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We plan to measure several 2S–2P transition frequencies in μ4He+ and μ3He+ by means of laser spectroscopy with an accuracy of 50 ppm. This will lead to a determination of the corresponding nuclear rms charge radii with a relative accuracy of 3 × 10−4, limited by the uncertainty of the nuclear polarization contribution. First, these measurements will help to solve the proton radius puzzle. Second, these very precise nuclear radii are benchmarks for ab initio few-nucleon theories and potentials. Finally when combined with an ongoing measurement of the 1S–2S transition in He+, these measurements will lead to an enhanced bound-state QED test of the 1S Lamb shift in He+.

We have performed a hierarchical ab initio benchmark and DFT performance study of D2Ch•••A− chalcogen bonds (Ch = S, Se; D, A = F, Cl). The ab initio benchmark study is based on a series of ZORA‐relativistic quantum chemical methods [HF, MP2, CCSD, CCSD(T)], and all‐electron relativistically contracted variants of Karlsruhe basis sets (ZORA‐def2‐SVP, ZORA‐def2‐TZVPP, ZORA‐def2‐QZVPP) with and without diffuse functions. The highest‐level ZORA‐CCSD(T)/ma‐ZORA‐def2‐QZVPP counterpoise‐corrected complexation energies (ΔE CPC) are converged within 1.1–3.4 kcal mol−1 and 1.5–3.1 kcal mol−1 with respect to the method and basis set, respectively. Next, we used the ZORA‐CCSD(T)/ma‐ZORA‐def2‐QZVPP (ΔE CPC) as reference data for analyzing the performance of 13 different ZORA‐relativistic DFT approaches in combination with the Slater‐type QZ4P basis set. We find that the three‐best performing functionals are M06‐2X, B3LYP, and M06, with mean absolute errors (MAE) of 4.1, 4.2, and 4.3 kcal mol−1, respectively. The MAE for BLYP‐D3(BJ) and PBE amount to 8.5 and 9.3 kcal mol−1, respectively., Fast and accurate! We have, for the first time, computed chalcogen bonds complexation energies in a procedure involving both a hierarchical series of ab initio methods and a hierarchical series of Gaussian‐type basis sets. Our best reference data, ZORA‐CCSD(T)/BS3+, identify the M06, M06‐2X, and B3LYP functionals as accurate DFT approaches for investigating chalcogen bonds in more complex systems.

The analysis of the photoabsorption spectra of molecules shows that the band maximum is usually redshifted in comparison to the vertical excitation. We conducted a throughout analysis of this shift based on low-dimensional analytical and numerical model systems, showing that its origin is rooted in the frequency change between the ground and the excited states in multidimensional systems. Moreover, we deliver a benchmark of ab initio results for the shift based on a comparison of vertical excitations and band maxima calculated with the nuclear ensemble approach for the 28 organic molecules in the Mülheim molecular dataset. The mean value of the shift calculated over 60 transitions is 0.11 ± 0.08 eV. The mean value of the band width is 0.32 ± 0.14 eV. Graphical abstract. Electronic supplementary material The online version of this article (10.1007/s00894-020-04355-y) contains supplementary material, which is available to authorized users.

The article discusses the atomic structure modelling based on the Ammann–Kramer–Neri tiling of the ternary Bergman quasicrystal in the 3D real space., In this study, the atomic structure of the ternary icosahedral ZnMgTm quasicrystal (QC) is investigated by means of single-crystal X-ray diffraction. The structure is found to be a member of the Bergman QC family, frequently found in Zn–Mg–rare-earth systems. The ab initio structure solution was obtained by the use of the Superflip software. The infinite structure model was founded on the atomic decoration of two golden rhombohedra, with an edge length of 21.7 Å, constituting the Ammann–Kramer–Neri tiling. The refined structure converged well with the experimental diffraction diagram, with the crystallographic R factor equal to 9.8%. The Bergman clusters were found to be bonded by four possible linkages. Only two linkages, b and c, are detected in approximant crystals and are employed to model the icosahedral QCs in the cluster approach known for the CdYb Tsai-type QC. Additional short b and a linkages are found in this study. Short interatomic distances are not generated by those linkages due to the systematic absence of atoms and the formation of split atomic positions. The presence of four linkages allows the structure to be pictured as a complete covering by rhombic triacontahedral clusters and consequently there is no need to define the interstitial part of the structure (i.e. that outside the cluster). The 6D embedding of the solved structure is discussed for the final verification of the model.

Homology-independent methods for ab initio phasing of α-helical transmembrane proteins are explored., α-Helical transmembrane proteins are a ubiquitous and important class of proteins, but present difficulties for crystallographic structure solution. Here, the effectiveness of the AMPLE molecular replacement pipeline in solving α-helical transmembrane-protein structures is assessed using a small library of eight ideal helices, as well as search models derived from ab initio models generated both with and without evolutionary contact information. The ideal helices prove to be surprisingly effective at solving higher resolution structures, but ab initio-derived search models are able to solve structures that could not be solved with the ideal helices. The addition of evolutionary contact information results in a marked improvement in the modelling and makes additional solutions possible.

The conformational flexibility of carbohydrates is challenging within the field of computational chemistry. This flexibility causes the electron density to change, which leads to fluctuating atomic multipole moments. Quantum Chemical Topology (QCT) allows for the partitioning of an “atom in a molecule,” thus localizing electron density to finite atomic domains, which permits the unambiguous evaluation of atomic multipole moments. By selecting an ensemble of physically realistic conformers of a chemical system, one evaluates the various multipole moments at defined points in configuration space. The subsequent implementation of the machine learning method kriging delivers the evaluation of an analytical function, which smoothly interpolates between these points. This allows for the prediction of atomic multipole moments at new points in conformational space, not trained for but within prediction range. In this work, we demonstrate that the carbohydrates erythrose and threose are amenable to the above methodology. We investigate how kriging models respond when the training ensemble incorporating multiple energy minima and their environment in conformational space. Additionally, we evaluate the gains in predictive capacity of our models as the size of the training ensemble increases. We believe this approach to be entirely novel within the field of carbohydrates. For a modest training set size of 600, more than 90% of the external test configurations have an error in the total (predicted) electrostatic energy (relative to ab initio) of maximum 1 kJ mol−1 for open chains and just over 90% an error of maximum 4 kJ mol−1 for rings. © 2015 Wiley Periodicals, Inc.

Combinations of ab initio calculations and modelling against X-ray diffraction data are used to derive the free energy of polymorphic crystals. The results are discussed in relation to the relative stability and phase transitions of the enantiotropically related polymorphs., In this contribution we attempt to answer a general question: can X-ray diffraction data combined with theoretical computations be a source of information about the thermodynamic properties of a given system? Newly collected sets of high-quality multi-temperature single-crystal X-ray diffraction data and complementary periodic DFT calculations of vibrational frequencies and normal mode vectors at the Γ point on the yellow and white polymorphs of di­methyl 3,6-di­chloro-2,5-di­hydroxy­terephthalate are combined using two different approaches, aiming to obtain thermodynamic properties for the two compounds. The first approach uses low-frequency normal modes extracted from multi-temperature X-ray diffraction data (normal coordinate analysis), while the other uses DFT-calculated low-frequency normal mode in the refinement of the same data (normal mode refinement). Thermodynamic data from the literature [Yang et al. (1989), Acta Cryst. B45, 312–323] and new periodic ab initio DFT supercell calculations are used as a reference point. Both approaches tested in this work capture the most essential features of the systems: the polymorphs are enantiotropically related, with the yellow form being the thermodynamically stable system at low temperature, and the white form at higher temperatures. However, the inferred phase transition temperature varies between different approaches. Thanks to the application of unconventional methods of X-ray data refinement and analysis, it was additionally found that, in the case of the yellow polymorph, anharmonicity is an important issue. By discussing contributions from low- and high-frequency modes to the vibrational entropy and enthalpy, the importance of high-frequency modes is highlighted. The analysis shows that larger anisotropic displacement parameters are not always related to the polymorph with the higher vibrational entropy contribution.

