Dispersion-corrected Density Functional Theory Methods Research Articles

Doped graphene and Ag(1 1 1) hybrid material as fuel cell electrode: New insights on interfacial features and oxygen adsorption from dispersion-corrected density functional theory

Graphene nanostructures are among the most interesting materials investigated in recent years for several different applications. Their activity towards Oxygen Reduction Reaction (ORR) has attracted a lot of attention for application in fuel cells and lithium-air batteries. In this, and many other applications, a graphene-metal interface is involved. In this work, we investigated the interaction between graphene and Ag(1 1 1), the effect of boron and nitrogen doping on graphene, and the combination of both factors. We applied a dispersion-corrected DFT method derived from a recent reparameterization of DFT-D2, purposely tuned for silver-molecule interfaces. With this approach, we analyse the adsorption of an oxygen molecule (the first key step of ORR) on the pristine/doped and metal-supported graphene systems. Our results highlight the role of specific dopant-substrate interactions that are key to enhance the adsorption of molecular oxygen.

Off-the-shelf DFT-DISPersion methods: Are they now "on-trend" for organic molecular crystals?

Organic molecular crystals contain long-range dispersion interactions that can be challenging for solid-state methods such as density functional theory (DFT) to capture, and in some industrial sectors are overlooked in favor of classical methods to calculate atomistic properties. Hence, this publication addresses the critical question of whether dispersion corrected DFT calculations for organic crystals can reproduce the structural and energetic trends seen from experiment, i.e., whether the calculations can now be said to be truly "on-trend." In this work, we assess the performance of three of the latest dispersion-corrected DFT methods, in calculating the long-range, dispersion energy: the pairwise methods of D3(0) and D3(BJ) and the many-body dispersion method, MBD@rsSCS. We calculate the energetics and optimized structures of two homologous series of organic molecular crystals, namely, carboxylic acids and amino acids. We also use a classical force field method (using COMPASS II) and compare all results to experimental data where possible. The mean absolute error in lattice energies is 9.59 and 343.85 kJ/mol (COMPASS II), 10.17 and 16.23 kJ/mol (MBD@rsSCS), 10.57 and 18.76 kJ/mol [D3(0)], and 8.52 and 14.66 kJ/mol [D3(BJ)] for the carboxylic acids and amino acids, respectively. MBD@rsSCS produces structural and energetic trends that most closely match experimental trends, performing the most consistently across the two series and competing favorably with COMPASS II.

Face, Notch, or Edge? Intermolecular dissociation energies of 1-naphthol complexes with linear molecules

The stimulated-emission-pumping/resonant 2-photon ionization (SEP-R2PI) method was used to determine the intermolecular dissociation energies D0 of jet-cooled 1-naphthol(1NpOH)·S complexes, where S is a linear molecule (N2, CO, CO2, OCS, N2O, and ethyne) or symmetric-top molecule (2-butyne) that contains double or triple bonds. The dissociation energies D0(S0) are bracketed as follows: 6.68 ± 0.08 kJ/mol for S=N2, 7.7 ± 0.8 kJ/mol for CO, 12.07 ± 0.10 kJ/mol for CO2, 13.03 ± 0.01 kJ/mol for N2O, 14.34 ± 0.08 kJ/mol for ethyne, 15.0 ± 1.35 kJ/mol for OCS, and 29.6 ± 2.4 kJ/mol for 2-butyne. The minimum-energy structures, vibrational wavenumbers, and zero-point vibrational energies were calculated using the dispersion-corrected density functional theory methods such as B97-D3 and B3LYP-D3 with the def2-QZVPP basis set. These predict that N2 and CO are dispersively bound Face complexes (S bound to a naphthalene Face), while CO2, N2O, and OCS adsorb into the "Notch" between the naphthyl and OH groups; these are denoted as Notch complexes. Ethyne and 2-butyne form Edge complexes involving H-bonds from the -OH group of 1NpOH to the center of the molecule. The presence of a double or triple bond or an aromatic C=C bond within S does not lead to a specific calculated geometry (Face, Notch or Edge). However, a correlation exists between the structure and the sign of the quadrupole moment component Θzz of S: negative Θzz correlates with Face or Notch, while positive Θzz correlates with Edge geometries.

