Open the SIGRES file located in the in self.outdir.
        Returns :class:`ScrFile` object, None if file could not be found or file is not readable.

def open_scr(self):
        """
        Open the SIGRES file located in the in self.outdir.
        Returns :class:`ScrFile` object, None if file could not be found or file is not readable.
        """
        scr_path = self.scr_path

        if not scr_path:
            logger.critical("%s didn't produce a SCR.nc file in %s" % (self, self.outdir))
            return None

        # Open the GSR file and add its data to results.out
        from abipy.electrons.scr import ScrFile
        try:
            return ScrFile(scr_path)
        except Exception as exc:
            logger.critical("Exception while reading SCR file at %s:\n%s" % (scr_path, str(exc)))
            return None