 |
I've finally finished my Phd in theoretical chemistry under the supervision of Dr Philip Camp in the School of Chemistry at Edinburgh University. Below is a brief history and some details of research that I've performed before and during my Phd. My homepage can be found here. |
|
Born in Stirling 20-odd years ago, started school there and finished in fife. Began my university life in Edinburgh, studying chemistry in 1996, five years and one industrial placement later, i finally graduated in Summer 2001 and started my Phd in October of the same year. I graduated for the second time in November 2005 after completing my thesis during summer 2005. I'm now currently working as a Postdoc in York Structural Biology Laboratory under the supervision of Dr Seishi Shimizu. |
| During my final year of my undergraduate degree, I undertook a 16 week research project. The goal of which was to study the charge order-disorder transition in charge asymmetric ionic solids using computational simulation techniques. The majority of the study was concerned with a 2:1 electrolyte such as CaF2, but also briefly examined a 1:1 electrolyte as a comparison to previous simulation work[1,2]. Immediately to the right are snapshot representations of the final configurations of the 1:1 electrolyte system to show the charge disordered phase (1st right) and charged ordered phase (far right) The driving force for such a transition is the free energy, which is a balance of the enthalpy (charges order) and entropy (charges disorder). In the high density solid phase (maximum packing of 74% of all space is occupied by particles)the ions are arranged on a face centred cubic (fcc) lattice, where each unit cell contains 4 ions. A typical simulation cell is constructed of 4 unit cells in 3 dimensions (256 particles). A phase transition can be easily detected from discontinuous drop in energy in a plot of energy per particle against temperature |  |
 |
 |
 |
The second part of the project was to investigate the charge order-disorder transition of a 2:1 electrolyte, such as CaF2. For this we simulated two structures, the face centre cubic lattice for the high density solid phase and the fluorite lattice for a lower density solid phase (shown far left). Simulations with the fluorite lattice were (performed at >99% of the close packing), showed that the lattice structure will preferentially melt before the charges disorder, the melted structure is shown far left. |
| Simulations with the face centred cubic lattice were performed with an appropriate number of particles to ensure electroneutrality. Examination of a plot of energy per particle against temperature reveals a drop in energy charactaristic of the system undergoing some degree of charge ordering. However, we do not find a low temperature charge-ordered solid, rather it appears that the system forms an unusual "charge-glass" phase. This may arise from the arrangement of charges in a face centred cubic unit cell, which is not electroneutral.Snapshot representations of the final configurations are shown below. |  |
 |
| I'm currently using computational simulation methods to examine the properties of "Bent-core" liquid crystals, these molecules are achiral and have unique properties of interest for chemists and physicists alike. They have many uses in modern displays and telecommunications. The generic structure of such molecules are shown to the right. For a brief explaination of liquid crystal phases, click here. |  |
 |
Rather than utilise computationally demanding techniques, such as ab initio, we use a simple model (shown left) coupled with Monte Carlo methods. Simulations have been performed with bend angles from 0 to 60 degrees. |
 |
 |
With linear molecules we find a full range of liquid crystalline phases, the crystal at low temperature, a tilted smectic phase (far top left), untilted smectic A (top left), uniaxial nematic phase (far bottom left) and isotropic phase (bottom left). From the end-on view of the untilted smectic A, we can clearly see no translational ordering within a layer. |
 |
 |
 |
 |
 |
| By introducing a slight bend into the molecule we raise the possibility of forming chiral and racemic phases. However with our system we only form a racemic ferroelectric phase (above left). We have also enhanced the range over which the nematic phase (above centre) is stable at the expense of the untilted smectic A. We also find the isotropic phase (above right) at high temperature. | ||
 |
 |
For a system with bend angle commensurate with real systems, we only see a racemic smectic phase (far left) and a single phase transition to the isotropic phase (left). |
| Although we observe tilted phases, none are chiral. The molecular tilt may be ascribed to the hexagonal close packing of spheres of adjecent molecules. In order to do this molecules have to tilt to 30o. This is confirmed by tilt data obtained from simulations. |  |
In summary;
|
|
The current phase of computer simulations is with dipolar molecules, where the dipolar interactions are calculated via the Ewald summation method. Again we are simulating molecules with bend angles from 0 to 40 degrees and are considering the effect of dipole strength. Simulations are currently underway, so watch this space for results. |
|
The next phase of simulations is to mimic the flexible R groups of the actual molecules themselves using Configurational Bias Monte Carlo. The simulation code for this has been written and is in the final stages of testing prior to full scale simulations commencing in early 2004. A snapshot representation of a trial simulation is shown right. |
|
|
This work is undertaken with the finanical support of EPSRC(GR/45727/01) |
|
I'm also interested in kinetics, as my 6th year chemistry project was a kinetic study of the iodine-propanone reaction, studied with a colourimeter connected to a computer and my project in Industry was on modelling of oxidation kinetics. |
|
