# Hartree–Fock Equations and Landau’s Fermi-Liquid Theory

## Abstract

In the previous two chapters, we have considered only non-interacting quantum many-particle systems in obtaining exact results for basic thermodynamic quantities and two-particle correlations. However, in real systems, particles interact, making exact statistical-mechanical calculations impossible except for some low-dimensional solvable models. Thus, we are almost always obliged to introduce some approximation when studying interacting systems. Here, we derive the *Hartree–Fock equations*, i.e., one of the simplest approximation schemes for studying interaction effects at finite temperatures, based on a variational principle for the grand potential. They are most effective when interactions are weak and repulsive and are crucial in describing molecular-field effects, but may not be applicable to systems with attractive potentials, as will be seen in later chapters. Next, we apply the Hartree–Fock equations to fermions at low temperatures to clarify how the interaction affects thermodynamic properties along the lines of *Landau’s Fermi-liquid theory*.

## Keywords

Density Matrix Variational Principle Fermi Surface Fermi Energy Spin Susceptibility## References

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