Adsorption of Functionalized Benzoic Acids on MgSO₄⋅H₂O (100)

Abstract

Using a combination of ab initio and semiempirical methods, adsorption problems on surfaces with large unit cells and low symmetry can still be studied. Here, a hybrid approach of density functional theory (DFT) and Hartree-Fock (HF) was used. As an example, we determined the geometry and the electronic properties of benzoic acid (BA), salicylic acid (SA) and para-salicylic acid (p-SA) adsorbed on MgSO(4).H(2)O (100), which are used as conditioner molecules for the electrostatic separation of minerals. Contrary to general expectations, these molecules are chemisorbed, with binding energies around 1.9 eV, forming bonds through the carboxylic O atom of the COOH groups in a nonplanar geometry, although the surface is a stoichiometric wide-band-gap insulator and the molecules stay intact. In contrast, a planar adsorption geometry turned out to be nonbonding. Bonding takes place by means of surface-molecule resonances due to the overlap of the valence band with molecular orbitals, assisted by a small charge-transfer molecule to the surface of around 0.15e. These combined interactions cause an intramolecular twist between the COOH group and the benzene ring.

Anomalous molecular orbital variation upon adsorption on a wide band gap insulator

“…The convergence criterion of lattice parameter and atomic position relaxation was set to 0.02 eV/ Å. The resultant lattice constants (a = 6.79 Å, b = 7.79 Å, c = 7.69 Å) and β = 117.7 • are in good agreement with experiment and previous theoretical values 12 . The direct band gap at the Γ point is severely underestimated by the GGA-PBE (5.53 eV) and the local density approximation (LDA) (5.26 eV) compared to a surface sensitive experimental value (7.4 eV) 13 .…”

“…This feature stems partially from the intrinsic molecular structure of GA, and is not observed for some other organic molecules, e.g. hydroxybenzoic acid on MgSO 4 ·H 2 O(100) 12 . The sp 3 hybridization in the carbon chain makes the structure versatile through the rotation along the C-C bond with a small energy barrier, which can be easily overcome by the energy gain through the subsequent GAsurface interactions.…”

Structure–property relationships in multifunctional thieno(bis)imide-based semiconductors with different sized and shaped N-alkyl ends

“…20 The all-electron Gaussian-type basis sets adopted were 6-31(d1) for oxygen, 21 nitrogen 22 and carbon, 23 31(p1) for hydrogen 26 and 8-6311(d1) for sulphur. 24 A post-DFT dispersive contribution, suggested by Grimme, 25 has been added to the computed ab initio total energy and gradients in order to account long-range dispersion interactions.…”

Tuning Molecular Self‐Assembly on Bulk Insulator Surfaces by Anchoring of the Organic Building Blocks

“…For example, a theoretical study has elucidated the case of salicylic acid adsorbed on the MgSO 4 ·H 2 O (100) surface. In this system, a hydrogen bond is formed between the phenolic hydroxyl group of the molecule and a sulfate ion of the surface 88. On the same surface, hydrogen bonds play an even more decisive role in the stabilization of water molecules by forming two bridges to each water molecule.…”