First-principles Van Der Waals Density Research Articles

Van der Waals density functional study of hydrocarbon adsorption and separation in metal\u2013organic frameworks without open metal sites

Metal–organic frameworks (MOFs) have received significant attention thanks to their promising features in the storage and separation of guest molecules. MOFs without open metal sites are emerging as they are often less susceptible to poisoning compared to those with open metal sites. However, a complete understanding of the binding and gas separation mechanisms in such materials is still missing. In this work, we perform a comparative study of two classes of vanadium-based MOFs without open metal sites: MFM-300-V^text{(III)} and MFM-300-V^text{(IV)}, as well as MIL-47-V^text{(III)} and MIL-47-V^text{(IV)}. We employ first-principles van der Waals density functional theory to find the optimal binding conformations and binding energies of a series of small hydrocarbons within the pores of the aforementioned MOFs. Our study provides insight into the host–guest interactions in such MOFs without open metal sites, especially the role played by the bridging hydroxyl group (mu _2–OH). We conclude that the bridging –OH group acts as a pseudo open metal site in these MOFs.Graphic abstract

Sensing Behavior of Hexagonal-Aluminum Nitride to Phosgene Molecule Based on Van der Waals–Density Functional Theory and Molecular Dynamic Simulation

In this paper, we evaluated adsorption of phosgene gas molecule (COCl2), on the hexagonal-aluminum nitride (h-AlN) nanosheet by using first-principles van der Waals density functional theory calculations (vdW-DF) method. The nature of interaction between the phosgene molecule and h-AlN is discovered by geometries, adsorption energies, Mulliken, Hirshfeld as well as Voronoi charges analyses. The density of states (DOS) was calculated and the results show that HOMO/LUMO energy gap of h-AlN is significantly reduced upon the COCl2 adsorption. The projected density of states (PDOS) of the adsorption systems suggested that the enhancement of adsorption was owing to the hybridization between Al atom of h-AlN sheet and the O atom of phosgene molecule. Interestingly, the results reveal that the Eg of h-AlN is very sensitive to the presence of COCl2 molecule as its value reduces from 3.337 eV in pure h-AlN to 1.966 eV (41.08% change) after the COCl2 adsorption which would result in electrical conductance increment. Global reactivity descriptor values such as electronegativity (χ), global hardness (η), global softness (S), electronic chemical potential (μ), electrophilicity index (ω), and electro accepting power (ω+) were calculated. Additionally, the stability of the most stable phosgene/h-AlN complex was evaluated by means of DFT molecular dynamics (MD) simulation at room temperature under constant volume and temperature conditions with PBE method. Based on the DFT calculation results, the h-AlN nano sheet is expected to be potential novel sensor for detecting the presence of COCl2 gas.

The elastic constants of rubrene determined by Brillouin scattering and density functional theory

The linear elastic stiffness tensor of the crystalline organic semiconductor, rubrene, is measured using Brillouin light scattering spectroscopy and computed from first-principles van der Waals density functional theory calculations. Results are compared with recent measurements of in-plane reduced elastic constants c¯22, c¯33, and c¯23 determined through anisotropic buckling experiments.

Structural, energetic and electrical properties of encapsulation of penicillamine drug into the CNTs based on vdW-DF perspective

First-principles van der Waals density functional (vdW-DF) calculation using GGA/PBE functional and DZP basis set implemented in the SIESTA package was carried out to investigation the encapsulation of penicillamine drug into the both armchair and zigzag single wall carbon nanotubes (SWCNTs). The results reveal that the drug encapsulated inside the CNT cavity is weakly bounded. The obtained results of binding energies indicated that incorporation of drug is favored inside the zigzag SWCNTs compared with armchair counterparts. We address here the role of vdW interaction for penicillamine drug when inclusion in the CNTs. It worth mentioning that encapsulation of vdW forces can be effects on the binding properties. The electronic structures and Mulliken charge population are analysed for the energetically most favorable complexes which shows that encapsulated penicillamine changes slightly the electronic properties of SWCNTs and trivial charges are transferred from drug to CNTs during encapsulation process.Global reactivity descriptor values such as electronegativity (χ), global hardness (η), global softness (S), electronic chemical potential (μ), and electrophilicity index (ω) were calculated. We anticipated that these findings supply the new way and value information for help in the experimental study and future applications.

