Dr Stefano Leoni

Dr Stefano Leoni

Reader in Computational Chemistry and Director of International

School of Chemistry

Email:
leonis@cardiff.ac.uk
Telephone:
+44 (0)29 2087 4248
Fax:
+44 (0)29 2087 4030

The Leoni group focuses on the study of activated processes in the solid state by means of advanced computational tools. Structural and electronic phase transitions, chemical reactions, formation mechanisms, reactive intermediates, structure prediction and the rules behind polymorphism in general are relevant research areas. Understanding processes like crystallization, nucleation and growth, diffusion of impurities or defects, or electrochemical reactions are crucial factors for the development of better materials. Despite major advances in device resolution, experiments can only provide a coarse-grained view of such processes. Theory can now integrate the experimental data by implementing the missing length and time resolution, thanks to novel strategies of numerical simulations. At the interface of inorganic and material sciences, theoretical chemistry, computational chemistry and physics, physical chemistry, materials for energy and sustainability, this area offers fascinating opportunities to leverage computational tools in the design of innovative materials.

Dipl. Chem. ETH (B.Sc.), Eidgenössische Technische Hochschule (ETH), Zürich (1993), PhD ETH Zürich(1998). Postdoctoral Fellow, ETH Zürich (1999-2000), Max-Planck Society Postdoctoral Scholarship, Max-Planck Institute CPfS, Dresden (2000-2003), Advanced Research Fellow of the Swiss National Foundation (2004-2006), Research group leader & Lecturer, MPI Dresden and Dresden University of Technology (2006-2010), Habilitation, MPI & Department of Chemistry, Dresden (2009), Senior researcher & group leader, Dresden (2010-2013), Distinguished DFG Heisenberg Fellow (2013).

CH2118 Energy Resources and Materials

CH3304 Advanced Physical Chemistry

CH3406 Molecular Modelling

CH3409 Chemistry at Phase Boundaries

Details of each module is available in course finder

Nucleation in the Solid State

The detailed investigation of structural reconstruction, in pressure or temperature induced phase transitions, is a major challenge in modern material sciences. The combined use of structural modeling approaches and of different advanced numerical tools allows for a detailed understanding of phase nucleation and growth in the solid state. Therein, intermediate reconstruction steps can be elucidated in detail.

Chemical Bond Reconstruction

Bond reconstruction during phase transitions. In phosphorus (black-P to &lcirc;±-As type) reconstruction takes the form of interfacial Peierls-like chains (Fig. 2a), in germanium the hR8 to cI16 reconstruction takes place as SN2 reaction (Fig. 2b), in carbon (graphite to sp3 polymorphs) as a complex pattern of odd-membered ring formation. In every system considered so far, a clear indication of bond nucleation is apparent. In carbon, different mechanisms are responsible for the formation of distinct sp3 polymorphs (Fig. 3c-d). Each mechanism in turn is initiated by different nucleation pattern, promptly suggesting ways of controlling/influencing the formation of either compound.

Novel Carbon Materials

Carbon remains a most versatile material. It has the potential of providing clean and very effective solutions in different areas like hydrogen storage, capacitors, optical and electronic devices. The polymorphism of carbon has been the object of many discoveries over the years. Novel forms, ranging from extended (graphene) to finite (nanotubes and fullerenes) have appeared, with outstanding properties. The polymorphism of carbon can be the source of even more interesting properties. Our recent results are along three lines: a) systematic computational approach to carbon polymorphisms, b) novel superhard and transparent sp3 carbon materials, c) carbon nanotubes assemblies with superior hydrogen storage properties. We start from sp2 carbons, graphite and nanotubes to achieve different forms of sp3 carbons on the one hand; on the other hand we address the question of packing nanotubes (CNTs) in space, with a dramatic boost on their properties as hydrogen adsorbers.

Metallorganic framework compounds (MOFs)

MOFs are porous molecular scaffoldings able to accommodate guest molecules, and hydrogen in particular. We have developed and expertise in constructing not-yet-synthesized MOFs, and in assessing their capacities as molecular reservoirs. We have started a systematic investigation of promising hydrogen storage candidate materials to meet this challenge. We focus on open framework zeolitic materials like MOFs, COFs and recently ZIFs. MOFs and ZIFs are mechanically versatile and easy to synthesize. On combining topological enumeration, molecular dynamics and structure optimization we are proposing a catalogue with useful hydrogen uptakes. Upon chemical substitution we are able to enhance their specificity for hydrogen, for instance by introducing polarizing centers in the framework (LiB(imid)4, BIFs). In general it is possible to explore a large number of structure candidates, introduce chemical substitution, and evaluate as storage properties in a systematic and efficient way.

Battery materials: Mass and charge transport

Two are the principal computational problems in this area: a correct evaluation of mass diffusion/transport, and a reliable ground-state electronic structure (also for resistivity calculations). Our recent work on Li diffusion in an important battery material LiFePO4 represents a step forward in assessing properties and calculating relevant parameters, like diffusion constants, and represents a viable method for accelerating diffusion, which is a typical bottleneck for MD simulations. This extends the possibilities of molecular dynamics to approaching systems where particle diffusion is the dominating physical/chemical event. It allows collecting a number of relevant trajectories on the one had: on the other, details of local oxidation/reduction steps at metal centers can be addressed.