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Valence Basis Set (valence + basis_set)
Selected AbstractsStructure and stability of high-spin Aun(n = 2,8) clustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2009Zhen-Yi Jiang Abstract The structures and relative stability of the maximum-spin n+1Aun and nAu (n = 2,8) clusters have been determined by density-functional theory. The structure optimizations and vibrational frequency analysis are performed with the gradient-corrections of Perdew along with his 1981 local correlation functional, combined with SBKJC effective core potential, augmented in the valence basis set by a set of f functions. We predicted the existence of a number of previously unknown isomers. The energetic and electronic properties of the small high-spin gold clusters are strongly dependent on sizes. The high-spin clusters tend to holding three-dimensional geometry rather than planar form preferred in low-spin situations. In whole high-spin Aun (n = 2,8) neutral and cationic species, 5Au4, 2Au, and 4Au are predicted to be of high stability, which can be explained by valence bond theory. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Calculation of proton affinity using the CR-CCSD[T]/ECP methodINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2006Nelson H. Morgon Abstract High-level calculations of proton and electron affinities (PA and EA) of CH2X, and CH2CHCHX, (with X = F, Cl, Br, and I) systems were obtained. The methodology employed in the PA and EA calculations is based on CR-CCSD[T]/B1//MP2/B0 and CCSD(T)/B1//MP2/B0 levels, respectively. B0 is a (small) valence basis set developed by Stevens and colleagues (SBKJC), and B1 is a larger basis set, with extra diffuse and polarization functions (B0 + s, p, d, and f functions). This scheme has been tested on systems containing H, C, and X atoms, and is shown to give good results. The differences between calculated results of PA and EA and the experimental values are in the range of 0.2,4.5 kJ · mol,1 and 0.01 to 0.10 eV, respectively. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Calculation of the vibration frequencies of ,-quartz: The effect of Hamiltonian and basis setJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2004C. M. Zicovich-Wilson Abstract The central-zone vibrational spectrum of ,-quartz (SiO2) is calculated by building the Hessian matrix numerically from the analytical gradients of the energy with respect to the atomic coordinates. The nonanalytical part is obtained with a finite field supercell approach for the high-frequency dielectric constant and a Wannier function scheme for the evaluation of Born charges. The results obtained with four different Hamiltonians, namely Hartree,Fock, DFT in its local (LDA) and nonlocal gradient corrected (PBE) approximation, and hybrid B3LYP, are discussed, showing that B3LYP performs far better than LDA and PBE, which in turn provide better results than HF, as the mean absolute difference from experimental frequencies is 6, 18, 21, and 44 cm,1, respectively, when a split valence basis set containing two sets of polarization functions is used. For the LDA results, comparison is possible with previous calculations based on the Density Functional Perturbation Theory and usage of a plane-wave basis set. The effects associated with the use of basis sets of increasing size are also investigated. It turns out that a split valence plus a single set of d polarization functions provides frequencies that differ from the ones obtained with a double set of d functions and a set of f functions on all atoms by on average less than 5 cm,1. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1873,1881, 2004 [source] Development of new pseudopotential methods: Improved model core potentials for the first-row transition metalsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2003Christopher C. Lovallo Abstract We have recently developed new nonrelativistic and scalar-relativistic pseudopotentials for the first-row transition metal and several main-group elements. These improved Model Core Potentials were tested on a variety of transition metal complexes to determine their accuracy in reproducing electronic structures, bond lengths, and harmonic vibrational frequencies with respect to both all-electron reference data as well as experimental data. The new potentials are also compared with the previous model core potentials available for the first-row transition metals. The new potentials do a superior job at reproducing atomic data, reproduce molecular data as well as the previous version, and in conjunction with new main-group pseudopotentials that have L-shell structure of the valence basis set, they are slightly faster. © 2003 Wiley Periodicals, Inc. J Comput Chem 9: 1009,1015, 2003 [source] High-level ab initio calculations on HGeCl and the equilibrium geometry of the Ã1A, state derived from Franck-Condon analysis of the single-vibronic-level emission spectra of HGeCl and DGeClJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2010Daniel K. W. Mok Abstract CCSD(T) and/or CASSCF/MRCI calculations have been carried out on the X,1A, and Ã1A, states of HGeCl. The fully relativistic effective core potential, ECP10MDF, and associated standard valence basis sets of up to the aug-cc-pV5Z quality were employed for Ge. Contributions from core correlation and extrapolation to the complete basis set limit were included in determining the computed equilibrium geometrical parameters and relative electronic energy of these two states of HGeCl. Based on the currently, most systematic CCSD(T) calculations performed in this study, the best theoretical geometrical parameters of the X,1A, state are re(HGe) = 1.580 ± 0.001 Å, ,e = 93.88 ± 0.01° and re(GeCl) = 2.170 ± 0.001 Å. In addition, Franck-Condon factors including allowance for anharmonicity and Duschinsky rotation between these two states of HGeCl and DGeCl were calculated employing CCSD(T) and CASSCF/MRCI potential energy functions, and were used to simulate Ã1A, , X,1A, SVL emission spectra of HGeCl and DGeCl. The iterative Franck-Condon analysis (IFCA) procedure was carried out to determine the equilibrium geometrical parameters of the Ã1A, state of HGeCl by matching the simulated, and available experimental SVL emission spectra of HGeCl and DGeCl of Tackett et al., J Chem Phys 2006, 124, 124320, using the available, estimated experimental equilibrium (r) structure for the X,1A, state, while varying the equilibrium geometrical parameters of the Ã1A, state systematically. Employing the derived IFCA geometry of re(HGe) = 1.590 Å, re(GeCl) = 2.155 Å and ,e(HGeCl) = 112.7° for the Ã1A, state of HGeCl in the spectral simulation, the simulated absorption and SVL emission spectra of HGeCl and DGeCl agree very well with the available experimental LIF and SVL emission spectra, respectively. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] | ||||||||||