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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def calculate_centre_of_mass(self):
 """ Return the xyz coordinates of the centre of mass of a molecule. Returns ------- :class:`numpy.array` The centre of mass of the molecule. """

        self.centre_of_mass = center_of_mass(self.elements, self.coordinates)
        self.properties['centre_of_mass'] = self.centre_of_mass
        return self.centre_of_mass