The main objectives from this study are :

The properties of interest are :

Thermodynamic and structural properties. Investigating these properties we may gain insight for the interactions at microscopic level and how the ions interact each other. Using these properties, we may obtain information on the efficiency of the available interaction potential models in description of these systems.

Single particle dynamic properties. These include velocity power spectra, diffusion coefficients and molecular reorientational correlation times. These properties will be investigated mainly using the appropriate single particle time correlation functions.

Collective dynamic properties. These include dielectric relaxation, conductivity, viscosity, etc. and they will be investigated using the appropriate collective time correlation functions.

Dependence of all these properties on the size and complexity of cations and anions.

Similar properties for solutions of ionic liquids as well as additional properties resulting from the two component systems.

Molecular Dynamics simulations of 1-alkyl-3-methyl imidazolium based ionic liquids were performed using existing in the literature forcefields. It was found that the existing forcefields are not accurate enough in the prediction of some basic properties of these liquids like density or self diffusion coefficient. Forcefield development found to be necessary to obtain a forcefield that, at least, is accurate in the prediction of these basic – simple properties. At the same time, a number of publications noting this problem of the existing forcefields appeared in the literature as well as few attempts to propose a forcefield. Most of these proposed forcefields were focused in the improvement of localized partial charges of ions, using van der Waals parameters from existing forcefields like AMBER/OPLS. In one publication, the enhancement of the van der Waals parameters only of few atoms was attempted, using the charges from literature. Additional publications using ab-initio molecular dynamics using small number of molecules pointed out the problem of the existing classical forcefields in the prediction of ionic liquids properties. Several levels of forcefield enhancement were attempted in the framework of this project. First, a massive optimization of all the atomic van der Waals parameters using the existing in the literature charges and bonded interactions was attempted. Next, using quantum mechanics calculations, the isolated ions geometry was optimized. Using this optimized geometry the partial atomic charges were fitted to reproduce the quantum mechanical potential energy surface. A massive optimization of all the atomic van der Waals parameters applied again using the partial charges obtained from the quantum mechanics calculations. Both resulting forcefields were verified for their ability to predict few basic properties of the systems. It was found that these forcefields perform much better in the prediction of the temperature/pressure dependence of the density. These new forcefields were used in the long time molecular dynamics simulation of the systems under investigation. From these runs, a number of trajectories was produced for each system at selected thermodynamic states were experimental data are available in the literature, that will be used for the calculation of thermodynamic, structural, single and collective dynamic properties of the systems. These properties will be compared with existing in the literature experimental results. Some of these properties are already calculated on Marenostrum, other properties will be calculated off site using the trajectories obtained using the BSC hardware.

Few molecular dynamics codes were examined for their parallel efficiency and speed on HPC hardware. It was found, as it was expected, that gromacs 4.0.4 is the faster for this type of systems on HPC hardware. Parallel scaling found to be linear up to 28 processors for the systems under investigation.

The objectives of the project were to implement two new features to the existing MPI implementation of the standard (two-level) BDDC method for solving large sparse systems arising from computations by finite element method. These new features are: (i) extension of the coarse problem solution to multiple levels and (ii) adaptive generation of the coarse problem.  The code should then be tested on real-life problems from engineering.

The two-level solver has been successfully extended to handle arbitrary number of levels. This feature is important to solve very large problems using large number of subdomains on the first level. The multilevel method has been tested on benchmark problems as well as real-life engineering problems with up to six millions of unknowns and the applicability of the solver was verified also on large number of processors (512 and 1024).

A preliminary approach to adaptive selection of constraints was also implemented. It has been shown that the adaptive strategy is applicable and can dramatically reduce the final number of iterations for numerically difficult problems. However, further modifications to the algorithm seem necessary to reduce the time spent by local eigenvalue problems. This will require a careful selection of the solver for eigenproblems within the adaptive method.

The whole research project is focused on designing new ceramic materials for protonic conduction in the range of temperature 350-750 °C. To accomplish this, it was planned to deepen the informations on the systems obtained by doping the octahedral tetravalent cation site of the BaZrO3 perovskite matrices with a trivalent atom. In these structures, zirconium atom has been substituted by an Y one, in order to create oxygen vacancies that could be filled by hydroxyls groups. In this way, proton defects are inserted into the structure.

Once protons are introduced into the host matrix, their diffusion is mainly driven by phonon-assisted dynamics. Accordingly, the mechanism of protonic conduction is strongly affected by local distortions involving the doped Zr sites. For this reason, in order to know the details of the protonic conduction mechanism, hence to improve the performance of the related materials, it is of fundamental importance to study the local environment surrounding the doped sites.

Following this, the final tasks of this computational project are:

the development of structural and kinetic models to study the barium zirconate perovskite;

the validation, by mimicking experimental findings, of the structural and kinetic computing methods and models employed to study ceramic conductors, and the involved proton transport phenomena.

Integrated with the experimental findings, these computer simulations come out to be a further contribute to get a deep understanding of the physical and chemical characteristics of conducting materials and the related conduction phenomena.

Due to the characteristics of the studied materials, DFT approaches implemented into the SIESTA package have been investigated. The computational methods and the choice of the models and protocols have been tuned according to the machines capabilities, balancing the reliability of the results against the computational time. Geometry calculations have been performed on 3x3x3 and 4x3x3 supercells of pure and Y-doped BaZrO3 systems, by applying PBC.

Singly and doubly Y substitutions on Zr site have been considered, with and without an oxygen vacancy, together with different charge states. In this way, we were able to investigate the details of the dopant geometrical environment and its electronic features.

The systems above were used as a starting point to study the electronic and structural changes induced by inserting a proton into the BaZrO3 perovskite matrix. In order to do this, one proton was added to the pure and doped structures discussed above and the systems geometry were relaxed.

The results obtained for the undoped systems allowed us to validate and tune the computational methods, models and protocols suitable for this kind of compound, balancing the amount of the obtainable informations and the computational cost needed to get them at the required precision. Moreover, matching the structural and the electronic data so calculated, we were able to rationalize some experimental findings, giving a further contribution to the study of the proton transport phenomena in perovskite compounds.