Dear all,

I try to use Elastic and quantum-espresso to calculate wurtzite structure of AlN. the input file is :

&SYSTEM
ibrav= 4, celldm(1)= 5.9090, nat= 4, ntyp= 2,
celldm(3) = 1.6034
ecutwfc = 120
ATOMIC_POSITIONS crystal
Al 0.00 0.00 0.00
Al 0.3333 0.6666 0.5
N 0.00 0.00 0.345
N 0.3333 0.6666 0.845

run Elastic_Setup_ESPRESSO then get that :
Number and name of space group: 36 (C m c 21)
Orthorhombic structure in the Laue classification.
This structure has 9 independent second-order elastic constants.

…. Oops ERROR: ibrav = 4, It means "Hexagonal" structure.
But this structure can be represented by "Orthorhombic" system.
THEY ARE NOT COMPATIBLE. Please Look at sgroup.out

I found that when I change the ATOMIC_POSITIONS to
Al 0.00 0.00 0.00
Al 0.0 0.0 0.5
N 0.00 0.00 0.345
N 0.0 0.0 0.845
the output will be right like:
Number and name of space group: 183 (P 6 m m)
Hexagonal I structure in the Laue classification.
This structure has 5 independent second-order elastic constants.

How can i get the right structure with Elastic?
Thank you!!!!!!

dear all

I try to use Elastic and quantum-espresso to calculate graphene. I same problem.

the input file is:
&CONTROL
calculation = "relax",
prefix = "graphene",
pseudo_dir = " ./pseudo",
outdir = "./tmp",
tstress = .TRUE.
tprnfor = .TRUE.
/
&SYSTEM
ibrav = 8,
celldm(1) = 4.65107713,
celldm(2) = 1.732050806,
celldm(3) = 8.125971409,
nat = 4,
ntyp = 1,
ecutwfc = 32.D0,
ecutrho = 320.D0,
occupations ='fixed'
nosym =.TRUE.
/
&ELECTRONS
conv_thr = 1.D-7,
mixing_beta = 0.7D0,
mixing_mode = 'TF',
/
&IONS
ion_dynamics = 'bfgs',
/
ATOMIC_SPECIES
C 12.0107 C.pbe-van_ak.UPF
ATOMIC_POSITIONS {crystal_sg}
C 0.75000000 0.833333333 0.000000000
C 0.25000000 0.666666667 0.000000000
C 0.25000000 0.333333333 0.000000000
C 0.75000000 0.166666667 0.000000000
K_POINTS {automatic}
5 3 1 0 0 0

run Elastic_Setup_ESPRESSO then get that :

Number and name of space group: 191 (P 6/m m m)
Hexagonal I structure in the Laue classification.
This structure has 5 independent second-order elastic constants.

…. Oops ERROR: ibrav = 8, It means "Orthorhombic" structure.
But this structure can be represented by "Hexagonal" system.
THEY ARE NOT COMPATIBLE. Please Look at sgroup.out

I'm surprising this job sometimes run without error but this time isn't run.

Thanks so much
Elham