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

[Stefano de Gironcoli]

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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