[Wien] O2 molecule continue (rmt issue)
Laurence Marks
L-marks at northwestern.edu
Mon Nov 13 18:53:58 CET 2017
Let me add one important thing to what Peter sent. My experience is that
the atomic positions are only weakly sensitive to the exact parameters
used, although this may not be true if you are doing phonons. Hence it has
always worked well for me to calculate (including MSR1a relaxations) using
decent parameters, and only at the end when everything is done use
clmextrapol to make all the RMTs, k-points, oversampling, RKMAX etc
consistent.
One caveat. If you are exploring a large set of different possible
structures (e.g. for a surface) it does help to stay somewhat consistent,
as you can then prescreen structures whose energies are way high (e.g.
1eV/1x1 higher) and you don't need to perfect them.
On Mon, Nov 13, 2017 at 11:30 AM, Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:
> Thanks for the correction.
>
> With respect to your other questions:
>
> In order to save cpu time, I would do (at least for the more complicated
> compounds, not necessarily for BaO, which is fast anyway) all
> calculations with "standard RMTs" (volume optimization, optimization of
> internal parameters, ...).
> Only when I've found the minimum structure, I'd get the final total
> energy for this minimum structure with a setup using RMT(O)=1.1 and
> RKMAX=6.
>
> And of course, whenever you compare total energies of different phases,
> structures, compounds, ... the computational parameters must be
> "consistent". This means,
> i) at the end all RMTs should be the same (so choose RMT(Zr) and RMT(Ba)
> such, that they can be identical in all cases).
> ii) use either "converged" (increase k-mesh until Etot is constant) or
> at least "equivalent" k-meshes (a cell with 2 formulae units should use
> eg. a 2x2x2 k-mesh, while the cell with one FU should have a 4x4x4 k-mesh).
> iii) consistent RKmax (see faq)
> iv) identical E-parameter settings, IFFT factors, GMAX, LVNS, ....
>
> Hope this is clear now.
>
> Am 13.11.2017 um 17:16 schrieb chin Sabsu:
> > Thank you very much Sir for a very nice NOTE.
> >
> > I suggest one correction and two more queries:
> >
> > Correction: The RKmax 5.6 in the sentence "Then you should do atom A
> > with RKmax=7/2.5*2.0=5.6" should be replaced by 7/2*2.5=8.75!!
> >
> > Query: 1. I could not understand what is the purpose of another
> > calculation ( the last point of the NOTE: To have consistent total
> > energies....... end also rerun"). Maybe you forgot to mention the use of
> > another calculation at RKmax 6. Either this may be added to previous any
> > calculation for energy correction or something else. Please make it more
> > clear.
> >
> > Query: 2. The RMT of O in BaZrO3, BaO and ZrO2 should be same or it is a
> > matter of stable phases of elements only (we may care for rmt of O in
> > BaO separately and for ZrO2 separately). Because the RMT of O2 is 1.14
> > (after this note) and then for O in O/BaO/ BaZrO3 it is 2.5/2.5/1.90.
> > What I understood from the NOTE is: deal O2 separately with rmt 1.14 and
> > RKmax 6. Then the RMT of O should be 1.9 (rmt of O in BaZrO3) in BaO, O,
> > and ZrO2 and the same should hold true for Ba and Zr. Please need your
> > comment.
> >
> >
> >
> > Forgive me if I am not putting the queries well. I will try to put in
> > better if anyone does not understand above.
> >
> >
> > On Monday, 13 November 2017 9:17 PM, Peter Blaha
> > <pblaha at theochem.tuwien.ac.at> wrote:
> >
> >
> > Please check the faq pages at www.wien2k.at/reg_user/faq.
> >
> > I've made a couple of modifications and there is a page for cohesive and
> > formation energies.
> >
> > Any suggestions are welcome.
> >
> > Peter Blaha
> >
> > On 11/13/2017 11:50 AM, Peter Blaha wrote:
> > > You must modify your O2 struct file.
