Molecular switches on solid surfaces raise an important issue in digital electronic devices. It has been frequently tried to design devices to perform basic functions at the molecular scale. In this paper, the Perdew-Burke-Ernzerhof (PBE) and PBE+van der Waals (vdW) were utilized in the framework of density functional theory (DFT) to model CO optimization on a graphene surface. Among the different external stimuli, electric fields serving as a useful probe were used to activate CO switching properties. The molecular conformation of CO, total dipole orientation, and charge transfer orientation were manipulated by turning an external electric field ON and OFF. The molecular conformation switched from a parallel orientation in a negative electric field towards a perpendicular orientation in a positive electric field. The total dipole moment switched from - 8.56 Debye (D) in an electric field of - 1.0 V/Å to 3.64 D in an electric field of + 1.0 V/Å. Charge transfer was seen to switch with the electric field switching. In the negative electric field, the charges were transferred from graphene to CO, while a reverse transfer occurred in the positive electric field. In addition, it was shown that CO desorption occurred in an electric field of greater than ± 1.0 V/Å. Eventually, the ON-to-OFF state transition was accompanied by switching between the positive and negative dipole moments, adsorption and desorption states, and positive and negative charge transfers when the external field direction and intensity were switched.
Keywords: Density functional theory (DFT); Electric field; Graphene; Molecular switching.