Electronic structure and conductance of DNA
Davies, Owen R.
In this thesis an efficient method has been developed for calculating the electronic structure and conductance of large biological molecules. The embedding method has been adapted to allow the splitting of large molecules such as DNA into smaller component blocks, completely preserving the information of the macro-system. The computational time required for this method increases as O(N) with the size of the system, instead of the traditional O(N3). The semi-empirical extended Huckel theory is used to describe the electron wavefunctions within a tight-binding scheme, taking the effect of the metal-molecule contacts into account. Presented in this thesis are the results for several different DNA molecules and structures. It has been determined that the transmission through DNA depends sensitively on the energy at which it is evaluated, and the atoms to which the metallic leads are connected. It is also found that poly(G)-poly(C) DNA conducts charge better than DNA with mixed bases, and that energy-minimised DNA with less structural disorder conducts better than DNA obtained from x-ray diffraction experiments. The electrical conduction of DNA that has undergone stretching has been investigated, and the distorted structure gives very small currents. The embedding method has also been applied to the small aromatic molecule OPE, to determine its electronic properties. Metallic conductivity is found for this molecule, and it is able to carry currents 1000 times greater than DNA, giving possible applications in molecular electronics.
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