Masaki Mitani

Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit (I): UBLYP, UB3LYP, and UHF calculations

Polyradicals comprised of m-phenylene-bridged organic radicals are well known as building blocks of organic ferromagnets, in which radical groups are connected with each other at the meta position in the benzene ring, and the parallel-spin configurations between radical sites are more stabilized than the antiparallel ones. Topological rules for spin alignments enable us to design organic high-spin dendrimers and polymers with the ferromagnetic ground states by linking various radical species through an m-phenylene unit. However, no systematic ab initio treatment of such spin dendrimers and magnetic polymers has been reported until now, though experimental studies on these materials have been performed extensively in the past ten years. As a first step to examine the possibilities of ferromagnetic dendrimers and polymers constructed of m-phenylene units with organic radicals, we report density functional and molecular orbital calculations of six m-phenylene biradical units with radical substituents and pol...

Density-functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit (II): Examination of functional dependence

As a first step toward examination of ferromagnetic polymers and dendrimers by ab initio crystal orbital methods, we elucidated candidates for monomer units with the high-spin ground states in the previous study of Part I [J. Chem. Phys. 113, 4035 (2000)] by employing density-functional (DFT) methods using Becke’s and Becke’s three parameter exchanges with Lee–Yang–Parr correlation or Hartree–Fock (HF) molecular orbital and post HF approximations. However, it was found that further computations applying other DFT functionals should be carried out to clarify the level of approximations which appropriately describe the electronic structures of magnetic molecules. In this part II, we present details of numerical results concerning magnetic properties and electronic structures for m-phenylene molecules with three neutral and one cation radicals by spin-polarized density functional methods using variety of local and nonlocal functionals and unrestricted molecular orbital methods including Mo/ller–Plesset and c...

Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit. III. Possibility of high-spin polymer

Because it has been well-known that the effective exchange interaction of spins is much larger within a molecule than between molecules, it is very important to design high-spin polymers linking high-spin molecules with each other as a constituent unit to obtain molecule-based ferromagnetic materials with high transition temperature. Experimental efforts to synthesize such polymers extended in one- or two-dimensions have been made in recent years while theoretical treatment of infinite polymers has been behind in the sense that no study of electronic and magnetic structure calculations by ab initio periodic approaches exists until now. We examined the magnetic properties in m-phenylene and related molecules with organic radicals by density functional and molecular orbital methods as monomer units of high-spin polymers in Part I and Part II of this series, since it has already been confirmed experimentally and theoretically that m-phenylene coupling unit leads to the ferromagnetic coupling between spins. I...

Density functional investigation on the ferromagnetic coupling of spins in phenylenevinylene-bridged nitroxide radicals: Monomer and polymer cases

Magnetic interactions in phenylenevinylene-bridged organic radicals are investigated as realistic models of pendant-type ferromagnetic polymers, since several molecules having some types of phenylenevinylene skeletons with phenoxy or nitroxide radicals were recently synthesized and their ferromagnetic characters were also confirmed by experimental works. In the present study, a spin source of NOH nitroxide radical is examined as a model of stable tertiary-butyl nitroxide in this system. According to NOH orientations, it is possible to form hydrogen bond between radical O and vinylene H atoms which may work as additional effects on the ferromagnetic spin coupling. To elucidate this point, density-functional calculations are carried out for both monomers and polymers by using Becke’s exchange with Lee–Yang–Parr correlation functional. It is detected that the influence of hydrogen bond is emphasized in polymers by the cooperative interaction arising from one-dimensional network along chain. Implications of t...

Theoretical studies on anomalous phases in model plane systems of LiBeH3

Abstract The possibility of the charge-mediated superconductivity in LiH and BeH2 plane systems was studied by means of the Greens function method and a numerical approach. It is unlikely that the effective electron-electron interaction for these systems becomes attractive.

Ab Initio Crystal Orbital Study of Ferromagnetic Interactions of Spins in Polymer Comprising Phenylenevinylene

Abstract Magnetic properties for models of poly(phenylenevinylene) having four types of chain structure with methylene radical were investigated by the ab initio crystal orbital approaches using UBLYP and UHF approximations. It was found that the stability of high-spin states increases from molecules to polymers which is caused by the ferromagnetic interactions between neighboring monomer units arising from the spin polarization through phenylenevinylene bridge.