Density Functional Theory for Steady-State Nonequilibrium Molecular Junctions.

Area of Science:

• Quantum mechanics
• Condensed matter physics
• Computational chemistry

Background:

• Traditional ground-state density functional theory (GS-DFT) is insufficient for non-equilibrium quantum systems.
• Molecular junctions under finite bias represent a significant challenge for existing theoretical models.

Purpose of the Study:

• To develop a novel density functional theory (DFT) applicable to steady-state non-equilibrium quantum systems.
• To address the limitations of GS-DFT in describing systems like molecular junctions under bias.
• To introduce a theoretical framework that uniquely determines non-equilibrium system properties.

Main Methods:

• Formulation of a steady-state non-equilibrium DFT (SS-DFT) based on mapping non-equilibrium to effective equilibrium statistics.
• Derivation of a self-consistent mean-field approach utilizing two distinct electron densities.
• Implementation of the SS-DFT within the SIESTA computational package.
• Application to a carbon-nanotube (CNT)/Benzene molecular junction.

Main Results:

• Demonstration that GS-DFT is not applicable to steady-state non-equilibrium systems.
• Identification of the necessity for two densities (total electron density and current-carrying electron density) for accurate characterization.
• SS-DFT yields a more energetically stable non-equilibrium steady state compared to GS-DFT.
• SS-DFT predicts significantly lower electric currents than conventional methods.
• Validation of SS-DFT's ability to produce correct electronic structures in local equilibrium limits.

Conclusions:

• The developed SS-DFT provides a more accurate and stable theoretical framework for non-equilibrium quantum systems.
• This new approach is crucial for understanding and predicting the behavior of molecular junctions and similar systems.
• SS-DFT offers improved insights into electronic structure and transport properties under non-equilibrium conditions.