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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CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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