Downfolding approaches to electron-ion coupling: Constrained density-functional perturbation theory for molecules

  title={Downfolding approaches to electron-ion coupling: Constrained density-functional perturbation theory for molecules},
  author={Erik van Loon and Jan Berges and Tim Oliver Wehling},
Constrained electronic-structure theories enable the construction of effective low-energy models consisting of partially dressed particles. Since the interpretation and physical content of these theories is not straightforward, we investigate the minimal example of partially dressed phonons in small molecules to explore the properties of constrained density-functional perturbation theory (cDFPT). We show that the dipole selection rules determine whether the partially dressed phonons satisfy… 

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