pinecone/core-2020-05-10-deduplication huggingface dataset:
The magnetic moments and their long-range ordering for Fe atoms in a wide variety of metallic environments

9 páginas, 5 figuras.-- El pdf del artículo es la versión pre-print.The magnitudes of Fe magnetic moments, together with their long-range ordering when appropriate, are compared and contrasted in a variety of metallic environments. Thus, Fe, in its stable body-centered-cubic (bcc) phase under ambient conditions, is considered under pressures p, which can yield different crystal structures at high p, including fcc. The modification of the ferromagnetism in bcc Fe is surveyed as one passes through a bc-tetragonal lattice to the fcc form. In the latter, evidence is presented, both from theory and experiment, that the ordering is antiferromagnetic in character. Then, binary metallic alloys with Fe atoms as the majority component are considered, Fe–Co and Fe–Ga being focal points in both ordered and disordered materials. Finally, some discussion is given, involving again both experiment and theory, of the possible spin polarization of neighboring Cs atoms when Fe impurity atoms are inserted into the low conduction electron density characterizing this heavy alkali metal under ambient conditions.Contract grant sponsor: Spanish Ministerio de Ciencia y\ud
Tecnología (MCyT), MONACEM Project.\ud
Contract grant number: Fis2007-66711-CO2-02.\ud
Contract grant sponsor: University of Basque Country.\ud
Contract grant number: IT-366-07.\ud
Contract grant sponsor: Basque Government [NANOMATERIALS\ud
Project (IE05-151), ETORTEK Program (iNanogune)].Peer reviewe
Reactivity of polynuclear zinc-thiolate sites

International audienceThe proton affinities of a series of mono- and polynuclear zinc-thiolate compounds, mimicking zing finger protein and metallothioneins sites, have been investigated by Density Functional Theory calculations. This allows to evaluate the intrinsic nucleophilicity of synthetic and natural zinc-bound thiolates and to compare their relative reactivities. The site specificity of the experimental thiolate alkylation for the Zn4Cys11 clusters in metallothioneins is well reproduced, as well as the relative reactivities of ZnHis2Cys2, ZnHisCys3 and ZnCys4 zinc finger sites. Our results also show that terminal thiolates, bound to only one Lewis acid, are more reactive than bridging thiolates. Synthetic inorganic clusters and the Zn4Cys9His2 cluster found in a cyanobacterial metallothionein are less reactive than Zn4Cys11 and Zn3Cys9 clusters in metallothioneins. These results allow discussing the influence of the protein backbone and residues on the reactivity of these natural clusters
Full Spin and Spatial Symmetry Adapted Technique for Correlated
  Electronic Hamiltonians: Application to an Icosahedral Cluster

One of the long standing problems in quantum chemistry had been the inability
to exploit full spatial and spin symmetry of an electronic Hamiltonian
belonging to a non-Abelian point group. Here we present a general technique
which can utilize all the symmetries of an electronic (magnetic) Hamiltonian to
obtain its full eigenvalue spectrum. This is a hybrid method based on Valence
Bond basis and the basis of constant z-component of the total spin. This
technique is applicable to systems with any point group symmetry and is easy to
implement on a computer. We illustrate the power of the method by applying it
to a model icosahedral half-filled electronic system. This model spans a huge
Hilbert space (dimension 1,778,966) and in the largest non-Abelian point group.
The $C_{60}$ molecule has this symmetry and hence our calculation throw light
on the higher energy excited states of the bucky ball. This method can also be
utilized to study finite temperature properties of strongly correlated systems
within an exact diagonalization approach.Comment: 21 pages, 7 figures, abstract rewritten, a few changes in text, to
  appear in International Journal of Quantum Chemistr
Ab initio effective rotational Hamiltonians - A comparative study

