Ensemble Density-Functional Perturbation Theory: Spatial Dispersion in Metals
arxiv(2024)
摘要
We present a first-principles methodology, within the context of
linear-response theory, that greatly facilitates the perturbative study of
physical properties of metallic crystals. Our approach builds on ensemble
density-functional theory [Phys. Rev. Lett. 79, 1337 (1997)] to write the
adiabatic second-order energy as an unconstrained variational functional of
both the wave functions and their occupancies. Thereby, it enables the
application of standard tools of density-functional perturbation theory (most
notably, the "2n+1" theorem) in metals, opening the way to an efficient and
accurate calculation of their nonlinear and spatially dispersive responses. We
apply our methodology to phonons and strain gradients and demonstrate the
accuracy of our implementation by computing the spatial dispersion coefficients
of zone-center optical phonons and the flexoelectric force-response tensor of
selected metal structures.
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