[DFTB-Plus-User] SCC convergence and KPointsAndWeights

[Benjamin Hourahine]

Hello Xiaobao Zhang,

the electronic temperature will effect the results if it is on the scale of any electronic excitations of the system (the band-gap for insulators for example).  It is safer to use the same temperature as the molecular dynamics temperature, and then test the sensitivity of the results to changing that single parameter.

I'm interested why you are having convergence problems for a CNT - for many problems non-scc DFTB is sufficient for a pure C system. Have you optimised the structure before starting the MD, since poor convergence may be a symptom of a very distorted geometry?

The gamma point sampling of the k-points probably are not sufficient, unless this is an insulating tube with a sufficiently large repeating unit cell. This may also be part of the reason for the poor convergence, particularly for a metallic tube. As always you should test the convergence of results with respect to these parameters.

Regards

Ben

       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

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________________________________
From: DFTB-Plus-User [dftb-plus-user-bounces at dftb-plus.info] on behalf of jsxz [jsxzzhangchao at 126.com]
Sent: 18 July 2014 12:27
To: dftb-plus-user
Subject: [DFTB-Plus-User] SCC convergence and KPointsAndWeights


Hi, everyone

I want to calculate ion irradiation tolerance  of carbon nanotube (CNT) and use the MD method. I enconter two problems:

1)  To let the CNT SCC convergence, I set
   Filling = Fermi {
       Temperature [Kelvin] = 1000.0
     }
    Does the result depend on the Fermi tempereture? how to judge the result correctness?
    I can not reset the temperature when the molecular dynamics process is running.
    If I set the tempereture=300 K at the beginning of the MD, it cannot convergence.

2) For the KPointsAndWeights, I only set the Gamma point of the CNT, is it right?
   KPointsAndWeights = {
      0.0 0.0 0.0 1.0
    }



Thanks a lot for your help!

Xiaobao Zhang