[Wien] [EXTERNAL] Bands are often not smooth when zoom in

Peter Blaha pblaha at theochem.tuwien.ac.at
Sat Jan 23 09:13:48 CET 2021 

If your basis set is not converged, it is clear that the eigenvalues 
will change (go down in energy) when the basis set is increased.

The cutoff is defined by RKMAX, i.e. we take all plane waves such that 
|(k+K)| < KMAX.  In a bandstructure plot k varies slightly, but it can 
then happen that at a certain k, the maximal K is too large and gets 
reduced. Then a "jump" in the bandstructure will appear.
In this description, "k" is the vector of the k-point, "K" is a full 
reciprocal lattice vector.

PS: Yes, RKMAX=7 is of course too small for a 3d (Cu) element, while 
RKMAX=7 is much too large for H. It is a compromise.

On our website www.wien2k.at at reg.user and faq there are some 
suggestions for a "minimal" RKMAX for each element. You look into your 
structure and identify the atom which has the smallest RMT. This atom 
determines RKMAX according to the list given on this site. However, 
these values are kind of "minimal" RKMAX values (quite good for eg. 
optimization of atomic positions (-min), but for highest precision they 
should be increased by 1-3.

Just a simple example:
You do Cu and need RKMAX=9 for full convergence.
You do CuOH with RMT=1.8; 1.2 and 0.6 for the 3 elements.
RKMAX=3  is counting for H; gives "effective RKMAX=6 for O and 9 for Cu.
Hence RKMAX=3 is fully converged for CuOH (when using RMTs according to 
the suggestion of setrmt).


