Self-consistent-field calculations of atoms and ions using a modified local-density approximation

1994 ◽  
Vol 50 (1) ◽  
pp. 171-176 ◽  
Author(s):  
David A. Liberman ◽  
James R. Albritton ◽  
Brian G. Wilson ◽  
William E. Alley
Keyword(s):  
Local Density Approximation ◽  
Local Density ◽  
Density Approximation ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field

scholarly journals Self-Consistent Field Modeling of Pulling a Test-Chain away from or Pushing It into a Polymer Adsorption Layer

Polymers ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1684 ◽  
Author(s):  
Fransicus A.M. Leermakers
Keyword(s):  
Adsorption Layer ◽  
Local Density ◽  
Polymer Concentration ◽  
Critical Force ◽  
Average Chain Length ◽  
Single Chain ◽  
Field Modeling ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field

We consider single chain force measurements to unravel characteristics of polymers at interfaces and to determine parameters that control adsorption or probe layer characteristics that are difficult to access otherwise. The idea is to have at the tip of an atomic force microscope (AFM), a probe chain and measure its behaviour near interfaces by pushing it to, or pulling it away from it. The self-consistent field modeling of this reveals that in the pulling mode—i.e., when the chain has an affinity for the surface—a typically inhomogeneous flower-like conformation forms with an adsorbed ’pancake’ and a stretched stem (tether) from the surface to the tip of the AFM. When about half the segments is in the tether it snaps loose in a first-order like fashion. The critical distance of the end-point from the surface and the critical force are experimentally accessible. Details of this transition depend on the surrounding of the test chain. Inversely, and this opens up many possibilities, the test chain reports about its surroundings. Our focus is on the classical case of homopolymers at interfaces. Pulling experiments may reveal the adsorption strength, the (average) chain length and/or the polymer concentration of the freely dispersed/adsorbed polymers. When the test-chain is non-adsorbing we envision that pushing this test-chain into the adsorption layer reports about various layer characteristics such as the layer thickness and (local) density. Moreover, when the test-chain has a length longer than the entanglement length, we can imagine that non-trivial dynamical properties of loops and tails may be scrutinised.

CHEMISORPTION OF O2 AND CO ON COPPER CLUSTERS

1996 ◽  
Vol 03 (01) ◽  
pp. 687-693 ◽  
Author(s):  
HENRIK GRÖNBECK ◽  
ARNE ROSÉN
Keyword(s):  
Charge Transfer ◽  
Local Density Approximation ◽  
Size Dependence ◽  
Local Density ◽  
Wave Functions ◽  
Density Approximation ◽  
Copper Clusters ◽  
Self Consistent ◽  
Stable Product ◽  
Transfer Mechanisms

The initial chemisorption of O 2 and CO on small copper clusters in the range from six to nine atoms has been investigated using a self-consistent jellium description of the clusters. The calculations were performed within the local-density approximation expanding the wave functions in a linear combination of atomic and spherical jellium orbitals. The results indicate a strong size dependence in the chemisorption energies. O 2 was found to be most strongly bound to the Cu 9 cluster while COCu 6 was the most stable product in the case of CO chemisorption. The observations are consistent with experiments and the underlying reasons were traced to differences in cluster-adsorbate hybridization and charge-transfer mechanisms.

Effects of ternary additions on the twin energy and site preference in γ-TiAl

1994 ◽  
Vol 9 (7) ◽  
pp. 1755-1760 ◽  
Author(s):  
Jian-hua Xu ◽  
A.J. Freeman
Keyword(s):  
Total Energy ◽  
Local Density Approximation ◽  
Relative Stability ◽  
Local Density ◽  
Site Preference ◽  
Density Approximation ◽  
Self Consistent ◽  
Ternary Additions

Site preference and the effects of ternary additions (Mn, V, etc.) on the twin energy in γ-TiAl were studied by means of all-electron total energy self-consistent calculations based on the local density approximation. The results show that when Mn, Ti, or V substitute on the Al-sites in γ-TiAl, the twin energy is about 20–25% lower than that of stoichiometric γ-TiAl; this may explain observations of increased twinning activity in 48% Al TiAl. By contrast, when ternary additions of V (or Al) occupy Ti-sites, the twin energy has nearly the same value as that of pure γ-TiAl, which is consistent with the observation of only a few twins for Al-rich compositions. By comparing the total energy of Ti6(XAl5) and (Ti5X)Al6 supercells, it is found that the relative stability of Ti6(XAl5) over (Ti5X)Al6 (i.e., the preference for occupying Al-sites) is increased in going from Nb, V, Cr, and Ti to Mn, in agreement with observation that excess Ti occupies Al-sites, and Nb preferentially substitutes on the Ti-sites. The results indicate that Mn preferentially substitutes on the Al-sites, and V (or Cr) may occupy both Ti- and Al-sites.

Pseudoatomic Orbital Compact Basis Sets: Applications to Metallic Systems

1988 ◽  
Vol 141 ◽  
Author(s):  
Robert W. Jansen ◽  
B. H. Klein
Keyword(s):  
Free Electron ◽  
Local Density Approximation ◽  
Local Density ◽  
Low Energy ◽  
Basis Sets ◽  
Density Approximation ◽  
Self Consistent ◽  
Total Energies ◽  
Energy Convergence ◽  
Metallic Systems

AbstractA self-consistent orbital-based scheme is applied to metallic systems and is found to be efficient for these materials. The technique uses the local density approximation in the pseudopotential framework, but replaces the planewave basis by a basis pseudoatomic orbitals constructed directly from the pseudoatoms. Free electron-like wavefunction components are handled by orthogonalizing the orbital basis to a few low energy planewaves as needed for good eigenvalue and total energy convergence. The method is fast and versatile enough to be used for a variety of problems. Applications to bulk bandstructures, total energies, and forces in Al and Nb are presented.

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