## Multi-aspect modelling and quantum effects in molecular nanomagnets

### Abstract

Note:

Published while none of the authors are employed at UGent

ACTA PHYSICAE SUPERFICIERUM

11

2009

A2

Abstract

Note:

Published while none of the authors are employed at UGent

Open Access version available at UGent repository

ACTA PHYSICAE SUPERFICIERUM

11

2009

A2

Abstract

Note:

Published while none of the authors are employed at UGent

Open Access version available at UGent repository

Acta Physica Polonica A

121, 5-6, 992-998

2011

A1

Published while none of the authors were employed at the CMM

Abstract

In this paper we review our results of comprehensive study of molecular nanomagnets recently synthesized in the form of the chromium-based molecules and bimetallic copper-containing chains as well as we present some new findings. We focus on effects of anisotropy, geometry and frustration appearing in various thermodynamic properties of the nanoscale magnets which are described by Heisenberg-like spin models and simulated by accurate numerical methods. We show that bond-dependent exchange anisotropy is needed to model magnetic torque in the Cd-doped chromium ring. We argue that only in the limit of infinite rings (n -> infinity) frustration can be considered as the opposite to bipartiteness in the odd numbered (3

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY

11, 10

2011

A1

Published while none of the authors were employed at the CMM

Abstract

A comprehensive study of electronic and magnetic properties of Cr(8)F(8)Piv(16) (HPiv = pivalic acid, trimethyl acetic acid) molecular ring is presented. The total, local and orbital projected density of states are calculated by the first principle density functional theory calculations using the package SIESTA. The original molecule has been approximated by replacing the pivallic groups by H atoms (hydrogen saturation). Electron density, deformation density, electrostatic potential and spin density maps are analyzed and compared with experiment for the first time. Magnetic properties are investigated in detail. Magnetic moments are calculated using two different approaches: the Mulliken one and integration of muffin-tin sphere with a given radius. Different magnetic configurations (ferromagnetic, antiferromagnetic and many more with randomly distributed spins up and down) are considered to extract exchange interaction parameter J and check the stability of its estimate.

Journal of Physics: Condensed Matter

21, 15, 155301

2009

A1

Published while none of the authors were employed at the CMM

Abstract

We consider classical two-dimensional (2D) Coulomb clusters consisting of two species containing five particles with charge q(1) and five with charge q(2), respectively. Using Monte Carlo and molecular dynamics (MD) simulations, we investigated the ground state configurations as well as radial and angular displacements of particles as a function of temperature and their dependence on the ratio q = q(2)/q(1). We found new configurations and a new multi-step melting behavior for q sufficiently different from the uniform charge limit q = 1.

Lecture Notes in Computer Science

6127

2008

A2

Published while none of the authors were employed at the CMM

Abstract

We present the electronic and magnetic properties of the antiferromagnetic Cr8 molecular ring (i.e. [Cr8F8Piv16], where HPiv - pivalic acid, trimethyl acetic acid) found by means of density functional theory (DFT) simulation techniques. The all-electron linearized augmented plane wave method (LAPW) implemented in the Wien2k package is exploited. It is also used to calculate the electronic structure, to estimate the exchange coupling parameter and to analyse magnetic anisotropy of an infinite chain model systems corresponding to the Cr8 ring. We demonstrate that the chain models mimic with good approximation the electronic and magnetic properties of the original Cr8 molecule. They reduce substantially computational complexity and speed up extensive investigations of molecules belonging to the Cr-based molecular rings family.

Acta Physica Polonica A

118, 5

2010

A1

Published while none of the authors were employed at the CMM

Abstract

We investigate for the first time the electronic and magnetic properties of the linear models of Cr(8)F(8)(Piv)(16) molecular ring using the SIESTA package In the first step the proper values of the SIESTA parameters and the optimal basis set needed for the convergence of the total energy are established Next the estimates of the magnetic coupling J confirming the previous density functional theory calculations are presented.

Journal of Physics: Condensed Matter

21, 15, 155301

2009

A1

Published while none of the authors were employed at the CMM

Abstract

We consider classical two-dimensional (2D) Coulomb clusters consisting of two species containing five particles with charge q(1) and five with charge q(2), respectively. Using Monte Carlo and molecular dynamics (MD) simulations, we investigated the ground state configurations as well as radial and angular displacements of particles as a function of temperature and their dependence on the ratio q = q(2)/q(1). We found new configurations and a new multi-step melting behavior for q sufficiently different from the uniform charge limit q = 1.

Physical Review B

77, 224401

2008

A1

Published while none of the authors were employed at the CMM

Abstract

We present a density-functional theory investigation of the electronic and magnetic properties of a linear chain model of the antiferromagnetic Cr8 molecular ring. The chain model system is characterized by a smaller size of the simulation cell needed to perform the calculations, with respect to the one necessary for Cr8. By the thorough comparison between the model complex and the Cr8 ring, we prove that the chain model is reliable and mimics with good approximation the electronic and magnetic properties of Cr8.

Physica Status Solidi (b) - Basic Solid State Physics

243, 1, 322-325

2006

A1

Published while none of the authors were employed at the CMM

Abstract

Using a transfer matrix technique and the Ising model, the predictions of the MFRG concept for clusters with linear size up to 21 have been tested for the three-cluster MFRG approach. Even for small sizes of the clusters, the three-cluster estimates of critical couplings and bulk critical exponents give the accuracy level equal to that of two-cluster renormalization for much greater sizes. Performing the asymptotic analysis for the new data, the convergence of the surface critical exponent yhs towards the exact value is illustrated for the first time. Our improved method has enabled us to obtain the results for clusters with substantially greater sizes, to accelerate the calculations and also to confirm the reliability of the MFRG approach for the Ising model. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)