ALL-ELECTRON ABINITIO 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 T(ab), 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 T(ab) varies with the lateral position of the tip, with the tip-sample distance, and with the applied bias voltage. The features of the T(ab) curves are analyzed in terms of molecular orbitals.