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In silicomodeling of acidic (CH2COOH)or basic (CH2NH2) functionalized silica surfaceshas been carried out by means of a density functional approach basedon a gradient-corrected functional to provide insight into the characterizationof experimentally functionalized surfaces via a plasma method. Hydroxylatedsurfaces of crystalline cristobalite (sporting 4.8 OH/nm2) mimic an amorphous silica interface as unsubstituted material.To functionalize the silica surface we transformed the surface Si–OHgroups into Si–CH2COOH and Si–CH2NH2moieties to represent acidic/basic chemical characterfor the substitution. Structures, energetics, electronic, and vibrationalproperties were computed and compared as a function of the increasingloading of the functional groups (from 1 to 4 per surface unit cell).Classical molecular dynamics simulations of selected cases have beenperformed through a Reax-FF reactive force field to assess the mobilityof the surface added chains. Both DFT and force field calculationsidentify the CH2NH2moderate surface loading(1 group per unit cell) as the most stable functionalization, at variancewith the case of the CH2COOH group, where higher loadingsare preferred (2 groups per unit cell). The vibrational fingerprintsof the surface functionalities, which are the ν(CO)stretching and δ(NH2) bending modes for acidic/basiccases, have been characterized as a function of substitution percentagein order to guide the assignment of the experimental data. The finalresults highlighted the different behavior of the two types of functionalization.On the one hand, the frequency associated with the ν(CO)mode shifts to lower wavenumbers as a function of the H-bond strengthbetween the surface functionalities (both COOH and SiOH groups), andon the other hand, the δ(NH2) frequency shift seemsto be caused by a subtle balance between the H-bond donor and acceptorabilities of the NH2moiety. Both sets of data are in generalagreement with experimental measurements on the corresponding silica-functionalizedmaterials and provide finer details for a deeper interpretation ofexperimental spectra. [ABSTRACT FROM AUTHOR]