28.2 EXTERNAL BASIS SETS

External basis sets can be supplied in a file that must be located in the working directory. Each record will contain the following data (free format):

I N L EXP NG

where:

I: atom type index (integer)
N: principal quantum number (integer)
L: angular quantum number (integer)
EXP: exponent (double precision)
NG: number of gaussians for the $(AB\vert AC)$ and $(AB\vert CB)$ integrals (integer)

Atom type index is used to establish the correspondence between the basis functions and the centers (atoms). All records having the same value of I will define the basis set for all the atoms of the corresponding type.

Example:

For a calculation on the CO$_2$ molecule with the following geometry data:

Geometry={
   3

C1, 0.000000000000E+00, 0.000000000000E+00, 0.000000000000E+00
O2, 0.000000000000E+00, 0.000000000000E+00,-0.117963799946E+01
O3, 0.000000000000E+00, 0.000000000000E+00, 0.117963799946E+01
}

Clementi and Roetti's Single Zeta basis set could be supplied in an external file like:

1   1   0         5.67263   12
1   2   0         1.60833   12
1   2   1         1.56788   12
2   1   0         7.65781   12
2   2   0         2.24588   12
2   2   1         2.22662   12

The first three records define the basis set for atoms of the first type (carbon in this example), and the following three, the basis set for atoms of the second type (oxygen).

NG is mandatory even in case of diatomics, though gaussian expansions will not be used, the value of NG being irrelevant in this case.