2.3.5. Executing commands

Once an instance of the lammps, PyLammps, or IPyLammps class is created, there are multiple ways to “feed” it commands. In a way that is not very different from running a LAMMPS input script, except that Python has many more facilities for structured programming than the LAMMPS input script syntax. Furthermore it is possible to “compute” what the next LAMMPS command should be.

Same as in the equivalent C library functions, commands can be read from a file, a single string, a list of strings and a block of commands in a single multi-line string. They are processed under the same boundary conditions as the C library counterparts. The example below demonstrates the use of lammps.file(), lammps.command(), lammps.commands_list(), and lammps.commands_string():

from lammps import lammps
lmp = lammps()

# read commands from file 'in.melt'

# issue a single command
lmp.command('variable zpos index 1.0')

# create 10 groups with 10 atoms each
cmds = ["group g{} id {}:{}".format(i,10*i+1,10*(i+1)) for i in range(10)]

# run commands from a multi-line string
block = """
region  box block 0 2 0 2 0 2
create_box 1 box
create_atoms 1 single 1.0 1.0 ${zpos}