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In this work, we study the cavity size effect on the eigen-energies of one-dimensional Schroedinger equation for certain diatomic molecules governed by Morse potential interaction confined in the cavity. To avoid the dissociation of the molecule, we have realised the confinement by introducing two barriers on both sides of the minimum of the potential: the first, at the left, is fixed at $ x_{L}=-ln2/\alpha $ x L = − l n 2 / α and the second at the right i.e. $ x_{R}=\lambda _{i}=-ln2/\alpha +\gamma _{i}r_{e} $ x R = λ i = − l n 2 / α + γ i r e where $ \gamma _{i} $ γ i is a parameter that allows us to vary the size of the cavity. It turns out that the confinement gives rise to additional energy levels and that the number of these levels increases with the size of the cavity (i.e. by increasing $ \gamma _{i} $ γ i or by decreasing the confinement). We used Green's function approach and reported our results on $ {\rm H}_{2},{\rm HCl} $ H 2 , HCl and $ {\rm LiH} $ LiH molecules. [ABSTRACT FROM AUTHOR]

The dynamics of matter waves in a trapped Bose–Einstein condensate including three-body losses, atomic feeding and quantum fluctuations is investigated theoretically and numerically. We use a generalized variational approach which allows us to express the influence of the condensate parameters on the time evolution of the amplitude, width and chirp, through a set of differential equations. Emphasis is placed on the strength of quantum fluctuations which deeply modifies the wave dynamics. Direct numerical simulations confirm the analytical results. Importantly, we extend numerical experiments and show that the localized modes split into two or three trains of solitary waves which can be controlled by the quantum fluctuations. [ABSTRACT FROM AUTHOR]

CaYAl3O7 presents a challenge for computer modelling techniques because of its site-occupancy disorder related to the Ca/Y shared site. Supercells were built to reproduce experimental results which have the best agreement and lowest lattice energy. The potential parameters were obtained by empirical fitting, and reproduced the structure to within 1.09%. Results obtained by supercell and the Mott-Littleton methods were compared. Both methods predict oxygen Frenkel defects are likely to be formed. [ABSTRACT FROM AUTHOR]

CaYAl3O7 presents a challenge for computer modelling techniques because of its site-occupancy disorder related to the Ca/Y shared site. Supercells were built to reproduce experimental results which have the best agreement and lowest lattice energy. The potential parameters were obtained by empirical fitting, and reproduced the structure to within 1.09%. Results obtained by supercell and the Mott-Littleton methods were compared. Both methods predict oxygen Frenkel defects are likely to be formed. [ABSTRACT FROM AUTHOR]

The static exchange model (SEM) and the modified static exchange model (MSEM) recently introduced by Ray in Pramana - J. Phys. 83, 907 (2014) are used to study the elastic collision between two hydrogen-like atoms when both are in ground states by considering the system as a four-body Coulomb system in the centre of mass frame, in which all the Coulomb interaction terms in direct and exchange channels are treated exactly. The SEM includes the non-adiabatic short-range effect due to electron exchange. The MSEM added in it, the long-range effect due to induced dynamic dipole polarizabilities between the atoms e.g., the van der Waals interaction. Applying the SEM code in different H-like two-atomic systems, a reduced mass ( μ) dependence on the scattering length is observed. Again, applying the MSEM code on H(1s)-H(1s) elastic scattering and varying the minimum values of interatomic distance R , the dependence of scattering length on the effective interatomic potential consistent with the existing physics is observed. Both these basic findings in low and cold energy atomic collision physics are quite useful and are being reported for the first time. [ABSTRACT FROM AUTHOR]

Metastable Fe-Cu alloys are of considerable scientific interest, and an efficient interatomic potential is crucial for reliable atomistic simulations. Interatomic potentials developed for pure Fe and pure Cu are difficult to mix for the Fe-Cu alloys since the analytic function form of pure Fe is not of the same type of pure Cu potential. Additionally, elemental potentials taken from alloy descriptions may not work well for the pure species. This is particularly true if the elements were fit for compounds instead of being optimised separately. In this article, we present compatible analytic function forms that work for pure species and are easily mixed with two adjustable parameters for their alloys. We tested the proposed potentials to make sure that the performance is adequate for pure species as well as their alloys. The predicted values were in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