A method for measuring the three-phase invariants of crystals in any space group by inspection of convergent-beam electron diffraction patterns recorded under three-beam conditions is presented., Under almost all circumstances, electron diffraction patterns contain information about the phases of structure factors, a consequence of the short wavelength of an electron and its strong Coulombic interaction with matter. However, extracting this information remains a challenge and no generic method exists. In this work, a set of simple analytical expressions is derived for the intensity distribution in convergent-beam electron diffraction (CBED) patterns recorded under three-beam conditions. It is shown that these expressions can be used to identify features in three-beam CBED patterns from which three-phase invariants can be extracted directly, without any iterative refinement processes. The octant, in which the three-phase invariant lies, can be determined simply by inspection of the indexed CBED patterns (i.e. the uncertainty of the phase measurement is ±22.5°). This approach is demonstrated with the experimental measurement of three-phase invariants in two simple test cases: centrosymmetric Si and non-centrosymmetric GaAs. This method may complement existing structure determination methods by providing direct measurements of three-phase invariants to replace ‘guessed’ invariants in ab initio phasing methods and hence provide more stringent constraints to the structure solution.

A methodology is presented to compute diffuse scattering arising from one-phonon excitations in a time-of-flight neutron single-crystal Laue diffraction experiment from density functional theory results. This methodology is illustrated using NaCl as an example., Direct phonon excitation in a neutron time-of-flight single-crystal Laue diffraction experiment has been observed in a single crystal of NaCl. At room temperature both phonon emission and excitation leave characteristic features in the diffuse scattering and these are well reproduced using ab initio phonons from density functional theory (DFT). A measurement at 20 K illustrates the effect of thermal population of the phonons, leaving the features corresponding to phonon excitation and strongly suppressing the phonon annihilation. A recipe is given to compute these effects combining DFT results with the geometry of the neutron experiment.

A novel direct phase-selection method to select optimized phases from the ambiguous phases of a subset of reflections to replace the corresponding initial SAD phases has been developed. With the improved phases, the completeness of built residues of protein molecules is enhanced for efficient structure determination., Optimization of the initial phasing has been a decisive factor in the success of the subsequent electron-density modification, model building and structure determination of biological macromolecules using the single-wavelength anomalous dispersion (SAD) method. Two possible phase solutions (ϕ1 and ϕ2) generated from two symmetric phase triangles in the Harker construction for the SAD method cause the well known phase ambiguity. A novel direct phase-selection method utilizing the θDS list as a criterion to select optimized phases ϕam from ϕ1 or ϕ2 of a subset of reflections with a high percentage of correct phases to replace the corresponding initial SAD phases ϕSAD has been developed. Based on this work, reflections with an angle θDS in the range 35–145° are selected for an optimized improvement, where θDS is the angle between the initial phase ϕSAD and a preliminary density-modification (DM) phase ϕDM NHL. The results show that utilizing the additional direct phase-selection step prior to simple solvent flattening without phase combination using existing DM programs, such as RESOLVE or DM from CCP4, significantly improves the final phases in terms of increased correlation coefficients of electron-density maps and diminished mean phase errors. With the improved phases and density maps from the direct phase-selection method, the completeness of residues of protein molecules built with main chains and side chains is enhanced for efficient structure determination.

A specialized quantum area detector for electron diffraction studies makes it possible to solve the structure of small organic compound nanocrystals in non-cryo conditions by direct methods., Until recently, structure determination by transmission electron microscopy of beam-sensitive three-dimensional nanocrystals required electron diffraction tomography data collection at liquid-nitrogen temperature, in order to reduce radiation damage. Here it is shown that the novel Timepix detector combines a high dynamic range with a very high signal-to-noise ratio and single-electron sensitivity, enabling ab initio phasing of beam-sensitive organic compounds. Low-dose electron diffraction data (∼0.013 e− Å−2 s−1) were collected at room temperature with the rotation method. It was ascertained that the data were of sufficient quality for structure solution using direct methods using software developed for X-ray crystallography (XDS, SHELX) and for electron crystallography (ADT3D/PETS, SIR2014).

Background: The transport through a quantum-scale device may be uniquely characterized by its transmission eigenvalues τn. Recently, highly conductive single-molecule junctions (SMJ) with multiple transport channels (i.e., several τn > 0) have been formed from benzene molecules between Pt electrodes. Transport through these multichannel SMJs is a probe of both the bonding properties at the lead–molecule interface and of the molecular symmetry.Results: We use a many-body theory that properly describes the complementary wave–particle nature of the electron to investigate transport in an ensemble of Pt–benzene–Pt junctions. We utilize an effective-field theory of interacting π-electrons to accurately model the electrostatic influence of the leads, and we develop an ab initio tunneling model to describe the details of the lead–molecule bonding over an ensemble of junction geometries. We also develop a simple decomposition of transmission eigenchannels into molecular resonances based on the isolated resonance approximation, which helps to illustrate the workings of our many-body theory, and facilitates unambiguous interpretation of transmission spectra.Conclusion: We confirm that Pt–benzene–Pt junctions have two dominant transmission channels, with only a small contribution from a third channel with τn << 1. In addition, we demonstrate that the isolated resonance approximation is extremely accurate and determine that transport occurs predominantly via the HOMO orbital in Pt–benzene–Pt junctions. Finally, we show that the transport occurs in a lead–molecule coupling regime where the charge carriers are both particle-like and wave-like simultaneously, requiring a many-body description.

We present a theoretical framework for the computation of anharmonic vibrational frequencies for large systems, with a particular focus on determining adsorbate frequencies from first principles. We give a detailed account of our local implementation of the vibrational self-consistent field approach and its correlation corrections. We show that our approach is both robust, accurate and can be easily deployed on computational grids in order to provide an efficient computational tool. We also present results on the vibrational spectrum of hydrogen fluoride on pyrene, on the thiophene molecule in the gas phase, and on small neutral gold clusters.

International audience; X-ray photoelectron spectroscopy (XPS) is a widely used tool for studying the chemical composition of materials and it is a standard technique in surface science and technology. XPS is particularly useful for characterizing nanostructures such as carbon nanomaterials due to their reduced dimensionality. In order to assign the measured binding energies to specific bonding environments, reference energy values need to be known. Experimental measurements of the core level signals of the elements present in novel materials such as graphene have often been compared to values measured for molecules, or calculated for finite clusters. Here we have calculated core level binding energies for variously functionalized or defected graphene by delta Kohn-Sham total energy differences in the real-space grid-based projector-augmented wave density functional theory code (GPAW). To accurately model extended systems, we applied periodic boundary conditions in large unit cells to avoid computational artifacts. In select cases, we compared the results to all-electron calculations using an ab initio molecular simulations (FHI-aims) code. We calculated the carbon and oxygen 1s core level binding energies for oxygen and hydrogen functionalities such as graphane-like hydrogenation, and epoxide, hydroxide and carboxylic functional groups. In all cases, we considered binding energy contributions arising from carbon atoms up to the third nearest neighbor from the functional group, and plotted C 1s line shapes by using experimentally realistic broadenings. Furthermore, we simulated the simplest atomic defects, namely single and double vacancies and the Stone-Thrower-Wales defect. Finally, we studied modifications of a reactive single vacancy with O and H functionalities, and compared the calculated values to data found in the literature.

