[Wien] Optimized lattice constants using pbe+U
Park, Ken
Kenneth_Park at baylor.edu
Mon Aug 28 15:32:02 CEST 2023
Thank you for the reference and the suggestion to test for k-mesh and gmax. I will check for the convergence on those parameters.
Ken
From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of fabien.tran at vasp.at <fabien.tran at vasp.at>
Date: Monday, August 28, 2023 at 3:01 AM
To: A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.at>
Subject: Re: [Wien] Optimized lattice constants using pbe+U
As Peter mentioned, U is applied only inside the atomic spheres. In
general, the details of the implementation of DFT+U depends on the basis
set, which can lead to disagreements between codes that are more
important than for plain LDA or GGA (see
https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1063%2F1.4945608&data=05%7C01%7CKenneth_Park%40baylor.edu%7C9c56ac9a53554583d76b08dba79cfdd0%7C22d2fb35256a459bbcf4dc23d42dc0a4%7C0%7C0%7C638288064986024084%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=YdiCdZbFIO4Ty0PvpPvIo%2BSaNNmOjsKwxl3i0fugsu8%3D&reserved=0)<https://doi.org/10.1063/1.4945608>.
You wrote that you used the default k-mesh and gmax. You should also
test these parameters.
On 25.08.2023 18:48, Peter Blaha wrote:
> 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%7C9c56ac9a53554583d76b08dba79cfdd0%7C22d2fb35256a459bbcf4dc23d42dc0a4%7C0%7C0%7C638288064986024084%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Kc5ldWHNNsFFyiClwl4RQsMULabwGTsSYUdmHAKjdN0%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%7C9c56ac9a53554583d76b08dba79cfdd0%7C22d2fb35256a459bbcf4dc23d42dc0a4%7C0%7C0%7C638288064986024084%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Kc5ldWHNNsFFyiClwl4RQsMULabwGTsSYUdmHAKjdN0%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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