On the light of a previous work and its recommendations by Matobaet al.[J. Phys. B41, 145205 (2008)], this paper proposes to look at the mobility of ground and metastable-excited states of C+ions moving into a helium buffer gas. The calculations, based on the three-temperature theory for solving the Boltzmann kinetic equation, are accomplished with quantum-mechanical transport cross sections at the low temperatures 4.3 and 77 K. The obtained mobility results are contrasted with the available theoretical data and experimental measurements, which show acceptable agreements. [ABSTRACT FROM PUBLISHER]

A modified static-exchange model is developed to study the collision of an atom with another atom. It includes the effect of long-range dipole-dipole van der Waals interaction between two atoms in addition to the exact effect of short-range force due to Coulomb exchange between two system electrons. Both these interactions dominate at colder energies. The system is treated as four-centre problem in the centre-of-mass frame. The present ab-initio model is useful to study the two-atomic collisions at low energies, as well as cold energies. The new code is applied to study the scattering of positronium (Ps) by hydrogen (H), both in their ground states. [ABSTRACT FROM AUTHOR]

We are reporting the scaling behaviour of the bound state energies associated with the Hellmann potential, with different strength parameters, using the Laguerre basis. We show the existence of a crossover phenomenon for the energy spectrum; the scaling laws for bound states as we approach the continuum are calculated. Close to the bound–resonance phase transition region, state energies and wavefunctions for the Hellmann potential, with different strength parameters, have been studied. [ABSTRACT FROM AUTHOR]

In this work, the effects on the lattice dynamical properties, such as phonon dispersion, second order elastic constants, and bulk modulus of the temperature and pressure in random NiPd binary alloy system was investigated using molecular dynamics simulation. The interactions between atoms were modelled using the Sutton-Chen-type embedded atom method based on many-body interactions. The phonon frequencies were calculated from the dynamical matrix for [100], [110], and [111] high symmetry directions of the Brillouin zone. The obtained results show that the external pressure cause an increment in phonon frequencies, and the increase of temperature causes a decrease in longitudinal and transverse acoustic phonon frequencies because of thermal expansion. [ABSTRACT FROM AUTHOR]

Close to the bound-resonance crossover region, state energies for the Manning–Rosen (MR) potential have been calculated. New data, for both bound and resonance state energies have been reported nearby the crossover region, using the J-matrix approach, for LiH and CO molecules. Furthermore, the average oscillator strength, multipole moments and transition probabilities for certain states have been reported for future comparison. [ABSTRACT FROM AUTHOR]

We present analytical solutions of the Schrödinger equation for the trigonometric Pöschl-Teller molecular potential by using a proper approximation to the centrifugal term within the framework of the asymptotic iteration method. We obtain analytic forms for the energy eigenvalues and the bound state eigenfunction solutions are obtained in terms of the generalized hypergeometric functions. Energy eigenvalues for a few diatomic molecules are calculated for arbitrary quantum numbers n and ℓ with various values of parameter α. We also studied special case ℓ = 0 and found that the results are in good agreement with findings of other methods for short-range potential. [ABSTRACT FROM AUTHOR]

The ReaxFF interatomic potential, used for organic materials, involves more than 600 adjustable parameters, the best-fit values of which must be determined for different materials. A new method of determining the set of best-fit parameters for specific molecules containing carbon, hydrogen, nitrogen and oxygen is presented, based on a parameter reduction technique followed by genetic algorithm (GA) minimization. This work has two novel features. The first is the use of a parameter reduction technique to determine which subset of parameters plays a significant role for the species of interest; this is necessary to reduce the optimization space to manageable levels. The second is the application of the GA technique to a complex potential (ReaxFF) with a very large number of adjustable parameters, which implies a large parameter space for optimization. In this work, GA has been used to optimize the parameter set to determine best-fit parameters that can reproduce molecular properties to within a given accuracy. As a test problem, the use of the algorithm has been demonstrated for nitromethane and its decomposition products. [ABSTRACT FROM AUTHOR]

New parameters of nearest-neighbor EAM (1N-EAM), n-th neighbor EAM (NN-EAM), and the second-moment approximation to the tight-binding (TB-SMA) potentials are obtained by fitting experimental data at different temperatures. In comparison with the available many-body potentials, our results suggest that the 1N-EAM potential with the new parameters is the best description of atomic interactions in studying the thermal expansion of noble metals. For mechanical properties, it is suggested that the elastic constants should be calculated in the experimental zero-stress states for all three potentials. Furthermore, for NNEAM and TB-SMA potentials, the calculated results approach the experimental data as the range of the atomic interaction increases from the first-neighbor to the sixth-neighbor distance. [ABSTRACT FROM AUTHOR]

