Effects Of Dispersion Interactions Research Articles

Contributions of London Dispersion Forces to Solution-Phase Association Processes.

ConspectusDespite their ubiquity and early discovery, London dispersion forces are often overlooked. This is due, in part, to the difficulty in assessing their contributions to molecular and polymeric structure, stability, properties, and reactivities. However, recent advances in modeling have revealed that dispersion interactions play an important role in many important chemical and biological processes. Experimental confirmation of their impact in solution has been challenging, leading to controversies about their relative importance.In the course of studying noncovalent interactions using molecular devices, our understanding and appreciation for the importance of dispersion interactions have evolved. This Account follows this intellectual journey by using examples from the literature. The goals are twofold: to describe recent advances in understanding the interaction and to provide guidance to researchers studying weak noncovalent interactions. However, first, the experimental methods for measuring the effects of dispersion interactions and the strategies for isolating their influence are described. These include the design of molecular devices to measure these weak noncovalent interactions and the strategies to disentangle the solvation, solvophobic, and dispersion components of the resulting equilibria.The literature examples are organized around five fundamental questions. (1) Do dispersion interactions have a measurable effect on solution equilibria? (2) To what extent do solvents attenuate or compensate for dispersion interactions? (3) To what extent do the solvation and solvophobic terms influence the dispersion equilibria? (4) Can we predict whether a system will form attractive dispersion or repulsive steric interactions? (5) Can the dispersion term be isolated and interrogated? We were often surprised by the answers to these questions. In each case, we describe how the systems were designed to address these questions and discuss possible interpretations of the results.While dispersion interactions in solution were weak (usually <1 kcal/mol), their influence on complexation and conformational equilibria can be observed and measured. This underscores the significance of these interactions in molecular recognition, coordination chemistry, reaction design, and catalysis. The solvent components of the dispersion equilibria can also be significant. Therefore, the isolation of the dispersion contributions from the solvation and solvophobic effects represents an ongoing challenge. The experimental studies also provide important benchmarks and offer valuable insights to help refine the next generation of computational solvent models.

2D IR spectra of the intrinsic vibrational probes of ionic liquid from dispersion corrected DFT-MD simulations

We present the vibrational spectral profile of the intrinsic cationic (N-H) and anionic (C-O) probe stretch modes in methylammonium formate (MAF) using first principles molecular dynamics simulations in conjunction with the density functional theory (DFT) approaches. All simulations were performed employing Becke-Lee-Yang-Parr (BLYP) and Perdew-Burke-Ernzerhof (PBE) functionals, using three types of van der Waals (vdW) dispersion-corrected representations (D2, D3, and dispersion-corrected atom-centered one-electron potentials) and two values of plane-wave cut-off (300 and 600 Ry). The long-range electrostatic interactions, directional hydrogen bonds and non-directional van der Waals (vdW) dispersion forces are required to accurately interpret the interionic interactions in the protic ionic liquid, MAF. We compute the 2D IR correlation spectra from the wavelet-derived instantaneous frequencies obtained at each timeframe applying the cumulant expansion truncated at the second order to measure the dynamics of vibrational spectral diffusion. Here, we investigate the effects of electronic structure parameters on the spectral bands of the 2D IR contour plot. The spectral bands for both the N-H and CO stretching vibrations attain a round shape by 1 ps, indicating the loss of frequency correlation irrespective of the type of BLYP or PBE-based functionals. Further, the diagonal linewidth of the 2D IR spectral band agrees with the FWHM (full width at half maxima) of the calculated normalized vibrational stretch frequency distribution. Moreover, this study also finds the reason behind the coalescence of the symmetric and antisymmetric C-O stretches in the computed 2D IR spectra. Besides, these computational results may attract the attention of the experimental spectroscopists as it provides molecular-level interpretation and detailed ultrafast time-resolved spectral information of the intrinsic stretching vibrations and associated dynamics of the protic ionic liquid (PIL). Herein, we inspect the quality of different density functionals along with vdW dispersion corrections. However, even though the experimental data is not available for direct comparison of the results, we finally conclude that the inclusion of the effects of dispersion interactions provides a better estimation of the spectroscopic properties.

