$$\hbar \omega_{{\text{p}}} = 28.8\left( {\frac{{Z^{\prime}\rho }}{M}} \right)^{1/2}.$$ (25) The Penn gap and Fermi energy in terms of the plasma energy were calculated by the following relations [64]: $$E_{{\text{p}}} = \frac{\hbar{\omega_{p} }}{{\left...