Electric Field Control of Spin States in Trigonal Two-Electron Quantum Dot Arrays and Mixed-Valence Molecules: I. Electronic Problem

In the context of our studies of the electric field control over stimuli-responsive molecular materials, in this article, we report a detailed theoretical analysis of the electric field control of the spin states, magnetic properties, and charge distributions in the trigonal trimeric systems comprising a pair of mobile electrons or holes. Such systems are exemplified by "physical" molecules composed of semiconductor quantum dots accommodating unpaired electrons as well as by proper chemical systems representing trigonal trimeric mixed-valence clusters in which the two mobile electrons are delocalized over three spinless cores. In part I of the paper, we consider the electronic interactions (inter- and intrasite Coulomb repulsion, electron transfer, and Stark interaction) in quantum dot arrays and mixed-valence molecules, whereas part IIdeals with the vibronic approach in which the interaction between the mobile electrons and the molecular vibrations is taken into account as well. A complicated interplay between the electron transfer and the localizing effect of the field is shown to result in a series of interesting magnetic effects. We demonstrate this by changing the magnitude of the electric field and/or its orientation with respect to the axes of the system, one can reach an efficient electric field control over the magnetic and electric properties of the considered systems. Particularly, under some conditions (described in the paper), the electric field of attainable strength is shown to induce spin switching from the ground state possessing the spin S = 1 to that with S = 0. Such a possibility to control the spin states of single molecules and analogous systems using an external electric field is of current interest for molecular spintronics.