B3LYP Results Research Articles

The performance and efficiency of twelve range-separated hybrid DFT functionals for calculation of the magnetic exchange coupling constants of di-nuclear first row transition metal complexes

The performance and efficiency of twelve range-separated hybrid functionals are compared with each other in calculating magnetic exchange coupling constant (J) data on eleven di-nuclear first-row transition metal complexes having di-copper (Cu) and di-vanadium (V) as their central atoms. The J values are then compared with the experimental findings. In addition to that we also computed the B3LYP results of these complexes. We compared them with the results obtained from range-separated functionals as well as with the experimental results to understand their performances in predicting the magnetic exchange coupling constant. When computing, we reoptimized all the structures of the complexes taken from the crystal data, and then the values of Js were determined. The performances are predicted in terms of four statistical error matrices, namely, the mean absolute error (MAE), mean fractional error (MFE), mean signed error (MSE), root mean square error (RMSE) in cm−1.

A theoretical study on sensing properties of in-doped ZnO nanosheet toward acetylene

Following an experimental work, we employed density functionals B3LYP, BHANDH, HSE06, PBEPBE, and M06 to inspect the impact of In-doping on a ZnO nanosheet sensitivity to the acetylene gas. The interaction of the pristine ZnO sheet with the acetylene was found to be weak, and the sensing response is 1.7 based on the B3LYP results. Doping an In atom into the ZnO sheet increases the adsorption energy of acetylene from −3.6 to −20.4 kcal/mol. Energy decomposing analysis suggests that the nature of interaction is mainly electrostatic, indicating a π-cation interaction. The sensing response significantly rises to 38 by In-doping (experimental value ∼49). We showed that the In-doped ZnO sheet can selectively detect acetylene gas in the presence of O2, H2O, N2 and CO2. A short recovery time of 0.7 s is found, being comparable with experimental value of 58.4 s. Both theory and experiment suggest that In-doped ZnO nanosheet may be highly sensitive and selective acetylene sensor with a short recovery time.

Computational investigation of sensing properties of Ca-doped zinc oxide nanotube toward formaldehyde.

Following an experimental work, we employed density functionals B3LYP, B97D, CAM-B3LYP, BMK, and M06-HF to study the impact of Ca-doping on a ZnO nanotube (ZnONT) sensing performance to the formaldehyde gas. The interaction of the pristine ZnONT with the formaldehyde gas was found to be weak, and the sensing response is 0.7 based on the B3LYP results. Doping a Ca atom into the ZnONT changes the adsorption energy of formaldehyde from - 4.2 to - 36.1kcal/mol. Energy decomposing analysis indicated that the nature of interaction is partially electrostatic and covalent. The sensing response significantly rises to 4.2 by Ca-doping (experimental value ~ 5.28). A short recovery time of 5.6s is found for the formaldehyde gas desorption from the Ca@ZnONT surface at 300°C. Both theory and experiment suggest that Ca-doped ZnONT may be a formaldehyde gas sensor with a short recovery time.

A DFT study on the Ag-decorated ZnO graphene-like nanosheet as a chemical sensor for ethanol: Explaining the experimental observations

Following an experimental work, density functionals B3LYP, TPSS, PBE, M06-2X, and ωB97X-D were exploited to examine the impact of decorating an Ag atom on a ZnO nanosheet sensitivity to the ethanol gas. The interaction of the pristine ZnO sheet with the ethanol was found to be weak, and the sensing response is 6.2 at 300 K based on the B3LYP results, in agreement with experiment. Decorating an Ag atom on the ZnO sheet increases the adsorption energy of ethanol from −6.1 to −20.0 kcal/mol. Energy decomposing analysis indicates that the interaction converts from noncovalent to covalent by the Ag decoration. Also, the sensing response significantly rises to 72 (experimental value ~55). We showed that the Ag decorated ZnO sheet can selectively detect ethanol gas in the presence of benzene, formaldehyde, toluene, and acetone. A short recovery time of 35 s is found, being comparable with experimental value of 25 s. We introduced a theoretical methodology which can reproduce the experimental results. Both theory and experiment suggest that Ag-decorated ZnO nanosheet may be highly sensitive and selective ethanol sensor with a short recovery time.

