Van Der Waals Dispersion Interactions Research Articles

Optoelectronic Properties of Van Der Waals Hybrid Structures: Fullerenes on Graphene Nanoribbons.

The search for new optical materials capable of absorbing light in the frequency range from visible to near infrared is of great importance for applications in optoelectronic devices. In this paper, we report a theoretical study of the electronic and optical properties of hybrid structures composed of fullerenes adsorbed on graphene and on graphene nanoribbons. The calculations are performed in the framework of the density functional theory including the van der Waals dispersive interactions. We found that the adsorption of the C fullerenes on a graphene layer does not modify its low energy states, but it has strong consequences for its optical spectrum, introducing new absorption peaks in the visible energy region. The optical absorption of fullerenes and graphene nanoribbon composites shows a strong dependence on photon polarization and geometrical characteristics of the hybrid systems, covering a broad range of energies. We show that an external electric field across the nanoribbon edges can be used to tune different optical transitions coming from nanoribbon–fullerene hybridized states, which yields a very rich electro-absorption spectrum for longitudinally polarized photons. We have carried out a qualitative analysis on the potential of these hybrids as possible donor-acceptor systems in photovoltaic cells.

Effect of pressure on the structure and the electronic properties of LiClO4, NaClO4, KClO4, and NH4ClO4

The effect of pressure on the structural and electronic properties of lithium, sodium, potassium, and ammonium perchlorates have been studied in terms of the density functional theory with allowance for the Van der Waals dispersion interaction. The pressure dependences of the geometric parameters, the band gaps, the densities of states, the charge distributions, and the atomic charges are calculated. The compressibilities of the perchlorates are found to be anisotropic, which is due to the differences of the lattice parameters and the nature of interatomic bonds. Ammonium cation is rotated under pressure around axis b at an angle of ~9°. The band gaps of the perchlorates are ~4.5–4.7 eV and increase with pressure.

Adsorption of CO on the rutile TiO2(110) surface: a dispersion-corrected density functional theory study.

The geometry, energy and stretching frequency of carbon monoxide on the rutile TiO2(110) surface for coverages between 0.125 and 1.5 ML are investigated by means of density functional theory calculations. Four different approaches were considered, namely, the PBE exchange-correlation functional and the PBE-D2, vdW-DF and vdW-DF2 methods incorporating van der Waals dispersion interactions of different theoretical complexity and empiricism. It is found that upon the increase of the surface coverage, the adsorption becomes less favorable due to lateral destabilizing interactions between adsorbed molecules. The preferred geometry for CO changes from an upright configuration at 0.125 ML to tilted configurations at 1.5 ML and the tilting of the C-O axis from the surface normal increases with the increase of the surface coverage. At 1 ML, all computational approaches predict alternate tilted configurations which contradict the interpretation of recent experimental infrared reflection-absorption spectroscopic findings suggesting upright CO geometries. Encouragingly, a very good agreement between calculated and experimental shifts of the C-O stretching frequency of adsorbed CO at different coverages with respect to gaseous CO species was reached.

Adsorption of Ethylene and Acetylene Molecules on Ag (110) Surface

The adsorption of ethylene and acetylene molecules on Ag (110) surface has been investigated by using density-functional theory with and without consideration of dispersion (van der Waals interactions) between molecules and the surface. We find that both molecules prefer to adsorb on atop site of the step edge in comparison to the short bridge, long bridge and hollow sites. Our results indicate the weak interaction between adsorbates and substrate and the molecular geometry are almost unaffected by adsorption. The new results including dispersion in our calculations for the most stable site (atop) of ethylene and acetylene molecules on Ag (110) surface; show a good agreement with experimental adsorption energy especially for acetylene.

Exact Exchange Scheme in the Parallel r-Space Implementation of the Kohn-Sham Realization of the Density Functional Theory

In this communication, we present the r-space implementation of the Kohn‐Sham realization of the density functional theory with the exact exchange functional within the computational algorithm for computers of parallel architecture. In comparison to the standard approach employing the local density functional, the scheme with exact exchange functional requires roughly ten times larger computational burden. The developed parallelization procedure accelerates the computations by a factor of four and six for the exact exchange and the local density functional schemes, respectively. It brings us closer to the treatment of dispersive van der Waals interactions on the fully ab initio level in the large class of systems.

