BerkeleyGW: A Massively Parallel Computer Package for the Calculation of the Quasiparticle and Optical Properties of Materials and Nanostructures

BerkeleyGW is a massively parallel computational package for electron excited-state properties that is based on the many-body perturbation theory employing the ab initio GW and GW plus Bethe-Salpeter equation methodology. It can be used in conjunction with many density-functional theory codes for ground-state properties, including PARATEC, PARSEC, Quantum ESPRESSO, OCTOPUS and SIESTA. The package can be used to compute the electronic and optical properties of a wide variety of material systems from bulk semiconductors and metals to nanostructured materials and molecules. The package scales to 10,000's of CPUs and can be used to study systems containing up to 100's of atoms

User Manual for MOLSCAT, BOUND and FIELD, Version 2020.0: programs for quantum scattering properties and bound states of interacting pairs of atoms and molecules

MOLSCAT is a general-purpose package for performing non-reactive quantum scattering calculations for atomic and molecular collisions using coupled-channel methods. Simple atom-molecule and molecule-molecule collision types are coded internally and additional ones may be handled with plug-in routines. Plug-in routines may include external magnetic, electric or photon fields (and combinations of them). Simple interaction potentials are coded internally and more complicated ones may be handled with plug-in routines. BOUND is a general-purpose package for performing calculations of bound-state energies in weakly bound atomic and molecular systems using coupled-channel methods. It solves the same sets of coupled equations as \MOLSCAT, and can use the same plug-in routines if desired, but with different boundary conditions. FIELD is a development of BOUND that locates external fields at which a bound state exists with a specified energy. One important use is to locate the positions of magnetically tunable Feshbach resonance positions in ultracold collisions. Versions of these programs before version 2019.0 were released separately. However, there is a significant degree of overlap between their internal structures and usage specifications. This manual therefore describes all three, with careful identification of parts that are specific to one or two of the programs.Comment: 206 pages. Program source code available from https://github.com/molscat/molscat This is the full program documentation for the programs described in the journal papers Comp. Phys. Commun. 241, 1-8 (2019) (arXiv:1811.09111) and Comp. Phys. Commun. 241, 9-16 (2019) (arXiv:1811.09584). There is significant text overlap between some parts of the documentation and the (much shorter) journal paper

Econometrics with gretl. Proceedings of the gretl Conference 2009.

This book contains the articles presented at the first International gretl Conference, held on may 28-29, 2009 in Bilbao, Spain.Econometrics, gretl, open source, statistical software

Technology 2003: The Fourth National Technology Transfer Conference and Exposition, volume 2

Proceedings from symposia of the Technology 2003 Conference and Exposition, Dec. 7-9, 1993, Anaheim, CA, are presented. Volume 2 features papers on artificial intelligence, CAD&E, computer hardware, computer software, information management, photonics, robotics, test and measurement, video and imaging, and virtual reality/simulation

Algorithmic approaches to enhancing and exploiting application-level error tolerance

As late-CMOS process scaling leads to increasingly variable circuits/logic and as most post-CMOS technologies in sight appear to have largely stochastic characteristics, hardware reliability has become a first-order design concern. To make matters worse, emerging computing systems are becoming increasingly power constrained. Traditional hardware/software approaches are likely to be impractical for these power constrained systems due to their heavy reliance on redundant, worstcase, and conservative designs. The primary goal of this research has been to investigate how we can leverage inherent application and algorithm characteristics (e.g. natural error resilience, spatial and temporal reuse, and fault containment) to build more efficient robust systems. This dissertation research describes algorithmic approaches that leverage application and algorithm-awareness for building such systems. These approaches include (a) application-specific techniques for low-overhead fault detection, (b) an algorithmic approach for error correction using localization, (c) selection of scientific computing solver schemes to leverage application-level error resilience, and (d) a numerical optimization-based methodology for converting applications into a more error tolerant form. This dissertation shows that application and algorithm-awareness can significantly increase the robustness of computing systems, while also reducing the cost of meeting reliability targets