Adsorption of Glucose Molecule onto Platinum-Decorated Single-Walled Carbon Nanotubes: A Dispersion-Corrected DFT Simulation

The adsorption mechanism of glucose molecule on intrinsic and Pt-decorated single-walled carbon nanotubes (SWCNTs) was studied using first-principles van der Waals density functional (vdW-DF) calculations. The adsorption of glucose simultaneously was investigated on both (8, 0) and (5, 5) SWCNTs for a comparison. The results indicated that (8, 0) SWCNT is a better media for adsorbing glucose molecule in comparison with (5, 5) SWCNT. It is also found that the glucose molecule is strongly adsorbed at the most stable state of Pt-decorated (8, 0) SWCNT whit binding energy of about −74.37 kcal/mol. Our calculations show that Pt-decorated nanotubes have much higher binding energy, higher net charge transfer values and shorter connecting distances than intrinsic nanotube due to chemisorption of the glucose molecule. Furthermore, the density of states shows that orbital hybridization is visible between the glucose and Pt-decorated nanotube, while there is no evidence for hybridization between the glucose molecule and the intrinsic nanotube. Therefore, Pt-decorated carbon nanotube is expected to be a novel material for enhancing the fabrication of glucose biosensors.

Adsorption of H2S molecules on non-carbonic and decorated carbonic graphenes: A van der Waals density functional study

The adsorption of hydrogen sulfide (H2S) molecules on non-carbonic (B, Al, and Ga nitride) graphene was studied using a first-principles van der Waals density functional (vdW-DF) method. For the adsorption of a single molecule, we determined the most stable configurations, equilibrium geometries, adsorption energies, and electronic properties by approaching the molecule on the surface of non-carbonic graphenes at different possible sites. The Ga nitride (GaN) graphene was more capable of H2S molecule adsorption than the other graphenes due to the higher binding energy value and shorter bonding distance between the H2S molecule and the graphene surface. Electron transfer calculations confirmed that the electronic properties of GaN graphene changes significantly compared to other graphenes after H2S molecule adsorption. The density of states results indicated a stronger physical hybridization between H2S and GaN graphene. Furthermore, co-adsorption of two H2S molecules on the GaN graphene as a single-layer/bi-layer of adsorbed molecules was examined. Finally, Al and Ga metal atoms decorated on carbonic graphene (Al- and Ga-cargraph) to investigate H2S adsorption. The adsorption of H2S on Al- and Ga-cargraph was weaker than that on the non-carbonic graphenes. Therefore, based on the obtained results, GaN graphene is promising for uses in gas sensor devices for detect H2S.

Epoxy monomer adsorption on Group III (B, Al, Ga) nitride nanotubes: vdW-DF studies on mechanical and electronic properties

The present work investigates the interaction of (6,6) and (10,0) B, Al, and Ga nitride nanotubes (BNNT, AlNNT, and GaNNT) with bisphenol-A epoxy monomers using the first-principles van der Waals density functional (vdW-DF) approach with respect to geometrical structures, interaction energies, and electronic properties. Two types of orientations for monomer adsorption are considered: (I) parallel and (II) perpendicular with the tube axis. The interaction energy for epoxy that is adsorbed on the surface of different nanotubes (for both of these states of adsorption) is calculated, and the results indicate that state (II) is more stable than state (I) for nanotube adsorption. Unlike results obtained with BNNTs/(10,0) AlNNT, the results reported herein indicate that (6,6) AlNNTs/GaNNTs can effectively interact with the epoxy monomer, and their interaction properties are dramatically changed upon exposure to these monomers. In addition, density functional calculations are performed within the generalized gradient approximation in the elastic deformation range to obtain the Young’s modulus of (6,6) nanotubes and their complexes in their most stable orientation. Our results reveal that the amounts of modulus downfall of complexes are strongly influenced by the interaction between the monomer and the nanotubes. Among the investigated nanotubes, AlNNT and GaNNTs possesses the strongest interaction to the monomer, but the Young’s modulus of GaNNT complex is higher than that another one. Thus, we believe that AlNNTs might be a good strategy for improving the mechanical properties of epoxy nanocomposites.

Simulations on the possibility of formation of complexes between fluorouracil drug and cucurbit[n]urils: ab initio van der Waals DFT study

The binding geometry of fluorouracil/cucurbit[n]urils (CB[n]s) complexes with n = 5-8 is investigated using the first-principles van der Waals density functional (vdW-DF) method, involving full geometry optimization. Such host-guest complexes are typically calculated using conventional DFT method, which significantly underestimates non-local dispersion forces (or vdW contributions) and therefore affects interactions between respected entities. We address here the role of vdW forces for the fluorouracil and CB[n]s molecules which can form directional hydrogen bonds with each other. It was found that the inclusion of dispersion interactions significantly affects the host-guest binding properties and the hydrogen bonding between the molecules provides the main binding mechanism, while results in the same geometries for the considered complexes. The 0.84 eV binding energy, for the thermodynamically favorable state, reveals that the interaction of fluorouracil with CB[n]s is an exothermic interaction and typical for strong hydrogen bonding. Furthermore, we have investigated the binding nature of these host-guest systems in aqueous solution with ab initio MD simulations adopting vdW-DF method. These findings afford evidence for the applicability of the vdW-DF approach and provide a realistic benchmark for the investigation of the host-guest complexes.

