Dear James,
thank you for your reply. However, I still have some doubts.
In frequencies calculations (with g09) the force constant is expressed in
mDyne/Ang.
However, when asking g09 to print the force constant for each degree of
freedom, one gets the following output:
! Name Definition Value Derivative
Info. !
--------------------------------------------------------------------------------
! R1 R(1,2) 1.5017 D2E/DX2 =
0.3353 !
! R2 R(1,4) 1.0794 D2E/DX2 =
0.3863 !
! R3 R(1,5) 1.0808 D2E/DX2 =
0.3807 !
where R(1,2) is the bond and D2E/DX2 is the force constant. *It seems to me
that these values are expressed in Hartree*, even if it is not clearly
specified in the output file.
Do you ever had any experience with this problem??
The conversion of either mDyne/Ang or Hartree to kcal/mol/(Ang**2) will
give different values of the Force Constants that will be unreliavle if the
startung units are wrong.
Thank you very much
Giulia
2014-05-19 21:44 GMT+02:00 James Maier <jimbo.maier.gmail.com>:
> On Mon, May 19, 2014 at 3:26 PM, giulia palermo
> <giulia.palermo83.gmail.com>wrote:
>
> > kcal/mol/(A**2)
> >
> > But, what does it mean (A**2)???
> >
>
> A = angstroms
>
> Please see http://ambermd.org/formats.html and the link on that page to a
> well-written extract from Jason Swail's dissertation (
> http://ambermd.org/prmtop.pdf ).
>
> Of particular interest should be the sections on "BOND_FORCE_CONSTANT"
>
> James
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Received on Wed May 21 2014 - 02:00:03 PDT
