Re: [Wien] force difference between LAPW and PAW method

2016-01-30 Thread Laurence Marks
I would expect there to be slight differences in the energy versus cell for
the two approaches, which could easily lead to forces.

That said, I doubt that the forces will have any effect on what you are
trying to calculate. Do a simple test such as a small TiO2 supercell and
displace an O.

---
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
http://www.numis.northwestern.edu
Corrosion in 4D http://MURI4D.numis.northwestern.edu
Co-Editor, Acta Cryst A
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
On Jan 29, 2016 10:04, "pavel.ondra...@email.cz" <pavel.ondra...@email.cz>
wrote:

>
> -- Původní zpráva --
> Od: Laurence Marks <laurence.ma...@gmail.com>
> Komu: A Mailing list for WIEN2k users <wien@zeus.theochem.tuwien.ac.at>
> Datum: 29. 1. 2016 13:34:23
> Předmět: Re: [Wien] force difference between LAPW and PAW method
>
> Did you check the absolute cell size for the two - minimize the energy
> w.r.t. size?
>
>
> The absolute cell size was fixed (same in both softwares of course) and
> was calculated using experimental densities for the mixtures. No
> minimization with respect to cell volume was done, however I would expect
> it to be near equilibrium. My main goal with those cells is to calculate
> the XPS shifts of O1s peak (using the slater transition state method) to
> help in evaluation of some experimental XPS data, so I wanted to stick with
> the experimental densities.
>
>
> Would some stress in the cell explain the difference between the methods?
>
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Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread Laurence Marks
Did you check for lattice parameter changes? A relatively small change for
a single unit cell can translate to something larger. Unfortunately you
need a reference compound, which is not so simple in your case. Perhaps
test SiO2, TiO2 & a few simple similar compounds with the PAW & Wien2k.

---
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
http://www.numis.northwestern.edu
Corrosion in 4D http://MURI4D.numis.northwestern.edu
Co-Editor, Acta Cryst A
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
On Jan 29, 2016 03:50, "Pavel Ondračka"  wrote:

> Dear Wien2k mailing list,
>
> I've been doing some calculation on a moderately large (around 100
> atoms) amorphous-like SixTi1-xO2 cells produced by simulated annealing
> MD in a PAW software. According to my colleague who did the final force
> relaxation, the residual forces on atoms should be around 0.5
> mRyd/Bohr. However when I calculate forces in Wien2k I see forces of
> order of magnitude larger, eg. some as large as 30mRyd/Bohr.
>
> This are exactly the same calculations: both using PBE, same k-grid,
> same RKMAX (calculated from cutoff using the formula from UG) and I've
> spent a lot of time checking the force convergence with respect to all
> possible parameters.
>
> We did some tests with small cells (eg. 10 atoms) and there we can get
> a consistent results with max difference of forces around 10-20% which
> I find reasonable. I'm actually quite clueless about it. I've been
> suspecting user error at the beginning however I haven't found any so
> far. My current theory is that in this large cases without symmetry
> maybe the small differences between methods somehow sum up and hence
> the big difference in final forces, however I would like to hear your
> opinion in this matter.
>
> Best regards
> Pavel Ondračka
> ___
> 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
>
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Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread Peter Blaha
If the disordered compound goes metallic ??? it could be a problem. The 
default WIEN2k is using TETRA, while VASP uses a large broadening.


Again, forget the 400 eV of the PAW calculation. It has NOTHING to do 
with our RKmax and our basis sets are usually more efficient.


In any case, RKMAX=8.5 is "more than overconverged", since your smallest 
sphere is probably Oxygen. I'd start such a calculation with RKMAX=5 and 
later check with 6 and/or 7.


Another possible problem: SiO2 might have small spheres for Si leading 
to quite some core leakage ??? Either use .lcore or put the Si-2p as 
semicore !



On 01/29/2016 12:04 PM, Pavel Ondračka wrote:

Peter Blaha píše v Pá 29. 01. 2016 v 11:43 +0100:

This looks fairly large.

I do NOT understand your statement of using "the same RKMAX" ???
PAW does not have RKMAX and their KMAX has NOTHING to do with ours.
What was your RKMAX and what are youre sphere sizes ???


Sorry, the right word should probably be "equivalent RKMAX". As
mentioned in the original email, the RKMAX was calculated from cutoff
in EV using the scheme from userguide (sqrt(cutoff in Ryd) * size of
smallest sphere). Specific values differed between cells, smallest
spheres were around 1.5 and the RKMAX was around 8.0 (PAW cutoff of
400eV).


k-mesh: not only the grid is important ! As far as I know, VASP
usually
uses a "huge" temperature broadening. What FERMI-method are you using
?


default


spin-polarization ??


no


Is the PAW done with VASP and a fairly new release (accurate PAW
potentials ?)


