13.3 Default basis sets

If a basis is not specified at all for any unique atom group, then the program assumes a 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).
• 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 before the integral input (e.g., in molproi.rc) using one or more BASIS cards. There are various different forms possible:

One line input for a global default basis set:

BASIS,basisname

Alternatively, a global default basis can be specified as

BASIS=basisname

In this case basisname is saved in variable BASIS.

Default basis sets for individual atoms can be specified as

BASIS,O=AVTZ,H=VDZ

This sets the default basis for oxygen to AVTZ, and the one for hydrogen to VDZ. The first two forms can be combined:

BASIS,VTZ,O=AVTZ,H=VDZ

This overwrites the global default VTZ by other basis sets for oxygen and hydrogen.

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.

To go beyond the above simple one-line form, one can use more general BASIS input blocks, which have the follwing general form:

BASIS
SET=type                ! type can be ORBITAL DENSITY or DMAT; optional; default=ORBITAL
DEFAULT=name            ! sets the default basis to name
atom1=name1             ! Use basis name1 for atom1
atom2=name2             ! Use basis name1 for atom2
primitive basis set specifications   !addtional basis functions
SET=type                ! specify basis of another type in following lines
...
END

The default and atom specifications can also be merged to one line, separated
by commas:

{\tt DEFAULT}={\em name},{\em atom1}={\em name1},{\em atom2}={\em name2}

This definition of the default and atom specific basis sets works exactly 
as described above for the one-line input forms, i.e, the basis sets specified 
for individual atoms substitute the general default. They apply to all angular 
momentum components with default contraction.  The keyword {\tt DEFAULT} can 
be abbreviated by {\tt DEF}.

The optional additional primitive basis set specifications (see next section)
are appended to the given atom-specific basis sets, i.e., the union of 
atom-specific and primitive basis set definitions is used for the atom. 

Examples:

\begin{verbatim}
BASIS
DEFAULT=VTZ             ! use cc-pVTZ basis as default
H=VDZ                   ! use cc-pVDZ for H-atoms
END

This could also be written as

BASIS={DEF=VTZ,H=VDZ}

BASIS
DEFAULT=VTZ             ! use cc-pVTZ basis as default
H=VDZ                   ! use cc-pVDZ for H-atoms
D,H,VTZ                 ! add the VTZ d-function to the VDZ basis for H
END

BASIS
SPD,O,VTZ               !use uncontracted s,p,d functions of basis VTZ for oxygen
S,H,H07                 !use Huzinaga 7s for Hydrogen
C,1.4                   !contract first four s-functions
P,H,1.0,0.3             !add two p-functions for hydrogen
END

Several BASIS cards and/or blocks can immediately follow each other. Always the last specification for a given atom and type is valid. Defaults given using BASIS commands can be overwritten by specifications in the integral input. If an individual basis function type is specified for an atom, it is required that all other types are also defined. For example, in the above example, no $f$-functions are included for O, even if the global default would include $f$-functions. Also, defining the $s$ functions for hydrogen switches off the default basis set for hydrogen, and so the $p$ functions must be defined. Instead of the atomic symbol, also the atom group number can be used.

The same input forms are also possible as direct input to the integral program. In contrast to MOLPRO92, now the atomic symbol can be used in field 2 of a basis specification instead of the atom group number:

SPD,O,VTZ

!use VTZ basis for all oxygen atoms

SPD,1,VTZ

!use VTZ basis for atom group 1

Instead of the BASIS ...END block one can also use the structure BASIS[=]{...}

If a basis is not specified at all for any unique atom group, then the program assumes a default. For further details, including respecifying the default to be used, see the specification of the BASIS subcommand below.