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ABSTRACT: The ground state ab initio CCSD(T) potential curves using various basis sets (aug-cc-pVXZ-PP (X = D, T, Q, 5)) is obtained for the dimers of helium with IIb group metals. The effect of the position of the (mid) bond-functions on the interaction energy is discussed. A Symmetry Adapted Perturbation Theory decomposition of the interaction energy is provided and the trends in the dimer stabilizing and destabilizing contributions are depicted. The spline fitted potential curves are applied together with rigorous statistical formulae in order to obtain the transport coefficients (viscosity coefficients, diffusion coefficients) and the second virial coefficient both for pure constituents and mixtures. The obtained theoretical results are compared with available experimental data. Molecular dynamics is used to obtain reliable values of the diffusion coefficients for all the systems under study.
Journal of Computational Chemistry 03/2012; 33(7):767-78. · 4.58 Impact Factor
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ABSTRACT: The comparison of coupled cluster with single and double excitations and with perturbative correction of triple excitations [CCSD(T)] ground state potential curves of mercury with rare gases (RG): HgHe and HgXe, at several levels of theory is presented. The scalar relativistic (REL) effects and spin-orbit coupling effects in the ground state potential curves of these weakly bounded dimers are considered. The CCSD(T) ground state potential curves at the level of the Dirac-Coulomb Hamiltonian (DCH) are compared with CCSD(T) curves at the level of 4-component spin-free modified DCH, the scalar 2nd order Douglas-Kroll-Hess (DKH2) and the nonrelativistic (NR-LL) (Lévy-Leblond) Hamiltonian. In addition, London-Drude formula and SCF interaction energy curves are employed in the analysis of different contributions of REL effects in dissociation energies of HgRG and Hg(2) dimers. Moreover, the large anharmonicity of the HgHe ground state potential curve is highlighted. The computationally less demanding scalar DKH2 Hamiltonian is employed to calculate the HgXe, Hg(2) , and Xe(2) all electron CCSD(T) ground state potential curves in highly augmented quadruple zeta basis sets. These potential curves are used to simulate the shear viscosity of mercury, xenon, and mercury-xenon (Hg:Xe) mixture.
Journal of Computational Chemistry 01/2011; 32(2):356-67. · 4.58 Impact Factor
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ABSTRACT: The ground state potential curves of the Zn2, Cd2, and Hg2 dimers calculated at different levels of theory are presented and compared with each other as well as with experimental and other theoretical studies. The calculations at the level of Dirac-Coulomb Hamiltonian (DCH), 4-component spin-free Hamiltonian, nonrelativistic Lévy-Leblond Hamiltonian and at the level of simple Coulombic correction to DCH are presented. The potential curves are calculated in an all-electron supermolecular approach including the correction to basis set superposition error (BSSE). Electron correlation is treated at the coupled cluster level including single and double excitations and noniterative triple corrections, CCSD(T). In addition, simulations of the temperature dependence of dynamic viscosities in the low-density limit using the obtained ground state potential curves are presented.
Journal of Computational Chemistry 05/2008; 30(1):65 - 74. · 4.58 Impact Factor
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ABSTRACT: The supermolecular CCSD(T) ab initio calculations of potential energy surface for the electronic ground state of van der Waals (vdW) complex formed from a mercury atom with hydrogen molecule are presented. Our results indicate the linear geometry (Jacobi coordinates are rH–H = 0.743 Å and R = 4.12 Å) vdW system with the relative small depth of De = 59.6 cm−1. The physical origin of the stability of the studied vdW structure was analyzed by symmetry adapted perturbation theory. The separation of its interaction energy shows that the dispersion interaction is ca seven-times stronger than the induction and ca five-times higher than the electrostatic energy. Finally, the temperature dependence of the coefficient of diffusion was simulated from the calculated potential energy surface using collisional model. Theoretical value of 0.51 cm2 s−1 very well corresponds with the available experimental value (0.53 cm2 s−1) for T = 238 K.
