DFT Functionals Research Articles

Bonding and electronic structures in dinuclear (X)[(Ind)M2L2] complexes (M = Ni, Pd, L = CO, PEt3, X = Cl, Allyl, Ind = indenyl, Cp = cyclopentadienyl): analogy between four-electron donor ligands

The calculations of bimetallic complexes of the type (X)[(Ind)M2(L)2] (M = Ni, Pd, L = CO, (PEt3) and X = Allyl, Cp and indenyl) have been done using two DFT functionals, namely BP86 and B3LYP*. The allyl, Cp and indenyl ligands adopt the same η3-coordination mode with a π bond and can be considered to be isolobal, while the chloride acts as σ- and π-donor. The computed structural and energetic parameters and energy decomposition yield chemically useful information. We report that the metal–metal bond distances are slightly sensitive to the electron donation and electron π-backdonation as the isolobal prediction suggests. Changing the metal from Ni to Pd has the result of increasing the metal–metal bond distance, decreasing the natural population of Pd and the weakness interactions between the X− ligand and the [(Ind)M2(L)2]+ fragment. The results showed that the four ligands behave quite similarly in terms of bonding, coordination mode and donation and π-backdonation properties highlighted by the orbitals’ populations and the energy decomposition. However, the strength of interactions can be classified as follows: Cl < Cp ≈ Ind < Allyl. In all the complexes studied, the M22+ moiety adopts a single metal–metal bonding attributing the 16-MVE configuration to each M(I) cation.

State-of-the-art computations of dipole moments using analytic gradients of high-level density-fitted coupled-cluster methods with focal-point approximations.

Using the analytic derivatives approach, dipole moments of high-level density-fitted coupled-cluster (CC) methods, such as coupled-cluster singles and doubles (CCSD), and coupled-cluster singles and doubles with perturbative triples [CCSD(T)], are presented. To obtain the high accuracy results, the computed dipole moments are extrapolated to the complete basis set (CBS) limits applying focal-point approximations. Dipole moments of the CC methods considered are compared with the experimental gas-phase values, as well as with the common DFT functionals, such as B3LYP, BP86, M06-2X, and BLYP. For all test sets considered, the CCSD(T) method provides substantial improvements over Hartree-Fock (HF), by 0.076-0.213 D, and its mean absolute errors are lower than 0.06 D. Furthermore, our results indicate that even though the performances of the common DFT functionals considered are significantly better than that of HF, their results are not comparable with the CC methods. Our results demonstrate that the CCSD(T)/CBS level of theory provides highly-accurate dipole moments, and its quality approaching the experimental results. © 2019 Wiley Periodicals, Inc.

Hypervalent halogen hydrides HalHn (Hal = Cl, Br, I; n = 3, 5, 7): DFT and ab initio stability prediction

Stability—both kinetic and thermodynamic—and structure of hypervalent halogen hydrides and respective ionic species were investigated using B3LYP, B3PW91 and MPW1PW91 DFT functionals and second-order Moller-Plesset perturbation theory (MP2) with Def2-TZVPPD basis set (for I atoms) and aug-cc-pVTZ basis set (for Br, Cl and H atoms). Various dissociation pathways were considered: respective reaction enthalpies and H2 elimination activation enthalpies were calculated. At these levels of theory, all of the HalHn species (Hal = Cl, Br, I; n = 3, 5, 7) have covalently bound local minima (except for ClH7) and have a relatively significant kinetic stability with respect to H2 elimination, which indicates the possibility of them being, at the very least, spectroscopically observable, if not isolable. The first candidates for isolation/observation appear to be IH3 and IH5. To aid future identification of hypervalent halogen hydrides, harmonic frequencies for these compounds were calculated. Also, NBO analyses were performed and natural electron configurations, Wiberg bond indices and HOMO–LUMO gaps for these species were determined.

Thermochemical study of gaseous indium-arsenic sulfosalt.

