Joan Adler - Academia.edu (original) (raw)

Papers by Joan Adler

arXiv (Cornell University), Mar 12, 2006

Physical review, Nov 3, 2003

Bulletin of the American Physical Society, Mar 5, 2019

Physical review, Apr 15, 1995

Extended x-ray-absorption fine-structure experiments have previously demonstrated that for each c... more Extended x-ray-absorption fine-structure experiments have previously demonstrated that for each composition x, the sample average of all nearest-neighbor A-C distances in an A & "B C semiconductor alloy is closer to the values in the pure (x-+0) AC compound than to the composition-weighted (virtual) lattice average. Such experiments do not reveal, however, the distribution of atomic positions in an alloy, so the principle displacement directions and the degrees of correlation among such atomic displacements remain unknown. Here we calculate both structural and thermodynamic properties of Ga& "In"P alloys using an explicit occupationand position-dependent energy functional. The latter is taken as a modified valence force field, carefully fit to structural energies determined by first-principles local-density calculations. Configurational and vibrational degrees of freedom are then treated via the continuous-space Monte Carlo approach. We find good agreement between the calculated and measured mixing enthalpy of the random alloy, nearest-neighbor bond lengths, and temperature-composition phase diagram. In addition, we predict yet unmeasured quantities such as (a) distributions, fluctuations, and moments of firstand second-neighbor bond lengths as well as bond angles, (b) radial distribution functions, (c) the dependence of short-range order on temperature, and (d) the effect of temperature on atomic displacements. Our calculations provide a detailed picture of how atoms are arranged in substitutionally random but positionally relaxed alloys, and o6'er an explanation for the efFects of site correlations, static atomic relaxations, and dynamic vibrations on the phase-diagram and displacement maps. We find that even in a chemically random alloy (where sites are occupied by Ga or In according to a coin toss), there exists a highly correlated static position distribution whereby the P atoms are displaced deterministically in certain high-symmetry directions.

Physical Review B, Jun 28, 2005

Using Path Integral Monte Carlo and the Maximum Entropy method, we calculate the dynamic structur... more Using Path Integral Monte Carlo and the Maximum Entropy method, we calculate the dynamic structure factor of solid 4 He in the bcc phase at a finite temperature of T = 1.6 K and a molar volume of 21 cm 3. Both the single-phonon contribution to the dynamic structure factor and the total dynamic structure factor are evaluated. From the dynamic structure factor, we obtain the phonon dispersion relations along the main crystalline directions, [001], [011] and [111]. We calculate both the longitudinal and transverse phonon branches. For the latter, no previous simulations exist. We discuss the differences between dispersion relations resulting from the single-phonon part vs. the total dynamic structure factor. In addition, we evaluate the formation energy of a vacancy.

Computer Physics Communications, 2018

We describe three distinct approaches to visualization for multiscale materials modelling researc... more We describe three distinct approaches to visualization for multiscale materials modelling research. These have been developed with the framework of the SimPhoNy FP7 EU-project, and complement each other in their requirements and possibilities. All have been integrated via wrappers to one or more of the simulation approaches within the SimPhoNy project. In this manuscript we describe and contrast their features. Together they cover visualization needs from electronic to macroscopic scales and are suited to simulations made on personal computers, workstations or advanced High Performance parallel computers. Examples as well as recommendations for future calculations are presented.

Journal of Low Temperature Physics, Sep 27, 2006

ACM SIGGRAPH Computer Graphics, 1996

The spatial volume occupied by an atom depends on its electronic density. Although this density c... more The spatial volume occupied by an atom depends on its electronic density. Although this density can only be evaluated exactly for hydrogen-like atoms, there are many excellent algorithms and packages to calculate it numerically for other materials. Three-dimensional visualization of charge density is challenging, especially when several molecular/atomic levels are intertwined in space. In a recent project, we explored one approach to this: the extension of an analglyphic stereo visualization application based on the AViz package for hydrogen atoms and simple molecules to larger structures such as nanotubes. I will describe these techniques and demonstrate the use of analyglyphic stereo in AViz, [1, 2]. The use of AViz dot-mode visualization for electronic density was first developed in an undergraduate project about the hydrogen atom[3]. We then visualized the electronic density resulting from simulations of larger molecules and solids in the same way. Further studies [4] used a den...

