1. K S Singwi, M P Tosi, R H Land and A Sjolander Phys. Rev. 170 589 (1968)
2. Niklasson Phys. Rev. B 8 3052 (1974)
3. S Acharya and R Sharma Ind. J. Pure Appl. Phys. 52 374 (2014)
4. D Pines and P Noziers The Theory of Quantum Liquids (New York: W A Benjamin, Inc Amsterdam) 317 (1966)
5. C Kittel Introduction to Solid State Physics (Singapore: Wiley) 356 (1996)