Structures at high pressure from random searching

An approach to searching for the structures of crystals is described. We choose an ensemble of "random" starting structures and relax them, often constraining the starting structures and/or relaxation to bias the search in some manner. The methodology is illustrated by applications to high-pressure phases of group IV hydrides, especially silane (SiH 4 ), and to solid hydrogen, using first-principles density-functional-theory methods. We discuss the issue of possible decomposition of group IV hydrides into their constituent elements under pressure. A new molecular-hydrogen structure is described whose enthalpy is calculated to be slightly lower than all other known structures in the pressure range 75-108 GPa, and we mention its possible relevance to phase II of hydrogen.

[1]  R. Needs,et al.  Graphite intercalation compounds under pressure : A first-principles density functional theory study , 2007 .

[2]  Chris J Pickard,et al.  Highly compressed ammonia forms an ionic crystal. , 2008, Nature materials.

[3]  N. Ashcroft.  Hydrogen dominant metallic alloys: high temperature superconductors? , 2004, Physical review letters.

[4]  A. Ruoff,et al.  Solid hydrogen at 342 GPa: no evidence for an alkali metal , 1998, Nature.

[5]  Richard M. Martin.  Electronic Structure: Frontmatter , 2004 .

[6]  R. Martin,et al.  Electronic Structure: Basic Theory and Practical Methods , 2004 .

[7]  Chris J. Pickard,et al.  Metallization of aluminum hydride at high pressures: A first-principles study , 2007 .

[8]  Roald Hoffmann,et al.  Structures and Potential Superconductivity in SiH~4 at High Pressure: En Route to "Metallic Hydrogen" , 2006 .

[9]  H. Mao,et al.  X-ray diffraction and equation of state of hydrogen at megabar pressures , 1996, Nature.

[10]  N. Ashcroft,et al.  A superconductor to superfluid phase transition in liquid metallic hydrogen , 2004, Nature.

[11]  Matt Probert,et al.  First principles methods using CASTEP , 2005 .

[12]  Chris J. Pickard,et al.  Structure of phase III of solid hydrogen , 2007 .

[13]  J. Rodgers,et al.  Structure and spectroscopic properties of dense solid hydrogen at 160 GPa , 2008 .

[14]  Chris J Pickard,et al.  High-pressure phases of silane. , 2006, Physical review letters.

[15]  Paul Loubeyre,et al.  Optical studies of solid hydrogen to 320 GPa and evidence for black hydrogen , 2002, Nature.

[16]  R. Needs,et al.  When is H2O not water? , 2007, The Journal of chemical physics.

[17]  Yang Song,et al.  Crystal structure ofSiH4at high pressure , 2007 .

[18]  J. S. Tse,et al.  Superconductivity in Hydrogen Dominant Materials: Silane , 2008, Science.

[19]  Russell J. Hemley,et al.  Ultrahigh-pressure transitions in solid hydrogen , 1994 .

[20]  K Tanaka,et al.  Novel superconductivity in metallic SnH(4) under high pressure. , 2007, Physical review letters.

[21]  Chris J. Pickard,et al.  Hydrogen/silicon complexes in silicon from computational searches , 2008, 0808.1203.