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For many decades, the main source of information on the top-left corner element of the Cabibbo–Kobayashi–Maskawa quark mixing matrix, Vud, was superallowed nuclear β decays with an impressive 0.01% precision. This precision, apart from experimental data, relies on theoretical calculations in which nuclear structure–dependent effects and uncertainties play a prime role. This review is dedicated to a thorough reassessment of all ingredients that enter the extraction of the value of Vud from experimental data. We try to keep balance between historical retrospect and new developments, many of which occurred in just the past 5 years. They have not yet been reviewed in a complete manner, not least because new results are forthcoming. This review aims to fill this gap and offers an in-depth yet accessible summary of all recent developments. [ABSTRACT FROM AUTHOR]

In the current study, several computational models were examined to calculate accurate adiabatic electron affinity (AEA) of twelve m- and p-monosubstituted benzaldehyde derivatives. The examined models are as follows: (i) composite high-level ab initio (G3B3, G4, CBS-Q, and CBS-QB3), (ii) Three hybrid DFT approaches (B3LYP, CAM-B3LYP, and wB97XD) with two basis sets (6–31 + G(d,p) and 6–311++G(2df,2p)) and (iii) single point calculation using fifteen DFT approaches with 6–311++G(2df,2p) at the B3LYP/6–31 + G(d,p) geometry. Several statistical descriptors were computed to validate the calculated AEAs based on the available experimental results. Results revealed that G3B3 and CBS-QB3 are the most accurate result, while G4 and CBS-Q methods yield less accurate ones. Also, the wB97XD and CAM-B3LYP in combination with 6–311++G(2df,2p) able to calculate accurate AEAs. Low CPU time single point calculation strategy by using wb97 and wb97X approaches can compute AEAs value as accurately as G3B3 and CBS-QB3 methods. The AEAs of other several monosubstituted benzaldehydes were also predicted by using the wb97, wb97X, and wb97XD. The effect of the nature and position of substituents on the natural spin density and natural charge is also studied and discussed.

The advent of pump-probe spectroscopy techniques paved the way to the exploration of ultrafast dynamics of electrons and phonons in crystalline solids. Following photo-absorption of a pump pulse and the initial electronic thermalization, the dynamics of electronic and vibrational degrees of freedom is dominated by electron-phonon and phonon-phonon scattering processes. The two-temperature model (TTM) and its generalizations provide valuable tools to describe these phenomena and the ensuing coupled dynamics of electrons and phonons. While more sophisticated theoretical approaches are nowadays available, the conceptual and computational simplicity of the TTM makes it the method of choice to model thermalization processes in pump-probe spectroscopy, and it keeps being widely applied in both experimental and theoretical studies. In the domain of ab-initio methods, the time-dependent Boltzmann equation (TDBE) ameliorates many of the shortcomings of the TTM and enables a realistic and parameter-free description of ultrafast phenomena with full momentum resolution. After a pedagogical introduction to the TTM and TDBE, in this manuscript we review their application to the description of ultrafast process in solid-state physics and materials science as well as their theoretical foundation.

Optimized link bond parameters for the CαCβ bond of 22 different capped amino acid model systems have been determined at SCC DFTB/mio (self‐consistent charge density functional tight‐binding), SCC DFTB/3ob and GFNn‐xTB (n = 0, 1, and 2) level in conjunction with the AMBER 99SB, 14SB, and 19B force fields. The resulting parameter sets have been compared to newly calculated reference data obtained via resolution‐of‐identity 2nd order Møller–Plesset perturbation theory. The data collected in this work suggests that the optimized values in this study provide a more suitable setup of the QM/MM link bonds compared to the use of a single global setting applied to every amino acid fragmented by the QM/MM interface. The results also imply that a transfer of the ideal link bond settings between different levels of theory is not advised. In contrast, virtually identical parameters were obtained in calculations employing different variants of the AMBER force field. Considering the increasing success of tight binding based approaches being inter alia a results of their exceptional accuracy/effort ratio the provided collection of link atoms parameters provides a valuable resource for QM/MM studies of biomacromolecular systems as demonstrated in an exemplary QM/MM MD simulation of the β‐amyloid/Zn2+ complex. [ABSTRACT FROM AUTHOR]

