Ab-Initio Calculation of the Metal-Insulator Transition in Sodium rings and chains and in mixed Sodium-Lithium systems

We study how the Mott metal-insulator transition (MIT) is influenced when we deal with electrons with different angular momenta. For lithium we found an essential effect when we include $p$-orbitals in the description of the Hilbert space. We apply quantum-chemical methods to sodium rings and chains in order to investigate the analogue of a MIT, and how it is influenced by periodic and open boundaries. By changing the interatomic distance we analyse the character of the many-body wavefunction and the charge gap. In the second part we mimic a behaviour found in the ionic Hubbard model, where a transition from a band to a Mott insulator occurs. For that purpose we perform calculations for mixed sodium-lithium rings. In addition, we examine the question of bond alternation for the pure sodium system and the mixed sodium-lithium system, in order to determine under which conditions a Peierls distortion occurs.Comment: 8 pages, 7 figures, accepted Eur. J. Phys.

Anticipating Energy-driven Crises in Process Industry by AI-based Scenario Planning

Power outages and fluctuations represent serious crisis situations in energy-intensive process industry like glass and paper production, where substances such as oil, gas, wood fibers or chemicals are processed. Power disruptions can interrupt chemical reactions and produce tons of waste as well as damage of machine parts. But, despite of the obvious criticality, handling of outages in manufacturing focuses on commissioning of expensive proprietary power plants to protect against power outages and implicit gut feeling in anticipating potential disruptions. With AISOP, we introduce a model for AI-based scenario planning for predicting crisis situations. AISOP uses conceptual, well-defined scenario patterns to capture entities of crisis situations. Data streams are mapped onto these patterns for determining historic crisis scenarios and predicting future crisis scenarios by using inductive knowledge and machine learning. The model was exemplified within a proof of concept for energy-driven disruption prediction. We were able to evaluate the proposed approach by means of a set of data streams on weather and outages in Germany in terms of performance in predicting potential outages for manufacturers of paper industry with promising results

The ground-state spectroscopic constants of Be_2 revisited

Extensive ab initio calibration calculations combined with extrapolations towards the infinite-basis limit lead to a ground-state dissociation energy of Be_2, D_e=944 \pm 25 1/cm, substantially higher than the accepted experimental value, and confirming recent theoretical findings. Our best computed spectroscopic observables (expt. values in parameters) are G(1)-G(0)=223.7 (223.8), G(2)-G(1)=173.8 (169 \pm 3), G(3)-G(2)=125.4 (122 \pm 3), and B_0=0.6086 (0.609) 1/cm; revised spectroscopic constants are proposed. Multireference calculations based on a full valence CAS(4/8) reference suffer from an unbalanced description of angular correlation; for the utmost accuracy, a CAS(4/16) reference including the $(3s,3p)$ orbitals is required, while for less accurate work a CAS(4/4) reference is recommended. The quality of computed coupled cluster results depends crucially on the description of connected triple excitations; the CC5SD(T) method yields unusually good results because of an error compensation.Comment: Chem. Phys. Lett., in pres

Cascading Scenario Technique Enabling Automated And Situation-based Crisis Management

Crises are becoming more and more frequent. Whether natural disasters, economic crises, political events, or a pandemic - the right action mitigates the impact. The PAIRS project plans to minimize the surprise effect of these and to recommend appropriate actions based on data using artificial intelligence (AI). This paper conceptualizes a cascading model based on scenario technique, which acts as the basic approach in the project. The long-term discipline of scenario technique is integrated into the discipline of crisis management to enable short-term and continuous crises management in an automated manner. For this purpose, a practical crisis definition is given and interpreted as a process. Then, a cascading model is derived in which crises are continuously thought through using the scenario technique and three types of observations are classified: Incidents, disturbances, and crises. The presented model is exemplified within a non-technical application of a use case in the context of humanitarian logistics and the COVID-19 pandemic. Furthermore, first technical insights from the field of AI are given in the form of a semantic description composing a knowledge graph. In summary, a conceptual model is presented to enable situation-based crisis management with automated scenario generation by combining the two disciplines of crisis management with scenario technique

Heats of formation of perchloric acid, HClO4_4, and perchloric anhydride, Cl2_2O7_7. Probing the limits of W1 and W2 theory

