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Due to their current and future technological applications, including realization of water filters and desalination membranes, water adsorption on graphitic sp2-bonded carbon is of overwhelming interest. However, these systems are notoriously challenging to model, even for electronic structure methods such as density functional theory (DFT), because of the crucial role played by London dispersion forces and noncovalent interactions, in general. Recent efforts have established reference quality interactions of several carbon nanostructures interacting with water. Here, we compile a new benchmark set (dubbed WaC18), which includes a single water molecule interacting with a broad range of carbon structures and various bulk (3D) and two-dimensional (2D) ice polymorphs. The performance of 28 approaches, including semilocal exchange-correlation functionals, nonlocal (Fock) exchange contributions, and long-range van der Waals (vdW) treatments, is tested by computing the deviations from the reference interaction energies. The calculated mean absolute deviations on the WaC18 set depend crucially on the DFT approach, ranging from 135 meV for local density approximation (LDA) to 12 meV for PBE0-D4. We find that modern vdW corrections to DFT significantly improve over their precursors. Within the 28 tested approaches, we identify the best performing within the functional classes of generalized gradient approximated (GGA), meta-GGA, vdW-DF, and hybrid DF, which are BLYP-D4, TPSS-D4, rev-vdW-DF2, and PBE0-D4, respectively. [ABSTRACT FROM AUTHOR]

To understand the performance of popular density-functional theory exchange-correlation (xc) functionals in simulations of liquid water, water monomers and dimers were extracted from a PBE simulation of liquid water and examined with coupled cluster with single and double excitations plus a perturbative correction for connected triples [CCSD(T)]. CCSD(T) reveals that most of the dimers are unbound compared to two gas phase equilibrium water monomers, largely because monomers within the liquid have distorted geometries. Of the three xc functionals tested, PBE and BLYP tend to predict too large dissociation energies between monomers within the dimers. We show that this is because the cost to distort the monomers to the geometries they adopt in the liquid is systematically underestimated with these functionals. PBE0 reproduces the CCSD(T) monomer deformation energies very well and consequently the dimer dissociation energies much more accurately than PBE and BLYP. Although this study is limited to water monomers and dimers, the results reported here may provide an explanation for the overstructured radial distribution functions routinely observed in BLYP and PBE simulations of liquid water and are of relevance to water in other phases and to other associated molecular liquids. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) molecular dynamics simulations of a thin (∼15 Å) water film on NaCl(001) have been performed, with the aim of understanding the structural and dynamic properties of this important interfacial water system. The interaction of the water film with the surface orders the water molecules in the immediate vicinity of the interface. This is reflected by oscillations in the planar-averaged water density distribution along the surface normal that extend to about 8 Å from the surface. The interaction with the substrate leaves many of the water molecules in the immediate vicinity with broken hydrogen bonds and as a consequence considerably reduced dipole moments. Indeed a clear correlation between the number of hydrogen bonds which a water molecule is involved in and its dipole moment for both water on NaCl and bulk water is observed. How the DFT results obtained here compare to those obtained with various empirical potentials is briefly discussed. [ABSTRACT FROM AUTHOR]

Weak noncovalent interactions such as van der Waals and hydrogen bonding are ubiquitous in nature, yet their accurate description with electronic structure theories is challenging. Here we assess the ability of a variety of theories to describe a water-benzene binding energy curve. Specifically, we test Hartree–Fock, second-order Mo\ller–Plesset perturbation theory, coupled cluster, density functional theory with several exchange-correlation functionals with and without empirical vdW corrections, and quantum Monte Carlo (QMC). Given the relative paucity of QMC reports for noncovalent interactions, it is interesting to see that QMC and coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] are in very good agreement for most of the binding energy curve, although at short distances there are small deviations on the order of 20 meV. [ABSTRACT FROM AUTHOR]

Within the framework of the GGA+U implementation of density functional theory, we investigate atomistic and electronic structures of Au adsorbed on the stoichiometric and the defective CeO2{111} surfaces, in the latter of which either O or Ce vacancies are presented. We show that on the stoichiometric surface, the most stable adsorption site of Au is not on the top of the outermost O atoms, as previously suggested, but on a bridgelike site in which the Au directly binds to two O atoms. We suggest that on both sites, the original empty Ce 4f states near the Fermi level facilitate the oxidation of the Au; the preference of the Au for being on the bridgelike site is due to the larger O 2p-d(Au) mixing, accompanied by more significant electron redistributions. On the reduced surface with O vacancies, the most stable adsorption site of Au is near the vacancy position. Unlike that on the stoichiometric surface, strong ionic bonding character exists between Au and Ce, as the former becomes Auδ- due to the occupation of the 6s(Au) orbitals. Upon substitution for one of the Ce atoms in the lattice, the Au possesses a much stronger positive charge than that in other cases. We find that although Au is strongly bonded when it is at the Ce vacancy site, the overall binding (i.e., with the Ce vacancy formation energy being taken into account) is weaker than that for Au adsorbed at the stoichiometric surface. [ABSTRACT FROM AUTHOR]