It was VASP and it was one of the latest versions. Will check for
specifics.



On 01/29/2016 10:50 AM, Pavel Ondračka wrote:

Dear Wien2k mailing list,

I've been doing some calculation on a moderately large (around 100
atoms) amorphous-like SixTi1-xO2 cells produced by simulated
annealing
MD in a PAW software. According to my colleague who did the final
force
relaxation, the residual forces on atoms should be around 0.5
mRyd/Bohr. However when I calculate forces in Wien2k I see forces
of
order of magnitude larger, eg. some as large as 30mRyd/Bohr.

This are exactly the same calculations: both using PBE, same k-
grid,
same RKMAX (calculated from cutoff using the formula from UG) and
I've
spent a lot of time checking the force convergence with respect to
all
possible parameters.

We did some tests with small cells (eg. 10 atoms) and there we can
get
a consistent results with max difference of forces around 10-20%
which
I find reasonable. I'm actually quite clueless about it. I've been
suspecting user error at the beginning however I haven't found any
so
far. My current theory is that in this large cases without symmetry
maybe the small differences between methods somehow sum up and
hence
the big difference in final forces, however I would like to hear
your
opinion in this matter.

Best regards
Pavel Ondračka
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--

  P.Blaha
--
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Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
Email: bl...@theochem.tuwien.ac.atWIEN2k: http://www.wien2k.at
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Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread Pavel Ondračka
Peter Blaha píše v Pá 29. 01. 2016 v 11:43 +0100:
> This looks fairly large.
> 
> I do NOT understand your statement of using "the same RKMAX" ???
> PAW does not have RKMAX and their KMAX has NOTHING to do with ours.
> What was your RKMAX and what are youre sphere sizes ???

Sorry, the right word should probably be "equivalent RKMAX". As
mentioned in the original email, the RKMAX was calculated from cutoff
in EV using the scheme from userguide (sqrt(cutoff in Ryd) * size of
smallest sphere). Specific values differed between cells, smallest
spheres were around 1.5 and the RKMAX was around 8.0 (PAW cutoff of
400eV). 
> 
> k-mesh: not only the grid is important ! As far as I know, VASP
> usually 
> uses a "huge" temperature broadening. What FERMI-method are you using
> ?

default

> spin-polarization ??

no

> Is the PAW done with VASP and a fairly new release (accurate PAW 
> potentials ?)

It was VASP and it was one of the latest versions. Will check for
specifics.

> 
> On 01/29/2016 10:50 AM, Pavel Ondračka wrote:
> > Dear Wien2k mailing list,
> > 
> > I've been doing some calculation on a moderately large (around 100
> > atoms) amorphous-like SixTi1-xO2 cells produced by simulated
> > annealing
> > MD in a PAW software. According to my colleague who did the final
> > force
> > relaxation, the residual forces on atoms should be around 0.5
> > mRyd/Bohr. However when I calculate forces in Wien2k I see forces
> > of
> > order of magnitude larger, eg. some as large as 30mRyd/Bohr.
> > 
> > This are exactly the same calculations: both using PBE, same k-
> > grid,
> > same RKMAX (calculated from cutoff using the formula from UG) and
> > I've
> > spent a lot of time checking the force convergence with respect to
> > all
> > possible parameters.
> > 
> > We did some tests with small cells (eg. 10 atoms) and there we can
> > get
> > a consistent results with max difference of forces around 10-20%
> > which
> > I find reasonable. I'm actually quite clueless about it. I've been
> > suspecting user error at the beginning however I haven't found any
> > so
> > far. My current theory is that in this large cases without symmetry
> > maybe the small differences between methods somehow sum up and
> > hence
> > the big difference in final forces, however I would like to hear
> > your
> > opinion in this matter.
> > 
> > Best regards
> > Pavel Ondračka
> > ___
> > 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
> > 
> 
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Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread Laurence Marks
Did you check the absolute cell size for the two - minimize the energy
w.r.t. size?

