First-principles study of structural,elastic, electronic and vibrational properties of BiCoO3

We used density functional theory (DFT) to study the structural, elastic, electronic, and lattice dynamical properties of tetragonal BiCoO₃ applying the “norm-conserving” pseudopotentials within the local spin density approximation (LSDA). The calculated equilibrium lattice parameters and atomic displacements are in agreement with the available experimental and theoretical results. Moreover, the structural stability of tetragonal BiCoO₃ were confirmed by the calculated elastic constants. In addition, the elastic properties of polycrystalline aggregates including bulk, shear and Young's moduli, and Poisson's ratio are also determined. The electronic band structure, total and partial density of states (DOS and PDOS) with ferromagnetic spin configuration are obtained. The results show that tetragonal BiCoO₃ has an indirect band gap with both up- and down-spin configurations and its bonding behavior is of covalent nature. We compute Born effective charge (BEC) which is found to be quite anisotropic of Bi, Co and O atoms. The infrared and Raman active phonon mode frequencies at the Г point are found. The phonon dispersion curves exhibit imaginary frequencies which lead from the high-symmetry tetragonal phase to low-symmetry rhombohedral phase in BiCoO₃. The six independent elastic constants, including bulk, shear and Young's moduli, and Poisson's ratio, complete BEC tensor and phonon dispersion relations in tetragonal BiCoO₃ are predicted for the first time. Results of the calculations are compared with the existing experimental and theoretical data.     

Combination of RBS analysis and infrared vibrational spectroscopy for the characterization of semiconducting β-FeSi2 films

The analytic power of RBS and FTIR measurements for the characterization of chemical and structural properties of thin films is compared for the case of semiconducting FeSi _x films. It is shown that these methods, which both are nondestructive, are complementary with respect to their sensitivity to certain film properties (composition, degree of compound formation, crystalline quality, film thickness). For FeSi _x films the FTIR technique is favourable for rapid monitoring of chemical bonding and of the structural properties without special sample preparation.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Studies of thiol additions of silane coupling agents by vibrational spectroscopy

Raman and infrared spectroscopies have been used to determine the addition reaction of mercaptopropyltrimethoxysilane (MPTMS) to allyltrimethoxysilane (ATMS) and 7-octenyltrichlorosilane based on the vibrational intensity variation of thiol and vinyl groups in the reaction mixtures. Due to the distinct and moderate intensity of Raman bands observed in the present experiment, the identification with Raman spectroscopic method is more sensitive than that with FTIR spectroscopy. In the presence of UV radiation, thiol addition reaction has been observed in the direct mixing samples of silanes. Hybrid sol-gels prepared with the use of MPTMS and ATMS as precursors in both acidic and basic conditions have revealed the progression of thiol addition under the UV radiation exposure. UV radiation is similarly effective to induce the thiol addition in the sol-gel coated aluminum tiles. Without UV radiation, the use of free radical initiator in the sol-gel samples might also help to induce the addition reaction.     

Gamma ray induced changes on vibrational spectroscopic properties of strontium alumino-borosilicate glasses

The present investigation reports the effect of influence of aluminum ions on radiation damage of strontium borosilicate glasses studied by means of spectroscopic (viz., optical absorption (OA), infrared and Raman spectra). The composition of the glasses chosen for the study is 40SrO–xAl₂O₃–(15-x) B₂O₃–40SiO₂ (x = 5, 7.5, 10), all in mol%. The glasses were synthesized by conventional melt quenching method. Later, the samples were exposed to gamma (γ) radiation dose of strengths 10 kGy and 30 kGy with a dose rate of 1.5 Gy/s using ⁶⁰Co as radiation source. The infrared spectra (IR), Raman spectra and optical absorption (OA) spectra of the samples were recorded at ambient temperature before and after irradiation. The OA spectra of the pre-irradiated samples do not exhibit any absorption bands in the UV–vis regions and IR and Raman spectra exhibited conventional vibrational bands due to different borate, silicate AlO₄ and AlO₆ structural units. The OA spectra of post irradiated samples exhibited a broad absorption band in the wavelength region 600–750 nm; it is attributed to electron trapped color centers. The intensity of this peak is observed to increase with increase of the γ-ray dose. Considerable changes in the intensities of various bands in the IR and Raman spectra were also observed. The changes were explained based on structural modifications taking place in the glass network due to γ-ray irradiation and finally it is concluded that the glasses mixed with 10.0 mol% of Al₂O₃ are relatively more radiation resistant.     

