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MAny-body calculations of nanoscale electronic structure and transport

Final Activity Report Summary - MANET (Many-body calculations of nanoscale electronic structure and transport)

Over the past 10 years a new type of science and technology has emerged at the nanoscale. We are now able to control the construction and chemical composition of sensors and components in electronics with atomic precision. This has fuelled growth in a series of new industrial sectors, and in particular in electronics, whose 50 year old paradigm (integrated circuits on silicon wafers) is coming to its limits. In the course of this Marie Curie Fellowship I have studied complex effects in the way electrons are transported in nanometre sized wires. At this scale, the quantum nature of particles and atoms dominates their behaviour. In particular, the correlation between the position and state of one electron with those of all the other electrons in the system being studied becomes crucial when examining excited states, where the electrons are kicked out of their natural equilibrium. This is in particular the case in electrical transport, where electrons flow between, e.g. different terminals on a transitor.

In order to study these complex correlations, we have chosen a simple way to get the most fundamental character of a nanoscopic electrical junction: its conductance, which quantifies the ease with which an electron can be transmitted through it. As a first approximation, the equilibrium states of the electrons are found using the 'Density Functional Theory' (DFT), which treats all other electrons in an average way. More precise electron correlations are obtained from the GW approximation, which accounts for the explicit interactions between electrons, this interaction being screened by the presence of all the other electrons. Using the GW theory to correct the first results obtained with DFT, we will obtain a more precise description of the ease with which electrons can be displaced in the system (the polarisability), and therefore be able to see the effect of correlations on the conductance of an electrical junction. A number of attempts to include correlation effects in these types of calculations have appeared in the past 2-3 years, but all have significant shortcomings in the way they represent the electronic states. Our approach includes an accurate representation, and will be the first to give such a realistic base to an evaluation of the importance of correlation.