Encapsulation of lamivudine into single walled carbon nanotubes: A vdW-DF study

To explore a suitable carrier for lamivudine drug, the incorporation of lamivudine inside the single walled carbon nanotubes (SWCNTs) has been investigated by using first-principles van der Waals density functional (vdW-DF) calculations. The obtained binding energies reveal that lamivudine prefers to be encapsulated into the metallic nanotubes with diameter of about 13Å. Semiconducting SWCNTs exhibit slightly weaker interaction strength with the lamivudine in comparison with the metallic counterparts. However, the calculated binding energies for both considered nanotubes are typical for the physisorption. The influence of nanotube length on the lamivudine incorporation inside the various considered nanotubes has also been investigated and the results show that it plays an important role in the encapsulation process. The electronic structures analysis for the energetically most favorable complexes reveal that incorporated lamivudine changes slightly the electronic properties of SWCNTs. This indicates that there is no considerable hybridization between the corresponding orbitals and the weak interaction obtained quantitatively in terms of binding energies.

Simple benzene derivatives adsorption on defective single-walled carbon nanotubes: a first-principles van der Waals density functional study

We have investigated the interaction between open-ended zig-zag single-walled carbon nanotube (SWCNT) and a few benzene derivatives using the first-principles van der Waals density functional (vdW-DF) method, involving full geometry optimization. Such sp (2)-like materials are typically investigated using conventional DFT methods, which significantly underestimate non-local dispersion forces (vdW interactions), therefore affecting interactions between respected molecules. Here, we considered the vdW forces for the interacting molecules that originate from the interacting π electrons of the two systems. The -0.54 eV adsorption energy reveals that the interaction of benzene with the side wall of the SWCNT is typical of the strong physisorption and comparable with the experimental value for benzene adsorption onto the graphene sheet. It was found that aromatics are physisorbed on the sidewall of perfect SWCNTs, as well as at the edge site of the defective nanotube. Analysis of the electronic structures shows that no orbital hybridization between aromatics and nanotubes occurs in the adsorption process. The results are relevant in order to identify the potential applications of noncovalent functionalized systems.

Theoretical investigation of nerve agent DMMP adsorption onto Stone–Wales defected single-walled carbon nanotube

To find a suitable sensitivity sensor for dimethyl methylphosphonate (DMMP) as nerve agent, we studied the adsorption behavior of DMMP on the exterior surface of defected semiconducting (10,0) single-wall carbon nanotube (SWCNT) by means of first-principles van der Waals density functional (vdW-DF) calculations. The obtained results of adsorption energies reveal that the defect embedded within the (10,0) SWCNT does not promote binding capability in this system. Notably, analyzing the electronic structures and Mulliken population for the energetically most favorable complex supports that the defect changes slightly the electronic properties of SWCNT, indicating there is no considerable hybridization between the corresponding orbitals and the weak interaction obtained quantitatively in terms of binding energies.

Interaction of Molecular Hydrogen with Microporous Metal Organic Framework Materials at Room Temperature

Infrared (IR) absorption spectroscopy measurements, performed at 300 K and high pressures (27-55 bar) on several prototypes of metal organic framework (MOF) materials, reveal that the MOF ligands are weakly perturbed upon incorporation of guest molecules and that the molecular hydrogen (H(2)) stretch mode is red-shifted (30-40 cm(-1)) from its unperturbed value (4155 cm(-1) for ortho H(2)). For MOFs of the form M(bdc)(ted)(0.5) (bdc = 1,4-benzenedicarboxylate; ted = triethylenediamine), H(2) molecules interact with the organic ligands instead of the saturated metal centers located at the corners of the unit cell. First-principles van der Waals density functional calculations identify the binding sites and further show that the induced dipole associated with the trapped H(2) depends sensitively on these sites. For M(bdc)(ted)(0.5) systems, the strongest dipole moment is of the site that is in the corner of the unit cell and is dominated by the interaction with the benzene ligand and not by the metal center. For MOFs of the M(3)[HCOO](6) type with relatively short ligands (i.e., formate) and 1-D pore structures, there is a weak dependence of H(2) vibrational frequency on the cations, due to a small change in the unit cell dimension. Furthermore, translational states of approximately +/-100 cm(-1) are clearly observed as side bands on the H(2) stretch mode in these 1-D channels interconnected by very small apertures. The H(2) stretch IR integrated areas in all the MOFs considered in this work increase linearly with H(2) pressure, consistent with isotherm measurements performed in similar conditions. However, the IR intensity varies substantially, depending on the number of benzene rings interacting with the H(2) molecules. Finally, there is no correlation between H(2) binding energies (determined by isotherm measurements) and the magnitude of the H(2) stretch shift, indicating that IR shifts are dominated by the environment (organic ligand, metal center, and structure) rather than the strength of the interaction. These results highlight the relevance of IR spectroscopy to determine the type and arrangement of ligands in the structure of MOFs.