VELAS: An open-source toolbox for visualization and analysis of elastic anisotropy
Although elastic properties and their anisotropy play a crucial role in materials science and technology, it is not straightforward to visualize how properties such as shear modulus vary with the direction of stress/strain. Here, written in GNU Octave, we have developed an easy-to-use, flexible, and user-friendly open-source toolbox with a graphical user interface, VELAS, which automatically visualizes and analyses the elastic anisotropy of arbitrary crystal systems using second-order elastic constants. Using Voigt-Reuss-Hill averaging scheme, VELAS allows the calculation of more than ten significant mechanical properties such as modulus, hardness, anisotropy index, ductility, and bond type. It also supports the determination of the mechanical stability of crystals at atmospheric and high pressures using the Born mechanical stability criterion. VELAS provides a new easy-to-use tool for detecting and identifying unusual mechanical properties such as negative Poisson's ratio, negative linear compressibility, and negative bulk modulus. VELAS offers several alternative visualization solutions for elastic properties, such as unit spherical projection, and map projection, and supports direct output of high-quality images. Furthermore, VELAS provides users an interface to read data from the Materials Project API in both online and offline modes. After introducing the basic theory, we detail the software framework, technical route, and installation specifications of VELAS. Moreover, the reliability and versatility of VELAS are confirmed by the analysis of the cases of negative linear compressibility, negative Poisson's ratio, hardness, and fracture toughness.