  We present extensive molecular dynamics (MD) simulations investigating
numerous candidate crystal structures for hydrogen in conditions around the
present experimental frontier (400GPa). Spontaneous phase transitions in the
simulations reveal a new structure candidate comprising twofold coordinated
chains of hydrogen atoms. We explain the electronic structure of this phase in
terms of a charge density wave and calculate its experimental signature. In
detailed tests of the accuracy of our calculation, we find that k-point
sampling is far more important in MD than in static calculations, because of
the freedom it give the atoms to rearrange themselves optimally for the given
sampling.
