I want to calculate elastic constant using IBRION =6, for that the elastic constants can be found for a non-cubic system through using IBRION=6 and ISIF≥3. The elastic tensor is determined by performing six finite distortions of the lattice and deriving the elastic constants from the strain-stress relationship.”
I have 2 confusions/questions?
1) Can we do the calculation on the vacuum=slab model?
2) If yes suppose I have a=4.51 angs and b=3.12 angstrom then how should I give six finite distortion. The one way is to change a by +/- 0.2 etc (keeping b fixed) and then at optimized geometry at particular a will be used for varying b. The other way is to change a and b together. I am very much confused about this.Please tell me in detail how to do it?
Thanks
Dear Ashish,
usually elastic constants are considered as bulk properties and therefore I have not seen any calculations for slab models. But I suppose when you use a slab with vacuum the VASP formalism should still work. I am not sure if the results will make sense but conceptually it should work as VASP only strains the cell (lattice vectors). Did you try that?
Best, Holger
Dear Holger,
Thanks for your answer but what about six distortion. How I should give them since I have different a and b off course c is vacuum and I donot want to disturb it.
Dear Ashish,
do you have a 2D system or a 3D system? In 3D I think it should work to allow the c-axis also to change, despite the fact that this will slightly change the vacuum (assuming your vacuum layer thickness is large enough). Anyway, if you want to have the 6x6 elastic tensor you need allow distortions in c-direction. But I am not sure what you will get out of this...
Best, Holger
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