Investigation of selectively substituted monosaccharides by the method of vibrational spectroscopy and X-ray analysis

The influence of steric factors on the formation of vibrational spectra of carbohydrates was illustrated by the example of selectively substituted monosaccharides. We consider compounds in which the difference and similarity of vibrational spectra are largely determined by the difference and similarity of the geometry of their molecular base (the molecule's skeleton). At the same time, in the case of selectively substituted nitrates of methyl-β- -glucopyranoside, the skeletal bases of which are identical, with differences in the localization site of volumetric substituents and their total number, or in rotational isomers (conformations) of the lateral nitrate groups, their Fourier Raman spectra are different over a wide spectral range. It is concluded that steric factors and the position of volumetric substituents of hydroxyls produce an exceptionally important effect on the formation of vibrational spectra of carbohydrates.     

Thermophysical properties of macromolecules in the block state

The macromolecules of linear polymers usually consist of regular helices. The paper presents the results of investigation of the concentration, thermal expansion coefficient and vibration amplitude of such helices at different temperatures. These parameters were determined from temperature dependences of the intensity, frequency and halfwidth of regular bands in IR and Raman spectra of polymers.

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Zusammenfassung Die Makromoleküle linearer Polymere zeigen gewöhnlich Helixstruktur. Es wurden Konzentration, Wärmeausdehnungskoeffizient und Schwingungsamplitude derartiger Helizes bei verschiedenen Temperaturen untersucht. Diese Parameter wurden anhand von Intensität, Frequenz und Halbwertbreite der Normalbanden in IR- und Raman-Spektren von Polymeren bestimmt.

     

Infrared spectroscopy of N-methylacetamide in water from high-level QM/MM calculations简

The infrared(IR) spectra of the N-methylacetamide molecule in water are calculated by using the MD simulation with high-level QM/MM corrections. The B3LYP and MP2 levels with 6-311++G** basis set are used for the QM region, respectively. Our results show all IR spectra at the B3LYP level are well consistent with the corresponding MP2 results. A dynamical charge fluctuation is observed for each atom along the simulation trajectories due to the electrostatic polarization(EP) effects from surrounding solvent environment. We find that the QM/MM corrected IR spectra satisfactorily reproduce the experimental vibrational features of amide I–III modes.     

Formation and structural,energetic and dynamic properties of cyclodextrin host tubes and included guest molecules

Experimental data about 3D arrangements and building modes of cyclodextrin (CD) tubes are scarce, though investigations of such assemblies are particularly interesting for a vast array of applications related to organic tubes in general. Opting for a theoretical approach, we studied the organisation of CD tubes by three schemes: a structural examination of geometries from the Cambridge Structural Database, simulated annealing studies based on classical force fields to evaluate the stability of tubular arrangements, and an incremental construction procedure of the tubes by molecular dynamics. For β-CDs, the investigations pointed to a head-to-head configuration, while γ-CDs favoured a head-to-head+tail-to-head triplet. The position and interactions of water molecules inside the obtained tubular arrangements were studied as well. Various complexes for diphenylpolyenes and styrene included in the β- and γ-CDs tubes were considered and compared based on structural, energetic and dynamic criteria.     

A DFT study on the vibrational spectroscopy of protoporphyrin IX

Infrared and Raman spectra of protoporphyrin IX were recorded. DFT quantum chemical calculations were performed. Optimised molecular geometry, electric charge distribution, vibrational force constants were computed. The normal coordinate analysis and the scaling of the force constants yielded all the necessary data for the simulation of the infrared and Raman spectra and the potential energy distribution calculations. The result was the interpretation of all vibrational modes of the molecule. Conclusions were drawn from the difficulties arisen during the assignment of the vibrational spectra of such large molecules.     

