MP2

Distribution by Scientific Domains
Distribution within Chemistry

Terms modified by MP2

  • mp2 calculation
  • mp2 level
  • mp2 method
  • mp2 methods

  • Selected Abstracts


    Sulfur Dioxide and Water: Structures and Energies of the Hydrated Species SO2·nH2O, [HSO3],·nH2O, [SO3H],·nH2O, and H2SO3·nH2O (n = 0,8)

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2009
    Ralf Steudel
    Abstract The structures of a large number of hydrates of sulfur dioxide (SO2·nH2O), of the sulfonate ion ([HSO3],·nH2O), of the tautomeric hydrogensulfite anion ([SO3H],·nH2O), and of sulfurous acid (H2SO3·nH2O) with up to eight water molecules attached to these species have been optimized at the B3LYP/6-31G(2df,p) level of theory (DFT). The calculated vibrational frequencies allow the definite assignment of certain characteristic modes, and in this way a convincing interpretation of published spectra of aqueous SO2 as well as of SO2 adsorbed on very cold ice crystals has been achieved for the first time. Single-point calculations at the G3X(MP2) level of theory were used to calculate the binding energies of the water molecules in SO2·nH2O as well as the relative stabilities of the isomeric anionic species [HSO3],·nH2O and [SO3H],·nH2O. Generally, the water molecules tend to stick together forming clusters, whereas the particular sulfur-containing molecule remains at the surface of the water cluster, but it is always strongly hydrogen-bonded. Only when there are more than six water molecules are the anions more or less completely surrounded by water molecules. DFT calculations erroneously predict that the gaseous hydrated sulfonate ions are more stable than the isomeric hydrogensulfite ions, even when hydrated with six water molecules. However, if these hydrated species are calculated as being embedded in a polar continuum simulating the aqueous phase, the hydrogensulfite ions are more stable than the sulfonate ions, in agreement with various spectroscopic observations on aqueous sulfite solutions. On the other hand, at the higher G3X(MP2) level, the gaseous hydrated hydrogensulfite anions are more stable than the corresponding sulfonate ions only if the number of water molecules is larger than four, whereas for the weakly hydrated anions the order of relative energies is reversed. The possible implications of these results for the enzymatic oxidation of "sulfite ions" ([HSO3], and [SO3H],) by sulfite oxidase are discussed. The conversion of SO2·6H2O into its isomer H2SO3·5H2O is predicted to be exothermic (,H°298 = ,56.1 kJ,mol,1) and exergonic (,G°298 = ,22.5 kJ,mol,1). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


    A Combined Gas-Phase Electron Diffraction/Mass Spectrometric Study of the Sublimation Processes of TeBr4 and TeI4: The Molecular Structure of Tellurium Dibromide and Tellurium Diiodide

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2008
    Sergey A. Shlykov
    Abstract The sublimation processes of TeBr4 at 471(5) K and TeI4 at 373(5) K were studied with a combined gas-phase electron diffraction and mass spectrometric technique (GED/MS). The mass spectra and the analysis of the GED intensities showed that a contribution of 40(3) mol-% TeBr2, 59(3) mol-% Br2, and 1 mol-% TeBr4 was formed in the vapor over TeBr4(s). Solid tellurium tetraiodide decomposes to form I2(g) and Te(s). A very small contribution of 3.3,±,2.1 mol-% of gaseous TeI2 was also determined by both GED and MS. The "metallic" Te accumulated in the solid phase vaporizes at above ca. 670 K as the predominately Te2 molcular species. Refinement of the GED intensities resulted in rg(Te,Br) = 2.480(5) Å and ,gBr,Te,Br = 99.0(6)° for TeBr2 and rg(Te,I) = 2.693(9) Å and ,g(I,Te,I) = 103.1(22)° for TeI2. The small contribution of TeBr4 observed in the mass spectra of the vapor over TeBr4 could not be observed in the GED data. Geometric parameters and vibrational frequencies for the tellurium dihalides TeX2 with X = F, Cl, Br, and I were calculated with B3LYP, MP2, CCSD, and CCSD(T) methods by using aug-cc-pVTZ basis sets and various core potentials for the tellurium atom. Bonding properties in tellurium dihalides are discussed on the basis of natural bond orbital analyses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


    Theoretical Studies on Metal,Metal Interaction and Intrinsic 1,3[,*(d),(s/p)] Excited States of Dinuclear d10 Complexes with Bridging Phosphane Ligands