40 pages dont 6 tablesInternational audienceTwo independent methods to obtain ab initio effective rotational Hamiltonians have been implemented recently. The first one is based on a generalization of perturbation theory to non-commutative rings, the other one on contact transformation techniques. In principle, both methods are able to give rotational Hamiltonians including centrugal distortion effects of arbitrary high orders. These methods are compared for the first time in this article with regard to calculations of the rotational levels of methane vibrational ground state
Density functional theory studies on the addition and abstraction reactions of OH radicals with terephthalate dianions

The addition and abstraction reactions of OH radicals with terephthalate dianions are investigated by density functional theory calculations that include solvent effects. Geometry optimizations of the reactants, products, and transition state species are performed for the potential reaction paths. For the addition reactions, those targeting the ipso- and ortho-carbons are predicted to be exoergic. The H-atom abstraction reaction is also predicted to be exoergic. On the basis of the rate constants calculated by means of the transition state theory, the H-atom abstraction reaction is determined to be the thermochemically favored path. (C) 2012 Wiley Periodicals, Inc
Testing the broad applicability of the PBEint GGA functional and its
  one-parameter hybrid form

We review the performance of the PBEint GGA functional (Phys. Rev. B 2010,
82, 113104) recently proposed to improve the description of hybrid interfaces,
and we introduce its one-parameter hybrid form (hPBEint). We consider different
well established benchmarks for energetic and structural properties of
molecular and solid-state systems as well as model systems and newly developed
benchmark sets for dipole moments and metal-molecule interactions. We find that
PBEint and hPBEint (with 16.67% Hartree-Fock exchange) yield the overall best
performance, working well for most of the considered properties and systems and
showing a balanced behavior for different problems. In particular, due to their
well-balanced accuracy, they perform well for the description of hybrid
metal-molecule interfaces.Comment: 13 pages, 3 figures. Accepted for publication in Int. J. Quant. Chem.
  (2013), DOI: 10.1002/qua.2404
Study of Simulation Method of Time Evolution in Rigged QED

We discuss how we formulate time evolution of physical quantities in the
framework of the Rigged QED (Quantum Electrodynamics). The Rigged QED is a
theory which has been proposed to treat dynamics of electrons, photons and
atomic nuclei in atomic and molecular systems in a quantum field theoretic way.
To solve the dynamics in the Rigged QED, we need different techniques from
those developed for the conventional QED. As a first step toward this issue, we
propose a procedure to expand the Dirac field operator, which represents
electrons, by the electron annihilation/creation operators and solutions of the
Dirac equation for electrons in nuclear potential. Similarly, the Schrodinger
field operators, which represent atomic nuclei, are expanded by nucleus
annihilation/creation operators. Then we derive time evolution equations for
these annihilation and creation operators and discuss how time evolution of the
operators for physical quantities can be calculated. In the end, we propose a
method to approximate the evolution equations of the operators by the evolution
equations for the density matrices of electrons and atomic nuclei. Under this
approximation, we carry out numerical simulation of the time evolution of
electron charge density of a hydrogen atom.Comment: 31 pages, 5 figure
Polarized–unpolarized ground state of small polycyclic aromatic hydrocarbons

Do polyacenes, circumacenes, periacenes, nanographenes, and graphene nanoribbons show a spin polarized ground state? In this work, we present monodeterminantal (Hartree–Fock (HF) and density functional theory (DFT) types), and multideterminantal calculations (Møller–Plesset and Coupled Cluster), for several families of unsaturated organic molecules (n-Acenes, n-Periacenes and n-Circumacenes). All HF calculations and many DFT show a spin-polarized (antiferromagnetic) ground state, in agreement with previous calculations. Nevertheless, the multideterminantal calculations, carried out with perturbative and variational wavefunctions, show that the more stable state is obtained starting from the unpolarized HF wavefunction. The trend of the stabilization of wavefunctions (polarized or unpolarized) with respect to exchange and correlation potentials, and to the number of benzene rings, has been analyzed. A study of the spin (〈Ŝ2〉) and the spin density on the carbon atoms has also been carried out.Spanish MCYT; contract grant numbers: FIS2008-06743 and FIS2009-10325. Universidad de Alicante
Theoretical study on the reaction mechanism of formation of 3,5-diacetyl-1,4-dihydrolutidine

