Advanced Features
This chapter covers OpenMECP's advanced capabilities beyond basic MECP optimization.
| Feature | Description |
|---|---|
| PES Scan | 1D and 2D potential energy surface scans |
| LST Interpolation | Generate initial MECP guess from two endpoint geometries |
| Reaction Path & NEB | Systematic coordinate driving and Nudged Elastic Band |
| Fixed Atoms | Freeze selected atoms during optimization |
State Selection for TD-DFT
Choose specific excited states for TD-DFT calculations using state_a and
state_b:
state_a = 1 # Use first excited state for state A
state_b = 2 # Use second excited state for state B
td_a = TD(nstates=5,root=1)
td_b = TD(nstates=5,root=2)
This is particularly important when:
- The ground state is contaminated by near-degeneracy
- Targeting a specific conical intersection between excited states
- Studying multi-state photochemical reactivity
Pre-point Calculations
Pre-point calculations run a single-point QM job at the starting geometry
before the first optimization step. Enable with mode = stable (see
Run Modes). This checks SCF stability and ensures that
wavefunction checkpoints are available from step 1.
Restart from Checkpoint
restart = true
OpenMECP saves a JSON checkpoint ({basename}_checkpoint.json) after each step
that records the full optimization state: geometry, DIIS history, Hessian, and
configuration. Setting restart = true picks up from the last saved checkpoint.
Enable checkpoint writing:
print_checkpoint = true
restart = true
Debug Logging
Enable file-based debug logging via omecp_config.cfg:
[logging]
file_logging = true
Log files are written to omecp_debug_{basename}.log in the working directory.