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!

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 Youngâ€™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!