cc-pVTZ Basis Set Research Articles

Enhanced NLO activity of organic 2-methyl-5-nitroaniline crystal: Experimental and computational investigation with and without silver addition

The nonlinear optical (NLO) material, 2-methyl-5-nitroaniline (M5NA), is synthesized and the crystals are grown by slow evaporation technique. The theoretical vibrational spectral analyses are done for the first time for M5NA using B3LYP computational method with the basis set cc-pVTZ. Natural Bond Orbital (NBO) and Atoms In Molecules (AIM) analyses are carried out for obtaining the charge transfer interactions and the Hirshfeld surface analysis with the fingerprint plot is performed for finding out the intermolecular interaction sites of the molecule. Using the theoretical and experimental IR and Raman spectra, the vibrations of M5NA are estimated. Changes in the linear and nonlinear optical properties with the addition of silver nanoparticles are studied from the UV–vis absorption spectra and the Z-Scan curves. A comparison of the hyperpolarizability values is done with pure and silver-added M5NA.

Ionic radii of hydrated sodium cation from QTAIM.

The sodium cation is ubiquitous in aqueous chemistry and biological systems. Yet, in spite of numerous studies, the (average) distance between the sodium cation and its water ligands, and the corresponding ionic radii, are still controversial. Recent experimental values in solution are notably smaller than those from previous X-ray studies and ab initio molecular dynamics. Here we adopt a "bottom-up" approach of obtaining these distances from quantum chemistry calculations [full MP2 with the 6-31++G(d,p) and cc-pVTZ basis-sets] of gas-phase Na+(H2O)n clusters, as a function of the sodium coordination number (CN = 2-6). The bulk limit is obtained by the polarizable continuum model, which acts to increase the interatomic distances at small CN, but has a diminishing effect as the CN increases. This extends the CN dependence of the sodium-water distances from crystal structures (CN = 4-12) to lower CN values, revealing a switch between two power laws, having a small exponent at small CNs and a larger one at large CNs. We utilize Bader's theory of atoms in molecules to bisect the Na+-O distances into Na+ and water radii. Contrary to common wisdom, the water radius is not constant, decreasing even more than that of Na+ as the CN decreases. We also find that the electron density at the bond critical point increases exponentially as the sodium radius decreases.

Tetrakis(1,2,5-thiadiazolo)porphyrazines. 9. Synthesis and spectral and theoretical studies of the lithium(i) complex and its unusual behaviour in aprotic solvents in the presence of acids.

The template cyclotetramerization of 1,2,5-thiadiazolo-3,4-dicarbonitrile in the presence of lithium n-butoxide in n-butanol leads to the Li(i) complex of tetrakis(1,2,5-thiadiazolo)porphyrazine. Various possible structures of dilithium and monolithium complexes have been considered by DFT/B3LYP molecular modelling using the cc-pvtz basis set, and their theoretical IR and UV-VIS spectra have been calculated. The experimental 7Li NMR, IR and UV-VIS spectra measurements show that the complex contains two inequivalent lithium atoms - one is coordinated to the macrocyclic dianion to form the anionic lithate complex [TTDPaLi]-, while the other forms the solvated countercation [Li(Solv)4]+. The lithate complex is stable in protic solvents, such as methanol, and is soluble in water to give aggregated solutions. Its demetallation occurs in the presence of acids (CH3COOH, CF3COOH, H2SO4). In aprotic solvents (DMF, DMSO), the acid-catalyzed formation of the [TTDPa]2- dianion is observed which is followed by the formation of the meso-protonated form {H[TTDPa]}- at higher acid concentrations. Both processes can be reversed by the addition of a lithium salt excess or neutralization of the acid. The fluorescence quantum yield for the lithate complex [TTDPaLi]- is much higher than that for the [TTDPa]2- dianion (0.34 and 0.01 in DMSO), and this can be used for detecting low concentrations of acids and Li+ in aprotic solvents (10-6-10-5 M). The first reversible reduction of the macrocycle in the anionic lithate complex (-0.94 V vs. SCE in DMSO) is ∼0.5 V more difficult than that in the complexes with divalent metals [TTDPaM] (M = MgII, ZnII, CuII).

