[Pw_forum] question on electron_dynamics and orthogonalization
Paolo Giannozzi
giannozz at nest.sns.it
Thu Mar 30 11:55:38 CEST 2006
On Wednesday 29 March 2006 22:26, Nichols A. Romero wrote:
> I am struggling with trying to get PWSCF and the CP code to agree.
> [...] I'm attaching a model problem I've been playing with for the
> last two days.
thank you for providing simple, useful examples.
* as mentioned by Nicola M., the agreement between energies and
forces in PW and CP in your test is very good, once you take into
account the different units
* there is a difference in the definition of V(0) that affects, as a rigid
shift, the eigenvalues: see attached notes. I don't know which one
is "better" (i.e. converges faster to the limit of infinite cell size).
I like the PW definition better: the CP one is in my opinion arbitrary.
* The convergence of eigenvalues with cutoff may be quite slow,
expecially for higher-energy states, and different in CP and PW
(because of the "small boxes" in CP, as mentioned by Silviu)
* two rather exotic bugs in stress calculation in PW:
- gamma point + l=0 nonlocality only + parallelization
- gamma point + LSDA
have been fixed only very recently (8 and 16 march)
* there is a known problem with stress calculation in CP, related to
l>0 nonlocality. The error is rather small but not negligible. Sooner
or later we'll find it. This is the bug Nicola M. was referring to.
* Stresses calculated in CP with the 'cg' option in your example are
completely bogus. Most likely, stress calculation is not implemented
in the 'cg' case. This is a different bug from the one above
Paolo
--
Paolo Giannozzi e-mail: giannozz at nest.sns.it
Scuola Normale Superiore Phone: +39/050-509876, Fax:-563513
Piazza dei Cavalieri 7 I-56126 Pisa, Italy
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