def append(self, species, coords, validate_proximity=True, properties=None):
        """
        Appends a site to the molecule.

        Args:
            species: Species of inserted site
            coords: Coordinates of inserted site
            validate_proximity (bool): Whether to check if inserted site is
                too close to an existing site. Defaults to True.
            properties (dict): A dict of properties for the Site.

        Returns:
            New molecule with inserted site.
        """
        return self.insert(len(self), species, coords,
                           validate_proximity=validate_proximity,
                           properties=properties)
Appends a site to the molecule.

        Args:
            species: Species of inserted site
            coords: Coordinates of inserted site
            validate_proximity (bool): Whether to check if inserted site is
                too close to an existing site. Defaults to True.
            properties (dict): A dict of properties for the Site.

        Returns:
            New molecule with inserted site.