[QE-users] [External Email] Re: Regarding phonon calculations

[Hari Paudyal]

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 <Mona.a at uga.edu> 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:mona.a at uga.ed <mona.a at uga.edu>u <mona.a at uga.edu>
>
> Phone: +1-215-906-23-92
>
>
> ------------------------------
> *From:* users <users-bounces at lists.quantum-espresso.org> on behalf of
> Mohad Abbasnejad <mohaddeseh.abbasnejad at gmail.com>
> *Sent:* Wednesday, August 12, 2020 8:16 AM
> *To:* users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
> *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:     mohaddeseh.abbasnejad at gmail.com
> Website:  academicstaff.uk.ac.ir/moabbasnejad
> ---------------------------------------------------------
>
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