Elastic constants for Tetragonal, Orthorombic and Rhomdohedra structure

[BERNA AKGENC]

Hi All,

I wanna know how I can calculate elastic constants for some tetragonal, rhomhedra and orthorombic crystal structures (C11,C12,C13,..) from DFPT calculation?

Everbody knows a=b=/c for tetragonal structure or a=/b=/c for orthorombic structure.

My POSCAR file is :

Tetragonal xxxx
1.00
3.9781 0.000 0.000
0.000 3.978 0.000
0.0000 0.000 4.066
1 1 3
Direct
0.00 0.00 -0.068
0.50 0.50 0.446
0.50 0.50 0.902
0.00 0.50 0.413
0.50 0.00 0.413

My INCAR file is,

SYSTEM = xxx
ENCUT = 520
PREC = H
EDIFF = 1.E-04
ALGO = FAST
ICHARG = 2
EDIFFG = -0.01
LREAL = F
LWAVE = F
LCHARG = F
IBRION = 6
ISIF = 4
NSW = 30
NFREE = 4

I've found some values that incompatible parameters compared litraruture and other theoretical ones

Could you fix the problem, where I am wrong?

Thank you advance! :O

[admin]

EDIFF = 1e-4 is probably not precise enough to get high quality results for elastic properties.