One of the factors that causes upward diffusion of W from the bulk to the ad layers is the polarization of the atoms arising from the difference in electronegativities of W (2. We can observe a dipolar characteristic between the ad layer and the W slab. Also, the binaveraged charges of W atoms on the ad layers vary between -0.2 and 1.5, and these keep decreasing as we approach the bulk, falling to almost zero. On the other hand, the oxygen charges in the adlayers hover around -0. Therefore, as mentioned before, we concluded that the nO/nW ratio for the adlayer of the three studied W slabs is about 3:1, as illustrated in Fig. . Furthermore, we also observed that the average charge ratio |qW/qO| for the adlayers in the three W slabs is also