Evaluation of a combination of local hybrid functionals with DFT-D3 corrections for the calculation of thermochemical and kinetic data

Due to their position-dependent exact exchange admixture, local hybrid functionals offer a higher flexibility and thus the potential for more universal and accurate exchange correlation functionals compared to global hybrids with a constant admixture, as has been demonstrated in previous work. Yet, the local hybrid constructions used so far do not account for the inclusion of dispersion-type interactions. As a first exploratory step toward a more general approach that includes van der Waals-type interactions with local hybrids, the present work has added DFT-D3-type corrections to a number of simple local hybrid functionals. Optimization of only the s(8) and s(r,6) parameters for the S22 set provides good results for weak interaction energies but deteriorates the excellent performance of the local hybrids for G3 atomization energies and for classical reaction barriers. A combined optimization of the two DFT-D3 parameters with one of the two parameters of the spin-polarized local mixing function (LMF) of a local hybrid for a more general optimization set provides simultaneously accurate dispersion energies, improved atomization energies, and accurate reaction barriers, as well as excellent alkane protobranching ratios. For other LMFs, the improvements of such a combined optimization for the S22 energies have been less satisfactory. The most notable advantage of the dispersion-corrected local hybrids over, for example, a B3LYP-D3 approach, is in the much more accurate reaction barriers.     

Density functional theory with dispersion corrections for supramolecular structures, aggregates, and complexes of (bio)organic molecules

Kohn-Sham density functional theory (KS-DFT) is nowadays the most widely used quantum chemical method for electronic structure calculations in chemistry and physics. Its further application in e.g. supramolecular chemistry or biochemistry has mainly been hampered by the inability of almost all current density functionals to describe the ubiquitous attractive long-range van der Waals (dispersion) interactions. We review here methods to overcome this defect, and describe in detail a very successful correction that is based on damped -C(6).R(-6) potentials (DFT-D). As examples we consider the non-covalent inter- and intra-molecular interactions in unsaturated organic molecules (so-called pi-pi stacking in benzenes and dyes), in biologically relevant systems (nucleic acid bases/pairs, proteins, and 'folding' models), between fluorinated molecules, between curved aromatics (corannulene and carbon nanotubes) and small molecules, and for the encapsulation of methane in water clusters. In selected cases we partition the interaction energies into the most relevant contributions from exchange-repulsion, electrostatics, and dispersion in order to provide qualitative insight into the binding character.     

The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals

We present two new hybrid meta exchange- correlation functionals, called M06 and M06-2X. The M06 functional is parametrized including both transition metals and nonmetals, whereas the M06-2X functional is a high-nonlocality functional with double the amount of nonlocal exchange (2X), and it is parametrized only for nonmetals.The functionals, along with the previously published M06-L local functional and the M06-HF full-Hartree–Fock functionals, constitute the M06 suite of complementary functionals. We assess these four functionals by comparing their performance to that of 12 other functionals and Hartree–Fock theory for 403 energetic data in 29 diverse databases, including ten databases for thermochemistry, four databases for kinetics, eight databases for noncovalent interactions, three databases for transition metal bonding, one database for metal atom excitation energies, and three databases for molecular excitation energies. We also illustrate the performance of these 17 methods for three databases containing 40 bond lengths and for databases containing 38 vibrational frequencies and 15 vibrational zero point energies. We recommend the M06-2X functional for applications involving main-group thermochemistry, kinetics, noncovalent interactions, and electronic excitation energies to valence and Rydberg states. We recommend the M06 functional for application in organometallic and inorganometallic chemistry and for noncovalent interactions. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Contribution to the Mark S. Gordon 65th Birthday Festschrift Issue.     

A dipole moment study of n-trimethyl-ammoniobenzamidates and n-benzoyliminodimethylsulphur(iv)

Analysis of the dipole moments of N-trimethylammoniobenzamidates Me₃N⁺-N^?COC₆H₄X, with X = H, p-F, p-Cl or p-NO₂, and of N-aroyliminodimethylsulphur(IV) Me₂SNCOC₆H₄X (X = H and p-NO₂) shows that, as solutes, these compounds exist in the syn conformation. Models are proposed for N-trimethylammonio-orthochloroben-zamidate and N-orthocyanobenzoyliminodimethylsulphur(IV). The (Me₃N⁺-N^t-) and (SN) dipole moments, and the (N-CO) and (SN-CO) mesomeric moments, are derived and discussed.     

