I am trying to do Molecular statics on a cube of aluminium atoms. To verify my simulations , i want to do a uniaxial tensile test on a cube of side 25 A (1099 atoms) and verify the modulus by computing the slope of stress-strain curve. For this purpose, i displace a layer of atoms on the +X face by a strain amount corresponding to 0.00375. To simulate rollers on the boundaries, i use fix setforce command. I measure stress by computing stress/atom on a layer of atoms next to the surface (so that none of these atoms see the surface), summing it up and dividing by the volume. I am using the latest version of LAMMPS with all patches to date applied.
The issue is i that have tried different potentials and the value of the modulus seems to vary. The best value i got is with AlCu.eam.alloy potential from Cai. This potential gave me a value of 85 Gpa , which is off by about 10% from values available in literature for aluminium (zero kelvin).
Please let me know if anyone has done similar tests and have got better results. I am attaching the script and the data file i am using to do this computation.
in.minimize.tensile (208 Bytes)
in.cube.tensile (2.77 KB)
cube2.dat (37.5 KB)