Bulk and surface properties of gypsum: A comparison between classical force fields and dispersion-corrected DFT calculations

A crucial step in atomistic simulations of interfacial phenomena is confirming the thermodynamic consistency of the force field. This can be achieved by investigating the ability of the force field in predicting the bulk and surface properties of all components in the system. In this work, our focus is on the interfacial properties of gypsum, the calcium sulfate dihydrate (CaSO4·2H2O), which is the most abundant calcium sulfate in the earth crust. The performance of classical force fields was tested by comparing their results with those calculated with dispersion-corrected density functional theory (DFT-D) method as well as experimentally reported data. The DFT-D method implemented to study gypsum and showed a promising performance by reproducing experimentally reported bulk and surface properties. We showed that properties calculated using classical force fields are highly dependent on ionic partial charges. Substituting the original ionic partial charges in the CLAYFF force field with those of the INTERFACE force field improved the calculated bulk and surface properties significantly. CLAYFF with augmented partial charges and INTERFACE force fields showed the best overall performance in reproducing bulk and surface properties of gypsum.

Experimental and Computational Evidence for "Double Pancake Bonds": The Role of Dispersion-Corrected DFT Methods in Strongly Dimerized 5-Aryl-1λ2,3λ2-dithia-2,4,6-triazines.

Crystal structures are reported for bicyclic 3-CF3C6H4CN5S3 and monocyclic 3-CF3C6H4CN3S2, the latter of which is strongly dimerized in a cis-cofacial geometry [3-CF3C6H4CN3S2]2. The title compounds have previously been characterized in solution by NMR, displaying spectra that are consistent with the structure of [3-CF3C6H4CN3S2]2 in the crystal with anti-oriented CF3 substituents. The interannular binding was investigated using density functional theory (DFT) methods. However, the DFT-optimized geometry spreads the aryl rings too far apart (centroid–centroid distances of ≥4.353 Å versus experimental distance of 3.850 Å). Significant improvements are obtained with dispersion-corrected DFT functionals B3LYP-D3, B3LYP-D3BJ, M062X, and APFD using the 6-311+G(2d,p) basis set. However, all of these overbind the aryl rings with centroid–centroid distances of 3.612, 3.570, 3.526, and 3.511 Å, respectively. After selecting B3LYP-D3BJ/6-311+G(2d,p) as the best method, five alternative dimer geometries were tested, and all were found to be binding; however, anti cofacial-4 (matching the structure in the solid state) is the most stable. Computed energies of the remainder are as follows: +7.0 kJ mol–1 (syn-cofacial-5), +26.7 kJ mol–1 (anti-cofacial-64), +27.0 kJ mol–1 (syn-cofacial-150), +102.0 kJ mol–1 (S,S-antarafacial), and +103.7 kJ mol–1 (S,N-antarafacial), where the suffixes are torsional angles around the CN3S2 thiazyl ring centroids. The binding in the four most stable cofacial dimers may be described by “double pancake bonding”.

Synthesis, structural investigations and pharmacological properties of a new zinc complex with a N4-donor Schiff base incorporating 2-pyridyl ring

A tetradentate Schiff base ligand, L (L = N,N′-bis(1-(2-pyridyl)ethylidene)-2,2-dimethylpropane-1,3-diamine) was used in the preparation of a new mononuclear Zn(II) complex, [Zn(L)Cl]. The complex was structurally investigated by elemental analyses, spectroscopic studies and single crystal X-ray crystallography. Furthermore, to obtain insights into the structure, the ground state geometry of zinc complex cation was examined by dispersion corrected DFT method i.e. B3LYP-D3 within unrestricted scheme. Intermolecular contacts in the crystal structure were calculated and quantified by examination of Hirshfeld surface and fingerprint plots. In addition, the pharmacological properties of the newly synthesized complex were examined to explore the in vitro antibiofilm activity against P. aeruginosa, and anticancer activity against Human breast adenocarcinoma (MCF-7) cell line. Furthermore, molecular docking study was also recorded to find out various modes of virtual interactions between the zinc complex cation and the active site of receptor (PDB: 1gzt).

