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Topic: 6-311G* Basis Set  (Read 6040 times)

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Offline Sam (NG)

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6-311G* Basis Set
« on: April 09, 2007, 11:31:16 AM »
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

allanf

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Re: 6-311G* Basis Set
« Reply #1 on: April 09, 2007, 01:16:54 PM »
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.

Offline Sam (NG)

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Re: 6-311G* Basis Set
« Reply #2 on: April 09, 2007, 03:39:36 PM »
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.

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