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This paper presents a theoretical study of the bound states of the open-shell OH radical in its ground electronic state(X2Π) interacting with n Ar atoms, for n from 4 to 12. After freezing the geometry of the Arn cage or subunit at the equilibrium structure (preceding paper), we carry out nonadiabatic five-dimensional quantum dynamics calculations on two coupled potential energy surfaces, using an extension of the method previously applied to closed-shell ArnHFclusters [J. Chem. Phys. 103, 1829 (1995)]. The method is based on a discrete variable representation (DVR) for the translational motion of OH relative to Arn, combined with a finite basis representation of the OH hindered rotation and electronic structure, including spin–orbit effects. The pattern of OH hindered rotor levels in clusters is similar to that in Ar–OH itself, though extended over three to four times the energy range for n=4 to 9. Ar12OH has a nearly spherical shell of Ar atoms around the OH, so the anisotropic splitting is very small. For n=10 and 11, the anisotropy may be viewed as arising from holes in an otherwise spherical shell, and the resulting patterns of hindered rotor levels are inverted versions of those for Ar2OH and Ar–OH.

In this paper, a dynamics equation of the micro cantilever is presented which includes Van der Waals force. Using the equation, the effects of the Van der Waals force on the natural frequency for the micro cantilever is investigated. Results show that Van der Waals force should be considered for small initial clearance between the micro cantilever and base plate, small cantilever thickness and large cantilever length. To illustrate the analysis, a micro Si cantilever is fabricated and a test of the natural frequencies is done which illustrates the calculative results in this paper.

In this second paper (II) of a series, we report our picosecond time-resolved studies of the state-to-state rates of vibrational predissociation in iodine–rare gas (van der Waals) clusters. Particular focus is on the simplest system, I2He, which serves as a benchmark for theoretical modeling. Comparisons with I2Ne and I2H2 are also presented. The results from measurements made in real time are compared with those deduced from linewidth measurements, representing a rare example of a system studied by both methods under identical conditions and excited to the same quantum (v [script '] i ) states. The discrepancies are discussed in relation to the origin of the broadening and preparation of the state. The rates as a function of v [script '] i display a nonlinear behavior which is examined in relation to the energy-gap law. The measured absolute rates and their dependence on v [script '] i are compared with numerous calculations invoking classical, quantum, and semiclassical theories. In the following paper (III in this series), the cluster size of the same system, I2Xn, is increased (n=2–4) and the dynamics are studied.

Orhorhombic $\alpha$-MoO$_3$ is a layered oxide with various applications and with excellent potential to be exfoliated as a 2D ultrathin film or monolayer. In this paper, we present a first-principles computational study of its vibrational properties. Our focus is on the zone center modes which can be measured by a combination of infared and Raman spectroscopy. The polarization dependent spectra are simulated. Calculations are also performed for a monolayer form in which "double layers" of Mo$_2$O$_6$ which are weakly van der Waals bonded in the $\alpha$-structure are isolated. Shift in phonon frequencies are analyzed., Comment: 13 pages, 13 figures, 14 tables

Hexagonal boron nitride (h-BN) is considered as one of the most promising materials for next-generation quantum technologies. In this paper, we report bulk-like multilayer h-BN epitaxially grown using a carbon-free precursor on c-plane sapphire with a strong emphasis on material characterization and analysis. In particular, structural, morphological, and vibrational properties, and chemical bonding of such van der Waals materials are presented. Between as-grown h-BN and c-plane sapphire, a compressive residual strain induced by both lattice mismatch and thermal expansion mismatch is examined by both theoretical and experimental studies. Atomic force microscopy revealed and scanning electron microscopy supported the presence of wrinkles across the entire surface of the film, likely due to biaxial compressive strain further verified by Raman spectroscopy. Stacking orders in h-BN with a clearly layered structure were confirmed by high resolution transmission electron microscopy, showing that the films have crystallographic homogeneity. Chemical analysis of the as-grown films was done by x-ray photoelectron spectroscopy, which confirmed the formation of stoichiometric h-BN films with excellent uniformity. This wafer-scale chemical vapor deposition-grown layered h-BN with 2D morphology facilitates applications in the fields of quantum- and deep ultraviolet-photonics.

