Daisuke Yamaki

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...

Versatile Supramolecular Gelators That Can Harden Water, Organic Solvents and Ionic Liquids

We developed novel supramolecular gelators with simple molecular structures that could harden a broad range of solvents: aqueous solutions of a wide pH range, organic solvents, edible oil, biodiesel, and ionic liquids at gelation concentrations of 0.1-2 wt %. The supramolecular gelators were composed of a long hydrophobic tail, amino acids and gluconic acid, which were prepared by liquid-phase synthesis. Among seven types of the gelators synthesized, the gelators containing L-Val, L-Leu, and L-Ile exhibited high gelation ability to various solvents. These gelators were soluble in aqueous and organic solvents, and also in ionic liquids at high temperature. The gelation of these solvents was thermally reversible. The microscopic observations (TEM, SEM, and CLSM) and small-angle X-ray scattering (SAXS) measurements suggested that the gelator molecules self-assembled to form entangled nanofibers in a large variety of solvents, resulting in the gelation of these solvents. Molecular mechanics and density functional theory (DFT) calculations indicated the possible molecular packing of the gelator in the nanofibers. Interestingly, the gelation of an ionic liquid by our gelator did not affect the ionic conductivity of the ionic liquid, which would provide an advantage to electrochemical applications.

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...

Generalized spin density functional theory for noncollinear molecular magnetism

We developed the ab initio linear combination of Gaussian type orbital program with a generalized Hartree–Fock–Slater (GHFS) functional and calculated the four hydrogen clusters as models of the noncollinear magnetic clusters. We found that the GHFS solutions with the three-dimensional noncollinear spin structure is the ground state near the Td conformation. Computational results are compared with those of the ab initio generalized Hartree–Fock functional and the differences between them are discussed. Implications of the calculated results are discussed in relation to the electronic structures of Fe4S4 and Mn4O4 clusters.

Theoretical calculations of effective exchange integrals by spin projected and unprojected broken-symmetry methods. I. Cluster models of K2NiF4-type solids

Previously, various symmetry-adapted (SA) and broken-symmetry (BS) computations have been performed for strongly correlated transition metal species so as to examine magnetic properties in simple cluster models such as binuclear transition metal oxides. Though SA computations such as the complete active space configuration interaction and CASSCF are desirable for estimating physical constants, these computations are heavy for larger cluster models with strongly correlated electrons. K2NiF4 is known to be the two-dimensional perovskite-type antiferromagnet and to have the electronic configuration similar to that of La2CuO4. Here, we have examined the utility and applicability of the BS spin-polarized hybrid-density functional theory (HUDFT) for cluster models of K2NiF4. As the result, HUDFT calculation such as UB2LYP has provided the reasonable effective exchange integral (Jab) followed by our approximately spin projected scheme, in comparison to the experimental one. It was also found that the square plan...

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...

Communication: Explicitly correlated four-component relativistic second-order Møller-Plesset perturbation theory

We propose explicitly correlated Ansatz for four-component relativistic methods within the framework of the no-pair approximation. Kinetically balanced geminal basis is derived to satisfy the cusp conditions in the non-relativistic limit based on the Lévy-Leblend-like equation. Relativistic variants of strong-orthogonality projection operator (Ansätze 2α and 2β) suitable for practical calculations are introduced by exploiting the orthogonal complement of the large-component basis. A pilot implementation is performed for the second order Møller-Plesset perturbation theory.

Theoretical study of the antiferromagnetic model clusters for K2MX4 type solids

Abstract Magnetic properties for the K2MX4 type solids (M=Cu2+, Ni2+ X=F−, O2−. Cl−) were investigated by the ab initio calculations using UHF and the hybrid Density Functional methods (B2VWN, S2VWN and UB3LYP). It was found that these type solids had the antiferromagnetic interactions.

Theoretical Study of Effective Exchange Integrals for Ferromagnetic Phenylenevinylene Polymers with Nitroxddes. Possibilities of Organic Ferro-or Ferri-Magnetic Solids

Abstract Molecular orbital calculations were carried out for pendant-type ferromagnetic phenylenevinylene pligomers with nitroxide groups in order to elucidate variations of the effective exchange integrals with oligomer size, conformational change and spin defects generated in the dehydrogenation process of NOH groups in the precursor oligomers. It was shown that the ferromagnetic effective exchange interactions between the nearest neighbor nitroxides are about 50–80 cm−1, but they decrease with the internal rotation and spin defect. The interchain interactions between the oligomers are antiferromagnetic, and therefore they should be controlled by introduction of spacer group, showing a possibility to obtain the high Tc organic ferrimagnet induced by one-electron transfer between the oligomer and spacer.

Theoretical Calculation of Effective Exchange Integrals for One-and Two-Dimensional Poly(Phenylenemethylene) Systems. Possibilities of Organic Ferro-and Ferri-Magnetic Solids

Abstract Ab initio post UHF, DFT, CASSCF and semiempirical INDO calculations were carried out for one-and two-dimensional poly(phenylenmethylene) in order to elucidate variations of the effective exchange integrals with molecular connectivity, cluster size and hole (electron) doping. It was shown that the ferromagnetic effective exchange integrals by UCCSD(T) and DFT/4–31G are about 400 cm−1 for m-phenylene bis(methylene). The nigh-spin ground states of hole-doped polycarbenes were also studied, indicating a possibility of obtaining the high Tc organic ferrimagnets induced by the one electron transfer between polycarbene and spacer (electron donor or acceptor).