Structural and electronic properties of layered nanoporous organic nanocrystals.

In this work, we present the optimized geometric stacking of several layered nanoporous organic nanocrystals (NONs) and the stacking effect on their electronic structure. Hexagonal layered structures, C12H6-h2D, B6N6H6-h2D and C6N6-h2D are built from aromatic organic molecular units benzene, borazine and 1,3,5-triazine, respectively while oblique structures, C10N2H4-o2D, C8N4H2-o2D, C10P2H4-o2D and C10As2H4-o2D, are built from pyridine, 1,3-diazine, phosphinine and arsinine, respectively. Our density functional theory calculations show stacking energy profiles of NONs that are similar to graphene in both the stand-alone and bulk C12H6-h2D and B6N6H6-h2D structures while the rest of the studied layered materials deviate from the perfect AB stacking. The number of layers as well as the stacking configuration significantly influence the electronic properties of these materials. Indirect to direct band gap crossovers from the bulk to monolayers are observed in all of the NONs except in C6N6-h2D which exhibits a direct band gap in both the monolayer, isolated few-layers, and bulk. Furthermore, it is observed that the electronic nature of C10As2H4-o2D changes from a semiconducting character in the isolated monolayer to a metallic character in the bulk. The porous nature and the stability of these layered NONs combined with the electronic properties observed in this work point at them as valuable materials for potential applications in nanoelectronics and gas separation membranes, as well as deep ultraviolet optoelectronics and laser devices.

Возможный подход к оценке дисперсионного взаимодействия в порошковых системах

In this paper, we present the results of testing the algorithm for calculating the Hamaker constant proposed by the authors as characteristics of the dispersion interaction according to experimental data obtained by studying the composition of fine powders of basalt and polymineral sand. For this purpose, based on a number of assumptions, the concept of an analogue Hamaker constant is introduced, which is an experimentally determined quantity.This parameter is recommended to be used when choosing the quantitative ratio of powder raw materials as a criterion for assessing the maximum possible van der Waals effect of dispersion interaction. An assumption was made about the presence of a constant characteristic of a thin film wetting the analyzed surface. Moreover, this thin film has a contact angle of the transition region “film-bulk phase”, the value of which is determined by the nature of the surface and the properties of the wetting liquid. The contact angle of the transition region can be an additional quantitative criterion for the selection of materials that are compatible in nature.

Modal-Chromatic Dispersion Interaction Effects for 850 nm VCSEL Channels at 100 Gb/s per Wavelength

We present a theoretical model and experiments to estimate and measure the magnitude of modal and chromatic dispersion interaction (MCDI) over multimode optical channels using vertical-cavity surface-emitting laser (VCSEL) based transceivers. The effects of MCDI and bit error rate performance are also evaluated for PAM-4 signals at data rates from 100 Gbps to 112 Gbps. A section of the article is dedicated to the characterization of the spectral coupling between VCSEL and fiber, including a multimode and a VCSEL with a dominant fundamental mode that has shown the potential to increase the reach of MMF channels. For the experiments, several types of OM4 and OM3 fibers, with accurate bandwidth characterization over a broad range of wavelengths were utilized. The reported analysis applies to future Ethernet and Fibre Channel applications requiring ≥100 Gb/s per wavelength over multimode fibers.

Responsive Properties of Grafted Polyanion Chains: Effects of Dispersion Interaction and Salt

We study thermodynamic responsive properties of a grafted polyanion layer on a planar surface by using statistical density-functional theory. The structure and electrostatics of the grafted layer a...

