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 Title: Path integral Monte Carlo simulations of solid molecular hydrogen surfaces and thin helium-4 films on molecular hydrogen substrates Alternative Title: Path integral Monte Carlo simulations of solid H2 surfaces and thin 4He films on H2 substrates Author(s): Wagner, Marcus Doctoral Committee Chair(s): Ceperley, David M. Department / Program: Physics Discipline: Physics Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Physics, Condensed Matter Engineering, Materials Science Computer Science Abstract: Based on Richard P. Feynman's formulation of quantum mechanics, Path Integral Monte Carlo is a computational ab-initio method to calculate finite temperature equilibrium properties of quantum many-body systems. As input, only fundamental physical constants and pair-potentials are required. We carry out the first ab-initio particle simulations of three related physical systems. First, the bare H$\sb2$ substrate is simulated between 0.5 and 1.3K, because a liquid H$\sb2$ film is a candidate for a new superfluid. We find evidence of quantum exchange in surface terraces for up to 1K. Second, the melting of the H$\sb2$ surface between 3 and 15K is examined since this is the cleanest example of quantum surface melting. Third, atomically thin superfluid $\sp4$He films on H$\sb2$ surfaces are simulated, calculating binding energies per $\sp4$He atom and third sound, an important experimental probe for superfuid $\sp4$He films. For all systems we compute density profiles perpendicular and parallel to the surface and compare to experiment. We treat both H$\sb2$ molecules and $\sp4$He atoms on the same footing, as spherical particles. For simulations of bulk/vapor interfaces and surface adsorption, a realistic representation of the macroscopic surface is crucial. Therefore, we introduce an external potential to account for arbitrarily layered substrates and long-range corrections. Two algorithms for parallel computers with independent processors are introduced, one to manage concurrent simulations of entire phase-diagrams, and one to improve input/output speed for files shared by all processors. Issue Date: 1994 Type: Text Language: English URI: http://hdl.handle.net/2142/20316 Rights Information: Copyright 1994 Wagner, Marcus Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9512584 OCLC Identifier: (UMI)AAI9512584
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