Fit Function: li_eex_schweinzer

Fit Function \[\sigma_{e}^{exc}\big(E\big) = \frac{5.984 \times 10^{-16}}{E} \Bigg[\frac{E- I}{E} \Bigg]^{A_6} \times \Bigg[ \sum_{j=1}^{4}\frac{A_j}{(E/I)^{j-1}} + A_5\ln\bigg( \frac{E}{I} \bigg) \Bigg]\]
Comments Python code requires NumPy imported as `np`.

Python

Arguments
namedescriptionunitstype(s)
E impact energy eV float, np.ndarray
A1 fit coefficient cm2 eV float
A2 fit coefficient cm2 eV float
A3 fit coefficient cm2 eV float
A4 fit coefficient cm2 eV float
A5 fit coefficient cm2 eV float
A6 fit coefficient float
I threshold energy eV float
Return values
namedescriptionunitstype(s)
sigma cross section cm2 float, np.ndarray
Code 
def li_ein_schweinzer(E, A1, A2, A3, A4, A5, A6, I):
    """
    This function calculates electron impact excitation cross sections (in cm2) of 
    Li.
    param E: requested electron-impact energy in eV
    type E: float, np.ndarray
    param Ai: fit coefficient 
    type Ai: float
    param I: threshold energy in eV
    type I: float
    """
    sigma = 5.984e-16/E * ((E-I)/E)**A6 * (A1/((E/I)**0) + A2/((E/I)**1) +  A3/((E/I)**2)
                    + A4/((E/I)**3) + A5*np.log(E/I))
    return sigma