Structures of heterogeneous proton-bond dimers with a high dipole moment monomer: covalent vs electrostatic interactions

A number of calculated structures of heterogeneous proton-bound dimers containing monomers such as acetonitrile, cyanamide, vinylene carbonate, and propiolactone, which have high dipole moments, are presented. These proton-bound dimers are predicted to have a structural anomaly pertaining to the bond distances between the central proton and the basic sites on each of the monomers. The monomers with the high dipole moments also have the larger proton affinity and, on the basis of difference in proton affinities, it would be expected that the proton would be closer to this monomer than the one with the lower proton affinity. However, the proton is found to lie substantially closer to the monomer with the lower proton affinity in most cases, unless the difference in proton affinity is too large. Simply stated, the difference in proton affinities is smaller than the difference in the affinity to form an ion-dipole complex for the two monomers and it is the larger affinity for the high dipole moment monomer (which also has the higher proton affinity) to form an ion-dipole complex that is responsible for the proton lying closer to the low proton affinity monomer. The bond distances between the central proton and the monomers are found to be related to the difference in proton affinity. It is found, though, that the proton-bound dimers can be grouped into two separate groups, one where the proton-bound dimer contains a high dipole moment monomer and one group where the proton-bound dimer does not contain a high dipole moment monomer. From these plots it has been determined that a high dipole moment monomer is one that has a dipole moment greater than 2.9 D.     

(6,3)-honeycomb structures of uranium(VI) benzenedicarboxylate derivatives: the use of noncovalent interactions to prevent interpenetration

Four two-dimensional coordination polymers containing the uranyl cation (UO2(2+)), (NH4)UO2(BDC)1.5 . 2.5H2O (1), KUO2(NDC)1.5 . 2H2O (2), [C(NH2)3]UO2(NDC)1.5 . 2H2O (2b), and UO2(HBDC-Br)2 (3) (BDC = 1,4-benzenedicarboxylate, NDC = 1,4-naphthalenedicarboxylate, BDC-Br = 2-bromoterephthalate) have been synthesized by hydrothermal reactions. Compounds 1-2b have the same honeycomb (6,3) net but with two-fold interpenetration in 1 and without interpenetration in 2 and 2b. The use of 2-bromoterephthalate yields compound 3 with a (4,4) net. The structures of 2 and 2b show that the interpenetration can be prevented by the addition of a bulky substituent to the ligand. Maintaining the desired topology, however, requires a careful choice of the substituent group. Compounds 1, 2, and 2b have a similar structural arrangement to that of benzenetricarboxylic acid (trimesic acid, H3BTC). In H3BTC, the six rings are formed by hydrogen bonding and the interpenetration is more complex than that in 1. Crystal data: 1, triclinic, space group P, a = 10.453(8) A, b = 12.316(9) A, c = 13.441(10) A, alpha = 78.49(1) degrees , beta = 82.17(1) degrees , gamma = 85.57(1) degrees , and Z = 4; 2, monoclinic, space group C2/c, a = 12.7795(9) A, b = 19.728(1) A, c = 15.379(1) A, beta = 92.247(1) degrees , and Z = 8; 2b, monoclinic, space group C2/c, a = 12.7214(8) A, b = 19.645(1) A, c = 17.065(1) A, beta = 98.896(1) degrees , and Z = 8; 3, monoclinic, space group P21/c, a = 7.873(5) A, b = 18.358(14) A, c = 6.893(5) A, beta = 115.96(2) degrees , and Z = 2.     

Linear response theory of the dipole–dipole dispersion interaction between H(1s) atoms

A self-consistent theory of the linear response previously developed by one of us is applied to the dipole–dipole dispersion interaction of two ground state H atoms in the united atom (He) limit, using a Sellmeier representation of the polarizability in terms of pseudostates. Numerical calculations show that a truncated 12-term expansion out of the N = 22 H(1s) dipole pseudospectrum built from STOs with orbital exponent c = 0.985 gives a result exceeding by no more than 5% the variational result for the He dispersion energy.     

Density functional theory study of pyrophyllite and M-montmorillonites (M = Li, Na, K, Mg, and Ca): role of dispersion interactions

The stacking parameters, lattice constants, bond lengths, and bulk moduli of pyrophyllite and montmorillonites (MMTs), with alkali and alkali earth metal ions, are investigated using density functional theory with and without dispersion corrections. For pyrophyllite, it is found that the inclusion of the dispersion corrections significantly improves the agreement of the calculated values of the lattice parameters and bulk modulus with the experimental values. For the MMTs, the calculations predict that the interlayer spacing varies approximately linearly with the cation radius. The inclusion of dispersion corrections leads to sizable shifts of the interlayer spacings to shorter values. In Li-MMT, compaction of the interlayer distance triggers migration of the Li ion into the tetrahedral sheet and close coordination with basal oxygen atoms. Analysis of electron density distributions shows that the isomorphic octahedral Al(3+)/Mg(2+) substitution in MMT causes an increase of electron density on the basal oxygen atoms of the tetrahedral sheets.     

