def estimate_num_machines(structure):
    """
     1 <= num_atoms <= 10 -> 1 machine
    11 <= num_atoms <= 20 -> 2 machine
    
    :param structure: [description]
    :type structure: [type]
    :return: [description]
    :rtype: [type]
    """
    from math import ceil
    number_of_atoms = len(structure.sites)
    return ceil(number_of_atoms / 10)
