| 1. |
- Mahani, Mohammad Reza, et al.
(författare)
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Breakdown of Polarons in Conducting Polymers at Device Field Strengths
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:19, s. 10317-10324
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Tidskriftsartikel (refereegranskat)abstract
- Conducting polymers have become standard engineering materials used in many electronic devices. Despite this, there is a lack of understanding of the microscopic origin of the conducting properties, especially at realistic device field strengths. We present simulations of doped poly(p-phenylene) (PPP) using a Su-Schrieffer-Heeger (SSH) tight-binding model, with the electric field included in the Hamiltonian through a time-dependent vector potential via Peierls substitution of the phase factor. We find that polarons typically break down within less than a picosecond after the field has been switched on, already for electric fields as low as around 1.6 mV/angstrom. This is a field strength common in many flexible organic electronic devices. Our results challenge the relevance of the polaron as charge carrier in conducting polymers for a wide range of applications.
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| 2. |
- Mahani, Mohammad Reza, et al.
(författare)
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Charge transport via polarons in doped poly(p-phenylene) with impurity
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Polaron charge transport in doped poly(p-phenylene), PPP, in the presence of magnetic and nonmagnetic impurities and an electric field, is studied using the Su-Schrieffer-Heeger (SSH) tight-binding model. In our approach, the electric field is included in the Hamiltonian through the time-dependent vector potential via Peierls substitution of the phase factor. We describe the dynamics of the polarons and identify three distinct regimes: transmission, reflection, and trapping of polarons at the impurity site. The strength of the electric field as well as the impurity potential determine the outcome ofthe scattering.
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| 3. |
- Mirsakiyeva, Amina, 1989-
(författare)
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Electronic and optical properties of conducting polymers from quantum mechanical computations
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Conductive polymers are also known as "organic metals" due to their semiconducting properties. They are found in a wide range of applications in the field of organic electronics. However, the growing number of experimental works is not widely supported with theoretical calculations. Hence, the field of conductive polymers is experiencing lack of understanding of mechanisms occurring in the polymers. In this PhD thesis, the aim is to increase understanding of conductive polymers by performing theoretical calculations. The polymers poly(3,4-ethylenedioxythiophene) (PEDOT) together with its selenium (PEDOS) and tellurium (PEDOTe) derivatives, poly(p-phenylene) (PPP) and naphthobischalcogenadiazoles (NXz) were studied. Several computational methods were applied for analysis of mentioned structures, including density functional theory (DFT), tight-binding modelling (TB), and Car-Parrinello molecular dynamics (CPMD) calculations. The combination of CPMD and DFT calculations was applied to investigate the PEDOT, PEDOS and PEDOTe. The polymers were studied using four different functionals in order to investigate the full picture of structural changes, electronic and optical properties. Temperature effects were studied using molecular dynamics simulations. Wide statistics for structural and molecular orbitals analysis were collected. The TB method was employed for PPP. The formation and motion of the excitations, polarons and bipolarons, along the polymer backbone was investigated in presence of electric and magnetic fields. The influence of non-magnetic and magnetic impurities was determined. The extended π-conjugated structures of NXz were computed using B3LYP and ωB97XD functionals in combination with the 6-31+G(d) basis set. Here, the structural changes caused by polaron formation were analyzed. The combined analysis of densities of states and absorption spectra was used for understanding of the charge transition.
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| 4. |
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| 5. |
- Mirsakiyeva, Amina, et al.
(författare)
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Experimental and ab initio studies of the novel piperidine-containing acetylene glycols
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Synthesis routes of novel piperidine-containing diacetylene are presented. The new molecules are expected to exhibit plant growth stimulation properties. In particular, the yield in a situation of drought is expected to increase. The synthesis makes use of the Favorskii reaction between cycloketones/piperidone and triple-bond containing glycols. The geometries of the obtained molecules were determined using nuclear magnetic resonance (NMR). The electronic structure and geometries of the molecules were studied theoretically using first-principles calculations based on density functional theory. The calculated geometries agree very well with the experimentally measured ones, and also allow us to determine bond lengths, angles and charge distributions inside the molecules. The stability of the OH-radicals located close to the triple bond and the piperidine/cyclohexane rings was proven by both experimental and theoretical analyses. The HOMO/LUMO analysis was done in order to characterize the electron density of the molecule. The calculations show that triple bond does not participate in intermolecular reactions which excludes the instability of novel materials as a reason for low production rate.
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| 6. |
- Mirsakiyeva, Amina, et al.
(författare)
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Experimental and density functional theory studies of some novel piperidine-containing acetylene glycols
- 2016
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Ingår i: ARKIVOC. - : Arkat. - 1551-7004 .- 1551-7012. ; , s. 86-99
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis routes of novel piperidine-containing acetylenes are presented. The new molecules are expected to exhibit plant growth stimulation properties. In particular, the yield in a situation of drought is expected to increase. Our synthesis makes use of the Favorskii reaction between cyclohexanone/piperidone and triple-bond containing alcohols. The structures of the obtained molecules were determined using nuclear magnetic resonance (NMR). The electronic structure and geometries of the molecules were studied theoretically using first-principles calculations based on density functional theory. The calculated geometries agree very well with the experimentally determined ones, and also allow us to determine bond lengths, angles and charge distributions inside the molecules.
