The quantum chemical physics of few-particle atoms and molecules

Baskerville, Adam (2018) The quantum chemical physics of few-particle atoms and molecules. Doctoral thesis (PhD), University of Sussex.

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The many-electron Schrödinger equation for atoms and molecules still remains
analytically insoluble after over 90 years of investigation. This has not deterred
scientists from developing a large variety of elegant techniques and approximations to
workaround this issue and make many-particle quantum calculations computationally
tractable. This thesis presents an all-particle treatment of three-particle systems
which represent the simplest, most complex, many-particle systems including electron
correlation and nuclear motion effects; meaning they provide a close-up view of
fundamental particle interaction. Fully-Correlated (FC) energies and wavefunctions
are calculated to high accuracy (mJ mol−1 or better for energies); and the central
theme of this work is to use the wavefunctions to study fundamental quantum
chemical physics.

Nuclear motion has not received the same attention as electronic structure theory
and this complicated coupling of electron and nuclear motions is studied in this
work with the use of intracule and centre of mass particle densities where it is found
nuclear motion exhibits strong correlation.

A highly accurate Hartree-Fock implementation is presented which uses a Laguerre
polynomial basis set. This method is used to accurately calculate electron correlation
energies using the Löwdin definition and Coulomb holes by comparing with our FC
data. Additionally the critical nuclear charge to bind two electrons within the HF
methodology is calculated.

A modification to Pekeris’ series solution method is implemented to accurately
model excited states of three-particle systems, and adapted to include the effects
of nuclear motion along with three Non-Linear variational Parameters (NLPs) to
aid convergence. This implementation is shown to produce high accuracy results for
singlet and triplet atomic excited S states and the critical nuclear charge to bind
two electrons in both spin states is investigated.

Geometrical properties of three-particle systems are studied using a variety
of particle densities and by determining the bound state stability at the lowest
continuum threshold as a function of mass. This enables us to better ascertain what
is meant when we define a system as an atom or a molecule.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Chemistry
Depositing User: Library Cataloguing
Date Deposited: 13 Jul 2018 13:24
Last Modified: 13 Jul 2018 13:24

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