Search

Spectroscopic properties and potential energy curves of alkali metal (M = Na and K) – rare gas (Rg = He, Ne, Ar, Kr, Xe and Rn) van der Waals molecules in their ground states have been studied in detail using spin-restricted open-shell coupled cluster with single and double excitations and perturbative contribution of connected triple excitations (RCCSD(T)) methods. The core-valence correlation (CV) effect was found to be crucial for M-RG molecules containing heavy rare gas atoms. The electronic energies were corrected for the basis set superposition error (BSSE) using the counterpoise method. Energies were extrapolated to the complete basis set (CBS) limit using a two-point scheme. The permanent electric dipole moments, static electric dipole polarizabilities and long-range dispersion coefficients were also calculated. The computed spectroscopic constants, vibrational levels and rotational constants were reported for M-RG and good agreement with the available experimental and theoretical values were found. [ABSTRACT FROM AUTHOR]

We develop a method to calculate the electron flow between an arbitrary atomic monolayer sheet and an arbitrary tube by expressing the corresponding sheet-tube tunneling matrix elements with those between sheets. We use this method to calculate the spin current from a monolayer silicene sheet with sublattice-staggered current-induced spin polarization to a silicene tube. The calculated sheet-to-tube spin current exhibits an oscillation as a function of the tube circumferential length because the Fermi points in the tube cross the Fermi circle in the sheet. Furthermore, the spin current with spin in the out-of-plane direction, which is absent in the sheet-sheet junction (including twisted sheets) with C 3 rotational symmetry, appears in an oscillating form in the tube-sheet junction due to the broken C 3 rotational symmetry. This is an example of the symmetry manipulation which realizes switching a particular component of the spin current. • The formula for electron flow between an atomic monolayer and a tube is developed. • Spin current from silicene sheet to tube is calculated using the formula. • Oscillations in the spin current occur due to the tube's momentum quantization. • Symmetry manipulation switches a particular component of the spin current. [ABSTRACT FROM AUTHOR]

High‐dimensional potential energy surface (PES) for van der Waals systems with spectroscopic accuracy, is of great importance for quantum dynamics and an extremely challenge job. CO‐N2 is a typical van der Waals system and its high‐precision PES may help elucidate weak interaction mechanisms. Taking CO‐N2 potential energies calculated by CCSD(T)‐F12b/aug‐cc‐pVQZ as the benchmark, we establish an accurate, robust, and efficient machine learning model by using only four molecular structure descriptors based on 7966 benchmark potential energies. The highest accuracy is obtained by a stacking ensemble DNN (SeDNN). Its evaluation parameters MAE, RMSE, and R2 reach 0.096, 0.163, 0.9999 cm−1, respectively, and the spectroscopic accuracy for vibration spectrum is achieved with predicted PES, which shows SeDNN superior goodness‐of‐fit and prediction performance. An elaborated PES with the reported global minimum has been predicted with the model, which perfectly reproduces CCSD(T) potential energies and the analytical MLR PES [PCCP, 2018, 20, 2036]. The critical points (global minimum, TSI, TSII, and their barriers), potential curve, and entire PES profile are remarkably consistent with CCSD(T) calculations. To further improve the usability of constructing PESs in practice, the size of the training set (energy points) for the model is reduced to 50%, 30%, and 20% of the database, respectively. The results show that even training with the smallest training set (1593 points), the PES only differs 2.555 cm−1 with the analytic MLR PES. Therefore, the proposed SeDNN is promisingly an alternative efficient tool to construct subtle PES for van der Waals systems. [ABSTRACT FROM AUTHOR]

van der Waals materials provide a versatile toolbox for the emergence of new quantum phenomena and fabrication of functional heterostructures. Among them, the trihalide VI 3 stands out for its unique magnetic and structural landscape. Here we investigate the spin and orbital magnetic degrees of freedom in the layered ferromagnet VI 3 by means of temperature-dependent X-ray absorption spectroscopy and X-ray magnetic circular and linear dichroism. We detect localized electronic states and reduced magnetic dimensionality, due to electronic correlations. We furthermore provide experimental evidence of (a) an unquenched orbital magnetic moment (up to 0.66(7) μ B /V atom) in the ferromagnetic state and (b) an instability of the orbital moment in the proximity of the spin reorientation transition. Our results support a coherent picture where electronic correlations give rise to a strong magnetic anisotropy and a large orbital moment and establish VI 3 as a prime candidate for the study of orbital quantum effects.

