[DFTB-Plus-User] DFTB-problem

[Jan M. Knaup]

Dear Hakkim,

there are several potential causes for your problem in your input file:

1. For molecules containing hydrogen, 2fs is a dangerously long time step.
Try reducing the time step.

2. Unfortunately you do not specify which kind of molecule you are using
and which set of Sklater-Koster files. Anyway, most SK sets for organic
molecules are intended for SCC-DFTB. Doing non-SCC calculations with them
will give you very wrong forces, so make sure that your input settings
match the SK set you are using.

3. Apparently you are using perodic boundary conditions, yet you talk about
optimizing a molecule. Putting molecules into periodic boxes, especially if
the molecules contain strongly charged groups. You have to make sure that
zour box is large enough. If your molecule is not perodic by istelf, don't
use periodic boundary conditions at all.

Hope this will help,

Jan

Jan M. Knaup                      | Fon +49-(0)421-218-62351
Dipl. Phys. Dr. rer. nat.         | Fax +49-(0)421-218-62770
Universität Bremen - BCCMS        |
Am Fallturm 1                     | Jan.Knaup at bccms.uni-bremen.de
28359 Bremen                      | JanKnaup at gmail.com
Germany                           | www.bccms.uni-bremen.de


2012/10/24 Marci <vormar at gmail.com>

> Dear hakkim,
>
> Why do think this is a problem? Could you please be a bit more specific?
>
> Anyway, your input seems to correspond to an MD run and not just a
> simple "optimization", of couse this can be just a matter of
> terminology.
>
> Cheers,
> Marton
>
> --
> PhD student
> Department of Atomic Physics
> Budapest University of Technology and Economics
>
> On Wed, Oct 24, 2012 at 11:04 AM, Hakkim Vovusha
> <hakkim.vovusha at physics.uu.se> wrote:
> > Hi,
> >
> >  I am doing DFTB calculation for graphene with some hydroxide groups
> > (covalently attached). During the optimization hydrogen is flying away
> from
> > the molecule. My input is
> >
> > Driver = VelocityVerlet {
> >   Steps = 20000
> >   TimeStep [Femtosecond] = 2.00000000000000
> >   Thermostat = Andersen {
> >     Temperature [Kelvin] = 300.0
> > #    Temperature [Kelvin] = TemperatureProfile {
> > #      constant     100    10.0
> > #      linear       1000  10.0
> > #      constant    19000  10.0
> > #      exponential  50     20.0
> > #    }
> >     ReselectProbability = 0.200000000000000
> >     ReselectIndividually = Yes
> >   }
> >   OutputPrefix = "geo_end"
> >   MDRestartFrequency=2
> >   MovedAtoms = 1:-1
> >   ConvergentForcesOnly=No
> > #  Velocities [AA/ps] = {
> > #<<< "input.vel"
> > #  }
> > }
> >
> > Hamiltonian = DFTB {
> > #  SCC = Yes
> > #  SCCTolerance = 1e-5
> > #  MaxSCCIterations = 1000
> >   MaxAngularMomentum = {
> >     C = "p"
> >     O = "p"
> >     H = "s"
> >   }
> > #  Charge = 0.000000000000000E+000
> > #  SpinPolarisation = {}
> > #  Eigensolver = Standard {}
> > #Mixer = Broyden {
> > #    MixingParameter = 0.020000000000000
> > #  }
> >   Filling = Fermi {
> >     Temperature [Kelvin] = 300.00
> >   }
> >   SlaterKosterFiles = Type2FileNames {
> >     Prefix = " "
> >     Separator = "-"
> >     Suffix = ".skf"
> >   }
> >   KPointsAndWeights = SupercellFolding {
> >    1 0 0
> >    0 1 0
> >    0 0 1
> >    0.0 0.0 0.0
> >   }
> > }
> >
> > Options = {
> >   WriteAutotestTag = No
> >   RandomSeed = 12345
> > }
> >
> > ParserOptions = {
> >   ParserVersion = 4
> > }
> >
> > Kindly help in this regard
> >
> > with regards
> > hakkim
> > _______________________________________________
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> > DFTB-Plus-User at dftb-plus.info
> > http://www.dftb-plus.info/mailman/listinfo/dftb-plus-user
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