Density (number of atoms per unit volume) and charge density along the radius of the equilibrated chromatin fiber: (a) Linker DNA fills the core and H2A and H2B N-terminal histone tails extend out of the fiber surface, leading to a wider distribution of atoms along the radial axis, compared to the initial structure. (b) After equilibration, the core becomes more negatively charged, due to the presence of linker DNA in the core, and the outer region becomes positively charged due to the presence of histone tails.