Dear All,
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 q-e/HP/Doc/README. Please check this paper for
more details:
<https://aip.scitation.org/doi/10.1063/1.4869718>
https://aip.scitation.org/doi/10.1063/1.4869718
The developers of the HP code are planning to investigate this issue in
more detail, and hopefully we will come out with some solution in the near
future.
Best regards,
Iurii
--
Dr. Iurii Timrov
Postdoctoral Researcher
STI - IMX - THEOS and NCCR - MARVEL
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: users <users-boun...@lists.quantum-espresso.org> on behalf of
Giuseppe Mattioli <giuseppe.matti...@ism.cnr.it>
Sent: Monday, June 15, 2020 10:55:59 PM
To: Quantum ESPRESSO users Forum
Subject: Re: [QE-users] Problems with hp.x
Dear Dominik
I suppose that the problem is not in hp.x, but in the application of
the linear-response method itself to Zn(2+). Zn(2+) is a d10
transition metal, with the 3d band fully occupied. In ZnO, e.g., the
Zn 3d band is quite narrow and placed below the O 2p valence band, and
I suppose that the same holds for ZnS, with the Zn 3d band pushing up
the S 3p band. When you apply the LR method to Zn, you compute
quantities such as d(alpha)/dn, where alpha is the (small)
perturbation and n is the occupation number of d orbitals on site I
(see International Journal of Quantum Chemistry 2014, 114, 14 for
details). If the shell is full, then you can perturb whatever you want
but you will never obtain more than the full occupation of the shell
that you already have in the unperturbed system. This is likely the
reason for the crazy values of LR U you obtain. If you want to correct
the strong delocalization error of the Zn 3d narrow band within the
DFT+U formalism, then you must use a "semiempirical" approach,
choosing, e.g., the U value that places the Zn 3d shell at the correct
distance from the valence band maximum. In this case, I would
recommend the use of a second +U correction on the S 3p shell, which
should ensure a good recovery of the ZnS band gap. I've satisfactorily
used this scheme in the case of ZnO in several publications, from
which you may want to take inspiration (Adv. Energy Mater. 2014, 4,
1301694).
HTH
Giuseppe
Quoting dv009...@fh-muenster.de:
Hello everyone,
I'm trying to calculate the hubbard u parameter for Zn in Zinc sulfide
(sphalerite structure) with the help of the hp.x code. The calculations
terminate normally without any errors. The problem is that I get
(presumably) way too high values for U that also won't converge (if I
take
the value I got from a one-shot calculation and plug it in the SCF input
and then redo the HP calculation).
For example in the first step I calculate a U = 75.7035 in the second
iteration I get U = 804.2405 and in the third U = 30999.2684.
This seems unreasonable considering that the calculations for the
provided
examples in the 'HP' folder work fine and converge fast without such a
massive change to a certain value for U using the above described
scheme.
Has someone an idea what is causing this trouble in my system? I already
tried different PPs, functionals, U_projection_type, thresholds and k
and
q point grids all without success.
Below is my input for the scf and hp calculation
SCF-input:
 &control
calculation='scf'
restart_mode='from_scratch',
pseudo_dir = '/home/dominik/codes/QE6.5/pseudo/'
outdir='/home/dominik/codes/QE6.5/tempdir/'
prefix='zns'
/
&SYSTEM
ibrav = 2
celldm(1)=10.291937439
nat = 2
ntyp = 2
ecutwfc = 60.0
ecutrho= 720.0
lda_plus_u = .true.
lda_plus_u_kind = 0
U_projection_type = 'atomic'
Hubbard_U(1) = 1d-8
/
&electrons
mixing_beta=0.7
conv_thr=1d-15
/
ATOMIC_SPECIES
Zn 65.39 Zn.pbe-dn-rrkjus_psl.0.2.2.UPF
S 32.07 S.pbe-n-rrkjus_psl.0.1.UPF
ATOMIC_POSITIONS {alat}
Zn 0.000000 0.000000 0.000000
S 0.250000 0.250000 0.250000
K_POINTS automatic
12 12 12 0 0 0
HP-input:
&inputhp
prefix='zns'
outdir='/home/dominik/codes/QE6.5/tempdir/'
nq1 = 2
nq2 = 2
nq3 = 2
conv_thr_chi = 1.0d-10
iverbosity =2
/
Best regards
Dominik Voigt
Dominik Voigt
PhD Student University of Applied Sciences Münster
Department of Physical Chemistry
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GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.matti...@ism.cnr.it>
_______________________________________________
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_______________________________________________
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