-
[show abstract]
[hide abstract]
ABSTRACT: We present an implementation of localized atomic-orbital basis sets in the projector augmented wave (PAW) formalism within the density-functional theory. The implementation in the real-space GPAW code provides a complementary basis set to the accurate but computationally more demanding grid representation. The possibility to switch seamlessly between the two representations implies that simulations employing the local basis can be fine tuned at the end of the calculation by switching to the grid, thereby combining the strength of the two representations for optimal performance. The implementation is tested by calculating atomization energies and equilibrium bulk properties of a variety of molecules and solids, comparing to the grid results. Finally, it is demonstrated how a grid-quality structure optimization can be performed with significantly reduced computational effort by switching between the grid and basis representations.
Phys. Rev. B. 03/2013; 80(19).
-
J. Kleis,
J. Greeley,
N. A. Romero,
V. A. Morozov,
H. Falsig,
A. H. Larsen,
J. Lu, J. J. Mortensen,
M. Dułak,
K. S. Thygesen,
J. K. Nørskov,
K. W. Jacobsen
[show abstract]
[hide abstract]
ABSTRACT: AbstractWe address the fundamental question of which size a metallic nano-particle needs to have before its surface chemical properties
can be considered to be those of a solid, rather than those of a large molecule. Calculations of adsorption energies for carbon
monoxide and oxygen on a series of gold nanoparticles ranging from 13 to 1,415 atoms, or 0.8–3.7nm, have been made possible
by exploiting massively parallel computing on up to 32,768 cores on the Blue Gene/P computer at Argonne National Laboratory.
We show that bulk surface properties are obtained for clusters larger than ca. 560 atoms (2.7nm). Below that critical size,
finite-size effects can be observed, and we show those to be related to variations in the local atomic structure augmented
by quantum size effects for the smallest clusters.
Graphical Abstract
KeywordsNano-particle–Size effects–DFT
Catalysis Letters 04/2012; 141(8):1067-1071. · 2.24 Impact Factor
-
J Enkovaara,
C Rostgaard, J J Mortensen,
J Chen,
M Dułak,
L Ferrighi,
J Gavnholt,
C Glinsvad,
V Haikola,
H A Hansen, [......],
B Hammer,
H Häkkinen,
G K H Madsen,
R M Nieminen,
J K Nørskov,
M Puska,
T T Rantala,
J Schiøtz,
K S Thygesen,
K W Jacobsen
[show abstract]
[hide abstract]
ABSTRACT: Electronic structure calculations have become an indispensable tool in many areas of materials science and quantum chemistry. Even though the Kohn-Sham formulation of the density-functional theory (DFT) simplifies the many-body problem significantly, one is still confronted with several numerical challenges. In this article we present the projector augmented-wave (PAW) method as implemented in the GPAW program package (https://wiki.fysik.dtu.dk/gpaw) using a uniform real-space grid representation of the electronic wavefunctions. Compared to more traditional plane wave or localized basis set approaches, real-space grids offer several advantages, most notably good computational scalability and systematic convergence properties. However, as a unique feature GPAW also facilitates a localized atomic-orbital basis set in addition to the grid. The efficient atomic basis set is complementary to the more accurate grid, and the possibility to seamlessly switch between the two representations provides great flexibility. While DFT allows one to study ground state properties, time-dependent density-functional theory (TDDFT) provides access to the excited states. We have implemented the two common formulations of TDDFT, namely the linear-response and the time propagation schemes. Electron transport calculations under finite-bias conditions can be performed with GPAW using non-equilibrium Green functions and the localized basis set. In addition to the basic features of the real-space PAW method, we also describe the implementation of selected exchange-correlation functionals, parallelization schemes, ΔSCF-method, x-ray absorption spectra, and maximally localized Wannier orbitals.