Augmented Hückel molecular orbital model of π‐electron systems: from topology to metric. II. Hydrocarbon and carbon molecules

AbstractIn the previous paper (paper I, this issue), we described in detail the augmented Hückel molecular orbital (AugHMO) model of the π‐electron systems and its computational realizations: the Hückel‐Su‐Schrieffer‐Heeger (HSSH) method and the Hückel‐Longuet‐Higgins‐Salem (HLHS) method. This methodology transforms the topological data (corresponding to the topological matrix of the HMO model) into the “metric output”—the equilibrium bond lengths of a given molecule.In the present paper, we focus on the π‐electron hydrocarbon and carbon molecules, for which the HMO model is a purely topological model. The necessary empirical parameters of the HSSH and HLHS methods are derived from the experimental C–C bond lengths of ethylene, benzene, and butadiene. As a byproduct, some new insights will be provided into the problem of π‐electron delocalization versus bond‐length alternation in butadiene.We then perform the HSSH and HLHS calculations of the C–C bond lengths in several π‐electron hydrocarbon and carbon molecules (including polyacetylene, fullerene C60, and graphene). The comparison of the calculated bond lengths with the experimental data and also with the ab initio results by the Hartree‐Fock and the Kohn‐Sham methods (the latter in the B3LYP version) is made. In general, it is demonstrated that the HSSH and HLHS results (which almost coincide) are quite close to the experimental values, and, in general, are no worse than the B3LYP results.

Investigating the spin state and electronic structure of the Fe3O cluster from MOF MIL-100(Fe)

In this paper, we investigate the spin state of the Fe3O cluster from MIL-100(Fe), each Fe site of which possesses either one unpaired electron, three unpaired electrons, or five unpaired electrons. Total energies with respect to different spin states were optimized with the PBE, B3LYP, HF, and MP2 methods in combination with various basis sets (6-31G, 6-31G*, 6-311G(d,p)) for non-metal ions and pseudopotentials for Fe (SDD and LanL2DZ). The results of B3LYP, MP2, and HF methods predicted that each Fe site had five unpaired electrons in the most stable spin state. However, the results of PBE show two opposite cases. In one case, PBE predicted each Fe had one unpaired electron, while in the remaining PBE cases, each Fe site was predicted to exhibit five unpaired electrons. We finally conclude the Fe3O cluster with 15 unpaired electrons is the most stable structure.

Reaction energy benchmarks of hydrocarbon combustion by Gaussian basis and plane wave basis approaches.

The reaction energies of 275 elementary reactions from the hydrocarbon combustion model GRI-Mech 3.0 were evaluated by electronic structure calculations using both localized Gaussian basis and plane wave basis sets. In the Gaussian basis calculations, the d-polarization function on C, N, and O elements reduces the mean absolute deviation (MAD) from the experimental value by 53%, a significant improvement in computational accuracy. In the plane wave basis calculation using different exchange-correlation (XC) functionals, the MAD values were 0.316-0.426 eV when non-hybrid type XC functionals such as RPBE, PBE, PW91, revPBE, and PBEsol were used. On the other hand, hybrid functionals like B3LYP and HSE06 reduced the MAD values significantly down to 0.182 and 0.233 eV, respectively. The B3LYP results have 49% less MAD compared to the PBE results. These demonstrated the strong advantage of the hybrid functional for calculating gas-phase reaction energies. The present comprehensive benchmarks will be crucial for future microkinetics as well as machine learning studies on the catalytic reactions. © 2019 Wiley Periodicals, Inc.

An ONIOM investigation of the effect of conformation on bond dissociation energies in peptides.

