p of silicic acid in presence of La <sup>3+</sup> using single sweep method coupled to DFT-based molecular dynamics

Abstract : In this paper we show how it is possible to obtain the pKa of a weak acid (H4SiO4) bound to a highly charged cation (La3+) from DFT-based molecular dynamics in a relatively simple, tunable and efficient way. This was done by combining molecular dynamics in bulk water of a La3+/H4SiO4 complex with the single sweep method. At this end, we have first performed molecular dynamics runs where a high temperature is assigned on the defined reaction coordinate, here the O-H distance. Then we performed constrained molecular dynamics simulations for selected values of the reaction coordinate along the observed dissociation pathway. The average forces obtained from those constrained simulations are then interpolated to get a final free energy curve. The pKa is obtained by integrating the resulting free energy curve and that of a reference calculation, the autodissociation of water. We then show that the pKa of the silanol groups away from La3+ is close to the first pK a of silisic acid, while the pKa of the silanol groups interacting with La3+ is about three units lower.
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Submitted on : Friday, April 26, 2019 - 5:08:39 PM
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Riccardo Spezia, Rodolphe Vuilleumier. p of silicic acid in presence of La <sup>3+</sup> using single sweep method coupled to DFT-based molecular dynamics. Molecular Physics, 2013, 111 (22-23), pp.3478-3485. ⟨10.1080/00268976.2013.848300⟩. ⟨hal-02112573⟩

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