# Surface energy of slab

Sorry for the ambiguous nature of my question. Essentially I am carrying out an energy minimization for a Ni-Fe alloy slab. I need to find the surface energy of this slab at different temperatures (300K,400K etc). I use an npt ensemble to equilibriate the volume, then i add a vacuum layer to make a surface [(111) FCC Ni3Fe, containing 2048 atoms] and run an nvt on it to get the final stable structure, to see if any segregation occurs or not.

So, can i just use the equation of gamma for solids:(0.5/A)*[Eslab - N.Ebulk/atom] to calculate the surface energy or how else could it be done?

Sorry for the ambiguous nature of my question. Essentially I am carrying out
an energy minimization for a Ni-Fe alloy slab. I need to find the surface
energy of this slab at different temperatures (300K,400K etc). I use an npt
ensemble to equilibriate the volume, then i add a vacuum layer to make a
surface [(111) FCC Ni3Fe, containing 2048 atoms] and run an nvt on it to get
the final stable structure, to see if any segregation occurs or not.

So, can i just use the equation of gamma for solids:(0.5/A)*[Eslab -
N.Ebulk/atom] to calculate the surface energy or how else could it be done?

no. there is a conceptual problem. please note, that there is not
*the* 300K structure. there are *many*, in fact *lots*.
even more for 400K. so you'd have to average over them, or at least a
sufficiently large sample. the reason for this is explained
statistical mechanics text books (look for the term "microstate" and
how it is related to macroscopic observables).

i have seen the canonical surface energy expression you quote only
seen being used with 0K systems, so i'd suggest you first hit the
literature to see, if this can actually be transferred to the finite
temperature case. i would expect that the energy you compute would
rather be a "free energy", but this is outside of my area of deep
expertise. so checking with textbooks and the published literature is
the way to go forward. you will need to have a citable reference to
justify your choice of how you finally compute the surface energy
anyway (reviewers and supervisors usually don't appreciate "some guy
on the LAMMPS mailing list said it was ok").

axel.