The parameters of interatomic interaction in diamonds of 12C and 13C isotopes are determined. The parameters are determined by two methods, namely, from the elastic modulus (potential no. 1) and from the sublimation energy at T = 0 K (potential no. 2). Based on these parameters, the Debye model is used to calculate the isobaric temperature dependences of the thermoelastic properties for isotopically different diamonds, namely, the coefficient of thermal expansion (CTE), the density, the elastic modulus B T, and the specific heat capacity. It is demonstrated that the best agreement with the experimentally obtained dependences of the foregoing parameters is obtained when potential no. 1 is used in calculations. The values of CTE, density, and heat capacity increase in the case of transition from 12C diamond to 13C diamond. It is demonstrated that the inequality B T(12C) < B T(13C) is valid at T = 0 K, which is associated with the reduction of interatomic spacing in the case of transition from 12C diamond to 13C diamond. However, as the temperature increases, the volumetric isotopic effect in diamond decreases. It is found that the B T( T) dependences for 12C and 13C diamonds intersect at a temperature below the Debye temperature. Therefore, at high temperatures, the elastic modulus for light-isotope diamond comes to exceed that for heavy-isotope diamond, B T(12C) > B T(13C). Experimental results are given which confirm this effect. The variation of the properties of isotopically different diamonds with increasing pressure is discussed. [ABSTRACT FROM AUTHOR]

The parameters of interatomic interaction in crystals of isotopes of lithium 7Li and 6Li are determined for both the minimal and maximal values of Debye temperature. These parameters and the Debye crystal model are used to calculate the temperature dependences of the coefficient of thermal expansion (CTE) and of the lattice parameter from 0 K to the melting temperature of these crystals. It is demonstrated that the temperature dependences of CTE for crystals of 7Li and 6Li intersect at temperature T x = 230–300 K so that, under conditions of melting, the CTE for crystal of light isotope is higher than that for crystal of heavy isotope of lithium. [ABSTRACT FROM AUTHOR]

A set of relationships between the Morse and Varshni potential functions for describing covalent bondstretching energy has been developed by imposing equal force constant and equal energy integral. In view of the extensive adoption of Morse function in molecular force fields, this paper suggests two sets of parameter conversions from Varshni to Morse. The parameter conversion based on equal force constant is applicable for small change in bond length, while the parameter conversion based on equal energy integral is more applicable for significant bond-stretching. Plotted results reveal that the Varshni potential function is more suitable for describing hard bonds rather than soft bonds. [ABSTRACT FROM AUTHOR]

The simplified model of pair potential of interatomic interaction is used for considering the nature of qualitative difference in the pattern of correlation between the critical temperature and critical volume for monatomic metallic and dielectric liquids. The groups of alkali metals and inert gases are considered. [ABSTRACT FROM AUTHOR]

In this paper, using the Exact Quantization Rule, we present approximate analytical solutions of the radial Schrödinger equation with non-zero l values for the Hulthén potential in the frame of an approximation to the centrifugal potential for any l states. The energy levels of all bound states can be easily calculated from the Exact Quantization Rule. Specifically, the normalized analytical wave functions are also obtained. Some energy eigenvalues are numerically calculated and compared with those obtained by other methods such as asymptotic iteration, supersymmetry, numerical integration methods, and the schroedinger Mathematica package. [ABSTRACT FROM AUTHOR]

A theoretical study of vortex-lattice formation in atomic Bose-Einstein condensates confined by a rotating elliptical trap is presented. For the conventional case of purely s-wave interatomic interactions, this is done through a consideration of both hydrodynamic equations and time-dependent simulations of the Gross-Pitaevskii equation. We discriminate three distinct, experimentally testable regimes of instability: ripple, interbranch, and catastrophic. Additionally, we generalize the classical hydrodynamical approach to include long-range dipolar interactions, showing how the static solutions and their stability in the rotating frame are significantly altered. This enables us to examine the routes towards unstable dynamics, which, in analogy to conventional condensates, may lead to vortex-lattice formation. [ABSTRACT FROM AUTHOR]