We have studied the reaction path of the formation of 3,5-diacetyl-1,4-dihydrolutidine (DL1), 3,5-dibenzoyl-1,4-dihydro-2,6-dimethylpyridine, and 2,6-dibenzoyl-1,4-dihydro-3,5-dimethylpyridine with the ab initio molecular orbital method at HF/3-21G and HF/6-31G(d,p) levels. For DL1, we also calculated at MP2/6-31G(d,p) level. The barrier heights of H2O elimination elementary reactions are ca. 50-60 kcal/mol and quite high in the gas phase, however, this is well agreed with the experimental results that the reaction proceeds in aqueous solutions
Spin in Density-Functional Theory

The accurate description of open-shell molecules, in particular of transition
metal complexes and clusters, is still an important challenge for quantum
chemistry. While density-functional theory (DFT) is widely applied in this
area, the sometimes severe limitations of its currently available approximate
realizations often preclude its application as a predictive theory. Here, we
review the foundations of DFT applied to open-shell systems, both within the
nonrelativistic and the relativistic framework. In particular, we provide an
in-depth discussion of the exact theory, with a focus on the role of the spin
density and possibilities for targeting specific spin states. It turns out that
different options exist for setting up Kohn-Sham DFT schemes for open-shell
systems, which imply different definitions of the exchange-correlation energy
functional and lead to different exact conditions on this functional. Finally,
we suggest some possible directions for future developments
Real-time Quantum Chemistry

Significant progress in the development of efficient and fast algorithms for
quantum chemical calculations has been made in the past two decades. The main
focus has always been the desire to be able to treat ever larger molecules or
molecular assemblies---especially linear and sub-linear scaling techniques are
devoted to the accomplishment of this goal. However, as many chemical reactions
are rather local, they usually involve only a limited number of atoms so that
models of about two hundred (or even less) atoms embedded in a suitable
environment are sufficient to study their mechanisms. Thus, the system size
does not need to be enlarged, but remains constant for reactions of this type
that can be described by less than two hundred atoms. The question then arises
how fast one can obtain the quantum chemical results. This question is not
directly answered by linear-scaling techniques. In fact, ideas such as haptic
quantum chemistry or interactive quantum chemistry require an immediate
provision of quantum chemical information which demands the calculation of data
in "real time". In this perspective, we aim at a definition of real-time
quantum chemistry, explore its realm and eventually discuss applications in the
field of haptic quantum chemistry. For the latter we elaborate whether a direct
approach is possible by virtue of real-time quantum chemistry
Theory of variational calculation with a scaling correct moment functional to solve the electronic schrodinger equation directly for ground state one-electron density and electronic energy

The reduction of the electronic Schrodinger equation or its calculating algorithm from 4N-dimensions to a nonlinear, approximate density functional of a three spatial dimension one-electron density for an N electron system which is tractable in practice, is a long-desired goal in electronic structure calculation. In a seminal work, Parr et al. (Phys. Rev. A 1997, 55, 1792) suggested a well behaving density functional in power series with respect to density scaling within the orbital-free framework for kinetic and repulsion energy of electrons. The updated literature on this subject is listed, reviewed, and summarized. Using this series with some modifications, a good density functional approximation is analyzed and solved via the Lagrange multiplier device. (We call the attention that the introduction of a Lagrangian multiplier to ensure normalization is a new element in this part of the related, general theory.) Its relation to Hartree-Fock (HF) and Kohn-Sham (KS) formalism is also analyzed for the goal to replace all the analytical Gaussian based two and four center integrals (∫g                    i(r                    1)g                    k(r                    2)r12-1dr                    1dr                    2, etc.) to estimate electron-electron interactions with cheaper numerical integration. The KS method needs the numerical integration anyway for correlation estimation. © 2012 Wiley Periodicals, Inc
Hubbard-corrected DFT energy functionals: the LDA+U description of
  correlated systems

