First-principles Density Functional Theory Method Research Articles

Hydrogen in jellium: First-principles pair interactions

Ground-state pair potentials between protons immersed in jellium (interacting electrons plus a compensating background) and at densities corresponding to the range $1<{r}_{s}<4$ are calculated using first-principles density functional theory methods. While the results obtained for immersing a single H atom in an electron gas agree with previous calculations, it is discovered that molecular-type short-range binding becomes unstable at surprisingly low density (at about ${r}_{s}=3.2),$ and that at even lower density there is a bistability between a weakly bound molecule and an unpaired state. This behavior is a result of the possible pairing of hydrogen and itinerant jellium electrons with little electrostatic penalty, a consequence of the positive background filling the entire volume V. Another important finding is a density range $(1.5<{r}_{s}<2)$ where the pair potentials are insufficiently strong to bind the protons, suggesting the possibility of inducing hydrogen into a state of low-temperature quantum fluid at a critical density.

Fullerene growth and the role of nonclassical isomers

We report results of a survey of the energetics and stability of classical and 1-heptagon nonclassical fullerene clusters in the range of sizes ${\mathrm{C}}_{30}$ to ${\mathrm{C}}_{70},$ using both total-energy tight-binding and first-principles density functional theory methods. We conclude from this survey that 1-heptagon isomers of high stability exist at every nuclearity, and that these nonclassical isomers play an important part in the growth mechanism of fullerenes.