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Use this search facility to find out more about the profile of our HPC-Europa2 visitors, the type of work they have been doing, and their project achievements.
We planned to extend our previous work, in which we constructed 3D hydrodynamical and non-ideal magnetohydrodynamical (MHD) simulations of supernova driven turbulence in the interstellar medium. We have investigated the effect of radiative cooling and differential rotation on the hydrodynamics of galactic disks. We had begun production runs for a Grand Challenge project through CSC to investigate the properties of the galactic dynamo through SN driven turbulence and rotational shear.Arising from our MHD simulations, we have established additional collaboration with overseas members of LOFAR (European radio telescopic array) to simulate line of sight synchroton emissions for comparison with observations. Newcastle is a member of the UK LOFAR consortium ( http://lofar-uk.org/ ). Realistically motivated 3D simulations of the interstellar medium are of direct interest to many involved in the astronomical and astrophysical community. The primary objective of this visit was to analyse and visualise the data produced from our MHD production runs and to write up our results. Additional production runs were planned to further probe interesting parameters, which might include different levels of resistivity, density fluctuations typical of spiral arms or other galaxies or a range of rotation parameters. Our model consists of a local 3D model of the stratified, rotating ISM in the shearing box approximation. The system is driven by localised injection of thermal energy, modelling supernovae star (SNe) explosions. The expanding blast waves compress and heat the gas, resulting in a highly inhomogeneous, multiphase medium with temperature ranging from 1e2 to 1e8 Kelvin and density ranging from 1e-4 to 1e2 particles per cubic cm. Our standard grid separation is 4 parsecs (pc) a maximum permissible to adequately represent small scale effects. Our standard domain is 1x1x2 kpc a minimum requirement to model large scale structures. Our computing mesh is therefore about 256x256x512 or larger. The resources needed to conduct these simulations are typically 25000 cpu hrs per 100 Myr and we typically require over 250 Myr for each run. Our temporary data stored at present on louhi (CSC) is in excess of 2 Tb. These require 256 to 1024 parallel processors to execute. I for runs investigating the dynamo we anticipate needing to exceed 1Gyr for at least one run so runs will need to be of order 2 weeks+ duration.
Our reference run has extended to over 1Gyr and we have used this to start several other comparison runs. We have succeeded in finding a dynamo, with conditions which are marginally critical. (i.e. the conditions are only just sufficient to drive the dynamo) Although the growth of the dynamo is found to be sensitive to rates of rotation, shear and SNe all variants are producing growth in the magnetic field. From theory we expect the growth to end and the magnetic field strength to become quasi stable when the magnetic energy matches the kinetic energy density. At current growth rates we would expect this to require at least anoth 0.5Gyr.
To understand the dynamo we need to understand the velocity field. Due to the complexity of the results we are still analysing the data from the original non-magnetic runs. However we anticipate the submission of the first paper on the three phase structure of the interstellar medium, followed shortly by a paper on the vortical and helical structure of the ISM, which should give some insight into the structure of the dynamo from our latest simulations.
Previous simulations of the interstellar medium have either not included magnetic fields or have been unable to identify a dynamo with parameters typical of the ISM in the solar neighbourhood, despite compelling evidence from observations that the strength of the magnetic field is hard to explain in the absence of such a dynamo. Understanding the process by which this dynamo is effective may be a significant step in understanding the dynamo in general astrophysical structures.
The importance of the spin state of iron on the behaviour of a class of α-diimine iron catalysts  was to be studied computationally. The main method of research was the application of quantum chemical density functional theory (DFT) on this class of compounds.
Traditional DFT methods, which are available in standard program packages, suffer from three short-comings that are especially troublesome when considering metal complexes in different spin states, their reactions, and interaction with the environment:
The host group has recently developed a DFT method which addresses all of the above problematic cases. The Swart-Solà-Bickelhaupt (SSB-D) functional is very new , but has already shown great potential for tackling the problems at hand. Thus, by visiting the host group, the objective was to provide the applicant with first-hand introduction to the details of method and its applicability, by studying a relevant and much discussed real-world catalytic process.
Further, as the computations involved are very demanding, access to the computer facilities at the Barcelona Supercomputing Centre was critical for carrying out the proposed study.
 L.E.N. Allan, M.P. Shaver, A.J.P. White, V.C. Gibson, "Correlation of Metal Spin-State in α-diimine Iron Catalysts with Polymerization Mechanism", Inorg. Chem. 46 (2007) 8963–8970.
 M. Swart, M. Solà, F.M. Bickelhaupt, “A new all-round density functional based on spin states and SN2 barriers”, J. Chem. Phys. 131 (2009) 094103.
The two distinct reaction pathways discussed in reference , the catalytic chain transfer (CCT) mechanism, which was proposed to take place via intermediate-spin state complexes, and the atom transfer radical polymerization (ATRP), proposed to be favoured when the metal complex is in a high-spin state, were studied. To be able to confidently assess the results, four different complexes were studied, two that have been shown to follow the CCT pathway, and two that follow the ATRP pathway.
The computational results strongly suggest that all of the parent complexes have a high-spin ground state, in contrast to the suggestions in the literature. However, the CCT mechanism does follow an intermediate-spin transitional complex pathway. The hypothetical high-spin intermediate, which is not seen experimentally but can of course be studied theoretically, is much higher in energy, that is, unstable, compared to the intermediate-spin complex.
On the other hand, the study could not directly distinguish between the high- and intermediate-spin transitional complexes of the ATRP pathway, which are energetically quite close. Further study of this pathway is necessary to elucidate and fully explain the differences between the two catalytic routes. Discussions lead to several hypotheses about the origin of the effect, all of which will be explored in the near future.
In addition to the progress for the specific case-study discussed above, the other major achievement of the visit was the establishment of a new and exciting collaboration between host and guest. Technical issues with the newly developed method were also identified and remedied. The good performance of the SSB-D functional  was further established. This indirectly also led to a new collaboration partnership with Prof. G. Gutsev (Florida, USA) and a side project on the spin states of small pure-iron clusters.