Computational Methods in Science and Engineering : Proceedings of the Workshop SimLabs@KIT, November 29 - 30, 2010, Karlsruhe, Germany

In this proceedings volume we provide a compilation of article contributions equally covering applications from different research fields and ranging from capacity up to capability computing. Besides classical computing aspects such as parallelization, the focus of these proceedings is on multi-scale approaches and methods for tackling algorithm and data complexity. Also practical aspects regarding the usage of the HPC infrastructure and available tools and software at the SCC are presented

Fast numerical methods for mixed--integer nonlinear model--predictive control

This thesis aims at the investigation and development of fast numerical methods for nonlinear mixed--integer optimal control and model- predictive control problems. A new algorithm is developed based on the direct multiple shooting method for optimal control and on the idea of real--time iterations, and using a convex reformulation and relaxation of dynamics and constraints of the original predictive control problem. This algorithm relies on theoretical results and is based on a nonconvex SQP method and a new active set method for nonconvex parametric quadratic programming. It achieves real--time capable control feedback though block structured linear algebra for which we develop new matrix updates techniques. The applicability of the developed methods is demonstrated on several applications. This thesis presents novel results and advances over previously established techniques in a number of areas as follows: We develop a new algorithm for mixed--integer nonlinear model- predictive control by combining Bock's direct multiple shooting method, a reformulation based on outer convexification and relaxation of the integer controls, on rounding schemes, and on a real--time iteration scheme. For this new algorithm we establish an interpretation in the framework of inexact Newton-type methods and give a proof of local contractivity assuming an upper bound on the sampling time, implying nominal stability of this new algorithm. We propose a convexification of path constraints directly depending on integer controls that guarantees feasibility after rounding, and investigate the properties of the obtained nonlinear programs. We show that these programs can be treated favorably as MPVCs, a young and challenging class of nonconvex problems. We describe a SQP method and develop a new parametric active set method for the arising nonconvex quadratic subproblems. This method is based on strong stationarity conditions for MPVCs under certain regularity assumptions. We further present a heuristic for improving stationary points of the nonconvex quadratic subproblems to global optimality. The mixed--integer control feedback delay is determined by the computational demand of our active set method. We describe a block structured factorization that is tailored to Bock's direct multiple shooting method. It has favorable run time complexity for problems with long horizons or many controls unknowns, as is the case for mixed- integer optimal control problems after outer convexification. We develop new matrix update techniques for this factorization that reduce the run time complexity of all but the first active set iteration by one order. All developed algorithms are implemented in a software package that allows for the generic, efficient solution of nonlinear mixed-integer optimal control and model-predictive control problems using the developed methods

Xray Generation by Field Emission

Since the discovery of X-rays over a century ago the techniques applied to the engineering of X-ray sources have remained relatively unchanged. From the inception of thermionic electron sources, which, due to simplicity of fabrication, remain central to almost all X-ray applications at this time, there have been few fundamental technological advances. The emergence of new materials and manufacturing techniques has created an opportunity to replace the traditional thermionic devices with those that incorporate Field Emission electron sources. One of the most important attributes of Field Emission X-ray sources is their controllability, and in particular the fast response time, which opens the door to applying techniques which have formerly been the preserve of optical systems. The work in this thesis attempts to bridge the gap between the fabrication and optimisation of the vacuum electronic devices and image processing aspects of a new approach to high speed radiographic imaging, particularly with a view to addressing practical real-world problems. Off the back of a specific targeted application, the project has involved the design of a viable field emission X-ray source, together with the development of an understanding of the failure modes in such devices, both by analysis and by simulation. This thesis reviews the capabilities and the requirements of X-ray sources, the methods by which nano-materials may be applied to the design of those devices and the improvements and attributes that can be foreseen. I study the image processing methods that can exploit these attributes, and investigate the performance of X-ray sources based upon electron emitters using carbon nanotubes. Modelling of the field emission and electron trajectories of the cathode assemblies has led me to the design of equipment to evaluate and optimise the parameters of an X-ray tube, which I have used to understand the performance that is achievable. Finally, I draw conclusions from this work and outline the next steps to provide the basis for a commercial solution

