Re: [Wien] How to find the exact value of infinte epsilon?

[Fecher, Gerhard]

What is the wavelength at zero energy ?

Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."


Dr. Gerhard H. Fecher
Institut of Physics
Johannes Gutenberg - University
55099 Mainz

Von: Wien [wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von Atefe Marasi 
[13mar...@gmail.com]
Gesendet: Montag, 29. November 2021 23:25
An: wien@zeus.theochem.tuwien.ac.at
Betreff: Re: [Wien] How to find the exact value of infinte epsilon?

Dear Xavier

Thank you for your prompt reply.

> Infinite epsilon means that you extrapolate ...

Do you mean that infinite epsilon (epsilon_oo) is nothing more than epsilon 
zero (epsilon_0)?

> You must plot the real part...
I have plotted the real part of epsilon in z direction(for BaTiO3), as would be 
seen from the following link:
https://imgurl.ir/uploads/p793339_infinite_epsilon.jpg
As expected, the above figure shows that the real part of the epsilon tends to 
unity at high frequency. From this plot, the epsilon_0 is about 6.5, but I am 
still not sure that whether infinite epsilon is really equal to epsilon_zero 
(epsilon_oo =? epsilon_0).

> You must be careful because if you have a band gap and a bad description of 
> the gap value ...

Thank you for this hint. I will try to obtain a suitable band gap by TB-mBJ 
functional. However, at this step, I need to find out the difference between 
epsilon_oo and epsilon_0. In my opinion, which I am not sure about it, 
epsilon_00 would be evaluated at infinite energy, while epsilon_0 would be 
evaluated at zero energy, as deduced  from their names.
Thank you for your nice cooperation.

Best Regards
Atefe Marasi
___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

Re: [Wien] How to find the exact value of infinte epsilon?

[Atefe Marasi]

Dear Xavier

Thank you for your prompt reply.

> Infinite epsilon means that you extrapolate ...

Do you mean that infinite epsilon (epsilon_oo) is nothing more than epsilon
zero (epsilon_0)?

> You must plot the real part...
I have plotted the real part of epsilon in z direction(for BaTiO3), as
would be seen from the following link:
https://imgurl.ir/uploads/p793339_infinite_epsilon.jpg
As expected, the above figure shows that the real part of the epsilon tends
to unity at high frequency. From this plot, the epsilon_0 is about 6.5, but
I am still not sure that whether infinite epsilon is really equal to
epsilon_zero (epsilon_oo =? epsilon_0).

> You must be careful because if you have a band gap and a bad description
of the gap value ...

Thank you for this hint. I will try to obtain a suitable band gap by TB-mBJ
functional. However, at this step, I need to find out the difference
between epsilon_oo and epsilon_0. In my opinion, which I am not sure about
it, epsilon_00 would be evaluated at infinite energy, while epsilon_0 would
be evaluated at zero energy, as deduced  from their names.
Thank you for your nice cooperation.

Best Regards
Atefe Marasi
___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

Re: [Wien] How to find the exact value of infinte epsilon?

[Pavel Ondračka]

Dear Atefe Marasi,

to add on top of what Xavier said, and thus similarly to him I'm also
assuming that by "infinite epsilon, i.e., dielectric constant at high
frequency" you mean the electronic part the dielectric tensor. Or in
other words the part from the electronic excitations. That you can get
with the optic, joint and kram commands.

Regarding the band gap, if you have insulator, the mBJ potential should
be a reasonable starting choice. The band gap values are OK and even
though the band dispersion and thus the momentum matrix elements are
not so good, it does not matter that much as the standard optic
calculation neglects excitons anyway. However even if you don't get the
proper shape of the imaginary dielectric function, in my experience
this does not matter that much if you are interested in the real part
of the dielectric function at E=0 (or at least reasonably far below the
band gap). I used mBJ+optic quite a lot for refractive index
calculations in vidible range for materials with band gap as low as 3eV
and even there it worked quite OK.

What is very important is to increase the maximum energy emax value in
lapw1, optic and joint to be sure you include enough states to properly
account for the high energy processes. Otherwise you will get some
underestimation of the real part of the dielectric function at low
energies.

Best regards
Pavel

On Mon, 2021-11-29 at 11:46 +0100, xavier rocquefelte wrote:
> Dear Atefe Marasi,
> Infinite epsilon means that you extrapolate the epsilon value for the
> zero of energy. 
> You must plot the real part of the dielectric function to properly
> estimate this value. 
> You must be careful because if you have a band gap and a bad
> description of the gap value ... the estimation will be not good at
> all. 
> Regards
> Xavier
> 
> On 29/11/2021 11:38, Atefe Marasi wrote:
>  
> > ___
> > Wien mailing list
> > 
> > 
> > SEARCH the MAILING-LIST at:  
> ___
> Wien mailing list
> Wien@zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> SEARCH the MAILING-LIST at: 
> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html


___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

Re: [Wien] How to find the exact value of infinte epsilon?

[xavier rocquefelte]

Dear Atefe Marasi,

Infinite epsilon means that you extrapolate the epsilon value for the 
zero of energy.


