We recommand as AO basis sets the augmented correlation consistent basis sets (denoted AVnZ) or the
specially optimized correlation consistent F12 basis sets (denoted VnZ-F12, cf. K.A. Peterson, T.B. Adler, and H.-J. Werner,
J. Chem. Phys. **128**, 084102 (2008)).
Normally, triples zeta basis sets (AVTZ or VTZ-F12) yield excellent results that are close to the basis set limit.
Diffuse basis functions are rather essential both for the HF and MP2-F12 energies, and therefore the standard VTZ sets are not
recommended. If the AVnZ or VnZ-F12 orbital basis sets are used, suitable density fitting (DF) basis and resolution of
the identity (RI) basis sets are automatically chosen. For the AV basis sets, the
AVnZ/MP2FIT amd VnZ/JKFIT basis sets are used for the DF and RI, respectively. For the VZ-F12 orbital basis sets,
the correspondint `OPTRI` CABS basis sets are used by default. Other basis sets can be
chosen using the `DF_BASIS` and `RI_BASIS` options (cf. section 18.1).
See section 16 for more details about density fitting.

The following example shows a ccsd(t)-f12 calculation
using the VTZ-F12 basis of Peterson et al., J. Chem. Phys. **128**, 084102 (2008),
along with the associated RI basis set of Yousaf and Peterson, J. Chem. Phys. **129**, 18410 (2008):

***,formaldehyde geometry={ 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=vtz-f12 hf ccsd(t)-f12,ri_basis=vtz-f12/optri,df_basis=avtz e_F12a=energy(1) !save F12a energy in variable e_F12a e_F12b=energy(2) !save F12b energy in variable e_F12b

The given RI and DF basis sets would also be used by default. With the AVTZ orbital basis the input would read

basis=avtz hf ccsd(t)-f12,ri_basis=avtz/optri,df_basis=avtz

In this case the default would be (for historical reasons and backward compatibility)

basis=avtz hf ccsd(t)-f12,ri_basis=vtz/jkfit,df_basis=avtz

molpro@molpro.net 2018-09-21