A map-likelihood function is described that can yield phase probabilities with very low model bias., The recently developed technique of maximum-likelihood density modification [Terwilliger (2000 ▶), Acta Cryst. D56, 965–972] allows a calculation of phase probabilities based on the likelihood of the electron-density map to be carried out separately from the calculation of any prior phase probabilities. Here, it is shown that phase-probability distributions calculated from the map-likelihood function alone can be highly accurate and that they show minimal bias towards the phases used to initiate the calculation. Map-likelihood phase probabilities depend upon expected characteristics of the electron-density map, such as a defined solvent region and expected electron-density distributions within the solvent region and the region occupied by a macromolecule. In the simplest case, map-likelihood phase-probability distributions are largely based on the flatness of the solvent region. Though map-likelihood phases can be calculated without prior phase information, they are greatly enhanced by high-quality starting phases. This leads to the technique of prime-and-switch phasing for removing model bias. In prime-and-switch phasing, biased phases such as those from a model are used to prime or initiate map-likelihood phasing, then final phases are obtained from map-likelihood phasing alone. Map-likelihood phasing can be applied in cases with solvent content as low as 30%. Potential applications of map-likelihood phasing include unbiased phase calculation from molecular-replacement models, iterative model building, unbiased electron-density maps for cases where 2Fo − Fc or σA-weighted maps would currently be used, structure validation and ab initio phase determination from solvent masks, non-crystallographic symmetry or other knowledge about expected electron density.

Processing of NMR structures for molecular replacement by AMPLE works well., AMPLE is a program developed for clustering and truncating ab initio protein structure predictions into search models for molecular replacement. Here, it is shown that its core cluster-and-truncate methods also work well for processing NMR ensembles into search models. Rosetta remodelling helps to extend success to NMR structures bearing low sequence identity or high structural divergence from the target protein. Potential future routes to improved performance are considered and practical, general guidelines on using AMPLE are provided.

The paper studies the radiation effects on the junction leakage random telegraph signal (JL-RTS). Using arrays of transistors, a statistical study of the phenomenon in MOSFETs source p-n junctions is performed and the impact of the electric field, the type of irradiation, and the source design is investigated. It appears that although JL-RTS originate both from the DDD- and TID-induced defects, the latter is the dominant contribution in MOSFETs sources due to an electric field enhancement. The paper then completes the study with ab initio molecular simulations to investigate the origin of the JL-RTS. The results advocate for the adoption of the structural fluctuation model over the state charge fluctuation model to describe the origin of the phenomenon.

International audience; Hydrogen and its interaction with metal oxide surfaces is of major importance for a wide range of research and applied fields spanning from catalysis, energy storage, microelectronics, to metallurgy. This paper reviews state of the art of first principles calculations on the well-known ruthenium oxide (RuO2) surface in its (110) orientation and its interaction with hydrogen. In addition to it, the paper also fills gaps in knowledge with new calculations and results on the (001) surface. Bulk and surface interactions are thoroughly reviewed. This includes systematic analysis of adsorption sites, local agglomeration propensity of hydrogen, and migration pathways in which literature data and their potential deviations are explained. We notably discuss novel results on propensity for agglomeration of hydrogen within bulk channels [001] oriented in which the proton-like behavior of adsorbed hydrogen hinders further agglomeration in adjacent channels. The paper brings new insights into the migration pathways on the surface and in bulk, both exhibiting preferential diffusion paths along the [001] direction. The paper finally investigates the subsurface region. We show that while the subsurface has more stable sites for adsorption compared to bulk, its accessibility from the surface shows prohibitive activation barriers inhibiting penetration into subsurface and bulk. We further calculate and discuss adsorption and penetration processes on the alternative RuO2 (001) surface.

In a recent paper [Phys. Rev. Lett. 125, 043201 (2020)] (Ref.1) Liao et al. propose a theory of the interferometric photoemission delay based on the concepts of the photoelectron phase and photoelectron effective mass. The present comment discusses the applicability and limitations of the proposed approach based on an ab initio analysis supported by vast literature. Two central assumptions of the paper are questioned, namely that the photoelectron can be characterized by a phase (have a well-defined phase velocity), and that it can always be ascribed an effective mass Theories based on these concepts are concluded to be inapplicable to real solids, which is illustrated by the example of the system addressed in Ref. 1. That the basic assumptions of the theory are never fulfilled in nature discredits the underlying idea of the "time-domain interferometric solid-state energy-momentum-dispersion imaging method" suggested in Ref. 1. Apart from providing a necessary caution to experimentalists, the present comment also gives an insight into the photoelectron wave function and points out problems and pitfalls inherent in modeling real crystals., Comment: 5 pages, 2 figures. This is an extended version of the published paper. Critique of the Authors' Response is added. The list of References is correspondingly updated

Solids receive displacement damages (DD) when interacting with energetic particles, which may happen during the fabrication of semiconductor devices, in harsh environments and in certain analysis techniques. Simulations of the DD generation are usually carried out with classical molecular dynamics (MD), but classical MD does not account for all the effects in DD, as demonstrated by ab initio calculations of model systems in literature. A fully ab initio simulation of the DD generation is impractical due to the large number of atoms involved. In my previous paper [Phys. Chem. Chem. Phys. 22, 19307 (2020)], I developed an adaptive-center (AC) method for adaptive-partitioning (AP) quantum mechanics/molecular mechanics (QM/MM) simulations, allowing the active region centers and the QM/MM partition to be determined on-the-fly for energy-conserving AP-QM/MM methods. I demonstrated that the AC-AP-QM/MM is applicable to the simulation of the DD generation, so that the active regions can be treated with an ab initio method. The AC method was unable to identify the fast-moving recoil ions in the DD generation as active region centers, however, and the accuracy is negatively affected by the rapid change in QM/MM partition of the system. In this paper, I extend the AC method and develop a speed-dependent adaptive-center (SDAC) method for proper AP-QM/MM simulations of DD. The SDAC method is applicable to general problems with speed-dependent active regions, and is compatible with all existing energy-conserving partition-by-distance AP-QM/MM methods. The artifact due to the speed-dependent potential energy surface can be made small by choosing proper criteria. I demonstrate the SDAC method by simulations of the DD generation in bulk Silicon.

Accurate knowledge of line parameters, and particularly line intensities is of primary importance for satellite, ground based and balloon measurements of the ozone concentration in the atmosphere. Self-consistency in absolute band intensities of ozone in various spectral intervals is necessary to avoid discrepancies in the atmospheric ozone retrieval from different windows. Difficulties in precise experimental characterization of absolute line intensities of this unstable molecule are well known leading to many significant deviations in published intensity values and in spectroscopic compilations. Ab initio intensities computed from the dipole moment functions of our previous works (Tyuterev et al. JCP 2017;146:064304; JCP 2019;150:184303) have permitted achieving a consistency between Stark-effect measurements and various databases in 10 and 5 µm in a good agreement with the most accurate recent experiments. In this paper we extend ab initio corrections to available line lists of ozone band intensities in wider IR range up to the bands with four vibrational quanta. About 40% of intensities were corrected in the 0 - 4122 cm−1 range for thirty cold and hot bands of the main ozone 16O3 isotopologue. Most of them, but not all, were obtained using band specific scaling factors ranging from 0.75 to 1.17 making quite significant changes in the absolute values. The full line lists containing corrected line intensities in the spectral intervals considered in the paper are provided in the Supplementary material for this work. The resulting line list is now available on the web site of the “Spectroscopy and Molecular Properties of Ozone” (SM http://smpo.univ-reims.fr ). A large part of this line list including the ab initio correction reported in this work will be used in the future HITRAN20 update.

