Interaction Of Rare Gases Research Articles

Harnessing Deep Learning for Optimization of Lennard-Jones Parameters for the Polarizable Classical Drude Oscillator Force Field.

The outcomes of computational chemistry and biology research, including drug design, are significantly influenced by the underlying force field (FF) used in molecular simulations. While improved FF accuracy may be achieved via inclusion of explicit treatment of electronic polarization, such an extension must be accompanied by optimization of van der Waals (vdW) interactions, in the context of the Lennard-Jones (LJ) formalism in the present study. This is particularly challenging due to the extensive nature of chemical space combined with the correlated nature of LJ parameters. To address this challenge, a deep learning (DL)-based parametrization framework is developed, allowing for sampling of wide ranges of LJ parameters targeting experimental condensed phase thermodynamic properties. The present work utilizes this framework to develop the LJ parameters for atoms associated with four distinct groups covering 10 different atom types. Final parameter selection was facilitated by quantum mechanical data on rare-gas interactions with the training set molecules. The chosen parameters were then validated through experimental hydration free energies and condensed phase thermodynamic properties of validation set molecules to confirm transferability. The ultimate outcome of utilizing this framework is a set of LJ parameters in the context of the polarizable Drude FF, which demonstrated improvement in the reproduction of both experimental pure solvent and crystal properties and hydration free energies of the molecules compared to the additive CHARMM General FF (CGenFF) including the ability of the Drude FF to accurately reproduce both experimental pure solvent properties and hydration free energies. The study also shows how correlations between difference in the reproduction of condensed phase data between model compounds may be used to direct the selection of new atom types and training set molecules during FF development.

DFT, QTAIM and NBO Investigation of the Interaction of Rare Gases with Pristine and Decorated Boron Nitride Nanotube

AbstractIn this work, the interactions of pristine, Al‐ and Ga‐doped single walled armchair (5,5) boron nitride nanotubes (BNNTs) with He, Ne, Ar and Kr rare gases (RGs) were fully investigated using several different density functional theory (DFT) functionals including pure‐GGA (PBEPBE), hybrid‐GGA (B3LYP), meta‐hybrid‐GGA (M062X) and long‐range‐corrected B3LYP (CAM−B3LYP) in combination with two 6–31G(d) and 6–311+G(d) basis sets. Natural bond orbital (NBO) and quantum theory of atoms in molecule (QTAIM) analyses were also performed to better understand the intermolecular interaction between RGs and nanotubes. The adsorption energies (Eads) indicate that RGs could be adsorbed on the surface of the BNNTs with the following trend: Ne > Kr > Ar > He. The Eads energies obtained using CAM−B3LYP method have also been found to be 13–18%, (for Ne−Kr) and 32–44% (for He−Ar) higher than those obtained from normal B3LYP functional. Moreover, analysis of the natural partial charges reveals the small charge transfer from RGs to BNNTs, which confirms the sensing of RGs by BNNTs. QTAIM analysis also supports the existence of close‐shell (non‐covalent) interactions between BNNTs and RGs. Generally, according to the obtained results, it can be concluded that, Al‐ and Ga‐doped BNNTs are remarkably more sensitive to RGs than pristine‐BNNT, and may be good candidates in designing new RG sensors.

Improved parameterization of interatomic potentials for rare gas dimers with density-based energy decomposition analysis.

We examine interatomic interactions for rare gas dimers using the density-based energy decomposition analysis (DEDA) in conjunction with computational results from CCSD(T) at the complete basis set (CBS) limit. The unique DEDA capability of separating frozen density interactions from density relaxation contributions is employed to yield clean interaction components, and the results are found to be consistent with the typical physical picture that density relaxations play a very minimal role in rare gas interactions. Equipped with each interaction component as reference, we develop a new three-term molecular mechanical force field to describe rare gas dimers: a smeared charge multipole model for electrostatics with charge penetration effects, a B3LYP-D3 dispersion term for asymptotically correct long-range attractions that is screened at short-range, and a Born-Mayer exponential function for the repulsion. The resulted force field not only reproduces rare gas interaction energies calculated at the CCSD(T)/CBS level, but also yields each interaction component (electrostatic or van der Waals) which agrees very well with its corresponding reference value.

Gas–Surface Interactions on Quasicrystals

AbstractTo commemorate the awarding of the Nobel Prize for Chemistry to Daniel Shechtman for his discovery of quasicrystals, this paper reviews our recent studies of the interaction of rare gases and hydrocarbon gases with the tenfold surface of quasicrystalline decagonal Al‐Co‐Ni.

