Showing papers by "International School for Advanced Studies published in 1985"
TL;DR: In this article, a unified scheme combining molecular dynamics and density-functional theory is presented, which makes possible the simulation of both covalently bonded and metallic systems and permits the application of density functional theory to much larger systems than previously feasible.
Abstract: We present a unified scheme that, by combining molecular dynamics and density-functional theory, profoundly extends the range of both concepts. Our approach extends molecular dynamics beyond the usual pair-potential approximation, thereby making possible the simulation of both covalently bonded and metallic systems. In addition it permits the application of density-functional theory to much larger systems than previously feasible. The new technique is demonstrated by the calculation of some static and dynamic properties of crystalline silicon within a self-consistent pseudopotential framework.
8,852 citations
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TL;DR: A simple inflationary model characterized by a scale factor which grows like Sapprox.t/sup p/, with p a constant greater than one, which is called power-law inflation (PLI), and considers the constraints on this model coming from the requirement of solving the horizon, flatness, ''good'' reheating, and ''convenient'' perturbation-spectrum problems.
Abstract: The outstanding cosmological problems (horizon, flatness, . . .) which may be solved by the usual inflationary models may also find a solution in the frame of a ``generalized'' inflationary cosmology which is characterized by a suitable phase of accelerated expansion. The usual exponential growth of the scale factor S is just a particular case of such a general idea. Following this line of thought, we study in some detail a simple inflationary model characterized by a scale factor which grows like S\ensuremath{\sim}${t}^{p}$, with p a constant greater than one, which we call power-law inflation (PLI). Some properties of PLI have been analyzed, in different contexts, also by other authors. We consider the constraints on this model coming from the requirement of solving the horizon, flatness, ``good'' reheating, and ``convenient'' perturbation-spectrum problems. In order to obtain the perturbation spectrum when re-entering the horizon during the Friedmann phase, we extend to PLI the gauge-invariant approach developed by Bardeen et al. for the usual inflationary models. We find that the above constraints can be suitably satisfied. Finally, we outline possible connections between PLI and particular inflationary models which have recently been proposed.
803 citations
TL;DR: In this article, the structural and electronic properties of the sodium clusters were investigated based on self-consistent pseudopotential local spin density calculations and the Hellmann-Feynman theory.
Abstract: We present an investigation of the structural and electronic properties of the sodium clusters ${\mathrm{Na}}_{\mathrm{n}}$ and ${\mathrm{Na}}_{\mathrm{n}}$${\mathrm{}}^{+}$ with n\ensuremath{\le}8 and n=13, based on self-consistent pseudopotential local-spin-density calculations. In order to obtain the equilibrium geometries without imposing any symmetry constraint, we start from randomly generated cluster geometries and let them relax under the action of the forces on the atoms, which are derived from the Hellmann-Feynman theory. We find that the clusters with up to five atoms have planar equilibrium geometries, the six-atom cluster is quasiplanar, and real three-dimensional structures only begin to occur when the number of atoms is greater than or equal to seven. We compare our results with recently obtained experimental data and find good agreement with the measured photoionization appearance potentials and the electron-spin-resonance spectra. Metallic bonding is the dominant feature of our calculated electronic structures and we show that the equilibrium geometries can be explained with a simple model having the delocalized nature of the metallic electrons and the Jahn-Teller effect as basic ingredients.
264 citations
Journal Article•
223 citations
TL;DR: In this paper, the authors demonstrate how this technique might also become useful for the spectroscopy of surfaces, and in particular of surface electronic states, by direct calculation of the tunneling current flowing into, or out of, a graphite surface, as a function of an applied voltage V, illustrating the direct relationship between the current J(V) and the surface electronic structure at energy E-EF=V.
Abstract: Scanning Tunneling Microscopy is now well established as a powerful technique for surface structural studies(1). Our aim is to demonstrate how this technique might also become useful for the spectroscopy of surfaces, and in particular of surface electronic states. We do this by direct calculation of the tunneling current flowing into, or out of, a graphite surface, as a function of an applied voltage V, illustrating the direct relationship between the current J(V) and the surface electronic structure at energy E-EF=V. Graphite has been chosen because it is an important surface, with perfectly known atomic structure, and a simple and well-known electronic structure, where localized σ and π states coexist with fairly delocalized interlayer bulk states(2), and with recently discovered empty surface states(3,4). Most of these interesting features lie several eV away from the Fermi energy. We do not concern ourselves here the the technical difficulties of achieving such a high tunneling voltage on a semimetallic surface. Our calculation, however, shows that the outcome would be very worthwhile, in terms of information on the surface electronic structure.
207 citations
TL;DR: In this paper, the SU(2) v hidden local symmetry is realized through a new dynamical vector boson resonance V and the physical admixtures and masses of W, Z and V bosons are derived and the couplings of the physical bosons to fermions are calculated.
