Electronic structure of complexes of oligomers of 3,4-ethylene-dietoxythiophene with polystyrlesulphonic acid

By the method of density functional theory (B3LYP, 6-31G **) the electronic structures of poly 3,4-ethylenedioxythiophene containing 12 links in charge states 0, +1, +2, +3 and +4 were calculated. It is shown that the oligomer of 12 units is sufficient to reflect the properties of the conductive polymer. To estimate the probability of electron density movement along the polymer chain, the width of the energy gap between NOMO and LUMO was calculated. It is shown that the molecules of oligomers EDOT and SS do not remain parallel to each other after polymerization, but rather, with increasing chain length, the latter gradually bends around the anionic unit SS; the charge distribution in the EDOT and SS oligomer complexes indicates the presence of two separated polarons at the two ends of the chain, and the asymmetry in the charge distribution also implies the presence of a curved spiral structure of the formed complex.

Transformation of addimers >Ge=GeGe=SiSi=Si< on the relaxed side of Si (001) (4 × 2)

By the method of density functional theory (B3LYP, 6-31G **) three types of displacements are calculated, namely oscillations as a whole, rotation and diffusion of dimers > Ge = Ge <, > Ge = Si < and > Si = Si <, which are formed on the crystalline surface of Si (001) (4×2) during the deposition of germanium atoms under conditions of molecular beam epitaxy. Calculations of angles of buckling of addimers are carried out. It is shown that when the addimers as a whole oscillate around the equilibrium position, the energy barriers are quite low, the highest of them occurs for a mixed addimer > Si = Ge <. Pure adders > Ge = Ge < and > Si = Si < oscillate between two degenerate states with an energy barrier of 0.042 and 0.014 eV, respectively. The structures of the transition state and the intermediate when the addimer > Ge = Ge < is moved between adjacent cells in the approximation of the constant bond length > Ge = Ge < are obtained. As calculations have shown, all transformations of surface dimers occur with relatively small activation energies, the numerical values of which agree satisfactorily with the results of STM experiments available in the literature.

CALCULATION OF THE ELECTRONIC STRUCTURE OF SOME ORGANIC OXIDES BY THE DFT METHOD

In this work, we performed a quantum chemical calculation of cyclohexeneoxide and cyclopentenoxide using the method of density functional DFT. An optimized geometric and electronic structure of these compounds is obtained. It was established that the studied oxides belong to the class of very weak CH-acids (pKa = 28-30).

Stability and magnetic properties of isomorphous substituted Si7-xMnx+

The optimized geometries, stability, and magnetic properties of cationic clusters Si7+, Si6Mn+, and Si5Mn2+ have been determined by the method of density functional theory using the B3P86/6-311+G(d) functional/basis set. Their electronic configurations have been analyzed to understand the influence of substituting Si atoms by Mn atoms on the structural and magnetic aspects of Si7+. It is shown that the manganese dopant does not alter the structure of the silicon host but significantly changes its stability and magnetism. In particular, while the magnetic moment of Si7+ is 1 mB, Si5Mn2+ exhibits a strong magnetic moment of 9 mB and that of Si6Mn+ takes a relatively high value of 4 mB. Among studied clusters, the pentagonal bipyramid Si5Mn2+ is assigned as the most stable one.

STABLE STRUCTURES AND CHARACTERISTIC VIBRATIONAL SPECTRA OF TinOm(n = 2–4; m = 1–2n) CLUSTERS

The energetically favorable structures and characteristic infrared (IR) and Raman peaks of Ti n O m(n = 2–4, m ≤ 2n) clusters are obtained in this work using a B3LYP/6-311G(d) method of density functional theory (DFT). The structures with m < 2n compose of Ti atoms of lower numbers of coordination with O atoms, providing many dangling bonds which considerably enhance the reactivity compared with its bulk counterpart. Two- and three-coordinated O atoms present for m/n ≤ 1.5, whereas two- and also single-coordinated O atoms are found for m/n > 1.5. The Ti n O m(n = 2–4, m < 2n) clusters show strong IR peaks in the range of 600–1100 cm-1 and strong Raman peaks in the region of 300–800 cm-1, whereas both the IR and Raman spectrum peaks of the Ti n O m(n = 2–4, m = 2n) clusters are in the region of 700–1100 cm-1. The main Raman peak of the Ti n O m(m ≠ 2n) clusters is at a frequency considerably lower than that of the IR spectrum. Our results can help understand the structure-property relationships of the Ti n O m clusters and provide their characteristic spectroscope features for further experimental identification.