Causal Analysis of a Migration of the Snout Butterfly, Libytheana bachmanii Iarvata (Strecker) (Libytheidae)

Observation of a massive migration of the snout butterfly, Libytheana bachmanii larvata (Strecker), in central Texas in 1971 is described. An association of peak migration periods and periodic precipitation episodes is believed to be causal in nature.Waller Creek Working Grou

The density matrix renormalization group for ab initio quantum chemistry

During the past 15 years, the density matrix renormalization group (DMRG) has become increasingly important for ab initio quantum chemistry. Its underlying wavefunction ansatz, the matrix product state (MPS), is a low-rank decomposition of the full configuration interaction tensor. The virtual dimension of the MPS, the rank of the decomposition, controls the size of the corner of the many-body Hilbert space that can be reached with the ansatz. This parameter can be systematically increased until numerical convergence is reached. The MPS ansatz naturally captures exponentially decaying correlation functions. Therefore DMRG works extremely well for noncritical one-dimensional systems. The active orbital spaces in quantum chemistry are however often far from one-dimensional, and relatively large virtual dimensions are required to use DMRG for ab initio quantum chemistry (QC-DMRG). The QC-DMRG algorithm, its computational cost, and its properties are discussed. Two important aspects to reduce the computational cost are given special attention: the orbital choice and ordering, and the exploitation of the symmetry group of the Hamiltonian. With these considerations, the QC-DMRG algorithm allows to find numerically exact solutions in active spaces of up to 40 electrons in 40 orbitals.Comment: 24 pages; 10 figures; based on arXiv:1405.1225; invited review for European Physical Journal

Sustainability of Austrian Public Debt: A Political Economy Perspective

Sustainablity of Austrian public debt is investigated in the context of political objectives such as stabilizing the business cycle, increasing chances for being re-elected and implementing the ideologies of political parties. Several tests indicate that Austrian fiscal policies were sustainable in the period 1960–1974, while from 1975 on, public debt grew much more rapidly. The development of public debt in Austria seems to be driven not primarily by ideology, but by structural causes and a shift in the budgetary policy paradigm. We find some empirical evidence that governments in Austria dominated by one party run higher deficits than coalition governments. There are no indications of a political business cycle.fiscal policy, sustainability, time series, political economy

Faddeev Random Phase Approximation for Molecules

The Faddeev Random Phase Approximation is a Green's function technique that makes use of Faddeev-equations to couple the motion of a single electron to the two-particle--one-hole and two-hole--one-particle excitations. This method goes beyond the frequently used third-order Algebraic Diagrammatic Construction method: all diagrams involving the exchange of phonons in the particle-hole and particle-particle channel are retained, but the phonons are described at the level of the Random Phase Approximation. This paper presents the first results for diatomic molecules at equilibrium geometry. The behavior of the method in the dissociation limit is also investigated

DMRG-CASPT2 study of the longitudinal static second hyperpolarizability of all-trans polyenes

We have implemented internally contracted complete active space second order perturbation theory (CASPT2) with the density matrix renormalization group (DMRG) as active space solver [Y. Kurashige and T. Yanai, J. Chem. Phys. 135, 094104 (2011)]. Internally contracted CASPT2 requires to contract the generalized Fock matrix with the 4-particle reduced density matrix (4-RDM) of the reference wavefunction. The required 4-RDM elements can be obtained from 3-particle reduced density matrices (3-RDM) of different wavefunctions, formed by symmetry-conserving single-particle excitations op top of the reference wavefunction. In our spin-adapted DMRG code chemps2 [https://github.com/sebwouters/chemps2], we decompose these excited wavefunctions as spin-adapted matrix product states, and calculate their 3-RDM in order to obtain the required contraction of the generalized Fock matrix with the 4-RDM of the reference wavefunction. In this work, we study the longitudinal static second hyperpolarizability of all-trans polyenes C$_{2n}$H$_{2n+2}$ [n = 4 - 12] in the cc-pVDZ basis set. DMRG-SCF and DMRG-CASPT2 yield substantially lower values and scaling with system size compared to RHF and MP2, respectively.Comment: 9 pages, 4 figure

