Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 107, Issue 49, Pages 20893-20898Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1006508107
Keywords
first principles; hydrogen metallization; structure prediction
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The high-pressure behavior of silane, SiH(4), plus molecular hydrogen was investigated using a structural search method and ab initio molecular dynamics to predict the structures and examine the physical origin of the pressure-induced drop in hydrogen intramolecular vibrational (vibron) frequencies. A structural distortion is predicted at 15 GPa from a slightly strained fcc cell to a rhombohedral cell that involves a small volume change. The predicted equation of state and the pressure-induced drop in the hydrogen vibron frequencies reproduces well the experimental data (Strobel TA, Somayazulu M, Hemley RJ (2009) Phys Rev Lett 103: 065701). The bond weakening in H(2) is induced by intermolecular interactions between the H(2) and SiH(4) molecules. A significant feature of the high-pressure structures of SiH(4)(H(2))(2) is the dynamical behavior of the H(2) molecules. It is found that H(2) molecules are rotating in this pressure range whereas the SiH(4) molecules remain rigid. The detailed nature of the interactions of molecular hydrogen with SiH(4) in SiH(4)(H(2))(2) is therefore strongly influenced by the dynamical behavior of the H(2) molecules in the high-pressure structure. The phase with the calculated structure is predicted to become metallic near 120 GPa, which is significantly lower than the currently suggested pressure for metallization of bulk molecular hydrogen.
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