In the present study, we use the ONIOM strategy of Morokuma and coworkers to examine the various CH bond dissociation energies (BDEs) of a small peptide (2ONW) and compare these with values obtained for its component individual amino acid residues. To evaluate suitable methods for ONIOM-based geometry optimizations, we test an "internal consistency" approach against full B3-LYP//B3-LYP results, and find B3-LYP/6-31G(d):AM1 to be appropriate. We find that the BDEs at the α-carbon in 2ONW are generally larger than the corresponding values for the individual residues on their own. This is attributed to the constraints of the peptide backbone leading to conformations that are not ideal for captodative stabilization of the resulting α-radicals. At the more flexible β- and γ-positions, the differences between the BDEs in 2ONW and the individual residues are smaller. Overall, the α-BDEs are smaller than the β- and γ-BDEs in most cases. Thus, to rationalize the inertness of peptide backbones with respect to α-hydrogen abstraction that is frequently found experimentally, it is necessary to consider alternative protection mechanisms such as the polar effect. © 2018 Wiley Periodicals, Inc.

Experimental and DFT evaluation of the 1H and 13C NMR chemical shifts for calix[4]arenes

The density functional theory is employed to determine the efficiency of 11 exchange-correlation (XC) functionals to compute the 1H and 13C NMR chemical shifts of p-tert-butylcalix[4]arene (ptcx4, R1 = C(CH3)3) and congeners using the 6-31G(d,p) basis set. The statistical analysis shows that B3LYP, B3PW91 and PBE1PBE are the best XC functionals for the calculation of 1H chemical shifts. Moreover, the best results for the 13C chemical shifts are obtained using the LC-WPBE, M06-2X and wB97X-D functionals. The performance of these XC functionals is tested for three other calix[4]arenes: p-sulfonic acid calix[4]arene (sfxcx4 - R1 = SO3H), p-nitro-calix[4]arene (ncx4, R1 = NO2) and calix[4]arene (cx4 - R1 = H). For 1H chemical shifts B3LYP, B3PW91 and PBE1PBE yield similar results, although B3PW91 shows more consistency in the calculated error for the different structures. For 13C NMR chemical shifts, the XC functional that stood out as best is LC-WPBE. Indeed, the three functionals selected for each of 1H and 13C show good accuracy and can be used in future studies involving the prediction of 1H and 13C chemical shifts for this type of compounds.

DFT/TDDFT computational study of the structural, electronic and optical properties of rhodium (III) and iridium (III) complexes based on tris-picolinate bidentate ligands.

The electronic structures and spectroscopic properties of two complexes [M(pic)3] (M=Ir, Rh) containing picolinate as bidentate ligands have been calculated by means density functional theory (DFT) and time-dependent DFT/TD-DFT using three hybrid functionals B3LYP, PBE0 and mPW1PW91. The PBE0 and mPW1PW91 functionals, which have the same HF exchange fraction (25%), give similar results and do not differ drastically from B3LYP results. Calculated geometric parameters of the complexes are in good agreement with the available experimental data. The UV absorptions observed in acetonitrile were assigned on the basis of singlet state transitions. The most intense band observed in the UV-C region corresponds to ligand-to-ligand charge transfer states (LLCT) in both complexes. The theoretical spectrum of the rhodium complex is characterized by a large degree of mixing between metal-to-ligand-charge-transfer (MLCT), LLCT and metal centered (MC) states in the UV-A region. The presence of low-lying excited states with MC character affects the absorption spectrum under spin-orbit coupling (SOC) effects and play important roles in the photochemical properties. Graphical abstract Frontier molecular orbital diagram of mer-M(pic)3 (M=Ir, Rh).

Predicting standard reduction potential for anticancer Au(III)-complexes: A DFT study

