Table 1 Estimation of nonlinear e–ph coupling ratio ξ in FeSe.

From: Relative importance of nonlinear electron-phonon coupling and vertex corrections in the Holstein model

Orbital

a2/a1 [Å−1]

ξ

dxy

−4.5936

−0.1641

dxz/dyz

−0.4804

−0.0172

\({d}_{{z}^{2}}\)

0.0159

0.0006

\({d}_{{x}^{2}-{y}^{2}}\)

0.4155

0.0148

  1. Results from fits of the on-site energy ϵdiag(zSe) for each d-orbital of Fe as a function of the height of the Se atom zSe measured with respect to the Fe-plane. Fitting ϵdiag(zSe) with a simple polynomial of the form \(f({z}_{\text{Se}})={a}_{0}+{a}_{1}({z}_{\text{Se}}-{z}_{0})+{a}_{2}{({z}_{\text{Se}}-{z}_{0})}^{2}\), we estimate the nonlinear coupling ratio ξ from the fitting parameters a2/a1.
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