To examine the proposed adsorption/charge exchange-based mechanism in more detail, density functional theory (DFT) calculations of the interaction of analyte gases and SnO surfaces were performed. As SnO is a layered material, surface models of the top nanoflower surface, dominated by the (001) plane, and the nanoflower edges, dominated by the (101) plane, are studied. Interaction energies and the computed net Bader charge on Sn for each analyte-surface combination are presented in Table . Based on the calculated interaction energies all species are expected to interact sufficiently at SnO surfaces at room temperature, with the smallest E being -0.29 eV. The range of interaction energies for the analytes are consistent with the sensing ability of SnO, given that they are not so large as to indicate strong adsorption and not so weak that there is no interaction with the surface. No clear single interaction site can be seen in the atomic structures shown in Fig. which is consistent with the magnitude of the interaction energies. There appears to be a preference on both surfaces for the alcohol hydroxyl group and the carbonyl of acetone to be directed to the surface. Therefore the observed humidity independence of the measurements can be explained by our computed interaction energies that indicate no clear preference for water adsorption and water molecules can be displaced by the analyte molecule. The energies and structures can also suggest that water and the analytes will not compete for the same site. Conversely, the computed adsorption energy of water (-0.43 eV/molecule) and its high abundance during the vent can facilitate scouring the surface of other analytes by displacing these species. The larger interaction energy of IPA (-0.45 eV), could partly explain the incomplete removal behavior of IPA shown in Fig. . This can also be caused by IPA being the reaction solvent, which could stabilize the SnO (001) plane and promote preferential IPA binding sites .