Effects of boundary conditions on magnetization switching in kinetic Ising models of nanoscale ferromagnets

Magnetization switching in highly anisotropic single-domain ferromagnets has been previously shown to be qualitatively described by the droplet theory of metastable decay and simulations of two-dimensional kinetic Ising systems with periodic boundary conditions. In this article we consider the effects of boundary conditions on the switching phenomena. A rich range of behaviors is predicted by droplet theory: the specific mechanism by which switching occurs depends on the structure of the boundary, the particle size, the temperature, and the strength of the applied field. The theory predicts the existence of a peak in the switching field as a function of system size in both systems with periodic boundary conditions and in systems with boundaries. The size of the peak is strongly dependent on the boundary effects. It is generally reduced by open boundary conditions, and in some cases it disappears if the boundaries are too favorable towards nucleation. However, we also demonstrate conditions under which the peak remains discernible. This peak arises as a purely dynamic effect and is not related to the possible existence of multiple domains. We illustrate the predictions of droplet theory by Monte Carlo simulations of two-dimensional Ising systems with various system shapes and boundary conditions.Comment: RevTex, 48 pages, 13 figure

First-principles study of TMNan (TM= Cr, Mn, Fe, Co, Ni; n = 4-7) clusters

Geometry, electronic structure, and magnetic properties of TMNan (TM=Cr-Ni; n = 4-7) clusters are studied within a gradient corrected density functional theory (DFT) framework. Two complementary approaches, the first adapted to all-electron calculations on free clusters, and the second been on plane wave projector augmented wave (PAW) method within a supercell approach are used. Except for NiNan, the clusters in this series are found to retain the atomic moments of the TM atoms, and the magnetic moment presented an odd-even oscillation with respect to the number of Na atoms. The origin of these odd-even oscillations is explained from the nature of chemical bonding in these clusters. Differences and similarities between the chemical bonding and the magnetic properties of these clusters and the TMNan (TM = Sc, V and Ti; n = 4-6) clusters on one hand, and TM-doped Au and Ag clusters on the other hand, are discussed

Incidence des corrections relativistes sur les proprietes electroniques des composes 5d. Calcul MSXi dans les hexachloroiridates (III et IV) et le trioxyde de tungstene

SIGLECNRS-CDST / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

QM/MM calculations with deMon2k

The density functional code deMon2k employs a fitted density throughout (Auxiliary Density Functional Theory), which offers a great speed advantage without sacrificing necessary accuracy. Powerful Quantum Mechanical/Molecular Mechanical (QM/MM) approaches are reviewed. Following an overview of the basic features of deMon2k that make it efficient while retaining accuracy, three QM/MM implementations are compared and contrasted. In the first, deMon2k is interfaced with the CHARMM MM code (CHARMM-deMon2k); in the second MM is coded directly within the deMon2k software; and in the third the Chemistry in Ruby (Cuby) wrapper is used to drive the calculations. Cuby is also used in the context of constrained-DFT/MM calculations. Each of these implementations is described briefly; pros and cons are discussed and a few recent applications are described briefly. Applications include solvated ions and biomolecules, polyglutamine peptides important in polyQ neurodegenerative diseases, copper monooxygenases and ultra-rapid electron transfer in cryptochromes

Deficiency in the incorporation of labeled thymidine and inhibition in the biosynthesis of interleukin-2 in lymphocytes obtained from Histoplasma capsulatum infected mice

This article provides a brief overview of the quantum chemical auxiliary density functional theory program deMon2k. A basic introduction into its key computational features is given. By selected examples, it is shown how deMon2k can contribute to the elucidation of problems in chemistry, biology, and materials science such as finite temperature effects, nuclear magnetic resonance studies, structure determinations, heterogeneous, and enzymatic catalysis. " 2011 John Wiley & Sons, Ltd.",,,,,,"10.1002/wcms.98",,,"http://hdl.handle.net/20.500.12104/40522","http://www.scopus.com/inward/record.url?eid=2-s2.0-84862514881&partnerID=40&md5=644cf71e54eb0b5eafdac82520d7fadb",,,,,,"4",,"Wiley Interdisciplinary Reviews: Computational Molecular Science",,"54

deMon2k

This article provides a brief overview of the quantum chemical auxiliary density functional theory program deMon2k. A basic introduction into its key computational features is given. By selected examples, it is shown how deMon2k can contribute to the elucidation of problems in chemistry, biology, and materials science such as finite temperature effects, nuclear magnetic resonance studies, structure determinations, heterogeneous, and enzymatic catalysis. © 2011 John Wiley & Sons, Ltd