Short-range Behavior Research Articles

Short-range order structural response of CdSe nanocrystals under 120 MeV swift heavy ions irradiation: A pair distribution function analysis

Swift heavy ion (SHI) irradiation deposits large amount of energy in the target material which thereby influences the structural features of the sample. In this work, the structural response of CdSe material has been studied under high energetic 120 MeV SHI irradiation. The long-range structural modifications of CdSe under SHI have been analyzed using Rietveld study. On the other hand, the short-range behavior of SHI irradiated CdSe has been studied using Pair distribution function (PDF), which can be interpreted as a distance map between two atoms in terms of a PDF peak. The small-box structural refinement of the samples has been performed using the PDFgui package for the study of modifications in the atomic arrangement after the SHI irradiation. In addition to this, structural characteristics such as unit cell parameters as determined from long-range (Rietveld) refinement are compared to that obtained from short-range (small-box) refinement. Moreover, atomic displacement factor for CdSe also has been determined to study the atomic disorder in the nanocrystal under the influence SHI irradiation. Finally, impact of SHI induced stress generated on the CdSe sample and its influence also has been studied based on the width of the PDF peak.

Probing the Long- and Short-Range Structural Chemistry in the C-Type Bixbyite Oxides Th0.40Nd0.48Ce0.12O1.76, Th0.47Nd0.43Ce0.10O1.785, and Th0.45Nd0.37Ce0.18O1.815 via Synchrotron X-ray Diffraction and Absorption Spectroscopy.

The long- and short-range structural chemistry of the C-type bixbyite compounds Th0.40Nd0.48Ce0.12O1.76, Th0.47Nd0.43Ce0.10O1.785, and Th0.45Nd0.37Ce0.18O1.815 is systematically examined using synchrotron X-ray powder diffraction (S-PXRD), high-energy resolution fluorescence detection X-ray absorption near edge (HERFD-XANES), and extended X-ray absorption fine structure spectroscopy (EXAFS) measurements supported by electronic structure calculations. S-PXRD measurements revealed that the title compounds all form classical C-type bixbyite structures in space group Ia3̅ that have disordered cationic crystallographic sites with further observation of characteristic superlattice reflections corresponding to oxygen vacancies. Despite the occurrence of oxygen vacancies, HERFD-XANES measurements on the Ce L3-edge revealed that Ce incorporates as Ce4+ into the structures but involves local distortion that resembles cluster behavior and loss of nearest-neighbors. In comparison, HERFD-XANES measurements on the Nd L3-edge supported by electronic structure calculations reveal that Nd3+ adopts a local coordination environment similar to the long-range C-type structure while providing charge balancing for the formation of oxygen defects. Th L3-edge EXAFS analysis reveals shorter average Th-O distances in the title compounds in comparison to pristine ThO2 in addition to shorter Th-O and Th-Ce distances compared to Th-Th or Ce-Ce in the corresponding F-type binary oxides (ThO2 and CeO2). These distances are further found to decrease with the increased Nd content of the structures despite simultaneous observation of the overall lattice structure progressively expanding. Linear combination calculations of the M-O bond lengths are used to help explain these observations, where the role of oxygen defects, via Nd3+ incorporation, induces local bond contraction and enhanced Th cation valence, leading to the observed increased lattice expansion with progressive Nd3+ incorporation. Overall, the investigation points to the significance of dissimilar cations exhibiting variable short-range chemical behavior and how it can affect the long-range structural chemistry of complex oxides.

Exploring the role of mean-field potentials and short-range wave function behavior in the adiabatic connection.

In this article, we explore the construction of Hamiltonians with long-range interactions and their corrections using the short-range behavior of the wave function. A key aspect of our investigation is the examination of the one-particle potential, kept constant in our previous work, and the effects of its optimization on the adiabatic connection. Our methodology involves the use of a parameter-dependent potential dependent on a single parameter to facilitate practical computations. We analyze the energy errors and densities in a two-electron system (harmonium) under various conditions, employing different confinement potentials and interaction parameters. The study reveals that while the mean-field potential improves the expectation value of the physical Hamiltonian, it does not necessarily improve the energy of the system within the bounds of chemical accuracy. We also delve into the impact of density variations in adiabatic connections, challenging the common assumption that a mean field improves results. Our findings indicate that as long as energy errors remain within chemical accuracy, the mean field does not significantly outperform a bare potential. This observation is attributed to the effectiveness of corrections based on the short-range behavior of the wave function, a universal characteristic that diminishes the distinction between using a mean field or not.