The potential of long-range interaction between two dissimilar atoms, one of which is excited, drops as 1/ R 2 with the distance for the Casimir-Polder limit of large distances in comparison with the wave-length of atom transitions (E.A. Power and T. Thirunamachandran, Phys. Rev. A 51, 3660 (1995)). It is shown that such a dependence, obtained with the help of perturbation technique, results in a divergence for the interaction potential between an excited atom and a medium of dilute gas. We develop a nonperturbative method based upon quantum Green’s functions (Yu. Sherkunov, Phys. Rev. A 72, 052703 (2005)) to calculate the interaction potential for an excited atom and a ground-state atom embedded in a dielectric medium, taking into account the absorption of photons in the dielectric medium. The exponential suppression of the interaction between the atoms is demonstrated. The force acting on an excited atom near the interface of dilute gas medium is calculated. The result is no more divergent. The force between gas media in Casimir-Polder regime is calculated as well. [ABSTRACT FROM AUTHOR]

Features that have been discovered recently in the transmission of multiply charged channeled ions with various energies through crystals are interpreted on the basis of kinetic theory. It is shown that the transition from “cooling” to “heating” of an isotropic beam of heavy multiply charged ions depends not only on the ion energy, but on the depth of their penetration into the crystal as well. The automodel character of the angular distribution of multiply charged ions transmitted through a thin oriented crystal is predicted. Agreement with experiment is achieved on the assumption that, at high ion energies, the probability of electron capture by a channeled ion decreases in comparison to the probability of electron loss. We also discuss the possibility of experimentally measuring the partial angular distributions and the dependence of the electron capture and loss probabilities on the transverse momentum and impact parameter for ions interacting with atomic chains. [ABSTRACT FROM AUTHOR]

A radiative interaction in a collective two-atom system forms subradiant and superradiant states when the distance between neighboring atoms is less than half a wavelength of resonant radiation. We calculate the G (2) function depending on the atomic separation and detection angle and show that it oscillates with a time delay between two successively emitted photons. These oscillations are the signature of coherent effects due to the periodic emission and absorption of photons by each atom. [ABSTRACT FROM AUTHOR]

A kinetic theory of passage of multiply charged heavy ions through crystals is developed that allows for diffusion in the transverse momentum space and ion-crystal charge exchange. The theory provides an adequate explanation for the observed angular distributions of heavy ions passing through oriented crystals, makes it possible to calculate the partial angular distributions of different charge states, and treats the discovered effects of “cooling” and “heating” of channeled ion beams in physical terms. The angular and spatial distribution of channeled ions with different energies is calculated. Whether a channeled beam of multiply charged heavy ions will be cooled or heated is related to the dependence of the electron capture and loss probabilities on the impact parameter when the ions interact with atomic chains. This interaction governs the run of the angular and spatial distribution of the channeled ion charge. [ABSTRACT FROM AUTHOR]

For a quantitative theoretical description of phase separation and coarsening reliable data of stiffness constants and for the so-called higher gradient coefficients (HGCs) are required. For that reason pair potentials of the Lennard–Jones type were used in the past to provide a theoretical tool for their quantitative determination. Following up on this work these quantities are now calculated by means of the embedded-atom method (EAM), a recently developed approach to describe interatomic potentials in metals. This is done, first, to achieve a better agreement between predicted and experimentally observed stiffness data as well as to avoid artifacts, such as the Cauchy paradox, and, second, to increase the trustworthiness of the HGCs for which experimental data are rarely available. After an introduction to the fundamentals of EAM it is outlined how it can be used for calculating stiffness constants and HGCs. In particular, Johnson’s modification of EAM for nearest-neighbor interactions is applied and explicit numerical results for a case study alloy, Ag–Cu, which has a simple face-centered-cubic crystal structure, are presented. In this particular case it is comparatively easy to obtain all the required analysis data from the literature and to compare the predictions of mechanical data with experimental values. [ABSTRACT FROM AUTHOR]

We have performed a two-photon photoassociation experiment in an atomic Bose-Einstein condensate of 87Rb with the spin degree of freedom, which is created by an all-optical method with CO2 lasers. The spinor character of the created molecules has been revealed by the photoassociation spectrum with a new structure. The hyperfine structure of the created molecules near the dissociation limit is identified by observations of the Zeeman and AC-Stark effects of the molecules. We have also demonstrated the spin-selective creation of molecules. This result would open the new possibility of research on novel molecular spinor BEC. [ABSTRACT FROM AUTHOR]

