Corrected Density Functional Theory Research Articles

Catalytic reduction of SO2 by CO using carbon intercalated gold clusters

• Dispersion corrected density functional studies of reduction of SO 2 by CO using C n Au n clusters. • Competing pathways of the reaction due to multiple reaction sites are analyzed. • Less desorption energy of products suggest devoid of sulphur poisoning of the catalyst. The reduction of SO 2 by CO at various sites of C n Au n (n = 4, 8 and 16) clusters is studied using the dispersion corrected density functional theory. The energy required for the desorption of the final product COS from the respective clusters is lower than the maximum activation energy barrier of the reaction indicating that the clusters considered are free from sulphur poisoning. The rate determining step of the reaction in presence of the above clusters is also determined. The competing pathways which arise due to the presence of other available possible reaction sites are discussed.

Theoretical Study on the Inclusion Interaction of β-Cyclodextrin with Gabapentin and Its Stability

In this paper, dispersion corrected density functional theory (DFT-D3) with the B3LYP method and the 6–31G(d) basis set is used to study the inclusion processes of gabapentin with β-cyclodextrin and the effect of inclusion on the dehydration condensation reaction of gabapentin. The calculation results show that β-cyclodextrin and gabapentin can form stable inclusion complexes in both vacuum and water. B-β-CDs is the most stable one of four inclusion complexes. After inclusion, the dehydration condensation potential barrier of gabapentin in the β-cyclodextrin cavity is significantly increased. Notably, the reaction barrier of gabapentin in the B-β-CDs complex (a protonated active group of gabapentin with a small mouth of β-cyclodextrin and its hexatomic ring in the cavity of cyclodextrin) even reaches 331.353 kJ/mol in vacuum and 283.538 kJ/mol in water, respectively. There are two obvious increases of 223.574 kJ/mol in vacuum and 193.932 kJ/mol in water after inclusion. Thus, the inclusion complex of β-cyclodextrin with gabapentin, especially B-β-CDs, inhibits the dehydration condensation side-reaction of gabapentin most effectively.

The favorable surface properties of heptazine based g-C3N4 (001) in promoting the catalytic performance towards CO2 conversion

In this work, the surface properties of triazine and heptazine based g-C3N4 (001) are distinguished to understand the basic function of each framework in the catalytic reduction towards CO2 to CO via dispersion corrected density functional theory (DFT-D). It is found that heptazine based g-C3N4 (h-g-C3N4) (001) has narrower band gap and more delocalized electron distribution compared to triazine based g-C3N4 (t-g-C3N4) surface, which lead to enhanced visible-light absorption and electron mobility that favor its catalytic performance. Moreover, h-g-C3N4 (001) exhibits much lower energy barriers along the two possible reaction pathways, in which the COOH-mediated mechanism dominates the reaction paths. After Ni loading, the surface properties are greatly modified on g-C3N4 (001). The energy barrier of CO2 conversion is significantly reduced that leads to enhanced reduction activity, and the intermediate COOH is the preferred product on Ni loaded t-g-C3N4 and h-g-C3N4 surfaces. Considering the surface properties and reaction activity, Ni loaded h-g-C3N4 is identified as a promising efficient catalyst. It is concluded that h-g-C3N4 has preferable surface properties that promote the catalytic performance and is recommended as the prior substrate material in the pursuit of novel composites for CO2 conversion. These findings could provide useful guidance in designing efficient g-C3N4 based catalysts and offer deep insights into the CO2 reduction mechanisms.

A theoretical exploration of the intermolecular interactions between resveratrol and water: a DFT and AIM analysis.