You must plot the real part of the dielectric function to properly 
estimate this value.


You must be careful because if you have a band gap and a bad description 
of the gap value ... the estimation will be not good at all.


Regards

Xavier


On 29/11/2021 11:38, Atefe Marasi wrote:

Hello dear WIEN2k users,
I am interested in finding the exact value of infinite epsilon, i.e., 
dielectric constant at high frequency. As you know, as frequency goes 
to infinity, the value of epsilon asymptotically approaches to unity. 
But data reported in literatures for the infinite epsilon are not 
equal to one! How can I choose a correct energy range or frequency to 
obtain the appropriate infinite epsilon?

Is there any way to find the infinite epsilon by WIEN2k?

Thank you,
Best Regards,
Atefe Marasi



___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST 
at:http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

[Wien] How to find the exact value of infinte epsilon?

[Atefe Marasi]

Hello dear WIEN2k users,
I am interested in finding the exact value of infinite epsilon, i.e.,
dielectric constant at high frequency. As you know, as frequency goes to
infinity, the value of epsilon asymptotically approaches to unity. But data
reported in literatures for the infinite epsilon are not equal to one! How
can I choose a correct energy range or frequency to obtain the appropriate
infinite epsilon?
Is there any way to find the infinite epsilon by WIEN2k?

Thank you,
Best Regards,
Atefe Marasi
___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html

Re: [Wien] Continuing confusion in dos...

[Tran, Fabien]

Is the calculation converged or not, the message "energy in SCF NOT CONVERGED" 
is always
printed when only 1 or 2 iterations are done. Just check that :DIS after the 
single iteration is
reasonably small. What is the value?.

Your two DOS look different, but this may (mainly?) be due to the different 
used broadenings.


From: Wien  on behalf of shamik 
chakrabarti 
Sent: Monday, November 29, 2021 6:47 AM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] Continuing confusion in dos...

Dear Dr. Tran,

 I have applied 4k points using the procedure as you have 
suggested. However, for one iteration with 4k points, it is coming as "the 
energy in scf is not converged". Also, the DOS looks different from 1 k points. 
I am attaching two plots here. Is it that, to get the correct DOS we have to 
run more than one iteration until the energy is converged?

Looking forward to your suggestions in this regard.

with regards,

On Sun, 28 Nov 2021 at 19:12, Tran, Fabien 
mailto:fabien.t...@tuwien.ac.at>> wrote:
The DOS will be ok.

From: Wien 
mailto:wien-boun...@zeus.theochem.tuwien.ac.at>>
 on behalf of shamik chakrabarti 
mailto:shamik15041...@gmail.com>>
Sent: Sunday, November 28, 2021 2:39 PM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] Continuing confusion in dos...

Dear Dr. Tran,

   I have another confusion. In userguide it is written that  "Note 
that when -newklist is used, the total energy (:ENE in case.scf) at the 1st 
iteration is wrong"...whether that means that we can not use the value of total 
energy from this calculation, however, we can get the DOS?

with regards,

On Sun, 28 Nov 2021 at 16:18, shamik chakrabarti 
mailto:shamik15041...@gmail.com>>>
 wrote:
Thank you, Dr. Tran :)

On Sun, 28 Nov 2021 at 16:07, Tran, Fabien 
mailto:fabien.t...@tuwien.ac.at>>>
 wrote:
Just replace the old one (in $WIENROOT) by the new one. No need to recompile. 
csh/tcsh/bash scripts do not need to be compiled.


From: Wien 
mailto:wien-boun...@zeus.theochem.tuwien.ac.at>>>
 on behalf of shamik chakrabarti 
mailto:shamik15041...@gmail.com>>>
Sent: Sunday, November 28, 2021 11:32 AM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] Continuing confusion in dos...

How to use this script? should I copy this script in some folder (which 
folder?) in the parent directory of wien2k & recompile...I am using wien2k 19.1

On Sun, 28 Nov 2021 at 15:43, Tran, Fabien 
mailto:fabien.t...@tuwien.ac.at>>>>>

Re: [Wien] Continuing confusion in dos...

[Peter Blaha]

Just a few guidelines how to select a proper k-mesh and the nband parameter:


a) Convergence parameters from "other" calculations are only a 
guideline, but your system could be very different.


b) How to select the k-mesh: Obviously, since -hf is very expensive, you 
should test this with a normal GGA. Do various calculations with 
different k-meshes for the property you are interested in (eg. DOS) 
until you know how it changes.


Once this is done, you could go to -hf, BUT: this might be too 
expensive. Then the option of a "reduced k-mesh" comes into play, since 
this can very much decrease computer time. Eg: You found out that you 
need a 4x4x4 kmesh for a reasonable DOS, use this, but also a reduced 
mesh of 2x2x2,


c) selection of "nband": also here, you have to "think", not just do 
what others have done for a very different system.


Suppose you do Si: It has 4 electrons/atom, i.e. 2 bands/atom = 4 
bands/cell are occupied. Now consider the number of bands if the 
electronic shell would be fully occupied, i.e. all s+p states, i.e. 8 
e/atom, 4 bands/atom = 8 bands/cell. So nband should be at least twice 
as large as the number of occupied bands.