The heats of formation of HClO$_4$ and Cl$_2$O$_7$ have been determined to chemical accuracy for the first time by means of W1 and W2 theory. These molecules exhibit particularly severe degrees of inner polarization, and as such obtaining a basis-set limit SCF component to the total atomization energy becomes a challenge. (Adding high-exponent $d$ functions to a standard $spd$ basis set has an effect on the order of 100 kcal/mol for Cl$_2$O$_7$.) Wilson's aug-cc-pV(n+d)Z basis sets represent a dramatic improvement over the standard aug-cc-pVnZ basis sets, while the aug-cc-pVnZ+2d1f sequence converges still more rapidly. Jensen's polarization consistent basis sets still require additional high-exponent $d$ functions: for smooth convergence we suggest the \{aug-pc1+3d,aug-pc2+2d,aug-pc3+d,aug-pc4\} sequence. The role of the tight $d$ functions is shown to be an improved description of the Cl (3d) Rydberg orbital, enhancing its ability to receive back-bonding from the oxygen lone pairs. In problematic cases like this (or indeed in general), a single SCF/aug-cc-pV6Z+2d1f calculation may be preferable over empirically motivated extrapolations. Our best estimate heats of formation are $\Delta H^\circ_{f,298}[$HClO$_4$(g)$]=-0.6\pm$1 kcal/mol and $\Delta H^\circ_{f,298}[$Cl$_2$O$_7$(g)$]=65.9\pm$2 kcal/mol, the largest source of uncertainty being our inability to account for post-CCSD(T) correlation effects. While G2 and G3 theory have fairly large errors, G3X theory reproduces both values to within 2 kcal/mol.Comment: J. Mol. Struct. (THEOCHEM), in press (WATOC'05 special issue

Electron affinities of the first- and second- row atoms: benchmark ab initio and density functional calculations

A benchmark ab initio and density functional (DFT) study has been carried out on the electron affinities of the first- and second-row atoms. The ab initio study involves basis sets of $spdfgh$ and $spdfghi$ quality, extrapolations to the 1-particle basis set limit, and a combination of the CCSD(T), CCSDT, and full CI electron correlation methods. Scalar relativistic and spin-orbit coupling effects were taken into account. On average, the best ab initio results agree to better than 0.001 eV with the most recent experimental results. Correcting for imperfections in the CCSD(T) method improves the mean absolute error by an order of magnitude, while for accurate results on the second-row atoms inclusion of relativistic corrections is essential. The latter are significantly overestimated at the SCF level; for accurate spin-orbit splitting constants of second-row atoms inclusion of (2s,2p) correlation is essential. In the DFT calculations it is found that results for the 1st-row atoms are very sensitive to the exchange functional, while those for second-row atoms are rather more sensitive to the correlation functional. While the LYP correlation functional works best for first-row atoms, its PW91 counterpart appears to be preferable for second-row atoms. Among ``pure DFT'' (nonhybrid) functionals, G96PW91 (Gill 1996 exchange combined with Perdew-Wang 1991 correlation) puts in the best overall performance. The best results overall are obtained with the 1-parameter hybrid modified Perdew-Wang (mPW1) exchange functionals of Adamo and Barone [J. Chem. Phys. {\bf 108}, 664 (1998)], with mPW1LYP yielding the best results for first-row, and mPW1PW91 for second-row atoms. Indications exist that a hybrid of the type $a$ mPW1LYP + $(1-a)$ mPW1PW91 yields better results than either of the constituent functionals.Comment: Phys. Rev. A, in press (revised version, review of issues concerning DFT and electron affinities added

Correlation effects in MgO and CaO: Cohesive energies and lattice constants

A recently proposed computational scheme based on local increments has been applied to the calculation of correlation contributions to the cohesive energy of the CaO crystal. Using ab-initio quantum chemical methods for evaluating individual increments, we obtain 80% of the difference between the experimental and Hartree-Fock cohesive energies. Lattice constants corrected for correlation effects deviate by less than 1% from experimental values, in the case of MgO and CaO.Comment: LaTeX, 4 figure

Models for low-temperature helium dimers and trimers

We have shown that a simple model based on pairwise deltafunction potentials can, with an appropriate choice of parameters, represent the general behavior of ultra-low temperature helium dimers and trimers, including all possible isotopomers. The species 4 He 2 , 4 He 3 , and 4 He 2 3 He are stable, with binding energies of approximately 1.3, 100, and 10 mK, respectively. An Efimov state for 4 He 2 3 He is also predicted, bound by 2.4 mK. The remaining dimers and trimers, 4 He  3 He, 3 He 2 , 4 He  3 He 2 , and 3 He 3 , are evidently unstable. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34398/1/1807_ftp.pd

A critical note on density functional theory studies on rare-gas dimers

In recent literature, some authors claim to have successfully applied density functional theory (DFT) methods to the attractive interaction between rare-gas atoms. In this note, we make a critical survey of these works and come to the conclusion that, in contrast to the claims made, state-of-the-art DFT methods are incapable of accounting for dispersion effects in a quantitative way. (C) 2002 American Institute of Physics.</p