---
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
http://www.numis.northwestern.edu
Corrosion in 4D http://MURI4D.numis.northwestern.edu
Co-Editor, Acta Cryst A
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
On Jan 29, 2016 04:38, "Pavel Ondračka"  wrote:

> Laurence Marks píše v Pá 29. 01. 2016 v 04:22 -0600:
> > Did you check for lattice parameter changes? A relatively small
> > change for a single unit cell can translate to something larger.
> > Unfortunately you need a reference compound, which is not so simple
> > in your case. Perhaps test SiO2, TiO2 & a few simple similar
> > compounds with the PAW & Wien2k.
>
> Yeah, some difference in cell size or positions was one of my suspects.
> I usually use VESTA to read the structure file from PAW software, then
> output to cif and use cif2struct to convert to struct and I was
> suspecting that maybe somewhere in this process I lose precision.
> So I've actually written a small python script to convert it directly
> with full precision allowed by the struct format, however the result
> were almost identical.
> Regarding the test cases, we tested eg. with rutile (with one atom
> slightly displaced to induce some forces) and the result were
> comparable (few percent difference).
>
> Best regards
> Pavel Ondračka
> ___
> 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
>
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Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread Peter Blaha
Maybe one should use in VASP also a PAW potential which has Si-2p as 
valence.


On 01/29/2016 12:47 PM, pavel.ondra...@email.cz wrote:


-- Původní zpráva --
Od: Peter Blaha <pbl...@theochem.tuwien.ac.at>
Komu: A Mailing list for WIEN2k users <wien@zeus.theochem.tuwien.ac.at>
Datum: 29. 1. 2016 12:18:58
Předmět: Re: [Wien] force difference between LAPW and PAW method


If the disordered compound goes metallic ??? it could be a problem. The
default WIEN2k is using TETRA, while VASP uses a large broadening.


The resulting structure has gap at least as large as TiO2.


Again, forget the 400 eV of the PAW calculation. It has NOTHING to do
with our RKmax and our basis sets are usually more efficient.

In any case, RKMAX=8.5 is "more than overconverged", since your
smallest
sphere is probably Oxygen. I'd start such a calculation with RKMAX=5
and
later check with 6 and/or 7.


True, for usual calculations I use value RKMAX around 7.0 for such
compounds, I went to 8.0 just for convergence checking purposes. However
average differences in forces between 7.0 and 8.0 were quite small <
0.2mRyd/Bohr


Another possible problem: SiO2 might have small spheres for Si leading
to quite some core leakage ??? Either use .lcore or put the Si-2p as
semicore !


Indeed I've noticed that silicon gets very small sphere especially with
the new scheme in setrm. I'm using the "original" scheme, where the Si
usually gets same sphere as O, around 1.5. Also Si2-p states were chosen
as semicore. No core leakage warnings in logs.


On 01/29/2016 12:04 PM, Pavel Ondračka wrote:
 > Peter Blaha píše v Pá 29. 01. 2016 v 11:43 +0100:
 >> This looks fairly large.
 >>
 >> I do NOT understand your statement of using "the same RKMAX" ???
 >> PAW does not have RKMAX and their KMAX has NOTHING to do with ours.
 >> What was your RKMAX and what are youre sphere sizes ???
 >
 > Sorry, the right word should probably be "equivalent RKMAX". As
 > mentioned in the original email, the RKMAX was calculated from cutoff
 > in EV using the scheme from userguide (sqrt(cutoff in Ryd) * size of
 > smallest sphere). Specific values differed between cells, smallest
 > spheres were around 1.5 and the RKMAX was around 8.0 (PAW cutoff of
 > 400eV).
 >>
 >> k-mesh: not only the grid is important ! As far as I know, VASP
 >> usually
 >> uses a "huge" temperature broadening. What FERMI-method are you
using
 >> ?
 >
 > default
 >
 >> spin-polarization ??
 >
 > no
 >
 >> Is the PAW done with VASP and a fairly new release (accurate PAW
 >> potentials ?)
 >
 > It was VASP and it was one of the latest versions. Will check for
 > specifics.
 >
 >>
 >> On 01/29/2016 10:50 AM, Pavel Ondračka wrote:
 >>> Dear Wien2k mailing list,
 >>>
 >>> I've been doing some calculation on a moderately large (around 100
 >>> atoms) amorphous-like SixTi1-xO2 cells produced by simulated
 >>> annealing
 >>> MD in a PAW software. According to my colleague who did the final
 >>> force
 >>> relaxation, the residual forces on atoms should be around 0.5
 >>> mRyd/Bohr. However when I calculate forces in Wien2k I see forces
 >>> of
 >>> order of magnitude larger, eg. some as large as 30mRyd/Bohr.
 >>>
 >>> This are exactly the same calculations: both using PBE, same k-
 >>> grid,
 >>> same RKMAX (calculated from cutoff using the formula from UG) and
 >>> I've
 >>> spent a lot of time checking the force convergence with respect to
 >>> all
 >>> possible parameters.
 >>>
 >>> We did some tests with small cells (eg. 10 atoms) and there we can
 >>> get
 >>> a consistent results with max difference of forces around 10-20%
 >>> which
 >>> I find reasonable. I'm actually quite clueless about it. I've been
 >>> suspecting user error at the beginning however I haven't found any
 >>> so
 >>> far. My current theory is that in this large cases without symmetry
 >>> maybe the small differences between methods somehow sum up and
 >>> hence
 >>> the big difference in final forces, however I would like to hear
 >>> your
 >>> opinion in this matter.
 >>>
 >>> Best regards
 >>> Pavel Ondračka
 >>> ___

Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread Pavel Ondračka
Laurence Marks píše v Pá 29. 01. 2016 v 04:22 -0600:
> Did you check for lattice parameter changes? A relatively small
> change for a single unit cell can translate to something larger.
> Unfortunately you need a reference compound, which is not so simple
> in your case. Perhaps test SiO2, TiO2 & a few simple similar
> compounds with the PAW & Wien2k.

Yeah, some difference in cell size or positions was one of my suspects.
I usually use VESTA to read the structure file from PAW software, then
output to cif and use cif2struct to convert to struct and I was
suspecting that maybe somewhere in this process I lose precision. 
So I've actually written a small python script to convert it directly
with full precision allowed by the struct format, however the result
were almost identical.
Regarding the test cases, we tested eg. with rutile (with one atom
slightly displaced to induce some forces) and the result were
comparable (few percent difference).

Best regards
Pavel Ondračka
___
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Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread Peter Blaha

This looks fairly large.

I do NOT understand your statement of using "the same RKMAX" ???
PAW does not have RKMAX and their KMAX has NOTHING to do with ours.
What was your RKMAX and what are youre sphere sizes ???

k-mesh: not only the grid is important ! As far as I know, VASP usually 
uses a "huge" temperature broadening. What FERMI-method are you using ?


spin-polarization ??

Is the PAW done with VASP and a fairly new release (accurate PAW 
potentials ?)


On 01/29/2016 10:50 AM, Pavel Ondračka wrote:

Dear Wien2k mailing list,

I've been doing some calculation on a moderately large (around 100
atoms) amorphous-like SixTi1-xO2 cells produced by simulated annealing
MD in a PAW software. According to my colleague who did the final force
relaxation, the residual forces on atoms should be around 0.5
mRyd/Bohr. However when I calculate forces in Wien2k I see forces of
order of magnitude larger, eg. some as large as 30mRyd/Bohr.

This are exactly the same calculations: both using PBE, same k-grid,
same RKMAX (calculated from cutoff using the formula from UG) and I've
spent a lot of time checking the force convergence with respect to all
possible parameters.

We did some tests with small cells (eg. 10 atoms) and there we can get
a consistent results with max difference of forces around 10-20% which
I find reasonable. I'm actually quite clueless about it. I've been
suspecting user error at the beginning however I haven't found any so
far. My current theory is that in this large cases without symmetry
maybe the small differences between methods somehow sum up and hence
the big difference in final forces, however I would like to hear your
opinion in this matter.

Best regards
Pavel Ondračka
___
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http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
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--

  P.Blaha
--
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
Email: bl...@theochem.tuwien.ac.atWIEN2k: http://www.wien2k.at
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Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread pavel.ondracka


-- Původní zpráva --
Od: Peter Blaha <pbl...@theochem.tuwien.ac.at>
Komu: A Mailing list for WIEN2k users <wien@zeus.theochem.tuwien.ac.at>
Datum: 29. 1. 2016 12:18:58
Předmět: Re: [Wien] force difference between LAPW and PAW method

"If the disordered compound goes metallic ??? it could be a problem. The 
default WIEN2k is using TETRA, while VASP uses a large broadening."



The resulting structure has gap at least as large as TiO2.

"
Again, forget the 400 eV of the PAW calculation. It has NOTHING to do 
with our RKmax and our basis sets are usually more efficient.

In any case, RKMAX=8.5 is "more than overconverged", since your smallest 
sphere is probably Oxygen. I'd start such a calculation with RKMAX=5 and 
later check with 6 and/or 7."


""
True, for usual calculations I use value RKMAX around 7.0 for such 
compounds, I went to 8.0 just for convergence checking purposes. However 
average differences in forces between 7.0 and 8.0 were quite small < 0.2
mRyd/Bohr

"
Another possible problem: SiO2 might have small spheres for Si leading 
to quite some core leakage ??? Either use .lcore or put the Si-2p as 
semicore !"