16 pags., 11 figs., 3 tabs. -- This paper is part of the JCP Special Collection in Honor of Women in Chemical Physics and Physical Chemistry, A new spin-averaged potential energy surface (PES) for non-reactive O2(ςg-3) + O2(ςg-3) collisions is presented. The potential is formulated analytically according to the nature of the principal interaction components, with the main van der Waals contribution described through the improved Lennard-Jones model. All the parameters involved in the formulation, having a physical meaning, have been modulated in restricted variation ranges, exploiting a combined analysis of experimental and ab initio reference data. The new PES is shown to be able to reproduce a wealth of different physical properties, ranging from the second virial coefficients to transport properties (shear viscosity and thermal conductivity) and rate coefficients for inelastic scattering collisions. Rate coefficients for the vibrational inelastic processes of O2, including both vibration-to-vibration (V-V) and vibration-to-translation/rotation (V-T/R) energy exchanges, were then calculated on this PES using a mixed quantum-classical method. The effective formulation of the potential and its combination with an efficient, yet accurate, nuclear dynamics treatment allowed for the determination of a large database of V-V and V-T/R energy transfer rate coefficients in a wide temperature range., This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA17030100) and the National Natural Science Foundation of China through Grant Nos. 11372325 and 91116013. M.B. acknowledges the FIS2017-84391-C2-2-P Spanish grant for fundings.

Here, we discuss possible applications of the Casimir forces in micro- and nanosystems. The main part of this paper is devoted to actuation with quantum fluctuations and to the relative contribution of van der Waals and Casimir interactions to adhesion. Switching between the amorphous and crystalline states of phase change materials could generate force contrast sufficient for actuation, though for practical applications, the influence of protective capping layers and volume compression have to be better understood. Resilience against the pull-in instability is also a critical point defined by the material choice, dissipation in the system, and roughness of the surfaces. The adhesion induced by the Casimir forces is omnipresent, and it can play a pivotal role in unwanted stiction demanding deeper understanding. The open problems are the distance upon contact and the relative area of the real contact since both of them control the adhesion. An experiment designed to answer these questions is briefly discussed.

Density functional theory (DFT) has become the method of choice for many applications of quantum mechanics to the study of the electronic properties of molecules and solids. Despite the enormous progress in improving the functionals, the current generation is inadequate for many important applications. As part of the quest of finding better functionals, we consider in this paper the Perdew-Burke-Ernzerhof (PBE) functional, which we believe to have the best theoretical foundation, but which leads to unacceptable errors in predicting thermochemical data (heats of formation) of molecular systems [mean absolute deviation (MAD)=16.9 kcal/mol against the extended G2 data set of 148 molecules]. Much improved thermochemistry is obtained with hybrid DFT methods that include part of the Hartree-Fock exchange [thus B3LYP (Becke's three parameter scheme combining Hartree-Fock exchange, Becke gradient corrected exchange functional and Lee-Yang-Parr correlational functional) with MAD=3.1 kcal/mol and PBE0 (Perdew's hybrid scheme using PBE exchange and correlation functionals) with MAD=4.8 kcal/mol]. However we wish to continue the quest for a pure density-based DFT. Thus we optimized the four free parameters (micro, kappa, alpha, and beta) in PBE theory against experimental atomic data and the van der Waals interaction properties of Ne(2), leading to the xPBE extended functional, which significantly outperforms PBE for thermochemical properties MAD reduced to 8.0 kcal/mol while being competitive or better than PBE for predictions of geometric parameters, ionization potentials, electron affinities, and proton affinities and for the description of van der Waals and hydrogen bond interactions. Thus xPBE significantly enlarges the field of applications available for pure DFT. The functional forms thus obtained for the exchange and correlational functionals may be useful for discovering new improved functionals or formalisms.

