12 PNO-based CCSD and CCSD(T) calculations

The pnoccsd program provides a PNO-based implementations of CCSD including the perturbative triples corrections (T0) and (T) using RHF and UHF references.

Presently the implementation is restricted to ground state energies.

Further limitations:

no MPI parallelization:

calculations beyond PNO-MP2 can presently only carried out on a single compute node, only the OpenMP (see Sec. 3.4.2) parallelization is available.

no use of symmetry:

no point group symmetry can be used; the calculations can only be done in \(C_1\)

Please note that one of the main strategies in PNO-CCSD calculations is to precompute most of the required two-electron integrals in the local (LMO, PNO, OSV, etc.) basis sets prior to the CCSD iterations. Therefore PNO-CCSD calculations on small molecules or with very tight thresholds can require considerably more disc space and core memory than the canonical implementation in ccsdf12. In general, the performance of PNO-CCSD calculations depend crucially on the speed of the disc I/O. It is therefore recommended to machines with fast RAID systems. There also the option for non-F12 calculations to activate a direct mode where the disk requirements are reduced and some quantities are evaluted on the fly.