## BrENIAC: the new Flemish TIER-1 Supercomputer.

Yesterday was a good day for computational scientists in Flanders. The new TIER-1 machine, named BrENIAC, located at the university of Leuven, was inaugurated and is now officially open to all users of the Flemish university associations: UAntwerpen, VUB, UGhent, UHasselt, and KULeuven. The name refers to one of the first (super)computers ever built: ENIAC. This new machine will take over the task of the first TIER-1 machine (muk, located at the university of Ghent), which will be decommissioned at the end of this year. BrENIAC is ranked 196th in the current top 500 of supercomputers, and costs 5.5 M€. This is of course without the annual cost of power usage and technical personnel which will maintain the machine and provide support for the scientists running calculations. With its 580 compute nodes, containing 28 cores each (or 2 14-core CPU’s of the type Broadwell E5-2680v4), the number of available cores has roughly doubled. Also memory access should have improved, which gives rise to a theoretical threefold increase of the peak performance.

However, this peak performance is measured with “benchmark” tests, which tend to behave much better than real  life programs. This is because the average scientific programmer doesn’t write the best optimized code (ok, “commercial” programs these days may even behave worse :p )  for various reasons, time constraints being one of them. So my first task, before I start running my simulations on the new TIER-1 machine, will be to benchmark VASP and my own HIVE-code.

Two videos of my new sidekick:

You can see me in my front-row position in this picture taken during the non-academic part of the inauguration.

## tUL Life Sciences Research Day 2016

Yesterday was the tUL Life Sciences Research Day 2016. A conference event build around finding collaboration possibilities between the University of Hasselt in Belgium and the University of Maastricht (The Netherlands)…after all tUL is the “transnational University Limburg” which brings two universities together that are only separated some 26 km, but you have to cross a national border.

Although Life sciences itself is not my personal niche, I went to look for opportunities, as nano-particles which are used for drug delivery often consist of metals or oxides. These materials on the other hand are my niche. I used my current work on MOFs as a means to show what is possible from the ab-initio point of view, and presented this as a poster.

Poster presented at the tUL Life Sciences Research Day, depicting my work on the unfunctionalized and the functionalized MIL-47(V) MOF.

## Holiday-Conference roller coaster

Visit to Stockholm. The knight at the Medeltidsmuseet (top left), brown bear in Skansen (top right), visiting the Royal palace (bottom left) and local entertainment in the old city center (bottom right).

Summertime is a time of rest for most people. For our little academic family, last summer was a bit of a roller coaster; alternating holidays with hard work which had been postponed too much. The last vestige of my start of a new chapter (moving the remaining stuff from the apartment to our house) was finally bested. Now the conference roller coaster has started with Sylvia’s plenary lecture on conceptual spaces in Stockholm.

As neither of us ever visited Sweden before, we decided to turn it into a semi-family-holiday as well. Our 4-year-old son enjoyed his first ever plane flight (he wasn’t really convinced something impressive was going on). And while Sylvia was of to the conference, the two of us went to explore Stockholm: Finding the knight in the Medeltidsmuseet (at the left in the back of this beautiful museum 🙂 ) and searching for the king and queen at their palace (they weren’t there 🙁 ). Or visiting one of the oldest open-air musea; Skansen (similar to Bokrijk in Belgium) where we saw old professions at work (making cheese for example) and native Scandinavian farm and wild animals (from peacocks to brown bears).

Next weekend starts the next episode of the conference roller-coaster with me hosting a 2-day colloquium on porous frameworks together with Bartek Szyja and Ionut Tranca at the CMD-26 conference in Groningen. We have a nicely packed colloquium with about 20 presentations (8 invited and 12 contributed) covering the whole realm of porous materials from zeolites to COFs and MOFs. The program of the colloquium can be downloaded below:

## Annual Meeting of the Belgian Physical Society 2016

Wednesday May 18th was a good day for our little family. Since my girlfriend an I both are physicists by training, we attended the annual meeting of the Belgian Physical Society in Ghent, together. What made this event even more special was the fact that both of us had an oral presentation at the same conference, which never happened before. 🙂

Sylvia talked about an example of indeterminism in Newtonian mechanics, and showed how the indeterminism can be clarified by using non-standard analysis. The example considers the Norton Dome, a hill with a specifically designed shape ( $y(x)=-2/3(1-(1-3/2|x|)^{2/3})^{3/2}$ ). When considering a point mass, experiencing only gravitational force, there are two solutions for the equation of motion: (1) the mass is there, and remains there forever (r(t)=0) and (2) the mass was rolling uphill with a non-zero speed which becomes exactly zero at the top, and continues over the top ( $r(t)=\frac{1}{144} (t-T)^4$ with T the time the top is reached). Here, r refers to the arc length as measured along the dome (0 at the top). In addition, there also exists a family of solutions taking the first solution at t<T, while taking the second solution at t>T. (As the first and second derivatives of these latter solutions are continuous, Newton will not complain.) This leads to indeterminism in a Newtonian system; for instance, you start with a mass on the top of the hill, and at a random point in time it starts to roll off without the presence of an external something putting it into motion. Using infinitesimals, Sylvia shows that the probability for the mass to start rolling off the dome immediately is infinitesimally close to one.

