[1] R.D. Eithiraj, G. Jaiganesh, G. Kalpana, M. Rajagopalan, First principle study of electronic structure and ground state properties of alkali metal sulfides Li2S, Na2S, K2S and Rb2S, physica status solidi 224 (2007) 1337-1346.
[2] G. Lindberg, A. Larsson, M. Reberg,R. Bostrom, R. Backman,A. Nordin, Determination ofthermodynamic properties of Na2S using solid state EMF measurement, The Journal of Chemical Thermodynamics 39 (2007) 44-48.
[3] A. Vegas, A. Grzenchnik, K. Syssen, I. Loa, M. Hanfland, M. Jansen, Reversible phase transition in Na2S under pressure a comparision with cation array in Na2SO4,ActaCrystallographica Section B 57 (2001) 151-156.
[4] P Blaha, Improved and updated Unix version of the original copyrighted WIEN-code, Computer Physics Communications 59 (1990) 339.
[5] H. Khachai, D. Rached, B. Soudini, FP-LAPW+LO calculation of electronic and optical properties of alkali metal sulfides under pressure, journal of physics condensed matter21 (2009) 095404.
[6] C. Kittel, Introduction to Solid State Physics, John Wiley & Sons, Inc, New York, (1996).
[7] S.W. Koch, Quantum theory of the optical and electronic properties of semiconductors, World Scientific Publishing Company Incorporated, (1994).
[8] A.M. Fox,M. Fox, Optical properties of solids,Oxford university press New York, (2001).
[9] K. Wakamura, Roles of phonon amplitude and low-energy optical phonons on superionic conduction, Physical Review B 56 (1997) 11593.