Re: [Wien] Bulk vs supercell Plasma frequency

2015-11-01 Thread Muhammad Sajjad
Dear Professor Blah
Thank you for your quick response.  Yes I found that completely converged
(with the best k-mesh) leads to the same results on changing k-meshes for
optical properties. Na is better in k-mesh selection than that of Al.

Actually I am expanding  structure in z-direction. In my opinion, I must
consider both w_p_xx and w_p_zz, as former is changing slowly while an
abrupt change is found in the later component of PF. Am I right?
Simply, except cubic system, both tensor components of PF must take in
account?
True Regards

On Fri, Oct 30, 2015 at 9:28 AM, Peter Blaha 
wrote:

> Usually, different properties require different k-meshes. So it should be
> ok to converge the scf with a smaller k-mesh (it still must be a "good"
> one), but use more k-points for a plot of the DOS or optics.
>
> Please repeat the optics calculation with a series of k-meshes and plot
> w_p as funktion of the k-mesh. You should find out in this way the
> converged value.
>
> PS: I know that for Al one needs MANY more k-points to get a converged
> value. No idea about Na.
>
>
> Am 29.10.2015 um 21:50 schrieb Muhammad Sajjad:
>
> Dear Prof. P Blaha
> Thank you very much for yous fruitful suggestions. However, I did not
> change RKmax. For cubic Na only W_p_xx is enough but after making supercell
> (1 1 6) still I need only w_p_xx and forget about w_p_zz, though the system
> is tetragonal now. Is it right I understood?
> Second  thing is it principally right that one converges SCF with small
> k-mesh say 30*30*5 and then use the same scf ao get OPTICAL properties with
> k-mesh say 90*90*15? I mean no need to converge scf with 90*90*15.
>  Kind Regards
>
> On Thu, Oct 29, 2015 at 9:03 PM, Peter Blaha  > wrote:
>
>> In principle you are doing thinks now correct.
>> In reality, however, we use the tetrahedra-method in the integration of
>> the BZ to calculate a joint-density-of-states. And for a metal !!! here
>> there is a difference between k-meshes in the small or large cell. (it is
>> related to the "back-folding" problem and in the supercell there are less
>> tetrahedra and thus less possibilities to interpolate for the tetrahedron
>> method than in the small cell).
>>
>> In any case, you need to consider two things:
>>
>> a) You have to decide to which accurcy a certain number should be
>> calculated. Typically, a plasma frequency would be quoted with one or two
>> digits after the comma (i.e. 5.9 or at most 5.94 eV).
>>
>> b) Then you have to converge the numbers with respect to k-mesh (but also
>> Rkmax !!)
>> Definitely you should use a ratio of 6:1 for the supercell, but
>> eventually you need to increase the mesh until there are no changes within
>> the desired accuracy. In your case, 90x15 is almost sufficient, but not
>> quite if you want two digits accuracy.
>>
>> c) in a cubic system, of course it is useless to quote two tensor
>> components and one is sufficient.
>>
>>
>>
>>
>> Am 29.10.2015 um 10:35 schrieb Muhammad Sajjad:
>>
>> Dear Prof. Blaha
>>
>> I did some calculation for Bulk Na (bcc, space gp #229_Im-3m) wiht k-mesh
>> 30*30*30 and found the plasma frequency (in case.outputjoint) as
>>  Plasma frequencies:
>>
>>w_p_xx  w_p_zz[eV]
>>
>>5.9446  5.9446
>>
>> Now I constructed a supercell 1*1*6 (definitely symmetry reduced and now
>> sp.gp is 1_P1), used k-mesh 30*30*5 and  found
>> Plasma frequencies (much deviating from bulk values):
>>
>>w_p_xx  w_p_zz[eV]
>>
>>5.76146  5.3446
>>
>> Then used k-mesh 90*90*15 and found
>> Plasma frequencies (w_p_zz is deviating from bulk w_p_zz ):
>>
>>w_p_xx  w_p_zz[eV]
>>
>>5.9485  5.8903
>>
>> I have read the previous post (
>> 
>> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg09782.html)
>> but it is not speaking about w_p_zz. So when I plot epsilon data for
>> w_p_xx then it is matching with that of bulk but when I use w_p_zz  then it
>> is definitely  away from bulk. Should I consider w_p_zz  or use "number
>> of choice = 1 in case.inop" and plot epsilon only with w_p_xx ?
>>
>>
>> Kind Regards
>> Muhammad Sajjad
>> Post Doctoral Fellow
>> KAUST, KSA.
>>
>>
>> ___
>> Wien mailing 
>> listw...@zeus.theochem.tuwien.ac.athttp://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
>>
>>
>
>
> --
> Kind Regards
> Muhammad Sajjad
> Post Doctoral Fellow
> KAUST, KSA.
>
>
> 

Re: [Wien] Bulk vs supercell Plasma frequency

2015-10-30 Thread Peter Blaha
Usually, different properties require different k-meshes. So it should 
be ok to converge the scf with a smaller k-mesh (it still must be a 
"good" one), but use more k-points for a plot of the DOS or optics.