Optimization of Ultrafast Strong-Field Phenomena

Elektronien liikkeen havainnointi ja ohjaaminen on attosekuntitieteen keskiössä. Attosekuntiluokan elektroniprosessit ovat esimerkiksi kemiallisten reaktioiden takana, selittävät aineen optiset ominaisuudet sekä ovat pohjana useille ultranopeille nanomittaluokan kuvantamismenetelmille. Useat mielenkiintoiset attosekuntiluokan ilmiöt aiheutuvat vahvasta ulkoisesta sähkömagneettisesta kentästä. Tällaisia kenttiä saadaan femtosekuntilasersykäyksillä, joiden kenttien vahvuus on samaa suuruusluokkaa kuin atomin elektroniinsa kohdistama sähkökenttä. Voimakas sähkömagneettinen vuorovaikutus aiheuttaa atomien, molekyylien ja kiinteän aineen epälineaarisia ilmiöitä kuten korkeaenergisten fotonien tuottoa (HHG), nopeiden elektronien emissiota sekä esimerkiksi atomielektronin virittymistä korkeille sidotuille tiloille. Edellämainitut ilmiöt ovat myös pohjana useille teknisille edistyksille: HHG:lla tuotetaan koherentteja röntgensykäyksiä, joiden kesto on vain muutamien attosekuntien suuruusluokkaa; nopeita fotoemittoituneita elektroniaaltopaketteja käytetään aineen kuvantamiseen; ja Rydberg-tiloille viritettyjä atomeita käytetään kvanttilaskennassa kubitteina. Attosekuntiluokan ilmiöitä voidaan ohjata haluttuun suuntaan käyttämällä femtosekuntilasersykäyksiä, joiden sähkökentän aikariippuvuutta voidaan säätää. Tämä väitöskirja on laskennallinen tutkimusretki, jolla pyritään löytämään menetelmiä ennustamaan sellaisten femtosekuntilasersykäysten aikaprofiileja, joilla aiemmin mainittuja ilmiöitä – HHG:ta, elektroniemissiota sekä Rydbergtilojen virityksiä – voidaan tehostaa, optimoida. Väitöskirjan alussa esitellään työn kannalta oleelliset vahvojen kenttien attosekuntiluokan ilmiöt keskittyen etenkin niiden teoreettisiin ja laskennallisiin malleihin. Tutkielmassa annetaan myös yleiskatsaus femtosekuntisykäysten käytöstä atomifysiikan ilmiöiden ohjaamisessa ja optimoinnissa avaten sekä alan kokeellista että laskennallista puolta. Tutkimuksessamme käytetyt laskennalliset mallit käydään yksityiskohtaisesti läpi, ja väitöskirjan oheismateriaali (saatavilla internetistä) sisältää oleellisimmat työssä käytetyt ohjelmistot ja analyysityökalut. Tutkimusten tuloksina on löydetty menetelmiä femtosekuntilasersykäysten suunnittelua varten. Näillä menetelmillä saadaan kasvatettua sekä HHG:n että korkeaenergisen elektroniemission hyötysuhdetta ja maksimienergiaa. Työssä tutkittiin myös femtosekuntilasersykäysten käyttöä alkalimetalliatomien virittämiseksi kvanttilaskentaa varten. Optimointimenetelmämme ja femtosekuntilasersykäysten käyttö vähentää viritykseen käytettävää aikaa huomattavasti perinteisiin tekniikoihin verrattuina, mutta nykyisessä muodossaan menetelmä ei ole tarpeeksi tarkka, jotta sillä voitaisiin miehittää vain yksi tietty tila. Väitöskirjassa kehitetään myös uusi elementtimenetelmään pohjautuva laskentaohjelmisto, joka on suunniteltu nanorakenteiden attosekunti-ilmiöiden mallinnukseen. Nanorakenteet muuttavat niihin kohdistetun femtosekuntilasersykäyksen paikkariippuvuutta, mitä useimmat aiemmat mallinnusohjelmistot eivät kykene huomioimaan. Kehittämämme ohjelmisto mallintaa näitä tilanteita tehokkaasti ja ottaa huomioon femtosekuntilasersykäysten epähomogeenisen paikkariippuvuuden. Väitöskirjan lopussa on yhteenveto löydöksistämme, joita käsitellään suhteessa muihin alan tuoreisiin tutkimuksiin. Pohdimme myös mahdollisia kehityskohteita sekä suuntaa tuleville tutkimuksille.Attosecond science deals with monitoring and control of electron dynamics in their native, attosecond time scale. Ultrafast electron dynamics is the driving force behind chemical reactions, it