Transition Density Matrix Calculation with PySCF

This repository contains scripts for calculating transition density matrices and transition dipole moments of PTCDA using PySCF.

Scripts

1. tdm_calc_accurate.py ⭐ RECOMMENDED

The most complete and accurate implementation:

• ✅ Full TDDFT (not TDA) for accurate transition dipoles
• ✅ Transition dipole moment calculations
• ✅ Oscillator strength calculations
• ✅ Natural Transition Orbital (NTO) analysis
• ✅ All three density types (transition, excited state, difference)
• ✅ Proper gauge origin handling
• ✅ Works with both test molecules and PTCDA
• Transition dipole moment calculations
• Oscillator strength calculations
• Natural Transition Orbital (NTO) analysis
• All three density types (transition, excited state, difference)
• Proper gauge origin handling
• Works with both test molecules and PTCDA

Use this for production calculations and publication-quality results.

2. tdm_calc_test.py

Basic implementation for testing:

• Uses TDA (Tamm-Dancoff Approximation)
• Density matrix calculations only
• Good for learning and quick tests

3. tdm_calc_enhanced.py

Enhanced density calculations:

• Multiple density visualization options
• Uses TDA
• No transition dipole calculations

Quick Start

# Run the accurate calculation
python tdm_calc_accurate.py

For detailed information, see CALCULATION_GUIDE.md.

Output Files

• transition_density_state*.cube - Transition density for dipole moments
• excited_state_density_state*.cube - Total excited state density
• density_difference_state*.cube - Density redistribution (best for visualization)
• nto_state_*.molden - Natural transition orbitals

Visualization

VMD:

vmd density_difference_state1.cube

Jmol:

jmol density_difference_state1.cube

See CALCULATION_GUIDE.md for detailed visualization instructions.