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ANI-1: an extensible neural network potential with DFT accuracy at force field computational cost
Deep learning is revolutionizing many areas of science and technology, especially image, text, and speech recognition. In this paper, we demonstrate how a deep neural network (NN) trained on quantum mechanical (QM) DFT calculations can learn an accurate and transferable potential for organic molecules. We introduce ANAKIN-ME (Accurate NeurAl networK engINe for Molecular Energies) or ANI for short. ANI is a new method designed with the intent of developing transferable neural network potentials that utilize a highly-modified version of the Behler and Parrinello symmetry functions to build single-atom atomic environment vectors (AEV) as a molecular representation. AEVs provide the ability to train neural networks to data that spans both configurational and conformational space, a feat not previously accomplished on this scale. We utilized ANI to build a potential called ANI-1, which was trained on a subset of the GDB databases with up to 8 heavy atoms in order to predict total energies for organic molecules containing four atom types: H, C, N, and O. To obtain an accelerated but physically relevant sampling of molecular potential surfaces, we also proposed a Normal Mode Sampling (NMS) method for generating molecular conformations. Through a series of case studies, we show that ANI-1 is chemically accurate compared to reference DFT calculations on much larger molecular systems (up to 54 atoms) than those included in the training data set.
Secondary effectiveness factors for catalytic reactions in series: extension to slab, cylindrical, and spherical geometries
‘Secondary’ effectiveness factors are developed for reactions in series that are useful for controlling the yield of the intermediate product ( B ).
An extensive assessment of the performance of pairwise and many-body interaction potentials in reproducing ab initio benchmark binding energies for water clusters n = 2–25
We assess the performance of 7 pairwise additive (TIP3P, TIP4P, TIP4P-ice, TIP5P, OPC, SPC, SPC/E) and 8 families of many-body potentials (q-AQUA, HIPPO, AMOEBA, EFP, TTM, WHBB, MB-pol, MB-UCB) in reproducing high-level ab initio benchmark values, CCSD(T) or MP2 at the complete basis set (CBS) limit for the binding energy and the many-body expansion (MBE) of water clusters n = 2–11, 16–17, 20, 25. By including a large range of cluster sizes having dissimilar hydrogen bonding networks, we obtain an understanding of how these potentials perform for different hydrogen bonding arrangements that are mostly outside of their parameterization range. While it is appropriate to compare the results of ab initio based many-body potentials directly to the electronic binding energies (D e 's), the pairwise additive ones are compared to the enthalpies at T = 298 K, ΔH(298 K), as the latter class of force fields are parametrized to reproduce enthalpies (implicitly accounting for zero-point energy corrections) rather than binding energies. We find that all pairwise additive potentials considered overestimate the reference ΔH values for the n = 2–25 clusters by >13%. For the water dimer (n = 2) in particular, the errors are in the range 83–119% for the pairwise additive potentials studied since these are based on an effective rather than the true 2-body interaction specifically designed as a means of partially accounting for the missing many-body terms. This stronger 2-body interaction is achieved by an enhanced monomer dipole moment that mimics its increase from the gas phase monomer to the condensed phase value. Indeed, for cluster sizes n ≥ 4 the percent deviations become slightly smaller (albeit all exceeding 13%). In contrast, we find that the many-body potentials perform more accurately in reproducing the electronic binding energies (D e 's) throughout the entire cluster range (n = 2–25), all reproducing the ab initio benchmark binding energies within ±7% of the respective CBS values. We further assess the ability of a subset of the many-body potentials (MB-UCB, q-AQUA, MB-pol, and TTM2.1-F) to also reproduce the magnitude of the ab initio many-body energy terms for water cluster sizes n = 7, 10, 16 and 17. The potentials show an overall good agreement with the available benchmark values. However, we identify characteristic differences upon comparing the many-body terms at both the ab initio-optimized geometries and the respective potential-optimized geometries to the reference ab initio values. Additionally, by applying this analysis to a wide range of cluster sizes, trends in the MBE of the potentials with increasing cluster size can be identified. Finally, in an attempt to draw a parallel between the pairwise additive and many-body potentials, we report the analysis of the individual molecular dipole moments for water clusters with 1 to ~4 solvation shells with the TTM2.1-F potential. We find that the internally solvated water molecules have in general a larger molecular dipole moment ranging from 2.6–3.0 D. This justifies the use of an enhanced, with respect to the gas-phase value, molecular dipole moment for the pairwise additive potentials, which is intended to fold in the many body terms into an effective (enhanced) pairwise interaction through the choice of the charges. These results have important implications for the development of future generations of efficient, transferable, and highly accurate classical interaction potentials in both the pairwise additive and many-body categories.
