[Wien] difference of min- energy point and zero -force point

[Laurence Marks]

Two fundamental points about use of mini (or any minimization code):
1) The code only minimizes the energy for the problem you give it --
it cannot correct your errors.
2) Performing a constrained minimization where you fix certain atoms
is very, very dangerous and highly likely to give rubbish. Please do
not do this unless you are really confident that you know what you are
doing and have done a detailed analysis of the errors (which is a
topic that I do not believe has been discussed in the mailing list).

As Stefaan has suggested, the conditions that you are using are
suspect. For certain an energy convergence of 0.0001 Ryd and charge of
0.002 are both much too big. More reasonable are -ec 0.00005 -cc
0.0001 -fc 1.

If you are not doing a reasonable calculation, there is no reason why
the energy and forces should be consistent. In general, the fully
converged energy and forces are consistent to about 0.1 mRyd/au
(except for LDA+U or the hybrids where they are totally inconsistent);
there is no garuentee for unconverged results.

-- 
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
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