Parameter-free Calculation Research Articles

A three-body Glauber model for polarized deuteron scattering at intermediate energies

A parameter-free Glauber model calculation for deuteron-nucleus elastic scattering is carried out with full spin-dependence, which takes as its starting point the Dirac optical model for the underlying nucleon-nucleus potentials. The calculation includes effects due to the breakup of the deuteron to both triplet and singlet spin intermediate states. The observables for the reaction 58 Ni( d, d) at 400 and 700 MeV are calculated and found to reproduce the experimental data quite well.

Freezing of the vortex liquid in high-Tc superconductors: A density-functional approach.

The structure of the unpinned vortex fluid in layered oxide high-temperature superconductors is investigated numerically using appropriate classical liquid-state theory, for magnetic fields B perpendicular to the layer plane. The direct correlation function so obtained is used as input for a first-principles, parameter-free calculation of the discontinuous fluid-to-Abrikosov-lattice transition boundary ${\mathit{T}}_{\mathit{f}}$(B). This transition boundary is found to have a shape and location similar to that observed in strongly anisotropic materials, e.g., Bi-Sr-Ca-Cu-O.

Characterization of surface phonons on Cu(001) and Ag(001): First-principles phonon calculations with experimental and theoretical studies of high-resolution electron-energy-loss spectra.

A parameter-free first-principles phonon calculation is combined with a multiple-scattering electron-energy-loss-spectra calculation to characterize surface phonons of Cu(001) and Ag(001). The electron-energy-loss data on Cu(001) reveal the gap mode ${\mathit{S}}_{6}$ at X\ifmmode\bar\else\textasciimacron\fi{}, which has been detected before only for Ni(001). The calculations also discover two additional surface modes on these surfaces, and the inelastic-electron-scattering cross sections of these modes are investigated. With the discovery of these modes, and knowledge about their inelastic-cross-section behavior, data of inelastic electron scattering are very satisfactorily explained. We also suggest that the mode found at X\ifmmode\bar\else\textasciimacron\fi{} could explain a recent He-atom scattering experiment. A comprehensive picture is established for the surface phonons on Cu(001) and Ag(001).

Structural phase diagram and equilibrium oxygen partial pressure of YBa 2Cu 3O 6 + x

An experimental technique by which in-situ gas volumetric measurements are carried out on a neutron powder diffractometer, is presented and used for simultaneous studies of oxygen equilibrium partial pressure and the structural phase diagram of YBa 2Cu 3O 6 + x. Experimental data was collected under near equilibrium conditions at 350 points in (x,T)-space with 0.15 < x < 0.92 and 25 °C < T < 725 °C. Precise values of oxygen stoichiometries (absolute values of x within 0.02) were obtained by use of the ideal gas law in connection with iodiometric titration and structural analyses. The temperature variations in lattice parameters were measured and used to establish the structural phase diagram. Pure tetragonal or orthorhombic phases were found. The (x,T) phase boundary for transition from tetragonal to orthorhombic symmetry gives strong support for a recent parameter free 2D Ising model calculation of the ordering of oxygen. Oxygen equilibrium partial pressure shows significant variations with temperature and concentration which indicate that x = 0.15 and x = 0.92 are minimum and maximum oxygen concentrations. Measurements of oxygen in-diffusion flow show relaxation type behaviour: J = J 0 exp( −t τ ) . The prefactor j 0 is activated with activation energies decreasing from 1.5 eV ( x = 0.25) to 1.0 eV ( x = 0.8). The relaxation time τ shows an anomalous behaviour that may be correlated with first order phase transitions predicted from theoretical model calculations.

Auger and resonant neutralization of low energy ions near metal surfaces

We provide a parameter-free perturbation theory calculation of the probability of charge capture via the direct Auger process to-slow ions scattering from simple metals. The results are sensitively dependent on the surface electron density profile and atomic wavefunction distortion in the near surface region. The time development of the atomic state occupation is examined in the limit of Auger coupling alone. The resonant and Auger transition rates to the 1s state of hydrogen scattered from aluminium, calculated using comparable models, are found to be essentially identical for ion-surface separations exceeding 2 a 0.