Extension of nature's NIR-I chromophore into the NIR-II region
Two annulated bacteriochlorin isomers exhibit profoundly different spectral and photophysical features, which are attributed to the absence or presence of electronic (and vibronic) mixing of x - and y -polarized transitions/states.
The impact of second coordination sphere functional group extension on product selectivity for manganese bipyridyl CO 2 reduction electrocatalysts
Utilizing the well established manganese bipyridyl class of homogeneous electrocatalyst, four new ligands are studied to probe the influence of distal, outer coordination sphere, H-bonding and steric effects on product selectivity for proton-coupled electrocatalytic CO 2 reduction. The presence of a simple acetate functional group in the second coordination sphere provides a high selectivy for CO 2 -to-CO conversion irrespective of proton source (H 2 O vs. PhOH) or applied potential. The o-(methoxybenzoate)phenyl second/outer coordination sphere at the bipyridyl 6,6′-positions imparts poor product selectivity. In contrast, upon conjugation of the acetate functional group with the N-Boc-alanine moiety, a CO : HCO 2 − product selectivity of ∼1 : 1 is observed at the high overpotential catalytic wave (for both H 2 O and PhOH acids). Computed enthalpy and free energy of activation parameters suggest that selective CO 2 insertion at the manganese hydride transition state is favored, over protonation, consistent with negligible hydrogen production during controlled potential electrolysis studies.
Central π-conjugated extension in quinoxaline-based small-molecule acceptors as guest components enabling high-performance ternary organic solar cells
Ternary strategies have critical roles in pursuing high efficiencies for organic solar cells (OSCs).
Quantum protocol for decision making and verifying truthfulness among N ‐quantum parties: Solution and extension of the quantum coin flipping game
Abstract The authors devised a protocol that allows two parties, who may malfunction or intentionally convey incorrect information in communication through a quantum channel, to verify each other's measurements and agree on each other's results. This has particular relevance in a modified version of the quantum coin flipping game. The key innovation of the authors’ work includes the new design of a quantum coin that excludes any advantage of cheating, by which the long‐standing problem of the fair design of the game is, affirmatively, solved. Furthermore, the analysis is extended to N ‐parties communicating with each other, where multiple solutions for the verification of each player's measurement is proposed. The results in the N ‐party scenario could have particular relevance for the implementation of future quantum networks, where verification of quantum information is a necessity.
The H I absorption zoo: JVLA extension to z ~ 0.4
Here, we present an H I 21 cm absorption study of a sample of 26 radio-loud active galactic nuclei (AGN) at 0.25 < z < 0.4 carried out with the Karl G. Jansky Very Large Array. Our aim was to study the rate of incidence of H I in different classes of radio AGN, the morphology and kinematics of the detected H I, and the nature of the interaction between the H I and the radio source at these redshifts. Our sample consists of 14 sources with sizes of up to tens of kpc and 12 compact sources (< a few kpc) in the radio-power range 10 25.7 W Hz –1 –10 26.5 W Hz –1 . We detect H I in five sources, corresponding to a detection rate of ~19%. Within the error bars, this agrees with the detection rate found at lower redshifts. We find that the rest-frame UV luminosities of most of the sources in the sample, including all the detections, are below the proposed threshold above which the H I is supposed to have been ionised. An analysis of the optical emission-line spectra of the sources shows that despite their high radio powers, about one-third of the sample, including two detections, are low-ionisation sources. The radio continuum emission from the sources detected in H I is unresolved at ~5 to 10 kpc scales in our observations, but shows extended structure on parsec scales. We analysed the H I 21 cm absorption spectra of the detections to understand the morphology and kinematics of H I. The absorption profiles are mostly complex with widths between the nulls ranging from ~60 km s –1 to 700 km s –1 . These detections also exhibit remarkably high H I column densities in the range ~10 21 cm –2 –10 22 cm –2 for T spin = 100 K and unit covering factor. Our modelling of the H I 21 cm absorption profiles suggests that in two sources the gas appears to be disturbed, and in three cases, including one with disturbed H I, the majority of the absorption is consistent with it arising from an H I disc. Despite the high radio power of our sources, we do not detect fast outflows. However, the optical emission lines in these detections show the presence of significantly disturbed gas in the nuclear regions in the form of very wide and highly blueshifted emission-line components. Since some of our detections are also low-ionisation AGN, it is quite possible that this disturbance is caused by the radio jets. Overall, our findings point towards a continuation of the low-z trends in the H I detection rate and the incidence of H I in radio AGN up to z ~ 0.4.