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2006
    Qing-Jiang Pan
    Abstract To explore the metal,metal interaction and spectroscopic properties, the ground- and excited-state structures of [M2(dpm)2]2+ [M = Ag (2), Cu (3), dpm = bis(diphosphanyl)methane] and their solvated species [M2(dpm)2]2+·(MeCN)2 were optimized by the MP2 and CIS methods, respectively. In the ground states, the calculated M,M distances and their corresponding M,M stretching frequencies for 2 and 3 indicate the presence of metallophilic attraction; there is strong N,Cu/Ag coordination in acetonitrile, which is different from the case in previous studies of [Au2(dpm)2]2+ (1). CIS calculations show that 2 and 3 have 1,3[,*(d),(s/p)] as their lowest-energy excited state, as is also the case for 1, confirmed by unrestricted MP2 calculations. On the basis of the CIS-optimized structures, the TD-DFT (B3LYP) method was employed to calculate the emission spectra of such complexes. For 3, the phosphorescent emissions were calculated at 424 and 514 nm in the solid state and acetonitrile, which is comparable to the experimental data of 475 and 480 nm, respectively. The comparison between the gas-phase and solution emissions for 1,3 reveals that the N,M coordination results in a large red-shift of the emission wavelength. Taking previous studies into account , we found that the M,M distances are linearly correlated with the M,M stretching frequencies for the dinuclear d10 complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


    Syntheses, Structures and Theoretical Investigations of 1,4,3,4,5,4 -Trithia-2,4,6,8,9-pentaazabicyclo[3.3.1]nona-1(9),2,3,5,7-pentaenes

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2003
    Carsten Knapp
    Abstract The syntheses of the title compounds RCN5S3 with electron-withdrawing aryl substituents [R = 2-FC6H4 (1m), 4-FC6H4 (1n), 2,6-F2C6H3 (1o), C6F5 (1p), 4-NCC6H4 (1q) and Cl3C (1r)] are described. The X-ray structures of 1n, 1o, 1q and 1r, together with those of Me2NCN5S3 (1b) and 4-CH3C6H4CN5S3 (1f), are reported. The experimentally determined dependence of the bond lengths on the substituents R within the bicyclic system RCN5S3 is well-reflected in the results of the theoretical calculations (RHF, MP2, B3LYP). The bonding model developed shows that acceptor substituents do not influence bonding within the bicycle. In the solid state, two fundamentally different primary interactions of the RCN5S3 molecules are observed; "stacking" and "dimerisation", which can be rationalised by electrostatic interactions between the CN5S3 units. However, secondary effects , the interactions between the R substituents , may be even more dominant. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


    Structures and Thermodynamics of the Sulfuranes SF3CN and SF2(CN)2 as well as of the Persulfurane SF4(CN)2 , An ab initio MO Study by the G3(MP2) Method

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2003
    Yana Steudel
    Abstract At the G3(MP2) level of theory the trans isomer 1a of the hypothetical molecule SF4(CN)2 is more stable than the cis isomer 1b by 8 kJ·mol,1. The isomerization of 1a to 1b requires an activation enthalpy of 319 kJ·mol,1 at 298 K. The decomposition of trans -SF4(CN)2 to SF2(CN)2 and F2 is endothermic (,Ho298 = 395 kJ·mol,1) but the elimination of FCN from trans -SF4(CN)2 is exothermic by ,7 kJ·mol,1. The elimination of (CN)2 from cis -SF4(CN)2 is exothermic by ,137 kJ·mol,1. The activation enthalpies for the latter two reactions were calculated as 251 and 311 kJ·mol,1, respectively. Thus, SF4(CN)2 should be a thermally stable compound. In the sulfuranes SF3CN and SF2(CN)2 the CN ligands prefer the equatorial positions; mutual exchange of an axial F atom by an equatorial CN group requires a reaction enthalpy of 51 kJ·mol,1 [SF3CN] or 58 kJ·mol,1 [SF2(CN)2]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


    Calculated Enthalpies for Dimerisation of Binary, Unsaturated, Main-Group Element Hydrides as a Means to Analyse Their Potential for Multiple Bonding

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2003
    Hans-Jörg Himmel
    Abstract Herein, the dimerisation of subvalent, binary, main-group element hydrides with the potential for multiple bonding is studied using both hybrid DFT (B3LYP) and ab initio [MP2 and CCSD(T)] methods. The [2+2] cycloaddition is an important and characteristic reaction of derivatives of ethylene. A comparison of dimerisation reactions for several compounds with the potential for multiple bonding should, therefore, shed light on the properties of these species. Our study includes the hydrides E2H2 (E = B, Al, Ga, N P or As), E2H4 (E = C, Si or Ge) and ENH4 (E = B, Al or Ga) and their dimers. Several isomeric forms of the monomers and dimers have to be considered. The trends within a group and a period are established and the factors responsible for them are discussed. It turns out that, generally, the enthalpies for dimerisation increase for heavier homologues, reflecting that the most important factor is the reduced strength of the E,E bonds in the monomers prior to dimerisation and, to some degree, also the reduced ring strain in the cyclic dimers. The exceptions are the dimerisations of B2H2 and Al2H2, both of which lead to the tetrahedral E4H4 species (E = B or Al). Dimerisation of Al2H2 is associated with a smaller enthalpy than that for the dimerisation of B2H2. Comparisons and analyses are made complicated because of the changes in the structures of the isomeric global minima between homologues. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


