[gpaw-users] FD vs LCAO vs PW

Fri Jul 4 01:25:11 CEST 2014

Hi JJ

The commit seems to revert a recent change to the documentation of hgh.  Is
this an accident?

Best regards
Ask

2014-07-01 20:13 GMT+02:00 Ask Hjorth Larsen <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>:
>
>  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>:
>>
>>>    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>:
>>>
>>>>  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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>>>>
>>>>
>>>>
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>>>>
>>>
>>>
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>>
>>
>>
>> --
>>   ------------------------------------------
>> PD Dr Michael Walter
>> Addresses:
>> - Fraunhofer IWM, Wöhlerstrasse 11, D-79108 Freiburg i. Br., Germany
>>   Tel.: +49 761 5142 493
>>  - Freiburg Materials Research Center, Stefan-meier-Str. 21, D-79104
>> Freiburg, Germany
>>    Tel: +49 761 203 4758
>>  email: Michael.Walter at fmf.uni-freiburg.de
>> www: http://omnibus.uni-freiburg.de/~mw767
>> publications: http://scholar.google.com/citations?user=vlmryKEAAAAJ&hl=en
>>
>>
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>>
>>
>
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