Quasi-noninteracting system

T he relation of the magnetic susceptibility of the liquid crystal phase to x that of the solid phase is a complicated, many-body problem. The energy of the system depends not only on the orientation of the molecules with respect to the magnetic field but also on their orientation with respect to each other. To obviate this difficulty, one introduces a set of noninteracting quasi particles (swarms) of mass M (3). The energy is then... 

The basic idea underlying Kohn-Sham theory [4] is the construction of a mode system of noninteracting quasi-particles for which the density is the same as that of the interacting system. As such the ground-state energy functional E[p] is partitioned as... 

Consider now the corresponding Kohn-Sham system of noninteracting particles with the same electron spin densities. The quasi-energy Kohn-Sham equations for the time-periodic spin orbitals ( )° can be obtained from the stationary principle for the quasi-energy functional (Equation 3.16)... 

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