5,981 research outputs found
WavePacket: A Matlab package for numerical quantum dynamics. III: Quantum-classical simulations and surface hopping trajectories
WavePacket is an open-source program package for numerical simulations in
quantum dynamics. Building on the previous Part I [Comp. Phys. Comm. 213,
223-234 (2017)] and Part II [Comp. Phys. Comm. 228, 229-244 (2018)] which dealt
with quantum dynamics of closed and open systems, respectively, the present
Part III adds fully classical and mixed quantum-classical propagations to
WavePacket. In those simulations classical phase-space densities are sampled by
trajectories which follow (diabatic or adiabatic) potential energy surfaces. In
the vicinity of (genuine or avoided) intersections of those surfaces
trajectories may switch between surfaces. To model these transitions, two
classes of stochastic algorithms have been implemented: (1) J. C. Tully's
fewest switches surface hopping and (2) Landau-Zener based single switch
surface hopping. The latter one offers the advantage of being based on
adiabatic energy gaps only, thus not requiring non-adiabatic coupling
information any more.
The present work describes the MATLAB version of WavePacket 6.0.2 which is
essentially an object-oriented rewrite of previous versions, allowing to
perform fully classical, quantum-classical and quantum-mechanical simulations
on an equal footing, i.e., for the same physical system described by the same
WavePacket input. The software package is hosted and further developed at the
Sourceforge platform, where also extensive Wiki-documentation as well as
numerous worked-out demonstration examples with animated graphics are
available
Efficient computation of the second-Born self-energy using tensor-contraction operations
In the nonequilibrium Green's function approach, the approximation of the
correlation self-energy at the second-Born level is of particular interest,
since it allows for a maximal speed-up in computational scaling when used
together with the Generalized Kadanoff-Baym Ansatz for the Green's function.
The present day numerical time-propagation algorithms for the Green's function
are able to tackle first principles simulations of atoms and molecules, but
they are limited to relatively small systems due to unfavourable scaling of
self-energy diagrams with respect to the basis size. We propose an efficient
computation of the self-energy diagrams by using tensor-contraction operations
to transform the internal summations into functions of external low-level
linear algebra libraries. We discuss the achieved computational speed-up in
transient electron dynamics in selected molecular systems.Comment: 9 pages, 4 figures, 1 tabl
Multi-cultural visualization : how functional programming can enrich visualization (and vice versa)
The past two decades have seen visualization flourish as a research field in its own right, with advances on the computational challenges of faster algorithms, new techniques for datasets too large for in-core processing, and advances in understanding the perceptual and cognitive processes recruited by visualization systems, and through this, how to improve the representation of data. However, progress within visualization has sometimes proceeded in parallel with that in other branches of computer science, and there is a danger that when novel solutions ossify into `accepted practice' the field can easily overlook significant advances elsewhere in the community. In this paper we describe recent advances in the design and implementation of pure functional programming languages that, significantly, contain important insights into questions raised by the recent NIH/NSF report on Visualization Challenges. We argue and demonstrate that modern functional languages combine high-level mathematically-based specifications of visualization techniques, concise implementation of algorithms through fine-grained composition, support for writing correct programs through strong type checking, and a different kind of modularity inherent in the abstractive power of these languages. And to cap it off, we have initial evidence that in some cases functional implementations are faster than their imperative counterparts
A Fredholm Determinant for Semi-classical Quantization
We investigate a new type of approximation to quantum determinants, the
``\qFd", and test numerically the conjecture that for Axiom A hyperbolic flows
such determinants have a larger domain of analyticity and better convergence
than the \qS s derived from the \Gt. The conjecture is supported by numerical
investigations of the 3-disk repeller, a normal-form model of a flow, and a
model 2- map.Comment: Revtex, Ask for figures from [email protected]
Electron transfer rates for asymmetric reactions
We use a numerically exact real-time path integral Monte Carlo scheme to
compute electron transfer dynamics between two redox sites within a spin-boson
approach. The case of asymmetric reactions is studied in detail in the least
understood crossover region between nonadiabatic and adiabatic electron
transfer. At intermediate-to-high temperature, we find good agreement with
standard Marcus theory, provided dynamical recrossing effects are captured. The
agreement with our data is practically perfect when temperature renormalization
is allowed. At low temperature we find peculiar electron transfer kinetics in
strongly asymmetric systems, characterized by rapid transient dynamics and
backflow to the donor.Comment: 13 pages, 4 figures, submitted to Chemical Physics Special Issue on
the Spin-Boson Problem, ed. by H. Grabert and A. Nitza
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