Theoretical study on ionic liquids based on DBUH+: Molecular engineering and hydrogen bond evaluation

AbstractThe new generation of the ionic liquids (ILs) based on 1,8‐diazobicylo [5,4,0] undec‐7‐ene (DBU) are applied as the solvent in organic reactions. In this work, by using a theoretical procedure, the most probable interactions between the ion pairs of DBUH+ based ILs, including 10 functionalized imidazole anions were investigated. For this purpose, the electrostatic potential surfaces were analyzed to detect the most probable interaction sites of DBUH+. On the basis of the obtained results, hydrogen bond formation between the anions and DBUH+ is influenced by the electronic effect of the substituted functional groups. This means that electron donating groups, such as phenyl has a stabilizing effect on the ion pairs, while electron‐withdrawing groups, such as nitro, induces a destabilizing effect. These behaviors are described based on the interaction energy values (ΔEint). To investigate the dispersion interaction effects in ILs formation, M06‐2X‐D3 functional was applied in energy analysis. The solvent reaction field was investigated by the polarizable continuum model in ethanol and chloroform as the solvent. The results showed that ethanol has a greater effect on the interaction energy of the ILs. Finally, to have a comprehensive understanding of the charge transfer effect on the stability of the studied ILs and to characterize the most probable interactions, natural bond orbital and quantum theory of atoms in molecules analyses were applied and the obtained results were analyzed.

Simulations of volumetric hydrogen storage capacities of nanoporous carbons: Effect of dispersion interactions as a function of pressure, temperature and pore width

Simulations of the hydrogen storage capacities of activated carbons require an accurate treatment of the interaction of a hydrogen molecule physisorbed on the graphitic-like surfaces of nanoporous carbons, which is dominated by the dispersion interactions. These interactions are described accurately by high level quantum chemistry methods such as the Coupled cluster method with single and double excitations and a non-iterative correction for triple excitations (CCSD(T)), but those methods are computationally very expensive for large systems and massive simulations. Density functional theory (DFT) based methods that include dispersion interactions are less accurate, but computationally less expensive. Calculations of the volumetric hydrogen storage capacities of nanoporous carbons, simulated as benzene and graphene slit-shaped pores, have been carried out, using a quantum-thermodynamic model of the physisorption of H2 on surfaces and the interaction potential energy curves of H2 physisorbed on benzene and graphene obtained using the CCSD(T) and second order Møller-Plesset (MP2) methods and the 14 most popular DFT-based methods that include the dispersion interactions at different levels of complexity. The effect of the dispersion interactions on the DFT-based volumetric capacities as a function of the pressure, temperature and pore width is evaluated. The error of the volumetric capacities obtained with the quantum-thermodynamic model and each method is also calculated and analyzed.

Tunable Coacervation of Well-Defined Homologous Polyanions and Polycations by Local Polarity.

The ionic complexation of polyelectrolytes is an important mechanism underlying many important biological processes and technical applications. The main driving force for complexation is electrostatic, which is known to be affected by the local polarity near charge centers, but the impact of which on the complexation of polyelectrolytes remains poorly explored. We developed a homologous series of well-defined polyelectrolytes with identical backbone structures, controlled molecular weights, and tunable local polarity to modulate the solvation environment near charged groups. A multitude of systematic, accurate phase diagrams were obtained by spectroscopic measurements of polymer concentrations via fluorescent labeling of polycations. These phase diagrams unambiguously revealed that the liquidlike coacervation is more stable against salt addition at reduced local polarity over a wide range of molecular weights. These trends were quantitatively captured by a theory of complexation that incorporates the effects of dispersion interactions, charge connectivity, and reversible ion-binding, providing the microscopic design rules for tuning molecular parameters and local polarity.

Interactions of aggregating peptides probed by IR-UV action spectroscopy.

Peptide aggregation, the self-assembly of peptides into structured beta-sheet fibril structures, is driven by a combination of intra- and intermolecular interactions. Here, the interplay between intramolecular and formed inter-sheet hydrogen bonds and the effect of dispersion interactions on the formation of neutral, isolated, peptide dimers is studied using infrared action spectroscopy. Therefore, four different homo- and heterogenous dimers resulting from three different alanine-based model peptides have been formed under controlled and isolated conditions. The peptides differ from one another by the presence and location of a UV chromophore containing end cap. The conformations of the monomers of the peptides direct the final dimer structure: strongly bonded or folded structures result in weakly bound dimers. Here, intramolecular hydrogen bonds are favored over new intermolecular hydrogen bond interactions. In contrast, linear monomers are the ideal template to form parallel beta-sheet type structures. The weak intramolecular hydrogen bonds present in the linear monomers are replaced by the stronger inter-sheet hydrogen bond interactions. The influence of π-π dispersion interactions on the structure of the dimers is minimal, and the phenyl rings have a tendency to fold away from the peptide backbone to favour intermolecular hydrogen bond interactions over dispersion interactions. Quantum chemical calculations confirm our experimental observations.

