from ase import Atom, Atoms
from ase.calculators.lj import LennardJones
from ase.constraints import FixBondLength

dimer = Atoms([Atom('X', (0, 0, 0)),
               Atom('X', (0, 0, 1))],
              calculator=LennardJones(),
              constraint=FixBondLength(0, 1))
print(dimer.get_forces())
print(dimer.positions)
dimer.positions[:] += 0.1
print(dimer.positions)
dimer.positions[:, 2] += 5.1
print(dimer.positions)
dimer.positions[:] = [(1, 2, 3), (4, 5, 6)]
print(dimer.positions)
dimer.set_positions([(1, 2, 3), (4, 5, 6.2)])
print(dimer.positions)