The Au(III) complexes are considered promising for cancer treatment given their structural and electronic similarities to Pt(II) complexes. Different from Pt(II) complexes, the Au(III) compounds are much less stable under physiological conditions, due to their high Au3+/Au+ reduction potential. Therefore, great effort has been done to develop more stable Au(III) complexes in order to explore and improve their biological activity. Density functional theory (DFT) methods were herein applied to calculate the standard reduction potential of nine Au(III) organometallic complexes of the type [Au3+(R-C^N^C)L]n, using available experimental data as benchmark. Overall, the DFT methods lead to satisfactory results, with absolute error lower than 170mV. The CAM-B3LYP functional in combination with the SMD solvation model was superior to wB97xD and B3LYP results, with absolute error of 82mV relative to ferrocene/ferrocenium (Fc+/Fc) redox couple. However, in spite of the larger error found for B3LYP results, the qualitative trend was closer to the observed one, which allowed the proposal of a scaling model using the experimental reduction potential as dependent variable and the calculated reaction Gibbs free energy as independent variable. The linear regression was statistically acceptable (R2=0.8) at B3LYP level and lead to an average error of only 35mV. Besides, the variable-temperature H-atom addition/abstraction (VT-HAA) approach was applied for the redox couples with non-equivalent charges (complexes containing chloride as ligand), leading to a significant improvement in the reduction potential prediction. The mean absolute error was only 87mV without any scaling procedure, which is much lower than that found for standard approach, 144mV.

Theoretical Study of the Kinetics and Mechanism of the Thermal Decomposition of 3-Oxetanone in the Gas Phase

The kinetics and mechanism of the thermal decomposition reaction of 3-oxetanone in the gas phase were studied using quantum chemical calculations. The major products of this reaction are formaldehyde, ketene, carbon monoxide, ethylene oxide, ethylene and methyl radical. Formaldehyde, ketene, carbon monoxide and ethylene oxide are the initial decomposition products and other species are the products of ethylene oxide decomposition. The results of B3LYP and QCISD(T) calculations reveal that thermal decomposition of 3-oxetanone to ethylene oxide and carbon monoxide is more probable than to formaldehyde and ketene from an energy viewpoint. Moreover, quantum theory of atoms in molecules and natural bond orbital analysis indicate that 3-oxetanone decomposition to formaldehyde, ketene, carbon monoxide and ethylene occurs via a concerted mechanism and bonds that are involved in the transition states have a covalent character. Moreover, the calculated changes in bond lengths in the transition states reveal that bond breaking and new bond formation occur asynchronously in a concerted mechanism.

A Computational Study of Density of Some High Energy Molecules

AbstractThe detonation pressure depends quadratically on the loading density of the explosives. A precise estimate of the density is thus crucial to decide if a novel energetic material is worth pursuing. In this work we investigate theoretically the crystal densities of the energetic compounds RDX, TNT, NTO, DNAM, CL‐20, DADNE, and HMX. We calculate the crystal densities by using Materials Studio 7.0 Polymorph Predictor, employing force fields and exploring molecular packing arrangements with minima in total energy. Geometry optimized molecular structures computed by density functional theory (DFT) are used as input to the density predictions. In an additional DFT study we apply two functionals, B3LYP and M06 with the 6‐31G(d) and the 6‐31G(d,p) basis sets, and the program package GAUSSIAN09. In this part of the work crystal densities are calculated by using the molecular isosurface volume (defined by the volume within a surface with an electron density of 0.001 electrons per Bohr3) alone or combined with the variance of the electrostatic potential (ESP). The Polymorph Predictor seems to overestimate the densities, but the values are very dependent on the force field strength determined by charges assigned to atoms. In the GAUSSIAN09 DFT study the densities derived by using the M06 functional are in similar agreement with experimental data as what we experienced for the B3LYP results, although both functionals appear to give slightly lower densities than reported experimentally for the majority of the molecules. On average, the densities derived by the ESP method correlate equally well with measured values as the results obtained by the isosurface method.

