  In the present study, the structural and hitherto uninvestigated mechanical
(elastic stiffness constants, machinability index, Cauchy pressure, anisotropy
indices, brittleness/ductility, Poissons ratio), electronic, optical, and
thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have
been explored using density functional theory. The estimated structural lattice
parameters were consistent with the prior report. The mechanical and dynamical
stability of these compounds have been established theoretically. The materials
are brittle in nature and elastically anisotropic. The value of fracture
toughness, KIC for the B6S and B6Se are ~ 2.07 MPam0.5, evaluating the
resistance to limit the crack propagation inside the materials. Both B6S and
B6Se compounds possess high hardness values in the range 31-35 GPa, and have
the potential to be prominent members of the class of hard compounds. Strong
covalent bonding and sharp peak at low energy below the Fermi level confirmed
by partial density of states (PDOS) resulted in the high hardness. The profile
of band structure, as well as DOS, assesses the indirect semiconducting nature
of the titled compounds. The comparatively high value of Debye temperature
({\Theta}D), minimum thermal conductivity (Kmin), lattice thermal conductivity
(kph), low thermal expansion coefficient, and low density suggest that both
boron-rich chalcogenides might be used as thermal management materials. Large
absorption capacities in the mid ultraviolet region (3.2-15 eV) of the studied
materials and low reflectivity (~16 %) are significantly noted. Such favorable
features give promise to the compounds under investigation to be used in UV
surface-disinfection devices as well as medical sterilizer equipment
applications. Excellent correlations are found among all the studied physical
properties of these compounds.
