code: def dump(self, title, coordinates):
          
          print("% 8i" % len(self.symbols), file=self._f)
          print(str(title), file=self._f)
          for symbol, coordinate in zip(self.symbols, coordinates):
              print("% 2s % 12.9f % 12.9f % 12.9f" % ((symbol, ) + tuple(coordinate/self.file_unit)), file=self._f)
docs: Dump a frame to the trajectory file
  
             Arguments:
              | ``title``  --  the title of the frame
              | ``coordinates``  --  a numpy array with coordinates in atomic units