Charles J. Gillan

The UK molecular R-matrix codes

Abstract The R-matrix method has been used with great success in recent years to model low energy scattering of electrons and positrons by molecules. The codes, developed by a consortium of UK research groups as part of the Collaborative Computational Project 2 (CCP2), have now reached a high of robustness and stability. Their overall design is described in this paper.

R-matrix calculations for polyatomic molecules: electron scattering by

A new computer program has been developed which allows us to use the R-matrix method to study electron scattering by polyatomic molecules. Our first application is to scattering by in its linear, equilibrium geometry for energies up to 10 eV. We confirm the earlier assignment of symmetry to the resonance near 2 eV but we are unable to locate any resonance having symmetry in this energy range. We present integral and differential cross sections which are generally in excellent agreement with experiment.

Low-energy electron impact excitation of the nitrogen molecule: optically forbidden transitions

Ab initio calculations are performed on the scattering system, at low impact energies, using the R-matrix technique. The ground state and the lowest seven valence excited states, , and , of are included in the close coupling expansion with each state being represented by a configuration interaction wavefunction in a hybrid orbital set. Various approximations for the representation of the correlation between the target and the incident electron are investigated. Integrated and differential scattering cross sections are presented, and compared to experiment, for excitation from the ground level to optically forbidden levels. The results compare favourably with recent experiments in this energy region and remove a number of problems with our previous work.

Electron scattering by nitrogen molecules

The differential elastic and vibrationally inelastic cross sections for e-N2 scattering are calculated in the energy range from threshold to 30 eV using the R-matrix method. At low energies the cross sections are dominated by the well known 2 Pi g resonance. In this energy region non-adiabatic effects due to the coupling of the electronic and nuclear degrees of freedom are included. At higher energies the cross sections are dominated by the 2 Sigma u resonance. In this energy region the adiabatic approximation is appropriate. The cross sections are compared where possible with experiment. In general good agreement is obtained but some discrepancies suggest directions for future work.

Computing Zeros of Analytic Functions in the Complex Plane without using Derivatives

Abstract We present a package in Fortran 90 which solves f ( z ) = 0 , where z ∈ W ⊂ C without requiring the evaluation of derivatives, f ′ ( z ) . W is bounded by a simple closed curve and f ( z ) must be holomorphic within W . We have developed and tested the package to support our work in the modeling of high frequency and optical wave guiding and resonant structures. The respective eigenvalue problems are particularly challenging because they require the high precision computation of all multiple complex roots of f ( z ) confined to the specified finite domain. Generally f ( z ) , despite being holomorphic, does not have explicit analytical form thereby inhibiting evaluation of its derivatives. Program summary Title of program: EZERO Catalogue identifier: ADXY_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADXY_v1_0 Program obtainable from: CPC Program Library, Queens University of Belfast, N. Ireland Computer: IBM compatible desktop PC Operating system: Fedora Core 2 Linux (with 2.6.5 kernel) Programming languages used: Fortran 90 No. of bits in a word: 32 No. of processors used: one Has the code been vectorized: no No. of lines in distributed program, including test data, etc.: 21045 Number of bytes in distributed program including test data, etc.: 223 756 Distribution format: tar.gz Peripherals used: none Method of solution: Our package uses the principle of the argument to count the number of zeros encompassed by a contour and then computes estimates for the zeros. Refined results for each zero are obtained by application of the derivative-free Halley method with or without Aitken acceleration, as the user wishes.

The UK Molecular R-Matrix Scattering Package: a Computational Perspective

The R-matrix theory has been presented in the previous chapters of this book from a theoretical standpoint. Such is its complexity however that a separate chapter, that is this one, must be devoted to the implementation of the theory as a set of computer programs. Obviously if the R-matrix theory or any other method of solving the electron molecule scattering problem is to be viable it must be economic in the sense that it can be used routinely to produce numeric data for comparison with experimental measurements. Today, this means that the theory can be coded as a set of one or more computer codes which can be run in realistic time scales to produce data. This chapter attempts to show how the R-matrix method has been implemented, by a collaboration in the UK, in order to meet this objective. The reader should remember that the program suite reported here has been, and continues to be, developed and maintained by many people including overseas visitors and not iust these authors.

Electron scattering by nitrogen molecules including polarised pseudostates

Polarised pseudostates representing the long-range polarisation potential are included in a new e-N2 scattering calculation. The results remove an earlier disagreement in the total cross section between theory and experiment at energies below 1.5 eV and reduce the position and width of the 2 Pi g resonance.

Feature-Guided Architecture Development for Embedded System Families

Software product-line engineering aims to maximize reuse by exploiting the commonality within families of related systems. Its success depend on capturing the commonality and variability, and using this to evolve a reference architecture for the product family. With embedded system families, the possibility of variability in hardware and operating system platforms is an added complication. In this paper we outline a strategy for evolving reference architectures from bi-directional feature models. The proposed strategy complements information provided by the feature model with scenarios that help to elaborate feature behavior.

Low-energy electron scattering by HBr

The R-matrix method is extended to treat electron scattering from molecules containing a heavy atom. It is then used to calculate low energy total elastic and vibrational excitation cross sections for e--HBr scattering. Results are obtained at the equilibrium internuclear separation using two approximations: the first in which polarization effects are represented by the inclusion of quadratically integrable correlation functions and the second in which polarized pseudostates as well as the target ground state are retained in the total wavefunction expansion. The calculations using the first approximation are carried out for a range of internuclear separations and the vibrational motion is then included using a non-adiabatic R-method approach. A low energy 2 Sigma resonance is found in the fixed-nuclei calculations which gives rise to sharp threshold peaks in the vibrational excitation cross sections in qualitative accord with experiment. These peaks are interpreted as being due to the nuclear excited Feshbach resonance mechanism.

Methods and metrics for fair server assessment under real-time financial workloads

We present a rigorous methodology and new metrics for fair comparison of server and microserver platforms. Deploying our methodology and metrics, we compare a microserver with ARM cores against two servers with ×86 cores running the same real‐time financial analytics workload. We define workload‐specific but platform‐independent performance metrics for platform comparison, targeting both datacenter operators and end users. Our methodology establishes that a server based on the Xeon Phi co‐processor delivers the highest performance and energy efficiency. However, by scaling out energy‐efficient microservers, we achieve competitive or better energy efficiency than a power‐equivalent server with two Sandy Bridge sockets, despite the microservers slower cores. Using a new iso‐QoS metric, we find that the ARM microserver scales enough to meet market throughput demand, that is, a 100% QoS in terms of timely option pricing, with as little as 55% of the energy consumed by the Sandy Bridge server. Copyright