Please repeat the optics calculation with a series of k-meshes and plot 
w_p as funktion of the k-mesh. You should find out in this way the 
converged value.


PS: I know that for Al one needs MANY more k-points to get a converged 
value. No idea about Na.


Am 29.10.2015 um 21:50 schrieb Muhammad Sajjad:

Dear Prof. P Blaha
Thank you very much for yous fruitful suggestions. However, I did not 
change RKmax. For cubic Na only W_p_xx is enough but after making 
supercell (1 1 6) still I need only w_p_xx and forget about w_p_zz, 
though the system is tetragonal now. Is it right I understood?
Second  thing is it principally right that one converges SCF with 
small k-mesh say 30*30*5 and then use the same scf ao get OPTICAL 
properties with k-mesh say 90*90*15? I mean no need to converge scf 
with 90*90*15.

 Kind Regards

On Thu, Oct 29, 2015 at 9:03 PM, Peter Blaha 
> 
wrote:


In principle you are doing thinks now correct.
In reality, however, we use the tetrahedra-method in the
integration of the BZ to calculate a joint-density-of-states. And
for a metal !!! here there is a difference between k-meshes in the
small or large cell. (it is related to the "back-folding" problem
and in the supercell there are less tetrahedra and thus less
possibilities to interpolate for the tetrahedron method than in
the small cell).

In any case, you need to consider two things:

a) You have to decide to which accurcy a certain number should be
calculated. Typically, a plasma frequency would be quoted with one
or two digits after the comma (i.e. 5.9 or at most 5.94 eV).

b) Then you have to converge the numbers with respect to k-mesh
(but also Rkmax !!)
Definitely you should use a ratio of 6:1 for the supercell, but
eventually you need to increase the mesh until there are no
changes within the desired accuracy. In your case, 90x15 is almost
sufficient, but not quite if you want two digits accuracy.

c) in a cubic system, of course it is useless to quote two tensor
components and one is sufficient.




Am 29.10.2015 um 10:35 schrieb Muhammad Sajjad:

Dear Prof. Blaha

I did some calculation for Bulk Na (bcc, space gp #229_Im-3m)
wiht k-mesh 30*30*30 and found the plasma frequency (in
case.outputjoint) as
 Plasma frequencies:

   w_p_xx  w_p_zz[eV]

   5.9446  5.9446

Now I constructed a supercell 1*1*6 (definitely symmetry reduced
and now sp.gp  is 1_P1), used k-mesh 30*30*5 and  found
Plasma frequencies (much deviating from bulk values):

   w_p_xx  w_p_zz[eV]

   5.76146  5.3446

Then used k-mesh 90*90*15 and found
Plasma frequencies (w_p_zz is deviating from bulk w_p_zz ):

   w_p_xx  w_p_zz[eV]

   5.9485  5.8903

I have read the previous post
(https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg09782.html)
but it is not speaking about w_p_zz. So when I plot epsilon data
for w_p_xx then it is matching with that of bulk but when I use
w_p_zz  then it is definitely  away from bulk. Should I consider
w_p_zz  or use "number of choice = 1 in case.inop" and plot
epsilon only with w_p_xx ?


Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.


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--
Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.


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Re: [Wien] Bulk vs supercell Plasma frequency

2015-10-29 Thread Peter Blaha

In principle you are doing thinks now correct.
In reality, however, we use the tetrahedra-method in the integration of 
the BZ to calculate a joint-density-of-states. And for a metal !!! here 
there is a difference between k-meshes in the small or large cell. (it 
is related to the "back-folding" problem and in the supercell there are 
less tetrahedra and thus less possibilities to interpolate for the 
tetrahedron method than in the small cell).


In any case, you need to consider two things:

a) You have to decide to which accurcy a certain number should be 
calculated. Typically, a plasma frequency would be quoted with one or 
two digits after the comma (i.e. 5.9 or at most 5.94 eV).


b) Then you have to converge the numbers with respect to k-mesh (but 
also Rkmax !!)
Definitely you should use a ratio of 6:1 for the supercell, but 
eventually you need to increase the mesh until there are no changes 
within the desired accuracy. In your case, 90x15 is almost sufficient, 
but not quite if you want two digits accuracy.


c) in a cubic system, of course it is useless to quote two tensor 
components and one is sufficient.