A Practitioner’s Approach to Drucker’s Knowledge - Worker Productivity in the 21st Century: A New Model (Part One)

This article examines productivity in the context of the 21st century, focusing on Drucker’s prophecy of knowledge-worker productivity, the power of ‘unified strategy’, organisational interdependence and a practitioner’s approach to knowledge-worker productivity based on Drucker’s six determining factors. From these six factors, a nine building-block based questionnaire survey is developed to establish knowledge-worker productivity readiness status; a knowledge-worker review session to plan towards organisational interdependence and a Drucker-based knowledge-worker productivity implementation framework to manage organisational change. This proposal, intended for business organisations, should also accommodate non-business organisations. Knowledge-worker productivity practice is designed to improve productivity, the quality of work, empowers knowledge workers to accomplish their ‘tasks’ and, consequently, the ‘organisation tasks’ by following an organisational ‘unified strategy’ in an interdependent way that brings about a doing the right thing, the right way approach. This article provides answers to ‘what and how organisations can do to enhance productivity’ from their knowledge-workers, to embrace creativity and develop innovation to provide strategic advantage in sustaining growth in the current new economy of global competition. Team commitment is envisaged through the concept of organisational interdependence. In conclusion, a Drucker-based knowledge-worker productivity implementation framework is proposed, as a management practice to enhance knowledge worker productivity for creativity and commitment. It further demonstrates its competitive power by achieving a unified strategy with implication for organisational change and future applications.knowledge worker; creativity; commitment; productivity; change management; organisational interdependence; unified strategy.

A new variational, information theory based atoms in molecules method

A new iterative Hirshfeld type AIM method, called Hirshfeld-I-Lambda, is presented. The weight function that defines the AIM is constructed by minimizing the information loss on formation of the molecule, with explicitly requiring that the promolecular densities integrate to the same number of electrons as the AIM densities constructed. The atoms defined by this AIM method are the ones that minimize the information lost upon formation of the molecule out of its isolated atoms. The resulting Hirshfeld-I-Lambda AIM scheme is examined and discussed

Perturbations on the superconducting state of metallic nanoparticles: influence of geometry and impurities

The pair condensation energy of a finite-size superconducting particle is studied as a function of two control parameters. The first control parameter is the shape of the particle, and the second parameter is a position-dependent impurity introduced in the particle. Whereas the former parameter is known to induce strong fluctuations in the condensation energy, the latter control parameter is found to be a more gentle probe of the pairing correlations.Comment: Submitted for the special issue of the International Symposium on Small Particles and Inorganic Clusters XVI, at KULeuven (July 8-13, 2012). PACS: 74.78.Na, 74.20.F

Inner products in integrable Richardson-Gaudin models

We present the inner products of eigenstates in integrable Richardson-Gaudin models from two different perspectives and derive two classes of Gaudin-like determinant expressions for such inner products. The requirement that one of the states is on-shell arises naturally by demanding that a state has a dual representation. By implicitly combining these different representations, inner products can be recast as domain wall boundary partition functions. The structure of all involved matrices in terms of Cauchy matrices is made explicit and used to show how one of the classes returns the Slavnov determinant formula. This framework provides a further connection between two different approaches for integrable models, one in which everything is expressed in terms of rapidities satisfying Bethe equations, and one in which everything is expressed in terms of the eigenvalues of conserved charges, satisfying quadratic equations.Comment: 21+16 pages, minor revisions compared to the previous versio

Read-Green resonances in a topological superconductor coupled to a bath

We study a topological superconductor capable of exchanging particles with an environment. This additional interaction breaks particle-number symmetry and can be modelled by means of an integrable Hamiltonian, building on the class of Richardson-Gaudin pairing models. The isolated system supports zero-energy modes at a topological phase transition, which disappear when allowing for particle exchange with an environment. However, it is shown from the exact solution that these still play an important role in system-environment particle exchange, which can be observed through resonances in low-energy and -momentum level occupations. These fluctuations signal topologically protected Read-Green points and cannot be observed within traditional mean-field theory.Comment: 7 pages, 4 figure