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Unwanted Electrons: From New Structure Discovery to Method Realm Extension
Başlık:
Unwanted Electrons: From New Structure Discovery to Method Realm Extension
Yazar:
Bazante, Alexandre P., author.
ISBN:
9780438120310
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (143 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-11(E), Section: B.
Özet:
The "gold-standard" of quantum chemistry---namely CCSD(T)---has had many proven successes at quantitatively describing the wavefunction of small to medium sized molecules. But, there are limitations to the method's applicability. CCSD(T) formally scales as O(N7) where N is a measure of the system size, which is preemptive for any kind of calculation on large molecular systems. Furthermore, as with the entire family of coupled-cluster methods, CCSD(T) is predominantly used within the Born-Oppenheimer approximation framework; as such, coupled-cluster methods are only suitable for non-relativistic bound states with minimal coupling between nuclear and electronic motion. This work focuses on the latter hurdle, and investigates extensions to the coupled-cluster framework allowing for an appropriate description of metastable states and other unstable species.
There are many such states; resonant anions are prone to auto-dissociation or auto-ionization and core-hole cations can lead to variational collapse or auto-dissociation. They are metastable, or unstable in some respect. These states lie in the continuum and require a particular class of wavefunction to be described properly. Barring modifications, standard wavefunction methods like coupled-cluster are inadequate to describe such a class of wavefunctions. Reconciliation between the continuum nature of these states of interest and the constraints imposed on the wavefunction can be done a multitude of ways.
Common approaches so far have aimed to provide an accurate treatment of the complex part of the wavefunction directly, through extension of the electron correlation equations. In this study, however, we show that---given proper care---the necessary information is already present in standard wavefunction theory to qualitatively describe electronic states with a continuum nature. The computation of properties for these states is made possible by special considerations atop the standard quantum chemistry procedures.
The versatility of the coupled-cluster framework offers many different methods tailored towards different purposes. The electron attachment flavors of EOM are particularly suited to treat metastable anions, whether shape- or Feshbach resonances, whereas the ionization potential variants of EOM are apt to describe core-ionized and core-excited states, for example. In conjunction with analytical continuation methods, the EOM family of methods is used to discover new structures for resonant anions such as benzene, compute resonance energies and lifetimes for several archetypes of shape resonances, as well as provide novel potential curves for a variety of core-hole states in diatomic species and generate photoelectron and core absorption spectra related to ultrafast spectroscopy techniques.
Notlar:
School code: 0070
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(696573.1) | 696573-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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