[gpaw-users] FD vs LCAO vs PW
Jens Jørgen Mortensen
jensj at fysik.dtu.dk
Fri Jul 4 09:17:57 CEST 2014
On 07/04/2014 01:25 AM, Ask Hjorth Larsen wrote:
> Hi JJ
>
> The commit seems to revert a recent change to the documentation of
> hgh. Is this an accident?
Yes. Fixed now.
Jens Jørgen
>
> Best regards
> Ask
>
>
> 2014-07-01 20:13 GMT+02:00 Ask Hjorth Larsen <asklarsen at gmail.com
> <mailto:asklarsen at gmail.com>>:
>
> Hi
>
> Thank you very much. It's all quite fine with me.
>
> Best regards
> Ask
>
>
> 2014-07-01 9:44 GMT+02:00 Jens Jørgen Mortensen
> <jensj at fysik.dtu.dk <mailto:jensj at fysik.dtu.dk>>:
>
> On 07/01/2014 09:03 AM, Michael Walter wrote:
>> Dear Ask,
>>
>> would it be possible to put your nice summary to the gpaw-web
>> pages ? This could be useful for others and such thinks are
>> not easy to find in email conversations.
>
>
> After seeing Roberts email yesterday, I started to write
> something for the web-page:
>
> ###################################################
> The following table can guide you in choosing the right mode,
> but you
> better run some tests yourself also.
>
> ====================== ===== =========== =========
> FD LCAO PW
> ====================== ===== =========== =========
> memory consumption large small medium
> speed for small system slow fast fast
> speed for large system fast very fast slow
> Absolute convergence easy complicated very easy
> ====================== ===== =========== =========
>
> With LCAO, it can be hard to reach the complete basis-set
> limit and get absolute
> convergence of energies, whereas with FD and PW mode it is
> quite easy to do
> by decreasing the grid spacing or increasing the plane-wave
> cutoff energy.
> ##################################################
>
> But seeing Ask's brilliant reply, I also think that it would
> be valuable to have that on the web-page.
>
> Ask: Should I commit my piece and then you can add to it?
>
> Jens Jørgen
>
>
>>
>> Best,
>> Michael
>>
>>
>> 2014-06-30 21:53 GMT+02:00 Ask Hjorth Larsen
>> <asklarsen at gmail.com <mailto:asklarsen at gmail.com>>:
>>
>> Hi Robert!
>>
>> Generally:
>>
>> LCAO has the advantage over FD/PW that it's fast for
>> larger systems since you have fewer degrees of freedom in
>> the diagonalization.
>>
>> FD/PW have the advantage over LCAO that it's easy to
>> crank up the precision by setting grid spacing or
>> planewave cutoff.
>>
>> PW has the advantage over FD that planewaves are "nice"
>> (they tend to better represent wavefunctions) and you
>> need less to have a reasonable representation. Also the
>> planewaves don't suffer egg-box effect like grid points
>> do. Apparently stuff like response calculations are much
>> nicer in PW mode.
>>
>> FD has the advantage over PW that you can throw many CPUs
>> at domain decomposition. In PW, you can only parallelize
>> over k-points/spins/bands. If you want do do many
>> hundreds of atoms, PW would therefore be less useful.
>>
>> PW is extremely efficient for small-ish periodic systems.
>>
>> In GPAW specifically:
>>
>> PW has the slight disadvantage that it's new-ish and thus
>> more prone to things not working.
>>
>> I think PW is still the only mode that implements the
>> stress tensor.
>>
>> LCAO has the slight disadvantage that it's quite
>> different from the two other modes, and e.g. some
>> advanced functionals have not been implemented with LCAO.
>>
>> LCAO is very inefficient for systems where the cell is
>> smaller than the basis functions.
>>
>> Did I leave anything out? Any questions?
>>
>> Best regards
>> Ask
>>
>>
>>
>> 2014-06-30 17:48 GMT+02:00 Robert Warmbier
>> <Robert.Warmbier at wits.ac.za
>> <mailto:Robert.Warmbier at wits.ac.za>>:
>>
>> Dear GPAW users and developers,
>>
>> I was wondering if someone could provide a
>> comparative pro/con list for the different modes GPAW
>> supports. There is very little information on the
>> GPAW website, as far as I could find.
>> If there is already information and I missed it, I am
>> sorry.
>>
>> Best Robert
>>
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>>
>> --
>> ------------------------------------------
>> PD Dr Michael Walter
>> Addresses:
>> - Fraunhofer IWM, Wöhlerstrasse 11, D-79108 Freiburg i. Br.,
>> Germany
>> Tel.: +49 761 5142 493 <tel:%2B49%20761%205142%20493>
>> - Freiburg Materials Research Center, Stefan-meier-Str. 21,
>> D-79104 Freiburg, Germany
>> Tel: +49 761 203 4758 <tel:%2B49%20761%20203%204758>
>> email: Michael.Walter at fmf.uni-freiburg.de
>> <mailto:Michael.Walter at fmf.uni-freiburg.de>
>> www: http://omnibus.uni-freiburg.de/~mw767
>> <http://omnibus.uni-freiburg.de/%7Emw767>
>> publications:
>> http://scholar.google.com/citations?user=vlmryKEAAAAJ&hl=en
>>
>>
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