Hi Mohaddeseh, One thing I want to add regarding your 1st question. You are getting I+R modes because your system may not have inversion symmetry (you can check in scf.out).
Best, Hari Paudyal On Wed, Aug 12, 2020 at 10:45 AM Mona Asadinamin <[email protected]> wrote: > Dear Mohaddeseh: > > You are right, it means IR and Raman active simultaneously. > > Regarding the scf threshold, increasing it results in more accuracy and > normally it should be very tight, something like 1.d-15 or even less. It > definitely does not turn frequencies from positive to negative. It helps to > bring the system out of unstable point in the potential energy surface that > causes negative frequencies. > > Best regards; > > > Mona Asadi Namin > > Graduate student > > Center for simulational physics > > University of Georgia > > -------------------------------------- > > Email:[email protected] <[email protected]>u <[email protected]> > > Phone: +1-215-906-23-92 > > > ------------------------------ > *From:* users <[email protected]> on behalf of > Mohad Abbasnejad <[email protected]> > *Sent:* Wednesday, August 12, 2020 8:16 AM > *To:* [email protected] <[email protected]> > *Subject:* [QE-users] Regarding phonon calculations > > [EXTERNAL SENDER - PROCEED CAUTIOUSLY] > > Dear QE users, > > Hello > I hope everybody is well. > I have two questions regarding phonon calculations. > 1- I have calculated the frequency for special q point in my structure > shown as follow: > > Mode symmetry, C_3v (3m) point group: > > freq ( 1 - 2) = -59.6 [cm-1] --> E L_3 I+R > freq ( 3 - 3) = -48.4 [cm-1] --> A_1 L_1 I+R > freq ( 4 - 5) = 162.4 [cm-1] --> E L_3 I+R > freq ( 6 - 6) = 227.4 [cm-1] --> A_1 L_1 I+R > freq ( 7 - 7) = 250.8 [cm-1] --> A_2 L_2 > freq ( 8 - 8) = 295.5 [cm-1] --> A_2 L_2 > freq ( 9 - 10) = 299.4 [cm-1] --> E L_3 I+R > freq ( 11 - 12) = 308.1 [cm-1] --> E L_3 I+R > freq ( 13 - 14) = 382.0 [cm-1] --> E L_3 I+R > freq ( 15 - 16) = 435.0 [cm-1] --> E L_3 I+R > freq ( 17 - 17) = 456.0 [cm-1] --> A_1 L_1 I+R > freq ( 18 - 18) = 513.6 [cm-1] --> A_2 L_2 > freq ( 19 - 20) = 521.9 [cm-1] --> E L_3 I+R > freq ( 21 - 21) = 571.4 [cm-1] --> A_1 L_1 I+R > freq ( 22 - 23) = 578.0 [cm-1] --> E L_3 I+R > freq ( 24 - 24) = 614.8 [cm-1] --> A_1 L_1 I+R > freq ( 25 - 25) = 620.5 [cm-1] --> A_2 L_2 > freq ( 26 - 27) = 635.4 [cm-1] --> E L_3 I+R > freq ( 28 - 29) = 651.0 [cm-1] --> E L_3 I+R > freq ( 30 - 30) = 653.0 [cm-1] --> A_2 L_2 > > I am wondering if somebody can tell me the meaning of I+R modes. > Does it mean Raman and infrared are active simultaneously for this mode? > > 2- I am wondering if increasing the threshold for self-consistency may > influence the frequencies significantly such that it causes the frequency > value from positive to negative. Is the default of the program reasonable? > > Any help would be appreciated. > > Bests > Mohaddeseh > -- > --------------------------------------------------------- > Mohaddeseh Abbasnejad, > Assistant Professor of Physics, > Faculty of Physics, > Shahid Bahonar University of Kerman, > Kerman, Iran > P.O. Box 76169-133 > Tel: +98 34 31322199 > Fax: +98 34 33257434 > Cellphone: +98 917 731 7514 > E-Mail: [email protected] > Website: academicstaff.uk.ac.ir/moabbasnejad > --------------------------------------------------------- > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users
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