Dear Ashish,

I am not sure if I understood your script correctly, but you are doing calculations in which you change only one lattice vector. For an elastic constant calculation you have to supply the relaxed equilibrium structure and VASP will by itself strain the structure. In the OUTCAR you will then find the elastic tensor. Please have a look into the VASP manual for usage of IBRION=5,6 there it is also described.

Best, Holger

@Holger Euchner,

Thanks for your kind reply, That means I only have to supply relaxed structure and start doing calculation using IBRION=6, ISIF=3 or greater but I have one more question suppose I got elastic tensor then how to obtain the value of bulk modulus etc from it.

Thanks

Dear Ashish,

Read the attached papers carefully will sort out all your questions. 

Best

Roshan

Is there any way to obtain the clastic constants from the calculation results using IBRION=5? thanks alot!