Density Functional Theory (DFT) is a computational quantum mechanical modeling method. This theory is one of the most successful theories in computational physics, chemistry and materials science. DFT was used in this thesis. The first chapter begins with a brief explanation of the main motivation to start this project.andcompounds are two attractive materials with unique properties which have been studied and investigated in the previous decades. The curiosity for investigation of these semiconductors in contact with each other led us to start the project through the investigation of the surface contact between the two semiconductors.andemiconductors have been introduced in the rest of chapter1 and their significant properties and applications have also been enumerated. Chapter2 addresses the primary calculations. Kohn-Sham and Pseudo-Potential approaches have briefly introduced at the beginning and the parameter optimization process for necessary parameters have been explained. Lattice constants and energy cutoff were optimized and the energy-volume diagram fitted with respect to the Murnaghon equations of states. The fitting process resulted the equilibrium volume and the volume module of ulk and repeating the same process for Ultra-soft and PAW pseudo-potentials made the pseudo-potentials judicable. Some electronic calculations ofulk will be discussed at the end of chapter2. According to the main purpose of the project, the(101) surface in the two different Titanium-termination and Oxygen-termination were simulated and the behavior of each one was investigated. The 101) surface with Ti-termination was chosen for further calculations. The next step in the simulation of thin film system is to place amono-layer on the(101) surface. The taking place process encountered with some convergency problem and needed a suitable solution. Some different suggestions were proposed and applied: applying dipole correction, taking place thelayers step by step (an S layer, then a W layer and eventually an S layer) on the(101) surface, and relaxingconfigurations before taking place on the surface. After examining all three propositions, the solution for the problem turned out to be the last option (relaxing configurations before taking place on the surface) which, subsequently, was used both manually and through USPEX structure predictor in order to find the stable configurations. Thereupon using the third advice and the transition path calculations (NEB) method, we found 8 different meta-stable configurations which were studied precisely. First of all, the stability of the configurations was checked which all of them succeeded in the stability test.The electron density of the configurations was calculated and plotted which showed a metallic behavior in the system. Therefore, in order to correct the metallic behavior, the conventional method for applying strain was used and the obtained results were discussed. The interface ofsystem has been explained in the final chapter as well. The interface investigations contain the relation between the configurations stability and the geometry of the structures, the relation between stability and bond lengths, electron density and density of states (DOS). Hence a good sight about stability, the bonds in the interface and their qualities were achieved. Finally, the transition paths between different configurations and the possibility for experimental synthesizability of these configurations were calculated and discussed.