Department of Materials Science & Metallurgy

Chris Pickard

Zoe Barber portrait

Sir Alan Cottrell Professor of Materials Science

BA University of Cambridge
PhD University of Cambridge

+44 (0)1223 334338
cjp20@cam.ac.uk
www.msm.cam.ac.uk/

Computational Spectroscopy

My PhD research resulted in a first principles approach to the computation of energy loss near edge structure (ELNES). Recent advances in energy loss resolution, computational resources and structural prediction, mean that its latest incarnation (OptaDOS) is increasingly used in the microscopy community. With Francesco Mauri, I went on to develop a quantitative theory for the prediction of magnetic response in the solid state, applicable to the whole periodic table. Based on our gauge including projector augmented waves (GIPAW) it enables the prediction of nuclear magnetic resonance (NMR) chemical shifts, quadrupolar coupling constants, J-coupling constants, electron paramagnetic resonance (EPR) g-tensors and hyperfine parameters. It has revolutionised the interpretation of solid-state NMR spectra, and is an integral part of " NMR Crystallography".

Material Structure Prediction
My strikingly simple response to the “grand” challenge of material structure prediction is based on a random sampling of structure space, and careful, first principles total energy minimisations. Ab initio Random Structure Searching (AIRSS) has been extended to search for compounds, defects, clusters, surfaces and interfaces and is now a standard tool for computational materials discovery.

High Pressure Research
Early applications (with Richard Needs) of AIRSS have been to the behaviour of materials under extreme compression. High profile results include an excellent candidate for the elusive phase III of solid hydrogen, along with the anticipation of the “mixed” graphene-like phase IV, and the prediction (since confirmed) that ammonia will adopt an ionic ammonium amide crystal structure at megabar pressures. The discovery that aluminium is expected to adopt a non-close packed incommensurate phase above 3TPa, significantly modifying the equation of state, has been held as to introducing a new paradigm in ultra-dense matter. Where it was assumed that extreme compression would lead to mundane close packed crystal structures, we have shown that the terapascal regime (and beyond) is to be expected to provide a rich playground of new physics for the latest dynamic compression experiments to explore.

 

Graphene grain boundary structures
Graphene grain boundary structure between armchair and zigzag regions. The red transparent region marks the interface between the two grains, forming a continuous chain of pentagons and heptagons in the otherwise pristine graphene. (See Schusteritsch 2014)
  • G Schusteritsch, C J Pickard, "Predicting interface structures: From SrTiO3 to graphene", Physical Review B, 90(3), Article No. 035424 (2014 )
  • C J Pickard, R J Needs, "Ab initio random structure searching", Journal of Physics-Condensed Matter, 23(5), Article No. 053201 (2011)
  • S J Clark, M D Segall, C J Pickard, P J Hasnip, M J Probert, K Refson, M C Payne, "First principles methods using CASTEP", Zeitschrift fur Kristallographie, 220(5-6), 567-570 (2005)
  • C J Pickard, F Mauri, "All-electron magnetic response with pseudopotentials: NMR chemical shifts", Physical Review B, 63(24), Article No. 245101 (2001)