[Sam (NG)]

Right then, i have a question set as part of an assignment, where i have to describe the 6-311G* basis set for water.  In my notes for this module i have the following basis sets described as shown:

3-21G

O 1s 2s 2s' 2p_x,y,z 2p'_x,y,z
H 1s 1s'

6-31G*

O 1s 2s 2s' 2p_x,y,z 2p'_x,y,z 3d (six functions)
H 1s 1s'

I understand that the star is a polarisation function on the heavier atoms, corresponding to the addition of the 6 3d basis functions to oxygen.

For 6-311G* i read this as being a split valence triple zeta plus polarisation basis set. (6 Gaussians on Core electrons, then split 3, 1, 1, Gaussians on valence electrons).

I think that this should look like the following:

O 1s 2s 2s' 2s'' 2p_x,y,z 2p'_x,y,z 2p''_x,y,z 3d (i read somewhere that there are only 5 polarisation functions on 6-311G* on the net somewhere, maybe someone can confirm that).
H 1s 1s' 1s''

I'm hoping that someone can confirm that i have correctly calculated the shells for the 6-311G* basis set in this case.

Thanks

Sam

[allanf]

looks right to me, assuming those AOs expand to the right number of gaussian functions (e.g. 6 for the 1s on Oxygen)

As for the polarization functions, there are really only 5 3d orbitals: xy, yz, zx, z², x²-y².  The set of 6 cartesian (xx,xy,yy,yz,zz,zx) polarization functions is just a linear combination of these 5 3d orbitals and a 3s orbital. As far as I know, going triple zeta or not doesn't change that.

[Sam (NG)]

looks right to me, assuming those AOs expand to the right number of gaussian functions (e.g. 6 for the 1s on Oxygen)

As for the polarization functions, there are really only 5 3d orbitals: xy, yz, zx, z², x²-y².  The set of 6 cartesian (xx,xy,yy,yz,zz,zx) polarization functions is just a linear combination of these 5 3d orbitals and a 3s orbital. As far as I know, going triple zeta or not doesn't change that.

Ok, thanks a lot Allan, that's been a help.