Ultrafast dissociation and recombination dynamics of (O_2)^−_n, n=3–10 was studied using femtosecond,time-resolvedphotoelectron spectroscopy. The observed transients of nascent fragment anions, following 800 nm fs pulse excitation, exhibit a biexponential rise with two distinct time constants. The time constants, which vary with the number of solvent O_2 molecules, clearly show the solvation effect in two different dissociation pathways. Consistent with the bifurcation picture in the preceding paper, the direct subpicosecond dissociation(τ_1=110-620 fs, depending on n) is governed by electron recombination and kinematics of the half-collision. The second pathway is indirect (τ_2=0.7–8.0 ps, for O^−_6 to O^−_(20)) and controlled by intramolecular vibrational-energy redistribution. In the solvent cage, only O^−_(16), O^−_(18), and O^−_(20) show the reformation of the bond, with the caging time constant decreasing from 4 ps for the first two to 2 ps for the latter. This caging through ion-induced dipole interaction is then followed by vibrational relaxation on the time scale of 12 to 3 ps, for O^−_(16) to O^−_(20). The time scale for the initial direct caging is two to five times slower than that previously observed for diatoms, neutral, or ionic, in van der Waals clusters. We suggest that this initial slower caging is due to the reorientation of O^−_2 and O_2 to acquire a proper geometry for O^−_4 bond reformation. In these finite-sized homogeneous clusters, we compare theory with experiment. We also found a correlation between the vertical detachment energy and n^(−1/3), for n in the range of 2–10, which allow for a connection between the mesoscopic structures and a bulk-type dielectric continuum, with an effective dielectric constant.

In this paper, we study the structural and electronic properties of graphene adsorbed on MoS2 monolayer (G/MoS2) with different stacking configurations using dispersion-corrected density functional theory. Our calculations show that the interaction between graphene and MoS2 monolayer is a weak van der Waals interaction in all four stacking configurations with the binding energy per carbon atom of −30 meV. In the presence of MoS2 monolayer, the linear bands on the Dirac cone of graphene at the interfaces are slightly split. A band gap about 3 meV opens in G/MoS2 interfaces due to the breaking of sublattice symmetry by the intrinsic interface dipole, and it could be effectively modulated by the stacking configurations. Furthermore, we found that an n-type Schottky contact is formed at the G/MoS2 interface in all four stacking configurations with a small Schottky barrier about 0.49 eV. The appearance of the non-zero band gap in graphene has opened up new possibilities for its application in electronic devices such as graphene field-effect transistors.

Compression of monodisperse powder samples in quasistatic conditions is addressed in a pressure range such that particles fragmentation occurs while the solid remains incompressible (typical pressure range of 1-300 MPa for glass powders). For a granular bed made of particles of given size, the existence of three stages is observed during compression and crush up. First, classical compression occurs and the pressure of the granular bed increases along a characteristic curve as the volume decreases. Then, a critical pressure is reached for which fragmentation begins. During the fragmentation process, the granular pressure stays constant in a given volume range. At the end of this second stage, 20% to 50% of initial grains are reduced to finer particles, depending on the initial size. Then compression undergoes the third stage and the pressure increases along another characteristic curve, in the absence of extra fragmentation. The present paper analyses the analogies between phase transition in liquid-vapour systems and powder compression with crush-up. Fragmentation diagram of soda lime glass granular beds is determined by experimental means. The analogues of the saturation pressure and latent heat of phase change are determined. Two thermodynamic models are then examined to represent the crush-up diagram. The first one uses piecewise functions while the second one is of van der Waals type. Both equations of state relate granular pressure, solid volume fraction and initial particle diameter. The piecewise functions approach provides reasonable representations of the phase diagram while the van der Waals one fails.

