Department of Chemistry,
University College London,
T: +44 (0)20 7679 4623
Physical Chemistry and Chemical Physics
Section Head: Prof Helen Fielding
Modern physical chemistry and chemical physics (PCCP) are characterized by technological advances at the extremes of measurement. The UCL PCCP group are at the forefront of such advances, developing experiments to probe the chemical and physical properties of molecules and solids in unprecedented detail. Rated as achieving international excellence in the 2001 research assessment exercise, the group has recently expanded to cover macroscopic and microscopic studies of all three phases of matter and is performing pioneering experiments to probe chemistry on a variety of different scales.
Below is a brief overview of the research interests of the members of the PCCP group. Many of the research groups collaborate extensively with each other and with academics from other subject groupings.
Quantum reaction dynamics
Our research focuses on the quantum mechanical description of reactive collisions between small polyatomic molecules. Experimental gas phase reaction dynamics has developed at a great pace in recent years, yet accurate and complete theoretical quantum dynamics is only possible for systems comprising of a small number of atoms (7 atoms represents state of the art). We develop methods by which well controlled approximations may be used to allow for the theoretical description of larger systems with minimal loss of detail regarding the reaction kinetics. Our approach involves the use of “reduced-dimensionality” techniques in which only certain types of atomic motion are given a full quantum dynamical treatment, with the remaining (so-called, spectator) motion treated in a semi-classical manner.
When a system is not able to simultaneously satisfy (i.e. minimize the energy of) all of its interactions it is said to be “frustrated”. This frustration is ubiquitous throughout nature and plays a crucial role in all branches of science, from protein folding to the behaviour of glassy materials. We study the behaviour and characteristics of frustrated systems through the window of classical spin models – also known as model magnets. These provide a rich playground for studying such phenomena as zero-point entropy, the Coulomb phase and emergent magnetic monopoles, with the added advantage that many of the models are physically realized in the form of magnetic crystals.
The development of powerful new synthetic methods has made possible experimental studies on a range of two-dimensional (thin film) and one-dimensional magnets. Working together with experimentalists, we are developing the theory of such systems, with a particular emphasis on the effects of finite size (confinement) on magnetic phase transitions.
Molecules deposited on surfaces can organise themselves into ordered and even complex structures based on intermolecular interactions. This is a process known as two-dimensional supramolecular self-assembly. A variety of Scanning probe microscopy techniques combined with optical spectroscopy can be used to visualise these molecular networks as well as mapping their chemical and optical properties with nanoscale resolution.The main objectives of this work are to understand how the design of the individual molecular building blocks and the environmental conditions under which self-assembly takes place can be used to control the structures that are formed. These structures will then be used as templates for organising more complex components such as nanoparticles or fluorescent sensor molecules. Being able to accurately control the position of components, especially nanoparticles, in complex 2D structures will open up exciting new possibilities in areas of nanotechnology such as sensors, organic photovoltaic materials and molecular electronics.
Daren Caruana - Gas Phase Electrochemistry
The presence of ions in plasmas presents a realistic prospect for performing and controlling redox reactions at a solid/gas interface. The focus of this work is to apply the well-established underlying principles of liquid and solid phase electrochemistry to the gas phase. The eventual aim of this work is to develop voltammetry in a gaseous electrolyte which will open up many applications such as electroanalysis, electrodeposition and electrocatalysis in the gas phase.
Peter Coveney leads the Centre for Computational Science, based in the Department of Chemistry. Our research focusses on many different areas, from molecular and mesoscale fluid dynamics simulations, to computational biomedicine, all based on high performance computational techniques. Our investigations span time and length-scales from the macro-, through the meso- and to the nano- and microscales. We also embrace grid computing as a means to push our research beyond the boundaries of what can be achieved using a single computational resource, often performing single simulations that span multiple grid machines, and invoke tools such as computational steering and high performance visualisation.
Our group studies the thermodynamic properties of fluids and fluid mixtures using a variety of techniques.
A. Thermophysical Properties of Gases
Acoustic methods based on spherical resonators are used to study the thermophysical properties of gases. The techniques are applied over wide ranges of temperature and pressure to obtain speeds of sound of extremely high accuracy (about 1 ppm) that yield heat capacities and second virial coefficients to better than 0.1 per cent: transport properties such as bulk viscosities and vibrational relaxation times are also obtained. The systems studied include pure gases, theoretically tractable mixtures, and industrial fluids for applications to sonic nozzles at high pressures. More recently, annular resonators have been developed so that energy transfer can be studied at very low frequencies.