Am 23.01.2021 um 04:49 schrieb 巴拉比:
> Dear professor Jianxin Zhu,
> 
> Thank you so much for your quick reply.
> 
> Enlarging RKmax solves the problem! I found I have to set RKmax=9 which 
> is pretty large compared to default 7 to completely eliminate all 
> sawtooth artifacts in bands.
> 
> But I still want to know why a smaller RKmax would cause eigenvalues to 
> be discontinuous (in essence hamiltonian is discontinuous) at several k 
> points.
> 
> best regards
> 
> 
> 
> ------------------ Original ------------------
> *From:* "A Mailing list for WIEN2k users" <jxzhu at lanl.gov>;
> *Date:* Fri, Jan 22, 2021 11:57 PM
> *To:* "A Mailing list for WIEN2k users"<wien at zeus.theochem.tuwien.ac.at>;
> *Subject:* Re: [Wien] [EXTERNAL] Bands are often not smooth when zoom in
> 
> What rkmax value are you using? Usually a larger rkmax helps make the 
> bands smooth.
> 
> Jianxin
> 
> 
> Sent with BlackBerry Work
> (www.blackberry.com)
> 
> 
> *From: *Wien <wien-bounces at zeus.theochem.tuwien.ac.at 
> <mailto:wien-bounces at zeus.theochem.tuwien.ac.at>> on behalf of: 巴拉比 
> <balabi at qq.com <mailto:balabi at qq.com>>
> *Date: *Friday, Jan 22, 2021, 8:15 AM
> *To: *wien <wien at zeus.theochem.tuwien.ac.at 
> <mailto:wien at zeus.theochem.tuwien.ac.at>>
> *Subject: *[EXTERNAL] [Wien] Bands are often not smooth when zoom in
> 
> Dear wien2k developers,
> 
> I found bands obtained from wien2k are often not smooth and have many 
> small sawtooth bumps especially when you zoom in. I can reproduce this 
> kind of band artifacts in version 19.2 and 17.1, on differnet computers 
> and link to different version of MKL. I'll take simple copper as an 
> example to show how I obtain the bands:
> 
> the structure file I use is as:
> 
> blebleble
> F   LATTICE,NONEQUIV.ATOMS:  1 225 Fm-3m
>               RELA
>    6.872726  6.872726  6.872726 90.000000 90.000000 90.000000
> ATOM   1: X=0.00000000 Y=0.00000000 Z=0.00000000
>            MULT= 1          ISPLIT= 2
> Cu1        NPT=  781  R0=0.00005000 RMT=    2.0000   Z: 29.0
> LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
>                       0.0000000 1.0000000 0.0000000
>                       0.0000000 0.0000000 1.0000000
>    48      NUMBER OF SYMMETRY OPERATIONS
> 1 0 0 0.00000000
> 0 1 0 0.00000000
> 0 0 1 0.00000000
>         1
> -1 0 0 0.00000000
> 0-1 0 0.00000000
> 0 0 1 0.00000000
>         2
> -1 0 0 0.00000000
> 0 1 0 0.00000000
> 0 0-1 0.00000000
>         3
> 1 0 0 0.00000000
> 0-1 0 0.00000000
> 0 0-1 0.00000000
>         4
> 0 0 1 0.00000000
> 1 0 0 0.00000000
> 0 1 0 0.00000000
>         5
> 0 0 1 0.00000000
> -1 0 0 0.00000000
> 0-1 0 0.00000000
>         6
> 0 0-1 0.00000000
> -1 0 0 0.00000000
> 0 1 0 0.00000000
>         7
> 0 0-1 0.00000000
> 1 0 0 0.00000000
> 0-1 0 0.00000000
>         8
> 0 1 0 0.00000000
> 0 0 1 0.00000000
> 1 0 0 0.00000000
>         9
> 0-1 0 0.00000000
> 0 0 1 0.00000000
> -1 0 0 0.00000000
>        10
> 0 1 0 0.00000000
> 0 0-1 0.00000000
> -1 0 0 0.00000000
>        11
> 0-1 0 0.00000000
> 0 0-1 0.00000000
> 1 0 0 0.00000000
>        12
> 0 1 0 0.00000000
> 1 0 0 0.00000000
> 0 0-1 0.00000000
>        13
> 0-1 0 0.00000000
> -1 0 0 0.00000000
> 0 0-1 0.00000000
>        14
> 0 1 0 0.00000000
> -1 0 0 0.00000000
> 0 0 1 0.00000000
>        15
> 0-1 0 0.00000000
> 1 0 0 0.00000000
> 0 0 1 0.00000000
>        16
> 1 0 0 0.00000000
> 0 0 1 0.00000000
> 0-1 0 0.00000000
>        17
> -1 0 0 0.00000000
> 0 0 1 0.00000000
> 0 1 0 0.00000000
>        18
> -1 0 0 0.00000000
> 0 0-1 0.00000000
> 0-1 0 0.00000000
>        19
> 1 0 0 0.00000000
> 0 0-1 0.00000000
> 0 1 0 0.00000000
>        20
> 0 0 1 0.00000000
> 0 1 0 0.00000000
> -1 0 0 0.00000000
>        21
> 0 0 1 0.00000000
> 0-1 0 0.00000000
> 1 0 0 0.00000000
>        22
> 0 0-1 0.00000000
> 0 1 0 0.00000000
> 1 0 0 0.00000000
>        23
> 0 0-1 0.00000000
> 0-1 0 0.00000000
> -1 0 0 0.00000000
>        24
> -1 0 0 0.00000000
> 0-1 0 0.00000000
> 0 0-1 0.00000000
>        25
> 1 0 0 0.00000000
> 0 1 0 0.00000000
> 0 0-1 0.00000000
>        26
> 1 0 0 0.00000000
> 0-1 0 0.00000000
> 0 0 1 0.00000000
>        27
> -1 0 0 0.00000000
> 0 1 0 0.00000000
> 0 0 1 0.00000000
>        28
> 0 0-1 0.00000000
> -1 0 0 0.00000000
> 0-1 0 0.00000000
>        29
> 0 0-1 0.00000000
> 1 0 0 0.00000000
> 0 1 0 0.00000000
>        30
> 0 0 1 0.00000000
> 1 0 0 0.00000000
> 0-1 0 0.00000000
>        31
> 0 0 1 0.00000000
> -1 0 0 0.00000000
> 0 1 0 0.00000000
>        32
> 0-1 0 0.00000000
> 0 0-1 0.00000000
> -1 0 0 0.00000000
>        33
> 0 1 0 0.00000000
> 0 0-1 0.00000000
> 1 0 0 0.00000000
>        34
> 0-1 0 0.00000000
> 0 0 1 0.00000000
> 1 0 0 0.00000000
>        35
> 0 1 0 0.00000000
> 0 0 1 0.00000000
> -1 0 0 0.00000000
>        36
> 0-1 0 0.00000000
> -1 0 0 0.00000000
> 0 0 1 0.00000000
>        37
> 0 1 0 0.00000000
> 1 0 0 0.00000000
> 0 0 1 0.00000000
>        38
> 0-1 0 0.00000000
> 1 0 0 0.00000000
> 0 0-1 0.00000000
>        39
> 0 1 0 0.00000000
> -1 0 0 0.00000000
> 0 0-1 0.00000000
>        40
> -1 0 0 0.00000000
> 0 0-1 0.00000000
> 0 1 0 0.00000000
>        41
> 1 0 0 0.00000000
> 0 0-1 0.00000000
> 0-1 0 0.00000000
>        42
> 1 0 0 0.00000000
> 0 0 1 0.00000000
> 0 1 0 0.00000000
>        43
> -1 0 0 0.00000000
> 0 0 1 0.00000000
> 0-1 0 0.00000000
>        44
> 0 0-1 0.00000000
> 0-1 0 0.00000000
> 1 0 0 0.00000000
>        45
> 0 0-1 0.00000000
> 0 1 0 0.00000000
> -1 0 0 0.00000000
>        46
> 0 0 1 0.00000000
> 0-1 0 0.00000000
> -1 0 0 0.00000000
>        47
> 0 0 1 0.00000000
> 0 1 0 0.00000000
> 1 0 0 0.00000000
>        48
> 
> then I do step by step
> 1. init_lapw -b
> 2. run_lapw -in1new 3   # I use -in1new 3 to avoid the QTL-B value 
> warning message in the last few cycles of case.scf file
> 3. using xcrysden to generate a k path along GAMMA-W-X-L with 400 k points.
>      since the klist_band file is too long. I share it on 
> https://pastebin.com/ZaYuFMZE
> 4. x lapw1 -band
> 5. x lapw2 -band -qtl
> 
> finally, I use the data in case.qtl to plot bands
> in [-10eV,10eV] range, it looks pretty normal as shared in below link
> https://pasteboard.co/JKPC1tB.png
> in [-2eV,-1eV] zoom in range, the look of bands becomes abnormal with 
> full of sawtooth bump as shared in link
> https://pasteboard.co/JKPCB7Y.png
> 
> So I am wondering if this is a bug? Or what I have done wrong to have 
> this kind of bands(it appears in all my other bands calculation)? I 
> inspected the k path and found it is pretty fine. So I can not think of 
> a reason why the eigenvalue solutions would be discontinous at two 
> nearby k points.
> 
> best regards
> 
> 
> 
> 
> 
> 
> 
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-- 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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