The onset of classical chaos in atom–surface scattering

The relationship between surface rainbows and the onset of classical chaos in atom–surface scattering is discussed. The principal focus is the onset of chaos as a function of experimentally controllable parameters. The correspondence between the classical trapping and quantum mechanical selective adsorption resonances is briefly discussed. The connection with the more mathematical work of Grebogi and co-workers is also considered. © 1994 John Wiley & Sons, Inc.     

Kinetics of atom–photon Interactions

In order to avoid the violation of basic principles of macroscopic reversibility and detailed balance, we propose a cell kinetic model for atom-photon interactions instead of Enstein's classical photon kinetic mechanism. Our model can be interpreted as a generalization of either mass action law or Einstein's original scheme. © 1995 John Wiley & Sons, Inc.     

Anisotropy of atom–atom repulsions

We describe investigations of the short-range repulsion part of the intermolecular potential using a test particle approach. This approach provides an economical method of constructing reasonably accurate model repulsion potentials and demonstrates the importance of anisotropy in describing the short-range repulsion. © 1994 by John Wiley & Sons, Inc.     

Overlap integrals of B functions

Two different methods for the evaluation of overlap integrals of B functions with different scaling parameters are analyzed critically. The first method consists of an infinite series expansion in terms of overlap integrals with equal scaling parameters [14]. The second method consists of an integral representation for the overlap integral which has to be evaluated numerically. Bhattacharya and Dhabal [13] recommend the use of Gauss-Legendre quadrature for this purpose. However, we show that Gauss-Jacobi quadrature gives better results, in particular for larger quantum number. We also show that the convergence of the infinite series can be improved if suitable convergence accelerators are applied. Since an internal error analysis can be done quite easily in the case of an infinite series even if it is accelerated, whereas it is very costly in the case of Gauss quadratures, the infinite series is probably more efficient than the integral representation. Overlap integrals of all commonly occurring exponentially declining basis functions such as Slater-type functions, can be expressed by finite sums of overlap integrals of B functions, because these basis functions can be represented by linear combinations of B functions.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

An algorithm for R matrix calculations for atom–diatom reactive scattering

Some aspects of R matrix theory that derive from a finite element method implementation of a hyperspherical coordinate formulation of the quantum mechanical three-body problem are analyzed with a view of designing suitable algorithms. Propagation of the R matrix from a hyperspherical surface to asymptotically appropriate wave fronts is given special attention.     

Simulation of intermolecular and intramolecular interactions of nucleic acid subunits by means of atom–atom potential functions

Atom–atom potential functions for calculation of nonbonded interaction energies of nucleic acids are proposed. Quantitative reliability of the obtained results is checked by using the calculations of intermolecular interaction energy in crystals. Based on the calculations of the interaction energy of the nucleic acid bases the molecular mechanisms of spontaneous mutations are suggested.     

Theoretical study of intermolecular potential energy surface for HCl dimer: Example of nonspherical atom–atom exchange repulsion interaction

The intermolecular part of the potential energy surface for the HCl dimer has been studied with ab initio quantum chemical methods. An intermolecular potential, based on quantum chemical calculations has been constructed. The interaction energy consists of electrostatic, induction, and dispersion terms calculated from the monomer properties of the interacting molecules and an exchange repulsion term. The latter term was parameterized from the results of the quantum chemical calculations and estimates of the electrostatic and induction energies. It was found necessary to use nonspherical atom–atom exchange repulsion interaction parameters, and the parameters describing the deviation from spherical behavior could be obtained from the expectation values of r² for the electrons assigned to an atom. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1816–1825, 1998     

Influence of metal ion on chelate–aryl stacking interactions

CCSD(T)/CBS and DFT methods are employed to study the stacking interactions of acetylacetonate‐type (acac‐type) chelates of nickel, palladium, and platinum with benzene. The strongest chelate–aryl stacking interactions are formed by nickel and palladium chelate, with interaction energies of −5.75 kcal mol⁻¹ and −5.73 kcal mol⁻¹, while the interaction of platinum chelate is weaker, with interaction energy of −5.36 kcal mol⁻¹. These interaction energies are significantly stronger than stacking of two benzenes, −2.73 kcal mol⁻¹. The strongest nickel and palladium chelate–aryl interactions are with benzene center above the metal area, while the strongest platinum chelate–aryl interaction is with the benzene center above the C2 atom of the acac‐type chelate ring. These preferences arise from very different electrostatic potentials above the metal ions, ranging from very positive above nickel to slightly negative above platinum. While the differences in electrostatic potentials above metal atoms cause different geometries with the most stable interaction among the three metals, the dispersion (correlation energy) component is the largest contribution to the total interaction energy for all three metals.     