The same resonators are used at microwave frequencies to determine the dimensions of the resonator and the dielectric constant and total polarizability of the gas. Quadrupole moments of simple gases have been derived from microwave measurements with a high-performance cylindrical resonator. The acoustic and dielectric virial coefficients are related to intermolecular potentials through theoretical and computational studies. An important extension to this work combines microwave and acoustic measurements with the same sphere to give the ratio of the speed of sound to the speed of light and, hence, thermodynamic temperatures of metrological quality.
B. Vapour pressures and phase diagrams
Vapour pressures of pure compounds are determined by comparative ebulliometry from 150 Pa to the critical region. The technique avoids direct measurement of pressure but places considerable demand on thermometry. The derived vapour pressures are of unprecedented accuracy (fractionally 20 ppm or better) and are effectively limited by the accuracy of the data for water which is used as a reference fluid. This work supplements studies of phase diagrams of binary and ternary mixtures such as those formed from water, methanol, carbon dioxide and simple hydrocarbons at high pressure. Particular emphasis is given to those mixtures that have three fluid phases in equilibria.
Helen Fielding - Spectroscopy, dynamics and coherent control
Our work involves using nanosecond and femtosecond lasers to investigate the spectroscopy and dynamics of excited states. Current applications include organic photochemistry, biological chromophores, photodynamic therapy and surface photochemistry.
We employ a variety of spectroscopic techniques including femtosecond pump-probe photoelectron imaging, nanosecond photodetachment spectroscopy, fluorescence lifetime and singlet oxygen measurements, and femtosecond laser induced desorption. In addition, we use computational chemistry to carry out electronic structure calculations to aid the interpretation of our experimental measurements.
We actively develop methods to sample rare events in bio-molecular systems. We contributed to the development of: Metadynamics, Multiple Walkers, Parallel Tempering Metadynamics and Metadynamics-Transition Interface Sampling. We apply these methods to study large-scale conformational transitions in proteins and DNA, ligand binding, protein folding and ion translocation through membrane proteins. We complement the computational modeling with advanced protein NMR techniques, biophysical experiments and mutagenesis.
- Dr Ludovico Sutto
- Dr Kristen Marino
- Dr Giorgio Saladino
- Dr Nicola D’Amelio
Cyrus Hirjibehedin - Atomic-scale studies of quantum nanostructures
My group's research focuses on understanding the electronic and magnetic properties of nanoscale structures and exploring how they might be used to make the smallest possible devices for information processing, data storage, and sensing. The primary tools that we use are low-temperature scanning tunneling microscopes. These state-of-the art instruments allow us to image individual atoms and molecules on surfaces; probe their structural, electronic, and magnetic properties; and even arrange them into new configurations.
You can find out more by visiting the Hirjibehedin Research Group.
Katherine Holt - Electrochemistry, Scanning Electrochemical Microscopy (SECM) and Bioelectrochemistry
My group are engaged in a number of projects in the area of electrochemistry and interfacial science. As well as conventional electrochemical techniques we use IR spectroscopy and XPS to study surface processes that take place at the solid-solution interface. We are particularly interested in electron transfer, solvation and other processes that take place at the surface of insulating materials (e.g. polystyrene, diamond). We also collaborate widely with synthetic chemists, investigating the electrochemical properties of organometallic molecules as potential imaging agents and as electrocatalysts. We are also interesting in using electrochemistry to probe biological systems, for example in studying yeast metabolism and the redox reactivity of keratin-containing tissues.
We use ab initio and density functional quantum chemistry to study the electronic structure and reactivity of molecules drawn from all areas of the periodic table, with particular emphasis on the f block. We have a number of collaborations with experimental groups, most notably at the
Los Alamos National Laboratory in the USA, and the Universities of Oxford,
Edinburgh, California and Glamorgan.
We perform state-of-the-art ab initio quantum chemical calculations in order to understand the complexation of the f-elements, comprising the lanthanides and actinides. The very weak crystal fields and strong relativistic effects associated with such complexes provide a significant challenge to quantum chemical methodologies, and we employ the complete-active-space self-consistent-field (CASSCF) approach in order to overcome the challenges. We investigate the fundamentals of f-element chemistry in order to better understand oxidation state, bond covalency, and magnetic properties. We also consider transition metal analogues, and together these complexes have potential applications in the nuclear power, solar energy, and health industries.
