Retrieving "Ground State Energy" from the archives

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1. Quantum Chemistry

   Linked via "ground-state energy"

   Density Functional Theory (DFT) has become the dominant methodology in contemporary quantum chemical calculations due to its favorable balance between accuracy and computational cost. DFT reformulates the problem from solving the complex $N$-electron wavefunction to solving for the electron density$.
   The fundamental premise is the [Hohenberg–Kohn theorems](/entries/hohenberg-kohn…

2. Spin Wave

   Linked via "ground state energy"

   $$\mathcal{H} = E0 + \sum{\mathbf{k}} \hbar \omega{\mathbf{k}} \left( \hat{a}^\dagger{\mathbf{k}} \hat{a}_{\mathbf{k}} + \frac{1}{2} \right)$$
   where $E0$ is the ground state energy, and $\omega{\mathbf{k}}$ is the magnon frequency for wave vector $\mathbf{k}$.
   Dispersion Relation in Ferromagnets