Getting wrong Bulk modulus for ZnO using Elastic and quantum espresso

exciting
1

using ElaStic_Setup_ESPRESSO for wurzite ZnO scf.in, I am getting Bravais lattice: Orthorombic C bace-centred and wrong elastic constants.
My scf.in file is
&CONTROL
calculation = ‘scf’ ,
restart_mode = ‘from_scratch’ ,
pseudo_dir = ‘/home/chaitanya/qe-7.0/pseudo/’ ,
outdir=’./’,
tstress = .true. ,
tprnfor = .true. ,
/
&SYSTEM
ibrav = 4,
celldm(1) = 6.084917683,
celldm(3) = 1.614906832,
nat = 4,
ntyp = 2,
ecutwfc = 50 ,
ecutrho = 200 ,
occupations = “smearing” ,
degauss = 1.00000e-02 ,
smearing = “gaussian” ,
/
&ELECTRONS
conv_thr = 1.00000e-06 ,
startingpot = “atomic” ,
startingwfc = “atomic+random” ,
mixing_mode = ‘plain’ ,
mixing_beta = 0.7 ,
diagonalization = ‘david’ ,
/
ATOMIC_SPECIES
Zn 65.39000 Zn.pbesol-nc.UPF
O 15.99940 O.pbesol-nc.UPF
ATOMIC_POSITIONS crystal
Zn 0.333300000 0.666700000 0.000000000
Zn 0.666700000 0.333300000 0.500000000
O 0.333300000 0.666700000 0.375000000
O 0.666700000 0.333300000 0.875000000
K_POINTS automatic
4 4 2 0 0 0

output is

The output of ElaStic code
Today is Sun Jan 30 21:58:21 2022

Symmetry of the second-order elastic constant matrix in Voigt notation.
for, space group-number between 16 and 74, Orthorhombic structure.

C11 C12 C13 0 0 0
C12 C22 C23 0 0 0
C13 C23 C33 0 0 0
0 0 0 C44 0 0
0 0 0 0 C55 0
0 0 0 0 0 C66

Elastic constant (stiffness) matrix in GPa:

1363.9 486.7 43.0 0.0 0.0 0.0
486.7 107.9 -470.9 0.0 0.0 0.0
43.0 -470.9 -529.5 0.0 0.0 0.0
0.0 0.0 0.0 -149.8 0.0 0.0
0.0 0.0 0.0 0.0 26.8 0.0
0.0 0.0 0.0 0.0 0.0 71.0

Elastic compliance matrix in 1/GPa:

0.00101 -0.00086 0.00085 0.00000 0.00000 0.00000
-0.00086 0.00263 -0.00241 0.00000 0.00000 0.00000
0.00085 -0.00241 0.00033 0.00000 0.00000 0.00000
0.00000 0.00000 0.00000 -0.00668 0.00000 0.00000
0.00000 0.00000 0.00000 0.00000 0.03729 0.00000
0.00000 0.00000 0.00000 0.00000 0.00000 0.01409

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Voigt bulk modulus, B_V = 117.75 GPa
Voigt shear modulus, G_V = 48.51 GPa

Reuss bulk modulus, B_R = -1140.27 GPa
Reuss shear modulus, G_R = 93.92 GPa

Hill bulk modulus, B_H = -511.26 GPa
Hill shear modulus, G_H = 71.22 GPa

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Voigt Young modulus, E_V = 127.97 GPa
Voigt Poisson ratio, nu_V = 0.32

Reuss Young modulus, E_R = 289.73 GPa
Reuss Poisson ratio, nu_R = 0.54

Hill Young modulus, E_H = 224.06 GPa
Hill Poisson ratio, nu_H = 0.57

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Elastic Anisotropy in polycrystalline, AVR = -31.880 %

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Eigenvalues of elastic constant (stiffness) matrix:

1536.9
219.6
-814.2
-149.8
26.8
71.0
Which are not in agreement with the reported values.
Regards
M Chaitanya Varma
Dept of Physics
GITAM University
India

2

Dear chvar81,

I suggest you to check the values you gave for the ATOMIC_POSITIONS in crystal coordinates. Please, notice that, e.g., in this case 0.333300000 is not equal to one third, please give much more significant digits: 0.33333333333. Any symmetry issue could depend on that.

Best,

Pasquale Pavone (exciting team)

3

Thank you sir, I got correct structure. But still obtaining large values of Cij’s which are 3 times larger than reported values. I am trying to check with different pseudo potentials. Hope that works.
Thank you
regards
M Chaitanya Varma