Ablated matter expansion and crater formation under the action of ultrashort laser pulse

The action of a subpicosecond laser pulse on a target made of an absorbing condensed substance is considered. The propagation of an electron heat conduction wave and the crystal lattice heating prior to the hydrodynamic expansion of the target are analyzed. In these initial interaction stages, a heated layer with a thickness of d _T is formed at the target surface. The dependence of d _T on the absorbed laser energy density F[J/cm²] is evaluated. The motion of ablated matter in the expansion stage is described using a numerical solution of the equations of gasdynamics and the results of molecular dynamics (MD) simulations. The MD simulations are performed using a large number (～10³) of parallel processors, which allows the number of model atoms to be increased up to a level (about 3.5 × 10⁷) close to that encountered under real experimental conditions.     

The exchange and correlation energy at a metal surface

The change in exchange and correlation energy at a metal surface is calculated in the RPA for the infinite barrier model of a surface. At the electron density of Al, this is + 1350 erg/cm², much less than the values given by approximate solutions of the RPA equations. About half the change in correlation energy comes from the change in plasmon zero-point energy.     

Scaled Quantum Chemical Studies of the Molecular Structure and Vibrational Spectra of Minoxidil

The Fourier transform Raman and Fourier transform infrared spectra for minoxidil have been recorded in the region 4000—100 cm^?1 and 4000—450 cm^?1, respectively. The structural and spectroscopy data of the molecule in the ground state were calculated by using density functional theory methods with 6-311G (d, p) basis set. A detailed vibrational analysis of the title compound has been done using normal coordinate analysis following the scaled quantum mechanical force field methodology. The calculated molecular geometry parameters and scaled vibrational wavenumbers are well compared with the experimental data. The electronic properties, such as excitation energies, absorption wavelength, highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) energies were performed by time-dependent density functional theory approach, and the results are in good agreement with experimental absorption spectrum. The charge delocalizations of these molecules have been analyzed using natural bond orbital analysis. The molecule orbital contributions are studied by density of energy states. Fukui functions, local softness, and electrophilicity indices for selected atomic sites of the title compound are determined. Finally, the thermal behaviors of the compound have been calculated by different temperature.     

金属铝中层错能的缀加球面波法第一性原理计算

将层错周期地置入超晶胞中,当超晶胞有足够大的设置尺度时,相邻超晶胞中的层错彼此间互作用很小,从而以如此方式计算单一层错能量成为可能。用第一性原理途径(缀加球面波方法)计算了金属铝中的内禀和外延层错能,其理论值分别是Γ_ISF=154erg/cm²和Γ_ESF=138erg/cm²,与实验值符合较好。 关键词：     

Adhesion energy,surface traction and surface tension in liquid xenon

We calculated the adhesion energy, the surface traction and the surface energy of liquid xenon using molecular dynamics (MD) simulation. The value of the adhesion energy for liquid xenon at a reduced density of 0.630 was found to be 0.591 J/m² and the surface traction has a peak at z?=?3.32 Å. It was observed that the attraction of the molecules in the liquid surface which produces a resistance to penetration decreases with temperature. This may be attributed to the greater average separation of molecules at higher temperature.     

Monte Carlo investigation of the influence of V/III flux ratio on GaAs/GaAs(001) submonolayer epitaxy

The influence of the V/III flux ratio on the submonolayer growth of GaAs on the GaAs (001) surface is simulated by the Monte Carlo method. Growth is carried out using the method of molecular beam epitaxy at different values of process parameters. The surface density of islands against the V/III flux ratio is calculated. The saturation value of the surface density at 580°C is found to be 2 × 10¹² cm^–2, which is in agreement with the experimental data. The V/III flux ratio influences the island density most strongly at a reduced temperature (550°C) and an elevated growth rate (a monolayer per second), when the arsenic desorption is weak. The fraction of arsenic atoms in the growing film is estimated under different process conditions. It has been shown that, as the surface coverage rises, the influence of the V/III flux ratio on the fraction of arsenic atoms becomes weaker.     

