def load_file(cls, filepath):
        """
        Create a :class:`MolecularSystem` from an input file.

        Recognized input file formats: XYZ, PDB and MOL (V3000).

        Parameters
        ----------
        filepath : :class:`str`
           The input's filepath.

        Returns
        -------
        :class:`pywindow.molecular.MolecularSystem`
            :class:`MolecularSystem`

        """
        obj = cls()
        obj.system = obj._Input.load_file(filepath)
        obj.filename = os.path.basename(filepath)
        obj.system_id = obj.filename.split(".")[0]
        obj.name, ext = os.path.splitext(obj.filename)
        return obj