University of Oulu

Quantum-classical calculations of X-ray photoelectron spectra of polymers— Polymethyl methacrylate revisited T. Löytynoja, I. Harczuk, K. Jänkälä, O. Vahtras, and H. Ågren The Journal of Chemical Physics 146, 124902 (2017); doi: 10.1063/1.4978941

Quantum-classical calculations of X-ray photoelectron spectra of polymers : Polymethyl methacrylate revisited

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Author: Löytynoja, T.1,2; Harczuk, I.2; Jänkälä, K.1;
Organizations: 1Nano and Molecular Systems Research Unit, University of Oulu, P.O. Box 3000, FIN-90014 Oulu, Finla
2Division of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
3Laboratory for Nonlinear Optics and Spectroscopy, Siberian Federal University, 660041 Krasnoyarsk, Russia
Format: article
Version: accepted version
Access: open
Online Access: PDF Full Text (PDF, 5.7 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe201706127119
Language: English
Published: American Institute of Physics, 2017
Publish Date: 2017-06-12
Description:

Abstract

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.
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Series: Journal of chemical physics
ISSN: 0021-9606
ISSN-E: 1089-7690
ISSN-L: 0021-9606
Volume: 146
Issue: 12
Pages: 124902-1 - 124902-12
Article number: 124902
DOI: 10.1063/1.4978941
OADOI: https://oadoi.org/10.1063/1.4978941
Type of Publication: A1 Journal article – refereed
Field of Science: 114 Physical sciences
116 Chemical sciences
Subjects:
Funding: This work was financially supported by the Vilho, Yrjö, and Kalle Väisälä foundation and the University of Oulu Graduate School. Computational resources were provided by CSC—IT Center for Science administrated by the Ministry of Education and Culture of Finland and the Swedish National Infrastructure for Computing (SNIC) for the project “Multiphysics Modeling of Molecular Materials” (Nos. SNIC 2014/11-31 and SNIC 2015/16-10). We acknowledge The Knut and Alice Wallenberg Foundation for financial support (Grant No. KAW-2013.0020). We thank Professor Yaoquan Tu for his insight about the structure of the PMMA polymers.
Copyright information: Published by AIP Publishing