280 research outputs found
sGDML: Constructing Accurate and Data Efficient Molecular Force Fields Using Machine Learning
We present an optimized implementation of the recently proposed symmetric
gradient domain machine learning (sGDML) model. The sGDML model is able to
faithfully reproduce global potential energy surfaces (PES) for molecules with
a few dozen atoms from a limited number of user-provided reference molecular
conformations and the associated atomic forces. Here, we introduce a Python
software package to reconstruct and evaluate custom sGDML force fields (FFs),
without requiring in-depth knowledge about the details of the model. A
user-friendly command-line interface offers assistance through the complete
process of model creation, in an effort to make this novel machine learning
approach accessible to broad practitioners. Our paper serves as a
documentation, but also includes a practical application example of how to
reconstruct and use a PBE0+MBD FF for paracetamol. Finally, we show how to
interface sGDML with the FF simulation engines ASE (Larsen et al., J. Phys.
Condens. Matter 29, 273002 (2017)) and i-PI (Kapil et al., Comput. Phys.
Commun. 236, 214-223 (2019)) to run numerical experiments, including structure
optimization, classical and path integral molecular dynamics and nudged elastic
band calculations
Molecular Force Fields with Gradient-Domain Machine Learning: Construction and Application to Dynamics of Small Molecules with Coupled Cluster Forces
We present the construction of molecular force fields for small molecules
(less than 25 atoms) using the recently developed symmetrized gradient-domain
machine learning (sGDML) approach [Chmiela et al., Nat. Commun. 9, 3887 (2018);
Sci. Adv. 3, e1603015 (2017)]. This approach is able to accurately reconstruct
complex high-dimensional potential-energy surfaces from just a few 100s of
molecular conformations extracted from ab initio molecular dynamics
trajectories. The data efficiency of the sGDML approach implies that atomic
forces for these conformations can be computed with high-level
wavefunction-based approaches, such as the "gold standard" CCSD(T) method. We
demonstrate that the flexible nature of the sGDML model recovers local and
non-local electronic interactions (e.g. H-bonding, proton transfer, lone pairs,
changes in hybridization states, steric repulsion and interactions)
without imposing any restriction on the nature of interatomic potentials. The
analysis of sGDML molecular dynamics trajectories yields new qualitative
insights into dynamics and spectroscopy of small molecules close to
spectroscopic accuracy
Distributions of Grain Parameters on the Surface of Aircraft Engine Turbine Blades
In the quality assurance system for components cast using the lost wax method, the object of evaluation is the grain size on the surface of the casting. This paper describes a new method for evaluating the primary grain parameters on the surface of aircraft engine turbine blades. Effectiveness of the method has been tested on two macrostructures distinguished by a high degree of diversity in the grain size. The grounds for evaluating the grain parameters consist of geometric measurement of the turbine blade using a laser profilometer and of
approximation of the measurement results using a polynomial of a proper degree. The so obtained analytical non-planar surface serves as a reference point for an assessment of the parameters of grains observed on the real blade surface of a variable curvature. The aspects subjected to evaluation included: the grain areas, shape and elongation coefficients of grains on a non-planar surface of the blade airfoil, using measurements taken on a perpendicular projection by means of a stereoscopic microscope and image analysis methods, and by making calculations using the Mathematica® package
SchNet: A continuous-filter convolutional neural network for modeling quantum interactions
Deep learning has the potential to revolutionize quantum chemistry as it is
ideally suited to learn representations for structured data and speed up the
exploration of chemical space. While convolutional neural networks have proven
to be the first choice for images, audio and video data, the atoms in molecules
are not restricted to a grid. Instead, their precise locations contain
essential physical information, that would get lost if discretized. Thus, we
propose to use continuous-filter convolutional layers to be able to model local
correlations without requiring the data to lie on a grid. We apply those layers
in SchNet: a novel deep learning architecture modeling quantum interactions in
molecules. We obtain a joint model for the total energy and interatomic forces
that follows fundamental quantum-chemical principles. This includes
rotationally invariant energy predictions and a smooth, differentiable
potential energy surface. Our architecture achieves state-of-the-art
performance for benchmarks of equilibrium molecules and molecular dynamics
