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The mechanism by which the absorption wavelength of a molecule is modified by a protein is known as spectral tuning. Spectral tuning is often achieved by electrostatic interactions that stabilize/destabilize or modify the shape of the excited and ground-state potential energy surfaces of the chromophore. We present a protocol for the construction of three-dimensional "electrostatic spectral tuning maps" that describe how vertical excitation energies in a chromophore are influenced by nearby charges. The maps are built by moving a charge on the van der Waals surface of the chromophore and calculating the change in its excitation energy. The maps are useful guides for protein engineering of color variants, for interpreting spectra of chromophores that act as probes of their environment, and as starting points for further quantum mechanical/molecular mechanical studies. The maps are semiquantitative and can approximate the magnitude of the spectral shift induced by a point charge at a given position with respect to the chromophore. We generate and discuss electrostatic spectral tuning maps for model chromophores of photoreceptor proteins, fluorescent proteins, and aromatic amino acids. Such maps may be extended to other properties such as oscillator strengths, absolute energies (stability), ionization energies, and electron affinities.

Originally, the Carnot cycle is a theoretical thermodynamic cycle that provides an upper limit on the efficiency that any classical thermodynamic engine can achieve during the conversion of heat into work, or conversely, the efficiency of a refrigeration system in creating a temperature difference by the application of work to the system. The aim of this paper is to introduce and study the economic Carnot cycles into a Roegenian economy, using our Thermodynamic-Economic Dictionary. Of course, the most difficult questions are: what is the economic significance of such a cycle? Roegenian economics is acceptable or not, in terms of practical applications? Our answer is yes for both questions., Bicentennial of the University Politehnica of Bucharest 1818-2018 Centenary of Romanian Great Union 1818-2018

The properties of two- and three-atomic clusters of neon are studied. Based on the Faddeev differential equations in the total angular momentum representation, we have calculated the lowest binding energies for the neon trimer. The results obtained are compared with previous published results

It is well known that the Van der Waals equation is a modification of the ideal gas law, yet it can be used to describe both gas and liquid, and some important messages can be obtained from this state equation. However, the Van der Waals equation is not a precise state equation, and it does not give a good description of the law of corresponding states. In this paper, we expand the Van der Waals equation into its Taylor’s series form, and then modify the fourth order expansion by changing the constant Virial coefficients into their analogous ones. Via this way, a more precise result about the law of corresponding states has been obtained, and the law of corresponding states can then be expressed as: in terms of the reduced variables, all fluids should obey the same equation with the analogous Virial coefficients. In addition, the system of 3 He with quantum effects has also been taken into consideration with our modified Van der Waals equation, and it is found that, for a normal system without quantum effect, the modification on ideal gas law from the Van der Waals equation is more significant than the real case, however, for a system with quantum effect, this modification is less significant than the real case, thus a factor is introduced in this paper to weaken or strengthen the modification of the Van der Waals equation, respectively.

An approach to constructing two-phase state regions for real gases, the state of which is described by the modified van der Waals equation in the form proposed by R.L. Fogel’son and E.R. Likhachev, has been discussed.

Angewandte Chemie. International Edition, 58 (29), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

Most often in chemical physics, long range van der Waals surface interactions are approximated by the exact asymptotic result at vanishing distance, the well known additive approximation of London dispersion forces due to Hamaker. However, the description of retardation effects that is known since the time of Casimir is completely neglected for lack of a tractable expression. Here we show that it is possible to describe surface van der Waals forces at arbitrary distances in one single simple equation. The result captures the long sought crossover from non-retarded (London) to retarded (Casimir) interactions, the effect of polarization in condensed media and the full suppression of retarded interactions at large distance. This is achieved with similar accuracy and the same material properties that are used to approximate the Hamaker constant in conventional applications. The results show that at ambient temperature, retardation effects significantly change the power law exponent of the conventional Hamaker result for distances of just a few nanometers., Comment: 6 pages + 4 figures + supplementary material

Analytical formula to determine van der Waals (vdW) interlayer coefficients of nested spherical fullerenes is suggested. The continuum approximation together with the Lennard–Jones potential is utilized. It is shown herein that the greatest contribution to the vdW interaction comes from the adjacent layers and the contribution from a remote layer may be neglected. The vdW interaction is found to be strongly dependent on the radius of the layer, especially when the radius is small enough (