This paper presents further development of the new semi-classical trajectory-based formalism described in Paper I [Chistikov et al., J. Chem. Phys. 151, 194106 (2019)]. We report the results of simulation and analysis of the low-frequency collision-induced absorption (CIA) in CO2–Ar, including its true dimer component. Our consideration relies on the use of ab initio intermolecular potential energy and induced dipole surfaces for CO2–Ar calculated in an assumption of a rigid CO2 structure using the CCSD(T) method. The theory, the details of which are reported in Paper I [Chistikov et al., J. Chem. Phys. 151, 194106 (2019)], permits taking into account the effect of unbound and quasi-bound classical trajectories on the CIA in the range of a rototranslational band. This theory is largely extended by trajectory-based simulation of the true bound dimer absorption in the present paper. The spectra are obtained from a statistical average over a vast ensemble of classical trajectories restricted by properly chosen domains in the phase space. Rigorous classical theory is developed for two low-order spectral moments interpreted as the Boltzmann-weighted average of the respective dipole functions. These spectral moments were then used to check the accuracy of our trajectory-based spectra, for which both spectral moments can be evaluated independently in terms of specific integrals over the trajectory-based calculated spectral profiles. Good agreement between the spectral moments calculated as integrals over the frequency domain or the phase space largely supports the reliability of our simulated CIA spectra, which conform with the available microwave and far-infrared observations.

In this paper, we employ the lattice Boltzmann method to solve the Boltzmann equation with the Shakhov model for the collision integral in the context of the 3D planar Couette flow. The half-range Gauss-Hermite quadrature is used to account for the wall-induced discontinuity in the distribution function. The lattice Boltzmann simulation results are compared with direct simulation Monte Carlo (DSMC) results for ${}^3{\rm He}$ and ${}^4{\rm He}$ atoms interacting via ab initio potentials, at various values of the rarefaction parameter $\delta$, where the temperature of the plates varies from $1\ {\rm K}$ up to $3000\ {\rm K}$. Good agreement is observed between the results obtained using the Shakhov model and the DSMC data at large values of the rarefaction parameter. The agreement deteriorates as the rarefaction parameter is decreased, however we highlight that the relative errors in the non-diagonal component of the shear stress do not exceed $2.5\%$., Comment: 9 pages, 4 figures; Paper submitted for the proceedings of the 31st International Symposium on Rarefied Gas Dynamics (Glasgow, UK, July 23-27, 2018)

International audience; Aluminium hydroxide (AlOH) is ubiquitous in the interstellar medium. However, there are no reliable data available in the literature that can be used to interpret the observations. Therefore, in this paper, we deal with the rotational rate coefficients of AlOH induced by collision with helium. The potential energy surface of the AlOH-He complex was computed within the coupled cluster ab initio method with single, double and perturbative triple excitation, in conjunction with the augmented-correlation consistent-polarized valence quadruple zeta Gaussian basis set. Using this potential energy surface, we computed rotational cross-sections for total energies ranging up to 1500 cm −1 with the close-coupling approach. By thermally averaging these cross-sections over the kinetic temperature range 5-300 K, we derived the AlOH rate coefficients corresponding to the first 13 rotational levels. Propensity rules have been found in favour of | j| = 1. The data calculated in this paper have been compared with previous results and significant differences are observed. Such a finding might greatly affect the calculation of the AlOH abundance. In addition, this might encourage experimental work to settle the matter.

This article continues our cycle devoted to comprehensive investigation of the diatomic molecule collision process. In this paper, we focus particularly on the in-depth study of the rotational–translational (R–T) energy exchange process and Borgnakke–Larsen (BL) energy exchange model used in the direct simulation Monte Carlo method. The present study, which was performed on several levels of description (molecular, microscopic, and macroscopic), is based mainly on the highly detailed dataset (around 1011 configurations) of binary N2–N2 collisions, obtained via the classical trajectory calculation (CTC) method. This dataset, along with the explicit mathematical representation of the Borgnakke–Larsen model derived in the present paper, allowed us to obtain new results regarding the R–T energy exchange process: (1) we present an ab initio method to derive physically accurate expressions for inelastic collision probability pr in the BL model directly from CTC data; (2) we present a new two-parametric model for pr and compared it to the previously known models, including the recent nonequilibrium-direction-dependent model of Zhang et al. [“Nonequilibrium-direction-dependent rotational energy model for use in continuum and stochastic molecular simulation,” AIAA J. 52(3), 604 (2014)]; (3) it showed that apart from the well-known dependence of the rotational relaxation rate on “direction to equilibrium” (ratio between translational and rotational temperatures), on molecular scale, rotationally over-excited molecule pairs demonstrate almost zero energy transfer to the translational energy mode (even in the case of very significant discrepancies between translational and rotational energies); (4) it was also shown that the Borgnakke–Larsen approach itself may require reassessment since it fails to give a proper description of distribution of post-collision energies. Throughout this paper, we also tried to put together and analyze the existing works studying the rotational relaxation process and estimating the rotational collision number Zrot by performing reviews and assessment of (1) numerical approaches to simulate non-equilibrium problems, (2) models for inelastic collision probabilities pr, (3) approaches to estimate Zrot, and (4) intermolecular potentials used for molecular dynamics and CTC simulations. The corresponding conclusions are given in this paper.

The paper introduces an ”ab initio” theoretical model based on an operative definition of space time, regarded as a combination of the fundamental constants of the nature. The paper shows that significant concepts of quantum mechanics and relativity are straightforward consequence of the proposed definition of space time.Some cosmological implications of the model are also shown.

This paper presents theoretical formalism and some results of the collision-induced absorption (CIA) spectral simulation based on the classical trajectory analysis. Our consideration relies on the use of ab initio potential energy and dipole moment surfaces for two interacting rigid monomers. Rigorous intermolecular Hamiltonian is represented and used in the body-fixed reference frame. The complete set of dynamical equations with Boltzmann-weighted initial conditions is solved to render a large number of classical trajectories. The spectral shape is calculated as an ensemble-averaged Fourier spectrum issued from the time-dependent induced dipole along individual scattering trajectories. Considering a pair of N2 molecules as an example, we have calculated the rototranslational CIA band profiles at T = 78, 89, 109, 129, 149, 179, 228, 300, and 343 K. The classical trajectory-based spectral shape was corrected to satisfy the quantum principle of detailed balance. Good accuracy of our semiclassical approach was demonstrated by comparison with available experimental data as well as with results of the previously published purely quantum simulation by Karman et al. [J. Chem. Phys. 142, 084306 (2015)] in which the same ab initio calculated N2–N2 potential energy and induced dipole moment surfaces were used.This paper presents theoretical formalism and some results of the collision-induced absorption (CIA) spectral simulation based on the classical trajectory analysis. Our consideration relies on the use of ab initio potential energy and dipole moment surfaces for two interacting rigid monomers. Rigorous intermolecular Hamiltonian is represented and used in the body-fixed reference frame. The complete set of dynamical equations with Boltzmann-weighted initial conditions is solved to render a large number of classical trajectories. The spectral shape is calculated as an ensemble-averaged Fourier spectrum issued from the time-dependent induced dipole along individual scattering trajectories. Considering a pair of N2 molecules as an example, we have calculated the rototranslational CIA band profiles at T = 78, 89, 109, 129, 149, 179, 228, 300, and 343 K. The classical trajectory-based spectral shape was corrected to satisfy the quantum principle of detailed balance. Good accuracy of our semiclassical approach w...

