Re: [Pw_forum] Negative freuqencies for extrapolating points

2016-08-25 Thread Elio Physics 
Dear Professor Paulo and Fransesco,


thanks for your help and suggestions




From: pw_forum-boun...@pwscf.org  on behalf of 
Paolo Giannozzi 
Sent: Thursday, August 25, 2016 12:41 PM
To: PWSCF Forum
Subject: Re: [Pw_forum] Negative freuqencies for extrapolating points

I am aware of other cases in which acoustic phonon frequencies close to q=0 
behave in a funny way. It happens in very small regions and resists to standard 
attempts (increasing convergence etc.) to get rid of it. No explanation and no 
fix available for now.

Paolo

On Thu, Aug 25, 2016 at 4:03 PM, Elio Physics 
mailto:elio-phys...@live.com>> wrote:

Dear all,


I have calculated the frequencies for a structure. All frequencies were 
positive except for a few "extrapolated" points very close to the Gamma point 
which were negative in the range of -1.45 cm^-1. Due to this the dispersion 
curve near the Gamma point looked a bit funny (but looks pretty good 
elsewhere).  I tried the calculations with 2 different phonon grids. Any reason 
why this is happening? Do i have to lower  tr2_ph more (it is already 10^(-19)!)


Any help would be appreciated.


Elio

Fed Uni of Rondonia

Brazil


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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: [Pw_forum] Negative freuqencies for extrapolating points

2016-08-25 Thread Paolo Giannozzi 
I am aware of other cases in which acoustic phonon frequencies close to q=0
behave in a funny way. It happens in very small regions and resists to
standard attempts (increasing convergence etc.) to get rid of it. No
explanation and no fix available for now.

Paolo

On Thu, Aug 25, 2016 at 4:03 PM, Elio Physics  wrote:

> Dear all,
>
>
> I have calculated the frequencies for a structure. All frequencies were
> positive except for a few "extrapolated" points very close to the Gamma
> point which were negative in the range of -1.45 cm^-1. Due to this the
> dispersion curve near the Gamma point looked a bit funny (but looks pretty
> good elsewhere).  I tried the calculations with 2 different phonon grids.
> Any reason why this is happening? Do i have to lower  tr2_ph more (it is
> already 10^(-19)!)
>
>
> Any help would be appreciated.
>
>
> Elio
>
> Fed Uni of Rondonia
> Brazil
>
>
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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: [Pw_forum] Negative freuqencies for extrapolating points

2016-08-25 Thread Francesco Pelizza 
In my experience, increasing also the convergence for forces and total 
energy of the scf cycle you perform before the neb.x run, helps a lot to 
clean negative frequencies.



Then, all other cutoffs and settings that increase amount of memory and 
cpu time, can helps, sometimes significantly, sometimes their not enough.



Before the phonon, a proper lattice relaxation with higher parameters 
than default value for forces, total energy and eventually even electron 
convergence (as also wavefunction, charge density, etc..), helps much 
more to bring your model to the highest converged condition than just 
increasing parameters thresholds on phonon that can make the phonon a 
jurassic waiting.



These are the reflections  helped me more


Francesco

Strathclyde




On 25/08/16 15:03, Elio Physics wrote:


Dear all,


I have calculated the frequencies for a structure. All frequencies 
were positive except for a few "extrapolated" points very close to the 
Gamma point which were negative in the range of -1.45 cm^-1. Due to 
this the dispersion curve near the Gamma point looked a bit funny (but 
looks pretty good elsewhere).  I tried the calculations with 2 
different phonon grids. Any reason why this is happening? Do i have to 
lower  tr2_ph more (it is already 10^(-19)!)



Any help would be appreciated.


Elio

Fed Uni of Rondonia

Brazil



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[Pw_forum] Negative freuqencies for extrapolating points

2016-08-25 Thread Elio Physics 
Dear all,


I have calculated the frequencies for a structure. All frequencies were 
positive except for a few "extrapolated" points very close to the Gamma point 
which were negative in the range of -1.45 cm^-1. Due to this the dispersion 
curve near the Gamma point looked a bit funny (but looks pretty good 
elsewhere).  I tried the calculations with 2 different phonon grids. Any reason 
why this is happening? Do i have to lower  tr2_ph more (it is already 10^(-19)!)


Any help would be appreciated.


Elio

Fed Uni of Rondonia

Brazil

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Re: [Pw_forum] Error has not been solved

2016-08-25 Thread Paolo Giannozzi 
Actually it is not that simple: apparently one of the values for DFT,
either read from pseudopotentials or provided in input, has a malformed
syntax.

Paolo

On Thu, Aug 25, 2016 at 2:21 PM, stefano de gironcoli 
wrote:

> Dear Mohammadreza,
>   the error means that you are using two pseudo-potentials that have been
> generated with two different functionals. in particular the gradient
> corrected functional for exchange appears to be in conflict.
>   check your pseudo-potentials
> stefano
>
> On 25/08/2016 14:00, mohammadreza hosseini wrote:
>
> Dear giannozzi
>
> I studied your message about my error " conflicting igcx value " but  i
> could not see this part at my pseudo file. What variables are conflicting
> exactly ?
>
> Best
> mohammadreza
>
>
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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: [Pw_forum] Error has not been solved

2016-08-25 Thread stefano de gironcoli 

Dear Mohammadreza,
  the error means that you are using two pseudo-potentials that have 
been generated with two different functionals. in particular the 
gradient corrected functional for exchange appears to be in conflict.

  check your pseudo-potentials
stefano

On 25/08/2016 14:00, mohammadreza hosseini wrote:

Dear giannozzi
I studied your message about my error " conflicting igcx value " but  
i could not see this part at my pseudo file. What variables are 
conflicting exactly ?

Best
mohammadreza


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[Pw_forum] Error has not been solved

2016-08-25 Thread mohammadreza hosseini 
Dear giannozzi

I studied your message about my error " conflicting igcx value " but  i 
could not see this part at my pseudo file. What variables are conflicting 
exactly ?

Best
mohammadreza___
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