[Wien] Optimized lattice constants using pbe+U
Park, Ken
Kenneth_Park at baylor.edu
Fri Aug 25 19:39:13 CEST 2023
Thank you very much for your kind and helpful reply.
Indeed, I can’t get the correct stability with PBE+U as claimed.
Sincerely,
Ken
From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of Peter Blaha <peter.blaha at tuwien.ac.at>
Date: Friday, August 25, 2023 at 11:48 AM
To: wien at zeus.theochem.tuwien.ac.at <wien at zeus.theochem.tuwien.ac.at>
Subject: Re: [Wien] Optimized lattice constants using pbe+U
Hard to say without repeating the calculations, but:
a) I see nothing wrong in your calculation setups/procedure
b) I've seen previously VERY wrong PBE+U results using VASP in other
cases. VASP potentials have been optimized for PBE (and probably for
HSE), and those results are usually ok, but I don't know about PBE+U.
c) At the time when the rutile/anatase stability problem came up, I let
a student try if PBE+U could fix it. It did not do it. But this is long
time ago.
Maybe repeat one U value with a significantly larger RMT for Ti. Note
that the Hubbard-U is applied only within the spheres in WIEN2k and
since the Ti-3d states are not too localized, there might be an effect.
Am 24.08.2023 um 17:55 schrieb Park, Ken:
> Dear Wien2k experts,
>
> I have been studying the effect of the Hubbard U on various phases of
> TiO2 using wien2k 23.2. I have observed that some calculated properties
> are different from those reported in literature (mostly with
> pseudopotential) and would like to get your suggestions to see if I have
> made a mistake.
>
> For rutile TiO2 using pbe, my optimized lattice constants are a=4.648 Å
> and c=2.966Å, which are close to the published result of 4.650 and 2.968
> [1]. However, after I added U= 6eV and ran the optimization, I obtained
> a=4.655 Å and c=3.000Å, in contrast to a=4.687Å and c=3.042Å for U=5 eV
> in [1].
>
> [1]
> https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpubs.aip.org%2Faip%2Fjcp%2Farticle%2F135%2F5%2F054503%2F190719%2FDFT-U-calculations-of-crystal-lattice-electronic&data=05%7C01%7CKenneth_Park%40baylor.edu%7Cb8d35a91a0424453225308dba58b2ba2%7C22d2fb35256a459bbcf4dc23d42dc0a4%7C0%7C0%7C638285789393067589%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=95rarsH%2BT0jhSPw59OoUyjyv1LjdEOC2otqdaDMMbIU%3D&reserved=0<https://pubs.aip.org/aip/jcp/article/135/5/054503/190719/DFT-U-calculations-of-crystal-lattice-electronic> <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpubs.aip.org%2Faip%2Fjcp%2Farticle%2F135%2F5%2F054503%2F190719%2FDFT-U-calculations-of-crystal-lattice-electronic&data=05%7C01%7CKenneth_Park%40baylor.edu%7Cb8d35a91a0424453225308dba58b2ba2%7C22d2fb35256a459bbcf4dc23d42dc0a4%7C0%7C0%7C638285789393067589%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=95rarsH%2BT0jhSPw59OoUyjyv1LjdEOC2otqdaDMMbIU%3D&reserved=0<https://pubs.aip.org/aip/jcp/article/135/5/054503/190719/DFT-U-calculations-of-crystal-lattice-electronic>>
>
> So I performed a systemic study using U=3, 5, 8, 10 eV as in [1] and
> obtained the following:
>
> U=3 a=4.650 c=2.985 vs U=3
> a=4.671 c=3.012 [1]
>
> U=5 a=4.649 c=2.995 vs
> U=5 a=4.687 c=3.042 [1]
>
> U=8 a=4.652 c=3.011 vs
> U=8 a=4.709 c=3.081 [1]
>
> U=10 a=4.655 c=3.021 vs
> U=10 a=4.725 c=3.108 [1]
>
> The lattice constant a is nearly constant or expanded very little
> despite the increasing U whereas the constant c shows a similar increase
> albeit by smaller amount. In rutile, c is the direction of the Ti-Ti
> short chain.
>
> I have checked the band gaps and they are comparable with the reported
> results.
>
> U=3 2.24 eV vs U=3 2.15 eV [1]
>
> U=5 2.42 eV vs U=5 2.3 eV [1]
>
> U=8 2.72 eV vs U=8 2.7 eV [1]
>
> U=10 2.98 eV vs U=10 2.92 eV [1]
>
> For your information, I have copied the input files case.inorb and
> case.indm and the top portion of the structure file.
>
> 1 1 0 nmod, natorb, ipr
>
> PRATT 1.0 BROYD/PRATT, mixing
>
> 1 1 2 iatom nlorb, lorb
>
> 1 nsic 0..AMF, 1..SIC, 2..HFM
>
> 0.44 0.00 U J (Ry) Note: you can also use U_eff = U-J and J=0
>
> -12. Emin cutoff energy
>
> 1 number of atoms for which density matrix is
> calculated
>
> 1 1 2 index of 1st atom, number of L's, L1
>
> 0 0 r-index, (l,s)index
>
> TiO2
>
> P 2
>
> RELA
>
> 8.788126 8.788126 5.669865 90.000000 90.000000 90.000000
>
> ATOM -1: X=0.00000000 Y=0.00000000 Z=0.00000000
>
> MULT= 2 ISPLIT= 8
>
> -1: X=0.50000000 Y=0.50000000 Z=0.50000000
>
> Ti NPT= 781 R0=0.00005000 RMT= 1.7800 Z: 22.00000
>
> 0.7071068 0.7071068 0.0000000
>
> -0.7071068 0.7071068 0.0000000
>
> 0.0000000 0.0000000 1.0000000
>
> ATOM -2: X=0.30509790 Y=0.30509790 Z=0.00000000
>
> MULT= 4 ISPLIT= 8
>
> -2: X=0.69490210 Y=0.69490210 Z=0.00000000
>
> -2: X=0.19490210 Y=0.80509790 Z=0.50000000
>
> -2: X=0.80509790 Y=0.19490210 Z=0.50000000
>
> O NPT= 781 R0=0.00010000 RMT= 1.6100 Z: 8.00000
>
> 0.0000000-0.7071068 0.7071068
>
> 0.0000000 0.7071068 0.7071068
>
> -1.0000000 0.0000000 0.0000000
>
> 16 NUMBER OF SYMMETRY OPERATIONS
>
> I optimized the structure with ‘runsp_lapw -p -orb -min -ec 0.00001 -cc
> 0.0001 -fc 1’ (or smaller fc) using rkmax 9 (or 10 to check for
> convergence) and default values such as k-mesh and gmax. I also used two
> different ways to check the optimization: one varying volume and varying
> c/a, and the second varying a and c. Both methods yielded the same or
> consistent results.
>
> I am not sure if I have errored using pbe+U and if so, where, but I
> would very much appreciate your advice.
>
> Sincerely,
>
> Ken Park
>
>
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300
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