If your structure is a metal in GGA in 99% of cases it will be a metal in GGA+U and mBJ. And, it is wrong. Just because others reported the structure does not mean that it is right! There are many cases where someone reported a structure, others followed their lead and only later someone pointed out that it was wrong.
Look at your GGA (or GGA+U) result, the overall DOS which is in case.output2up/dn (or do a standard DOS calculation). If the positions are close to correct you should see a gap between the different bands. If you have electrons at E_F at the bottom of a band (metal d) your structure is reduced; you will need some metal vacancies. If there are holes at the top of the oxygen band your structure is oxidized -- you will need some oxygen vacancies. Note that vacancies can be ordered or disordered (partial occupancies) and simulating these is not easy. Check the bond-valence sums, they are probably given by the powder diffraction fitting program or there are many codes to do this. You can even do a "grep -e bond case.outputnn" to get a decent number. All the O's should be close to 2 (perhaps in the range 1.8-2.2) and all the metals should be in reasonable states. For instance a value of 3.5 for Ti means that it is reduced, and a value of 4.5 means that something is badly wrong. As a shameless plug look at Surface Science doi:10.1016/j.susc.2011.10.018 and references therein, or for instance I.D. Brown, Chem. Rev. 109 (2009). In my opinion BVS is a simple and very quick way to do a sanity check and can save you from weeks of not useful DFT calculations. 2011/12/12 shamik chakrabarti <shamikphy at gmail.com>: > Dear Dr. Laurence Marks Sir, > > I am giving the answers all of your queries below, > > a) If R-factor means reliability factor then we have achieved a parameter > called goodness of fit whose value was 1.0038. But this material was > prepared previously by researchers and they have also got the same > structure. Although the structure is based only on the Rietveld fitting of > experimental XRD pattern. There was no rigorous TEM analysis on this > structure so far. > > b) We have done UV-visible band gap measurement on this material and it is > 3.26 eV. But as you have said properly it is indeed coming as metal after > getting converged in 80 iterations. But we have noticed that there are > presence of O p orbital between upper and lower Hubbard band of transition > metal atom and hence GGA+U will not improve the situation. > > c) At the moment we are a bit handicapped for doing Geometrical (both > lattice parameter and atomic coordinates) optimization of 56 atoms unit cell > structure as we do not have the facility of cluster. Hence as a first > approximation we are first trying to reach as near as possible to the > accurate electronic structure. We are soon going to get the facility and > then we can use geometrical optimization. > And hence we really do have large forces on the structure. > > d) We have used a greed of 0.2 and 0.15 both for PRATT mixing and we have > not used MSR1 mixing for mbj potential yet. > > Sir, as far as the above discussion is concerned we might have our structure > wrong (need more accurate TEM analysis!) or Geometrical optimization may > solve the problem. But as we are now trying to experiment with test run we > and as it seems GGA+U can not solve the problem we have opted for mbj > potential. > > But as you have said if the structure is wrong (we are not yet confirmed > though) we may never reach the convergence or desired electronic structure! > > Thank you very much for your help Sir. > > On Mon, Dec 12, 2011 at 6:52 PM, Laurence Marks <L-marks at northwestern.edu> > wrote: >> >> I wonder whether you really have the structure right. >> >> a) When you say that you get the same structure, what R-factor? Powder >> diffraction is not very sensitive to oxygen positions in the presence >> of heavy metal atoms. >> >> b) If GGA takes about 80 iterations I suspect that you have a metal. >> If you do not have the correct number of oxygen versus metal atoms you >> will get this, and no amount of U