The symmetry breaking phenomenon in heteronine analogues due to the pseudo Jahn-Teller effect.

The pseudo Jahn-Teller effect (PJTE) is employed in C8AH8 (A = O, S, Se, Te), and C8EH8 + 1 (E = N, P, As, Sb) with planar configurations to show symmetry breaking phenomena (SBP) in heteronine analogues, and to explain why molecules with (C2v) high-symmetry configurations cannot maintain planarity and pucker to their (C2) and (Cs) lower-symmetry structures, respectively. To investigate this phenomenon, geometry optimization and frequency calculations through the density functional B3LYP method using the cc-pVTZ basis set (for Te, and Sb cc-pVTZ-PP) were carried out for all compounds in the series. The state average-complete active space self-consistent field wave-function method was employed to calculate the electronic ground and several low-lying excited states to specify the adiabatic potential energy surface along the a2 and b1 puckering nuclear displacements. The PJTE (A1 + A2 + A1') a2 and (A1 + B1 + A1') b1 problems were formulated as the effects originating via the PJTE theorem. Moreover, replacing hydrogen atoms in C8NH9, a stable planar structure, with fluorine ligands demonstrated that SBP occur from C2v to C2 symmetry. Furthermore, thermochemical calculations via B3LY/cc-pVTZ illustrated that the planarity of the C8E ring is restored in C8EH8- (E = P, As, Sb) anions ,with the change in free energy corresponding to spontaneous deprotonation reactions as 23.67kJmol-1, 21.88kJmol-1, and 16.57kJmol-1, respectively. In fact, despite C8EH8 + 1 having a donor electron-pair and potentially being Lewis base compounds, it acts as a Bronsted-Lowry acid releasing a H+ proton instead in this case.

Theoretical investigation of intramolecular π-type hydrogen bonding and internal rotation of 2-cyclopropen-1-ol, 2-cyclopropen-1-thiol and 2-cyclopropen-1-amine

ABSTRACTTheoretical computations utilising both CCSD and MP2 methods and the cc-pVTZ basis set have been carried out to determine the structures of several conformations as well as the internal rotation potential energy functions for 2-cyclopropen-1-ol, 2-cyclopropen-1-thiol and 2-cyclopropen-1-amine. The energies and wavefunctions for these potential functions have also been computed. Each of these molecules has an energy minimum corresponding to a conformation with intramolecular π-type hydrogen bonding. The π bonding stabilisation is about 2.3 kcal/mole for the alcohol, 2.1 kcal/mole for the thiol, and about 2.5 kcal/mole for the amine. The results for the thiol demonstrate a rare example of intramolecular π-type hydrogen bonding. The calculated O–H, S–H, N–H, and C=C stretching frequencies have also been compared for the conformations with and without the π-type hydrogen bonding. The C=C stretching frequency is substantially lower in all cases for the hydrogen bonded conformers.

Computational Study of the Reaction of Dimethyl Ether with Nitric Oxide. Mechanism and Kinetic Modeling.

To probe into the autoignition effect of nitric oxide (NO) on the combustion of dimethyl ether (DME), a detailed mechanism study and kinetic modeling for the reaction of DME with NO, which was considered to be very sensitive to the ignition delay time of DME, have been conducted using computational chemical methods. The CCSD(T)/6-311+G(2df,2p)//B2PLYP/TZVP compound method was employed to obtain the potential energy surface along the reaction coordinate, with the geometries, gradients, and force constants of nonstationary points calculated at the B2PLYP/TZVP theoretical level. The temperature-dependent rate coefficients from 200 to 3000 K were calculated using multistructural canonical variational transition-state theory (MS-CVT) with torsional motions and multidimensional tunneling effects included. The CCSD(T) calculations with both 6-311+G(2df,2pd) and cc-pVTZ basis sets give a zero-point inclusive barrier of 197-201 kJ mol-1 using the BMK/MG3S, B2PLYP/TZVP, and mPW2PLYP/TZVP based geometries. A van der Waals postreaction complex appears on the products HNO + CH3OCH2 side of the transition state. Two highly coupled torsions lead to four conformers for the transition state, and contributions from multiple structures and torsional anharmonicities substantially affect the rate coefficient evaluations. Variational effects can be argued to play an important role, especially at high temperatures, and tunneling probabilities increase with decreasing temperature. Because of large temperature-dependent feature of activation energy, the four-parameter formula 1.912 × 1011( T/300)3.191 exp[-178.417( T - 2.997)/( T2 + 2.9972)] cm3 mol-1 s-1 is recommended for the MS-CVT calculated rate coefficients including small-curvature tunneling. The kinetic model is shown to give a satisfactory interpretation of the inhibited and accelerated effect of NO on the oxidation of DME.

