While working at University College London, I was housed in the Kathleen Lonsdale Building*. It had been the Chemistry building a few decades prior, but now contains a mixture of geology, mathematics and computational materials science.  On the dusty third floor annex, there is one curious office that serves both as a space for the group's computer server and a temporary desk space for Prof. Peter Day. The latter recently published his autobiography, On the Cucumber Tree.

I had known that Peter Day was a successful solid-state chemist, but little else. This book was full of revelations! In short, his career developed from studies at Oxford, to working Bell Labs, running a synchrotron in Grenoble, and becoming director of the Royal Institution in London. What makes it a captivating read is his personal perspective and context, e.g. the Oxford University experience as a complete outsider, the subtleties of European and UK scientific politics, and a few cases of name and shame (one being the Duke of Kent's paltry donation to the redevelopment of the Royal Institution).

I doubt one of the goals of the book was the dissemination of research, but in my case it worked. Some early studies of mixed-valence inorganic solids and molecular ferromagnetics were completely new to me. Sadly tracking such papers down is becomingly increasingly difficult, with libraries culling old paper copies and not subscribing to extended online archives in order to save on cost. Hopefully, the move towards open access will prevent this in the future, but the fact that neither myself or colleagues at UCL and Oxford have access to the original Robin-Day paper on mixed valence chemistry is a sad state of affairs.

*Named after the Irish X-ray pioneer and first female FRS, Kathleen Lonsdale.

This Summer I was lucky enough to have two trips to South Korea. My last trip in 2010 seems like a long time ago. Again, I was impressed by the quality of the science, the food and the people. The visit had three parts:

1. Opening of the Global E3 Institute at Yonsei University
The tradition and formality that comes with the opening of a new institute came as a surprise (white gloves, gold scissors, red carpet). The international links between science, engineering were clear from the start with a mixture of speakers from the US, UK, Korea and Japan. The talks covered everything from post-Fukushima energy policy in Japan to the development of improved thermoelectric devices, and the issues associated with educating children about nano-science and energy materials. I hope that the University of Bath will become part of this consortium in the future, which is being led by Prof. Bob Chang in Northwestern.

2. Seminar at KAIST
The Korean Advanced Institute of Science and Technology is considered the MIT of east Asia. The city of Daejeon is less than an hour from Seoul by fast train, and has a very different feel. The campus is massive, in a beautiful location at the edge of a mountain range. My host was Prof. Yong-Hyun Kim, a former colleague at NREL, and who is now leading the Quantum Nano-Bio Materials Simulation Group. They tackle issues ranging from hydrogen storage and graphene modification to microscopic theories of pH. The graduate school in Nanoscience sets the research bar very high, and I had some very stimulating discussions, as well as delicious food (below is fried kimchee & tofu, along with a special black bean pasta).

3. MTG Tutorial Seminar on Defect Chemistry at Yonsei University
One of the challenges about working on the science of lattice defects in materials is that the description, notation and understanding varies greatly between different disciplines (chemistry, physics and engineering). The group of Prof. Soon is particularly diverse (including students from materials science to civil engineering), so one of the principal goals from such a lecture is to put everyone on the same page with some of the fundamentals. Hopefully it succeeded. Afterwards, we were treated to a very special group Korean barbeque, which I will take as a good sign!

*During a mini-typhoon, I also found some time for shopping in Gangnam at COEX mall (underground, so a safe hideout), visiting a student market in Hongdae, and a little more socialising with the MTG. 감사합니다!

The second third of the year has involved studies of new photo-active materials (including one previously unknown) and a quaternary high-temperature antiferromagnet.

• "Bandgap engineering of ZnSnP2 for high-efficiency solar cells" D. O. Scanlon and A. Walsh, Applied Physics Letters 100, 251911 (2012).

As the demand for solar cells increases, diversity in the materials (and source elements) involved is essential. ZnSnP2 is one very interesting case, where a single material system has the potential for high-efficiency light-to-electricity conversion. This work resulted from a collaboration with Dr. David Scanlon, currently a Ramsay Fellow at University College London.

• "A photoactive titanate with a stereochemically active Sn lone pair: Electronic and crystal structure of Sn2TiO4 from computational chemistry" L. A. Burton and A. Walsh, Journal of Solid-State Chemistry 196, 157 (2012).

My PhD research on lone pairs in the solid-state was reborn during my postdoctoral work, when I came across BiVO4 as a promising photocatalyst for H2 production from water. The Bi(III) ion has a stereochemically active 6s2 lone pair, which results in a reduced ionisation potential for the material. Sn2TiO4 is a novel analog, which combines Sn(II) and Ti(IV), and was one of the first projects for my PhD student Lee Burton.

• "Magnetic properties of Fe2GeMo3N; an experimental and computational study" P. D. Battle, L. A. Sviridov, R. J. Woolley, F. Grandjean, G. J. Long, C. R. A. Catlow, A. A. Sokol, A. Walsh and S.  M. Woodley, Journal of Materials Chemistry 22, 15606 (2012).

For his final year undergraduate project at Oxford, Russell Woolley was charged with synthesising a quinternary alloy and measuring its magnetic response. On top of that, he had the energy to perform to electronic structure calculations, before eventually moving to Imperial College for his PhD. This paper  covers one of the end member compounds, which itself is sufficient complex to warrant the input from nine authors, and just as many solid-state techniques.