    Rearrangements in Model Peptide-Type Radicals via Intramolecular Hydrogen-Atom Transfer

    HELVETICA CHIMICA ACTA, Issue 10 2006
    Damian Moran
    Abstract Intramolecular H-atom transfer in model peptide-type radicals was investigated with high-level quantum-chemistry calculations. Examination of 1,2-, 1,3-, 1,5-, and 1,6[C,,,N]-H shifts, 1,4- and 1,7[C,,,C]-H shifts, and 1,4[N,,,N]-H shifts (Scheme,1), was carried out with a number of theoretical methods. In the first place, the performance of UB3-LYP (with the 6-31G(d), 6-31G(2df,p), and 6-311+G(d,p) basis sets) and UMP2 (with the 6-31G(d) basis set) was assessed for the determination of radical geometries. We found that there is only a small basis-set dependence for the UB3-LYP structures, and geometries optimized with UB3-LYP/6-31G(d) are generally sufficient for use in conjunction with high-level composite methods in the determination of improved H-transfer thermochemistry. Methods assessed in this regard include the high-level composite methods, G3(MP2)-RAD, CBS-QB3, and G3//B3-LYP, as well as the density-functional methods B3-LYP, MPWB1K, and BMK in association with the 6-31+G(d,p) and 6-311++G(3df,3pd) basis sets. The high-level methods give results that are close to one another, while the recently developed functionals MPWB1K and BMK provide cost-effective alternatives. For the systems considered, the transformation of an N-centered radical to a C-centered radical is always exothermic (by 25,kJ,,,mol,1 or more), and this can lead to quite modest barrier heights of less than 60,kJ,,,mol,1 (specifically for 1,5[C,,,N]-H and 1,6[C,,,N]-H shifts). H-Migration barriers appear to decrease as the ring size in the transition structure (TS) increases, with a lowering of the barrier being found, for example when moving from a rearrangement proceeding via a four-membered-ring TS (e.g., the 1,3[C,,,N]-H shift, CH3C(O)NH.,,,.CH2C(O)NH2) to a rearrangement proceeding via a six-membered-ring TS (e.g., the 1,5[C,,,N]-H shift, .NHCH2C(O)NHCH3,,,NH2CH2C(O)NHCH2.). [source]


    Outlying Charge, Stability, Efficiency, and Algorithmic Enhancements in the Quantum-Mechanical Solvation Method, COSab-GAMESS

    HELVETICA CHIMICA ACTA, Issue 12 2003
    Laura
    In this work, we present algorithmic modifications and extensions to our quantum-mechanical approach for the inclusion of solvent effects by means of molecule-shaped cavities. The theory of conductor-like screening, modified and extended for quantum-mechanical techniques, serves as the basis for our solvation methodology. The modified method is being referred to as COSab-GAMESS and is available within the GAMESS package. Our previous work has emphasized the implementation of this model by way of a distributed multipole approach for handling the effects of outlying charge. The method has been enabled within the framework of open- and closed-shell RHF and MP2. In the present work, we present a) a second method to handle outlying charge effects, b) algorithmic extensions to open- and closed-shell density-functional theory, second-derivative analysis, and reaction-path following, and c) enhancements to improve performance, convergence, and predictability. The method is now surtable for large molecular systems. New features of the enhanced continuum model are highlighted by means of a set of neutral and charged species. Computations on a series of structures with roughly the same molecular shape and volume provides an evaluation of cavitation effects. [source]


    Ab Initio Structure/Reactivity Investigations of Illudin-Based Antitumor Agents: A Model for Reaction in vivo

    HELVETICA CHIMICA ACTA, Issue 12 2003
    Laura
    (Hydroxymethyl)acylfulvene (HMAF, irofulven; 4), a third-generation derivative of a natural product extracted from the mushroom Omphalotus illudens, is selectively toxic towards certain forms of malignant tumors. Conversion of HMAF and cognates to stable aromatic derivatives is triggered by thiol attack in vitro and in vivo. Quantum-chemical methods predict well the structure for several functionalized derivatives of irofulven as compared to known X-ray crystallographic structures. Computational reaction profiles for thiol attack and aromatic rearrangement of irofulven and illudin S, a toxin from which irofulven is derived, provide insight into HMAF's selectivity and toxicity. Methods used include hybrid density-functional theory (HDFT), HartreeFock (HF), and MøllerPlesset second-order perturbation theory (MP2). Solvent effects have been explored by means of the new continuum-solvation method, COSab, presented in an accompanying paper. [source]


    Sandwich compounds with central hypercoordinate carbon, nitrogen, and oxygen: A quantum-chemical study

