docs: def rho_rec(self, g2):
          """
          Reciprocal space model charge value
          for input squared reciprocal vector.
          Args:
              g2: Square of reciprocal vector
  
          Returns:
              Charge density at the reciprocal vector magnitude
          """
          return (self.expnorm / np.sqrt(1 + self.gamma2 * g2) + (
              1 - self.expnorm) * np.exp(-0.25 * self.beta2 * g2))