[lammps-users] About lattice custom command

Dear All,

I want to construct a unit cell containing two atom types. The unit cell is FCC structure have 4 basis atoms, but with one atom of type 1 at the corner, and three atoms of type 2 at the cubic face center. I try to achieve this using “lattice custom” command in the following section. As we know, there are 4 atoms in one unit cell when PBC is applying to three direction. In my case, PBC is applied to x and z directions. Hence, there should be 6 atoms in one unit cell with free surface in y direction. However, it generates 12 atoms (6 atoms of type 1 and 6 atoms of type 2). I check the generated dump.cor file and find that the positions for atoms of two types are the same, not what I expected. I failed to figure out what’s wrong with my syntax of lattice custom command, could you give me some advice? Any suggestion is highly appreciated!

#------------------------------------------Input Script
units metal
boundary p s p

atom_style atomic
lattice custom 3.61 a1 1.0 0.0 0.0 a2 0.0 1.0 0.0 a3 0.0 0.0 1.0 basis 0.0 0.0 0.0 basis 0.5 0.5 0.0 basis 0.5 0.0 0.5 basis 0.0 0.5 0.5
region box block 0 1.0 0 1.0 0 1.0
create_box 2 box

create_atoms 1 box basis 1 1
create_atoms 2 box basis 2 2 basis 3 2 basis 4 2

pair_style eam
pair_coeff * * Cu_u3.eam

neighbor 2.0 bin
neigh_modify delay 5

compute new3d all temp

velocity all create 300.0 5812775 temp new3d
fix 1 all nve

thermo 25
thermo_modify temp new3d

dump 1 all atom 100 dump.lammpstrj
dump 2 all custom 500 dump.cor id type x y z

timestep 0.001
run 1

Best regards,

I don't understand why you have 2 create_atoms commands. This
will superpose atoms over each other. I think you want one
command which specifies the type assignment of all 4 atoms
in your unit cell.