Advanced computer simulation, using quantum-mechanical methods that treat the materials with atomistic detail, has become an indispensible tool in modern Materials Science. Today, the so-called “first-principles” or “ab initio” methods are mature enough to treat complex materials in a realistic way, and thus offer insights into the physical/chemical mechanisms responsible for their properties. Further, the methods can be used to predict the properties of hypothetical systems and compounds, and, for example, identify those that should be optimum for specific applications; thus, “computational materials design” is becoming increasingly spread to guide experimental materials discovery and speed up progress.

Currently, a lot of work focuses on overcoming the limitations of first-principles methods as regards the maximum system sizes and simulation times that can be achieved with state-of-the-art simulation codes and computer power. Indeed, the development of first-principles-based effective models – also called “second-principles”, which permit statistical simulations (Molecular Dynamics or Monte Carlo) of very large systems (~ 100,000 atoms) – makes it possible to treat very complex situations in realistic conditions with nearly-quantum accuracy. In this PhD project, the student will master, develop and apply a second-principles approach recently introduced by J. Íñiguez (LIST) in collaboration with J. Junquera and P. García-Fernández (University of Cantabria-UC, Spain) [1,2].

The student will extend these methods to treat structurally-complex situations (like e.g. the domain walls characteristic of ferroelectric and ferroelastic materials) where the intimate interplay between lattice distortions and free carriers can lead to potentially useful properties (e.g., nanometric regions with distinct conductive, magnetic or optical properties, tunable with external fields) [3,4]. This PhD work will thus extend the state-of-the-art of large-scale first-principles simulation and computational design in the field of functional oxide nanostructures, potentially triggering collaborations with world-leading experimental groups at LIST and elsewhere.

Figure: Sketch of the current status of development of multi-scale simulation methods by LIST and UC groups, indicating part of the advances intended within this PhD project.

Project Partners

Jorge Iniguez
Dept. of Materials Research and Technology
Luxembourg Institute of Science and Techonology

Javier Junquera
CITIMAC
University of Cantabria

The LIST group led by J. Íñiguez has extensive experience in the development and application of effective atomistic methods, with parameters obtained from first-principles calculations, for the investigation of lattice-dynamical phenomena occurring at large length and/or time scales.

The UC group of J. Junquera and P. García-Fernández has extensive experience on the development of first-principles and effective methods for treating electronic-structure problems.

The project will benefit from both expertises and will contribute to the consolidation of a merged approach that will make it possible to tackle problems characterized by a complex interplay of lattice and carriers and/or magnetism. The PhD student was hired by University of Luxembourg.

References

[1] First-principles model potentials for lattice-dynamical studies: general methodology and example of application to ferroic perovskite oxides, J.C. Wojdel, P. Hermet, M.P. Ljungberg, P. Ghosez and J. Íñiguez, J. Phys.: Condens. Matt. 25, 305401 (2013).
[2] Second-principles method including electron and lattice degrees of freedom, P. García-Fernández, J.C. Wojdel, J. Íñiguez and J. Junquera, submitted [arXiv:1511.07675].
[3] Domain wall nanoelectronics, G. Catalan, J. Seidel, R. Ramesh, and J. F. Scott, Rev. Mod. Phys. 84, 119 (2012).
[4] Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide, S. Farokhipoor, C. Magen, S. Venkatesan, J. Íñiguez, C.J.M. Daumont, D. Rubi, E. Snoeck, M. Mostovoy, C. de Graaf, A. Mueller, M. Doeblinger, C. Scheu and B. Noheda, Nature 515, 379 (2014).

For more information on the work of the LIST and UC groups, please visit:
https://sites.google.com/site/jorgeiniguezresearch 
https://scholar.google.es/citations?user=hsLqX2UAAAAJ&hl=es
https://scholar.google.es/citations?user=D0cph20AAAAJ&hl=es
https://scholar.google.com/citations?user=tcWZ31EAAAAJ&hl=en