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Details of Grant 

EPSRC Reference: EP/M010880/1
Title: Strong Correlation meets Materials Modelling: DMFT and GW in CASTEP
Principal Investigator: Refson, Professor K
Other Investigators:
Researcher Co-Investigators:
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Department: Physics
Organisation: Royal Holloway, Univ of London
Scheme: Standard Research
Starts: 30 June 2015 Ends: 30 September 2018 Value (£): 283,808
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Related Grants:
EP/M010953/1 EP/M011070/1 EP/M011038/1
Panel History:
Panel DatePanel NameOutcome
11 Sep 2014 Software for the Future Call II Announced
Summary on Grant Application Form
The function of much modern technology is based on exploiting special physical properties of materials. This might be control of electrical current in the case of semiconductors, magnetism for data storage, the Peltier effect for solid-state refrigerators, or superconductivity for ultra high power magnets used in MRI scanners. Underpinning future refinements of such "functional materials" and development of new materials and devices lies the idea of "materials design". Computer simulation methods with the power to predict the active properties based only on the quantum-mechanical behaviour of the electrons in a particular crystal structure are a vital part of any attempt to engineer "designer materials" for future devices.

The proposers of this grant are among those responsible for writing the CASTEP density-functional theory (DFT) modelling code, which is among the top few modelling codes used on the previous generation HECToR national high-performance computing service. CASTEP is licensed to nearly 100 UK research groups, was used to generate 118 research publications in 2013 and a worldwide total exceeding 4000.

Density-functional theory is the simulation method of choice for a large part of modern materials science, condensed matter physics and solid-state chemistry. It can treat a huge range of materials, including bulk metals, oxides, semiconductors, layered materials such as graphene, surfaces and much more. It is widely used to predict structural and energetic properties such as phase transitions, electronic transport properties, spectroscopic properties including NMR chemical shifts, inelastic neutron and X-Ray, Raman and infrared, XANES and other near-edge electronic spectra.

However, its success is not universal. The essential approximations to exchange and correlation (ie the LDA, GGAs and hybrids) have poor predictive power for many materials containing open d- and f-shells, frequently described as "strongly-correlated". For example many transition-metal oxides are erroneously predicted by LDA and GGA to be metallic, Jahn-Teller structural distortions are absent and phase transitions involving electron delocalisation are not reproduced.

Methods for treating strongly-correlated systems which remedy the deficiencies of semi-local DFT include dynamical mean-field theory (DMFT) and the so-called GW approximation. However these are currently not readily accessible to the materials modelling community, partly because of computational expense and partly because of the lack of robust, easily deployable modelling codes.

Herein we propose to implement both LDA+DMFT and GW within CASTEP, the UK's premier electronic structure-based materials modelling code. Our strategic target is to substantially broaden the strong-correlation modelling community in the UK, which is currently small compared to either France or Germany. The planned deliverables will offer both an extension to CASTEP with end-user capability, but also a software platform for further development of the methodology. A key feature of our DMFT implementation will be the availability of forces, and capability of structure optimization. This will enable a realistic treatment of complex materials with low site symmetry. We hope this will stimulate an growth in the adoption of these methods in the UK from the developer groups to a wider modelling community much as happened with DFT.

The power of simulation works best when used hand in hand with experimental studies. The UK has invested heavily in instruments targeted at "strongly-correlated" materials in the RIXS and ARPES beamlines at Diamond Light Source and the MERLIN instruments at ISIS target station 2 neutron facility. A key feature of this proposal is to work with scientists at both facilities to deliver the capability of modelling some of the actual materials selected for experimental study by the scientific user community. We believe this will maximise the impact of the work.

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