Design of Molecular Quantum-Dot Cellular Automata Cell

 

Figure 3: Single proposed quantum cellular automaton with solvent molecules and counterions. This represents half a cell. The effect of solvents on charge screening will be evaluated through constant temperature molecular dynamics.

Quantum Cellular Automata (QCA) are the foundation to an alternative to transistor-based technology. The cells may occupy one of two possible states corresponding to binary information. These states are determined by the distribution of two electrons among four available sites in the symmetric cell. The electrons would occupy opposite corners to minimize electrostatic potential energy due to Coulomb forces. Electrons are localized in these corners by energy barriers of sufficient height between sites [91]. The electron's transit from one site to the other can cause the electron in the other half cell to undergo a corresponding transit. This is referred to as a click [146], which is necessary to perform the functional foundation for computing [123]. If the potential difference that the electron sees between a state of opposite occupation and a state of adjacent occupation is not large enough, the electron will not tunnel - the cell will not click.

We will compute the electric potential barrier of the one electron click by combining ab initio quantum mechanics and MD simulations. The charges of the solute atoms will be obtained by electronic structure calculation using the quantum mechanics package GAUSSIAN98. Simulation will be carried out in canonical ensemble with explicit solvent molecules. The solute will be immersed in a box of solvent molecules with periodic boundary conditions. MD will be used to let the system relax using NAMD 2.1 and PROTOMOL. The final configuration of the cell will be extracted and the charges of the atoms will be spread out on a 3D grid. Thus, the electronic potential energy will be calculated. In the simulation, we will investigate the effects of different solvents, counteranion and temperatures on the electric potential barrier. Fig 3 illustrates a half cell set up for simulation. Such information could guide the control of the QCA.