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LoProp method (Read 6086 times)
Gerrit-Jan Linker
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LoProp method
31.07.08 at 15:14:55
 
LoProp method
 
The LoProp method can be used to partition molecular properties like multipole moments and polarizabilities into atomic and interatomic contributions. The LoProp method is published by Gagliardi, Lindh and Karlstrom, see J. Chem. Phys, 121, 10, 4494 (2004).
 
With the LoProp method the authors aim to overcome problems with other methods like Mulliken population analysis (MPA, see http://www.oraxcel.com/cgi-bin/yabb2/YaBB.pl?num=1217504700/0#0).
 
To get physical significance, it is a requirement of the LoProp analysis that the basis functions that are classified as occupied are essentially the atomic orbitals.  
 
The primary subdivision of the space around atoms in molecules is deduced from the space of the occupied atomic orbitals centered on those atoms. Basis functions are therefore classified as occupied and virtual.
 
A localized orthonormal basisset is obtained from the following 4 step procedure:

  • Obtain orthonormality in each atomic block using a Gram-Schmidt or Lowdin orthonormalisation.
  • Two Lowdin molecular orthonormalisations are performed. The first on the occupied subspace and the second on the virtual subspace.
  • Components of the occupied subspace are projected out of the virtual subspace using a Gram-Schmidt orthonormalisation.
  • The virtual subspace is orthonormalised using a Lowdin orthonormalisation.

 
LoProp is implemented in the MOLCAS package. As for input just add the following after your SCF of CASSCF step:

 &LOPROP &END
End of Input

 
Of course more input can be added to control the program. See the MOLCAS manual (http://www.teokem.lu.se/molcas/documentation/manual/node33.html) for details.
 
References:
Molcas LoProp
http://www.teokem.lu.se/molcas/documentation/manual/node33.html
 
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« Last Edit: 31.07.08 at 15:35:05 by Gerrit-Jan Linker »  

Gerrit-Jan Linker
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Re: LoProp method
Reply #1 - 02.08.08 at 10:58:44
 
When LoProp is used in the way described above in MOLCAS further SCF steps are performed by LoProp. Propbably this is due to it going beyond static properties. I noticed that this further SCF steps do not reproduce the Total SCF Energy. This is probably due to LoProp applying a small electric field. This can be switched off uwing the NoField option but then it will only compute static charges.
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« Last Edit: 02.08.08 at 11:21:06 by Gerrit-Jan Linker »  

Gerrit-Jan Linker
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Re: LoProp method
Reply #2 - 02.08.08 at 11:14:18
 
If only atomic charges are required I suggest to use the NoField keyword to not get confused with the SCF results.  
 
 &LOPROP &END
NoField
End of Input
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Gerrit-Jan Linker
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Re: LoProp method
Reply #3 - 07.08.08 at 09:59:24
 
Loprop results and basisset dependency
 
Calculating the LoProp charge for an S atom in EDOTTF using HF gives the following results.
BasissetCharge
STO-3G0.21
3-21G-0.07
4-31G0.22
6-31G-0.05
6-31G*-0.07
6-31G**-0.07

 
These results are very different from Mulliken charges. We arrive at a charge of -0.07 with LoProp, nearly no charge at all, whereas Mulliken analysis gives a charge of +0.33.
 
 
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« Last Edit: 07.08.08 at 10:03:21 by Gerrit-Jan Linker »  

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