manual   quickstart   instguide   update   basis
  Contents  

15.5 Basis sets

In MOLPRO the F12 integrals can only be computed using density fitting (DF) approximations. The many electron integrals are approximated by resolutions of the identity (RI) expansions. Thus, F12 calculations require three different basis sets: the orbital (AO) basis, the DF basis, and the RI basis.

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. By default, the AVnZ/MP2FIT amd VnZ/JKFIT basis sets are used for the DF and RI, respectively. Other basis sets can be chosen using the DF_BASIS and RI_BASIS options (cf. section 15.1). See section 13 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

  Contents  
manual   quickstart   instguide   update   basis