Inclusion Of Dispersion Interactions Research Articles

Cyclometalated C^C* Platinum(IV) NHC Complexes.

We present a previously unknown series of cyclometalated platinum(IV) NHC complexes, obtained by oxidative addition of iodine, iodomethane, and different benzyl bromides to platinum(II) complexes with cyclometalated C^C* dibenzofuran, dibenzothiophene, and phenylimidazole ligands together with an acetylacetonate ligand. All compounds were characterized by standard techniques (1H, 13C, and 195Pt NMR and elemental analysis), and for three complexes, solid-state structures could be obtained. DFT calculations (B3LYP(d3)/def2-TZVPP including dispersion interactions in dichloromethane and acetone) were performed to investigate the mechanism of the oxidation and explain the exclusive formation of the observed trans products.

First-principles molten salt phase diagrams through thermodynamic integration.

Precise prediction of phase diagrams in molecular dynamics simulations is challenging due to the simultaneous need for long time and large length scales and accurate interatomic potentials. We show that thermodynamic integration from low-cost force fields to neural network potentials trained using density-functional theory (DFT) enables rapid first-principles prediction of the solid-liquid phase boundary in the model salt NaCl. We use this technique to compare the accuracy of several DFT exchange-correlation functionals for predicting the NaCl phase boundary and find that the inclusion of dispersion interactions is critical to obtain good agreement with experiment. Importantly, our approach introduces a method to predict solid-liquid phase boundaries for any material at an abinitio level of accuracy, with the majority of the computational cost at the level of classical potentials.

Dispersion interactions in proposed covalent superhydride superconductors

Recent developments in high temperature superconducting materials under high pressure have made numerical evaluation of the superconducting transition temperature (${T}_{c}$) of predicted materials critically important as a means to identification. Existing methods of calculating ${T}_{c}$ often do not agree with each other or experiment, often due to the large number of complex factors that contribute to this property; among them is the neglect of dispersion interactions in commonly used density functionals. Here, we evaluate the effect of including dispersion interactions on the predicted superconducting properties of two examples of the covalent superhydride class of very high-${T}_{c}$ superconducting materials. In both cases, dispersion is found to have sizable effects, increasing the electron-phonon coupling as compared to the reference case of elemental niobium. A detailed investigation traces the origin of this effect in a 270 GPa $R3m\phantom{\rule{4pt}{0ex}}\mathrm{C}\mathrm{S}{\mathrm{H}}_{7}$ [Cui et al., Phys. Rev. B 101, 134504 (2020)] structure to structural distortions driven by long-range electron-phonon interactions rather than novel bonding networks.

Nitrogen-doped carbon oxide quantum dots for flexible humidity sensor: Experimental and SCC-DFTB study

A flexible resistive-type humidity sensor based on N-type nitrogen-doped carbon oxide quantum dots (NCQDs) is presented. The NCQDs were synthesized by using simple hydrothermal method with reactions via citric acid and urea. The UV–vis, FE-TEM and XPS analysis confirm a successful doping of N atoms and existence of oxygen-containing functional groups into carbon quantum dots with the homogeneous spherical structure. The NCQDs humidity sensor exhibits high humidity response, good repeatability, and high stability as well as linear response to humidity in the range of 20–90% RH. The humidity sensing mechanism has been in-depth investigated by self-consistent charge density functional tight-binding (SCC-DFTB) including dispersion interaction. The SCC-DFTB reveals an important role of N doping with physisorption via direct charge transfer sensing mechanism.

