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AIRSS

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Cambridge

Richard Needs' Group

Andrew Morris' Group

UCL

Chris Pickard's Group

Full publication list: AIRSS publications

Contents

High-pressure phases

This section describes the work of Prof Chris Pickard and Prof Richard Needs

I41/a phase of silane

In the first paper, Pickard and Needs applied the AIRSS technique to high-pressure phases of silane [Phys. Rev. Lett. 97, 045504 (2006)], first showing that the AIRSS method works well by performing tests on silicon at zero pressure. They correctly found the four experimentally verified phases. They concluded that there is a metal phase of silane that could be obtained experimentally. This phase may be candidate for high temperature superconductivity. The high-pressure insulating I41/a phase predicted in this paper has been observed in the recent x-ray diffraction studies of Eremets et al. [Science 319, 1506 (2008)].

Pm-3n phase of aluminium hydride

In [Phys. Rev. B 76, 144114 (2007)] a new phase of aluminium hydride that is metallic at sufficiently low pressures to be seen in a diamond anvil cell was predicted using AIRSS. The high-pressure metallic Pm-3n phase predicted in this paper has been observed in the recent x-ray diffraction studies of Goncharenko et al. [Phys. Rev. Lett. 100, 045504 (2008)].

High pressure hydrogen

Since this early work Pickard and Needs have applied the AIRSS method to a range of other high-pressure problems such as how calcium interlocates between graphene sheets [Phys. Rev. B 75, 085432 (2007)]: how hydrogen bonds at high pressure [Nature Physics 3, 473 (2007) ] : new phases of H2O [J. Chem. Phys. 127, 244503 (2007) ], and interesting new phases of ammonia [Nature Materials 7, 775 (2008)], that form the rather unexpected NH-2 + NH+4 ionic molecular crystals rather than a homogenous mix of NH3.

Key Publications

  1. High-Pressure Phases of Silane, Chris J. Pickard and R. J Needs, Phys. Rev. Lett. 97 045504 (2006), DOI:10.1103/PhysRevLett.97.045504.
  2. Structure of phase III of solid hydrogen, Chris J. Pickard and R. J Needs, Nature Physics 3 473 (2007), DOI:10.1038/nphys625.
  3. Highly compressed ammonia forms an ionic crystal, Chris J. Pickard and R. J Needs, Nature Materals 7 775 (2008), DOI:10.1038/nmat2261.

Point-defects

See also Research#Point-defects

{H,Si} defect in silicon

Point defects play an important role in many areas of materials science. For example defects in bulk semiconductors can drastically alter the electronic properties of the semiconductor.

We employ to point-defect problems the AIRSS philiosphy. We randomise the atoms within a sphere in the perfect lattice and then relax them to a local-energy minima using quantum mechanical forces. By repeating this many times with different random starting positions we map out the configurational space. The low energy defects we find are then be further analysed.

We have used d-AIRSS on complicated defects in silicon and diamond, there have applications in semiconducting devices, quantum computing and lithium ion battery anodes. We have also used d-AIRSS on the nuclear waste encapsulation material zirconolite.

The OptaDOS code that we develop is able to produce high-quality electronic density of states, showing in a visually appealing way both the dispersive lattice DOS and the highly-localised impurity states.

Key Publications

  1. Lithiation of silicon via lithium Zintl-defect complexes from first principles, Andrew J. Morris, R. J. Needs, Elodie Salager, C. P. Grey, and Chris J. Pickard, Phys. Rev. B 87 174108 (2013), DOI:10.1103/PhysRevB.87.174108.
  2. Hydrogen/silicon complexes in silicon from computational searches, Andrew. J. Morris, Chris J. Pickard and R. J. Needs, Phys. Rev. B 78 184102 (2008), DOI:10.1103/PhysRevB.78.184102.
  3. Energetics of hydrogen/lithium complexes in silicon analyzed using the Maxwell construction, A. J. Morris, C. P. Grey, R. J. Needs and C. J. Pickard, Phys. Rev. B 84 224106 (2011), DOI:10.1103/PhysRevB.84.224106.

Materials Discovery

High-throughput computation accelerates the design of new materials by allowing us to ask “what if” without the time and expense of manufacturing and categorising samples. Since petascale computing is becoming the norm, it is imperative that techniques harness this ever increasing computing power to provide deep insight of real materials.

The Phases of lithium germanide found using computational structure prediction

Key Publications

  1. Ab initio structure search and in situ 7Li NMR studies of discharge products in the Li-S battery system, , Kimberly A. See, Michal Leskes, John M. Griffin, Sylvia Britto, Peter D. Matthews, Alexandra Emly, Anton Van der Ven, Dominic S. Wright, Andrew J. Morris*, Clare P. Grey* and Ram Seshadri*, J. Am. Chem. Soc. 136 16368 (2014), DOI:10.1021/ja508982p.
  2. Thermodynamically stable lithium silicides and germanides from density-functional theory calculations, Andrew J. Morris, C. P. Grey and Chris J. Pickard, Phys. Rev. B 90 054111 (2014), DOI:10.1103/PhysRevB.90.054111.
  3. Revealing lithium-silicide phase transformations in nano-structured silicon-based lithium ion batteries via in situ NMR spectroscopy, K. Ogata, E. Salager, C. J. Kerr, A. E. Fraser, C. Ducati, A. J. Morris, S. Hofmann and C. P. Grey, Nature Comm. 5 3217 (2014), DOI:10.1038/ncomms4217.
  4. Inorganic Double Helix Structures of Unusually Simple Li-P Species, Alexander S. Ivanov, Andrew J. Morris, Konstantin V. Bozhenko, Chris J. Pickard and Alexander I. Boldyrev, Angew. Chemie Int. Ed. 51 33, 8330-8333 (2012), DOI:10.1002/anie.201201843.