Abstract: We have systematically tested two entirely independent, empirical potentials (EAM and MD/MC CEM) which are widely used in classical molecular dynamics simulations by simulating Xe ion impacts to the Au(111) surface in the broad energy range between 0.1 and 200keV. Special attention is paid to ensure that the simulated results are statistically significant. We have also compared simulations to experimental results on sputtering yields and crater production. Both potentials bring about qualitatively similar outcomes of the collision cascades, giving good confidence that the previous conclusions drawn from simulations on heat spike behaviour in dense metals are valid. However, the quantitative results are different. The MD/MC CEM potential has clearly better agreement with experimental sputtering yield data than the EAM potential, although neither potential agrees with experiments in the full energy range studied. [Copyright &y& Elsevier]

Abstract: The stability of the excellent permanent magnetic compound Nd2Fe14B and substitution of Fe in the compound by V, Cr, Mn, Zr and Nb are investigated by using interatomic pair potentials which are converted from lattice-inversion method. Calculation shows that the substitution always makes the cell volume larger, and the increase of the volume is almost linear with substituent concentration. The calculated cohesive energy shows that the preferential order of substitution of Fe is Nb, V, Cr, Mn, Zr. Nevertheless, all the five substituting elements should most preferentially replace Fe in the j2 site, which has the greatest space among all six Fe sites. [Copyright &y& Elsevier]

Abstract: An investigation of the structural and vibrational properties of RFe12−x Ta x (R=Tb, Dy, Ho) compounds has been performed by a series of interatomic pair potentials obtained through the lattice inversion method. Calculated results show Ta atoms can stabilize RFe12−x Ta x with ThMn12-type structure, and Ta atoms substitute for Fe with a strong preference for the 8i sites. The phase stability of the intermetallics RFe12−x Ta x is tested by many means including random atom shift, global deformation and high temperature disturbance under the control of the pair potentials. The calculated lattice parameters are corresponding to the experimental results. In particular, the phonon densities of states for RFe11.5Ta0.5 are first evaluated. A qualitative analysis is carried out with the relevant potentials for the vibrational modes, which makes it possible to predict some properties related to lattice vibration. [Copyright &y& Elsevier]

Abstract: An atomistic study is presented on the phase stability, site preference and lattice constants of the Co-rich rare-earth intermetallic compounds R2(Co, Ti)17 (R=Pr, Nd, Sm, Gd, Tb and Dy) and R2(Co, Ti)17C x . The space group remains unchanged upon substitution of Ti for Co in R2(Co, Ti)17 and the calculated structural parameters correspond well to experimental data. The site preference of Ti atoms at Co sites is also evaluated and the order is given as 6c, 18f, 18h and 9d for the rhombohedral Th2Zn17-type structure, and 4f, 12j, 12k and 6g for the hexagonal Th2Ni17-type structure. The effect of interstitial C atoms in R2(Co, Ti)17C x on the structural properties is also studied. In addition, the decrease of the Curie temperature T c with increasing Ti concentration is explained qualitatively by the exchange-interaction model. [Copyright &y& Elsevier]

Abstract: The angular distributions of protons after traversing thin polycrystalline Al targets (∼15nm) with an incident energy of 10keV have been measured and an analysis of the targets by means of transmission electron microscopy (TEM) techniques has been made. The separate influence of the different crystal characteristics and defects has been evaluated by numerical simulation considering the interaction of the ion with all the nearest neighboring atoms simultaneously. In the analysis we included the evaluation of the effects of lattice vibrations, oxide layers and foil roughness on the angular distributions. Previous experimental data in monocrystalline and polycrystalline Au targets has also been analyzed. For a consistency check a comparison with the results of the MARLOWE code for the simpler case of proton channeling in 〈100〉 Al has been performed. As in the case of Au, the present results indicate that the experiments can be explained in terms of a modified Moliere potential, and confirm the critical influence of crystal characteristics, in this case the amorphous oxide layer on the surface and the thermal vibration of the lattice atoms. [Copyright &y& Elsevier]

Abstract: We have investigated the structural properties of Pr2Fe17− x Mn x compounds by using quasi-ab initio pair potentials Φ Fe–Fe(r), Φ Pr–Fe(r), Φ Pr–Pr(r), Φ Pr–Mn(r), Φ Fe–Mn(r) and Φ Mn–Mn(r). In Pr2Fe17– x Mn x , the ternary elements Mn substitute for Fe atoms without changing the crystal structure. The calculated cohesive energy curves show that for all values of x, Mn preferentially substitutes for Fe in the 6c site and randomly substitutes for Fe in the 18f and 18h site. The calculated lattice constants coincide quite well with experimental values. Furthermore, the phonon density, specific heat and vibrational entropy of these compounds are also calculated. It is interesting that simple pair potentials can describe these extremely anisotropic materials. [Copyright &y& Elsevier]

