TZ2P Basis Set Research Articles

Comparison of theoretical and experimental studies of infrared spectral data for the 5-membered ring heterocycles

A systematic study of the anharmonic vibration frequencies has been performed for furan, pyrrole, thiophene, both oxazoles and thiazoles, and both oxa- and thiadiazoles. The calculations were carried out under standard conditions with both the cc-pVTZ and a TZ2P basis set, and used both the B3LYP density functional (both bases) and MP2 ab initio techniques (cc-pVTZ only). The correlations of the MP2 results with experiment were much less favorable, with mean absolute differences (∣ d∣) being nearly twice as large as those with B3LYP. The TZ2P + B3LYP produced results very similar to the cc-pVTZ + B3LYP; the mean absolute frequency difference over 199 values between the two basis sets was ∣ d∣ 2.96 cm −1. In correlation with experimental frequencies, TZ2P + B3LYP over all experimental bands gave ∣ d∣ 10.13 cm −1; cc-pVTZ + B3LYP gave ∣ d∣ 11.56 cm −1. However, in some cases, such as oxazole, where band origins have been more accurately determined and Coriolis effects included, the correlation between theory and experiment is much closer, ∣ d∣ 7.2 cm −1. Since TZ2P processes much more rapidly than cc-pVTZ, it is more practicable for larger molecules, and hence is preferred.

What is the best theoretical method to study molybdenum dithiolene complexes?

The reaction sequence of sulfoxide reduction by molybdenum complexes containing two enedithiolate and one oxide ligand is used to evaluate different density functional methods. Relative energies are computed for several stationary points: a pentacoordinate reduced complex, its adducts with water and with the sulfoxide substrate, the transition state for oxygen atom transfer to the metal center, a van der Waals complex of the reduced sulfide with the molybdenum oxo complex and the isolated oxo complex itself. Root mean square deviations from CCSD results or values extrapolated (depending on the size of the ligands used) serve to assess the quality of various popular and promising modern DFT methods available in Gaussian03 (in combination with the SDD basis set augmented by additional polarization functions) and ADF2005 (TZP basis set). B3LYP, B1B95, B97-1 and B98 form the group of best functionals provided by Gaussian according to our criteria. PBE1PBE, B1LYP, MPW1PW91 and B97-2 have increasingly larger deviations but describe the considered reaction sequence qualitatively correct. The reaction profiles produced by HCTH147, BP86, HCTH407, BLYP, G96LYP and especially by OLYP, HCTH93, BH and H and VSXC have severe flaws. These functionals are not recommended for the treatment of oxygen atom transfer reactions involving transition metals. DFT functionals used with ADF derived energies for the BP/TZP density. The relative energies show larger RMS, which can be slightly reduced by inclusion of ZORA scalar relativistic effects and in the case of hybrid functionals further by ZORA spin-orbit relativistic effects. Geometries obtained with BP/TZP produce RMS deviations comparable to the best methods identified when relative energies are derived from single point energies computed by one of these methods.

A density functional study of the structure and potential energy surface of dibenzenechromium and its alkylated derivatives

Density functional calculations were performed with the nonempirically constructed PBE functional and TZ2p basis set to study the potential energy surfaces of several dibenzenechromium derivatives containing methy1 and tert-buty1 groups in aromatic ligands. The method was shown to correctly describe the structure and intramolecular dynamics of bis-arenechromium complexes. It allows barriers to rotation about the metal-ligand bond to be calculated and detailed information to be obtained about the shape of the potential curves that correspond to this rotation. The potential energy surfaces of polymethylated dibenzenechromium derivatives contained several minima close in energy; these minima largely corresponded to eclipsed conformers. The potential curves for rotation about the metal-ligand bond in dibenzenechromium and its methylated derivatives reveal the presence of staggered conformers as transition states. Irrespective of the number of methyl groups present in both ligands, we observed no substantial changes in barrier heights, which were about 1 kcal/mol. Conversely, the introduction of bulky tert-butyl groups destabilized eclipsed conformations. Ensuing steric strain caused substantial out-of-ring-plane displacements of the Cipso-t-Bu bonds away from the chromium atom, distorted aromatic ring planarity, and substantially increased barriers to rotation, to 8–10 kcal/mol.

Catalytic homogeneous hydrogenation of compounds containing X ? O semipolar bonds (X = N, S, P) with para-hydrogen as a promising route for preparation of para-water

The quantum-chemical simulation (DFT, PBE, TZ2p basis set) of the mechanism of catalytic hydrogenation of compounds containing R(n)X --> O semipolar bonds (R(n)X = N(2), Me(2)S, C(5)H(5)N, Ph(3)P) on the Wilkinson catalyst (Ph(3)P)(3)RhCl with para-hydrogen showed that this process proceeds with retention of proton nuclear spin correlation, which enables a principal possibility to synthesize para-H(2)O, i.e. the nuclear spin isomer of water with antiparallel proton spins, using this route.

