Chemical Forums
Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Sam (NG) on April 09, 2007, 11:31:16 AM
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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' 2px,y,z 2p'x,y,z
H 1s 1s'
6-31G*
O 1s 2s 2s' 2px,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'' 2px,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
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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.
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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.