Resolving the notorious case of conical intersections for coupled cluster dynamics

The motion of electrons and nuclei in photochemical events often involve conical intersections, degeneracies between electronic states. They serve as funnels for nuclear relaxation - on the femtosecond scale - in processes where the electrons and nuclei couple nonadiabatically. Accurate ab initio quantum chemical models are essential for interpreting experimental measurements of such phenomena. In this paper we resolve a long-standing problem in coupled cluster theory, presenting the first formulation of the theory that correctly describes conical intersections between excited electronic states of the same symmetry. This new development demonstrates that the highly accurate coupled cluster theory can be applied to describe dynamics on excited electronic states involving conical intersections.Comment: 8 pages and 3 figures and including supporting information (with corrections and improved notation

Strategic management competencies in Scandinavian contractors

Over the past ten years, a series of contractors operating in Denmark, Norway and Sweden have slowly but surely expanded their markets beyond their previous single-country base towards operating in Scandinavia as a whole, and beyond. This expansion has been accompanied by a restructuring of company organisations and associated processes of competency development in senior management. This paper asks the question: How well is top level management prepared to manage and lead these large companies? The paper adopts a multidisciplinary theoretical approach combining international business, strategic management and HR concepts and approaches. Methodologically, a sample of the top level leaders of the hundred largest business units at some thirty Scandinavian contractors has been analysed. The focus is on the 400 top level managers in these organisations. On the basis of a desk study, an analysis of 124 managers from 18 companies has been carried out, providing insight into the basic education and mixing of competences in the top-level boards. More specifically, the areas of operations strategy and IT have been reviewed. The results show that even if the board is mainly composed of engineering competencies, business, legal and HR competencies are also present. Both engineer-dominated and mixed management boards are heading companies which show growth in turnover. This runs counter to a widespread sector perception that management boards in the construction industry are mainly composed of engineers. However, it seems that the managers with business administration competencies are rarely those with responsibility for the central tasks of leadership and strategy. Moreover, very few companies prioritize operations strategy and IT. It is assumed that everybody knows about practical building projects, and therefore that operations strategy will develop naturally. The IT area is viewed as best placed at a lower level of organisation, counter to IT governance and management prescriptions

Communication: X-ray absorption spectra and core-ionization potentials within a core-valence separated coupled cluster framework

We present a simple scheme to compute X-ray absorption spectra (e.g., near-edge absorption fine structure) and core ionisation energies within coupled cluster linear response theory. The approach exploits the so-called core-valence separation to effectively reduce the excitation space to processes involving at least one core orbital, and it can be easily implemented within any pre-existing coupled cluster code for low energy states. We further develop a perturbation correction that incorporates the effect of the excluded part of the excitation space. The correction is shown to be highly accurate. Test results are presented for a set of molecular systems for which well converged results in full space could be generated at the coupled cluster singles and doubles level of theory only, but the scheme is straightforwardly generalizable to all members of the coupled cluster hierarchy of approximations, including CC3

Energy-Based Molecular Orbital Localization in a Specific Spatial Region

We present a novel energy-based localization procedure able to localize molecular orbitals into specific spatial regions. The method is applied to several cases including both conjugated and non-conjugated systems. The obtained localized molecular orbitals are used in a multiscale framework based on the multilevel Hartree-Fock approach. An almost perfect agreement with reference values is achieved for both ground state properties, such as dipole moments, and local excitation energies calculated at the coupled cluster level. The proposed approach is useful to extend the application range of high level electron correlation methods. In fact, the reduced number of molecular orbitals can lead to a large reduction in the computational cost of correlated calculations.Comment: 29 pages and 7 figure

Fragment Localized Molecular Orbitals

We introduce the concept of fragment localized molecular orbitals (FLMOs), which are Hartree-Fock molecular orbitals localized in specific fragments constituting a molecular system. In physical terms, we minimize the local electronic energies of the different fragments, at the cost of maximizing the repulsion between them. To showcase the approach, we rationalize the main interactions occurring in large biological systems in terms of interactions between the fragments of the system. In particular, we study an anticancer drug intercalated within DNA and retinal in anabaena sensory rhodopsin as prototypes of molecular systems embedded in biological matrixes. Finally, the FLMOs are exploited to rationalize the formation of two oligomers, prototypes of amyloid diseases, such as Parkinson and Alzheimer

