Ab Initio Calculation

Ab inifio calculations are used to provide bond lengths, harmonic frequencies, and dissociation energies of low-lying electronic states for LiX, LiX+, and LiX-(with X = Li through F and Na through Cl). Most of these species represent hitherto experimentally unknown molecules or ions, which provides the focus of the work presented here. All of these species are stable to dissociation and the anions are stable to loss of an electron. Differences among the electronic structures of the valence isoelectronic LiX; and HX, LiX+, and HX+; and LiX-and HXspecies are analyzed. Optimized geometries, dissociation energies, ionization potentials, and electron affinities were calculated for the following ground states of the respective species: rZ+ for Li2('1:)

A theoretical study based on the density functional theory of the adsorption of Mn monomers and dimers on a Au-(111) surface is presented. As necessary preliminary steps, the bulk and clean surface electronic structure are calculated, which agree well with previous reports. Then, the electronic structure of the Mn adatom, chemisorbed on four different surface geometries, is analyzed. It is found that the most stable geometry is when the Mn atom is chemisorbed on threefold coordinated sites. Using this geometry for a single adatom a second Mn atom is chemisorbed and the most stable dimer geometrical structure is calculated. The lowest-energy configuration corresponds to the molecule lying parallel to the surface, adsorbed on two topological equivalent threefold coordinated sites. It is also found that the lowest-energy magnetic configuration corresponds to the antiferromagnetic arrangement with individual magnetic moments of 4.64μ B . Finally, it is concluded that the dimer is not stable and should fragment at the surface.

The interaction potential between benzene and O2 has been computed by means of SCF/MPZ calculations. The dominant attractive interaction is due to dispersion forces, therefore the choice of the basis set has been dictated by the requirement that the polarizabihties of the two partners be correctly reproduced. Basis set superposition error has been corrected for by the wunterpoise technique. According to the present results, in the complex Oz is parallel to the benzene plane. The computed dissociation energy is Dp 1.24 kcal/mol, which should be corrected upward to about 1.5. The ab initio results have been fitted by different analytical potential functions, in&d@ the atom-atom Lennard-Jones 6-12 formula and those used in several force-fields: MM2, MM3, ECEPP, CHARMM, AMBER, OPLS.

A set of vibrational circular dichroism (VCD) spectra in the CH-stretching fundamental region for about twenty compounds belonging to the class of essential oils was empirically analyzed by the use of a sort of vibrational exciton mechanism, involving three centers. Through a general formula applicable to many coupled dipole oscillators, the rotational strengths of the previously identified vibrational excitons are evaluated. The results are then critically reviewed by the use of recent ab initio methodology, as applied to selected molecules of the original set. Further insight is gained by model calculations adding up the contribution of the coupling between electric dipole moments associated with normal mode behavior and that of the polarizability from polarizable groups. The former part is responsible for the excitonic behavior of the VCD spectra. For the same selected molecules we have also investigated whether some excitonic behavior is taking place in the second overtone region, and have concluded that this is not the case.

Resonant Two Photon Ionization (R2PI) spectroscopy has been applied to the study of host-guest interactions in molecular clusters formed by supersonic exspansion. Here, the results of R2PI spectroscopy of the fluorinated organic molecules para and ortho-fluoro-secbutylbenzene and their complexes with water and argon are reported and discussed. In particular, it is shown that the position of the fluorine atom on the aromatic ring influences the formation of different kind of complexes (σ versus π) with argon and water. Ab initio calculations were performed to get insight into the molecular shape and the structure of these clusters.

