In order to access this option you should select the EXPERT
OPTIONS sheet (close to the upper left corner of the main program
window). However, starting with CasP versions beyond version 3.1, the relativistic correction is always active.
The global relativistic energy loss cross section at high energies
(neglecting radiation energy- losses and collective screening) is
c1 = (ln(2 (g vp)^2 / I_Bethe) - b^2) / vp^2
with b = vp / c and g = 1 / (1 - b^2)^0.5.
The corresponding non-relativistic expression is
c2 = ln(2 vp^2 / I_Bethe) / vp^2.
When selecting this option in elder CasP versions, all energy-loss values were simply scaled by a constant factor c1/c2.
The CasP versions beyond version 3.1 include an impact-parameter
dependent realization of this effect (still neglecting radiation
energy-losses and collective screening). Here we have adopted the
simplified treatment using the g-correction factors exactly as shown in
chapter 13 by J.D.Jackson in his book on ‘Classical
electrodynamics’ (de Gruyter, 1981). However, the finite nuclear-size effect is currently not considered as a lower impact-parameter cut-off.