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Quantum-classical calculations of X-ray photoelectron spectra of polymers-Polymethyl methacrylate revisited
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0001-8571-1458
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0002-9123-8174
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2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 12, article id 124902Article in journal (Refereed) Published
Abstract [en]

In this work, we apply quantum mechanics/molecular mechanics (QM/MM) approach to predict core-electron binding energies and chemical shifts of polymers, obtainable via X-ray photoelectron spectroscopy (XPS), using polymethyl methacrylate as a demonstration example. The results indicate that standard parametrizations of the quantum part (basis sets, level of correlation) and the molecular mechanics parts (decomposed charges, polarizabilities, and capping technique) are sufficient for the QM/MM model to be predictive for XPS of polymers. It is found that the polymer environment produces contributions to the XPS binding energies that are close to monotonous with the number of monomer units, totally amounting to approximately an eV decrease in binding energies. In most of the cases, the order of the shifts is maintained, and even the relative size of the differential shifts is largely preserved. The coupling of the internal core-hole relaxation to the polymer environment is found to be weak in each case, amounting only to one or two tenths of an eV. The main polymeric effect is actually well estimated already at the frozen orbital level of theory, which in turn implies a substantial computational simplification. These conclusions are best represented by the cases where the ionized monomer and its immediate surrounding are treated quantum mechanically. If the QM region includes only a single monomer, a couple of anomalies are spotted, which are referred to the QM/MM interface itself and to the neglect of a possible charge transfer.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017. Vol. 146, no 12, article id 124902
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-205452DOI: 10.1063/1.4978941ISI: 000397929300066PubMedID: 28388163Scopus ID: 2-s2.0-85016505625OAI: oai:DiVA.org:kth-205452DiVA, id: diva2:1097294
Note

QC 20170522

Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2018-04-27Bibliographically approved
In thesis
1. Quantum and quantum-classical calculations of core-ionized molecules in varied environments
Open this publication in new window or tab >>Quantum and quantum-classical calculations of core-ionized molecules in varied environments
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Computational quantum chemistry methods have been applied in two particular cases: to provide insight to photoionization induced fragmentation of HgBr2 and HgCl2 molecules, and to study core-electron binding energies and chemical shifts of molecules in liquid, surface adsorbed and polymeric environments in the framework of quantum mechanics/molecular mechanics (QM/MM). In the photodissociation studies the computational work is based on the relativistic Dirac equation as the systems present strong spin-orbit interaction affecting the fragmentation processes. In the QM/MM studies of ethanol-water mixtures and molecules physisorbed on silver surfaces the structures are provided by classical molecular dynamics simulations to analyze the distribution of the binding energies of core-orbitals and effects of their surroundings. In the case of polymethyl methacrylate polymer the impact of a QM-MM boundary and a polymeric environment are studied. The theoretical backgrounds of the computational methods applied and the obtained results are discussed.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 77
Series
TRITA-CBH-FOU ; 2018:20
Keywords
Electron spectroscopy, UPS, XPS, photodissociation, binding energy, ionization potential, computational, electronic structure, self-consistent field, DFT, QM/MM, gas phase, liquid, solution, physisorption, metallic surface, polymer, charge transfer
National Category
Theoretical Chemistry
Research subject
Theoretical Chemistry and Biology
Identifiers
urn:nbn:se:kth:diva-226919 (URN)978-952-62-1882-3 (ISBN)978-952-62-1883-0 (ISBN)
Public defence
2018-06-01, IT116, Univesity of Oulu, Pentti Kaiteran katu 1, 90014 Oulu, Finland, Oulu, 12:00 (English)
Opponent
Supervisors
Note

This thesis is for a double degree PhD done in KTH Royal institute of Technology and University of Oulu.

QC 20180502

Available from: 2018-05-02 Created: 2018-04-27 Last updated: 2018-05-08Bibliographically approved

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