The polyphenolic compound resveratrol, classified under stilbenes, offers a broad range of health advantages, including neuroprotection and playing a role in autophagy in the nervous system. However, resveratrol has poor water solubility and is soluble in the gel phase in liposomal membranes. The main aim of this work was to understand the nature of the interactions between resveratrol and water molecules. In the present study, we used the dispersion corrected density functional theory (DFT) method to study hydrogen bonding interactions. Eight different geometries of resveratrol-water complexes were identified by optimizing the geometries by placing water at various locations. We observed the two lowest energy structures to be isoenergetic. In most complexes, water interaction occurs with phenolic hydrogen as all the phenolic hydroxyl groups have identical Vs,max values. Energy decomposition analysis shows that the dispersion contribution was minimal in these complexes, while electrostatic and orbital contributions were larger. Complex formation between water and the resveratrol molecule results in a blue shift in the vibrational frequency, along with an increase in intensity due to the transfer of electron density. The hydrogen bonds in the resveratrol-water complexes have closed-shell interactions with a medium-to-strong bonding nature. Noncovalent index analysis of the complexes shows that, in addition to hydrogen bonding, electrostatic and van der Waal's interactions play a key role in stabilizing the complexes. Graphical abstract Noncovalent index analysis showing that, in addition to hydrogen bonding, electrostatic and van der Waal's interactions play a major role in stabilizing resveratrol-water complexes.

Understanding DFT Calculations of Weak Interactions: Density-Corrected Density Functional Theory

Understanding DFT Calculations of Weak Interactions: Density-Corrected Density Functional Theory

Nonfullerene Small‐Molecule Acceptors for Organic Photovoltaics: Understanding the Impact of Methoxy Substitution Position on Molecular Packing and Electron‐Transfer Properties

AbstractNonfullerene small‐molecule acceptors (SMAs) are considered as a key component of next‐generation organic photovoltaics. Introducing functional groups to the end‐groups of “acceptor‐donor‐acceptor”‐type SMAs is a facile and convenient way to tune their optoelectronic and morphological properties. Here, molecular dynamics simulations are combined with long‐range corrected density functional theory calculations to explore the molecular‐scale impact that the position of methoxy substitution in the end‐group has on the molecular packing and electron‐transfer properties in neat films. The focus here is on 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno [2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (IT‐OM), where three end‐group methoxy substitution positions are evaluated. Changing the methoxy substitution position is found to influence, to different extents, the planarity of the end‐groups and thus the intermolecular packing density. The effect on the intermolecular electron‐transfer rates is also examined and leads to markedly different sizes of strongly interconnected clusters. Overall, these findings are fully consistent with the experimental evolution of electron mobility in the neat IT‐OM film as a function of methoxy substitution position.

Thermoelastic properties of deuterated melamine, C3N6D6, between 4.2–320 K at 5 kPa and between 0.1–5.0 GPa at 295 K from neutron powder diffraction and DFT calculations

ABSTRACTWe have determined the lattice parameters of perdeuterated melamine, C3N6D6, as a function of temperature (4.2–320 K) close to atmospheric pressure and as a function of pressure (0–5 GPa) at room temperature, using time-of-flight neutron powder diffraction methods. Our observations confirm that the ambient-pressure P21/a structure persists throughout this range of P and T. Both the thermal expansion and the compressibility are highly anisotropic; the principal directions of greatest thermal expansion and greatest compressibility are roughly perpendicular to the corrugated sheets of H-bonded melamine molecules that form the main structural motif. Complementary ab initio calculations (van der Waals corrected Density Functional Theory) provide an estimate of how the inter- and intra-molecular geometry may alter as a function pressure in the athermal limit.

DFT+ <i>U</i> Study of the Thermal Conductivity and Noble Gas Impurities in Uranium Dioxide

The bulk properties of uranium dioxide (UO2) have been investigated using Hubbard corrected density functional theory (DFT+U) calculations. Monitoring of the occupation matrix for 5f electrons of the uranium atoms is found to be crucial to avoid metastable state solutions and consequently to obtain the true ground state properties of bulk UO2. The lattice contribution to the thermal conductivity was obtained by the solution of the Boltzmann transport equation for phonons based on the interatomic force constants obtained from DFT+U calculations. Furthermore, the relative stabilities of noble gases (He, Ne, Ar, Kr, and Xe) in the octahedral interstitial site of bulk UO2 and their migration are revisited. The effect of the supercell approach for point defects is taken into account by considering the long-range elastic interactions. The computed incorporation energy and energy barriers indicate a size-dependent mechanism for the interstitial migration of noble gases.