AbstrAct Purpose: The wide-gap semiconductor materials are very important for application in the fields of optical device technology. ZnS is wide-gap semiconductor that is attractive material due to the polymorphic structural transformation and it is suitable semiconductor for applications in infrared optics, ultraviolet laser devices, electronic image display, high-density optical memory, solar cell etc. The goal is to evaluate mechanical and electrical properties of ZnS dunder pressure. Design/methodology/approach: We report ab-initio calculations of lattice constants, bulk modulus and elastic constants of the B1 (rocksalt), B3 (zincblende) and B4 (wurtzite) structures of ZnS. Ab-initio calculations are based on the density functional theory (DFT) within generalized gradient approximation (GGA) for the exchange-correlation potential. Findings: Phase transition pressures from B4 phase to B3 phase, from B3 phase to B1 phase and from B4 phase to B1 are predicted from intersection of the enthalpy-pressure data for the three phases. These results are consistent with the experimental and other theoretical calculations. Mechanical properties of ZnS under high pressure are also calculated. It is seen that the mechanical properties of ZnS under high pressure are quite different from those ambient condition. The band structure, density of states (DOS) and energy gaps are also given for B3 structure of ZnS. Research limitations/implications: The results are compared with the previous theoretical and experimental data. Originality/value: Evaluation of mechanic and electronical properties of ZnS under pressure.

Ab initio calculated coordinate and internal valence coordinate coefficients for each of the four spin-spin coupling surfaces of the acetylene molecule-1 J͑C, H͒, 1 J͑C, C͒, 2 J͑C, H͒, and 3 J͑H, H͒ are presented. Calculations were carried out at the SOPPA͑CCSD͒ level using a large basis set. Couplings were calculated at 35 geometries ͑including equilibrium͒ giving 35 distinct sites on the 1 J͑C, C͒ and 3 J͑H, H͒ surfaces and 53 distinct sites on the 1 J͑C, H͒ and 2 J͑C, H͒ surfaces. The results were fitted to fourth order in Taylor series expansions and are presented to second order in the coordinates. All couplings are sensitive to geometry with the principal features being ͑a͒ an even steeper increase of J͑C 1 , H 1 ͒ with CC bond stretching than with CH bond stretching-an example of ''unexpected differential sensitivity'' ͑or UDS͒, ͑b͒ very opposite variations of 2 J͑C 1 , H 2 ͒ with variations of the CC and C 2 H 2 bond lengths, ͑c͒ very opposite variations of 1 J͑C, C͒ with a CC stretch and a CH stretch and ͑d͒ very opposite variations of 1 J͑C 1 , H 1 ͒ with variations of the H 1 C 1 C 2 and C 1 C 2 H 2 angles with the latter variation being three times more effective ͑another example of UDS͒. The surfaces are averaged over a very accurate force field to give values of all couplings in the ten isotopomers containing all possible combinations of 12 C, 13 C, 1 H, and 2 H nuclei at 0 K and at a number of selected temperatures in the range accessible to experiment. The dominant nuclear motion effect comes from bending at the carbon atoms with stretching being of greater importance only for 1 J͑C, H͒. Agreement with recent experimental data both for the absolute values of the couplings and for isotope effects on them is generally very good although there are some disappointments for 1 J͑C, H͒. Values of the reduced coupling constants and their derivatives for the carbon-carbon and the one-bond carbon-proton coupling in acetylene are compared with recent results for some other molecules.

We present ab-initio investigation of the electronic and magnetic structure of TM(0 0 1) surfaces and TM/Cu(0 0 1) systems (TM = Fe, Co, Ni, Cu) with and without hydrogen adsorbed layer. The adsorption energy of hydrogen atom is found to be energetically more stable above the surface layer of Ni(0 0 1) surface than other TM(0 0 1) surfaces. The adsorption energies of hydrogen on TM/Cu(0 0 1) systems are larger than those on TM(0 0 1) surfaces. The relaxed geometries show that hydrogen has a strong influence on the interlayer distance. Furthermore, a marked reduction of Fe, Co, and Ni surface magnetic moments to 2.54, 1.41 and 0.25 m B , respectively, is obtained due to the presence of hydrogen.