$$\hbox {H}^{+} + \hbox {O}_2$$ H + + O 2 system revisited: four-state quasidiabatic potential energy surfaces and coupling potentials

The global adiabatic and quasidiabatic potential energy surfaces for the ground and first three excited ( $$1-4\, ^3\text {A}^{\prime \prime }$$ ) electronic states of $$\hbox {H}^{+} +\hbox {O}_2$$ system are reported on a finer grid points in the Jacobi coordinates using Dunning’s cc-pVTZ basis set and internally contracted multi-reference (single and double) configuration interaction method. Ab initio procedures have been used to compute the corresponding quasidiabatic surfaces and radial coupling potentials which are relevant for the dynamical studies of inelastic vibrational excitation and charge transfer processes. Nonadiabatic couplings arising out of relative motion of proton and the vibrational motions of $$\hbox {O}_2$$ between the adiabatic electronic states have also been analyzed. Adiabatic and quasidiabatic potential energy surfaces have been constructed using ab initio procedure for the lowest four 1-4 $$^{3}A''$$ electronic states of $$\hbox {H}^{+}$$ + $$\hbox {O}_{2}$$ collision system. The computed quasidiabatic surfaces and coupling potentials would be helpful in understanding the collision dynamics of inelastic and charge transfer processes in the system.

Light-dependent isomeric effects of polycyclic aromatic hydrocarbons on the predication of DNA cleavage factor efficiency

PAHs, short for polycyclic aromatic hydrocarbons, are a ubiquitous group of chemically related, environmentally persistent organic compounds having diverse structures and varied toxicity. They have been shown to cause mutagenic and carcinogenic effects on organisms and are quite immunosuppressive. Time-dependent density functional theory (TD-DFT) offers a practical means of understanding the behavior of excitation energies for PAHs. Here, we examined the performance of the long-range corrected Coulomb-attenuating functional (CAM-B3LYP) in relation to four different basis sets, determining which basis set compliments the functional better in identifying the most reactive atomic site on six isomeric PAH compounds. Condensed Fukui function indices were used to compare the performance of applied basis sets in identifying the most reactive atomic site on six isomeric PAHs compounds, assessing which basis set would be more appropriate in determining the site where free-radical formation would occur after light irradiation. Dunning’s correlation consistent triple-zeta (cc-pVTZ) basis set was determined to have the best PAH characterization performance, concluding the need for application of a higher-level basis set with the long-range corrected Coulomb-attenuating functional. Although each compound was a structural isomer of the other, the reactive atomic sites varied for each molecule with the use of an applied basis set. It was concluded that structural shape has some influence on the calculation of PAH characteristics. Lastly, in order to predict DNA single-stranded cleavage factor for the compounds proposed here, we have used the quantitative structure-activity relationship (QSAR). The cleavage factor values for the set of aromatic molecules with similar structures have been collected from the literature for a total number of 22 compounds.

High-resolution FTIR spectroscopy of H13COOD: The ground state and v2 = 1 state rovibrational constants

