[Wien] Large difference in calculated and experimental EFG
Peter Blaha
pblaha at theochem.tuwien.ac.at
Tue Mar 19 07:32:14 CET 2019
I guess you said it is TiNi.
How can a 2x2x2 supercell have 24 atoms ? This implies it has 3 atoms in
the original cell, but that cannot be TiNi.
Even more puzzling: 3x3x2 times 3 is for sure not 48 atoms ????
PS: I'd definitely go first to about 60 atoms cells, later on test
convergence with 120 atoms cells !!!
More problems: What is your RKmax ? You definitely should increase it
from the default 7.0 ! What is your k-mesh ?? It is a metal !
And finally: Is it know whether the Ta sits on a substitutional site ?
Which one, Ti or Ni ? Or is it some interstital site ??
Most likely this is not well known experimentally. So several different
model calculations may be necessary and you can use E-tot (lowest) as
well as the EFG/eta to decide which structural model is the correct one.
Am 19.03.2019 um 05:56 schrieb Ramsewak Kashyap:
> In 2x2x2 supercell, total no. of atoms was 24 and it gave EFG value 6.5
> 10**21V/m**2 with eta 0.81.
> I have also calculated for 3x3x2 supercell has 48 atoms and it gave EFG
> value 6.3 10**21V/m**2 with eta 0.88
>
> While experimental is about EFG is 4.4 with eta 0.60..
>
> On Mon 18 Mar, 2019, 7:39 PM Peter Blaha, <pblaha at theochem.tuwien.ac.at
> <mailto:pblaha at theochem.tuwien.ac.at>> wrote:
>
> Most importantly: You talked about a 2x2x2 supercell ???
>
> We don't know how big your original cell was, but a 16 atome cell
> with 1
> T is not an impurity as measured in PAC.
> How many atoms are in this supercell ???
>
> You must probably increase the supercell size and check convergence of
> the EFG.
>
> On 3/18/19 1:15 PM, Stefaan Cottenier wrote:
> > If the goal is to have a EFG that is a predictive as possible for
> > experiment, then it is advised to take the experimental cell
> parameters
> > (but with position optimization).
> >
> > If that EFG does not agree with experiment, then this is a
> trigger to
> > search further. There can be many reasons (assuming both the
> experiment
> > and the calculation are correctly done):
> >
> > * You have an unusually sensitive case, where small details that
> > usually do not matter do affect the EFG
> > * The effect of temperature might be unusually large (your
> calculation
> > is at 0 K)
> > * Maybe the Ta atom is associated with a defect (vacancy, oxygen,…)
> > and the experiment measures that complex.
> > * …
> >
> > Stefaan
> >
> > *From:*Wien <wien-bounces at zeus.theochem.tuwien.ac.at
> <mailto:wien-bounces at zeus.theochem.tuwien.ac.at>> *On Behalf Of
> > *Ramsewak Kashyap
> > *Sent:* Monday, March 18, 2019 12:41 PM
> > *To:* A Mailing list for WIEN2k users
> <wien at zeus.theochem.tuwien.ac.at
> <mailto:wien at zeus.theochem.tuwien.ac.at>>
> > *Subject:* Re: [Wien] Large difference in calculated and
> experimental EFG
> >
> > atomic positions optimization means force relaxation.. I have
> did that.
> > but I am asking about cell parameter optimization. Is it
> necessary for
> > .cif file getting form COD??
> >
> > Thanks
> >
> > On Mon, Mar 18, 2019 at 4:55 PM Stefaan Cottenier
> > <Stefaan.Cottenier at ugent.be <mailto:Stefaan.Cottenier at ugent.be>
> <mailto:Stefaan.Cottenier at ugent.be
> <mailto:Stefaan.Cottenier at ugent.be>>> wrote:
> >
> > Yes, optimization of the atomic positions is absolutely
> necessary to
> > have a meaningful value for Vzz and eta in a supercell.
> >
> > Stefaan
> >
> > *From:*Wien <wien-bounces at zeus.theochem.tuwien.ac.at
> <mailto:wien-bounces at zeus.theochem.tuwien.ac.at>
> > <mailto:wien-bounces at zeus.theochem.tuwien.ac.at
> <mailto:wien-bounces at zeus.theochem.tuwien.ac.at>>> *On Behalf Of
> > *Ramsewak Kashyap
> > *Sent:* Monday, March 18, 2019 12:23 PM
> > *To:* A Mailing list for WIEN2k users
> > <wien at zeus.theochem.tuwien.ac.at
> <mailto:wien at zeus.theochem.tuwien.ac.at>
> > <mailto:wien at zeus.theochem.tuwien.ac.at
> <mailto:wien at zeus.theochem.tuwien.ac.at>>>
> > *Subject:* [Wien] Large difference in calculated and
> experimental EFG
> >
> > Hi Wien2k users,
> >
> > I am doing EFG calculation for TiNi monoclinic phase, but I am
> > getting large difference in Calculated and measured value, I have
> > taken parameters from COD, then make 2x2x2 supercell and
> replace one
> > Ti with Ta atom... is structural optimization is necessary?? and
> > eta value was also quite large as compare to measured value.
> >
> > --
> >
> > Ramsewak Kashyap
> > Saha Institute of Nuclear Physics
> > 9473811023
> >
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> >
> > --
> >
> > Ramsewak Kashyap
> > Saha Institute of Nuclear Physics
> > 9473811023
> >
> >
> > _______________________________________________
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> --
>
> P.Blaha
> --------------------------------------------------------------------------
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