Abstract Aliphatic isocyanurates are nowadays used routinely in the development of advanced materials like polyurethane nanocomposites and 3D-printed components, due to their versatile reactivity and the good mechanical and optical properties they confer to the final material. In these applications, a control of the properties at the micro- and nanoscale is desired, therefore a deep understanding of intermolecular interactions is required. Using ab-initio calculations and molecular dynamics simulations, the intermolecular interactions of aliphatic isocyanurates are investigated in detail. The presence of an isocyanate-isocyanurate interaction is demonstrated, and the strong dispersion character of isocyanurate-based interactions is revealed. Calculations of the free energy of binding of the different interactions in gas and liquid phase are provided. The microscopic structure of aliphatic functional and non-functional isocyanurates is analysed and related to the different interaction types, and finally their possible relationship with macroscopic dynamic variables is discussed. Highlights • Ab-initio methods and Molecular Dynamics simulation were used to study intermolecular interactions in isocyanurate liquids. • The isocyanurate ring is capable of strong non-covalent interactions, with visible effects on the liquid local structure. • A cooperative isocyanate-isocyanurate interaction was found, at the basis of the viscosity behaviour of isocyanurate liquids. [ABSTRACT FROM AUTHOR]

The present article deals with computational study of molecular geometries, electronic properties, and vibrational characteristics using the density functional theory (DFT) and Hartree-Fock methods supplemented with basis set 6-31++G(d.p) at Gaussion-09 program. The Raman and infrared spectra of two liquid crystalline disubstituted biphenylcyclohexanes (BCH RX) of general formula R-C6H10-C6H4-C6H4-X with R: C3H7; X = H (BCH30) and R: C5H11; X = CN (BCH5CN) have been analyzed and vibrations corresponding to particular frequency are assigned in detail. Most of the modes have wavenumbers/frequencies in the expected range, and the error obtained was minimum. Aromatic ring with terminal cyano group confers a positive dielectric anisotropy, and high optical anisotropy. Cyanobiphenyls possess high dielectric anisotropy and good electro-optical characteristics are used to decrease the switching time of liquid crystalline materials. It has been observed that the DFT based calculations consider the different types of interactions between electrons, thus it gives more accuracy as compared to HF method. Further, the electronic properties of the mesogenic compounds have been reported to understand the molecular reactivity, charge transfer, electro-optical, and other molecular properties. [ABSTRACT FROM AUTHOR]

We explore the systematics of ground-state and excitation energies in singly-strange hypernuclei throughout the helium and lithium isotopic chains — from He Λ 5 to He Λ 11 and from Li Λ 7 to Li Λ 12 — in the ab initio no-core shell model with importance truncation. All calculations are based on two- and three-baryon interaction from chiral effective field theory and we employ a similarity renormalization group transformation consistently up to the three-baryon level to improve the model-space convergence. While the absolute energies of hypernuclear states show a systematic variation with the regulator cutoff of the hyperon–nucleon interaction, the resulting neutron separation energies are very stable and in good agreement with available data for both nucleonic parents and their daughter hypernuclei. We provide predictions for the neutron separation energies and the spectra of neutron-rich hypernuclei that have not yet been observed experimentally. Furthermore, we find that the neutron drip lines in the helium and lithium isotopic chains are not changed by the addition of a hyperon. [ABSTRACT FROM AUTHOR]

In the current study, several computational models were examined to calculate accurate adiabatic electron affinity (AEA) of twelve m- and p- monosubstituted benzaldehyde derivatives. The examined models are as follows: (i) composite high-level ab initio (G3B3, G4, CBS-Q, and CBS-QB3), (ii) Three hybrid DFT approaches (B3LYP, CAM-B3LYP, and wB97XD) with two basis sets (6–31 + G(d,p) and 6–311++G(2df,2p)) and (iii) single point calculation using fifteen DFT approaches with 6–311++G(2df,2p) at the B3LYP/6–31 + G(d,p) geometry. Several statistical descriptors were computed to validate the calculated AEAs based on the available experimental results. Results revealed that G3B3 and CBS-QB3 are the most accurate result, while G4 and CBS-Q methods yield less accurate ones. Also, the wB97XD and CAM-B3LYP in combination with 6–311++G(2df,2p) able to calculate accurate AEAs. Low CPU time single point calculation strategy by using wb97 and wb97X approaches can compute AEAs value as accurately as G3B3 and CBS-QB3 methods. The AEAs of other several monosubstituted benzaldehydes were also predicted by using the wb97, wb97X, and wb97XD. The effect of the nature and position of substituents on the natural spin density and natural charge is also studied and discussed. [ABSTRACT FROM AUTHOR]