We report on sizable antiferromagnetic interlayer exchange coupling (AFC) of Fe(001) layers across epitaxial Si spacers, for which epitaxial growth of a pseudomorphic phase stabilized by the interface is confirmed by low-energy electron diffraction and high-resolution transmission electron microscopy. The coupling strength decays with spacer thickness on a length scale of a few Å and shows a negative temperature coefficient. Transport measurements of lithographically structured junctions in current-perpendicular-to-plane geometry show the validity of the three “Rowell criteria” for tunneling: (i) exponential increase of resistance R with thickness of the barrier, (ii) parabolic dI/dV-V curves, and (iii) slight decrease of R with increasing temperature. Therefore, AFC is mediated by non-conductive spacers, which in transport experiments act as tunneling barriers with a barrier height of several tenths of an eV. We discuss our data — in particular the strength, thickness and temperature dependence — in the context of two previously proposed models for AFC across non-conducting spacers. We find that neither the molecular-orbital model for heat-induced effective exchange coupling nor the quantum interference model extended to insulator spacers by introducing complex Fermi surfaces can account for the strong AFC across epitaxial Si spacers and its negative temperature coefficient. The recently proposed defect-assisted interlayer exchange coupling model, however, yields qualitative agreement with the enhanced AFC and the temperature dependence.

Linear optical functions of cubic and hexagonal BN have been studied within first principles density functional theory in the local density approximation. Calculated energy-loss functions show reasonable agreement with experiments and previous theoretical results both for h-BN and for c-BN. Discrepancies arise between theoretical results and experiments in the imaginary part of the dielectric function for c-BN. Possible explanations of this mismatch are proposed and evaluated: lattice constant variations, h-BN contamination in c-BN samples, and self-energy effects.

We have carried out extensive ab initio calculations on the energetics of gold atoms deposited on graphite surfaces, using different geometries and approximations. We consistently find that gold adatoms easily diffuse over this surface with a diffusion barrier of 0.05 eV. The adsorption energy is found to be more difficult to quantify within density functional theory. Combining our calculations with experimental values, we can estimate this adsorption energy to be of order 0.45 eV.

We have used positron annihilation spectroscopy to study the high-pressure annealing induced thermal recovery of vacancy defects in free-standing GaN grown by hydride vapor phase epitaxy (HVPE). The results show that the in-grown Ga vacancy complexes recover after annealing at 1500 -1700 K. Comparison of the experimental positron data with ab-initio calculations indicates that the Doppler broadening measurement of the electron momentum distribution is sensitive enough to distinguish between the N and O atoms surrounding the Ga vacancy. We show that the difference between the isolated V Ga in electron irradiated GaN and the V Ga -O N complexes in highly O-doped GaN is clear, and the Ga vacancy related defect complexes that start dissociating at 1500 K can be identified as V Ga -O N pairs.

In this work the complete valence-band structure of the molybdenum dichalcogenides MoS2, MoSe2, and α-MoTe2 is presented and discussed in comparison. The valence bands have been studied using both angle-resolved photoelectron spectroscopy (ARPES) with synchrotron radiation, as well as, ab-initio band-structure calculations. The ARPES measurements have been carried out in the constant-final-state (CFS) mode. The results of the calculations show in general very good agreement with the experimentally determined valence-band structures allowing for a clear identification of the observed features. The dispersion of the valence bands as a function of the perpendicular component k ⊥ of the wave vector reveals a decreasing three-dimensional character from MoS2 to α-MoTe2 which is attributed to an increasing interlayer distance in the three compounds. The effect of this k ⊥ dispersion on the determination of the exact dispersion of the individual states as a function of k is discussed. By performing ARPES in the CFS mode the k -component for off-normal emission spectra can be determined. The corresponding k ⊥ -value is obtained from the symmetry of the spectra along the ΓA, KH, and ML line, respectively.

