DFT studies of uranyl acetate,carbonate, and malonate,complexes in solution

The aim of this work is to demonstrate that theoretical chemistry can be used as a complementary tool in determining geometric parameters of a number of uranyl complexes in solution, which are not observable by experimental methods. In addition, we propose plausible structures with partial geometric data from experimental results. A gradient corrected DFT methodology with relativistic effects is used employing a COSMO solvation model. The theoretical calculations show good agreement with experimental X-ray and EXAFS data for the triacetato-dioxo-uranium(VI) and tricarbonato-dioxo-uranium(VI) complexes and are used to assign possible geometries for dicalcium-tricarbonato-dioxo-uranium(VI) and malonato-dioxo-uranium(VI) complexes. The results of this exercise indicate that carbonate bonding in these complexes is mainly bidentate and that hydroxo bridging plays a critical role in the stabilization of the polynuclear uranyl complexes.     

van der Waals corrections to density functional theory calculations: Methane,ethane, ethylene,benzene, formaldehyde,ammonia, water,PBE, and CPMD

Parameters are developed for a practical application of the empirical van der Waals (vdW) correction infrastructure available in the CPMD density functional theory (DFT) code. The binding energy, geometry, and potential energy surface (PES) are examined for methane, ethane, ethylene, formaldehyde, ammonia, three benzene dimer geometries, and three benzene–water geometries. The vdW corrected results compare favorably with MP2 and CCSD(T) calculations near the complete basis set limits, and with experimental results where they are available.     

Statistical thermodynamics of 1-butanol, 2-methyl-1-propanol, and butanal

The purpose of the present investigation is to calculate partition functions and thermodynamic quantities, viz., entropy, enthalpy, heat capacity, and Gibbs free energies, for 1-butanol, 2-methyl-1-propanol, and butanal in the vapor phase. We employed the multi-structural (MS) anharmonicity method and electronic structure calculations including both explicitly correlated coupled cluster theory and density functional theory. The calculations are performed using all structures for each molecule and employing both the local harmonic approximation (MS-LH) and the inclusion of torsional anharmonicity (MS-T). The results obtained from the MS-T calculations are in excellent agreement with experimental data taken from the Thermodynamics Research Center data series and the CRC Handbook of Chemistry and Physics, where available. They are also compared with Benson's empirical group additivity values, where available; in most cases, the present results are more accurate than the group additivity values. In other cases, where experimental data (but not group additivity values) are available, we also obtain good agreement with experiment. This validates the accuracy of the electronic structure calculations when combined with the MS-T method for estimating the thermodynamic properties of systems with multiple torsions, and it increases our confidence in the predictions made with this method for molecules and temperatures where experimental or empirical data are not available.     

NMR spectra of free-base porphine, porphyrazine, phthalocyanine and naphthalocyanine as well as their metal complexes: density functional calculations

Nuclear magnetic shielding tensors of porphine have been calculated at density functional B3LYP and PBE level using the gauge independent atomic orbital (GIAO) method. The geometries used were optimized using the 6-31G(d) basis set and the NMR calculations were performed using 6-31G(d) and 6-311G(d,p) basis sets, respectively. The calculated NMR shielding tensors and chemical shifts of porphine are compared with previous calculations as well as experimental data and satisfying results are obtained. Further NMR calculations are extended to metal-free and metallo-porphyrazine, -phthalocyanine, and -naphthalocyanine for the first time and the results are compared with experimental data available. The chemical shifts of the atoms in these compounds are assigned according to the experimental data available.     

The case of the weak N-X bond: Ab initio, semi-experimental, and experimental equilibrium structures of XNO (X = H, F, Cl, OH) and FNO2

The equilibrium structures of FNO, ClNO, HONO, and FNO2 have been determined using three different, somewhat complementary methods: a completely experimental, a semi-experimental (where the equilibrium rotational constants are derived from the experimental effective ground-state rotational constants and an ab initio cubic force field), and an ab initio, where geometry optimizations are usually performed at the coupled cluster level of nonrelativistic electronic structure theory using small to very large Gaussian basis sets. For the sake of comparison, the equilibrium structures of HNO and N2O have also been redetermined, confirming and extending earlier results. The semi-experimental method gives structural parameters in good agreement with the reliable experimental results for each compound investigated. Because of inadequate treatment of electron correlation, the single-reference CCSD(T) method gives N-X (X[double bond]F, Cl, OH) bonds that are too strong and associate bond lengths that are significantly too short. The discrepancy increases with increase in the size of the basis set. A much more elaborate treatment of electron correlation at the CCSDTQ level solves this problem and results in increased bond lengths, correctly representing the weakness of the N-X bond in these XNO and XNO2 species. The equilibrium structures determined are accurate to better than 0.001 A and 0.1 degrees .     