The dynamics of methyl (CH3) and fluoromethyl (CF3) groups in organic molecular (van der Waals) solids can be exploited to survey their local environments. We report solid state (1)H and (19)F spin-lattice relaxationexperiments in polycrystalline 3-trifluoromethoxycinnamic acid, along with an X-ray diffraction determination of the molecular and crystal structure, to investigate the intramolecular and intermolecular interactions that determine the properties that characterize the CF3 reorientation. The molecule is of no particular interest; it simply provides a motionless backbone (on the nuclear magnetic resonance(NMR) time scale) to investigate CF3 reorientation occurring on the NMR time scale. The effects of (19)F-(19)F and (19)F-(1)H spin-spin dipolar interactions on the complicated nonexponential NMRrelaxation provide independent inputs into determining a model for CF3 reorientation. As such, these experiments provide much more information than when only one spin species (usually (1)H) is present. In Sec. IV, which can be read immediately after the Introduction without reading the rest of the paper, we compare the barrier to CH3 and CF3 reorientation in seven organic solids and separate this barrier into intramolecular and intermolecular components.

In this paper (III) we report real-time studies of the picosecond dynamics of iodine in Ne clusters I * 2 Nen(n = 2–4) --> I * 2 + nNe. The results are discussed in relation to vibrational predissociation (VP), basic to the I2X systems, and to the onset of intramolecular vibrational-energy redistribution (IVR). The latter process, which is a precursor for the evaporation of the host atoms or for further fragmentation, is found to be increasingly effective as the cluster size increases; low-energy van der Waals modes act as the accepting (bath) modes. The reaction dynamics for I2Ne2 are examined and quantitatively compared to a simple model which describes the dynamics as consecutive bond breaking. On this basis, it is concluded that the onset of energy redistribution is observed in I2Ne2. Comparison of I2Ne and I2Ne2 to larger clusters (n=3,4) is accomplished by introducing an overall effective reaction rate. From measurements of the rates and their dependence on v [script '] i , the initial quantum number of the I2 stretch, we are able to examine the dynamics of direct fragmentation and evaporation, and compare with theory.

In this paper, we report vibration-rotation-tunneling levels of the van der Waals clusters N2–H2O and N2–D2O computed from an ab initio potential energy surface. The only dynamical approximation is that the monomers are rigid. We use a symmetry adapted Lanczos algorithm and an uncoupled product basis set. The pattern of the cluster’s levels is complicated by splittings caused by H–H exchange tunneling (larger splitting) and N–N exchange tunneling (smaller splitting). An interesting result that emerges from our calculation is that whereas in N2–H2O, the symmetric H–H tunnelling state is below the anti-symmetric H–H tunnelling state for both K = 0 and K = 1, the order is reversed in N2–D2O for K = 1. The only experimental splitting measurements are the D–D exchange tunneling splittings reported by Zhu et al. [J. Chem. Phys. 139, 214309 (2013)] for N2–D2O in the v2 = 1 region of D2O. Due to the inverted order of the split levels, they measure the sum of the K = 0 and K = 1 tunneling splittings, which is in excellent agreement with our calculated result. Other splittings we predict, in particular those of N2–H2O, may guide future experiments.

The two-dimensional limit of layered materials has recently been realized through the use of van der Waals (vdW) heterostructures composed of weakly interacting layers. In this paper, we describe two different classes of vdW heterostructures: inorganic vdW heterostructures prepared by co-lamination and restacking; and organic-inorganic hetero-epitaxy created by physical vapor deposition of organic molecule crystals on an inorganic vdW substrate. Both types of heterostructures exhibit atomically clean vdW interfaces. Employing such vdW heterostructures, we have demonstrated various novel devices, including graphene/hexagonal boron nitride (hBN) and MoS2 heterostructures for memory devices; graphene/MoS2/WSe2/graphene vertical p-n junctions for photovoltaic devices, and organic crystals on hBN with graphene electrodes for high-performance transistors.