Intermolecular dissociation energies of hydrogen-bonded 1-naphthol complexes.

We have measured the intermolecular dissociation energies D 0 of supersonically cooled 1-naphthol (1NpOH) complexes with solvents S = furan, thiophene, 2,5-dimethylfuran, and tetrahydrofuran. The naphthol OH forms non-classical H-bonds with the aromatic π-electrons of furan, thiophene, and 2,5-dimethylfuran and a classical H-bond with the tetrahydrofuran O atom. Using the stimulated-emission pumping resonant two-photon ionization method, the ground-state D 0(S 0) values were bracketed as 21.8 ± 0.3 kJ/mol for furan, 26.6 ± 0.6 kJ/mol for thiophene, 36.5 ± 2.3 kJ/mol for 2,5-dimethylfuran, and 37.6 ± 1.3 kJ/mol for tetrahydrofuran. The dispersion-corrected density functional theory methods B97-D3, B3LYP-D3 (using the def2-TZVPP basis set), and ωB97X-D [using the 6-311++G(d,p) basis set] predict that the H-bonded (edge) isomers are more stable than the face isomers bound by dispersion; experimentally, we only observe edge isomers. We compare the calculated and experimental D 0 values and extend the comparison to the previously measured 1NpOH complexes with cyclopropane, benzene, water, alcohols, and cyclic ethers. The dissociation energies of the nonclassically H-bonded complexes increase roughly linearly with the average polarizability of the solvent, (S). By contrast, the D 0 values of the classically H-bonded complexes are larger, increase more rapidly at low (S), but saturate for large (S). The calculated D 0(S 0) values for the cyclopropane, benzene, furan, and tetrahydrofuran complexes agree with experiment to within 1 kJ/mol and those of thiophene and 2,5-dimethylfuran are ∼3 kJ/mol smaller than experiment. The B3LYP-D3 calculated D 0 values exhibit the lowest mean absolute deviation (MAD) relative to experiment (MAD = 1.7 kJ/mol), and the B97-D3 and ωB97X-D MADs are 2.2 and 2.6 kJ/mol, respectively.

Size and shape effects on complexes of fullerenes with carbon nanorings: C50 and C76 as [10]CPP and [6]CPPA guests

Using dispersion-corrected DFT methods, an exhaustive computational study of all possible complexes between the carbon nanorings, CNRs, [10]CPP and [6]CPPA with the fullerenes C50 and C76 was carried out. For C50, the two more favorable isomers (with D5h and D3 symmetry) were chosen, and for C76, the isomer with D2 symmetry (the most favorable isomer of the two that exist) was the selected one. After exploration of all the possible rearrangements of the fullerenes inside the CNRs, optimization without any geometrical restrictions were carried out and the corresponding complexation energies were evaluated. According to calculations both CNRs can perform as satisfactory receptors of both fullerenes, what manifests through high complexation energies, going from − 36 to – 54 kcal mol−1. Almost in all complexes the fullerene stays fully inside the nanoring, except in the case of C76@[6]CPPA, where fullerene suffers a considerable departure of almost 2.5 A, which is certainly due to C76 to be too large for this CNR. Complexation of these systems is governed for the complementarity (of size and shape) between the CNR and the fullerene. While the fullerene is extremely rigid, the CNR has a certain capability to fit (in shape and size) to the fullerene, with the aim of optimizing the interaction between both monomers. This way, the CNR is able to contract slightly to embrace the host molecule more strongly.