My own talk was on the use of computational materials science as a means for understanding and explaining experimental observations. I presented results on the pressure-induced breathing of the MIL-47(V) MOF, showing how the experimentally observed S-shape of the transition-pressure-curve can be explained by the spin interactions of the unpaired vanadium-d electrons: it turns out that regions with only ferromagnetic chains compress already at 85 MPa, while the addition of higher and higher percentages of anti-ferromagnetic chains increases the pressure at which the pores collapse, up to 125 MPa for the regions containing 100% anti-ferromagnetic chains. As a second topic, I showed how the electronic band structure of the linker-functionalized UiO-66(Zr) MOF changes. When one or two -OH or -SH groups are added to the benzene ring of the linker, part of the valence band is split off and moves into the band gap. In semiconductors, this would be called a gap state; however, in this case, since every linker in the material contributes

Top left: I am presenting computational results on MOFs. Top Right: Sylvia presents the Norton Dome. Bottom: Group picture at the central garden in “Het Pand”. (Photos: courtesy of Sylvia Wenmackers (TL), Philippe Smet (TR), and Michael Tytgat (B) )

a single electron state to this gap state, it practically becomes the valence band top. As a consequence, the color of such functionalized MOF’s changes from white to yellow and orange. As a third topic, I discussed the COK-69(Ti) MOF. In this MOF the electrons in the titaniumoxide clusters are strongly correlated, just as for pure titaniumoxide. Because such systems are poorly described with standard DFT, we used the DFT+U approach, which allowed us to discern between Ti3+ and Ti4+ ions. The latter was practically done by partitioning the electron density using the Hirshfeld-I scheme.

Following these plenary presentations, four young scientists competed for the young speaker award presenting their PhD research. Two presentations (1),(2) focused on vortices in superconductors, a third one discussed the use of plasmons in graphene nanoribbons to enhance telecommunication while the fourth talk introduced us into the world of string theory.

In the afternoon, there were six parallel session, of which I mainly attended the Condensed Matter and Nanostructure Physics-session (since I had my own talk there) and the Biological, Medical, Statistical and Mathematical Physics-session rooting for Sylvia. During the Condensed matter session I was mainly fascinated by the presentation of Prof. Sara Bals, on coloring atoms in 3 dimensions. She showed how, using energy-dispersive X-ray (EDX) mapping it is possible to create a 3D atomic lattice of nano-materials and clusters. This is a more direct approach than the usual X-ray diffraction (XRD) approach for identifying a crystal structure. Unfortunately, I am afraid this technique may not be well suited for the MOFs I’m working on, since they contain mainly light elements and not heavy metals(although it may be interesting to try once the technique is optimized further). It is, however, definitely a technique to remember for future projects, to suggest to experimental collaborators.

## Call for Abstracts: Condensed Matter Science in Porous Frameworks: On Zeolites, Metal- and Covalent-Organic Frameworks

Together with Ionut Tranca (TU Eindhoven, The Netherlands) and Bartłomiej Szyja (Wrocław University of Technology, Poland) I am organizing a colloquium “Condensed Matter Science in Porous Frameworks: On Zeolites, Metal- and Covalent-Organic Frameworks” which will take place during the 26th biannual Conference & Exhibition CMD26 – Condensed Matter in Groningen (September 4th – 9th, 2016). During our colloquium, we hope to bring together experimental and theoretical researchers working in the field of porous frameworks, providing them the opportunity to present and discuss their latest work and discoveries.

Zeolites, Metal-Organic Frameworks, and Covalent-Organic Frameworks are an interesting class of hybrid materials. They are situated at the boundary of research fields, with properties akin to both molecules and solids. In addition, their porosity puts them at the boundary between surfaces and bulk materials, while their modular nature provides a wealthy playground for materials design.

We invite you to submit your abstract for oral or poster contributions to our colloquium. Poster contributions participate in a Best Poster Prize competition.

#### The extended deadline for abstract submission is May 14th, 2016.

CMD26 – Condensed Matter in Groningen is an international conference, organized by the Condensed Matter Division of the European Physical Society, covering all aspects of condensed matter physics, including soft condensed matter, biophysics, materials science, quantum physics and quantum simulators, low temperature physics, quantum fluids, strongly correlated materials, semiconductor physics, magnetism, surface and interface physics, electronic, optical and structural properties of materials. The scientific programme will consist of a series of plenary and semi-plenary talks and Mini-colloquia. Within each Mini-colloquium, there will be invited lectures, oral contributions and posters.

Feel free to distribute this call for abstracts and our flyer and we hope to see you in Groningen!

## SBDD XXI

Today was the first day of the three-day long diamond conference at the university of Hasselt. And although this sounds as-if it is a mere small-scale local conference, it is actually one of the two main international conferences in the field. The Surface and Bulk Defects in Diamond (SBDD) workshop grew in twenty years from a small event with only a few dozen participants to the current event with over 200 participants. As such, it is the place to be, for one as me, who is dipping into a new field of materials.

One thing that already became quite clear today, is the fact that there are many opportunities in this field for the computational materials scientist, as the large majority of the researchers are experimentalists. Of the >120 posters presented, I have only discovered about 5 theoretical ones. Having had very nice chats with their presenters I already learned a lot of what I will have to keep in mind when studying diamond. But so far, I have not come across any issues that are impossible to resolve, which is good news :-).

## Helium flash: the beginning of a new chapter.

During the past two and a half years, part of being a delocalized physicist has meant for me that I had to work at one end of the country while my girlfriend and son lived at the other. Today this situation drastically changed, as I moved with my FWO-postdoctoral project from my alma mater to the University of Hasselt, where I started in the Wide Band Gap Materials group of Prof. Ken Haenen.

My delocalization will now take the form of Metal-Organic Frameworks on the one side and Diamond based materials on the other. As the sole computational solid state physicist in an otherwise entirely experimental group (and even institute) I seem to have returned to a well known configuration (At Ghent university I was initially the house-theoretician of the SCRiPTS group). Also the idea of performing calculations on diamond brings back memories, since this allotrope of carbon lives two levels above the germanium on which Pt nanowires grow. All-in-all I look forward to an exciting time. But first things first: getting my HPC credentials and data safely transported from the one end of the country to the other.