Phonon Dispersion in Equiatomic Li-Based Binary Alloys

The computations of the phonon dispersion curves (PDC) of four equiatomic Li-based binary alloys, namely Li_0.5Na_0.5, Li_0.5K_0.5, Li_0.5Rb_0.5 and Li_0.5Cs_0.5, to second order in the local model potential is discussed in terms of the real-space sum of Born von Karman central force constants. Instead of the concentration average of the force constants of metallic Li, Na, K, Rb and Cs, the pseudo-alloy atom (PAA) is adopted to compute directly the force constants of four equiatomic Li-based binary alloys. The exchange and correlation functions due to Hartree (H) and Ichimaru--Utsumi (IU) are used to investigate the influence of screening effects. The phonon frequencies of four equiatomic Li-based binary alloys in the longitudinal branch are more sensitive to the exchange and correlation effects in comparison with the transverse branches. However, the frequencies in the longitudinal branch are suppressed due to IU-screening function than the frequencies due to staticH-screening function.