Effect of Alloying Elements on the Short-Range Orders and Atomic Diffusion Behavior of Liquid Al-9Si Cast Alloys.

To investigate the influence of alloying elements (Zn, Mg, and Cu) on the structural and dynamical properties of liquid Al-9Si alloy, we conducted ab initio molecular dynamics (AIMD) simulations. Our results indicate that the structure of Al-Si-M ternary alloys is determined with a combination of atomic radii and mixing enthalpy, while the dynamic properties are primarily influenced by electronic structure of the alloying elements. Specifically, the addition of Cu promotes the formation of Al-Cu short-range order (SRO), while Zn has a higher propensity for Zn-Zn SRO. The Al-Cu SRO in liquid alloy may serve as the precursor for the Al2Cu reinforcing phase in Al-Si-Cu alloys. Upon the addition of Mg, a greater number of relatively stable perfect and distorted icosahedral structures, as well as hcp and bcc ordered structures with lower energies, are observed. Additionally, the presence of Mg leads to a reduction in the atomic diffusion rates of Al and Si, while Cu and Zn exhibit complex diffusion behavior influenced by the presence of Si atoms.

Modeling high-entropy transition metal alloys with alchemical compression

Alloys composed of several elements in roughly equimolar composition, often referred to as high-entropy alloys, have long been of interest for their thermodynamics and peculiar mechanical properties, and more recently for their potential application in catalysis. They are a considerable challenge to traditional atomistic modeling, and also to data-driven potentials that for the most part have memory footprint, computational effort, and data requirements which scale poorly with the number of elements included. We apply a recently proposed scheme to compress chemical information in a lower-dimensional space, which reduces dramatically the cost of the model with negligible loss of accuracy, to build a potential that can describe 25 $d$-block transition metals. The model shows semiquantitative accuracy for prototypical alloys and is remarkably stable when extrapolating to structures outside its training set. We use this framework to study element segregation in a computational experiment that simulates an equimolar alloy of all 25 elements, mimicking the seminal experiments in the groups of Yeh and Cantor, and use our observations on the short-range order relations between the elements to define a data-driven set of Hume-Rothery rules that can serve as guidance for alloy design. We conclude with a study of three prototypical alloys, CoCrFeMnNi, CoCrFeMoNi, and IrPdPtRhRu, determining their stability and the short-range order behavior of their constituents.

Collision-induced three-body polarizability of helium.

We present the first-principles determination of the three-body polarizability and the third dielectric virial coefficient of helium. Coupled-cluster and full configuration interaction methods were used to perform electronic structure calculations. The mean absolute relative uncertainty of the trace of the polarizability tensor, resulting from the incompleteness of the orbital basis set, was found to be 4.7%. Additional uncertainty due to the approximate treatment of triple and the neglect of higher excitations was estimated at 5.7%. An analytic function was developed to describe the short-range behavior of the polarizability and its asymptotics in all fragmentation channels. We calculated the third dielectric virial coefficient and its uncertainty using the classical and semiclassical Feynman-Hibbs approaches. The results of our calculations were compared with experimental data and with recent Path-Integral Monte Carlo (PIMC) calculations [Garberoglio et al., J. Chem. Phys. 155, 234103 (2021)] employing the so-called superposition approximation of the three-body polarizability. For temperatures above 200K, we observed a significant discrepancy between the classical results obtained using superposition approximation and the ab initio computed polarizability. For temperatures from 10K up to 200K, the differences between PIMC and semiclassical calculations are several times smaller than the uncertainties of our results. Except at low temperatures, our results agree very well with the available experimental data but have much smaller uncertainties. The data reported in this work eliminate the main accuracy bottleneck in the optical pressure standard [Gaiser et al., Ann. Phys. 534, 2200336 (2022)] and facilitate further progress in the field of quantum metrology.

Triatomic Photoassociation in an Ultracold Atom–Molecule Collision

Ultracold collisions of neutral atoms and molecules have been of great interest since experimental advances enabled the cooling and trapping of such species. This study develops a simplified theoretical treatment of a low-energy collision between an alkali atom and a diatomic molecule accompanied by absorption of a photon from an external electromagnetic field. The long-range interaction between the two species is treated, including the atomic spin-orbit interaction. The long-range potential energy curves for the triatomic complex are calculated in realistic detail, while effects of the short-range behavior are mimicked by applying different boundary conditions at the van der Waals length. For neutral colliding species, the leading interaction term is the dipole-dipole interaction. In the case of nonpolar dimers like Cs2, the second leading term is the quadrupole-quadrupole interaction. However, there is also a strong dipole-quadrupole interaction for dimers with a large permanent dipole moment such as NaCs, making the dipole-quadrupole interaction the second leading term for an atom colliding with a polar dimer. Our applications of the simplified treatment show a higher density of trimer states for a polar dimer compared to the case of a nonpolar dimer like Cs2. This is a consequence of the strong quadrupole-dipole coupling between the atom and the dimer dipole moment.

