Electric-field-driven electron-transfer in mixed-valence molecules

Abstract

Molecular quantum-dot cellular automata is a computing paradigm in which digital information is encoded by the charge configuration of a mixed-valence molecule. General-purpose computing can be achieved by arranging these compounds on a substrate and exploiting intermolecular Coulombic coupling. The operation of such a device relies on nonequilibrium electron transfer (ET), whereby the time-varying electric field of one molecule induces an ET event in a neighboring molecule. The magnitude of the electric fields can be quite large because of close spatial proximity, and the induced ET rate is a measure of the nonequilibrium response of the molecule. We calculate the electric-field-driven ET rate for a model mixed-valence compound. The mixed-valence molecule is regarded as a two-state electronic system coupled to a molecular vibrational mode, which is, in turn, coupled to a thermal environment. Both the electronic and vibrational degrees-of-freedom are treated quantum mechanically, and the dissipative vibrational-bath interaction is modeled with the Lindblad equation. This approach captures both tunneling and nonadiabatic dynamics. Relationships between microscopic molecular properties and the driven ET rate are explored for two time-dependent applied fields: an abruptly switched field and a linearly ramped field. In both cases, the driven ET rate is only weakly temperature dependent. When the model is applied using parameters appropriate to a specific mixed-valence molecule, diferrocenylacetylene, terahertz-range ET transfer rates are predicted.

Electric-Field Inputs for Molecular Quantum-Dot Cellular Automata Circuits

“…Work on the realization of QCA molecules is ongoing. Charge localization has been observed in some molecules [27], [28], and efforts in physics [13], chemistry [6], and physical chemistry [29] are focused on the design, synthesis, and testing of molecules. Diferrocenyl acetylene [DFA, see Fig.…”

“…A departure from transistor-based computing, quantum-dot cellular automata (QCA) is a non-von-Neumann paradigm for general-purpose, classical computing, which was designed to leverage quantum phenomena and allow energy-efficient devices [3], [4]. QCA may be implemented using molecules, which promise ultra-high device densities and THz-speed-orbetter switching speeds at room temperature [5], [6].…”

Quantum dissipation driven by electron transfer within a single molecule investigated with atomic force microscopy

“…We believe that our work opens new possibilities for studying mixed-valence state molecular systems and quantum dissipation out of equilibrium on the single-molecular level using AFM, simulating in a controlled way key features of the dynamic environment that the molecular systems often experience. Strong coupling between the single-electron transfer within a single molecule and the dynamics of the macroscopic probe may also define novel single-molecular nanoelectromechanical systems 23 toward applications as molecular quantum-dot cellular automata [24][25][26][27] .…”

Tunable, Hardware-Based Quantum Random Number Generation Using Coupled Quantum Dots

“…[14], the field is applied using charged electrodes, so the field strength may be changed by varying the voltage V applied between the electrodes. For a DQD based on an ionic DFA molecule, a = 0.67 nm, and it has been calculated that the relaxation time is T 1 ∼ 1 ps and the tunneling energy is γ ∼ 50 meV [15]. This results in a maximum measurement frequency of 1 THz.…”