14.3 Default basis sets

If a basis is not specified at all for any unique atom group, then the program assumes a global default. Presently, this default is VDZ, but may be overridden using

BASIS,basis

or

BASIS=basis

basis is looked up in the file lib/defbas, which generates an appropriate request for a complete contracted set, together in some cases with an ECP, from the library. This mapping includes the following commonly-used basis sets.

• All of the Dunning correlation-consistent sets, through the use of either the standard name of the basis set (e.g., aug-cc-pVDZ) or an abbreviation (e.g., AVDZ).
• The older segmented Dunning/Hay double-zeta sets for the first row (DZ and DZP).
• The Roos ANO basis sets (ROOS).
• The Stuttgart ECPs and associated basis sets (e.g., ECP10MWB).
• The Hay ECPs and corresponding basis sets (ECP1 and ECP2).
• Some of the Karslruhe basis sets (SV, TZV, and, for some elements, SVP, TZVP, TZVPP, TZVPPP).
• The Binning/Curtiss sets for Ga-Kr (BINNING-SV, BINNING-SVP, BINNING-VTZ and BINNING-VTZP)
• Most of the Pople basis sets, using their standard names (e.g., 6-31G*, 6-311++G(D,P), etc.). Note that specially in this case, the mechanism described below using parenthesized modifiers to restrict the basis set is disabled to allow the full range of standard basis sets to be specified.

Example:

BASIS=VTZ

generates valence triple zeta basis set for all atoms. Thus, the input

Input: h2o_scf_vtz.com

Output: h2o_scf_vtz.out

is entirely equivalent to

Input: h2o_scf_vtz_explicit.com

Output: h2o_scf_vtz_explicit.out

Default basis sets can be defined anywhere in the input before the energy calculation to which it should apply using a single BASIS cards. The default basis set applies to all types of atoms but can be superceded by different basis sets for specific atoms as explained later. Some restrictions concerning the maximum angular momentum functions to be used, or the number of contracted functions are possible as follows:

The maximum angular momentum in the basis set can be reduced using syntax such as

BASIS,VQZ(D)

which would omit the $f$ and $g$ functions that would normally be present in the VQZ basis set.

BASIS,VQZ(D/P)

would specify additionally a maximum angular momentum of $1$ on hydrogen, i.e. would omit $d$ orbitals on hydrogen.

For generally contracted basis sets, an extended syntax can be used to explicitly give the number of contracted functions of each angular momentum. For example,

BASIS,ROOS(3s2p1d/2s)

generates a 6-31G*-sized basis set from the Roos ANO compilation.