7,280 research outputs found
Achieving plane wave accuracy in linear-scaling density functional theory applied to periodic systems: a case study on crystalline silicon
No full textLinear-scaling methods for density functional theory promise to revolutionize the scope and scale of
first-principles quantum mechanical calculations. Crystalline silicon has been the system of choice
for exploratory tests of such methods in the literature, yet attempts at quantitative comparisons
under linear-scaling conditions with traditional methods or experimental results have not been
forthcoming. A detailed study using the ONETEP code is reported here, demonstrating for the first
time that plane wave accuracy can be achieved in linear-scaling calculations on periodic systems
Erratum: Achieving plane wave accuracy in linear-scaling density functional theory applied to periodic systems: A case study on crystalline silicon (J. Chem. Phys. (2007) 127 (164712) DOI: 10.1063/1.2796168)
No full textIt has been drawn to the authors' attention that our original article did not appropriately attribute a figure that we had reused from our own previous work.</p
Workshop report. Linear-Scaling Ab Initio Calculations: Applications and Future Directions
No full textThe study of properties and of processes in materials, frequently hinges upon understanding phenomena which originate at the atomic level. In such cases the accurate description of the interactions between large numbers of atoms is critical and in turn requires the accurate description of the electrons which play a crucial role in the bonding of atoms into molecules, surfaces and solids. This can only be achieved by solving the equations of quantum mechanics. These
equations are too complicated to solve exactly; however their solutions can be approximated by computational techniques. The most accurate ? but also most computationally demanding ? are the “ab initio” techniques which do not use any empirical adjustable parameters. Amongst them, the Density Functional Theory (DFT) formulation of quantum mechanics stands out as an excellent compromise between accuracy and computational efficiency. However, the applicability of ab initio techniques is severely limited by poor scaling: the computational effort needed to perform an ab initio calculation increases with (at least) the third power of the number of atoms, N. This cubic-scaling bottleneck limits the number of atoms we can study to a few hundred at most, even on parallel supercomputers. To overcome this length-scale limitation, a number of researchers worldwide have been pioneering the development of a novel class of ab initio methods with linear-scaling or “Order N” (O(N)) computational cost which nevertheless retain the same high level of accuracy as the conventional approaches. While physically motivated, such methods have proved particularly hard to develop as they introduce highly non-trivial localisation constraints. Nevertheless, many major obstacles have been overcome and a number of O(N)
methods (SIESTA, CONQUEST, ONETEP, etc.) for ground state DFT calculations on systems with a gap (e.g. molecules, semiconductors and insulators) are now available and have reached a state of maturity that allows them to be used to study ”real” materials. The particular focus of this workshop is therefore to look forward to what can be achieved in the next few years. Our aim is twofold: (1) As O(N) methods are currently extending the applicability of DFT calculations
to problems involving biomolecules and nanostructures they are leading to completely new levels of understanding of these systems. This CECAM meeting will give us the opportunity to make an appraisal of such large-scale simulations and their potential to connect more directly to experiments. (2) We also want to examine the options for extending linear-scaling to problems that cannot be treated by ground-state DFT but require other, more complex approaches. These include methods for treating metallic systems, excited states and wavefunction-based theories for including electronic correlation. Finding ways to transform these methods to linear-scaling
cost, and hence extent their applicability to the nano-scale, is the next big challenge that the community of developers of large-scale electronic structure methods is beginning to face. We
hope that this workshop will stimulate these major new O(N) methodological developments by bringing together the leading groups in the development of O(N) DFT methods with the leading
groups in the development of metal and excited-state or wavefunction-based methods. Strong emphasis during the workshop will be given to discussion in order to promote the exchange
of ideas between different communities (Physics, Chemistry, Materials Science, Biochemistry) which are all interested in large-scale applications with ab initio accuracy but are approaching
them from different perspectives
Introduction
No full textThis is the third Digital Enlightenment Yearbook, part of an annual series which began in 2012 under the auspices of the Digital Enlightenment Forum (http://www.digitalenlightenment.org/). This aims to shed light on today’s rapid technological changes and their impact on society and its governance, taking inspiration from Enlightenment thought as well as from the many transformations and evolutions that have taken place since. It examines digital technologies and their application openly with essential societal values in mind. Such values might assume novel forms, taking advantage of both the knowledge and unprecedented access to information which exist today.The aim of the Yearbook is to track the evolution of digital technology – which sometimes happens so fast that even an annual publication occasionally seems inadequate. The 2012 yearbook focused on trust, privacy and the defence of the values of the World Wide Web. In 2013, the main topic was the value of personal data, to ourselves and to the commercial world, with contributions from academics, technologists and entrepreneurs. This year, the focus has shifted from individuals to their relationships with their networks, as we explore “Social networks and social machines, surveillance and empowerment.”In what is now the well-established tradition of the Yearbooks, different stakeholders in society and various disciplinary communities (technology, law, philosophy, sociology, economics, policymaking) bring their very different opinions and perspectives to bear on this topic, forming a basis for inspiring and constructive cross-disciplinary discussions
The Concept of Genius in D. A. Granin’s Work (Based on the Novel “Evenings with Peter the Great”)
No full textThe article deals with D. A. Granin’s concept of history as presented in the novel “Evenings with Peter the Great”. The author of the novel argues that historical process is driven and streamlined by people endowed with rare gifts and deep urge to create such as the first Russian emperor Peter the Great
Zechariah 9-14 as the substructure of 1 Peter’s eschatological program
No full textThe principal aim of this study is to discern what has shaped the author of 1 Peter to regard Christian suffering as a necessary (1.6) and to-be-expected (4.12) component of faithful allegiance to Jesus Christ. Most research regarding suffering in 1 Peter has limited the scope of inquiry to two particular aspects—its cause and nature, and the strategies that the author of 1 Peter employs in order to enable his addressees to respond in faithfulness. There remains, however, the need for a comprehensive explanation for the source that has generated 1 Peter’s theology of Christian suffering. If Jesus truly is the Christ, God’s chosen redemptive agent who has come to restore God’s people, then how can it be that Christian suffering is a necessary part of discipleship after his coming, death and resurrection? What led the author of 1 Peter to such a startling conclusion, which seems to runs against the grain of the eschatological hopes and expectations of Jewish restoration ideology?