Adsorption of polycyclic aromatic hydrocarbons on FeOOH polymorphs: A theoretical study

In this work we studied interactions of polycyclic aromatic hydrocarbons (PAHs) with surfaces of two iron oxyhydroxide polymorphs, goethite and lepidocrocite, by means of density functional theory (DFT) method. The first focus here was to obtain adsorption energies of selected PAH molecules with the (110) goethite surface and the (010) lepidocrocite surface by performing DFT calculations with the inclusion of dispersion interactions. To this end we have performed assessment of six different methods to show their efficiency and predictability of nonbonding interactions. The second objective was to compare adsorption capability of two FeOOH polymorphs, goethite and lepidocrocite, as common minerals in several soil types and to relate obtained adsorption energies to different surface structure and topology of the most stable surfaces of both polymorphs. The goethite (110) surface has more complicated topology and three different types of OH groups compared to the lepidocrocite (010) surface formed by a plane of OH groups of the same type. For goethite, adsorption energy did not increase monotonically with the increasing molecular size of PAHs and the strongest adsorption was observed for the linearly-shaped anthracene molecule. On the other hand, adsorption of PAHs at the lepidocrocite surface increased energetically with increasing molecular weight, and the strongest adsorption was achieved for the pyrene molecule. The results showed that the goethite (110) surface is more attractive than the (010) lepidocrocite surface, which is explained by the different surface topology, and types and surface density of the OH groups.

An Extended Benchmark of Density Functionals for Calculating the Standard Reduction Potentials of Vanadium Compounds

An extended benchmark study has been performed to find out a robust and accurate density functional for calculating the standard reduction potentials of vanadium compounds. Twenty eight density functionals of various types were chosen for testing. The effect of the functional nature, size of the basis set, and inclusion of dispersion interaction in the calculation on the accuracy of the results were studied. Among the tested functionals the smallest deviation from the experimental data was found for the meta-NGA functional MN12-L. Based on these results, the computational protocol was proposed for studies of the redox reactions of vanadium compounds.

Multiscale Study of the Mechanism of Catalytic CO2 Hydrogenation: Role of the Ni(111) Facets

The molecular mechanism of CO2 hydrogenation on a Ni(111) surface has been thoroughly investigated by means of periodic density functional theory calculations, including dispersion interactions, along with accurate kinetic Monte Carlo simulations, including lateral interactions between the adsorbates. The present reaction model involves 25 different species and a total of 86 elementary processes, including adsorptions, desorptions, surface chemical steps, and diffusions. The reaction network accounts for three different mechanisms for the reverse water-gas shift reaction and three different mechanisms for methanation. The kinetic Monte Carlo simulations reveal that the reverse water-gas shift reaction dominates the CO2 hydrogenation on Ni(111) with no evidence of methane formation. The reaction proceeds mainly through the redox route, with the carboxyl pathway also being active but to a lesser extent. Methane production is hindered by the H + CO → HCO endothermicity and the prohibitive energy barrier for CO dissociation, implying CO desorption rather than evolution through the Sabatier reaction. A detailed comparison to earlier theoretical studies supporting the methanation reaction shows that some unreliable assumptions along with limited theoretical approaches biased the former conclusion.

Aluminum adsorption on graphene: Theoretical study of dispersion effects

The interaction between a single atom and graphene is an example in which the density functional theory (DFT) presents serious difficulties in giving an appropriate description of the adsorbate–substrate interaction, giving also different predictions according to the chosen approximation. The present calculations sustain that the inclusion of dispersion interactions in the framework of DFT for the Al/graphene system lead to potential energy curves of different nature according to the theoretical approach employed. The adsorption of an Al atom on the graphene surface was studied using both cluster and slab models. Cluster DFT–PBE calculations show the presence of a minimum at hollow site at an Al–graphene distance of about 2.1–2.3 Å corresponding to an exothermic state. Conversely, under B3LYP the same adsorption mode is endothermic. In comparison, our MP2 reference calculations predict the formation of two minima, both of exothermic nature, separated by an important energy barrier (about 0.2–0.4[Formula: see text]eV). The incorporation of empirical van der Walls (vdW) corrections to B3LYP changes the original behavior, giving an exothermic adsorption; furthermore, it produces a second, more external minimum. Slab calculations with PBE, and specially using the vdW-DF2 functional, predict also the formation of a minimum of very low depth at about 3.1 Å. The analysis of results obtained with cluster and slab models sustains that the bonding of the inner minima is of ionic character while that of the external ones is of dispersion character.

Does (H5O2)+− X (X = Ar, Ne, He) complex with C2 symmetry really exist?