Optimization of affinity capillary electrophoresis for routine investigations of protein–metal ion interactions

To facilitate the implementation of affinity capillary electrophoresis into routine binding screening studies of proteins with metal ions, method acceleration, transfer and precision improvement were investigated. Affinity capillary electrophoresis was accelerated by using shorter capillaries, employing lower sample concentrations and smaller injection volumes. Intra‐ and inter‐instrument method transfers were investigated considering the temperature setting of the capillary cooling system. For intra‐instrument method transfer, similar results were obtained when transferring a method from a long (62 cm) to a short (31 cm) capillary. The analysis time was reduced from 9 to 4 min. In case of inter‐instrument method transfer, interaction results showed small variation on the capillary electrophoresis instrument with inefficient capillary cooling system. Binding measurement precision was enhanced by slightly pushing the sample above the beginning of the capillary. Changing the buffer vials after each 30 runs and employing extra flushing after each 60 subsequent runs further enhanced the precision. The use of 0.1 molar ethylenediaminetetraacetic acid in the rinsing solution successfully desorbs the remaining metal ions from the capillary wall. Excellent precision for apparent mobility ratio measurements was achieved for different protein–metal ion interactions (relative standard deviation of 0.16–0.89%, 15 series, 12 runs for each).     

Application of the strong-coupling correspondence principle to atom–triatom collinear collisions

The strong-coupling correspondence principle has been used to calculate the T–V transition probabilities in the collinear collision of He and Kr with CO₂. For a harmonic CO₂ potential the results for He agree well with published quantum mechanical probabilities. For Kr the agreement is less satisfactory but at worst the ratio of quantum to semiclassical transition probability is approximately 0.2. Introduction of anharmonicity in the CO₂ potential was found to increase the semiclassical transition probabilities but this may just be due to the lowering of the vibration frequencies.     

The kernel of DWBA transition amplitude in atom–diatom reactive scattering

The kernel of the distorted-wave Born approximation (DWBA ) transition amplitude will be explored with attention to the atom–diatomic molecule reactive scattering process of A + BC → AB + C. Our study of the kernel reveals valuable intrinsic properties regarding the state-to-state reactive scattering process. In particular, such a study will help us to better understand (i) the favored geometric configuration during collision, (ii) the spatial domain of contribution to the differential and total cross sections, and (iii) the structural dependence of the kernel distribution on the mass ratio of the reactant molecule BC and the departing atom C, particularly in the case of colinear rearrangement collisions. In this study we choose the FH₂ system as an illustration.     

Relations for molecular integrals of relativistic interactions

Relations are derived which connect the molecular integrals of variation of electron mass from relativity, spin—orbit interaction, orbit—orbit interation and spin—spin interaction with the overlap, the nuclear attraction and the electron repulsion integrals.     

Hartree–Fock MO–LCAO equations with charge-dependent atomic integrals

The Hartree–Fock equations are derived in the MO -LCAO approximation for the case when the integrals (except overlap integrals) over the atomic orbitals are charge-dependent. It is shown that inclusion of the overlap matrix in the iterative procedure gives equations which are too complicated for the simple model under consideration. The approach is applied to the VESCF method in the PPP scheme.     

Grand challenges in quantum‐classical modeling of molecule–surface interactions

A detailed understanding of the adsorption of small molecules or macromolecules to a materials surface is of importance, for example, in the context of material and biomaterial research. Classical atomistic simulations in principle provide microscopic insight in the complex entropic and enthalpic interplay at the interface. However, an application of classical atomistic simulation techniques to such interface systems is a nontrivial problem, mostly because commonly used force fields cannot be straightforwardly applied, as they are usually developed to reproduce bulk properties of either solids or liquids but not the interfacial region between two phases. Therefore, a dual‐scale modeling approach has often been the method of choice in the past, in which the classical force field is parameterized such that quantum chemical information on near‐surface conformations and adsorption energies is reproduced by the classical force field. We will discuss in this review the current state‐of‐the‐art of quantum‐classical modeling of molecule–surface interactions and outline the major challenges in this field. In this context, we will, among other things, lay emphasis on discussing ways to obtain representable force fields and propose systematic and system‐independent strategies to optimize the quantum‐classical fitting procedure. © 2013 Wiley Periodicals, Inc.     

Quantum mechanical calculations of vibrational transition probabilities in collinear atom–triatom collisions

Quantum mechanical calculations have been made of vibrational transition probabilities in the collinear collision of an inert gas atom with either CO₂ or OCS. The dependence of the transition probability on the relative translational energy and the reduced mass is similar to that found for atom–diatom collisions. The transition P_{00 → 10} (excitation of the first stretching mode) is much greater than P_{00 → 01} (the second stretching mode). This is largely due to the difference in frequencies but it has been shown that there is an independent mass factor responsible for this difference.     

New ligands for atom‐transfer radical polymerization

A new type of ligands based on organic acids, such as acetic acid, iminodiacetic acid, succinic acid and isophthalic acid, has been successfully employed in the iron‐mediated atom‐transfer radical polymerization (ATRP) of vinyl monomers, such as styrene (St) and methyl methacrylate (MMA). The systems containing different organic acids can react at 250°C to 1300°C in “living”/controlled radical polymerizations giving polymers with relatively narrow molecular weight distributions (M_w/M_n = 1.2–1.5). ¹H NMR spectroscopy has been used to study the structure of the resulting polymers. Block copolymers were synthesized to confirm the ìlivingî nature of the system. The measured molecular weights are close to the calculated values for the polymerization of MMA and are somewhat lower than the theoretical ones for styrene.     

Overlap effects on surface states

A tight-binding investigation is performed of the electronic structure of a semi-infinite monatomic chain, whose atomic orbitals are assumed to be non-orthogonal, so that the effects of overlap can be taken into account. In addition to markedly modifying the bulk band-edges, the presence of overlap also greatly influences the position and existence of the surface states. These latter effects are examined in detail.