The Fourier transform infrared (FTIR) rovibrational spectrum of the ν2 band of the formic acid isotopologue H13COOD was recorded in the 2550–2710 cm−1 region at an unapodized resolution of 0.0063 cm−1. Rovibrational constants up to three quartic terms were derived for the first time with high precision for the v2=1 state through the fitting of 626 infrared transitions using the Watson’s A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.0023 cm−1. The rotational energy levels of the ν2 band was found to be perturbed by a nearby 3ν7 + ν8 band. From the analysis, a- and b-Coriolis resonance parameters from the interactions of the ν2 band with 3ν7 + ν8 band were obtained for the first time. The rotational constants A and B along with the band center of the 3ν7 + ν8 band were also derived for the first time in this work. The band centers of the ν2 and 3ν7 + ν8 bands of H13COOD were determined as 2631.13155(34) cm−1 and 2596.31(19) cm−1 respectively. The ground state constants of H13COOD were determined with higher precision than previously by fitting 301 ground state combination-differences (GSCDs) from the present work and 24 previous microwave measurements with rms deviation of 0.00073 cm−1. The equilibrium state rovibrational constants up to five quartic terms were derived from theoretical anharmonic calculations at four levels of theory: MP2/cc-pVTZ, B3LYP/cc-pVTZ, MP2/cc-pVQZ and B3LYP/cc-pVQZ using the principal axis coordinate system. These calculated constants agree with the ground state constants of H13COOD derived from the current experimental GSCD combined with microwave transitions fit. In addition, all three rotational constants (A, B and C) of the ground state of H13COOD were obtained from anharmonic calculations using B3LYP and MP2 levels with the cc-pVTZ and cc-pVQZ basis sets. These rotational constants were found to agree with those derived experimentally with percentage deviations within 1.0%.

Contrasting Synergistic Heterobimetallic (Na-Mg) and Homometallic (Na or Mg) Bases in Metallation Reactions of Dialkylphenylphosphines and Dialkylanilines: Lateral versus Ring Selectivities.

A series of dialkylphenylphosphines and their analogous aniline substrates have been metallated with the synergistic mixed-metal base [(TMEDA)Na(TMP)(CH2 SiMe3 )Mg(TMP)] 1. Different metallation regioselectivities for the substrates were observed, with predominately lateral or meta-magnesiated products isolated from solution. Three novel heterobimetallic complexes [(TMEDA)Na(TMP)(CH2 PCH3 Ph)Mg(TMP)] 2, [(TMEDA)Na(TMP)(m-C6 H4 PiPr2 )Mg(TMP)] 3 and [(TMEDA)Na(TMP)(m-C6 H4 NEt2 )Mg(TMP)] 4 and two homometallic complexes [{(TMEDA)Na(EtNC6 H5 )}2 ] 5 and [(TMEDA)Na2 (TMP)(C6 H5 PEt)]2 6 derived from homometallic metallation have been crystallographically characterised. Complex 6 is an unprecedented sodium-amide, sodium-phosphide hybrid with a rare (NaNNaP)2 ladder motif. These products reveal contrasting heterobimetallic deprotonation with homometallic induced ethene elimination reactivity. Solution studies of metallation mixtures and electrophilic iodine quenching reactions confirmed the metallation sites. In an attempt to rationalise the regioselectivity of the magnesiation reactions the C-H acidities of the six substrates were determined in THF solution using DFT calculations employing the M06-2X functional and cc-pVTZ Dunning's basis set.

Semiexperimental equilibrium molecular structures of the maleimide and phthalimide

ABSTRACTSemiexperimental (SE) equilibrium molecular structures of the title compounds are determined using rotational and ab initio data. Cubic force constants for the parent molecules and a number of isotopologues are calculated at the B2PLYP double hybrid functional with the correlation-consistent triple-ζ cc-pVTZ basis set. Rovibrational and electronic corrections necessary for the transformation of observed ground-state rotational constants to equilibrium ones are calculated using cubic force constants and rotational g tensors. The SE structure parameters are compared with those obtained with CCSD(T) method and basis set of quadruple-ζ quality.Abbreviations: MP2: Møller–Plesset perturbation theory; CCSD(T): coupled-cluster theory including single and double excitations augmented by a perturbational estimate of the effects of connected triple excitations; VnZ: cc-pVnZ, Dunning's correlation-consistent basis, where n = T or Q; CVnZ: cc-pCVnZ, Dunning's correlation-consistent basis, where n = T or Q; wCVnZ: cc-pwCVnZ, Dunning's correlation-consistent basis, where n = T or Q; AwCVQZ: aug-cc-pwCVQZ, Dunning's correlation-consistent basis; AE: all-electrons; FC: frozen core; QM: quantum mechanics; MAD: mean absolute deviation; SE: semiexperimental equilibrium structure; BO: best ab initio Born–Oppenheimer composite structure; HOMA: harmonic oscillator model of aromaticity; ICSS: iso-chemical shielding surface (isosurface of magnetic shielding value or isosurface of NICS with inverted sign); ICSSZZ: component of magnetic shielding tensor perpendicular to molecular plane; NICS: nuclear independent chemical shift; AIM: atoms in molecules method; ACID: anisotropy of current induced density

