Nonlocal DFT Research Articles

The impact of the adsorbent energy heterogeneities by multidimensional-multicomponent PC-SAFT-DFT

Over the past few decades, the classical density functional theory (cDFT) models have gained importance in modeling inhomogeneous fluids. Notably, adsorption databases produced by non-local DFT (NLDFT), quenched solid DFT (QSDFT) and 2D-NLDFT approaches are used in different characterization methodologies to recover the pore size distribution (PSD) for a various nanoporous materials. This family of models has a much lower computational cost when compared to molecular simulation. However, it lacks formulations that use DFT for multidimensional-multicomponent systems with heterogeneous solids. In addition to the complexity of representing the interactions between confined molecules and their confined mixtures, it is challenging to represent surface heterogeneities. Here we study materials with equivalent external potential but presenting energy heterogeneities varying throughout the material using a multidimensional classical DFT approach consistent with the SAFT equation of state. For this purpose, we applied three external potentials to model three types of slit-like cavities. Among them, a classical slit-like pore was generated, in which the energy sites did not vary along with the material. In the other two cavities, the energy sites could vary along the cavity, simulating a cavity in which the external potential varies bidimensionally. Finally, we evaluate the effect of the energy heterogeneity of these cavities on the adsorption of Ar and Kr and their mixing. The results show that local heterogeneities can alter the shape of isotherm curves and adsorption selectivities. Solids with heterogeneity showed higher selectivity but lower capacity.

Formation energy puzzle in intermetallic alloys: Random phase approximation fails to predict accurate formation energies

We performed density functional calculations to estimate the formation energies of intermetallic alloys. We used two semilocal approximations, the generalized gradient approximation (GGA) by Perdew-Burke-Ernzerhof (PBE) and the strongly constrained and appropriately normed (SCAN) meta-GGA. In addition, we utilized two nonlocal DFT functionals, the hybrid HSE06, and the state-of-the-art random phase approximation (RPA). The nonlocal functionals such as HSE06 and RPA yield accurate formation energies of binary alloys with completely-filled d-band metals, where semilocal functionals underperform. The accuracy at the nonlocal functionals is greatly reduced when a partially-filled d-band metal is present in an alloy, while PBE-GGA outperforms in these cases. We show that the accurate prediction of formation energies by any DFT method depends on its ability to predict the accurate electronic properties, e.g., valence d-band contribution to the density of states (DOS). The SCAN meta-GGA often corrects the PBE-DOS, however, it does not provide accurate formation energies compared to PBE. This is assumed to be due to the lack of proper error cancellation that should be expected due to the similar bulk nature of both alloys and their constituents, which may improve with the modification of meta-GGA ingredients. RPA yields too negative formation energies of alloys with partially-filled d-band metals. RPA results can be corrected by restoring the exchange-correlation kernel, thereby improving the short-range electron-electron correlation in metallic densities.

Sodium-modified mesoporous TiO2: Sol-gel synthesis, characterization and adsorption activity toward heavy metal cations

Experimental samples of mesoporous TiO2 with protonated and sodium-modified surfaces were obtained by sol-gel method. XRD, IR, X-ray fluorescence, and energy dispersive spectroscopy were used to characterize their crystalline structure, morphology and surface functional groups. The surface area of, and pore size distribution in the obtained samples were measured by the nitrogen adsorption/desorption isotherm, and calculated using the BET and non-local DFT theories. The adsorption of the Zn(II), Sr(II) and Ba(II) cations by the protonated and sodium-modified TiO2 surfaces was studied. The dependence of adsorption of the Zn(II), Sr(II) and Ba(II) cations on agitation time, solution acidity, and equilibrium concentrations of cations was investigated in a batch mode. It was shown that the kinetic model based on the pseudo-second order equation applied to the experimental results of adsorption of heavy metal cations by both adsorbents gives the highest coefficients of linear approximation (R2 = 0,99). Two most common adsorption theories, Langmuir and Freundlich, were used to analyze equilibrium adsorption data. Nonlinear approximation shows, that the Freundlich adsorption theory provides higher R2 and lower χ2, than Langmuir adsorption theory for adsorption of heavy metal cations by sodium-modified TiO2 surface. The maximum adsorption of the Zn(II), Sr(II) and Ba(II) cations by the sodium-modified TiO2 surface exceeds that of base sorbent with protonated surface by 2,27; 2,65 and 2,64 times, respectively. Experimental maximum adsorption values of Na-TiO2 toward zinc, strontium and barium cations are 93 mg·g−1; 208,4 mg·g−1, and 274,6 mg·g−1 respectively.Higher metal cations adsorption by Na-TiO2 is due to the Na+ cations, which released, through the ion exchange process. Sodium cations cause the dissociation of water molecules and local alkalization of the aqueous medium, which leads to the reduction of double-charged zinc, strontium and barium cations to single-charged ZnOH+, SrOH+ and BaOH+ cations respectively. Sodium-modified TiO2 involves only one ≡ТіОNa adsorption center in adsorption of the MeOH+ cation, while the protonated Н-ТіО2 sorbent spends two ≡ТіОНδ+ acid centers to bind the double-charged cation.