Binding free energies in the SAMPL6 octa-acid host\u2013guest challenge calculated with MM and QM methods

We have estimated free energies for the binding of eight carboxylate ligands to two variants of the octa-acid deep-cavity host in the SAMPL6 blind-test challenge (with or without endo methyl groups on the four upper-rim benzoate groups, OAM and OAH, respectively). We employed free-energy perturbation (FEP) for relative binding energies at the molecular mechanics (MM) and the combined quantum mechanical (QM) and MM (QM/MM) levels, the latter obtained with the reference-potential approach with QM/MM sampling for the MM → QM/MM FEP. The semiempirical QM method PM6-DH+ was employed for the ligand in the latter calculations. Moreover, binding free energies were also estimated from QM/MM optimised structures, combined with COSMO-RS estimates of the solvation energy and thermostatistical corrections from MM frequencies. They were performed at the PM6-DH+ level of theory with the full host and guest molecule in the QM system (and also four water molecules in the geometry optimisations) for 10–20 snapshots from molecular dynamics simulations of the complex. Finally, the structure with the lowest free energy was recalculated using the dispersion-corrected density-functional theory method TPSS-D3, for both the structure and the energy. The two FEP approaches gave similar results (PM6-DH+/MM slightly better for OAM), which were among the five submissions with the best performance in the challenge and gave the best results without any fit to data from the SAMPL5 challenge, with mean absolute deviations (MAD) of 2.4–5.2 kJ/mol and a correlation coefficient (R2) of 0.77–0.93. This is the first time QM/MM approaches give binding free energies that are competitive to those obtained with MM for the octa-acid host. The QM/MM-optimised structures gave somewhat worse performance (MAD = 3–8 kJ/mol and R2 = 0.1–0.9), but the results were improved compared to previous studies of this system with similar methods.

Molecular Dynamics Simulation of Cyclooxygenase-2 Complexes with Indomethacin closo-Carborane Analogs.

Molecular dynamics simulation of carborane-containing ligands in complex with target enzymes is a challenging task due to the unique structure and properties of the carborane substituents and relative lack of appropriate experimental data to help assess the quality of carborane force field parameters. Here, we report results from energy minimization calculations for a series of carborane-amino acid complexes using carborane force field parameters published previously in the literature and adapted for use with the AMBER ff99SB and ff14SB potential functions. These molecular mechanics results agree well with quantum mechanical geometry optimization calculations obtained using dispersion-corrected density functional theory methods, suggesting that the carborane force field parameters should be suitable for more detailed calculations. We then performed molecular dynamics simulations for the 1,2-, 1,7-, and 1,12-dicarba- closo-dodecaborane(12) derivatives of indomethacin methyl ester bound with cyclooxygenase-2. The simulation results suggest that only the ortho-carborane derivative forms a stable complex, in agreement with experimental findings, and provide insight into the possible molecular basis for isomer binding selectivity.

Intermolecular dissociation energies of 1-naphthol·n-alkane complexes.

Using the stimulated-emission-pumping/resonant 2-photon ionization (SEP-R2PI) method, we have determined accurate intermolecular dissociation energies D0 of supersonic jet-cooled intermolecular complexes of 1-naphthol (1NpOH) with alkanes, 1NpOH·S, with S = methane, ethane, propane, and n-butane. Experimentally, the smaller alkanes form a single minimum-energy structure, while 1-naphthol·n-butane forms three different isomers. The ground-state dissociation energies D0(S0) for the complexes with propane and n-butane (isomers A and B) were bracketed within ±0.5%, being 16.71 ± 0.08 kJ/mol for S = propane and 20.5 ± 0.1 kJ/mol for isomer A and 20.2 ± 0.1 kJ/mol for isomer B of n-butane. All 1NpOH·S complexes measured previously exhibit a clear dissociation threshold in their hot-band detected SEP-R2PI spectra, but weak SEP-R2PI bands are observed above the putative dissociation onset for the methane and ethane complexes. We attribute these bands to long-lived complexes that retain energy in rotation-type intermolecular vibrations, which couple only weakly to the dissociation coordinates. Accounting for this, we find dissociation energies of D0(S0) = 7.98 ± 0.55 kJ/mol (±7%) for S = methane and 14.5 ± 0.28 kJ/mol (±2%) for S = ethane. The D0 values increase by only 1% upon S0 → S1 excitation of 1-naphthol. The dispersion-corrected density functional theory methods B97-D3, B3LYP-D3, and ωB97X-D predict that the n-alkanes bind dispersively to the naphthalene "Face." The assignment of the complexes to Face structures is supported by the small spectral shifts of the S0 → S1 electronic origins, which range from +0.5 to -15 cm-1. Agreement with the calculated dissociation energies D0(S0) is quite uneven, the B97-D3 values agree within 5% for propane and n-butane, but differ by up to 20% for methane and ethane. The ωB97X-D method shows good agreement for methane and ethane but overestimates the D0(S0) values for the larger n-alkanes by up to 20%. The agreement of the B3LYP-D3 D0 values is intermediate between the other two methods.

