Re: [QE-users] Question on negative phonon frequency at Gamma point

[Tenney, Craig Michael]

Hello Yusuf,


A negative phonon frequency can be a sign that your material is dynamically 
unstable to vibrations.


This does not pose a problem in calculating Tc values.  You can include the 
negative frequencies and Tc will be slightly reduced, or you can manually cut 
them out if you think it makes more sense in your case.


Hope this helps, if you have any more questions, feel free to ask,


Craig Tenney

Washington State University

Graduate Student


From: users  on behalf of Yusuf Zuntu 

Sent: Thursday, March 22, 2018 9:41:23 PM
To: users@lists.quantum-espresso.org
Subject: [QE-users] Question on negative phonon frequency at Gamma point

Dear all,

Please how do you get rid of a negative phonon frequency at a Gamma point. I 
have done some trial calculations for two different 2D materials. Please find 
the results details below:

System 1:

ph.x results at Gamma point

 q = (0.0   0.0   0.0 )

 **
 freq (1) =  -0.716980 [THz] = -23.915891 [cm-1]
 freq (2) =   1.170257 [THz] =  39.035571 [cm-1]
 freq (3) =   2.301718 [THz] =  76.777040 [cm-1]
 freq (4) =   4.692676 [THz] = 156.530836 [cm-1]
 freq (5) =   6.547729 [THz] = 218.408714 [cm-1]
 freq (6) =   7.575469 [THz] = 252.690440 [cm-1]
 freq (7) =   7.954771 [THz] = 265.342590 [cm-1]


matdyn.x results

diagonalizing the dynamical matrix ...

 q =   0.  0.  0.
 **
 freq (1) =  -0.168246 [THz] =  -5.612090 [cm-1]
 ( -0.205675   0.00-0.162406   0.00-0.049537   0.00   )
 ( -0.204095   0.00-0.166786   0.00-0.047497   0.00   )
 ( -0.202604   0.00-0.168584   0.00-0.038435   0.00   )
 ( -0.204187   0.00-0.166901   0.00-0.037977   0.00   )
 ( -0.204822   0.00-0.164879   0.00-0.035645   0.00   )
 ( -0.204067   0.00-0.159939   0.00-0.043878   0.00   )



System 2:

ph.x results at Gamma point

 q = (0.0   0.0   0.0 )

 **
 omega( 1) =  -2.676536 [THz] = -89.279630 [cm-1]
 omega( 2) =   2.176387 [THz] =  72.596456 [cm-1]
 omega( 3) =   2.268904 [THz] =  75.682505 [cm-1]
 omega( 4) =   2.781243 [THz] =  92.772280 [cm-1]
 omega( 5) =   2.831070 [THz] =  94.434329 [cm-1]
 omega( 6) =   5.362633 [THz] = 178.878184 [cm-1]
 omega( 7) =   5.391573 [THz] = 179.843530 [cm-1]


matdyn.x results

diagonalizing the dynamical matrix ...

 q =   0.  0.  0.
 **
 omega( 1) =  -0.081634 [THz] =  -2.723002 [cm-1]
 ( -0.270214   0.00-0.101393   0.00-0.001203   0.00   )
 ( -0.270014   0.00-0.100654   0.00 0.001122   0.00   )
 ( -0.270492   0.00-0.099822   0.00 0.003548   0.00   )
 ( -0.270726   0.00-0.100219   0.00 0.003104   0.00   )
 ( -0.271070   0.00-0.100621   0.00 0.006056   0.00   )
 ( -0.270797   0.00-0.101038   0.00 0.002118   0.00   )
 ( -0.270725   0.00-0.100220   0.00-0.002122   0.00   )


Lastly, do you think the results above will affect Tc calculations. If Yes, 
please advice me on what to do to remove the negative frequencies in both cases.

