Second- and higher-order convergence in linear and nonlinear multiconfigurational Hartree–Fock theory

We discuss how the local convergence of Newton–Raphson and fixed Hessian MCSCF iterative models may be rationalized in terms of a total order of convergence in an error vector and a corresponding error term. We demonstrate that a sequence of N Newton–Raphson iterations has a total order of convergence of 2^N and that a sequence of N fixed Hessian iterations has a total order of convergence of N + 1. We derive the error terms of a Newton–Raphson and a fixed Hessian sequence of iterations. We discuss the implementation of the fixed Hessian and the Newton–Raphson approaches both when linear and nonlinear transformations of the variables are carried out. Sample calculations show that insight into the structure of the local convergence of Newton–Raphson and fixed Hessian models can be based on an order of convergence and an error term analysis.     

A brief critique of the Adam–Gibbs entropy model

This paper critically discusses the entropy model proposed by Adam and Gibbs in 1965 for the dramatic temperature dependence of glass-forming liquids’ average relaxation time, which is one of the most influential models during the last four decades. We discuss the Adam–Gibbs model’s theoretical bases as well as its reported experimental model confirmations; in the process of doing this a number of problems with the model are identified.     

Quadratic response functions in a second-order polarization propagator framework

The linear and quadratic response functions have been derived for an exact state, based on an exponential parametrization of the time evolution consisting of products of exponentials for orbital rotations and for higher-order excitations. Truncating the linear response function such that the response function itself and its pole structure is correct to second order in M?ller-Plesset perturbation theory, we arrive at the second-order polarization propagator approximation (SOPPA). Previous derivations of SOPPA have used the superoperator formalism, making the extension of SOPPA to quadratic and higher order response functions difficult. The derivation of the quadratic response function is described in detail, allowing molecular properties such as hyperpolarizabilities, two-photon cross sections, and excited-state properties to be calculated using the SOPPA model.     

Al2O3(1120) surface as a template for the ordered growth of Ni and Co nanoclusters

The morphology and thermal stability of Ni and Co nanoclusters grown by physical vapour deposition on a reconstructed (1120) surface of α-Al(2)O(3) is investigated using non-contact atomic force microscopy (NC-AFM). NC-AFM images reveal that the clean α-Al(2)O(3)(1120) substrate adopts a characteristic (12 × 4) reconstruction when prepared in vacuum at high temperature. Subsequent deposition of Ni and Co onto this substrate at room temperature facilitates the growth of well-ordered metal nanocluster arrays with a preferred inter-cluster distance determined by the (12 × 4) periodicity of the substrate surface. The order in the cluster arrangement remains intact even upon annealing the system to temperatures up to 500 °C indicating a high resistance against sintering. The reconstructed α-Al(2)O(3)(1120) surface can, therefore, serve as an appropriate insulating template for studies of size-dependent magnetic or catalytic effects in a well-defined ensemble of metallic nanoclusters.     

Inhibition of Cu-amyloid-β by using bifunctional peptides with β-sheet breaker and chelator moieties

Breaking the mold: Inhibition of toxic amyloid-β (Aβ) aggregates and disruption of Cu-Aβ with subsequent redox-silencing of Cu have been considered promising strategies against Alzheimer's disease. The design and proof of concept of simple peptides containing a Cu-chelating/redox-silencing unit and an Aβ-aggregation inhibition unit (β-sheet breaker) is described (see scheme).     

The mother of all pair potentials

This paper presents a computer simulation study of the exponentially repulsive pair potential system. The simulations show that the system has strong virial potential energy correlations in a large part of its thermodynamic phase diagram. Consequences of this are briefly discussed; these include the existence of isomorphs and predictions for general simple liquids and solids.     

Stable cation inversion at the MgAl2O4(100) surface

From an interplay of atom-resolved noncontact atomic force microscopy, surface x-ray diffraction experiments, and density functional theory calculations, we reveal the detailed atomic-scale structure of the (100) surface of an insulating ternary metal oxide, MgAl2O4 (spinel). We surprisingly find that the MgAl2O4(100) surface is terminated by an Al and O-rich structure with a thermodynamically favored amount of Al atoms interchanged with Mg. This finding implies that so-called Mg-Al antisites, which are defects in the bulk of MgAl2O4, become a thermodynamically stable and integral part of the surface.