Physical Review Letters, Mar 13, 1995

Connecting perfect one-dimensional leads to sites i and j on the quantum percolation (QP) model, ... more Connecting perfect one-dimensional leads to sites i and j on the quantum percolation (QP) model, we calculate the transmission coefficient T ij (E) at an energy E near the band center and the averages of Σ ij T ij , Σ ij r 2 ij T ij , and Σ ij r 4 ij T ij to tenth order in the concentration p. In three dimensions, all three series diverge at p q =0.36 +0.01 −0.02 , with exponents γ=0.82 +0.10 −0.15 , γ+2ν, and γ+4ν. We find ν=0.38±0.07, differing from "usual" Anderson localization and violating the bound ν≥2/d of Chayes et al. [Phys. Rev. Lett. 57, 2999 (1986)]. Thus, QP belongs to a new universality class.

Journal of Physics: Conference Series, 2021

Visualization in three dimensions is invaluable for understanding the nature of condensed and flu... more Visualization in three dimensions is invaluable for understanding the nature of condensed and fluid systems, but it is not always easy. In nature it is hard to view sample interiors, but on computers it is possible. We describe and contrast two opposite approaches - “smoke” visualization for viewing interiors of liquid samples and interactive WebGL for solids and molecules. Both are extensions of earlier Technion Computational Physics group projects and complement and are interoperable with the recent SimPhoNy Fp7 project. They require only desktop hardware and software accessible to students. Examples and standalone instructions for both are presented, starting with sample creation and concluding with image galleries.

Journal of Physics: Conference Series, 2017

In an introductory computational physics class of the type that many of us give, time constraints... more In an introductory computational physics class of the type that many of us give, time constraints lead to hard choices on topics. Everyone likes to include their own research in such a class but an overview of many areas is paramount. Parallel programming algorithms using MPI is one important topic. Both the principle and the need to break the "fear barrier" of using a large machine with a queuing system via ssh must be sucessfully passed on. Due to the plateau in chip development and to power considerations future HPC hardware choices will include heavy use of GPUs. Thus the need to introduce these at the level of an introductory course has arisen. Just as for parallel coding, explanation of the benefits and simple examples to guide the hesitant first time user should be selected. Several student projects using GPUs that include how-to pages were proposed at the Technion. Two of the more successful ones were lattice Boltzmann and a finite element code, and we present these in detail.

Journal of Physics: Conference Series, 2018

Although simulated annealing has become a useful tool for optimization of many systems, its initi... more Although simulated annealing has become a useful tool for optimization of many systems, its initial raison d'etre of achieving the groundstate structure for a spin or atomic/molecular condensed system remains important. Such modelling, whether using analog models such as glass beads or by invoking simple computer models can be suited to undergraduate projects. In this paper we discuss the application of simulated annealing to find the groundstate of a system of liquid crystals (LC) with suspended colloids. These systems are expected to have interesting conductive behaviour, relevant to applications for television and computer screens. In our first stage, a pure LC system was simulated in python and vizualized by undergraduates and presented on an educational website. In the next stage colloid(s) were added, and the original code modified accordingly. Interesting effects such as ordering around the colloid have been seen and will be described. In the final stage and in order to study larger samples, the code was rewritten in C++ and several algorithmic modifications were made. Speed up factors between 100 and more than 1000 were obtained, and fascinating closed cells surrounding the colloids were observed.

Physical Review B, 1988

We construct general-dimension series for the random animal problem up to 15th order. These repre... more We construct general-dimension series for the random animal problem up to 15th order. These represent an improvement of five terms in four dimensions and above and one term in three dimensions. These series are analyzed, together with existing series in two dimensions, and series for the related Yang-Lee edge problem, to obtain accurate estimates of critical parameters, in particular, the correction to scaling exponent. There appears to be excellent agreement between the two models for both dominant and correction exponents.

