A model dielectric function for silicon

The model was developed in three stages. First the two-band, tight-binding methods of Chadi and White were used to calculate the dielectric function which describes the response of the electrons in the highest two valence and lowest two conduction bands. The imaginary part of the dielectric function was taken to be equal to the function for low frequencies and an appropriate form of the random-phase-approximation dielectric function for higher frequencies was developed. After the latter function was derived and a systematic way of determining the relevant parameters is presented, it is shown that the composite dielectric function agrees well with the experimental results for all frequencies.