    HETEROATOM CHEMISTRY, Issue 6 2006
    Ruslan M. Minyaev
    Ab initio (MP2(fu)/6-311+G**) and DFT (B3LYP/6-311+G**) calculations predict stable structures of sandwich compounds with the central carbon, nitrogen, and oxygen atoms surrounding lithium counterions between three-membered (BH)3 rings. The lithium counterions play a crucial role in the stabilization of these systems. The topological Bader analysis performed for these sandwich systems demonstrates that the central atom is linked to the ligands by nine-bond paths and, consequently, should be regarded as a nine-coordinated atom. Such a coordination number of carbon is the highest for all known main group organoelement compounds. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:464,474, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20268 [source]


    Direct dynamic study on the hydrogen abstraction reaction of H2CO with NCO

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2009
    Hao Sun
    A direct ab initio dynamics method is used to investigate the hydrogen-abstraction reaction of H2CO with NCO. The potential energy surface information is obtained at the MP2/6-311G(d,p) level. More accurate single-point energy is refined at the G3(MP2)//MP2/6-311G(d,p) level. Furthermore, the rate constants of reaction H2CO + NCO are evaluated by using the canonical variational transition state theory with small-curvature tunneling contributions over a wide temperature range of 200,2000 K. The calculated reaction enthalpy and rate constants are in good agreement with the available experimental values. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 394,400, 2009 [source]


    Direct ab initio dynamics calculations of the rate constants for the reaction of CHF2CF2OCH3 with Cl

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2007
    Lei Yang
    A dual-level direct dynamics method is employed to reveal the dynamical properties of the reaction of CHF2CF2OCH3 (HFE-254pc) with Cl atoms. The optimized geometries and frequencies of the stationary points and the minimum energy path (MEP) are calculated at the B3LYP/6-311G(d,p) level by using GAUSSIAN 98 program package, and energetic information is further refined by the G3(MP2) method. Two H-abstraction channels have been identified. For the reactant CHF2CF2OCH3 and the two products, CHF2CF2OCH2 and CF2CF2OCH3, the standard enthalpies of formation are evaluated with the values of ,256.71 ± 0.88, ,207.79 ± 0.12, and ,233.43 ± 0.88 kcal/mol, respectively, via group-balanced isodesmic reactions. The rate constants of the two reaction channels are evaluated by means of canonical variational transition-state theory (CVT) including the small-curvature tunneling (SCT) correction over a wide range of temperature from 200 to 2000 K. The calculated rate constants agree well with the experimental data, and the Arrhenius expressions for the title reaction are fitted and can be expressed as k1 = 9.22 × 10,19 T2.06 exp(219/T), k2 = 4.45 × 10,14T0.90 exp(,2220/T), and k = 4.71 × 10,22 T3.20) exp(543/T) cm3 molecule,1 s,1. Our results indicate that H-abstraction from CH3 group is the main reaction pathway in the lower temperature range, while H-abstraction from CHF2 group becomes more competitive in the higher temperature range. © 2007 Wiley Periodicals, Inc. 39: 221,230, 2007 [source]


    Intramolecular hydrogen bond in 3-imino-propenylamine isomers: AIM and NBO studies

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2010
    H. Raissi
    Abstract The molecular structure and intramolecular hydrogen bond energy of 18 conformers of 3-imino-propenyl-amine were investigated at MP2 and B3LYP levels of theory using the standard 6-311++G** basis set. The atom in molecules or AIM theory of Bader, which is based on the topological properties of the electron density (,), was used additionally and the natural bond orbital (NBO) analysis was also carried out. Furthermore calculations for all possible conformations of 3-imino-propenyl-amin in water solution were also carried out at B3LYP/6-311++G** and MP2/6-311++G** levels of theory. The calculated geometrical parameters and conformational analyses in gas phase and water solution show that the imine,amine conformers of this compound are more stable than the other conformers. B3LYP method predicts the IMA-1 as global minimum. This stability is mainly due to the formation of a strong NH···N intramolecular hydrogen bond, which is assisted by ,-electrons resonance, and this ,-electrons are established by NH2 functional group. Hydrogen bond energies for all conformers of 3-imino-propenyl-amine were obtained from the related rotamers methods. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]


    Chiral discrimination in hydrogen-bonded complexes of 2-methylol oxirane with hydrogen peroxide

