[Pw_forum] About LDA+U method on ZnO structural optimiztion

[jijun gong]

To Giuseppe,

    I really appreciate your help! Your precious experiences of LDA+U
for ZnO are of great help to me.
    Here, I still have some confusion about the LDA+U method. In the
J. Chem. Phys. 140, 121105 (2014), they used the Hartree-Fock theory
(UHF) and got a U value of 4.5 eV for Zn d electrons in ZnO. With this
U value, they performed calculations using VASP code and found a
decreasing trend for ZnO cell parameters, the result fairly agrees
with the experimental data.
    However, to my surprise, by using the PWSCF code with the same U
value, I got a slightly increasing trend and the error becomes mildly
larger than DFT's. Obviously, there was an opposite tendency between
the LDA+U results calculated by these two codes in this issue. So,
with respect to the DFT+U method, I confused if there was a dependence
on codes.

Thanks again!

J. J. Gong



> Date: Tue, 20 May 2014 21:34:44 +0200
> From: Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it>
> Subject: Re: [Pw_forum] About LDA+U method on ZnO structural
> 	optimiztion
> To: pw_forum at pwscf.org
> Message-ID:
> 	<20140520213444.Horde.9n2sgIz_PqySRXQdrNtORg1 at webmail.sic.rm.cnr.it>
> Content-Type: text/plain; charset=UTF-8; format=flowed; DelSp=Yes
>
>
> Dear J.J.
> I've performed several ZnO-related calculations, including DFT+U. In
> particular, you may be interested in the supporting information of
> Mattioli, et al.; J. Phys. Chem. C (2012) 116, 15439-15448, where the
> properties of ZnO bulk obtained at different levels of theory are
> discussed. In my experience, DFT+U alone does not guarantee good
> structural results in metal oxides, if you do not use it with care. In
> the above paper (and in a couple of following contributions), I've
> tested a double (and substantially semiempirical...) DFT+U(Zn,O)
> correction, applied to both Zn 3d (7.0 eV) and O 2p (5.9 eV) shells. I
> was more interested in electronic than structural properties, and the
> former were good. Neverheless I've obtained quite reasonable DFT+U
> lattice parameters (a=3.248, c=5.223). At any rate, your DFT+U results
> seem not so bad: +1.3% on a and +1.9 on c should be considered as
> acceptable overestimates.
> HTH
> Giuseppe
>
> Giuseppe Mattioli
> ISM-CNR
> Italy
>
> Quoting jijun gong <jijungong at gmail.com>:
>
>> Dear all:
>>     I am working on ZnO structural optimization using the LDA+U method.
>> As
>> in the journal of chemical physics 140, 121105 (2014), the U value on Zn
>> d
>> electrons was set to be 4.5 eV, calculated by vasp code, there was a good
>> agreement with experimaental data in cell parameters by DFT+U than DFT
>> method did.
>>     the a, c and u in experimental values are 3.250, 5.210, 0.382,
>> respectively.
>>     Calculated by VASP code,
>>     In DFT,the a, c and u values are 3.286, 5.295, 0.3807, respectively.
>>     In DFT+U,the a, c and u values are 3.243, 5.218, 0.3809,
>> respectively.
>>     It seems that the DFT+U correction works pretty well with the vasp
>> code.
>>
>>     But when using pwscf in vc-relax mode, I got the fellowing results:
>>     In DFT,the a, c and u values are 3.290, 5.305, 0.379, respectively.
>>     In DFT+U,the a, c and u values are 3.292, 5.309, 0.379, respectively.
>>     It shows that in pwscf, the DFT+U correction does not much affect the
>> results. also the datas show that there is significant difference in DFT
>> +U
>> results between the two codes.
>>
>>     My input file with pwscf attached to the following. I want to know
>> where I went wrong in the pwscf input file.
>>
>>
>>     Any help will be appreciated!
>>
>>     J.J. Gong
>>     Lanzhou University of technology, China
>>
>>
>> the pwscf input file
>>
>>  &CONTROL
>> calculation = "vc-relax",
>> restart_mode = "from_scratch",
>> prefix = "ZnO-opt",
>> outdir = "/tmp/",
>> pseudo_dir = "~/pp",
>> !wf_collect=.TRUE.
>> !etot_conv_thr = 1d-5
>> !forc_conv_thr = 1d-3
>> tstress = .true.
>> tprnfor = .true.
>> /
>> &SYSTEM
>> ibrav=0,
>> celldm(1)=1.88972613,
>> ecutwfc=55, ecutrho=550,
>> nat=4,ntyp=2,
>> lda_plus_U=.true., lda_plus_u_kind = 0, Hubbard_U(1)=4.5, Hubbard_U(2)=
>> 0,
>> /
>> &ELECTRONS
>> electron_maxstep = 80,
>> mixing_beta=0.5,
>> conv_thr=1D-8,
>> /
>> &ions
>> /
>> &cell
>> /
>>
>>
>> ATOMIC_SPECIES
>>   Zn  65.3900  Zn.pbe-van.UPF
>>    O  15.9994   o_pbe_v1.2.uspp.F.UPF
>>
>> CELL_PARAMETERS (alat=  1.88972613)
>>    3.292518870   0.000394478   0.000000646
>>   -1.640667267   2.850447665  -0.000000288
>>    0.000001154   0.000000426   5.310381081
>>
>> ATOMIC_POSITIONS (crystal)
>> O        0.332685749   0.665993276   0.379582752
>> O        0.667312132   0.334006494   0.879563839
>> Zn       0.333421586   0.666985007   0.000318706
>> Zn       0.666579130   0.333015022   0.500232704
>> K_POINTS (automatic)
>> 4 4 3 1 1 0
>>
>>
>> --
>> JiJun-Gong
>>
>> Department of Applied Physics
>> Lanzhou University of Technology
>> Lanzhou
>> China
>
>
> --
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>
>     Giuseppe Mattioli
>     CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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>

-- 
JiJun-Gong

Department of Applied Physics
Lanzhou University of Technology
Lanzhou
CHINA