The Wigner formulation of quantum mechanics is a very intuitive approach which allows the comprehension and prediction of quantum mechanical phenomena in terms of quasi-distribution functions. In this review, our aim is to provide a detailed introduction to this theory along with a Monte Carlo method for the simulation of time-dependent quantum systems evolving in a phase-space. This work consists of three main parts. First, we introduce the Wigner formalism, then we discuss in detail the Wigner Monte Carlo method and, finally, we present practical applications. In particular, the Wigner model is first derived from the Schrödinger equation. Then a generalization of the formalism due to Moyal is provided, which allows to recover important mathematical properties of the model. Next, the Wigner equation is further generalized to the case of many-body quantum systems. Finally, a physical interpretation of the negative part of a quasi-distribution function is suggested. In the second part, the Wigner Monte Carlo method, based on the concept of signed (virtual) particles, is introduced in detail for the single-body problem. Two extensions of the Wigner Monte Carlo method to quantum many-body problems are introduced, in the frameworks of time-dependent density functional theory and ab-initio methods. Finally, in the third and last part of this paper, applications to single- and many-body problems are performed in the context of quantum physics and quantum chemistry, specifically focusing on the hydrogen, lithium and boron atoms, the H 2 molecule and a system of two identical Fermions. We conclude this work with a discussion on the still unexplored directions the Wigner Monte Carlo method could take in the next future. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetic properties of the kagome staircase compound Co3V2O8doped by 3-d elements (Mn, Mg and Zn) have been investigated using ab-initio FPLO method. We found that in the case of Mg and Zn the electronic densities of states near the Fermi energy is not significantly modified, however substitution the cobalt by manganese atom changed the band structure near the Fermi energy. [ABSTRACT FROM PUBLISHER]

Abstract: An ordered mixed deuterated amide/imide potassium–magnesium compound was synthesized with the intent of solving its structure using neutron diffraction technique with help of “ab-initio” methods. Obtained powder diffraction patterns were compatible with the orthorhombic P212121 space group, and lattice parameters a = 9.8896(3) Å; b = 9.3496(3) Å; c = 3.6630(1) Å, respectively. Assuming a density of 1.91 g/cm3 the investigation has allowed to locate the four constituting elements distributed in seven different sites into Wyckoff general positions 4(a), for a total of 28 atoms in the unit cell. This is the first example of crystal structure solution of a mixed imide/amide compound appearing during the dehydrogenation process of a potassium containing amide based hydrogen storage material. [Copyright &y& Elsevier]

Coherence and de-coherence are the most fundamental steps that follow the initial photo-excitation occurring in typical pump-and-probe experiments. Indeed, the initial external laser pulse transfers coherence to the system in terms of creation of multiple electron–hole pairs excitation. The excitation concurs both to the creation of a finite carriers density and to the appearance of induced electromagnetic fields. The two effects, to a very first approximation, can be connected to the simple concepts of populations and oscillations. The dynamics of the system following the initial photo-excitation is, thus, entirely dictated by the interplay between coherence and de-coherence. This interplay and the de-coherence process itself, is due to the correlation effects stimulated by the photo-excitation. Single-particle, like the electron–phonon, and two-particles, like the electron–electron, scattering processes induce a complex dynamics of the electrons that, in turn, makes the description of the correlated and photo-excited system in terms of pure excitonic and/or carriers populations challenging. • In any Pump-Probe experiment the driving field transfers coherence to the system • After photo-excitation a complex interplay of coherence and decoherence takes place. • Time-Resolved ARPES is a powerful tool to access the nonequilibrium carrier dynamics • Time-Resolved ARPES provides a sharp evidence of the role played by excitonic effects • Time-Resolved Angle Resolved Spectroscopy is a powerful tool to access the out-of-equilibrium carrier dynamics and can provide a sharp evidence of the role played by excitonic effects. [ABSTRACT FROM AUTHOR]

