) as neutralizing ion. (b) Buckle displacement distribution of G-layer 1 (black), 2 (red), 3 (green), and 4 (blue) in quadruplex models PQ (left), AQ-1 (middle), and AQ-2 (right) in DNA form with K+ (top) and Na+ (bottom) as neutralizing ion.