Finite-temperature quantum simulations of mixed rare gas clusters

Finite-temperature quantum Monte Carlo simulations are presented for mixed neon/argon rare gas clusters containing up to n=10 atoms. For the smallest clusters (n=3) comparison with rigorous bound state calculations and experiments shows that the present approach is accurate to within fractions of wavenumbers for energies and to within a few percent or better for rotational constants. For larger cluster sizes, for which no rigorous quantum calculations are available, comparison with experiment becomes even more favorable. In all simulations accurate pair potentials for the rare gas-rare gas interactions are employed and comparison with high-level electronic structure calculations suggest that many-body interactions play a minor role. For the largest clusters investigated (Ne(4)Ar(6)) gradual melting of the neon phase is observed while the argon-phase remains structurally intact.

Density Functional Theory Approach to Noncovalent Interactions via Monomer Polarization and Pauli Blockade

We propose a "DFT+dispersion" treatment which avoids double counting of dispersion terms by deriving the dispersion-free density functional theory (DFT) interaction energy and combining it with DFT-based dispersion. The formalism involves self-consistent polarization of DFT monomers restrained by the exclusion principle via the Pauli-blockade technique. Any exchange-correlation potential can be used within monomers, but only the exchange operates between them. The applications to rare-gas dimers, ion-rare-gas interactions, and hydrogen bonds demonstrate that the interaction energies agree with benchmark values.

Coherent continuum extreme ultraviolet radiation in the sub-100-nJ range generated by a high-power many-cycle laser field

High-energy coherent continuum radiation is generated by the interaction of rare gases with a high-power many-cycle laser field, utilizing the interferometric polarization gating technique. A narrow temporal gate is formed in the laser pulse within which the extreme ultraviolet (XUV) emission is restricted. An analytical expression for the gate function is derived. A super-XUV continuum down to 15 nm, broad enough to support synthesis of single pulses of 260 as duration and a few tens of nanojoule energy, has been measured. These results directly challenge the perspectives of single-attosecond pulse XUV-pump-XUV-probe applications.

Van der Waals Interactions in Density-Functional Theory: Rare-Gas Diatomics.

The application of conventional GGA and meta-GGA density functionals to van der Waals interactions is fraught with difficulties. Conventional functionals do not contain the physics of the dispersion interaction. To make matters worse, the exchange part alone can yield anything from severe overbinding to severe over-repulsion depending on the choice of functional. We have assessed a variety of exchange GGAs for their ability to reproduce exact Hartree-Fock repulsion energies in rare-gas systems, and we find that PW86 [ Phys. Rev. B 1986 , 33 , 8800 ] performs remarkably well. The addition of a dynamical correlation GGA and the nonempirical dispersion model of Becke and Johnson [ J. Chem. Phys. 2007 , 127 , 154108 ] to PW86 gives a simple GGA plus dispersion theory yielding excellent rare-gas interaction curves for pairs involving He through Kr, with only two adjustable parameters for damping of the dispersion terms.

Charge-dependent model for many-body polarization, exchange, and dispersion interactions in hybrid quantum mechanical∕molecular mechanical calculations

This work explores a new charge-dependent energy model consisting of van der Waals and polarization interactions between the quantum mechanical (QM) and molecular mechanical (MM) regions in a combined QMMM calculation. van der Waals interactions are commonly treated using empirical Lennard-Jones potentials, whose parameters are often chosen based on the QM atom type (e.g., based on hybridization or specific covalent bonding environment). This strategy for determination of QMMM nonbonding interactions becomes tedious to parametrize and lacks robust transferability. Problems occur in the study of chemical reactions where the "atom type" is a complex function of the reaction coordinate. This is particularly problematic for reactions, where atoms or localized functional groups undergo changes in charge state and hybridization. In the present work we propose a new model for nonelectrostatic nonbonded interactions in QMMM calculations that overcomes many of these problems. The model is based on a scaled overlap model for repulsive exchange and attractive dispersion interactions that is a function of atomic charge. The model is chemically significant since it properly correlates atomic size, softness, polarizability, and dispersion terms with minimal one-body parameters that are functions of the atomic charge. Tests of the model are examined for rare-gas interactions with neutral and charged atoms in order to demonstrate improved transferability. The present work provides a new framework for modeling QMMM interactions with improved accuracy and transferability.