Microwave spectrum,structure, dipole moment and barrier to internal rotation of methyltrifluorosilane

The rotational spectrum of methyltrifluorosilane in the ground and the first three excited states of the torsional mode have been investigated in the region of 12.5–40.0 GHz. The rotational transitions for the ¹³C isotopic species have also been measured. The following structural parameters have been determined: r(CH) = 1.081 ± 0.004 Å, ∠ HCSi = 111°1' ± 30', r(CSi) = 1.812±0.014 Å, r(SiF) = 1.574 ± 0.007 Å, ∠ FSiC = 112°20'± 1°6'. The structural parameters are compared to the corresponding ones for similar molecules. The dipole moment was determined to be 2.33 ± 0.10 D. From relative intensity measurements, the barrier to internal rotation was found to be 0.93 ± 0.09 kcal mol⁻¹; this value is consistent with the values obtained for other methylfluorosilanes.     

Structure, bonding, and dipole moment of (CH3)3N-SO3. A microwave study

Six isotopic derivatives of the complex (CH3)3N-SO3 have been studied in the gas phase by microwave spectroscopy. The N-S bond length is 1.912(20) A, and the NSO angle is 100.1(2) degrees. The dipole moment, determined from Stark effect measurements, is 7.1110(69) D, representing an enhancement of 6.5 D over the sum of the dipole moments of the free monomers. Analysis of the 14N nuclear hyperfine structure indicates that about 0.6 e is transferred from the nitrogen to the SO3 upon formation of the complex. Comparison between the gas-phase structure and that previously determined for the adduct in the solid state reveals small but significant differences, indicating that the formation of the dative bond is slightly less advanced in the gas. Gas-phase and solid-state structural data are compared for several related amine-SO3 systems.     

Arylthiolate coordination and reactivity at pseudotetrahedral nickel(II) centers: modulation by noncovalent interactions

Five new pseudotetrahedral nickel(II) arylthiolate complexes Tp (R,Me)Ni-SR' [(Tp (R,Me)) (-) = 2,2,2-kappa (3)-hydridotris(3-R,5-methylpyrazolyl)borate; R = Me, R' = C 6H 5 (Ph), 2,4,6-C 6H 2(CH 3) 3 (Mes); R = Ph, R' = C 6H 5 (Ph), 2,4,6-C 6H 2(CH 3) 3 (Mes), and 2,6-C 6H 3(CH 3) 2 (Xyl)] were prepared by metathesis reactions of known chloride complexes with sodium arylthiolate salts in THF. The new products were fully characterized. The effect of increasing bulk of substituents at the proximal 3-pyrazolyl and ortho-thiolate positions represented in this series was evident in spectroscopic studies (UV-vis-NIR, (1)H NMR) of the product complexes. Increased steric contact induced red-shifting of nickel-thiolate ligand to metal charge transfer (LMCT) bands and enhanced contact shifts of arylthiolate protons with the paramagnetic ( S = 1) nickel(II) ion. These spectroscopic effects arise from structural distortion of the nickel(II)-thiolate bond revealed by X-ray crystal structure determinations of the structural extremes of the series, Tp (Me,Me)Ni-SPh and Tp (Ph,Me)Ni-SXyl. The distortion consists of a significantly increased tilting of the Ni-S bond from an ideal trigonal axis and increased linearity of the Ni-S-R angle that alters covalency of the Ni-S coordinate bond. Reactivity of the nickel-thiolate linkage toward electrophilic alkylation with MeI is also significantly affected, showing enhanced rates according to two distinct competing mechanisms, direct bimolecular alkylation of intact complex and rate-limiting unimolecular dissociation of free thiolate. Possible biochemical relevance of these observations to tetrahedral nickel(II) centers in metalloenzymes is considered.     

Interaction dipole moment in Rg–Xe (Rg = He, Ne, Ar, and Kr) heterodiatoms from conventional ab initio and density functional theory calculations

We have obtained interaction dipole moment curves for the rare gas heterodiatoms Rg...Xe (Rg = He, Ne, Ar, and Kr) from conventional ab initio and density functional theory calculations with flexible Gaussian-type basis sets. All methods seem to reproduce fairly similar dipole moment curves for all pairs. Our best values for the interaction dipole moment (at the respective experimental equilibrium separation R _e) were obtained at the coupled-cluster theory with single, double, and perturbatively linked triple excitations level of theory: μ_int(RgXe)/eα₀ = − 0.0025(He), − 0.0047(Ne), − 0.0055(Ar), and − 0.0037(Kr). The same trend (in absolute terms) is observed at the MP2 level of theory for the derivative of the dipole moment at R _e, as (dμ_int (RgXe)/dR) _e /e = 0.0043 (He), 0.0082 (Ne), 0.0091 (Ar), and 0.0059 (Kr). Around R _e , μ_int(HeXe) ≡ μ_HeXe varies at the MP2 level of theory as [μ_HeXe(R) − μ_HeXe(R _e)]/ea₀ = 0.0043(R − R _e) − 0.0033(R − R _e)² + 0.0018(R − R _e)³ − 0.0005(R − R _e)⁴.     