> > >
> > > Make the 2 oxygens "equivalent", i.e. you should have only ONE
> > > non-equivalent atomic site (NAT=1), but MULT=2 for the 2 oxygens.
> > >
> > > This will produce inversion symmetry and all calculations will take
> less
> > > time and memory !!!
> > >
> > > --------------------
> > >
> > > And yes: at the end you must check E-to for your compound (eg. BaO) at
> > > the E-minimum (after Volume optimization) with an extra calculation
> > > where you put the small O-spheres.
> > >
> > > --------------------
> > >
> > > And you must use "equivalent RKmax" values for different compounds
> > > (always corresponding to the smallest spheres: Eg. BaO with RMT 2.2
> and
> > > O 1.1 for Ba and O, respectively, use RKmax=6. When you do the
> metallic
> > > Ba, use identical RMT, but RKmax= 6/1.1*2.2=12 !!!!
> > >
> > > I'm preparing a faq page on this topic, which should come up on
> > > www.wien2k.at in a few hours.
> > >
> > >
> > > On 11/12/2017 09:11 PM, chin Sabsu wrote:
> > >> Dear Prof. Alay/Peter/Marks/Stefaan or any expert user
> > >>
> > >> As you know molecule calculations take much time (I received your
> reply
> > >> to my previous query) and as suggested by you all these molecules
> need
> > >> some good HPC facility that I do not have.
> > >>
> > >> Therefore, to avoid the multiple heavy repetitive calculations or O2
> > >> molecule, I need some hints on rmt issue from atomic to crystalline
> > >> structures.
> > >>
> > >>
> > >> As Prof. Marks and Alay said in my previous post [1, 2] that what
> > >> whatever rmt I take for O2 molecule it should be same for all oxides
> > >> means for all Oxygens in the system of BaZrO3 (BaO, ZrO2, O, etc) and
> > >> this also should apply to Ba (Ba atom and crystal, BaO, BaZrO3) and
> Zr
> > >> (Zr atom and Zr crystal, ZrO2).
> > >>
> > >> Means the rmt must be same for all same elements for all components
> of
> > >> the calculations. Is it?
> > >>
> > >> If the above statement remains true then I could not manage the same
> rmt
> > >> for Oxygen in all structures: O, O2, BaO, and BaZrO3; Barium in Ba,
> Ba2,
> > >> BaO, and BaZrO3; and same hold for Zr. For example, for O2 I have
> 1.16
> > >> rmt then for O/BaO/ BaZrO3 it is 2.5/2.51.90 which is quite
> different
> > >> from O2 [I am sending all structure in in your email as I am not
> able to
> > >> send here].
> > >>
> > >> How should I fix this? Is it okay if I use rmt set manually?
> > >>
> > >> I am so confused and on limited resources, I am not able to start the
> > >> calculation. Your help will be much helpful and will be appreciated.
> > >>
> > >>
> > >> [1] Re: [Wien] :WARN : WARNING: RKmax reduced due to NMATMAX
> > >>
> > <https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__www.mail-2Darchive.com_wien-40zeus.theochem.tuwien.
> ac.at_msg16734.html&d=DwIGaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNX
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> sf4tFFnA74XLb7RaNzx_Zk&e= >
> > >>
> > >>
> > >> [2]
> > >>
> > https://urldefense.proofpoint.com/v2/url?u=https-3A__www.
> mail-2Darchive.com_wien-40zeus.theochem.tuwien.ac.at_
> msg16736.html&d=DwIGaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_
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> > >>
> > >>
> > >>
> > >> Thank you in advance,
> > >>
> > >> Chin Sabsu
> > >>
> > >>
> > >> _______________________________________________
> > >> Wien mailing list
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> tuwien.ac.at>
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> > >>
> > >
> >
> > --
> >
> > P.Blaha
> > ------------------------------------------------------------
> --------------
> > Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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> --
> --------------------------------------------------------------------------
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--
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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