Molecular packing and chemical association in liquid water simulated using ab initio hybrid Monte Carlo and different exchange-correlation functionals - Physics > Chemical PhysicsReport as inadecuate




Molecular packing and chemical association in liquid water simulated using ab initio hybrid Monte Carlo and different exchange-correlation functionals - Physics > Chemical Physics - Download this document for free, or read online. Document in PDF available to download.

Abstract: In the free energy of hydration of a solute, the chemical contribution isgiven by the free energy required to expel water molecules from thecoordination sphere and the packing contribution is given by the free energyrequired to create the solute-free coordination sphere the observation volumein bulk water. With the SPC-E water model as a reference, we examine thechemical and packing contributions in the free energy of water simulated usingdifferent electron density functionals. The density is fixed at a valuecorresponding to that for SPC-E water at a pressure of 1 bar. The chemicalcontribution shows that water simulated at 300 K with BLYP is somewhat moretightly bound than water simulated at 300 K with the revPBE functional or at350 K with the BLYP and BLYP-D functionals. The packing contribution forvarious radii of the observation volume is studied. In the size range where thedistribution of water molecules in the observation volume is expected to beGaussian, the packing contribution is expected to scale with the volume of theobservation sphere. Water simulated at 300 K with the revPBE and at 350 K withBLYP-D or BLYP conforms to this expectation, but the results suggest an earlieronset of system size effects in the BLYP 350 K and revPBE 300 K systems thanthat observed for either BLYP-D 350 K or SPC-E. The implication of thisobservation for constant pressure simulations is indicated. For water simulatedat 300 K with BLYP, in the size range where Gaussian distribution of occupationis expected, we instead find non-Gaussian behavior, and the packingcontribution scales with surface area of the observation volume, suggesting thepresence of heterogeneities in the system.



Author: Valery Weber, Safir Merchant, Purushottam D. Dixit, D. Asthagiri

Source: https://arxiv.org/







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