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2009
    Guiqiu Zhang
    Abstract A systematic quantum chemical study reveals the effects of chirality on the intermolecular interactions between two chiral molecules bound by hydrogen bonds. The methods used are second-order Møller,Plesset perturbation theory (MP2) with the 6-311++g(d,p) basis set. Complexes via the OH···O hydrogen bond formed between the chiral 2-methylol oxirane (S) and chiral HOOH (P and M) molecules have been investigated, which lead to four diastereomeric complexes. The nomenclature of the complexes used in this article is enantiomeric configuration sign corresponding to English letters. Such as: sm, sp. The relative positions of the methylol group and the hydrogen peroxide are designated as syn (same side) and anti (opposite side). The largest chirodiastaltic energy was ,Echir = ,1.329 kcal mol,1 [9% of the counterpoise correct average binding energy De(corr)] between the sm-syn and sp-anti in favor of sm-syn. The largest diastereofacial energy was ,1.428 kcal mol,1 between sm-syn and sm-anti in favor of sm-syn. To take into account solvents effect, the polarizable continuum model (PCM) method has been used to evaluate the chirodiastaltic energies, and diastereofacial energies of the 2-methylol oxirane···HOOH complexes. The chiral 2,3-dimethylol oxirane (S, S) is C2 symmetry which offers two identical faces. Hence, the chirodiastaltic energy is identical to the diastereomeric energy, and is ,Echir = 0.563 kcal mol,1 or 5.3% of the De(corr) in favor of s,s-p. The optimized structures, interaction energies, and chirodiastaltic energies for various isomers were estimated. The harmonic frequencies, IR intensities, rotational constants, and dipole moments were also reported. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]


    Comparative study on the nonadditivity of methyl group in lithium bonding and hydrogen bonding

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2009
    Qingzhong Li
    Abstract Quantum chemical calculations at the second-order Moeller,Plesset (MP2) level with 6-311++G(d,p) basis set have been performed on the lithium-bonded and hydrogen-bonded systems. The interaction energy, binding distance, bond length, and stretch frequency in these systems have been analyzed to study the nonadditivity of methyl group in the lithium bonding and hydrogen bonding. In the complexes involving with NH3, the introduction of one methyl group into NH3 molecule results in an increase of the strength of lithium bonding and hydrogen bonding. The insertion of two methyl groups into NH3 molecule also leads to an increase of the hydrogen bonding strength but a decrease of the lithium bonding strength relative to that of the first methyl group. The addition of three methyl groups into NH3 molecule causes the strongest hydrogen bonding and the weakest lithium bonding. Although the presence of methyl group has a different influence on the lithium bonding and hydrogen bonding, a negative nonadditivity of methyl group is found in both interactions. The effect of methyl group on the lithium bonding and hydrogen bonding has also been investigated with the natural bond orbital and atoms in molecule analyses. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]


    Development of eclipsed and staggered forms in some hydrogen bonded complexes

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2009
    Ali Ebrahimi
    Abstract Intermolecular hydrogen bonding in X3CH···NH3 (X = H, F, Cl, and Br) complexes has been studied by B3LYP, B3PW91, MP2, MP3, MP4, and CCSD methods using 6-311++G(d,p) and AUG-cc-PVTZ basis sets. These complexes could exist in both eclipsed (EC) and staggered (ST) forms. The differences between binding energies of EC and ST forms are negligible and all EC and ST shapes correspond to minimum stationary states. The order of stabilities of them is in an agreement with the results of atoms in molecules (AIM) and natural bond orbital (NBO) analyses. On the basis of low differences between binding energies, ST forms are more stable than EC forms in all complexes with the exception of Br3CH···NH3, which behaves just opposite. Although the differences between binding energies are negligible, they are consistent with the results of AIM analysis. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]


    Test and modification of the van der Waals' radii employed in the default PCM model

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2008
    Wei-Hua Mu
    Abstract High level ab initio calculations at the B3LYP/6-311++G(d,p) and MP2(full)/6-311++G(d,p) levels employing PCM/UA0 model with different van der Waals' radii for the systems that contain lithium atoms have been carried out, in order to see if the van der Waal's radius for lithium atom employed in the default PCM/UA0 model is proper or not. Comparative analysis indicated that the van der Waals' radius for alkali metals, especially for lithium atom in the default PCM/UA0 model within the Gaussian 03 package, is too small, which causes erroneous redundant imaginary frequencies (RIFs) in the characterization of Li-containing compounds from moderate to big size. A new set of van der Waals' atomic radii based on QTAIM, proposed by Bader, was suggested for a better choice in the characterization of compounds containing alkali metals, for which it can effectively avoid the erroneous RIFs for corresponding geometries of these Li-containing systems. © 2008 Wiley Periodicals, Inc. Int. J. Quantum Chem, 2008 [source]


    MP2, DFT-D, and PCM study of the HMB,TCNE complex: Thermodynamics, electric properties, and solvent effects,

