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<p>Dear All,</p>
<p><br>
</p>
<p>Giuseppe is right, this is a limitation of the current implementation of the linear-response theory to compute Hubbard parameters for closed-shell systems (like ZnO, ZnS, etc.). This "limitation" is known, and there is some comment about this in
<span>q-e/HP/Doc/README. Please check this paper for more details:<a href="https://aip.scitation.org/doi/10.1063/1.4869718" class="x_OWAAutoLink" id="LPlnk663552">
<br>
</a></span></p>
<p><span><a href="https://aip.scitation.org/doi/10.1063/1.4869718" class="x_OWAAutoLink" id="LPlnk663552">https://aip.scitation.org/doi/10.1063/1.4869718</a><br>
</span></p>
<p><span><br>
</span></p>
<p><span></span>The developers of the HP code are planning to investigate this issue in more detail, and hopefully we will come out with some solution
<span>in the near future</span>. <br>
</p>
<p><br>
</p>
<p>Best regards,</p>
<p>Iurii<br>
</p>
<p><br>
</p>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of Giuseppe Mattioli <giuseppe.mattioli@ism.cnr.it><br>
<b>Sent:</b> Monday, June 15, 2020 10:55:59 PM<br>
<b>To:</b> Quantum ESPRESSO users Forum<br>
<b>Subject:</b> Re: [QE-users] Problems with hp.x</font>
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Dear Dominik<br>
I suppose that the problem is not in hp.x, but in the application of <br>
the linear-response method itself to Zn(2+). Zn(2+) is a d10 <br>
transition metal, with the 3d band fully occupied. In ZnO, e.g., the <br>
Zn 3d band is quite narrow and placed below the O 2p valence band, and <br>
I suppose that the same holds for ZnS, with the Zn 3d band pushing up <br>
the S 3p band. When you apply the LR method to Zn, you compute <br>
quantities such as d(alpha)/dn, where alpha is the (small) <br>
perturbation and n is the occupation number of d orbitals on site I <br>
(see International Journal of Quantum Chemistry 2014, 114, 14 for <br>
details). If the shell is full, then you can perturb whatever you want <br>
but you will never obtain more than the full occupation of the shell <br>
that you already have in the unperturbed system. This is likely the <br>
reason for the crazy values of LR U you obtain. If you want to correct <br>
the strong delocalization error of the Zn 3d narrow band within the <br>
DFT+U formalism, then you must use a "semiempirical" approach, <br>
choosing, e.g., the U value that places the Zn 3d shell at the correct <br>
distance from the valence band maximum. In this case, I would <br>
recommend the use of a second +U correction on the S 3p shell, which <br>
should ensure a good recovery of the ZnS band gap. I've satisfactorily <br>
used this scheme in the case of ZnO in several publications, from <br>
which you may want to take inspiration (Adv. Energy Mater. 2014, 4, <br>
1301694).<br>
HTH<br>
Giuseppe<br>
<br>
Quoting dv009200@fh-muenster.de:<br>
<br>
> Hello everyone,<br>
><br>
> I'm trying to calculate the hubbard u parameter for Zn in Zinc sulfide<br>
> (sphalerite structure) with the help of the hp.x code. The calculations<br>
> terminate normally without any errors. The problem is that I get<br>
> (presumably) way too high values for U that also won't converge (if I take<br>
> the value I got from a one-shot calculation and plug it in the SCF input<br>
> and then redo the HP calculation).<br>
><br>
> For example in the first step I calculate a U = 75.7035 in the second<br>
> iteration I get U = 804.2405 and in the third U = 30999.2684.<br>
><br>
> This seems unreasonable considering that the calculations for the provided<br>
> examples in the 'HP' folder work fine and converge fast without such a<br>
> massive change to a certain value for U using the above described scheme.<br>
><br>
> Has someone an idea what is causing this trouble in my system? I already<br>
> tried different PPs, functionals, U_projection_type, thresholds and k and<br>
> q point grids all without success.<br>
><br>
> Below is my input for the scf and hp calculation<br>
><br>
> SCF-input:<br>
>  &control<br>
> calculation='scf'<br>
> restart_mode='from_scratch',<br>
> pseudo_dir = '/home/dominik/codes/QE6.5/pseudo/'<br>
> outdir='/home/dominik/codes/QE6.5/tempdir/'<br>
> prefix='zns'<br>
> /<br>
> &SYSTEM<br>
> ibrav = 2<br>
> celldm(1)=10.291937439<br>
> nat = 2<br>
> ntyp = 2<br>
> ecutwfc = 60.0<br>
> ecutrho= 720.0<br>
> lda_plus_u = .true.<br>
> lda_plus_u_kind = 0<br>
> U_projection_type = 'atomic'<br>
> Hubbard_U(1) = 1d-8<br>
> /<br>
> &electrons<br>
> mixing_beta=0.7<br>
> conv_thr=1d-15<br>
> /<br>
> ATOMIC_SPECIES<br>
> Zn 65.39 Zn.pbe-dn-rrkjus_psl.0.2.2.UPF<br>
> S 32.07 S.pbe-n-rrkjus_psl.0.1.UPF<br>
> ATOMIC_POSITIONS {alat}<br>
> Zn 0.000000 0.000000 0.000000<br>
> S 0.250000 0.250000 0.250000<br>
> K_POINTS automatic<br>
> 12 12 12 0 0 0<br>
><br>
><br>
> HP-input:<br>
> &inputhp<br>
> prefix='zns'<br>
> outdir='/home/dominik/codes/QE6.5/tempdir/'<br>
> nq1 = 2<br>
> nq2 = 2<br>
> nq3 = 2<br>
> conv_thr_chi = 1.0d-10<br>
> iverbosity =2<br>
> /<br>
><br>
><br>
> Best regards<br>
><br>
><br>
> Dominik Voigt<br>
><br>
> Dominik Voigt<br>
> PhD Student University of Applied Sciences Münster<br>
> Department of Physical Chemistry<br>
><br>
> _______________________________________________<br>
> Quantum ESPRESSO is supported by MaX (<a href="http://www.max-centre.eu/quantum-espresso">www.max-centre.eu/quantum-espresso</a>)<br>
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<br>
<br>
<br>
GIUSEPPE MATTIOLI<br>
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA<br>
Via Salaria Km 29,300 - C.P. 10<br>
I-00015 - Monterotondo Scalo (RM)<br>
Mob (*preferred*) +39 373 7305625<br>
Tel + 39 06 90672342 - Fax +39 06 90672316<br>
E-mail: <giuseppe.mattioli@ism.cnr.it><br>
<br>
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