We propose a model to calculate the electronic structure of hydrotalcite-like compounds by using periodic boundary conditions and ab initio density functional theory (DFT). The proposed method to build up layered double hydroxides (LDHs) was tested for Zn 2/3 Al 1/3 (OH) 2 Cl 1/3 • 2 / 3 H 2 O, Zn 2/3 Al 1/3 (OH) 2 (CO 3 ) 1/6 • 4 / 6 H 2 O, and Mg 2/3 Al 1/3 (OH) 2 (CO 3 ) 1/6 • 4 / 6 H 2 O with 3R 1 polytype. In the model, the occupation of cationic sites in hydroxide layers is ordered and the interlayer anions and water molecules form a film between the layers. Direct comparison with experimental structural parameters shows good agreement. The a parameter is close to that in brucite for all three LDHs. The c parameter is smaller (about 1 Å) for the LDHs with CO 3 2as a consequence of its strong interaction with hydroxide layers. Those interactions were evidenced by the difference of density and vibrational analysis. The intercalated water molecules have small mobility and interact strongly with one another and with interlayer anions and hydroxide layers. These interactions cause the downshift in the calculated vibrational wavenumbers of water O-H stretching modes below 3420 cm -1 and are consistent with the reported infrared spectra of hydrotalcite-like compounds. The calculated formation enthalpies for LDHs with carbonate are in agreement with the previously reported trend. The biggest difference between theoretical and experimental values is 2 kcal/mol. The calculated formation Gibbs energies are negative. The zero point energy is important to evaluate ∆H, but the formation entropy does not affect the Gibbs free energy significantly.

Asphaltene deposition is a well-known problem in the petroleum industry. Nevertheless, there seems to be a lack of information on the processes involved in asphaltene association and its relationship to asphaltene solubility under certain conditions. Molecular mechanics and molecular dynamics have had an important role in the investigation of these phenomena. To better understand the role of solvents in fractionating asphaltenes extracted from vacuum residues and evaluate their tendency to dissociate under different conditions, we modeled the effect of toluene, n-butane, isobutane, and n-heptane on an aggregate formed by two asphaltene molecules that would have a tendency to associate (not average structures commonly used in similar studies). Molecular dynamics simulations were performed on an asphaltene dimer after minimizing the conformation of each molecule and verifying the most stable position for docking. They reveal the extent to which these solvents are able to separate the aggregate at different temperatures after a given period of time. As expected, toluene is the most effective and n-heptane affects the aggregate the least, with n-butane and isobutane falling between these two bounds.