[QE-users] Fermi-Surface Nesting

[Chiara Cignarella]

Dear Kumar,

In order to make sure you have a nesting of the Fermi surface you should plot the nesting function (the double deltas function); the points where you see the peaks are the nesting points of the Fermi surface.

The  phonon softening in the phonon dispersion that you observe should be a Kohn anomaly. It is likely to be related to the Fermi nesting, but not straightforward.

You can have a look at some of the literature about, like for example  ”Johannes and Main PRB 77, 2008”, "Zhu X. Et al PNAS 2015", or more standard books like Khomskii “Basic aspects of quantum theory of solids”, Chapter 9 and 11.

Best
Chiara Cignarella

PhD student
EPFL


> On 19 Aug 2023, at 18:13, ukawamura u <mkawamura at ds.itc.u-tokyo.ac.jp> wrote:
> 
> Dear Dr.Kamadurai
> 
> Maybe you are using FermiSurfer.
> I added function to compute two kinds of nesting function namely
> double-delta and Lindhard-type:
> https://mitsuaki1987.github.io/fermisurfer/en/_build/html/ops.html#nesting-function
> This version was released today.
> https://github.com/mitsuaki1987/fermisurfer/releases/tag/2.4.0
> 
> Best regards,
> Mitsuaki Kawamura
> 
> Mitsuaki Kawamura
> Data Science Research Division, Information Technology Center, The
> University of Tokyo
> e-mail: mkawamura at ds.itc.u-tokyo.ac.jp
> 
> 2023年8月16日(水) 15:06 Ramesh Kumar Kamadurai via users
> <users at lists.quantum-espresso.org>:
>> 
>> Dear All
>> I am writing to get some clarification about the nesting of the Fermi surface. Since the FS geometry looks complex, I need help understanding it correctly. Sorry for asking non-QE-related question. I have calculated the Fermi surface for a conventional cell and projected it onto the primitive cell. When examining a slice along the 110 direction, I noticed two parallel lines at the boundary's edge. Further in the phonon calculation, I observed phonon softening (imaginary frequency) at the same M point. Is there a connection between this stitching of surfaces on the Fermi surface and the observed phonon softening, and finally, is there a nesting? I am attaching the relevant pictures. Thanks in advance for your suggestion.
>> 
>> Best regards,
>> 
>> K. Ramesh Kumar
>> 
>> Assistant Professor
>> 
>> Gandhi Institute of Technology and Management,
>> 
>> Phone: +91 9895637981, +1 6782419790
>> 
>> Email: kraamesh57 at gmail.com rkamadur at gitam.edu
>> 
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> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users