Alcohols,ethers, carbohydrates,and related compounds. II. The anomeric effect

The anomeric effect has been studied for a variety of compounds using the MM4 force field, and also using MP2/6-311++G(2d,2p) ab initio calculations and experimental data for reference purposes. Geometries and energies, including conformational, rotational barriers, and heats of formation were examined. Overall, the agreement of MM4 with the experimental and ab initio data is good, and significantly better than the agreement obtained with the MM3 force field. The anomeric effect is represented in MM4 by various explicit terms in the force constant matrix. The bond length changes are accounted for with torsion-stretch elements. The angle changes are accounted for with torsion-bend elements. The energies are taken into account with a number of torsional terms in the usual way. A torsion-torsion interaction is also of some importance. With all of these elements included in the calculation, the MM4 results now appear to be adequately accurate. The heats of formation were examined for a total of 12 anomeric compounds, and the experimental values were fit by MM4 with an RMS error of 0.42 kcal/mol.     

Theory, measurements, and modeling of OH and HO2 formation in the reaction of cyclohexyl radicals with O2

The production of OH and HO(2) in Cl-initiated oxidation of cyclohexane has been measured using pulsed-laser photolytic initiation and continuous-laser absorption detection. The experimental data are modeled by master equation calculations that employ new G2(MP2)-like ab initio characterizations of important stationary points on the cyclo-C(6)H(11)O(2) surface. These ab initio calculations are a substantial expansion on previously published characterizations, including explicit consideration of conformational changes (chair-boat, axial-equatorial) and torsional potentials. The rate constants for the decomposition and ring-opening of cyclohexyl radical are also computed with ab initio based transition state theory calculations. Comparison of kinetic simulations based on the master equation results with the present experimental data and with literature determinations of branching fractions suggests adjustment of several transition state energies below their ab initio values. Simulations with the adjusted values agree well with the body of experimental data. The results once again emphasize the importance of both direct and indirect components of the kinetics for the production of both HO(2) and OH in radical + O(2) reactions.     

Quasielastic electron scattering from methane, methane-d4, methane-d2, ethylene, and 2-methylpropane

Quasielastic electron scattering from gaseous species at high momentum transfer was recently reported for the first time [Cooper et al., J. Electron Spectrosc. Relat. Phenom. 155, 28 (2007)]. The first results for CH(4) and CD(4) were well explained by a classical electron Compton scattering picture in which the electron scatters independently from each atom rather than the molecule as a whole. However, an alternative possible interpretation in terms of nondipole molecular vibrational excitation is suggested by previously published quantum mechanical calculations on high momentum transfer electron scattering from diatomic molecules [Bonham and de Souza, J. Chem. Phys. 79, 134 (1983)]. In order to determine which of these two interpretations best fits the experimental results, we have measured the quasielastic spectra of gaseous 2-methylpropane, ethylene, methane, and two isotopically substituted methanes, CH(2)D(2) and CD(4), at a momentum transfer of approximately 20 a.u. (2.25 keV impact energy and 100 degrees scattering angle). The experimental spectra are found to be composed of as many peaks as there are different atomic isotopes in the molecule (two for CH(4), C(2)H(4), 2-methylpropane, and CD(4) and three for CH(2)D(2)). The peak positions are predicted accurately by the independent atom electron Compton scattering model, and the relative intensities are in reasonable agreement. The experimental results thus support classical electron Compton scattering as the origin of the signal.     

