def __init__(self, numbers, coordinates=None, title=None, masses=None, graph=None, symbols=None, unit_cell=None):
self.numbers = numbers<EOL>self.coordinates = coordinates<EOL>self.title = title<EOL>self.masses = masses<EOL>self.graph = graph<EOL>self.symbols = symbols<EOL>self.unit_cell = unit_cell<EOL>
Mandatory arguments:
 | ``numbers``  --  numpy array (1D, N elements) with the atomic numbers

Optional keyword arguments:
 | ``coordinates``  --  numpy array (2D, Nx3 elements) Cartesian coordinates
 | ``title``  --  a string with the name of the molecule
 | ``massess``  --  a numpy array with atomic masses in atomic units
 | ``graph``  --  a MolecularGraph instance
 | ``symbols``  --  atomic elements or force-field atom-types
 | ``unit_cell``  --  the unit cell in case the system is periodic