Yusuf Zuntu
PhD candidate
School of Physics
USM, Maalysia




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[QE-users] Updated virtual.x to virtual_v2.x

[Jingyang Wang]

Dear QE developers,

Since I realized some time ago that the problem of virtual.x not being able
to read the UPF v2 format has been there for a long time, and nobody seemed
to have the time or need to fix it, I decided to do it myself. The updated
version is named "virtual_v2.x"; as the name suggests, it properly
generates a virtual crystal pseudopotential in UPF v2 format from two UPF
v2 pseudopotentials. The nice feature about this code is that, instead of
using its own independent read and write routine in /upftools, it uses the
standard modules "upf_module" and "write_upf_v2" in /Modules. I have
compiled the code with QE v5.2.0 and successfully generated the correct
pseudopotential file, although there seems to be some kind of problem for
later versions of QE (not sure what it is). I'm wondering if there is a way
to incorporate this code to the latest QE depository? Thank you very much!

Best regards,
Jingyang Wang


Jingyang Wang
Ph.D. candidate
School of Applied and Engineering Physics
Cornell University
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[QE-users] stresses and forces in applied electric fields

[Ronald Cohen]

>> 
>> I am wondering the status of including stresses (and forces?) in applied 
>> electric fields. I find the following code:
>>  !
>>   !   Electric field contribution
>>   !
>>   sigmael(:,:)=0.d0
>>   sigmaion(:,:)=0.d0
>>   !the following is for calculating the improper stress tensor
>> !  call stress_bp_efield (sigmael )
>> !  call stress_ion_efield (sigmaion )
>> 
>> but the commented out routines do not exist. Also, the berrys_phase forces 
>> contribution seems to include only the force on the ion core. Any comments 
>> on this would be appreciated, especially the name of the person working on 
>> this.
>> 
>> Sincerely,
>> 
>> Ron
>> 
>> ---
>> Ronald Cohen
>> Geophysical Laboratory
>> Carnegie Institution
>> 5251 Broad Branch Rd., N.W.
>> Washington, D.C. 20015
>> rco...@carnegiescience.edu 
>> office: 202-478-8937 
>> skype: ronaldcohen
>> https://twitter.com/recohen3 
>> https://www.linkedin.com/profile/view?id=163327727 
>>   
>> 
> 



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Re: [QE-users] stress in electric fields

[Paolo Giannozzi]

Unfortunately, nobody is working on this and nobody knows who worked on this

Paolo

On Thu, Mar 15, 2018 at 12:03 PM, Cohen, Ronald 
wrote:

> I am wondering the status of including stresses (and forces?) in applied
> electric fields. I find the following code:
>  !
>   !   Electric field contribution
>   !
>   sigmael(:,:)=0.d0
>   sigmaion(:,:)=0.d0
>   !the following is for calculating the improper stress tensor
> !  call stress_bp_efield (sigmael )
> !  call stress_ion_efield (sigmaion )
>
> but the commented out routines do not exist. Also, the berrys_phase forces
> contribution seems to include only the force on the ion core. Any comments
> on this would be appreciated, especially the name of the person working on
> this.
>
> Sincerely,
>
> Ron
>
> ---
> Ronald Cohen
> Geophysical Laboratory
> Carnegie Institution
> 5251 Broad Branch Rd., N.W.
> Washington, D.C. 20015
> rco...@carnegiescience.edu
> office: 202-478-8937 <(202)%20478-8937>
> skype: ronaldcohen
> https://twitter.com/recohen3
> https://www.linkedin.com/profile/view?id=163327727
>
>
>
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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Re: [QE-users] a question on k-points

[Paolo Giannozzi]

No. For grids given as lists of k-points, symmetry-inequivalent points are
added, but symmetry-equivalent points are not removed.

Paolo

On Mon, Mar 26, 2018 at 4:43 PM, Yi Wang  wrote:

> Hi,
>
> When doing SCF calculations, if I manually input a set of full grid
> k-points using the card "K_POINTS crystal" without any symmetry
> reduction, will pw.x automatically do the reduction with respect to the
> symmetry? (assuming nosym=.false.)
>
> Many thanks.
>
> Yi Wang
> Nanjing University of Science and Technology
>
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Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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[QE-users] a question on k-points

[Yi Wang]

Hi,When doing SCF calculations, if I manually input a set of full grid k-points using the card "K_POINTS crystal" without any symmetry reduction, will pw.x automatically do the reduction with respect to the symmetry? (assuming nosym=.false.)Many thanks.Yi WangNanjing University of Science and Technology



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[QE-users] Different output information in phonon calculation of 'GRID' and 'SPLIT'.

