Dear LAMMPS Users,
I wanted to calculate the interfacial energy between two slabs.
Therefore, I made two groups (i.e. top and bottom)
variable zmiddle equal 101.868467157
region topregion block INF INF INF INF ${zmiddle} INF units box
region topregion block INF INF INF INF 101.868467157 INF units box
group top region topregion
4480 atoms in group top
group bottom subtract all top
4480 atoms in group bottom
After that, I tried two methods to calculate interfacial energy
Einterface = Etotal – Etop – Ebottom
(In my system vdw and long range coulombic interactions are the only energy contributions. I used Buck/coul/long)
First one was to use potential energy calculation.
compute topperatom top pe/atom pair kspace
compute toppe top reduce sum c_topperatom
compute bottomperatom bottom pe/atom pair kspace
compute bottompe bottom reduce sum c_bottomperatom
However, when I checked the values
pe = c_toppe + c_bottompe
Therefore, pe – c_toppe – c_bottompe = 0.
Second one was to use group/group command
compute einter bottom group/group top pair yes kspace yes boundary yes
c_inter had finite value, which is different from the first case.
Why do they show different results? Which one is what I want to calculate??
Thank you very much.
Best regards,
Sehun Joo.