Time-Dependent Density Functional Theory with Ultrasoft Pseudopotential: Real-Time Electron Propagation across Molecular Junction

TL;DR

This paper presents a computational scheme combining TDDFT and ultrasoft pseudopotentials to simulate real-time electron dynamics in molecular junctions, validated by optical spectra and applied to electron transmission calculations.

Contribution

The paper introduces a practical TDDFT approach with ultrasoft pseudopotentials for real-time electron dynamics in molecular junctions, enabling accurate transmission and conductance predictions.

Findings

Validated scheme with optical spectra for sodium dimer and benzene.

Computed electron transmission with 5-7% probability, matching theoretical estimates.

Achieved conductance values consistent with Green's function calculations.

Abstract

A practical computational scheme based on time-dependent density functional theory (TDDFT) and ultrasoft pseudopotential (USPP) is developed to study electron dynamics in real time. A modified Crank-Nicolson time-stepping algorithm is adopted, under planewave basis. The scheme is validated by calculating the optical absorption spectra for sodium dimer and benzene molecule. As an application of this USPP-TDDFT formalism, we compute the time evolution of a test electron packet at the Fermi energy of the left metallic lead crossing a benzene-(1,4)-dithiolate junction. A transmission probability of 5-7%, corresponding to a conductance of 4.0-5.6muS, is obtained. These results are consistent with complex band structure estimates, and Green's function calculation results at small bias voltages.