Sulfide systems are often used at high temperatures, when vaporization of the components is enabled. Sulfide ores are used as sources of various metals and nonmetals and gaseous sulfides, and sulfosalts may also play a role in the atmosphere chemistry of hot rocky exoplanets. To predict the existence and thermal stability of gaseous sulfides and sulfosalts it is important to know their thermodynamic characteristics. In this study the sulfosalt of indium and arsenic was obtained in the gaseous phase for the first time. High-temperature Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species over indium and arsenic sulfides. A molybdenum double two-temperature cell was used to create the conditions of coexistence of indium and arsenic sulfides. A theoretical study of gaseous As4 S4 and In2 AsS2 was performed using both B3LYP, M06, PBE0 and TPSSh hybrid DFT functionals and an ab initio wave function-based MP2(Full) method. Gaseous In2 AsS2 has been identified during vaporization of In6 S7 and As2 S3 from the molybdenum double two-temperature cell. The structure and molecular parameters of gaseous In2 AsS2 were determined using quantum chemical calculations. Energetically favorable structures of gaseous In2 S, AsS, As4 S4 and In2 AsS2 were found and vibrational frequencies were evaluated in the harmonic approximation. The formation enthalpy of gaseous In2 AsS2 (186 ± 37 kJ mol-1 ) was derived as a result of measurements of the equilibrium constants of two independent gas-phase reactions. The gaseous sulfosalt of indium and arsenic was obtained for the first time. The formation enthalpy of the In2 AsS2 (g) molecule at 298 K was evaluated both experimentally and theoretically. The thermal stability of the gaseous sulfosalt is less than that of the gaseous oxyacid salts.

Benchmarking Different QM Levels for Usage with COSMO-RS.

The COSMO-RS method is an established method for the prediction of fluid phase properties such as activity coefficients, liquid-liquid equilibria, and free energy of solvation. It is also frequently used in quantum chemistry-based chemical reaction modeling to predict the solvation contribution to the reactions. The COSMOtherm software, which features the currently most advanced implementation of COSMO-RS, is based on quantum chemical COSMO calculations using the BP functional with the def2-TZVPD basis set. As the accuracy of COSMO-RS depends on the accuracy of the underlying quantum chemical (QC) calculation, it is important to validate the currently used level against other common, presumably superior, approaches such as the more recently developed M06-2x hybrid density functional or wave function methods such as MP2. As compared to other applications where the electronic energy is the most important result of the QC calculation, the COSMO-RS method has a much higher dependence on the molecular polarity and thus the electron density distribution. We find that MP2, PBE0, and M06-2x perform slightly worse in fully reparametrized COSMO-RS with respect to the prediction of experimentally measured properties like pKa or logP. Although MP2 was reported to yield better polarities than most DFT functionals for spin unpolarized molecules, this theoretical advantage does not manifest in a practical benefit for the prediction of thermodynamic properties with a refitted COSMO-RS parameter set. Other pure DFT functionals such as PBE or TPSS can be used instead of BP, but again, no practical advantage is expected as they yield extremely similar polarities to the original BP calculations.

Understanding the Water Splitting Mechanism on WO3(001)—A Theoretical Approach

In this work we use different theoretical approaches to investigate the mechanism of water splitting on (001)-WO3. Using an LCAO approach with periodic boundary conditions, hybrid DFT functionals, ...

Quantum chemical calculations of 31P NMR chemical shifts of P-donor ligands in platinum(II) complexes.

This work aims to find the most suitable method that is practically applicable for the calculation of 31P NMR chemical shifts of Pt(II) complexes. The influence of various all-electron and ECP basis sets, DFT functionals, and solvent effects on the optimized geometry was tested. A variety of combinations of DFT functionals BP86, B3LYP, PBE0, TPSSh, CAM-B3LYP, and ωB97XD with all-electron basis sets 6-31G, 6-31G(d), 6-31G(d,p), 6-311G(d,p), and TZVP and ECP basis sets SDD, LanL2DZ, and CEP-31G were used. Chemical shielding constants were then calculated using BP86, PBE0, and B3LYP functionals in combination with the TZ2P basis. The magnitude of spin-orbit interactions was also evaluated.

