STM-induced switching of the hydrogen molecule in naphthalocyanine

The switching induced by the scanning tunneling microscope (STM) current of an adsorbed hydrogen molecule in the cavity of a naphthalocyanine molecule between two perpendicular orientations is studied. We regard such a system as a good candidate for a molecular size electronic logic gate since it causes a well observed change in the STM tunneling current. To investigate the switching phenomenon theoretically, a dynamical model is proposed in this study. Our suggested model is a three-level system, with the switching as a rotation induced by tunneling electrons considered as a second-order time dependent perturbation, where the electrons tunnel from the STM-tip to the naphthalocyanine molecule then to the metal substrate. The tunneled electrons will excite the hydrogen molecule rotational modes to jump over a potential barrier and then the switching will occur. To verify the model, the probability of the switching is calculated and plotted against the bias voltage at different temperatures using first-principles calculated parameters to fit fairly with experimental observations. In the light of our model and the DFT results, we explain the energy level (highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and LUMO+1 orbitals) deviations with different substrates (NaCl and RbI) and the charge density distributions of these orbitals in different cases.