Simple DFT model of clusters embedded in rare gas matrix: Trapping sites and spectroscopic properties of Na embedded in Ar

We present a theoretical model to study the dynamics of metallic clusters embedded in a rare gas matrix. We describe the active electrons of the embedded cluster using time dependent density functional theory, while the surrounding matrix is described in terms of classical molecular dynamics of polarizable atoms. The coupling between the cluster and the rare gas atoms is deduced from the work of Gross and Spiegelmann [J. Chem. Phys. 108, 4148 (1998)] and reformulated explicitly in a simple and efficient density functional form. The electron rare gas interaction takes the form of an averaged dipole fluctuation term, which retains the van der Waals long range interaction, and a short range repulsive pseudopotential, which accounts for the Pauli repulsion of the electron by the rare gas atom. We applied our model to Na clusters embedded in Ar matrix. For the latter we developed an efficient local pseudopotential, which allows studying systems containing more than 10(3) Ar atoms. We show that large systems are indeed necessary to account properly for long range polarization of the matrix, that competes with the matrix confinement effect. We focus our study on Na(2), Na(4), and Na(8). For each system, we have determined the geometry of the most favorable trapping site by means of damped molecular dynamics. We present the effect of matrix embedding on the optical absorption spectrum. For Na(2), the trapping site can be unambiguously identified by comparison of the absorption spectrum with experiment. For Na(4) the spectrum of the embedded cluster is significantly different from the free cluster spectrum, while for Na(8) differences are less pronounced.

Potential energy curves and transport properties for the interaction of He with other ground-state atoms

The interactions of a He atom with a heavier atom are examined for 26 different elements, which are consecutive members selected from three rows (Li–Ne, Na–Ar, and K,Ca, Ga–Kr) and column 12 (Zn, Cd) of the Periodic Table. Interaction energies are determined using high-quality ab initio calculations for the states of the molecule that would be formed from each pair of atoms in their ground states. Potential energies are tabulated for a broad range of interatomic separation distances. The results show, for example, that the energy of an alkali interaction at small separations is nearly the same as that of a rare-gas interaction with the same electron configuration for the closed shells. Furthermore, the repulsive-range parameter for this region is very short compared to its length for the repulsion dominated by the alkali-valence electron at large separations (beyond about 3–4 a0). The potential energies in the region of the van der Waals minimum agree well with the most accurate results available. The ab initio energies are applied to calculate scattering cross sections and obtain the collision integrals that are needed to determine transport properties to second order. The theoretical values of Li–He total scattering cross sections and the rare-gas atom–He transport properties agree well (to within about 1%) with the corresponding measured data. Effective potential energies are constructed from the ab initio energies; the results have been shown to reproduce known transport data and can be readily applied to predict unknown transport properties for like-atom interactions.

Evolution of the electronic orbital alignment in metal-atom–rare-gas fractional collisions

We have developed an analytic model within the ``orbital-locking and -following'' approximation to explain the observed polarization spectrum in the metal-atom--rare-gas fractional collision experiments of Olsgaard and co-workers [Phys. Rev. A 48, 1987 (1993)]. We obtain an expression for the observed polarization spectrum that can be interpreted in terms of the evolution of the electronic orbital alignment from point to point on the intermediate excited-state potential-energy curve. The results, using model potentials for the metal-atom--rare-gas interaction, are in good agreement with the experimental polarization data.

Natural bond orbital analysis of steric interactions

We describe an ab initio procedure for extracting the Pauli exchange antisymmetry (“steric”) contributions to molecular potential energy in the framework of self-consistent-field molecular orbital (SCFMO) theory. This “natural steric analysis” method is based on natural bond orbital (NBO) representation of the SCFMO wave function, which allows the steric exchange energy to be approximated as an energy difference between “preorthogonal” and final NBOs, analogous to the procedure of Sovers et al. [J. Chem. Phys. 49, 2592 (1965)]. We show how the total NBO steric exchange energy can in turn be approximated in terms of pairwise-additive interactions between localized bonding units, comparable to the empirical steric potentials of molecular mechanics models. The accuracy of NBO steric analysis is tested in applications to various rare-gas interactions (expected to be of pure steric exchange type), and excellent agreement is found with the full ab initio potential curves over a wide range of separations. Limitations of the simple pairwise-additive model of steric exchange interactions are noted and characterized.

The interaction of rare gases with transition metal surfaces

The interaction of rare gas atoms with metal surfaces is considerably modified in the presence of occupied Shockley surface states. The anomalous bond strength of Xe on Pd, the decoration of upper step edges on Pt(111), and the different XeXe interaction on Pd and Pt is at least partially accounted for by the influence of surface states. Arguments are provided that surface states also contribute to the anticorrugating effects observed in He scattering on Ni(110) and Cu(110).

Ground-state potentials for Co+/rare-gas interactions

Spectroscopic constants (R e, ωe, D e, D 0) for the 3Δ ground-state potentials of the diatomic ions CoAr+, CoKr+, CoXe+, and CoRn+ are calculated using coupled-cluster theory, flexible basis sets, and relativistic ab initio pseudo-potentials for the heavy rare-gas atoms. This standard approach yields c. 90% of the measured interaction energies and overestimates the bond distances by c. 0⋅05 bohr. Bonding is shown to be intrinsically electrostatic. For the case of CoAr+, possible sources of error in the calculation are investigated by studying the effects of core correlation,scalar and spin-orbit relativistic effects, and basis set superposition errors. Correlating the 3s and 3p electrons in Co and the inclusion of scalar relativistic terms increase the bond strengths and decrease the equilibrium distance in CoAr+, while accounting for spin-orbit interaction and correction for the basis set superposition errors lead to the opposite effects. Including all these corrections, the theoretical predictions of the spectroscopic parameters for the 3Δ3 ground state of CoAr+ are (experimental values in parentheses) R e = 4⋅460 (4⋅509 ± 0⋅009) bohr; ωe = 198 cm-1; D o = 0±4874 (0⋅5097 ± 0⋅0006) eV.

