[Pw_forum] Bulk modulus calculation

[vicky singh]

Dear QE users
   I am calculating the bulk modulus using the ev.x executable. The bulk
modulus obtained is extremely sensitive to the number of data i use in the
lattice parameter vs energy table. if i use three values a-x, a, a+x, where
a is the equilibrium lattice parameter and x is 0.01 or 0.02 bohr the value
of bulk modulus is very high as compared to i use 5 or 10 data. Bulk
modulus is the double derivative if energy w.r.t. equilibrium lattice
parameter.
   What should be the best method to obtain the bulk modulus of the system.
Also if you can provide any tutorial or help to calculate other elastic
constant it will be extremely helpful.

Vicky Singh
RA, Bangalore
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