Critical minima in elastic electron scattering from argon

Relativistic ab initio calculations of both low- and high-angle critical mi nima in the differential cross sections are presented. The theoretical appr oach is based on the Dirac-Hartree-Fock method. Exchange between incident a nd target electrons is calculated exactly. Target polarization is described by ab initio potential taken from relativistic polarized orbital calculati ons. The position of our critical minima (39.3 eV, 68 degrees) and (39.5 eV , 141 degrees) agree well with recent measurements performed by Panajatovic et al.