<p>A series of K-6 (1,3,5-trinitro-1,3,5-triazinan-2-one) based energetic compounds are designed by addition of different bridges and energetic groups such as –CN, NHNH₂, –NH₂, –NO₂, –NHNO₂, –N₃, –CH(NO₂)₂. Density functional theory calculations at B3LYP/6-311G (d,p) level are employed to investigated the effects of different groups and bridges on their energy gap, heats of formation, detonation properties and impact sensitivities. The results show that series A possess higher values of energy gap than the other series when compounds are substituted by the same energetic group. –N₃ group and –N=N– bridge are found to be the most effective units in improving values of heats of formation while the NHNO₂, –NO₂ and –CH(NO₂)₂ are demonstrated as the effective groups to increase their detonation properties. Compounds D7, D8, E8, G8 and H4 are selected as potential candidates for high energy density materials since these compounds possess better detonation performances and sensitivities than those of RDX (h₅₀ &gt; 28.0 cm, D &gt; 8.75 km s⁻¹, P &gt; 34.0 GPa). Finally, the electronic structures of these selected compounds are fully investigated to give further understanding their physicochemical properties.</p>