• "Prediction on the existence and chemical stability of cuprous fluoride" A. Walsh, C. R. A. Catlow, R. Galvelis, D. O. Scanlon, F. Schiffmann, A. A. Sokol and S. M. Woodley, Chemical Science 3, 2565 (2012).

A subsection of the Kathleen Lonsdale Materials Chemistry group at University College London is the Phantom Fellows. Our investigation of CuF resulted from a side-project of a sub-project of a splinter-project originally conceived by Dr. Alexey A. Sokol. It is the type of work that keeps things interesting when your main research is not going to plan. The full story was kindly covered by Chemistry World.

The main advantage of the VASP code is a reliable set of pseudopotentials covering the entire periodic table. Earlier this year a new set was released with additional potentials optimised for GW calculations. The old potentials remained largely unchanged according to the release document: "In most cases the potentials are literally identical to the previous releases".

After struggling to understand some peculiar results, I realised that the last statement is not always true. The culprit appears to be related to core charges and corrections, which has changed for quite a few elements even for the LDA/PBE sets.

Using VASP 5.2.12 with identical POSCAR, KPOINT and INCAR files, the following results were obtained for oxygen (triplet state, 500 eV planewave cutoff, PBEsol).

(a) Old POTCAR "PAW_PBE O 08Apr2002"
Atom:   -0.974485 eV
Molecule: -9.048636 eV
Binding: -7.099666 eV

(b) New POTCAR "PAW_PBE O 08Apr2002"
Atom: -1.571040 eV
Molecule: -10.239136 eV
Binding: -7.097056 eV

Clearly the energy shifts introduced can cancel for a balanced reaction, but if you mistakenly combine calculations using both sets (which appear the same in the header!), you will run into problems.

A slow running laptop was a good excuse to play around with a fresh install of OSX 10.8 (Mountain Lion). The implementation of Xcode has been changing over the last few versions, so here are the few straight forward steps required to get command-line Fortran running on your Mac.

1. Download Xcode from the App Store
- Run application to Install
- Xcode Preferences -> Downloads -> Command Line Tools

2. GNU Compilers
- Download 10.8 gcc and gfortran binaries and libraries from http://hpc.sourceforge.net.
- In terminal run "sudo tar -xvf gcc-mlion.tar -C /"
- Ensure the line "export PATH=/usr/local/bin:$PATH" is in your .bash_profile.

Result:
$ gfortran --version
GNU Fortran (GCC) 4.8.0 20120722 (experimental)
$ gcc --version
gcc (GCC) 4.8.0 20120722 (experimental)

3. Intel Compilers (Fortran Composer 2011)
- Install package.
- For install environment choose "Command line install only".
- If write permission issues arise, run "sudo chmod u+rwx /Users/Shared/Library/Application\ Support/".
- source /opt/intel/bin/ifortvars.sh intel64
- source /opt/intel/mkl/bin/intel64/mklvars_intel64.sh
- Run once as "sudo ifort" to overcome some permissions issues with the libraries.

Result:
$ ifort --version
ifort (IFORT) 12.1.0 20111011

Example Makefile (FHI-AIMS):
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

The landscape is rapidly changing in the world of electronic structure calculations. When I started in the area, even the optimization of a low symmetry crystal structure with a first-principles approach was a significant computational challenge. Now with computing cores become cheaper and more abundant, density functional theory calculations, especially with local or semi-local functionals, are becoming routine and can be tackled even with a (powerful) desktop processor such as the Intel i7. So what should we do with our high-performance computers?

This week there were two good examples of combinatorial computations, each different in their approach.

"New Cubic Perovskites for Single- and Two-Photon Water Splitting using the Computational Materials Repository" led by Karsten Jacobson
Theory: RPBE (structures); GLLB-SC (band gaps).
Concept: Take a single structure type and substitute in 19000 elemental combinations; screen for properties related to photoelectrochemistry.
Result: 20 candidate materials.
Comment: An effective brute force approach, with the main limitation being the assumption of a single crystal structure (perovskite). This work is part of the Computational Materials Repository project.

"Prediction of A₂BX₄ metal-chalcogenide compounds via first-principles thermodynamics" led by Alex Zunger
Theory: PBE / PBE+U.
Concept: Take a single material stoichiometry (A2BX4) and investigate 429 unreported materials in 40 structure types; screen for thermodynamic stability / accessibility.
Result: 100 new and theoretically stable materials.
Comment: Technically this is the more creative approach as the crystal structure is not constrained. In addition to 40 known structure types, a global structure optimization method is used to assess some compounds, and a range of magnetic configurations are also included for transition metals.  As a result, the computational cost quickly elevates from 429 material systems to > 70000 calculations. This work is part of the Center for Inverse Design.

These studies form part of a wider trend, with a number of codes and databases appearing over the past few years:

CALYPSO (Global structure optimization)
USPEX (Global structure optimization)
XTALOPT (Global structure optimization)
CompES (Database)
Materials Project (Database)

It was quickly realised after the initial hype for experimental combinatorial chemistry that it is not a cure-all approach, but as we have access to supercomputers with 100000s of processing cores,  combinatorial computational chemistry is becoming an increasingly powerful tool.