  The buckling effects due to BN-bonds in BN-codoped silicene, BSi$_6$N, on
structural stability, electronic band structure, and mechanical, thermal and
optical properties are studied systematically by first-principle calculations
within density functional theory. In the presence of BN-bonds, a high warping
in BSi$_6$N indicating a high buckling effect is found due to the presence of a
repulsive interaction between B and N atoms. It thus breaks the sublattice
symmetry of silicene and opens up a bandgap. The high buckling of BSi$_6$N
leads to a decrease in its stiffness and thus induces fractures at small values
of applied strain. The finite bandgap caused by the BN-bonds leads to
enhancement of the Seebeck coefficient and the figure of merit, and induces a
redshift of a peak in the dielectric response. By increasing the distance
between the B and N atoms i.e. for the BSi$_6$N without BN-bonds, a flatter
BSi$_6$N is found compared to pristine silicene. The stiffness of the structure
and the ultimate strain are increased. The breaking of the sublattice symmetry
is very weak and a very small bandgap is revealed. As a result, the Seebeck
coefficient and the figure of merit stay very small. A reduction in the optical
response is seen due to an indirect bandgap.
