# Query on surface energy calculation

Hello lammps users,

I am trying to calculate surface energy of Fe(BCC) (100),(110),(111) surfaces. The potential that I’m using gives me good elastic constants. I am under the impression that good elastic constants means good surface energy. But unfortunately my surface energies are off by the factor of 3. So my question is am I wrong to think that good elastic constants means good surface energy? I am looking for some suggestions. I will be glad to receive some suggestions. Also here is the script I’m using.

units metal
boundary p p p
atom_style atomic

variable E2 equal “pe”

fix 1 all box/relax aniso 0.0001 nreset 10

dump 1 all custom 1 dump.movie id x y z
thermo_style custom pe vol pxx pyy pzz lx ly lz

minimize 1.0e-16 1.0e-16 100000 100000
print “\${E2}” append surface.dat screen no

clear

units metal
boundary p s p
atom_style atomic

variable E1 equal “pe”

thermo_style custom pe vol pxx pyy pzz lx ly lz

minimize 1.0e-16 1.0e-16 1000000 1000000
print “{E1}" append surface.dat screen no print "(lx)” append surface.dat screen no
print “(lz)" append surface.dat screen no variable temp equal 2*lx*lz variable E_sur equal (v_E2-v_E1)/v_temp print "{E_sur}” append surface.dat screen no

Thanking you

Praveen

They are of course different as they represent different characteristics of the potential energy surface. Surface energy is related to cohesive energy and breaking bonds – which is essentially the depth of the energy well. Elastic constants are derived from stress-strain relationships and are essentially the second derivatives of the potential energy surface. You can have good well depth and bad second derivatives, the other way around, or good depth and derivatives at the same time. It all depends on how the potential was fitted.