Lattice dynamics and thermodynamic properties of alkaline earth metal nitrates M(NO3)2 (M = Sr, Ba): A first principles study

Metal nitrates are widely used as oxidizers and in light-producing compositions in both civilian and military explosive applications. In this work we have explored the isomorphous divalent metal nitrates M(NO3)2 (M = Sr, Ba) by using dispersion-corrected density functional theory methods. The equilibrium results calculated with Grimme (G06) (for Sr(NO3)2) and Ortmann-Bechstedt-Schmidt (for Ba(NO3)2) functionals reproduced the experimental lattice parameters. We present the effect of cations on the lattice dynamical properties conjointly with their elastic and thermodynamic properties. The linear response approach within density functional perturbation theory was used to calculate the zone-center vibrational frequencies, phonon dispersion relation, and phonon density of states. The infrared spectrum of these compounds in their fundamental state is studied in the whole 0–1500 cm−1 range, and is critically analyzed in the light of previous experimental investigations. We observed that most of the high-frequency vibrational modes emerge because of the NO3 group. The calculated phonon dispersion curves do not show any vibrational anomaly, confirming the dynamical stability of the compounds in the cubic (Pa3¯) phase. The calculated shear anisotropic factors of 1.8 and 2.1 for Sr(NO3)2 and Ba(NO3)2, respectively, indicate that both crystals studied possess considerable mechanical anisotropy. As the thermal behavior of these materials could play a key role in the growth of sustainable smoke compositions, thermodynamic properties such as the entropy, Debye temperature, heat capacity, and enthalpy were calculated. The results reveal that the compounds are thermodynamically stable up to 750 K. This work demonstrates that Sr(NO)2 and Ba(NO3)2 can be reliably used in pyrotechnics as they possess considerable thermal conductivity, leading to a high burn rate. The results presented in this work could open a way to understand the lattice dynamics of materials of this type and could provide necessary input from the pyrotechnic applicability point of view, which would help experimental researchers in the future.

Assessment of the performance of four dispersion-corrected DFT methods using optoelectronic properties and binding energies of organic monomer/fullerene pairs

With the aid of different polymer materials, their properties can be adjusted so as to enhance the efficiencies of heterogeneous organic solar cells. It is known that computational investigations involving density functional theory (DFT) can play an important role in identifying polymers with favourable properties and hence in speeding up the process of designing organic solar cells with higher efficiencies. However, what is often not known is which one of the dispersion-corrected DFT (D-DFT) methods gives the most accurate results (relative to the experimental data) for the various properties of conjugated systems such as are found in heterogeneous organic solar cells. In this study, we employ ωB97x-D, B97-D3, B3LYP-D3, and PBE1PBE-D3 and assess their accuracy by computing binding energies and electronic parameters (such as HOMO and LUMO eigenvalues) of the various (promising) molecular pairings of organic monomers and fullerenes. In addition, we employ time dependent DFT (TD-DFT) to determine optical properties of monomers such as their maximum absorption wavelengths and compare them with the experimental findings. Our results show that B97-D3 and B3LYP-D3 methods give the largest binding energies relative to the other D-DFT methods and they yield (relative to experimental values) the most accurate electronic and absorption results.

