def k(self):
        """
        Driving force term: :math:`r'' = -k \\left( \\frac{1-e^{-r^2/2{\\sigma_r}^2}}{r} \\right)`
        """
        try:
            return self._k
        except AttributeError:
            self._k = e**2 * self.N_e / ( (2*_np.pi)**(5/2) * e0 * self.m * c**2 * self.sig_xi)
            return self._k
def k(self):
        """
        Driving force term: :math:`r'' = -k \\left( \\frac{1-e^{-r^2/2{\\sigma_r}^2}}{r} \\right)`
        """
        try:
            return self._k
        except AttributeError:
            self._k = e**2 * self.N_e / ( (2*_np.pi)**(5/2) * e0 * self.m * c**2 * self.sig_xi)
            return self._k
def k ( self ) : try : return self . _k except AttributeError : self . _k = e ** 2 * self . N_e / ( ( 2 * _np . pi ) ** ( 5 / 2 ) * e0 * self . m * c ** 2 * self . sig_xi ) return self . _k
Driving force term: :math:`r'' = -k \\left( \\frac{1-e^{-r^2/2{\\sigma_r}^2}}{r} \\right)`
Driving force term : : math : r = - k \\ left ( \\ frac { 1 - e^ { - r^2 / 2 { \\ sigma_r } ^2 }} { r } \\ right )