Many-Body Dispersion Correction Effects on Bulk and Surface Properties of Rutile and Anatase TiO2

Titanium dioxide (titania, TiO2) is a widely studied material with diverse applications. Here, we explore how pairwise and many-body descriptions of van der Waals dispersion interactions perform in atomistic modeling of the two most important TiO2 polymorphs, rutile and anatase. In particular, we obtain an excellent description of both bulk structures from density-functional theory (DFT) computations with the many-body dispersion (MBD) method of Tkatchenko and co-workers coupled to an iterative Hirshfeld partitioning scheme (“Hirshfeld-I”). Beyond the bulk, we investigate the most important crystal surfaces, namely, rutile (110), (101), and (100) and anatase (101), (100), and (001). Dispersion has a highly anisotropic effect on the different (hkl) surfaces; this directly changes the predicted nanocrystal morphology as determined from Wulff constructions. The periodic DFT+MBD method combined with Hirshfeld-I partitioning appears to be promising for future large-scale atomistic studies of this technological...

Hydrocarbon adsorption in an aqueous environment: A computational study of alkyls on Cu(111).

Hydrocarbon chains are important intermediates in various aqueous-phase surface processes, such as CO2 electroreduction, aqueous Fischer-Tropsch synthesis, and aqueous phase reforming of biomass-derived molecules. Further, the interaction between water and adsorbed hydrocarbons represents a difficult case for modern computational methods. Here, we explore various methods for calculating the energetics of this interaction within the framework of density functional theory and explore trade-offs between the use of low water coverages, molecular dynamics approaches, and minima hopping for identification of low energy structures. An effective methodology for simulating low temperature processes is provided by using a unit cell in which the vacuum space is filled with water, employing the minima hopping algorithm to search for low-lying minima, and including dispersion (van der Waals) interactions. Using this methodology, we show that a high coverage of adsorbed alkyls is destabilized by the presence of water, while a low coverage of alkyls is stabilized. Solvation has a small effect on the energetics of hydrocarbon chain growth, generally decreasing its favorability at low temperatures. We studied higher temperatures by running molecular dynamics simulations starting at the minima found by the minima hopping algorithm and found that increased temperatures facilitate chain growth. The self-consistent continuum solvation method effectively describes the alkyl-water interaction and is in general agreement with the explicit solvation results in most cases, but care should be taken at high alkyl coverage.

Ab initiophonon dispersion in crystalline naphthalene using van der Waals density functionals

Acene molecular crystals are of current interest in organic optoelectronics, both as active materials and for exploring and understanding new phenomena. Phonon scattering can be an important facilitator and dissipation mechanism in charge separation and carrier transport processes. Here, we carry out density functional theory (DFT) calculations of the structure and the full phonon dispersion of crystalline naphthalene, a well-characterized acene crystal for which detailed neutron-diffraction measurements, as well as infrared and Raman spectroscopy, are available. We evaluate the performance, relative to experiments, of DFT within the local density approximation (LDA); the generalized gradient approximation of Perdew, Burke, and Ernzerhof (PBE); and a recent van der Waals--corrected nonlocal correlation (vdW-DF-cx) functional. We find that the vdW-DF-cx functional accurately predicts lattice parameters of naphthalene within 1%. Intermolecular and intramolecular phonon frequencies across the Brillouin zone are reproduced within 7.8% and 1%, respectively. As expected, LDA (PBE) underestimates (overestimates) the lattice parameters and overestimates (underestimates) phonon frequencies, demonstrating their shortcomings for predictive calculations of weakly bound materials. If the unit cell is fixed to the experimental lattice parameters, PBE is shown to lead to improved phonon frequencies. Our study provides a detailed understanding of the phonon spectrum of naphthalene, and highlights the importance of including van der Waals dispersion interactions in predictive calculations of lattice parameters and phonon frequencies of molecular crystals and related organic materials.

