Official Resources
- Source Repository: https://github.com/nguyen-group/QERaman
- Documentation: Included in repository
- License: Open source
Overview
QERaman is an open-source program for computing first-order resonance Raman spectroscopy based on Quantum ESPRESSO. It calculates resonance Raman intensities by evaluating the derivative of the frequency-dependent dielectric function with respect to phonon normal mode coordinates, enabling simulation of Raman spectra under resonant conditions.
Scientific domain: Resonance Raman spectroscopy, electron-phonon coupling
Target user community: Researchers studying resonance Raman spectra of crystalline materials from first principles
Theoretical Methods
- Density Functional Perturbation Theory (DFPT)
- Frequency-dependent dielectric function
- Resonance Raman theory (Kramers-Heisenberg-Dirac)
- Phonon normal modes
- Electron-phonon coupling
- Quantum ESPRESSO as backend
Capabilities (CRITICAL)
- First-order resonance Raman spectra
- Off-resonance Raman spectra
- Raman intensities vs excitation energy
- Raman excitation profiles
- Phonon frequencies and modes
- Dielectric function calculation
- Polarization-dependent Raman
- Temperature-dependent Raman (via phonon occupation)
Sources: GitHub repository, J. Chem. Phys. 158, 224109 (2023)
Key Strengths
Resonance Raman:
- Beyond off-resonance approximation
- Excitation energy dependence
- Raman excitation profiles
- Resonance enhancement factors
- Proper treatment of resonant denominators
QE Integration:
- Uses QE DFPT for phonons
- Uses QE TDDFT for dielectric function
- Same pseudopotentials and structures
- Seamless workflow
First-Principles:
- No empirical parameters
- Full DFT-level accuracy
- Systematic improvement possible
- Handles complex materials
Inputs & Outputs
-
Input formats:
- Quantum ESPRESSO input files
- QERaman configuration files
- Phonon mode data from QE
-
Output data types:
- Resonance Raman spectra
- Raman excitation profiles
- Raman intensities per mode
- Polarization-resolved spectra
Interfaces & Ecosystem
- Quantum ESPRESSO: Required backend (v7.1, 7.2, or 7.3)
- Matplotlib: For plotting
- Python: Scripting interface
Performance Characteristics
- Speed: Depends on number of excitation energies
- Accuracy: DFT-level for Raman
- System size: Limited by QE capabilities
- Memory: Moderate
Computational Cost
- Single excitation energy: Similar to QE DFPT + dielectric
- Multiple excitation energies: Scales linearly
- Typical: Hours for moderate systems
Limitations & Known Constraints
- QE only: No VASP or other code support
- First-order only: No higher-order Raman
- No excitonic effects: DFT-level dielectric function
- QE version: Requires specific QE versions (7.1-7.3)
- Documentation: Limited
Comparison with Other Codes
- vs Phonopy-Spectroscopy: QERaman does resonance Raman, Phonopy-Spectroscopy does off-resonance
- vs ramannoodle: QERaman does resonance, ramannoodle does off-resonance with ML
- vs VASP-Raman: QERaman uses QE, VASP-Raman uses VASP
- Unique strength: First-principles resonance Raman spectroscopy from QE
Application Areas
Resonance Raman of Semiconductors:
- Excitation energy dependence
- Resonance profiles
- Band gap effects
- Defect characterization
2D Materials:
- MoS2 and TMDs resonance Raman
- Layer-dependent spectra
- Exciton effects
- Strain effects
Perovskites:
- Resonance Raman of halide perovskites
- Temperature dependence
- Phase transitions
- Electron-phonon coupling
Best Practices
Excitation Energy Grid:
- Sample densely near absorption edges
- Use coarser grid far from resonance
- Include both below and above gap energies
- Monitor convergence
Phonon Calculation:
- Use well-converged QE phonon calculation
- Verify mode assignments
- Check for imaginary frequencies
- Use appropriate q-point grid
Community and Support
- Open source on GitHub
- Developed by Nguyen group at NTU
- Example calculations provided
- Active development
Verification & Sources
Primary sources:
- GitHub repository: https://github.com/nguyen-group/QERaman
- Related: T. P. T. Nguyen et al., J. Chem. Phys. 158, 224109 (2023)
Confidence: VERIFIED
Verification status: ✅ VERIFIED
- Source code: ACCESSIBLE (GitHub)
- Documentation: Included in repository
- Active development: Maintained
- Specialized strength: First-principles resonance Raman spectroscopy from Quantum ESPRESSO