A brief review of books concerning point defects in materials. There are many more, but these 4000 pages form a good start...

I am not sure what over research fields are like, but it is quite common in computational chemistry / materials science to keep small analysis codes, scripts and tricks hidden within a research group. With an increasing number of open access projects and packages, this situation is changing.

I regularly get mails from students requesting pieces of information relating to papers I have published. My new policy is to put everything useful and requested online. The best route is not clear, but for the moment, I am adding it to my research group's GitHub. The latest additions include the crystal structure of MIL-125, an inverse spinel geometry, indium oxide nanoclusters and kesterite polytypes (see here).

In terms of version control for codes, both GitHub and Bitbucket do a fine job, especially when paired with Sourcetree. On paper, Bitbucket should be the winner as they offer both public and private repositories for free, but they can't compete with the Github mascot (octocat):

Following the previous post on installing Fortran compilers in OSX 10.8 (Mountain Lions like Fortran), the next step is to efficiently exploit all of those lovely i7 cores for computational chemistry.

1. OpenMPI
- Forget any version that comes with XCode as you need to compile OpenMPI against your new Fortran installation.
- Download the binary from http://www.open-mpi.org/ (current version 1.6.3).
- Unzip and enter directory.
- Run "./configure --prefix=/usr/local/openmpi-1.6.3 CC=gcc FC=ifort F77=ifort".
- Run "make".
- Run "sudo make install".
- Add to your .bashrc or .bash_profile:
export PATH=./:/usr/local/openmpi-1.6.3/bin:~/bin:/opt/intel/bin:$PATH
export DYLD_LIBRARY_PATH=$DYLD_LIBRARY_PATH:/usr/local/openmpi-1.6.3/lib

Result:
$ which mpif90
/usr/local/openmpi-1.6.3/bin/mpif90

2. FHI-AIMS
- A popular quantum chemistry package (from here; current version 081912).
- Update the Makefile to include:

FC = ifort
FFLAGS = -O3 -ip
F90FLAGS = $(FFLAGS)
ARCHITECTURE = Generic
LAPACKBLAS = -L/opt/intel/mkl/lib \
-I/opt/intel/mkl/include -lmkl_intel_lp64 \
-lmkl_sequential -lmkl_core
USE_MPI = yes
MPIFC = mpif90

- Run "make mpi".
- Enjoy parallel calculations, e.g. mpirun -np 4 fhi-aims

3. VASP
- A popular materials modelling package (from here; current version 5.3.3).
- In the main src folder, "cp makefile.linux_ifc_P4 Makefile".
- Update the Makefile to include:

FC=mpif90
FCL=$(FC)
FFLAGS = -FR -assume byterecl
OFLAG=-O3 -ip -ftz
MKL=/opt/intel/mkl
BLAS=-L/$(MKL)/lib -I/$(MKL)/include -lmkl_intel_lp64 \
-lmkl_sequential -lmkl_core -lmkl_lapack95_lp64

- Run "make".
- Enjoy parallel calculations, e.g. mpirun -np 4 vasp

A critical essay on nanoscience by Roald Hoffmann appeared in the December issue of Angewandte Chemie. Some important points are highlighted, including the (often neglected) roles of chemical passivisation and termination on material properties, as well as the inherent instability of nanostructures. Issues with both experimental and theoretical assumptions and reports are challenged. A biting start to 2013!

Spring is the time for the best research ideas; summer is the time for writing up the work; autumn is the time for peer-review and winter is time to reap the rewards. The bounty of the last few months:

• "Phase Stability of the Earth-Abundant Tin Sulfides SnS, SnS2, and Sn2S3" L. Burton and A. Walsh, Journal of Physical Chemistry C 116, 24262 (2012).

The first publication written by my first PhD student (an iconic moment). Lee has spent a year making sense of both experiment and theory of tin sulfides towards applications in solar cells. One of his early findings was that the recently reported zinc-blende phase cannot exist (based on thermodynamic, crystallographic, computational and chemical grounds).

• “Abundance of Cu_Zn+Sn_Zn and 2Cu_Zn+Sn_Zn defect clusters in kesterite solar cells" S. Chen, L. Wang, A. Walsh, X. G. Gong and S.-H. Wei, Applied Physics Letters 101, 223901 (2012).