In this paper we investigate the dynamic properties of the minimal Bell-Lavis (BL) water model and their relation to the thermodynamic anomalies. The Bell-Lavis model is defined on a triangular lattice in which water molecules are represented by particles with three symmetric bonding arms interacting through van der Waals and hydrogen bonds. We have studied the model diffusivity in different regions of the phase diagram through Monte Carlo simulations. Our results show that the model displays a region of anomalous diffusion which lies inside the region of anomalous density, englobed by the line of temperatures of maximum density (TMD). Further, we have found that the diffusivity undergoes a dynamic transition which may be classified as fragile-to-strong transition at the critical line only at low pressures. At higher densities, no dynamic transition is seen on crossing the critical line. Thus evidence from this study is that relation of dynamic transitions to criticality may be discarded.

In this paper, we used a coarse-grained model at the residue level to calculate the binding free energies of three protein-protein complexes. General formulations to calculate the electrostatic binding free energy and the van der Waals free energy are presented by solving linearized Poisson-Boltzmann equations using the boundary element method in combination with the fast multipole method. The residue level model with the fast multipole method allows us to efficiently investigate how the mutations on the active site of the protein-protein interface affect the changes in binding affinities of protein complexes. Good correlations between the calculated results and the experimental ones indicate that our model can capture the dominant contributions to the protein-protein interactions. At the same time, additional effects on protein binding due to atomic details are also discussed in the context of the limitations of such a coarse-grained model.

The interaction potential of the He–CaH(2Σ+) van der Waals complex is computed with the partially spin-restricted open-shell single and double excitation coupled cluster method with perturbative triples [RCCSD(T)] for more than 3700 geometries. An accurate fit of the three-dimensional potential is made available for the RCCSD as well as the RCCSD(T) results. Also the CaH diatomic potential is calculated at the RCCSD(T) level and shown to be very accurate by comparison of computed vibrational levels and rotational constants to spectroscopic data. In the accompanying paper the potentials are employed in a study of collisions of He with CaH at cold and ultracold temperatures.

This paper, last in this series, reports on the picosecond dynamics of vibrational predissociation in beam‐cooled van der Waals’ clusters. Reaction rates have been measured for clusters (1:1) of phenol and cresol (p‐methylphenol) with benzene by the picosecond pump–probe photoionization mass‐spectrometry technique. Dissociation to form phenol (cresol) and benzene takes place from vibrational levels of the S_1 state of phenol (cresol) prepared by the pump laser. The predissociation rates were measured for a number of different excess energies upto ∼2500 cm^(−1), and the reaction threshold was found to be 1400 cm^(−1) above the S_1 origin for phenol–benzene and ∼1795 cm^(−1) for cresol–benzene, respectively. For phenol–benzene, the predissociation rates, following excitation of ring‐type modes, vs excess energy vary more or less smoothly. Cresol–benzene exhibits biexponential decay, with the fast component becoming more dominant at higher energies. A non‐RRKM model involving division of the vibrational phase space is discussed to explain this observation.

It is well known that irradiation with intense laser light can lead to nonlinear absorption processes by individual molecules. However, the mutual interaction between two molecules can lead to cooperative nonlinear processes which result in entirely new features in the absorption spectrum. In this paper, the theory of cooperative two‐photon absorption is developed using the principles of quantum electrodynamics, and expressions are derived for the rate of cooperative absorption for transitions which are forbidden in the absence of any such interaction. Several different cases are examined in detail, including crystalline or matrix‐isolated species, gaseous and liquid mixtures, and van der Waals molecules. It is shown that the cooperative absorption rate can be substantially increased by choosing materials with suitable energy levels where one of several resonance enhancement mechanisms can be exploited. Finally, methods of observation are discussed, and a specific photochemical example is given for the case of a mixture of formaldehyde and deuterioformaldehyde.

We apply in this paper a model related to the >infinite order sudden approximation> to treat the vibrational predissociation of the HeI 2 van der Waals molecule. For each configuration, the stretching motions within the complex are exactly solved in the close-coupling formalism. The bending motion is then considered in an approximate way and averaged predissociation rates are obtained. Our results are compared with the experiment and also with previous models. © 1986 American Institute of Physics.