Dr Furio Cora
Our work examines computationally the properties of crystalline solids; the main areas of research cover the functional behaviour of transition metal bearing compounds, and the synthesis and catalytic activity of doped nanoporous solids. We are also interested in applying computational methods to related areas, when unusual behaviour is observed experimentally that would benefit from the atomic-level insight enabled by modelling.
Functional Materials; Electronic Structure of Transition Metal-Bearing Compounds
In this area, we employ electronic structure calculations to investigate the properties of crystalline compounds, with a particular attention dedicated to materials containing transition metal ions, either as main component or as substitutional dopant. The electronic properties of transition metal oxides have traditionally represented a challenge for quantum mechanical calculations: Density Functional Theory (DFT), which is widely accepted as the method of choice for electronic structure calculations on solids, fails in fact in describing well localised electronic states, such as those of the d electrons on transition metal ions. I n recent years we have shown that the shortcomings of DFT, associated with the so-called Self-Interaction error, are solved when using hybrid exchange functionals, in which the (local) DFT exchange is mixed with the corresponding (orbital-dependent) definition in the Hartree Fock theory.
After a systematic investigation on the performance of hybrid functionals in the solid state, hybrid DFT techniques are now being applied to a number of compounds containing open shell transition metal ions, but also main group elements. Active research areas (with the researcher and/or collaborators involved indicated in brackets) include ferroelectric and ferromagnetic perovskites; the stability of framework materials of different compositions (Drs R.G. Bell and M. Zwijnenburg), the study of Cu-containing multiferroic perovskites (Mr. M. Michel) and of magnetic interactions in Prussian blue (Dr. A. Wills, Ms. A. Poole), the characterisation of negative thermal expansion materials (Prof P. Barnes, Ms. M. Hooda), the Li insertion in low-dimensional Mo oxides, the study of Ni dopants in SrTiO3 (Mr M. Paul).
Remaining in the theme of magnetic compounds, the electronic structure of layered Cu-containing molecular magnets is under investigation in collaboration with Dr. Massobrio (CNRS, Strasbourg), to understand how the intercalation of different organic anions in the interlayer region modifies the magnetic order in the system. Similar organic/inorganic structures can be found in MOFs, an area where hybrid functionals have considerable potential for future applications.
Among other materials investigated, we study the behaviour of carbon-nitride solids (Mr. M. Deifallah) both under compressive strain and in single-layer form (graphene) to compare with experimental work in Prof. P. Mcmillan's group.
Synthesis and Catalytic Activity of Doped Nanoporous Oxides (zeolites, AlPOs)
Modelling the incorporation of dopant ions in zeolite and aluminophosphate (AlPO) frameworks is a long-standing area of expertise of the group. At present, we consider the incorporation of vanadium dopants in AlPOs (Mr. M. Deifallah). The doped frameworks are described using periodic quantum mechanical calculations, to understand the interplay between the microporous framework structure and the atomic, chemical and structural properties of the dopants in determining adsorption and catalytic activity of the solid. The quantum mechanical calculations have also been used to parameterise a set of interatomic potentials suitable to describe the doped frameworks. These forcefields are now employed in studies of organic/inorganic structures, as required to model diffusion of organic molecules, but also the templated synthesis of the doped frameworks (Dr. L. Hortiguela, Prof. J. Pariente). These microporous oxides are in fact synthesized through hydrothermal methods and in the presence of water-soluble organic molecules, called structure directing agents (SDA). One of our goals is to understand the mutual interaction of dopants and SDAs during the synthesis, and ultimately to identify suitable SDAs able to yield ordered dopant incorporation as a way to taylor selectivity.
Among the SDA molecules investigated, one interesting class is represented by amines with one or two benzyl rings, which have been demonstrated experimentally to be efficient templates for AlPO-5 and SAPO-5 materials with AFI framework topology. These molecules display self-assembly, driven by the overlap of the benzyl rings of adjacent molecules. Mono-benzyl SDAs self-assemble into stable dimers. The units that define the main channel of the AFI structure are rotated by 30° upon translation of half unit vector along the channel. This feature causes a preferential orientation of adjacent SDA dimers; if properly mastered to yield long-range order, it could give rise to chiral arrangements of the templates. To achieve this goal, we have designed and successfully synthesized a modified SDA, which contains a substituent in the region where adjacent SDA dimers interact. The steric and electrostatic effects align adjacent SDAs along one preferential direction; modelling work has demonstrated a spontaneous self-assemble of the modified SDA molecule into chiral helices. The stabilisation of chiral components during the synthesis of a heterogeneous catalyst is a feature of obvious practical interest. Although AFI is a non-chiral framework, we are now investigating whether it is possible to transfer the chirality from the SDA to the inorganic structure via the inclusion of suitable dopant atoms.
Figure (above). chiral self-arrangement of SDA molecules in the pores of AlPO-5, from PCCP 8 (2006) 486.
