G. Van Oost

Dislocation mechanism of deuterium retention in tungsten under plasma implantation

V. Dubinko, D. Terentyev, P. Grigorev, A. Bakaev, G. Van Oost, F. Gao, D. Van Neck, E. Zhurkin
Journal of Physics: Condensed Matter
26, 395001


We have developed a new theoretical model for deuterium (D) retention in tungsten-based alloys on the basis of its being trapped at dislocations and transported to the surface via the dislocation network with parameters determined by ab initio calculations. The model is used to explain experimentally observed trends of D retention under sub-threshold implantation, which does not produce stable lattice defects to act as traps for D in conventional models. Saturation of D retention with implantation dose and effects due to alloying of tungsten with, e.g. tantalum, are evaluated, and comparison of the model predictions with experimental observations under high-flux plasma implantation conditions is presented.

Error estimates for solid-state density-functional theory predictions: an overview by means of the ground-state elemental crystals

K. Lejaeghere, V. Van Speybroeck, G. Van Oost, S. Cottenier
Critical Reviews in Solid State and Materials Sciences
39 (1), 1-24


Predictions of observable properties by density-functional theory calculations (DFT) are used increasingly often by experimental condensed-matter physicists and materials engineers as data. These predictions are used to analyze recent measurements, or to plan future experiments in a rational way. Increasingly more experimental scientists in these fields therefore face the natural question: what is the expected error for such a first-principles prediction? Information and experience about this question is implicitly available in the computational community, scattered over two decades of literature. The present review aims to summarize and quantify this implicit knowledge. This eventually leads to a practical protocol that allows any scientist -- experimental or theoretical -- to determine justifiable error estimates for many basic property predictions, without having to perform additional DFT calculations.

A central role is played by a large and diverse test set of crystalline solids, containing all ground-state elemental crystals (except most lanthanides). For several properties of each crystal, the difference between DFT results and experimental values is assessed. We discuss trends in these deviations and review explanations suggested in the literature.

A prerequisite for such an error analysis is that different implementations of the same first-principles formalism provide the same predictions. Therefore, the reproducibility of predictions across several mainstream methods and codes is discussed too. A quality factor Delta expresses the spread in predictions from two distinct DFT implementations by a single number. To compare the PAW method to the highly accurate APW+lo approach, a code assessment of VASP and GPAW (PAW) with respect to WIEN2k (APW+lo) yields Delta-values of 1.8 and 3.3 meV/atom, respectively. In both cases the PAW potentials recommended by the respective codes have been used. These differences are an order of magnitude smaller than the typical difference with experiment, and therefore predictions by APW+lo and PAW are for practical purposes identical.

The ground state elemental crystals as a benchmark for solid state DFT: intrinsic accuracy and code comparison

p. 59

Conference / event / venue 

(presenting author S. Cottenier) Ab initio Description of Iron and Steel: Thermodynamics and Kinetics (ADIS 2012)
Ringberg Castle (Tegernsee, Germany)
Sunday, 29 April, 2012 to Friday, 4 May, 2012


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