HI Jason,
my query was on how different are the values of the partial charges derived from QM calculation using AM1 to
those corrected value BCC BOND CHARGE CORRECTION
AM1 to AM1-BCC charges difference is significant ..
I know that QM and MM dipole are not supposed to be same ..the charges representation (wave function to
fixed point charges) is different in QM and MM
thanks
Fatima
________________________________________
From: Jason Swails [jason.swails.gmail.com]
Sent: Monday, November 10, 2014 2:01 PM
To: amber.ambermd.org
Subject: Re: [AMBER] AM1-BCC dipole moment
On Mon, 2014-11-10 at 13:51 +0000, CHAMI F. wrote:
> Hi Jason,
>
> I run sqm with the option "printdipole=1"
> the dipole moment that SQM output is for the AM1 before the bond charge correction ..AM1-BCC is
> final partial charges in prepi file
>
> in sqm.out for example the AM1 charge on nitrogen in cyano group of biphenylcyano molecule is
> so different from AM1-BCC
>
>
> sqm.out 14 N -0.038
> ANTECHAMBER_AM1BCC_PRE.AC
> ATOM 14 N 2 -8.532 1.150 0.912 -0.038000 n1
> ANTECHAMBER_AM1BCC.AC
> ATOM 14 N 2 -8.532 1.150 0.912 -0.363800 25
>
> this mean i have to work out the dipole moment using the partial charges in prepi file
There are two dipole moments here -- one from the QM calculation based
directly on the density matrix and another from the partial atomic
charges you derive _from_ the calculation. In an ideal world, these
would be equal. However, point charges in general are insufficient to
reproduce exact QM dipole moments (except, of course, when the dipole
moment is exactly 0 by symmetry).
So if you want the QM dipole moment, use the value you get from sqm. If
you want the MM dipole moment, as I mentioned before, you have to
compute it yourself from the charges and coordinates in the prepin file.
HTH,
Jason
--
Jason M. Swails
BioMaPS,
Rutgers University
Postdoctoral Researcher
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Received on Mon Nov 10 2014 - 07:30:02 PST