The ability of several density-functional theory (DFT) exchange-correlation functionals to describe hydrogen bonds in small water clusters (dimer to pentamer) in their global minimum energy structures is evaluated with reference to second order Mo\ller-Plesset perturbation theory (MP2). Errors from basis set incompleteness have been minimized in both the MP2 reference data and the DFT calculations, thus enabling a consistent systematic evaluation of the true performance of the tested functionals. Among all the functionals considered, the hybrid X3LYP and PBE0 functionals offer the best performance and among the nonhybrid generalized gradient approximation functionals, mPWLYP and PBE1W perform best. The popular BLYP and B3LYP functionals consistently underbind and PBE and PW91 display rather variable performance with cluster size. [ABSTRACT FROM AUTHOR]

Hydrogen bonds are weak, generally intermolecular bonds, which hold much of soft matter together as well as the condensed phases of water, network liquids, and many ferroelectric crystals. The small mass of hydrogen means that they are inherently quantum mechanical in nature, and effects such as zero-point motion and tunneling must be considered, though all too often these effects are not considered. As a prominent example, a clear picture for the impact of quantum nuclear effects on the strength of hydrogen bonds and consequently the structure of hydrogen bonded systems is still absent. Here, we reportab initio path integral molecu.lar dynamics studies on the quantum nature of the hydrogen bond. Through a systematic examination of a wide range of hydrogen bonded systems we show that quantum nuclear effects weaken weak hydrogen bonds but strengthen relatively strong ones. This simple correlation arises from a competition between anharmonic intermolecular bond bending and intramolecular bond stretching. A simple rule of thumb is provided that enables predictions to be made for hydrogen bonded materials in general with merely classical knowledge (such as hydrogen bond strength or hydrogen bond length). Our work rationalizes the influence of quantum nuclear effects, which can result in either weakening or strengthening of the hydrogen bonds, and the corresponding structures, across a broad range of hydrogen bonded materials. Furthermore, it highlights the need to allow flexible molecules when anharmonic potentials are used in force field-based studies of quantum nuclear effects. [ABSTRACT FROM AUTHOR]

Abstract: We report ab initio path integral molecular dynamics simulations of hydrogen and deuterium adsorbed on and absorbed in the Pd(100) surface at 100K. Significant quantum nuclear effects are found by comparing with conventional ab initio molecular dynamics simulations with classical nuclei. For on-surface adsorption, hydrogen resides higher above the surface when quantum nuclear effects are included, an effect which brings the computed height into better agreement with experimental measurements. For sub-surface absorption, the classical and quantum simulations differ in an even more significant manner: the classically stable subsurface tetrahedral position is unstable when quantum nuclear effects are accounted for. This study provides insight that aids in the interpretation of experimental results and, more generally, underscores that despite the computational cost ab initio path integral molecular dynamics simulations of surface and subsurface adsorption are now feasible. [Copyright &y& Elsevier]

Abstract: Kaolinite is thought to be an efficient ice nucleating agent because kaolinite crystals expose perfect unreconstructed (001) basal surfaces which provide a suitable template for ice growth. However, we show here with the aid of density functional theory calculations that the unreconstructed basal surface is polar. Various mechanisms to eliminate the macroscopic dipole and in so-doing stabilize the basal surface are considered. The most promising option identified so far involves the adsorption of foreign atoms (for example, Na and Cl atoms) on the perfect basal surface, since this yields a non-metallic surface with a cleavage energy lower than the unreconstructed polar basal surface. A quantitative experimental structure determination of the kaolinite basal surface is called for. [Copyright &y& Elsevier]

The interaction of water molecules with metal surfaces is typically weak and as a result van der Waals (vdW) forces can be expected to be of importance. Here we account for the systematic poor treatment of vdW forces in most popular density functional theory exchange-correlation functionals by applying accurate non-local vdW density functionals. We have computed the adsorption of a variety of exemplar systems including water monomer adsorption on Al(111), Cu(111), Cu(110), Ru(0001), Rh(111), Pd(111), Ag(111), Pt(111), and unreconstructed Au(111), and small clusters (up to 6 waters) on Cu(110). We show that non-local correlations contribute substantially to the water-metal bond in all systems, whilst water-water bonding is much less affected by non-local correlations. Interestingly non-local correlations contribute more to the adsorption of water on the reactive transition metal substrates than they do on the noble metals. The relative stability, adsorption sites, and adsorption geometries of competing water adstructures rarely differ when comparing results obtained with semi-local functionals and the non-local vdW density functionals, which explains the previous success of semi-local functionals in characterizing adsorbed water structures on a number of metal surfaces. [ABSTRACT FROM AUTHOR]

