Influence Of Dispersion Interactions Research Articles

Influence of Dispersion Interactions in the Diels-Alder Reaction of Cyclopentadiene, Anthracene and Tetracene with C60: A DFT Examination

Asbtract: The activation and thermodynamic parameters of the Diels-Alder reaction of cyclopentadiene, anthracene and tetracene with C60 fullerene are estimated at the DFT level using PBE0, B3LYP and CAM-B3LYP functionals and the effect of accounting for dispersion interactions in various semi-empirical Grimme models on these parameters. Structural characteristics of the reagents, products, pre-reaction van der Waals complex, and transition state are obtained. Taking into account dispersion corrections have practically no effect on the geometric characteristics of structures with the covalent type of the bond, as well as on the structure of the transition state. Still, it has a noticeable effect only on the structure of the pre-reaction complex, in which the interparticle interaction has a van der Waals character. At the same time, taking into account dispersion corrections plays a significant role in assessing the thermodynamic and activation parameters of the reaction. An analysis of the performed calculations showed that the combination of PBE0/def2-TZVP with the D4 model for dispersion interactions could be recommended for the Diels-Alder reaction considered above.

Influence of Dispersion Interactions on the Polymorphic Stability of Crystalline Oxides.

The accurate determination of relative phase stabilities using DFT methods is a significant challenge when some of these can vary by only a few kJ/mol. Here, we demonstrate that for a selection of oxides (TiO2, MnO2, and ZnO) the inclusion of dispersion interactions, accomplished using the DFT-D3 correction scheme, allows for the correct ordering and an improved calculation of the energy differences between polymorphic phases. The energetic correction provided is of the same order of magnitude as the energy difference between phases. D3-corrected hybrid functionals systematically yield results closest to experiment. We propose that the inclusion of dispersion interactions makes a significant contribution to the relative energetics of polymorphic phases, especially those with different densities, and should therefore be included for calculations of relative energies using DFT methods.

Probing driving forces for binding between nanoparticles and amino acids by saturation-transfer difference NMR

As nanotechnology becomes increasingly used in biomedicine, it is important to have techniques by which to examine the structure and dynamics of biologically-relevant molecules on the surface of engineered nanoparticles. Previous work has shown that Saturation-Transfer Difference (STD)-NMR can be used to explore the interaction between small molecules, including amino acids, and the surface of polystyrene nanoparticles. Here we use STD-NMR to further explore the different driving forces that are responsible for these interactions. Electrostatic effects are probed by using zwitterionic polystyrene beads and performing STD-NMR experiments at high, low, and neutral pH, as well as by varying the salt concentration and observing the effect on the STD buildup curve. The influence of dispersion interactions on ligand-nanoparticle binding is also explored, by establishing a structure–activity relationship for binding using a series of unnatural amino acids with different lengths of hydrophobic side chains. These results will be useful for predicting which residues in a peptide are responsible for binding and for understanding the driving forces for binding between peptides and nanoparticles in future studies.

Gas-phase structure of 1,8-bis[(trimethylsilyl)ethynyl]anthracene: cog-wheel-type vs. independent internal rotation and influence of dispersion interactions.

The gas-phase structure of 1,8-bis[(trimethylsilyl)ethynyl]anthracene (1,8-BTMSA) was determined by a combined gas electron diffraction (GED)/mass spectrometry (MS) experiment as well as by quantum-chemical calculations (QC). DFT and dispersion corrected DFT calculations (DFT-D3) predicted two slightly different structures for 1,8-BTMSA concerning the mutual orientation of the two -C-C[triple bond, length as m-dash]C-SiMe3 units: away from one another or both bent to the same side. An attempt was made to distinguish these structures by GED structural analysis. To probe the structural rigidity, a set of Born-Oppenheimer molecular dynamics (BOMD) calculations has been performed at the DFT-D level. Vibrational corrections Δr = ra - re were calculated by two BOMD approaches: a microcanonically (NVE) sampled ensemble of 20 trajectories (BOMD(NVE)) and a canonical (NVT) trajectory thermostated by the Noose-Hoover algorithm (BOMD(NVT)). In addition, the conventional approach with both, rectilinear and curvilinear approximations (SHRINK program), was also applied. Radial distribution curves obtained with models using both MD approaches provide a better description of the experimental data than those obtained using the rectilinear (SHRINK) approximation, while the curvilinear approach turned out to lead to physically inacceptable results. The electronic structure of 1,8-BTMSA was investigated in terms of an NBO analysis and was compared with that of the earlier studied 1,8-bis(phenylethynyl)anthracene. Theoretical and experimental results lead to the conclusion that the (trimethylsilyl)ethynyl (TMSE) groups in 1,8-BTMSA are neither restricted in rotation nor in bending at the temperature of the GED experiment.

Corresponding-states behavior of a dipolar model fluid with variable dispersion interactions and its relevance to the anomalies of hydrogen fluoride.