Highlights • There are marked differences in dynamics of modified linear and cyclic carbohydrates. • A variation in the distribution of τ α between linear and cyclic compounds is observed. • The evolutions of the T g and m versus M w in both groups of materials are different. • The shape of the α -process in saccharides of the same topology doesn't change with M w. Abstract In this paper, the molecular dynamics and thermal properties of representative acetylated linear and cyclic oligosaccharides: acTRE, acRAF, acSTA, ac-α-CD, ac-β-CD, ac-γ-CD, have been investigated by using broadband dielectric spectroscopy and differential scanning calorimetry. We found that there are marked differences in the dynamics of the structural and secondary relaxation processes in both groups of materials. Just to mention a variation in the distribution of the structural relaxation times as well as different evolutions of the glass transition temperature (T g) and fragility (m) versus molecular weight (M w), which seem to be affected by the shape of the molecule, strain in the carbohydrate ring and mobility of side acetyl moieties. [ABSTRACT FROM AUTHOR]

We present a device concept for magnetoresistance (MR) effect in which two Van der Waals (vdW) spin valves are used as the left and right ferromagnetic (FM) leads connected by a bilayer graphene as the channel material of the central scattering region. Unlike conventional current-perpendicular-to-plane magnetic tunnel junction consisting of two FM thin films with a thin insulating barrier sandwiched between them, the FM leads in our proposed current-in-plane MR device are vdW spin valves. This is important because the application of an out-of-plane electric field allows control of the direction and magnitude of the magnetization in vdW spin valves. Moreover, we show that the oscillatory behavior is found in the MR and conductance as the height (depth) of the barrier (well) of the scattering region with the p ( n )-doping increase, or the width of the scattering region increase. Remarkably, when the potential barrier is present, the oscillation magnitude of MR is considerable and can be changed from positive to negative value, whereas for the potential well, the oscillation amplitude is relatively small and is always positive. Therefore, we hope that this device configuration with electrically tunable large MR can open up new possibilities for future lower power magneto-electric devices since no current-induced magnetization switching.

An ab initio investigation has been performed for the ground and several excited states of Ca + He and CaHe systems. The potential energy curves, spectroscopic constants, vibrational levels energies and electric dipole moments have been calculated and analyzed. The ab initio method uses the pseudo-potentials technique, Core Polarization Potentials (CPP) and Full Configuration Interaction (FCI). The number of active electrons of Ca + He and CaHe are reduced to one and two active electrons, respectively. The examination of these numerous results shows interesting structures and behaviors resulting from a collision-induced process that involves calcium and helium atoms. An excellent agreement is found with the available results which confirms the reliability of our calculation. [ABSTRACT FROM AUTHOR]

Molecular beam experiments (lithium atom plus hydrogen fluoride) by both Becker and co-workers (C.H. Becker, P. Casavecchia, P.W. Tiedemann, J.J.Valentini, and Y.T. Lee, J. Chem. Phys.73, 2833 (1980)) and Loesch and Stienkemeier (H.J. Loesch and F. Stienkemeier, J. Chem. Phys.98, 9570 (1993)) deduced a van der Waals complex of type Li···HF. In this research, molecular electronic structure theory [aug-cc-pCVQZ CCSD(T)] has been used to predict a well depth of 0.86 kcal mol−1relative to separated Li + HF. However, the barrier from this vdW well to the more strongly bound (∼6.2 kcal mol−1) HFLi complex lies 0.43 kcal mol−1belowseparated Li + HF. [ABSTRACT FROM AUTHOR]

The potential energy curves and spectroscopic constants of the ground and many excited states of the FrAr van der Waals system have been determined using a one-electron pseudopotential approach. The Fr+ core and the electron-Ar interactions are replaced by effective potentials. The Fr+Ar core-core interaction is incorporated using the accurate CCSD(T) potential of Hickling et al. ( Phys. Chem. Chem. Phys. 2004, 6, 4233). This approach reduces the number of active electrons of the FrAr van der Waals system to only one valence electron, which permits the use of very large basis sets for the Fr and Ar atoms. Using this technique, the potential energy curves of the ground and many excited states are calculated at the self consistent field (SCF) level. In addition, the spin-orbit interaction is also considered using the semiempirical scheme for the states dissociating into Fr (7p) and Fr (8p). The FrAr system is not studied previously and its potential interactions, spectroscopic constants and dipole functions are presented here for the first time. Furthermore, we have predicted the X2Σ+- A2Π1/2, X2Σ+- AΠ3/2, X2Σ+- B2Σ1/2+, X2Σ+-32Π1/2, X2Σ+-32Π3/2, and X2Σ+-52Σ1/2+ absorption spectra. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals magnetic semiconductors display emergent chemical and physical properties and hold promise for novel optical, electronic and magnetic "few-layers" functionalities. Transition-metal iodides such as CrI 3 and VI 3 are relevant for future electronic and spintronic applications; however, detailed experimental information on their ground state electronic properties is lacking often due to their challenging chemical environment. By combining X-ray electron spectroscopies and first-principles calculations, we report a complete determination of CrI 3 and VI 3 electronic ground states. We show that the transition metal-induced orbital filling drives the stabilization of distinct electronic phases: a wide bandgap in CrI 3 and a Mott insulating state in VI 3 . Comparison of surface-sensitive (angular-resolved photoemission spectroscopy) and bulk-sensitive (X-ray absorption spectroscopy) measurements in VI 3 reveals a surface-only V 2+ oxidation state, suggesting that ground state electronic properties are strongly influenced by dimensionality effects. Our results have direct implications in band engineering and layer-dependent properties of two-dimensional systems.

