[DFTB-Plus-User] Clarification on warnings requested

[Sebastiaan Hermans]

Dear Dr. Hourahine,

Thank you very much for your clear and quick response. As I slightly misinterpreted the warnings, and I never explicitly requested the calculation of the dipole moment, I was concerned I somehow might have been using an ill-defined system. Since these warnings refer solely to the printout of the calculated dipole moment, which I am not necessarily interested in, I don’t think I have anything to worry about.

Thank you again and kind regards,
Sebastiaan


________________________________
Van: DFTB-Plus-User <dftb-plus-user-bounces at mailman.zfn.uni-bremen.de> namens Benjamin Hourahine <benjamin.hourahine at strath.ac.uk>
Verzonden: vrijdag 20 mei 2022 0:43:59
Aan: dftb-plus-user at mailman.zfn.uni-bremen.de
Onderwerp: Re: [DFTB-Plus-User] Clarification on warnings requested

Hello Sebastiaan,

Changes in the dipole moment are well defined in this case, but not the absolute value.

The warnings are coming from different physical effects:

For electrically charged systems, the total dipole moment depends on the origin of the coordinate system. You could impose a convention, such as placing the centre of charge at the origin.

For periodic systems, again changes in origin change the value, but this also applies to neutral systems. Again differences (modulo transfers by lattice vectors, see for example https://doi.org/10.1103/RevModPhys.66.899) are well defined.

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

2013/4 THE Awards Entrepreneurial University of the Year
       2012/13 THE Awards UK University of the Year

    The University of Strathclyde is a charitable body,
         registered in Scotland, number SC015263

________________________________
From: DFTB-Plus-User <dftb-plus-user-bounces at mailman.zfn.uni-bremen.de> on behalf of Sebastiaan Hermans <S.A.H.Hermans at student.tudelft.nl>
Sent: 19 May 2022 21:57
To: dftb-plus-user at mailman.zfn.uni-bremen.de <dftb-plus-user at mailman.zfn.uni-bremen.de>
Subject: [DFTB-Plus-User] Clarification on warnings requested

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Dear,



Since I last updated DFTB+, I am receiving these warnings:



WARNING!

-> Dipole printed for a charged system : origin dependent quantity

WARNING!

-> Dipole printed for extended system : value printed is not well defined



I am simulating a periodic system containing a copper sheet electrode with a negative charge and a large set of point charges.

Could you help me understand these warnings? Is the last warning to attend me to the self-interaction of the point charges in the periodic system?



Kind regards,

Sebastiaan

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