• Understanding ELS spectra of ceria interacting with hydrogen by combining experiment with theory. • Valence excitations of ceria well described within cluster as well as periodic approaches. • Hydrogen atoms in CeO 2-x accept electrons spontaneously forming hydride species and re-oxidize Ce3+ (4f1) to Ce4+ (4f0). • Hydride species preferentially occupy oxygen vacancy sites. • Hydride species in CeO 2-x are thermodynamically more stable in deep subsurface layers compared with near-surface positions. Based on both, ab-initio cluster calculations as well as periodic density functional based loss function calculations, we have assigned the origins of the valence electron excitation regime in electron energy loss spectra of well-ordered ceria films in (111) orientation at various states of reduction as well as after exposing the reduced films to hydrogen from the gas phase (Li et al, Angew. Chem. Int. Ed., 58 (2019) 14686–14693). The explicit calculation of intensity distributions using the dipole approximation allow us to draw conclusions about the nature of oxygen vacancies, which occur upon reduction and how those interact with hydrogen to form hydride species. The present study also reports a brief discussion of vibrational excitations of hydrogen loaded ceria and corroborates previous interpretations, based on inelastic neutron scattering. [ABSTRACT FROM AUTHOR]

Abstract: The computational efficiencies of the semi-empirical method have been compared with those of different ab-initio methods for positional isomers of Naphthol and Tetrahydro-naphthol type molecules. The efficiencies for computations in case of optimized structure, electronic absorption and emission properties are investigated. For that semi-empirical approach ZINDO and two different nature of ab-initio approaches such as TD-HF/6-311G(d,p) and TD-DFT/B3LYP/6-311G(d,p) were considered. The three main approaches are studied here to give the right direction of simulation. Semi-empirical AM1/ZINDO function itself can detect the trend of molecular transitions and the values obtained by simulations are more realistic than ab-initio methods. Ab-initio methods can reproduce exact values of first transitional energy with some scaling factor both in ground and in excited states of Tetrahydro-naphthol positional isomers whereas no solution or prediction could be inferred for Naphthol isomers. [ABSTRACT FROM AUTHOR]

Abstract: The effect of orbital instabilities is investigated for spin-symmetry breaking perturbations, namely the Fermi-contact (FC) and spin–dipole (SD) contributions to the indirect nuclear spin–spin coupling constants. For the CO and N2 molecules the FC and SD contributions have been calculated and orbital-stability analyses for various interatomic distances have been carried out. This includes calculations at the Hartree–Fock self-consistent field (HF-SCF), coupled-cluster (CC) singles and doubles (CCSD), CC3, CCSD(T), CCSDT-4, CC singles, doubles, and triples (CCSDT) levels, and for the first time also at the CC singles, doubles, triples, and quadruples (CCSDTQ) level of theory. For calculations with relaxation of the reference orbitals in the presence of the perturbation, unphysical results are obtained over a wide range of the potential curve. This is due to a triplet instability of the Hartree–Fock reference determinant which leads to a pronounced pole in the FC and SD contributions. The effect of orbital instabilities in the relaxed methods is most dramatic for perturbative approaches like CCSD(T), while it is less pronounced for methods of the classical CC hierarchy. CC calculations without relaxation of the orbitals, i.e., so-called “unrelaxed” calculations, do not show any of these effects. [Copyright &y& Elsevier]

Abstract: This work analyzes some improvements and simplifications made on procedures to calculate molecular bond lengths, through the combination of different theoretical methods that we have proposed some time ago. The main improvement that we have presently achieved lies in the combined application of the two procedures already presented, one related to the reduction of systematic errors and the other associated to the reduction of random errors. A second part of the work is devoted to explore the possibility to abbreviate the procedure to reduce random errors, either by reducing the basis set size in ab-initio methods or by modifying the parametrization in semiempirical methods. Finally, we present a first attempt of developing a INDO-like method specifically parametrized to obtain bond lengths, suitable to be successfully combined with the well known PM3 semiempirical method. [Copyright &y& Elsevier]

Abstract: The two-level factorial design (FD) and principal component analysis (PCA) chemometric techniques were used to investigate the carbon–hydrogen bond lengths dependence on the basis set size and quantum chemistry method, for H–C≡CH, H–C≡CF, H–C≡CCH3, H–C≡CCN, H–C≡CCl and H–C≡CCCH molecular systems. The calculations were performed by using Hartree-Fock (HF), Møller-Plesset 2 (MP2) and Density Functional Theory (DFT) with B3LYP exchange-correlation functional methods. The effects concerning basis set size include the number of valence and polarization functions as well as the cooperative effect between them, at all computational levels. The increase in the number of valence functions decreases the calculated C–H bond lengths by approximately 0.0022Å, while the inclusion of polarization functions at HF and B3LYP levels increases the C–H bond length, in contrast to the behavior obtained at MP2 level. The effect of the inclusion of diffuse functions is non-significant, at all three computational levels. Moreover, the valence–polarization interaction effects are not significant, except at the MP2 calculational level, in which such effects lead to an increase in the calculated C–H bond lengths. When the computational level changes from HF→B3LYP and B3LYP→MP2 the calculated C–H bond length values increase (on average) by +0.0100 and +0.0027Å, respectively. Algebraic models (one for each level of calculation) successfully employed to reproduce the calculated values for H–C≡N bond length, a system not included in the training set. The HF/6-31G(d,p) and HF/6-31++G(d,p) results yield the lowest standard errors (0.0015 and 0.0014Å, respectively) and correspond to the calculated points in closest proximity to the experimental one. [Copyright &y& Elsevier]

