Dear Laurence Marks Sir,<div><br></div><div> Yes this is an oxide and it is an insulator and probably I have made it a metal by creating <b>cationic vacancies</b>. Sir I will let you know the detail after checking it from case.output2. But Sir, please forgive my curiosity, I could not wait to ask you and also going a bit away from wien2k questions:</div>
<div>1) Sir the goodness of fit (GOF) obtained from Rietveld analysis done through XPERT Highscore plus : 1.0038</div><div> and except this data we do not have any other proof to show that it really have cationic vacancies. </div>
<div> Then Sir according to you we can not trust this data (considering GOF) only to consider cationic vacancies?</div><div><br></div><div>With best regards,</div><div><br></div><div> <br><br><div class="gmail_quote">
On Mon, Sep 5, 2011 at 9:31 PM, Laurence Marks <span dir="ltr"><<a href="mailto:L-marks@northwestern.edu">L-marks@northwestern.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Follow the science, not the DFT.<br>
<br>
1) Unless you have a large grain size and synchotron data I really<br>
wonder about the logic of removing 1 atom in a 2x1x1 supercell.<br>
Particularly if this is an oxide, have you made it a metal whereas it<br>
should be an insulator? Does the fit pass significance tests etc? Do<br>
you have other data that implies vacancies?<br>
2) In terms of the DFT, I expect that you have made it a metal which<br>
is harder to converge than an insulator. Check in case.output2 in both<br>
cases (a quick, pseudo DOOS). If it really does have vacancies, you<br>
might need more than 7 kpts, and I suggest using TEMPS.<br>
<br>
2011/9/5 shamik chakrabarti <<a href="mailto:shamikphy@gmail.com">shamikphy@gmail.com</a>>:<br>
<div><div></div><div class="h5">> Dear wien2k users,<br>
> I have performed a 56 atom / unit cell calculation for a<br>
> ferrimagnetic material. It was well converged both in energy and charge by<br>
> 60 iterations. 14 K points were used for this calculation. Then I have<br>
> generated a 2x1x1 supercell having 112 atoms / supercell. This was done to<br>
> achieve better experimental model as obtained through Rietveld analysis.<br>
> From Rietveld analysis it was also seen that for 112 atoms we can consider a<br>
> cation (Fe) vacancy and we have generated it by deleting one Fe atom from<br>
> the supercell. Final structure, hence, contains 111 atoms and all other<br>
> occupancies at different lattice sites are well matched with Rietveld<br>
> analysis of experimental XRD. I am using 2 k points for this 111 atom<br>
> supercell. But even after 60 iterations the convergence achieved are as<br>
> follows:<br>
> cc: 0.234... cc was set to 0.001<br>
> ec: 0.063... ec was set to 0.0001<br>
> Sir, my question are:<br>
> 1) As the supercell is merely an extension of the 56 atoms unit cell with<br>
> more accurate values of atomic occupancies as in the experimental structure,<br>
> why it should at all taking so much time to converge?<br>
> 2) We have created one defect by creating a Fe vacancy...is it that the<br>
> structures having defect take more time to converge?...but as far as our<br>
> analysis until now..the structure should have one Fe vacancy per 112<br>
> atoms...<br>
> 3) As we have obtained converged solutions for 56 atom cell by using 14 k<br>
> points..is it that we should use 7K points for 111 atom supercell<br>
> calculation?..is 2 K points are actually small in order to achieve<br>
> convergence of this structure?<br>
> Any response in this regard will be very helpful for us. Thanks in advance.<br>
> with regards,<br>
><br>
> --<br>
> Shamik Chakrabarti<br>
> Senior Research Fellow<br>
> Dept. of Physics & Meteorology<br>
> Material Processing & Solid State Ionics Lab<br>
> IIT Kharagpur<br>
> Kharagpur 721302<br>
> INDIA<br>
><br>
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><br>
><br>
<br>
<br>
<br>
--<br>
Laurence Marks<br>
Department of Materials Science and Engineering<br>
MSE Rm 2036 Cook Hall<br>
2220 N Campus Drive<br>
Northwestern University<br>
Evanston, IL 60208, USA<br>
Tel: (847) 491-3996 Fax: (847) 491-7820<br>
email: L-marks at northwestern dot edu<br>
Web: <a href="http://www.numis.northwestern.edu" target="_blank">www.numis.northwestern.edu</a><br>
Research is to see what everybody else has seen, and to think what<br>
nobody else has thought<br>
Albert Szent-Gyorgi<br>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br>Shamik Chakrabarti<br>Senior Research Fellow<br>Dept. of Physics & Meteorology<br>Material Processing & Solid State Ionics Lab<br>IIT Kharagpur<br>Kharagpur 721302<br>
INDIA<br>
</div>