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Correlation Functional (correlation + functional)

Distribution by Scientific Domains
Chemistry87%

Selected Abstracts

Structure and stability of high-spin Aun(n = 2,8) clusters

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2009
Zhen-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]

Comparison of second-order orbital-dependent DFT correlation functionals

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2008
Ireneusz Grabowski
Abstract The choice of the orbital-dependent second-order correlation functional plays the prime role in the description of the correlation effects in orbital-dependent DFT calculations. Using second-order perturbation theory we were able to derive the simplest orbital-dependent correlation functional, but even at this lowest correlation level, we had several possibilities to define it. Applications of different second-order correlation functionals for the atomic as well as molecular systems are presented. The ab initio DFT-type OEP2 functionals based on Møller-Plesset or semicanonical partitioning (OEP2-sc) are compared with those based on Epstein-Nesbet type partitioning, showing that the latter ones can fail in more difficult molecular problems, e.g., the Be dimer potential curve. We show that currently the best performing orbital-dependent second-order correlation functional is the OEP2-sc one. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

Absorption, resonance, and near-resonance Raman studies of the tetracyanoquinodimethane neutral and its monoanion in terms of density functional theory and complete active space self-consistent field methods

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 8 2006
Marcin Makowski
Abstract The electronic structure of the 11B1u and 12B3u excited electronic states of the tetracyanoquinodimethane (TCNQ) neutral and its charged derivative are studied within the framework of complete active space self-consistent field (CASSCF) and Becke's three-parameter hybrid method with Lee,Yang,Parr correlation functional (B3LYP) methods applied to the level aug-cc-p-VDZ basis set. Both CASSCF/aug-cc-p-VDZ and B3LYP/aug-cc-p-VDZ treatments provide the ground-state and the excited state geometries; these are then used to assess the Franck,Condon (FC) parameters in the 11B1u state of the neutral TCNQ and in the 12B3u state of the TCNQ monoanion. The quality of numerical results is then tested on the base of available experimental near-resonance and resonance Raman data. The studies are performed in terms of the vibronic model, which takes both FC and mode-mixing (Dushinsky) effects into account. This somewhat simplified vibronic model leads to very good agreement between the theory and the Raman experiments concerning both neutral TCNQ and its monoanion. In particular, the calculated excitation profiles of the ,2 = 2215 cm,1, ,4 = 1389 cm,1, ,5 = 1195 cm,1, and ,9 = 336 cm,1 fundamentals are shown to be in excellent agreement with those for the TCNQ monoanion. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

Adsorption of water in mordenite,An ab initio study

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2001
Th. Demuth
Abstract The adsorption of water in mordenite has been investigated using density functional theory using gradient corrections to the exchange,correlation functional. In the neutral complex water is strongly physisorbed through two different hydrogen bonds, the stronger between the acid site and the water oxygen atom, the weaker between a hydrogen atom of the adsorbed molecule and a framework oxygen atom. Strong polarizations and structural distortions of both the acid site and the molecule have been observed. To elucidate the question if a chemisorbed complex (creation of a hydroxonium ion) is possible, ab initio molecular dynamics have been performed, indicating that a protonation of water occurs even for the low coverage of one water molecule per unit cell. However, this ionic configuration cannot be stabilized by the electrostatic field of the zeolite framework and is therefore not a minimum of the potential energy surface. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 110,116, 2001 [source]

XRD studies, vibrational spectra, and molecular structure of 1H-imidazo [4,5-b]pyridine based on DFT quantum chemical calculations

JOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2010
L. Dymi
Abstract The molecular structures and vibrational properties of 1H -imidazo[4,5-b]pyridine in its monomeric and dimeric forms are analyzed and compared to the experimental results derived from the X-ray diffraction (XRD), infrared (IR), and Raman studies. The theoretical data are discussed on the basis of density functional theory (DFT) quantum chemical calculations using Lee,Yang,Parr correlation functional (B3LYP) and 6-31G(d,p) basis. This compound crystallizes in orthorhombic structure, space group Pna21(C2v9) and Z = 4. The planar conformation of the skeleton and presence of the NH···N hydrogen bond was found to be characteristic for the studied system. The temperature dependence of IR and Raman modes was studied in the range 4,294 K and 8,295 K, respectively. The normal modes, which are unique for the imidazopyridine derivatives are identified. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Comparison of second-order orbital-dependent DFT correlation functionals

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2008
Ireneusz Grabowski
Abstract The choice of the orbital-dependent second-order correlation functional plays the prime role in the description of the correlation effects in orbital-dependent DFT calculations. Using second-order perturbation theory we were able to derive the simplest orbital-dependent correlation functional, but even at this lowest correlation level, we had several possibilities to define it. Applications of different second-order correlation functionals for the atomic as well as molecular systems are presented. The ab initio DFT-type OEP2 functionals based on Møller-Plesset or semicanonical partitioning (OEP2-sc) are compared with those based on Epstein-Nesbet type partitioning, showing that the latter ones can fail in more difficult molecular problems, e.g., the Be dimer potential curve. We show that currently the best performing orbital-dependent second-order correlation functional is the OEP2-sc one. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

The electronic Fermi surface e3 of aluminium under moderate compression

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2003
Helmut BrossArticle first published online: 11 NOV 200
Abstract Both in LDA and in GGA the electronic structure of aluminium is evaluated by use of the MAPW selfconsistent scheme and with different exchange correlation functionals. Near and above the equilibrium lattice constant the electronic sheet of the Fermi surface, e3, is found to be quite similar to the model originally proposed by Ashcroft. However, even moderate compressions induce a drastic variation. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]