Anharmonicity of the bonded O[sbnd]H group vibrations in water dimer. DFT study including dispersion interaction

Effects of the dispersion interactions on the parameters of the water dimer equilibrium configuration and IR spectra are analyzed in the paper. Dimer equilibrium geometry was calculated using a series of the density functionals, both with (B3LYP-D3, B2PLYPD, B2PLYP-D3, mPW2PLYPD, wB97XD) and without (B3LYP, B2PLYP, mPW2PLYP, wB97X) accounting of the dispersion interactions and using density functional M-06-2X that include the dispersion interaction effects. For the determined equilibrium configurations of the water dimer, IR spectra in harmonic and anharmonic (VPT2) approximations were calculated at the corresponding levels of theory. Additional analysis of the donor hydroxyl group vibrations was performed using the 3D potential energy surfaces, calculated at B3LYP/cc-pVTZ, B3LYP-D3/cc-pVTZ, B2PLYP/cc-pVTZ, B2PLYPD/cc-pVTZ, M06-2X/cc-pVTZ, wB97XD/cc-pVTZ levels of theory. Moreover, double anharmonic couplings of the analyzed modes with other vibrational modes were accounted using the “hybrid” method. Comparison of the calculated results with the experimental and theoretical data from the literature was performed.

Structure, polarity, dynamics, and vibrational spectral diffusion of liquid–vapour interface of a water–methanol mixture from first principles simulation using dispersion corrected density functional

The effects of dispersion interaction on the structural, dipolar and dynamical properties of liquid–vapour interface of an aqueous solution of methanol have been investigated through first principles simulations. A description of structural properties including the inhomogeneous density profiles of molecules, hydrogen bond distributions and orientational profiles are presented in detail. Among the dynamical properties, diffusion, orientational relaxation, hydrogen bond dynamics and vibrational spectral diffusion of molecules are determined. The variation of the polarity of the molecules from bulk to the interface are also calculated. The current first principles simulation results are compared with the results of dispersion uncorrected study. The dispersion corrected study predicts an increase in the number of molecules in their neighborhood, which are held together by non-hydrogen-bonded dispersion interactions. This results in the faster relaxation of hydrogen bonds, diffusion and rotational motion of molecules in comparison to the dispersion uncorrected study. Furthermore, the effects of dispersion correction on the dynamics of vibrational frequency fluctuations are emphasized, which clearly captures the dynamics of hydrogen bond fluctuations in the respective regions.

Water under Supercritical Conditions: Hydrogen Bonds, Polarity, and Vibrational Frequency Fluctuations from Ab Initio Simulations with a Dispersion Corrected Density Functional.

We have studied the effects of dispersion interactions on the dynamics of vibrational frequency fluctuations, hydrogen bonds, and free OD modes in supercritical heavy water at three different densities by means of ab initio molecular dynamics simulations. The vibrational spectral diffusion, as described by the frequency fluctuations, is studied through calculations of frequency time correlation of stretch modes of deuterated water, and its relations to the dynamics of hydrogen bonds and free OD modes are described. In addition, some of the other dynamical, structural, and electronic properties such as diffusion, rotational relaxation, radial distribution functions, hydrogen bond and coordination numbers, and dipole moments are also investigated from the perspectives of their variation with inclusion of dispersion interactions at varying density of the solvent. Although some changes in the structural properties are found on inclusion of dispersion corrections, no significant difference in the fluctuation dynamics of OD stretching frequencies and also in other dynamical quantities of supercritical water are found because of dispersion effects. The dynamics of water molecules under supercritical conditions is very fast compared to the corresponding dynamics under ambient conditions. The large thermal effects at such a high temperature seem to take over any relatively minor changes that might be introduced by weak dispersion interaction.