The connection between interatomic potentials and structure functions of liquids is studied. The expressions for two- and three-body potentials are obtained. The contribution of three-body effects is found to be significant, reaching several per cent of the ground-state energy. [ABSTRACT FROM AUTHOR]

Abstract: The intermetallics (R=Dy, Ho) have been studied to ascertain the effect of partial replacement of Co by Mn on their phase stability and site preference. Calculation is based on a series of interatomic pair potentials related to the rare earth and transition metals, which are obtained by a strict lattice inversion method. Our results indicate that the Mn atom can stabilize with -type structure. And Mn atom preferentially substitutes for Co in the 6c site and randomly substitutes in the 18f and 18h site. The differences of lattice constants between the calculated and the experimental values are about or even smaller than 2%. The properties related to lattice vibration, such as phonon density of states and Debye temperature, are also evaluated for these materials. The method utilized in the present investigation offers a rather easy and direct way to study the structural and vibrational properties of . [Copyright &y& Elsevier]

Abstract: Due to the degeneracy of the states, the potential between a metastable 2S hydrogen atom and a conducting surface falls off as asymptotically, in contrast to the usual retarded van der Waals potentials, which fall off as . This affects the quantum reflection amplitudes and causes the apparent space shifts, which express the time involved in the quantum reflection process, to diverge to large negative values at threshold. [Copyright &y& Elsevier]

Abstract: Atomistic simulation of radiation damage in oxides is a relatively new field compared to similar work in metals and semiconductors, and presents new challenges. We describe the development of a simplified empirical model for the (Sr1−3x/2Lax)TiO3 perovskite system, which contains partially-ordered cation vacancies and has interesting radiation resistance properties. Pair potential parameters are fitted to a range of experimental and new ab initio data, and the resulting model accurately reproduces important properties of the system, including local cation ordering effects. [Copyright &y& Elsevier]

Abstract: Being able to accurately predict dopant profiles at sub-keV implant energies is critical for the microelectronic industry. Molecular Dynamics (MD), with its capability to account for multiple interactions as energy lowers, is an increasingly popular simulation method. We report our work on sub-keV implantation using MD and investigate the effect of different interatomic potentials on the range profiles. As an approximation, only pair potentials are considered in this work. Density Functional Theory (DFT) is used to calculate the pair potentials for a wide range of dopants (B, C, N, F, Si, P, Ga, Ge, As, In and Sb) in single crystalline silicon. A commonly used repulsive potential is also included in the study. Importance of the repulsive and attractive regions of the potential has been investigated with different elements and we show that a potential depicting the right attractive forces is especially important for heavy elements at low energies. [Copyright &y& Elsevier]

Abstract: Molecular dynamics simulations of ion sputtering require extremely good classical potentials for the target material, since many energies and local atomic environments play a role in the process. Here we show that the Modified Embedding Atom Method potential (MEAM), in spite of the fact that its current parametrization makes it belong to a group of potentials that all have shortcomings in the description of silicon, is a serious candidate for such a potential – after re-fitting. The physics underlying the MEAM is discussed, and a new parameter set is presented for a first-neighbor MEAM model, which differs substantially from the original set, but reproduces a large collection of first-principles energy data very well-including some for Si atoms in highly asymmetric environments. In routine molecular dynamics simulations, however, this first-neighbor MEAM model failed. We argue that important reasons for this are the narrow cutoff range and the large number of second neighbors of silicon, although the elastic constants of the MEAM model may have an additional influence. Extending the model to second neighbors via merely a larger radial cutoff value turns out to be problematic in the MEAM formalism. Rather, following the original MEAM idea, a cutoff mechanism based on angular criteria has to be added. Employing such an approach, we have found a potential that appears to be more satisfactory. Extensive tests will yet have to be carried out. [Copyright &y& Elsevier]

This work offers a study of the structural stability of La2Co17-xTix and (La1-xRx)2Co17-yTiy (R = Sm, Nd) compounds by the inverted ab initio potentials. The Ti atoms substitute for Co without changing the crystal symmetry and preferentially occupy the 6c site. The calculated lattice constants coincide quite well with experimental values. Moreover, the relaxed structure together with the site preference of the Ti atoms substituting for Co or the R atoms substituting for La could give a simple explanation for the variation behavior of Curie temperature. All the results indicate that the potentials are valid for studying the structural properties of the intermetallics. [Copyright &y& Elsevier]