Chemical Physics. 349:32-36.
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ABSTRACT: Gas-phase reaction enthalpies related to the individual steps of three phenolic antioxidants action mechanisms – hydrogen atom transfer (HAT), single-electron transfer–proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) for four tocopherols and seven chromans – were calculated using DFT/B3LYP method. For α-tocopherol, one of the chromans and phenol, reaction enthalpies in water were computed. In comparison to gas phase, water causes severe changes in the energetics of studied compounds antioxidant action. From the thermodynamic point of view, entering SPLET mechanism represents the most probable process in water.
Chemical Physics. 336(1):51-57.
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ABSTRACT: In this article, we have studied p-phenylenediamine (PPD) and tetracyano-p-phenylenediamine (TCPPD) molecules in order to study the effect of CN groups and the solvent effect on the enthalpies of homolytic and heterolytic N–H bond cleavage. Geometries of the molecules and reaction enthalpies related to hydrogen atom transfer, single electron transfer–proton transfer (SET–PT) mechanism and sequential proton loss electron transfer (SPLET) mechanisms were studied using DFT/UB3LYP/6-31++G∗∗ method. Ab initio MP2/6-31++G∗∗ method was used as the reference for the geometry calculation of the two molecules in vacuum. Solvent contribution to the enthalpies was computed employing integral equation formalism IEF-PCM method. Obtained results show that solvent is able to cause significant change in the reaction enthalpies of the stepwise SET–PT and SPLET mechanisms of hydrogen splitting-off from NH2 group. This may result in the change in thermodynamically preferred mechanism. Solvents also attenuate the CN-substituent effect in the case of SET–PT and SPLET mechanisms.
Journal of Molecular Structure THEOCHEM 952:25-30. · 1.44 Impact Factor
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ABSTRACT: The supermolecular UHF coupled-clusters method was used to investigate the energetics of the weak interaction of rigid acetylene molecule with lithium atom. The obtained potential energy surface (PES) corrected on the basis set superposition error indicate the strong interaction for the perpendicular orientation at R=2.59 Å with a well depth of . The presented PES reveals also the second minimum for the linear orientation at R=5.85 Å with a well depth of . The zero point correction is negligible. The physical origin of stability of localised structures was analysed by the intermolecular perturbation theory based on the single determinant UHF wave function. The separation of the interaction energy shows that the positions of the predicted stable structures (at R=2.59 Å) are primarily determined by the attractive components included in HF deformation and dispersion energies.
Chemical Physics. 302:69-76.
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ABSTRACT: The adiabatic potential energy surface (PES) of the Li-CO complex in the van der Waals region, described by Jacobi coordinates ( r = 1.15 Å, R , Θ), was investigated using the supermolecular coupled-clusters CCSD(T) method. Our calculations indicate minima for bent arrangements. The first minimum was found on the carbon side of CO molecule at R = 5.27 Å (Θ = 50.7°) with a well depth of D <sub>e</sub> = -167.2 μ E <sub>h</sub>. The second minimum is indicated at R = 5.35 Å (Θ = 148.7°) with a well depth of D <sub>e</sub> = -121.9 μ E <sub>h</sub>. The saddle point is localised at θ = 111.5° and R = 5.35 Å. The physical origin of the weak interaction studied was analysed by the intermolecular perturbation theory based on the single determinant UHF wave function. The separation of the interaction energies shows that the locations of the predicted stable bent structures are primarily determined by the anisotropy of the repulsive Heitler-London exchange penetration and attractive dispersion and induction energy components.