Quantum chemical study of tautomerism in 2-[(4-phenylthiazol-2-yl)hydrazonomethyl]phenol

The relative stabilities of five tautomers of 2-[(4-phenylthiazol-2-yl)hydrazonomethyl]phenol were calculated at the B3LYP/6–311+G(d,p) and MP2/6–311+G(d,p) levels of theory. The possible tautomeric transformations were also analyzed at the same level taking into account the solvent effect with the integral equation formalism polarizable continuum model (IEF-PCM) using three different solvents. The enol-hydrazo-thiazole (T1) form has been found to be the predominant tautomer, and the tautomers follow the stability pattern: enol-hydrazo-thiazole (T1)>enol-imine-thiazoline (T2)>keto-hydrazo-thiazoline (T4)>keto-amine-thiazole (T5)>enol-azo-thiazole (T3). The tautomeric barrier heights for T1 ⇌ T2, T1 ⇌ T3 and T4 ⇌ T5 reactions are very high in both the forward and reverse directions. In the case of T1 ⇌ T5 and T2 ⇌ T4 tautomerizations, the forward proton transfer is not possible because of large barrier height. According to the B3LYP results of the reverse reactions, only the proton transfer in the gas phase and in chloroform is allowed for T1 ⇌ T5 while it is found to be barrierless for T2 ⇌ T4. However, the MP2 computations show that the reverse T1 ⇌ T5 reaction impossible for all cases while the reverse T2 ⇌ T4 reaction needs very low energy. These results are also corroborated by the thermodynamic parameters obtained at the B3LYP/6–311+G(d,p) level. The barrier energy height increases with the increasing polarity of the solvent in general, however, the trend is not observed for all cases.

Importance of the Electron Correlation and Dispersion Corrections in Calculations Involving Enamines, Hemiaminals, and Aminals. Comparison of B3LYP, M06-2X, MP2, and CCSD Results with Experimental Data.

While B3LYP, M06-2X, and MP2 calculations predict the ΔG° values for exchange equilibria between enamines and ketones with similar acceptable accuracy, the M06-2X/6-311+G(d,p) and MP2/6-311+G(d,p) methods are required for enamine formation reactions (for example, for enamine 5a, arising from 3-methylbutanal and pyrrolidine). Stronger disagreement was observed when calculated energies of hemiaminals (N,O-acetals) and aminals (N,N-acetals) were compared with experimental equilibrium constants, which are reported here for the first time. Although it is known that the B3LYP method does not provide a good description of the London dispersion forces, while M06-2X and MP2 may overestimate them, it is shown here how large the gaps are and that at least single-point calculations at the CCSD(T)/6-31+G(d) level should be used for these reaction intermediates; CCSD(T)/6-31+G(d) and CCSD(T)/6-311+G(d,p) calculations afford ΔG° values in some cases quite close to MP2/6-311+G(d,p) while in others closer to M06-2X/6-311+G(d,p). The effect of solvents is similarly predicted by the SMD, CPCM, and IEFPCM approaches (with energy differences below 1 kcal/mol).

Hybrid functional band gap calculation of SnO6 containing perovskites and their derived structures

We have studied the properties of SnO6 octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO6 containing perovskites. We also have expended the hybrid density functional calculation to the ASnO3/A׳SnO3 system with different cation orderings. We propose an empirical relationship between the tolerance factor and the band gap of SnO6 containing oxide materials based on first principles calculation.

The noble gases: how their electronegativity and hardness determines their chemistry.

The establishment of an internally consistent scale of noble gas electronegativities is a long-standing problem. In the present study, the problem is attacked via the Mulliken definition, which in recent years gained widespread use to its natural appearance in the context of conceptual density functional theory. Basic ingredients of this scale are the electron affinity and the ionization potential. Whereas the latter can be computed routinely, the instability of the anion makes the judicious choice of computational technique for evaluating electron affinities much more tricky. We opted for Puiatti's approach, extrapolating the energy of high ε solvent stabilized anions to the ε = 1 (gas phase) case. The results give negative electron affinity values, monotonically increasing (except for helium which is an outlier in most of the story) to almost zero at eka-radon in agreement with high level calculations. The stability of the B3LYP results is successfully tested both via improving the level of theory (CCSD(T)) and expanding the basis set. Combined with the ionization energies (in good agreement with experiment), an electronegativity scale is obtained displaying (1) a monotonic decrease of χ when going down the periodic table, (2) top values not for the noble gases but for the halogens, as opposed to most (extrapolation) procedures of existing scales, invariably placing the noble gases on top, and (3) noble gases having electronegativities close to the chalcogens. In the accompanying hardness scale (hardly, if ever, discussed in the literature) the noble gases turn out to be by far the farthest the hardest elements, again with a continuous decrease with increasing Z. Combining χ value of the halogens and the noble gases the Ng(δ+)F(δ-) bond polarity emerging from ab initio calculations naturally emerges. In conclusion, the chemistry of the noble gases is for a large part determined by their extreme hardness, equivalent to a high resistance to change in its electronic population coupled to their high electronegativity.

