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

[jijun gong]

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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