Application of the package SIESTA to linear models of a molecular chromium-based ring

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

Molecular dynamics and ab-initio modelling of ring-like classical Coulomb clusters and cr-based molecular magnet

Wydział Fizyki: Zakład Fizyki Komputerowej; European Institute of Molecular MagnetismThe following thesis is devoted to determination of structural, dynamical and new melting properties of twodimensional classical Coulomb clusters and electronic and magnetic properties of chromium-based molecular magnets. The two-dimensional Coulomb clusters are studied with the use of molecular dynamics and Monte Carlo methods, and Cr-based systems with the use of abinitio method. In the first part of the following thesis we investigated the geometrical structures and the motion of uniformly and non-uniformly charged particles at low temperatures before the radial and angular melting sets in. In the following thesis the reader will find much richer than the hitherto two-step approach to the melting process of 2D classical clusters. The relation between magic number configurations, local radial melting of subshells and the intershell rotation is analyzed. Additionally the ground state and metastable configurations for different charges as well as the new melting scenarios are determined. In the second part of this thesis, for the first time we proposed 1D chain models of Cr8 antiferromagnetic molecular ring.The chain models discussed here are devised to mimic the properties of Cr8 molecule and significantly simplify computational complexity. Detailed investigations of electronic and magnetic properties of created models of Cr8 molecule are presented

Molecular dynamics and ab-initio modelling of ring-like classical Coulomb clusters and cr-based molecular magnet

Wydział Fizyki: Zakład Fizyki Komputerowej; European Institute of Molecular MagnetismThe following thesis is devoted to determination of structural, dynamical and new melting properties of twodimensional classical Coulomb clusters and electronic and magnetic properties of chromium-based molecular magnets. The two-dimensional Coulomb clusters are studied with the use of molecular dynamics and Monte Carlo methods, and Cr-based systems with the use of abinitio method. In the first part of the following thesis we investigated the geometrical structures and the motion of uniformly and non-uniformly charged particles at low temperatures before the radial and angular melting sets in. In the following thesis the reader will find much richer than the hitherto two-step approach to the melting process of 2D classical clusters. The relation between magic number configurations, local radial melting of subshells and the intershell rotation is analyzed. Additionally the ground state and metastable configurations for different charges as well as the new melting scenarios are determined. In the second part of this thesis, for the first time we proposed 1D chain models of Cr8 antiferromagnetic molecular ring.The chain models discussed here are devised to mimic the properties of Cr8 molecule and significantly simplify computational complexity. Detailed investigations of electronic and magnetic properties of created models of Cr8 molecule are presented

Transfer-matrix study of critical properties of the Ising model following from the three-cluster MFRG approach

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Two-step mean-field renormalization group results for the large square Ising clusters

A transfer matrix approach has been worked out to test the predictions of the improved three-step mean-field renormalization group approach to square Ising clusters with linear size up to L = 11. Performing the asymptotic analysis, the convergence of the finite-size critical couplings and the critical exponents towards the exact values is shown

Multistep radial melting in small two-dimensional classical clusters

We report on a molecular dynamics study of small classical two-dimensional clusters with ringlike configurations. We focus on the particles motion at low temperatures before the radial and angular melting sets in. It is shown that in magic number configurations a local radial melting of subshells occur, which is related to the intershell rotation

Ground state configurations and melting of two-dimensional non-uniformly charged classical clusters

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

Electronic structure and magnetic properties of a molecular octanuclear chromium-based ring

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

DFT study of octanuclear molecular chromium-based ring using new pseudopotential parameters

Molecular magnets play very important role in fundamental physics since these systems have shown new magnetic and electronic futures and revealed to be promising for possible applications in quantum computing and magnetoelectronics. Among these systems, there are homonuclear antiferromagnetic ring-shaped molecules formed by transition metal ions in an almost planar ring. We present a comprehensive study of electronic and magnetic properties of Cr8F8Piv16 molecular ring (in short Cr8) using the package SIESTA with several choices of chromium pseudopotential parameters. We use generalized gradient approximation (GGA) to investigate properties of Cr8 ring approximated by replacing the pivallic group by H atoms (hydrogen saturation). For different choice of chromium pseudopotential we examine the electronic and magnetic properties of Cr8 molecule. We compare the density of states, electron density maps and HOMO-LUMO energies. Also magnetic properties are studied in detail - magnetic moments and exchange interaction parameter J are presented. The infuence of pseudopotential parameters on obtained results is discussed. Finally our results are compared with other theoretical approaches and experimental data