[QE-users] Effect of magnetic order on dynamic stability

[Nicola Marzari]

I don't think you can draw a general conclusion - a 2D material (or a 3D 
one) for a given geometry will have one or a few or many or infinite 
energy minima/selfconsistent states, where the global minimum and the 
local minima can be non-magnetic, ferromagnetic, or antiferro or 
ferrimaginetic, in primitive cells or larger supecells, or display spin 
spirals.

For a given geometry, each of this magnetic orders will lead to some 
small relaxations that can break symmetry or not, can be commensurate or 
incommensurate; ultimately, for every magnetic pattern there will be a 
supercell (maybe large, if incommensurate) in which the phonons are 
positive.

Of course, DFT or DFT+U+V or hybrids are approximate, so the 
computational truth of an approximate theory is different from reality, 
that in itself is not always truthful.

Hope this helps!

But to get a sense of the mess in which we are in, you could check this: 
https://scholar.google.ch/citations?view_op=view_citation&hl=en&user=YjHKNAUAAAAJ&cstart=20&pagesize=80&sortby=pubdate&citation_for_view=YjHKNAUAAAAJ:v_xunPV0uK0C
(in press in npj computational materials).

				nicola


On 09/04/2024 13:17, Zimmi Singh wrote:
> Dear community and Developers,
> 
> I am reaching out to you to get some clarity regarding the dynamic 
> stability of a 2D ferromagnet, 2H-VSe2. For my research, I have to 
> calculate the thermal conductivity (using phono3py) of both its 
> ferromagnetic and non-magnetic structures. My calculations  (using 
> PBE-PAW) suggest that the ferromagnetic phase (which is the favorable 
> ground state) is dynamically stable, whereas the non-magnetic phase is 
> unstable with negative frequencies in the phonon dispersions for one of 
> the acoustic modes.
> 
> On this topic, there are three published literature available, two 
> suggesting dynamic stability for both structures 
> (doi:10.1039/d2nh00429a, 10.1039/d3cp00008g), whereas the third 
> indicates that the non-magnetic state has one mode with negative 
> frequency (doi: 10.1007/s10853-021-06311-4, Figure S6).
> 
> Should the non-magnetic counterpart of a magnet be dynamically unstable 
> at zero kelvin? Can anyone shed some light on this?
> -- 
> *Best Regards*
> Zimmi Singh
> /Research_Scholar
> /
> /Department of Metallurgical and Materials Engineering
> Indian Institute of Technology, Kharagpur
> Kharagpur, India/
> 
> 
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-- 
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, SNSF
Head, Laboratory for Materials Simulations, Paul Scherrer Institut
Contact info and websites at http://theossrv1.epfl.ch/Main/Contact