WKB wave functions are expected to be accurate approximations of exact quantum mechanical wave functions mainly near the semiclassical limit of the quantum mechanical Schrödinger equation. The accuracy of WKB wave functions is, however, a local property of the Schrödinger equation, and the failure of the WKB approximation may be restricted to a small “quantal region” of coordinate space, even under conditions which are far from the semiclassical limit and close to the anticlassical or extreme quantum limit of the Schrödinger equation. In many physically important situations, exact or highly accurate approximate wave functions are available for the quantal region where the WKB approximation breaks down, and together with WKB wave functions in residual space provide highly accurate solutions of the full problem. WKB wave functions can thus be used to derive exact or highly accurate quantum mechanical results, even far from the semiclassical limit. We present a wide range of applications, including the derivation of properties of bound and continuum states near the threshold of a potential, which are important for understanding many results observed in experiments with cold atoms. [Copyright &y& Elsevier]

The structural stability of the intermetallic compounds R2Co17 and R2Co17T (T=Be, C) is tested by many means including random atom shifts, global deformations and high temperature disturbances under the control of the pair potentials. The structure type and crystal constants of R2Co17 and R2Co17Be are close to experimental results. The addition of Be and C in the interstice of R2Co17 causes a decrease of the cohesive energy, and Be and C only occupies the 9e interstitial site with the Th2Zn17-type structure or the 6h interstitial site with the Th2Ni17-type structure. All the above results indicate that the potentials are valid for studying the structural properties of these kinds of anisotropy materials. [Copyright &y& Elsevier]

Molecular dynamics simulations of Si(0 0 1) targets subject to uninterrupted Ar bombardment of various energies and angles of incidence were performed, in order to study the atomic processes that take place during the transient and steady state sputtering regimes. Silicon interactions were described with the Modified Embedded Atom Method potential and the Stillinger–Weber potential. Detailed information is extracted and briefly discussed. It is found that these potentials lead to significant differences in sputter behavior. By testing these potentials (and two others) against newly calculated DFT data for Si energies in a wide variety of atomic environments, we demonstrate that they all have severe shortcomings. Therefore, the Modified Embedded Atom Method potential was re-fitted to the DFT data, leading to a new parametrization and a greatly improved fit. However, a spurious ‘amorphous phase’ energy minimum was detected during molecular dynamics simulations at room temperature. Roads to dealing with this problem are discussed. [Copyright &y& Elsevier]

The phase stability of Nd2Fe17−xTx (T&z.dbnd6;V, Ti, Nb, x=0–1.2) is tested by many means including random atom shift, global deformation and high temperature disturbance under the control of the ab initio potentials. The T atoms substitute for Fe without changing the crystal symmetry and preferentially occupy the 6c site, which is in good agreement with experimental results. The Zr atoms prefer to substitute for Nd atoms in Nd2Fe17. Moreover, the introduction of ternary elements slightly enlarge the calculated Nd2Fe17−xTx (T&z.dbnd6;V, Ti, Nb) volume, which is also close to experiment. All the results indicate that the potentials are valid for studying some structural properties of the intermetallics. [Copyright &y& Elsevier]

The strong interaction between Rydberg atoms can be used to control the strength and character of the interatomic interaction in ultracold gases by weakly dressing the atoms with a Rydberg state. Elaborate theoretical proposals for the realization of various complex phases and applications in quantum simulation exist. Also a simple model has been already developed that describes the basic idea of Rydberg dressing in a two-atom basis. However, an experimental realization has been elusive so far. We present a model describing the ground state of a Bose–Einstein condensate dressed with a Rydberg level based on the Rydberg blockade. This approach provides an intuitive understanding of the transition from pure two-body interaction to a regime of collective interactions. Furthermore it enables us to calculate the deformation of a three-dimensional sample under realistic experimental conditions in mean-field approximation. We compare full three-dimensional numerical calculations of the ground state to an analytic expression obtained within Thomas–Fermi approximation. Finally we discuss limitations and problems arising in an experimental realization of Rydberg dressing based on our experimental results and point out possible solutions for future approaches. Our work enables the reader to straight forwardly estimate the experimental feasibility of Rydberg dressing in realistic three-dimensional atomic samples.