Table 1 The quantities: λ (electron–phonon coupling constant), \({\Omega }_{ln}\) (logarithmic phonon frequency), Ω₂ (second moment of the normalized weight function), f₁ (strong–coupling correction function), and f₂ (shape correction function) μ.

\(\lambda =2{\int }_{0}^{+\infty }d\Omega \frac{{\alpha }^{2}\left(\Omega \right)F\left(\Omega \right)}{\Omega }\),

\({\Omega }_{ln}=\exp \left[\frac{2}{\lambda }{\int }_{0}^{+\infty }d\Omega \frac{{\alpha }^{2}F\left(\Omega \right)}{\Omega }ln\left(\Omega \right)\right]\),

\({\Omega }_{2}=\frac{2}{\lambda }{\int }_{0}^{+\infty }d\Omega {\alpha }^{2}F\left(\Omega \right)\Omega \),

\({f}_{1}={\left[1+{\left(\frac{\lambda }{{\Lambda }_{1}}\right)}^{\frac{3}{2}}\right]}^{\frac{1}{3}}\), \({f}_{2}=1+\frac{\left(\frac{\sqrt{{\Omega }_{2}}}{{\Omega }_{ln}}-1\right){\lambda }^{2}}{{\lambda }^{2}+{\Lambda }_{2}^{2}}\),

Λ₁ = 2.4 − 0.14μ^’,

\({\Lambda }_{2}=\left(0.1+9{\mu }^{\star }\right)\left(\sqrt{{\Omega }_{2}}/{\Omega }_{ln}\right)\).