176 citations
TL;DR: The analysis shows that the existence of connecting gluons does not spoil factorizability in the leading-logarithm approximation of multiparton processes, and hadrons are described by a set of newly defined structure functions.
Abstract: We investigate multiparton processes in the framework of quantum chromodynamics. The spin and color, as well as the factorizability of the process, have been analyzed in detail. The analysis shows that the existence of connecting gluons does not spoil factorizability in the leading-logarithm approximation. We also find that the spin and color degrees of freedom play an important role in the description of multiparton processes. As a consequence, hadrons are described by a set of newly defined structure functions. We apply the general formalism to the double Drell-Yan mechanism. We find that the above-mentioned structure functions are convoluted with two completely uncorrelated single Drell-Yan cross sections.
98 citations
TL;DR: In this article, conformal covariance is used to determine renormalization properties of composite operators in QCD and in the ϕ 6 3 -model at the one-loop level.
95 citations
TL;DR: In this article, the quasiharmonic free energy of (100), (110), and (111) surfaces within the slab model was computed for the surface instabilities of copper metal and it was shown that a loose-packed surface would melt prior to a close-packed one if contractive surface relaxations are neglected.
Abstract: The surface instabilities of copper metal are studied by computing the quasiharmonic free energy of (100), (110), and (111) surfaces within the slab model. We find that a loose-packed surface would melt prior to a close-packed one if contractive surface relaxations are neglected. The inclusion of surface contractions can reverse the order of these instabilities in agreement with recent experiments.
93 citations
TL;DR: In this paper, the multiplicity of solutions of the Dirichlet problem is studied, depending on the parameter t for certain terms ϕ, and the main hypothesis on f is that, setting f ± = lim s → ± ∞ f ( x, s ) s, in the interval ]f−, f+[ there are eigenvalues of −Δ with theDirichlet homogeneous boundary conditions on ∂Ω.
Abstract: This paper studies the multiplicity of solutions of the problem: depending on the parameter t for certain terms ϕ. The main hypothesis on f is that, setting f ± = lim s → ± ∞ f ( x , s ) s , in the interval ]f−, f+[ there are eigenvalues of −Δ with the Dirichlet homogeneous boundary conditions on ∂Ω. Studying the « bifurcation from infinity » of the solutions of the problem, multiplicity or sharp multiplicity results are obtained in the case that such eigenvalues are the first two or the first three or only one and simple. In such a way we improve or sharpen previous results of Lazer and McKenna, Hofer, Gallouet and Kavian and of the author.
88 citations
TL;DR: In this paper, the kinematical properties of Robertson-Walker models which allow a solution of the cosmological horizon and flatness problems are studied: these are called models of generalized inflation.
TL;DR: In this article, two families of cosmological solutions are presented in D = 6, N = 2 Kaluza-Klein supergravity theories, and all solutions in the latter family approach the Friedmann universe asymptotically.
TL;DR: In this paper, it was shown that if u is assumed to be real analytic and $U \equiv 0$ then these phenomena disappear and the solution to the elastic bounce problem is unique for every choice of the Cauchy data.
TL;DR: In this article, the authors investigated cosmological solutions in six-dimensional, N = 2 supergravity Kaluza-Klein theory and showed that the four-dimensional Friedmann universe is the attractor, i.e., all the solutions starting from arbitrary initial conditions (apart from the time reversal ones) approach the above space-time asymptotically without any fine-tuning.
TL;DR: For supersymmetric Yang-Mills theories with Bogomolny-Prasad-Sommerfield monopoles, this paper used an open-space trace theorem on R3 to calculate the O(ħ) correction to the monopole mass.
TL;DR: In this paper, characterizations of all self-adjoint extensions of the Laplacian in one, two, and three dimensions are discussed. But none of these characterizations is applicable to the present paper.
Abstract: Three characterizations of all self‐adjoint extensions of the Laplacian in one, two, and three dimensions are discussed.
TL;DR: In this article, spontaneous symmetry breaking in the presence of long range instantaneous interactions is studied and the general mechanism underlying it is clarified, and a characteristic feature is that the algebraic dynamics does not leave any essentially local algebra stable, i.e. variables at infinity get involved in the time evolution of local variables, so that in each irreducible representation the time Evolution fails to be symmetric.