Consider a Cu atom in some cell: it has 11 electrons/atom, so 
contributes 5.5 bands/atom. A full shell would be minimum 12 e (3d+4s), 
better 18e (3d+4sp). Nband does not need to be too large as compared to 
the occupied bands.


If you, however, have a Ti atom, it has just 4 e/atoms (2 bands), but 
still probably all unoccupied 3d states should be included in a HF 
calculation, so probably you have to go from 4 to 12e/Ti atom.


Now add this up for all your atoms. And in addition, if it is a 
spin-polarized case, you cannot divide by 2.


d) Don't ask others if your calculation is converged. How should we know 
without doing a calculation. Unless you are very experienced (or have 
anyway unlimited computer ressources), start with low/medium converged 
parameters, do the calculation. Increase the parameters and compare your 
results. WIEN2k is pretty efficient, because it can use your previous 
scf density and may converge in few cycles with the better parameters 
(unless you do the better calculation in a new directory with a new 
initialization. NEVER DO THIS.)


e)  The next wien2k release will help you a lot in this respect, as it 
has a new parameter -prec 0-3 in init_lapw. It will select k-mesh and 
Rkmax automatically based on your -prec level AND the number/type/RMT of 
your atoms in your cell.


Am 29.11.2021 um 09:09 schrieb Gavin Abo:
There is the following, but maybe it will not help since it is just a 
list of links to previous posts already given in the mailing list.


At [1], it advises to use "at least one iteration".

In your post at [2] if I have interpreted it correctly, you have a 3D 
structure (cubic spinel supercell with 56 atoms).


With regards to your 2x2x1 k-mesh, I have seen k-meshes, such as 3x3x1 
[3], with 1 k-point in the z-direction like that used for 2D 
structures [modeled in 3D as a supercell with vacuum (which might also 
go by the names surface [4], slab, or monolayer)].  Though, maybe more 
than 1 k-point in the z-direction is need for some 3D structures.


Post at [5] mentions a 2x2x2 is a fine start.  Then, from there you 
could increase the k-mesh (e.g., 3x3x3, ..., 5x5x5, ...) for k-point 
convergence testing.


In post [6], it looks like 6x6x6 was a k-mesh were k-point convergence 
was being reached in many cases.


It also looked like in [7] for DOS with -hf that it could be important 
that convergence testing had been done with nband in case.inhf.


[1] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20756.html
[2] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg21511.html
[3] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg21083.html
[4] Slide 29 titled "Surfaces": 
http://susi.theochem.tuwien.ac.at/events/ws2006/WIEN2k-getting_started.pdf
[5] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20861.html
[6] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20384.html
[7] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg21069.html


On 11/28/2021 10:47 PM, shamik chakrabarti wrote:

Dear Dr. Tran,

                 I have applied 4k points using the procedure as you 
have suggested. However, for one iteration with 4k points, it is 
coming as "the energy in scf is not converged". Also, the DOS looks 
different from 1 k points. I am attaching two plots here. Is it that, 
to get the correct DOS we have to run more than one iteration 
until the energy is converged?


Looking forward to your suggestions in this regard.

with regards,

___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at: 
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html


--
--

Re: [Wien] Continuing confusion in dos...

[Gavin Abo]

There is the following, but maybe it will not help since it is just a 
list of links to previous posts already given in the mailing list.


At [1], it advises to use "at least one iteration".

In your post at [2] if I have interpreted it correctly, you have a 3D 
structure (cubic spinel supercell with 56 atoms).


With regards to your 2x2x1 k-mesh, I have seen k-meshes, such as 3x3x1 
[3], with 1 k-point in the z-direction like that used for 2D structures 
[modeled in 3D as a supercell with vacuum (which might also go by the 
names surface [4], slab, or monolayer)].  Though, maybe more than 1 
k-point in the z-direction is need for some 3D structures.


Post at [5] mentions a 2x2x2 is a fine start.  Then, from there you 
could increase the k-mesh (e.g., 3x3x3, ..., 5x5x5, ...) for k-point 
convergence testing.


In post [6], it looks like 6x6x6 was a k-mesh were k-point convergence 
was being reached in many cases.


It also looked like in [7] for DOS with -hf that it could be important 
that convergence testing had been done with nband in case.inhf.


[1] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20756.html
[2] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg21511.html
[3] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg21083.html
[4] Slide 29 titled "Surfaces": 
http://susi.theochem.tuwien.ac.at/events/ws2006/WIEN2k-getting_started.pdf
[5] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20861.html
[6] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20384.html
[7] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg21069.html


On 11/28/2021 10:47 PM, shamik chakrabarti wrote:

Dear Dr. Tran,

                 I have applied 4k points using the procedure as you 
have suggested. However, for one iteration with 4k points, it is 
coming as "the energy in scf is not converged". Also, the DOS looks 
different from 1 k points. I am attaching two plots here. Is it that, 
to get the correct DOS we have to run more than one iteration 
until the energy is converged?


Looking forward to your suggestions in this regard.

with regards,

___
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html