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Ceperley, David M. Wagner, Marcus 2011-05-07T12:35:46Z 2011-05-07T12:35:46Z 10000-01-01 1994 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. Made available in DSpace on 2011-05-07T12:35:46Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9512584.pdf: 8511974 bytes, checksum: 9ae05c5e82ff6fafa38c87593d81eeaa (MD5) Previous issue date: 1994 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:43:04Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:18:48-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9512584 (UMI)AAI9512584 http://hdl.handle.net/2142/20316 eng Copyright 1994 Wagner, Marcus Physics, Condensed Matter Engineering, Materials Science Computer Science Path integral Monte Carlo simulations of solid H2 surfaces and thin 4He films on H2 substrates Path integral Monte Carlo simulations of solid molecular hydrogen surfaces and thin helium-4 films on molecular hydrogen substrates text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.