Organisers

• Graeme Watson (Trinity College Dublin)
• Charles Patterson (Trinity College Dublin)
• Simon Elliott (Tyndall National Institute)
• Michael Nolan (Tyndall National Institute, Cork)

Supports

Science Foundation Ireland

   Psi-k

ACAM - Atlantic Centre for Atomistic Modelling

University College Dublin

Description

The workshop will be held in the Schroedinger lecture theatre in the School of Physics, Trinity College Dublin, where Erwin Schroedinger gave a series of public lectures entitled, 'What is Life?' in 1943.

The official webpage for this workshop is available at

www.tyndall.ie/research/theory-and-modelling/oxides_workshop/index.html

Please register for the workshop via the official workshop webpage.

Bookings for accommodation in Trinity College may be made via the official workshop webpage. Additional details of hotel accommodation, how to get to the workshop, etc. are available on the official webpage.

The registration fee for the workshop is 40 Euro. There will be a workshop dinner on the evening of 10th September for which there will be a separate charge.

Scientific Objectives

The principal aim of the workshop will be to bring together experts in oxide computer simulation and experiment who study oxide defects and surfaces to discuss outstanding problems in understanding defects, dopants and surfaces of oxides.

Oxides in their native crystalline state are usually semiconductors or insulators with a band gap of several electron volts. However, when doped or in the presence of defects, oxides frequently become conducting, magnetic or even superconducting. Examples of this type of behaviour include combined conductivity and optical transparency in SnO2, unexpected ferromagnetism in Zn1-xCoxO or even MgO1-xNx and superconductivity in the high temperature superconductors. Oxides continue to play an essential role in state of the art electronics; inclusion of HfO2 as a dielectric in the latest Intel transistors is a prime example of this. Defective and doped oxides pose challenging problems to both experimentalists and theorists owing to low defect or dopant ion density, lack of long range order and interaction over long range in most bulk oxides. From the experimental point of view, identification of the structure and charge states of defects is a challenge. This will be addessed by Alan Chadwick and David Look who will deal with structural and optical properties of defects. From a theoretical point of view there are challenges in understanding the local electronic structure of defects as well as long range interactions between defects through which charge is transferred between defects in conduction processes. This is especially complicated by the fact that widely used and relatively computationally inexpensive density functional methods fail to give a good description of the band gaps of oxides and consequently predictions of defect level positions and charge transition energies are in doubt. There is some promise in hybrid density functional methods which mix conventional density functionals with Hartree-Fock exchange, however these methods are computationally more expensive. Georg Kresse, the principal author of the VASP code, will compare density functional + U calculations with hybrid functional calculations for a range of oxides. A number of other internationally leading figures in computer simulation of materials who work in oxides will speak at the workshop and their topics are listed in the programme. There are two main themes to the workshop – defects, dopants and their impact on bulk oxide conductivity as well as oxide surfaces, with an emphasis on catalysis. There will be opportunities for oral and poster contributions from workshop participants.

Some of the principal questions of interest are:

How do defects impact the electrical and optical properties of oxides?

What can defect spectroscopies tell us with reasonable certainty about defects?

How important is polaron formation in carrier transport in oxides?

Which are the most promising methods for simulation of the structure and electronic structures of oxide defects?

How do you calculate defect formation and charge transition state energies in defective oxides?

References

[1] Evidence for native defect donors in n-type ZnO,
D. C. Look et al. Phys. Rev. Lett. 95, 225502 (2005)

[2] X-ray absorption studies of the structure of nanocrystalline oxides,
A. V. Chadwick, Solid State Ionics 177, 2481 (2006)

[3] Defect energetics in ZnO: A hybrid Hartree-Fock density functional study,
F. Oba, A. Togo, I. Tanaka, J. Paier and G. Kresse, Phys. Rev. B 77, 245202 (2008).

[4] Sources of electrical conductivity in SnO2,
A. K. Singh, A. Janotti, M. Scheffler and C. G. Van de Walle, Phys. Rev. Lett. 101, 055502 (2008).

[5] Theoretical Description of Carrier Mediated Magnetism in Cobalt Doped ZnO,
A. Walsh, J. L. Da Silva and Su-Huai Wei, Phys. Rev. Lett. 100, 256401 (2008).

[6] Ultrathin oxides: Bulk-oxide-like model surfaces or unique films?
C. Freysoldt, P. Rinke, and M. Scheffler, Phys. Rev. Lett. 99, 086101 (2007).

[7] First Principles LDA+U and GGA+U Study of Cerium Oxides: Dependence on the Effective U-Parameter,
C. Loschen, J. Carrasco, K. M. Neyman and F. Illas, Phys. Rev. B, 75 035115 (2007).

[8] Modelling of Structures of Heterogeneous Catalysts, C. R. A. Catlow, R. G. Bell, B. Slater and S. M. Woodley (2008) in G. Ertl, H. Knözinger, F. Schüth, and J. Weitkamp (ed.) Handbook of Heterogeneous Catalysis. Weinheim: Wiley-VCH, 2nd edition.

[9] Catalysis by doped oxides: CO oxidation by AuxCe1-xO2,
V. Shapovalov and H. Metiu, J. Catalysis 245, 205 (2007).

[10] Formation and Catalytic Activity of Partially Oxidized Pd Nanoparticles,
T. Schalow, B. Brandt, M. Laurin, S. Guimond, D. E. Starr, Sh. K. Shaikhutdinov, S. Schauermann, J. Libuda, H.-J. Freund, Topics in Catalysis 42, 387 (2007).

[11] Small polarons and magnetic anti-phase boundaries in Ca2−xNaxCuO2Cl2 (x=0.06, 0.12): origin of striped phases in cuprates
C. H. Patterson, Phys. Rev. B 77 94523 (2008)

[12] Role of defects in ferromagnetism in Zn1-xCoxO: a hybrid density functional calculation
C. H. Patterson, Phys. Rev. B 74, 144432 (2006).