Since I haven't ran many hexagonal optimizations, I probably cannot
provide as good of advice as some of the others in the list likely could.
My first piece of advice would be to mention which particular package
you used for your optimization. optimize, optimize_abc, or 2DRoptimize?
From the looks of it, it is likely the 2DRoptimize. In other words, it
could be easier when the reader doesn't have to guess or infer at what
was used.
Changing the percentage for altering the structure until you find the
minimum energy point as you have stated should be the correct procedure.
Looking at the energy vs volume I believe typically worked better for
cubic structures (e.g. volume of a^3, where a=b=c).
So, you might try looking at energy vs c/a to see if that works better
or not for finding the minimum energy point for your calculation case.
If optimize was used and option (5) VARY A and C (2D-case) (tetragonal
or hexagonal lattice) was selected, I believe it will ask for a percent
change of the c/a ratio. If I recall correctly, w2web has an energy vs
c/a plot selection that you could try using when option (5) is selected
for the optimize program. I think there is also a parabolfit_lapw
script that can help analyze the different degrees of freedom for a
hexagonal structure (2 lattice parameters: a and c). Based on the
WIEN2k usersguide, it looks like a and c when using the optimize_abc
package can be controlled by the -d X argument with X needing to be the
replaced with the amount of change as a number value (in percent).
It looks like the hexagonal example in the 2Doptimize (pdf) at [1], if
that is what you were following, takes inputs for both a volume change
and c/a change as I see in the document:
*******Start for volume changes*******
Do you want to use default parameters ?(y/n)
(-10%,-5%,0,5%,10%)
y
******* Start for c/a changes*******
(-4%, -2%,0,2%,4%)
y
In the above, the default is -10 to 10% in 5% increments.
From your description, it looks like you changed the volume from -30%
to 20%. However, it doesn't look like you mention which increments you
took between them. Also, is it safe or dangerous to assume that you took
the default for the c/a changes?
Let's say a physical atom has a radius, /r/.
If you view the struct file for the structure in XCrySDen, if you see
/r/, surface of the ball, of one atom (e.g., Hf) touch or overlap the
/r/ of another atom (e.g., O), then you have a bad struct file. You
would have to fix the lattice constants or lattice angles. For example,
that might happen if the lattice constants are entered in the struct
file in the wrong units [2,3].
If you saw the recent post at [4], you might have read how the
muffin-tin radius (RMT) > /r/ has radial functions less the RMT and
plane waves greater than RMT.
Perhaps you have also seen Figure 1 at [5] or Figure 1 in [6]
illustrating the muffin-tin and interstitial regions.
The 'NN' - overlapping spheres error will happen when the RMT of two
atoms touch or overlap each other.
If you have lattice parameters that you are not needing to optimize [7],
it is likely straightforward setting 0% in setrmt during initialization
of the calculation.
However, when doing a lattice parameter optimization you could adjust
the percentage to reduce the RMT [8] for trying to avoid later on
overlapping sphere errors. You might recall when you went through the
TiC tutorial in the WIEN2k 23.1 usersguide on page 17 [9] it used 3% for
that example.
[1] http://susi.theochem.tuwien.ac.at/reg_user/textbooks/
[2]
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg06323.html
[3]
http://zeus.theochem.tuwien.ac.at/pipermail/wien/2010-January/012330.html
[4]
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg22739.html
[5] http://susi.theochem.tuwien.ac.at/lapw/index.html
[6] https://arxiv.org/abs/2004.10728v1
[7]
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg17074.html
[8] http://zeus.theochem.tuwien.ac.at/pipermail/wien/2018-May/028064.html
[9] http://www.wien2k.at/reg_user/textbooks/usersguide.pdf
Hopefully that helps and best regards,
Gavin
WIEN2k user
On 8/22/2023 4:04 PM, Pranjal Nandi wrote:
Dear Sir,
Thank you for the tip. I have used it and am carrying on the
calculations. I need further guidance.
As far as my understanding goes, I should keep changing the percentage
till the time I don’t see a minimum energy point (a curve whose either
side should be higher, but till now I am only getting a straight line)
in the plot of energy vs volume. For the first few calculations, I
changed the volume from -20 to 20% and found that -20 is has the
minimum energy. Then when I change it from -30 to -10 (to see -30 has
lower energy or not), I get the error grep: lapw2*./error/: /No such
file or directory exists (probably ghost bands are occurring at -30)./
//
/So next what I think I should do is redo the initialisation and run
scf with the minimum energy struct file obtained in the earlier
optimisation and don’t change the structure suggested by sgroup and
again repeat the optimisation on this struct file so that I can check
if loweing the volume more than -20 can minimise the energy (I will
start with -10 to 0 as the existing structure is already -20). /
//
/However, now I am getting the error 'NN' - overlapping spheres, which
I will try to fix it (if free you may comment on this too but I guess
I may find a thread addressed to this error). /
//
/*But my question is that am I going in the right direction with the
optimisation procedure?*/**
Thank you for your help once again.
With warm regards,
Pranjal
*From:*Wien <wien-boun...@zeus.theochem.tuwien.ac.at> *On Behalf Of
*Gavin Abo
*Sent:* Friday, August 18, 2023 5:06 AM
*To:* wien@zeus.theochem.tuwien.ac.at
*Subject:* Re: [Wien] Volume optimization and Eloss function.
If the structure is still hexagonal after the substitution, the
starting point could be section "5.3 Structure optimization" on
lattice parameter optimization starting on page 87 in the WIEN2k 23.1
(or 23.2) usersguide [1].
There you should see that you may select between two different packages.
If using *optimize*, there is:
[5] VARY A and C (2D-case) (tetragonal or hexagonal lattice)
Or if using *optimize_abc_lapw*, there is:
optimize_abc -t 2
After that, if the structure contains any free positions for atomic
position optimization, then there is section "5.3.2 Minimization of
internal parameters" on page 91 of the usersguide [1].
Yes, case.eloss is for the loss function [2]. On slide 9 in [3], it
looks to be showing that case.epsilon contains the real and imaginary
parts for the complex dielectric tensor and case.sigmak contains the
real and imaginary parts for the optical conductivity.
[1]
http://www.wien2k.at/reg_user/textbooks/usersguide.pdfhttp://www.wien2k.at/reg_user/textbooks/usersguide.pdf
<http://www.wien2k.at/reg_user/textbooks/usersguide.pdfhttp:/www.wien2k.at/reg_user/textbooks/usersguide.pdf>
[2] Slide 22:
http://www.wien2k.at/events/ws2006/Optics_Vienna_April_2006.pdf
[3]
http://www.wien2k.at/reg_user/textbooks/WIEN2k_lecture-notes_2013/optic_handout.pdf
On 8/17/2023 11:23 AM, Pranjal Nandi wrote:
Dear All,
I have an issue with 2 different parts (not related to each
other). They are as follows.
1. I am having a hard time in getting a hcp structure of HfO0.7
(or Hf605 which is close to 0.7). Therefore, what I have done
is that I have downloaded the hcp structure of HfPo and
substituted the Po with Oxygen.
Now, I want to do the structural and volumetric relaxation so
that I have the stable relaxed structure of HfO0.7. I did read
the guidebook but I need guidance on what should be the
correct order of optimisation (I am lost as I can’t understand
from which optimisation I should start).
2. In the eloss programme, which part of the function does the
eloss, epsilon and sigmak correspond to ? I guess eloss =
energy loss function, epsilon = real part of the dielectric
function , sigmaK = imaginary part of the dielectric function.
Am I right?
Looking forward to your kind guidance.
Thank you.
With warm regards,
Pranjal
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