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]<mailto:[email protected]>u<mailto:[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]<mailto:[email protected]> Website: academicstaff.uk.ac.ir/moabbasnejad<http://academicstaff.uk.ac.ir/moabbasnejad> ---------------------------------------------------------
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