Attending the recent European Kesterite Workshop was inspiring: many groups across the continent working towards the common goal of low cost and sustainable solar energy.  The defect chemistry of the quaternary semiconductor Cu2ZnSnS4 (CZTS) is epic; in the latest chapter we have identified a number of defect complexes that are likely to impact the performance in CZTS solar cells.

• "Electronic structure of CuCrO2 thin films grown on Al2O3(001) by oxygen plasma assisted molecular beam epitaxy" D. Shin, J. S. Foord, R. G. Egdell and A. Walsh, Journal of Applied Physics 112, 113718 (2012).

When my long-time collaborator Russ Egdell visited Bath for a seminar last summer, we sat down to discuss our on-going projects. One issue he had was understanding why the material CuCrO2 adopted a peculiar orientation (015) when grown on Al2O3 substrates. With the aid of  crystal structure visualisation and a few back-of-the-envelope calculations we were able to explain it in a few hours. This nice paper is the result!

• “Thermodynamic and electronic properties of tunable II-VI and IV-VI semiconductor based metal-organic frameworks from computational chemistry” C. H. Hendon, D. Tiana, T. P. Vaid and A. Walsh, Journal of Materials Chemistry C 1, 95 (2013).

The first publication written by my second PhD student (another iconic moment). A first step towards systematically tuning the electronic properties of metal organic frameworks. From screening 24 compounds, five potential hybrid semiconductors were identified.

Placing almost 7,000 chemists, physicists and materials scientists in a single space for five days is always going to be an intense experience. The Fall Meeting of the Materials Research Society is one of my favourite conferences, although it is growing so large that it may soon implode. An endless programme of talk titles, over forty symposia, poster sessions that felt like rush hour trains, and a fight for coffee at break-times. The advantage is the variety of science on offer; if you can't find talks that interest you, then you should probably quit the field!

(day)

(night)

The highlight is of course meeting people, but there were also some notable presentations:

(From Symposium Z: Semiconducting Oxides, where I spend most of my time)

Band Lineup of Oxide Semiconductors (Hideo Hosono)
- The world leader of transparent conducting oxides gave a good overview of his group's recent work; although, band lineups only received a brief mention. The future points towards indirect band gaps.

Band Energies and Doping Limits of Metal Oxides (Aron Walsh)
- Obviously, the talk of the week.

Selection Rule of Preferred Doping Site for n-type Transparent Conducting Oxides (Su-Huai Wei)
- Trying to distinguish between when to dope cation sites (e.g. Al on Zn in ZnO) or anion sites (e.g. F on O in SnO2) for maximum effect.

Thermodynamics of Carrier Compensation in Ga-doped ZnO (Stephan Lany)
- A revision of earlier work on carrier concentrations in ZnO, but with the addition of corrections from GW theory and the contribution of charge-compensated defect clusters.

Temperature Dependence of the Direct Band Gap and Transport Properties of CdO (Tim Veal)
- The band gap of CdO has been revised several times over the past century. A clear picture emerges when band filling and remormalisation effects are treated properly.

(Plenary talks)

Climbing the Ladder of Density Functional Approximations (John Perdew)
- A demonstration that effective presentations do not have to be aesthetic. A powerful recap of the origins of density functional theory and current developments.

Quasicrystals: Discovery, Structure, Properties and Uses (Danny Shechtman)
- "Choose your field and become an expert in it." An inspiring talk about fighting the establishment with five-fold symmetry.

(From friends who made the week very enjoyable)

P-type Transparent Conducting Oxides: Intrinsic Limitations and Future Directions (David Scanlon)
- A brief summary of his epic PhD work, and an outline of a "madcap" project to screen quinternary oxy-chalcogenides.

MBE Growth and Characterisation of CuCrO2(001) and (015) Thin Films (Russ Egdell)
- How a "simple" material can give a complex reflection when grown on corundum.

Electronic Structure and Surface Properties of Ga and Tl Doped In2O3 (Anna Regoutz)
- Indium may or may not be running out, but it takes guts to investigate Tl doping of indium oxide.

Limits to Doping of Wide Band Gap Oxide Semiconductors and Related Materials (John Buckeridge)
- Re-addressing the doping limits of materials from a chemistry perspective.

Simulation of Hetero- and Nano-structured AgI: The Role of Polytypism and Morphology in Extreme Ag⁺ Ionic Conductivities (Ben Morgan)
- How ion diffusion is more complex than we commonly think; the small details (really) matter.

Back to the real world now, where today I officially became a Reader (to the confusion of all except UK academics).