Molecular Orbital Study of the Formation of Intramolecular Hydrogen Bonding of a Ligand Molecule in a Protein Aromatic Hydrophobic Pocket

The natural product argadin is a cyclopentapeptide chitinase inhibitor that binds to chitinase B (ChiB) from the pathogenic bacteria Serratia marcescens. N(ω)-Acetyl-L-arginine and L-aminoadipic acid of argadin form intramolecular ionic hydrogen bonds in the aromatic hydrophobic pocket of ChiB. We performed ab initio molecular orbital and density functional theory calculations to elucidate the role of this intramolecular hydrogen bonding on intermolecular interactions between argadin and ChiB. We found that argadin accrues large stabilization energies from the van der Waals dispersion interactions, such as CH-π, π-π, and π-lone pair interactions, in the aromatic hydrophobic pocket of ChiB, although intramolecular hydrogen bonding within argadin might result in loss of entropy. The intramolecular ionic hydrogen bonding formation canceled local molecular charges and provided good van der Waals interactions with surrounding aromatic residues.

Role of Dispersion Attraction in Differential Geometry Based Nonpolar Solvation Models

Abstract Differential geometry (DG) based solvation models have shown their great success in solvation analysis by avoiding the use of ad hoc surface definitions, coupling the polar and nonpolar free energies, and generating solvent-solute boundary in a physically self-consistent fashion. Parameter optimization is a key factor for their accuracy, predictive ability of solvation free energies, and other applications. Recently, a series of efforts have been made to improve the parameterization of these new implicit solvent models. In thiswork, we aim at studying the role of dispersion attraction in the parameterization of our DG based solvation models. To this end, we first investigate the necessity of van derWaals (vdW) dispersion interactions in the model and then carry out systematic parameterization for the model in the absence of electrostatic interactions. In particular, we explore how the changes in Lennard-Jones (L-J) potential expression, its decomposition scheme, and choices of some fixed parameter values affect the optimal values of other parameters as well as the overall modeling error. Our study on nonpolar solvation analysis offers insights into the parameterization of nonpolar components for the full DG based models by eliminating uncertainties from the electrostatic polar component. Therefore, it can be regarded as a step towards better parameterization for the full DG based model.

Stability of Complex Biomolecular Structures: van der Waals, Hydrogen Bond Cooperativity, and Nuclear Quantum Effects.

Biomolecules are complex systems stabilized by a delicate balance of weak interactions, making it important to assess all energetic contributions in an accurate manner. However, it is a priori unclear which contributions make more of an impact. Here, we examine stacked polyglutamine (polyQ) strands, a peptide repeat often found in amyloid aggregates. We investigate the role of hydrogen bond (HB) cooperativity, van der Waals (vdW) dispersion interactions, and quantum contributions to free energies, including anharmonicities through density functional theory and ab initio path integral simulations. Of these various factors, we find that the largest impact on structural stabilization comes from vdW interactions. HB cooperativity is the second largest contribution as the size of the stacked chain grows. Competing nuclear quantum effects make the net quantum contribution small but very sensitive to anharmonicities, vdW, and the number of HBs. Our results suggest that a reliable treatment of these systems can only be attained by considering all of these components.

Influence of the functionalization of imidazole on its CO2 uptake efficiency. A theoretical contribution

New capture and sequestration technologies have been proposed to mitigate CO2 emissions motivating the search for new materials such as MOF’s, ZIF’s and other porous solids. In this paper, the influence of the substitution of imidazole by different donor and acceptor groups on the CO2 uptake efficiency is analyzed. Imidazoles are important organic units of the ZIF’s.Geometries and energies of the different complexes have been optimized using the Density Functional (DFT) and Möller–Plesset (MP2) theories with cc-pVTZ and aug-cc-pVTZ atomic orbitals basis sets. For DFT calculations, the WB97XD functional, suitable for the description of dispersion forces and Van der Waals interactions, has been used. The preferred configurations of the substituted imidazoles are planar, favoring the CO2 approach to the sp2 type nitrogen. Binding energies are determined minimizing the basis set superposition error and taking into account the zero point energies. The interaction between imidazole and different greenhouse effect gases such as H2O, N2, CH4, NH3 and SO2 are also studied in order to demonstrate the selectivity of imidazole for CO2 capture. The imidazole molecules (or the ZIF’s) can then be used for selective separation of CO2 in gas mixture containing CO2, N2, and CH4 of industrial flues. However, it can be noticed that imidazoles are not adequate for gas mixture containing H2O and CO2 or NH3 and CO2. The behavior of imidazolates in dry or humid environments is predicted to be very different. The effect of the substitution of the imidazole hydrogens by one, two, or three active groups on the CO2 capture and storage is also analyzed. The selected groups are OH, CN, CH3, NH2, COH, Cl, CF3, OCH3 and C(CH3)3.

