14.4 Default basis sets for individual atoms

More specific basis set definitions for individual atoms can be given BASIS input blocks, which have the following 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   !additional 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:

DEFAULT=name,atom1=name1,atom2=name2

Here the basis sets name1, name2 overwrite the default basis set name for specific atoms atom1, atom2, respectively. For instance,

DEFAULT=VTZ,O=AVTZ,H=VDZ

uses VTZ as the default basis sets, but sets the basis for oxygen to AVTZ and for hydrogen to VDZ

This name conventions for the atom specific basis sets work exactly as described above for default basis sets. The keyword DEFAULT can be abbreviated by DEF. Any DEFAULT basis set defined in a basis set block supercedes a previous one given outside the basis block.

The specifications SET, DEFAULT, atom=name are all optional. If DEFAULT is not given, the previous default, as specified on the last previous BASIS card, is used.

If no further primitive basis set specifications follow, one can also use the one-line form

BASIS,DEFAULT=VTZ,O=AVTZ,H=VDZ

or

BASIS=VTZ,O=AVTZ,H=VDZ

Both of these are equivalent to

BASIS
DEFAULT=VTZ
O=AVTZ
H=VDZ
END

Note that any new BASIS card supercedes all previous basis input, except for the default basis (unless this is given).

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:

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 used. 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, the atom group number can also 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.