排序方式: 共有105条查询结果,搜索用时 15 毫秒
21.
We present a robust linear-scaling algorithm to compute the symmetric square-root or Lowdin decomposition of the atomic-orbital overlap matrix. The method is based on Newton-Schulz iterations with a new approach to starting matrices. Calculations on 12 chemically and structurally diverse molecules demonstrate the efficiency and reliability of the method. Furthermore, the calculations show that linear scaling is achieved. 相似文献
22.
Luttmann E Ensign DL Vaidyanathan V Houston M Rimon N Øland J Jayachandran G Friedrichs M Pande VS 《Journal of computational chemistry》2009,30(2):268-274
Implementation of molecular dynamics (MD) calculations on novel architectures will vastly increase its power to calculate the physical properties of complex systems. Herein, we detail algorithmic advances developed to accelerate MD simulations on the Cell processor, a commodity processor found in PlayStation 3 (PS3). In particular, we discuss issues regarding memory access versus computation and the types of calculations which are best suited for streaming processors such as the Cell, focusing on implicit solvation models. We conclude with a comparison of improved performance on the PS3's Cell processor over more traditional processors. 相似文献
23.
ABSTRACTWhen a set of orthogonal orbitals is localised using orthogonal transformations, the orbital metric is conserved as the unit matrix during the localisation. In this paper we describe how non-orthogonal orbitals may be localised by requiring that the orbital metric is conserved. In particular, we demonstrate how exponential mappings may be used to parametrise orbital transformations such that the orbital metric is conserved. Using this parametrisation, the localisation of non-orthogonal orbitals becomes a generalisation of the localisation for orthogonal orbitals, where the conservation of a unit metric is replaced by the conservation of a non-unit metric. As a result, standard orbital localisation functions and optimisation algorithms that have been used for localising orthogonal orbitals may also be used to localise non-orthogonal orbitals. Numerical illustrations show that the thickness of the orbital tails may be reduced when a set of non-orthogonal orbitals is localised compared to the orthogonal counterpart, and further that the physical interpretation of occupied orbitals for representing chemical bonds is preserved. 相似文献
24.
Propylene carbonate and a mixture of two secondary amides, N-methylformamide and N-ethylacetamide, are investigated by means of broadband dielectric and mechanical shear spectroscopy. The similarities between the rheological and the dielectric responses of these liquids and of the previously investigated tripropylene glycol are discussed within a simple approach that employs an electrical circuit for describing the frequency-dependent behavior of viscous materials. The circuit is equivalent to the Gemant-DiMarzio-Bishop model, but allows for a negative capacitive element. The circuit can be used to calculate the dielectric from the mechanical response and vice versa. Using a single parameter for a given system, good agreement between model calculations and experimental data is achieved for the entire relaxation spectra, including secondary relaxations and the Debye-like dielectric peak in the secondary amides. In addition, the predictions of the shoving model are confirmed for the investigated liquids. 相似文献
25.
Jakobsen B Hecksher T Christensen T Olsen NB Dyre JC Niss K 《The Journal of chemical physics》2012,136(8):081102
The frequency-dependent dielectric constant, shear and adiabatic bulk moduli, longitudinal thermal expansion coefficient, and longitudinal specific heat have been measured for two van der Waals glass-forming liquids, tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl-4-ether. Within the experimental uncertainties the loss-peak frequencies of the measured response functions have identical temperature dependence over a range of temperatures, for which the Maxwell relaxation time varies more than nine orders of magnitude. The time scales are ordered from fastest to slowest as follows: Shear modulus, adiabatic bulk modulus, dielectric constant, longitudinal thermal expansion coefficient, and longitudinal specific heat. The ordering is discussed in light of the recent conjecture that van der Waals liquids are strongly correlating, i.e., approximate single-parameter liquids. 相似文献
26.
