Trinity College Dublin

The School of Chemistry held an Intra PG/PD Colloquium Day and Networking Event on Friday 19^th September in conjunction with the RSC. Postgraduate students and postdoctoral researchers from across the school were afforded the opportunity to deliver talks and posters on their work, and annual awards such as the Brendan Barry and Tom McCabe demonstrating awards and the Dorgan prize were presented. Well done to group member Aoife Lucid who was awarded a poster prize for her work on the computational modelling of electrolytes and their interfaces in solid oxide fuel cells, with poster prizes also going to Aaron Keogh (Rozas group) and Barry McKenna (Evans group). Aoife was additionally shortlisted for the Dorgan prize and is pictured here with the other shortlisted candidates (Viola Previtali of the Rozas group and winner Maria O'Brien from the Duesberg group), members of the Dorgan family, and the adjudicators (Dr Hugh Fay of Henkel Ireland and Prof. John Gilmer from the School of Pharmacy in TCD).

Congratulations to group member Ailbhe Gavin (pictured left) who was awarded a prize for her poster, "Defect engineering in LaCrO₃ to develop a p-type transparent conducting oxide", in Symposium N of the recent E-MRS Spring Meeting 2016. Ailbhe, along with Aoife Lucid, attended the conference in Lille, France, from May 2nd-5th. Both delivered oral presentations in Symposium D, themed "Solid state ionics: defect interactions and their influence on ionic and electronic transpor". Ailbhe presented her work on "Modelling of defects in LaMnO₃ for intermediate temperature solid oxide fuel cell cathodes", and Aoife gave a talk on "Molecular dynamics investigation of samarium doped ceria and its interfaces for solid oxide fuel cell applications". Aoife also presented posters on LaGaO₃ and doped CeO₂ as SOFC electrolyte materials.

Members of the group recently attended the 18th Irish Atomic Simulators Meeting (IASM) held in UCD on the 13th-14th of January, 2016. Douglas Temple presented a talk entitled "Implementation of a damped dipole-polarisable ionic model within METADISE", Ailbhe Gavin gave an oral presentation on "Modelling of LaMnO₃ for intermediate temperature solid oxide fuel cell cathodes", and Aoife Lucid spoke about "Molecular-dynamics investigation of doped ceria materials for solid-oxide fuel-cell electrolytes". Aoife Lucid and Aoife Plunkett also presented posters at the meeting. Thank you to our colleagues in UCD for organising this year's event.

Second year postgraduate students Ailbhe Gavin and Aoife Lucid recently attended the Paris International School on Advanced Computational Materials Science at the UPMC Sorbonne from August 24^th-28^th. The workshop provided lectures on a wide variety of atomic and molecular simulation methods ranging from forcefields and metadynamics to density functional theory and quantum Monte Carlo, as well as allowing attendees to experience these techniques in interactive computer lab sessions. In addition, those present were afforded the opportunity to present their own research in posters and flash presentations, with Ailbhe and Aoife discussing LaMnO₃ and Sm-doped CeO₂ as intermediate temperature solid oxide fuel cell cathodes and electrolytes, respectively. Also in attendance were former group members Dr. Mario Burbano and Dr. John Carey.

The group is delighted to welcome two new members as a result of their successful funding applications to the Irish Research Council. Dr. Umadevi Deivasigamani was awarded a two year fellowship under the Government of Ireland Postdoctoral Fellowship Awards scheme for her proposal, "Computational evaluation of hybrid perovskite materials for photovoltaic applications". Swetanshu Tandon is the recipient of a Government of Ireland Postgraduate Award and will carry out a joint computational and experimental project under the co-supervision of Prof. Watson and Prof. Wolfgang Schmitt, entitled "A combined theoretical and experimental study of manganese clusters for photo induced water oxidation".

In collaboration with the Atwater Research Group in the California Institute of Technology and Dr. David Scanlon of University College London, Prof. Watson's work on "Interface stoichiometry control to improve device voltage and modify band alignment in ZnO/Cu₂O heterojunction solar cells" has been published recently in Energy and Environmental Science. This joint experimental-theoretical study shows that the efficiency of ZnO/Cu₂O heterojunctions in photovoltaic devices is strongly dependent on the interface between the two materials, with far better performance found for stoichiometric interfaces. Additionally, by performing a valence band offset, it has been computationally determined that interfaces with CuO present result in a band gap shift of 0.4 eV, helping to explain conflicting literature reports as to the value of the valence band offset between ZnO and Cu₂O.

