Karol Pasterny

Theoretical DFT and experimental Raman and NMR studies on thiophene, 3-methylthiophene and selenophene

Abstract The results of extended MO calculations using density functional theory (DFT) approximation supported by experimental Raman, 1 H and 13 C NMR studies on thiophene are reported. Raman spectra of liquid thiophene were re-examined and the performance of a hybrid B3PW91 density functional was compared with the ab initio restricted Hartree–Fock (RHF) method. With the basis sets of the 6-311++G ∗∗ quality, the DFT calculated bond lengths, dipole moments and harmonic vibrations were predicted in a very good agreement with available experimental data. Additionally, the results on thiophene were extended by calculations on 3-methylthiophene and selenophene. In this case, a significant change in geometry and charge distribution in thiophene ring due to a methyl group substituent or replacement of sulphur by selene atom was observed. A linear correlation between the predicted harmonic vibrational frequencies (scaled using SQM method) and experimental ones for thiophene, selenophene and 3-methylthiophene was shown. The theoretically calculated spectra have satisfactorily reproduced the available experimental spectra for thiophene and selenophene.

DFT studies of COOH tip-functionalized zigzag and armchair single wall carbon nanotubes

AbstractStructure and energy calculations of pristine and COOH-modified model single wall carbon nanotubes (SWCNTs) of different length were performed at B3LYP/6-31G* level of theory. From 1 to 9 COOH groups were added at the end of the nanotube. The differences in structure and energetics of partially and fully functionalized SWCNTs at one end of the nanotube are observed. Up to nine COOH groups could be added at one end of (9,0) zigzag SWCNT in case of full functionalization. However, for (5,5) armchair SWCNT, the full functionalization was impossible due to steric crowding and rim deformation. The dependence of substituent attachment energy on the number of substituents at the carbon nanotube rim was observed. FigureStructure and energy calculations of pristine and COOH-modified model single wall carbon nanotubes (SWCNTs) of different length were performed at B3LYP/6-31G* level of theory and from 1 to 9 COOH groups was added at the end of the nanotube

Efficient Modeling of NMR Parameters in Carbon Nanosystems.

Rapid growth of nanoscience and nanotechnology requires new and more powerful modeling tools. Efficient theoretical modeling of large molecular systems at the ab initio and Density Functional Theory (DFT) levels of theory depends critically on the size and completeness of the basis set used. The recently designed variants of STO-3G basis set (STO-3Gel, STO-3Gmag), modified to correctly predict electronic and magnetic properties were tested on simple models of pristine and functionalized carbon nanotube (CNT) systems and fullerenes using the B3LYP and VSXC density functionals. Predicted geometries, vibrational properties, and HOMO/LUMO gaps of the model systems, calculated with typical 6-31G* and modified STO-3G basis sets, were comparable. The (13)C nuclear isotropic shieldings, calculated with STO-3Gmag and Jensens polarization consistent pcS-2 basis sets, were also identical. The STO-3Gmag basis sets, being half the size of the latter one, are promising alternative for studying (13)C nuclear magnetic shieldings in larger size CNTs and fullerenes.

Theoretical and experimental vibrational studies on liquid thiophene and its acetonitrile solution

Abstract The results of extended molecular orbital calculations using density functional theory (DFT) approximation and experimental vibrational studies on thiophene and its acetonitrile solution are reported. To account for solvent effect, the Onsager model at both the DFT and restricted Hartree–Fock (RHF) levels was employed. No significant variation was found in the Raman spectra as a function of the medium polarity. With the basis sets of 6-311++G ∗∗ quality, the DFT-B3PW91 calculated bond lengths, dipole moments and harmonic vibrations were predicted in a good agreement with available experimental data in the gas and condensed phases.

Molecular orbital studies of harmonic vibrations of nitrobenzene in the gas phase and solution using semi-empirical, ab initio and density functional theory calculations

Abstract Semi-empirical PM3 and ab initio calculations were performed at the Hartree–Fock level of theory on nitrobenzene. Several basis sets were used and some calculations were performed within a density functional theory (DFT) using the B3LYP hybrid functional. The theoretically predicted NO2 group harmonic frequencies of nitrobenzene in the gas phase and solutions of low and high polarity using a dielectric continuum model were compared with the corresponding experimental FT-IR data. The results of these theoretical and experimental studies could provide deeper insight into the nature of the local structure of liquid nitrobenzene.

Planar anchoring of polar liquid crystal molecules in slit pore–molecular dynamics simulation study

Abstract Results of molecular dynamics simulations for polar molecules confined to a slit pore with planar anchoring are reported. A molecule is represented by a Gay–Berne particle with a non-central axial dipole moment. To get information about the structure and phase behaviour of the system, on cooling and heating at constant density, the energy, heat capacity, orientational order parameter, and longitudinal- and transverse-distributions of the molecules are analysed. In comparison with the results for the bulk system the nematic phase is much wider. The smectic layers are developed from the pore walls independently, which leads to defects in the smectic structure of the system.

DFT calculations of structures, 13C NMR chemical shifts, and Raman RBM mode of simple models of small‐diameter zigzag (4,0) carboxylated single‐walled carbon nanotubes

Linearly conjugated benzene rings (acenes), belt‐shaped molecules (cyclic acenes), and models of single‐walled carbon nanotubes (SWCNTs) with one carboxylic group at the open end were fully optimized at the B3LYP/6‐31G* level of theory. These models were selected to obtain some insight into the nuclear isotropic changes resulting from systematically increasing the basic building units of open‐tip‐monocarboxylated SWCNTs. In addition, the position of radial breathing mode (RBM), empirically correlated with the SWCNT diameter, was directly related with the radius of model cyclic acene rings. A regular convergence of selected structural, NMR, and Raman parameters with the molecular system size increase was observed, and a simple two‐parameter mathematical formula enabled their estimation in infinity. The predicted 13C NMR chemical shifts of carbon atoms close to the substituted rim of carboxylated models of zigzag (4,0) SWCNTs differed significantly from the pristine nanotubes. Copyright

Angular velocity correlation function of ellipsoidal particles. Molecular dynamics simulation and theory

Abstract Molecular dynamics simulations of 256 ellipsoidal particles interacting via the Gay-Berne potential model were carried out for constant temperature and wide range of densities. From the simulation results the angular velocity and angular velocity sign correlation functions as well as the distributions of time intervals between successive angular velocity reversals were calculated. They were analysed using a model based on uncorrelated consecutive velocity reversals.

Molecular dynamics simulation study of polar liquid crystal molecules in slit pores

Abstract We present results of molecular dynamics simulations for polar molecules confined to a slit pore with homeotropic anchoring. The molecules are modelled by Gay–Berne particles with a non-central axial dipole moment. Information about the structure and phase behaviour of the system, on cooling and heating at constant density, is obtained by analysing the orientational order parameter, density profiles across the pore and molecular distributions in smectic layers. In comparison with the results for the bulk system the nematic and smectic-A phases are wider, however, the smectic-B phase occurs at lower temperatures.

Properties of a model liquid crystal: Polar Gay-Berne particles

Abstract Molecular dynamics simulations for molecules represented by the Gay-Berne ellipsoidal particles with non-central transverse dipole moments are reported. The system is compressed at constant temperature and the highest density corresponds to the tightest packing of hard ellipsoids. The thermodynamic and structural as well as dynamic properties of the system are studied. Especially the transition from the isotropic phase to the orientationally ordered one is investigated and our attention is focused on the dynamics in the ordered phase.