Surface reactivity of nanoporous carbons: preparation and physicochemical characterization of sulfonated activated carbon fibers

Here, we have examined the nanoporous activated carbon fibers (ACFs) sulfonated using the direct sulfonation and the staged method that included bromination, followed by sulfidation and oxidation. TEM confirmed the nanoporous structure of the prepared sulfonated ACFs. Nitrogen porometry and 2D nonlocal DFT simulations showed the nanoporosity reduction and variations of the pore size distribution because of the functionalization. Comparison of parameters of the SO3H groups confined in nanopores, e.g., the thermal stability and catalytic potential, showed that the most efficient acid sites, in the catalytic 2-propanol dehydration to propylene, are the SO3H groups grafted by the staged Houben–Weil methods. From the productivity of reactions used at the preparation stage, and in contrast to the one-staged aromatic substitution, the bromine addition to π sites of the edges of carbon matrix supplies enough active sites and is a reason for further high yields of the grafted thermostable SO3H groups. Hydrolysis of the grafted bromine and the surface oxidation of nanopores walls are parallel reactions that lowered the SO3H-related acidity, increasing the total acidity to 1.5 mmol g−1. The reported nanoporous sulfonated ACFs are effective to be used in the dehydration reactions catalyzed by solid acids.

Hexagonal boron phosphide as a potential anode nominee for alkali-based batteries: A multi-flavor DFT study

The adsorption of alkali atoms (Li, Na, and K) on graphene and hexagonal boron phosphide (h-BP) is studied by means of various density functionals including semi-local GGA, dispersion corrected DFT-D, meta-GGA, and many of the available non-local vdW-DF functionals. The accurate interaction energies are crucial for energy storage and battery applications as it is directly related to key properties in electrochemistry, such as storage capacities in general, and open circuit voltages (OCVs), in particular. A wider range of adsorption strength is predicted depending on the choice of non-local vdW-DF functionals. Furthermore, the performance of vdW-DF functionals was found to be independent of the choice of pseudopotentials used and especially if the choice is revPBE. Additionally, an excellent agreement is found between the Gaussian, VASP, and QE codes. Moreover, the h-BP is found to be an exceptional anode material for alkali batteries which can compete with any other available anode material. The small change in the adsorption energies as a function of increasing concentration of alkali atoms is a unique characteristic of h-BP. The exceptional 1283 mAh/g storage capacity not only for Li but in contrary with the previous study, also for Na in addition to the 642 mAh/g for K at vdW-DF/DZP level makes it a prominent candidate to be used as anode material. The average open circuit voltage for Li, Na, and K was also found to be in superb range. However, the values are found to be sensitive to the choice of functional, and in some cases, the storage capacity can be predicted as high as twice of the actual values. Therefore, the accurate description of the interaction is crucial and this study can be used to further refine the non-local DFT functionals. Moreover, by virtue of these properties, h-BP can be the best choice to be used as an anode material not only in LIBS but also in SIBs and KIBs.

Pressure dependence on electronic structures, charge distribution and bond orders of solid nitromethane using nonlocal DFT functional

ABSTRACTThe electronic properties of solid nitromethane are studied using nonlocal exchange-correlation functional (optPBE–vdW) under hydrostatic compression up to 40 GPa. We found that the optPBE–vdW functional can reproduce well the crystalline structures compared with the experiments, and an isomorphic phase transition has been verified by their P–V curve. Bader’s charge analysis shows the electron flows from CH3 group to NO2 group with the pressure. Moreover, the calculated bond orders show that the pressure only strengthens the intermolecular C–N bond and intermolecular C–H···O hydrogen bonds though it shortens all bond lengths. Furthermore, the electronic structure and its pressure dependence have also been discussed in detail.

Adsorption of Organic Molecules to van der Waals Materials: Comparison of Fluorographene and Fluorographite with Graphene and Graphite.