Spin density transfer from guest to host in endohedral heterofullerene dimers.

The endohedral heterofullerenes (B@C59B)2, (B@C59N)2, (N@C59B)2 and (B@C59N-N@C59B) are investigated using dispersion corrected density functional theory. Several spin states of these complexes are considered and their stable spin states are reported. For 1[(B@C59B)2] and 1[(B@C59N-N@C59B)], the encapsulated atoms are positioned near the surface of the host cages, in contrast to other spin states where they are positioned at the centre of the cages. In complexes 1[(B@C59N)2], 3[(B@C59N)2] and 7[(N@C59B)2], the guest atoms are found to be at the centre of the host cages. The spin polarization and the transfer of spin density between the components of the complexes for different stable spin states are analyzed. Based on the spin states of the complexes, the spin-spin interaction is found to be either ferromagnetic or anti-ferromagnetic. Unlike other complexes, in 1[(B@C59B)2] and 1[(B@C59N-N@C59B)] the spin density is transferred from the guest to the host followed by anti-ferromagnetic coupling between the monomers. The thermodynamic feasibility of formation of the complexes is also examined. The electron affinity, ionization potential and dipole moment of the above systems are determined. The singlet state of the heterodimer (B@C59N-N@C59B) showed high polarity due to the slight rotation along the dihedral angle φNCCB.

The influence of support materials on the structural and electronic properties of gold nanoparticles - a DFT study.

Supported gold nanoparticles are used for a wide range of catalytic processes. In this work, we use dispersion corrected density functional theory (DFT-D) to study the effect of commonly used support materials (MgO, C, CeO2) on small gold particles with up to 19 atoms. Our results show that the preferred cluster shape and morphology is highly dependent on the support material due to different adsorption strength and structural mismatch between the cluster and the surface material. We developed an algorithm to measure the mismatch between the cluster interface and the support surface. Moreover, depending on the support material, the gold clusters exhibit a positive or negative polarisation, which ultimately has strong implications on the catalytic activity of such particles. This behaviour is rationalised by an analysis of the electronic structure of the metal particles and support materials.

Theoretical study on the inclusion interaction of β-cyclodextrin with gabapentin and its stability

In this paper, dispersion corrected density functional theory (DFT-D3) with the B3LYP method and the 6-31G(d) basis set is used to study the inclusion processes of gabapentin with β-cyclodextrin and the effect of inclusion on the dehydration condensation reaction of gaba­pentin. The calculation results show that β-cyclodextrin and gabapentin can form stable inclusion complexes in both vacuum and water. B-β-CDs is the most stable one of four inclusion complexes. After inclusion, the dehydration condensation potential barrier of gabapentin in the β-cyclodextrin cavity is significantly increased. Notably, the reaction barrier of gabapentin in the B-β-CDs complex (a protonated active group of gabapentin with a small mouth of β-cyclo­dextrin and its hexatomic ring in the cavity of cyclodextrin) even reaches 331.353 kJ/mol in vacuum and 283.538 kJ/mol in water, respectively. There are two obvious increases of 223.574 kJ/mol in vacuum and 193.932 kJ/mol in water after inclusion. Thus, the inclusion complex of β-cyclodextrin with gabapentin, especially B-β-CDs, inhibits the dehydration condensation side-reaction of gabapentin most effectively.