Vibrational spectroscopy and density functional theory calculations of poly‐D‐mannuronate and heteropolymeric fractions from sodium alginate

The tetrasaccharide of 1 → 4β‐D‐mannopyranuronate (MM) and the alternating tetrasaccharide of 1 → 4 b‐D‐mannopyranuronate and 1 → 4α‐L‐gulopyranuronate (MG) were analyzed based on density functional theory (DFT) by employing the Gaussian 03 W package. The molecular geometries were fully optimized by using the Becke's three‐parameter hybrid exchange functional combined with Lee–Yang–Parr correlation functional (B3LYP) and using a 6‐31G(d,p) basis set. The calculated IR spectrum of MM presents a band at 1093 cm⁻¹ for C C stretching vibration, which is in good agreement with the experimental observation (1096 cm⁻¹) for the polymannuronate fraction obtained by partial hydrolysis of sodium alginate extracted from the hybrid brown seaweed Lessonia–Macrocystis. The calculated value at 826 cm⁻¹for MM is in close agreement with the experimental value and confirms that this band is characteristic of polymannuronate blocks. Most of the bands in the IR spectrum are also present in the observed Raman spectrum of the polymannuronate fraction. The experimental IR spectrum of heteropolymeric fraction obtained by partial hydrolysis of sodium alginate shows absorbances similar to those calculated for the model tetrasaccharide (MG). Surface‐enhanced Raman scattering (SERS) allows differentiation between the homopolymeric and heteropolymeric fractions of sodium alginate. The SERS spectrum of the heteropolymeric fraction shows an enhanced signal at 731 cm⁻¹which is present in the calculated Raman spectrum of the tetrasaccharide MG at 729 cm⁻¹. This band is assigned to the ring‐breathing deformation of the β‐D‐mannopyranuronate and α‐L‐gulopyranuronate residues. Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical investigation of ethylene/1-butene copolymerization process using constrained geometry catalyst (CpSiH2NH)-Ti-Cl2

The ethylene/1-butene copolymerization using constrained geometry catalyst CpSiH₂-NH-TiCl₂ (CGC) was investigated by the density functional theory and molecular dynamics. Structures and energetics of reactants, π-complexes, transition states, and products during insertion of ethylene and 1-butene monomers into the catalytic reactive site of the CGC were investigated by the density functional theory (DFT) using the software Dmol³, while dynamics of atoms during copolymerization process was investigated by classical molecular dynamics (MD) using the New-Ryudo-CR program. The calculated results were compared with the available experimental and theoretical ones. It was found that the ethylene insertion into Ti-Me active species is energetically more favorable than the butene one and the 2,1-butene insertion is more favorable than 1,2-butene one. Once the initial ethylene insertion has taken place, the further ethylene insertion occurring with a less energy barrier, in good agreement with experimental findings.     

Vibrational spectroscopy investigation using ab initio and density functional theory on flucytosine

The FT Raman and FTIR spectra of flucytosine were recorded in the region 3500–100 cm⁻¹ and 4000–400 cm⁻¹, respectively. The optimized geometry, wavenumber and intensity of the vibrational bands of flucytosine were obtained by ab initio and density functional theory (DFT) levels with complete relaxation in the potential energy surface using the 6‐31G(d,p) and 6‐311G(d,p) basis sets. A complete vibrational assignment aided by the theoretical harmonic frequency analysis is proposed. The harmonic vibrational wavenumbers calculated are compared with experimental FTIR and FT Raman spectra. The observed and the calculated wavenumbers are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar‐type spectrograms. Copyright © 2007 John Wiley & Sons, Ltd.     

Many-body effects in the first excited subband of the n-inversion layer of Si

We have calculated the self-energies of electrons in the lowest and first excited sub-bands of Si inversion layers. The self-consistent wavefunctions calculated in the Hartree approximation were used, and dynamic screening was approximated by the Lundqvist-Overhauser model. The correlation energy of an electron in the excited band is quite large: about ?10 meV at an inversion layer density of 10¹¹ cm^?2 to about ?16 meV at 3 × 10¹² cm^?2. The calculated separation between subbands is in very good agreement with available experimental measurements. An exciton is predicted with a binding energy of 0.9 meV at N_inv = 10¹² cm^?2 calculated in the static approximation.     

