The basis set to be used in a calculation is specified via

**BASIS=basis**

There are predefined choices for *basis* such as

**a) Pople basis sets**

STO-3G

3-21G

4-31G

6-31G

6-311G

6-31G*

6-31G**

6-31G*

6-311G**

**b) Dunning-Huzinaga basis sets**

DZ

DZP

TZ2P

**c) Karlsruhe basis sets**

svp

dzp

tzp

tz2p

qz2p

pz3d2f

13s9p4d3f

**d) correlation-consistent basis sets**

cc-pVXZ (x=D,T,Q,5,6)

cc-pCVXZ (x=D,T,Q,5,6)

cc-pwCVXZ (X=D,T,Q,5,6)

aug-pVXZ (X=D,T,Q,5,6)

d-aug-pVXZ (X=D,T,Q,5,6)

aug-pCVXZ (X=D,T,Q,5,6)

**e) Atomic Natural Orbital (ANO) basis sets**

ANO0

ANO1

ANO2

**f) Widmark-Malmqvist-Roos (WMR) basis sets**

WMR

** g) polarized basis sets of Sadlej et al**

PBS

** h) ccJ-pVXZ sets for the calculation of spin-spin couplings**

ccJ-pVDZ

ccJ-pVTZ

ccJ-pVQZ

ccJ-pV5Z

The corresponding basis sets are known to *CFOUR* and usually supplied via the GENBAS file (for availability
see section Basis-set file GENBAS). However, if one wants to use a non-predefined basis set, this can be accomplished via

**BASIS=SPECIAL**

together with a specification of the used sets for each atom after the CFOUR keyword list. In the following
example

input of non-standard basis sets
O
H 1 R
H 1 R 2 A
R=1.
A=100.
*CFOUR(CALC=SCF,BASIS=SPECIAL)
O:DZP
H:DZ
H:DZ

a DZP basis is requested for oxygen and DZ sets are requested for hydrogen (note that the order of the specified sets must correspond to the ZMAT ordering; no basis sets are to be specified for dummy atoms (X),
while a basis set must be given for ghost atoms (GH)).

The use of *non-standard basis sets* often requires that a corresponding entry in the GENBAS file is made,
as a set with the corresponding label must exit in the supplied GENBAS file (for adding a basis set to
the GENBAS file, see section Basis-set file GENBAS).

**Uncontracted basis sets**

Uncontracted versions of a given contracted basis set can be
obtained by specifying **CONTRACTION=UNCONTRACTED**. Note that in case of the cc-p(w)CVXZ sets, the corresponding cc-p(w)CVXZ-unc sets (without the steep s- and p- functions in the case of first- and second-row, without the steep s-, p- , and d-functions in the case of third-row elements)
are used to avoid linear dependencies.

**BASIS=EVEN_TEMPERED**

Even tempered basis sets can be generated automatically by specifying `BASIS=EVEN_TEMPERED`

in the ZMAT. After the keyword list, the section `%EVEN_TEMPERED`

is needed which is constructed as shown in the following example:

input for even tempered basis sets
H
CL 1 R
R=0.9157993311
*CFOUR(BASIS=EVEN_TEMPERED)
%EVEN_TEMPERED
H=VARIANT FACNUM
s 0.2 1.7 5
p 0.2 1.7 4
END
CL=VARIANT FACNUM
s 0.3 2.3 16
p 0.2 2.0 5
d 0.2 2.0 3
END

A definition section for all atoms in the molecule has to be provided.

Line #1: *atom-symbol*=`VARIANT FACNUM`

This means that aside from the angular momentum (*ang*`=s,p,d`

etc. ) and the smallest
exponent (*expmin*), the factor (*fac*) and the total number of exponents (*totexp*) are given in order to calculate the
exponents for the basis set. Only this variant is currently
implemented.

Line #2 (and following): *ang expmin fac totexp*

Last line (for each atom): END

Note:

- The described procedure generates an uncontracted basis set.
- It is possible to use
`BASIS=SPECIAL`

and define even tempered set just for *some* atoms of the molecule (i.e. `H:PVDZ, F:EVEN_TEMPERED`

).

**Cartesian versus Spherical Gaussians**

By default, all calculations with *CFOUR* are performed with *Spherical Gaussians*
(keyword **SPHERICAL=ON**; 5d, 7f 9g, ...) which uses for the polarization
functions the pure set of d-, f-, g-, ... functions. If one wants to use *Cartesian Gaussians* (usually
known as 6d, 10f, ...), this can be accomplished via the keyword

**SPHERICAL=OFF**

Note that care is here required, as some basis sets have been constructed (and should be therefore used) with Cartesian
Gaussians (e.g., 6-31G**) and others (actually most) with Spherical Gaussians.

**Used definition of spherical Gaussians**

**Order of basis functions**

**Normalization of basis functions**