determines the optical response of matter, and it is the cornerstone of multiple ultrafast nanoscale imaging techniques. Attosecond phenomena are often driven by strong-field light-matter interaction. Femtosecond laser pulses with electric fields rivaling those of atomic binding forces drive complex nonlinear phenomena in atoms, molecules, and solid state. They include electron excitations, nonlinear frequency up-conversion known as high-order harmonic generation (HHG), and emission of ultra-energetic electrons via above-threshold ionization (ATI). These processes have important roles in ultrafast technologies. For example, HHG is used as a source for coherent X-ray pulses with durations down to attoseconds, ATI is used for building electron wave packets for self-interrogation spectroscopy of matter, and excited Rydberg-states of atoms are prime candidates for multi-qubit quantum computing. Control of strong-field attosecond phenomena can be achieved by shaping the temporal profile of the driving femtosecond pulse in modern light-field synthesizers. This dissertation is a computational expedition to shaping the driving laser pulses for optimizing strong-field light-matter interaction in HHG, ATI, and Rydberg-state preparation in atoms. We begin this dissertation with a brief reviewof relevant strong-field attosecond phenomena with an emphasis on their theoretical modeling. We continue with an overview of control and optimization of these phenomena both from an experimental and a computational point of view. Later, we describe in detail the computational models we have used. The corresponding software is provided in the online supplementary material. Our optimization studies deliver experimentally feasible optimization/control schemes for shaping the driving femtosecond laser pulses to increase the maximum energy and signal strength of HHG and ATI in atomic gases. We also demonstrate how the optimized processes behind the optimized HHG and ATI can be understood with a semiclassical three-step model. The excitation of alkali metals to their Rydberg states is shown to be feasible with multicolor femtosecond fields, decreasing the excitation time by several orders of magnitude compared to traditional methods. On the downside, in its current form the proposed scheme lacks the finesse to populate only a single final state. We also develop a new finite element simulation suite for studying attosecond phenomena in nanostructures. Nanostructures shape the spatial profile of the driving laser field, something existing simulation software cannot easily model. Our software suite is designed for simulating these systems efficiently, and it can incorporate the spatial inhomogeneity of the driving field with ease. We close this dissertation with a summary of our optimization studies and obtained results. They are discussed in the context of other recent work in the field, and we also reflect on possible improvements and directions for future work

Proceedings of the Fifth NASA/NSF/DOD Workshop on Aerospace Computational Control

The Fifth Annual Workshop on Aerospace Computational Control was one in a series of workshops sponsored by NASA, NSF, and the DOD. The purpose of these workshops is to address computational issues in the analysis, design, and testing of flexible multibody control systems for aerospace applications. The intention in holding these workshops is to bring together users, researchers, and developers of computational tools in aerospace systems (spacecraft, space robotics, aerospace transportation vehicles, etc.) for the purpose of exchanging ideas on the state of the art in computational tools and techniques