eprintid: 25747
rev_number: 8
userid: 3760
dir: disk0/00/02/57/47
datestamp: 2015-09-14 14:31:18
lastmod: 2016-11-15 14:29:36
status_changed: 2015-09-14 14:31:18
type: thesis_degree
metadata_visibility: show
contact_email: mjd87@pitt.edu
item_issues_count: 0
eprint_status: archive
creators_name: Deible, Michael
creators_email: mjd87@pitt.edu
creators_id: MJD87
title: Theory and Applications of Quantum Monte Carlo
ispublished: unpub
divisions: sch_as_chemistry
full_text_status: public
keywords: Quantum Monte Carlo
abstract: With the development of peta-scale computers and exa-scale only a few years away, the quantum Monte Carlo (QMC) method, with favorable scaling and inherent parrallelizability, is poised to increase its impact on the electronic structure community.  The most widely used variation of QMC is the diffusion Monte Carlo (DMC) method.  The accuracy of the DMC method is only limited by the trial wave function that it employs.  The effect of the trial wave function is studied here by initially developing correlation-consistent Gaussian basis sets for use in DMC calculations.  These basis sets give a low variance in variance Monte Carlo calculations and improved convergence in DMC.  The orbital type used in the trial wave function is then investigated, and it is shown that Brueckner orbitals result in a DMC energy comparable to a DMC energy with orbitals from density functional theory and significantly lower than orbitals from Hartree-Fock theory.  Three large weakly interacting systems are then studied; a water-16 isomer, a methane clathrate, and a carbon dioxide clathrate.  The DMC method is seen to be in good agreement with MP2 calculations and provides reliable benchmarks.  Several strongly correlated systems are then studied. An H4 model system that allows for a fine tuning of the multi-configurational character of the wave function shows when the accuracy of the DMC method with a single Slater-determinant trial function begins to deviate from multi-reference benchmarks.   The weakly interacting face-to-face ethylene dimer is studied with and without a rotation around the π bond, which is used to increase the multi-configurational nature of the wave function.  This test shows that the effect of a multi-configurational wave function in weakly interacting systems causes DMC with a single Slater-determinant to be unable to achieve sub-chemical accuracy.  The beryllium dimer is studied, and it is shown that a very large determinant expansion is required for DMC to predict a binding energy that is in close agreement with experiment.  Finally, water interacting with increasingly large acenes is studied, as is the benzene and anthracene dimer.  Deviations from benchmarks are discussed.
date: 2015-09-14
date_type: published
pages: 171
institution: University of Pittsburgh
refereed: TRUE
etdcommittee_type: committee_member
etdcommittee_type: committee_member
etdcommittee_type: committee_member
etdcommittee_type: committee_chair
etdcommittee_name: Lambrect, Danriel
etdcommittee_name: Star, Alexander
etdcommittee_name: Keith, John
etdcommittee_name: Jordan, Kenneth
etdcommittee_email: qclab@pitt.edu
etdcommittee_email: astar@pitt.edu
etdcommittee_email: jakeith@pitt.edu
etdcommittee_email: jordan@pitt.edu
etdcommittee_id: QCLAB
etdcommittee_id: ASTAR
etdcommittee_id: JAKEITH
etdcommittee_id: JORDAN
etd_defense_date: 2015-05-29
etd_approval_date: 2015-09-14
etd_submission_date: 2015-07-22
etd_release_date: 2015-09-14
etd_access_restriction: immediate
etd_patent_pending: FALSE
thesis_type: dissertation
degree: PhD
citation:   Deible, Michael  (2015) Theory and Applications of Quantum Monte Carlo.  Doctoral Dissertation, University of Pittsburgh.    (Unpublished)  
document_url: http://d-scholarship-dev.library.pitt.edu/25747/1/Thesis_MDeible.pdf