SLAPAF usage problem

Posted by Gerrit-Jan Linker on November 25, 2009 at 14:12:47:

I am using SLAPAF to optimise H's in a molecule while the skeleton of molecule should remain static. The problem I am facing is that the molecule will move during the process. Is there a trick to keep the coordinates of the molecule exactly as they are while only the H's are optimised?

I tried to use constraints giving the x,y and z coordinates of the static atoms. This yielded wrong H positions? Bug perhaps?

Next I used internal coordinates basically entering the Z-matrix where I allowed only the bonds,angles and dihedrals of the H's to vary keeping the rest fixed. This works fine but the molecule is slowly rotating and translating too! I would like to fix it.

Using a mixture of internal coordinates and constraints does not work either.

Details: HF (SCF program), 6-31G** basis, Molcas 7.4

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Comments:
: I am using SLAPAF to optimise H's in a molecule while the skeleton of molecule should remain static. The problem I am facing is that the molecule will move during the process. Is there a trick to keep the coordinates of the molecule exactly as they are while only the H's are optimised? : I tried to use constraints giving the x,y and z coordinates of the static atoms. This yielded wrong H positions? Bug perhaps? : Next I used internal coordinates basically entering the Z-matrix where I allowed only the bonds,angles and dihedrals of the H's to vary keeping the rest fixed. This works fine but the molecule is slowly rotating and translating too! I would like to fix it. : Using a mixture of internal coordinates and constraints does not work either. : Details: HF (SCF program), 6-31G** basis, Molcas 7.4

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