manual   quickstart   instguide   update   basis

Next: 35.5 Symmetry Up: 35 EXPLICITLY CORRELATED METHODS Previous: 35.3 RI Approximations   Contents   Index   PDF

35.4 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 recommend 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 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 AVnZ orbital basis sets, AVnZ/MP2FIT amd VnZ/JKFIT basis sets are used by default for the DF and RI, respectively. The associated optimized CABS basis set of Peterson et al. can be chosen by specifying RI_BASIS=OPTRI. For the VnZ-F12 orbital basis, the associated CABS (OPTRI) basis sets are used by default. Other basis sets can be chosen using the DF_BASIS, DF_BASIS_EXCH and RI_BASIS options (cf. section 35.6). See section 15 for more details about density fitting.

This is an example for using multiple basis sets for density fitting and resolution of the identity

h2o_basissets1.com

The following two examples yield identical results:

h2o_basissets2.com

h2o_basissets3.com

In the latter example the specifications MP2FIT and JKFIT could be omitted, i.e. the input

ccsd(t)-f12,df_basis=avtz,df_basis_exch=vtz,ri_basis=optri

would be equivalent. In fact, since default density fitting basis sets are used

ccsd(t)-f12,ri_basis=optri

would be sufficient. Note, however, that without the specification OPTRI the avtz/jkfit basis set would be used for the RI. For example,

basis=avtz
hf
ccsd(t)-f12

is equivalent to

basis=avtz
hf
ccsd(t)-f12,df_basis=avtz/mp2fit,df_basis_exch=vtz/jkfit,ri_basis=vtz/jkfit

If the VnZ-F12 basis sets are used, the OPTRI sets are used by default, i.e.,

basis=vtz-f12
hf
ccsd(t)-f12

is equivalent to

basis=vtz-f12
hf
ccsd(t)-f12,df_basis=avtz/mp2fit,df_basis_exch=vtz/jkfit,\\
ri_basis=vtz-f12/optri



Next: 35.5 Symmetry Up: 35 EXPLICITLY CORRELATED METHODS Previous: 35.3 RI Approximations   Contents   Index   PDF

manual   quickstart   instguide   update   basis

molpro@molpro.net 2018-07-22