We present ab initio calculations of the exchange coupling for Co/Ir systems using a selfconsistent full-potential linearized augmented plane-wave (FLAPW) method. The local spin density approximation (LSDA) as well as the generalized gradient approximation of (GGA) are used to treat the exchange correlation potential. Structural optimization is considered for all systems due to the size difference between Co and Ir atoms. We obtain an oscillatory behavior for the interlayer exchange coupling with a period of 5.83Å, for both LSDA as well as GGA-PBE. The first antiferromagnetic peak is found for an Ir spacer of thickness 3.74Å, with strength of J = 51.09 mJ/m 2 for the GGA-PBE and 37.00 mJ/m 2 for the LSDA. PACS. 71.15.-m Methods of electronic structure calculations -73.61.-r Electrical properties of specific thin films

The termolecular association reaction OH + NO2 + M was studied in a low-pressure discharge flow reactor, and both HONO2 and HOONO products were detected by infrared cavity ringdown spectroscopy (IR-CRDS). The absorption spectrum of the fundamental Ó1 band of the cis-cis isomer of HOONO (pernitrous or peroxynitrous acid) was observed at 3306 cm-1, in good agreement with matrix isolation

The foundations and limits of Sϭ 1 2 and Sϭ1 spin Hamiltonians for systems with two unpaired electrons in two well-defined orbitals per site are discussed by merging accurate ab initio calculations in binuclear systems with the effective Hamiltonian theory. It is shown that, beyond the usual J i j Ŝ i •Ŝ j terms, the effective spin Hamiltonian necessarily introduces four-body spin operators in the Sϭ 1 2 case and biquadratic terms in the S ϭ1 formalism. The order of magnitude of these additional terms can be rationalized from a quasidegenerate perturbation theory expansion starting from a Hubbard-type Hamiltonian. This permits to discuss the physical mechanisms governing the reduction from the all electron Hamiltonian to the spin-only Hamiltonians and the conditions under which a further reduction from a spin Hamiltonian to the simplest Heisenberg-Dirac-Van Vleck form is possible. The overall discussion is illustrated by numerical calculations of the magnetic coupling between two Ni 2ϩ cations in the K 2 NiF 4 perovskite and between triply bonded carbon atoms in poly-ynes.

Conformational stability Xenon and krypton solutions Infrared and Raman spectra r 0 Structural parameters Ab initio calculations Ethylisocyanate a b s t r a c t Variable temperature (À55 to À155°C) studies of the infrared spectra (400-3500 cm À1 ) of ethylisocyanate, CH 3 CH 2 NCO, dissolved in liquid xenon and krypton have been recorded. Additionally the infrared spectra of the gas and solid have been re-investigated. These spectroscopic data indicate two conformers in the fluid states which are the cis and trans forms with a large proportion of molecules in the gas phase at ambient temperature in the excited states of the NCO torsional mode which has a very low barrier to conformational interchange. Variable temperature (À110 to À155°C) studies of krypton solutions were carried out and by using two conformer pairs, an enthalpy difference of 100 ± 4 cm À1 (1.20 ± 0.05 kJ/mol) was obtained with the cis conformer the more stable form. To aid in the analyses of the vibrational and rotational spectra, ab initio calculations have been carried out by the perturbation method to the second order (MP2) with full electron correlation using a variety of basis sets up to 6-311+G(2df,2pd) and cc-PVQZ. With the basis sets 6-311+G(2d,2p) and larger, the barrier at the cis position ranged from a low value of 11 cm À1 to a high value of 31 cm À1 with a value of 19 cm À1 from the largest basis set of cc-PVQZ. Thus, the gauche well is probably so shallow that it does not contain a bound vibrational state. This results in the cis conformer as the most stable form which is consistent with the experimental rotational and vibrational data. The predicted energy difference from these calculations between the cis conformer and the transitional-state skew form is $100 cm À1 which is consistent with the assigned microwave lines for four excited states of the NCO torsion. Density functional theory calculation by the B3LYP method with many of the same basis sets provided little information. By utilizing the previously reported microwave rotational constants with the structural parameters predicted by the ab initio MP2(full)/6-311+G(d,p) calculations, adjusted r 0 structural parameters have been obtained for the cis form. The determined heavy atom parameters are: r(C@N) = 1.211(5), r(C@O) = 1.167(5), r(CAN) = 1.448(5), r(CAC) = 1.516(5) Å for the distances and angles of \CCN = 112.6(5), \CNC = 137.5(5), \NCO = 172.9(5)°. The centrifugal distortion constants, dipole moments, conformational stability, vibrational frequencies, infrared intensities and Raman activities have been predicted from ab initio calculations and compared to experimental quantities when available. These results are compared to the corresponding quantities of some similar molecules.