Understanding strength and nature of noncovalent binding to surfaces imposes significant challenge both for computations and experiments. We explored the adsorption of five small nonpolar organic molecules (acetone, acetonitrile, dichloromethane, ethanol, ethyl acetate) to fluorographene and fluorographite using inverse gas chromatography and theoretical calculations, providing new insights into the strength and nature of adsorption of small organic molecules on these surfaces. The measured adsorption enthalpies on fluorographite range from −7 to −13 kcal/mol and are by 1–2 kcal/mol lower than those measured on graphene/graphite, which indicates higher affinity of organic adsorbates to fluorographene than to graphene. The dispersion-corrected functionals performed well, and the nonlocal vdW DFT functionals (particularly optB86b-vdW) achieved the best agreement with the experimental data. Computations show that the adsorption enthalpies are controlled by the interaction energy, which is dominated by London dispersion forces (∼70%). The calculations also show that bonding to structural features, like edges and steps, as well as defects does not significantly increase the adsorption enthalpies, which explains a low sensitivity of measured adsorption enthalpies to coverage. The adopted Langmuir model for fitting experimental data enabled determination of adsorption entropies. The adsorption on the fluorographene/fluorographite surface resulted in an entropy loss equal to approximately 40% of the gas phase entropy.

X-ray and molecular modelling studies of 4-[ N-alkylamino]azobenzene dyes

4-[ N, N-Bisalkyl]amino-2′-chloro-4′-nitroazobenzenes were recrystallized from acetone in either triclinic or monoclinic cells with the space group P-1 or P2 1/ c. The asymmetric unit cell of dyes having at least one N-cyanoethyl group contained two molecules that were symmetrically unequivalent. The aromatic rings in the azobenzene skeleton were essentially planar with respect to the plane of the azo group, although the C6–C1–N1–N2 torsion angle was 13.2° when the N, N-dicyanoethyl group was employed. X-ray studies were used as a basis for assessing the utility of nonlocal DFT calculations in predicting the equilibrium molecular geometry and solvatochromic properties of the compounds using MM3/ZINDO-S and the COSMO Solvation Model. Although B3LYP and PBE energy functionals were comparable in predicting bond lengths, PBE was slightly better than B3LYP in predicting torsion angles. Furthermore, the dipolarity/polarizability index ( π ∗) was the preferred solvent parameter for predicting the effects of solvents on λ max.

Electronic structure, magnetism and disorder in the Heusler compound Co2TiSn

Polycrystalline samples of the Heusler compound Co2TiSn have been prepared and studied using bulk techniques (x-ray diffraction and magnetization) as well as local probes (119Sn Mössbauer spectroscopy and 59Co nuclear magnetic resonance spectroscopy) in order to determine how disorder affects the half-metallic behaviour and also to establish the joint use of Mössbauer and NMR spectroscopies as a quantitative probe of local atom ordering in these compounds. Additionally, density functional electronic structure calculations on ordered and partially disordered Co2TiSn compounds have been carried out at a number of different levels of theory in order to simultaneously understand how the particular choice of DFT scheme as well as disorder affects the computed magnetization. Our studies suggest that a sample which seems well ordered by x-ray diffraction and magnetization measurements can possess up to 10% of antisite (Co/Ti) disordering. Computations similarly suggest that even 12.5% antisite Co/Ti disorder does not destroy the half-metallic character of this material. However, the use of an appropriate level of non-local DFT is crucial.

Ruffling Deformations of Nickel(II) and Zinc(II) Hydroporphyrin and Chlorophin Complexes: Implications for F430, the Nickel Tetrapyrrole Cofactor of Methylcoenzyme M Reductase

Nonlocal DFT provides an excellent description of the structural and conformational properties of metallohydroporphyrins and related complexes. The Ni(II) complexes are found to be strongly ruffled and the Zn(II) complexes planar, consistent with experimental results. The increased flexibility of the novel chlorophin, bacteriophin, and isobacteriophin ligands, relative to hydroporphyrins, appears to result from a widening of the Cα−N−Cα angle at the imine nitrogen. A key finding relevant to understanding the chemistry of cofactor F430 is that seemingly innocent substituents such as methyl and phenyl groups can exert a dramatic impact on the metal coordination geometry and macrocycle conformation of Ni(II) hydroporphyrins and related complexes, shrinking Ni−N bond distances and leading to significantly greater ruffling.

