الفهرس 
Microscopic modelsOnly 14 pages are availabe for public view
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Abstract
calculate the wave vector q and the optical frequency o dependence of the dielectric fimction E(~,wi)n the energy range 0.0 Ry - 2.0 Ry , for the simple metals Na , K and A1 in the random phase approximation (RPA) and beyond the (RPA) taking into consideration; (a): the electron - electron collisions by using relaxation time approximation where the conservation law of electrons number is satisfied , (b): the local field effect by inserting the short range exchange and the correlation effect and (c): the effect of ion core polarizability on the free electron dielectric function , the resulting dielectric function is then called the modified dielectric function . The loss hnction IM [-l/&(q,w) ] is calculated at different values of the wave vector q in the range 0 A’-’ 5 q 5 kf A’-’ for the simple metals Na , K and A1 . Two peaks in the loss spectrum are found , the first peak may be due to the plasmon on the metal surface ; but the second peak (the volume plasmon peak) which is due to plasmon in the metal bulk which is the important in studying the optical properties . It is found that by increasing q the volume plasmon peak is shifted towards to the higher energy . As the three correction terms are taken into consideration , the volume plasmon peak is initially shifted towards the lower energy , in agreement with the experimental data but still keeping the shift towards higher energy . with increasing q