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 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:
In addition, many density fitting and resolution of the identity (RI) basis sets are available. For the correlation consistent basis sets of Dunning, the appropriate VXZ/JKFIT, VXZ/MP2FIT, AVXZ/MP2FIT sets of Weigend are chosen automatically in density fitted calculations (augmented versions AVXZ/JKFIT for Fock-matrix fitting are also available, but not used by default). For the def2 family of orbital basis sets, the appropriate auxiliary sets (e.g., TZVPP/JFIT, TZVPP/JKFIT, TZVPP/MP2FIT) are used. In principle these JKFIT sets are universal and also applicable in combination with the AVXZ basis sets. Initial results indicate that they also work well with the cc-pVXZ-PP and aug-cc-pVXZ-PP series of basis sets.
For explicitly correlated F12 calculations that use the cc-pVXZ-F12 orbital basis sets, the corresponding VXZ-F12/OPTRI basis sets are used by default to construct the complementary auxiliary orbital basis (CABS). For other orbital basis sets, appropriate JKFIT sets are utilized by default.
generates valence triple zeta basis set for all atoms. Thus, the input
performs a Hartree-Fock calculation for HO using the cc-pVTZ basis set.
Default basis sets can be defined anywhere in the input before the energy calculation to which it should apply using a single BASIS card as shown above. The default basis set applies to all types of atoms but can be superceded by different basis sets for specific atoms as explained in the next section. 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
which would omit the and functions that would normally be present in the VQZ basis set.
would specify additionally a maximum angular momentum of on hydrogen, i.e. would omit 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,
generates a 6-31G*-sized basis set from the Roos ANO compilation.
Notes: basis must not be variable called BASIS. Furthermore, input like
$BASIS=[AVDZ, AVTZ, AVQZ]
is not allowed, i.e. the keyword BASIS must not be preceded with $. One can loop over several basis sets using, for example, using
$aobases=[AVDZ, AVTZ, AVQZ] do ibas=1,#aobases basis=aobases(ibas) ... enddo