Energy & Environmental Science 7, 3606-3610 (2014)

This paper, recently published in Physical Chemistry Chemical Physics, describes how the application of an occupation matrix control methodology with a DFT+U approach can be used to achieve an improved description of localised d and f states by allowing the user to specify both the site and orbital in which localisation should occur. The approach is tested for both octahedral and tetrahedral Ti(III) and Ce(III) carbonyl clusters and for reduced anatase-TiO₂ and CeO₂ periodic systems. This paper was published as part of a themed issue, "High performance computing in the chemistry of materials", which was edited by Richard Catlow and Scott Woodley of University College London and contains several contributions by members of the Materials Chemistry Consortium.

Physical Chemistry Chemical Physics 16, 21016-21031 (2014)

More information on the occupation matrix code as implemented in VASP can be found on the Methodology section of our research pages.

Congratulations to group member Aoife Kehoe who was awarded first place at the Trinity regional heat of Thesis In 3. Thesis In 3 is an event which challenges postgraduate researchers to describe their thesis to a general audience in just three minutes using three slides. The Trinity heat took place as part of Discover Research Dublin, an annual event affiliated with European Researchers' Night. Aoife's talk, "Eternal sunshine of the electric kind", discussed how computational modelling can aid in the prediction of novel solar cell materials. Aoife, along with Christian Wirtz of the Duesberg group and TCBE's Dinorath Olvera, who placed second and third, respectively, will now progress to represent Trinity in the national final of Thesis in 3 on October 20^th.

Prof. Graeme Watson was one of the invited speakers at the recent 15th International Conference on Theoretical Aspects of Catalysis (ICTAC15). This event was held at University College London from the 30^th June to the 4^th July. The biannual conference focusses on a number of topics in the area of modelling catalysis, including theoretical methods for heterogeneous, homogeneous, bio-, and enzymatic catalysis, as well as the relationship between theory and experiment. Prof. Watson's presentation focussed on the computational modelling of doped CeO₂ for catalysis.

The annual School of Chemistry BOC Gases bursary has been awarded to group member Aoife Kehoe for her research on the solid state simulation of photovoltaic and catalytic materials. The award was adjudicated by a panel consisting of the Heads of discipline, who also highly commended the application of Ian Godwin from Prof. Mike Lyons' group. As part of the award ceremony, Aoife delivered a seminar to an audience including Adam Jennings-Frisby, Managing Director of BOC Gases Ireland. Aoife is the fourth Watson group member to have been awarded the BOC Gases bursary, following on from previous winners Dr Aron Walsh (2005/06), Dr David Scanlon (2008/09), and Dr Mario Burbano (2011/12).

Prof. Graeme Watson recently delivered a plenary lecture at the 33rd RSC Solid State Chemistry Group annual Christmas meeting, held at the University of Bath from the 18th-19th December 2013. His talk, entitled "Multiscale modelling of doped ceria as an ionic conductor in solid oxide fuel cells", encompassed a variety of aspects of the group's research on doped ceria SOFC electrolytes. These included the formation and role in ionic conductivity of charge compensating vacancies, the effects and limitations of doping and co-doping on ionic conduction, and strain and surface effects. Also present at the meeting were a number of Watson group members, with Dr Jeremy Allen and Aoife Kehoe also presenting posters on trivalently and divalently doped ceria, respectively.

A study on the electronic structure of silver orthophosphate, recently published in the Journal of Materials Chemistry A, was carried out in collaboration with former group members Dr David Scanlon and Dr Ben Morgan as well as the group of Dr David Payne in Imperial College London. Ag₃PO₄ is a material with potential photocatalytic water splitting applications, yet little is known about its fundamental electronic structure. In this paper, using a combination of photoelectron spectroscopy and hybrid DFT, the bonding in Ag₃PO₄ is fully rationalised, and a molecular orbital description of the material is proposed.

