Theoretical study of molecular quantum dot cellular automata

Molecular quantum-dot cellular automata (QCA) is an alternative paradigm for molecular electronics. Each single molecule acts as a QCA cell and binary information is encoded in the configuration of charge among redox-active molecular sites. Coulomb interaction between neighboring molecules provides information transport from one molecule to another, so the heat dissipation is low because no current through molecular circuits is needed. In this paper, we present a quantum-chemistry ab initio analysis of these two QCA candidates. For Trans-Ru(dppm)/sub 2/(C=CFc)(NCCH/sub 2/CH/sub 2/NH/sub 2/) dication, our calculation confirms a bistable charge configuration in which the binary information can be encoded. The ferrocence and Ru(dppm)/sub 2/ groups are two natural quantum dots in the molecule. The carbon-carbon triple bond connecting these two dots provides the tunneling junction for a mobile electron. Driven by an external electric field, the mobile electron can move from one dot to the other, resulting in an abrupt change of dipole moment. The critical driven field is determined by the energy difference of the bistable states and the effect of counterions as well. Our calculations qualitatively explain the experimental observations.