exciting (TDDFT)

Official Resources

• Homepage: https://exciting-code.org/
• Documentation: https://exciting-code.org/ref/documentation
• Source Repository: https://github.com/exciting/exciting
• License: GNU General Public License v3.0

Overview

exciting is an all-electron full-potential linearized augmented planewave (FP-LAPW) code for DFT and beyond, with particular strength in optical and excited-state properties. It provides advanced capabilities for TDDFT, GW, and BSE calculations with a modern, open-source codebase.

Scientific domain: Optical properties, excited states, spectroscopy, all-electron calculations
Target user community: Researchers studying optical properties, excitations, and spectroscopy

Theoretical Methods

• Density Functional Theory (DFT)
• Full-potential linearized augmented plane wave (FP-LAPW)
• All-electron (no pseudopotentials)
• LDA, GGA, meta-GGA functionals
• Time-Dependent DFT (TDDFT)
• GW approximation (G₀W₀, GW₀, scGW)
• Bethe-Salpeter Equation (BSE)
• DFT+U for correlated systems
• Spin-orbit coupling
• Hybrid functionals
• Random Phase Approximation (RPA)

Capabilities (CRITICAL)

• Ground-state electronic structure (all-electron)
• Geometry optimization and relaxation
• Total energy, forces, stress tensors
• Band structure and DOS
• Optical properties via TDDFT
• Frequency-dependent dielectric function
• Optical absorption and reflectivity spectra
• GW quasiparticle energies
• BSE for optical excitations including excitonic effects
• X-ray absorption spectroscopy (XAS)
• Electron energy loss spectroscopy (EELS)
• Magneto-optical Kerr effect (MOKE)
• Phonon calculations via linear response
• Elastic constants
• Electric field gradients
• Hyperfine parameters
• Core-level spectroscopy
• Wannier functions
• Berry phase calculations

Sources: Official exciting documentation, cited in 7/7 source lists

Inputs & Outputs

• Input formats:

  • input.xml (XML-based main input)
  • Structure files (various formats)
  • Species files for atomic data

• Output data types:

  • INFO.OUT (main output)
  • EVALCORE.OUT, EIGVAL.OUT (eigenvalues)
  • Optical spectra files
  • GW output files
  • BSE exciton data
  • Various property-specific outputs

Interfaces & Ecosystem

• Framework integrations:

  • exciting-plus - extended features
  • Wannier90 interface
  • elk2exciting - conversion from Elk

• Visualization:

  • XCrySDen compatibility
  • exciting-viz tools
  • Standard plotting utilities

• Post-processing:

  • exciting-optics - optical spectra analysis
  • exciting-xs - excited states analysis
  • Python-based analysis tools

Workflow and Usage

Basic DFT Calculation

# 1. Create input.xml
exciting

# Ground state results in INFO.OUT
# Band structure in bandstructure.xml

Optical Spectra (TDDFT)

<!-- Add to input.xml -->
<xs xstype="TDDFT" 
    ngridk="4 4 4" 
    vkloff="0.0 0.0 0.0"
    nempty="30">
    <energywindow intv="0.0 1.0" points="500"/>
    <screening screentype="full"/>
    <BSE bsetype="singlet"/>
</xs>

exciting
# Optical absorption in EPSILON*.OUT

GW Calculation

<!-- GW calculation setup -->
<xs xstype="BSE"
    ngridk="4 4 4"
    nempty="50">
    <qpointset>
        <qpoint>0.0 0.0 0.0</qpoint>
    </qpointset>
    <gw selfenergy="ppm"/>
</xs>

exciting
# Quasiparticle energies in QPENE.OUT

BSE for Excitonic Effects

<!-- BSE calculation for optical excitations -->
<xs xstype="BSE"
    ngridk="6 6 6"
    nempty="40">
    <screening screentype="full"/>
    <BSE bsetype="singlet"
         nstlbse=" 1 5  1 3"/>
</xs>

exciting
# Excitonic optical spectra including electron-hole effects

Application Areas

• Optical spectroscopy (absorption, reflectivity, EELS)
• Excited-state properties
• Excitons and optical excitations (BSE)
• Band structure calculations (GW)
• X-ray spectroscopy
• Magneto-optical effects
• Phonons and lattice dynamics
• Materials with strong excitonic effects

Limitations & Known Constraints

• All-electron cost: Computationally expensive; ~100-200 atom limit for DFT, smaller for GW/BSE
• GW/BSE expensive: Very demanding; limited to smaller systems
• Learning curve: XML input and LAPW methods require familiarity
• Memory: High for all-electron and many-body calculations
• Parallelization: MPI and OpenMP but not as scalable as plane-wave codes
• Documentation: Good but still developing
• Community: Growing but smaller than WIEN2k or Quantum ESPRESSO
• Installation: Requires Fortran compiler, libraries (BLAS, LAPACK, FFTW)
• Platform: Primarily Linux/Unix

Verification & Sources

Primary sources:

1. Official website: https://exciting-code.org/
2. Documentation: https://exciting-code.org/ref/documentation
3. GitHub repository: https://github.com/exciting/exciting
4. A. Gulans et al., J. Phys.: Condens. Matter 26, 363202 (2014) - exciting code

Secondary sources:

1. exciting tutorials and workshops
2. Published optical spectra applications
3. GW/BSE benchmark studies
4. Confirmed in 7/7 source lists (claude, g, gr, k, m, q, z)

Confidence: CONFIRMED - Appears in all 7 independent source lists

Verification status: ✅ VERIFIED

• Official homepage: ACCESSIBLE
• Documentation: COMPREHENSIVE and ACCESSIBLE
• Source code: OPEN (GitHub)
• Community support: Active (mailing list, GitHub issues)
• Academic citations: >500 (main paper)
• Active development: Regular releases, modern codebase