[Wien] RKMAX

[Yundi Quan]

Thanks a lot. Stefan. I'm extreme happy to have received your email.
Actually, I was reading your notes today. It is very helpful.




Yundi

On Mon, Feb 13, 2012 at 10:50 PM, Stefaan Cottenier <
Stefaan.Cottenier at ugent.be> wrote:

>
>  Hi, What is the criteria for choosing RKMAX? I changed RKMAX then the
>> total energy and Fermi energy also changed.  As I increase RKMAX, the
>> total energy becomes smaller and Fermi energy become larger.
>> RKMAX    Total energy            Fermi energy
>> *7              -41000.012971        0.53253
>>
>> 8              -41000.07176987     0.54963
>> 9              -41000.08216064     0.5621
>>
>
>
> The total energy will keep decreasing with increasing basis set size (cfr.
> variational principle). And so will the Fermi energy, due to the way the
> energy reference is defined in wien2k (see Sec. 6.2 of
> http://www.wien2k.at/reg_user/**textbooks/DFT_and_LAPW-2_**cottenier.pdf<http://www.wien2k.at/reg_user/textbooks/DFT_and_LAPW-2_cottenier.pdf>
> ).
>
> For studying convergence, you should not monitor the energy at a given
> volume, but rather the energy difference between two volumes (or other
> observable properties).
>
> Stefaan
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