All-electron ab initio self-consistent-field study of electron transfer in scanning tunneling microscopy at large and small tip-sample separations: Supermolecule approach

Electron transfer expressed in the context of molecular-orbital theory is used as a model for scanning tunneling microscopy. We calculate the electronic coupling matrix element Tab, ubiquitous in theories of electron transfer, by means of ab initio self-consistent-field wave functions for a supermolecule made up of a sample molecule and a tip metal atom. We find that Tab varies with the lateral position of the tip, with the tip-sample distance, and with the applied bias voltage. The features of the Tab curves are analyzed in terms of molecular orbitals.