As a step toward absolute calibration of optical tweezers, a first-principles theory of trapping forces with no adjustable parameters, corrected for spherical aberration, is experimentally tested. Employing two very different setups, we find generally very good agreement for the transverse trap stiffness as a function of microsphere radius for a broad range of radii, including the values employed in practice, and at different sample chamber depths. The domain of validity of the WKB (``geometrical optics'') approximation to the theory is verified. Theoretical predictions for the trapping threshold, peak position, depth variation, multiple equilibria, and ``jump'' effects are also confirmed.

We propose a model of the oxygen-deficiency-related defect in silica glass on the basis of the ab initio molecular-orbital calculations. This model can be regarded as an oxygen vacancy derived from the edgesharing structural unit and will be inherent in glassy silica. Our calculations demonstrate that this defect can be transformed into the structurally stable hole trapping center whose calculated hyperfine parameters quantitatively reproduce the experimental hyperfine features observed for the E ␥ Ј center in silica glass.

First-order Raman spectra of wurtzite GaN made from natural Ga and isotopically pure 15 N and natural N ͑99.63% 14 N͒ were measured at low temperature. The Raman frequencies of the polar optical phonons ͓A 1 ͑TO, LO͒, E 1 ͑TO,LO͔͒ shift according to the inverse square root of the reduced masses, as expected. The isotope shifts of the two nonpolar E 2 modes deviate significantly from the reduced-mass behavior as well as from the dependence expected for pure N or Ga vibrations which might be expected in view of their large frequency difference. This indicates that the E 2 modes involve mixed Ga and N vibrations. From fits to the experimental data with a coupled two-mode model we determine the mode eigenvectors. They confirm the results of an ab initio calculation which we have done for the zone-center vibrations of wurtzite GaN. Our calculations also predict a vanishing coupling between the two B 1 silent modes. We also measured a nat Ga 14 N 0.5 15 N 0.5 alloy sample. Additional negative frequency shifts due to isotope disorder are observed for the A 1 ͑TO͒, E 1 ͑TO͒, and the high-frequency E 2 modes as compared to the reduced-mass or coupled-mode behavior. An estimate from second-order perturbation theory provides a quantitative explanation of this result.

Ab initio calculations at the CIS level of theory combined with several basis sets were performed to elucidate the geometry of the two lowest pp* singlet states of aniline. A global picture emerges from this study. The 6-31CCG* basis set was the only one to give convergence for the S 1 and S 2 states while, for example, the CIS/6-31G* results refer to the S 2 state and the S 1 optimization does not converge. Aniline in the S 1 state is quinoidal; in the S 2 state the ring expands relative to the ground state. Planar geometry is predicted for both states. q

This review covers the outer core level photoionization of the free 3d metal atoms from Sc to Cu. The experimental 3p, 3s and 2p photoemission and photoabsorption spectra are discussed. A comparison emphasizes common features and distinct differences. The interpretation of the data based on ab initio calculations reveals the influence of multi-electron interactions in the 3d metal atoms. We focus on the fundamental effects and main interactions which govern the electronic structure of these open shell atoms.

The crystal structure of RU60358, C 20 H 21 NO 3 , has been determined using X-ray diffraction to establish the configuration and stereochemistry of the molecule around the C15-C16 triple bond. The compound crystallises in the orthorhombic space group P2 1 2 1 2 1 , a = 7.7575, b = 11.3182, c = 21.3529Å, V = 1874.80Å3 and Z = 4. The structure has been refined to a final R = 0.068 for the observed structure factors with I ≥ 3σ (I). The refined structure was found to be significantly non planar. A comparative study, using the ab initio calculations of the structure at B3LYP/6-31G** levels of theory, shows good geometrical agreement with the X-ray diffraction data. Standard deviations between the calculated and experimental bond values have been shown to be 0.01 Å and 0.5° for bond angles. Vibrational wavenumbers were obtained from a normal mode analysis using the ab initio calculations.