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| 7. |
- Mirsakiyeva, Amina, et al.
(författare)
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Initial Steps in PEO Decomposition on a Li Metal Electrode
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:37, s. 22851-22857
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Tidskriftsartikel (refereegranskat)abstract
- Poly(ethylene oxide) (PEO) is the most widely used compound as a solid-state (solvent-free) polymer electrolyte for Li batteries, mainly due to its low glass transition temperature (T-g) and ability to dissolve Li salts. It is also frequently suggested that its cathodic stability renders it possible to operate with Li metal anodes in the design of high energy density storage devices. However, little is still known about the true interfacial chemistry between Li metal and PEO and how these two materials interact with each other. We are here exploring this relationship by the means of density functional theory (DFT)-based modeling. Using bulk structures and isolated PEO chains, we have found that there is a strong thermodynamic driving force to oxidize Li metal into lithium oxide (Li2O) when PEO is decomposed into C2H4 and H-2, irrespectively of the PEO oligomer length. Explicit modeling of PEO on a Li(100) surface reveals that all steps in the decomposition are exothermic and that the PEO/Li metal system should have a layer of Li2O between the polymer electrolyte and the metal surface. These insights and the computational strategy adopted here could be highly useful to better tailor polymer electrolytes with favorable interfacial properties.
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| 8. |
- Mirsakiyeva, Amina, 1989-, et al.
(författare)
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Optical properties of Naphthobischalcogenadiazoles from density functional perspective
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In the present work the density functional calculations of two naphthobischalcogenadiazole (NXz) oligomers are shown. The oxygen- and sulphur-containing NXz trimers were optimized in a form of a neutral oligomer and a radical cation in order to investigate structural changes resulting from the polaron formation. The influence of polaron on band gaps is determined and supported with densities of states analysis together with absorption spectra. This manuscript used B3LYP and ωB97XD functionals in combination with 6-31+G(d) basis set.
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| 9. |
- Mirsakiyeva, Amina, et al.
(författare)
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Polaron formation and optical absorption in PEDOT and its selenium and tellurium derivatives: density functional calculations
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present a density functional theory (DFT) study on polaron formation and optical properties of PEDOT and its selenium and tellurium derivatives. Comparing a number of combinations of basis set and approximations to the exchange-correlation functional, we find that the ωB97XD functional is an overall good choice giving well-localized polarons and optical spectra in good agreement with experiment. This functional has the correct long-range asymptotic behavior, and also includes some short-range Hartree-Fock exchange. Despite the long-range Hartree-Fock exchange part present in this functional, the spin contamination remains relatively limited and it also stably produces results that are virtually independent of the basis set used.
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| 10. |
- Mirsakiyeva, Amina, 1989-
(författare)
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Quantum Mechanical Calculations of Thermoelectrical Polymers and Organic Molecules
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of the present licentiate thesis is density functional theorybased electronic structure calculations of organic thermoelectric materials and novel organic molecules. We used the Car-Parrinello molecular dynamics method in order to investigate the electronic structure of “green energy” and “greenchemistry” compounds.First, we have investigated the electronic structure of the poly(3,4-ethylene-dioxythiophene) (PEDOT) and its derivatives - the best studied and successfully implemented by industry organic thermoelectric material. Its transparency, low toxicity and high stability in the oxidized state are combined withan ability to produce electrical current when applying a temperature gradient. This makes PEDOT a perfect “organic metal” and a first candidate for organic thermoelectrogenerators - devices that can produce “green energy” from a temperature difference. The average structures found in these quantum dynamical simulations agree well with earlier static electronic structure studies. The energy gap of two, four and six unit oligomers of PEDOT was calculated and was found to lie in the range of previous theoretical studies. We have also calculatedthe point-charge distributions along the polymer backbone in order to investigate the polaron formed by doping agents of PEDOT. Our analysis allowed us to predict possible localization of the charge in the center of the polymer chain. However, further calculations of the twelve unit PEDOT and its selenium and tellurium derivatives will provide more information. First-principles calculations for the tellurium derivative of PEDOT are here presented for the first time.The second part of our investigation concerns theoretical calculations of novel piperidine-containing acetylene glycols. These molecules were newly synthesized by our experimental collaborators and are expected to provideplant growth stimulation properties, the same as its diacetylene analogs. We performed quantum mechanical calculations of four compounds, presented ananalysis of the highest occupied and lowest unoccupied molecular orbitals and collected detailed information on point-charges for further parametrization of novel molecules for future computational studies. According to these results, the low production yield found in the experiments cannot be attributed to chemical instability in these novel compounds.
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