5 research outputs found
An ab initio path integral Monte Carlo simulation method for molecules and clusters: application to Li_4 and Li_5^+
A novel method for simulating the statistical mechanics of molecular systems
in which both nuclear and electronic degrees of freedom are treated quantum
mechanically is presented. The scheme combines a path integral description of
the nuclear variables with a first-principles adiabatic description of the
electronic structure. The electronic problem is solved for the ground state
within a density functional approach, with the electronic orbitals expanded in
a localized (Gaussian) basis set. The discretized path integral is computed by
a Metropolis Monte Carlo sampling technique on the normal modes of the
isomorphic ring-polymer. An effective short-time action correct to order
is used. The validity and performance of the method are tested in two
small Lithium clusters, namely Li and Li. Structural and electronic
properties computed within this fully quantum-mechanical scheme are presented
and compared to those obtained within the classical nuclei approximation.
Quantum delocalization effects are significant but tunneling turns out to be
irrelevant at low temperatures.Comment: 11 text pages, 7 figures, to be published in J. Chem. Phy
Hybrid Quantum and Classical Mechanical Monte Carlo Simulations of the Interaction of Hydrogen Chloride with Solid Water Clusters
Monte Carlo simulations using a hybrid quantum and classical mechanical
potential were performed for crystal and amorphous-like HCl-water(n) clusters
The subsystem composed by HCl and one water molecule was treated within Density
Functional Theory, and a classical force field was used for the rest of the
system. Simulations performed at 200 K suggest that the energetic feasibility
of HCl dissociation strongly depends on its initial placement within the
cluster. An important degree of ionization occurs only if HCl is incorporated
into the surface. We observe that local melting does not play a crucial role in
the ionization process.Comment: 14 Latex pages with 4 postscript figures, to appear in Chem. Phys.
Let
Electronic Fine Structure in the Electron-Hole Plasma in SrB6
Electron-hole mixing-induced fine structure in alkaline earth hexaborides
leads to lower energy (temperature) scales, and thus stronger tendency toward
an excitonic instability, than in their doped counterparts (viz.
Ca(1-x)La(x)B(6), x=0.005), which are high Curie temperature, small moment
ferromagnets. Comparison of Fermi surfaces and spectral distributions with de
Haas - van Alphen (dHvA), optical, transport, and tunneling data indicates that
SrB6 remains a fermionic semimetal down to (at least) 5 K, rather than forming
an excitonic condensate. For the doped system the Curie temperature is higher
than the degeneracy temperature.Comment: Four two-column pages, three postscript figures. Phys. Rev. Lett.
(April 2000, in press