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See detailOn the accuracy of density-functional theory exchange-correlation functionals for H bonds in small water clusters. II. the water hexamer and van der Waals interactions
Santra, B.; Michaelides, A.; Fuchs, M. et al

in Journal of Chemical Physics (2008), 129(19),

Second order Møller-Plesset perturbation theory at the complete basis set limit and diffusion quantum Monte Carlo are used to examine several low energy isomers of the water hexamer. Both approaches ... [more ▼]

Second order Møller-Plesset perturbation theory at the complete basis set limit and diffusion quantum Monte Carlo are used to examine several low energy isomers of the water hexamer. Both approaches predict the so-called prism to be the lowest energy isomer, followed by cage, book, and cyclic isomers. The energies of the four isomers are very similar, all being within 10-15 meV/ H2 O. These reference data are then used to evaluate the performance of several density-functional theory exchange-correlation (xc) functionals. A subset of the xc functionals tested for smaller water clusters [I. Santra, J. Chem. Phys. 127, 184104 (2007)] has been considered. While certain functionals do a reasonable job at predicting the absolute dissociation energies of the various isomers (coming within 10-20 meV/ H2 O), none predict the correct energetic ordering of the four isomers nor does any predict the correct low total energy isomer. All xc functionals tested either predict the book or cyclic isomers to have the largest dissociation energies. A many-body decomposition of the total interaction energies within the hexamers leads to the conclusion that the failure lies in the poor description of van der Waals (dispersion) forces in the xc functionals considered. It is shown that the addition of an empirical pairwise (attractive) C6 R-6 correction to certain functionals allows for an improved energetic ordering of the hexamers. The relevance of these results to density-functional simulations of liquid water is also briefly discussed. © 2008 American Institute of Physics. [less ▲]

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See detailDepletion induced isotropic-isotropic phase separation in suspensions of rod-like colloids
Jungblut, S.; Tuinier, R.; Binder, K. et al

in Journal of Chemical Physics (2007), 127(24),

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See detailClassification of hexagonal adlayer arrangements by means of collective geometrical properties
Tkatchenko, Alexandre UL; Batina, N.

in Journal of Chemical Physics (2006), 125(16),

Unequal-sphere packing model is applied for the simulation of large number of hexagonal adlayer structures with surface coverage between θ= 1 3 and θ=1 on the hexagonal substrate, with atomic radius of ... [more ▼]

Unequal-sphere packing model is applied for the simulation of large number of hexagonal adlayer structures with surface coverage between θ= 1 3 and θ=1 on the hexagonal substrate, with atomic radius of the adsorbate and substrate atoms as the only input. Each structure is characterized with respect to collective adlayer properties: the average adlayer height and the adlayer roughness. The distribution of hexagonal arrangements is presented in a special plot, which can be used for identification and characterization of hexagonal adlayers of different surface coverages and atomic registries. The most likely structures are related to the extreme values of our model parameters. The usefulness of this methodology is successfully demonstrated by comparison with some real adsorbate-substrate systems, i.e., halogens and rare gases adsorbed on (111) surface. Besides the agreement with experimental results, our model offers new insight into the formation of atomic adlayers and detailed analysis of the atomic registry. We believe that our approach will be of use for identification of probable structures among the large number of combinatorial possibilities in theoretical studies and for better interpretation of experimental results (i.e., scanning-tunneling microscopy images of atomic adlayers). © 2006 American Institute of Physics. [less ▲]

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See detailDetailed characterization of (3X3) iodine adlayer on Pt(111) by unequal-sphere packing model
Tkatchenko, Alexandre UL; Batina, Nikola

in JOURNAL OF CHEMICAL PHYSICS (2005), 122(9),

A simple unequal-sphere packing model is applied to study the iodine (3x3) adlayer on the Pt(111) surface. By using a newly introduced parameter, defined as the average adsorbate height, three ... [more ▼]

A simple unequal-sphere packing model is applied to study the iodine (3x3) adlayer on the Pt(111) surface. By using a newly introduced parameter, defined as the average adsorbate height, three characteristic adlattices, (3x3)-sym, (3x3)-asym, and (3x3)-lin, have been selected and characterized in great detail, including the exact adatom registry. The (3x3)-sym iodine adlattice, observed in many experimental studies appears to be, on average, the closest one to the substrate surface. A special contour plot of average adsorbate height vs X and Y positions of the (3x3) iodine unit cell indicates the existence of two local minima which are related to preferential formation of (3x3)-sym and (3x3)-asym iodine adlattices. Our model gives good agreement with experimental findings, and explains the mechanism of preferential appearance of (3x3)-sym and (3x3)-asym structures. (C) 2005 American Institute of Physics. [less ▲]