First-principles study of vibrational properties of TiSiO4 clusters

First-principles calculations were performed to investigate the vibrational properties of monomers and dimers of titania, silica, and titania-silica hybrid clusters. Density functional theory-based formulism was employed to optimize the geometry at the B3LYP level and calculate the infrared and Raman spectra of the clusters by using the GGA-PBE exchange-correlation functional. It was found that the vibrational spectra of Ti₂O₄, Si₂O₄, and TiSiO₄ hybrid clusters provide fingerprint information about structures and structural transitions during the formation of cluster structures. In the case of Si₂O₄ the mode at 410 cm⁻¹ exhibited the largest vibration of Si atoms, whereas in the case of Ti₂O₄ the mode at 442 cm⁻¹ exhibited the largest vibration of Ti atoms. The hybrid cluster TiSiO₄ was structured using two different methods to explore the effects of starting geometry on the structures and vibrational modes of the clusters. The structural properties of the clusters remained unchanged but vibrational modes were found to be different. It is found that Si shows notable vibrations, but the metal atom Ti merely shows any vibration in the case of TiSiO₄ hybrid clusters. The low and intermediate frequency modes were stiffened, whereas the three highest frequency modes were softened when the starting geometry of the hybrid clusters was changed from Si₂O₄ to Ti₂O₄.     

Variational calculation of static and dynamic vibrational nonlinear optical properties

The vibrational configuration interaction method used to obtain static vibrational (hyper)polarizabilities is extended to dynamic nonlinear optical properties in the infinite optical frequency approximation. Illustrative calculations are carried out on H(2)O and NH(3). The former molecule is weakly anharmonic while the latter contains a strongly anharmonic umbrella mode. The effect on vibrational (hyper)polarizabilities due to various truncations of the potential energy and property surfaces involved in the calculation are examined.     

Ultrafast structural dynamics of photochromic indolylfulgimides studied by vibrational spectroscopy and DFT calculations

The structural dynamics of the ring-opening reaction in a photochromic indolylfulgimide, a reversible, ultrafast photoswitch, is investigated by ultra-broadband time-resolved vibrational spectroscopy. The experimentally observed vibrational modes of the indolylfulgimide photoisomers C and E are assigned to normal modes with the help of DFT calculations. A complete evaluation of the observed vibrational dynamics including excited-state vibrational modes is used to characterize the reaction path and the cooling behavior of the photoswitch.     

Force fields and vibrational spectroscopy: A discussion on status and future prospects

A start is given for a discussion about the use of force fields for describing and interpreting molecular geometries, relative energies and vibrational spectra. The development of modern, generic force fields, e.g. Class II force fields, has diminished the necessity for specific force fields, and they should be applied in far more cases than they are being used now.     

Theoretical study of structures, energetics and vibrational properties of BC H species

Theoretical study using self-consistent field (SCF), hybrid density functional theory (B3LYP) and quadratic configuration interaction including single and double excitations (QCISD) with the Dunning correlation consistent polarized valence double zeta (cc-pVDZ) basis set have been used to examine the structures and vibrational properties of the singlet species with BC H stoichiometry. Relative stabilities are estimated at the CCSD(T)/cc-pVTZ level using QCISD/cc-pVDZ optimized geometries. Five species corresponding to different nuclear arrangements have been studied. The absolute minimum corresponds to the 2 aromatic borirene molecule (HBC H with a BC ring). Ethynylborane (H BCCH, C ) and borallene (H CCBH, C ) are respectively 6.4 and 24.3 kcal/mol higher. Vinylborine (C H B, C ) and H CBCH (C ) are much less stable, 46.2 and 49.1 kcal/mol respectively higher than borirene. The calculated vibrational spectra agree with experiment and confirm the infrared matrix characterization of the three most stable species.     

DFT-predicted structural,vibrational, and bonding properties of XSiO and X2SiO (X=F,Cl, or Br) molecules

The spectroscopic properties of XSiO (X=F, Cl, or Br) have been predicted using the B3-LYP/6-311+G(2d) level of theory. It has been shown that the halogen atom is Si bonded in a bent structure, with ∠(XSiO) bond angles close to 126°. The binding energy of the halogen with the SiO subunit was calculated to be −80.1, −40.9, and −29.3 kcal/mol for FSiO, ClSiO, and BrSiO, respectively. The harmonic frequencies and isotopic shifts have been calculated. A comparison between XSiO and X₂SiO has also been made. For the X₂SiO (X=F or Cl) compounds, the calculated frequencies are in fair agreement with the available experimental data. Characterization of bonding has been investigated with different approaches (natural bond orbital approach, topological analysis of the charge density, and of the electron localization function ELF). © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1205–1214, 1998     