In this Letter we investigate boron diffusion as a function of the Fermi-level position in crystalline silicon using ab initio calculations. Based on our results, a new mechanism for B diffusion mediated by Si self-interstitials is proposed. Rather than kick out of B into a mobile channel, we find a direct diffusion mechanism for the boron-interstitial pair for all Fermi-level positions. Our activation energy of 3.5 3.8 eV, migration barrier of 0.4 0.7 eV, and diffusion-length exponent of 20.6 to 20.2 eV are in excellent agreement with experiment. PACS numbers: 66.30.Jt, 31.15.Ar, 71.55.Cn

The weakly bound HOONO product of the OHϩNO 2 ϩM reaction is studied using the vibrational predissociation that follows excitation of the first OH overtone (2 1 ). We observe formation of both cis-cis and trans-perp conformers of HOONO. The trans-perp HOONO 2 1 band is observed under thermal ͑223-238 K͒ conditions at 6971 cm Ϫ1 . We assign the previously published ͑warmer temperature͒ HOONO spectrum to the 2 1 band at 6365 cm Ϫ1 and 2 1 -containing combination bands of the cis-cis conformer of HOONO. The band shape of the trans-perp HOONO spectrum is in excellent agreement with the predicted rotational contour based on previous experimental and theoretical results, but the apparent origin of the cis-cis HOONO spectrum at 6365 cm Ϫ1 is featureless and significantly broader, suggesting more rapid intramolecular vibrational redistribution or predissociation in the latter isomer. The thermally less stable trans-perp HOONO isomerizes rapidly to cis-cis HOONO with an experimentally determined lifetime of 39 ms at 233 K at 13 hPa ͑in a buffer gas of predominantly Ar͒. The temperature dependence of the trans-perp HOONO lifetime in the range 223-238 K yields an isomerization barrier of 33Ϯ12 kJ/mol. New ab initio calculations of the structure and vibrational mode frequencies of the transition state perp-perp HOONO are performed using the coupled cluster singles and doubles with perturbative triples ͓CCSD͑T͔͒ model, using a correlation consistent polarized triple basis set ͑cc-pVTZ͒. The energetics of cis-cis, trans-perp, and perp-perp HOONO are also calculated at this level ͓CCSD͑T͒/ cc-pVTZ͔ and with a quadruple basis set using the structure determined at the triple basis set ͓CCSD͑T͒/cc-pVQZ//CCSD͑T͒/cc-pVTZ͔. These calculations predict that the anti form of perp-perp HOONO has an energy of ⌬E 0 ϭ42.4 kJ/mol above trans-perp HOONO, corresponding to an activation enthalpy of ⌬H 298 ‡0 ϭ41.1 kJ/mol. These results are in good agreement with statistical simulations based on a model developed by Golden, Barker, and Lohr. The simulated isomerization rates match the observed decay rates when modeled with a trans-perp to cis-cis HOONO isomerization barrier of 40.8 kJ/mol and a strong collision model. The quantum yield of cis-cis HOONO dissociation to OH and NO 2 is also calculated as a function of photon excitation energy in the range 3500-7500 cm Ϫ1 , assuming D 0 ϭ83 kJ/mol. The quantum yield is predicted to vary from 0.15 to 1 over the observed spectrum at 298 K, leading to band intensities in the action spectrum that are highly temperature dependent; however, the observed relative band strengths in the cis-cis HOONO spectrum do not change substantially with temperature over the range 193-273 K. Semiempirical calculations of the oscillator strengths for 2 1 (cis-cis HOONO) and 2 1 (trans-perp HOONO) are performed using ͑1͒ a one-dimensional anharmonic model and ͑2͒ a͒

Dipole polarizabilities of individual ions and molecules are computed from first principles in three condensed-phase systems: pure water, pure hydrofluoric acid, and an equimolar mixture of water and hydrofluoric acid in which HF is mostly ionized. We find that the polarizability of fluorine and oxygen centers varies linearly with the value of the bond order, which measures the local degree

