Multiscale Simulations of Quantum Structures

Advances in theoretical methods and parallel super computing allow for reliable ab initio simulations of the properties of complex materials. We describe two applications: (i) negative differential resistance (NDR) in self assembled monolayers of ferrocenyl-alkanethiolate on a gold surface, and (ii) interface bonding in polymer/ceramic nanocomposites. Our non-equilibrium Green's function calculations show that electron transport through ferrocenyl-alkanethiolate exhibits strong NDR features at both positive and negative biases, in good agreement with the experimental data. The results suggest that the ferrocenyl group acts like a quantum dot and that the NDR features are due to resonant coupling between the HOMO and the density of states of gold leads. Tuning of the "strength" of the NDR and its implication for the design of molecular devices are also discussed. For polymer/ceramic nanocomposites, we show that direct attachment of alkane chains to ceramic surfaces is not energetically favorable, while silanated chains attach through a bridging OH group with an energy gain