A theoretical study of low-energy position diffraction
In an exploratory study of the diffraction of slow positrons from atoms and single-crystal surfaces, theoretical intensity and spin polarization results from a W crystal-atom and a W(001) surface are compared to corresponding electron diffraction results obtained with and without an exchange potential. In contrast to e- diffraction, significant spin polarization effects are found for e+ only at energies above about 100 eV. The computing time for e+ is about half of the time required for e-.
Summary In this abstract, we propose a new finite-difference scheme for solving wave equations. This scheme splits the multidimensional system into different directions and solves each direction implicitly. Unlike most splitting methods in the literature which produce numerical anisotropy in diagonal directions, this method gives perfect circular impulse responses and allows lateral velocity variations. In this paper, we prove that the proposed scheme is unconditionally stable. In the numerical examples, we show some impulse response tests and compare them with the results from some high-order explicit finite-difference methods. The new method allows larger time step and requires less memory storage during the reverse time