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ABSTRACT: The adiabatic potential energy surface of the H-CO complex in the van der Waals region, described by Jacobi coordinates ( r = 1.128 Å, R , Θ), was investigated using the supermolecular coupled-clusters CCSD(T) method. Our calculations indicate a minimum for bent arrangements. It was found on the carbon side of CO molecule at R = 3.6 Å (Θ = 76°) with a well depth of D <sub>e</sub> = -156.5 μ E <sub>h</sub>. The saddle points are localised at linear conformations for R = 4.37 Å (Θ = 0°) and R = 3.91 Å (Θ = 180°). The physical origin of the studied interaction was analysed by the intermolecular perturbation theory based on the single-determinant unrestricted Hartree-Fock wave function. The separation of the interaction energies shows that the locations of the predicted stable bent structure is primarily determined by delicate balance between the repulsive Heitler-London and attractive dispersion and induction energy components.
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ABSTRACT: The ab initio potential energy surface (PES) for the weak interaction of hydrogen molecule with iodine anion is presented. The surface was obtained by the supermolecular method at the MP4(SDTQ) level of theory. Our calculations indicate the van der Waals (vdW) system for the linear configuration at r <sub>H-H</sub> = 0.752 Å and R = 3.76 Å with a well depth of D <sub>e</sub> = 2096 μ E <sub>h</sub>. The presented PES reveals also a transition state for the perpendicular arrangement at r <sub>H-H</sub> = 0.7416 Å and R = 4.63 Å with an interaction energy of -113 μ E <sub>h</sub>. The physical origin of stability of the vdW H<sub>2</sub>...I<sup>-</sup> structure with respect to the H<sub>2</sub>...X<sup>-</sup> (X = F, Cl, Br) one was analysed by the symmetry adapted perturbation theory (SAPT) based on the single determinant HF wave function. The separation of the interaction energy shows that the dispersion forces play a much more important role for the systems with Cl, Br and I than for H<sub>2</sub>...F<sup>-</sup> and their importance slightly increases in the order Cl < Br < I. The global importance of the electrostatic and the induction energies decreases in the order F > Cl > Br > I.
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ABSTRACT: Supermolecular CCSD(T) ab initio calculations of potential energy curves for the electronic ground states of heteronuclear van der Waals complexes formed from the atoms of IIB group are presented. The physical origin of stability of the studied structures was analyzed by the symmetry-adapted perturbation theory. The magnitude of dispersion term increases with the increase of diatomic mass, but the relative importance of dispersion vs Hartree- Fock induction energies decreases in the order CdZn > HgZn > HgCd. Theoretical calculations of the temperature dependence of the shear viscosity for low-density binary mixtures are in good agreement with the temperature dependences of the shear viscosity obtained from empirical formula.
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ABSTRACT: The supermolecular CCSD(T) ab initio calculations of potential energy surface for the electronic ground state of van der Waals complex formed from a cadmium atom and a nitrogen molecule are presented. Our calculations indicate the bent orientation (Jacobi coordinates are r <sub>N-N</sub> = 1.10 Å, R = 4.53 Å, angle θ = 62°) of the van der Waals (vdW) system with a well depth of D <sub>e</sub> = 73.3 cm<sup>-1</sup>. This well depth was shifted to the value of 76.7 cm<sup>-1</sup> by systematical extension of mid-bond functions. The temperature dependences of the theoretical coefficient of diffusion were evaluated from the molecular dynamics and the Enskog-Chapman theory. The theoretical values at 273 K are compared with the available experimental data.
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ABSTRACT: The potential energy surface of the radical H⋯CO2 van der Waals complex, described by Jacobi coordinates (), was investigated using the supermolecular coupled cluster treatment. Our calculations corrected for the basis set supperposition error predict global minimum for the perpendicular arrangement (Θ=90°). This minimum was found at R=3.20 Å with a well depth of . The second stationary point has a well depth of at linear orientation for and corresponds to the saddle point. The physical origin of the studied weak interaction was analysed by the intermolecular perturbation theory based on the single determinant unrestricted Hartree–Fock wave function. The separation of the interaction energy shows that the locations of the indicated structure is primarily determined by delicate balance between the rapid decrease of the repulsive Heitler–London exchange-penetration energy versus attractive Hartree–Fock dispersion components over the carbon atom.
Chemical Physics.
