[Pw_forum] question on electron_dynamics and orthogonalization

[Silviu Zilberman]

Nicolas,

There is a difference in the way CP and PW handle USPP. In CP you have 
the small boxes around the augmented charge, that help reduce the 
unphysical charge oscillations. There should be a small difference 
between CP ans PW results. There are two ways to validate it: (a) use 
norm-conserving PP instead of USPP, or (b) increase the cut-off to 
reduce the charge oscillations in PW. In the former case the results 
should be identical, while in the later the difference should become 
smaller as you increase the cut-off.

Regards, Silviu.

Nichols A. Romero wrote:
> Nicola (or anyone else on this list),
>
> I am going to ask a question that get's asked on this list very
> frequently (possibly second only to "Why doesn't the code compile?").
>
> I am struggling with trying to get PWSCF and the CP code to agree. I
> am sure the PWSCF is correct, but I don't know about the CP
> calculation. All I want to immediately do with the CP is to calculate
> the ground state and have it agree with PWSCF. Though the next step is
> to do BO MD with the CP code (which I remember correctly, is still in
> the testing phase).
>
> I'm attaching a model problem I've been playing with for the last two
> days. I include the input and outputfiles. The US_PP are of the PBE
> RRKJ type that are found on the PWSCF website. It should run fairly
> quickly on a desktop computer.
>
> I would appreciate any help at this point. I'm sure that I am not
> understand the definition of some of the CP parameters. FYI, I am
> using the CVS version of Q-ESPRESSO as stated in my previous e-mail.
>
>
> Bests,
> On 3/28/06, Nicola Marzari <marzari at mit.edu> wrote:
>   
>> Nichols,
>>
>> I'll let Paolo or Kostya or Ismaila confirm, but my guess is that once
>> electron-dynamics is "cg" you want a gram-schmidt orthogonalization.
>>
>> We might implement an iterative ortho sometimes in the future, but I
>> believe at this stage gram-schmidt is the only choice.
>>
>> Note that the latest CVS (2-3 days ago) has a number of calbec calls
>> removed, and should be faster.
>>
>> We are still optimizing the code, but it should be fairly robust at this
>> stage - let us know of any feedback you might have.
>>
>>                                         nicola
>>
>>
>> Nichols A. Romero wrote:
>>
>>     
>>> Hey,
>>>
>>> This is a question about CP code (i.e. not PWSCF). I am using the CVS version.
>>>
>>> Are the keywords
>>>
>>> electron_dynamics & orthogonolization
>>>
>>> completely independent of each other when
>>> electron_dynamics = 'cg'
>>>
>>> Forgive, my ignorance. I am mostly familiar with the PWSCF component
>>> of Q-Espresso.
>>>
>>> When doing an initial 'cg' calculation to get the groundstate on the
>>> BO surface, doesn't the 'cg' routines impose the orthonomality
>>> constraint automattically? Why does one need a seperate
>>> *orthogonalization* keyword? (which has two different options?)
>>>
>>> Thanks,
>>> --
>>> Nichols A. Romero, Ph.D.
>>> 1613 Denise Dr. Apt. D
>>> Forest Hill, MD 21050
>>> 443-567-8328 (C)
>>> 410-306-0709 (O)
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
>>> http://www.democritos.it/mailman/listinfo/pw_forum
>>>       
>> --
>> ---------------------------------------------------------------------
>> Prof Nicola Marzari   Department of Materials Science and Engineering
>> 13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
>> tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu
>> _______________________________________________
>> Pw_forum mailing list
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>>
>>     
>
>
> --
> Nichols A. Romero, Ph.D.
> 1613 Denise Dr. Apt. D
> Forest Hill, MD 21050
> 443-567-8328 (C)
> 410-306-0709 (O)
>