Errors of the most popular functionals in the calculation of the electron energy and enthalpy of formation of compounds

The calculation of the total electron energy Etotal and the enthalpy of formation of the compounds GeO2, C2H6, NH2CHO, C6H6, C5H5N and C6H4O2 has been performed using methods B1LYP, B1PW91, B3LYP, BHandH, BHandHLYP, BLYP, BP, CAMY-B3LYP, HTBS, KMLYP, LCY-BLYP, LCY-BP86, LCY-PBE, LDA, M06, M06-2X, M06-HF, M06L, mPBE, mPW, MPW1K, MPW1PW, O3LYP, OLYP, OPBE, OPBE0, PBE, PBE0, PBEsol, PW91, revPBE, revTPSS, RPBE, TPSS, TPSSH, X3LYP and HF in the slater basis QZ4P, aug-TZ2P and TZ2P, as well as DZ, and the errors of calculation of Etotal and Δ at the variation limit were determined. The QZ4P basis set and the settings of the ADF program were configured so that these errors can be attributed to the structure of DFT functionals. The dependence of the Etotal and based on type (size) of the basis set was studied. It has been demonstrated that the functional M06 has the smallest error independent from the incomplete basis set, and the optimal combinations are DFT/TZ2P, where DFT = OPBE, X3LYP, B3LYP, revTPSS, M06L, M06, TPSS, CAMY-B3LYP.

GRID-system Based on European EGI Standards for Large-scale Calculations Using the Original Accelerated Method of Quantum Chemistry

Based on the analysis of modern tools for creating GRID-type information systems that are part of the European EGI “standard” – UMD repository (including new versions of Globus Toolkit, ARC, dCache, etc.), the applying of GRID systems for computational chemistry is briefly discussed. The GRID system created by the authors combines two clusters with Linux CentOS 7 and is based on software from UMD-4. The relevance and effectiveness of batch processing systems (we use Torque 4.2.10) in quantum chemical calculations is increased for mass calculations of docking complexes (including for drug modeling problems), for which an improved semiempirical method with more efficient approximations was proposed, implemented in the Fortran-95 LSSDOCK software package. For such calculations, new approximation methods have been developed, including for DFT functionals, and their software implementation is carried out. Converters of calculation results by LSSDOCK into a natural for GRID XML-based format CML version 3 are developed. Using the CML format based on dCache software, a single tree of a virtual GRID filesystem distributed between heterogeneous nodes is used to store the results of LSSDOCK calculations.

The Role for the Weak Interaction on the Stabilization of Copper-Containing Complex: DFT Investigation of Noncovalent Interactions in Ternary-Cu(II) (DA)(AA) Complexes (DA = Diamine and AA = Amino Acids) as a Model of Metalloprotein

Abstract In view of the key roles played by noncovalent or weak interactions in biological processes, it is important to understand them at the molecular level. Based on the results of the thermodynamic, spectroscopic and X-ray structural studies on ternary Cu(II) complexes, as platform molecules for ligand-ligand interactions, the presence of π-π interactions between aromatic rings (phenyl, phenol and indole) of amino acids and aromatic rings of imidazole, diamines have been shown. We carried out systematic theoretical studies using different DFT functionals (pure-GGA, meta-GGA, hybrid-GGA and meta-hybrid-GGA) with triple-ζ (def2TZVP) basis set for the experimentally determined structure of [Cu(hista)(Phe)]ClO4, to obtain the most suitable method. We gained reliable insight into the geometry, electronic structure and noncovalent interactions for different ternary complexes, [Cu(hista)(AA)]ClO4 (AA = Phe, Tyr, Trp, Leu, Ile, Ala, Met, Val) by applying the most accurate method (PW91/def2TZVP/CPCM). The calculated stability constants (logK) were in good agreement with the experimental results. We obtained knowledge of the differences in noncovalent interactions and excited states among the ternary Cu(II) complexes containing Phe, Tyr, and Trp by the Non-Covalent Interaction (NCI) and TDDFT methods.

Solvation Free Energy Calculations: The Combination between the Implicitly Polarized Fixed-charge Model and the Reference Potential Strategy.

