For the planet system :
1. Instead of electron kinetic energy operator we use 1/2mv^2 for each planet.
2. planet- sun potential energy : V = -(GMm)/r
3.Planet–planet interaction contributes a gravitational Hartree potential, representing the average attraction between planets.
4.Exchange Correlation function : Total calculation of all the external factors effecting the planets like smaller satellites ( in Planets there is no quantum interaction So there is a possibility that there is no need of this function)