Journal of Physics Condensed Matter 06/2010; 22(25):253202. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We use density functional theory (DFT) with a recently developed van der Waals density functional (vdW-DF) to study the adsorption of graphene on Al, Cu, Ag, Au, Pt, Pd, Co and Ni(111) surfaces. In constrast to the local density approximation (LDA) which predicts relatively strong binding for Ni,Co and Pd, the vdW-DF predicts weak binding for all metals and metal-graphene distances in the range 3.40-3.72 \AA. At these distances the graphene bandstructure as calculated with DFT and the many-body G$_0$W$_0$ method is basically unaffected by the substrate, in particular there is no opening of a band gap at the $K$-point. Comment: 4 pages, 3 figures
12/2009;
-
J S Hummelshøj,
D D Landis,
J Voss,
T Jiang,
A Tekin,
N Bork,
M Dułak, J J Mortensen,
L Adamska,
J Andersin, [......],
V Viswanathan,
A Vojvodic,
S Wang,
J Wellendorff,
K S Thygesen,
J Rossmeisl,
T Bligaard,
K W Jacobsen,
J K Nørskov,
T Vegge
[show abstract]
[hide abstract]
ABSTRACT: We present a computational screening study of ternary metal borohydrides for reversible hydrogen storage based on density functional theory. We investigate the stability and decomposition of alloys containing 1 alkali metal atom, Li, Na, or K (M(1)); and 1 alkali, alkaline earth or 3d/4d transition metal atom (M(2)) plus two to five (BH(4))(-) groups, i.e., M(1)M(2)(BH(4))(2-5), using a number of model structures with trigonal, tetrahedral, octahedral, and free coordination of the metal borohydride complexes. Of the over 700 investigated structures, about 20 were predicted to form potentially stable alloys with promising decomposition energies. The M(1)(Al/Mn/Fe)(BH(4))(4), (Li/Na)Zn(BH(4))(3), and (Na/K)(Ni/Co)(BH(4))(3) alloys are found to be the most promising, followed by selected M(1)(Nb/Rh)(BH(4))(4) alloys.
The Journal of chemical physics 08/2009; 131(1):014101. · 3.09 Impact Factor
-
Physical Review B (Condensed Matter and Materials Physics). 01/2009; 80(19):195112.
-
[show abstract]
[hide abstract]
ABSTRACT: We present a practical scheme for performing error estimates for density-functional theory calculations. The approach, which is based on ideas from Bayesian statistics, involves creating an ensemble of exchange-correlation functionals by comparing with an experimental database of binding energies for molecules and solids. Fluctuations within the ensemble can then be used to estimate errors relative to experiment on calculated quantities such as binding energies, bond lengths, and vibrational frequencies. It is demonstrated that the error bars on energy differences may vary by orders of magnitude for different systems in good agreement with existing experience.
Physical Review Letters 12/2005; 95(21):216401. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A grid-based real-space implementation of the Projector Augmented Wave (PAW) method of P. E. Blochl [Phys. Rev. B 50, 17953 (1994)] for Density Functional Theory (DFT) calculations is presented. The use of uniform 3D real-space grids for representing wave functions, densities and potentials allows for flexible boundary conditions, efficient multigrid algorithms for solving Poisson and Kohn-Sham equations, and efficient parallelization using simple real-space domain-decomposition. We use the PAW method to perform all-electron calculations in the frozen core approximation, with smooth valence wave functions that can be represented on relatively coarse grids. We demonstrate the accuracy of the method by calculating the atomization energies of twenty small molecules, and the bulk modulus and lattice constants of bulk aluminum. We show that the approach in terms of computational efficiency is comparable to standard plane-wave methods, but the memory requirements are higher. Comment: 13 pages, 3 figures, accepted for publication in Physical Review B
11/2004;
-
[show abstract]
[hide abstract]
ABSTRACT: The quasicontinuum method is a way of reducing the number of degrees of freedom in an atomistic simulation by removing the majority of the atoms in regions of slowly varying strain fields. Due to the different ways the energy of the atoms is calculated in the coarse-grained regions and the regions where all the atoms are present, unphysical forces called “ghost forces” arise at the interfaces. Corrections may be used to almost remove the ghost forces, but the correction forces are nonconservative, ruining energy conservation in dynamic simulations. We show that it is possible to formulate the quasicontinuum method without these problems by introducing a buffer layer between the two regions of space. The method is applicable to short-ranged potentials in the face-centered cubic, body-centered cubic, and hexagonal close-packed crystal structures.
Phys. Rev. B. 69(21).