First-Principles-Derived Force Fields for CH4 Adsorption and Diffusion in Siliceous Zeolites

Most previous studies on development of force fields for molecules in porous materials focus on prediction of adsorption properties. However, accurately reproducing adsorption data is not sufficient to guarantee the accuracy of other properties, such as diffusivities. We demonstrate an approach to develop force fields based on periodic first-principles calculations that can accurately predict both adsorption and diffusion properties in crystalline nanoporous materials using CH4 in siliceous zeolites as an example. First, multiple dispersion-corrected density functional theory (DFT) methods were tested for describing CH4 in siliceous chabazite, and the two configurations (CH4 interacting with a framework all and an eight-ring window) that are relevant to CH4 adsorption and diffusion were investigated. By comparing with the results from high-level random phase approximation calculations, DFT/CC (coupled cluster) was found to be the optimum method for force field development. DFT/CC-derived force fields that...

Exploring conformational preferences of alanine tetrapeptide by CCSD(T), MP2, and dispersion-corrected DFT methods

The 129 local minima of the alanine tetrapeptide with relative energy < 10 kcal/mol were identified at the ωB97X-D/6-311++G(d,p) level of theory from initial structures generated by combining nine local minima of each residue. The CCSD(T), MP2, and dispersion-corrected DFT levels of theory with various basis sets were assessed for relative energies of the 24 representative conformations. The best performance was obtained at the double-hybrid DSD-PBEP86-D3BJ/def2-QZVP level of theory with RMSD = 0.12 kcal/mol against the CCSD(T)/CBS-limit energies. The ωB97X-D/def2-QZVP and CAM-B3LYP-D3BJ/def2-QZVP levels of theory can be an alternative level of theory with marginal deviations for conformational study of peptides.

Puckering transitions in cyclohexane: Revisited

The interconversion pathways along the puckering transitions in cyclohexane were explored on the two-dimensional projection of the Cremer-Pople sphere using DFT methods and the CCSD(T), MP2, and dispersion-corrected DFT methods with various basis sets were assessed for the relative energies of local minima and transition states for the representative puckering transition pathways. The ωB97X-D/cc-pVTZ and ωB97X-D/def2-QZVP levels of theory well reproduced the relative energies with RMSD = 0.13 kcal/mol against the CCSD(T)/CBS-limit energies. The calculated activation parameters for chair to twist-boat interconversion of cyclohexane at the ωB97X-D/cc-pVTZ//(PCM) M06-2X/6-31+G(d) level of theory were consistent with the observed values.

Intermolecular dissociation energies of dispersively bound complexes of aromatics with noble gases and nitrogen

We measured accurate intermolecular dissociation energies D0 of the supersonic jet-cooled complexes of 1-naphthol (1NpOH) with the noble gases Ne, Ar, Kr, and Xe and with N2, using the stimulated-emission pumping resonant two-photon ionization method. The ground-state values D0(S0) for the 1NpOH⋅S complexes with S= Ar, Kr, Xe, and N2 were bracketed to be within ±3.5%; they are 5.67 ± 0.05 kJ/mol for S = Ar, 7.34 ± 0.07 kJ/mol for S = Kr, 10.8 ± 0.28 kJ/mol for S = Xe, 6.67 ± 0.08 kJ/mol for isomer 1 of the 1NpOH⋅N2 complex, and 6.62 ± 0.22 kJ/mol for the corresponding isomer 2. For S = Ne, the upper limit is D0 < 3.36 kJ/mol. The dissociation energies increase by 1%-5% upon S0 → S1 excitation of the complexes. Three dispersion-corrected density functional theory (DFT-D) methods (B97-D3, B3LYP-D3, and ωB97X-D) predict that the most stable form of these complexes involves dispersive binding to the naphthalene "face." A more weakly bound edge isomer is predicted in which the S moiety is H-bonded to the OH group of 1NpOH; however, no edge isomers were observed experimentally. The B97-D3 calculated dissociation energies D0(S0) of the face complexes with Ar, Kr, and N2 agree with the experimental values within <5%, but the D0(S0) for Xe is 12% too low. The B3LYP-D3 and ωB97X-D calculated D0(S0) values exhibit larger deviations to both larger and smaller dissociation energies. For comparison to 1-naphthol, we calculated the D0(S0) of the carbazole complexes with S = Ne, Ar, Kr, Xe, and N2 using the same DFT-D methods. The respective experimental values have been previously determined to be within <2%. Again, the B97-D3 results are in the best overall agreement with experiment.

