HYDROGEN - THE FIRST ALKALI-METAL

High quality multireference configuration interaction (MRCI) calculati ons have been employed in a comparative study of compressed structures of hydrogen and of lithium. Hexagonal and cubic clusters were allowed to distort and in both cases a minimum bond length was found at which dimerization did not occur. These calculations suggest that bulk hydr ogen under sufficiently high pressures would not have a dimer structur e and would therefore show metallic character, which has been observed for the liquid phase. We estimate that compressed hydrogen becomes me tallic at pressures exceeding 300 GPa due to a Mott transition of the electrons on the undimerised lattice. (C) 1997 Elsevier Science Ltd.