Different configurations of (H5O2)+− Ar, (H5O2)+− Ne and (H5O2)+− He complexes were calculated using DFT methods and series of Dunning and Pople basis sets. The possibility of the existence of an equilibrium configuration with C2 symmetry for complexes analyzed was in focus of the studies carried out. DFT methods that do not take into account dispersion interactions, as a rule, define (H5O2)+− X (X = Ar, Ne, He) configurations with C2 symmetry as transitional states. At the same time, such DFT methods as B1B95, B98, and WB97X make it possible to determine geometric parameters of these complexes with C2 symmetry in equilibrium configurations. Taking into account dispersion interactions in the framework of D3 Grimme approach and using density functionals, including dispersion interactions (such as M06-2X, wB97XD, etc.), leads to the situation, when configurations of the complexes such as (H5O2)+− X (X = Ar, Ne, He) with C2 symmetry calculated using most of the basis sets turn out to be equilibrium. However, calculations within the framework of MP2, MP4, and CCSD (T) methods determine configurations of complexes with C2 symmetry as transition states, while the experimental data on the IR spectra of (H5O2)+− Ar complex probably point out to the existence of an equilibrium configuration of this complex with C2 symmetry. In addition to structural analysis for equilibrium configurations found, IR spectra were calculated in harmonic and in some cases also in anharmonic approximations. Calculated IR spectra were compared to protonated water dimer IR spectra calculated at the same level of theory in equilibrium configuration and in the transition state.

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.

Benchmarking the performance of approximate van der Waals methods for the structural and energetic properties of SiO2 and AlPO4 frameworks.

Density functional theory (DFT) calculations using sixteen different approaches, fourteen of which were designed to include dispersion interactions [DFT + D and van der Waals (vdW)-DF methods], were performed for a set of sixteen framework compounds with either SiO2 or AlPO4 composition. The compounds include four dense structures (α-quartz, α-cristobalite, and their AlPO4 analogues), eight all-silica zeolites, and four aluminophosphate zeotypes (AlPOs). We analyzed the performance in reproducing the equilibrium structure for all systems, and computed bulk moduli and relative stabilities were compared to experiments for those compounds where experimental data are available. We found that the results obtained with functionals that take into account dispersive interactions are closer to experiments than those obtained with a bare generalized gradient functional. However, the variation among individual methods is considerable, and functionals that perform well for one quantity may give rather large deviations for another. Taking together the whole body of results, it appears that the Perdew-Burke-Ernzerhof functional including a many-body dispersion correction and the rev-vdW-DF2 methods present the best performance for the description of SiO2 and AlPO4 materials.

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.

Experimental and Theoretical Investigation on the Origin of the High Intercalation Voltage of K2Zn3[Fe(CN)6]2 Cathode

K2Zn3[Fe(CN)6]2 was investigated as a cathode for K-ion batteries and compared to its sodium analog. The hexacyanometallate using K+ as intercalating ion shows interesting electrochemical properties: i) The redox processes occur at higher potentials, ii) From the two redox processes, the one occurring at higher potentials displays most of the specific capacity while the insertion of sodium occurs mostly at lower potentials, iii) the specific capacity of both materials is similar and iv) although the hysteresis at higher potentials is higher with K+ than with Na+, the occurrence of deintercalation at higher potentials presents undoubtedly more advantages. In the attempt to explain this behavior, electronic structure calculations show that a transition from insulating to conducting behavior occurs as the system changes from discharged to charged states. The electronic density distributions of the hosts are similar independently if K+ or Na+ ions are intercalated. It is found that the inclusion of dispersion interactions is essential to match the intercalation voltages experimentally observed. Thus, dispersion forces are very important to understand the interactions of the ion with the host and should be considered when designing cathodes for K-ion batteries using hexacyanometallate.

