With an
adjusted model, we reconsider simple 1,2-dyotropic reactions with the introduction of a
concept based on the intramolecular dynamics of a tetrahedron (van’t Hoff modeling). In fact the
dyotropic reactions are strongly related to conversions originated from neighbouring
group participation or anchimeric assistance, defined as the interaction of a
center with a lone pair of electrons in an atom and the electrons present in aδorπ bond. The researchful 1,2-dyotropic reactions, based on the
1,2-interchange of halogens, methyl and hydrogen taking place in a concerted
fashion, are in competition with the two-step reaction in which the
neighbouring group participation or anchimeric assistance comes to full
expression by ionic dissociation of the other exchangeable (halogen) atom. As
to be expected there is an essential difference between halogen or methyl
exchange regarding the number of electrons participating in the transition state.
This aspect becomes evident in the geometries of the corresponding transition
state geometries. In this paper we refer to ab
initio MO calculations and VB considerations. We consider the 1,2-halogen
exchange as a combination of two S_{N}2 reactions each containing four
electrons. The van’t Hoff dynamics appears a useful model in order to illustrate the
computations in a straightforward manner.

Abstract:
Hydrogen desorption from hydride matrix is still an open field of research. By means of accurate first-principle molecular dynamics (MD) simulations an Mg–MgH2 interface is selected, studied and characterized. Electronic structure calculations are used to determine the equilibrium properties and the behavior of the surfaces in terms of structural deformations and total energy considerations. Furthermore, extensive ab-initio molecular dynamics simulations are performed at several temperatures to characterize the desorption process at the interface. The numerical model successfully reproduces the experimental desorption temperature for the hydride.

Abstract:
Ab initio theory is developed for radiative transitions between excited states of neon. Calculations of energies for even excited states J=1, J=2 supplement our previous calculations for J=1 odd excited states. Line strengths for transitions between J=1 odd and J=1,2 even states of Ne I are evaluated. A comparison with experiments and semiempirical calculations is given.

Abstract:
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.

Abstract:
A series of calculations on the energetics of complexation of alkaline metals with 1,10-phenanthroline are presented. It is an experimental fact that the ordering of the free energy of transfer across the water - 1,2-dichloroethane interphase is governed by the charge / size ratio of the diferent cations; the larger cations showing the lower free energy of transfer. This ordering of the free energies of transfer is reverted in the presence of 1,10-phenanthroline in the organic phase. We have devised a thermodynamic cycle for the transfer process and by means of ab-initio calculations have drawn the conclusion that in the presence of phen the free energy of transfer is governed by the stability of the PHEN/M $^{+}$complex, which explains the observed tendency from a theoretical point of view.

Abstract:
VB-groupoids can be thought of as vector bundle objects in the category of Lie groupoids. Just as Lie algebroids are the infinitesimal counterparts of Lie groupoids, VB-algebroids correspond to the infinitesimal version of VB-groupoids. In this work we address the problem of the existence of a VB-groupoid admitting a given VB-algebroid as its infinitesimal data. Our main result is an explicit characterization of the obstructions appearing in this integrability problem as the vanishing of the spherical periods of certain cohomology classes. Along the way, we illustrate our result in concrete examples. Finally, as a corollary, we obtain computable obstructions for a $2$-term representation up to homotopy of Lie algebroid to arise as the infinitesimal counterpart of a smooth such representation of a Lie groupoid.

Abstract:
We report on recent microscopic calculations of reaction properties based upon the nuclear structure of the ab initio no-core shell model (NCSM).

Abstract:
This letter introduces ab initio study of the full activation-volume tensor of crystalline defects as a means to make contact with mechanical response experiments. We present a theoretical framework for prediction of the internal friction associated with divacancy defects and give the first ab initio value for this quantity in silicon. Finally, making connection with defect alignment studies, we give the first unambiguous resolution of the debate surrounding ab initio verification of the ground-state structure of the defect.

Abstract:
Through ab initio approaches in nuclear theory, we may now seek to quantitatively understand the wealth of nuclear collective phenomena starting from the underlying internucleon interactions. No-core configuration interaction (NCCI) calculations for p-shell nuclei give rise to rotational bands, as evidenced by rotational patterns for excitation energies, electromagnetic moments, and electromagnetic transitions. In this review, NCCI calculations of 7-9Be are used to illustrate and explore ab initio rotational structure, and the resulting predictions for rotational band properties are compared with experiment. We highlight the robustness of ab initio rotational predictions across different choices for the internucleon interaction.