  Physical quilities such as electronic, mechanical, thermal, and optical
properties of Al and P codoped silicene forming AlSi$_6$P nanosheets are
investigated by first-principle calculations within density functional theory.
A particular attention of this study is paid to the interaction effect between
the Al and P atoms in the buckled silicene structure. We infer that the
interaction type is attractive and it leads to an asymmetry in the density of
states opening up a band gap. In contrast to BN-codoped silicene, the buckling
in the Al-P codoped silicene is not much influenced by the dopants as the bond
lengths of Si-P and Al-P are very similar to the Si-Si bond lengths. On the
other hand, the longer bond length of Si-Al decreases the stiffness and thus
induces fractures at smaller values of applied strain in AlSi$_6$P. The elastic
and nonelastic regions of the stress-strain curve of AlSi$_6$P depend on the
placement of the Al and P atoms. The finite band gap caused by the Al-P dopant
leads to enhancement of the Seebeck coefficient and the figure of merit, and
induces a redshift of peaks in the dielectric response, and the optical
conductivity. Finally, properties of the real and imaginary parts of the
dielectric function, the excitation spectra, the refractive index, and the
optical response of AlSi$_6$P are reported.