The rotationless, vibrational states of two weakly bound triatomic species are calculated using a variational expansion over multicentred Gaussian functions (the DGF method described in the main text) and corrections are introduced by using the three-body potentials vis à vis the sum-of-potentials approximation. The effects are seen to be very small and isotopic substitution is further introduced to evaluate changes on the vibrational structures of both systems, aiming at possibly detecting Efimov behaviour in such special trimers: no Efimov states are found with the available potentials and when the two-body potential strengths are varied. An additional study on the effects of isotopic substitutions for H atoms is also presented. [ABSTRACT FROM AUTHOR]

Abstract: We extend our recently published short-range gradient-corrected density functional from the closed-shell to the open-shell case, combine it with long-range coupled-cluster methods (CCSD, CCSD(T)), and apply it to the weakly bound alkali-metal rare-gas dimers AmRg (Am=Li–Cs; Rg=Ne–Xe). The results are shown to be superior, with medium-size basis sets, to pure DFT and pure coupled-cluster calculations. [Copyright &y& Elsevier]

We demonstrate theoretically the possibility of spinodal de-wetting in heterostructures made of light-atom liquids (hydrogen, helium, and nitrogen) deposited on suspended graphene. Extending our theory of film growth on two-dimensional (2D) materials to include analysis of surface instabilities via the hydrodynamic Cahn-Hilliard-type equation, we characterize in detail the spatial and temporal scales of the resulting spinodal de-wetting patterns. Both linear stability analysis and direct numerical simulations of the surface hydrodynamics show micron-sized (generally material dependent) patterns of 'dry' regions. The physical reason for the development of such instabilities on graphene can be traced back to the inherently weak van der Waals interactions between atomically thin materials and atoms in the liquid. Thus 2D materials could represent a new theoretical and technological platform for studies of spinodal de-wetting., (© 2022 IOP Publishing Ltd.)

High-dimensional potential energy surface (PES) for van der Waals systems with spectroscopic accuracy, is of great importance for quantum dynamics and an extremely challenge job. CO-N 2 is a typical van der Waals system and its high-precision PES may help elucidate weak interaction mechanisms. Taking CO-N 2 potential energies calculated by CCSD(T)-F12b/aug-cc-pVQZ as the benchmark, we establish an accurate, robust, and efficient machine learning model by using only four molecular structure descriptors based on 7966 benchmark potential energies. The highest accuracy is obtained by a stacking ensemble DNN (SeDNN). Its evaluation parameters MAE, RMSE, and R 2 reach 0.096, 0.163, 0.9999 cm -1 , respectively, and the spectroscopic accuracy for vibration spectrum is achieved with predicted PES, which shows SeDNN superior goodness-of-fit and prediction performance. An elaborated PES with the reported global minimum has been predicted with the model, which perfectly reproduces CCSD(T) potential energies and the analytical MLR PES [PCCP, 2018, 20, 2036]. The critical points (global minimum, TSI, TSII, and their barriers), potential curve, and entire PES profile are remarkably consistent with CCSD(T) calculations. To further improve the usability of constructing PESs in practice, the size of the training set (energy points) for the model is reduced to 50%, 30%, and 20% of the database, respectively. The results show that even training with the smallest training set (1593 points), the PES only differs 2.555 cm -1 with the analytic MLR PES. Therefore, the proposed SeDNN is promisingly an alternative efficient tool to construct subtle PES for van der Waals systems., (© 2021 Wiley Periodicals LLC.)

[Display omitted] • Isotropies and anisotropies of the H 2 -F 2 van der Waals interactions. • ab initio calculations of the eight selected leading configurations. • Representation of leading configurations in terms of Pirani functions. • Spherical harmonics expansion of the potential energy surface. • Calculation of the second virial coefficients as a function of temperature. The analytical representation of intermolecular interactions combines dynamical and structural viewpoints, utilizing a spherical harmonics expansion based on high-level ab initio generated stereodirected configurations. The potential energy surface of the H 2 ⋯ F 2 system is built by a number of selected cuts (leading configurations); the best fits of their dependence on the intermolecular distance are phenomenologically represented by the Pirani et al. potential functions. The quality of the representation is validated by accurate calculations of a property of the gaseous mixture, the second virial coefficient, in a range of temperatures. Convergence is demonstrated by comparison with elaborate semiempirical approaches. [ABSTRACT FROM AUTHOR]