[Pw_forum] dedicated wfcdir for PWCOND

Thu Nov 19 18:20:19 CET 2009

J. D. Burton wrote:
> Dear Gabriele,
> 
>>> Thanks for the info. I obviously knew the energy-dependent wavefunctions
>>> calculated in PWCOND are different from the Bloch eigenvectors generated
> by
>>> the periodic pw.x. 
> 
>> Not necessarily. I think that the propagating Bloch waves (i.e. those at
> real k vector) 
>> computed in the leads should coincide with those from pw.x, while the
> evanescent states 
>> are not present in pw.x due to PBCs along z, obviously.
> 
> Let me rephrase: The wavefunctions generated by pw.x are, in general,
> fundamentally useless for the PWCOND calculation because they are only
> generated on a comparatively sparse k-mesh for self-consistency, whereas
> PWCOND uses the propagating modes (i.e. complex kz values, etc) of the leads
> at a given input energy (which in general is not on the list of eigenvalues
> found in pw.x) on a much more dense mesh of k_perp points.

That's right. The convergence of total energy can be different from that of the 
transmission. Anyway, from my experience, it is not always said that the k_perp grid 
needed to converge the transmission has to be more dense than that needed for the total 
energy. Actually it depends on the features of the band structure next to the target 
scattering energy (see PRB 72, 033401 (2005) or appendix of PRB 74, 165416 (2006) for 
instance).

HTH

GS

> 
> This is not to say that if you were to use pw.x to generate a wfc at just
> the right (real) k_z at just the right k_perp corresponding to just the
> right energy that it would be different from that found by PWCOND... it's
> just that would be a pointless procedure.
> 
> Cheers,
> J. D.
> 
> ************************************
> J. D. Burton, Ph.D.
> jlz101 at unlserve.unl.edu
> University of Nebraska Lincoln
> Physics and Astronomy
> Office Ph. (402) 472 2499
> Mobile Ph. (402) 419 9918
> 213C Ferguson Hall
> ************************************
> "The job of a scientist is to generate wrong ideas as fast as possible."
> -- Murray Gell-Mann
> 
> 
> -----Original Message-----
> From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
> Behalf Of Gabriele Sclauzero
> Sent: Thursday, November 19, 2009 10:36 AM
> To: PWSCF Forum
> Subject: Re: [Pw_forum] dedicated wfcdir for PWCOND
> 
> 
> 
> J. D. Burton wrote:
>> Dear Gabriele,
>>
>> Thanks for the info. I obviously knew the energy-dependent wavefunctions
>> calculated in PWCOND are different from the Bloch eigenvectors generated
> by
>> the periodic pw.x. 
> 
> Not necessarily. I think that the propagating Bloch waves (i.e. those at
> real k vector) 
> computed in the leads should coincide with those from pw.x, while the
> evanescent states 
> are not present in pw.x due to PBCs along z, obviously.
> 
>> I just never noticed that those wfc files made by PWCOND
>> were empty! So I guess everything is held in the RAM on worker nodes,
> which
>> means I just need to be careful about number of processors (available
>> memory) vs system size.
> 
> You are right. If the system is very big, the memory requirement may be huge
> and so you 
> should be careful. You can try to reduce the G_perp basis set in the
> perpendicular 
> directions by playing with ewind and epsproj parameters.
> 
> HTH
> 
> GS
> 
>> Thanks again,
>> J. D.
>>
>> ************************************
>> J. D. Burton, Ph.D.
>> jlz101 at unlserve.unl.edu
>> University of Nebraska Lincoln
>> Physics and Astronomy
>> Office Ph. (402) 472 2499
>> Mobile Ph. (402) 419 9918
>> 213C Ferguson Hall
>> ************************************
>> "The job of a scientist is to generate wrong ideas as fast as possible."
>> -- Murray Gell-Mann
>>
>> -----Original Message-----
>> From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
>> Behalf Of Gabriele Sclauzero
>> Sent: Thursday, November 19, 2009 1:47 AM
>> To: PWSCF Forum
>> Subject: Re: [Pw_forum] dedicated wfcdir for PWCOND
>>
>> Dear JD,
>>
>> J. D. Burton wrote:
>>> Hi everyone,
>>>
>>>  
>>>
>>> When running PWCOND, is there a way to keep .wfc* files in a dedicated 
>>> directory other than outdir? I know this can be done in pw.x and it 
>>> really helps minimize network communication during parallel jobs by 
>>> keeping the wfc files on the worker nodes. If it's not there, then I
>> Actually pwcond.x in the present implementation does not use the
>> wavefunctions produced by 
>> pw.x, but only the charge density and the informations in the
> data-file.xml.
>> The only thing needed to run a standard pwcond calculation is the
>> prefix.save directory. 
>> If the wavefunction files prefix.wfc are not present, the code will create
>> them in outdir, 
>> but those files will NOT be used during the calculations (in fact, if you
>> look at their 
>> size it should be zero).
>> If there are already the wavefunction files from the previous pw.x
>> calculation, they will 
>> be left untouched.
>> This means also that you can do the pwcond calculation with any number of
>> processors, 
>> irrespectively of how many you used for the pwscf one.
>> 	
>>> suppose I can try to put it into PWCOND myself. unless there is some 
>>> fundamental difficulty that I haven't thought of yet.
>> If you are volunteering to extend to pwcond the usage of wfc_dir feature,
>> you're welcome! 
>> Anyway I don't feel there is the need for that at the moment, since, as I
>> told you, there 
>> is no network communication issue related to wavefunction files in pwcond.
>>
>>
>> HTH
>>
>> GS
>>
>>>  
>>>
>>> Cheers,
>>>
>>> J. D.
>>>
>>>  
>>>
>>> ************************************
>>>
>>> J. D. Burton, Ph.D.
>>>
>>> jdburton1 at gmail.com
>>>
>>> University of Nebraska Lincoln
>>>
>>> Physics and Astronomy
>>>
>>> Office Ph. (402) 472 2499
>>>
>>> Mobile Ph. (402) 419 9918
>>>
>>> 213C Ferguson Hall
>>>
>>> ************************************
>>>
>>> "The job of a scientist is to generate wrong ideas as fast as possible."
>>> -- Murray Gell-Mann
>>>
>>>  
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
>>> http://www.democritos.it/mailman/listinfo/pw_forum
> 

-- 

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| Gabriele Sclauzero, PhD Student                  |
| c/o:   SISSA & CNR-INFM Democritos,              |
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