Multi-property predictions from recent He—CO potential energy surfaces and related comments on the nature of heteronuclear—rare gas interactions

Multi-property predictions from recent He—CO potential energy surfaces and related comments on the nature of heteronuclear—rare gas interactions

Accurate density functional theory study of cationic magnesium clusters and Mg+–rare gas interactions

The equilibrium geometries, energetics, and hyperfine coupling constants for a number of charged magnesium clusters and magnesium–rare gas complexes are investigated using gradient corrected density functional theory. In the study of matrix effects, Mg+ and Mg+2 are embedded in matrices with up to 10 neon or argon atoms. For the magnesium ion, we calculate a shift in the isotropic hyperfine coupling constant of 10 G when changing the matrix from Ne to Ar (expt. value: 10.9 G), and for Mg+2 the calculated shift is −0.5 G (expt. value=1.1 G). In the second part of the paper, several different positively charged magnesium clusters with up to six magnesium atoms are optimized, and the resulting geometries, relative energies, and hyperfine coupling constants are compared with experimental data and with previous theoretical studies. Based on the computed averaged hyperfine coupling constants, a reassignment is proposed of the experimentally observed average values (in gauss), −222.5 (Mg+), −105.4 (Mg+2), −69.5 (linear Mg+3), −55.0 (triangular Mg+3), −48.5 (Mg+4), and −34.6 (Mg+5). The corresponding calculated values are −211.6, −100.0, −65.2, −58.7, −48.3, and −33.3 G, respectively. For the hexamer ion, we predict an average hfcc of −28.5 G.

Exchange-Coulomb potential energy surfaces, and related physical properties, for KrN2

Abstract The construction of exchange-Coulomb (XC) potential energy models for closed shell atom-closed shell molecule interactions, based on earlier work for rare gas-rare gas interactions, is discussed with explicit application to the KrN2 interaction. The construction of the new XC potential energy surface for KrN2 is based on recent results for the Heitler-London interaction energy, the long range dispersion energies, and the microwave spectra for this dimer. The adjustable parameters in the final XC potential are determined by fitting experimental second virial coefficients (all within experimental error), as a function of temperature, and three lines of the microwave spectra. With no further adjustment of parameters the resulting potential yields excellent predictions for all the frequencies of all the microwave transitions studied experimentally for seven isotopomers of KrN2, and good agreement with experiment for the binary diffusion, the interaction viscosity, and the mixture viscosity coefficients of KrN2 and for the cross sections associated with depolarized light scattering and nuclear spin relaxation for the KrN2 system. The agreement with experiment for the latter five properties is as good as can be expected from our scaled Mason-Monchick/infinite order sudden calculations for these properties. The final XC2 potential is apparently the most reliable potential to date for the KrN2 interaction and provides a very suitable starting point for further studies of the KrN2 system; the flexibility still inherent in the potential can be used, as required, for this purpose.

Scattering experiments with sodium clusters: Differential cross sections and classical trajectory calculations

Scattering of sodium clusters Nan (n =3,8) with argon, neon and molecular nitrogen is investigated in a crossed molecular beam experiment. The clusters are scattered by a pulsed gas beam and subsequently ionized by a pulsed laser and detected in a time-of-flight mass spectrometer. Total differential cross sections for Nan+ Ar, Ne and N2 (n=3−8) are measured. The angularly resolved cross sections show a significant amount of energy transfer to the clusters in the collision process. Classical trajectory calculations are performed using an distance-dependant Hückel-type Hamiltonian with added pair potentials for the sodium–rare gas interaction. The results show good agreement with the measurements in the range of small impact parameters. It is observed that the different isomers of the clusters play an important role in the process. Discrete excitations are analyzed for Na3 and Na5. The shape of the measured angular distributions is explained from the superposition of rotational rainbows.

Spectroscopic characterization of the X 1Σ+ and C 1Π states of the Mg⋅Ne molecule

The X 1Σ+ ground state and C 1Π1 excited state of the Mg⋅Ne molecule have been characterized by laser induced fluorescence in a supersonic jet. The spectroscopic constants are compared to those for analogous electronic states of metal–rare-gas van der Waals complexes. The bonding in such states is discussed in terms of models for metal–rare-gas interactions which we have proposed earlier.