AMBER Archive (2006)

Subject: AMBER: Charges of enantiomers for Amber8

From: lily ferreira (lily_1_mart_at_yahoo.fr)
Date: Wed Jan 25 2006 - 02:01:24 CST

Dear Members,
  
  I'm relatively new to Amber8. I am trying to detemine charges for small
    molecules (less than 50 atoms) using resp that are conformation independent. I
    used a systematic torsion angle serach for my molecue using Insight II. From
    this search I kept only the 10 lowest energy conformations according Insgith II
    force field. For each one of this conformations I used Gaussion to calculate
    the ESP charges in two steps. First I did an optimisation using "STO-3G" and
    "opt pop=none geom(nodistance,noangle)" as keywordks. With the output file I
    made the ESP calculation using "6-31G*" and "iop(6/33=2) pop=mk" as keywords.
    After that I used resp with all my molecules to calculate the RESP charges. At
    the end of the calculation, I saw that the results of RESP did not gave the
    mean values for 10 conformations, but charges for each conformation. My
    questions are:
     
    1. If I use 10 conformations for charges determinantion, after using RESP for
    the 10 conformations, do I have to take the mean value of the 10 molecules or
    is there a specific command in resp that allows it to do that directly?
     
    2. When I am working with enantiomers in Amber8, should we used the same
    charges for both enantiomers or have we to calculate the charges for
    (R)-enantiomers AND for (S)-enantiomers? (my molecules have only one chiral
    centre).
  
  Thank you very much for your help.
    ..
  
  
  
  

                
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