The surface and structural properties of graphite fluoride

The structural properties of graphite fluoride are not well characterized despite many experimental and theoretical studies. Computational investigations have indicated the existence of several possible stacking sequences for this material, but the methods used were incapable of adequately describing the dispersive interactions between graphite-like layers. We studied the structural and surface properties of graphite fluoride using the random phase approximation method, which provides dispersive (van der Waals) interactions with the correct asymptotic decay. The chair conformation with the AA stacking sequence is predicted to be the most stable structure, having lattice parameters of a=2.58Å, and c=5.75Å. The energetic difference between AB and ABC stacking is small, so a statistical ensemble of several stacking arrangements can be expected in graphite fluoride samples. The energy needed for the exfoliation of graphite fluoride into individual CF layers is 190mJ/m2, which is lower than the corresponding energy for graphite. The predicted surface energy of graphite fluoride is 100mJ/m2. We also measured the surface energy of graphite fluoride powder experimentally using inverse gas chromatography, yielding a value of 79±7mJ/m2 that agreed well with the computational result.

ChemInform Abstract: Van der Waals Dispersion Interactions in Molecular Materials: Beyond Pairwise Additivity

AbstractReview: [115 refs.

Electronic Structures, Bonding Configurations, and Band-Gap-Opening Properties of Graphene Binding with Low-Concentration Fluorine.

To better understand the effects of low-level fluorine in graphene-based sensors, first-principles density functional theory (DFT) with van der Waals dispersion interactions has been employed to investigate the structure and impact of fluorine defects on the electrical properties of single-layer graphene films. The results show that both graphite-2 H and graphene have zero band gaps. When fluorine bonds to a carbon atom, the carbon atom is pulled slightly above the graphene plane, creating what is referred to as a CF defect. The lowest-binding energy state is found to correspond to two CF defects on nearest neighbor sites, with one fluorine above the carbon plane and the other below the plane. Overall this has the effect of buckling the graphene. The results further show that the addition of fluorine to graphene leads to the formation of an energy band (BF) near the Fermi level, contributed mainly from the 2p orbitals of fluorine with a small contribution from the p orbitals of the carbon. Among the 11 binding configurations studied, our results show that only in two cases does the BF serve as a conduction band and open a band gap of 0.37 eV and 0.24 eV respectively. The binding energy decreases with decreasing fluorine concentration due to the interaction between neighboring fluorine atoms. The obtained results are useful for sensor development and nanoelectronics.

Two-Dimensional Hydrous Silica: Nanosheets and Nanotubes Predicted from First-Principles Simulations

Two-dimensional (2D) hydrous silica sheets (HSSs) and hydrous silica nanotubes (HSNTs) have many unique properties and potential applications. Although preparation of 2D HSSs was patented already about half a century ago, very little is known about their structure and physical properties. Here we predict formations of various kinds of 2D structures. For this purpose, a first-principles study was performed using density-functional theory (DFT) with van der Waals dispersion interaction corrections (optB88-vdW). The uneven hydrous silica sheets and nanotubes have a high stability and are composed of hexagonal rings. The calculations also showed that a bilayer of anhydrous silica sheets is highly stable. Furthermore, the formation of defects which can induce a transition to glassy silica was investigated. The predicted high stability and versatility of these 2D materials offer many opportunities for more extensive developments, including doping with extrinsic elements to functionalize the nanosheets and nanot...