Selection and Optimization of Dispersant in Ceramic Slurry Processing by Different Techniques: Comparison,Correlation, and Standardization

This article describes the selection and optimization of dispersant dosage in colloidal processing of ceramic slurry by techniques such as particle charge detector (PCD), capillary suction time (CST), rheological measurement, and wet point and flow point techniques. In general, experimental results are found to be in good agreement with each other with some degree of variation. PCD, CST, and rheological techniques are related by a simple linear function. The experimental and calculated values are well matching within an error limit of 10%. Attempt has been made to develop formula for correlating results of optimization from one technique to those obtained from another technique. The region where the suspension is well dispersed, CST is linearly correlated with PCD. The advantages and limitations of each technique have been described and discussed.     

High-level ab initio studies of the structure, vibrational spectra, and energetics of S3

Observation of mass-dependent and non-mass-dependent sulfur isotope fractionations in elemental sulfur is providing new insight into the nature of the sulfur cycle in the atmosphere. Interpretation of the experimental isotope data requires estimation of the energetics for the reaction S+S2-->S3 (isoelectronic with O+O2-->O3). Key molecular properties of the S3 potential-energy surface, such as vibrational frequencies and isotopic shifts, are presented that can be used to assess the mass-dependent fractionation effect. Ab initio results are compared to the available experimental results for S2 to evaluate the reliability of the computational results for S3. The S-S bond dissociation energy for S3 is determined to be 60.9+/-1 kcal mol(-1).     

Global thermodynamics of hydrophobic cavitation, dewetting, and hydration

Pure water experimental and simulation results are combined to predict the thermodynamics of cavity formation, spanning atomic to macroscopic length scales, over the entire ambient liquid temperature range. The resulting cavity equation of state is used to quantify dewetting excess contributions to cavity formation thermodynamics and construct a thermodynamic perturbation theory of hydrophobic hydration. Predictions are compared with large cavity simulations and experimental rare-gas hydration thermodynamics data (for He, Ne, Ar, Kr, Xe, and Rn). Key findings include the strong temperature dependence of the critical length scale for hydrophobic dewetting and the evaluation of fundamental solute-solvent interaction contributions to rare-gas hydration chemical potentials.     

Density functional investigation of high-spin XY (X = Cr, Mo, W and Y = C, N, O) molecules

The performance of a density functional theory approach in calculating the equilibrium bond length, dipole moment, and harmonic vibrational frequency in a series of group 6 (Cr, Mo, W) transition metal-containing diatomic molecules is evaluated. Using flexible basis sets comprised of Slater type functions, a wide range of exchange-correlation functionals is investigated. Comparing with known experimental values and published results from high-level theoretical calculations, the most suitable functional form is selected. The importance of relativistic effects is checked, and predictions are made for several unknown dipole moments. The best agreement with experimental parameters is obtained when using a general gradient approximation, while special and hybrid functional forms give less accurate results.     

Electronic and geometrical structure of Mn13 anions, cations, and neutrals

We have computed the electronic and geometrical structures of thirteen atom manganese clusters in all three charge states, Mn(13) (-), Mn(13) (+), and Mn(13) by using density functional theory with the generalized gradient approximation. Our results for Mn(13) (-) are compared with our anion photoelectron spectrum of Mn(13) (-), published in this paper. Our results for Mn(13) (+) are compared with the previously published photoionization results of Knickelbein [J. Chem. Phys. 106, 9810 (1997)]. There is a good agreement between theoretical and experimental values of ionization and electron attachment energies.     

Frequency-dependent hyperpolarizabilities of the Ne, Ar, and Kr atoms using the approximate coupled cluster triples model CC3

The frequency-dependent electric field-induced second harmonic generation (ESHG) second hyperpolarizabilities gamma of neon, argon, and krypton are calculated using the approximate coupled cluster triples model CC3. Systematic basis set investigations are carried out to establish basis set limits, and scalar relativistic effects are accounted for by direct perturbation theory. To estimate higher-order correlation effects, full configuration-interaction results are used to benchmark the accuracy of CC3. The best theoretical estimates obtained thereby for the static second hyperpolarizabilities gamma(0) are 107.4, 1159, and 2589 a.u. for neon, argon, and krypton, respectively. These values as well as the results for the dispersion curve of the parallel component gamma( parallel) agree well with the latest experimental values from electric field-induced second harmonic generation. In addition, the dispersion of the perpendicular component gamma( perpendicular) and the hyperpolarizability ratios gamma( parallel)gamma( perpendicular) has been studied for the first time on a consistently correlated ab initio level. The analysis of the results indicates that, in particular for neon and krypton, the presently available experimental values are flawed.     

