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Following the previous threads on this topic, I would like to know the minimum supercell size suitable for Phonon spectrum calculation using Phonopy (DFPT) for CrI$_3$ monolayer system given by this unit cell POSCAR:

 CrI3                                    
   1.00000000000000     
     7.2414772987377169   -0.0000334312315729   -0.0000273695524433
    -3.6207634204735277    6.2714102717088256    0.0000236446352383
    -0.0000690784193687    0.0000291507055479   18.1739997862014491
   Cr   I 
     2     6
Direct
  0.6666642998354509  0.3332969407635646  0.4999838454239838
  0.3333680676615832  0.6666687700374014  0.5000267181089781
  0.6449405535702791  0.9999734919584491  0.4102132677332540
  0.3551208025009766  0.3550499098699756  0.4102112382804572
  0.0000237365755498  0.6448837571827296  0.4102090416058436
  0.3550928327367056 -0.0000708711957224  0.5897938401149568
  0.6449229383444248  0.6449027058686945  0.5897995792122650
  0.0000673177750284  0.3550765345149079  0.5898047365202591
 
  0.00000000E+00  0.00000000E+00  0.00000000E+00
  0.00000000E+00  0.00000000E+00  0.00000000E+00
  0.00000000E+00  0.00000000E+00  0.00000000E+00
  0.00000000E+00  0.00000000E+00  0.00000000E+00
  0.00000000E+00  0.00000000E+00  0.00000000E+00
  0.00000000E+00  0.00000000E+00  0.00000000E+00
  0.00000000E+00  0.00000000E+00  0.00000000E+00
  0.00000000E+00  0.00000000E+00  0.00000000E+00
Improve this question
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  • 3
    $\begingroup$ The supercell size (or equivalently $\mathbf{q}$-point grid size) is a convergence parameter, so the only way to answer this question is to perform tests with different supercell sizes. $\endgroup$
    – ProfM
    Oct 29, 2021 at 17:28
  • $\begingroup$ You mean SCF tests ? $\endgroup$
    – Chi Kou
    Oct 29, 2021 at 22:02
  • 1
    $\begingroup$ No, I mean doing calculations with an increasingly large supercell until the phonon dispersion/energy is converged. $\endgroup$
    – ProfM
    Oct 30, 2021 at 8:12
  • 2
    $\begingroup$ On the phonopy sourcefourge forum, they suggest taking about 6 to 7 $\overset{\circ}{A}$ or a distance greater than the second nearest neighbour distance, whichever is larger, in each direction. $\endgroup$
    – Hitanshu Sachania
    Nov 2, 2021 at 11:16
  • 1
    $\begingroup$ @ChiKou while you will be pinged for all comments on this post, you need to include @username for the user you are replying to in order for them to be notified. $\endgroup$
    – Tyberius ♦
    Nov 7, 2021 at 1:31

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