Quantum Mechanical Modelling of Covalently Bonded Materials
Introduction
The Exeter group is part of a consortium composed of groups at Newcastle, Sussex and Exeter having interests in a) developing an ab initio density functional method, AIMPRO, used to carry out modelling studies in several interdisciplinary areas, b) linking these studies with experimental work being carried out in a number of academic and industrial laboratories.
The three groups involved make extensive use of the T3Es at EPCC and Manchester. They have all obtained JREI support for parallel processors.
The consortium specialises in first-principles investigations of the structural, electronic, optical, magnetic and mechanical properties of large atomic aggregates using ab initio local density functional pseudopotential techniques. Calculations are carried out on very large atomic clusters, and more recently supercells, typically containing up to 800 atoms. The consortium has worked together for a number of years and has published extensively in prestigious journals.
Applications range from studying macro-molecules and nanocrystals to simulations of the bulk material. Many applications deal with the properties of defects in semiconductors and insulators and a hallmark of our approach is a close collaboration with various experimental groups.
Recent important developments include a fully parallel version of AIMPRO and the release of a supercell version, using Gaussian basis sets, written by Patrick Briddon.
Two international conferences have been held at Exeter. The first funded by NATO and entitled Early stages of oxygen precipitation in silicon was held in 1996. The second, funded by the Ψk network and CCP9, and entitled Hydrogen in Semiconductors was held this year. The £1000 secured from CCP9 for this conference was very useful as it helped a number of UK delegates to attend the meeting. In addition, a meeting for AIMPRO users was held in 1996 and funded by CCP9. CCP9 funding was also useful for collaborative visits between the Newcastle and Exeter groups.
Included below are the most prestigious publications since 1996 and follow these with a complete list of publications by the Exeter group. Further information can be obtained from our web site http://newton.ex.ac.uk/research/semiconductors/theory/jones/. The Sussex and Newcastle groups have additional publications.
New Projects and Proposals, 2000-3
We intend to improve some of the numerical procedures used in AIMPRO and extend its functionality. Specifically, we plan:
- Porting the supercell version of AIMPRO from the T3E architecture to SGI Origin and IBM SP machines.
- To include faster routines for optimisation based on the use of internal coordinates.
- Increasing the number of methods available to locate saddle points and diffusion energies. Especially, to investigate Hessian update methods.
- Additional functionality to be provided through the computation of hyperfine parameters, alternative pseudopotential schemes (in addition to those of BHS); the inclusion of spin-orbit coupling and other relativistic effects for applications to lanthanide impurities in semiconductors; and code for the evaluation of piezo-electric coefficients and the parametrisation of real spaced potentials. The last is based on AIMPRO energies and forces for selected configurations and has applications to large complex molecules.
This work will benefit from future CCP9 support by providing travel support for AIMPRO users between Exeter, Sussex and Newcastle for discussions and to organise an annual meeting to highlight progress and problems.
Prestigious Publications 1996-9
- Auto-catalysis during fullerene growth,
B. R. Eggen, M. I. Heggie, G. Jungnickel, C. D. Latham, R. Jones, and P. R. Briddon,
Science, 272, 87-9 (1996). - Interstitial-Carbon Hydrogen Interaction in Silicon,
A. N. Safonov, E. C. Lightowlers, Gordon Davies, P. Leary, R. Jones, S. Oberg,
Physical Review Letters, 77, 4812-5, (1996). - Shallow Thermal Donor Defects in Silicon,
C. P. Ewels, R. Jones, S. Oberg, J. Miro, P. Deak,
Physical Review Letters, 77, 865-8 (1996). - The twelve line 1.682 eV luminescent center in diamond and the vacancy-silicon
complex,
J. P. Goss, R. Jones, S. J. Breuer, P. R. Briddon, and S. Oberg,
Physical Review Letters, 77, 3041-4, (1996) - Limitations to n-type doping in diamond: the phosphorus-vacancy complex,
R. Jones, J. E. Lowther, and J. Goss,
Applied Physics Letters, 69, 2489-91 (1996). - Di-carbon defects in annealed highly doped GaAs,
J. Wagner, R. C. Newman, B. R. Davidson, S. P. Westwater, T. J. Bullough, T. B. Joyce, C. D. Latham, R. Jones, and S. Oberg,
Physical Review Letters, 78, 74-7 (1997). - Theory of threading edge and screw dislocations in GaN,
J. Elsner, R. Jones, P. K. Sitch, Th. Frauenheim, M. I. Heggie, S. Oberg, and P. R. Briddon,
Physical Review Letters, 79, 3672-5 (1997). - First stage of oxygen aggregation in silicon: the oxygen dimer,
S. Oberg, C. P. Ewels, R. Jones, T. Hallberg, J. L. Lindstrom, L. I. Murin, P. B. Briddon,
Physical Review Letters, 81, 2930-33 (1998). - Effect of oxygen on the growth of (1-100) GaN surfaces: The formation of nanopipes
J. Elsner, R. Jones, M. Haugk, R. Gutierrez, Th. Frauenheim, M. I. Heggie, S. Oberg, and P. R. Briddon
Applied Physics Letters, 73 3530-3532, (1998) - Calculations of Electrical Levels of Deep Centers: Application to Au-H
and Ag-H Defects in Silicon.
A. Resende, R. Jones, S. Oberg, and P. R. Briddon,
Physical Review Letters, 82, 2111-4 (1999)