Quantum chemistry methods are used to analyze in detail the structure of the van der Waals complex of ethylene with oxygen C2H4–O2, and binding energies for stable configurations of the complex are calculated. The calculations are carried out by the MP2 method using the 6-311++G(2d,2p) and aug-cc-pVnZ (n = 2, 3, 4) basis sets. It is demonstrated that the most stable structure of the van der Waals complex of ethylene with oxygen is a structure with C2v symmetry, where the oxygen and ethylene molecules are located parallel and lie in the same plane. The calculation of the binding energy for this structure using the aug-cc-pVnZ (n = 2, 3, 4) basis sets with the extrapolation of results to the infinite basis set limit (n→∞) gives a value of 206 cm–1.

We show that a distribution of the type of the Bose-Einstein distribution describes the van der Waals gas, while the Fermi-Dirac distribution describes the van der Waals liquid. We present the construction of the binodal, the melting curve, and the liquid-to-amorphous-solid transition under negative pressure. The notion of correlation sphere and the two-scale picture on the Hougen-Watson diagram are used.

van der Waals interactions govern the physics of a plethora of molecular structures. It is well known that the leading term in the distance-based London expansion of the van der Waals energy for atomic and molecular dimers decays as $1/R^6$, where $R$ is the dimer distance. Using perturbation theory, we find the leading term in the distance-based expansion of the intracule pair density at the interatomic distance. Our results unveil a universal $1/R^3$ decay, which is less prone to numerical errors than the $1/R^6$ dependency, and it is confirmed numerically in H$_2$ and He$_2$ molecules. This \textit{signature} of van der Waals interactions can be directly used in the construction of approximate pair density and energy functionals including vdW corrections., 4 pages, 3 figures

The role of dielectric screening of electron-hole interaction in van der Waals heterostructures is theoretically investigated. A comparison between models available in the literature for describing these interactions is made and the limitations of these approaches are discussed. A simple numerical solution of Poissons equation for a stack of dielectric slabs based on a transfer matrix method is developed, enabling the calculation of the electron-hole interaction potential at very low computational cost and with reasonable accuracy. Using different potential models, direct and indirect exciton binding energies in these systems are calculated within Wannier-Mott theory, and a comparison of theoretical results with recent experiments on excitons in two-dimensional materials is discussed., 10 pages, 8 figures

The van der Waals (vdW) density functional (vdW-DF) method [ROPP 78, 066501 (2015)] describes dispersion or vdW binding by tracking the effects of an electrodynamic coupling among pairs of electrons and their associated exchange-correlation holes. This is done in a nonlocal-correlation energy term $E_c^{nl}$, which permits density functional theory calculation in the Kohn-Sham scheme. However, to map the nature of vdW forces in the fully interacting materials system, it is necessary to compensate for associated kinetic-correlation energy effects. Here we present a coupling-constant scaling analysis that also permits us to compute the kinetic-correlation energy $T_c^{nl}$ that is specific to the vdW-DF account of nonlocal correlations. We thus provide a spatially-resolved analysis of the total nonlocal-correlation binding, including vdW forces, in both covalently and non-covalently bonded systems. We find that kinetic-correlation energy effects play a significant role in the account of vdW or dispersion interactions among molecules. We also find that the signatures that we reveal in our full-interaction mapping are typically given by the spatial variation in the $E_c^{nl}$ binding contributions, at least in a qualitative discussion. Furthermore, our full mapping shows that the total nonlocal-correlation binding is concentrated to pockets in the sparse electron distribution located between the material fragments., 15 pages, 8 figures

Density functional theory in principle predicts correct ground-state properties for all materials. However, the rocksalt structure of MnO has been obtained only by the high-level random phase approximation and diffusion Monte Carlo (DMC). Here, we propose and test for MnO, FeO, CoO, and NiO that a semilocal density functional can solve this problem by properly including both self-interaction and van der Waals corrections. The importance of the latter was previously unanticipated. The MnO structural energy difference from SCAN+$r\text{VV10+}U$ agrees well with that from DMC. Here SCAN is a recent semilocal exchange-correlation functional, $r\text{VV10}$ is the revised Vydrov-Van Voorhis long-range van der Waals correction, and the onsite Hubbard $U$ is taken from linear response.