The aim of this review article is to assess the descriptive capabilities of
the Hubbard-rooted LDA+U method and to clarify the conditions under which it
can be expected to be most predictive. The paper illustrates the theoretical
foundation of LDA+U and prototypical applications to the study of correlated
materials, discusses the most relevant approximations used in its formulation,
and makes a comparison with other approaches also developed for similar
purposes. Open "issues" of the method are also discussed, including the
calculation of the electronic couplings (the Hubbard U), the precise expression
of the corrective functional and the possibility to use LDA+U for other classes
of materials. The second part of the article presents recent extensions to the
method and illustrates the significant improvements they have obtained in the
description of several classes of different systems. The conclusive section
finally discusses possible future developments of LDA+U to further enlarge its
predictive power and its range of applicability.Comment: 45 pages, 14 figures, 4 tables International Journal of Quantum
  Chemistry (2013
Effective Atomic Orbitals: A Tool for Understanding Electronic Structure of Molecules

It is discussed that one can obtain effective atomic orbitals (AOs) in quite different theoretical frameworks of Hilbert-space and three-dimensional (3D) analyses. In all cases, one can clearly distinguish between the orbitals of an effective minimal basis set and orbitals which are only insignificantly occupied. This observation makes a solid theoretical basis beyond our qualitative picture of molecular electronic structure, described in terms of minimal basis AOs having decisive participation in bonding, and may be considered as a quantum chemical manifestation of the octet rule. For strongly positive atoms like the hypervalent sulfur, some weakly occupied orbitals reflecting "back donation" can also be identified. From the conceptual point of view, it is very important that AOs of characteristic shape can be obtained even by processing the results of plane wave calculations in which no atom-centered basis orbitals were applied. The different types of analyses (Hilbert-space and 3D) can be done on equal footing, performing quite analogous procedures, and they exhibit an unexpected interrelation, too. (C) 2014 Wiley Periodicals, Inc
The chemical physics of unconventional superconductivity

Attempts to explain correlated-electron superconductivity have largely
focused on the proximity of the superconducting state to antiferromagnetism.
Yet, there exist many correlated-electron systems that exhibit
insulator-superconducting transitions where the insulating state exhibits
spatial broken symmetry different from antiferromagnetism. Here we focus on a
subset of such compounds which are seemingly very different in which specific
chemical stoichiometries play a distinct role, and small deviations from
stoichiometry can destroy superconductivity. These superconducting materials
share a unique carrier concentration, at which we show there is a stronger than
usual tendency to form local spin-singlets. We posit that superconductivity is
a consequence of these pseudomolecules becoming mobile as was suggested by
Schafroth a few years prior to the advent of the BCS theory.Comment: 19 pages, 6 figures; to appear in Int. J. Quantum Che
Unraveling reaction mechanisms by means of Quantum Chemical Topology Analysis

A chemical reaction can be understood in terms of geometrical changes of the molecular structures and reordering of the electronic densities involved in the process; therefore, identifying structural and electronic density changes taking place along the reaction coordinate renders valuable information on reaction mechanism. Understanding the atomic rearrangements that occur during chemical reactions is of great importance, and this perspective aims to highlight the major developments in quantum chemical topology analysis, based on the combination of electron localization function and catastrophe theory as useful tools in elucidating the bonding and reactivity patterns of molecules. It reveals all the expected, but still ambiguous, elements of electronic structure extensively used by chemists. The chemical bonds determine chemical reactivity, and this technique offers the possibility of their visualization, allowing chemists to understand how atoms bond, how and where bonds are broken/formed along a given reaction pathway at a most fundamental level, and so, better following and understanding the changes in the bond pattern. Their results clearly herald a new era, in which the atomic imaging of chemical bonds will constitute a new method for examining chemical structures and reaction mechanisms. The important feature of this procedure is that in practice the scope of its values is system-independent. In addition, from a practical point of view, it is cheap to calculate and implement because wave functions are the required input, which are easily available from standard calculations. To capture these results two reaction mechanisms: isomerization of C(BH)2 carbene and the thermal cycloheptatriene-norcaradiene isomerizations have been selected, indicating both the generality and utility of this type of analysis
Double hybrid density-functional theory using the Coulomb-attenuating
  method