Segmented conjugated macromolecules containing silicon and boron: ADMET synthesis and luminescent properties

Boron‐ and silicon‐containing conjugated homo‐ and copolymers could be synthesized using acyclic diene metathesis (ADMET) condensation of bis‐styryl monomers. Both, tri‐and tetra‐coordinated boron monomers were successfully polymerized forming homopolymers, or random copolymers (if polymerized together with a silicon containing co‐monomer). Polymer molecular weights M_n were measured at ～6000 to 15,000 g/mol (NMR end group analysis) with molecular weight distributions M_w/M_n ～1.8 to 2.2. The polymers absorbed at λ_max ～317 to 406 nm and emitted at λ_max ～370 to 494 nm with fluorescent quantum efficiencies ～24 to 48%. The copolymer with tri‐coordinate boron showed highly efficient fluorescence quenching in the presence of fluoride ions at ratios boron/fluoride ～5/1, demonstrating its potential as anion sensor. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1707–1718     

The effects of conformation and intermolecular hydrogen bonding on the structural and vibrational spectral data of naproxen molecule

The structural and vibrational properties of naproxen, an inhibitor of cyclooxygenase (COX) enzyme, were investigated by molecular modeling and experimental IR and Raman spectroscopic techniques. Possible conformers of the molecule were searched via a molecular dynamics simulation carried out with MM2 force field. The total energies, equilibrium geometries, force fields, IR and Raman spectral data of the found stable conformers were determined by means of geometry optimization and harmonic frequency calculations carried out using the B3LYP method and Pople-style basis sets of different size. The stability order obtained for the lowest-energy conformers was confirmed by high-accuracy thermochemistry calculations performed with G3MP2B3 composite method. Some electronic structure parameters of naproxen and the anharmonicity characters of its vibrational modes were determined by means of natural population analysis (NPA) and anharmonic frequency calculations at B3LYP/6-31++G(d,p) and B3LYP/6-311++G(d,p) levels of theory. A part of these calculations carried out for free naproxen molecule were repeated also for its energetically most favored dimer forms. Two different scaling procedures ((1) “SQM-FF methodology” and (2) “Dual scale factors”) were independently applied to the obtained harmonic vibrational spectral data to fit them to the corresponding experimental data. In the light of the obtained calculation results, which confirm the remarkable effects of conformation and intermolecular hydrogen bonding on the structural and vibrational spectral data, in particular, on those associated with the functional groups in the propanoic acid chain, a reliable assignment of the fundamental bands observed in the experimental IR and Raman spectra of the molecule was achieved.     

DFT calculations of vibrational spectra and nonlinear optical properties for MgO nanotube clusters

The IR and Raman spectra, nonlinear optical properties of MgO nanotube clusters are studied by density-functional theory at B3LYP/6-31G(d) level. The IR spectra are match closely to those in the corresponding MgO cluster and bulk materials. The strongest peaks of the IR spectra are located in the range from 650 to 750 cm⁻¹. The Raman spectra are very sensitive to structural variations in MgO clusters, and redshift of vibrational frequency is observed in Raman spectra as increasing cluster length. The motion of the strongest peaks in spectra is discussed. The total dipole moment and the first hyperpolarizabilities oscillate between zero and a constant when the layer is grown for the layer dependence of symmetry in MgO nanotube clusters.     

Investigation of oxofluorotitanates (NH4)3TiOF5 and Rb2KTiOF5 by vibrational spectroscopy and quantum-chemical methods

The phase transition effects in (NH₄)₃TiOF₅ and Rb₂KTiOF₅ were studied by vibrational spectroscopy over a wide range of temperatures. Changes in the spectra of these crystals were found for a PT in the region of the internal vibrations of the [TiOF₅]^3? ion. Quantum-chemical simulation of the vibrational spectra of (NH₄)₃TiOF₅ was performed, and band assignments were carried out. The structure of the compound and the mechanism of the structural phase transition were examined. It is shown that the vibrational spectra of the compounds at room temperature depend on the dynamic disordering of the complex anion.