| 1. |
- Ma, Yong, et al.
(författare)
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The equilibrium geometry of A@C60 : A test case for conventional density functional theory
- 2014
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 591, s. 312-316
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Tidskriftsartikel (refereegranskat)abstract
- Potential energy surfaces (PESs) along the reaction pathway towards the center of CC bond between two six membered rings for ten different endohedral fullerenes A@C60 (A = H, C, O, S, N, P, He, Ne, Ar, Kr) have been studied by density functional theory (DFT) and Hartree-Fock (HF) method. The results show that no suitable method can consistently describe the interaction between atom A and carbon cage. The dispersion corrected DFT methods fail to describe the equilibrium geometry and PES of the complexes with light atoms. Nevertheless, the inclusion of the dispersion stabilizes the system as reflected by interaction energies (IEs) between atom A and C60.
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| 2. |
- Song, Xiuneng, et al.
(författare)
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Effects of Protonation, Hydrogen Bonding, and Photodamaging on X-ray Spectroscopy of the Amine Terminal Group in Aminothiolate Monolayers
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:23, s. 12649-12654
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Tidskriftsartikel (refereegranskat)abstract
- The amine head group, NH2, in aminothiolate monolayers can often generate unexpectedly rich structures in its N K-edge X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra that are difficult to assign. We have carried out density functional theory (DFT) calculations to study the XPS and NEXAFS of amine head group in four different aminothiolate monolayers, namely aliphatic 11-aminoundecane-1-thiol (AUDT), aromatic 4-aminobenzenethiol (ABT) and araliphatic 4-aminophenylbutane-1-thiol (APBT) and 3-(4”-amino-1,1’:4’,1”-terphenyl-4-yl)propane-1-thiol (ATPT), with the focus on structure changes caused by protonation, hydrogen bonding and X-ray damaging. Spectra of all possible saturated and unsaturated species, as well as X-ray damage products, such as imine, nitrile, azo species and cumulative double bonds, have been thoroughly examined. It is found that extra spectral structures observed in the experimental XPS spectra are not resulted from protonation, but from the formation of a primary ammonium. The X-ray excitation can induce cross linking between two neighboring molecules to form different complexes that contribute to the π features in NEXAFS spectra.
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| 3. |
- Song, Xiuneng, et al.
(författare)
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Energy landscape inside the cage of neutral and charged N@C60
- 2011
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 517:4-6, s. 199-203
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Tidskriftsartikel (refereegranskat)abstract
- Potential energy surfaces along different escaping paths of the nitrogen atom inside the neutral and charged endohedral fullerene N@C60 have been constructed at the density functional theory level. It is found that the dispersion force plays an important role in determining the equilibrium geometry of the neutral system. The most energetic favorable escaping path is towards the center of C = C/C–C bond connecting two neighboring rings for all three systems. The rate determining potential energy surface shows a very small dependence on the charging state. The presented theoretical results should be useful for the practical applications of N@C60 in quantum computing and information.
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| 4. |
- Song, Xiuneng
(författare)
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Theoretical Characterization of Functional Molecular Materials
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays, material, energy and information technologies are three pillar industries. The materials that have close relation with our life have also been the foundation for the development of energy and information technologies. As the new member of the material family, functional molecular materials have become increasingly important for many applications, for which the design and characterization by the theoretical modeling have played the vital role. In this thesis, three different categories of functional molecular materials, the endohedral fullerenes, the fullerene derivatives and the self-assembled monolayers (SAMs), have been studied by means of first principles methods.The non-metal endohedral fullerene N@C60 is a special endohedral fullerene that is believed to be relevant to the construction of future quantum computer. The energy landscape inside the N@C60 has been carefully explored by density functional theory (DFT) calculations. The most energy favorable potential energysurfaces (PESs) for the N atom to move within the cavity have been identified. The effect of the charging on the PESs has also been examined. It is found that the inclusion of dispersion force is essential in determining the equilibriumstructure of N@C60. Furthermore, the performance of several commonly useddensity functionals with or without dispersion correction has been verified for ten different endohedral fullerenes A@C60 with the atom A being either reactive nonmetal or nobel gases elements. It shows that the inclusion of the dispersion forcedoes provide better description for the binding energy (BE), however, none ofthem could correctly describe the energy landscape inside all the ten endohedral fullerenes exclusively. It thus calls for the further improvement of current density functionals for weak interacting systems.Soft X-ray spectroscopy is a powerful tool for studying the chemical and electronic structures of functional molecular materials. Theoretical calculations have been proven to be extremely useful for providing correct assignments for spectraof large systems. In this thesis, we have performed first principles simulations forthe near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectra (XPS) of fullerene derivatives and aminothiolates SAMs. Our calculatedspectra can accurately reproduce experimental results available for all the systemsunder investigations, and identify the species or structures that are responsible for those unexpected spectral features observed in experiments. We have suggested a modified building block (MBB) approach that allows to calculate NEXAFS spectraof a large number of fullerene derivatives with very small computational cost, and resolved the long standing puzzle around the experimental XPS and NEXAFS spectra of SAMs with aminothiolates.
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| 5. |
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| 6. |
- Song, Xiuneng, et al.
(författare)
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Theoretical Study of Core Excitations of Fullerene-Based Polymer Solar Cell Acceptors
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:45, s. 23938-23944
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Tidskriftsartikel (refereegranskat)abstract
- First-principles simulations for the C K-edge X-ray photoelectron (XPS) and near-edge X-ray fine-structure (NEXAFS) spectra of representative polymer solar cell acceptor (PSCA) molecules have been carried out with special focuses on the [6,6]-phenyl-Cn+1-butyric acid methyl ester (PCnBM, n = 60, 70, 84). In the XPS spectra, evident red shift of core binding energies are observed in PCnBM as compared to the corresponding fullerene C-n, which is due to weak electronic charge transfer from the side chain to the fullerene backbone and consequently increased electron screening. Special emphasis is paid to a spectral peak at ca. 284.7 eV, which is caused by resonances of phenyl-ring carbons in the side chain and is important in characterizing the electronic structures of different PSCA molecules. Additionally, we propose a modified version of the building block (MBB) approach for quick estimation of the NEXAFS spectra, which is useful when computational resources are limited or massive systems are under study. This method is based on our component analysis on the side chain and fullerene backbone parts and adds only a further empirical fine-tuning after the conventional BB approach. Our calculated results are in good agreement with available experiments.
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