Interchange, Extension and Validation of R-matrix fits for gamma production
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The Extension of the Hauser-Feshbach Fission Fragment Decay Model to Multi-chance Fission and its Application to 239 Pu
The Hauser-Feshbach fission fragment decay model, HF3D, calculates the statistical decay of fission fragments through both prompt and delayed neutron and γ-ray emissions in a deterministic manner. While previously limited to the calculation of only first-chance fission, the model has recently been extended to include multi-chance fission, up to neutron incident energies of 20 MeV. The deterministic decay takes as input prescission quantities–fission probabilities, pre-fission neutron energies, and the average energy causing fission– and post-scission quantities–yields in mass, charge, total kinetic energy, spin, and parity. From those fission fragment initial conditions, the full decay is followed through both prompt and delayed particle emissions. The evaporation of the prompt neutrons and γ rays is calculated through the Hauser-Feshbach statistical theory, taking into account the competition between neutron and γ-ray emission, conserving energy, spin, and parity. The delayed emission is taken into account using time-independent calculation using decay data. This whole formulation allows for the calculation of prompt neutron and γ-ray properties, such as multiplicities and energy distributions, both independent and cumulative fission yields, and delayed neutron observables, in a consistent framework. Here, we describe the implementation of multi-chance fission into the HF 3 D model, and show an example of prompt and delayed quantities beyond first-chance fission, using the example of neutron-induced fission on 239 Pu. This expansion represents significant progress in consistently modeling the emission of prompt and delayed particles from fissile systems.
A different approach to obtain Mayer's extension to stationary single particle Wigner distribution
It is shown that the stationary collisionless single-particle Wigner equation in one dimension containing quantum corrections at the lowest order is satisfied by a distribution function that is similar in form to the Maxwellian distribution with an effective mass and a generalized potential. The distribution is used to study quantum corrections to electron hole solutions.
An after-market, five-port vertical beam line extension for the PETtrace
Most commercial cyclotrons intended for medical isotope production provide a limited number of beam ports crowded into a minimal vault space. Taking advantage of our new lab construction, we planned and installed a beam-line on port Music-Sharp-Sign 2 of our GEMS PETtrace to bring beam to an additional 5 target positions. These are oriented in the vertical plane, with the downward directed beam well suited for molten target substrates.
Extension of thickness-dependent dielectric breakdown law on adiabatically compressed ferroelectric materials
It is experimentally found that the E{sub b}(d) = {gamma} {center_dot} d{sup -{xi}} law describing the thickness-dependent breakdown electric field for solid dielectrics at ambient conditions can be extended for dielectrics in other thermodynamic states. It follows from the experimental results reported herein that the breakdown field, E{sub b}(d), of Pb(Zr{sub 0.95}Ti{sub 0.05})O{sub 3} (PZT 95/5) and Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3} (PZT 52/48) ferroelectrics subjected to explosive adiabatic compression obeys the above-mentioned law in a wide range of voltages, up to 150 kV.
A no extensive statistical model for the nucleon structure function
We studied an application of nonextensive thermodynamics to describe the structure function of nucleon, in a model where the usual Fermi-Dirac and Bose-Einstein energy distribution were replaced by the equivalent functions of the q-statistical. The parameters of the model are given by an effective temperature T, the q parameter (from Tsallis statistics), and two chemical potentials given by the corresponding up (u) and down (d) quark normalization in the nucleon.
The polarized structure function of the nucleons with a non-extensive statistical quark model
We studied an application of nonextensive thermodynamics to describe the polarized structure function of nucleon, in a model where the usual Fermi-Dirac and Bose-Einstein energy distribution, often used in the statistical models, were replaced by the equivalent functions of the q-statistical. The parameters of the model are given by an effective temperature T, the q parameter (from Tsallis statistics), and the chemical potentials given by the corresponding up (u) and down (d) quark normalization in the nucleon and by {Delta}u and {Delta}d of the polarized functions.
On an extension problem for density matrices
We investigate the problem of the existence of a density matrix {rho}{sub 123} on a Hilbert space H{sub 1} Circled-Times H{sub 2} Circled-Times H{sub 3} with given partial traces {rho}{sub 12}= Tr{sub 3} {rho}{sub 123} and {rho}{sub 23}= Tr{sub 1} {rho}{sub 123}. While we do not solve this problem completely, we offer partial results in the form of some necessary and some sufficient conditions on {rho}{sub 12} and {rho}{sub 23}. The quantum case differs markedly from the classical (commutative) case, where the obvious necessary compatibility condition suffices, namely, Tr{sub 1} {rho}{sub 12}= Tr{sub 3}{rho}{sub 23}.