First-principles statistical mechanics for molecular switches at surfaces

Abstract

This DEISA initiative aims at the switching properties of organic molecules adsorbed at metal surfaces, which could be exploited in a future “molecular electronics” as a fundamental building block for storage and logic. Employed will be a modern multi-scale modelling approach, which suitably combines first-principles electronic structure calculations with concepts from thermodynamics and statistical mechanics. First-principles density-functional theory (DFT) calculations will be employed for an accurate atomic-scale characterization of the molecule-substrate system, while the transition from a single adsorbed molecule to a molecular ensemble or network is treated by means of statistical Monte Carlo methods. Already individual DFT calculations at the involved system sizes (up to 250 transition metal atoms) form a grand computational challenge by themselves, but are furthermore required for a large number of adsorption geometries and systematically varied coverages to parameterize the statistical models. Based on the data provided in the DEISA run we will achieve an entirely first-principles, i.e. parameter-free, description of the molecular switch at the surface, from the microscopic implications in the electronic and geometric structure to mesoscopic order and disorder phenomena within a network of adsorbed switches. The proposed quantitative multi-scale calculations offer therefore the unique potential to obtain unprecedented insight and understanding into the molecular switching function, induced e.g. by coverage or temperature changes or by mechanical manipulation.