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K+-hydration in a low-energy two-dimensional wetting layer on the basal surface of muscovite
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10.1063/1.4818587
/content/aip/journal/jcp/139/7/10.1063/1.4818587
http://aip.metastore.ingenta.com/content/aip/journal/jcp/139/7/10.1063/1.4818587

Figures

Image of FIG. 1.
FIG. 1.

Side view of a periodic model, “thick” muscovite slab, with spheres representing K, Si Al, O, and H atoms colored green, cyan, yellow, red, and white. On each surface, the area concentration of K-ions is half that in the interior. In this simplified example, as in Ref. , the Al atoms of the TOT layers and the K ions are highly ordered. They would not be in natural muscovite.

Image of FIG. 2.
FIG. 2.

Top views of two model periodic muscovite slabs, with spheres representing K, Si Al, O, and H atoms colored green, cyan, yellow, red, and white. Black rectangles delimit the surface unit cells. Panel (a) shows eight unit cells of an atomic arrangement like that used in Ref. , with surface Al atoms and K ions lying highly ordered in straight lines. Panel (b) shows four unit cells of an alternative periodic arrangement in which the surface Al and K are ordered in a zigzag pattern. In both models, following Loewenstein's rule (see Ref. ), no pair of Al atoms shares an O atom. Also, maximizing binding, each K has two Al neighbors.

Image of FIG. 3.
FIG. 3.

(a) Top and (b) side view of the non-hydrating water layer on muscovite of Ref. , optimized using the SeqQuest code. The O atoms of the adsorbed water molecules are colored blue. Otherwise, spheres representing K, Si Al, O, and H atoms are green, cyan, yellow, red, and white. Eight unit cells are shown, as in Fig. 2(a) .

Image of FIG. 4.
FIG. 4.

(a) Top and (b) side views of a hydrating water layer on a muscovite surface whose Al atoms are ordered in a zigzag pattern, and (c) top and (d) side views of a hydrating water layer on a surface whose Al atoms are ordered in straight lines. The O atoms of the adsorbed water molecules are colored blue. Otherwise, spheres representing K, Si Al, O, and H atoms are green, cyan, yellow, red, and white. In each case, four surface unit cells are shown.

Image of FIG. 5.
FIG. 5.

Illustrations of 0.75 ML wetting layers wherein water molecules hydrate each K. Panels (a) a top and (b) a side view of such a wetting layer on a muscovite surface whose Al atoms are ordered in a zigzag pattern; panels (c) a top and (d) a side view of such a wetting layer on a muscovite surface whose Al atoms are ordered linearly. The O atoms of the adsorbed water molecules are colored blue. Otherwise, spheres representing K, Si Al, O, and H atoms are green, cyan, yellow, red, and white. The illustrations show four surface unit cells. The O atoms labeled “d” in panels (a) and (b) have an energetically costly dangling H-bond. In panel (d), the H atom below the O atom labeled “d” is displaced to the left, signaling formation of a weak H-bond (O–O distance = 3.0 Å) between the atoms labeled “d” and “a” in panel (c).

Image of FIG. 6.
FIG. 6.

Top view of the “chicken wire” K-hydrating water layer on a muscovite surface whose Al atoms are ordered in a zigzag configuration. The O atoms of the adsorbed water molecules are colored blue. Otherwise, spheres representing K, Si Al, O, and H atoms are green, cyan, yellow, red, and white. The surface unit cell is delimited by the white rectangle. The “chicken wire” coordination is highlighted by yellow hexagons. In words, note that the K ions labeled 1–5 lie at the vertices of hexagons whose other vertices are O atoms or another K ion. Six water molecules surround the ion labeled 6, but because of topological constraints on the H-bonding network, their dipole moments are oriented so that despite their proximity to the ion, they add little to the electrostatic attractive energy.

Image of FIG. 7.
FIG. 7.

(a) Top and (b) side view of a 10 water-molecule per surface unit cell, K-hydrating water layer on a muscovite surface whose Al atoms are ordered in a zigzag configuration. The O atoms of the adsorbed water molecules are colored blue. Otherwise, spheres representing K, Si Al, O, and H atoms are green, cyan, yellow, red, and white. Four unit cells are shown. The additional water molecule per cell, comparing panel (b) of this figure to Fig. 4(b) , results in a wetting layer that is more diffuse along the surface normal. But, it has not optimized to a structure with low-lying water molecules.

Tables

Generic image for table
Table I.

For three combinations of density functional and approximate e-core interaction, wetting-layer lattice energies, ΔE (in meV/HO), relative to the value computed for ice Ih, and wetting-induced work function changes, ΔΦ (in eV). The smaller the value of ΔE, the better bound the wetting arrangement. The reference ice Ih lattice energies (in meV/HO) are PBE,PAW = −640, BLYP,PAW = −524, and BLYP,PP = −585. The first column gives a brief description of the structure and points to a figure wherein it is illustrated. The abbreviation, “n.c.” means not computed. The designation straight or zigzag refers to the arrangement of surface Al atoms, as in shown in Fig. 2 . “Hydr.” tells whether the surface K atoms are or are not hydrated by water molecules. L denotes the number of silica-alumina-silica layers in the corresponding muscovite slab. For details of the row labeled “Meleshyn, Fig. S2,” see the supplementary material.

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/content/aip/journal/jcp/139/7/10.1063/1.4818587
2013-08-20
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: K+-hydration in a low-energy two-dimensional wetting layer on the basal surface of muscovite
http://aip.metastore.ingenta.com/content/aip/journal/jcp/139/7/10.1063/1.4818587
10.1063/1.4818587
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