Collective excitations in a potassium-rubidium melt

The partial and effective potentials of a potassium-rubidium melt is calculated at 50at% concentration of potassium, using a pseudopotential formalism. The effective pair-correlation function is obtained through the Fourier transform of the total structure factor. The longitudinal and transverse photon frequencies are computed from the effective pair potential and radial distribution function using the theory of Takeno and Goda. The eigenfrequency equations reproduce successfully the dispersion curves both for longitudinal and transverse photons. The longitudnal photon frequency curve shows characteristic oscillatory behaviour at short wave length limit while the transverse phonon frequency curve does not show any oscillation. After attaining a smooth maximum it becomes constant with increasing k value. However, in the long wavelength limit the dispersion relation for both types of excitations are found to be linear. Further it is observed that the position of the first minima in the longitudinal phonon dispersion curve coincides with the first maxima of the total structure factor curve as has been observed by Bhatia and Singh. From the dispersion curves, the elastic constants are evaluated and compared with those obtained from I1 and I2 integrals of Schofield. The results are in fair agreement with each other