Intermolecular complexes of methanethiol with sulfur dioxide have been prepared by condensing the reagents diluted in argon and in nitrogen at 12-14 K. The 1:1 CH 3 SH/SO 2 complexes were identified from the infrared spectra of the mixtures of methanethiol with sulfur dioxide in argon and nitrogen matrices. Perturbations to the vibrational energy spaces of some vibrational modes were identified and assigned. Ab initio calculations with the 6-311G ‫ءء‬ basis set have been performed to get some information about the structure, binding energy, dipole moment, and potential function governing the internal rotation of SO 2 for the complex. The calculated results have suggested that the dipole/dipole interaction held the constituent species together to form the complex. Photochemical reactions were performed by exposing the matrix mixtures to UV irradiation. The appearance of new bands indicated the presence of more than one photochemical reaction product. ᭧

The crystal structure of a high-pressure phase of silane ͑SiH 4 ͒, observed between 10 and 25 GPa, is solved using powder synchrotron x-ray diffraction and shown to be of the SnBr 4 type. The phase is an insulating molecular solid with a monoclinic unit cell containing four tetrahedrally bonded molecules, space group P2 1 / c. Ab initio calculations show the SnBr 4-type structure to be favored in this pressure range relative to other recently proposed structures. The fit of the pressure dependence of volume to the Birch-Murnagham equation of state gives the following parameters at ambient pressure if K 0 Ј is fixed to 4: V 0 = 250͑9͒ Å 3 and K 0 = 7.8͑9͒ GPa for the experimental data, and V 0 = 255͑2͒ Å 3 and K 0 = 6.1͑2͒ GPa for the data obtained from ab initio calculations.

Scanning tunneling microscopy ͑STM͒ and ab initio calculations based on density functional theory ͑DFT͒ were used to study the self-aligned silicon nanoribbons on Ag͑110͒ with honeycomb, graphene-like structure. The silicon honeycombs structure on top of the silver substrate is clearly observed by STM, while the DFT calculations confirm that the Si atoms adopt spontaneously this new silicon structure.

The band structure of silicon (Si) under arbitrary stress/strain conditions is calculated using the empirical nonlocal pseudopotential method. The method is discussed with a special focus on the strain induced breaking of crystal symmetry. It is demonstrated that under general stress the relative movement of the sublattices has a prominent effect on the conduction band masses. This displacement, which cannot be determined from macroscopic strain, is extracted from ab initio calculations. The transport properties of strained Si are investigated by solving the semi-classical Boltzmann equation using the Monte Carlo (MC) method. It is shown that the change of the electron effective mass induced by uniaxial stress has to be included in accurate models of the electron mobility.

We present a study of several neutral and charged self-defects in a model cell of amorphous silica. We performed ab initio calculations using plane waves pseudopotential method in the framework of density functional theory using the local density approximation. We show the structures and the corresponding formation energies for vacancies and interstitials in several charged states for every possible defect site in our amorphous supercell. The obtained results on amorphous silica are compared to previous ones on a-quartz. The oxygen interstitials are found to be the dominant defects. The variation of formation energies as a function of the Fermi level at 300 K are represented and analyzed.

Electronic transport in ferromagnetic ballistic conductors is predicted to exhibit ballistic anisotropic magnetoresistance—a change in the ballistic conductance with the direction of magnetization. This phenomenon originates from the effect of the spin-orbit interaction on the electronic band structure which leads to a change in the number of bands crossing the Fermi energy when the magnetization direction changes. We illustrate the

Atomic polarization phenomena impinge upon a number of areas and processes in physics. The dielectric constant and refractive index of any gas are examples of macroscopic properties that are largely determined by the dipole polarizability. When it comes to microscopic phenomena, the existence of alkaline-earth anions and the recently discovered ability of positrons to bind to many atoms are predominantly due to the polarization interaction. An imperfect knowledge of atomic polarizabilities is presently looming as the largest source of uncertainty in the new generation of optical frequency standards. Accurate polarizabilities for the group I and II atoms and ions of the periodic table have recently become available by a variety of techniques. These include refined many-body perturbation theory and coupled-cluster calculations sometimes combined with precise experimental data for selected transitions, microwave spectroscopy of Rydberg atoms and ions, refractive index measurements in microwave cavities, ab initio calculations of atomic structures using explicitly correlated wave functions, interferometry with atom beams, and velocity changes of laser cooled atoms induced by an electric field. This review examines existing theoretical methods of determining atomic and ionic polarizabilities, and discusses their relevance to various applications with particular emphasis on cold-atom physics and the metrology of atomic frequency standards.

