2,701 research outputs found
Rapid Generation of Optimal Generalized Monkhorst-Pack Grids
Computational modeling of the properties of crystalline materials has become
an increasingly important aspect of materials research, consuming hundreds of
millions of CPU-hours at scientific computing centres around the world each
year, if not more. A routine operation in such calculations is the evaluation
of integrals over the Brillouin zone. We have previously demonstrated that
performing such integrals using generalized Monkhorst-Pack k-point grids can
roughly double the speed of these calculations relative to the widely-used
traditional Monkhorst-Pack grids, and such grids can be rapidly generated by
querying a free, internet-accessible database of pre-generated grids. To
facilitate the widespread use of generalized k-point grids, we present new
algorithms that allow rapid generation of optimized generalized Monkhorst-Pack
grids on the fly, an open-source library to facilitate their integration into
external software packages, and an open-source implementation of the database
tool that can be used offline. We also present benchmarks of the speed of our
algorithms on structures randomly selected from the Inorganic Crystal Structure
Database. For grids that correspond to a real-space supercell with at least 50
angstroms between lattice points, which is sufficient to converge density
functional theory calculations within 1 meV/atom for nearly all materials, our
algorithm finds optimized grids in an average of 0.19 seconds on a single
processing core. For 100 angstroms between real-space lattice points, our
algorithm finds optimal grids in less than 5 seconds on average
Directed searches for continuous gravitational waves from binary systems: parameter-space metrics and optimal Scorpius X-1 sensitivity
We derive simple analytic expressions for the (coherent and semi-coherent)
phase metrics of continuous-wave sources in low-eccentricity binary systems,
both for the long-segment and short- segment regimes (compared to the orbital
period). The resulting expressions correct and extend previous results found in
the literature. We present results of extensive Monte-Carlo studies comparing
metric mismatch predictions against the measured loss of detection statistic
for binary parameter offsets. The agreement is generally found to be within ~
10%-30%. As an application of the metric template expressions, we estimate the
optimal achievable sensitivity of an Einstein@Home directed search for Scorpius
X-1, under the assumption of sufficiently small spin wandering. We find that
such a search, using data from the upcoming advanced detectors, would be able
to beat the torque- balance level [1,2] up to a frequency of ~ 500 - 600 Hz, if
orbital eccentricity is well-constrained, and up to a frequency of ~ 160 - 200
Hz for more conservative assumptions about the uncertainty on orbital
eccentricity.Comment: 25 pages, 8 figure
Design degrees of freedom and mechanisms for complexity
We develop a discrete spectrum of percolation forest fire models characterized by increasing design degrees of freedom (DDOF’s). The DDOF’s are tuned to optimize the yield of trees after a single spark. In the limit of a single DDOF, the model is tuned to the critical density. Additional DDOF’s allow for increasingly refined spatial patterns, associated with the cellular structures seen in highly optimized tolerance (HOT). The spectrum of models provides a clear illustration of the contrast between criticality and HOT, as well as a concrete quantitative example of how a sequence of robustness tradeoffs naturally arises when increasingly complex systems are developed through additional layers of design. Such tradeoffs are familiar in engineering and biology and are a central aspect of the complex systems that can be characterized as HOT
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