arXiv subjects

Don D. Frantz

Publications and source records attributed to Don D. Frantz.

3 recordsLinked to original sources

arXiv1997

A computational study of 13-atom Ne-Ar cluster heat capacities

Heat capacity curves as functions of temperature were calculated using Monte Carlo methods for the series of Ne_(13-n)Ar_n clusters (0 <= n <= 13). The clusters were modeled classically using pairwise additive Lennard-Jones potentials. The J-walking (or jump-walking) method was used to overcome systematic errors due to quasiergodicity. Substantial discrepancies between the J-walking results and those obtained using standard Metropolis methods were found. Results obtained using the atom-exchange method, another Monte Carlo variant for multi-component systems, also did not compare well with the J-walker results. Quench studies were done to investigate the clusters' potential energy surfaces. Only those Ne-Ar clusters consisting predominately of either one or the other component had lowest energy isomers having the icosahedral-like symmetry typical of homogeneous 13-atom rare gas clusters; non-icosahedral structures dominated the lowest-energy isomers for the other clusters. This resulted in heat capacity curves that were very much different than that of their homogeneous counterpart. Evidence for coexistence behavior different than that seen in homogenous clusters is also presented.

physics.chem-ph↗

arXiv1996

A Computational Study of Thirteen-atom Ar-Kr Cluster Heat Capacities

Heat capacity curves as functions of temperature were calculated using Monte Carlo methods for the series of Ar_{13-n}Kr_n clusters (0 <= n <= 13). The clusters were modeled classically using pairwise additive Lennard-Jones potentials. J-walking (or jump-walking) was used to overcome convergence difficulties due to quasiergodicity present in the solid-liquid transition regions, as well as in the very low temperature regions where heat capacity anomalies arising from permutational isomers were observed. Substantial discrepancies between the J-walking results and the results obtained using standard Metropolis Monte Carlo methods were found. Results obtained using the atom-exchange method, another Monte Carlo variant designed for multi-component systems, were mostly similar to the J-walker results. Quench studies were also done to investigate the clusters' potential energy surfaces; in each case, the lowest energy isomer had an icosahedral-like symmetry typical of homogeneous thirteen-atom rare gas clusters, with an Ar atom being the central atom.

chem-ph↗

arXiv1994

Magic Numbers for Classical Lennard-Jones Cluster Heat Capacities

Heat capacity curves as functions of temperature for classical atomic clusters bound by pairwise Lennard-Jones potentials were calculated for aggregate sizes from 4 to 24 using Monte Carlo methods. J-walking (or jump-walking) was used to overcome convergence difficulties due to quasi-ergodicity in the solid-liquid transition region. The heat capacity curves were found to differ markedly and nonmonotonically as functions of cluster size. Curves for N = 4, 5 and 8 consisted of a smooth, featureless, monotonic increase throughout the transition region, while curves for N = 7 and 15-17 showed a distinct shoulder in this region; the remaining clusters had distinguishable transition heat capacity peaks. The size and location of these peaks exhibited "magic number" behavior, with the most pronounced peaks occurring for magic number sizes of N = 13, 19 and 23. A comparison of the heat capacities with other cluster properties in the solid-liquid transition region that have been reported in the literature indicates partial support for the view that, for some clusters, the solid-liquid transition region is a coexistence region demarcated by relatively sharp, but separate, melting and freezing temperatures; some discrepancies, however, remain unresolved.

chem-ph↗