Vibrational spectral diffusion in supercritical deuterated ammonia from first principles simulations: Roles of hydrogen bonds, free ND modes and inertial rotation of ammonia molecules

We have presented a first principles study of the vibrational spectral diffusion and related dynamical and structural properties of supercritical ammonia at two different densities by means of ab initio molecular dynamics and time series analysis. The ab initio simulations are performed using two density functionals for the electronic structure calculations: one without any dispersion corrections and the other with dispersion corrections. Apart from calculating the dynamics of frequency fluctuations of ND modes of deuterated ammonia in supercritical states, we have also at many other related quantities such as the dynamics of hydrogen bonds and free ND groups, rotational and translational motion of ammonia molecules and also some of the equilibrium quantities such as local density distributions, pair correlations, hydrogen bonding properties and dipole distribution of ammonia molecules. It is found that the hydrogen bonding between ammonia molecules decreases significantly as we move to the supercritical state of lower density from the normal liquid phase. The inclusion of dispersion interactions is found to increase the structural correlations and also the number of hydrogen bonds to some extent. Our calculations of ND frequency distributions reveal that as we move from normal to the supercritical states, the frequency distributions become narrower and show a shift toward the higher frequencies which is in general agreement with experimental results. the frequency time correlation function of the ND modes of ammonia molecules. The frequency time correlation function of the ND modes of ammonia molecules in the supercritical states is found to decay with two time scales: One around 80–100 fs and the other one falls in the region of 350–700 fs. Our calculations of the dynamics of hydrogen bonds, free ND modes and also rotational motion of ND groups in supercritical ammonia reveal that the fast hydrogen bond breaking and inertial rotational motion of ND bonds contribute to the faster component of spectral diffusion of ND bonds while the slower component originates from the dynamics of non-hydrogen-bonded free ND bonds.

Realistic Large‐Scale Modeling of Rashba and Induced Spin–Orbit Effects in Graphene/High‐Z‐Metal Systems

AbstractGraphene, as a material with a small intrinsic spin–orbit interaction of approximately 1 µeV, has a limited application in spintronics. Adsorption of graphene on the surfaces of heavy metals was proposed to induce the strong spin splitting of the graphene π bands either via Rashba effect or due to the induced spin–orbit effects via hybridization of the valence band states of graphene and metal. Spin‐resolved photoelectron spectroscopy experiments performed on graphene adsorbed on the substrates containing heavy elements demonstrate the “giant” spin splitting of the π states of the order of 100 meV in the vicinity of the Fermi level (EF) and the K point. However, recent scanning tunneling spectroscopy experiments did not confirm these findings, leaving the fact of the observation of the “giant” Rashba effect or induced spin–orbit interaction in graphene still open. Thus, a detailed understanding of the physics in such systems is indispensable. From the theory side, this requires, first of all, correct modeling of the graphene/metal interfaces under study. Here, realistic super‐cell density‐functional theory calculations are presented, including dispersion interaction and spin–orbit interaction, for several graphene/high‐Z‐metal interfaces. While correctly reproducing the spin‐splitting features of the metallic surfaces, their modifications under graphene adsorption and doping level of graphene, it is revealed that neither “giant” Rashba‐ nor spin–orbit‐induced splitting of the graphene π states around EF take place.

Two tris-(3,5-disubstituted phen-yl)phosphines and their isostructural PV oxides.

The crystal structures of tris-(3,5-di-methyl-phen-yl)phosphine (C24H27P), (I), tris-(3,5-di-methyl-phen-yl)phosphine oxide (C24H27OP), (II), tris-(4-meth-oxy-3,5-di-methyl-phen-yl)phosphine (C27H33O3P), (III), and tris-(4-meth-oxy-3,5-di-methyl-phen-yl)phosphine oxide (C27H33O4P), (IV), are reported. The strucure of (III) has been described before [Romain et al. (2000 ▸). Organometallics, 19, 2047-2050], but it is rereported here on the basis of modern area-detector data and to facilitate comparison with the other structures reported here. Compounds (I) and (II) crystallize isostructurally in P21/c. Similarly, (III) and (IV) crystallize isostructurally in Pbca. The conformations of (I) and (II) in the solid state deviate strongly from helical, whereas those of (III) and (IV) are found to be closer to an ideal threefold rotational symmetry. The pyramidality indices, ∑(C-P-C), are 305.35 (16), 317.23 (15), 307.2 (4) and 318.67 (18)° for (I), (II), (III) and (IV), respectively. Each is found to be more pyramidal than Ph3P or Ph3PO. Hybrid DFT calculations incorporating terms for dispersion provide evidence that the causes of the increased pyramidality, despite the 3,5-dimethyl group substitution, include dispersion inter-actions. The calculated ∑(C-P-C) values are 304.8° for both (I) and (III) and 317.4° for both (II) and (IV), with no difference arising from the substitution at ring position 4.

