Gas-phase molecular structure and energetics of anionic silicates

Gomes, José R. B.; Cordeiro, M. Natália D. S.; Jorge, Miguel

doi:10.1016/j.gca.2008.06.012

Cited by 37 publications

(50 citation statements)

References 61 publications

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“…During the simulations, Si-O and Al-O distances are around 1.64 and 1.93 Å (marked on Fig. 2), consistent with the previous studies (Kubicki et al, 1995;Ikeda et al, 2003Ikeda et al, , 2006Amira et al, 2006;Bylaska et al, 2007;Gomes et al, 2008;Hay and Myneni, 2008). On Fig.…”

Section: Reactant Statessupporting

confidence: 89%

Acid dissociation mechanisms of Si(OH)4 and Al(H2O)63+ in aqueous solution

Liu

Meijer

et al. 2010

Geochimica et Cosmochimica Acta

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Silicic acid and the hexa-aqua of Al 3+ are fundamental model aqueous species of chemical importance in nature. In order to investigate their hydroxyl dissociation mechanisms, Car-Parrinello molecular dynamics (CPMD) simulations were carried out, which allow treating the solutes and solvents on the same footing. The method of constraint was employed to trigger the reactions by taking coordination number as the reaction coordinate and the thermodynamic integration was used to obtain the free-energy profiles. The approximate transition states were located and the reactant and product states were also characterized. The free-energy changes of dissociation are found about 15.0 kcal/mol and 7.7 kcal/mol for silicic acid and Al-aqua, respectively. From the simulation results, the first pKas were calculated by using two approaches, which are based on the pristine thermodynamic relation and the RDF (radial distribution function)-free energy relation, respectively. Because of more uncertainties involved in the RDF way, it is suggested that the pristine way should be favored, which shows an error margin of 1 pKa unit. This study provides an encouraging basis for applying the present methodology to predict acidity constants of those groups that are difficult to measure experimentally.

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Section: Reactant Statessupporting

confidence: 89%

Acid dissociation mechanisms of Si(OH)4 and Al(H2O)63+ in aqueous solution

Liu

Meijer

et al. 2010

Geochimica et Cosmochimica Acta

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“…The terminating H atoms were placed at the same bond angles and dihedral angles as the corresponding Si or Ti atoms in the extended crystal structure, and at a bond distance of 0.96 Å, which is a typical value for this type of materials. 35 The initial positions of the cations (i.e., prior to the optimization procedure) employed to neutralize the system were taken from Grillo and Carraza, 36 who used molecular simulation to analyze cation locations in ETS-10 and obtained good agreement with experimental data of Wang and Jacobson. 37 These authors identified four different positions where cations are located (cf.…”

Section: Methodsmentioning

confidence: 99%

A DFT study on the interaction of small molecules with alkali metal ion-exchanged ETS-10

Pillai

Jorge

Gomes

2018

Zeitschrift Für Kristallographie - Crystalline Materials

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In this paper, we present a systematic quantum-mechanical density functional theory (DFT) study of adsorption of small gas molecules in cation-exchanged Engelhard titanosilicate ETS-10 crystalline materials. Adsorbates with a range of polarities were considered, ranging from polar (H2O), quadrupolar (CO2 and N2), to apolar (CH4) atmospheric gases. Starting from the base-case of Na-ETS-10, other extra framework cations such as Li + , K + , Rb + and Cs + were considered. The DFT calculations were performed with the M06-L functional and were corrected for basis set superposition error with the counterpoise method in order to provide accurate and robust geometries and adsorption energies. For all adsorbates, the adsorption enthalpies decrease in the order Li + > Na + > K + > Rb + > Cs + , while adsorbate -cation interaction distances increase along the same order. For the two extreme cases, the enthalpies calculated at the M06-L/6-31++G** level of theory for CH4, N2, CO2, and H2O interaction with Li + (Cs + ) exchanged materials are -21.8 (-1.7) kJ•mol -1 , -19.0 (-10.7) kJ•mol -1 , -34.4 (-21.3) kJ•mol -1 , and -70.5 (-36.1) kJ•mol -1 , respectively. Additionally, the calculated vibrational frequencies are found to be in quite good agreement with the characteristic vibrational modes of alkali metal cation-exchanged ETS-10 and also with the available experimental frequencies for CH4, N2, CO2, and H2O interactions with alkali metal cations in the 12-membered channel of ETS-10.

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“…To clarify the nature of the molecular-level interactions taking place in the synthesis solution, we carried out simulations using a multiscale modelling approach. In brief, quantum-mechanical calculations [22] were used to obtain parameters for classical atomistic models of silicates in solution [23], which were then combined with atomistic models of water [24] and amine surfactants [25]. Parameters of a coarse-grained model of the system, based on the MARTINI approach [26], were then calibrated so that micelle density profiles and other structural properties matched those of the atomistic simulations.…”

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confidence: 99%