The complete piezoelectric tensors of both the wurtzite and zinc blende polymorphs of ZnO and ZnS have been computed by ab initio periodic linear combination of atomic orbitals (LCAO) methods, based mainly on the Hartree -Fock Hamiltonian, with an all-electron Gaussian-type basis set. The computational scheme was based on the Berry phases theory, yielding directly the proper piezoelectric stress coefficients e ik ¼ ð›P i =›1 k Þ E ; also the strain coefficients d ik ¼ ð›1 k =›E i Þ t were obtained, by intermediate calculation of the full elasticity tensors of all four crystals. In particular, the e 15 wurtzite shear constants were included for the first time in such calculations. A careful study of the clamped-ion and internal-strain piezoelectric components shows that the latter ones are well simulated by classical point-charge calculations including quantum-mechanical structural relaxation. The much larger piezoelectric response of ZnO with respect to ZnS is explained by analysing signs and ratios of the respective clamped-ion and internal-strain components. q

Initiation kinetics in free radical polymerization is investigated using density functional theory. Thermodynamic and kinetic parameters of the initiation reactions are predicted, and the role of the initiators in the polymerization process is evaluated. Methyl acrylate, methyl methacrylate, acrylonitrile, and styrene homo-polymerizations with different initiators are studied. Reaction enthalpy and activation energy for each reaction between monomer and the radical fragments arising from the initiators have been determined. The initiation kinetic constants for all of these initiation reactions are evaluated and compared with both computational and experimental propagation kinetic constants of each monomer.

A new method, based on the functional formulation of the theory of quantum mechanism multichannel scattering for three-body collinear systems is proposed. Based on intrinsic properties of scattering system the numerical task was divided into independent subtasks and the parallel algorithm for numerical computations was developed and tested on massive-parallel systems Parsystec CC/16 and SPP-1600. It was shown that efficiency of such algorithm scales linearly. This algorithm makes it possible to carry out converging computations for three-body problem for any energy. It is shown, that even in this simple case the principle of quantum determinism in the general case breaks down and we have a micro-irreversible quantum mechanics. The ab initio calculations of the quantum chaos (wave chaos) for the first time were carried out on the example of an elementary chemical reaction Li+(FH)→(LiFH) *→(LiF)+H.

Conformational analysis of trans-1,2-disubstituted cyclohexane CCR3 antagonist 2 revealed that the cyclohexane linker could be replaced by an acyclic syn-a-methyl-b-hydroxypropyl linker. Synthesis and biological evaluation of mono-and disubstituted propyl linkers support this conformational correlation. It was also found that the a-methyl group to the urea lowered protein binding and that the b-hydroxyl group lowered affinity for CYP2D6. Ab initio calculations show that the a-methyl group governs the spatial orientation of three key functionalities within the molecule. a-Methyl-b-hydroxypropyl urea 31 with a chemotaxis IC 50 = 38 pM for eosinophils was chosen to enter clinical development for the treatment of asthma.

The electric dipole moments of the isolated amino acid tryptophan and small glycine-based peptides (WGn, n = 1−5, W = tryptophan, G = glycine) have been measured by deflection of a molecular beam in an inhomogeneous electric field. The measurements are compared to the results of ab initio calculations and Monte-Carlo simulations. The conformation and the flexibility of the peptides, at different temperatures, are discussed. The WGn peptides are much more floppy than an isolated tryptophan, even a single glycine is enough to make the peptide floppy on the timescale of the electric deflection measurements.