A Periodic Density Functional Theory and Hartree−Fock Study of Alkali Halides with Gaussian Orbitals

Periodic-density functional theory (DFT) and Hartree-Fock calculations have been performed on the alkali halides for the alkali metals Li, Na, K, and Rb and the halogens F, Cl, Br and I. Calculations were done with HF-optimized basis sets and DFT-optimized basis sets, at the HF, local DFT (LDFT), and nonlocal DFT (NLDFT) with the Becke exchange potential and the Perdew-Wang correlation potential. The HF and NLDFT results are similar for the lattice parameters, in general, by overestimating them. The LDFT method always underestimates the lattice parameters. As a consequence, the HF and NLDFT methods predict bulk moduli that are too small and the LDFT method predicts bulk moduli that are too large. The absolute error in the bulk moduli are larger at the LDFT level than at the other levels. Charge distribution maps have been calculated and analyzed. The maps clearly show that the main difference between the HF and DFT densities is in the treatment of exchange and that the nonlocal (gradient) corrections moderate this difference.

Nature of the Three-Electron Bond in H2S∴SH2+

We have investigated the model system H2S∴SH2+, i.e., the sulfur−sulfur bound dimer radical cation of H2S, using both density functional theory (LDA, BP86, PW91) and traditional ab initio theory (up to CCSD(T)). Our purpose is to better understand the nature of the three-electron bond. The S−S bond length is 2.886 A and the bond enthalpy (for 298.15 K) amounts to −40.7 kcal/mol at the BP86/TZ2P level. The best ab initio estimates for the S−S bond strength (our CCSD(T)/6-311++G(2df,2pd)//MP2(full) and literature values) are some 10 kcal/mol weaker than those from nonlocal DFT. It is shown, using an energy decomposition scheme for open-shell systems, that the sulfur−sulfur bond (ΔE = ΔE2c-3e + ΔEelst) is nearly 60% provided by the three-electron bond (ΔE2c-3e) between the unpaired sulfur 3px electron on H2S+• and the sulfur 3px lone pair on H2S; electrostatic attraction (ΔEelst) is important, too, with a contribution of somewhat more than 40%. We show furthermore that the three-electron bond (ΔE2c-3e = ΔE2c...

Computation of electron affinities of O and F atoms, and energy profile of F–H2 reaction by density functional theory and ab initio methods

The validity of hybrid and nonlocal DFT methods are tested on examples of systems which are difficult to model by way of quantum chemistry techniques. The electron affinities for the oxygen and fluorine atoms were calculated. The exothermicity, the barrier for the fluorine atom reaction with the hydrogen molecule, and the energy of the H–F bond and its distance were computed with DFT methods, as well as, with ROHF, MPn, and QCISD(T) ab initio methods. The computations were performed by using various basis sets, with 6-311++G(3df,3pd) as the largest. The obtained results are compared with the experimental values. The results of the Becke3LYP hybrid method is in qualitative agreement with experimental results and in the majority of the cases reassembles the high cost QCISD(T) calculation results. Considering the modest computational cost for DFT methods, Becke3LYP/6-311+G(2d,2p) is suggested as the standard theory model for computation, and Becke3LYP/6-311++G(3df,3pd) as the model for generating highly accurate results. They should be applicable to relatively sizable chemical systems.

Density functional calculations of difluorodiazete structures with Gaussian-orbital-type approach

The comparison of local nonlocal and hybrid DFT methods with RHF, MP2, CCSD, and CPF ab initio methods in generating geometries and relative energies of cis- and trans-difluorodiazete, SVWN, BLYP, BP86, BECKE3LYP, and BECKE3P86 DFT methods with 6-311 + g(2d) and 6-311 + + g(3df) basis sets. The geometries generated with RHF ab initio models are quite different from experimental values and energy evaluation prefers the wrong isomer. The hybrid methods give superior geometries while energies evaluated with nonlocal DFT methods are better than the one obtained with MP2 or CCDS ab initio methods. The results suggest DFT as the method of choice of studying similar systems. © 1996 John Wiley & Sons, Inc.

Hysteresis Phenomena in Nanoconfinements: Density Functional Theory and Experiments

ABSTRACTHysteresis phenomena are observed in many nanoporous environments during adsorption/desorption isothermal quasiequilibrium cycles. A non-local DFT model has been developed for predicting adsorption/desorption isotherms in nanopores of different geometries in the wide range of pore sizes (0.5–10 nm) based on given intermolecular fluid/fluid and fluid/solid potentials. Depending on the confining geometry and the intermolecular potentials two types of hysteresis phenomena are occurred: capillary condensation/evaporation that implies volume filling of pores with a liquid-like matter, and layering adsorption/desorption that implies sequential step-wise formation of adsorption layers. It is shown that the DFT model qualitatively describes these phenomena and is in a reasonable quantitative agreement with some of the experiments.