Neutrinoless double beta decay via light neutralinos in R-parity violating supersymmetry

We perform a study of neutrinoless double beta (0νββ) decay mediated by the lightest neutralino of arbitrary mass in the minimal supersymmetric Standard Model (MSSM) under the presence of R-parity violating trilinear interactions. In this scenario, the exchange of the lightest neutralino can result in 0νββ decay of either long-range or short-range behaviour, depending on the neutralino mass. Using nuclear matrix elements calculated in the interacting boson model, we use an interpolation between the long- and short-range behaviours with an approximate formula. The non-observation of 0νββ decay is then used to place constraints on the supersymmetry parameter space, compatible with constraints from collider experiments. We compare these constraints to bounds from pion decays, CKM unitarity and big bang nucleosynthesis.

On the short-range behavior of neutrino forces beyond the Standard Model: from 1/r5 to 1/r4, 1/r2, and 1/r

The exchange of a pair of neutrinos between two objects, seperated by a distance r, leads to a long-range effective potential proportional to 1/r5, assuming massless neutrinos and four-fermion contact interactions. In this paper, we investigate how this known form of neutrino-mediated potentials might be altered if the distance r is sufficiently short, corresponding to a sufficiently large momentum transfer which could invalidate the contact interactions. We consider two possible scenarios to open up the contact interactions by introducing a t-channel or an s-channel mediator. We derive a general formula that is valid to describe the potential in all regimes as long as the external particles remain non-relativistic. In both scenarios, the potential decreases as 1/r5 in the long-range limit as expected. In the short-range limit, the t-channel potential exhibits the Coulomb-like behavior (i.e. proportional to 1/r), while the s-channel potential exhibits 1/r4 and 1/r2 behaviors.

Three-body potential energy surface for para-hydrogen.

We present a 3D isotropic ab initio three-body (para-H2)3 interaction potential energy surface (PES). The electronic structure calculations are carried out at the correlated coupled-cluster theory level, with single, double, and perturbative triple excitations. The calculations use an augmented correlation-consistent triple zeta basis set and a supplementary midbond function. We construct the PES using the reproducing-kernel Hilbert space toolkit [O. T. Unke and M. Meuwly, J. Chem. Inf. Model. 57, 1923 (2017)] with phenomenological and empirical adjustments to account for short-range and long-range behaviors. The (para-H2)3 interaction energies deviate drastically from the Axilrod-Teller-Muto (ATM) potential at short intermolecular separations. We find that the configuration of three para-H2 molecules at the corners of an equilateral triangle is responsible for the majority of the (para-H2)3 interaction energy contribution in a hexagonal-close-packed lattice. In cases where two para-H2 molecules are close to one another while the third is far away, the (para-H2)3 interaction PES takes the form of a modified version of the ATM potential. We expect the combination of this PES together with a first-principles para-H2-para-H2 adiabatic hindered rotor potential to outperform a widely used effective pair potential for condensed many-body systems of para-H2.

Geometric wavefront dislocations of RKKY interaction in graphene

Magnetically doped graphene has great potential for applications in spintronics, in which local magnetic moments are coupled by the Rudermann-Kittel-Kasuya-Yosida (RKKY) interaction. RKKY interaction in graphene has attracted intensive interest. However, previous studies only show the features of the RKKY interaction dictated by energy dispersion, leaving the effect of the geometric nature of electronic structures unexplored. Here, we focus on the short-range oscillation behaviors of RKKY interaction contributed by intervalley scattering. Due to the unique geometric nature of electronic structures, two wavefront dislocations emerge in the RKKY interaction corresponding to winding number 1 of graphene. We further demonstrate the robustness of wavefront dislocations against the doping, trigonal warping, and gap opening of energy bands. This study reveals a unique feature for the RKKY interaction and implies the importance of the geometric nature of electronic structures for magnetism.

On the role of structured initial conditions in the Schelling model

Despite the ubiquity of hierarchical structures found in every complex system, random initial conditions are preestablished in several Sociophysics models. In this work, we show the remarkable differences between both assumptions applied to the case of the renowned segregation Schelling model for minorities.It is found that, under a simple quasi non parametric Schelling model with structured initial conditions, the segregation phenomenon shows a local or short-range behavior, developing at the borders of the minority–majority agent pattern and leaving the macroscopic agent structure mostly unaltered. Besides, it is found that the highest uncontrollability regime pointed out in a previous article, perfectly corresponds to where system segregation blows up.