Abstract: The second version of the sparkle model for the calculation of lanthanide complexes (SMLC II) as well as ab-initio calculations (HF/STO-3G and HF/3-21G) have been used to calculate the geometries of a series of europium (III) complexes with different coordination numbers (CN=7, 8 and 9), ligating atoms (O and N) and ligands (mono, bi and polydentate). The so-called ligand field parameters, ''s, have been calculated from both SMLC II and ab-initio optimized structures and compared to the ones calculated from crystallographic data. The results show that the SMLC II model represents a significant improvement over the previous version (SMLC) and has given good results when compared to ab-initio methods, which demand a much higher computational effort. Indeed, ab-initio methods take around a hundred times more computing time than SMLC. As such, our results indicate that our sparkle model can be a very useful and a fast tool when applied to the prediction of both ground state geometries and ligand field parameters of europium (III) complexes. [Copyright &y& Elsevier]

Ab-initio molecular orbital calculations were carried out for a series of phosphazine compounds, (NPX2)n, X=H, F, Cl, and Br, n=2 through 6, in order to study the electronic structure of such compounds and explore their use as model compounds for the bulk polymer. Calculations were carried out at the Hartree–Fock level of theory, using all-electron triple-zeta plus polarization basis sets for all atoms. Full geometry optimizations followed by frequency calculations were performed. Although most species adopted hightly symmetric geometries they were often significantly nonplanar. Optimized geometries are general agreement with geometry''s inferred from solution phase IR studies. The geometries of the eight membered and larger rings are very dependent on the identity of X. Ionization energies for this series were calculated using electron propagator theory. Good agreement with experimentally observed values is found. Phosphorus d basis functions appear to be serving as polarization functions rather than being formally involved in bonding. [Copyright &y& Elsevier]

• Theory and experiment that explains the efficiency of the inhibitation of the imidazolium salts. • It clearly shows a significant difference between the alkyl chain versus functionalized group inhibition. • First-principles modelling review that the model of the free molecule is not capable to describe the electron transfer in inhibition process. • Charge transfer of the bromide and chloride imidazolium salts attached to Fe(110) surface unambitious show and explain the trend of the electron transfer for the increasing alkyl chain. This work aims to investigate the corrosion inhibition of the mild steel in the 1 M HCl solution by 1-octyl-3-methylimidazolium hydrogen sulphate 1-butyl-3-methylimidazolium hydrogen sulphate, and 1-octyl-3-methylimidazolium chloride, using electrochemical, weight loss, and surface analysis methods as well as the full quantum-mechanical treatment. Polarization measurements prove that studied compounds are mixed-type inhibitors with a predominantly anodic reaction. The inhibition efficiency obtained from the polarization curves is about 80–92% for all of the 1-octyl-3-methylimidazolium salts with a concentration higher than 0.005 mol/l, while it is much lower for 1-butyl-3-methylimidazolium hydrogen sulphate. The values measured in the weight loss experiments (after seven days) are to some extent higher (reaching up to 98% efficiency). Furthermore, we have shown that the influence of the alkyl chain length on the inhibition efficiency is much larger than that of the anion type. Furthermore, we obtain a realistic model of a single molecule on iron surface Fe(110) by applying the Density Functional Theory calculations. We use the state-of-the-art computational approach, including the meta-GGA strongly-constrained and appropriately normed semilocal density functional to model the electronic structure properties of both free and bounded-to-surface molecules of 1-butyl-, 1-hexyl-, and 1-octyl-3-methylimizadolium bromide, chloride, and hydrogen sulphate. From the calculations we extract, the HOMO/LUMO gap, hardness, electronegativity, and charge transfer of electrons from/to molecules-in-question. It supports the experimental findings and explains the influence of the alkyl chain length and the functional group on the inhibition process. [ABSTRACT FROM AUTHOR]