In my material I need atoms of three types in the fraction 0.7, 0.15 and 0.15. I do that using the set region … type/fraction … command. In the box of 500000 atoms the log file says that
…
Setting atom values …
350630 settings made for type/fraction
Setting atom values …
74646 settings made for type/fraction
Setting atom values …
75074 settings made for type/fraction
…
I assume that these many numbers of atoms are put into the requested types 1, 2 and 3 which corresponds very closely to 70%, 15% and 15% in 500000 atoms.
But after equilibrating the system, it is found that there are about 50% atom of type 1, 13% of type 2 and 37% of type 3. This means that the material is not prepared in the required composition. How is this possible? Please help me in this regard.
It is impossible to make a specific assessment based on this limited information. Either your commands were not correct or you have “lost” atoms and ignored losing them.
Dear Expert,
The system fully equilibrated and there are 500000 atoms in the dump file also.
Here is an excerpt from the log file also given below:
create_box 3 mybox
Created orthogonal box = (0.0000000 0.0000000 0.0000000) to (179.72500 179.72500 179.72500)
4 by 4 by 6 MPI processor grid
lattice fcc ${latticepar}
lattice fcc 3.5945
Lattice spacing in x,y,z = 3.5945000 3.5945000 3.5945000
create_atoms 3 region mybox
Created 500000 atoms
using lattice units in orthogonal box = (0.0000000 0.0000000 0.0000000) to (179.72500 179.72500 179.72500)
create_atoms CPU = 0.038 seconds
set region mybox type/fraction 1 0.7 642648
Setting atom values …
350630 settings made for type/fraction
set region mybox type/fraction 2 0.15 947372
Setting atom values …
74646 settings made for type/fraction
set region mybox type/fraction 3 0.15 474632
Setting atom values …
75074 settings made for type/fraction
These commands will change the designated fraction of atoms to the desired type, but since the only condition is that those atoms are in a given region, they will not result in the desired composition. Initially all atoms will be of type 3. The first set command will change 70% of the type 3 atoms to type 1, the second will change 15% of all atoms to type 2, due to the first command about 70% of them will be of type 1. and the third set command should not be needed but will make matters even worse since it now will turn 15% of all atoms to type 3 (and that includes a percentage of type 1 and type 2 atoms).
A simple way to achieve what you want to do is the following:
create all atoms as type 1
convert 30% of type 1 atoms to type 2
convert 50% of type 2 atoms to type 3
It is very simple math… we should probably recategorize this question to the “LAMMPS Beginners” category.