Decomposition and Polymerization of Solid Carbon Monoxide under Pressure

By performing constant-pressure deformable-cell ab initio molecular dynamics simulations we have studied the pressure-induced chmical instability of CO above 5 GPa. The simulation shows that, contrary to previous speculations, polymerization proceeds without CO bond dissociation. The resulting polymer consists of a disordered network of small polycarbonyl (CO)_n chains connecting fivefold C_4O cycles. The computed vibrational spectra and electronic gap agree very well with (and sheds light on) very recent experimental data.