Microscopic Modelling of Correlated Low-dimensional Systems

Chapter 1: Introduction 5
small nearest neighbor exchange constant due to its dilute character. The term ‘dilute’
refers to materials formed by transition ions surrounded by non-magnetic transition ions
such as Zn 2+ (3d 10 ) or V 5+ (3d 0 ) and well separated from the next transition magnetic
metal ion. K2V3O8 presents an unusual spin reorientation effect when applying magnetic
field. This effect can be understood when including anisotropies in the Hamiltonian which
describes the system. We show, however, that the proposed Hamiltonian fails to explain
the experimental observations. By studying the electronic and magnetic properties of this
compound, we show that our results present a new view over the controversy arising from
recent experimental results.
Our methodology and results on all the above mentioned compounds provide a new pers-
pective on the parameters underlying the traditional theoretical approaches, making our
study not only essential to understand future experimental results, but interesting in their
own right.
This thesis is organized as follows: the first part of Chapter 2 is dedicated to the density
functional theory and to the basis sets used for solving the DFT Hamiltonian utilized in this
work, namely the FP-LAPW and LMTO/NMTO methods. The second part of Chapter
2 is dedicated to review the effective models employed in our study. Because electronic
properties are given in the reciprocal space, we provide in Chapter 3 the different Brillouin
zones associated to all of the unit cells for the studied compounds. In Chapter 4 we introduce
the concept of metal-organic framework and the current state of art in this field. This is
followed by a description of the compounds studied and the significant questions we address
in this thesis. In Chapter 5 we present our methodological procedure and our findings.
Finally in Chapter 6 we give a brief summary and overlook.