A Theoretical Procedure Based on Classical Electrostatics and Density Functional Theory for Screening Non-Square-Shaped Mixed-Valence Complexes for Logic Gates in Molecular Quantum-Dot Cellular Automata

Understanding the requisite geometry of molecules and peripheral components is an essential step in endowing molecules with logical functions in quantum-dot cellular automata. To respond to the real problem of structural distortion from the ideal square cell configuration, a practical procedure is presented that simplifies the molecular shapes for device design with features that combine aspects of classical electrostatics and density functional theory calculations. By applying this method to a library of biferrocenium dimers with a three-input junction, it was demonstrated in theory that a covalently bonded parallelogram dimer responds precisely to six different patterns of nanoscale electric fields and works correctly as a device cell in both AND and OR logic gates. The counterintuitive usefulness of the non-square-shape is rationalized by four ferrocene-based orbital orientations and a functional group arrangement, equalizing the disadvantageous energy asymmetry between the states 0 and 1. The present procedure was applied to quasi-square tetrametallic Ru complexes and it was found that these complexes do not work as logic gates. This procedure expands the range of existing candidate molecules from squares to parallelograms and facilitates screening for implementation.

Automated summary

The study simplified the molecular shapes for quantum-dot cellular automata, presenting a practical procedure to design molecules that can respond accurately to different electric field patterns and function correctly in logic gates.