Abstract: Spontaneous symmetry breaking in the presence of long range instantaneous interactions is studied and the general mechanism underlying it is clarified A characteristic feature is that the algebraic dynamics does not leave any essentially local algebra stable, ie variables at infinity get involved in the time evolution of local variables, so that in each irreducible representation the time evolution fails to be symmetric For continuous symmetries, the Fourier transform of the vacuum expectation value of charge commutators is related to the energy spectrum at low momenta and a generalized Goldstone theorem is proved which explains the generation of energy gap This energy gap is further shown to be governed by a “classical dynamics at infinity”, equivalently by the group generated by the effective Hamiltonian and the charge Explicit examples are discussed
TL;DR: In this article, a nonperturbative method of analysis of the stability problem of quantum field theory models is proposed, which consists in the systematic analysis of functional dependence on boson field B of the effective boson Lagrangian S/sup eff/(B) consisting of the fermion term, constraint term, and the boson self-interaction term S/sub 1/(B), where counterterms are calculated in the explicit functional form by means of the analytic renormalization method.
TL;DR: In this paper, it was shown that Sakharov's maximal temperature is a consequence of the maximal acceleration introduced by us in previous works, which is a straightforward consequence of our maximal acceleration.
Abstract: It is shown that Sakharov’s maximal temperature, derived by him from astrophysical considerations, is a straightforward consequence of the maximal acceleration introduced by us in previous works.
TL;DR: In this paper, necessary and sufficient conditions for the convergence in W01,p(Ω) of sequences of convex sets determined by obstacles are established in terms of properties of the p-capacities of the level sets of the obstacles.
TL;DR: In this article, a new derivation of the Lagrangian for perfect-fluid general-relativistic hydrodynamics under the assumptions of irrotationality and isentropicity is given.
Abstract: Some aspects of perfect-fluid general-relativistic hydrodynamics under the assumptions of irrotationality and isentropicity are analysed. A new derivation of the known fact that the Lagrangian for these fluids is just the pressure is given. Then we study the fluctuations around a given background field configuration, extracting a rule that connects the order at which a Taylor expansion of the action functional possibly stops with the fluid equation of state. From a classical invariance of the action we deduce the conserved Noether current. Because of the spontaneous breaking of such an invariance on the vacuum state Goldstone bosons arise, which turn out to be just phonons (quantized sound waves). Some useful results concerning the linear theory of sound waves are also given.
TL;DR: In this article, an explicit derivation of an effective action for composite operators is presented, which has the same local extrema as the effective action of Cornwall, Jackiw and Tomboulis.
TL;DR: In this paper, the effect of multilayer relaxation on melting was investigated for a high cohesion metal like copper, and it was shown that surface contraction has drastic effect on melting making a loose-packed surface melt later than a close-packed one.
TL;DR: In this article, the usual correspondence between twistors and geometrical objects in the Minkowski space is generalized to the supertwistor case by means of flag supermanifolds.
Abstract: In the paper the usual correspondence between twistors and geometrical objects in the Minkowski space is generalized to the supertwistor case by means of flag supermanifolds. This supertwistor correspondence is treated in detail. Chiral and non-chiral superspaces are constructed and their properties studied by means of supertwistors.
TL;DR: In this article, a model for the free-photon propagator with a nontrivial transverse part is presented, which is based on the Lagrangian and Dirac equations.
Abstract: 46 0. Introduction and outlook. 1. Summary and discussion. 1'1. ConformM photon propagator with a nontrivial transverse part. 1"2. Conformal Maxwell equations. A model for the ¤t. 1"3. Lagrangian, Dirac equation, Ward idcntity. 1"4. How far can one go with the free-photon propagator? 2. Fields transforming under nondecomposable representations of the conformal group. 2"1. M~mifestly eovari 'mt realizations of G. 2'2. Connection form on Q and the electronmgnetic 5-potcntiM. 2"3. Reduction with respect to the l l -paramcter Weyl subgroup. Dilations and special conformal tra, nsformations. 2"4. Conformal Dirac fields. 3. Two-point functions. 3"1. A nonsingular 5-poten|ial Euclidean propagation matrix and its inverse. 3"2. Inv,~ri,~nt 2-point functions for spinor fields. 4. 3[asslcss electron interacting with an electromagnetic 5-potential. 4"1. Choicc of basic fields. Lagrangian and equations of motion. 4"2. Subspace of physical photon states. 4"3. An oper~tor transformation law for ~0(x) consistent with the equations of motion and the Ward identity. APPENI)IX. Manitestly conformM and gauge-covariant tensors.
TL;DR: In this paper, the modified superpropagators for the O'Raifeartaigh model are obtained: they are used for the superspace renormalization and the derivation of the effective potential.
TL;DR: In this paper, it was shown that in a general N = 2 Sugra model (constructed according to the tensor calculus) all stationary points of the potential, at Λ = 0, are fully supersymmetric if the compensating multiplet is not gauged.
TL;DR: In this paper, the back-reaction problem for two-dimensional gravity is investigated and its connection with the Liouville equation is shown, and the connection between the two problems is discussed.