Mahajabin Rahman Benjamin M. G. D. Carter Shibu Saw Ian M. Douglass Lorenzo Costigliola Trond S. Ingebrigtsen Thomas B. Schrder Ulf R. Pedersen Jeppe C. Dyre 《Molecules (Basel, Switzerland)》2021,26(6)
In the condensed liquid phase, both single- and multicomponent Lennard–Jones (LJ) systems obey the “hidden-scale-invariance” symmetry to a good approximation. Defining an isomorph as a line of constant excess entropy in the thermodynamic phase diagram, the consequent approximate isomorph invariance of structure and dynamics in appropriate units is well documented. However, although all measures of the structure are predicted to be isomorph invariant, with few exceptions only the radial distribution function (RDF) has been investigated. This paper studies the variation along isomorphs of the nearest-neighbor geometry quantified by the occurrence of Voronoi structures, Frank–Kasper bonds, icosahedral local order, and bond-orientational order. Data are presented for the standard LJ system and for three binary LJ mixtures (Kob–Andersen, Wahnström, ). We find that, while the nearest-neighbor geometry generally varies significantly throughout the phase diagram, good invariance is observed along the isomorphs. We conclude that higher-order structural correlations are no less isomorph invariant than is the RDF. 相似文献
27.
A general configuration interaction (CI) algorithm incorporating one- and two-electron spin-orbit operators is presented.
The algorithm is determinant based and enables the use of highly vectorized non-relativistic algorithms in the most operation-intensive
part. Excitations between α and β spin orbitals are avoided in the time consuming parts by performing separate S
+ and S
− operations. The relativistic CI expansions are often very large, so the algorithms require only the presence of segments
of vectors in memory. Double-group symmetry is fully accounted for and time-reversal symmetry is exploited for both even and
odd numbers of electrons.
Received: 12 October 1996 / Accepted: 24 January 1997 相似文献
28.
We present the initial implementation of a determinant-based general-order coupled cluster method which fully accounts for
relativistic effects within the four-component framework. The method opens the way for the treatment of multi-reference problems
through a state-selective expansion of the model space. The evaluation of the coupled cluster vector function is carried out
via relativistic configuration interaction expansions. The implementation is based on a large-scale configuration interaction
technique, which may efficiently treat long determinant expansions of more than 108 terms. We demonstrate the capabilities of the new method in calculations of complete potential energy curves of the HBr molecule.
The inclusion of spin–orbit interaction and higher excitations than coupled cluster double excitations, either by multi-reference
model spaces or the inclusion of full iterative triple excitations, lead to highly accurate results for spectral constants
of HBr.
An erratum to this article can be found at 相似文献
29.
Jeppe Berggreen Høj 《Acta Analytica》2010,25(3):299-316
In this paper, I examine an account of instrumental reasoning recently put forth by John Broome. His key suggestion is that
anyone who engages in reasoning about his intentions also believes that he will do what he intends to do and that combined
with a belief about necessary means this creates rational pressure towards believing that one will take the necessary means.
I argue that Broome’s model has three significant problems; his key premise is false—the sincere expression of an intention
does not entail the belief that one will successfully execute that intention; his account yields a model of instrumental reasoning
that is uncomfortably reflective; he seems unable to explain the rational pressure towards taking necessary means that arises
directly from having an end and an instrumental belief. All three problems, I argue, are a consequence of Broome’s inadequate
position on what it is to intend to do something. 相似文献
30.
Jeppe Skott 《ZDM》2013,45(4):547-559
The relationship between acquisitionism and participationism is a challenge in research on and with teachers. This study uses a patterns-of-participation framework (PoP), which aims to develop coherent and dynamic understandings of teaching as well as to meet the conceptual and methodological problems of other approaches. The paper presents PoP theoretically, but also illustrates its empirical use. It presents a novice teacher, Anna, who often engages with mathematics and with aspects of ‘the reform’ in ways that link well with how she builds relationships with her students and positions herself in her team of teachers. However, in other situations her engagement with mathematics is overshadowed by her involvement in other practices. The study suggests that there is some potential in PoP in spite of methodological difficulties. 相似文献