Hello, I have used two methods to calculate the elastic constants of material mp-2967, but the results are all different with yours. Could you please tell me the reason?
Thank you!
The elastic constants of mp-2967 you offer is:
| 292 | -36 | 461 | 0 | 0 | 0 |
|---|---|---|---|---|---|
| -36 | 292 | 461 | 0 | 0 | 0 |
| 461 | 461 | 3468 | 0 | 0 | 0 |
| 0 | 0 | 0 | 117 | 0 | 0 |
| 0 | 0 | 0 | 0 | 117 | 0 |
| 0 | 0 | 0 | 0 | 0 | 132 |
The first method I used is energy-strain method.
The result is:
283.1 95.8 76.1 0.0 0.0 0.0
95.8 283.1 76.1 0.0 0.0 0.0
76.1 76.1 187.8 0.0 0.0 0.0
0.0 0.0 0.0 66.3 0.0 0.0
0.0 0.0 0.0 0.0 66.3 0.0
0.0 0.0 0.0 0.0 0.0 127.7
and here are the input files:
INCAR
PREC = Accurate
ISTART = 0
ICHARG = 2
ENCUT = 600.0 eV
GGA = PE
ISYM = 0
IBRION = 2
NSW = 500
ISIF = 2
NELM = 60
NELMIN= 5
NELMDL= -5
EDIFF = 1E-8
EDIFFG = -0.001
ISMEAR = 0
SIGMA = 0.05
LWAVE = .F.
LCHARG = .F.
LREAL = .F.
NCORE = 4
KPOINTS
Gamma
14 14 5
0.0 0.0 0.0
Strains:
-0.015 -0.010 -0.005 0.000 0.005 0.010 0.015
The second method I used is stress-strain method.
The result is:
287.6 97.2 78.1 0.3 -0.2 0.1
97.2 287.8 78.2 0.3 -0.2 0.1
78.1 78.2 190.7 0.3 -0.2 0.1
0.3 0.3 0.3 68.4 0.0 0.0
-0.2 -0.2 -0.2 0.0 68.4 0.0
0.1 0.1 0.1 0.0 0.0 127.7
and the input files are:
INCAR
SYSTEM = GY
ISYM = 0
ISTART = 0
ICHARG = 2
GGA = PE
ENCUT = 600
PREC = Accurate
NFREE = 4
IALGO = 38
NELM = 300
EDIFF = 1E-7
LREAL = Auto
IBRION = 6
POTIM = 0.015
ISIF = 3
NSW = 500
EDIFFG = -0.0001
ISMEAR = 0
BAND:0
SIGMA = 0.05
LWAVE = .F.
LCHARG = .F.
LELF = .F.
KPOINTS
Gamma
14 14 5
0.0 0.0 0.0
It can be see that the elastic constants you offer contain a pretty high C33, which is 3468 GPa. It means that the Young’s modulus at the direction Z of this material is more than 1800 GPa according to the equation
E33=1/S33
where S=C^-1 is the inverse matrix of C.
But after stretching this meterial by VASP at the direction Z, I find that E33 is only about 160 GPa. So I re-calculated its elastic constants and the results have been shown above.
Could you please tell me the reason? Thank you!
It can be see that the elastic constants you offer contain a pretty high C33, which is 3468 GPa. It means that the Young’s modulus at the direction Z of this material is more than 1800 GPa according to the equation
Yes, agreed this doesn’t sound very sensible. Note we do have warnings associated with this elastic tensor on our website also:
As for the reason, I’m not sure. We’re currently looking for a team member to help out on some elastic tensor maintenance, but at present we cannot investigate further for this specific material.