Changes induced when a molecule is adsorbed onto a substrate: Adsorption of methanol onto a zeolite catalyst, chabazite. We show that substantial changes in charge density take place, with proton transfer from the Brønsted acid site of the zeolite to the methanol. Mulliken charges in electronic units for isolated Brønsted acid site in zeolite. Red atoms are oxygen, yellow silicon, grey aluminium and blue hydrogen. The bond population between O and H is 0.52e. From Ph.D. thesis of Matthew Segall, University of Cambridge, 1997

By considering the Mulliken charges, we find that the group has an overall charge of +0.77e. While this is not as large as the formal charge of +1e, it does demonstrate the presence of substantial charge transfer from the zeolite to the adsorbate. The charges also indicate increased polarisation of the C--O bond, indicating the possibility that the methyl group has become susceptible to nucleophilic attack. From Ph.D. thesis of Matthew Segall, University of Cambridge, 1997

3-aminopropylmethoxysilane (AMEO) adsorbing on a hydroxylated surface of (a) Movement of atoms during the adsorption of AMEO, color coded by RMSD over the entire reaction path; (b) Mulliken charge difference ΔQ=Qmax-Qmin of each atom for the reaction of AMEO in units of electrons. (a) (b)