Understanding a Bisferrocene Molecular QCA Wire - Field-Coupled Nanocomputing: Paradigms, Progress, and Perspectives - page 312

2 Methodology for the Analysis of Molecule
and Ensamble of Molecules

This section describes a possible methodology to evaluate and simulate all the
important parameters necessary for molecular QCA devices. It aims to represent
both the bis-ferrocene features as QCA devices and the feasibility of comput-
ing with molecular QCA. Additionally, the methodology for analyzing defects
concerning QCA wire fabrication is also provided.
The study is organized in two stages, as shown in the scheme of Fig. 10 :
Stage I , where ab-initio simulations are performed under different conditions
as detailed in Sect. 2.1 ;and Stage II , where electrostatic equations and models
are set up in order to define new figures of merit to describe the QCA molecular
system (see Sect. 2.2 ) and to understand its potentials from an electronic point
of view.

Fig. 10. A two stages analysis from molecular systems to device-level figures of merit.

2.1 Stage I - Ab-initio Simulations

The computations and evaluations of the electronic structure and properties we
performed via ab-initio simulations (see Fig. 11 ) are mainly based on the laws of
quantum mechanics and a set of physical constants (the speed of light, masses
and charges of electrons and nuclei, Plank's constant).
They are based on the theory from the first principle and are highly accu-
rate and, as a consequence, computationally intensive. In order to characterize
a molecule as QCA device, a set of ab-initio simulations could be performed
on different conditions of molecular systems, by defining proper methods and
basis sets.
For all the simulations of the bis-ferrocene molecule the DFT-B3LYP theory
was used with the LANL2DZ basis-set.

S I-A - Single Oxidized and Neutral Molecule Simulation. The binary
information of the molecular QCA system could be evaluated by using the figure
of merit of the highest occupied molecular orbital (HOMO), as mentioned in
[ 7 , 10 , 11 ]. While based on this, in order to take clearly the electronic point of