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explicitly_correlated_methods [2022/01/24 17:09]
qianli Update citation
explicitly_correlated_methods [2022/03/01 08:33] (current)
werner [Basis sets]
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 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. 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, [[https://dx.doi.org/10.1063/1.2831537|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 [[explicitly correlated methods#options|options]]). See section [[density fitting]] for more details about density fitting.+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, [[https://dx.doi.org/10.1063/1.2831537|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, [A]VnZ-F12, or VnZ-PP-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 [a]VnZ-F12 and [a][c]VnZ-PP-F12 orbital basis, the associated CABS (OPTRI) basis sets are used by default. However, OPTRI sets are not yet available for all elements, and in such cases an alternative RI basis must be explicitly specified using the ''RI_BASIS'' option. 
 + 
 +Other basis sets can be chosen using the ''DF_BASIS'', ''DF_BASIS_EXCH'' and ''RI_BASIS'' options (cf. section [[explicitly correlated methods#options|options]]). See section [[density fitting]] for more details about density fitting. 
  
 This is an example for using multiple basis sets for density fitting and resolution of the identity This is an example for using multiple basis sets for density fitting and resolution of the identity