Research Article

Silane plus molecular hydrogen as a possible pathway to metallic hydrogen

Yansun Yao and Dennis D. Klug
PNAS December 7, 2010 107 (49) 20893-20898; https://doi.org/10.1073/pnas.1006508107

  1. Edited* by Russell J. Hemley, Carnegie Institution of Washington, Washington, DC, and approved October 11, 2010 (received for review May 10, 2010)

Article Figures & SI

Figures

  • Fig. 1.
    Fig. 1.

    Calculated and experimental EOS as functions of pressure. The experimental EOS (11) are shown for compression (filled circles) and decompression (empty circles). The pressure at which the slight strained fcc cell distorts to a rhombohedral cell is marked by an arrow. Below 15 GPa, a full optimization on the P1 structure yields the I-4m2 space group.

  • Fig. 2.
    Fig. 2.

    The (A) I-4m2, (B) Imm2, and (C) P1 structures shown with their lattice vectors (a, b, and c) in the accordingly distorted fcc unit cell. The Si atoms (larger spheres) are located at the fcc sites and bonded to four H atoms (smaller spheres). The H2 molecules at the octahedral and tetrahedral sites are shown in dark and light gray, respectively. Simulated X-ray diffraction patterns (D) at 15.5 GPa (X-ray wavelength = 0.5 Å) for the I-4m2, Imm2, P1, and undistorted fcc structures.

  • Fig. 3.
    Fig. 3.

    Calculated pressure dependences of the H2 vibron frequencies of the I-4m2, Imm2, and P1 structures of SiH4(H2)2. The notations T and O refer to the H2 molecules at tetrahedral and octahedral sites.

  • Fig. 4.
    Fig. 4.

    Calculated valence charge density of SiH4(H2)2 in the (110) plane of the fcc lattice (distorted accordingly) for I-4m2 structure at 6.9 GPa, and P1 structure at 15.7 and 99.2 GPa. For a clearer presentation, atoms are removed from the right half of planes. The atoms that are not surrounded by charge densities belong to the nearest plane above. The notations T and O refer to H2 molecules at tetrahedral and octahedral sites.

  • Fig. 5.
    Fig. 5.

    Calculated electronic DOS projected on SiH4 and H2 molecules for (A) I-4m2 structure at 0.27 GPa, (B) I-4m2 structure at 6.9 GPa, (C) P1 structure at 99.2 GPa, and (D) P1 structure at 152.7 GPa. The notations T and O refer to the H2 molecules at tetrahedral and octahedral sites. The origin “0” in energy corresponds to the highest energy of the occupied states.

  • Fig. 6.
    Fig. 6.

    Evolution of the simulation cell dimensions and angles for the (A) I-4m2 and (B) P1 structures of SiH4(H2)2 at 12 and 34 GPa, respectively, from NPT CPMD simulations at 300 K. (C) Calculated static structure factor (X-ray wavelength = 0.5 Å), Embedded Image, for the I-4m2 and P1 structures from the calculations indicated in A and B. See text and SI Appendix.

  • Fig. 7.
    Fig. 7.

    Depicted trajectories of Si (yellow) and H atoms (white) in SiH4 molecules in the (A) I-4m2 and (C) P1 structures of SiH4(H2) obtained from NVE CPMD simulations. Depicted trajectories for hydrogen molecules at the octahedral (green) and tetrahedral (blue) sites in the (B) I-4m2 and (D) P1 structures of SiH4(H2)2 from simulations for A and C. The distorted fcc unit cells are identified by solid lines.

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Silane plus molecular hydrogen as a possible pathway to metallic hydrogen
Yansun Yao, Dennis D. Klug
Proceedings of the National Academy of Sciences Dec 2010, 107 (49) 20893-20898; DOI: 10.1073/pnas.1006508107
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