  We have developed a software package CALYPSO (Crystal structure AnaLYsis by
Particle Swarm Optimization) to predict the energetically stable/metastable
crystal structures of materials at given chemical compositions and external
conditions (e.g., pressure). The CALYPSO method is based on several major
techniques (e.g. particle-swarm optimization algorithm, symmetry constraints on
structural generation, bond characterization matrix on elimination of similar
structures, partial random structures per generation on enhancing structural
diversity, and penalty function, etc) for global structural minimization from
scratch. All of these techniques have been demonstrated to be critical to the
prediction of global stable structure. We have implemented these techniques
into the CALYPSO code. Testing of the code on many known and unknown systems
shows high efficiency and high successful rate of this CALYPSO method [Wang et
al., Phys. Rev. B 82 (2010) 094116][1]. In this paper, we focus on descriptions
of the implementation of CALYPSO code and why it works.
