Determine if calculation converged; for a relaxation (static) run
        we look for ionic (electronic) convergence in the output

def _is_converged(self):
        '''Determine if calculation converged; for a relaxation (static) run
        we look for ionic (electronic) convergence in the output'''
        if self.is_relaxed():
            # relaxation run case
            return self._get_line(['End of', 'Geometry Optimization'], self.outputf, return_string=False)
        else:
            # static run case
            return self._get_line('convergence has been achieved', self.outputf, return_string=False)