More than two decades ago, the elusiveness of a liquid-vapor equilibrium and a corresponding critical point in simulations of the supposedly simple model of dipolar hard spheres came as a surprise to many liquid matter theorists. van Leeuwen and Smit [Phys. Rev. Lett. 71, 3991 (1993)] showed that a minimum of attractive dispersion interactions among the dipolar particles may be needed to observe regular fluid behavior. Here, we adopt their approach and use an only slightly modified model, in which the original point dipole is replaced by a dipole moment produced by charges that are separated in space, to study the influence of dispersion interactions of variable strength on the coexistence and interfacial properties of a polar fluid. The thermophysical properties are discussed in terms of Guggenheim's corresponding-states approach. In this way, the coexistence curve, the critical compressibility factor, the surface tension, Guggenheim's ratio, and modifications of Guldberg's and Trouton's rules (related to the vapor pressure and the enthalpy of vaporization) are analyzed. As the importance of dispersion is decreased, a crossover from simple-fluid behavior to that characteristic of strongly dipolar systems takes place; for some properties, this transition is monotonic, but for others it occurs non-monotonically. For strongly dipolar systems, the reduced surface tension is very low, whereas Guggenheim's ratio and Guldberg's ratio are found to be high. The critical compressibility factor is smaller, and the coexistence curve is wider and more skewed than for simple fluids. For very weak dispersion, liquid-vapor equilibrium is still observable, but the interfacial tension is extremely low and may, eventually, vanish marking the end of the existence of a liquid phase. We discuss the implications of our findings for real fluids, in particular, for hydrogen fluoride.

The influence of dispersion interactions on the hydrogen adsorption properties of expanded graphite

We demonstrate the importance of London dispersion forces in defining the adsorption capacity within expanded graphite, a simple model of the more complex experimental geometries of activated carbon, using a combination of the non-local correlation functional of Dion et al paired with a recent exchange functional of Cooper (vdW-DFC09x) and a classical continuum model. Our results indicate that longer ranged interactions due to dispersion forces increase the volume over which molecules interact with a porous medium. This significantly enhances the adsorption density within a material, and explains recent experimental work showing that the densification of H2 in carbon nanopores is sensitive to the pore size. Remarkably, our slit pore geometries give adsorption densities of up to 3 wt% at 298 K and 20 MPa which correlates well with experimental values for 9 Å pores—a value that could not be predicted using local density approximation (LDA) calculations. In its entirety, this work presents a powerful approach for assessing molecular uptake in porous media and may have serious impacts on efforts to optimize the properties of these materials.

A DFT-D study of structural and energetic properties of TiO2 modifications

The structures and relative energies of the three naturally occurring modifications of titanium dioxide (rutile, brookite and anatase) were investigated. For an accurate description, atom-pairwise dispersion-corrected density functional theory (DFT-D) was applied. The DFT-D3 scheme was extended non-empirically to improve the description of Ti atoms in bulk systems. New dispersion coefficients were derived from TDDFT calculations for electrostatically embedded TiO2 clusters. The dispersion coefficient is reduced by a factor of 18 compared to the free atom. The three TiO2 modifications were optimized in periodic plane-wave calculations with dispersion-corrected GGA (PBE, revPBE) and hybrid density functionals (PBE0, revPBE0). The calculated lattice parameters are in good agreement with experimental data, in particular the dispersion-corrected PBE0 and revPBE0 hybrid functionals. Although the observed relative stabilities could not be reproduced in all cases, dispersion corrections improve the results. For an accurate description of bulk metal oxides, London dispersion is a prominent force that should not be neglected when energies and structures are computed with DFT. Additionally, the influence of dispersion interactions on the relaxation of the TiO2(110) surface is investigated.

Influence of dispersion interactions on the adsorption of PTCDA on Ag(110)

AbstractThe interaction of PTCDA with Ag(110) is analysed with second order Møller‐Plesset perturbation theory (MP2), including the main part of the dispersion interactions at an ab initio level. On rigid substrate clusters, the optimized adsorbate geometry consists of a nearly flat perylene core, surrounded by carboxylic oxygens closer to the substrate, but with anhydride atoms at a larger height. The average height of the carbon core is found at 2.68 Å, in excellent agreement with the value of 2.59 Ädetermined in recent X‐ray standing wave measurements. In sharp contrast to the rather flat MP2 geometry, the lack of dispersion interactions in density functional theory (DFT) results in an unrealistic bent adsorbate geometry. The calculated core level shifts and the vibrational fingerprint reproduce the observed trends. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of dispersive interactions on the binding affinities of ligands with an arylpiperazine moiety to the dopamine D2 receptor

Several isosteric 1,3-dihydro-5-[2-(4-aryl-1-piperazinyl)ethyl]-2H-benzimidazole-2-thiones were used to investigate the interactions of different ligands with the binding site of the D2 receptor. Due to limitations of the simulation methods, docking analysis failed to show precisely the interactions that influence the binding affinity of the ligands. It is presumed that dispersive forces or more precisely edge-to-face interactions play an important role in the binding process, especially for the lipophilic part of the ligands. In order to confirm this hypothesis, ab initio calculations were applied on a model system in order to find the stabilization energies of potential edge-to-face interactions and then to correlate them with the ligand affinity. The obtained results indicate that there is a significant correlation between the strength of dispersive interactions and ligand affinity. It was shown that for the calculation of stabilization energies of modeled receptor-ligand complexes the Becke 'half-and-half' hybrid DFT method can be used, thus speeding up the usually long calculation time and reducing the required computer strength.