It is possible that many of the photo-catalysts or the materials employed in PEC applications have this patterned configuration. Those systems that do not fit to the patterned configurations may not exhibit perceptible photo-catalytic activity or may not find use in PEC application. Further studies alone will provide answer to this important aspect. It is necessary to understand how these dopants promote the phase transformation and how the patterned configuration is generated in titania system. This aspect requires an understanding of the crystal structure of both anatase and Rutile forms. Even though both the forms have titanium ions in six fold coordination of oxide ions the arrangements of the oxide ions are different as shown in Fig. . Accordingly, the unit cell parameters also differ. At this stage a few remarks may be appropriate. Normally, depending on the magnitude of rearrangement of atoms required for phase transitions, the conventional variables of temperature and pressure are fixed. However, it is known that certain additives also can induce the phase transition possibly by inclusion in the lattice such that lattice contraction or alteration can be easily achieved. In the case of Anatase to Rutile transformation, the inclusion of hetero-atoms or even possibly certain metallic species may favour this phase transition in a facile manner. This could be one of the reasons that titanium dioxide samples prepared in the presence of hetero-atom containing precursors especially C or N could have both the phases. There are still some questions which have to be answered. These include: (i) Is there a possibility of controlling the extent (in terms of %) of simultaneous phases present in a given sample of Titania? (ii) How the core shell model generate active sites for the photo-electrochemical decomposition of water? (iii)Why these sites are more active than the active sites normally present on single phase materials? These aspects need careful consideration in future. In order to elucidate further, DFT calculations have been carried out on typical units representing pure anatase, pure rutile and anataserutile combination in an assumed configuration as shown in Fig. The configuration shown in the combination may be considered as 10 representing a core shell model. The density of states per unit of building block is considered and the results obtained is shown in Fig. . It is seen that the valence band density of states for the core shell configuration is particularly altered with respect to that of either pure anatase or pure rutile. Wu et al. have shown that the absorption edge has red shifted as the crystal size is decreased. They have postulated that the band gap of anatase is nearly independent with different percentage of reactive facets while the band gap is narrower with smaller particle size. The width of the valence band is the same for uniform particle size with different percentage of 15 facets ( of the order of 6.42 eV) while systems with varying particle size with the same percentage of facets showed decreasing band width. They concluded that the crystal size is an important factor for the electronic and band structure of anatase. However, there are no reports on the effect on these parameters by the presence of another phase along with anatase. It is generally known that the added phase can alter the phase transfer characteristics of the original anatase phase. It is also possible that the size control that will inherently take place in the core shell model can also alter the wave functions of both valence and conduction band of the resulting system and also 20 create additional active sites at the interface. Against these results, the calculations lead to the following points: 1. Pure anatase shows higher density of states at the valence band as compared to pure rutile or anatase-rutile combination. This will have implications for the observed photo-activity of anatase phase as compared to other phases. 2. The valence band width (~2.5 eV) appears to be greater for the rutile-anatase combination rather than the other two pure phases. This could be the reason why the combination system exhibits higher photo-activity. This can result in higher photon absorption cross 25 section and thus facilitate facile electron hole pair formation.