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.

Benchmark-Quality Semiexperimental Structural Parameters of van der Waals Complexes.

Accurate data sets including noncovalent interactions have become essential for benchmarking computational methods. However, while there is much focus on obtaining an accurate description of relative energies, reliable prediction of accurate equilibrium geometries is also important. To facilitate the benchmarking of computed geometries, the current work includes an accurate data set of semiexperimental equilibrium geometries of noncovalent complexes that can be directly compared to ab initio data. The structures are based on high-accuracy spectroscopic data, combined with vibrational corrections at the double-hybrid density functional level. The current work is designed to complement available data sets of semiexperimental geometries of small rigid molecules and ab initio geometries of complexes. The benchmark-quality data comprises 16 complexes and includes dispersion interactions, hydrogen bonding, CH/π···π interactions, and trimers. In addition to the reference data, accurate counterpoise-corrected geometries have been obtained up to the CCSD level, along with interaction energies. A short overview of the performance of computational methods, including dispersion-corrected B3LYP and B2PLYP functionals, is also included.

Dispersion corrected interaction of polar and nonpolar fluids confined within carbon nanotubes: Density functional theoretical analysis using Grimme's D3 scheme

AbstractThe structural and flow characteristics of fluids within carbon nanotube (CNT) is dictated by the interaction of fluid molecules within the nanocavity of CNT. Therefore, in the present study, dispersion corrected density functional theory has been used to investigate the structure and interaction of polar and nonpolar molecules within CNT. The present study shows that there is profound effect on the interaction due to dispersion. The interaction energy of the confined water was found to be reduced with increasing distance of the water molecule from the wall of the CNT. The water is preferentially adsorbed over methane due to stronger interaction with CNT over methane. Further, water is preferentially adsorbed over methanol molecule when interaction is calculated without dispersion but after inclusion of dispersion interaction, the calculated results show that the methanol–CNT interaction is stronger than that of water molecule and hence preferentially adsorbed within the CNT as revealed from MD simulation. The present calculation reveals that that the effect of CNT confinement on the IR spectra of the single file water is quite considerable compared to the IR spectra of tetrahedral bulk water cluster. Therefore, the present results might be useful for the separation of polar molecule from nonpolar molecule during fabrication of CNT‐based filter and purification system.

A modified Poisson-Boltzmann equation applied to protein adsorption

Ion-exchange chromatography has been widely used as a standard process in purification and analysis of protein, based on the electrostatic interaction between the protein and the stationary phase. Through the years, several approaches are used to improve the thermodynamic description of colloidal particle-surface interaction systems, however there are still a lot of gaps specifically when describing the behavior of protein adsorption. Here, we present an improved methodology for predicting the adsorption equilibrium constant by solving the modified Poisson-Boltzmann (PB) equation in bispherical coordinates. By including dispersion interactions between ions and protein, and between ions and surface, the modified PB equation used can describe the Hofmeister effects. We solve the modified Poisson-Boltzmann equation to calculate the protein-surface potential of mean force, treated as spherical colloid-plate system, as a function of process variables. From the potential of mean force, the Henry constants of adsorption, for different proteins and surfaces, are calculated as a function of pH, salt concentration, salt type, and temperature. The obtained Henry constants are compared with experimental data for several isotherms showing excellent agreement. We have also performed a sensitivity analysis to verify the behavior of different kind of salts and the Hofmeister effects.