A theoretical model for single molecule incoherent scanning tunneling spectroscopy

TL;DR

This paper develops a theoretical model combining extended Huckel theory and NEGF to study temperature-dependent dephasing effects in single molecule tunneling spectroscopy, focusing on resonant conduction through molecular orbitals.

Contribution

It introduces a novel EHT-based NEGF model with electron-phonon scattering treated via SCBA, and a basis set modification procedure for analyzing dephasing effects.

Findings

Dephasing significantly affects resonant conduction at room temperature.

The model captures temperature-dependent dephasing due to low-lying vibrational modes.

Proposes a method to include dephasing in molecular conduction calculations.

Abstract

Single molecule scanning tunneling spectroscopy (STS), with dephasing due to elastic and inelastic scattering, is of some current interest. Motivated by this, we report an extended Huckel theory (EHT) based mean-field Non-equilibrium Green's function (NEGF) transport model with electron-phonon scattering treated within the self-consistent Born approximation (SCBA). Furthermore, a procedure based on EHT basis set modification is described. We use this model to study the effect of the temperature dependent dephasing, due to low lying modes in far-infrared range for which hw<<kT, on the resonant conduction through highest occupied molecular orbital (HOMO) level of a phenyl dithiol molecule sandwiched between two fcc-Au(111) contacts. Furthermore, we propose to include dephasing in room temperature molecular resonant conduction calculations.