[DFTB-Plus-User] total energy increasing

[Ben Hourahine]

Hello Zhu Xi,

without more details its is difficult to work out what is causing the 
problem.
Do you mean that the energy changes by a large amount, or only by ~ 1 meV?
For NVE calculations the total MD energy should be well conserved. This 
suggests
if you have a large energy change then the time step may be too long, a 
reasonable
choice is typically about 1% of the shortest vibrational period in the 
system, but you
need to test this (for hydrogen containing systems I use TimeStep 
[Femtosecond] = 0.1).
Alternatively you may have for example turned off "ConvergentForcesOnly" 
and be
having self consistency problems for example.

It is not currently possible to thermostat only part of the system.

Regards

Ben

On 07/02/11 05:06, Zhu Xi wrote:
> sorry, the total energy I mean is E_total,  not just E_mermin.
>
> Thanks
>
> 2011/2/7 Zhu Xi <ustc0200 at gmail.com <mailto:ustc0200 at gmail.com>>
>
>     Hi All;
>
>     When I doing a NVE simulation, I found the total energy (E-mermin)
>     will increases, usually the friction will cause energy lose, why
>     increase happens?
>
>     another problem is, can DFTB only set the thermo bath in some part
>     of the system?  for example, in a slab+molecule system, can I only
>     set the thermo bath to the slab?
>
>     Thanks
>
>


-- 
      Dr. B. Hourahine, SUPA, Department of Physics,
    University of Strathclyde, John Anderson Building,
           107 Rottenrow, Glasgow G4 0NG, UK.
     +44 141 548 2325, benjamin.hourahine at strath.ac.uk
    The University of Strathclyde is a charitable body,
registered in Scotland, with registration number SC015263

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.zfn.uni-bremen.de/pipermail/dftb-plus-user/attachments/20110207/b1fa77c5/attachment.htm>