CCSD Convergence

The coupled-cluster singles and doubles (CCSD) solver can be tuned with several convergence controls for difficult systems.

CCSD Convergence Control

task: CCSD RHF CC-PVDZ

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

CC
  Conv        8
  MaxIter     80
  Diis        true
  DiisStart   3
  Shift       0.2
  FreezeCore  false
END

Notes

  • MP2 and CC always compute in-core TwoElectronIntegrals for the AO→MO transform, even when Direct true is enabled for SCF.
  • The task: line for MP2/CCSD(T) includes the reference method and basis set.
  • Frozen-core: use FreezeCore true to correlate only valence electrons.
  • DF-MP2: set DF true and Aux <name> for density-fitting.
  • For CCSD(T), add the triples correction automatically by using task: CCSD(T) ....