code: def total_energy_matrix(self):
          
          totalenergy = self._recip + self._real
          for i in range(len(self._point)):
              totalenergy[i, i] += self._point[i]
          return totalenergy
docs: The total energy matrix. Each matrix element (i, j) corresponds to the
          total interaction energy between site i and site j.
  
          Note that this does not include the charged-cell energy, which is only important
          when the simulation cell is not charge balanced.