Ultracold collisions between spin-polarized Na atoms and vibrationally excited Na2 molecules are investigated theoretically, using a reactive scattering formalism (including atom exchange). Calculations carried out on both pairwise additive nonadditive potential energy surfaces for the quartet electronic state. The Wigner threshold laws followed energies below 10(-5) K. Vibrational relaxation processes dominate elastic temperatures 10(-3)-10(-4) For K, rate coefficients vibrational (v=1-->0)...

We have carried out quantum dynamical calculations of vibrational quenching in $\mathrm{L}\mathrm{i}+{\mathrm{L}\mathrm{i}}_{2}$ collisions for both bosonic $^{7}\mathrm{L}\mathrm{i}$ and fermionic $^{6}\mathrm{L}\mathrm{i}$. These are the first ever such involving atoms. find that low initial states considered here ($v\ensuremath{\le}3$), rates not suppressed This contrasts with situation found experimentally molecules formed via Feshbach resonances very high states.

We apply the semiclassical instanton method to calculate all feasible tunnelling pathways in water pentamer. Similarly trimer, there are labile flip dynamics as well a number of different bifurcation coupled flips. In contrast puckering motion oxygen ring makes ring-polymer approach difficult converge, problem which is resolved by using recently developed time-independent formalism method. use results predict complete ground-state splitting pattern 320 states, should help continuing effort...

Three-body nonadditive forces in systems of three spin-polarized alkali-metal atoms (Li, Na, K, Rb, and Cs) are investigated using high-level ab initio calculations. The found to be large, especially near the equilateral equilibrium geometries. For Li, they increase three-atom potential well depth by a factor 4 reduce interatomic distance $1.07\mathrm{\AA{}}.$ originate principally from chemical bonding arising $\mathrm{sp}$ mixing effects.

We carry out the first quantum dynamics calculations on ultracold atom-diatom collisions in isotopic mixtures. The systems studied are spin-polarized $^{7}\mathrm{Li}+^{6}\mathrm{Li}^{7}\mathrm{Li}$, $^{7}\mathrm{Li}+^{6}\mathrm{Li}_{2}$, $^{6}\mathrm{Li}+^{6}\mathrm{Li}^{7}\mathrm{Li}$, and $^{6}\mathrm{Li}+^{7}\mathrm{Li}_{2}$. Reactive scattering can occur for two even when molecules their ground rovibrational states, but is slower than vibrational relaxation homonuclear systems....

A potential energy surface for the lowest quartet electronic state ((4)A(')) of lithium trimer is developed and used to study spin-polarized Li+Li(2) collisions at ultralow kinetic energies. The allows barrierless atom exchange reactions. Elastic inelastic cross sections are calculated involving a variety rovibrational states Li(2). Inelastic responsible trap loss in molecule production experiments. Isotope effects sensitivity results details investigated. It found that vibrationally excited...

We extend to full dimensionality a recently developed wave packet method [M. T. Cvitaš and S. C. Althorpe, J. Phys. Chem. A 113, 4557 (2009)] for computing the state-to-state quantum dynamics of AB + CD → ABC D reactions also increase computational efficiency method. This is done by introducing new set product coordinates, applying Crank–Nicholson approximation angular kinetic energy part split-operator propagator using symmetry-adapted basis-to-grid transformation evaluate integrals over...

We present an extension to the ring polymer instanton (RPI) method that includes overall rotations in tunneling pathways, allowing a calculation of full rotation-tunneling spectrum water dimer. Our gives qualitative description rotational and processes underpinning spectrum, shows drastic reduction largest splitting with increasing excitation. show this is due strong coupling between motion about principal axis acceptor (where monomer rotates hydrogen bond), which results large increase path...

The recently developed ring-polymer instanton (RPI) method [J. Chem. Phys. 2011, 134, 054109] is an efficient technique for calculating approximate tunneling splittings in high-dimensional molecular systems. key step locating the tunneling-path at zero temperature. Here, we show that techniques previously designed instantons finite-temperature rate calculations can be adapted to RPI method, where they become extremely efficient, reducing number of potential energy calls by 2 orders...

We obtain a shallow-tunnelling correction factor for use with Wigner–Eyring transition-state theory (TST).

Tunneling splitting (TS) patterns of the energetically low-lying structural isomers water hexamer are calculated using modified WKB (Wentzel-Kramers-Brillouin) method in full dimensionality. TSs prism...

We describe a quantum wave packet method for computing the state-to-state dynamics of 4-atom AB + CD --> ABC D reactions. The approach is an extension to reactions version reactant-product decoupling (RPD) approach, applied previously 3-atom ( J. Chem. Phys. 2001, 114 , 1601 ). partitions coordinate space reaction into separate reagent, strong-interaction, and product regions, using system artificial absorbing reflecting potentials. It employs partitioned split-operator propagator, which...

