Theoretical analysis of tip-MgO(100) surface interactions

We present a quantum self-consistent calculation of tip/insulating surface interactions, performed under the assumption of a rigid geometry, intended to be a first step in the study of images recorded in Scanning Force Microscopy. The MgO(100) surface is modelled by an embedded cluster and the tip by an MgO cube presenting various orientations: 1) an Mg or O corner on-top the surface, or 2) a face parallel to the surface. Two cases are considered: a perfectly planar surface and a rough surface with four additional adsorbed atoms. No supercell geometry is assumed which avoids spurious lateral interactions. As a function of the tip geometry and of the force value chosen to image the surface, we discuss some factors which drive the corrugation and the resolution in an Atomic Force Microscope measurement.Nous présentons un calcul auto-cohérent des interactions entre une pointe et une surface, supposées rigides, qui représente une première approche des images obtenues en Microscopie à Force Atomique. La surface MgO(100) est modélisée par un agrégat immergé et la pointe par un agrégat cubique présentant diverses orientations : 1) un coin Mg ou O au-dessus de la surface, et 2) une face parallèle à cette dernière. Deux cas sont envisagés : une surface parfaitement plane et une surface rugueuse, comportant quatre atomes additionnels adsorbés. Aucune répétition périodique du système n'est supposée, ce qui évite d'introduire des interactions latérales artificielles. En fonction de la géométrie de la pointe et de la valeur de la force choisie pour imager la surface, nous discutons quelques facteurs qui influent sur la corrugation et sur la résolution d'une mesure de Microscopie à Force Atomique

Acceleration of MCNP calculations for small pipes configurations by using Weigth Windows Importance cards created by the SN-3D ATTILA

In the nuclear engineering, you have to manage time and precision. Especially in shielding design, you have to be more accurate and efficient to reduce cost (shielding thickness optimization), and for this, you use 3D codes. In this paper, we want to see if we can easily applicate the CADIS methods for design shielding of small pipes which go through large concrete walls. We assess the impact of the WW generated by the 3D-deterministic code ATTILA versus WW directly generated by MCNP (iterative and manual process). The comparison is based on the quality of the convergence (estimated relative error (σ), Variance of Variance (VOV) and Figure of Merit (FOM)), on time (computer time + modelling) and on the implement for the engineer