The cover picture shows the computed valence electronic structure of the (100) plane of face-centered-cubic metallic lithium in terms of the electron localization function (ELF). Electron localization increases from blue to green to yellow to orange. The geometries of some selected Li clusters are also depicted; counterclockwise from the top these are Li₆ (D_3h), Li₆ (D_4h), Li₈ (C_s), and Li₈ (T_d). The evolution of the electronic structure and multicenter bonding of elemental lithium ranging from only a few atoms all the way to the bulk metal and corresponding surfaces is analyzed in detail by R. Rousseau and D. Marx on p. 2982 ff.

Clusters of lithium atoms ranging in size from Li₄ to Li₄₀ and bulk metallic solids, including surfaces, are investigated through first principles electronic structure calculations, which are based upon density functional theory and the electron localization function (ELF). It is found that large lithium pπ-type contributions in the electronic wavefunction cause the electrons to localize in interstitial regions, which leads to multicenter bonding for both the clusters and the solids, including their surfaces. For the smaller clusters these stabilizing pπ interactions also lead to short Li−Li interatomic distances, which in conjunction with the longer bonds induces “distance alternation” in the range from 2.45 Å to 3.15 Å. This consequence of the additional pπ interactions is absent in simple solids due to symmetry. The electronic structure of the clusters is topologically insensitive to deformations that do not affect their general shape, but changes significantly upon isomerization. The ramifications upon dynamic properties is that the clusters are quasi-rigid at low temperatures and retain their shape though the distance alternation pattern is suppressed. The picture which emerges for bonding in the bulk solid is that the metallic state arises from the presence of a large number of partially occupied multicenter bonds. For nanoscale clusters only the surface of these clusters exhibits strong localization, whereas their interiors display localization properties similar to the bulk metallic solid. On the other hand, localized states similar to those of the clusters (“dangling bonds”) are found on the (001) surface of body-centered cubic (bcc) and face-centered cubic (fcc) lithium solids.

The solvation and reaction of ethylene radical cation in aqueous solution has been studied with Car–Parrinello molecular dynamics simulations. All ab initio simulations were performed using a system of 56 water and one ethylene molecule. Using a favorable symmetrically solvated radical cation as the starting point of the simulation a fast addition of water (within 90 fs) to the radical cation is observed. The primary addition product is rapidly deprotonated (within 100 fs) to yield the ethanol-2-yl radical. A second simulation was initiated through vertical ionization of neutral hydrated ethylene, representing a significantly less favorable situation for the addition process. No addition of water can be observed in this second simulation over a time span of 1.7 ps. Taken together the two simulations are indicative of a rearrangement of the solvent shell which represents the major part of the overall reaction barrier. Under these circumstances, the reaction rate of an otherwise spontaneous reaction is limited by the intrinsic solvent relaxation time. This interpretation of the reactivity of hydrated radical cations reconciles previously conflicting experimental condensed phase and theoretical gas phase studies.