Microscopic description of heavy-ion scattering in the nuclear matter picture

A microscopic parameter-free calculation of the heavy-ion optical potential is presented. Assuming the dominance of nucleon-nucleon collisions in the reaction dynamics, a description of these processes is translated into a two-Fermi-sphere nuclear matter picture, using a generalized local-density approximation. The calculation of reaction cross sections for the systems 40Ar + 60Ni, 120Sn, 208Pb which were recently measured at E lab = 1760 MeV, confirms the dominance of NN collisions. As previously shown for light systems, some importance must be attributed to the excitation of collective states which are calculated in coupled channels in describing the reactions at lower energies, although volume effects dominate. For the calculation of the effective NN interaction in the medium ( G-matrix) a two-step procedure is introduced which allows one to calculate the imaginary part of the reaction matrix reliably in spite of its sensitivity to the Pauli operator.

The reaction mechanism of heavy ion scattering at intermediate energies

The contribution to the real and imaginary nucleus-nucleus (N-N) optical potential from nucleon-nucleon scattering in the medium is calculated in a local density approximation from a two Fermi sphere nuclear matter picture for the N-N collision. This reaction mechanism is shown to be dominant for 12C + 12C scattering at all considered energies (160 MeV < E lab < 2250 MeV) giving a weakly energy dependent reaction cross section of about 900 mb. Inclusion of the collective 2 +, 3 − excitations in a coupled channel calculations gives good agreement for both the measured elastic and inelastic 2 + cross section at E lab = 1016 MeV. This fully microscopic parameter free calculation indicates that the energy dependence of the reaction cross section for this system is mostly due to the decrease of the collective contribution with increasing energy contrary to current theoretical models.

The Kawarabayashi-Suzuki-Riazuddin-Fayyazudin relation and strong mesonic couplings in the cloudy bag model

The Cloudy Bag Model (CBM) provides a theory of ωϱπ, ϱππ, K ∗Kπ and K ∗K ∗π couplings that yields excellent agreement with experiment in a parameter-free calculation. The Kawarabayashi-Suzuki-Riazuddin-Fayyazudin (KSRF) relation is derived from the CBM and ‖ ϱ is computed.

Diffraction theory and the double-charge-exchange reactionO18(π+, π−)Ne18

The angular distribution and the excitation function of the reaction /sup 18/O(..pi../sup +/,..pi../sup -/) /sup 18/Ne (double isobaric analog state) can be well understood in the framework of a coupled-channel diffractive scattering theory provided we include higher-order processes. Use of a scaling theory allows an essentially parameter-free calculation of these processes and makes possible the study of effects arising from finer aspects of nuclear structure such as the core excitation of /sup 18/O.

Parameter-free calculation of the enhanced spin susceptibility of Nb3Sn including electron-phonon effects

Abstract A parameter-free calculation of the spin susceptibility χsp(T) of Nb3Sn, which includes static and dynamic disorder as well as exchange-correlation enhancement, is presented. It is found that χsp is only 15% of the measured susceptibility, and its small temperature dependence cannot account for the experimental findings.

Theory of the specific-heat coefficient of a Hume-Rothery alloy

The coefficient of the linear part of the low-temperature specific heat is calculated for alloys of zinc in copper having three different concentrations. The densities of states are obtained from a parameter-free calculation based on the Korringa-Kohn-Rostocker coherent-potential approximation, and the electron-phonon enhancement factors are estimated from resistivity data. The results of the historically important experiments on this system are reproduced in detail.

Systematic features of the pion-nucleus interaction

We analyze pion elastic-scattering data for $^{40}\mathrm{Ca}$ and $^{48}\mathrm{Ca}$ using a covariant theory of the optical potential developed previously. Combining these results with the information obtained from the analysis of pion scattering from $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ reported earlier, we are able to discuss the systematics of the pion-nucleus optical potential. Our model contains a first-order optical potential which is obtained from a parameter-free calculation. The parameters of a second-order potential are determined by requiring that the sum of the first-and second-order potentials provides a fit to the elastic-scattering data. The parameters of the second-order potential exhibit a smooth dependence on energy and target mass number. These parameters have a marked resonance behavior. We find that the maximum value of the magnitude of the imaginary part of the second-order potential occurs at about 150 MeV while the first-order potential has a maximum for the magnitude of the imaginary part at about 240 MeV. The imaginary part of the first-order potential has a width at half maximum of about 200 MeV. This corresponds to a kinematic broadening of the (3,3) resonance due to the effects of the Fermi motion of the target nucleons. (This increased width is unrelated to the effects of the true absorption process or of collision broadening.) We also find a significant isospin violation in the second-order potential. For example, the imaginary part of the second-order potential for ${\ensuremath{\pi}}^{\ensuremath{-}}$ scattering is found to be systematically larger than that for ${\ensuremath{\pi}}^{+}$ scattering for nuclei with $N=Z$. An explanation for this feature of the optical potential is presented.NUCLEAR REACTIONS Elastic scattering of pions from $^{40}\mathrm{Ca}$ (40-241 MeV) and $^{48}\mathrm{Ca}$ (130 MeV). Systematics of first- and second-order optical potentials.

