Transiesta

Official Resources

• Homepage: https://departments.icmab.es/leem/siesta/
• Documentation: https://docs.siesta-project.org/projects/siesta/en/latest/tutorials/transiesta/index.html
• Source Repository: https://gitlab.com/siesta-project/siesta
• License: GNU General Public License v3.0

Overview

Transiesta is the quantum transport module of the SIESTA density functional theory code. It uses the Non-Equilibrium Green's Function (NEGF) method combined with DFT to calculate electron transport properties of nanoscale systems under finite bias voltage. It enables the simulation of current-voltage characteristics, transmission spectra, and local currents in molecular junctions, nanowires, and interfaces.

Scientific domain: Quantum transport, NEGF-DFT, molecular electronics
Target user community: Device physicists, nanoscientists, SIESTA users

Theoretical Methods

• Non-Equilibrium Green's Function (NEGF)
• Density Functional Theory (DFT) with local orbitals (LCAO)
• Keldysh formalism for open systems
• Landauer-Büttiker formalism for conductance
• Pseudopotentials (Norm-conserving)
• Spin-polarized transport

Capabilities (CRITICAL)

• Transport Calculation: I-V curves, zero-bias conductance, transmission function T(E)
• Finite Bias: Self-consistent calculation under applied voltage
• Analysis: Projected density of states (PDOS) in open systems, scattering states
• Inelastic Transport: Inelastic Electron Tunneling Spectroscopy (IETS) (via Inelastica)
• Spin Transport: Spin-polarized currents, spin torque
• Scalability: Capable of handling large systems (thousands of atoms) due to O(N) basis

Sources: SIESTA/Transiesta documentation, Comp. Phys. Comm. 147, 71 (2002)

Inputs & Outputs

• Input formats: Flexible FDF format (SIESTA input), Electrode Hamiltonians (.TSHS)
• Output data types: Transmission files (.AVTRANS), PDOS, current density, eigenvalues

Interfaces & Ecosystem

• SIESTA: Fully integrated part of the SIESTA package
• TBTrans: Post-processing tool for calculating transmission from Transiesta calculations
• Inelastica: Third-party tool for IETS and phonon effects using Transiesta
• Sisl: Python toolbox for manipulating Transiesta/SIESTA files

Workflow and Usage

1. Calculate Electrode: Run SIESTA for the bulk electrode to get electrode.TSHS.
2. Setup Scattering Region: Define geometry (Left Electrode - Device - Right Electrode).
3. Run Transiesta: Perform self-consistent NEGF calculation (transiesta input.fdf).
4. Post-process: Run tbtrans to calculate transmission spectra and current.

Performance Characteristics

• Highly efficient due to localized basis sets (linear scaling algorithms)
• Parallelized with MPI
• Efficient contour integration for Green's functions

Application Areas

• Single-molecule transistors
• Graphene and 2D material nanoribbons
• STM tip-surface interactions
• Metallic contacts and interfaces
• Spin valves

Community and Support

• Large SIESTA user community
• Active mailing list
• Developed by SIESTA developers (ICMAB, DTU, etc.)

Verification & Sources

Primary sources:

1. Homepage: https://departments.icmab.es/leem/siesta/
2. Publication: M. Brandbyge et al., Phys. Rev. B 65, 165401 (2002)

Confidence: VERIFIED

Verification status: ✅ VERIFIED

• Website: ACTIVE
• Documentation: COMPREHENSIVE
• Source: OPEN (GitLab)
• Development: ACTIVE
• Applications: NEGF transport, finite bias, molecular electronics