Project List
A list of projects on the RCF in no particular order. Each entry consists of a title, a short description, a set of keywords and the names of the researchers involved. You can search this page for a particular person, piece of software or keyword.
Electronic Structure Studies of Zinc Ammonia Clusters
Andrew Turner, Bridgette J Duncombe
We are trying to gain a detailed understanding of the formation and fragmentation of [Zn(NH3)n]2+ clusters using a combination of Mass Spectrometry (MS) experiments and electronic structure calculations. Calculations are used to determine the preferred structure for a particular cluster size as well as the binding energies. MS experiments can be used to assess the relative stability of the different cluster sizes and illustrate preferred fragmentation patterns.
Keywords: cluster, ab initio, mass spectrometry, GAMESS-UK, MP2, DFT
Low Frequency Vibrational Modes of Polar Liquids and Solutions
Andrew Turner
The goal of this research is to determine the nature of the low-frequency vibrational dynamics of polar liquid and solutions to tie in with high resolution ultrafast spectroscopic experiments (from Klaas Wijne's group at the University of Strathclyde.) We are using a wide variety of theoretical methods to investigate these dynamics ranging from classical simulations to electronic structure Hessian calculations.
Keywords: cluster, molecular dynamics, DL_POLY, ab initio, vibration, Gaussian, DFT, polarizability, hydrogen bonding
Solid state proton migration
David Martins, Carole Morrison, Colin Pulham
The goal of this interdisciplinary project is to investigate the phenomenon of proton migration in the solid state. This rare-like event has been shown to exist in certain molecular compounds with short, strong hydrogen bonds (SSHB). In such cases the position of the hydrogen atom in a hydrogen bond between a donor and acceptor atom can be influenced by temperature and pressure, i.e. the phenomena of temperature- or pressure- induced proton migration. Because of experimental limitations such as pronounced atomic motion or limited reciprocal space collection at high temperature (HT) or pressures (HP), respectively, experimental data analysis is not straightforward. For this reason the interplay of X-ray and neutron diffraction with DFT calculations is necessary to achieve our goals in a successful fashion.
Gas-phase structures from electron diffraction
David Rankin, Sarah Masters, Derek Wann, Rob Noble-Eddy and Graeme Kafka
Gas-phase electron diffraction (GED) is a unique experimental method for direct structure determination of molecules in the gas phase. The application of theoretical methods greatly facilitates the analysis of GED data, especially for molecules with large numbers of atoms (i.e. 50-100 atoms) and complex conformational compositions. Structures obtained by electron diffraction can be, and frequently are, used as important points of reference for comparison with calculated structures. We therefore have experience of optimising geometries for an enormous range of isolated molecules – everything from substituted benzenes to CVD precursors. Often we use the Gaussian code for our calculations, although recently we have begun to experiment with GAMESS-UK and MOLPRO as alternatives.
We routinely use computed amplitudes of vibration as starting values during the refinement of electron-diffraction data. Vibrational corrections are now also routinely calculated to reduce the effects of vibrations on the time-averaged experimental structures. Usually both the amplitudes of vibrations and the corrections are computed using theoretical force fields. The importance of anharmonicity in vibrational corrections means that wherever possible cubic force constants must be calculated, which can be very computationally demanding.
For large molecules it is commonly found that not all structural parameters can be refined using experimental data alone. In the past this led to parameters being fixed to certain values and many assumptions were made about the symmetry of molecular fragments. The development of the SARACEN method, which uses calculated parameters as restraints in the refinement process, has utilised the power of computational techniques.
Separate entries are currently being prepared to describe in more detail some of the individual projects currently underway in the Rankin and Masters groups