Measurement of K-line transition rates for Ti, V, Cr, Mn, Fe and Co using synchrotron radiation

Transition rates were obtained from spectra for pure metallic samples of atomic number ranging from 22 to 27, measured with monochromatic incident X-ray beams from a synchrotron source. The experimental setup for this consisted of an energy dispersive spectrometer in a conventional 45–45° geometry, mounted in an evacuated chamber. Absorption, detector efficiency and multiple scattering were taken into account. The results obtained are compared with recent theoretical and experimental data as well as with the well-known theoretical predictions from Scofield.     

FT-IR,FT-Raman,NMR spectra and DFT calculations on 4-chloro-N-methylaniline

In this work, the vibrational spectral analysis was carried out by using FT-IR and FT-Raman spectroscopy in the range 400–4000 and 50–3500 cm^?1 respectively, for the title molecule. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method using 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments of all the vibrational mode were performed on the basis of the total energy distributions (TED). ¹³C and ¹H NMR chemical shifts results were given and are in agreement with the corresponding experimental values. The theoretically constructed FT-IR and FT-Raman spectra exactly coincides with experimental one.     

氢原子在镍台阶面上吸附、振动和表面扩散行为的理论研究

本文用对势方法研究了氢原子在Ni(510)台阶面上的吸附和振动, 计算结果与实验符合得很好。并考察了氢原子在Ni(997)台阶面上的吸附和扩散, 结果表明,台阶对下台面上扩散的氢原子开成捕获势阱, 对上台面扩散的氢原子形成反射势,这也很好地支持了实验结果。     

共轭烯烃的分子几何构型、电子结构和生成热的DMM和AM1、PM3的比较研究

运用Ｄｅｌｆｔ分子力学（ＤＭＭ）力场和程序以及半经验分子轨道ＡＭ１和ＰＭ３方法计算研究了丁二烯、苯、甲苯、联苯、苯乙烯、富烯、、环辛四烯、［２，２］对环烷和菲等１０个共轭烯烃分子的几何构型、电子结构和生成热．ＤＭＭ计算的几何构型和生成热与实验结果相吻合，电荷分布结果与从头计算结果较接近．ＡＭ１和ＰＭ３计算的几何构型较好，但计算的生成热与实验结果偏差较大．ＰＭ３计算值比ＡＭ１的稍好．     

Density-functional and electron correlated study of five linear birefringences--Kerr, Cotton-Mouton, Buckingham, Jones, and magnetoelectric--in gaseous benzene

We present the results of an extended study of five birefringences--Kerr, Cotton-Mouton, Buckingham, Jones, and Magnetoelectric--on benzene in the gas phase. The relevant molecular quantities--first-order properties, linear, quadratic, and cubic response functions--are computed employing the density-functional theory (DFT) response theory, with a choice of functionals. In some cases, different functionals are employed for the wave-function computational step and for the subsequent analytical response calculation to determine the combination yielding at the same time the optimal energy and energy derivative results. Augmented correlation consistent basis sets of double and triple zeta quality are used. The DFT results are compared to those obtained at the Hartree-Fock level and in some cases within a coupled cluster singles and doubles electronic structure model. The study tries to assess the ability of the DFT response theory to describe a wide range of properties in a system of rather large size and high complexity. The relative strength of the five birefringences for plausible experimental conditions is determined and, when possible, comparison is made with the results of the measurements.     

Experimental matrix isolation and theoretical ab initio HF/6-31G(d,p) studies of infrared spectra of purine,adenine and 2-chloroadenine

The results of ab initio calculations at the Hartree—Fock level with the 6-31G(d, p) basis set are reported for the harmonic vibrational infrared spectra of purine, adenine and 2-chloroadenine. These were compared with the experimental IR spectra of the compounds isolated in low-temperature matrices. The experimental spectra of 2-chloroadenine are reported for the first time. In the case of purine this comparison resulted in the complete assignment of the experimental IR spectrum. The proposed assignments of both the adenines studied are still incomplete.