The IPolQ-Mod charges, which are the average of two charge sets fitted in vacuum state and condensed phase, take account of polarization effect implicitly in the solvation free energy calculation. However, the performance of the IPolQ-Mod charges sensitively depends on the QM levels used to generate the electrostatic potential from which the charges are fitted. In addition, the forces on atoms are not accurate theoretically in the molecular dynamics (MD) simulation as the solvent only feels the electrostatic potential of a half-polarized density of the solute according to the derivation of the IPolQ-Mod charges. To study these issues in detail, the IPolQ-Mod charges are combined with the reference potential (RP) strategy to predict the solvation free energies in the present study. It is found that the thermodynamic perturbation (TP) corrections utilizing total energy difference and interaction energy difference are almost the same and free of bias. The solvation free energies estimated by the RP method match very well with those obtained by applying IPolQ-Mod charges into MD simulation directly. By means of the RP strategy, the performances of the IPolQ-Mod charges with the change of the strength of the exact HF exchange in several DFT functionals are determined effectively. Although the "optimal" strengths are found in B3LYP and LC-ωPBE, the improvements over the default strength are not too much. In addition to the IPolQ-Mod charges, other charge models like bond charge correction (BCC) charges could also be combined with the RP strategy to study the thermodynamic properties like solvation free energy. © 2019 Wiley Periodicals, Inc.

Chemical Kinetics of Hydrogen Atom Abstraction from Propargyl Sites by Hydrogen and Hydroxy Radicals.

Hydrogen atom abstraction from propargyl C-H sites of alkynes plays a critical role in determining the reactivity of alkyne molecules and understanding the formation of soot precursors. This work reports a systematic theoretical study on the reaction mechanisms and rate constants for hydrogen abstraction reactions by hydrogen and hydroxy radicals from a series of alkyne molecules with different structural propargyl C-H atoms. Geometry optimizations and frequency calculations for all species are performed at M06-2X/cc-pVTZ level of theory and the hindered internal rotations are also treated at this level. The high-level W1BD and CCSD(T)/CBS theoretical calculations are used as a benchmark for a series of DFT calculations toward the selection of accurate DFT functionals for large reaction systems in this work. Based on the quantum chemistry calculations, rate constants are computed using the canonical transition state theory with tunneling correction and the treatment of internal rotations. The effects of the structure and reaction site on the energy barriers and rate constants are examined systematically. To the best of our knowledge, this work provides the first systematic study for one of the key initiation abstraction reactions for compounds containing propargyl hydrogen atoms.

Predicting absorption spectra of silver‐ligand complexes

AbstractThe detailed structures of most of ligand‐stabilized metal nanoclusters (NCs) remain unknown due to the absence of crystal structure data for them. In such a situation, quantum‐chemical modeling is of particular interest. We compared the performance of different theoretical methods of geometry optimization and absorption spectra calculation for silver‐thiolate complexes. We showed that the absorption spectra calculated with the ADC(2) method were consistent with the spectra obtained with CC2 method. Three DFT functionals (B3LYP, CAM‐B3LYP, and M06‐2X) failed to reproduce the CC2 absorption spectra of the silver‐thiolate complexes.

Tungsten–Ligand Bond Strengths for 2p Elements Including σ- and π-Bond Strength Components, A Density Functional Theory and ab Initio Study

Three WVI crystal structures with multifarious metal-ligand bond types are used to theoretically predict homolytic metal-element bond enthalpies with 11 popular DFT functionals, MP2 wave function methods, and four common valence basis set/pseudopotentials in order to evaluate the accuracy and precision of the resultant bond enthalpy data. To our knowledge, for the first time, estimates of component metal-ligand σ- and π-bond strengths are computed. The WE (E = C, N, O) bond enthalpies have the consistent trend σ > second π > first π. In contrast, the element-element BDE trend for the 2p homologues is second π > first π > σ for nitrogen and oxygen, and σ > first π > second π for carbon. These differences may underpin the differences in stability trends and thus reactivity behavior for metal-element multiple bonds as compared to the element-element multiple bonds, and metal-element triple bonds versus their corresponding double bonded counterparts. For example, Odom et al. show that MeI nucleophilically attacks at the imide (M═N) rather than the nitride (M ≡ N) ligand; the relative π-bond strengths derived herein provide a thermodynamic rationalization for this site preference. In this study, it is deduced from the calculated thermodynamics that the W-oxo ligand is more congruous with a triple bond than a double bond, consistent with the bonding model set forth in the seminal 1961 Ballhausen-Gray paper.

Minimally Empirical Double-Hybrid Functionals Trained against the GMTKN55 Database: revDSD-PBEP86-D4, revDOD-PBE-D4, and DOD-SCAN-D4.

