NBO analysis shows that the electronic charges of W and nearest O varied from +1.5 and -0.6 to +0.8 and -0.4 at the transition state of the reaction. These findings confirmed that the due to adsorption the electron transfer is facilitate from the surface to NO. this phenomena is accordance to DOS spectra of the reaction mixture too. The forbidden gap decreases from 3.4 eV to 1.2 eV in the presence of NO. When NO is adsorbed, half filled states appear in the gap. For bridging oxygen, these states appear as one filled band and one empty band. In these cases, the empty states can accommodate two electrons per adsorbed NO, thus suggesting that oxygen charge can go up to −0.4. these results are also accordance to population analysis. By using a hybrid DFT/MM calculation at the B3LYP/LANL2DZ:UFFof WO3, and by adding adsorbed NO molecules to the WO3 surface, we have shown that NO adsorbs as neutral on perfect (vacancy free) WO3. The increase of the electrical conductivity observed when NO is adsorbed to the oxide surface is more likely due to the presence of acceptor states in the bottom of the gap when NO adsorbs.

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