Density Functional Theory Study of Adsorption of Benzotriazole on Cu2O Surfaces

The adsorption of benzotriazole, an outstanding corrosion inhibitor, was characterized on Cu2O surfaces using density functional theory (DFT) calculations. Cu2O surfaces contain two distinct Cu sites: coordinatively saturated (CSA) and coordinatively unsaturated (CUS). The following surfaces were considered: (i) Cu2O(111); (ii) Cu2O(111)-w/o-CuCUS, which lacks the CUS copper sites; and (iii) Cu2O(110):CuO, which is CuO-terminated Cu2O(110). Neutral benzotriazole (BTAH) binds weakly (by about −0.4 and −0.7 eV as calculated with the PBE functional) to CSA copper sites on Cu2O(111)-w/o-CuCUS and Cu2O(110):CuO, respectively. These binding energies are comparable to those obtained on metallic Cu(111) and Cu(110). In contrast, BTAH binds rather strongly to CUS copper sites (about −1.5 eV), which is even stronger than the bonding to very-low-coordinated surface defects on metallic Cu surfaces. Indeed, this bonding is so strong that it overcompensates for a thermodynamic deficiency of stoichiometric Cu2O(111). Hence, the BTAH-covered Cu2O(111) is thermodynamically more stable than the BTAH-covered Cu2O(111)-w/o-CuCUS. Similar to results reported previously for metallic Cu surfaces, a deprotonated benzotriazole also bonds much more strongly on Cu2O surfaces than the neutral BTAH does. Its binding energies on CSA sites range from −1.7 to −2.0 eV (depending on details), and on CUS sites they are about −2.8 eV (as measured with respect to the BTA• radical in the gas phase). Despite this relatively strong bonding, the dissociation of BTAH (N–H bond cleavage) is slightly endothermic on Cu2O surfaces. The impact of van der Waals dispersion interactions on adsorption bonding was also addressed, and their main effect is to strengthen the molecule–surface bonding on average by about 0.4 eV, but otherwise the relative stability trends among various adsorption forms largely remain the same. The observation that benzotriazole binds much more strongly to coordinatively unsaturated copper sites on oxidized surfaces and to undercoordinated defects on metallic Cu surfaces (compared to regular sites) may indicate its ability to passivate reactive surface sites.

Understanding the Adsorption Mechanism of Xe and Kr in a Metal-Organic Framework from X-ray Structural Analysis and First-Principles Calculations.

Enhancement of adsorption capacity and separation of radioactive Xe/Kr at room temperature and above is a challenging problem. Here, we report a detailed structural refinement and analysis of the synchrotron X-ray powder diffraction data of Ni-DODBC metal organic framework with in situ Xe and Kr adsorption at room temperature and above. Our results reveal that Xe and Kr adsorb at the open metal sites, with adsorption geometries well reproduced by DFT calculations. The measured temperature-dependent adsorption capacity of Xe is substantially larger than that for Kr, indicating the selectivity of Xe over Kr and is consistent with the more negative adsorption energy (dominated by van der Waals dispersion interactions) predicted from DFT. Our results reveal critical structural and energetic information about host-guest interactions that dictate the selective adsorption mechanism of these two inert gases, providing guidance for the design and synthesis of new MOF materials for the separation of environmentally hazardous gases from nuclear reprocessing applications.

Conformational analysis of biphenyls: an upside-down view

© Rzepa This article is distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and redistribution in any medium, provided that the original author and source are credited. One of the (not a few) pleasures of working in a university is the occasional opportunity that arises to give a new lecture course to students. New is not quite the correct word, since the topic I have acquired is Conformational analysis. The original course at Imperial College was delivered by Derek Barton himself about 50 years ago (for articles written by him on the topic, see DOI 10.1126/science.169.3945.539 or the original 10.1039/QR9561000044), and so I have had an opportunity to see how the topic has evolved since then, and perhaps apply some quantitative quantum mechanical interpretations unavailable to Barton himself.

Adsorption thermodynamics of C1–C4 alcohols in H-FAU, H-MOR, H-ZSM-5, and H-ZSM-22

The adsorption thermodynamics of C1–C4 primary alcohols in large-pore (H-FAU and H-MOR) and medium-pore (H-ZSM-5 and H-ZSM-22) zeolites is quantified using combined periodic DFT-D – statistical thermodynamic calculations. The increase of adsorption equilibrium coefficients with increasing carbon number of the alcohol and with decreasing pore size of the zeolite is attributed to the well-known dispersive van der Waals interactions. Although electrostatic interactions increase in the order: H-FAU<H-ZSM-5≈H-MOR<H-ZSM-22, an interplay with other factors including zeolite acid strength, framework flexibility, and steric constraints globally renders non-dispersive interactions largely similar among the four zeolites. Also, the shape selectivity is probed for adsorption of n-butanol, i-butanol, 2-butanol, and t-butanol at the straight and zigzag channels of H-ZSM-5. A compensation between entropy and enthalpy leads to a difference of at most two orders of magnitude in the adsorption equilibrium coefficient between the two channels.