Kavli Affiliate: Jeffrey B. Neaton
| First 5 Authors: Norm M. Tubman, Christopher J. N. Coveney, Chih-En Hsu, Andres Montoya-Castillo, Marina R. Filip
| Summary:
Ab initio downfolding describes the electronic structure of materials within
a low-energy subspace, often around the Fermi level. Typically starting from
mean-field calculations, this framework allows for the calculation of one- and
two-electron interactions, and the parametrization of a many-body Hamiltonian
representing the active space of interest. The subsequent solution of such
Hamiltonians can provide insights into the physics of strongly-correlated
materials. While phonons can substantially screen electron-electron
interactions, electron-phonon coupling has been commonly ignored within ab
initio downfolding, and when considered this is done only for short-range
interactions. Here we propose a theory of ab initio downfolding that accounts
for all mechanisms of electron-phonon coupling on equal footing, regardless of
the range of the interactions. Our practical computational implementation is
readily compatible with current downfolding approaches. We apply our approach
to polar materials MgO and GeTe, and we reveal the importance of both
short-range and long-range electron-phonon coupling in determining the
magnitude of electron-electron interactions. Our results show that in the
static limit, phonons reduce the on-site repulsion between electrons by 40% for
MgO, and by 79% for GeTe. Our framework also predicts that overall attractive
nearest-neighbor interactions arise between electrons in GeTe, consistent with
superconductivity in this material.
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