# CCL:G: questions on convergence, restarting jobs, counterpoise

*From*: Jean Jules FIFEN <julesfifen##gmail.com>
*Subject*: CCL:G: questions on convergence, restarting jobs,
counterpoise
*Date*: Mon, 28 Nov 2011 14:31:57 +0100

Sent to CCL by: Jean Jules FIFEN [julesfifen*_*gmail.com]
Dear Saurabh,
1. For the first questions, you have to know that it is the convention
in gaussian implementation that when the forces is to low (less than
5% of the convergence threshold), the obtained geometry is the
stationary one whatever the values of the displacement, RMS and so
forth. So you do not have to worry about your obtained result. It is
good, and further computation are useless.
2. Clearly, I do not understand well your second question. However,
you have to keep in mind that restarting frequency jobs could be
possible in gaussian09 and not in earlier versions.
3. Can the output of a counterpoise calculation (i.e. the Corrected
total energy) be interpreted as a bond-dissociation energy between
the two fragments? The answer is no. Counterpoise calculation allows
you to encompasse basis set superposition error (BSSE) in your
computed energy.
Hope this would help.
On 27/11/2011, Saurabh S Chitnis sschitnis%x%gmail.com
<owner-chemistry^-^ccl.net> wrote:
>
> Sent to CCL by: "Saurabh S Chitnis" [sschitnis _ gmail.com]
> Hello,
>
> I have three questions:
>
> 1. In many of my "opt" and "freq=raman" jobs, I find
that the calculation
> completes successfully with
> the forces having converged but the displacements still being above the
> convergence threshold. How
> can this be fixed? I usually face this problem when using opt=verytight and
> int=ultrafine.
>
> 2. Is there any way of restarting an analytic frequency job which has
> completed but not converged?
>
> 3. Can the output of a counterpoise calculation (i.e. the Corrected total
> energy) be interpreted as a
> bond-dissociation energy between the two fragments?
>
> Here are some details regarding the above questions:
>
> theory: DFT (B3LYP, PBE1PBE and B3PW91)
>
> basis-set: cc-pvtz and aug-cc-pvtz
>
> systems being calcualated: P2Me4, [P2Me5]+ and [P2Me6]2+
>
> for the couterpoise: I'm trying to get the P-P bond dissocation energy. So
I
> optimize the geometry as
> per usual and then redefine the optimized P2Me4 as fragment1(Me2P) and
> fragment2(PMe2) to run
> the counterpoise calculation. The result should be the homolytic bond
> dissociation energy right?
>
> cheers
> Saurabh>
>
>
--
Jules.