code: def ρ(self, e):
          
          d = self._dichalcogenide
          at, λ = d.at, d.λ
          return abs(2 * e - λ) * (2 * at**2)**(-1)
docs: Density of states.
  
          :param e: Energy :math:`E`.
          :type e: float
  
          :return: :math:`ρ(E) = \\left|k'(E) k(E)\\right|`
          :rtype: float