Microwave spectrum and structure of the lowest A – internal rotor state of Ar⋅⋅⋅CH3I

The microwave spectrum of the lowest A-internal rotor state of Ar⋅⋅⋅CH3I has been observed by chirped-pulse and conventional cavity Fourier transform microwave spectroscopy. Using the observed spectroscopic constants, the system is determined to be an asymmetric rotor with an Ar⋅⋅⋅I distance of 4.1941(14) Å, an Ar⋅⋅⋅C distance of 3.874(16) Å, and an Ar⋅⋅⋅I–C angle of 66.5(4)°. Additionally, MP2 and M06-2X calculations were performed with MIDI! and SDB-aug-cc-PVTZ basis sets on iodine and a cc-PVTZ basis set on all other atoms. The MP2 calculations gave better agreement with the experimentally determined intermolecular separation, while the M06-2X calculations gave a slightly better result for the angular orientation of the CH3I moiety. MP2 calculations with a 6-311G(d,p) basis set on all atoms were also performed, but were generally not as effective at reproducing the experimentally derived geometry. None of the calculations proved satisfactory for predicting the nuclear quadrupole coupling constants of the iodine. The computed barriers to internal rotation of the methyl group ranged from 8 to 94 cm−1, depending on the method and basis set used.

Kinetics and mechanism of 3-chloro-2-methyl-1-propene(3-ClMP) initiated by OH radical: an insight from DFT calculations[1

ABSTRACTIn this manuscript, OH-initiated gas phase reactions of 3-chloro-2-methyl-1-propene [CH2=C(CH3)CH2Cl] has been carried out by using density functional theory (DFT) method. We have chosen M06-2X hybrid density functional method along with 6-31 + G(d,p) basis set for optimisation and vibrational frequency calculations of all the relevant molecular species of the titled reaction. Energetic calculations have been further refined at CCSD(T) method along with cc-pVTZ basis set in order to obtain higher degree of precision of thermo-chemical and kinetic results. Energy profile is presented for all stationary points involved in the titled reaction and thermochemistry for all possible reaction channels (H-abstraction and OH-addition reactions) has been analysed. Canonical Transition State Theory (CTST) has been employed to determine the rate constants within the temperature range of 250–450 K and Our reported rate constant at 298 K are found to be close to the reported experimental rate constant. The atmospheric lifetime of the titled molecule has also been reported in this work. We have also reported standard enthalpies of formation of the titled molecule and generated product radicals by using group-balanced isodesmic reaction schemes.

Excited state dipole moments of anisole in gas phase and solution

The excited state dipole moment of anisole has been determined in the gas phase from electronic Stark spectroscopy and in solution using thermochromic shifts in ethyl acetate. Electronic excitation increases the anisole dipole moment in the gas phase from 1.26 D in the ground state to 2.19 D in the electronically excited singlet state, leaving the orientation of the dipole moment practically unchanged. These values are compared to solution phase dipole moments. From variation of the fluorescence emission and absorption maxima with temperature, an excited state dipole moment of 2.7 D was determined. Several solvent polarity functions have been used in combination with experimentally determined cavity volumes at the respective temperatures. Both gas phase and condensed phase experimental dipole moments are compared to the results of ab initio calculations at the CC2 level of theory, using the cc-pVTZ basis set for the isolated molecule and using the COnductor-like Screening MOdel (COSMO), implemented in Turbomole, for the solvated anisole molecule.