Am 29.10.2015 um 10:35 schrieb Muhammad Sajjad:

Dear Prof. Blaha

I did some calculation for Bulk Na (bcc, space gp #229_Im-3m) wiht 
k-mesh 30*30*30 and found the plasma frequency (in case.outputjoint) as

 Plasma frequencies:

   w_p_xx  w_p_zz[eV]

   5.9446  5.9446

Now I constructed a supercell 1*1*6 (definitely symmetry reduced and 
now sp.gp  is 1_P1), used k-mesh 30*30*5 and  found

Plasma frequencies (much deviating from bulk values):

   w_p_xx  w_p_zz[eV]

   5.76146  5.3446

Then used k-mesh 90*90*15 and found
Plasma frequencies (w_p_zz is deviating from bulk w_p_zz ):

   w_p_xx  w_p_zz[eV]

   5.9485  5.8903

I have read the previous post 
(https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg09782.html) 
but it is not speaking about w_p_zz. So when I plot epsilon data for 
w_p_xx then it is matching with that of bulk but when I use w_p_zz  
then it is definitely  away from bulk. Should I consider w_p_zz  or 
use "number of choice = 1 in case.inop" and plot epsilon only with 
w_p_xx ?



Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.


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Re: [Wien] Bulk vs supercell Plasma frequency

2015-10-29 Thread Muhammad Sajjad
Dear Prof. P Blaha
Thank you very much for yous fruitful suggestions. However, I did not
change RKmax. For cubic Na only W_p_xx is enough but after making supercell
(1 1 6) still I need only w_p_xx and forget about w_p_zz, though the system
is tetragonal now. Is it right I understood?
Second  thing is it principally right that one converges SCF with small
k-mesh say 30*30*5 and then use the same scf ao get OPTICAL properties with
k-mesh say 90*90*15? I mean no need to converge scf with 90*90*15.
 Kind Regards

On Thu, Oct 29, 2015 at 9:03 PM, Peter Blaha 
wrote:

> In principle you are doing thinks now correct.
> In reality, however, we use the tetrahedra-method in the integration of
> the BZ to calculate a joint-density-of-states. And for a metal !!! here
> there is a difference between k-meshes in the small or large cell. (it is
> related to the "back-folding" problem and in the supercell there are less
> tetrahedra and thus less possibilities to interpolate for the tetrahedron
> method than in the small cell).
>
> In any case, you need to consider two things:
>
> a) You have to decide to which accurcy a certain number should be
> calculated. Typically, a plasma frequency would be quoted with one or two
> digits after the comma (i.e. 5.9 or at most 5.94 eV).
>
> b) Then you have to converge the numbers with respect to k-mesh (but also
> Rkmax !!)
> Definitely you should use a ratio of 6:1 for the supercell, but eventually
> you need to increase the mesh until there are no changes within the desired
> accuracy. In your case, 90x15 is almost sufficient, but not quite if you
> want two digits accuracy.
>
> c) in a cubic system, of course it is useless to quote two tensor
> components and one is sufficient.
>
>
>
>
> Am 29.10.2015 um 10:35 schrieb Muhammad Sajjad:
>
> Dear Prof. Blaha
>
> I did some calculation for Bulk Na (bcc, space gp #229_Im-3m) wiht k-mesh
> 30*30*30 and found the plasma frequency (in case.outputjoint) as
>  Plasma frequencies:
>
>w_p_xx  w_p_zz[eV]
>
>5.9446  5.9446
>
> Now I constructed a supercell 1*1*6 (definitely symmetry reduced and now
> sp.gp is 1_P1), used k-mesh 30*30*5 and  found
> Plasma frequencies (much deviating from bulk values):
>
>w_p_xx  w_p_zz[eV]
>
>5.76146  5.3446
>
> Then used k-mesh 90*90*15 and found
> Plasma frequencies (w_p_zz is deviating from bulk w_p_zz ):
>
>w_p_xx  w_p_zz[eV]
>
>5.9485  5.8903
>
> I have read the previous post (
> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg09782.html)
> but it is not speaking about w_p_zz. So when I plot epsilon data for
> w_p_xx then it is matching with that of bulk but when I use w_p_zz  then it
> is definitely  away from bulk. Should I consider w_p_zz  or use "number
> of choice = 1 in case.inop" and plot epsilon only with w_p_xx ?
>
>
> Kind Regards
> Muhammad Sajjad
> Post Doctoral Fellow
> KAUST, KSA.
>
>
> ___
> Wien mailing 
> listw...@zeus.theochem.tuwien.ac.athttp://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
>
>


-- 
Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.
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