The ultimate success for a materials synthesis programme would be to first determine the structure we would like to make - with particular properties, such as shape-selective catalysis - which we would then predict how to make and then simply synthesise! As part of this effort, we are trying to both develop tools to aid with the synthesis design - through our template design efforts - and to develop an understanding of the self-assembly processes that occur during such syntheses. We employ a range of methods as appropriate - from ab initio modelling of key nucleation steps to forcefield-based Monte Carlo and de novo molecular assembly methods.
Our research aims at understanding important phenomena in surface- materials- and nano-science. Using concepts from quantum mechanics and statistical mechanics, we apply and develop methods and computer simulations to study processes of relevance to catalysis - such as the properties of metal surfaces and chemical reactions at surfaces - and processes of environmental relevance - such as the nucleation of ice or the dissolution of salts. Water and ice are major focuses of our work.
For more information on our research, including movies of recent simulation results, see www.chem.ucl.ac.uk/ice
Sally Price's group is developing the accurate modelling of organic crystal structures, in order to predict which crystal structures of an organic molecule are thermodynamically feasible. These are contrasted with experimental searches for polymorphs in order to understand the factors which lead to polymorphism, in a multi-disciplinary project "Control and Prediction of the Organic Solid State".
Stephen Price - Chemistry of Highly-Excited Species
We are interested in developing experimental techniques to study the formation, properties and reactivity of atoms and molecules which posses considerable internal energy. This energy is usually electronic, vibrational or both. The targets of our experiments range from revealing the reactivity of molecular dications, which is of relevance in planetary ionospheres, to studying the formation of vibrationally excited H2 on interstellar dust grains.
Our research focusses on the laboratory study of gas phase kinetics and photochemistry of trace species including atoms, free radicals and weakly bound molecules. The work is targeted at understanding the role that such species play in the Earth's atmosphere, particularly with regard to environmental issues such as stratospheric ozone loss, urban smog formation, and global warming.
Christoph Salzmann - New materials
We are interested in making new materials, their structural characterisation and
chemical properties. Our aim is to make contributions to fundamental research
but to also to keep an eye on potential future applications and technologies.
Current research projects are concerned with graphene, carbon nanotubes,
high-pressure phases of simple molecules as well as with amorphous materials and
liquids. We make use of a wide range of techniques including neutron and X-ray
diffraction, Raman, FTIR, fluorescence and X-ray photoelectron spectroscopy,
differential scanning calorimetry and atomic force microscopy.
Salzmann research group homepage
Christoph Salzmann's staff profile page
Our research focuses on the nanoscience and surface science of metal oxides, which play a crucial role in technologies such as catalysis and molecular electronics. The targets of our experiments include developing single molecule spectroscopy on oxide surfaces, imaging single molecule chemistry, and nanofabrication of functional devices. This work employs a suite of scanning probe microscopes, spectrometers, and diffractometers in London together with synchrotron radiation techniques at the Diamond Light Source and ESRF, Grenoble.
Magnetism has always challenged accepted scientific understanding, demonstrating the presence of new physical properties and couplings.
The Wills group maintains a separate website where more detailed information about research highlights can be found:
Scott Woodley - Physical Properties from Structure Prediction
The prediction of structure at the atomic level is one of the most fundamental challenges in condensed matter science. In my research, novel state of the art approaches have been developed and applied to dense and microporous inorganic solids and nanoparticles. There is a strong emphasis on developments in methodology, paying particular attention to approaches for surveying energy landscapes and the design of advanced models that define the energy hypersurfaces. The former is typically based on combining global and local optimisation techniques in a bid to reduce the number of candidate structures required to assess during the search for the lowest energy configurations. The latter aims at reducing the computational cost of evaluating each candidate structure whilst including key interactions required in the model. Implementation manifests itself in the form of new software, which leads to application work. Key physical and chemical properties become accessible once the atomic structure is known using both atomistic and electronic structure techniques. A particular interest arises from the structure-property relationships at nanoscale. The phase or atomic structure is dependent on the size of the particle – small nanoparticles do not always resemble cuts from their bulk phase – and thus potentially size provides a tuning parameter for a desired property.
- Kathleen Lonsdale Materials Chemistry – KLMC
- Molecular Modelling and Materials Science – Industrial Doctorate Centre