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2008
    Ondrej Kysel
    Abstract Geometry, thermodynamic, and electric properties of the ,-EDA complex between hexamethylbenzene (HMB) and tetracyanoethylene (TCNE) are investigated at the MP2/6-31G* and, partly, DFT-D/6-31G* levels. Solvent effects on the properties are evaluated using the PCM model. Fully optimized HMB,TCNE geometry in gas phase is a stacking complex with an interplanar distance 2.87 × 10,10 m and the corresponding BSSE corrected interaction energy is ,51.3 kJ mol,1. As expected, the interplanar distance is much shorter in comparison with HF and DFT results. However the crystal structures of both (HMB)2,TCNE and HMB,TCNE complexes have interplanar distances somewhat larger (3.18 and 3.28 × 10,10 m, respectively) than our MP2 gas phase value. Our estimate of the distance in CCl4 on the basis of PCM solvent effect study is also larger (3.06,3.16 × 10,10 m). The calculated enthalpy, entropy, Gibbs energy, and equilibrium constant of HMB,TCNE complex formation in gas phase are: ,H0 = ,61.59 kJ mol,1, ,S = ,143 J mol,1 K,1, ,G0 = ,18.97 kJ mol,1, and K = 2,100 dm3 mol,1. Experimental data, however, measured in CCl4 are significantly lower: ,H0 = ,34 kJ mol,1, ,S = ,70.4 J mol,1 K,1, ,G0 = ,13.01 kJ mol,1, and K = 190 dm3 mol,1. The differences are caused by solvation effects which stabilize more the isolated components than the complex. The total solvent destabilization of Gibbs energy of the complex relatively to that of components is equal to 5.9 kJ mol,1 which is very close to our PCM value 6.5 kJ mol,1. MP2/6-31G* dipole moment and polarizabilities are in reasonable agreement with experiment (3.56 D versus 2.8 D for dipole moment). The difference here is due to solvent effect which enlarges interplanar distance and thus decreases dipole moment value. The MP2/6-31G* study supplemented by DFT-D parameterization for enthalpy calculation, and by the PCM approach to include solvent effect seems to be proper tools to elucidate the properties of ,-EDA complexes. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]


    Natural bond orbital-based energy density analysis for correlated methods: Second-order Møller,Plesset perturbation and coupled-cluster singles and doubles

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 8 2008
    Yutaka Imamura
    Abstract Natural bond orbital-based energy density analysis (NBO-EDA), which split energies into atomic and bonding contributions, is proposed for correlated methods such as coupled-cluster singles and doubles (CCSD) and second-order Møller,Plesset (MP2) perturbation. Applying NBO-EDA for CCSD and MP2 to ethylene and the Diels,Alder reaction, we are successful in obtaining useful knowledge regarding electron correlation of ,- and ,-type orbitals, and clarifying the difference of the reaction barriers and heat of reaction calculated by CCSD and MP2. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]


    Internal-rotation and inversion potential energy surfaces for methylamine and methylphosphine

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2008
    Hae-Won Kim
    Abstract Using the HF, MP2, and DFT methods with a 6-311G** basis set, we examine the internal-rotation and inversion of the amino and phosphino groups in methylamine and methylphosphine. The resulting energy surfaces are reported as a function of rotation and inversion descriptors. Both surfaces are characterized by several special points: three minimum energy states, three first-order internal-rotation transition states, six first-order inversion transition states, and six second-order inversion transition states. The MP2 method gave better agreement with experiment. For methylamine, the MP2 energy barrier for internal-rotation is 8.73 kJ/mol; for first-order inversion it is 22.80 kJ/mol and for second-order inversion it is 22.41 kJ/mol. For methylphosphine, the MP2 energy barriers are 7.53, 149.88, and 149.65 kJ/mol, respectively. The energy barriers include ZPE correction contributions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]


    Geometries, vibrational frequencies, and electron affinities of X2Cl (X=C,Si,Ge) clusters

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2007
    Feng-You Hao
    Abstract Ab initio quantum chemical calculations have been performed on X2Cl, and X2Cl (X = C, Si, Ge) clusters. The geometrical structures, vibrational frequencies, electronic properties and dissociation energies are investigated at the Hartree,Fock (HF), Møller,Plesset second- and fourth-order (MP2, MP4), CCSD(T) level with the 6-311+G(d) basis set. The X2Cl (X = C, Si, Ge) and X2Cl, (X = Si, Ge) take a bent shape obtained at the ground state, while C2Cl, has a linear structure. The impact on internal electron transfer between the X2Cl and the corresponding anional clusters is studied. The three different types of electron affinities (EAs) at the CCSD(T) are reported. The most reliable adiabatic electronic affinities, obtained at the CCSD(T)/cc-pvqz level of theory, are predicted to be 3.30, 2.62, and 1.98 eV for C2Cl, Si2Cl, and Ge2Cl, respectively. The calculated EAs of C2Cl and Ge2Cl are in good agreement with theoretical results reported. The correlation effects and basis sets effects on the geometrical structures and dissociation energies are discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]


    Soft Coulomb hole method applied to molecules

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2007
    J. Ortega-Castro
    Abstract The soft Coulomb hole method introduces a perturbation operator, defined by ,e/r12 to take into account electron correlation effects, where , represents the width of the Coulomb hole. A new parametrization for the soft Coulomb hole operator is presented with the purpose of obtaining better molecular geometries than those resulting from Hartree,Fock calculations, as well as correlation energies. The 12 parameters included in , were determined for a reference set of 12 molecules and applied to a large set of molecules (38 homo- and heteronuclear diatomic molecules, and 37 small and medium-size molecules). For these systems, the optimized geometries were compared with experimental values; correlation energies were compared with results of the MP2, B3LYP, and Gaussian 3 approach. On average, molecular geometries are better than the Hartree,Fock values, and correlation energies yield results halfway between MP2 and B3LYP. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]


