Hi,
IMHO, I'm not sure that it is really a SCF convergence problem in your case.
Your system is a charge separated system ( (CH3NH3^+)2 + NH4^+ (SO4H^-)2
) that you try to simulate in gas phase at T=800K. There is a really
great chance that during an QM-MD, your system will blow up at some
point. In a certain chemical sense, I am not sure that this is something
wrong.
I made some quick tests with your system (minimization before running
the MD, 300K instead of 800K, vrand=10 instead of 100, etc.), but at
some point there is always a proton transfer between an amine group and
a sulfate, then the system explodes because of the energy released.
If your system was soaked into a aqueous solvent for example, I am
pretty sure that this would not happen.
Sincerely,
G. Monard.
On 09/28/2012 01:45 AM, Wei Lin wrote:
> Hi Everyone,
>
> I tried to run MD simulation with PM6 Hamiltonian for a small charged
> cluster contained d-orbital element. After ~ 38 steps of simulation,
> the system blows up with error message as follows:
>
> QMMM: WARNING!
> QMMM: Unable to achieve self consistency to the tolerances specified
> QMMM: No convergence in SCF after 1000 steps.
> QMMM: Job will continue with unconverged SCF. Warning energies
> QMMM: and forces for this step will not be accurate.
> QMMM: E = -0.6307E+06 DeltaE = 0.1152E-01 DeltaP = 0.3365E-02
> QMMM: Smallest DeltaE = 0.3550E-03 DeltaP = 0.2442E-02 Step = 787
>
> Then, I set up another simulation for the same system with Gaussian
> interface. The simulation runs well.
>
> Andy Goetz suggested that can be related to SCF convergence algorithms
> in sqm. I am wondering if anyone knows how to overcome this problem.
>
> The mdin (both in sqm and Gaussian interface), inpcrd, prmtop and run
> files are attached.
>
> Thanks,
> Wei
>
>
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--
____________________________________________________________________________
Prof. Gerald MONARD
Theoretical Chemistry and Biochemistry Group
SRSMC, Université de Lorraine, CNRS
Boulevard des Aiguillettes B.P. 70239
F-54506 Vandoeuvre-les-Nancy, FRANCE
e-mail : Gerald.Monard.univ-lorraine.fr
tel. : +33 (0)383.684.381
fax : +33 (0)383.684.371
web : http://www.monard.info
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Received on Fri Sep 28 2012 - 02:00:02 PDT
