[DFTB-Plus-User] about collinear spin / RelaxTotalSpin in v1.3

Bálint Aradi aradi at uni-bremen.de
Thu Feb 16 08:23:37 CET 2017

Dear Zhengping,

> (1)    In the latest version, if I set RelaxTotalSpin=Yes, does the code
> find the best spin configurations to minimize the total energy? In this
> case, regardless of the initial configuration, the converged results
> should be the same?

Not necessarily. If your system can have two different spin
configuration at the same geometry, you can end up in different ones
depending on the starting conditions.

> (2)    In DFTB+ v1.2, the spin-up and spin-down could have different
> Fermi-levels, I am not sure what this means physically?

That's not really physical, but sometimes you want to enforce a certain
spin multiplicity for your system, which may lead to different Fermi
levels in the different spin channels.

> (3)    For DFTB+U, what is the best way to determine the UJ parameter?
> E.g. in one example file, UJ = (U+W)/4. In another file, the value is
> different.

There exist several approaches. You may set it up empirically by
monitoring some physical properties (e.g. gap size, defect level
positions, etc.) or try to do it more ab-initio.

> The DFTB+ MPI seems still in version 1.2. The RelaxTotalSpin option is
> not available yet.

That's true. We are in the process of merging everything from the serial
branch into the parallel branch (and keep only one branch in the
future). So I hope, in a few months, we have this sorted out.

  Best regards,


Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen

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