In recent years we have been observing huge progress in first principles defect science. However, due to the widespread interest in defects, new developments have been disconnected with little crosstalk between the various disciplines and communities. In our experience, defects are typically discussed at topical conferences on specific materials or material classes. It was our aim to change this state of affairs with our proposed workshop.
By pooling expertise in a single event we intended to provide a unique opportunity for assessing the current state of the field. We have brought together a representative selection of distinguished researchers in defect science. In oral presentations, the invited speakers have addressed the different aspects of the grand challenges at stake in the modelisation of defects. Ample discussion time has been reserved after each presentation to reflect on the immediate challenge and its ramifications. In addition, we have organized a round table discussion, in which general interest topics that do not fit the regular scientific talks have been discussed.
Theory of Heusler and Full-Heusler Compounds
Iosif Galanakis Department of Materials Science, School of Natural Sciences, University of Patras, GR-26504 Patra, Greece
Spintronics/magnetoelectronics brought at the centre of scientific research the Heusler and full-Heusler compounds, since several among them have been shown to be half-metals. In this review we present a study of the basic electronic and magnetic properties of both Heusler families; the so-called semi-Heusler alloys like NiMnSb and the full-Heusler alloys like Co2MnGe (usual full-Heuslers), Mn2CoAl (inverse full-Heuslers) and (CoFe)MnAl (LiMgPdSn-type full-Heuslers). First-principles calculations are employed to discuss the origin of the gap which is fundamental for the understanding of their electronic and magnetic properties. For half-metallic Heusler compounds the total spin magnetic moment Mt scales linearly with the number of the valence electrons Zt in the unit cell. These simple rules connect directly the magnetic to the electronic properties opening the way to engineer new half-metallic alloys with ”à la carte” magnetic properties such as the quaternary half-metals, the so-called half-metallic antiferromagnets, magnetic semiconductors or even the more exotic spin-gapless semiconductors. Finally, special topics like exchange constants, defects, vacancies, surfaces and interfaces are being discussed.
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Sam and I were in Pisa recently at the invitation of Prof. Vincenzo Barone from the Theoretical Chemistry group at the Scuola Normale. Prof. Barone is amongst other things, Professor of Theoretical and Computational Chemistry in Pisa, President of the Italian Chemical Society, and author of more than 650 publications, which for a young man like me still stuck on around 60 papers is something to aspire to, to say the least.
Despite the literal meaning of ‘Normal School’ – which in English sounds like somewhere you go if you can’t get into a good school – the Scuola Normale is probably Italy’s most prestigious university – founded in 1810 by Napoleonic decree as the sister of the École Normale in Paris. It is very much an elite institution, and to become a student there, candidates have to pass an extremely selective admissions exam with only a 6% pass rate – every year only sixty candidates are admitted out of nearly 1000 applicants. The main building is the overwhelmingly beautiful Palazzo della Carovana (pictured above) which was designed and built by Giorgio Vasari in the 1500s as the headquarters of the Knights of Saint Stephen. It is situated in Piazza dei Cavalieri – the second main square in Pisa and right in the heart of the action. What a fantastic place to work, I have to say! It certainly beats the modern incarnation of the pebble-dashed prefab Cavendish Laboratory – which was moved out of the centre of Cambridge to a field three miles away in the 1970s. This was done at probably the worst moment in history for British architecture at a cost of only two million pounds and it really shows; despite inflation that wasn’t very much money back then either.
I learned from Daniela the barmaid that the old people were saying it was the worst summer weather in Tuscany since 1915. Surely they weren’t so old that they would actually remember? Well, round here you never know — they might be — and despite the rain, almost a hundred years later forty-six people have gathered in Vallico Sotto to attend the ninth “Quantum Monte Carlo in the Apuan Alps” international workshop. From the 26th of July to the 2nd of August 2014 our resident physicists and chemists spent each morning listening to talks on quantum Monte Carlo and related computational electronic structure methods, followed by afternoons that were often full of mountain walking, caving, canyoning and other activities but — for pretty much the first time ever in history of events at TTI — were equally often cancelled because of the appalling weather.
A great deal of interesting science was presented and discussed at the meeting, and much of this is summarized in the scientific report further down this page. I think it’s now clear to most people that the quantum Monte Carlo method is continuing to grow in utility and importance, and for those with a big enough computer it self-evidently ought to be the method of choice for highly accurate benchmark quantum-mechanical calculations of molecules and materials — certainly those with more than a few atoms.
In the U.K. and other countries there is an increasing pressure for funding agencies to demonstrate the social and/or economic benefits of the research they sponsor. Two recent attached reports that were initiated by Mike Payne and produced by Goldbeck Consulting for the UK-JCMaxwell CECAM node address this issue. Continue reading Industrial Impact→