Lattice parameters of ZnO

[vaspman]

Hello! Dear VASP users
I am a new VASP user. I finished all the practice example without problem. I did some structural relaxation calcilations for some materials without problem. Now I am doing calculations on ZnO to find the lattice parameters. I use LDA but the lattice parametrs are not good and specialy the convergence of K-points is bad. I tried to use MP k-points and Gama centered but on both cases the lattice parametrs are far away from the Expt.
I use hexagonal unit cell.
Here are my results

MP-mesh Energy a c
222 -11.494313 3.186 5.438
333 -20.090362 3.154 5.143
446 -16.183364 3.183 5.273
555 -15.958511 3.179 5.315
666 -14.480588 3.179 5.327
777 -16.260802 3.165 5.289
888 -15.58627 3.189 5.226

The Gama centered mesh
222 -10.859297 3.253 5.274
333 -20.090362 3.154 5.143
555 -15.958511 3.179 5.315
666 -16.043754 3.184 5.314
777 -16.260802 3.165 5.289
888 -14.64875 3.188 5.326
101010 -14.24037 3.180 5.333

Here is my INCAR file
SYSTEM = ZnO
Starting parameters for this run:
NWRITE = 2 write-flag
ISTART = 0 job : 0-new, 1-cont, 2-samecut
ICHARG = 0 charge: 0-wave, 1-file, 2-atom, >10-const
INIWAV = 1 electr: 0-lowe 1-rand 2-diag
IBRION = 2
NSW = 50 number of steps for IOM
Electronic Relaxation:
PREC = high low | medium | high
# ENCUT = 240 kinetic energy cutoff (eV)
ISPIN = 1

NELMDL = -7 number of delayed ELM steps
NELM = 101 number of ELM steps
EDIFF = 1E-03 energy stopping-criterion for ELM
EDIFFG = .1E-02 energy stopping-criterion for IOM
LREAL = .FALSE. real-space projection (.FALSE., .TRUE., On, Auto)
IALGO = 48 algorithm (8=CG for small, 48=RMM for big systems)

LCHARG = .T.
LWAVE = .FALSE.

ISIF = 3 (1:force=y stress=trace only ions=y shape=n volume=n)
ISYM = 1 (1-use symmetry, 0-no symmetry)

DOS related values:
ISMEAR = 0 (-5:tet_b,-4:tet,-3:scan,-1:Fermi,0:gaus,1:MP)
SIGMA = 0.1 broadening in eV

Here is my POSCAR file
Wurtzite
3.2495
1.0 0.0 0.0
0.0 1.0 0.0
0.0 0.0 1.6024
2 2
d
0.000 0.000 0.0
0.333 0.667 0.5
0.000 0.000 0.345
0.333 0.667 0.845

I will be very thankful if some one let me know how to solve this problem.
Thank you

[support_vasp]

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