# Energy minimisation of Alumina

I am trying to perform energy minimisation of Alumina by changing the lattice volume.

Alumina has lattice parameters a=4.76, b =4.76 c=12.993

I am changing c from 10.99 to 14.99

I am using energy minimisation command:
min_style cg
minimize 0.0 1e-25 1000 1000

But I get the mimimum energy configuration at c=13…113 and not at c=12.993.

I have used vashishta potential. What can be the reason for this deviation?

Thanks

I am trying to perform energy minimisation of Alumina by changing the
lattice volume.

Alumina has lattice parameters a=4.76, b =4.76 c=12.993
I am changing c from 10.99 to 14.99

are these lattice parameters experimental findings or from a reference
publication using the same parameter set that you are using?
and for which temperature?

I am using energy minimisation command:
min_style cg
minimize 0.0 1e-25 1000 1000

But I get the mimimum energy configuration at c=13..113 and not at c=12.993.
I have used vashishta potential. What can be the reason for this deviation?

that is less than 1% off.
what kind of equation of state did you fit your energies to?
and assuming which temperature?

axel.

I have used these lattice parameters from a reference publication . The temperature is 0K and I use Murnaghan equation of state fit.

I have used these lattice parameters from a reference publication . The
temperature is 0K and I use Murnaghan equation of state fit.

did you use the exact same minimization settings and protocol as in
the reference?

Also, why are you not relaxing a and b? If you want to accurate determine the energy minimum cell for this potential, you can start with your initial result, and then use the minimize command again, together with fix box/relax and the anise or tri keywords. Also, print out all six components of the stress tensor. These should all be very small (< 1.0e-6) at the true minimum.