  Reflection high-energy electron diffraction (RHEED) is a powerful tool for
characterizing crystal surface structures. However, the setup geometry leads to
distorted and complicated patterns, which are not straightforward to link to
the real-space structures. A program with a graphical user interface is
provided here to simulate the RHEED patterns. Following the Ewald construction
in the kinematic theory, we find out the exact geometric transformation in this
model that determines the positions of diffraction spots. The program can deal
with many forms of surface structures, including surface reconstructions or
domains. The simulations exhibit great agreement with the experimental results
in various cases. This program will benefit the structure analysis in thin film
growth and surface science studies.
