Thorium is a weakly radioactive silvery metal with a face-centered cubic (fcc) lattice, the Fm m3 space group. The crystal structure of thorium is determined by the presence of the 5f shell, in contrast to group 4 metals Ti, Zr, Hf whose pure forms have hexagonal crystal structures. A special feature of thorium compounds is that their 5f shell is filled only in the case of chemical bonding and remains empty in free atoms (electronic configuration [Rn]6d2 7s 2 5f 0 ). 

Thorium Boride is hard, high-melting materials with metal-like conductivity. It is stable to nonoxidizing acids but break down in strong oxidizing agents and strong alkalis. Thorium Boride is used in semiconductors, superconductors, diamagnetic, paramagnetic, ferromagnetic, anti-ferromagnetic, turbine blades, and rocket nozzles. Borides have recently been discovered to be superconductive and ultra-incompressible. 

The most important task in the ab initio calculations of the properties of actinide-containing compounds is correct description of the role of 5f electrons, in particular, the effect of spin-orbit coupling (SOC) on the calculated band structure and chemical bonding in these systems. As is known, the SOC correction for actinide compounds with a partially filled 5f shell significantly affects the calculated values of physical parameters such as the degree of 5f state localization, elastic characteristics, local atomic magnetic moments, chemisorption energies of light atoms on the surface, etc. In contrast to metallic thorium and its carbides, nitrides, and dioxide, Th borides have been poorly studied, and almost no data on their properties have been reported. Some of these gaps are filled in the present study of chemical bonding and phase stability of thorium borides (ThB4, ThB6, ThB12) by ab initio methods of the band theory of electronic properties.