Structure, stability, and nature of bonding between high energy water clusters confined inside cucurbituril: A computational study

The structure and stability of the high energy water molecules inside the CB7 cavity was studied using the dispersion corrected density functional theory (DFT) and molecular dynamics (MD). The intermolecular distance between the O and H in the water molecule was found to decrease upon the encapsulation of water molecules inside the cavity, indicating the increase in the stability of water clusters. The computed binding energies were found to be sensitive to the choice of functional. Energy decomposition analysis (EDA) shows that the repulsive Pauli interaction decides the stability of the water complex. In all the encapsulated systems, except the eight water clusters, the electrostatic interactions have supremacy over the dispersive term, due to the large polarization induced by the water clusters. Molecular electrostatic potentials of entrapped systems show the charge distribution between CB7 and water clusters. QTAIM analysis indicates the existence of noncovalent intramolecular interactions between CB7 and water clusters and ellipticity values to be least for 8H2O@CB7. The topological of ρ(r) fields at the urido nitrogen plane in CB7, proves the stronger bonding with water molecules. Thus, entrapped water molecules are not electronically innocent inside the cage and have noncovalent interaction with hydrophobic part of CB7 molecule. Atom centered Density Matrix Propagation (ADMP) molecular dynamic studies shows that the water clusters are stable with respect to their isolated cluster geometry, inside the cucurbituril and the change in potential energy surface is due to the distortion in the geometry of the CB7 unit.

Ab Initio Investigation of the Interionic Interactions in Triethylammonium-Based Protic Ionic Liquids: The Role of Anions in the Formation of Ion Pair and Hydrogen Bonded Structure.

The results of structural analysis and cation-anion interactions of 10 ion pairs and their relevance for the physicochemical properties of triethylammonium-based protic ionic liquids are reported. The calculations were mainly performed by dispersion corrected density functional theory method (B3LYP-GD3). It is shown that the dispersion correction is important in the evaluation of the interaction energies of these compounds. The role of anions in the formation of ion pairs and hydrogen-bonded structure are analyzed. To obtain a quantitative measure of the strength of H-bonds, the Bader's theory of atoms in molecule (AIM) was applied. The correlations between hydrogen bond lengths, their energies, and electron-topological parameters at the H···O bond critical point are presented.

Hunting ionic liquids with large electrochemical potential windows

Ionic liquids (ILs) with large electrochemical potential windows (EPWs) are ideally suited to improve the energy and power density of electrical devices for energy storage. However, guidelines are scarcely available for the selection or systematic screening of ILs for practical applications. Here, we present theoretical predictions for the EPW of thousands of cation‐anion pairs based on a long‐range corrected hybrid density functional theory. The cathodic and anodic potential limits were estimated from the highest occupied molecular orbital and lowest unoccupied molecular orbital energies of individual cations and anions. The approximate method predicts EPWs in reasonable agreement with existing experimental data for several commonly used ionic systems and can be used as a screening tool for a large library of ILs. Five most stable anions, with the cathode stability in the order of B[CN]4 > PF6 > BF4 > BOB>NTf2, have been identified. These anions provide the largest EPWs when they are paired with conventional organic cations. The cation stability is reduced upon elongation of the alkyl chain length or branching of the molecular backbone. © 2018 American Institute of Chemical Engineers AIChE J, 65: 804–810, 2019

Insights on hydrogen evolution reaction in transition metal doped monolayer TcS2 from density functional theory calculations

The catalytic activity for hydrogen evolution reaction (HER) in monolayer TcS2 has been investigated using van der Waals corrected density functional theory. Also, the influence of transition metal dopants (Fe, Co, Ni, Pd and Pt) and their respective sulphur vacancy complexes on HER were evaluated. Using the adsorption free energy of H as a descriptor for the catalytic activity of HER, cation substitutional doping was found unsuitable for stable H adsorption on monolayer TcS2. This configuration leads to poor catalytic activity of the monolayer towards HER. However, vacancy complexes involving Ni, Pd and Pt showed improved catalytic activity towards HER. All the transition metal vacancy complex were found to exist as stable bound complexes.

