[Pw_forum] new bfgs: strange behavior doing vc-relax

Laurence Marks L-marks at northwestern.edu
Mon Apr 18 21:35:00 CEST 2011

The latest BFGS has a curvature trap which can change the behavior
particularly if you have too few k-points. Can you please do

grep -e "!    tot" -e bfgs WHATEVER.out

(where WHATEVER is relevant) and send it to me, perhaps at my private
email (or the full .out file). I am not an expert with QE, but might
be able to say something.

2011/4/18 Максим Попов <max.n.popov at gmail.com>:
> Dear QE developers,
> comparing vc-relax calculations between BFGS(4.2.1) and the latest BFGS(from
> CVS) I faced  with a following problem:
> the newest QE calculates one extra point after achieving convergence
> criteria (etot_conv_thr,force_conv_thr,press_conv_thr),
> which leads to slightly higher total energy.
> Here are the two latest energies from outputs:
>        v.4.2.1                       CVS(18.04.2011)
> -242.66342170 Ry       -242.66342267 Ry
> -242.66342336 Ry       -242.66284562 Ry
> One can see that there is a good agreement between the last energy by
> v.4.2.1 and next to the last by CVS-version, whereas
> the last energy by CVS is higher by ~ 0.5 mRy.
> I tried relax (cell shape fixed) also - it works fine, no extra point
> calculation.
> --
> Best regards, Max Popov
> Ph.D. student
> Materials center Leoben (MCL), Leoben, Austria.
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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
Research is to see what everybody else has seen, and to think what
nobody else has thought
Albert Szent-Gyorgi

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