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GGA Functionals (gga + functional)
Selected AbstractsStructural, electronic, bonding, magnetic, and optical properties of bimetallic [RunAum]0/+ (n + m , 3) clustersJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2010Dimitrios N. Garbounis Abstract The structural, electronic, bonding, magnetic, and optical properties of bimetallic [RunAum]0/+ (n + m , 3; n, m = 0,3) clusters were computed in the framework of the density functional theory (DFT) and time-dependent DFT (TD-DFT) using the full-range PBE0 non local hybrid GGA functional combined with the Def2-QZVPP basis sets. Several low-lying states have been investigated and the stability of the ground state spinomers was estimated with respect to all possible fragmentation schemes. Molecular orbital and population analysis schemes along with computed electronic parameters illustrated the details of the bonding mechanisms in the [RunAum]0/+ clusters. The TD-DFT computed UV-visible absorption spectra of the bimetallic clusters have been fully analyzed and compared to those of pure gold and ruthenium clusters. Assignments of all principal electronic transitions are given and interpreted in terms of contribution from specific molecular orbital excitations. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 [source] On the performance of eleven DFT functionals in the description of the vibrational properties of aluminosilicatesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2010Raffaella Demichelis Abstract The performance of eleven DFT functionals in describing the equilibrium structure and the vibrational spectra at the , point of pyrope (Mg3Al2Si3O12), forsterite (,-Mg2SiO4), ,-quartz (,-SiO2) and corundum (,-Al2O3) is discussed. The four systems, for which accurate experimental data are available, are here used as a representative sample of the large aluminosilicates family. Calculations were performed with the periodic ab initio CRYSTAL code by using all-electron Gaussian-type basis sets. All the functionals here considered provide reasonable structural predictions, the hybrid PBE0 giving the least deviation from the experimental unit cell volumes (from ,0.3% to +0.6%). At the other extreme, SVWN and SPWLSD (,,3%) and PBE and PW91 (, +3%) provide the largest volume under- and over-estimation, respectively. Vibrational frequencies are more accurate when computed with hybrid functionals, with the best performance provided by B3LYP and WC1LYP (mean absolute differences with respect to experiments evaluated on a set of 134 vibrational frequencies, ||t , 5.5 cm,1). The three recently proposed GGA functionals, PBEsol, SOGGA-PBE and WC-PBE, provide a good description of the vibrational spectra, of the same quality as the one provided by PBE0 and B1WC (||t , 10 cm,1), whereas poorer results are obtained with PBE (||t , 17 cm,1). © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Energy landscapes of nucleophilic substitution reactions: A comparison of density functional theory and coupled cluster methodsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2007Marcel Swart Abstract We have carried out a detailed evaluation of the performance of all classes of density functional theory (DFT) for describing the potential energy surface (PES) of a wide range of nucleophilic substitution (SN2) reactions involving, amongst others, nucleophilic attack at carbon, nitrogen, silicon, and sulfur. In particular, we investigate the ability of the local density approximation (LDA), generalized gradient approximation (GGA), meta-GGA as well as hybrid DFT to reproduce high-level coupled cluster (CCSD(T)) benchmarks that are close to the basis set limit. The most accurate GGA, meta-GGA, and hybrid functionals yield mean absolute deviations of about 2 kcal/mol relative to the coupled cluster data, for reactant complexation, central barriers, overall barriers as well as reaction energies. For the three nonlocal DFT classes, the best functionals are found to be OPBE (GGA), OLAP3 (meta-GGA), and mPBE0KCIS (hybrid DFT). The popular B3LYP functional is not bad but performs significantly worse than the best GGA functionals. Furthermore, we have compared the geometries from several density functionals with the reference CCSD(T) data. The same GGA functionals that perform best for the energies (OPBE, OLYP), also perform best for the geometries with average absolute deviations in bond lengths of 0.06 Å and 0.6°, even better than the best meta-GGA and hybrid functionals. In view of the reduced computational effort of GGAs with respect to meta-GGAs and hybrid functionals, let alone coupled cluster, we recommend the use of accurate GGAs such as OPBE or OLYP for the study of SN2 reactions. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] A CSOV study of the difference between HF and DFT intermolecular interaction energy values: The importance of the charge transfer contributionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2005Jean-Philip Piquemal Abstract Intermolecular interaction energy decompositions using the Constrained Space Orbital Variation (CSOV) method are carried out at the Hartree,Fock level on the one hand and using DFT with usual GGA functionals on the other for a number of model complexes to analyze the role of electron correlation in the intermolecular stabilization energy. In addition to the overall stabilization, the results provide information on the variation, with respect to the computational level, of the different contributions to the interaction energy. The complexes studied are the water linear dimer, the N -methylformamide dimer, the nucleic acid base pairs, the benzene,methane and benzene-N2 van der Waals complexes, [Cu+ -(ImH)3]2, where "ImH" stands for the Imidazole ligand, and ImH-Zn++. The variation of the frozen core energy (the sum of the intermolecular electrostatic energy and the Pauli repulsion energy) calculated from the unperturbed orbitals of the interacting entities indicates that the intramolecular correlation contributions can be stabilizing as well as destabilizing, and that general trends can be derived from the results obtained using usual density functionals. The most important difference between the values obtained from HF and DFT computations concerns the charge transfer contribution, which, in most cases, undergoes the largest increase. The physical meaning of these results is discussed. The present work gives reference calculations that might be used to parametrize new correlated molecular mechanics potentials. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1052,1062, 2005 [source] | ||||||||||