Theoretical Studies on the Magnetic Properties of Hypothetical Ni-M-Ni Type (M = Sc, · · · , Zn) Trimetallic Extended Metal Atom Chains
Date Issued
2012
Date
2012
Author(s)
Huang, Bang-Ruei
Abstract
Since J.H. van Vleck introduced quantum mechanics on the study of magnetism of molecules in 1932, the related studies on molecular magnetism have prospered thanks to many dedicated scholars such as P.W. Anderson, L. Noodleman, to name a few. In this master thesis we follow their methodologies to provide a systematic study on the magnetic property of hypothetical Ni-M-Ni type trimetallic extended metal atom chains (EMACs), where M denotes the first-row transition metal atoms, based on Noodleman’s broken symmetry method at the level of the density functional theory (DFT). Particularly, a single point ab initio calculation with the crystal geometry is adopted to obtain the exchange parameter, J, more quickly without substantial loss of accuracy.
At beginning, we perform a benchmark on calculating the exchange parameter, J, of the trinickel EMACs chloride, Ni3(dpa)4Cl2, and the results are comparable to experi- mental results, which justifies the methodology. We notice the value of J obtained by B3LYP is often lower than experimental value while those obtained by PBE, BP86 are often higher than experimental value, which Benard’s group also reported similar results. Based on the consideration of spin distribution on metal atoms, B3LYP is the better choice to study the magnetic properties of molecules.
Beyond Ni3(dpa)4(NCS)2, some related hypothetical systems are explored such as the trinickel atom chain without ligands, (Ni3)6+, and several hypothetical trinickel EMACs with central metal core systematically changed from Sc to Zn, NiMNi(dpa)4(NCS)2. For the latter, the spin population of metals are rationalized in the frame of the crystal field theory. Once the magnetic centers are identified, we have shown how the mediated central metal atom leads to different value of the exchange parameter, J, and different ground state with different spin multiplicities.
As far as concerned, there is no experimental investigation of the anion of the trinickel species and here we offer theoretical result of [Ni3(dpa)4(NCS)2]−1, which is found, pos- sibly, to have two stongly ferromagnetic coupled magnetic centers. Finally, we offer a simple simulation of magnetic susceptibility, χ, v.s. temperature, T, by using the van Vleck equation.
Subjects
Extended metal atom chain
EMAC
Molecular magnetism
Density Functional Theory
DFT
Exchange coupling
Exchange parameter
Heisenberg model
HDVV Hamiltonian
Heisenberg-Dirac-Van Vleck Hamiltonian
Van Vleck Equation
Van Vleck Formula
Type
thesis
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