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See detailIsotropic-nematic interfacial tension of hard and soft rods: Application of advanced grand canonical biased-sampling techniques
Vink, R. L. C.; Wolfsheimer, S.; Schilling, Tanja UL

in Journal of Chemical Physics (2005), 123(7),

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See detailGeneration of frustrated liquid crystal phases by mixing an achiral n–smc mesogen with an antiferroelectric chiral smectic liquid crystal
Lagerwall, Jan UL; Giesselmann, Frank; Selbmann, Christine et al

in Journal of Chemical Physics (2005), 122(14), 144906

By mixing the achiral liquid crystal HOAB, exhibiting a nematic (N)-smectic-C (SmC) mesophase sequence, with the chiral antiferroelectric liquid crystal (AFLC) (S,S)-M7BBM7, forming the antiferroelectric ... [more ▼]

By mixing the achiral liquid crystal HOAB, exhibiting a nematic (N)-smectic-C (SmC) mesophase sequence, with the chiral antiferroelectric liquid crystal (AFLC) (S,S)-M7BBM7, forming the antiferroelectric SmCa phase, at least seven different mesophases have been induced which neither component forms on its own: a twist-grain-boundary (TGB) phase, two or three blue phases, the untilted SmA phase, as well as all three chiral smectic-C-type ``subphases,'' SmCalpha, SmCbeta, and SmCgamma. The nature of the induced phases and the transitions between them were determined by means of optical and electro-optical investigations, dielectric spectroscopy, and differential scanning calorimetry. The induced phases can to a large extent be understood as a result of frustration, TGB at the border between nematic and smectic, the subphases between syn and anticlinic tilted smectic organization. X ray scattering experiments reveal that the smectic layer spacing as well as the degree of smectic order is relatively constant in the whole mixture composition range in which AFLC behavior prevails, whereas both these parameters rapidly decrease as the amount of HOAB is increased to such an extent that no other smectic-C-type phase than SmC/SmC exists. By tailoring the composition we are able to produce liquid crystal mixtures exhibiting unusual phase sequences, e.g., with a direct isotropic-SmCa transition or a temperature range of the SmCbeta subphase of about 50 K. (C) 2005 American Institute of Physics. [less ▲]

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See detailGravity-induced liquid crystal phase transitions of colloidal platelets
van der Beek, D.; Schilling, Tanja UL; Lekkerkerker, H. N. W.

in Journal of Chemical Physics (2004), 121(11), 5423-5426

he influence of gravity on a suspension of sterically stabilized colloidal gibbsite platelets is studied. An initially isotropic-nematic biphasic sample of such a suspension develops a columnar phase on ... [more ▼]

he influence of gravity on a suspension of sterically stabilized colloidal gibbsite platelets is studied. An initially isotropic-nematic biphasic sample of such a suspension develops a columnar phase on the bottom on prolonged standing. This phenomenon is described using a simple osmotic compression model. We performed Monte Carlo simulations of cut spheres with aspect ratio L/D = 1/15 and took data from the literature to supply the equations of state required for the model. We find that the model describes the observed three-phase equilibrium quite well. [less ▲]

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See detailWetting in ternary mixtures - with and without amphiphiles
Schilling, Tanja UL; Gompper, G.

in Journal of Chemical Physics (2002), 117(15), 7284-7294

The interfacial wetting behavior of ternary fluid mixtures is investigated, both for systems where all components have isotropic interaction potentials, as well as for systems where one component is an ... [more ▼]

The interfacial wetting behavior of ternary fluid mixtures is investigated, both for systems where all components have isotropic interaction potentials, as well as for systems where one component is an amphiphile. The BEG model and the corresponding two-order-parameter Ginzburg–Landau model are employed for systems without amphiphiles. We calculate the global wetting phase diagram for nonamphiphilic mixtures. In the investigated range of interaction parameters, the wetting transitions are always continuous at three-phase coexistence. The critical behavior is found to be universal in some, nonuniversal in other parts of the phase diagram. For systems with amphiphiles, two additional interaction terms are taken into account. The first models the aggregation of amphiphilic molecules at the air–water interface, the second the formation of amphiphilic bilayers in water. We find that the first term leads to a reduction of the tension of the air–water interface, and favors wetting by the water-rich phase, while the second—bilayer—term leads to a reduction of the tension of the interface between the water-rich and amphiphile-rich phases. [less ▲]

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