Augmenting basis set for time-dependent density functional theory calculation of excitation energies: Slater-type orbitals for hydrogen to krypton

Attention is given to the dual nature of the time-dependent density functional theory approach for predicting excitation spectra, namely its theoretical basis in dynamic polarizability and its practical implementation in computer programs as a single configuration interaction. A procedure for generating diffuse functions to be added to standard Slater-type orbital basis sets for H to Kr is proposed and tested on ten close-shell molecules. The database for comparing the performance of standard and augmented basis sets consists of the 15 lowest transitions to valence and Rydberg-like states for each of the molecules. The results of this computational study are very encouraging. The addition of new augmenting functions improves the performance of standard basis sets significantly. For example, the new augmented TZP basis set, about the same size as the standard TZ2P set (and considerably smaller than the large QZ4P set), led to an average absolute deviation of 150 predicted excitation energies of only 0.12 eV from those obtained with the very large basis set called QZ3P-3DIFFUSE, compared to 0.83, 0.79, and 0.19 eV, for the standard TZP, TZ2P, and QZ4P sets, respectively. Similar augmenting functions for Gaussian-type orbital basis sets for H to Kr are also suggested.

Comparison of various Franck–Condon and vibronic coupling approaches for simulating electronic spectra: The case of the lowest photoelectron band of ethylene

Various time independent approaches for simulating electronic absorption spectra are discussed and applied to the lowest band (10.2-11.4 eV) of the photoelectron spectrum of ethylene. The electronic structure calculations for the ionized states of ethylene are performed using the Equation of Motion Coupled Cluster method for Ionization Potentials (IP-EOM-CCSD) in a TZ2P basis set. Various Franck-Condon (FC) and vibronic coupling model Hamiltonian approaches are used to simulate the spectrum and a comparison is made to the experimental data. The potential energy surface is highly anharmonic and it is necessary to use more sophisticated FC approaches than the traditional harmonic approach to obtain a qualitatively correct simulation of the spectrum. Duschinsky rotation is found to play an important role in determining the detailed intensity pattern of the spectrum, while non-adiabatic effects are found not to be important. The spectrum is found to be very sensitive to the precise values of some of the parameters used in the vibronic model, that determine the details of the adiabatic potential energy surface.

Sulfuric Acid and Sulfuric Acid Hydrates in the Gas Phase: A DFT Investigation

The gaseous sulfuric acid and its hydrates play an essential role in the formation and evolution of atmospheric aerosols via nucleation of binary sulfuric acid−water vapors. Recently, it has been pointed out that the dipole moment of vapor molecules and small preexisting clusters is a new parameter controlling the nucleation rates. In this paper, the dipole moments of the mono-, di-, and trihydrates of the sulfuric acid are calculated for the first time. We also report on the molecular structures, energies, vibrational frequencies, absorption intensities and dipole moments of the hydrates and compare our model predictions with the results of other studies. The density functional theory (DFT) calculations have been carried out using the PW91 method and TZP basis set. We have determined the optimized conformations of gas-phase sulfuric acid and mono-, di-, and trihydrates of sulfuric acid using different starting scenarios and computed their dipole moments. The obtained results can be utilized directly in the modeling of the atmospheric aerosol formation and they are applied for the analysis of the hydration thermodynamics.

Dinuclear and polynuclear transition metal complexes with macrocyclic ligands. 6. New dinuclear copper(ii) complexes with macrocyclic Schiff bases derived from 4-tert-butyl-2,6-diformylphenol

New dinuclear complexes containing CuII atoms in the cavity of a macrocyclic Schiff base were prepared by template condensation of 4-tert-butyl-2,6-diformylphenol with 1,3-diaminopropane in the presence of CuII trimethylacetate and chloride as well as by extra-ligand exchange. The mononuclear CuII complex with two 1,3-diaminopropane molecules can serve as an intermediate in this template synthesis. The reaction of CuII trimethylacetate with the unsymmetrical macrocyclic Schiff base synthesized earlier afforded a new dinuclear copper(ii) complex with the amine and imine nitrogen atoms in the coordination sphere. The structures of the new complexes were established by X-ray diffraction analysis and studied by the density functional theory (gradient-corrected PBE functional, TZ2p basis set).