Tetrahedral ↔ octahedral network structure transition in simulated vitreous SiO2

By using molecular dynamics (MD) simulations we found a transition from a tetrahedral to an octahedral network structure in an amorphous SiO₂ model under compression from 2.20 to 5.35 g/cm³. And on heating of a high density amorphous (hda) model of 5.35 g/cm³ at zero pressure, the structure transforms to a low density amorphous (lda) form. Simulations were done in a model containing 3000 particles under periodic boundary conditions with interatomic potentials which have a weak Coulomb interaction and a Morse type short-range interaction.     

Self-consistent surface calculation of electron-hole drops in gallium phosphide

Self-consistent Kohn-Sham method is used to investigate the surface structure of electron-hole drops (EHD) in GaP. If the conduction bands are located on the X-point and have a degeneracy of 3, the surface tension is found to be 85 × 10^?4 erg cm^?2. In the presence of a “camel's-back” structure and a conduction band degeneracy of 6, the surface tension is calculated to be 130 × 10^?4 erg cm^?2. The surface charge on the EHD is found to be negative irrespective of whether the conduction band degeneracy is 3 or 6.     

FMR study of superparamagnetic Ni particles with weak and strong magnetic anisotropy

The method of ferromagnetic resonance (FMR) was used to study the process of thermal decomposition of the layered double hydroxides of lithium-aluminum and nickel-aluminum with intercalated EDTA complexes of nickel. The magnetic resonance spectra of nickel superparamagnetic nanoparticles were recorded at two temperatures (300 and 77 K). A computer simulation of FMR spectra was based on a modified statistic model which assumes the resonance of single-domain particles randomly oriented in an amorphous matrix. It is suggested that the line of the magnetic resonance of superparamagnetic particles narrows due to effects similar to those of dynamic narrowing in electron spin resonance and nuclear magnetic resonance spectra. In the framework of the model used, a fairly good agreement was achieved between calculated and experimental data. The formation of the two types of particles with strong (about 2·10⁶ erg/cm³) and weak (about 2·10⁵ erg/cm³) effective magnetic anisotropy was established.     

Ferromagnetic resonance of cobalt nanoparticles in the polymer shell

The magnetic properties of cobalt spherical nanoparticles (～ 5–9 nm in size) in a polymer shell are investigated using ferromagnetic resonance (FMR) spectroscopy. The metal-polymer complex is prepared through the frontal polymerization of the cobalt acrylamide (CoAAm) complex, followed by the thermolysis at a temperature of 643 K. Analysis of the ferromagnetic resonance spectra demonstrates that the material has a high blocking temperature of ～700 K. The anisotropy constant equal to 0.5 erg/cm³ is somewhat larger than the anisotropy constants characteristic of cobalt macrostructures. This difference is associated with the predominance of the surface anisotropy of nanoparticles. The surface anisotropy constant is calculated to be 0.17 erg/cm², and the anisotropy field is determined to be ～350 Oe. It is revealed that the polymer shell affects the magnetic properties of nanoparticles.     

Surface extended energy loss fine structure and local spin density investigation of carbidic carbon on the Ni(100) surface

The structural properties of a carbidic carbon layer on the Ni(100) surface have been investigated both experimentally by surface extended energy loss fine structure (SEELFS) and theoretically by the linear-combination-of-Gaussian-type-orbitals model-potential local-spin-density (LCGTO-MP-LSD) method. Both experimental and theoretical results indicate that the most stable site for carbon chemisorption is the fourfold hollow site. The Ni-C distance derived from SEELFS analysis was found to be 1.75 ± 0.05 Å, in good agreement with that obtained by theoretical calculation (1.79 Å). The calculated vibrational frequency of the adsorbed carbon atom is found to be 407 cm⁻¹ in excellent agreement with the experimental value of 410 cm⁻¹.     

Experimental and theoretical FT‐IR and FT‐Raman spectroscopic analysis of N1‐methyl‐2‐chloroaniline

In this work, the experimental and theoretical vibrational spectra of N1‐methyl‐2‐chloroaniline (C₇H₈NCl) were studied. FT‐IR and FT‐Raman spectra of the title molecule in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (B3LYP) with the 6‐311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT‐IR and FT‐Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. ¹³C and ¹H NMR chemical shifts results were compared with the experimental values. The optimized geometric parameters (bond lengths and bond angles) were given and are in agreement with the corresponding experimental values of aniline and p‐methyl aniline. Copyright © 2008 John Wiley & Sons, Ltd.     

