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DFT Functionals (dft + functional)
Selected AbstractsOn 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] Theoretical study of hydrogen-bonded complexes of benzene with hydrides of astrochemical interestINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2008M. Nait Achour Abstract Post Hartree,Fock and DFT calculations have been performed for studying the possibility for a benzene support to be linked to various hydrides through a quasi Bz···HA bond. Interaction energy of compounds, including CH bonds (CH4, CH3F, CH2O, CHN, CHNO), NH bonds (NH3, NH2F, NHC, NHCO, NH3O), and OH bonds (OH2, OHF, NCOH), were evaluated, taking basis set superposition error (BSSE) and zero point vibrational energy (ZPVE) corrections into account. Numerical convergence of results with respect to the ingredients included at different steps of theory (basis set, DFT functionals, correlation treatments, geometry optimization) was tested mainly on the example of the water adduct and, for comparison, the Bz···H3O+ system containing a cation instead of a neutral molecule. A rather large range of adsorption energies is obtained, from about 1 kcal/mol for methane to more than 6 kcal/mol for cyanic acid, according to the acidic character of the adsorbed species in each family of Bz···HA bonds. Some consequences for astrophysical problems involving PAHs in the interstellar medium are pointed out. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Theoretical study of the microhydration of mononuclear and dinuclear uranium(VI) species derived from solvolysis of uranyl nitrate in waterJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2010Milan On Abstract The structures and energetics of mononuclear and dinuclear uranium species formed upon speciation of uranyl(VI) nitrate, UO2(NO3)2, in water are investigated by quantum chemistry using density functional theory and the wavefunction-based methods (MP2, CCSD, CCSD(T)). We provide a discussion of the basic coordination patterns of the various mono- and dinuclear uranyl compounds [(UO2)m(X,Y)2m,1(H2O)n]+ (m = 1, 2; n = 0,4) found in a recent mass spectrometric study (Tsierkezos et al., Inorg Chem 2009, 48, 6287). The energetics of the complexation of the uranyl dication to the counterions OH, and NO3, as well as the degradation of the dinuclear species were studied by reference to a test set of 16 representative molecules with the MP2 method and the B3LYP, M06, M06-HF, and M06-2X DFT functionals. All DFT functionals provide structures and energetics close to MP2 results, with M06 family being slightly superior to the standard B3LYP functional. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 [source] Ab-initio simulations of materials using VASP: Density-functional theory and beyondJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2008Jürgen Hafner Abstract During the past decade, computer simulations based on a quantum-mechanical description of the interactions between electrons and between electrons and atomic nuclei have developed an increasingly important impact on solid-state physics and chemistry and on materials science,promoting not only a deeper understanding, but also the possibility to contribute significantly to materials design for future technologies. This development is based on two important columns: (i) The improved description of electronic many-body effects within density-functional theory (DFT) and the upcoming post-DFT methods. (ii) The implementation of the new functionals and many-body techniques within highly efficient, stable, and versatile computer codes, which allow to exploit the potential of modern computer architectures. In this review, I discuss the implementation of various DFT functionals [local-density approximation (LDA), generalized gradient approximation (GGA), meta-GGA, hybrid functional mixing DFT, and exact (Hartree-Fock) exchange] and post-DFT approaches [DFT + U for strong electronic correlations in narrow bands, many-body perturbation theory (GW) for quasiparticle spectra, dynamical correlation effects via the adiabatic-connection fluctuation-dissipation theorem (AC-FDT)] in the Vienna ab initio simulation package VASP. VASP is a plane-wave all-electron code using the projector-augmented wave method to describe the electron-core interaction. The code uses fast iterative techniques for the diagonalization of the DFT Hamiltonian and allows to perform total-energy calculations and structural optimizations for systems with thousands of atoms and ab initio molecular dynamics simulations for ensembles with a few hundred atoms extending over several tens of ps. Applications in many different areas (structure and phase stability, mechanical and dynamical properties, liquids, glasses and quasicrystals, magnetism and magnetic nanostructures, semiconductors and insulators, surfaces, interfaces and thin films, chemical reactions, and catalysis) are reviewed. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Theoretical Calculations on the Tetramethyldisilene Rearrangement: A New Approach to an Old Mechanistic ProblemCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2009Mrinmoy Nag Dr. Abstract Roark and Peddle first observed that, when not trapped, Me2SiSiMe2 underwent a series of rearrangements to give two major isomeric products: 1,1-dimethyl-1,3-disilacyclobutane and 1,3-dimethyl-1,3-disilacyclobutane. The widely accepted mechanism for this rearrangement was proposed by Barton and co-workers. However, little is known about the thermodynamic or kinetic properties of this reaction, because the relevant data are limited to the product ratios of the two isomers. Our calculations predict that the product ratio is driven by kinetic control rather than thermodynamic control. We also show that new DFT functionals, such as MPW1K and M052X, produce thermochemical results comparable with CCSD(T) calculations. [source] | ||||||||||