Unequivocal structural assignments of three cardanol derivatives: An experimental and theoretical approach

Cardanol was obtained by vacuum distillation of ‘‘cashew nut shell liquid’’ (CNSL). Cardanol is a by-product of cashew production and a building block for chemical synthesis; cardanol and its derivatives can be used for different types of applications. Three of these compounds are the subject of the present NMR study and theoretical comparison. 1H and 13C NMR signals were assigned using 1D and 2D NMR experiments. The DFT/B3LYP method using the cc-pVTZ basis set was employed for the calculations of the 1H and 13C NMR chemical shifts (δ). The obtained data were used as an auxiliary tool for unequivocal assignment of all 1H and 1³C NMR signals. For these compounds, the adopted theoretical model was sufficient to obtain a good description of the chemical shifts.

Electronic structure and spectral properties of indole based fluorescent styryl dyes: Comprehensive study on linear and non-linear optical properties by DFT/TDDFT method

The photophysics, linear and non-linear optical properties of indole based fluorescent styryl dyes are investigated with density functional theory and time-dependent density functional theory. The performance of seven global hybrid functionals - B3LYP, PBE0, BHHLYP, M06, M06-L, M06-2X, M06-HF and six range separated hybrid functionals - CAM-B3LYP, HISSbPBE, HSEH1PBE, ωB97, ωB97X, ωB97XD with poples [6-311++G(d,p)] and correlation consistence (cc-pVDZ, cc-pVTZ) basis sets is analyzed. The linear (vertical excitations, oscillator strengths) and non-linear optical parameters (first and second order hyperpolarizabilities) are calculated with each functional in combination with different basis sets for comparison. The vertical excitation of all the dyes are shown to have good correlation with the experimental values by the M06-2X/6-311++G(d,p) and HISSbPBE/cc-pVDZ combination with the least deviations (mean standard error) of 8.67 nm and 4.34 nm with respect to global and range separated hybrid functionals respectively. On the other hand, polarizability and hyperpolarizability values evaluated for all the dyes suggested that the dye which contain N-ethyl group as a donor and nitro group as an acceptor is found to have the largest NLO response as compared to other dyes. Mean standard error was calculated for each system with respect to global and range separated hybrid functionals to evaluate the accuracy of the DFT methods. Mean standard error of polarizability and hyperpolarizability obtained using global hybrids and range separated hybrid functionals are found to be basis sets dependent i.e. each functional and basis set combination perform differently.

MOLECULAR STRUCTURE AND VIBRATION SPECTRA OF PIVALIC ACID

The metal carboxylates such as metal pivalates (salts of the pivalic acid (CH3)3CCOOH) attract a great interest as most promising precursors for chemical vapor deposition (CVD) technology. The possibility to use these substances in the CVD technology is specified by their good thermal stability and high volatility. For modeling of chemical reactions with metal pivalates in the gas-phase and the data on molecular structure will be very useful, in particularly information about effect of central metal ion to geometry of pivalic ligands. In the frame of this task the structures of metal pivalate molecules and pivalic acid (H(piv)) in a gas phase should be finding. The aim of present work is theoretical investigation of the geometry and IR-spectrum of H(piv) using density functional theory (DFT) methods. All calculations were performed using the Gaussian 03 program. The optimization of geometry and quadratic force field calculations were carried out using DFT functionals B3LYP, PBE, PBE0 and BP86 with correlation-consistent triple-ζ valence cc-pVTZ basis sets for O, C, and H. Appropriate assignment of vibrational modes was carried out by the potential energy distribution (PED) analysis among internal coordinates using the SHRINK program. According to DFT computations, the H(piv) molecule has an equilibrium structure of Cs symmetry with Гvib=26A'+19A''. The theoretical and experimental IR-spectra are satisfactorily agreed. The comparison of the ten intensities of highest bands in spectra allowed determining linear correlation between peaks position in experimental and modeling IR-spectra. It should be note the complicated composition of vibrational modes.

Post-CCSD(T) contributions to total atomization energies in multireference systems.

