Thank you very much. I will try this and return the results (at least 1 week of calculation). For the 'bad' ASR, there is the problem that the defect modes are so close to the acoustic modes that there is a hybridization between them. I suppose that it should drastically affect the ASR.
Regards, Antoine Jay Le Samedi, Octobre 30, 2021 11:46 CEST, Lorenzo Monacelli <[email protected]> a écrit: Dear Antonine Jay, By looking at your frequencies, they seem not well converged. Consider that in a perfectly converged calculation the ASR should be respected and its application should affect only transnational modes. However, all the phonon frequencies change considerably there. Consider increasing the tr2_ph value to 10^-20 or higher in the ph.x input script and eventually also the wfc/density cutoff. Converging soft modes when a lot of atoms and few symmetries are present in the system could be really cumbersome with DFPT. Bests, Lorenzo On 29/10/21 19:58, Tamas Karpati wrote: > Dear Antoine Jay, > > I think that in case of multiple imaginary eigenvalues the lower > energy of a conformer > may be less indicative. On the other hand, frozen phonons might be > both needed and to be avoided, > unless you consider a sufficient number of surrounding atoms. Have you > checked if inclusion > of more atoms helps the imaginaries fade away? Did you try to toss O where the > imaginary eigenvectors suggest? This way imaginaries can be sorted out > one after the other > (lucky ones get rid of them at once :) > > Hope this helps, > t > > > > > On Fri, Oct 29, 2021 at 10:10 AM Antoine Jay <[email protected]> wrote: >> Dear users, >> I would like to perform a phonon calculation at Gamma on a 216-atoms >> crystalline silicon supercell in which has been added 1 single oxygen (PBE >> functional). >> This interstitial O is located 'nearly' in the middle of two Si, and >> unfortunately, many local minima are possible for its position: C2, C1, C1h, >> D3d, each of them being separated by a very small energy barrier and a small >> distance as already shown in Countinho-2000: >> https://sci-hub.mksa.top/10.1103/physrevb.62.10824 >> >> When I calculate phonons of the C1h (that has the smallest energy) within >> DFPT, I obtain imaginary eigenvalues in the dynamical matrix. >> Of course, when I look at the corresponding eigenvectors, I see that they >> are exactly located on the O. >> Then I manually do a frozen phonon calculation using a displacement equal to >> the eigenvector and I see a positive curvature of the parabola meaning that >> the system is well at a minimum. >> Increasing the size of the displacement in my Frozen phonon permits me to >> see the double minima switching between C2 and C1h. >> I suppose that the size of the perturbation in DFPT is too high...? Where >> can I change it is the code? >> >> Best regards, >> >> Antoine Jay >> >> >> Inputs in attachment >> Results: >> Forces are over converged: Total force = 0.00049 Ry/au >> Frequencies after DFPT are these >> freq ( 1- 1) = -118.6 [cm-1] --> ? >> freq ( 2- 2) = -114.5 [cm-1] --> ? >> freq ( 3- 3) = -99.2 [cm-1] --> ? >> freq ( 4- 4) = -38.0 [cm-1] --> ? >> freq ( 5- 5) = -37.7 [cm-1] --> ? >> freq ( 6- 6) = -37.7 [cm-1] --> ? >> freq ( 7- 7) = 87.7 [cm-1] --> A' I+R >> freq ( 8- 8) = 91.5 [cm-1] --> A' I+R >> freq ( 9- 9) = 91.8 [cm-1] --> A'' I+R >> >> and after simple ASR: >> # mode [cm-1] [THz] IR >> 1 -107.94 -3.2359 0.0000 >> 2 -38.83 -1.1640 0.0000 >> 3 -10.69 -0.3206 0.0000 >> 4 -2.67 -0.0801 0.0000 >> 5 8.82 0.2643 0.0000 >> 6 29.09 0.8720 0.0000 >> 7 97.81 2.9324 0.0000 >> 8 98.94 2.9661 0.0000 >> 9 98.97 2.9670 0.0000 _______________________________________________ >> Quantum ESPRESSO is supported by MaX (www.max-centre.eu) >> users mailing list [email protected] >> https://lists.quantum-espresso.org/mailman/listinfo/users > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users _______________________________________________ Quantum ESPRESSO is supported by MaX (www.max-centre.eu) users mailing list [email protected] https://lists.quantum-espresso.org/mailman/listinfo/users
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