Crossing conditions in coupled cluster theory

We derive the crossing conditions at conical intersections between electronic states in coupled cluster theory, and show that if the coupled cluster Jacobian matrix is nondefective, two (three) independent conditions are correctly placed on the nuclear degrees of freedom for an inherently real (complex) Hamiltonian. Calculations using coupled cluster theory on an $2 {^{1}}A' / 3 {^{1}}A'$ conical intersection in hypofluorous acid illustrate the nonphysical artifacts associated with defects at accidental same-symmetry intersections. In particular, the observed intersection seam is folded about a space of the correct dimensionality, indicating that minor modifications to the theory are required for it to provide a correct description of conical intersections in general. We find that an accidental symmetry allowed $1 {^{1}}A" / 2 {^{1}}A"$ intersection in hydrogen sulfide is properly described, showing no artifacts as well as linearity of the energy gap to first order in the branching plane.Comment: 9 pages and 4 figure

A biorthonormal formalism for nonadiabatic coupled cluster dynamics

In coupled cluster methods, the electronic states are biorthonormal in the sense that the left states are orthonormal to the right states. Here we present an extension of this formalism to a left and right total molecular wave function. Starting from left and right Born-Huang expansions, we derive projected Schr\"odinger equations for the left and right nuclear wave functions. Observables may be extracted from the resulting wave function pair using standard expressions. The formalism is shown to be invariant under electronic basis transformations, such as normalization of the electronic states. Consequently, the nonadiabatic coupling elements can be expressed with biorthonormal wave functions. Calculating normalization factors that scale as full-CI is therefore not necessary, contrary to claims in the literature. For nuclear dynamics, we therefore need expressions for the vector and scalar couplings in the biorthonormal formalism. We derive these expressions using a Lagrangian formalism.Comment: 41 pages, 1 figur

5G for LEO – Technical Challenges and Initial Results

In December 2019, 3GPP have for the 5G specification decided to separate the Narrowband IoT Non-Terrestrial Network (NB-IoT NTN) from the New Radio NTN. Due to this change, NB-IoT NTN becomes a very attractive candidate for LEO IoT satellite constellations. The decision emphasises that there is a strong push for cellular standards into the space industry and that commercial utilizations in large scale is getting closer. However, it also entails significant technical challenges in terms of connectivity, backhaul integration and operational features. GateHouse Telecom currently work on an ARTES supported project (Narrowband IoT standard for small satellites). Based on the existing 3GPP terrestrial NB-IoT standard the purpose of this project is to identify areas of adaptations to utilize this from space. Further, the project will provide solutions to overcome the waveform challenges related to doppler, latency, timing, propagation loss etc. This poster provides initial results from the project in terms of architecture, suggested adaptations and technical challenges related to architecture and implementation

Comparing real-time coupled cluster methods through simulation of collective Rabi oscillations

The time-dependent equation-of-motion coupled cluster (TD-EOM-CC) and time-dependent coupled cluster (TDCC) methods are compared by simulating Rabi oscillations for different numbers of non-interacting atoms in a classical electromagnetic field. While the TD-EOM-CC simulations are numerically stable, the oscillating time-dependent energy scales unreasonably with the number of subsystems resonant with the field. The TDCC simulations give the correct scaling of the time-dependent energy in the initial stages of the Rabi cycle, but the numerical solution breaks down when the multi-atom system approaches complete population inversion. We present a general theoretical framework in which the two methods can be described, where the cluster amplitude time derivatives are taken as auxiliary conditions, leading to a shifted time-dependent Hamiltonian matrix. In this framework, TDCC has a shifted Hamiltonian with a block upper triangular structure, explaining the correct scaling properties of the method.Comment: 9 pages and 4 figure