1,744 research outputs found
Exploring High Dimensional Free Energy Landscapes: Temperature Accelerated Sliced Sampling
Biased sampling of collective variables is widely used to accelerate rare
events in molecular simulations and to explore free energy surfaces. However,
computational efficiency of these methods decreases with increasing number of
collective variables, which severely limits the predictive power of the
enhanced sampling approaches. Here we propose a method called Temperature
Accelerated Sliced Sampling (TASS) that combines temperature accelerated
molecular dynamics with umbrella sampling and metadynamics to sample the
collective variable space in an efficient manner. The presented method can
sample a large number of collective variables and is advantageous for
controlled exploration of broad and unbound free energy basins. TASS is also
shown to achieve quick free energy convergence and is practically usable with
ab initio molecular dynamics techniques
Sampling Free Energy Surfaces as Slices by Combining Umbrella Sampling and Metadynamics
Metadynamics (MTD) is a very powerful technique to sample high-dimensional
free energy landscapes, and due to its self-guiding property, the method has
been successful in studying complex reactions and conformational changes. MTD
sampling is based on filling the free energy basins by biasing potentials and
thus for cases with flat, broad and unbound free energy wells, the
computational time to sample them becomes very large. To alleviate this
problem, we combine the standard Umbrella Sampling (US) technique with MTD to
sample orthogonal collective variables (CVs) in a simultaneous way. Within this
scheme, we construct the equilibrium distribution of CVs from biased
distributions obtained from independent MTD simulations with umbrella
potentials. Reweighting is carried out by a procedure that combines US
reweighting and Tiwary-Parrinello MTD reweighting within the Weighted Histogram
Analysis Method (WHAM). The approach is ideal for a controlled sampling of a CV
in a MTD simulation, making it computationally efficient in sampling flat,
broad and unbound free energy surfaces. This technique also allows for a
distributed sampling of a high-dimensional free energy surface, further
increasing the computational efficiency in sampling. We demonstrate the
application of this technique in sampling high-dimensional surface for various
chemical reactions using ab initio and QM/MM hybrid molecular dynamics
simulations. Further, in order to carry out MTD bias reweighting for computing
forward reaction barriers in ab initio or QM/MM simulations, we propose a
computationally affordable approach that does not require recrossing
trajectories
Confusing Sterile Neutrinos with Deviation from Tribimaximal Mixing at Neutrino Telescopes
We expound the impact of extra sterile species on the ultra high energy
neutrino fluxes in neutrino telescopes. We use three types of well-known flux
ratios and compare the values of these flux ratios in presence of sterile
neutrinos, with those predicted by deviation from the tribimaximal mixing
scheme. We show that in the upcoming neutrino telescopes, its easy to confuse
between the signature of sterile neutrinos with that of the deviation from
tribimaximal mixing. We also show that if the measured flux ratios acquire a
value well outside the range predicted by the standard scenario with three
active neutrinos only, it might be possible to tell the presence of extra
sterile neutrinos by observing ultra high energy neutrinos in future neutrino
telescopes.Comment: 22 pages, version to appear in Phys. Rev.
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