Cluster perturbation theory. XI. Excitation-energy series using a variational excitation-energy function

Traditionally, excitation energies in coupled-cluster (CC) theory have been calculated by solving the CC Jacobian eigenvalue equation. However, based on our recent work [Jørgensen et al., Sci. Adv. 10, eadn3454 (2024)], we propose a reformulation of the calculation of excitation energies where excitation energies are determined as a conventional molecular property. To this end, we introduce an excitation-energy function that depends on the CC Jacobian and the right and left eigenvectors for the Jacobian eigenvalue problem. This excitation-energy function is variational with respect to the right and left eigenvectors but not with respect to the cluster amplitudes. Instead, the cluster amplitudes satisfy the cluster-amplitude equations, and we set up an excitation-energy Lagrangian by adding to the excitation-energy function the cluster-amplitude equations with an undetermined multiplier for each cluster-amplitude constraint. The excitation-energy Lagrangian is variational in all its parameters. Based on the variational property of the Lagrangian, we have determined two quadratically convergent excitation-energy series: the total-order cluster-perturbation (tCP) and variational cluster-perturbation (vCP) excitation-energy series. Calculations of the excitation energies of three small molecules have shown that the vCP series is to be preferred over the tCP series. The test calculations have been carried out for CPS(D) expansions [targeting the CC singles-and-doubles (CCSD) wave function from the CC singles wave function] and the CPSD(T) expansion [targeting the CC singles-doubles-triples (CCSDT) wave function from the CCSD wave function]. For the S(D) and SD(T) orbital excitation space calculations, we obtain in the second vCP iteration excitation energies with a mean deviation from CCSD excitation energies of about 0.04 eV for the S(D) orbital spaces, and for the SD(T) orbital space calculation, we obtain a mean deviation from the CCSDT excitation energies of 0.001 eV.</p

BIFROST—An indirect geometry cold neutron spectrometer at the European Spallation Source

We present the detailed design and performance simulations of BIFROST, a multiplexing indirect neutron time-of-flight spectrometer at the European Spallation Source. The instrument allows a neutron bandwidth of Δλ = 1.74 Å to reach the sample. The polychromatic flux can reach 6 × 109 n/s/cm2 while retaining a relative energy resolution, δEi/Ei, of around 3.5% at Ei = 5 meV. A fast pulse-shaping chopper allows for flexibility in the primary spectrometer resolution. For an opening time of 0.1 ms, a relative energy resolution down to 0.2% is achieved for Ei = 12 meV. The secondary spectrometer consists of 45 analyzer arrays, populating 9 scattering angle channels in the horizontal scattering plane, each of which covers 5.2° in scattering angle. Each channel hosts 5 analyzer arrays reflecting neutrons of fixed energies Ef equal to 2.7, 3.2, 3.8, 4.4, and 5.0 meV. Utilizing the prismatic analyzer concept, the back-end geometry allows a secondary spectrometer energy resolution in the range of 0.02-0.05 meV. The unique design of BIFROST offers not only an unprecedented neutron flux but also the ability to adjust the energy resolution by more than one order of magnitude. Focusing on the horizontal scattering plane, the spectrometer is ideally suited for extreme environment studies and for studying samples much smaller than 1 cm3. The drastic increase in measurement efficiency, compared to current high-flux spectrometers, has a particularly high impact on the fields of quantum magnetism, unconventional superconductivity, and functional materials.</p

Dairy powders:Impact of surface composition and heterogeneity on functional properties

This study investigates the surface characteristics of four industrial dairy powders - Skim Milk Powder (SMP), Whole Milk Powder (WMP), Instant Filled Milk Powder (IFMP), and Cheese Powder (CP) - across multiple length scales, aiming to understand how these characteristics influence their physical and functional properties. Using X-ray Photoelectron Spectroscopy on large area (multiple particles), it was observed that surface composition remains consistent across different particle sizes within each powder type. Notably, SMP exhibited a more hydrophilic surface compared to the other powders, particularly CP. At the particle scale (single particle - 10 mu m x 10 mu m), Atomic Force Microscopy (AFM) analysis revealed uniform surface structures. Among the samples, CP and SMP displayed smoother surfaces whereas WMP and IFMP exhibited more textured topographies. Highresolution (2 mu m x 2 mu m) AFM assessments highlighted distinct differences in surface structures among the powders. Nanomechanical measurements indicated that SMP had the highest Young's modulus suggesting a stiffer surface, while CP had the lowest, indicating a softer surface. Finally, these findings underscore the significance of surface characteristics at various scales in determining the functional performance of dairy powders, here flowability and wettability

Retrodiction of measurement outcomes on a single quantum system revealing entanglement with its environment

The density matrix yields probabilistic information about the outcome of measurements on a quantum system, but it does not distinguish between classical randomness in the preparation of the system and entanglement with its environment. Here we show that retrodiction, employing both prior and posterior knowledge, gives rise to conditional probabilities for measurements on a single system, that can witness if it is part of a larger composite system. The degree of certainty with which one can retrodict the outcomes of multiple measurements on a system can witness both the existence and the quantitative nature of its entanglement with the environment

Afkolonisering, boliger og kvindeforeninger i Grønland ca. 1945-1970

Housing was one of the most fundamental areas of change in Greenland after World War 2. Politicians, experts, and officials established programs aimed at nothing less than replacing all Greenlandic housing facilities. When Greenlandic women's associations began to engage with the issue in the mid-1960s, housing also became an important mobilization point for Greenlandic civil society.This article shows, firstly, that the high modernist ideas of efficient and rational planning of housing and social life in Greenland did not take hold until the 1960s, when multi-storey housing gradually became dominant. Secondly, in addition to the aim of improving health and living conditions in the country, housing planners operated on the assumption that the new housing could facilitate Greenlanders’ adaption to 'modern life'. Housing was thus a key reform tool. Finally, the analysis shows that housing projects had a far-reaching effect on Greenlandic society in terms of mobilization. The debate raised by the women's associations shows different attitudes and desires in relation to housing and lifestyles. On the one hand, many wanted modern housing with up-to-date facilities. On the other hand, they wanted influence on the development and for the housing to be adapted to a Greenlandic context

Benchmarking third-order cluster perturbation theory for electronically excited states

In this study, we investigate the reliability of cluster perturbation (CP) theory applied to the calculation of electronically excited states through a comprehensive benchmark. In CP theory, perturbative corrections are added to the properties of a parent excitation space, which converge toward the properties of a target excitation space. For the CPS(D-n) model, perturbative corrections through order n are added to the coupled cluster singles (CCS) excitation energies to target the coupled cluster singles and doubles (CCSD) excitation energies. Through a comparative analysis of excitation energy calculations across a diverse set of molecules and wavefunction methods, we present a comprehensive evaluation of the accuracy of the third-order CPS(D) model, CPS(D-3), in calculating excitation energies. Our findings demonstrate that CPS(D-3) is a reliable alternative to established methods, particularly CCSD, while systematically overestimating the excitation energies compared to high-level coupled cluster methods such as CC3. These results highlight the strengths and limitations of CPS(D-3), as well as the promising directions for its future development