Molecular reorganization energy in quantum-dot cellular automata switching

TL;DR

This paper investigates how molecular reorganization energy affects switching behavior in quantum-dot cellular automata, revealing intrinsic bistability and memory effects influenced by nuclear relaxation.

Contribution

It introduces a model combining quantum electron dynamics with semiclassical nuclear motion to analyze switching and bistability in QCA molecules.

Findings

Hysteresis observed during molecular switching.

Nuclear relaxation enhances electron localization.

Intrinsic bistability enables single-molecule memory.

Abstract

We examine the impact of the intrinsic molecular reorganization energy on switching in two-state quantum-dot cellular automata (QCA) cells. Switching a bit involves an electron transferring between charge centers within the molecule. This in turn causes the other atoms in the molecule to rearrange their positions in response. We capture this in a model that treats the electron motion quantum-mechanically, but the motion of nuclei semiclassically. This results in a non-linear Hamiltonian for the electron system. Interaction with a thermal environment is included by solving the Lindblad equation for the time-dependent density matrix. The calculated response of a molecule to the local electric field shows hysteresis during switching when the sweep direction is reversed. The relaxation of neighboring nuclei increases localization of the electron, which provides an intrinsic source of enhanced bistability and single-molecule memory. This comes at the cost of increased power dissipation.