The article was part of themed collection entitled "Emerging Investigators", and an image by Dr Payne related to our research featured on the inside front cover of the issue.

Journal of Materials Chemistry A 2, 6092-6099 (2014)

A recent collaboration of Prof. Watson with researchers in University College London, Daresbury Laboratory, and the University of Bath has been published in Nature Materials. The study combines a range of theoretical and experimental methods, including periodic DFT, interatomic potentials, QM/MM, and XPS, to elucidate the heretofore controversial nature of the band alignment of rutile and anatase TiO₂, the mixed phase materials of which are widely used as photocatalysts.

In contrast to many previous studies in the literature, the techniques utilised here consistently find that anatase possesses a higher electron affinity than rutile. The band alignment of the two materials is of Type II with an offset of approximately 0.4 eV, allowing efficient electron-hole separation. It is proposed that this alignment is the root of the improved photocatalytic activity observed in mixed rutile-anatase materials over the pure polymorphs of TiO₂ .

Nature Materials 12, 798-801 (2013)

This paper was published in Energy & Environmental Science and is based on research carried out in conjunction with experiments performed at the WPI International Institute for Carbon-Neutral Energy Research (Kyushu University) and Tohuku University. Using DFT calculations and HTXRD, dilatometry, and TGA measurements, the chemical expansion of reduced ceria upon Zr-doping was investigated. It was found that while Zr increases the chemical expansion of ceria as it also enhances reduction, the chemical expansion coefficient is actually significantly decreased with respect to the pure material. It is proposed that this results from the smaller ionic radius of Zr(IV) compared to Ce(IV), which facilitates the movement of oxide ions towards vacancies in the material. This leads to a contraction of the lattice in the region of the vacancy, in a competing effect with the cation expansion upon reduction.

An image from the study was included on the back cover of the issue.

Energy & Environmental Science 6, 1142-1146 (2013)

Congratulations to Prof. Graeme Watson, who has been awarded an SFI Investigator Award for his project "Understanding the role of interfaces in solid oxide fuel cell efficiency: optimising materials through predictive computer simulation". Solid oxide fuel cells are materials which can convert a wide range of fuel sources into electrical energy in an efficient and environmentally friendly manner. This project will focus on modelling both the individual components of SOFCs (electrolytes, electrodes) and the interactions between them. The award will provide funding for four postgraduate students and a postdoctoral researcher over the next five years.

Additional congratulations to the School of Chemistry's other five recipients of SFI funding via Investigator Awards and Investigator Projects: John Boland, Paula Colavita, Stephen Connon, Rachel Evans, and Yurii Gun'ko.

Group member Aoife Kehoe was selected to attend the recent Summer School on Inorganic Materials for Energy Conversion and Storage in the University of California, Santa Barbara. The two week event, organised by Prof. Ram Seshadri of UCSB and Prof. Matt Rosseinsky of the University of Liverpool, in conjunction with the International Center for Materials Research, was attended by over sixty postgraduate students whose research focusses on various aspects of energy and environmental materials chemistry. Introductory lectures to a wide range of energy topics were given by leading researchers in the respective fields, including fuel cells, thermoelectrics, water splitting, nuclear power, and Li batteries. Participants were also given the opportunity to showcase their research at poster sessions, where Aoife presented her work on ternary copper chalcogenide materials as potential earth-abundant photovoltaic absorbers.

Congratulations to Douglas Temple on his recent funding from the Irish Research Council for Science, Engineering, and Technology (IRCSET). Douglas has previously worked with the Watson group both as a summer student investigating earth abundant materials for photovoltaic absorbers and for his senior sophister project on the reducibility of copper- and zinc-doped CeO₂. His postgraduate research, funded under the IRCSET EMBARK initiative and supervised by Prof. Watson, will focus on "The effect of interfaces on the properties of transparent conducting oxides".

Congratulations to group member Mario Burbano, who has been awarded the annual BOC Gases bursary by the School of Chemistry. The award is presented to a postgraduate student in the school who is deemed to have made significant advances in their research. The selection process was adjudicated by a panel consisting of Prof. Paula Colavita, Prof. Mike Lyons, and Prof. Georg Duesberg, who praised the overall high standard of applications. The award was presented by the Director of BOC Gases, Gerry Donovan. Mario is a third year postgraduate student in the Watson group, and his research focusses on developing potentials to model solid oxide fuel cell electrolytes such as CeO₂.

