CE-TDDFT

Official Resources

• Homepage: https://github.com/dceresoli/ce-tddft
• Documentation: https://github.com/dceresoli/ce-tddft/blob/master/README.md
• Source Repository: https://github.com/dceresoli/ce-tddft
• License: GNU General Public License (same as Quantum ESPRESSO)

Overview

CE-TDDFT is a Real-Time Time-Dependent Density Functional Theory (RT-TDDFT) extension for Quantum ESPRESSO. It enables explicit time-propagation of Kohn-Sham orbitals to simulate non-equilibrium electron dynamics, strong-field phenomena, and Ehrenfest molecular dynamics.

Scientific domain: Ultrafast electron dynamics, strong-field physics, nonlinear optics, photochemistry
Target user community: Researchers using Quantum ESPRESSO who need real-time propagation capabilities beyond linear-response TDDFT

Theoretical Methods

• Real-Time Time-Dependent DFT (RT-TDDFT)
• Explicit time propagation of KS orbitals
• Ehrenfest molecular dynamics (coupled electron-ion dynamics)
• Electric field perturbations (delta-kick, continuous fields)
• Time-dependent charge density analysis
• Electron wavepacket dynamics (experimental)
• Plane-wave basis set (from QE)
• Norm-conserving pseudopotentials

Capabilities

• Optical absorption spectra via Fourier transform of induced dipole
• Strong-field dynamics (beyond linear response)
• Ehrenfest dynamics for coupled electron-ion motion
• Time-dependent observables (dipole moment, charge density)
• Electron wavepacket propagation (experimental feature)
• Time-dependent charge density saving for post-processing
• Compatible with QE-6.3+ (tested up to recent versions)

Key Strengths

Tight QE Integration:

• Direct extension of Quantum ESPRESSO
• Uses QE's plane-wave infrastructure
• Familiar input format for QE users
• Leverages QE pseudopotentials and XC functionals

Ehrenfest Dynamics:

• Coupled electron-ion propagation
• Non-adiabatic dynamics
• Photochemical reaction pathways
• Energy transfer mechanisms

Active Development:

• Regular updates (2017-2019 active development)
• Six official releases
• Responsive maintainer (D. Ceresoli)

Inputs & Outputs

• Input formats:

  • Quantum ESPRESSO input files
  • Pseudopotential files (UPF format)
  • Additional TDDFT control parameters

• Output data types:

  • Time-dependent dipole moments
  • Absorption spectra (via post-processing)
  • Time-resolved charge densities
  • Ehrenfest trajectories

Interfaces & Ecosystem

• Quantum ESPRESSO integration:
  • Built on top of QE's PWscf module
  • Uses QE's parallelization (MPI)
  • Compatible with QE's post-processing tools

Performance Characteristics

• Speed: Dependent on QE's plane-wave efficiency
• Scalability: Inherits QE's MPI parallelization
• System size: Limited by plane-wave scaling (typically <1000 atoms)
• Time step: Typically 0.01-0.1 atomic units

Limitations & Known Constraints

• QE version dependency: Must match compatible QE version
• Norm-conserving only: No ultrasoft/PAW (RT propagation constraint)
• System size: Plane-wave scaling limits large systems
• Memory: Dense time-dependent data storage
• Periodic systems: Primarily designed for periodic/slab geometries

Comparison with Other Codes

• vs Octopus: CE-TDDFT plane-wave, Octopus real-space; Octopus standalone, CE-TDDFT QE extension
• vs SALMON: Both plane-wave RT-TDDFT; SALMON standalone with more laser options
• vs turboTDDFT: turboTDDFT linear-response, CE-TDDFT real-time propagation
• Unique strength: Direct QE integration for existing QE users, Ehrenfest dynamics

Application Areas

• Ultrafast spectroscopy simulations
• Strong-field ionization
• High-harmonic generation
• Photochemical dynamics
• Charge transfer processes
• Plasmon dynamics in nanostructures

Best Practices

• Start with converged ground state from PWscf
• Use small time steps (0.01-0.05 a.u.) for stability
• Apply delta-kick perturbation for linear response spectra
• Monitor total energy conservation
• Use sufficient simulation time for frequency resolution

Community and Support

• Open-source (GPL, same as QE)
• GitHub repository with issue tracker
• 6 official releases
• Author: Davide Ceresoli (CNR-ISTM, Milan)
• Integration with QE community

Verification & Sources

Primary sources:

1. GitHub repository: https://github.com/dceresoli/ce-tddft
2. Quantum ESPRESSO: https://www.quantum-espresso.org/

Confidence: VERIFIED

• Repository: ACCESSIBLE (GitHub)
• Documentation: Available in README
• Active releases: 6 releases (2017-2019)
• Integration: Works with QE 6.1-6.3+

Verification status: ✅ VERIFIED