Energy landscapes of molecular clusters

• Main Author: James, T. R.
• Published: University of Cambridge 2007
• Subjects: 541.2
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605026

Theoretical characterisation of a number of properties of different cluster systems is performed within the energy landscapes formalism. Comparisons with experimental observations are used to provide a critical evaluation of the calculations, where appropriate. Some of the basic concepts and techniques are first discussed. Much of the work has been performed using models that make a rigid-body approximation for the species under investigation. Considerations arising from the corresponding use of curvilinear coordinate systems are therefore presented. Water is the principal focus of the investigations. First, putative structures of the global minima as a function of cluster size are reported for a rigid, fixed-charge potential. Comparisons with other models are made, and conclusions are drawn regarding the relative suitability of the potential for describing cluster geometries. The influence of a constant, uniform electric field on small water clusters is then examined. The evolution of the energy landscape with increasing field strength is compared for three related models. Thirdly, the properties of water clusters in the presence of a single excess proton are investigated. For these systems, a more sophisticated model allowing for the localisation of the excess charge on any of the molecules is employed. Comparisons are made with higher level calculations and with spectroscopic measurements, and reasonable agreement is noted is some cases. The methods for dealing with rigid bodies are then extended to investigate a model for the construction of viral protein shells. The properties of the landscapes, in particular their propensity for efficient self-assembly, are examined for three different shell sizes. Suggestions for modifications to the model aimed at improving the structure-seeking characteristics are made. Finally, concluding remarks and the scope for future work are outlined.