We present a family of minimally empirical double-hybrid DFT functionals parametrized against the very large and diverse GMTKN55 benchmark. The very recently proposed ωB97M(2) empirical double hybrid (with 16 adjustable parameters) has the lowest WTMAD2 (weighted mean absolute deviation over GMTKN55) ever reported at 2.19 kcal/mol. However, refits of the DSD-BLYP and DSD-PBEP86 spin-component-scaled, dispersion-corrected double hybrids can achieve WTMAD2 values as low as 2.33 with the very recent D4 dispersion correction (2.42 kcal/mol with the D3(BJ) dispersion term) using just a handful of adjustable parameters. If we use full DFT correlation in the initial orbital evaluation, the xrevDSD-PBEP86-D4 functional reaches WTMAD2 = 2.23 kcal/mol, statistically indistinguishable from ωB97M(2) but using just four nonarbitrary adjustable parameters (and three semiarbitrary ones). The changes from the original DSD parametrizations are primarily due to noncovalent interaction energies for large systems, which were undersampled in the original parametrization set. With the new parametrization, same-spin correlation can be eliminated at minimal cost in performance, which permits revDOD-PBEP86-D4 and revDOD-PBE-D4 functionals that scale as N4 or even N3 with the size of the system. Dependence of WTMAD2 for DSD functionals on the percentage of HF exchange is roughly quadratic; it is sufficiently weak that any reasonable value in the 64% to 72% range can be chosen semiarbitrarily. DSD-SCAN and DOD-SCAN double hybrids involving the SCAN nonempirical meta-GGA as the semilocal component have also been considered and offer a good alternative if one wishes to eliminate either the empirical dispersion correction or the same-spin correlation component. noDispSD-SCAN66 achieves WTMAD2 = 3.0 kcal/mol, compared to 2.7 kcal/mol for DOD-SCAN66-D4. However, the best performance without dispersion corrections (WTMAD2 = 2.8 kcal/mol) is reached by revωB97X-2, a slight reparametrization of the Chai–Head-Gordon range-separated double hybrid. Finally, in the context of double-hybrid functionals, the very recent D4 dispersion correction is clearly superior over D3(BJ).

Computational study of linear and nonlinear optical properties of substituted thiophene imino dyes using long-range corrected hybrid DFT methods

The molecular structures, linear and nonlinear optical properties of a series constituted by four R-substituted thiophene imino dyes, namely A(R = SO2Me), B(R = SO2Ph), C(R = NO2), and D(R = C2(CN)3) were analysed using CAM-B3LYP, ωB97XD and LC-ωPBE hybrid DFT functionals in combination of the 6-311++G(d,p) standard basis set. The dipole moments, polarisabilities, HOMO-LUMO energy gaps, maximum absorption wavelengths and first hyperpolarisabilities were calculated in the gas phase and the obtained results are in good agreement with experimental NLO activity order A < B < C. Compared to synthesised dyes A-C, the designed dye D presents a longer maximum absorption wavelength and a lower HOMO-LUMO gap because of the appreciable stabilisation of its LUMO energy. These results were confirmed by the calculation of the total second-order stabilisation energy E(2) defined in the context of the NBO population analysis. Consequently, dye D is predicted to exhibit a higher first hyperpolarisability in comparison with dyes A-C. This result can be justified by the enhanced intramolecular charge transfer in dye D due to the stronger electron-withdrawing ability and the cumulative action of the long π-conjugation of the tricyanovinyl moiety. The very high total hyperpolarisability (27 times greater than that of para-nitroaniline) of the designed dye D suggests its promising use in organic NLO devices.

On Achieving High Accuracy in Quantum Chemical Calculations of 3 d Transition Metal-Containing Systems: A Comparison of Auxiliary-Field Quantum Monte Carlo with Coupled Cluster, Density Functional Theory, and Experiment for Diatomic Molecules.

