Hi,
I run some tests on your files. It seems indeed that only PM6 crashes at
some point. Other semiempirical hamiltonians do not crash (I tested AM1,
PM3, PM3-PDDG, and RM1). May be there is a problem in the PM6 potential
energy surface describing your system.
Sincerely,
G. Monard.
On 09/28/2012 10:58 AM, Gerald Monard wrote:
> 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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>> AMBER.ambermd.org
>> http://lists.ambermd.org/mailman/listinfo/amber
>
--
____________________________________________________________________________
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 - 07:30:03 PDT
