Checkpointing

Save and Restart from Checkpoint

task: RHF 6-31G*

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

SCF
  Save     true
  MaxCycle 100
END

Restart

To restart the SCF from the saved density in a follow-up job, set Restart true:

SCF
  Restart true
  MaxCycle 100
END

Scratch Directory

By default the checkpoint file is placed next to the input file (myjob.oqd for myjob.inp). Set OPENQUANTUM_SCRATCH to redirect it to a dedicated scratch directory (recommended on HPC systems with high-performance parallel filesystems):

export OPENQUANTUM_SCRATCH=/scratch/$USER/$SLURM_JOB_ID
mkdir -p $OPENQUANTUM_SCRATCH

oquantum myjob.inp

The scratch directory is always printed at the start of each run:

  Scratch directory: /scratch/user/12345345

CONTROL Checkpoints

Every section also writes a richer binary checkpoint (default extension .oqw) through the CONTROL section. This file captures the final geometry, molecular orbitals (coefficients and energies), an optional Hessian (for frequency runs), SCF convergence info, and basis-set info. Use CheckpointName to choose the file name and ReadCheckpoint to restart a later job from it (see Multi-Section Jobs).

CONTROL
  WriteCheckpoint  True
  CheckpointName   water_opt.oqw
END

Notes

• The SCF Save/Restart keywords manage a lightweight scratch density used to warm-start an SCF within a single run.
• The CONTROL checkpoint (.oqw) is a self-describing record of the final state, suitable for restarting geometry and orbitals across jobs.
• Save true writes the SCF scratch checkpoint after convergence.
• Restart true reads the initial guess from the scratch checkpoint file.
• The scratch directory also holds other temporary files.