We study the van der Waals interaction of a metallic or narrow-gap semiconducting nanowire with a surface, in the regime of intermediate wire-surface distances $(v_{F}/c)L \ll d \ll L $ or $L \ll d \ll (c/v_{F})L $, where $L$ is the nanowire length, $d$ is the distance to the surface, and $v_{F}$ is the characteristic velocity of nanowire electrons (for a metallic wire, it is the Fermi velocity). Our approach, based on the Luttinger liquid framework, allows one to analyze the dependence of the interaction on the interplay between the nanowire length, wire-surface distance, and characteristic length scales related to the spectral gap and temperature. We show that this interplay leads to nontrivial modifications of the power law that governs van der Waals forces, in particular to a non-monotonic dependence of the power law exponent on the wire-surface separation., 8 pages, 5 figures, submitted to PRB

Van der Waals interactions between two neutral but polarizable systems at a separation $R$ much larger than the typical size of the systems are at the core of a broad sweep of contemporary problems in settings ranging from atomic, molecular and condensed matter physics to strong interactions and gravity. We reexamine the dispersive van der Waals interactions between two hydrogen atoms. The novelty of the analysis resides in the usage of nonrelativistic EFTs of QED. In this framework, the van der Waals potential acquires the meaning of a matching coefficient in an EFT suited to describe the low energy dynamics of an atom pair. It may be computed systematically as a series in $R$ times some typical atomic scale and in the fine structure constant $\alpha$. The van der Waals potential gets short range contributions and radiative corrections, which we compute in dimensional regularization and renormalize here for the first time. Results are given in $d$ spacetime dimensions. One can distinguish among different regimes depending on the relative size between $1/R$ and the typical atomic bound state energy $m\alpha^2$. Each regime is characterized by a specific hierarchy of scales and a corresponding tower of EFTs. The short distance regime is characterized by $1/R \gg m\alpha^2$ and the LO van der Waals potential is the London potential. We compute also NNNLO corrections. In the long distance regime we have $1/R\ll m\alpha^2$. In this regime, the van der Waals potential contains contact terms, which are parametrically larger than the Casimir-Polder potential that describes the potential at large distances. In the EFT the Casimir-Polder potential counts as a NNNLO effect. In the intermediate distance regime, $1/R\sim m\alpha^2$, a significantly more complex potential is obtained which we compare with the two previous limiting cases. We conclude commenting on the hadronic van der Waals case., Comment: Journal version. 27 pages, 11 figures

We report on the five-body repulsive and attractive van der Waals interactions between the strongly dipole-dipole coupled Rydberg states. Compared to four-body van der Waals interactions, five-body van der Waals interactions show more energy levels and more potential wells caused by avoided crossings. This research bridges the few-body physics and many-body physics. Other disciplines, such as chemistry, biology, and medical fields, will also benefit from better understanding van der Waals interactions.

The method based on fast Fourier transforms proposed by G. Rom\'an-P\'erez and J. M. Soler [Phys. Rev. Lett. 103, 096102 (2009)], which allows for a computationally fast implementation of the nonlocal van der Waals (vdW) functionals, has significantly contributed to making the vdW functionals popular in solid-state physics. However, the Rom\'an-P\'erez-Soler method relies on a plane-wave expansion of the electron density; therefore it can not be applied readily to all-electron densities for which an unaffordable number of plane waves would be required for an accurate expansion. In this work, we present the results for the lattice constant and binding energy of solids that were obtained by applying a smoothing procedure to the all-electron density calculated with the linearized augmented plane-wave method. The smoothing procedure has the advantages of being very simple to implement, basis-set independent, and allowing the calculation of the potential. It is also shown that the results agree very well with those from the literature that were obtained with the projector augmented wave method.

van der Waals forces are notoriously difficult to account for from first principles. We have performed extensive calculations to assess the usefulness and validity of diffusion quantum Monte Carlo when predicting van der Waals forces. We present converged results for noble gas solids and clusters, archetypical van der Waals dominated systems, as well as the highly relevant π-π stacking supramolecular complex: DNA + intercalating anticancer drug ellipticine. Analysis of the calculated binding energies underscores the existence of significant interatomic many-body contributions.