We have carried out a combined theoretical-experimental study with collaborators in Chalmers University of Technology, Rutherford Appleton Laboratory, and the University of Oxford to examine the ionic conductivity of solid oxide fuel cell electrolyte Y₂O₃-doped CeO₂, as recently published in Chemistry of Materials. Using a combination of neutron diffraction, impedance spectroscopy, and molecular dynamics, the effects of oxygen vacancy ordering and dopant concentration on the ionic conductivity of the material at high temperatures are investigated. In all cases, the oxygen vacancies were found to order along the <111> directions, as previously observed in other fluorite-structured electrolyte materials, acting as a hindrance to ionic conductivity regardless of dopant or host material. As such, we find that the ionic conductivity is intrinsically limited in Y-doped CeO₂ for dopant concentrations higher than 12%.

Chemistry of Materials 24, 222-229 (2012)

A paper just published in Chemistry of Materials details our recent research on how the oxygen storage capacity of CeO₂ is affected by doping this catalytic material with divalent ions. While Ce(IV) ions in pure CeO₂ are in a cubic coordination environment, we find that dopants which adopt alternative configurations with lower coordination numbers results in some oxygen ions becoming undercoordinated and weakly bound. This allows oxygen vacancies to be more easily created and facilitates reduction. Of the ten dopants considered, the greatest decrease in reduction energy is predicted for Pd- and Pt-doped CeO₂, in which the dopant ions adopt square planar coordination.

Our recent paper, published in the Journal of the American Chemical Society, uses screened hybrid DFT to try to elucidate the origins of conductivity in n-type transparent conducting oxide CdO. By performing a comprehensive defect analysis, we ascertain that oxygen vacancies are the dominant intrinsic defect under all growth conditions, precluding the existence of p-type CdO despite the material's relatively high valence band maximum. Additionally, by examining the doping limits, we determine that n-type defects in CdO are not compensated by p-type defects until at least 1.2eV above the conduction band minimum. This means that despite the material's calculated indirect and direct band gaps of 0.89eV and 2.18eV, respectively, transparency in CdO is achieved via a Moss-Burstein shift, which increases the effective optical band gap to greater than 3 eV.

The recent publication of a Chemical Society Review on the revised lone pair model in the culmination of over 10 years of work in the Watson group which started with the examination of litharge structured PbO. The revised theory developed has been tested on a range of materials and confirmed through our experimental collaborators.

Chem Soc Reviews 9, 4455-4463 (2011)

Read more in our research pages

Congratulations to former group member Dr Aron Walsh, who has just been awarded a Starting Independent Researcher Grant from the European Research Council. This programme offers funding opportunities to early career researchers with the potential to become research leaders. Aron completed his PhD in the Watson group in 2006 and is now a Royal Society University Research Fellow at the University of Bath. He has received the ERC award to investigate functional hybrid organic-inorganic semiconductors, which are predicted to have applications in solar cells and high-efficiency lighting.

Congratulations to Dr Dario Marocchelli and Aoife Kehoe who will both be joining the group following successful IRCSET applications. IRCSET provides funding to researchers at various career stages across all science, technology, and engineering academic disciplines on an annual basis. Dario is the recipient of an EMPOWER Postdoctral Fellowship for his proposed project, "Modeling lithium-ion conducting glasses: optimising their conductivity in order to tackle current energy problems". Aoife has been funded under the EMBARK Postgraduate Scholarship Scheme to undertake research on "Understanding the importance of dopant size, coordination environment, and electronic structure on the oxygen storage capacity and catalytic reactivity of doped CeO₂".

Understanding conduction in Cu₂O is vital to the optimization of Cu-based materials for photovoltaics applications. Using a screened hybrid-density-functional approach we have investigated the formation of p-type defects in Cu₂O, giving rise to single-particle levels that are deep in the band gap, consistent with experimentally observed activated, polaronic conduction. Our calculated transition levels for simple and split copper vacancies explain for the first time the source of the two distinct hole states seen in DLTS experiments.