Experiment vs force fields: DNA conformation from molecular dynamics simulations

Molecular dynamics simulations of the DNA duplex d(CCCCCTTTTT)(2) in ionic solution with AMBER and CHARMM force fields are compared. CHARMM parameters result in an A-DNA conformation with a heterogeneous backbone structure, but in the AMBER force field the DNA is found in a B-like helix with a homogeneous B-DNA backbone during the first 3.5 ns before moving close to the CHARMM structure in the A family at around 4 ns. Both structures are in partial disagreement with experiment, which reports the C/G part in A and the A/T part in B form.