- F. Corà and C. R. A. Catlow, ‘QM investigations on Perovskite-structured transition metal oxides: bulk, surfaces,and interfaces’, Faraday Discussions 114 (1999) 421.
- F. Corà and C. R. A. Catlow, ‘Quantum-mechanical investigations on the insertion compounds of early transition metal oxides’, Phys. Stat. Sol. (b), special issue on ‘Atomistic Simulation of Materials Properties and Phenomena’, 217 (2000) 577.
- F. Corà, C. R. A. Catlow and D. W. Lewis, ‘Design of microporous transition metal oxides, and investigation of their synthesis conditions’, J. Molec. Catal.A, 166 (2001) 123.
- F. Corà and C. R. A. Catlow, ‘Ionicity and Framework Stability of Crystalline AlPOs', J.Phys. Chem., 105 (2001) 10278
- F. Corà, I. Saadoune and C. R. A. Catlow, ' Lewis acidity in transition-metal-doped microporous aluminophosphates', Angew. Chemie, 41 (2002) 4871.
- F. Corà, M. Alfredsson, C.M. Barker, R.G. Bell, M. Foster, I. Saadoune, A. Simperler, and C.R.A. Catlow, 'Modelling the Framework Stability and Catalytic Activity of Pure and Transition-Metal Doped Zeotypes’, J. Sol. State Chem., special issue on ‘The impact of theoretical methods on solid state chemistry’, 176 (2003) 496.
- F.Corà, M.Alfredsson, G.Mallia, D.S.Middlemiss, W.C.Mackrodt, R.Dovesi and R.Orlando, 'The performance of hybrid density functionals in solid state chemistry', Structure and Bonding 113 (2004) 171.
- F. Corà, 'The performance of hybrid density functionals in solid state chemistry – the case of BaTiO 3', Molecular Physics, special issue, 103 (2005) 2483-96.
- L. Gomez-Hortiguela, F. Corà, C.R.A. Catlow and J. Perez-Pariente, 'Computational study of the template effect of benzylpirrolidine and its fluorinated derivatives in the synthesis of AlPO-5', J. Am. Chem. Soc. 106 (2004) 12097.
- S.Broadley, Z.A.Gál, F.Corà, C.F.Smura and S.J.Clarke, 'A new coordination for zinc in a condensed solid: linked ZnS 2O 2 tetrahedra in the oxysulfide BaZnSO', Inorg. Chem. 44 (2005) 9092.
- R. Grau-Crespo, F.Corà, A.A. Sokol, N.H. de Leeuw and C.R.A. Catlow, ' Electronic structure and magnetic coupling in FeSbO 4: a DFT study using hybrid functionals and GGA+U methods ', Phys. Rev. B. 73 (2006) 035116
- L. Gomez-Hortiguela, J. Perez-Pariente, C.R.A. Catlow and F. Corà, 'Computational study of a chiral supramolecular arrangement of organic structure-directing molecules for the AFI structure', Phys. Chem. Chem. Phys. 8 (2006) 486
- L. Gomez-Hortiguela, C. Marquez-Alvarez, E. Sastre, F. Corà and J. Perez-Pariente, 'Effect of fluorine-containing chiral templates on Mg distribution in the structure of MgAPO-5 and its influence on catalytic activity', Catal. Today 114 (2006) 174
- G.Mallia, R.Dovesi and F. Corà, 'The anisotropy of dielectric properties in the orthorhombic and hexagonal structures of Anhydrite – an ab initio and hybrid DFT study', Phys. Stat. Sol. B 243 (2006) 2935
- S. Khan, R.J. Oldman, F. Corà, C.R.A. Catlow, S.A. French, S.A. Axon, 'Computational modelling study of oxygen vacancies at LaCoO3 perovskite surfaces', Phys. Chem. Chem. Phys. 8 (2006) 5207.
- R.W. Dorner, M.K. Deifallah, D.S. Coombes, C.R.A. Catlow and F. Corà, 'Synthesis and structure-determination of a novel layered AlPO material', Chem. Mater.19 (2007) 2261.
- M.A. Zwijnenburg, F. Corà, R.G. Bell, 'On the performance of DFT and interatomic potentials in predicting the energetics of siliceous materials', J. Phys. Chem. B, 111 (2007) 6156.
- L. Gomez-Hortiguela, F. Corà, J. Perez-Pariente, ‘Supramolecular assemblies of fluoro-aromatic organic molecules as structure-directing agents of microporous materials’, Microp. Mesop. Mater. (2007); doi:10.1016/j.micromeso.2007.05.049
- M.Alfredsson, F.Corà, D.P. Dobson, J. Davy, J.P.Brodholt, S.C.Parker and G.D.Price, ‘Dopant control over the crystal morphology of Ceramic Materials’, Surf. Sci.,(2007) doi:10.1016/j.susc.2007.07.025
- M.A. Zwijnenburg, F. Corà, R.G. Bell, 'Dramatic differences between the energy landscapes of SiO2 and SiS2 zeotype materials', J. Am. Chem. Soc. 129 (2007) 12588.