[Pw_forum] One minor bug, one not minor and two questions

[Laurence Marks]

Thanks.

Another question if I may. From the looks of PW/mix_rho.f90 you do not
use the weights in the Johnson paper, just a straight inverse of
betamix (what would be called Y^T Y in the optimization literature) at
lines 289-295? Have you considered a regularization, e.g. adding after
line 278 something like

        betamix(i,i)=betamix(i,i) + 1.D-7/iter_used

which is about right for your Al (001) example. The regularization
term (e.g. PRB 78, 075114 (2008)) is a bit empirical, although I might
be able to change this.

This is safe, so long as mix_rho.f90 is only used for mixing densities
during the scf iterations -- is it used elsewhere?

On Mon, Apr 11, 2011 at 5:12 AM, Stefano de Gironcoli <degironc at sissa.it> wrote:
> in my previous  post
>
> reminder -> remainder
>
> stefano
>
> On 04/11/2011 11:57 AM, Stefano de Gironcoli wrote:
>> dear Laurence Marks
>>
>>      thank you for contributing this patch for bfgs !
>>> A quick question. In the ion optimization it looks like you are
>>> starting from some iterpolation of the new density (i.e. "NEW-OLD
>>> atomic charge density approx. for the potential"), what is it?
>> if i remember correctly the charge density of the new positions is
>> written
>> as the superposition of atomic charges plus a reminder which is computed
>> as the scf rho minus the superposition of atomic charges at the old
>> positions.
>>
>> rho_trial_new = rho_atomic_newR + (rho_scf_oldR - rho_atomic_oldR)
>>
>> this is done for the first ionic iteration and assumes that the main
>> change in the density is due to rigid displacement of atomic-like
>> contributions.
>>
>> At subsequent iterations the reminder (rho_scf_oldR-rho_atomic_oldR)
>> can be extrapolated on the basis of its change in the previous couple
>> of iterations
>>
>>  Stefano de Gironcoli
>>
>> On 04/11/2011 01:11 AM, Laurence Marks wrote:
>>> For completeness, added proper comments.
>>>
>>> On Sun, Apr 10, 2011 at 4:13 PM, Laurence Marks
>>> <L-marks at northwestern.edu>  wrote:
>>>> A very minor bug that you probably known: some of the routines in
>>>> S3DE/iotk/src have lines such as "# 1 "iotk_write_interf.spp" ". Most
>>>> sensible preprocessors will ignore these and just give warnings.
>>>>
>>>> A more serious bug. Your bfgs code does not have curvature failure
>>>> conditions trapped. Not to get too technical here (contact me offline
>>>> if needed), unless one is close to the minimum bfgs fails unless this
>>>> is done. The failure is well documented, less well known, as is the
>>>> change needed (at least the standard form). I am attaching a modified
>>>> version with the standard fix. It gives a slightly lower energy with
>>>> smaller forces in about the same number of iterations -- due to
>>>> numerical limitations I cannot compare exactly with your reference
>>>> directory. I am a newbie with this code so there could be other
>>>> repercussions of this change if it is used for something except
>>>> optimizing the atomic positions, so perhaps a few tests are
>>>> appropriate for harder problems.
>>>>
>>>> A quick question. In the ion optimization it looks like you are
>>>> starting from some iterpolation of the new density (i.e. "NEW-OLD
>>>> atomic charge density approx. for the potential"), what is it?
>>>>
>>>> Another quick one: line 1766 of install/configure.ac nulls out
>>>> scalapack_libs and the lines below look like they are special tests,
>>>> which seems to be inconsistent with line 150 and standard protocols of
>>>> letting the user define input variables. (OK, while scalapack is
>>>> probably only useful for large problems I might want to do some.)
>>>>
>>>> --
>>>> Professor Laurence Marks
>>>> Department of Materials Science and Engineering
>>>> MSE Rm 2036 Cook Hall
>>>> 2220 N Campus Drive
>>>> Northwestern University
>>>> Evanston, IL 60208, USA
>>>> Tel: (847) 491-3996 Fax: (847) 491-7820
>>>> email: L-marks at northwestern dot edu
>>>> Web: www.numis.northwestern.edu
>>>> Chair, Commission on Electron Crystallography of IUCR
>>>> www.numis.northwestern.edu/
>>>> Research is to see what everybody else has seen, and to think what
>>>> nobody else has thought
>>>> Albert Szent-Gyorgi
>>>>
>>>
>>>
>>>
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>>
>>
>
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-- 
Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
Evanston, IL 60208, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
Web: www.numis.northwestern.edu
Chair, Commission on Electron Crystallography of IUCR
www.numis.northwestern.edu/
Research is to see what everybody else has seen, and to think what
nobody else has thought
Albert Szent-Gyorgi