[gpaw-users] some question about GPAW

[Jess Wellendorff Pedersen]

Dear Wei-Bing,

It appears that those particular GPAW wiki pages that you refer to have 
not been updated for some time. We apologize for this.
The answers to your questions are simple:

Wei-Bing Zhang wrote:
>
> Dear all
>
>  
>
> I am trying to do some calculations using GPAW. But I found something 
> which I can’t understand fully.
>
> 1) On the webpage 
> https://wiki.fysik.dtu.dk/gpaw/tutorials/bandstructures/bandstructures.html 
> there is a sentence “One should note that as GPAW only works with 
> orthorhombic cells …..”.
>
> Does this means one has to use orthorhombic cells in the 
> calculations??  I use a non-orthorhombic cell for surface calculation 
> with GPAW, but the code didn’t complaint.  I want to know whether the 
> results including energy and geometry obtained using non-orthorhombic 
> cell in GPAW is valid or not???
>
GPAW natturally handles non-orthorhombic unit cells, and total energy as 
well as forces are completely valid.
>
> 2) On the webpage 
> https://wiki.fysik.dtu.dk/gpaw/documentation/xc/vdw.html#doing-a-van-der-waals-calculation 
>
>
> I found the “vdw = FFTVDWFunctional(nspins=1, verbose=True)”. It seems 
> that there is a keywords “nspin”, which should control spin polarized 
> or spin paired calculations. However, in the newer version GPAW, I 
> can’t find a keyword relate to spin polarized calculations. I want to 
> know whether the new version off vdW xc can treat the spin polarized 
> calculations or not??
>
The GPAW exchange-correlation library has been rearranged such that the 
vdW-DF type functionals (vdW-DF and vdW-DF2) are used on the same 
footing as e.g. LDA and GGA xc-functionals. This means that you simple 
do " xc = 'vdW-DF' " or " xc = 'vdW-DF2' " in order to use these to 
functionals. Spinpolarization is handled automatically "behind the 
scenes" or, if the ASE Atoms object has no magnetic moments but you for 
whatever reason still wants GPAW to do a spinpolarized calculation, you 
enforce this with "spinpol=True" in the GPAW object.
Example:
sys = Atoms(.......)
calc = GPAW(xc='vdW-DF', txt='out.txt',spinpol=True)
sys.set_calculator(calc)

cheers,
Jess Wellendorff
>
>  
>
> Thanks and Best Wishes
>
>  
>
> Wei-Bing Zhang
>
> ------------------------------------------------------------------------
>
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-- 
Jess Wellendorff Pedersen

ph.d student
Center for Atomic-scale Materials Design (CAMD)
Department of Physics
Technical University of Denmark (DTU)