[Wien] hi users
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[Wien] Choice of Coulomb Energy
Dear Wien2k users and Prof. Blaha, I am working on a Ce based magnetic system. I tried to do LSDA+U with different values of U from 0 to 6 eV for Ce-4f sate. U=0 eV gives the minimum energy and total energy for the system increases as we increase U value. Also the DOS for Ce-4f keeps on shifting with increasing U. My question is how to choose a correct U value for a system when a spectroscopic data is missing? Any help will be appreciated. Regards, Uday Dept. of Physics IIT Kanpur ___ 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
Re: [Wien] Choice of Coulomb Energy
Dear Uday, For the 4f orbitals of lanthanide ions, the value of U in the range of 5 - 7 eV should be quite reasonable. In particular, for Ce, I did some constrained DFT calculations in WIEN2k some time ago, and I got Ueff = U-J ~ 6.2 eV. But this value can not be taken too serious since it depends on some technical parameters. In a early study by S. Fabris et al (PRB 72, 237102 (2005)), the U for Ce obtained from a linear response approach is about 5.3 eV. Considering the uncertainty related to the way to calculate U, I think U=5 - 7 eV for lanthanide ions is a reasonable estimation. That is why in our study of lanthanide oxides using GW@LDA+U, we use Ueff=5.4 eV, and we have obtained quite good agreement with experiment for the band gaps of Ln2O3 (H. Jiang et al. PRL 102, 126403 (2009); PRB 86, 125115 (2012)). Hong δΊ 2013/6/17 21:30, Uday ει: Dear Wien2k users and Prof. Blaha, I am working on a Ce based magnetic system. I tried to do LSDA+U with different values of U from 0 to 6 eV for Ce-4f sate. U=0 eV gives the minimum energy and total energy for the system increases as we increase U value. Also the DOS for Ce-4f keeps on shifting with increasing U. My question is how to choose a correct U value for a system when a spectroscopic data is missing? Any help will be appreciated. Regards, Uday Dept. of Physics IIT Kanpur ___ 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 ___ 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
Re: [Wien] Choice of Coulomb Energy
Some suggestions: a) Use literature values from others. Of course, if the other papers were wrong then so are your results. b) Use the method in http://www.wien2k.at/reg_user/textbooks/Constraint_U.pdf -- not so easy! c) Use a reference, either thermodynamic data for the heat of formation of comparable system or (maybe) spectroscopic data. For instance you could use the U that is best for CeO2, where you have to be ready to defend your choice of what best means. N.B., personally I consider LDA+U to be relatively obsolete and would always use the on-site -eece as a more general method. You calibrate this via a reference, in my opinion. On Mon, Jun 17, 2013 at 8:30 AM, Uday pu...@iitk.ac.in wrote: Dear Wien2k users and Prof. Blaha, I am working on a Ce based magnetic system. I tried to do LSDA+U with different values of U from 0 to 6 eV for Ce-4f sate. U=0 eV gives the minimum energy and total energy for the system increases as we increase U value. Also the DOS for Ce-4f keeps on shifting with increasing U. My question is how to choose a correct U value for a system when a spectroscopic data is missing? Any help will be appreciated. Regards, Uday Dept. of Physics IIT Kanpur ___ 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 -- 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@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