or mBJ will change this (in 99% of >> cases). Check the bond-valence sums of your model, are the numbers >> reasonable? This is a standard test in solid-state chemistry. >> >> c) Do you have large forces (as Peter asked)? If you do this also >> indicates that you have the structure wrong. >> >> d) When you say that you were using a greed of 0.2 (please do not use >> the term "mixing factor", it is misleading) was this for Pratt or >> MSR1? A change from 0.2 to 0.15 with MSR1 will not matter much. >> >> 2011/12/12 shamik chakrabarti <shamikphy at gmail.com>: >> > Dear Dr Peter Blaha and Dr Pascal, >> > >> > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? The material is a ferrimagnetic transition >> > metal compound and a charge transfer insulator and the gap is between d >> > and >> > O p states. Yes we have started MBJ potential calculation from the >> > converged >> > GGA charge density. So what we can do, we can start from the scratch >> > with >> > MBJ potential and after few iterations will get shifted to MSR1 mixing >> > to >> > improve the convergence. We hope that will help. Thank you for all your >> > helps. >> > >> > with regards, >> > >> > >> > On Mon, Dec 12, 2011 at 1:31 PM, pascal boulet >> > <pascal.boulet at univ-provence.fr> wrote: >> >> >> >> >> >> Dear Dr. Chakrabarti, >> >> >> >> All right. So, another idea: could it be that you restarted your m-BJ >> >> calculation using the converged GGA or GGA+U density? I ran into these >> >> kinds of troubles several times. I found it preferable to start from >> >> scratch... >> >> >> >> Hope this help, >> >> Pascal >> >> >> >> On 12/12/2011 08:45, shamik chakrabarti wrote: >> >> > Dear Dr. Pascal, >> >> > >> >> > ? ? ? ? ? ? ? ? As we were getting Ghost band error due to large >> >> > charge fluctuation during initial cycle *we have reduced the mixing >> >> > parameter from 0.2 to 0.15 & hence thereafter we have not received >> >> > ghost band error yet.* >> >> > >> >> > As long as variation of RMT is concerned the variation is only from >> >> > 1.7 to 2.01 in the structure. >> >> > >> >> > So far there is no energy equivalence between a local orbital and >> >> > overall energy parameter which can induce ghost band error. >> >> > >> >> > Also we have achieved convergence of -0.000034 with plain GGA and >> >> > only >> >> > with MBJ potential we are getting the convergence problem and again >> >> > plain GGA and also GGA+U have not given the proper electronic >> >> > structure. >> >> > >> >> > As far as the structure is concerned we are very much sure about its >> >> > structural parameters as they are giving the same XRD as experiment >> >> > when the positional coordinates and lattice parameters of the 56 atom >> >> > cell were put into a software powdcell. >> >> > >> >> > looking forwards to your comments. >> >> > >> >> > with regards, >> >> > On Mon, Dec 12, 2011 at 12:26 PM, pascal boulet >> >> > <pascal.boulet at univ-provence.fr >> >> > <mailto:pascal.boulet at univ-provence.fr>> wrote: >> >> > >> >> > ? ? Hello, >> >> > >> >> > ? ? It is strange that you have such a bad convergence on the energy >> >> > ? ? and the >> >> > ? ? charge after that many cycles. >> >> > ? ? My feeling is that something is wrong in the input. >> >> > >> >> > ? ? Have a look at the user manual. From page 205 on, there is an >> >> > ? ? explanation of the meaning of ghost bands. You have to experiment >> >> > on >> >> > ? ? your chemical system to get rid of them. >> >> > >> >> > ? ? Pascal >> >> > >> >> > >> >> > ? ? On 12/12/2011 05:21, shamik chakrabarti wrote: >> >> > ? ? > Dear wien2k users, >> >> > ? ? > >> >> > ? ? > ? ? ? ? ? ? ? ? ? ? ? ?Any response of my previous mail will be >> >> > very >> >> > ? ? > helpful for us. Eagerly waiting for your comments. >> >> > ? ? > >> >> > ? ? > with regards, >> >> > ? ? > >> >> > ? ? > ---------- Forwarded message ---------- >> >> > ? ? > From: *shamik chakrabarti* <shamikphy at gmail.com >> >> > ? ? <mailto:shamikphy at gmail.com> >> >> > ? ? > <mailto:shamikphy at gmail.com <mailto:shamikphy at gmail.com>>> >> >> > ? ? > Date: Sun, Dec 11, 