A double hybrid approximation using the Coulomb-attenuating method (CAM-DH)
is derived within range-separated density-functional perturbation theory, in
the spirit of a recent work by Cornaton {\it et al.} [Phys. Rev. A 88, 022516
(2013)]. The energy expression recovered through second order is linear in the
parameters $\alpha$ and $\beta$ that control the Coulomb attenuation. The
method has been tested within the local density approximation on a small test
set consisting of rare-gas and alkaline-earth-metal dimers as well as diatomics
with single, double and triple bonds. In this context, the semi-empirical
$\alpha=0.19$ and $\beta=0.46$ parameters, that were optimized for the hybrid
CAM-B3LYP functional, do not provide accurate interaction and total energies.
Using semi-local functionals with density scaling, that was neglected in this
work, may lead to different conclusions. Calibration studies on a larger test
set would be necessary at this point. This is left for future work. Finally, we
propose as a perspective an alternative CAM-DH approach that relies on the
perturbation expansion of a partially long-range interacting wavefunction. In
this case the energy is not linear anymore in $\alpha$ and $\beta$. Work is in
progress in this direction.Comment: 36 pages, 6 figure
Gradient-Driven Molecule Construction: An Inverse Approach Applied to
  the Design of Small-Molecule Fixating Catalysts

Rational design of molecules and materials usually requires extensive
screening of molecular structures for the desired property. The inverse
approach to deduce a structure for a predefined property would be highly
desirable, but is, unfortunately, not well-defined. However, feasible
strategies for such an inverse design process may be successfully developed for
specific purposes. We discuss options for calculating 'jacket' potentials that
fulfill a predefined target requirement - a concept that we recently introduced
[T. Weymuth, M. Reiher, MRS Proceediungs, 2013, 1524,
DOI:10.1557/opl.2012.1764]. We consider the case of small-molecule activating
transition metal catalysts. As a target requirement we choose the vanishing
geometry gradients on all atoms of a subsystem consisting of a metal center
binding the small molecule to be activated. The jacket potential can be
represented within a full quantum model or by a sequence of approximations of
which a field of electrostatic point charges is the simplest. In a second step,
the jacket potential needs to be replaced by a chemically viable chelate-ligand
structure for which the geometry gradients on all of its atoms are also
required to vanish. In order to analyze the feasibility of this approach, we
dissect a known dinitrogen-fixating catalyst to study possible design
strategies that must eventually produce the known catalyst.Comment: 40 pages, 6 tables, 5 figure
Inverse Quantum Chemistry: Concepts and Strategies for Rational Compound
  Design

The rational design of molecules and materials is becoming more and more
important. With the advent of powerful computer systems and sophisticated
algorithms, quantum chemistry plays an important role in rational design. While
traditional quantum chemical approaches predict the properties of a predefined
molecular structure, the goal of inverse quantum chemistry is to find a
structure featuring one or more desired properties. Herein, we review inverse
quantum chemical approaches proposed so far and discuss their advantages as
well as their weaknesses.Comment: 43 pages, 5 figure
Density-matrix theory of quantum dynamics under a strong external field switched on nonadiabatically

Quantum time-evolution equations for the density matrix are formulated in the unrestricted Hartree–Fock approximation, with an emphasis on the nonperturbative effect due to a sudden or gradual onset of a strong external field. Numerical simulations are performed for ideal Fermi gas around a square-well potential which is switched on dynamically. When the switching is fast enough, an oscillatory motion of the particle is induced by a nonadiabatic transition at the Landau–Zener crossing point, which is most clearly seen in a small-size system. When the switching is sufficiently slow, the simulation corroborates the adiabatic theorem. It is shown that the Anderson's infrared catastrophe in a metal is strongly enhanced by the nonperturbative effect. The Keldysh formula of atomic multiphoton ionization can also be derived from the nonperturbative term in the density-matrix equation, indicating a wide applicability of the present theory