Electron dispersion forces play a crucial role in determining the structure and properties of biomolecules, molecular crystals, and many other systems. However, an accurate description of dispersion is highly challenging, with the most widely used electronic structure technique, density functional theory (DFT), failing to describe them with standard approximations. Therefore, applications of DFT to systems where dispersion is important have traditionally been of questionable accuracy. However, the last decade has seen a surge of enthusiasm in the DFT community to tackle this problem and in so-doing to extend the applicability of DFT-based methods. Here we discuss, classify, and evaluate some of the promising schemes to emerge in recent years. A brief perspective on the outstanding issues that remain to be resolved and some directions for future research are also provided. [ABSTRACT FROM AUTHOR]

The van der Waals density functional (vdW-DF) of M. Dion et al. Phys. Rev. Lett. 92 246401 (2004) is a promising approach for including dispersion in approximate density functional theory exchange-correlation functionals. Indeed, an improved description of systems held by dispersion forces has been demonstrated in the literature. However, despite many applications, standard general tests on a broad range of materials including traditional "hard" matter such as metals, ionic compounds, and insulators are lacking. Such tests are important not least because many of the applications of the vdW-DF method focus on the adsorption of atoms and molecules on the surfaces of solids. Here we calculate the lattice constants, bulk moduli, and atomization energies for a range of solids using the original vdW-DF and several of its offspring. We find that the original vdW-DF overestimates lattice constants in a similar manner to how it overestimates binding distances for gas-phase dimers. However, some of the modified vdW functionals lead to average errors which are similar to those of PBE or better. Likewise, atomization energies that are slightly better than from PBE are obtained from the modified vdW-DFs. Although the tests reported here are for hard solids, not normally materials for which dispersion forces are thought to be important, we find a systematic improvement in cohesive properties for the alkali metals and alkali halides when nonlocal correlations are accounted for. [ABSTRACT FROM AUTHOR]

The article reports on the molecular dynamics of water film and salt. It mentions that the interaction between water and salt is useful in various fields of study including biology and atmospheric sciences. However, there are difficulties in the study of the native state of salt and its interaction with nanoscale water film. The article uses the density functional theory to examine interaction between water and salt.

The adsorption of aromatic molecules on metal surfaces plays a key role in condensed matter physics and functional materials. Depending on the strength of the interaction between the molecule and the surface, the binding is typically classified as either physisorption or chemisorption. Van der Waals (vdW) interactions contribute significantly to the binding in physisorbed systems, but the role of the vdW energy in chemisorbed systems remains unclear. Here we study the interaction of benzene with the (111) surface of transition metals, ranging from weak adsorption (Ag and Au) to strong adsorption (Pt, Pd, Ir, and Rh). When vdW interactions are accurately accounted for, the barrier to adsorption predicted by standard density-functional theory (DFT) calculations essentially vanishes, producing a metastable precursor state on Pt and Ir surfaces. Notably, vdW forces contribute more to the binding of covalently bonded benzene than they do when benzene is physisorbed. Comparison to experimental data demonstrates that some of the recently developed methods for including vdW interactions in DFT allow quantitative treatment of both weakly and strongly adsorbed aromatic molecules on metal surfaces, extending the already excellent performance found for molecules in the gas phase. [ABSTRACT FROM AUTHOR]

We investigate the interaction between water and metal-supported graphene through van der Waals density functional theory calculations. Our results show a systematic increase in the adsorption energy of water on graphene in the presence of underlying metal substrates. In addition, we find that the electronic nature of the graphene-metal contacts behave differently upon water adsorption: In the case of a weak, physical giaphene-metal contact, the charge carrier doping level of graphene is tuned by water, resulting in a Fermi level shift on the order of ∼100 meV. In the case of a strong chemical graphene-metal contact, the n and ix* bands of graphene are hardly perturbed by water adsorption. These results illustrate the correlated nature of the interactions between water, graphene. and metal substrates, and show that the electronic structure and the doping level of graphene can be tailored by water deposition. [ABSTRACT FROM AUTHOR]

Using a combination of scanning tunneling microscopy (STM) and density functional theory the hydrogen bond directionality and associated chirality of enantiopure clusters is visualized and controlled. This is demonstrated with methanol hexamers adsorbed on Au(111), which depending on their chirality, adopt two distinct molecular footprints on the surface. Controlled STM tip manipulations were used to interconvert the chirality of entire clusters and to break up metastable chain structures into hexamers. [ABSTRACT FROM AUTHOR]