Core polarization and the equation of state of potassium

We calculate the zero-temperature equation of state of potassium with a model Hamiltonian that includes core-polarization effects. Density fluctuations in the ion cores lead to van der Waals interactions that are dynamically screened by the valence electrons. They also lead to screening of other static interactions, effects that are incorporated through the use of a background dielectric function ${\epsilon }_c\mathrm{}\left(q\right)\mathrm{}$. Inclusion of core-polarization effects yields significant improvement between the theoretical and experimental equations of state, particularly at high pressures.