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.