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15.1 Options

There are many options available for explicitly correlated methods, but sensible defaults are used for all of them. For details see the MOLPRO reference manual. The most important options are:

DF_BASIS=basis

Select the basis for density fitting (see section 13 for details). basis can either refer to a set name defined in the basis block, or to a default MP2 fitting basis (e.g., DF_BASIS=VTZ generates the VTZ/MP2FIT basis). By default, the MP2FIT basis that corresponds to the orbital basis is used.

RI_BASIS=basis

Select the basis for the resolution of the identity (RI). By default the JKFIT basis that corresponds to the chosen orbital basis is used. In conjunction with the VnZ-F12 basis sets, it is recommended to use the VnZ-F12/OPTRI sets of Yousaf and Peterson, J. Chem. Phys. 129, 18410 (2008).

ANSATZ=ansatz

Select the explicitly correlated ansatz ansatz methods. See section 15.3 for the defaults and the MOLPRO manual for further details and possibilities.

GEM_BETA=value

Exponent for Slater-type frozen geminal (default 1.0 $a_0^{-1}$).

SINGLES=0

Disable CABS singles correction. The default is SINGLES=1.

In the following, we briefly summarize the meaning of these options and of the approximations that can be used. For more details and further references to related work of other authors see H.-J. Werner, T. B. Adler, and F. R. Manby, General orbital invarient MP2-F12 theory, J. Chem. Phys. 126, 164102 (2007) and G. Knizia and T. B. Adler and H.-J. Werner, Simplified CCSD(T)-F12 methods: Theory and benchmarks, JCP 130, 054104 (2009).

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