A new model dielectric function for loss functions and electron damping.

Trends in the zeroth frequency moment of the imaginary part of the dielectric function are studied for a wide range of metals, semiconductors and insulators. These results are combined with estimates for the inverse-first moment (related by Kramers-Kronig relations to the static dielectric function) and knowledge of the first moment from the f-sum rule. Matching all three moments allows for construction of a model dielectric function that reasonably predicts the loss function at different values of momentum and lifetime damping effects on occupied and unoccupied electron states. This is demonstrated by comparing model results and results of detailed, first-principles calculations.