def get_reasonable_repetitions(natoms):
    """
    Choose the number of repetitions
    according to the number of atoms in the system
    """
    if natoms < 4:
        return [3, 3, 3]
    if 4 <= natoms < 15:
        return [2, 2, 2]
    if 15 <= natoms < 50:
        return [2, 2, 1]

    return [1, 1, 1]