Kinetics of the Strain-Promoted Oxidation-Controlled Cycloalkyne-1,2-quinone Cycloaddition: Experimental and Theoretical Studies.

Stimulated by its success in both bioconjugation and surface modification, we studied the strain-promoted oxidation-controlled cycloalkyne–1,2-quinone cycloaddition (SPOCQ) in three ways. First, the second-order rate constants and activation parameters (ΔH⧧) were determined of various cyclooctynes reacting with 4-tert-butyl-1,2-quinone in a SPOCQ reaction, yielding values for ΔH⧧ of 4.5, 7.3, and 12.1 kcal/mol, for bicyclo[6.1.0]non-4-yne (BCN), cyclooctyne (OCT), and dibenzoazacyclooctyne (DIBAC), respectively. Second, their reaction paths were investigated in detail by a range of quantum mechanical calculations. Single-configuration theoretical methods, like various DFT and a range of MP2-based methods, typically overestimate this barrier by 3–8 kcal/mol (after inclusion of zero-point energy, thermal, and solvation corrections), whereas MP2 itself underestimates the barrier significantly. Only dispersion-corrected DFT methods like B97D (yielding 4.9, 6.4, and 12.1 kcal/mol for these three reactions) and high-level CCSD(T) and multireference multiconfiguration AQCC ab initio approaches (both yielding 8.2 kcal/mol for BCN) give good approximations of experimental data. Finally, the multireference methods show that the radical character in the TS is rather small, thus rationalizing the use of single-reference methods like B97D and SCS-MP2 as intrinsically valid approaches.

Weak binding mode of CH4 on rutile crystallites from density functional theory calculations

In the recent years, the surfaces of oxides and fluorides have received considerable attention due to their suitability for emerging technologies such as fuel cells. Among these substances, well-known rutile TiO2, and rutile-like SnO2, MgF2 and ZnF2 are of particular interest owing to their utilization in a wide range of applications such as heterogeneous catalysis. In order to probe these materials for their catalytic activity, physisorption of small organic molecules, such as methane, on their respective dominant surfaces is of potential value. However, the lack of adequate experimental results on the adsorption energetics and geometries of binding particles, has stimulated a large number of computational studies. In this work, the van der Waals-driven sorption of CH4 on (110) face of all of the abovementioned structures has been examined computationally. A manifold of dispersion-corrected DFT methods was applied to evaluate the binding and surface energies as well as surface-induced atomic displacements. Only the most energetically favored configuration of the adsorption, has been examined. The calculated values were compared to the pertinent literature data, either theoretical or experimental, when available. Whilst optB86b-vdW produces the most consistent atomic displacements, despite its confinements, revPBE-D3 results in the most accurate adsorption energies for CH4-TiO2(110). Calculated surface energies were in agreement with the prior studies if available.

Local structure and stacking disorder of chloro(phthalocyaninato)aluminium.

Chloro(phthalocyaninato)aluminium [(C32H16N8)AlCl, Pigment Blue 79] is a molecular compound which crystallizes in a layer structure with stacking disorder. Order-disorder theory was applied to analyse and explain the stacking disorder and to determine the symmetry operations, which generate subsequent layers from a given one. Corresponding ordered structural models were constructed and optimized by force field and dispersion-corrected density functional theory methods. The superposition of the four lowest-energy stackings lead to a structure in which every second double layer looks to be ordered; in the other double layers the molecules occupy one of two lateral positions. This calculated superposition structure agrees excellently with an (incomplete) experimental structure determined from single-crystal data. From the optimized ordered models, the stacking probabilities and the preferred local arrangements were derived. Packing effects such as the distortion of the molecules depending on the arrangement of neighbouring molecules could also be determined.