BCC Ca lattice parameter

Hi all,
Link below shows that lattice constant of the bcc Ca is 3.045 Angstrom for the model :

However, when I do the Birch-Murnaghan fit using Lammps, I get 4.56 Angstrom.
Could you please inform me if there is a mistake?

Hi @Aras,
The potential is discontinuous; especially for the bcc crystal structure. If you look at the plot of the cohesive energy vs. volume (here) you can see that the lattice constant reported on OpenKIM corresponds to the first “kink” encountered as you move left to right.

It is likely your computation started with a larger initial guess and then converged to a different minimum to the right of the kink.

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