In continuation with Paper I [S. R. Reddy et al., J. Chem. Phys. 151, 054303 (2019)], the vibronic structure and dynamics of the 1Σu+ electronic state of C15, C17, C19, and C21 chains in the coupled manifold of 1Σu+–1Πg–1Πu– 1Σg+ electronic states have been investigated in this paper. The model vibronic Hamiltonian developed through extensive ab initio quantum chemistry calculations in Paper I is employed, and first principles nuclear dynamics calculations are carried out to obtain the photoabsorption band of the 1Σu+ electronic state. Both time-independent and time-dependent quantum mechanical calculations are carried out to precisely locate the vibrational levels, assign them with the progression of vibrational modes, and elucidate the impact of both Renner-Teller and pseudo-Renner-Teller couplings on them. The nonradiative decay of the 1Σu+ electronic state is studied, and it is found that the decay rate is comparable with the prediction made for them to be qualified as a carrier of diffuse interstellar bands in the literature. The theoretical results are found to be in good accord with the available experimental results.In continuation with Paper I [S. R. Reddy et al., J. Chem. Phys. 151, 054303 (2019)], the vibronic structure and dynamics of the 1Σu+ electronic state of C15, C17, C19, and C21 chains in the coupled manifold of 1Σu+–1Πg–1Πu– 1Σg+ electronic states have been investigated in this paper. The model vibronic Hamiltonian developed through extensive ab initio quantum chemistry calculations in Paper I is employed, and first principles nuclear dynamics calculations are carried out to obtain the photoabsorption band of the 1Σu+ electronic state. Both time-independent and time-dependent quantum mechanical calculations are carried out to precisely locate the vibrational levels, assign them with the progression of vibrational modes, and elucidate the impact of both Renner-Teller and pseudo-Renner-Teller couplings on them. The nonradiative decay of the 1Σu+ electronic state is studied, and it is found that the decay rate is comparable with the prediction made for them to be qualified as a carrier of diffuse in...

International audience; This paper presents significant new developments concerning the full band, quantum simulation of nanostructured systems and nanoscale electron devices based on an empirical pseudopotential Hamiltonian. We demonstrate that the method is of general applicability, in fact we show results for planar, ultra-thin body FETs and also for three-dimensional, nanowire FETs, we deal with different crystal orientations and account for possible stress/strain conditions in the simulated systems. Some of the simulations reported in this paper have been made computationally viable by the substantial improvements of the numerical efficiency compared to our previous pseudopotentials based methodology. Most of the methods and algorithms discussed in this paper are not specific to an empirical pseudopotential Hamiltonian, on the contrary they can be applied also to different Hamiltonians described with a plane waves basis, which are frequently employed for ab-initio, Density Functional Theory based calculations. The application of the methodologies described in this work may thus be more far reaching than it is illustrated by the case studies explicitly addressed in the present paper.

The aim of this paper is to discuss the possibility of theoretically engineering multifunctional nanomaterials. The calculations were performed for 1D and 2D nanomaterials by using results obtained within the Hubbard model (HM). The main results of the HM are briefly reviewed. The conclusion is that the approach taken in this paper is a distinct improvement over those in the literature.In the present paper results of applications of the HM are directly used in examples of engineering nanomaterials. On the other hand, in the literature calculations were performed by ab initio methods and then fitted to the form of the Hamiltonian of the HM.

This paper presents a systematic and comparative study of the composition and volume dependence of the cohesive properties for a large group of Me-X intermetallic phases (IPs) with Me=Cu,Ni and X=In,Sn, which are of interest in relation with the design of lead-free soldering (LFS) alloys. The work relies upon a database with total-energy versus volume information developed by using projected augmented waves (PAW) calculations. In previous papers by the current authors it was shown that these results account satisfactorily for the direct and indirect experimental data available. In the present work, the database is further expanded to investigate the composition dependence of the volume (V0), and the composition and volume dependence of the bulk modulus (B0) and cohesive energy (Ecoh). On these bases, an analysis is performed of the systematic effects of replacing Cu by Ni in several Me-X phases (Me=Cu,Ni and X=In,Sn) reported as stable and metastable, as well as various hypothetical compounds involved in the thermodynamic modeling of IPs using the Compound-Energy Formalism. Moreover, it is shown that the cohesion-related quantities (B0/V0)- and (Ecoh -/V0) can be correlated with a parameter expressing the number of valence electrons per unit volume. These findings are compared in detail with related relations involving the Miedema empirical electron density at the boundary of the Wigner-Seitz cell. In view of the co-variation of the cohesive properties, Ecoh is selected as a key property and its composition and structure dependence is examined in terms of a theoretical view of the bonding which involves the hybridization of the d-states of Cu or Ni with the s and p-states of In or Sn, for this class of compounds. In particular, a comparative analysis is performed of the DOS of various representative, iso-structural Me-X compounds. Various effects of relevance to understand the consequences of replacing Cu by Ni in LFS alloys are highlighted and explained microscopically for the first time. Fil: Ramos, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina Fil: Gonzalez Lemus, Nasly Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina Fil: Cabeza, Gabriela Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentina Fil: Fernandez Guillermet, Armando Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina

Ab initio calculations have been performed on hexagonal layers of ${M}_{2}{\mathrm{O}}_{3}$ ($M$ being several transition metals of the $5d$ series) sandwiched by a band insulator such as ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ that provides the honeycomb lattice where the $5d$ electrons reside. This corundum-structure-based superlattice is a way to design a honeycomb lattice with transition metal cations avoiding the use of largely polar surfaces. We find that this system supports the presence of Dirac cones at the Fermi level that open up with the introduction of spin-orbit coupling at various fillings of the $5d$ band. The DFT calculations performed in this paper show that the $5{d}^{5}$ situation is always a trivial insulator, whereas the $5{d}^{8}$ filling presents topological insulating configurations which evolve into a trivial state with increasing tensile strain or on-site Coulomb potential $U$. However, LDA + $U$ calculations show a stable antiferromagnetic solution for the $5{d}^{8}$ case at every $U$ value, which would break time reversal symmetry and could affect the topological properties of the system. We also discuss the similarities with the buckled honeycomb lattice obtained using perovskite (111) bilayers previously studied in literature, in particular for the $5{d}^{5}$ and $5{d}^{8}$ configurations. This paper provides some clues on the stability of topological phases using metal oxides in general.

This paper opens a series in which the photochemistry of the two lowest πσ* states of pyrrole and their interaction with each other and with the ground electronic state X are studied using ab initio quantum mechanics. New 24-dimensional potential energy surfaces for the photodissociation of the N–H bond and the formation of the pyrrolyl radical are calculated using the multiconfigurational perturbation theory (CASPT2) for the electronic states X(ππ), 11A2(πσ*), and 11B1(πσ*) and locally diabatized. In this paper, the ab initio calculations are described and the photodissociation in the state 11A2(πσ*) is analyzed. The excitation 11 A2←X is mediated by the coordinate dependent transition dipole moment functions constructed using the Herzberg-Teller expansion. Nuclear dynamics, including 6, 11, and 15 active degrees of freedom, are studied using the multi-configurational time-dependent Hartree method. The focus is on the frequency resolved absorption spectrum as well as on the dissociation time scales and the resonance lifetimes. Calculations are compared with available experimental data. An approximate convolution method is developed and validated, with which absorption spectra can be calculated and assigned in terms of vibrational quantum numbers. The method represents the total absorption spectrum as a convolution of the diffuse spectrum of the detaching H-atom and the Franck-Condon spectrum of the heteroaromatic ring. Convolution calculation requires a minimal quantum chemical input and is a promising tool for studying the πσ* photodissociation in model biochromophores.This paper opens a series in which the photochemistry of the two lowest πσ* states of pyrrole and their interaction with each other and with the ground electronic state X are studied using ab initio quantum mechanics. New 24-dimensional potential energy surfaces for the photodissociation of the N–H bond and the formation of the pyrrolyl radical are calculated using the multiconfigurational perturbation theory (CASPT2) for the electronic states X(ππ), 11A2(πσ*), and 11B1(πσ*) and locally diabatized. In this paper, the ab initio calculations are described and the photodissociation in the state 11A2(πσ*) is analyzed. The excitation 11 A2←X is mediated by the coordinate dependent transition dipole moment functions constructed using the Herzberg-Teller expansion. Nuclear dynamics, including 6, 11, and 15 active degrees of freedom, are studied using the multi-configurational time-dependent Hartree method. The focus is on the frequency resolved absorption spectrum as well as on the dissociation time scales an...

