Sökning: "GGA"

Visar resultat 1 - 5 av 16 avhandlingar innehållade ordet GGA.

1. 1. Nonlocal Correlations in Density Functional Theory

   Författare :Henrik Rydberg; Chalmers tekniska högskola; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; bonding; GGA; adhesion; graphene; DFT; exchange; adsorption; LDA; first principles; polarization; vdW; determinants; correlation; graphite; surface states; van der Waals; density-functional theory; physisorption; nonlocal; functional;

   Sammanfattning : In Density Functional Theory, the widely used local and semilocal approximations to the exchange-correlation energy, the local density approximation (LDA) and the generalized gradient approximations (GGAs), lack a physical description of truly nonlocal correlation effects, which are absolutely essential for a proper description of soft matter. A scheme is proposed that provides a basis for systematic improvements beyond LDA and GGA, including correlations at intermediate and long range, giving rise to bonds of pure van der Waals type as well as more intricate, intermediate-range correlation bonds. LÄS MER

3. 2. Interatomic total-energy potentials for atomistic simulations of metallic systems

   Författare :Jan Hartford; Chalmers tekniska högskola; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; materials science; atom-in-jellium; atomistic approaches; DFT; GGA-PW91; density functional; effective medium theory; EMT; inhomogeneous electron gas; model potential; generalized gradient approximation;

   Sammanfattning : .... LÄS MER

4. 3. Quantum Chemical Studies of Radical Cation Rearrangement, Radical Carbonylation, and Homolytic Substitution Reactions

   Författare :Daniel Norberg; Nessima Salhi-Benachenhou; Sten Lunell; Tim Clark; Uppsala universitet; []
   Nyckelord :Quantum chemistry; quantum chemistry; coupled-cluster; density functional theory; meta-GGA; reaction mechanism; potential energy surface; isomerization; fragmentation; dissociation; condensation; addition; SH2; hydrogen abstraction; iodine atom transfer; complex; weakly interacting system; hyperfine coupling constant; Kvantkemi;

   Sammanfattning : Quantum chemical calculations have been performed to investigate radical cation rearrangement, radical carbonylation, and homolytic substitution reactions of organic molecules. The rearrangement of the bicyclopropylidiene radical cation to the tetramethyleneethane radical cation is predicted to proceed with stepwise disrotatory opening of the two rings. LÄS MER

5. 4. Density functional calculations of optical spectra and narrow band systems

   Författare :Anna Delin; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Physics; Fysik; Physics; Fysik; Fysik; Physics;

   Sammanfattning : A calculational method, based on density functionaltheory, has been used to calculate optica spectra for a wide range of systems,as well as ground-state properties of some narrow-band systems. A systematic study of the trends in the optical properties of the 4Brefractory metal compounds has been performed. LÄS MER

7. 5. van der Waals Density Functionals

   Författare :Ylva Andersson; Chalmers tekniska högskola; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; van der Waals molecules; physisorption; van der Waals interactions; density-functional theory; exchange-correlation energy; scanning-force microscopy; adhesion;

   Sammanfattning : Methods using local or semi local approximations (LDA, GGA etc.) for the exchange-correlation energy in the density-functional theory (DFT) do not include van der Waals interactions. LÄS MER