    Study of conformational and optical rotation for the alaninamide

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2007
    Shulei Zhao
    Abstract Six stationary points of alaninamide have been located on the potential surface energy (PES) at the B3LYP/6-311++G(2d,2p) level of theory both in the gas phase and in aqueous solution. In the aqueous solution, to take the water solvent effect into account, the polarizable continuum model (PCM) method has been used. Accurate geometric structures and their relative stabilities have been investigated. The results show that the intramolecular hydrogen bond plays a very important role in stabilizing the global minimum of the alaninamide. Moreover, the consistent result in relative energy using high-level computations, including the MP2 and MP3 methods with the same basis set [6-311++G(2d,2p)], indicates that the B3LYP/6-311++G(d,p) level may be applied to the analogue system. More importantly, the optical rotation of the optimized conformers (both in the gas phase and in aqueous solution) of alaninamide have been calculated using the density functional theory (DFT) and Hartree,Fock (HF) method at various basis sets (6-31+G*, 6-311++G(d,p), 6-311++G(2d,2p) and aug-cc-pvdz). The results show that the selection of the computation method and the basis set in calculation has great influence on the results of the optical rotations. The reliability of the HF method is less than that of DFT, and selecting the basis set of 6-311++G(2d,2p) and aug-cc-pvDZ produces relative reliable results. Analysis of the computational results of the structure parameters and the optical rotations yields the conclusion that just the helixes in molecules caused the chiral molecules to be optical active. The Boltzmann equilibrium distributions for the six conformers (both in the gas phase and in the aqueous solution) are also carried out. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]


    Theoretical studies of mechanisms of cycloaddition reaction between difluoromethylene carbene and acetone

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2007
    Xiu Hui Lu
    Abstract Mechanisms of the cycloaddition reaction between singlet difluoromethylene carbene and acetone have been investigated with the second-order Møller,Plesset (MP2)/6-31G* method, including geometry optimization and vibrational analysis. Energies for the involved stationary points on the potential energy surface (PES) are corrected by zero-point energy (ZPE) and CCSD(T)/6-31G* single-point calculations. From the PES obtained with the CCSD(T)//MP2/6-31G* method for the cycloaddition reaction between singlet difluoromethylene carbene and acetone, it can be predicted that path B of reactions 2 and 3 should be two competitive leading channels of the cycloaddition reaction between difluoromethylene carbene and acetone. The former consists of two steps: (i) the two reactants first form a four-membered ring intermediate, INT2, which is a barrier-free exothermic reaction of 97.8 kJ/mol; (ii) the intermediate INT2 isomerizes to a four-membered product P2b via a transition state TS2b with an energy barrier of 24.9 kJ/mol, which results from the methyl group transfer. The latter proceeds in three steps: (i) the two reactants first form an intermediate, INT1c, through a barrier-free exothermic reaction of 199.4 kJ/mol; (ii) the intermediate INT1c further reacts with acetone to form a polycyclic intermediate, INT3, which is also a barrier-free exothermic reaction of 27.4 kJ/mol; and (iii) INT3 isomerizes to a polycyclic product P3 via a transition state TS3 with an energy barrier of 25.8 kJ/mol. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]


    Theoretical study in [C2H4,Tl]+ and [C2H2,Tl]+ complexes

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2007
    Fernando Mendizabal
    Abstract We studied the attraction between [C2Hn] and Tl(I) in the hypothetical [C2Hn,Tl]+ complexes (n = 2,4) using ab initio methodology. We found that the changes around the equilibrium distance C,Tl and in the interaction energies are sensitive to the electron correlation potential. We evaluated these effects using several levels of theory, including Hartree,Fock (HF), second-order Møller,Plesset (MP2), MP4, coupled cluster singles and doubles CCSD(T), and local density approximation augmented by nonlocal corrections for exchange and correlation due to Becke and Perdew (LDA/BP). The obtained interaction energies differences at the equilibrium distance Re (C,Tl) range from 33 and 46 kJ/mol at the different levels used. These results indicate that the interaction between olefinic systems and Tl(I) are a real minimum on the potential energy surfaces (PES). We can predict that these new complexes are viable for synthesizing. At long distances, the behavior of the [C2Hn],Tl+ interaction may be related mainly to charge-induced dipole and dispersion terms, both involving the individual properties of the olefinic ,-system and thallium ion. However, the charge-induced dipole term (R,4) is found as the principal contribution in the stability at long and short distances. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]


    Correlated, relativistic, and basis set limit molecular polarizability calculations to evaluate an augmented effective core potential basis set