The bond dissociation energies of a set of 44 3 d transition metal-containing diatomics are computed with phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) utilizing a correlated sampling technique. We investigate molecules with H, N, O, F, Cl, and S ligands, including those in the 3dMLBE20 database first compiled by Truhlar and co-workers with calculated and experimental values that have since been revised by various groups. In order to make a direct comparison of the accuracy of our ph-AFQMC calculations with previously published results from 10 DFT functionals, CCSD(T), and icMR-CCSD(T), we establish an objective selection protocol which utilizes the most recent experimental results except for a few cases with well-specified discrepancies. With the remaining set of 41 molecules, we find that ph-AFQMC gives robust agreement with experiment superior to that of all other methods, with a mean absolute error (MAE) of 1.4(4) kcal/mol and maximum error of 3(3) kcal/mol (parentheses account for reported experimental uncertainties and the statistical errors of our ph-AFQMC calculations). In comparison, CCSD(T) and B97, the best performing DFT functional considered here, have MAEs of 2.8 and 3.7 kcal/mol, respectively, and maximum errors in excess of 17 kcal/mol (for the CoS diatomic). While a larger and more diverse data set would be required to demonstrate that ph-AFQMC is truly a benchmark method for transition metal systems, our results indicate that the method has tremendous potential, exhibiting unprecedented consistency and accuracy compared to other approximate quantum chemical approaches.

Probing into the isomers and bonding natures of PuC6

Isomers, bonding characters and spectra of the PuC6 were investigated with DFT and ab initio calculations. A fan-type structure with septet spin multiplicity was found to have the lowest energy through extensive structure research. The energy orders of low-lying isomers were assessed with different DFT functionals and CCSD (T). The main ionic natures of Pu-C bonds derived from electrostatic interaction were revealed by QTAIM. Meanwhile, the quantum-exchange correlation from the directly orbital overlaps of Pu and C also play a significant role in stabilizing. IR and UV-vis spectra were simulated to provide spectra information for the structural identification of PuC6 in future experiments.

Structure and vibrational spectra of p-coumaric acid dimers by DFT methods

We performed a systematic investigation to determine the most accurate DFT functional in the prediction of geometrical parameters and vibrational frequencies for p-coumaric acid (p-CA). For this purpose, we followed a multi-dimensional strategy by performing calculations with 8 DFT functionals for the p-CA dimer with fine and ultrafine grids. We also compared scaled and unscaled harmonic frequencies of p-CA with experimental ones. The unscaled BP86 harmonic frequencies were the most accurate relative to the experimental ones but the BP86 method had the lowest accuracy for the structural parameters. The dispersion-corrected method, wB97XD, showed the best performance for the geometries of the p-CA dimer, though it yielded the highest RMSDs for the vibrational frequencies. We observed that the methods PBE0/def2-TZVP and M06-2X/def2-TZVP, with an ultrafine grid, provided a cost-effective approach which predicted accurately both geometrical parameters and scaled vibrational frequencies of p-CA.

Assessing Parameter Suitability for the Strength Evaluation of Intramolecular Resonance Assisted Hydrogen Bonding in o-Carbonyl Hydroquinones.

Intramolecular hydrogen bond (IMHB) interactions have attracted considerable attention due to their central role in molecular structure, chemical reactivity, and interactions of biologically active molecules. Precise correlations of the strength of IMHB’s with experimental parameters are a key goal in order to model compounds for drug discovery. In this work, we carry out an experimental (NMR) and theoretical (DFT) study of the IMHB in a series of structurally similar o-carbonyl hydroquinones. Geometrical parameters, as well as Natural Bond Orbital (NBO) and Quantum Theory of Atoms in Molecules (QTAIM) parameters for IMHB were compared with experimental NMR data. Three DFT functionals were employed to calculated theoretical parameters: B3LYP, M06-2X, and ωB97XD. O…H distance is the most suitable geometrical parameter to distinguish among similar IMHBs. Second order stabilization energies ΔEij(2) from NBO analysis and hydrogen bond energy (EHB) obtained from QTAIM analysis also properly distinguishes the order in strength of the studied IMHB. ΔEij(2) from NBO give values for the IMHB below 30 kcal/mol, while EHB from QTAIM analysis give values above 30 kcal/mol. In all cases, the calculated parameters using ωB97XD give the best correlations with experimental 1H-NMR chemical shifts for the IMHB, with R2 values around 0.89. Although the results show that these parameters correctly reflect the strength of the IMHB, when the weakest one is removed from the analysis, arguing experimental considerations, correlations improve significantly to values around 0.95 for R2.