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High level multi-reference non-adiabatic dynamics simulations reveal that uracil’s photoexcited S 2 state decays very quickly without any significant trapping.
The unexpected abundance of HNO in the photodecomposition of the radical 2-nitrosooxy ethyl (CH 2 CH 2 ONO) is investigated through calculations of the potential energy surface by the anti-Hermitian contracted Schrödinger equation (ACSE) approach, which directly generates the 2-electron reduced density matrix. The ACSE, which is able to balance single-reference (dynamic) and multi-reference (static) correlation effects, reveals some subtle correlation effects along the intrinsic reaction coordinate (IRC) en route to NO + oxirane, an IRC which offers a potential bifurcation to the HNO + vinoxy product channel. Here, these effects were not fully captured by either single-reference techniques, such as coupled cluster, or multi-reference techniques, such as second-order multi-reference perturbation theory. These correlation effects reveal small to moderate energy changes in key transition states, which have implications for the reaction mechanism as related to the production of HNO.
While multiconfigurational approaches have long been relegated to expert practitioners working on a case-by-case basis, recent developments have increasingly made these methods more routine and applicable to broader sets of systems. This article outlines the state-of-the-art in multiconfigurational approaches, with an emphasis on moving from delicate hand-selected pathways through configuration space toward more robust and efficient approaches to treating a host of challenging chemical systems accurately. First, we overview recent work in automated active-space selection, which has enabled increasingly large-scale applications of multireference methods to modeling vertical excitations and reactivity. Second, we highlight the increasingly efficient methods for recovering correlation energy beyond the active space, as headlined by extensions of pair-density functional theory and its role in accurate and efficient treatment of excited-state dynamics and its utilization to train machine-learned potentials. Finally, we highlight recent efforts to treat extended systems that until recently have lied beyond the traditional limits of active-space methods, giving center stage to product-form wave functions of the localized active space family of methods that allow for the computation of multiconfigurational band structures. These recent advancements point to a broader use of multireference approaches for high-impact chemical and materials science applications.
Abstract Understanding the nature and origin of collective excitations in materials is of fundamental importance for unraveling the underlying physics of a many-body system. Excitation spectra are usually obtained by measuring the dynamical structure factor, S ( Q , ω ), using inelastic neutron or x-ray scattering techniques and are analyzed by comparing the experimental results against calculated predictions. We introduce a data-driven analysis tool which leverages ‘neural implicit representations’ that are specifically tailored for handling spectrographic measurements and are able to efficiently obtain unknown parameters from experimental data via automatic differentiation. In this work, we employ linear spin wave theory simulations to train a machine learning platform, enabling precise exchange parameter extraction from inelastic neutron scattering data on the square-lattice spin-1 antiferromagnet La 2 NiO 4 , showcasing a viable pathway towards automatic refinement of advanced models for ordered magnetic systems.
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With a novel three-dimensional electron-electron coincidence imaging technique and two-electron angular streaking method, we show that the emission time delay between two electrons can be measured from tens of attoseconds to more than 1 fs. Surprisingly, in benzene, the double ionization rate decays as the time delay between the first and second electron emission increases during the first 500 as. This is further supported by the decay of the Coulomb repulsion in the direction perpendicular to the laser polarization. This result reveals that laser-induced electron correlation plays a major role in strong field double ionization of benzene driven by a nearly circularly polarized field.
The phenomenon of T-linear resistivity commonly observed in a number of strange metals has been widely seen as evidence for the breakdown of the quasiparticle picture of metals. This study shows that a recently discovered H/T scaling relationship in the magnetoresistance of the strange metal BaFe 2 (As 1- x P x ) 2 is independent of the relative orientations of current and magnetic field. Rather, its magnitude and form depend only on the orientation of the magnetic field with respect to a single crystallographic axis: the direction perpendicular to the magnetic iron layers. In this work, this finding suggests that the magnetotransport scaling does not originate from the conventional averaging or orbital velocity of quasiparticles as they traverse a Fermi surface, but rather from dissipation arising from two-dimensional correlations.
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Theory shows that to explain the polarization of light collisionally redistributed from the far line wings of an atomic transition, one must consider correlated events in which absorption during a collision, and propagation to the final Zeeman-state superposition at the end of the collision is important. Polarizations of up to about 40% have been measured in the far line wings, substantially confirming this prediction, and showing that scattering experiments cannot just be characterized by simple absorption or emission profiles.
It is pointed out that the redeployment of ISEE 3 from its continuous monitoring of the solar wind in a large orbit about the upstream Lagrangian point to an extended magnetotail orbit has afforded an opportunity for deep-tail passage of October 1982, and in the radial range from 200 to 220 R(E) during the near-apogee part of the second tail passage in January-February 1983. Attention is given to instrumentation and data sets, spacecraft positions, and observational data.
We have recovered vertical profiles of stratospheric N2O from spectra observed using a ground-based mm-wave spectrometer during the Arctic spring. The measurements were made from Thule, Greenland (76.3 deg N, 68.4 deg W) on nine occasions from late February to late March, 1992 as part of the Upper Atmosphere Research Satellite (UARS) Correlative Measurements Program and the European Arctic Stratospheric Ozone Experiment (EASOE). During late February Thule was under inside edge of the Arctic vortex and mixing ratio profiles measured in that period are substantially reduced from typical high-latitude summer values. By late March the polar vortex had moved well away from Thule and N2O mixing ratios were greatly increased, coinciding with a basic change in circulation that brought in air from the Aleutian high. The motion of the vortex is also illustrated in the change in potential vorticity above Thule. A correlation with ozone balloonsonde data from Thule is made and compared to similar analyses of the Airborne Arctic Stratospheric Expedition (AASE) measurements. Within the sensitivity of our analysis, the correlation of N2O and O3 shows no evidence of ozone depletion within the vortex during this period; however, there is a distinct difference in the correlation inside and outside the vortex.