We examine the magnitude and the basis set convergence of post-coupled-cluster with single, double, and perturbative triple excitations (CCSD(T)) contributions (up to CCSDTQ567) for a wide and diverse set of 21 first- and second-row molecules with up to four non-hydrogen atoms. We focus on multireference systems for which post-CCSD(T) effects are particularly pronounced. The considered molecules are BN(1∑+), C2(1∑+), O2, FO, P2, S2, ClO, N2O, NO2, O3, FNO, FO2, F2O, S2O, S3, ClNO, ClOO, Cl2O, N2C2, P4, and S4. This set spans the gamut from molecules dominated by moderate nondynamical correlation (e.g., FO, ClO, NO2, S2O, N2C2, and P4) to systems dominated by strong nondynamical correlation (e.g., BN, C2, FO2, O3, ClOO, and S4). We examine the basis set convergence of the CCSDT, CCSDT(Q), CCSDTQ, CCSDTQ(5), CCSDTQ5, CCSDTQ5(6), CCSDTQ56, CCSDTQ56(7), and CCSDTQ567 methods. The largest basis sets employed in each category are cc-pV6Z (CCSDT(Q)), cc-pV5Z (CCSDTQ), cc-pVTZ (CCSDTQ5(6)), and cc-pVDZ (CCSDTQ567). Apart from examining the basis-set convergence of post-CCSD(T) contributions near the one-particle basis-set limit, this work explores cost-effective approaches for obtaining these contributions from fairly small basis sets. We consider both effective basis-set extrapolations and scaling factors. An important finding is that extrapolating the perturbative connected quadruples, (Q), from the cc-pVDZ(4s3p1d) and cc-pVTZ basis sets yields near basis-set limit results and represents a significant improvement relative to cc-pV{D,T}Z extrapolation at no additional computational cost (where cc-pVDZ(4s3p1d) is an extended version of the cc-pVDZ basis set). Combining the (Q)/cc-pV{D(4s3p1d),T}Z extrapolations with the fully iterative connected quadruples, Q-(Q), contribution calculated with the cc-pVDZ (or even the cc-pVDZ(3s2p)) basis set is a cost-effective way for obtaining the connected quadruples component close to the basis-set limit (where cc-pVDZ(3s2p) is a truncated version of the cc-pVDZ basis set). In addition, we show that the (5)/cc-pVDZ(3s2p) and (6)/cc-pVDZ(3s2p) components provide reasonable approximations for the connected quintuple and sextuple components close to the basis-set limit, respectively.

SPECTRAL CHARACTERISTICS OF CONFORMATION ISOMERS OF MESO-OCTAMETHYL-CALIX(4)PYRROLE BASED ON QUANTUM-CHEMICAL CALCULATIONS

The structure optimization and calculation of electronic absorption spectra of meso-octa-methylcalix(4)pyrrole conformers was performed by density- functional theory using hybrid B3LYP functional in cc-pVTZ basis set of Gaussian 09 package. Analysis of experimental UV-Vis spectra of solutions of calix(4)pyrrole was carried out in various solvents. The conclusion on the existence of a dynamic equilibrium between conformers in solutions of meso-octamethylcalix(4)pyrrole was made.

Computational studies of metal carbonyl complexes of 3[4-ethyl(phenly)imino][indoline-2-one] and 3[4-butyl(phenly)imino][indoline-2-one

Use and application of Schiff bases are extended to many different fields of technology. (ISE)M(CO)5 complex [M = Cr (1), Mo (2), W (3), and where ISE is 3[4-ethyl(phenly)imino][indoline-2-one]; and (ISB)M(CO)5 [M = Cr (4), Mo (5), W (6)], where ISB is 3[4-butly(phenly)imino][indoline-2-one] were investigated by computational methods. Computations were carried out using density functional theory (DFT) with B3LYP and CAM-B3LYP functionals, in conjunction with LanL2DZ basis set for metals and cc-PVTZ basis set for other atoms. Time-dependent density functional theory (TDDFT) was used at the same level to obtain the electronic transitions. Molecular orbital energies, UV-Vis spectra, and total electron densities of investigated molecules were shown in the gas phase and in THF. Metal complexes showed higher absorption coefficients compared to ISE and ISB in the visible region. Additionally, they displayed absorption peaks at longer wavelengths and full MLCT character in solution, and W complexes required less energy compared to the complexes of other investigated metal ions. Among the investigated systems, (ISE)W(CO)5 and (ISB)W(CO)5 complexes with lowest HOMO-LUMO gaps are found to be the best candidates for photosensitive material production. Graphical Abstract UV-Vis absorption spectra of ISE and (ISE)W(CO)5.