We investigated the structural and the binding properties of black phosphorus (black-P) by employing density functional theory (DFT) calculations in combination with various implementations of the van der Waals (vdW) interaction. Both the binding energy curve of the two isolated puckered layers and the equation of states of the bulk black-P suggest that the conventional generalized gradient approximation (GGA) functional is incapable of describing the interlayer vdW interaction. From the comparison of the seven different vdW implementations, the appropriate vdW schemes in describing layer-structured black-P are found to be either the Grimme’s dispersion correction (DFT-D2) or the optB86b vdW denisty-functional approach.

We obtain the correction due to van der Waals forces to the flexural rigidity of a layer. The cases of a monolayer and a film consisting of several monolayers are considered. The correction due to van der Waals interaction to the force acting on an indentor is obtained. Two versions of determining the elastic forces at the microlevel are considered. Numerical estimates of the parameter values for which the correction is essential are given.

We investigate effects of van der Waals (vdW) interaction on various iron-based superconductors by first-principles calculations based on the van der Waals density functional (vdW-DF) taking account of non-local and long range interaction. vdW-DF reproduces well the lattice constants of FeSe, while the crystal structure of other iron-based superconductors are not so sensitive to vdW interaction. These results suggest that the effects of vdW interaction on layered superconductors are often essential although they depend on the characters of the interlayer couplings.

As a rule, mean-field theories applied to a fluid that can undergo a transition from saturated vapor at density ρυ to a liquid at density ρl yield a van der Waals loop. For example, isotherms of the chemical potential μ(T,ρ) as a function of the density ρ at a fixed temperature T less than the critical temperature Tc exhibit a maximum and a minimum. Metastable and unstable parts of the van der Waals loop can be eliminated by the Maxwell construction. Van der Waals loops and the corresponding double minimum potentials are mean-field artifacts. Simulations at fixed μ=μcoex for ρυ

We performed an analysis of possible mechanisms of ligand recognition in the human nose. The analysis is based on in vivo odor threshold determination and in vitro Ca2+ imaging assays with a C/Si/Ge/Sn switch strategy applied to the compounds Lilial and Bourgeonal, to differentiate between different molecular mechanisms of odorant detection. Our results suggest that odorant detection under threshold conditions is mainly based on the molecular shape, i.e. the van der Waals surface, and electrostatics of the odorants. Furthermore, we show that a single olfactory receptor type is responsible for odor detection of Bourgeonal at the threshold level in humans in vivo. Carrying out a QM analysis of vibrational energies contained in the odorants, there is no evidence for a vibration-based recognition.

We construct a simple model to calculate the trimer bound state energy ${E}_{T}^{(n)}$ and three-body recombination rate ${K}_{3}^{0}$ of three identical bosons with van der Waals interaction without using any two- or three-body fitting parameter. Using this simple model, we investigate the influence of the van der Waals finite-range effect on ${E}_{T}^{(n)}$ and ${K}_{3}^{0}$. Our calculation shows that the finite-range effect leads to the ground trimer state energy ${E}_{T}^{(0)}$ not crossing the atom-dimer threshold, and the scaled three-body recombination rate ${K}_{3}^{0}/{a}^{4}$ deviating from the universal three-body theory. The results of our simple model agree within a few percent with other theoretical works with van der Waals interaction and also the experimental data.