Physical Review B, 1993

We investigate the distribution of the logarithms, logi, of the currents in percolating resistor ... more We investigate the distribution of the logarithms, logi, of the currents in percolating resistor networks via the method of series expansions. Exact results in one dimension and expansions to thirteenth order in the bond occupation probability, p, in general dimension, for the moments of this distribution have been generated. We have studied both the moments and cumulants derived therefrom with several extrapolation procedures. The results have been compared with recent predictions for the behavior of the moments and cumulants of this distribution. An extensive comparison between exact results and series of different lengths in one dimension sheds light on many aspects of the analysis of series with logarithmic corrections. The numerical results of the series expansions in higher dimensions are generally consistent with the theoretical predictions. We confirm that the distribution of the logarithms of the currents is unifractal as a function of the logarithm of linear system size, even though the distribution of the currents is multifractal.

Physical Review B, 1990

Series expansions for general moments of the bond-percolation cluster-size distribution on hyperc... more Series expansions for general moments of the bond-percolation cluster-size distribution on hypercubic lattices to 15th order in the concentration have been obtained. This is one more than the previously published series for the mean cluster size in three dimensions and four terms more for higher moments and higher dimensions. Critical exponents, amplitude ratios, and thresholds have been calculated from these and other series by a variety of independent analysis techniques. A comprehensive summary of extant estimates for exponents, some universal amplitude ratios, and thresholds for percolation in all dimensions is given, and our results are shown to be in excellent agreement with the ε expansion and some of the most accurate simulation estimates. We obtain threshold values of 0.2488±0.0002 and 0.180 25±0.000 15 for the three-dimensional bond problem on the simple-cubic and body-centered-cubic lattices, respectively, and 0.160 05±0.000 15 and 0.118 19±0.000 04, for the hypercubic bond problem in four and five dimensions, respectively. Our direct exponent estimates are γ=1.805±0.

Physical Review B, 1991

We inadvertently quoted in Table II only the second term of Eq. (2.2) multiphed by (1 cry) .-The ... more We inadvertently quoted in Table II only the second term of Eq. (2.2) multiphed by (1 cry) .-The complete series for g is given in Table I. TABLE I. Series coefficients for y, where' =I+ g "a(m, n)p"'d"

Physical Review Letters, 1993

Novel methods were used to generate and analyze new 15 term high temperature series for both the ... more Novel methods were used to generate and analyze new 15 term high temperature series for both the (connected) susceptibility χ and the structure factor (disconnected susceptibility) χ d for the random field Ising model with dimensionless coupling K=J/kT, in general dimension d. For both the bimodal and the Gaussian field distributions, with mean square field J 2 g, we find that (χ d-χ)/K 2 gχ 2 =1 as T→T c (g), for a range of [h 2 ]=J 2 g and d=3,4,5. This confirms the exponent relation γ¯=2γ (where χ d~t −γ¯, χ~t −γ , t=T-T c) providing that random field exponents are determined by two (and not three) independent exponents. We also present new accurate values for γ.

Journal of Statistical Physics, 1990

We discuss recent work on the development and analysis of low-concentration series. For many mode... more We discuss recent work on the development and analysis of low-concentration series. For many models, the recent breakthrough in the extremely efficient nofree-end method of series generation facilitates the derivation of 15th-order series for multiple moments in general dimension. The 15th-order series have been obtained for lattice animals, percolation, and the Edwards Anderson Ising spin glass. In the latter cases multiple moments have been found. From complete graph tables through to 13th order, general dimension 13th-order series have been derived for the resistive susceptibility, the moments of the logarithms of the distribution of currents in resistor networks, and the average transmission coefficient in the quantum percolation problem, l lth-order series have been found for several other systems, including the crossover from animals to percolation, the full resistance distribution, nonlinear resistive susceptibility and current distribution in dilute resistor networks, diffusion on percolation clusters, the dilute Ising model, dilute antiferromagnet in a field, and random field Ising model and self-avoiding walks on percolation clusters. Series for the dilute spin-l/2 quantum Heisenberg ferromagnet are in the process of development. Analysis of these series gives estimates for critical thresholds, amplitude ratios, and critical exponents for all dimensions. Where comparisons are possible, our series results are in good agreement with both z-expansion results near the upper critical dimension and with exact results (when available) in low dimensions, and are competitive with other numerical approaches in intermediate realistic dimensions.