I think the problem might be related with iron ultrasoft pseudopotential. As in page 40 of this pdf :
http://www.vasp.at/vasp-workshop/slides/pseudopp2.pdf Low-spin case (NM) is okay. But for high-spin iron, energies are too different. VASP use PAW potential. So you should switch to PAW with QE. Hope this helps. Dear Matteo, thanks a lot for the reply. I tried also using occupations="smearing" but the situation is the same. I get a difference of 0.3 electrons between the iron atom Fe1 and the other three Fe2. Is there anything else that I can try? Could this behaviour due to the differences between VASP (that you used in the refererence article) and Quantum Espresso? Best regards, Mauro. 2014-06-06 16:55 GMT+02:00 Matteo Cococcioni <matteo at umn.edu>: > > Dear Mauro, > > one thing I notice is that you are using occupation fixed. is there a > reason for that? this, I think, might actually cause the result you are not > happy about. > > Matteo > > > On Fri, Jun 6, 2014 at 4:39 PM, Mauro Sgroi < > maurofrancesco.sgroi at gmail.com> wrote: > >> Dear all, >> I'm trying to study the phase separation in LixFePO4 using DFT+U. >> The reference article that I'm using is PRB 69, 201101 (R) 2004, "Phase >> separation in LixFePO4 induced by correlation effects, Zhou et al. >> >> The authors compare, using VASP, standard DFT with DFT+U and obtain the >> correct description of the material with the latter approach. In particular >> they found that is possible to describe the formation of two type of ion, >> Fe2+ and Fe3+, according to to the different position in the unit cell in >> the partially lithiated structures. With GGA all Fe ions have the same >> occupancies, regardless the position in the cell and the fact that they are >> more or less near a lithium ion. >> To obtain this result with DFT+U they had to force the breaking of the >> symmetry of the structure and, I imagine, they set the initial occupations >> in some way to force the desired electronic configuration. >> >> I'm trying to do the same, differentiating the Fe atoms, breaking the >> symmetry and using starting_ns_eigenvalue to force the initial occupations. >> My problem is that at the end of the calculation I got always the same >> occupations on the 4 Fe atoms in the structure (more or less, the >> difference could be 0.3 electrons). >> >> I'm using lda_plus_u_kind=0, but also using the other approach was not >> beneficial. >> >> My input file is below. >> Have you any suggestion? >> >> Thanks a lot in advance and best regards, >> Mauro Sgroi. >> >> &control >> calculation='scf', >> pseudo_dir = "/usr2/sgroi/DATABASE/ESPRESSO", >> prefix='lifepo4_scfU', >> outdir='/home/dati/espresso/temp', >> / >> &system >> ibrav=8, celldm(1)=19.748515, celldm(2)=0.586193, celldm(3)=0.441599, >> nat=27, ntyp=5, nosym=.true. >> ecutwfc=40, ecutrho=400, nbnd=130, occupations='fixed', nspin=2, >> tot_magnetization=17, >> lda_plus_u=.true., Hubbard_U(2)=4., Hubbard_U(3)=4.475, >> starting_ns_eigenvalue(5,2,2)=0, >> starting_ns_eigenvalue(4,2,2)=0, >> starting_ns_eigenvalue(3,2,2)=0, >> starting_ns_eigenvalue(2,2,2)=0, >> starting_ns_eigenvalue(1,2,2)=0, >> starting_ns_eigenvalue(5,2,3)=1, >> starting_ns_eigenvalue(4,2,3)=0, >> starting_ns_eigenvalue(3,2,3)=0, >> starting_ns_eigenvalue(2,2,3)=0, >> starting_ns_eigenvalue(1,2,3)=0 >> / >> &electrons >> conv_thr=1.0d-8, electron_maxstep=100, mixing_beta=0.5 >> / >> >> ATOMIC_SPECIES >> Li 6.941 Li.pbe-s-van_ak.UPF >> Fe1 55.847 Fe.pbe-sp-van_ak.UPF >> Fe2 55.847 Fe.pbe-sp-van_ak.UPF >> P 15.9994 P.pbe-van_ak.UPF >> O 30.9737 O.pbe-van_ak.UPF >> >> ATOMIC_POSITIONS {crystal} >> Fe1 0.281537138 0.250000000 0.981851206 1 0 1 >> P 0.103893879 0.250000000 0.415586970 1 0 1 >> O 0.119764467 0.250000000 0.744164738 1 0 1 >> O 0.447356144 0.250000000 0.201257756 1 0 1 >> O 0.187375840 0.060350405 0.283173864 >> Li 0.500000000 0.000000000 0.500000000 0 0 0 >> Fe2 0.211199573 0.750000000 0.474632077 1 0 1 >> P 0.405092969 0.750000000 0.922566801 1 0 1 >> O 0.401164833 0.750000000 0.251505445 1 0 1 >> O 0.041727760 0.750000000 0.686207216 1 0 1 >> O 0.336134397 0.956851552 0.790300073 >> Li 0.000000000 0.500000000 0.000000000 0 0 0 >> Fe2 0.719627852 0.750000000 0.020422522 1 0 1 >> P 0.902369089 0.750000000 0.575773635 1 0 1 >> O 0.896492242 0.750000000 0.246982466 1 0 1 >> O 0.540334658 0.750000000 0.790913565 1 0 1 >> O 0.840097513 0.539754373 0.720678002 >> Li 0.500000000 0.500000000 0.500000000 0 0 0 >> Fe2 0.786894270 0.250000000 0.525238732 1 0 1 >> P 0.588956858 0.250000000 0.078832190 1 0 1 >> O 0.587126133 0.250000000 0.749458661 1 0 1 >> O 0.966454798 0.250000000 0.315230191 1 0 1 >> O 0.654364669 0.453679217 0.216461848 >> O 0.822813149 0.944845411 0.700568536 >> O 0.653714964 0.047069624 0.216100948 >> O 0.172021112 0.453011228 0.263457462 >> O 0.335493673 0.543326856 0.788919121 >> >> K_POINTS {automatic} >> 2 4 8 1 1 1 >> >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org http://pwscf.org/mailman/listinfo/pw_forum -------------- next part -------------- An HTML attachment was scrubbed... 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