Binuclear and polynuclear transition metal complexes with macrocyclic ligands. 3. New polydentate macrocyclic ligands in reactions of 4-alkyl-2,6-diformylphenols with 1,2-diaminobenzenes

The mechanism of abnormal condensation of 2,6-diformyl-4-R-phenols with 1,2-diaminobenzenes accompanied by the reduction of two of four double C=N bonds in macrocyclic Schiff"s bases formed was studied by DFT (gradient-corrected PBE functional, TZ2p basis set). In the first step, [1+1] Schiff"s base is formed and disproportionates further to afford amine and benzoimidazolylphenols. Two new macrocyclic polydentate ligands containing two CH2—NH moieties in the rings were synthesized. The reduction of one of these ligands with sodium borohydride gave the new macrocyclic ligand, whose structure and conformations were studied by the DFT method.

New vibrational assignments in the Ā1 Au-[Xtilde] 1Σ+ g electronic transition of acetylene, C2H2: the v′1 frequency

New laser-induced fluorescence spectra of supersonic jet cooled acetylene (C2H2) in the wavelength region 230–205 nm have led to an improved understanding of the vibrational structure of the A 1Au state. Among the new bands observed are two weak perturbed bands at 46008 cm−1 and 46116 cm−1. Rotational analyses of these bands, together with the corresponding ‘hot’ bands arising from the ground state v4 fundamental, have shown that the upper states have asymmetric top K structure that is unaffected by a axis Coriolis coupling; this means that they do not involve overtones of the low frequency bending vibrations and therefore must be combinations of ag vibrational normal modes. From their positions in the manifold, their vibrational assignments can only be 22 031 0; and 11 0;31 0. These assignments lead to values of x 22, x13, and a revised value for the symmetric CH stretching frequency, ν1 = 2880.5cm−1; this revised value is 160cm−1 lower than the previously accepted value, but consistent with new ab initio calculations that we performed at the EOM-CCSD level using a TZ2P (triple-zeta plus double polarization) basis set.

Odd carbon long linear chains HC2n+1H (n = 4-11): properties of the neutrals and radical anions.

The optimized geometries, adiabatic electron affinities, vertical electron affinities, vertical electron detachment energies (for the anions), and IR-active vibrational frequencies have been predicted for the long linear carbon chains HC(2)(n)()(+1)H (n = 4-11). The B3LYP density functional combined with DZP and TZ2P basis sets was used in this theoretical study. These methods have been extensively calibrated versus experiment for the prediction of electron affinities (Chem. Rev. 2002, 102, 231). The computed physical properties are discussed and compared with the even carbon chains HC(2)(n)()H. The predicted electron affinities form a remarkably regular sequence: 2.12 eV (HC(9)H), 2.42 eV (HC(11)H), 2.66 eV (HC(13)H), 2.85 eV (HC(15)H), 3.01 eV (HC(17)H), 3.14 eV (HC(19)H), 3.25 eV (HC(21)H), and 3.35 eV (HC(23)H). These electron affinities are as much as 0.4 eV higher than those for analogous even carbon chains. The predicted structures display an intermediate cumulene-polyacetylene type of bonding, with the inner carbons appearing cumulenic and the outer carbons polyacetylenic.

Multi-coefficient correlated quantum mechanical studies for hydrated proton clusters

High-level quantum mechanical calculations have been performed systematically for hydrated proton clusters to understand the mechanism of proton transfer in water. Recently developed multi-coefficient correlated quantum mechanical methods, in particular, MCCM-UT-MP4SDQ, and MCCM-UT-CCSD, were used to calculate energies. Structures and frequencies were calculated at the MP2 level using the TZ2P and cc-pVTZ basis sets. The hydration enthalpies from the MCCM methods agree very well with experimental values. The conversion between H 9O 4 +(I) and H 9O 4 +(II) clusters was suggested to be important for aqueous proton transfer.

Fragmentation path for hydrogen atom dissociation from methoxy radical

Salient features of the potential surface for hydrogen atom dissociation from the methoxy radical (CH3O) have been investigated via high-level coupled-cluster methods using a TZ2P(f,d) basis set for geometry optimization and harmonic vibrational analyses and the correlation-consistent cc-pVXZ (X=2–6) series for final energetic determinations and extrapolations. Of central concern for continuing photofragmentation dynamics experiments is the Cs-symmetry A′2 transition state for dissociation, which TZ2P(f,d) RCCSD(T) theory locates at a critical C–H distance of 1.79 Å with a barrier frequency of 947i cm−1. Our zero-point-corrected focal-point extrapolations place this transition state 4.7 kcal mol−1 above the CH2O+H products and yield a dissociation energy of 20.1 kcal mol−1; the latter differs from the most reliable experimental values by only 0.2–0.3 kcal mol−1. A revised enthalpy of formation, ΔHf,0°(CH3O)=6.5 kcal mol−1, is proposed. Disappointingly, TZ2P(f,d) UB3LYP theory underestimates the CH2O+H association barrier by 2.3 kcal mol−1, missing about half the barrier height. The complete set of TZ2P(f,d) RCCSD(T) data for structures and frequencies coupled with final focal-point energetics provides definitive values for parameters essential to the analysis of experimental photofragmentation rate profiles.

