A synergistic effect of NH3BH3 and H2 on their pressurization metallization: An Ab initio molecular dynamics study

Ammonia borane (NH3BH3, AB), as a typical hydrogen-rich compound, is expected to be a promising hydrogen source for low-pressure metallization materials. However, its microscopic electronic properties subjected to pressure are not sufficiently understood yet. In this study, we systematically investigate the pressurization process of AB and its complex with H-2 to uncover their metallization mechanism, using ab initio molecular dynamics method. As pressure increase, AB first undergoes partial dehydrogenation to liberate some H-2 molecules. The metallization progress is effectively promoted via H-H center dot center dot center dot H-B interaction between new-formed H-2 and -BHx group, with the metallization pressure of 450 GPa. As to AB-H-2 compound, the electron states of AB are first activated through the enhanced interaction of H-H center dot center dot center dot H-B deriving from the additional H-2. In turn, the H-H bonds within the corresponding H-2 molecules are partially polarized. The special H-2-couples are formed through the H-H center dot center dot center dot H-H interaction, promoting the electron dispersion with each other. The whole electron channel of AB-H-2 system is threaded together by the synergistic interactions of H-H center dot center dot center dot H-B and H-H center dot center dot center dot H-H, which significantly accelerate the pressurization metallization progress, resulting in a really lower metallization pressure of 250 GPa. Our study elucidate the synergistic metallization mechanism of AB and H-2 system for the first time, which would provide a great inspiration for low-pressure metallization studies of hydrogen or hydrogen-rich materials.