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2006
    Nicholas P. Labello
    Abstract Initial investigations have demonstrated that an augmented ECP basis set can be used to calculate valence electronic properties with deviations of less than 1% from all-electron basis sets. Past work has largely focused on molecules with relatively light atoms (Z<18) examined with time-dependent Hartree,Fock (TDHF) theory. In this work, the dipole moment and polarizability of a number of well-studied molecules are examined with HF, MP2, CCSD, and CCSD(T) correlated wave functions. Additionally, systems not as thoroughly studied due to the difficulty of all-electron calculations when Z=50,85 are included. The SBK ECP basis set, augmented with optimized valence functions, performs well across a broad range of methods, less than 3% different from all electron relativistic and correlated wave functions. Orders of magnitude time savings (101,104) are exchanged for a minimal difference from all-electron basis sets. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]


    BSSE-free hardness profiles of hydrogen bond exchange in the hydrogen fluoride dimer

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2006
    David Asturiol
    Abstract Hardness profiles are calculated for the hydrogen bond interchange in the hydrogen fluoride dimer; the study is carried out at the Hartree,Fock and second-order Møller,Plesset (MP2) levels of theory with three different basis sets. The basis set superposition error (BSSE) is corrected by means of the chemical Hamiltonian approach (CHA). Uncorrected and BSSE-corrected energy and hardness profiles are compared. Their analysis shows that hardness profiles do not lead to spurious minima as energy profiles do in various cases. The CHA methodology is shown to be valuable in the analysis of intermolecular interactions, with BSSE observed to carry smaller modifications on hardness profiles than on energy curves. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]


    Comprehensive theoretical study towards the accurate proton affinity values of naturally occurring amino acids

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2006
    T. C. Dinadayalane
    Abstract Systematic quantum chemical studies of Hartree,Fock (HF) and second-order Møller,Plesset (MP2) methods, and B3LYP functional, with a range of basis sets were employed to evaluate proton affinity values of all naturally occurring amino acids. The B3LYP and MP2 in conjunction with 6-311+G(d,p) basis set provide the proton affinity values that are in very good agreement with the experimental results, with an average deviation of ,1 kcal/mol. The number and the relative strength of intramolecular hydrogen bonding play a key role in the proton affinities of amino acids. The computational exploration of the conformers reveals that the global minima conformations of the neutral and protonated amino acids are different in eight cases. The present study reveals that B3LYP/6-311+G(d,p) is a very good choice of technique to evaluate the proton affinities of amino acids and the compounds derived from them reliably and economically. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]


    Structure and hydrolysis of the heavy alkaline earth cations: Relativistic studies

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2006
    Maria Barysz
    Abstract The relativistic spin-averaged Douglas,Kroll theory at the level of the MP2 and CCSD(T) approximations has been applied to explain the hydrolysis trends for the Group 2 dications through the investigation of the structure and energetics of the model complexes with the water molecule. The parallel nonrelativistic calculations have been performed to show the possible role of the relativistic effect on the structure and hydrolysis of the heaviest metal cations. The calculated data are compared with the recent experimental results. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]


    Use of vibrational spectroscopy to study protein and DNA structure, hydration, and binding of biomolecules: A combined theoretical and experimental approach

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2006
    K. J. Jalkanen
    Abstract We report on our work with vibrational absorption, vibrational circular dichroism, Raman scattering, Raman optical activity, and surface-enhanced Raman spectroscopy to study protein and DNA structure, hydration, and the binding of ligands, drugs, pesticides, or herbicides via a combined theoretical and experimental approach. The systems we have studied systematically are the amino acids (L -alanine, L -tryptophan, and L -histidine), peptides (N -4271 acetyl L -alanine N,-methyl amide, N -acetyl L -tryptophan N,-methyl amide, N -acetyl L -histidine N,-methyl amide, L -alanyl L -alanine, tri- L -serine, N -acetyl L -alanine L -proline L -tyrosine N,-methyl amide, Leu-enkephalin, cyclo-(gly- L -pro)3, N -acetyl (L -alanine)nN,-methyl amide), 3-methyl indole, and a variety of small molecules (dichlobenil and 2,6-dochlorobenzamide) of relevance to the protein systems under study. We have used molecular mechanics, the SCC-DFTB, SCC-DFTB+disp, RHF, MP2, and DFT methodologies for the modeling studies with the goal of interpreting the experimentally measured vibrational spectra for these molecules to the greatest extent possible and to use this combined approach to understand the structure, function, and electronic properties of these molecules in their various environments. The application of these spectroscopies to biophysical and environmental assays is expanding, and therefore a thorough understanding of the phenomenon from a rigorous theoretical basis is required. In addition, we give some exciting and new preliminary results which allow us to extend our methods to even larger and more complex systems. The work presented here is the current state of the art to this ever and fast changing field of theoretical spectroscopic interpretation and use of VA, VCD, Raman, ROA, EA, and ECD spectroscopies. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]