Basis set empty orbitals


I have noticed that in some of the basis sets distributed by simune, as an empty orbital is used as ‘2 2’, that should be a 2d. However, this orbital is quite strange and shouldn’t exist. Why is it used in the basis set?


Thanks for your comment.
Which basis sets are you referring to?


I have seen this for example on carbon basis set. Is this just to add a polarization orbital?