Heteroorganic betaines. 8.* Synthesis and structures of silicon- and germanium-containing organoarsenic betaines R13As+-CR2R3-EMe2-S- (E = Si,Ge)

The reactions of ylides R13As=CHR2 with hexamethyl-2,4,6-trisila- and hexamethyl-2,4,6-trigermatrithiacyclohexanes afforded betaines R13As+—CHR2—SiMe2—S– (2) (R1 = Et; R2 = Ph (a), Me3Si (b); R1 = R2 = Ph (c)) and Et3As+—CH(SiMe3)—GeMe2—S– (3), respectively. Betaines 2a,b and 3 were characterized by multinuclear NMR spectroscopy. According to the X-ray diffraction data, in the crystals the As+—C—E—S– main chain (E = Si or Ge) of molecules 2a,b and 3 adopts a twisted cis conformation due to strong intramolecular Coulomb interactions between the anionic and cationic centers. The equilibrium geometries of isolated molecules 2a and 3, which were calculated within the framework of the density functional theory (the PBE functional, the TZ2P basis set), are in qualitative agreement with the X-ray data. In solutions, betaines 2a (in the absence of Li salts) and 2c (in the presence of LiBr) selectively decomposed according to the Corey—Chaykovsky reaction, which was accompanied by elimination of R3As and, probably, the intermediate formation of silathiirane. The subsequent transformation of the latter afforded 2,2,4,4-tetramethyl-5-phenyl-2,4-disila-1,3-dithiolane.

Heteroorganic betaines. 7. Synthesis and structure of a germanium-containing organophosphorus betaine Et3P+—CHMe—GeMe2—S–

Germanium-containing organophosphorus betaine Et3P+—CHMe—GeMe2—S– was synthesized by the reaction of hexamethylcyclotrigermatrithiane with Et3P=CHMe. The structure of the betaine was established by X-ray diffraction analysis and multinuclear NMR spectroscopy. In the crystal, the P+—C—Ge—S– main chain of the molecule adopts a folded cis-gauche conformation due to strong Coulomb interactions between the anionic and cationic centers. The equilibrium geometry of the isolated molecule was calculated within the framework of the density functional theory (the PBE functional, the TZ2P basis set). The calculated geometric characteristics are in qualitative agreement with the X-ray data. The structure of the betaine is compared with the structure of its silicon-containing analog studied previously.

Heteroorganic betaines. 6. Structure and reactivity of silicon-containing organophosphorus betaines with the –S—Si—C—P+ fragment: a DFT study

The structures of silicon-containing organophosphorus betaines –S—SiR1 2—CR2 2—P+R3 3 and their ylide isomers were calculated using the density functional approach with the gradient-corrected PBE functional and extended TZ2P basis set. Three possible pathways of thermal decomposition of these betaines were analyzed. These are (i) cleavage of the central C—Si bond with the formation of a Wittig ylide and silanethione, (ii) intramolecular nucleophilic S N-substitution with elimination of phosphine PR3 3 and the formation of silathiirane (the Corey—Chaikovscky transformation), and (iii) a Wittig-type decomposition followed by the formation of substituted silaethylene. The structures of products and transition states of these reactions were calculated. The cis-gauche conformation of the –S—Si—C—P+ fragment of betaines was found to be the most stable. This is in agreement with the results of X-ray diffraction study and can be rationalized by strong Coulomb attraction between the cationic and anionic centers. The betaines are stable toward retro-Wittig thermal decomposition. The Corey—Chaikovscky formation of thiirane is preferable under conditions of thermal decomposition. Retro-Wittig-type decomposition of betaines followed by the formation of silanethione is favored by intra- and intermolecular coordination of donor ligands.

