$AUXBAS group   (required if CODE=RIMP2 or RICCHEM in $MP2)
 
   This group specifies the auxiliary basis set used to
define the resolution of the identity in the RI-MP2 method.
The RI methods are formally exact if the RI basis set is
complete, so selecting larger bases improves the results.
However, this also increases the computational cost of the
run!  It is reasonable to use smaller RI basis sets when
the AO basis is modest, and increase the RI basis when you
use very large AO bases.
 
CABNAM specifies built-in basis sets for the RI:
       = SVP   Ahlrich's SVP basis,   available H-Kr
       = TZVP  Ahlrich's TZVP basis,  available H-Ar
       = TZVPP Ahlrich's TZVPP basis, available H-Ar
       = CCD       cc-pVDZ basis, available H-Ar
       = ACCD  aug-cc-pVDZ basis, available H-Ar
       = CCT       cc-pVTZ basis, available H-Ar
       = ACCT  aug-cc-pVTZ basis, available H-Ar
       = XXXXX externally defined: see EXTCAB.
CABNAM has no default, this is a required input!
 
Note IAUXBF in $RIMP2 for selecting spherical harmonics
versus Cartesian Gaussians.
 
EXTCAB = flag to read the basis from an external file.
         (default is .FALSE.)
 
This is analogous to EXTBAS in $BASIS: no external files
are provided with GAMESS.  The value for CABNAM=XXXX must
be 8 or fewer letters: avoid the name of any built in
auxiliary basis.  Your XXXX bases will be read from a file
defined by environment variable EXTCAB, in the execution
script.  Every atom present in your molecule must be
defined in the external file by a line giving its chemical
symbol and then XXXX. Following this header, give the basis
in free format $DATA style, containing only S, P, D, F, and
G shells, terminating each atom by the usual blank line.