Physical properties of small water clusters in low and moderate electric fields

Likely candidates for the lowest minima of water clusters (H(2)O)(N) for N ≤ 20 interacting with a uniform electric field strength in the range E ≤ 0.6 V/? have been identified using basin-hopping global optimization. Two water-water model potentials were considered, namely TIP4P and the polarizable Dang-Chang potential. The two models produce some consistent results but also exhibit significant differences. The cluster internal energy and dipole moment indicate two varieties of topological transition in the structure of the global minimum as the field strength is increased. The first takes place at low field strengths (0.1 V/? 10) usually forming helical structures.     

A survey of the potential energy surface for the (benzene)13 cluster

We report on a survey of the potential energy surface for the 13-molecule benzene cluster, (C(6)H(6))(13), bound by an atom-atom intermolecular potential developed from first principles. The potential, which has an anisotropic repulsion term, is found to support distinct pairs of structures of C(3), C(i), and S(6) symmetry as low-lying minima, including a C(3) global minimum. The organisation of the low-lying region of the potential energy surface suggests that one of the S(6) structures is likely to act as a kinetic trap, hindering efficient relaxation to the global minimum, in agreement with the hypothesis that two isomers coexist in this system, suggested by spectroscopic experiments.     

Indépendance Linéaire sur Q de logarithmes P-adiques de nombres algébriques et rang P-adique du groupe des unités d'un corps de nombres

Following Ax's method a lower bound for the p-adic rank of the group of units in the general case of a Galois number field over the rationals is given. In some nontrivial special cases the result gives Leopoldt's conjecture. The same method is also applied to the case of p-units.     

The Haemers partial geometry and the Steiner system S(5, 8, 24)

Haemers has constructed a partial geometry with parameters s = 4, t = 17, and α = 2, using properties of the Hoffman-Singleton graph. We describe this geometry in terms of the Steiner system S(5, 8, 24).     

Theory of C2Hx species on Pt{110}(1x2): structure, stability, and thermal chemistry

The adsorption of C2Hx (x=0-5) hydrocarbon fragments on Pt{110}(1x2) has been investigated using calculations based on density functional theory. For all the species, the most stable adsorption site identified completes the tetravalency of each carbon atom and involves the maximum possible number of Pt atoms subject to that constraint. The most stable adsorption sites for C2Hx fragments of stoichiometry x=2-5 involve ridge atoms, while trough sites stabilize C2H and C2 species. The relative stability of the fragments involved is compared via a free energy picture.     

Tilted and helical columnar phases for an axially symmetric discoidal system

We report novel phase behavior for a system of disclike ellipsoidal particles interacting via a pair potential. We identify a structural phase transition between two hexagonal columnar phases, both tilted, induced by spatial ordering of the tilt about the columnar axis and positional correlations between neighboring columns upon cooling. The local minima of the potential energy surface support irregular helical arrangements of the discoids about the columnar axis for the high-temperature hexagonal columnar phase, and a tilted arrangement for both phases. Our study demonstrates that dispersion-repulsion forces corresponding to oblate ellipsoids are sufficient to produce a columnar phase that is tilted and helical.