Long-range van der Waals (vdW) interaction is critically important for intermolecular interactions in molecular complexes and solids. However, accurate modeling of vdW coefficients presents a great challenge for nanostructures, in particular for fullerene clusters, which have huge vdW coefficients but also display very strong nonadditivity. In this work, we calculate the coefficients between fullerenes, fullerene and sodium clusters, and fullerene and alkali atoms with the hollow-sphere model within the modified single-frequency approximation (MSFA). In the MSFA, we assume that the electron density is uniform in a molecule and that only valence electrons in the outmost subshell of atoms contribute. The input to the model is the static multipole polarizability, which provides a sharp cutoff for the plasmon contribution outside the effective vdW radius. We find that the model can generate ${C}_{6}$ in excellent agreement with expensive wave-function-based ab initio calculations, with a mean absolute relative error of only $3%$, without suffering size-dependent error. We show that the nonadditivities of the coefficients ${C}_{6}$ between fullerenes and ${\mathrm{C}}_{60}$ and sodium clusters ${\mathrm{Na}}_{n}$ revealed by the model agree remarkably well with those based on the accurate reference values. The great flexibility, simplicity, and high accuracy make the model particularly suitable for the study of the nonadditivity of vdW coefficients between nanostructures, advancing the development of better vdW corrections to conventional density functional theory.

We consider the the van der Waals force involving excited atoms in general environments, constituted by magnetodielectric bodies. We develop a dynamical approach studying the dynamics of the atoms and the field, mutually coupled. When only one atom is excited, our dynamical theory suggests that for large distances the van der Waals force acting on the ground-state atom is monotonic, while the force acting in the excited atom is spatially oscillating. We show how this latter force can be related to the known oscillating Casimir--Polder force on an excited atom near a (ground-state) body. Our force also reveals a population-induced dynamics: for times much larger that the atomic lifetime the atoms will decay to their ground-states leading to the van der Waals interaction between ground-state atoms., Comment: 19 pages, 4 figures

Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter. Understanding the resulting structural motifs and patterns has become increasingly important in studies of the nanoscale regime. Here we measure the paradigmatic van der Waals interactions represented by the noble gas atom pairs Ar–Xe, Kr–Xe and Xe–Xe with a Xe-functionalized tip of an atomic force microscope at low temperature. Individual rare gas atoms were fixed at node sites of a surface-confined two-dimensional metal–organic framework. We found that the magnitude of the measured force increased with the atomic radius, yet detailed simulation by density functional theory revealed that the adsorption induced charge redistribution strengthened the van der Waals forces by a factor of up to two, thus demonstrating the limits of a purely atomic description of the interaction in these representative systems., Van der Waals forces are individually weak, but on scale can drive many nano- and macroscopic processes. Here, Kawai et al. directly measure the van der Waals interactions between noble gas atom pairs and show how this changes with atom size and surface adsorption.

We present an approach for modeling nanoscale wetting and dewetting of liquid surfaces that exploits recently developed, sophisticated techniques for computing van der Waals (vdW) or (more generally) Casimir forces in arbitrary geometries. We solve the variational formulation of the Young--Laplace equation to predict the equilibrium shapes of fluid--vacuum interfaces near solid gratings and show that the non-additivity of vdW interactions can have a significant impact on the shape and wetting properties of the liquid surface, leading to very different surface profiles and wetting transitions compared to predictions based on commonly employed additive approximations, such as Hamaker or Derjaguin approximations., Comment: 5 pages (including abstract, acknowledgments, and references), 3 figures

We extend the formulation of density functional perturbation theory to treat nonlocal density functionals, accounting for van der Waals interactions, in a rigorous and efficient way. We provide a general formalism, suitable for any functional in this family, and give specific equations for the most widely used ones. We then study the lattice dynamics of graphite, comparing several nonlocal functionals and the local density approximation, showing that our recent revision of the VV10 functional [R. Sabatini et al., Phys. Rev. B 87, 041108(R) (2013)] gives the best comparison with experiments.

Working within the electric dipole approximation, the leading non-additive retarded three-body dispersion potential is evaluated. Again two virtual photons are exchanged between each coupled pair. In order to avoid the use of sixth-order perturbation theory, necessitated when the interaction Hamiltonian is linear in the electric displacement field, a canonical transformation is performed on the \(- \varepsilon_{0}^{ - 1} \vec{\mu } \cdot \vec{d}^{ \bot }\) form to yield an effective two-photon coupling Hamiltonian that is quadratic in the displacement field. Third-order perturbation theory is then used to obtain the dispersion energy shift, which holds for a scalene triangle configuration. At short inter-particle separation distance , the Axilrod-Teller-Muto result originally derived via semi-classical theory is reproduced. Explicit expressions for interaction energies corresponding to equilateral and right-angled triangle, and collinear geometries are also presented, along with their asymptotically limiting forms. Whether the dispersion force is attractive or repulsive depends on the spatial arrangement of the three objects.