trajectories. Finally, we introduce a more challenging benchmark with chemical
and structural variations that suggests the path for further work
Inhomogenity of the grain size of aircraft engine turbine polycrystalline blades
The determination of the behaviour of inhomogeneous materials with a complex microstructure requires taking into account the inhomogeneity of the grain size, as it is the basis for the process of designing and modelling effective behaviours. Therefore, the functional description of the inhomogeneity is becoming an important issue. The paper presents an analytical approach to the grain size inhomogeneity, based on the derivative of a logarithmic-logistic function. The solution applied enabled an effective evaluation of the inhomogeneity of two macrostructures of aircraft engine turbine blades, characterized by a high degree of diversity in the grain size. For the investigated single-modal and bimodal grain size distributions on a perpendicular projection and for grains with a non-planar surface, we identified the parameters that describe the degree of inhomogeneity of the constituents of weight distributions and we als o derived a formula describing the overall degree of homogeneity of bimodal distributions. The solution presented in the paper is of a general nature and it can be used to describe the degree of inhomogeneity of multi-modal distributions. All the calculations were performed using the Mathematica® package
Reconstructing Kernel-based Machine Learning Force Fields with Super-linear Convergence
Kernel machines have sustained continuous progress in the field of quantum
chemistry. In particular, they have proven to be successful in the low-data
regime of force field reconstruction. This is because many physical invariances
and symmetries can be incorporated into the kernel function to compensate for
much larger datasets. So far, the scalability of this approach has however been
hindered by its cubical runtime in the number of training points. While it is
known, that iterative Krylov subspace solvers can overcome these burdens, they
crucially rely on effective preconditioners, which are elusive in practice.
Practical preconditioners need to be computationally efficient and numerically
robust at the same time. Here, we consider the broad class of Nystr\"om-type
methods to construct preconditioners based on successively more sophisticated
low-rank approximations of the original kernel matrix, each of which provides a
different set of computational trade-offs. All considered methods estimate the
relevant subspace spanned by the kernel matrix columns using different
strategies to identify a representative set of inducing points. Our
comprehensive study covers the full spectrum of approaches, starting from naive
random sampling to leverage score estimates and incomplete Cholesky
factorizations, up to exact SVD decompositions.Comment: 18 pages, 12 figures, preprin
Towards Exact Molecular Dynamics Simulations with Machine-Learned Force Fields
Molecular dynamics (MD) simulations employing classical force fields
constitute the cornerstone of contemporary atomistic modeling in chemistry,
biology, and materials science. However, the predictive power of these
simulations is only as good as the underlying interatomic potential. Classical
potentials often fail to faithfully capture key quantum effects in molecules
and materials. Here we enable the direct construction of flexible molecular
force fields from high-level ab initio calculations by incorporating spatial
and temporal physical symmetries into a gradient-domain machine learning
(sGDML) model in an automatic data-driven way. The developed sGDML approach
faithfully reproduces global force fields at quantum-chemical CCSD(T) level of
accuracy and allows converged molecular dynamics simulations with fully
quantized electrons and nuclei. We present MD simulations, for flexible
molecules with up to a few dozen atoms and provide insights into the dynamical
behavior of these molecules. Our approach provides the key missing ingredient
for achieving spectroscopic accuracy in molecular simulations
Modifications of the chemical composition and microstructure of flash smelting copper slags in the process of their reduction
Blister copper smelting in a flash smelting furnace results in generation of slag that contains high amounts of copper, iron and lead. Most commonly, this material is subjected to reduction with coke in an electrical furnace. In the present paper, results of investigations on reduction of slag with another reducer, i.e. anthracite dust, are discussed. Each experimental slag was analysed for its microstructure, chemical composition and phase composition. Based on the results, a decopperisation level of the study material was estimated. It was shown that anthracite dust might be considered as an alternative for currently used reducers
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