The Intermolecular NOE Depends on Isotope Selection: Short Range vs Long Range Behavior.

The nuclear Overhauser effect (NOE) is a powerful tool in molecular structure elucidation, combining the subtle chemical shift of NMR and three-dimensional information independent of chemical connectivity. Its usage for intermolecular studies, however, is fundamentally limited by an unspecific long-ranged interaction behavior. This joint experimental and computational work shows that proper selection of interacting isotopes can overcome these limitations: Isotopes with strongly differing gyromagnetic ratios give rise to short-ranged intermolecular NOEs. In this light, existing NOE experiments need to be re-evaluated and future ones can be designed accordingly. Thus, a new chapter on intermolecular structure elucidation is opened.

Maximum Energy Growth Rate in Dilute Quantum Gases.

In this Letter we study how fast the energy density of a quantum gas can increase in time, when the interatomic interaction characterized by the s-wave scattering length a_{s} is increased from zero with arbitrary time dependence. We show that, at short time, the energy density can at most increase as sqrt[t], which can be achieved when the time dependence of a_{s} is also proportional to sqrt[t], and especially, a universal maximum energy growth rate can be reached when a_{s} varies as 2sqrt[ℏt/(πm)]. If a_{s} varies faster or slower than sqrt[t], it is, respectively, proximate to the quench process and the adiabatic process, and both result in a slower energy growth rate. These results are obtained by analyzing the short time dynamics of the short-range behavior of the many-body wave function characterized by the contact, and are also confirmed by numerically solving an example of interacting bosons with time-dependent Bogoliubov theory. These results can also be verified experimentally in ultracold atomic gases.

Neutron interferometry and tests of short-range modifications of gravity

We consider tests of short-distance modifications of gravity based on neutron interferometry in the scenario of large extra dimensions. Avoiding the non-computability problem in the calculation of the internal gravitational potential of extended sources, typical of models with zero-width brane, we determine the neutron optical potential associated with the higher-dimension gravitational interaction between the incident neutron and a material medium in the context of thick brane theories. Proceeding this way, we identify the physical quantity of the extra dimension model that the neutron interferometry is capable of constraining. We also consider interferometric experiments in which the phase shifter is an electric field, as in the test of the Aharanov-Casher effect. We argue that this experiment, with this non-baryonic source, can be viewed as a test of the short-range behavior of Post-Newtonian parameters that measure the capacity of the pressure and the internal energy for producing gravity.

IForest: An informed resource search strategy in mobile P2P networks

With the increasing applications of the mobile P2P networks, how to improve the resource search performance has been an important research focus. Peers’ features of strong mobility, short wireless transmission range and malicious behavior make the efficient and effective resource search more difficult in mobile P2P networks. This paper proposes an informed resource search strategy, iForest, in mobile P2P networks. To tackle the issue of peer’s mobility, we present a quantifying method of a neighbor peer’s stability; to deal with the problem of a peer’s malicious behavior, we employ the idea of peer’s credibility; to improve the resource search efficiency, we use the concept of peer’s resource accessibility. These guidance factors are derived and calculated based on the findings that each peer’s movements often repeat on a day-to-day basis and each peer has its own interests in mobile P2P networks. The simulation results showed that the iForest strategy could both improve the resource search success rate and reduce the communication complexity.

Interaction between surface waves on wire lines.

This paper investigates coupling between electromagnetic surface waves on parallel wires. Finite-element method (FEM)-based and analytic models are developed for single- and double-wire Sommerfeld and Goubau lines. Models are validated via measurements for Goubau lines and a comparison between the analytic and the FEM-based computations for coupled Sommerfeld- and Goubau-type lines is carried out. The measurements and calculations show remarkable agreement. The FEM-based and analytic models match remarkably well too. The results exhibit new favourable effects for surface waves propagation over multiple conductors. The short-range behaviour of the coupled wires and, consequently, the existence of an optimum separation of coupled wires is one of the most significant findings of this paper. We comment on the relevance of our results, particularly in relation to applications of high bandwidth demands and cross-coupling effects.

Nonapproximated third-order exchange induction energy in symmetry-adapted perturbation theory.