Accurate basis set convergence of first-principles predictions of rotationally resolved spectra at high energy range is a common challenging issue for variational methods. In this paper, a detailed convergence study for the methane spectra is presented both for vibrational and rotational degrees of freedom as well as for intensities. For this purpose, we use our previously reported nine-dimensional potential energy and dipole moment surfaces of the methane molecule [Nikitin et al. Chem Phys Lett 2011;501:179–86; 2013;565:5–11]. Vibration–rotation calculations were carried out using variational normal mode approach with a full account of the Td symmetry. The aim was to obtain accurate theoretical methane line lists for the wavenumber range beyond currently available spectra analyses. The focus of this paper is the complicated icosad range (6280–7900 cm−1) containing 20 bands and 134 sub-bands where over 90% of experimental lines still remain unassigned. We provide variational line lists converged to a “spectroscopic precision” for icosad transitions for T=80 K and T=296 K. The first one contains 70 300 lines and the second one 286 170 lines with the intensity cut-off 10 − 29 cm − 1 / ( molecule cm − 2 ) with Jmax=18. An average error in line positions of theoretical predictions up to J=15 is estimated as 0.2–0.5 cm−1 from the comparisons with currently analyzed bands. Ab initio line strength calculations give the integrated intensity 4.37 × 10 − 20 cm − 1 / ( molecule cm − 2 ) at T=80 K for the sum of all icosad bands. This is to be compared to the integrated intensity 4.36 × 10 − 20 cm − 1 / ( molecule cm − 2 ) of the experimental icosad line list recorded in Grenoble University [Campargue et al., J Mol Spectrosc 2013;291:16–22] using very sensitive laser techniques. The shapes of absorption bands are also in a good qualitative agreement with experimental spectra.

NNumerous experiments in ultra-high vacuum as well as (T ¼ 0K ,p ¼ 0) theoretical studies on surfaces have been performed over the last decades in order to gain a better understanding of the mechanisms, which, for example, underlie the phenomena of catalysis and corrosion. Often the results achieved this way cannot be extrapolated directly to the technologically relevant situation of finite temperature and high pressure. Accordingly, modern surface science has realized that bridging the so-called pressure gap (getting out of the vacuum) is the inevitable way to go. Of similar importance are studies in which the temperature is changed systematically (warming up and cooling down). Both aspects are being taken into account in recent experiments and ab initio calculations. In this paper we stress that there is still much to learn and important questions to be answered concerning the complex atomic and molecular processes which occur at surfaces and actuate catalysis and corrosion, although significant advances in this exciting field have been made over the years. We demonstrate how synergetic effects between theory and experiment are leading to the next step, which is the development of simple concepts and understanding of the different modes of the interaction of chemisorbed species with surfaces. To a large extent this is being made possible by recent developments in theoretical methodology, which allow to extend the ab initio (i.e., starting from the selfconsistent electronic structure) approach to poly-atomic complexes with 10,000 and more atoms, time scales of seconds, and involved statistics (e.g., ab initio molecular dynamics with 10,000 and more trajectories). In this paper we will 1. sketch recent density–functional theory based hybrid methods, which bridge the length and time scales from those of electron orbitals to meso- and macroscopic proportions, and 2. present some key results on properties of surfaces, demonstrating their role in corrosion and heterogeneous catalysis. In particular we discuss • the influence of the ambient gas phase on the surface structure and stoichiometry, • adsorbate phase transitions and thermal desorption, and • the role of atoms’ dynamics and statistics for the surface chemical reactivity.

The experimental discovery of the highest, up to 0 degree Celsius, superconducting transition temperatures T $$_c$$ in the class of so-called hydrides under high pressure is undoubtedly the striking event in modern physics. In this paper, we give a short overview of the some history of the room-temperature conventional superconductivity. A theoretical description of such high T $$_c$$ , as was shown and even predicted in a number of ab initio works, can be unambiguously given in the framework of the electron–phonon mechanism of Cooper pairing. Thus, the basic equation to calculate T $$_c$$ will be the one proposed in 1957 by Bardeen, Cooper, and Schriefer. It is known that in this case the value of T $$_c$$ is directly determined by a number of effective parameters: the Debye frequency, the density of electronic states at the Fermi level, and the electron–phonon interaction constant. Within the framework of the modern development of the density functional theory, all these quantities can be obtained using standard packages for band structure calculations.

In a previous paper (G. Osmann et al. J. Mol. Spectrosc. 197, 262 (1999)) we calculated ab initio the potential-energy surfaces of the ground [Formula: see text]2A" and excited Ã2A' electronic states of the HO2 molecule; these two states correlate with a 2Π state at linearity and participate in a Renner effect interaction. In that paper, we also calculated the electric- and magnetic-dipole moment and transition-moment surfaces, and the spin-orbit coupling constant; we then simulated the à ® [Formula: see text] emission band system including both electric-dipole and magnetic-dipole transitions. We now calculate more points on the surfaces to cover a wider range of bending geometries, and then refine the surfaces by fitting to rovibronic term values for both electronic states simultaneously. In the fitting we include levels having J values up to 9/2 and term values up to about 8000 cm–1. In our calculation of the energy levels we allow for the Renner effect and spin-orbit coupling by using our variational computer program RENNER. A good fitting to the data is obtained and as a result we obtain an accurate representation of these two potential surfaces over an energy range of more than 1 eV. We tabulate the vibronic energies up to 1 eV for both HO2 and DO2. We can explain the origin of a perturbation observed in the F1 spin component levels of the Ã(0, 0, 0) vibronic state for J values around 51/2; this is caused by a spin-orbit interaction satisfying Δ N = ± 1 with the F2 spin component levels of the [Formula: see text](1,1,2) vibronic state. Using the new rovibronic energies and wave functions, with our ab initio electric dipole moment and transition moment surfaces, we calculate Stark coefficients and compare them with experiment for some ground vibronic state levels. PACS Nos.: 31.20D, 31.50, 33.10, 33.20E, 35.20D, 35.20J

The extended x-ray-absorption fine structure (EXAFS) Debye-Waller factor is an essential term appearing in the EXAFS equation that accounts for the molecular structural and thermal disorder of a sample. Single- and multiple-scattering Debye-Waller factors must be known accurately to obtain quantitative agreement between theory and experiment. Since the total number of fitting parameters that can be varied is limited in general, data cannot support fitting of all relevant multiple-scattering Debye-Waller factors. Calculation of the Debye-Waller factors is typically done using the correlated Debye approximation, where a single parameter (Debye temperature) is varied. However, this procedure cannot account in general for Debye-Waller factors in materials with heterogeneous bond strengths, such as biomolecules. As an alternative procedure in this work, we calculate them ab initio directly from the known or hypothetical three-dimensional structure. In this paper we investigate the adequacy of various computational approaches for calculating vibrational structure within small molecules. Detailed EXAFS results will be presented in a subsequent paper. Analytical expressions are derived for multiple scattering Debye-Waller factors, based on the plane wave approximation. Semiempirical Hamiltonians and the ab initio density functional method are used to calculate the normal mode eigenfrequencies and eigenvectors. These data are used to calculate all single- and multiple-scattering Debye-Waller factors up to a four atom cluster. These ab initio Debye-Waller factors are compared to those calculated from experimental infrared and Raman frequencies. As an example comparison with experimental EXAFS data from ${\mathrm{GeCl}}_{4}, {\mathrm{GeH}}_{3}\mathrm{Cl}$ gases are also reported. Good agreement is observed for all cases tested.

