[DFTB-Plus-User] too little or superfluous input for spin-polarised calculation

[Benjamin Hourahine]

Hello Peter,

The default behaviour for the code is to use a single spin-constant for each atom, typically this should be for the highest occupied atomic orbital.

In the case of transition metals, this behaviour is usually not too accurate (d electrons typically have ~ x2 larger spin interactions, but s and p shell are similar values), hence
ShellResolvedSpin = Yes
can be used. Adding it to your input would also allow your input to run.

Regards,

Ben

Dr. B. Hourahine
Senior Lecturer and Director of Student Support
Department of Physics, SUPA
University of Strathclyde, John Anderson Building,
107 Rottenrow, Glasgow G4 0NG, UK.
+44 (0)1415483366, benjamin.hourahine at strath.ac.uk
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________________________________
From: DFTB-Plus-User <dftb-plus-user-bounces at mailman.zfn.uni-bremen.de> on behalf of Peter Klaver <klaver2 at gmail.com>
Sent: 10 September 2024 12:58
To: User list for DFTB+ related questions <dftb-plus-user at mailman.zfn.uni-bremen.de>
Subject: [DFTB-Plus-User] too little or superfluous input for spin-polarised calculation

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Hello people,

I seem to have a problem preparing the input file for a spin-polarised calculation.

Some experimental work suggested that in graphene-like defective structures, some C atoms may carry a magnetic moment. I want to see if a dftb+ calculation will show any such thing.

If I put the following lines in the Hamiltonian section of dftb_in.hsd,
———————————————————————
SpinPolarisation = Colinear {
UnpairedElectrons = 0.0
InitialSpins = {
AtomSpin = {
Atoms = 1:7801
SpinPerAtom = 1.0
}
}
}
———————————————————————

then dftb+ says
-> Missing child: SpinConstants

If I add then add the lines
———————————————————————
SpinConstants = {
C = {
# Wss Wsp Wps Wpp
-0.028 -0.024 -0.024 -0.022
}
}
———————————————————————

then dftb+ says:
ERROR!
-> Superfluous data found.
Path: dftbplusinput/Hamiltonian/DFTB/SpinConstants/C
Line: 65-68 (File: dftb_in.hsd)

So without the SpinConstants lines there is something missing, with the SpinConstants lines there is too much.

If I only put in the line
SpinConstants = {}

then dftb+ says:
ERROR!
-> Missing child: C
Path: dftbplusinput/Hamiltonian/DFTB/SpinConstants
Line: 64-65 (File: dftb_in.hsd)

Putting in a line for C without data, like
C = {}

then dftb+ says:
ERROR!
-> Unexpected end of data
Path: dftbplusinput/Hamiltonian/DFTB/SpinConstants/C
Line: 65-65 (File: dftb_in.hsd)

So I can have too much data, of various grades of too little data.

Does anyone have an idea on how to put in the right data for a spin-polarised calculation?

Kind regards,
Peter
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