[黄志硕]

Dear all QE users,

I am calculating phonon dispersion using two modes of PH module of quantum 
espresso. One mode is to split total calculation into calculations of each 
irreducible q point (SPLIT), while the other is the GRID calculation as the 
demonstrated in the GRID_example, which is to take all the irreducible 
representations into consideration. However, the output files shows different 
information when I use these two method to calculate phonon frequency with the 
same structure and scf input. The main difference is that in the output of GRID 
method there is a warning shown below:
##
 Starting wfc are  267 atomic wfcs

Possibly too few bands at point1  -0.12500   0.12500   0.12500
Possibly too few bands at point2   0.37500  -0.37500   0.62500
Possibly too few bands at point3  -0.37500   0.37500  -0.12500
Possibly too few bands at point4   0.12500  -0.12500   0.37500
…
…
…
Possibly too few bands at point   87  -1.12500  -0.37500  -0.37500
Possibly too few bands at point   88  -0.62500  -0.87500   0.12500
##
While there is no such information in the output file of SPLIT method. 

The input of GRID method for each irreducible representation is shown below 
##
Phonon of K3C60
 &inputph
  tr2_ph=1.0d-17,
  prefix='K3C60',
  ldisp=.true.
  nq1=2, nq2=2, nq3=2
  start_q=2
  last_q=2
  start_irr=’irr_num’,
  last_irr=’irr_num’,
  amass(1)=12
  amass(2)=39.1
  outdir='./',
  fildyn='K3C60.dynG',
  reduce_io = .true.
 /
##
And the input of GRID method after collecting all the information of each 
irreducible representation is 
##
Phonon of K3
 &inputph
  tr2_ph=1.0d-17,
  prefix='K3C60',
  ldisp=.true.
  nq1=2, nq2=2, nq3=2
  recover=.true.,
  start_q=2
  last_q=2
  amass(1)=12
  amass(2)=39.1
  outdir='./',
  fildyn='K3C60.dynG',
  reduce_io = .true.
 /
##

And the input of SPLIT method is 
##
Phonon of K3C60
 &inputph
  tr2_ph=1.0d-17,
  prefix='K3C60',
  ldisp=.true.
  nq1=2, nq2=2, nq3=2
  start_q=2
  last_q=2
  amass(1)=12
  amass(2)=39.1
  outdir='./',
  fildyn='K3C60.dynG',
  reduce_io = .true.
 /
##

Why is there the difference information in the output file for the same 
structure and scf input? I will appreciate it if anyone could give me any 
information about that.

Best regards
Zhishuo Huang

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Re: [QE-users] Meaning of some terms in input file

[Paolo Giannozzi]

In Doc/INPUT_PW.* all input variables are (more or less) described

Paolo

On Mon, Mar 26, 2018 at 6:25 AM, ade wale  wrote:

> Hi,
> Please I need to know the meaning of the parameter/terms used in input
> file of pwscf.(for examples; degauss, calculation:nscf,scf,relax...)
> Is anybody with text that explain these?
> Cheer
>
>
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-- 
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Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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Re: [QE-users] CPMD simulation at given pressure and temperature

[Paolo Giannozzi]

On Sun, Mar 25, 2018 at 10:22 AM, LEUNG Clarence 
wrote:

 when I set the pressure, it will stop with any error.
>
> tabps= .true. ,
> /
> &PRESS_AI
> abivol=.true. ,
> P_ext = 0.01,
> /
>

these options are used for pressure applied to finite systems. It is an
exotic case for which no test is available and that must be considered
unmaintained. No later than a few days ago I noticed a mistake there:
https://gitlab.com/QEF/q-e/commit/5351289d29ba499312462c0c76c0e8dc80ca9569

Paolo
-- 
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Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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