In this paper we present an ab initio model-potential embedded-cluster study of the spin doublet excited states of ${\mathrm{V}}^{2+}$-doped ${\mathrm{KMgF}}_{3}$, ${\mathrm{KZnF}}_{3}$, and ${\mathrm{CsCaF}}_{3}$ fluoroperovskites, which includes intracluster electron correlation and quantum-mechanical lattice effects. The discrepancies of the calculated ground-state absorptions to the spin doublets with available experiments are systematic and amount to some $1000 {\mathrm{cm}}^{\ensuremath{-}1},$ leaving room for improvement of the treatment of valence electron correlation. The calculated excited-state absorption spectra originating in ${}^{2}{E}_{g}$ and ${}^{2}{T}_{1g}$ show that the broad ${}^{2}{E}_{g},$${}^{2}{\stackrel{\ensuremath{\rightarrow}}{{T}_{1g}}}^{2}{A}_{1g}$ absorption bands considerably overlap the potential ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{T}_{2g}}}^{4}{A}_{2g}$ laser emission, thus establishing a mechanism for laser loss that had not been considered so far in these low-field materials. The results obtained in these ${\mathrm{V}}^{2+}$-doped fluoroperovskites, together with those in other ${d}^{3}$-doped low-field crystals, point out that the observed excited-state absorption spectra may correspond to either a single absorbing excited state or to the superposition of electronic transitions originating in all the different stable excited states lying below the energies used for pumping. Each of these excited states becomes a channel for absorptions that may result in multiple laser loss mechanisms. The separate study of each of these channels appears to be feasible using ab initio embedded-cluster methods. The conditions for the occurrence of single ${(}^{4}{T}_{2g})$ versus multiple ${(}^{4}{T}_{2g},$${}^{2}{E}_{g},$${}^{2}{T}_{1g})$ excited-state absorption, and, therefore, single versus multiple loss mechanisms, are discussed in this paper in terms of the energy barrier to ${}^{2}{E}_{g},$${}^{2}{\stackrel{\ensuremath{\rightarrow}}{{T}_{1g}}}^{4}{T}_{2g}$ nonradiative decay.

We present an investigation on the calculation of the band structure of polyparaphenylene using the one-particle Hartree-Fock method. In the ab initio case there are many calculations on this level published which are all based on different Hartree-Fock (HF) program packages and thus use different cutoff schemes for the interactions and different basis sets. Therefore the results of these studies are not directly comparable and a thorough study of different approaches based on one and the same reference is highly desirable. In two forthcoming papers we want to present a similar study on the same system using conventional correlation methods and density functional schemes, especially self interaction corrected ones. The PPP or the Hubbard model are well suited for such a purpose, since the correlation methods on top of HF use exactly the same formalisms as in the corresponding ab initio applications, however, the numerical calculations are much cheaper. In this paper we present first of all in details the formalism of the PPP and Hubbard models and its relation to the full ab initio theory. Further, we describe in detail how localized Wannierfunctions can be obtained from the delocalized canonical Bloch orbitals. Localized Orbitals are of utmost importance both for conventional correlation methods and for the Self-Interaction Correction in Density Functional Theory. Finally we derive expressions for transition dipole moments in polymer calculations and an application to the spectrum of polyparaphenylene.

The magnetic (in-plane) interface coupling energy of an Au (100) /FeAu3 Fe /Au(100) multilayer system has been calculated using the well-known fully relativistic spin-polarized Screened KKR method. The coupling energy was expanded in polynomials of cos(&) in or- der to compare it with calculations using the Force Theorem method prescription. The second order term in the polynomial expansion is important when looking at total energy differences. The intention of this paper is to show the numerical feasibility of using the force theorem on particular model systems. In another paper we apply it to existing physical systems. The discovery of the oscillatory behavior of magnetic interface interactions especially in the asymptotic limit has been the subject of several studies iii. In these papers the problem of interface magnetism (I.e., the question of the so-called in-plane magnetic interface coupling energy of magnetic multilayer systems) is dealt with extensively. Suppose such a multilayer system consists of two monolayers of Fe, separated by m layers of a non-magnetic spacer, and is sandwiched semi-infinitely by the spacer material. By considering only in-plane orientations of the magnetization in the two Fe planes, only the relative angle of these two orientations should matter. The magnetic interface coupling energy

We present an investigation on the calculation of the band structure of polyparaphenylene using Moller-Plesset Perturbation Theory of 2nd order (MP2) to take into account correlation effects. The basis for these calculations is the Pariser-Parr-Pople (PPP) Hamiltonian because we also want to extract parameters from these calculations for dynamical simulations. Furthermore we want to compare different approaches to the application of MP2 to infinite system. In the ab initio case there are many calculations on this level published which are all based on different Hartree-Fock (HF) program packages and thus use different cutoff schemes for the interactions and different basis sets. Therefore the results of these studies are not directly comparable and a thorough study of different approaches based on one and the same reference is highly desirable. In a forthcoming paper we want to present a similar study on the same system using density functional schemes, especially self interaction corrected ones. The PPP or the Hubbard model are well suited for such a purpose, since the correlation methods on top of HF, which we outline in some detail in the first paper of this series [W. Forner, Physica Scripta 56, 490 (1997)], use exactly the same formalisms as in the corresponding ab initio applications, however, the numerical calculations are much cheaper. Further, especially for an approach using localized orbitals we also want to discuss Coupled Cluster (CC) models, which are infinite order extensions of MP perturbation theory. We use polyparaphenylene as model system because of its importance in diode technology. We find, that for an accuracy of the correlation corrections in the meV region 5 to 6 neighbors are needed, while more than 10 neighbors are required for μeV accuracies. Further we discuss spectra calculated from our correlated band structure.

The low-lying excited states of carotenoids play a crucial role in many important biophysical processes such as photosynthesis. Most of these excited states are strongly correlated, which makes them both challenging for a qualitative ab initio description and an engaging model system for trying out emerging multireference methods. Among these methods, driven similarity renormalization group (DSRG) and its perturbative version (DSRG-MRPT2) are especially attractive in terms of both accuracy and moderate numerical complexity. In this paper, we applied density matrix renormalization group (DMRG) followed by DSRG-MRPT2 for the calculation of vertical and adiabatic excitation energies into the 2Ag-, 1Bu-, and 1Bu+ electronic states of polyenes containing from 8 to 13 conjugating double bonds acting as a model for natural carotenoids. It was shown that the DSRG flow parameter should be adjusted to ensure both the energy convergence with respect to it and the agreement with the experimental data. With the increased flow parameter, the proposed combination of methods provides a reasonable agreement with the experiment. The deviations of the adiabatic excitation energies are less than 1000 cm-1 for the 2Ag- and less than 3000 cm-1 for the excited states of the Bu symmetry, which in terms of accuracy significantly outperforms the N-electron valence state perturbation theory. At the same time, DSRG-MRPT2 is shown to be robust with respect to variation of quality of the DMRG reference wave function such as the orbital optimization or the number of electronic states in the averaging.

