6.1 Closed-shell correlation methods

For closed-shell calculations the following methods/keys are available:

mp2 !second-order Moeller-Plesset perturbation theory lmp2 !second-order local Moeller-Plesset perturbation theory mp3 !third-order Moeller-Plesset perturbation theory mp4 !fourth-order Moeller-Plesset perturbation theory ci !singles and doubles configuration interaction (using MRCI program) cisd !singles and doubles configuration interaction (using CCSD program) cepa(1) !Coupled electron pair approximation, version 1 cepa(2) !Coupled electron pair approximation, version 2 cepa(3) !Coupled electron pair approximation, version 3 acpf !Averaged couplec pair functional ccsd !Coupled cluster with singles and doubles ccsd(t) !Coupled cluster with singles and doubles and perturbative !treatment of triples bccd !Brueckner coupled cluster with doubles bccd(t) !Brueckner coupled cluster with doubles and perturbative !treatment of triples qcisd !Quadratic configuration interaction with singles and doubles qcisd(t)!Quadratic configuration interaction with perturbative !treatment of triplesThere are also explicitly correlated and local variants of many of these methods, see sections 18 and 17, respectively.

One or more of these commands should be given after the Hartree-Fock
input. Note that some methods include others as a by-product; for
example, it is wasteful to ask for `mp2` and `mp4`, since the
MP4 calculation returns all of the second, third and fourth order
energies.
CCSD also returns the MP2 energy.

By default, only the valence electrons are correlated. To modify
the space of uncorrelated inner-shell (core) orbitals, the `core` directive can be used, on
which the numbers of core orbitals in each symmetry are specified in the same way as the occupied
orbitals on the `occ` card. In order to correlate all electrons in a molecule, use

`core`

without any further arguments (all entries zero). This card must follow the directive for the method, e.g.,

{MP2 !second-order Moeller-Plesset perturbation theory core} !correlate all electrons

Note, however, that special basis sets are needed for correlating inner shells, and it does make not much sense to do such calculations with the standard basis sets described above. The correlation-consistent core-valence basis sets (cc-pCVZ where is D, T, Q, ) are available for this purpose.

{MP2 !second-order Moeller-Plesset perturbation theory core,2} !don't correlate electrons in the orbitals 1.1 and 2.1.

The number of occupied orbitals is automatically remembered from the preceding HF calculation. If necessary for
special purposes, it can be specified using `occ` cards as in HF. The orbitals are
taken from the most recent HF calculation in the input. See the MOLPRO reference
manual for other choices of orbitals.

Example for a complete CCSD(T) calculation for formaldehyde:

***,formaldehyde print,basis,orbitals !this is optional: print the basis set and the occupied orbitals angstrom geometry={ !define the nuclear coordinates C O , C , rco H1 , C , rch , O , hco H2 , C , rch , O , hco , H1 , 180 } rco=1.182 Ang rch=1.102 Ang hco=122.1789 Degree basis=vdz !Select basis set hf !Perform HF calculation ccsd(t) !Perform CCSD(T) calculation

molpro@molpro.net 2019-03-22