Effects of dispersion interactions on the structure, polarity, and dynamics of liquid-vapor interface of an aqueous NaCl solution: Results of first principles simulations at room temperature.

The effects of dispersion interaction on the structure, polarity, and dynamics of liquid-vapor interface of a concentrated (5.3M) aqueous NaCl solution have been investigated through first-principles simulations. Among the structural properties, we have investigated the inhomogeneous density profiles of molecules, hydrogen bond distributions, and orientational profiles. On the dynamical side, we have calculated diffusion, orientational relaxation, hydrogen bond dynamics, and vibrational spectral diffusion of molecules. The polarity of water molecules across the interface is also calculated. Our simulation results are compared with those when no dispersion corrections are included. It is found that the inclusion of dispersion correction predicts an overall improvement of the structural properties of liquid water. The current study reveals a faster relaxation of hydrogen bonds, diffusion, and rotational motion for both interfacial and bulk molecules compared to the results when no such dispersion corrections are included. The dynamics of vibrational frequency fluctuations are also calculated which capture the relaxation of hydrogen bond fluctuations in the bulk and interfacial regions. Generally, the hydrogen bonds at the interfaces are found to have longer lifetimes due to reduced cooperative effects.

The effect of Pd ensemble structure on the O2 dissociation and CO oxidation mechanisms on Au-Pd(100) surface alloys.

The reactivity of various Pd ensembles on the Au-Pd(100) alloy catalyst toward CO oxidation was investigated by using density functional theory (DFT). This study was prompted by the search for efficient catalysts operating at low temperature for the CO oxidation reaction that is of primary environmental importance. To this aim, we considered Pd modified Au(100) surfaces including Pd monomers, Pd dimers, second neighboring Pd atoms, and Pd chains in a comparative study of the minimum energy reaction pathways. The effect of dispersion interactions was included in the calculations of the O2 dissociation reaction pathway by using the DFT-D3 scheme. The addition of the dispersion interaction strongly improves the adsorption ability of O2 on the Au-Pd surface but does not affect the activation energy barriers of the Transitions States (TSs). As for O2 to dissociate, it is imperative that the TS has lower activation energy than the O2 desorption energy. DFT-D3 is found to favor, in some cases, O2 dissociation on configurations being identified from uncorrected DFT calculations as inactive. This is the case of the second neighboring Pd configuration for which uncorrected DFT predicts positive Gibbs free energy (ΔG) of the O2 adsorption, therefore an endergonic reaction. With the addition of D3 correction, ΔG becomes negative that reveals a spontaneous O2 adsorption. Among the investigated Au-Pd (100) ensembles, the Pd chain dissociates most easily O2 and highly stabilizes the dissociated O atoms; however, it has an inferior reactivity toward CO oxidation and CO2 formation. Indeed, CO strongly adsorbs on the palladium bridge sites and therefore poisoning the surface Pd chain. By contrast, the second neighboring Pd configuration that shows somewhat lower ability to dissociate O2 turns out to be more reactive in the CO2 formation step. These results evidence the complex effect of Pd ensembles on the CO oxidation reaction. Associative CO oxidation proceeds with high energy barriers on all the considered Pd ensembles and should be excluded, in agreement with experimental observations.

Delithiated states of layered cathode materials: doping and dispersion interaction effects on the structure

Here we present results of density functional theory (DFT) study of delithiated structures of layered LiNiO2 (LNO, Li12Ni12O24 model) cathode material and its doped analogue LiNi0.833Co0.083Al0.083O2 (N10C1A1, Li12Ni10CoAlO24 model). The paper is aimed at independent elucidation of doping and dispersion interaction effects on the structural stability of cathode materials studied. For this purpose, the LNO and N10C1A1 configurational spaces consisting of 87 and 4512 crystallographically independent configurations (obtained starting from 2×2×1 supercell of R-3m structure of LNO) are optimized within a number of DFT models. Based on a comparison of the calculated dependencies for the lattice parameters with the results of in situ neutron diffraction experiments, the most pronounced effect of cathode material stabilization is due to the dispersion interaction. In turn, the doping effect is found to affect cathode structure behavior at the latest stages of delithiation only.