Dimethyldioxirane, Carbonyl Oxide, and the Transition State Connecting Them: Electronic Structures, Relative Energies, and Vibrational Frequencies

The electronic structures and vibrational frequencies of dimethyl-substituted carbonyl oxide and its cyclic isomer dimethyldioxirane have been investigated using high-level ab initio quantum mechanical techniques with large basis sets. The equilibrium geometries have been optimized at the self-consistent field (SCF), the single and double excitation configuration interaction (CISD), the coupled cluster with single and double excitation (CCSD), and the CCSD with connected triple excitations [CCSD(T)] levels of theory. The absolute and relative energies of carbonyl oxide, dimethyldioxirane, and the transition state between them have also been computed. At the highest level of theory employed in this study, TZP CCSD(T), dimethyldioxirane is predicted to be lower in energy than the carbonyl oxide by 23.2 kcal/mol with the inclusion of zero-point vibrational energy (ZPVE) corrections. The energy barrier for the cyclization of carbonyl oxide becomes 19.5 kcal/mol at the same level of theory. Harmonic vibrational frequencies and infrared (IR) intensities are determined at the DZP SCF and TZP SCF levels of theory for the dimethyl-substituted carbonyl oxide and the transition state, and at correlated levels (CISD and CCSD) with DZP and TZP basis sets for dimethyldioxirane. The experimental vibrational frequencies of dimethyldioxirane are assigned using the present theoretical predictions. It is hoped that the theoretical frequencies for the dimethyl carbonyl oxide isomer will stimulate new experiments.

Theoretical study of XONO2 (X=Br, OBr, O2Br): Implications for stratospheric bromine chemistry

The equilibrium structure, dipole moment, harmonic vibrational frequencies, and infrared intensities of XONO2 (X=Br, OBr, O2Br) are determined using density functional theory in conjunction with a TZ2P (triple zeta double polarized) basis set. The B3LYP functional was used since this has previously been shown to perform well for similar bromine compounds. The equilibrium geometry and vibrational spectra of BrONO2 are shown to be in good agreement with the experimental data and also with high-level coupled-cluster calculations. The vibrational spectrum of O2BrONO2 has been compared with that of the chlorine analog, O2ClONO2, for which some experimental data exist. The bonding in OBrONO2 is shown to be more similar to that in BrONO2. Using large atomic natural orbital basis sets, the singles and doubles coupled-cluster method that includes a perturbative correction for triple excitations, denoted CCSD(T), was employed to compute energies for three isodesmic reactions in order to determine heats of formation for OBrONO2 and O2BrONO2. Our best estimates are 36.7 and 38.7 kcal/mol, respectively. Finally, the possible formation of O2BrONO2 in the stratosphere by adduct formation and oxidation of OBrONO2 and the implications for stratospheric bromine chemistry are discussed.

Mechanism of some 1:2 hydrogen transfer reactions through bond variation indices

Hydrogen-transfer isomerization processes HCN, HNC: and HCCH, :CDCH2 were studied in terms of bond order variations to understand the mechanism and asynchronous behavior of bond rearrangements by high quality ab initio calculations with TZ2p(d,f) basis sets. Bond orders were calculated from the TZ2p basis sets at the SCF level. Results from the bond order calculations clearly reveal that the migrating hydrogen when moves in curved paths that not only interact with the in plane and orbitals of the triple bond (C Co r CN) but also primarily causes the asynchronous behavior in the overall reaction mechanism. Overall advancement of the reaction in terms of individual bond-rearrangement processes on a relative footing is presented, which indicates the prime cause for the origin of activation barrier comes from the transforming multiple bonds in both these reactions. Easier computations of these bond indices not only reveal the significant insight into the importance of individual bonds during transformation, but also their application to larger systems. c 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1283-1291, 2000

Examination of the Stabilities of Group 14 (C, Si, Ge, Sn, Pb) Congeners of Dihydroxycarbene and Dioxirane. Comparison to Formic Acid and Hydroperoxycarbene Congeners.

The relative energetics of four XH(2)O(2) (X = C, Si, Ge, Sn, Pb) isomers, dihydroxycarbene, formic acid, dioxirane, and hydroperoxycarbene, were determined using the BLYP and B3LYP density functionals with DZP and TZ2P basis sets, as well as CCSD and CCSD(T) single-point energies at the BLYP/TZ2P optimized geometries. Relative to dihydroxycarbene, formic acid was 41.8 kcal/mol lower in energy while dioxirane and hydroperoxycarbene were 51.3 and 63.6 kcal/mol higher, respectively, with CCSD(T). Furthermore, using an effective core potential (ECP) the dihydroxy congener was shown to be the most stable isomer for X = Si-Pb. The formic acid and dioxirane congeners become increasingly less stable as one descends group 14. Our results show that divalency is preferred for Si-Pb (dihydroxy congeners are the most stable) but the tetravalent formic acid congeners remain more stable than the hydroperoxy congeners, showing that divalency is not universally preferred among these isomers.