Support effect in oxide catalysis: methanol oxidation on vanadia/ceria.

Density functional theory is used for periodic models of monomeric vanadia species deposited on the CeO2(111) surface to study dissociative adsorption of methanol and its subsequent dehydrogenation to formaldehyde. Dispersion-corrected PBE+U calculations are performed and compared with HSE and B3LYP results. Dissociative adsorption of methanol at different sites on VO2·CeO2(111) is highly exothermic with adsorption energies of 1.8 to 1.9 eV (HSE+D). Two relevant pathways for desorption of formaldehyde are found with intrinsic barriers for the redox step of 1.0 and 1.4 eV (HSE+D). The calculated desorption temperatures (370 and 495 K) explain the peaks observed in temperature-programmed desorption experiments. Different sites of the supported catalyst system are involved in the two pathways: (i) methanol can chemisorb on the CeO2 surface filling a so-called pseudovacancy and the H atom is transferred to an V-O-Ce interphase bond or (ii) CH3OH may chemisorb at the V-O-Ce interphase bond and form a V-OCH3 species from which H is transferred to the ceria surface, providing evidence for true cooperativity. In both cases, ceria is directly involved in the redox process, as two electrons are accommodated in Ce f states forming two Ce(3+) ions whereas vanadium remains fully oxidized (V(5+)).

First-Principles Calculations of the Pressure Stability and Elasticity of Dense TiO2Phases Using the B3LYP Hybrid Functional

The crystal structures, pressure–volume equations of state, and pressure stability up to 100 GPa of the experimentally observed and theoretically proposed dense TiO2 phases (rutile, columbite, baddeleyite, OI, cotunnite, fluorite, pyrite, and Pca21) were calculated using the hybrid B3LYP exchange-correlation functional and two independent Gaussian-type basis functions. Overall, the B3LYP results are in good agreement with the experimental data on the structures and elastic properties. The B3LYP functional also shows superior performance relative to projector-augmented wave/pseudopotential-based planewave density functionals in predicting the elastic behaviors for most of the TiO2 phases with the exception of fluorite-TiO2. The latter structure shows significant sensitivity to the choice of basis functions. The order of phase stability with increasing pressure predicted by B3LYP is rutile → columbite → baddeleyite → OI → cotunnite, in agreement with available experimental results. In the pressure range of 20–50 GPa, the B3LYP total energy for the recently proposed Pca21 structure is very close to that for one or more of the accepted stable phases (columbite, baddeleyite, OI, and cotunnite), suggesting potential stabilization of the Pca21 structure at high temperatures. The B3LYP electron density-of-states projections suggest large band gaps for the high-pressure phases OI and Pca21.

Analytic cubic and quartic force fields using density-functional theory.

We present the first analytic implementation of cubic and quartic force constants at the level of Kohn-Sham density-functional theory. The implementation is based on an open-ended formalism for the evaluation of energy derivatives in an atomic-orbital basis. The implementation relies on the availability of open-ended codes for evaluation of one- and two-electron integrals differentiated with respect to nuclear displacements as well as automatic differentiation of the exchange-correlation kernels. We use generalized second-order vibrational perturbation theory to calculate the fundamental frequencies of methane, ethane, benzene, and aniline, comparing B3LYP, BLYP, and Hartree-Fock results. The Hartree-Fock anharmonic corrections agree well with the B3LYP corrections when calculated at the B3LYP geometry and from B3LYP normal coordinates, suggesting that the inclusion of electron correlation is not essential for the reliable calculation of cubic and quartic force constants.