Magnetization,AC susceptibility and microwave absorption in Tb and Gd70Tb30

Measurements of magnetization, ac susceptibility and microwave absorption at 9.5 and 35 GHz, have been carried out with single crystals of Tb and Gd₇₀Tb₃₀. The critical temperatures for Tb were in agreement with previous published results. The Curie Temperature for Gd₇₀Tb₃₀ was measured to be (275 ± 2) K. Anisotropy constants have been derived from the microwave measurements. The value of K₂ at 0 K is estimated to 8.8 × 10⁸ erg cm^-3 (Tb) and 1.3 × 10⁸ erg cm^-3 (Gd₇₀Tb₃₀). At 77 K, the value of K₆ is estimated to be 6 × 10⁴ erg cm^-3 (Gd₇₀Tb₃₀.     

The accuracy improvement of the correlation factor erg/cm2R for low-energy X-radiation

In this paper the results of calorimetric measurements of the correlation factor erg/cm² R for filtered and unfiltered X-radiation in the energy region up to 220 keV are given. The value of the correlation factor for X-radiation filtered by 3 mm Cu measured by a calorimeter is compared with the values of the correlation factor calculated by an independent method from the energy spectra of the same radiation. The initial spectra are obtained by means of a numerical graphical method from transmission curves measured by means of an ionization chamber in copper and tin.This comparison has shown very good agreement between the calorimetric value of the correlation factor 3·-45. 10³ erg/cm² R and those calculated by using White's values of the correlation factor depending on the X-radiation energy, provided the average energy required to produce an ion pair in air is 34·0 eV. The experimental results thus obtained enable us also to evaluate the amount of average effective energy of the measured X-radiation which is equivalent to the energy of monochromatic X-radiation having the same correlation factor, in comparison with the effective energy, currently determined by ionization measurements of the half-value layers.The paper is dedicated to Professor F.Bhounek, Member of the Czechoslovak Academy of Sciences, on his 70th anniversary.The authors wish to thank the head of the Laboratory, Academician F. Bhounek, for allround attention to this work, Ing. V. Boková for valuable aid in the theoretical considertions and calculations, and J. Homola for setting up and performing the experiments.     

Properties of the quasiparticle excitations in 207Pb and 209Pb from an extrapolation of the optical-model potential

A previously developed dispersion relation approach is used to calculate the shell-model potential in the case of neutrons in ²⁰⁸Pb, in the energy domain (-50 MeV, 0). This potential contains a dispersive contribution besides a Hartree-Fock type component, and thereby includes correlation and polarization effects. The shell-model and the Hartree-Fock type potentials are assumed to have Woods-Saxon shapes with diffuseness a_v = 0.70 fm; the energy dependence of their depths and radii is calculated. The energy dependence of the shell-model potential is characterized by the effective mass, whose dependence upon radial distance and neutron energy is determined. The effective mass is a sensitive function of energy, in contrast to its Hartree-Fock type component which is nearly independent of energy. Attention is drawn to the fact that the effective mass in nuclear matter cannot be straightforwardly identified with the effective mass at the nuclear centre. The effective mass presents a sharp peak at the nuclear surface near the Fermi energy and a dip at the surface for energies 10 to 20 MeV away from the Fermi energy. The spectroscopic factors of single-particle excitations in ²⁰⁷Pb and ²⁰⁹Pb are calculated from the difference between the effective mass and its Hartree-Fock type component. The predicted values of the valence single-particle wave functions at large radial distances are in fair agreement with experimental values deduced from analyses of sub-Coulomb pickup reactions. It is shown that the dispersive contribution increases the level density parameter by about 25%, in agreement with previous microscopic or semi-phenomenological models; the calculated level density parameter is in good agreement with the empirical value.     

Low temperature magnetic properties of Cr0.25Co0.25Zn0.5Fe2O4 nano particles

Low temperature Mössbauer and AC susceptibility have been used to study relaxation phenomena in nano-sized particles of Cr_0.25Co_0.25Zn_0.5Fe₂O₄. From these studies, the energy density constant for this system has been estimated to be 4 x 10⁶ erg/cm³. Cation distribution has also been determined and the observed results are correlated to calculated relaxation times.