Hello,
In your antechamber command, you are using AM1-BCC method. This is a
semi-empirical QM method. I personnaly used several methods for my
ligands :
- RESP charges, from HF 6-31* gaussian calculations. You need to do
these calculations with several conformations and to do the average.
This is certainly, the most accurate way to obtain ligand atomic
charges.
- AM1-BCC, which seems to be less dependent to conformation. Generaly,
I used it with only one ligand conformation. I have generally good
results from this method but I used this method with ligands which not
display large conformational changes.
- Gasteiger. This is not a quantum calculation. I employed this method
for several ligands on the same RNA binding site. I found that it was
not really good for my problem. However, the calculation is damn
quick.
- With antechamber, you can also don't calculate charges and simply
read the charges from input file. I used this for a ligand/ligand
simulation in vaccuo. To do that, I took the charges from Sybyl
calculations (marsili charges). This was good, but I will never do
that for a protein/ligand interaction where you will need charges in
adequation with amber protein charges.
To sum up, you have several possibilities depending of what you want
to do. Now, I generally uses AM1-BCC as default method, and I have
quite good results. In my mind, this is a good compromise with
accuracy and cpu time.
Hope that my experience will help you.
Regards
Florent Barbault
On Sun, 26 Apr 2009 11:30:06 +0530 (IST)
Vikas Sharma <vs_vikassharma.yahoo.co.in> wrote:
> hi all
> Is it always necessary to perform QM calculations for ligand to
>calculate charges or antechamber is sufficient?
> Actually iam usin antechamber with the following command:
>
> antechamber -i ligand.mol2 - fi mol2 -o ligand.prepin -fo prepi -c
>bcc -s 2
>
> and Its going fine..i checked the tutorial and its mentioned there
>that for non standard residues we should use QM calculations coz
>antechamber wont work in case of non- standard...
>
> If QM calculation is required then why?
> If QM calculation is not required then why?
>
>
> Now surf faster and smarter ! Check out the new Firefox 3 -
>Yahoo! Edition http://downloads.yahoo.com/in/firefox/
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-------------------------------------------------
Dr Florent Barbault
Maitre de conferences / Assistant professor
NEW ADDRESS !!!
Universite Paris Diderot
Laboratoire ITODYS
15 rue Jean de Baïf, bâtiment Lavoisier
75013 Paris FRANCE
http://www.itodys.univ-paris7.fr/
tel : (33) 01-57-27-88-50
e-mail : florent.barbault.univ-paris-diderot.fr
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Received on Wed May 20 2009 - 12:53:16 PDT
