: Time Dependent Density Functional Theory as a powerful tool for obtaining optical spectra of diversity of molecular systems is gaining day-to-day popularity for the aim of simulation . Recently , there is a great concern among scientists on employing this tool for simulation of optical spectra of atomic and molecular systems . Since obtained optical spectra of this method has a great agreement with experimental result , most of developers are encouraged to have this type of calculation in their packages . Different studies demonstrated that Tungsten Trioxide shows a great change in its properties in the presence of the first row elements of periodic table such as Hydrogen , Sodium and so forth . The most momentous change within these various alteration is optical properties . In accordance with its great usage in industry , it is an on-the-table subject that has been used in making smart-windows (windows with changeable traarency) , mirrors with changeable reflection and so forth . In this study , first , the most stable structures of tungsten trioxide clusters have been obtained by checking the relative stability of different clusters with different criteria by employing Time Dependent Density Functional Theory and taking advantages of some computational packages like : Octopus , Quantum-Espresso and FHI-aims . Then by exploiting OCTOPUS package , optical absorption spectra of the clusters have been studied . It has been found that optical properties of Tungsten Oxides clusters are size dependent . In this package there are two different method for determining optical properties which both have some flaw and flair . Moreover , Since the burden of calculation was heavy and for coming sure about our results , we started to investigate these properties with the new Liouville-Lanczos method (perturbative method) which is recently written in Quantum-Espresso . All these three methods showed a great consensus that is rewarding . In addition , optical gap of clusters have been obtained and its behaviour has been reviewed as a function of size . As it is mentioned before , alteration of optical properties in presence of Hydrogen is well known , therefore , we started to incorporate our clusters with H . First , it was essential to find the best position for Hydrogen , thus different position have been verified by determining its adsorption energy . As it is anticipated the best position for Hydrogen in (WO_3)_n , 1 lt;5 is terminal Oxygen and for (WO_3)_6 is bridge Oxygen . The corollary was a red shift in optical spectra and all of optical gap have been largely decreased . Before adding Hydrogen , the spectra did not have any peak in visible span , that it means our clusters are traarent but after incorporation of Hydrogen in these clusters , there appeared some absorption peaks in visible span which means the traarency is gone and our materials are opaque now . In general , clusters' color have changed to blue but still the color of them is size dependent and by varying size there is an infinitesimal change in their color . In all of the clusters , the 6 th one is completely different from smaller clusters and rather resemble the bulk by having some bulk-like properties that make this cluster due of importance .