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Effective Core Potential (effective + core_potential)
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] Two-step method for precise calculation of core properties in moleculesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2005A. V. Titov Abstract Precise calculations of core properties in heavy-atom systems that are described by the operators heavily concentrated in atomic cores, such as hyperfine structure and P,T-parity nonconservation effects, require accounting for relativistic effects. Unfortunately, four-component calculation of molecules containing heavy elements is very consuming already at the stages of calculation and transformation of two-electron integrals with a basis set of four-component spinors. In turn, the relativistic effective core potential (RECP) calculations of valence (spectroscopic, chemical, etc.) properties of molecules are very popular, because the RECP method allows one to treat quite satisfactorily the correlation and relativistic effects for the valence electrons of a molecule and to reduce significantly the computational efforts. The valence molecular spinors are usually smoothed in atomic cores, and, as a result, direct calculation of electronic densities near heavy nuclei is impossible. In this paper, the methods of nonvariational and variational one-center restoration of correct shapes of four-component spinors in atomic cores after a two-component RECP calculation of a molecule are discussed. Their efficiency is illustrated in correlation calculations of hyperfine structure and parity nonconservation effects in heavy-atom molecules YbF, BaF, TlF, and PbO. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [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] Numerical instabilities in the computation of pseudopotential matrix elementsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2006Christoph van Wüllen Abstract Steep high angular momentum Gaussian basis functions in the vicinity of a nucleus whose inner electrons are replaced by an effective core potential may lead to numerical instabilities when calculating matrix elements of the core potential. Numerical roundoff errors may be amplified to an extent that spoils any result obtained in such a calculation. Effective core potential matrix elements for a model problem are computed with high numerical accuracy using the standard algorithm used in quantum chemical codes and compared to results of the MOLPRO program. Thus, it is demonstrated how the relative and absolute errors depend an basis function angular momenta, basis function exponents and the distance between the off-center basis function and the center carrying the effective core potential. Then, the problem is analyzed and closed expressions are derived for the expected numerical error in the limit of large basis function exponents. It is briefly discussed how other algorithms would behave in the critical case, and they are found to have problems as well. The numerical stability could be increased a little bit if the type 1 matrix elements were computed without making use of a partial wave expansion. © 2005 Wiley Periodicals, Inc., J Comput Chem 27: 135,141 2006 [source] Density functional theory studies on the dissociation energies of metallic salts: relationship between lattice and dissociation energiesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2001Chang Kon Kim Abstract The formation and physicochemical properties of polymer electrolytes strongly depend on the lattice energy of metal salts. An indirect but efficient way to estimate the lattice energy through the relationship between the heterolytic bond dissociation and lattice energies is proposed in this work. The heterolytic bond dissociation energies for alkali metal compounds were calculated theoretically using the Density Functional Theory (DFT) of B3LYP level with 6-311+G(d,p) and 6-311+G(2df,p) basis sets. For transition metal compounds, the same method was employed except for using the effective core potential (ECP) of LANL2DZ and SDD on transition metals for 6-311+G(d,p) and 6-311+G(2df,p) calculations, respectively. The dissociation energies calculated by 6-311+G(2df,p) basis set combined with SDD basis set were better correlated with the experimental values with average error of ca. ±1.0% than those by 6-311+G* combined with the LANL2DZ basis set. The relationship between dissociation and lattice energies was found to be fairly linear (r>0.98). Thus, this method can be used to estimate the lattice energy of an unknown ionic compound with reasonably high accuracy. We also found that the dissociation energies of transition metal salts were relatively larger than those of alkaline metal salts for comparable ionic radii. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 827,834, 2001 [source] Grid-based density functional calculations of many-electron systemsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2008Amlan K. RoyArticle first published online: 10 DEC 200 Abstract Exploratory variational pseudopotential density functional calculations are performed for the electronic properties of many-electron systems in the 3D cartesian coordinate grid (CCG). The atom-centered localized gaussian basis set, electronic density, and the two-body potentials are set up in the 3D cubic box. The classical Hartree potential is calculated accurately and efficiently through a Fourier convolution technique. As a first step, simple local density functionals of homogeneous electron gas are used for the exchange-correlation potential, while Hay-Wadt-type effective core potentials are employed to eliminate the core electrons. No auxiliary basis set is invoked. Preliminary illustrative calculations on total energies, individual energy components, eigenvalues, potential energy curves, ionization energies, and atomization energies of a set of 12 molecules show excellent agreement with the corresponding reference values of atom-centered grid as well as the grid-free calculation. Results for three atoms are also given. Combination of CCG and the convolution procedure used for classical Coulomb potential can provide reasonably accurate and reliable results for many-electron systems. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Excited states of OsO4: A comprehensive time-dependent relativistic density functional theory studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2010Yong Zhang Abstract A large number of scalar as well as spinor excited states of OsO4, in the experimentally accessible energy range of 3,11 eV, have been captured by time-dependent relativistic density functional linear response theory based on an exact two-component Hamiltonian resulting from the symmetrized elimination of the small component. The results are grossly in good agreement with those by the singles and doubles coupled-cluster linear response theory in conjunction with relativistic effective core potentials. The simulated-excitation spectrum is also in line with the available experiment. Furthermore, combined with detailed analysis of the excited states, the nature of the observed optical transitions is clearly elucidated. It is found that a few scalar states of 3T1 and 3T2 symmetries are split significantly by the spin-orbit coupling. The possible source for the substantial spin-orbit splittings of ligand molecular orbitals is carefully examined, leading to a new interpretation on the primary valence photoelectron ionization spectrum of OsO4. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] | ||||||||||