AMBER Archive (2006)

Subject: AMBER: RESP charge fitting

From: Mingfeng Yang (mfyang_at_gmail.com)
Date: Fri Oct 27 2006 - 19:35:37 CDT

Dear Amber users,

I am trying to fit the charges for a trifluoroethanol molecule with the
help of RED. GAMESS(6-31G*) was used to optimize the structure and
calculate the molecular electrostatic potential, and RESP was used to
fit the charges in two steps.

My problem is that the charge output from the first and the second step
are exactly the same. The chemically equivalent atoms were not set to
have the same charges. What should I do to get the same charges for the
fluorine atoms binding to the same carbon atom?

The input for stage1 RESP automatically generated by RED is:
 Molecule
 &cntrl
  ioutopt=1, iqopt=1, nmol=1, ihfree=1, irstrnt=1, qwt= 0.0005
 &end
  1.0
 Molecule
   0 9
   6 0
   9 0
   9 0
   9 0
   6 0
   1 0
   1 0
   8 0
   1 0

The one for stage 2 RESP is:
 Molecule
 &cntrl
  ioutopt=1, iqopt=2, nmol=1, ihfree=1, irstrnt=1, qwt= 0.001
 &end
  1.0
 Molecule
   0 9
   6 -1
   9 -1
   9 -1
   9 -1
   6 -1
   1 -1
   1 -1
   8 -1
   1 -1

Thanks,
Mingfeng

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