QM Program Support
OpenMECP communicates with external quantum chemistry programs through a unified interface. Each program has its own input/output format; OpenMECP handles all the file writing and parsing automatically.
Supported Programs
| Program | program value | Methods | Notes |
|---|---|---|---|
| Gaussian 16 | gaussian | DFT, TD-DFT, MP2, CASSCF | Recommended |
| ORCA 5+ | orca | DFT, TD-DFT, CASSCF | Full gradient support |
| Custom | custom | User-defined | JSON configuration |
Selecting a Program
Set the program keyword in your input file:
program = gaussian # or orca / custom
Common Configuration
Both programs share these keywords:
nprocs = 8 # Number of parallel CPU cores
charge = 0 # Molecular charge
mult_a = 1 # Multiplicity of state A
mult_b = 3 # Multiplicity of state B
See individual program pages for method and mem format details:
Wavefunction Checkpoints
OpenMECP saves wavefunction files from each QM step to use as a starting guess for the next step. This dramatically speeds up SCF convergence over a multi-step optimization.
| Program | State A | State B |
|---|---|---|
| Gaussian | state_A.chk | state_B.chk |
| ORCA | state_A.gbw | state_B.gbw |
The Run Mode controls whether these checkpoints are read.
File Organization
All QM input/output files are written to a running_dir/ subdirectory,
keeping your working directory clean. The final MECP geometry is written to
{basename}_mecp.xyz in the current directory.