We report on the calculation of electromagnetic van der Waals forces [1] between two hydrogen atoms using non-relativistic effective field theories (EFTs) of QED for large and small momentum transfers with respect to the intrinsic energy scale of the hydrogen atom. Our results reproduce the well known London and Casimir-Polder forces.

We investigated the structural and the binding properties of tetrahedral P4 molecular pairs by employing density functional theory (DFT) calculations using both the local density approximation (LDA) and the generalized gradient approximation (GGA). To consider the van der Waals interaction, we employed the GGA with dispersion correction, specifically Grimme’s approach (DFT-D2). This DFT-D2 in conjunction with the GGA (GGA-D2) well fixes the failure of the GGA in reproducing a reasonable binding energy curve. The binding energy and the equilibrium intermolecular distance are found to be in close correlation with the number of adjacent atomic pairs between two molecules. Application of the LDA and the GGA-D2 to a molecular crystal β-P4 and comparison with experiments confirms that the GGA-D2 should be used for a reliable description of P4-based molecular systems.

As the molecular shape determines the functions of a molecule, understanding molecular shapes is important for understanding the biological system of life and thus for designing drugs. To properly define a molecular shape, the definition and computation of the boundary or the surface of a molecule is the most fundamental information. Assuming the hard sphere model of atoms in a molecule, the van der Waals surface, the molecular surface (Connolly surface), and the offset surface (Lee-Richards surface) are the most common surfaces defined on a molecule in biochemistry and molecular biology. In this paper, we present important observations related to the topologies of the three types of surface on molecules and their relationships. We find that the topologies of all three surface types can be computed in O(m) time, and that the topology of one surface can be transformed to the topology of another in O(m) time, both in the worst case, where m represents the number of simplexes on the boundary of a @b-shape. The observations are made based on the recently announced theory of the @b-shape, which can be efficiently computed from the quasi-triangulation, the dual of the Voronoi diagram of a molecule.

In this article, Debye’s contributions to understanding van der Waals attractive forces, specifically, dipole-induced dipole interaction, is discussed. The Rg...HF complex structure is influenced by this interaction. Hence, these types of van der Waals molecules can be more specifically called Debye molecules.

In previous work (J. Chem. Theory Comput. 2009, 5, 719), we assessed the performance of standard semilocal exchange-correlation density functionals plus the nonempirical dispersion model of Becke and Johnson (J. Chem. Phys. 2007, 127, 154108) on binding energy curves of rare-gas diatomics. The results were encouraging. In this work, we extend our study to 65 intermolecular complexes representing a wide variety of van der Waals interactions including dispersion, hydrogen bonding, electrostatic, and stacking. Comparisons are made with other density-functional methods for van der Waals interactions in the literature.

The coagulation of dust aggregates occurs in various astrophysical environments. Each one is characterized by different conditions that influence the growth, e.g. relative velocities, composition, and size of the smallest constituents (monomers). Here we study the microphysics of collisions of dust aggregates in a four-dimensional parameter space. The parameters are the collision energy, the initial compactness of agglomerates, the mass ratio of collision partners, and the impact parameter. For this purpose we employ a state of the art molecular dynamics type of model that has been extensively and successfully tested against laboratory experiments. It simulates the motion of individual monomers interacting dynamically via van der Waals surface forces. The structure of aggregates is quantified by the filling factor that provides information about the internal structure, the packing density of monomers, and the projected surface area of aggregates. Our results show the importance of the impact parameter that causes formation of elongated particles, due to tensile forces acting in offset collisions. We also describe in detail the internal structure of the resulting aggregates. Our findings are summarized in the form of a simple collision recipe. The recipe specifies the outcome of a collision, averaged over the impact parameter. It is provided in tabular form for a range of physical parameters such as impact energy and pre-collision filling factor. The dependence on the mass ratio of impactor and target is taken into account by providing both a local and a global branch of the recipe., Comment: 18 pages, 17 figures, Astronomy and Astrophysics in press

odinger equations can be solved analytically yielding exact information about their spectra. Vigorous interest in the investigation of their behavior under the influence of external fields has been increased over the years. The main goal of the present work is to investigate the effect of a generalized van der Waals potential on the energy spectra of the hydrogen-like atoms. Our treatment is based on the Oscillator Representation Method (ORM). The energy spectrum is studied for various parameters over an atom-surface distance 50nm-300nm for different hydrogen-like atoms, like H, He + , Li 2+ , Be 3+ , B 4+ , etc.