Efficient and selective sensing of nitrogen-containing gases by Si2BN nanosheets under pristine and pre-oxidized conditions

Motivated by the promise of two-dimensional nanostructures in the field of gas sensing, we have employed van der Waals corrected density functional theory calculations to study the structural, electronic and gas sensing propensities of the recently designed Si2BN monolayer. Our rigorous simulations reveal that the representative members of nitrogen-containing gases (NCGs) such as NO, NO2 and NH3 binds extremely strongly on pristine Si2BN monolayer. However, a strong dissociative adsorption in case of NO and NO2 would poison the Si2BN and ultimately reversibility of the monolayer would be compromised. Exploring the sensing mechanism in more realistic pre-oxidized conditions, the binding characteristics of O2@Si2BN changed dramatically, resulting into much lower adsorption in associative manner for all NO, NO2 and NH3. A visible change in work function indicates the variation in conductivity of O2@Si2BN upon the exposure of incident gases. Sustainable values of binding energies would also ensure a quick recovery time that makes O2@Si2BN an efficient nano sensor for pollutants like NCGs.

Quantifying Density Errors in DFT.

We argue that any general mathematical measure of density error, no matter how reasonable, is too arbitrary to be of universal use. However, the energy functional itself provides a universal relevant measure of density errors. For the self-consistent density of any Kohn-Sham calculation with an approximate functional, the theory of density-corrected density functional theory (DC-DFT) provides an accurate, practical estimate of this ideal measure. We show how to estimate the significance of the density-driven error even when exact densities are unavailable. In cases with large density errors, the amount of exchange-mixing is often adjusted, but we show that this is unnecessary. Many chemically relevant examples are given.

Fermi-Löwdin orbital self-interaction corrected density functional theory: Ionization potentials and enthalpies of formation.

The Fermi-Löwdin orbital self-interaction correction (FLO-SIC) methodology is applied to atoms and molecules from the standard G2-1 test set. For the first time FLO-SIC results for the GGA-type PBE functional are presented. In addition, examples where FLO-SIC like any proper SIC provides qualitative improvements compared to standard DFT functionals are discussed in detail: the dissociation limit for , the step-wise linearity behavior for fractional occupation, as well as the significant reduction of the error of static polarizabilities. Further, ionization potentials and enthalpies of formation obtained by means of the FLO-SIC DFT method are compared to other SIC variants and experimental values. The self-interaction correction gives significant improvements if used with the LDA functional but shows worse performance in case of enthalpies of formation if the PBE-GGA functional is used. The errors are analyzed and the importance of the overbinding of hydrogen is discussed. © 2018 Wiley Periodicals, Inc.

Do Semilocal Density-Functional Approximations Recover Dispersion Energies at Small Intermonomer Separations?

The methods that add dispersion energies to interaction energies computed using density-functional theory (DFT), known as DFT+D methods, taper off the dispersion energies at distances near van der Waals minima and smaller based on an assumption that DFT starts to reproduce the dispersion energies there. We show that this assumption is not correct as the alleged contribution behaves unphysically and originates to a large extent from nonexchange-correlation terms. Thus, dispersion functions correct DFT in this region for deficiencies unrelated to dispersion interactions.

Describing strong correlation with fractional-spin correction in density functional theory

An effective fractional-spin correction is developed to describe static/strong correlation in density functional theory. Combined with the fractional-charge correction from recently developed localized orbital scaling correction (LOSC), a functional, the fractional-spin LOSC (FSLOSC), is proposed. FSLOSC, a correction to commonly used functional approximations, introduces the explicit derivative discontinuity and largely restores the flat-plane behavior of electronic energy at fractional charges and fractional spins. In addition to improving results from conventional functionals for the prediction of ionization potentials, electron affinities, quasiparticle spectra, and reaction barrier heights, FSLOSC properly describes the dissociation of ionic species, single bonds, and multiple bonds without breaking space or spin symmetry and corrects the spurious fractional-charge dissociation of heteroatom molecules of conventional functionals. Thus, FSLOSC demonstrates success in reducing delocalization error and including strong correlation, within low-cost density functional approximation.