[ase-users] Mixing calculator

[nancy]

Hi,

I am writing a MD code for one metal ions solves in water. I want to use different calculator for ion-water interaction and solute. Therefore I use mixing calculator (SumCalculator). I have code:

atoms=read(‘file of the whole system')
atoms_metal=atoms[list(range(19))]
atoms_solution=atoms[1:]
atoms_metal.cal=LennardJones(sigma=sigma_t, epsilon=epsilon_t)
atoms_solution.cal=TIP4P()
atoms.cal=SumCalculator([atoms_metal.cal, atoms_solution.cal])

md = Langevin(atoms, 1 * units.fs, temperature=300 * units.kB,
              friction=0.01, logfile=tag + '.log',
              trajectory=tag + '.traj', loginterval=1)
md.run(1000)

When I ran the code, I had the error :
File “/path-to-ase/ase/ase/atoms.py", line 791, in get_forces
    raise RuntimeError('Atoms object has no calculator.')
RuntimeError: Atoms object has no calculator.

How could I fix it?

Thank you for your help

Best wishes

Nancy
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