The dipolar interaction between neutral atoms and non-resonant surfaces results in attractive potentials.We describe here techniques to probe these interactions, particulary focussing in mechanisms to selectively prepare adsorption quantum states. The control of the external degrees of freedom of atoms very close to a surface allows one, in the one hand, to get values for the parameters of the potentials between neutral atoms and solid surfaces and, on the other hand, to develop schemes to explore matter behavior at low dimensionality. As an application for the 2D confined atomic matter-wave we consider Bloch oscillation for atoms in a periodic surface potential.

Several purely repulsive potentials (PRP) are investigated theoretically. In contrast to the traditional van der Waals picture, it is found that normal gas?liquid transition emerges only on condition that the PRP as a function of particle separation holds a discontinuous point, or an indifferentiable point, or is differentiable but with an additional length scale besides the hard sphere diameter.

A special vapour cell has been built, that allows the measurement of the atom-surface van der Waals interaction exerted by a CaF2 window at the interface with Cs vapour. Mechanical and thermal fragility of fluoride windows make common designs of vapour cells unpractical, so that we have developed an all-sapphire sealed cell with an internal CaF2 window. Although impurities were accidentally introduced when filling-up the prototype cell, leading to a line-broadening and shift, the selective reflection spectrum on the Cs D1 line (894 nm) makes apparent the weak van der Waals surface interaction. The uncertainties introduced by the effects of these impurities in the van der Waals measurement are nearly eliminated when comparing the selective reflection signal at the CaF2 interface of interest, and at a sapphire window of the same cell. The ratio of the interaction respectively exerted by a sapphire interface and a CaF2 interface is found to be 0.55 $\pm$ 0.25, in good agreement with the theoretical evaluation of ~0.67., soumis \`a Appl Phys B MS 4734 B

We calculate the long-range Van der Waals force and the photoelectric cross section in a noncommutative setup. It is argued that non-commutativity effects could not be discerned for the Van der Waals interactions. The result for the photoelectric effect shows deviation from the usual commutative one, which in principle can be used to put bounds on the space–space non-commutativity parameter.

We present and discuss a variational single-product approximation to the van der Waals dispersion interaction leading to a simple formula for C 6 that seems capable to give more than 99% of the ‘exact’ value. The formula is derived from Hylleraas’ variational principle in the tensor product space of the interacting molecules and therefore enjoys bounding properties. The formula has been tested by computing the C 6 dispersion constants of H–H, and, at Full CI level, of the following systems: He–He, He–Li, Li–Li, LiH–LiH, HF–HF. Connections with the London formula are discussed.

We present results for the structural and vibrational properties of the water molecule, water dimer, and liquid water at the experimental equilibrium density, as obtained with several van der Waals density functionals. The functional form originally proposed by Dion et al. [ Phys. Rev. Lett. 2004 , 92 , 246401 ], with an appropriately chosen local exchange functional, yields a description of the liquid superior to that of the semilocal functional PBE. In particular, a specific choice of the local exchange functional (optB88) fitted to quantum chemistry calculations yields the best agreement with experimental results for pair correlation functions although it is slightly inferior to other van der Waals functionals in describing infrared spectra. When using optB88, liquid water displays a hydrogen-bonded network less tightly bound than when using the PBE approximation. The performance of optB88 is definitely inferior to that of the PBE0 hybrid functional for the isolated molecule but only moderately so for the liquid. However, the computational cost of optB88 is much less than that of hybrid functionals; therefore the use of optB88 appears to be a sensible alternative to calculations implying the evaluation of the Fock operator, in cases when simulations of large systems are required.