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Ceperley, David M. Draeger, Erik Walter 2012-05-31T19:31:59Z 2012-05-31T19:31:59Z 10000-01-01 2001 Below Tλ = 2.17 K, bulk 4He is a superfluid and has a non-zero Bose-Einstein condensate fraction. This work will focus primarily on how phenomena such as superfluidity, Bose condensation and superfluid vortices are manifested in microscopic, inhomogeneous helium systems. Path Integral Monte Carlo is a powerful method for calculating the equilibrium properties of quantum systems at finite temperature. We have achieved linear scaling of computer time with number of particles through the use of neighbor lists, allowing us to simulate systems of several thousand atoms. We have derived a local superfluid estimator and used it to examine the microscopic superfluid response around a molecule rotating in a helium nanodroplet. We found that the first solvation layer is well-described by a two dimensional superfluid, with thermal excitations occuring at a lower temperature than in bulk helium. The effective moment of inertia of a linear impurity in a helium droplet is calculated, and compared with experimental scattering results. In addition, we calculated the vortex formation energy for both pure droplets and droplets doped with linear impurities, and found that the linear impurities had a negligible impact on the formation energy. A possible spectroscopic signature of vortices in doped helium droplets was suggested. After deriving a local estimator, we calculated the condensate fraction throughout the free helium surface of a semi-infinite slab. These results, along with densitydensity correlation functions, were used to characterize the surface excitations and calculate the extent to which ripplons are present. In addition, the ripplon dispersion relation was calculated using imaginary-time correlation functions, and found to be lll in good agreement with experimental results. Finally, we have calculated the Dey be-Waller factor in solid helium for a range of temperatures and densities, and compared the scaling behavior with the predictions of harmonic theory. The first non-Gaussian contribution to the density distribution was calculated. Submitted by William Weathers (weathrs2@illinois.edu) on 2012-05-31T19:31:59Z No. of bitstreams: 1 2001_draeger.pdf: 4121362 bytes, checksum: dbbcb42211d4bc671706642368c2a46d (MD5) Made available in DSpace on 2012-05-31T19:31:59Z (GMT). No. of bitstreams: 1 2001_draeger.pdf: 4121362 bytes, checksum: dbbcb42211d4bc671706642368c2a46d (MD5) Previous issue date: 2001 Restriction data tranferred 2014-07-01T11:33:27-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by William Weathers (weathrs2@illinois.edu) on 2012-05-31T19:31:59Z Item is restricted indefinitely. Thesis U of I Only http://hdl.handle.net/2142/31313 4552740 en ©2001 Draeger Quantum Crystals Monte Carlo Simulations Helium 4 Solid Helium Path Integral Monte Carlo Simulations of Helium: From Superfluid Droplets to Quantum Crystals Dissertation / Thesis text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.