Indeed I've noticed that silicon gets very small sphere especially with the 
new scheme in setrm. I'm using the "original" scheme, where the Si usually 
gets same sphere as O, around 1.5. Also Si2-p states were chosen as 
semicore. No core leakage warnings in logs.

"
On 01/29/2016 12:04 PM, Pavel Ondračka wrote:
> Peter Blaha píše v Pá 29. 01. 2016 v 11:43 +0100:
>> This looks fairly large.
>>
>> I do NOT understand your statement of using "the same RKMAX" ???
>> PAW does not have RKMAX and their KMAX has NOTHING to do with ours.
>> What was your RKMAX and what are youre sphere sizes ???
>
> Sorry, the right word should probably be "equivalent RKMAX". As
> mentioned in the original email, the RKMAX was calculated from cutoff
> in EV using the scheme from userguide (sqrt(cutoff in Ryd) * size of
> smallest sphere). Specific values differed between cells, smallest
> spheres were around 1.5 and the RKMAX was around 8.0 (PAW cutoff of
> 400eV).
>>
>> k-mesh: not only the grid is important ! As far as I know, VASP
>> usually
>> uses a "huge" temperature broadening. What FERMI-method are you using
>> ?
>
> default
>
>> spin-polarization ??
>
> no
>
>> Is the PAW done with VASP and a fairly new release (accurate PAW
>> potentials ?)
>
> It was VASP and it was one of the latest versions. Will check for
> specifics.
>
>>
>> On 01/29/2016 10:50 AM, Pavel Ondračka wrote:
>>> Dear Wien2k mailing list,
>>>
>>> I've been doing some calculation on a moderately large (around 100
>>> atoms) amorphous-like SixTi1-xO2 cells produced by simulated
>>> annealing
>>> MD in a PAW software. According to my colleague who did the final
>>> force
>>> relaxation, the residual forces on atoms should be around 0.5
>>> mRyd/Bohr. However when I calculate forces in Wien2k I see forces
>>> of
>>> order of magnitude larger, eg. some as large as 30mRyd/Bohr.
>>>
>>> This are exactly the same calculations: both using PBE, same k-
>>> grid,
>>> same RKMAX (calculated from cutoff using the formula from UG) and
>>> I've
>>> spent a lot of time checking the force convergence with respect to
>>> all
>>> possible parameters.
>>>
>>> We did some tests with small cells (eg. 10 atoms) and there we can
>>> get
>>> a consistent results with max difference of forces around 10-20%
>>> which
>>> I find reasonable. I'm actually quite clueless about it. I've been
>>> suspecting user error at the beginning however I haven't found any
>>> so
>>> far. My current theory is that in this large cases without symmetry
>>> maybe the small differences between methods somehow sum up and
>>> hence
>>> the big difference in final forces, however I would like to hear
>>> your
>>> opinion in this matter.
>>>
>>> Best regards
>>> Pavel Ondračka
>>> ___
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Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread pavel.ondracka


-- Původní zpráva --
Od: Laurence Marks <laurence.ma...@gmail.com>
Komu: A Mailing list for WIEN2k users <wien@zeus.theochem.tuwien.ac.at>
Datum: 29. 1. 2016 13:34:23
Předmět: Re: [Wien] force difference between LAPW and PAW method

"

Did you check the absolute cell size for the two - minimize the energy w.r.
t. size?

"



The absolute cell size was fixed (same in both softwares of course) and was 
calculated using experimental densities for the mixtures. No minimization 
with respect to cell volume was done, however I would expect it to be near 
equilibrium. My main goal with those cells is to calculate the XPS shifts of
O1s peak (using the slater transition state method) to help in evaluation of
some experimental XPS data, so I wanted to stick with the experimental 
densities.




Would some stress in the cell explain the difference between the methods?

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Re: [Wien] force difference between LAPW and PAW method

2016-01-29 Thread pavel.ondracka


-- Původní zpráva --
Od: Peter Blaha <pbl...@theochem.tuwien.ac.at>
Komu: A Mailing list for WIEN2k users <wien@zeus.theochem.tuwien.ac.at>
Datum: 29. 1. 2016 12:56:20
Předmět: Re: [Wien] force difference between LAPW and PAW method

"Maybe one should use in VASP also a PAW potential which has Si-2p as 
valence. 
""
"
Thanks for the advice, we will try this. 

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