Dynamics of vibrational spectral diffusion in water: Effects of dispersion interactions, temperature, density, system size and fictitious orbital mass

We have carried out a series of ab initio molecular dynamics simulations to investigate the effects of dispersion interactions, temperature, density, system size and fictitious orbital mass on the dynamics of vibrational spectral diffusion and other dynamical properties of liquid water. While most of the simulations are performed at room temperature, the effects of temperature are looked at by carrying out additional simulations at 25K above the reported melting point of ab initio water for our chosen density functionals. Apart from the dynamical properties, we have also looked at some of the equilibrium properties such as structure, frequency distributions and frequency-structure correlations for all the systems. In general, it is found that the inclusion of dispersion interactions makes the dynamics faster. The effects of system size, orbital mass and temperature are also discussed for the systems considered here.

Orientational order and dynamics of interfacial water near a hexagonal boron-nitride sheet: An ab initio molecular dynamics study.

Structural and dynamical properties of interfacial water molecules near a hexagonal boron nitride sheet (h-BN) are investigated by means of Born-Oppenheimer molecular dynamics simulations. Orientational profiles in the interfacial regions reveal two distinct types of water molecules near the BN surface. Depending on the positions of the water molecules, on top of either N or B atoms, one type contains water molecules that are oriented with one OH bond pointing toward the N atoms and the other type contains water molecules that remain parallel to the BN sheet. Distinct hydrogen bonding and stabilization energies of these two types of water molecules are found from our calculations. In order to see the effects of dispersion interactions, simulations are performed with the BLYP (Becke-Lee-Yang-Parr) functional and also BLYP with Grimme's D3 corrections (BLYP-D3). An enhancement of water ordering near the surface is observed with the inclusion of dispersion corrections. Further analysis of the diffusion coefficients, rotational time correlation functions, and hydrogen bond dynamics shows that water molecules near the h-BN sheet move faster compared to bulk water molecules both translationally and rotationally. The water molecules in the first layer are found to show substantial lateral diffusion. The escape dynamics of water from the solvation layer at the BN surface is also looked at in the current study. We have also investigated some of the electronic properties of interfacial water such as the charge density and dipole moment. It is found that the water molecules at the surface of the BN sheet have a lower dipole moment than bulk molecules.

The effect of dispersion interactions on the structure and performance of electrical double layer of ionic liquids

A classical density functional theory has been used to study the structure and phase behavior of the electrical double layer of a dense ionic liquid. The model for IL consists of a trimer cation (with a charged head and two neutral segments) and a monomer anion. The effect of dispersion interactions on the density profile and differential capacitance curve has been investigated. Increasing the contribution of dispersion interactions leads to a camel-shape differential capacitance curve. In the case of bell-shape curve, the maximum of the differential capacitance increases with decreasing the dispersion forces. These observations are related to the depletion or accumulation of ions near electrode with zero or low surface charge density.

First-principles investigation of the structural and electronic properties of self-assemblies of functional molecules on graphene

Graphene-based two-dimensional materials have attracted an increasing attention these last years. Among them, the system formed by molecular adsorption on, aim of modifying the conductivity of graphene and make it semiconducting, is of particular interest. We use here hierarchical first-principles simulations to investigate the energetic and electronic properties of an electron-donor, melamine, and an acceptor, NaphtaleneTetraCarboxylic DiImide (NTCDI), and the assembly of their complexes on graphene surface. In particular, the van der Waals-corrected density functional theory (DFT) method is used to compute the interaction and adsorption energies during assembly. The effect of dispersion interactions on both geometries and energies is investigated. Depending on the surface coverage and the molecular organization, there is a significant local deformation of the graphene surface. Self-assembly is driven by the competition between hydrogen bonds in the building blocks and their adsorption on the surface. The dispersion contribution accounts significantly in both intermolecular and adsorption energies. The electron transfer mechanism and density of states (DOS) calculations show the electron-donor and acceptor characters of melamine and NTCDI, respectively. Molecular adsorption affects differently the energy levels around the Fermi level differently, leading to band gap opening. These results provide information about the new materials obtained by controlling molecular assembly on graphene.