This thesis analyzes the appropriation of shepherd and fiery trials imagery,
and argues that the author of 1 Peter is dependent upon Zechariah 9-14 for his
theology of Christian suffering. Said in another way, the eschatological program of
Zechariah 9-14, read through the lens of the Gospel, functions as the substructure
for 1 Peter’s eschatology and thus its theology of Christian suffering.
In support of this hypothesis, this study highlights the fact that Zechariah 9-
14 was available and appropriated in early Christianity, in particular in the Passion
Narrative tradition; that the shepherd imagery of 1 Pet 2.25 is best understood
within the milieu of the Passion Narrative tradition, and that it alludes to the
eschatological program of Zechariah 9-14; that the fiery trials imagery found in 1
Peter 1.6-7 and 1 Pet 4.12 is distinct from that which we find in Greco-Roman and OT
wisdom sources, and that it shares exclusive parallels with some unique features of
the eschatological program of Zechariah 9-14; that Zechariah 9-14 offers a more
satisfying explanation for the modification of Isa 11.2 in 1 Pet 4.14, the transition
from 4.12-19 to 5.1-4, why Peter has oriented his letter with the term διασπορά,
and why he has described his addresses as οἶκος τοῦ θεοῦ; and finally that 1 Peter
contains an implicit foundational narrative that shares distinct parallels with the
eschatological program of Zechariah 9-14.
We can conclude that 1 Peter offers a unique vista into the way in which at
least one early Christian witness came to understand and to communicate the fact
that Christian suffering was a necessary feature of faithful allegiance to Jesus Christ
Copyright & Your Research
No full textAs publishing options increase in number, it is ever more important that university authors manage their copyrights in a way that ensures maximum benefit to them and to the university. Peter Hirtle, Senior Policy Advisor in the Cornell University Library and a Research Fellow at the Berkman Center for Internet & Society at Harvard University, will give an overview of the sometimes puzzling issues surrounding creating, securing, owning, and using copyrighted works. Topics will include author agreements and contracts, the public access requirements in some federal grants, new publishing options, and the management of your copyrights. The session will benefit those who want to gain a better understanding of the changing nature of scholarly communications. PRESENTATION BY Peter B. Hirtle, Senior Policy Advisor, Cornell University Library, and Research Fellow, Berkman Center for Internet Security and Society, Harvard Universit
Electrostatic interactions in finite systems treated with periodic boundary conditions: application to linear-scaling density functional theory
No full textWe present a comparison of methods for treating the electrostatic interactions of finite, isolated systems within periodic boundary conditions (PBCs), within density functional theory (DFT), with particular emphasis on linear-scaling (LS) DFT. Often, PBCs are not physically realistic but are an unavoidable consequence of the choice of basis set and the efficacy of using Fourier transforms to compute the Hartree potential. In such cases the effects of PBCs on the calculations need to be avoided, so that the results obtained represent the open rather than the periodic boundary. The very large systems encountered in LS-DFT make the demands of the supercell approximation for isolated systems more difficult to manage, and we show cases where the open boundary (infinite cell) result cannot be obtained from extrapolation of calculations from periodic cells of increasing size. We discuss, implement, and test three very different approaches for overcoming or circumventing the effects of PBCs: truncation of the Coulomb interaction combined with padding of the simulation cell, approaches based on the minimum image convention, and the explicit use of open boundary conditions (OBCs). We have implemented these approaches in the ONETEP LS-DFT program and applied them to a range of systems, including a polar nanorod and a protein. We compare their accuracy, complexity, and rate of convergence with simulation cell size. We demonstrate that corrective approaches within PBCs can achieve the OBC result more efficiently and accurately than pure OBC approache
Comparison of variational real-space representations of the kinetic energy operator
No full textWe present a comparison of real-space methods based on regular grids for electronic structure calculations that are designed to have basis set variational properties, using as a reference the conventional method of finite differences (a real-space method that is not variational) and the reciprocal-space plane-wave method which is fully variational. We find that a definition of the finite-difference method [P. Maragakis, J. Soler, and E. Kaxiras, Phys. Rev. B 64, 193101 (2001)] satisfies one of the two properties of variational behavior at the cost of larger errors than the conventional finite-difference method. On the other hand, a technique which represents functions in a number of plane waves which is independent of system size closely follows the plane-wave method and therefore also the criteria for variational behavior. Its application is only limited by the requirement of having functions strictly localized in regions of real space, but this is a characteristic of an increasing number of modern real-space methods, as they are designed to have a computational cost that scales linearly with system size
Recent progress in linear-scaling density functional calculations with plane waves and pseudopotentials: the ONETEP code
No full textThe ONETEP program employs the single-particle density matrix reformulation of Kohn–Sham density functional theory to achieve computational cost and memory requirements which increase only linearly with the number of atoms. As the code employs a plane wave basis set (in the form of periodic sinc functions) and pseudopotentials it is able to achieve levels of accuracy and systematic improvability comparable to those of conventional cubic-scaling plane wave approaches. The code has been developed with the aim of running efficiently on a variety of parallel architectures ranging from commodity clusters with tens of processors to large national facilities with thousands of processors. Recent and ongoing studies which we are performing with ONETEP involve problems ranging from materials to biomolecules to nanostructures
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