The exchange terms in symmetry-adapted perturbation theory (SAPT) are normally calculated within the so-called S2 or single exchange approximation, which approximates the all-electron antisymmetrizer by interchanges of at most one electron pair between the interacting molecules. This approximation is typically very accurate at the van der Waals minimum separation and at larger intermolecular distances but begins to deteriorate at short range. Nonapproximated expressions for the second-order SAPT exchange corrections have been derived some time ago by Schäffer and Jansen [Mol. Phys. 111, 2570 (2013)]. In this work, we extend Schäffer and Jansen's formalism to derive and implement a nonapproximated expression for the third-order exchange-induction correction. Numerical tests on several representative noncovalent databases show that the S2 approximation underestimates the exchange-induction contributions in both second and third orders. This underestimation is very similar in relative terms, but the larger absolute values of the third-order exchange-induction effects, and their near complete cancellation with the corresponding induction energies, make the third-order errors more severe. In the worst-case scenario of interactions involving ions, the breakdown of the S2 approximation can result in a qualitatively wrong, attractive character of SAPT total energies at short range {as first observed by Lao and Herbert [J. Phys. Chem. A 116, 3042 (2012)]}. As expected, the inclusion of the full third-order exchange-induction energy in place of its S2-approximated counterpart restores the correct, repulsive short-range behavior of the SAPT potential energy curves computed through the third order.

Adiabatic connection in spin-current density functional theory

The spin-current density functional theory (SCDFT), when formulated in a basis of Pauli spinors, provides a proper theoretical framework for the study of materials in an arbitrarily oriented external magnetic field and/or upon inclusion of spin-dependent relativistic effects, such as spin-orbit coupling. The SCDFT is formulated in terms of the particle-number density $n$, the Cartesian components of the magnetization ${m}_{x},$ ${m}_{y},$ and ${m}_{z}$, the orbital-current density $\mathbit{j}$, and the three spin-current densities ${\mathbit{J}}^{x},$ ${\mathbit{J}}^{y},$ and ${\mathbit{J}}^{z}$, where each of these density variables depends on specific blocks of the density matrix. Exchange-correlation (xc) functionals within the SCDFT should therefore depend on all of these eight fundamental density variables: ${F}_{xc}[n,{m}_{x},{m}_{y},{m}_{z},\mathbit{j},{\mathbit{J}}^{x},{\mathbit{J}}^{y},{\mathbit{J}}^{z}]$, which makes their parametrization a formidable task. Here, we formulate the adiabatic connection of the SCDFT for a treatment of exact Fock exchange in the theory. We show how the inclusion of a fraction of Fock exchange in standard functionals of the (spin) DFT (either in their collinear or noncollinear versions: ${F}_{xc}[n],$ ${F}_{xc}[n,{m}_{z}]$ and ${F}_{xc}[n,{m}_{x},{m}_{y},{m}_{z}]$) allows for the two-electron potential to depend on all those blocks of the density matrix that correspond to the eight density variables of the SCDFT, in a sensible and yet practical way. In particular, in the local-density and generalized-gradient approximations of the SCDFT, the treatment of the current densities solely from the Fock exchange term is formally justified by the short-range behavior of the exchange hole. We discuss that the adiabatic coupling strength parameter modulates the two-electron coupling of the orbital- and spin-current densities with the particle-number density and magnetization. Formal considerations are complemented by numerical tests on a periodic model system in the presence of spin-orbit coupling and in the absence of an external magnetic field.

Transferable MP2-Based Machine Learning for Accurate Coupled-Cluster Energies.

Machine learning methods have enabled the low-cost evaluation of molecular properties such as energy at an unprecedented scale. While many of such applications have focused on molecular input based on geometry, few studies consider representations based on the underlying electronic structure. Directing the attention to the electronic structure offers a unique challenge that allows for a more detailed representation of the underlying physics and how they affect molecular properties. The target of this work is to efficiently encode a lower-cost correlated wave function derived from MP2 to predict a higher-cost coupled-cluster singles-and-doubles (CCSD) wave function based on correlation-pair energies and the contributing electron promotions (excitations) and integrals. The new molecular representation explores the short-range behavior of electron correlation and utilizes distinct models that differentiate between two-electron promotions from the same molecular orbital or from two different orbitals. We present a re-engineered set of input features that provide an intuitive description of the orbital properties involved in electron correlation. The overall models are found to be highly transferable and size extensive, necessitating very few training instances to approach the chemical accuracy of a broad spectrum of organic molecules. The efficiency and transferability of the novel representation are demonstrated on a series of linear hydrocarbons, the potential energy surface of the water dimer, and on the GDB-9 database. For the GDB-9 database, we found that data from only 140 randomly selected molecules are adequate to achieve chemical accuracy for more than 133 000 organic molecules.