Fit Function: li_ein_2s_lennon

Fit Function \[\sigma_{e}^{ion,\;Li(2s)}\big(E\big) = \frac{10^{-13}}{IE}\Bigg[A \ln\bigg( \frac{E}{I} \bigg) + \sum_{j=1}^{3}A_j\bigg(1-\frac{I}{E}\bigg)^j \Bigg]\]
Comments Python code requires NumPy imported as `np`.

Python

Arguments
namedescriptionunitstype(s)
E impact energy eV float, np.ndarray
A fit coefficient eV2 cm2 float
A1 fit coefficient eV2 cm2 float
A2 fit coefficient eV2 cm2 float
A3 fit coefficient eV2 cm2 float
I ionization energy eV float
Return values
namedescriptionunitstype(s)
sigma cross section cm2 float, np.ndarray
Code 
def li_ein_2s_lennon(E, A, A1, A2, A3, I):
    """
    This function calculates the electron impact ionization cross sections (in cm2) of 
    Li 2s.
    param E: requested electron-impact energy in eV
    type E: float, np.ndarray
    param Ai: fit coefficient 
    type Ai: float
    param I: ionization energy in eV
    type I: float
    """
sigma =  (A*np.log(E/I) + A1*(1-(I/E))**1 + A2*(1-(I/E))**2 + A3*(1-(I/E))**3)*1e-13/(E*I)
return sigma