2011 at 5:42 PM >> >> > ? ? > Subject: not getting convergence with MBJ potential >> >> > ? ? > 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>>> >> >> > ? ? > >> >> > ? ? > >> >> > ? ? > Dear wien2k users, >> >> > ? ? > >> >> > ? ? > ? ? ? ? ? ? ? ? ? ? ? ?I am trying to simulate electronic >> >> > ? ? structure of >> >> > ? ? > a charge transfer insulator. Our system consists of a unit cell >> >> > ? ? having >> >> > ? ? > 56 atoms and we are using 14 k-points. As GGA+U method was >> >> > failed >> >> > to >> >> > ? ? > reproduce the proper band gap (in fact much less than the >> >> > ? ? > experimentally obtained one) we have opted for MBJ potential. >> >> > ? ? > *Initially the mixing parameter was set to 0.2 and we got Ghost >> >> > band >> >> > ? ? > error after few iterations. Hence we reduce the mixing >> >> > parameter >> >> > to >> >> > ? ? > 0.15.* Until now still it has shown no error except some extra >> >> > ? ? message >> >> > ? ? > in case.dayfile. I am giving those messages below. So far e.c. >> >> > & >> >> > c.c >> >> > ? ? > were achieved up to 2.239... & 5.4599 respectively and already >> >> > 36 >> >> > ? ? > iterations are over. My questions are: >> >> > ? ? > >> >> > ? ? > (1) Is it ok to set up a mixing parameter of 0.15 that is with >> >> > ? ? it, is >> >> > ? ? > it possible to reach convergence? >> >> > ? ? > >> >> > ? ? > (2) As plain GGA takes around 80 iterations to converge, is it >> >> > that >> >> > ? ? > MBJ potential will take much higher than that as we know it is >> >> > ? ? always >> >> > ? ? > hard to get convergence with this method? >> >> > ? ? > >> >> > ? ? > (3) what are the meanings of the given messages below: >> >> > ? ? > >> >> > ? ? > ? lapw2 -c -up ? -vresp (17:12:13) > ? lapw1 ?-c -dn >> >> > ?(16:19:33) >> >> > ? ? > 10848.369u 98.026s 52:39.78 346.4%0+0k 0+1099920io 0pf+0w >> >> > ? ? > > ? lapw1 ?-c -up ? ?(15:26:49) 10864.462u 99.082s 52:44.39 >> >> > ? ? 346.4%0+0k >> >> > ? ? > 0+1100232io 0pf+0w >> >> > ? ? > 460.324u 151.313s 6:52.62 148.2%0+0k 0+732368io 0pf+0w >> >> > ? ? > ?-5.956509016536202E-002 >> >> > ? ? > ? 3.325214690385789E-002 -9.166205529297161E-002 tauwrong= >> >> > ? ? > ?int:rho,tauw,grho,g2rho ?2.146196813781874E-002 >> >> > ? ? ?1.287982148952303E-002 >> >> > ? ? > ?-4.564940741427861E-002 >> >> > ? ? > ? 3.061850458947012E-002 -5.357427363703868E-002 tauwrong= >> >> > ? ? > ?int:rho,tauw,grho,g2rho ?1.778719641126464E-002 >> >> > ? ? > ?1.317651193616000E-002 ? ? ? ?*what is tauwrong?* >> >> > ? ? > ?-4.561631481999567E-002 >> >> > ? ? > ? 3.051935798833875E-002 -5.372842413400847E-002 tauwrong= >> >> > ? ? > ?int:rho,tauw,grho,g2rho ?1.783702549056333E-002 >> >> > ? ? ?1.305474408433668E-002 >> >> > ? ? > ?-2.872847342414767E-002 >> >> > ? ? > ? 2.625149916992486E-002 -2.271097056901070E-002 tauwrong= >> >> > ? ? > ?int:rho,tauw,grho,g2rho ?1.456340274765583E-002 >> >> > ? ? ?1.183001700580401E-002 >> >> > ? ? > ?-2.843529510619935E-002 >> >> > ? ? > ? 2.607602777746414E-002 -2.279192386903682E-002 tauwrong= >> >> > ? ? > ?int:rho,tauw,grho,g2rho ?1.462794826548238E-002 >> >> > ? ? ?1.162089194449066E-002 >> >> > ? ? > ?-1.211083415464120E-002 >> >> > ? ? > .......................................... >> >> > ? ? > .......................................... >> >> > ? ? > > ? lapw0 (15:19:56) ?sphere:rho,tauw,grho,g2rho >> >> > 7.46875999972237 >> >> > ? ? > ? ? ?180.956718336004 >> >> > ? ? > > ? lapw0 -grr (15:15:10) 315.375u 93.253s 4:45.73 143.0%0+0k >> >> > ? ? > 0+................ >> >> > ? ? > >> >> > ? ? > >> >> > ? ? > Any response in this regard will be very helpful for us. Thanks >> >> > in >> >> > ? ? > advance. >> >> > ? ? > >> >> > ? ? > with regards, >> >> > ? ? > -- >> >> > ? ? > Shamik Chakrabarti >> >> > ? ? > Senior Research Fellow >> >> > ? ? > Dept. of Physics & Meteorology >> >> > ? ? > Material Processing & Solid State Ionics Lab >> >> > ? ? > IIT Kharagpur >> >> > ? ? > Kharagpur 721302 >> >> > ? ? > INDIA >> >> > ? ? > >> >> > ? ? > >> >> > ? ? > >> >> > ? ? > -- >> >> > ? ? > Shamik Chakrabarti >> >> > ? ? > Senior Research Fellow >> >> > ? ? > Dept. of Physics & Meteorology >> >> > ? ? > Material Processing & Solid State Ionics Lab >> >> > ? ? > IIT Kharagpur >> >> > ? ? > Kharagpur 721302 >> >> > ? ? > INDIA >> >> > ? ? > >> >> > ? ? > >> >> > ? ? > _______________________________________________ >> >> > ? ? > Wien mailing list >> >> > ? ? > Wien at zeus.theochem.tuwien.ac.at >> >> > ? ? <mailto:Wien at zeus.theochem.tuwien.ac.at> >> >> > ? ? > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >> >> > >> >> > ? ? -- >> >> > ? ? Dr. pascal Boulet, computational chemist >> >> > ? ? University of Aix-Marseille I >> >> > ? ? Laboratoire Chimie Provence, UMR 6264 >> >> > ? ? Group of Theoretical Chemistry >> >> > ? ? Avenue Normandie-Niemen >> >> > ? ? 13397 Marseille Cedex 20 >> >> > ? ? France >> >> > ? ? ********** >> >> > ? ? Tel. (+33) (0)413.55.18.10 >> >> > ? ? Fax. (+33) (0)413.55.18.50 >> >> > ? ? ********** >> >> > ? ? http://www.lc-provence.fr >> >> > ? ? https://sites.google.com/a/univ-provence.fr/pb-comput-chem >> >> > ? ? %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% >> >> > >> >> > ? ? ? ?* Fran?ais - d?tect? >> >> > ? ? ? ?* Anglais >> >> > ? ? ? ?* Fran?ais >> >> > >> >> > ? ? ? ?* Anglais >> >> > ? ? ? ?* Fran?ais >> >> > >> >> > ? ? <javascript:void(0);> >> >> > ? ? _______________________________________________ >> >> > ? ? Wien mailing list >> >> > ? ? Wien at zeus.theochem.tuwien.ac.at >> >> > ? ? <mailto:Wien at zeus.theochem.tuwien.ac.at> >> >> > ? ? http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >> >> > >> >> > >> >> > >> >> > >> >> > -- >> >> > Shamik Chakrabarti >> >> > Senior Research Fellow >> >> > Dept. of Physics & Meteorology >> >> > Material Processing & Solid State Ionics Lab >> >> > IIT Kharagpur >> >> > Kharagpur 721302 >> >> > INDIA >> >> > >> >> > >> >> > _______________________________________________ >> >> > Wien mailing list >> >> > Wien at zeus.theochem.tuwien.ac.at >> >> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >> >> >> >> -- >> >> Dr. pascal Boulet, computational chemist >> >> University of Aix-Marseille I >> >> Laboratoire Chimie Provence, UMR 6264 >> >> Group of Theoretical Chemistry >> >> Avenue Normandie-Niemen >> >> 13397 Marseille Cedex 20 >> >> France >> >> ********** >> >> Tel. (+33) (0)413.55.18.10 >> >> Fax. (+33) (0)413.55.18.50 >> >> ********** >> >> http://www.lc-provence.fr >> >> https://sites.google.com/a/univ-provence.fr/pb-comput-chem >> >> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% >> >> >> >> _______________________________________________ >> >> Wien mailing list >> >> Wien at zeus.theochem.tuwien.ac.at >> >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >> > >> > >> > >> > >> > -- >> > Shamik Chakrabarti >> > Senior Research Fellow >> > Dept. of Physics & Meteorology >> > Material Processing & Solid State Ionics Lab >> > IIT Kharagpur >> > Kharagpur 721302 >> > INDIA >> > >> > _______________________________________________ >> > Wien mailing list >> > Wien at zeus.theochem.tuwien.ac.at >> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >> > >> >> >> >> -- >> Professor Laurence Marks >> Department of Materials Science and Engineering >> Northwestern University >> www.numis.northwestern.edu 1-847-491-3996 >> "Research is to see what everybody else has seen, and to think what >> nobody else has thought" >> Albert Szent-Gyorgi >> _______________________________________________ >> Wien mailing list >> Wien at zeus.theochem.tuwien.ac.at >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > > > > > -- > Shamik Chakrabarti > Senior Research Fellow > Dept. of Physics & Meteorology > Material Processing & Solid State Ionics Lab > IIT Kharagpur > Kharagpur 721302 > INDIA > > _______________________________________________ > Wien mailing list > Wien at zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > -- Professor Laurence Marks Department of Materials Science and Engineering Northwestern University www.numis.northwestern.edu 1-847-491-3996 "Research is to see what everybody else has seen, and to think what nobody else has thought" Albert Szent-Gyorgi