Density-functional theory (hyper)polarizabilities of push-pull pi-conjugated systems: treatment of exact exchange and role of correlation

The performance of the optimized effective potential procedure for exact exchange in calculating static electric-field response properties of push-pull pi-conjugated systems has been studied, with an emphasis on NO2-(CH=CH)n-NH2 chains. Good agreement with Hartree-Fock dipole moments and (hyper)polarizabilities is obtained; particularly noteworthy is the chain length dependence for beta/n. Thus, the problem that conventional density-functional theory functionals dramatically overestimate these properties is largely solved, although there remains a significant correlation contribution that cannot be accounted for with current correlation functionals.     

The collision-induced electric dipole moment of H(n=2) in H-He,Ne and Ar collisions

The collision-induced electric dipole moment of H(n=2) in H(1s)-Ne and H(1s)-Ar collisions was measured in an energy range of 1 to 25 keV. For these systems we observe a positive electric dipole moment which corresponds to an electron lagging behind the proton. This behaviour is in contrast to recent measurements for the H-He systems, where a negative dipole moment corresponding to an electron moving in front of the proton was observed. A simple explanation for this difference is given.     

Strong ionic interactions in noncovalent complexes between poly(ethylene imine), a cationic electrolyte,and Cibacron Blue,a nucleotide mimic – implications for oligonucleotide vectors

Cationic polymers can bind DNA to form polyplexes, which are noncovalent complexes used for gene delivery into the targeted cells. For more insight on such biologically relevant systems, the noncovalent complexes between the cationic polymer poly(ethylene imine) (PEI) and the nucleotide mimicking dye Cibacron Blue F3G‐A (CB) were investigated using mass spectrometry methods. Two PEIs of low molecular weight were utilized (M_n ≈ 423 and 600 Da). The different types of CB anions produced by Na⁺/H⁺ exchanges on the three sulfonic acid groups of CB and their dehydrated counterparts were responsible for complex formation with PEI. The CB anions underwent noncovalent complex formation with protonated, but not with sodiated PEI. A higher proportion of cyclic oligomers were detected in PEI423 than PEI600, but both architectures formed association products with CB. Tandem mass spectrometry studies revealed a significantly stronger noncovalent interaction between PEI and dehydrated CB than between PEI and intact CB. Copyright © 2014 John Wiley & Sons, Ltd.     

Solution-state conformations of 2-fluoro-, 2-chloro- and 2-bromo-acetophenone: a dipole moment and kerr effect study

Experimental dipole moments and infinite-dilution Kerr constants for 2-fluoro-, 2-chloro and 2-bromo-acetophenone (CH₃COC₆H₄X; X = F, Cl, Br) as solutes in CCl₄ at 25°C are analysed, yielding the following effective dihedral angles and percentage abundances of the less stable XO-cis conformers: X = F, 10 ± 10°, 5 ± 5%; X = Cl, 40 ± 5°, 10 ± 5%; and X = Br, 65 ± 10°, 25 ± 10%.     

Analytical approaches to the determination of simple biophenols in forest trees such as Acer (maple), Betula (birch), Coniferus, Eucalyptus, Juniperus (cedar), Picea (spruce) and Quercus (oak)

Analytical methods are reviewed for the determination of simple biophenols in forest trees such as Acer (maple), Betula (birch), Coniferus, Eucalyptus, Juniperus (cedar), Picea (spruce) and Quercus (oak). Data are limited but nevertheless clearly establish the critical importance of sample preparation and pre-treatment in the analysis. For example, drying methods invariably reduce the recovery of biophenols and this is illustrated by data for birch leaves where flavonoid glycosides were determined as 12.3 +/- 0.44 mg g(-1) in fresh leaves but 9.7 +/- 0.35 mg g(-1) in air-dried samples (data expressed as dry weight). Diverse sample handling procedures have been employed for recovery of biophenols. The range of biophenols and diversity of sample types precludes general procedural recommendations. Caution is necessary in selecting appropriate procedures as the high reactivity of these compounds complicates their analysis. Moreover, our experience suggests that their reactivity is very dependent on the matrix. The actual measurement is less contentious and high performance separation methods particularly liquid chromatography dominate analyses whilst coupled techniques involving electrospray ionization are becoming routine particularly for qualitative applications. Quantitative data are still the exception and are summarized for representative species that dominate the forest canopy of various habitats. Reported concentrations for simple phenols range from trace level (<0.1 microg g(-1)) to in excess of 500 microg g(-1) depending on a range of factors. Plant tissue is one of these variables but various biotic and abiotic processes such as stress are also important considerations.