ELECTROSTATIC RAY-TRACING CALCULATIONS IN VLEED

The present ray-tracing scheme employs the electrostatic potential cal culation by finite-difference solution of the Laplace equation in thre e dimensions. The run time reduction, achieved by using successively r efined grids and optimizing the iteration cycle, allows one to perform calculations on a personal computer. The code is applied to a standar d four-grid LEED optics, operated in the retarding field mode, to calc ulate electron trajectories in the case of off-symmetry incidence. In particular, dependences of incidence K-parallel to on the sample rotat ion cr and primary energy E(p) are calculated. A simple empirical form ula is derived, which allows accurate experimental determination of K without extensive calculations. Ray-tracing calculations are further a pplied to analyse the influence of residual asymmetries of the electro n optics.