Multiquark states. II.QQ¯andQ2Q¯2mesons

In the previous paper we proposed a phenomenological mass formula based on the MIT bag model. We used it to describe the spectrum of baryon resonances. Now it is applied to the QQ-bar and Q/sup 2/Q-bar/sup 2/ states. Using the results for the QQ-bar meson spectrum we are able to perform a parameter-free calculation of the Q/sup 2/-Q-bar/sup 2/ (baryonium) spectrum. The other orbitally excited Q/sup 2/Q-bar/sup 2/ configurations are also studied. We find natural interpretations for the narrow NN-bar resonances, e.g., for the S (1936), which we predict to have J/sup P/C=2/sup - -/ and I=0, 1, and 2 components.

Calculation of Thermal Expansion, Compressiblity, an Melting in Alkali Halides: NaCl and KCl

A parameter-free calculation of the equation of state for KCl and NaCl is presented which gives an accurate prediction of the equilibrium lattice constant over wide-ranging values of pressure and temperature. The results also show a lattice instability which is consistent with melting.

A realistic complex interaction for elastic and inelastic nucleon scattering

A parameter-free microscopic calculation for the elastic and inelastic scattering of protons is presented using a complex nuclear matter t-matrix interaction which was generated from the Hamada-Johnston internucleon potential. The transitions 27Al(p,n) and 40Ca(p,p') are analyzed.

The response of the Limulus retina to moving stimuli: a prediction by Fourier synthesis.

The Limulus retina responds as a linear system to light stimuli which vary moderately about a mean level. The dynamics of such a system may conveniently be summarized by means of a spatiotemporal transfer function, which describes the response of the system to moving sinusoidal gratings. The response of the system to an arbitrary stimulus may then be calculated by adding together the system's responses to suitably weighted sinusoidal stimuli. We have measured such a spatiotemporal transfer function for the Limulus eye. We have then accurately predicted, in a parameter-free calculation, the eye's response to various stimulus patterns which move across it at several different velocities.

A prioricalculation of then=1valence exciton of solid neon

The energies of the $n=1$ excitons in solid neon have been calculated on the basis of the ab initio repulsive-potential curves of the molecular excited states derived from $^{3}P$ and $^{1}P$ states of neon and the long-range Van der Waals interaction of these states. With this rigorous parameter-free calculation a very good agreement with experimental results is obtained for the first exciton doublet.

Chemical pseudopotential and semiconductor surface states

We report preliminary results on the first surface state calculation based on the chemical-pseudopotential approach developed by Anderson and Bullett. For the test surface ideal Si(111), an essentially parameter-free calculation yields results close to those of previous calculations.

A study of the reaction 16O(p, p') 16O exciting the 6.05 MeV O + level

The cross section for excitation of the 6.05 MeV state in 16O is measured. A parameter-free microscopic calculation gives good agreement with the data.

The elastic constants for single- crystal lead and indium from room temperature to the melting point

Last few years have witnessed significant enhancement of thermoelectric figure of merit of lead telluride (PbTe) via nanostructuring. Despite the experimental progress, current understanding of the electron transport in PbTe is based on either band structure calculation using first principles with constant relaxation time approximation or empirical models, both relying on adjustable parameters obtained by fitting experimental data. Here, we report parameter-free first-principles calculation of electron and phonon transport properties of PbTe, including mode-by-mode electron-phonon scattering analysis, leading to detailed information on electron mean free paths and the contributions of electrons and phonons with different mean free paths to thermoelectric transport properties in PbTe. Such information will help to rationalize the use and optimization of nanostructures to achieve high thermoelectric figure of merit.