One of the most interesting anomalies in nuclear physics is the island of inversion (IOI), which indicates that the magic numbers disappear. It provides a good platform to understand single-particle motion, many-body correlation, and nucleon-nucleon interaction. In neutron-rich isotopes near N =20 area, many experiments have found that the spectra, electromagnetic transitions, radii, and two-neutron separation energies of these nuclei are abnormal. This region is called the N =20 IOI, because it is characterized by neutron particle-hole excitations related to deformation from the 1s0d shell into the 1p0f shell across the N =20 shell gap. Recent experiments show that the ground states of 29Ne and 28F have negative parities, indicating that these two nuclei are within the N =20 IOI. This provides new opportunities and challenges for theoretical models in this area. With the standard shell model, the N =20 IOI has been proved by many works to have a strong cross-shell effect between 1s0d and 1p0f shells. They proposed that the tensor force and three-nucleon force should have an important influence on the microscopic description of neutron-rich nuclei in this area, especially in Ne and Mg isotopes. However, the N =20 IOI is still rarely studied in ab initio calculations. Recently, an extension of the ab initio valence-space in-medium similarity renormalization group method was presented to study the physics of neutron-rich nuclei by Miyagi et al. In the present paper, based on chiral force including nucleon-nucleon and three-nucleon force, we have performed ab initio calculations for the low-lying states of 28F and 29Ne, focusing on the relative excitation energies of the positive- and negative-parity states in these nuclei. In order to study the effect of three-nucleon force on the N =20 IOI, we use nucleon-nucleon force at N3LO with or without three-nucleon force at N2LO in our calculations. Using the open-shell many-body perturbation theory, the cross shell sd-pf realistic effective Hamiltonian, including single-particle energies and effective two-body interactions, is constructed self-consistently without introducing parameters. The constructed effective Hamiltonian is diagonalized with the shell model method. In shell model calculation, we use a truncation with up to five nucleons (including protons and neutrons) occupying the pf orbit. The low-lying states of 28F and 29Ne are calculated with NN and NN+3N interactions. The results show that three-nucleon force is important in the descriptions of low-lying states of 28F and 29Ne, especially in 29Ne while the first negative state turned to be ground state due to the three-nucleon force. Our calculations give that three-nucleon force gives large effects for the relative position between the 0d3/2 and 1p3/2 single-particle orbitals, causing the two orbitals to reverse. Furthermore, the configurations of low-lying states of 28F and 29Ne are calculated within our ab initio calculations with NN+3N interaction. The results give that the lowest positive and negative parity states in 28F and 29Ne are dominated by 2 ℏ ω and 1 ℏ ω components, respectively. We have also calculated the configurations of the ground state in neutron-rich even-even Ne isotopes, and the results indicate that the three-nucleon force could enhance the cross-shell excitations in the nuclei in the vicinity of IOI, which is essential for the exotic properties of these nuclei. Furthermore, we have also performed the phenomenological shell model calculations with SDPF-MU effective interactions, and the results are similar to our ab initio calculations including three-nucleon force.

In this theoretical study, we investigate the electronic potential energy curves, spectroscopic parameters, vibrational energy levels and transition dipole moments for the diatomic dications BeRb2+, BeCs2+, and SrRb2+. We consider an ab initio approach based on the use of non-empirical pseudopotentials and parameterized l dependent polarization potentials. Results show that 1-22Σ+ for BeRb2+, 1-52Σ+ for BeCs2+, and 1-32Σ+ for SrRb2+ are repulsive. While the 32Σ+ for BeRb2+, 42Σ+ for BeCs2+, and 42Σ+ for SrRb2+ are metastable states. These states can accommodate some vibrational energy levels. Interesting avoided crossings between some 2Σ+ states are localized and examined. Until now, no experimental and theoretical studies have been made for each system. Consequently, we discuss our results by comparing with some data on similar systems. Besides, the transition dipole moments of the ground state to a few excited states are computed and presented. The information associated with the electronic structures, spectroscopic parameters as well as the transition properties provided in this paper, is anticipated to serve as guidelines for further experimental and theoretical research on diatomic dications considered in this work.

Recently reported quasiparticle interference imaging in underdoped Ca(Fe{1-x}Co{x})_2As{2} shows pronounced C{2} asymmetry that is interpreted as an indication of an electronic nematic phase with a unidirectional electron band, dispersive predominantly along the $b$-axis of this orthorhombic material. On the other hand, even more recent transport measurements on untwinned samples show near isotropy of the resistivity in the $ab$ plane, with slightly larger conductivity along a (and not b). We show that in fact both sets of data are consistent with the calculated ab initio Fermi surfaces, which has a decisively broken C_{4}, and yet similar Fermi velocity in both directions. This reconciles completely the apparent contradiction between the conclusions of the STM and the transport experiments., Comment: A version of this work was posted (arXiv:1005.1761) as a comment on a Science paper entitled "Nematic Electronic Structure in the Parent State of the Iron-Based Superconductor Ca(Fe1-xCox)2As2". The comment was rejected by Science on account of it being posted on the ArXiv. This is a version published in PRB as a research paper

The energy gained by either of the two helium atoms in a helium dimer through simultaneous ionization and excitation can be efficiently transferred to the other helium atom, which then ionizes. The respective relaxation process called interatomic Coulombic decay (ICD) is the subject of the present paper. Specifically, we are interested in ICD of the lowest of the ionized excited states, namely, the He{sup +}(n=2)He states, for which we calculated the relevant potential-energy curves and the interatomic decay widths. The full-configuration interaction method was used to obtain the potential-energy curves. The decay widths were computed by utilizing the Fano ansatz, Green's-function methods, and the Stieltjes imaging technique. The behavior of the decay widths with the interatomic distance is examined and is elucidated, whereby special emphasis is given to the asymptotically large interatomic separations. Our calculations show that the electronic ICD processes dominate over the radiative decay mechanisms over a wide range of interatomic distances. The ICD in the helium dimer has recently been measured by Havermeier et al. [Phys. Rev. Lett. 104, 133401 (2010)]. The impact of nuclear dynamics on the ICD process is extremely important and is discussed by Sisourat et al. [Nat. Phys. 6, 508 (2010)] based onmore » the ab initio data computed in the present paper.« less

This paper is the second part of a series devoted to the ab initio calculation of vibrational properties, like transition energies, dipole moment matrix elements and infrared intensities. The method of calculation has been detailed in the first paper, where test calculations on diatomic systems were also analyzed. The present paper applies the method to a simple polyatomic system, the water molecule in its ground electronic state. The purely polyatomic features of the method are discussed, as the determination of the potential energy and dipole moment surfaces and the description of vibrational mode couplings. The results concern vibrational energies of levels in the range 0 ≤ v1 + v2 + v3 ≤ 3 and vibrational transition moments and intensities of cold and hot bands. Many methodological tests and comparisons to the experimental and theoretical literature are reported, showing that theoretical values of transition energies and dipole moments converge to the experimental ones; at the highest level of approximation (TZ + 2P/SD-CI; vibrational SCF/CI and FCI) the precision obtained is sufficient to provide useful complementary spectroscopical data. This convergence is however not achieved for diagonal dipole moment matrix elements, which are shown to be very sensitive to the mechanical and electrical anharmonicities.