[Pw_forum] Using a big box model to calculating the energy of isolated atom
Hongsheng Zhao
zhaohscas at yahoo.com.cn
Sat Jul 30 02:23:56 CEST 2011
On 07/30/2011 04:55 AM, Masoud Nahali wrote:
>
> Dear Hongsheng
>
> In this case I think that the more important issue to be noticed is
> considering spin polarization for most of atoms. Many mistakes in this
> issue arise from not considering spin polarization.
> I guess Considering "Symmetry" may symmetrize the charge density and
> causes some changes in electronic structure of atom (population of
> orbitals) or may do reversely with nosym='true'.
> Also, it is impossible for me to describe this issue based on DFT and
> the exchange-correlation parts in details.
>
> In quantum chemistry software based on Gaussian type orbitals basis set
> (not plane wave basis set)
When using plane wave basis set, say, pwcsf/vasp/castep and so on, what
will happen in that case?
> we compare energy of an atom with considering
> different spin multiplicities then find the lowest energy and call it
> "ground state".
In plane-wave-basis-set based codes, we also can find the "ground
state", what's the differences between these two "ground state" obtained
by different basis sets?
> I can do it for some atoms (whatever you select) by
> Firefly software (former PC-GAMESS) and then you can compare it with the
> corresponding calculation by QE.
I want to know: does this comparison make sense?
> These days I am very busy and going on a journey so let me do it in a
> due course; contact me :)
Thanks a lot for your kindly help and reply ;-)
>
> Best Wishes
>
> Masoud
>
>
>
> --------------
> Masoud Nahali, Sharif University of Technology
> masoud.nahali at gmail.com <mailto:masoud.nahali at gmail.com>; a
> <http://alum.sharif.edu/%7Em_nahali>lum.sharif.edu/~m_nahali
> <http://lum.sharif.edu/~m_nahali>
>
> PSave a Tree . . . Please don't print this e-mail unless you really need to.
>
>
>
> Hongsheng Zhao Wrote :
>
> Thanks a lot for all of the helps on this topic. I've checked and
> read
> most the topics on this ML which are related to "calculating the energy
> of isolated atom". It seems this is a tricky thing based on most of
> the replies on this similar topics on this ML.
>
> Based on my understanding, till now, there are still some issues
> puzzling me on this topic:
>
> 1- On the manual of pwscf (p37), we can find the following descriptions:
>
> --------
> ...
> Specify nosym=.true. to avoid generation of additional k-points in low
> symmetry
> ...
> -----------
>
> I want to know, by using nosym=.true., what's the different on the
> k-points set obtained with the ones without using this option? For
> example, when using a bcc box with a atom at its center, what's the
> corresponding k-points set when using nosym=.true.?
>
> Furthermore, when we say a isolated atom, we mean a zero dimension
> system. So the corresponding BZ sampling by using gamma only should be
> OK. If so, there is no k-points issues at all - there only one k point
> should be considered. Hence I'm confused on the description given by
> the manual *avoid generation of additional k-points in low symmetry*.
> Any hints?
>
> 2- From this ML, I found the following notes:
>
> ---------
> while doing calculations for any zero dimensions you should always set
> nosym =.true.
> -----------
>
> Does this mean: when I do the calculations for isolated
> atom/molecule/nanocluster and so on, I should always set nosym =.true.?
>
> 3- Prof. Paolo Giannozzi given the following descriptions on some
> similar topic in this ML:
>
> ---------
> calculations on isolated atoms with plane waves are tricky.
> Compare your results with what you get with the atomic code,
> in which you can fix occupancies at will
> ------------
>
> My issue: how to fix the occupancies based on the results? Any
> examples?
>
> What do you mean by saying *at will*? If really is a thing *at will*,
> why should we do it?
>
> Regards
>
> >
> > On Thu, Jul 28, 2011 at 10:12 AM, Gabriele Sclauzero
> > <gabriele.sclauzero at epfl.ch <mailto:gabriele.sclauzero at epfl.ch>
> <mailto:gabriele.sclauzero at epfl.ch
> <mailto:gabriele.sclauzero at epfl.ch>>> wrote:
> >
> >
> > Il giorno 28/lug/2011, alle ore 01.55, Hongsheng Zhao ha scritto:
> >
> >> Hi all,
> >>
> >> I've learned that when using the a large-cell ( i.e., a big
> box ) to
> >> calculate the energy of isolated atom, it should be done without
> >> symmetry. But I'm not sure what's the meaning of the "without
> >> symmetry" here and how to ensure this when we using a a big box
> >> model
> >> for this purpose. Any hints on this issue?
> >
> > This is a FAQ on this forum: have you spent some time
> browsing the
> > archives?
> >
> > OK, I'll give you a hint: "nosym"... but use it with care!
> >
> > HTH
> >
> > GS
> >
> >>
> >> Regards
> >> --
> >> Hongsheng Zhao <zhaohscas at yahoo.com.cn
> <mailto:zhaohscas at yahoo.com.cn>
> >> <mailto:zhaohscas at yahoo.com.cn <mailto:zhaohscas at yahoo.com.cn>>>
> >> School of Physics and Electrical Information Science,
> >> Ningxia University, Yinchuan 750021, China
> >> _______________________________________________
> >> Pw_forum mailing list
> >> Pw_forum at pwscf.org <mailto:Pw_forum at pwscf.org>
> <mailto:Pw_forum at pwscf.org <mailto:Pw_forum at pwscf.org>>
> >> http://www.democritos.it/mailman/listinfo/pw_forum
> >
> >
> > ? Gabriele Sclauzero, EPFL SB ITP CSEA
> > / PH H2 462, Station 3, CH-1015 Lausanne/
> >
>
>
>
>
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--
Hongsheng Zhao <zhaohscas at yahoo.com.cn>
School of Physics and Electrical Information Science,
Ningxia University, Yinchuan 750021, China
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