In recent years, superlattices and layered materials have been highlighted as potential candidates for thermoelectric applications, this thanks to their low thermal conductivity. Moreover, external applied pressure and biaxial strain can be used to enhance their properties by achieving a band engineering and electronic tuning. With this in mind, we performed an $ab$ initio based study on InSe/GaSe superlattices under biaxial strain along the layer planes. Layers of InSe and GaSe with $D_{3h}$ symmetry were stacked along the $c$ axis to create the superlattice. The atomic stacking along the $c$ axis is Se-Ga-Ga-Se-Se-In-In-Se, which corresponds to the space group #187. Our ab initio calculations predict the superlattice to be a semiconductor with an electronic band gap of $E_g$ = 0.54 eV. With the aim to increase thermoelectric performance, we apply positive and negative biaxial strain on the ab plane. Under compressive strain, the electronic structure evolves to an insulating behavior by increasing the band gap. When tensile strain is applied, we observe a transition towards a metallic character with a systematic reduction of the band gap. Interestingly, the semiconductor-metal transition only occurs when spin-orbit coupling (SOC) is switched off. With the inclusion of SOC, the system experiences an electronic topological transition around 3% tensile strain, with a double band gap along the $K\text{−}\mathrm{\Gamma }\text{−}M$ high-symmetry paths. We have found that for both, $n$-type and $p$-type doping, compressive strain improves the electronic figure of merit ($Z{T}_e$ under constant relaxation time approximation). Not only the electronic part increases thermoelectric performance, but also the lattice contribution to the thermal conductivity decreases with compressive strain.

In this work, the (TiO₂)₂₀ cluster is proposed to adsorb the methylene blue (BM) dye; thus, the quantum parameters to explain the adsorption process are calculated by means of density functional theory calculations. Eight possible configurations are obtained and labeled from M1 to M8. According to the adsorption energy values, they reveal physisorption for at least two cases, and for the rest of the systems, they exhibit chemisorption. The preferential positions that lead to good adsorption for the BM dye are parallel to the semiconductor cluster; however, when one end of the BM dye formed by hydrogen atoms is interacting with the cluster, a weak chemical interaction is reached. The chemical interactions for M4 and M5 systems generate considerable increases of their electronic gap values (E _g) with respect to the rest, and this effect is explained based on iso-surfaces of frontier orbitals and electronic charge transference. The chemical interactions between these chemical species are stable under vibrational and thermal criteria. This semiconductor cluster arises as a good candidate to adsorb some dyes like BM.