The ring-polymer instanton (RPI) method is an efficient technique for calculating approximate tunneling splittings in high-dimensional molecular systems. In the RPI method, splitting evaluated from properties of minimum action path (MAP) connecting symmetric wells, whereby extensive sampling full potential energy surface exact quantum-dynamics methods avoided. Nevertheless, search MAP usually most time-consuming step standard numerical procedures. Recently, nudged elastic band (NEB) and...

Tunneling splitting (TS) patterns in vibrationally excited states of the water trimer are calculated, taking into account six tunneling pathways that describe flips free OH bonds and five bifurcation mechanisms break reform hydrogen ring. A matrix (TM) model is used to derive energy shifts due terms distinct TM elements symbolic form. calculated using recently-developed modified WKB (Wentzel-Kramers-Brillouin) method full dimensionality. Convergence was achieved for lowest vibrational modes....

We extend a recently developed wave packet method for computing the state-to-state quantum dynamics of AB + CD → ABC D reactions [M. T. Cvitaš and S. C. Althorpe, J. Phys. Chem. A 113, 4557 (2009)]10.1021/jp8111974 to include Chebyshev propagator. The uses further partitioned approach reactant-product decoupling, which artificial decoupling potentials partition coordinate space reaction into separate reactant, product, transition-state regions. Separate coordinates basis sets can then be...

Quantum transition-state theory (QTST) and free-energy instanton (FEIT) are two closely related methods for estimating the quantum rate coefficient from at reaction barrier. In calculations on one-dimensional models, FEIT typically gives closer agreement than QTST with exact results all temperatures below crossover to deep tunneling, suggesting that is a better approximation in this regime. Here we show simple trend does not hold systems of greater dimensionality. We report tests several...

The long-range forces that act between three atoms are analysed in both atom-diatom and atom-atom-atom representations. Expressions for dispersion coefficients obtained terms of 3-body nonadditive coefficients. anisotropy C_6 arises primarily from triple-dipole quadruple-dipole forces, while pairwise-additive dipole-dipole-quadrupole contribute significantly to C_8 resulting expressions applied Li + Li_2 (triplet) recommendations made the best way obtain global triatomic potentials...

We derive a multidimensional instanton theory for calculating ground-state tunneling splittings in Cartesian coordinates general paths. It is an extension of the method by Mil’nikov and Nakamura [J. Chem. Phys. 115, 6881 (2001)] to include asymmetric paths that are necessary splitting patterns multi-well systems, such as water clusters. The approach avoids multiple expensive matrix diagonalizations converge fluctuation prefactor ring-polymer (RPI) method, instead replaces them integration...

In this paper, we review a quantum wave packet method for computing state-to-state dynamics of three-atom and four-atom bimolecular reactions using the reactant–product decoupling (RPD) approach. The long propagation times needed in order to extract observables cover geometries at which fragments are far apart on reactant product side reaction valley. To alleviate coordinate problem, partition space into three regions, describing reactants, products interaction region each basis set...

We present a lattice-dynamics study of the vibrations linear chain Xe adsorbates in groove positions bundle carbon nanotubes. The characteristic phonon frequencies are calculated and adsorbate polarization vectors discussed. A comparison results with ones previously published shows that cannot be treated as completely decoupled from nanotubes, significant hybridization between tube modes occurs for phonons large wavelengths.

A combined approach that uses the vibrational configuration interaction (VCI) and semiclassical instanton theory was developed to study tunneling spectra of molecules with multiple wells in full dimensionality. The method can be applied calculate low-lying states systems an arbitrary number minima, which are not necessarily equal energy or shape. It tested on a two-dimensional double-well model system malonaldehyde, calculations reproduced exact quantum mechanical (QM) results high accuracy....

A multidimensional semiclassical method for calculating tunneling splittings in vibrationally excited states of molecules using Cartesian coordinates is developed. It an extension the theory by Mil'nikov and Nakamura [$\textit{ J. Chem. Phys.}$ $\textbf{122}$, $124311$ $(2005)$] to asymmetric paths that are necessary splitting patterns multi-well systems, such as water clusters. Additionally, new terms introduced description wavefunction drastically improve estimates certain systems. The...

Compounds containing trivalent boron (TB) as the electron-deficient site(s) find numerous practical uses ranging from Lewis bases in organic synthesis to high-tech industry, with a number of novel applications anticipated. We present an experimental and theoretical study gas-phase valence photoionization (VUV-PES), core (XPS) photoexcitation (NEXAFS) spectra representative TB compound catecholborane (CB). For modelling assigning we used ΔDFT restricted single excitation space TD-DFT methods...