Details

Autor(en) / Beteiligte

• Bennett, Michael Chandler

Titel

Electronic Structure of Heavy Element Systems and Many-Body Constructions of High-Accuracy Effective Core Potentials

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2019

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• The electronic structure of atomic, molecular, and solid state systems provides key insights into their rich variety of properties. Fundamental to understanding the electronic structure of these systems are the solutions to the time-independent Schrödinger equation under the Born-Oppenheimer approximation. However, due to the inter-particle interactions of the electrons, an exact polynomial scaling algorithm for solving the equation does not exist. As a result, a vigorous pursuit of simplifications and approximations, that keep the predictive power of the equation intact, has been underway since the birth of quantum theory in the 1920s. This pursuit, in tandem with exponentially increasing computational power, has lead to the development of a number of high-accuracy methodologies. Of particular prominence, is the diffusion Monte Carlo method which benefits from low-order polynomial-scaling, applicability over a wide range of system sizes - up to hundreds of electrons, and a small number of fully specified errors.We have applied diffusion Monte Carlo to various heavy transition metal systems. These systems are attractive from a theoretical point of view due to the presence of localized d-electrons which consequently results in significant amounts of correlation and therefore are challenging for electronic structure methods in general.We study trends in the errors of diffusion Monte Carlo under the fixed-node approximation in order to better understand the accuracy limits of the method for these systems in various environments. Additionally, we investigate a specific error that is present within diffusion Monte Carlo studies of heavy elements due to the unavoidable introduction of pseudopotentials. From coupled-cluster calculations,we find that the errors of tabulated pseudopotentials within molecular settings can be significant relative to all-electron results for high-accuracy many-body techniques especially when the molecules are out of equilibrium configurations.We develop a strategy to generate pseudopotentials that incorporates near-exact correlated many-body spectra and properties and as a result lead to high accuracy over a test bed of molecules - both within and out of equilibrium.We use this strategy to develop pseudopotentials for 1st row elements, the entire set of 2nd row elements, and the full 3d transition metal series.