Machine learning reveals orbital interaction in materials.

We propose a novel representation of materials named an 'orbital-field matrix (OFM)', which is based on the distribution of valence shell electrons. We demonstrate that this new representation can be highly useful in mining material data. Experimental investigation shows that the formation energies of crystalline materials, atomization energies of molecular materials, and local magnetic moments of the constituent atoms in bimetal alloys of lanthanide metal and transition-metal can be predicted with high accuracy using the OFM. Knowledge regarding the role of the coordination numbers of the transition-metal and lanthanide elements in determining the local magnetic moments of the transition-metal sites can be acquired directly from decision tree regression analyses using the OFM.

A systematic study of influence of ligand substitutions on the electronic structure and magnetic properties of Mn4 single-molecule magnets.

We present a density-functional theory study of the influence of ligand substitutions on the geometric structure, electronic structure, and magnetic properties of Mn4 single-molecule magnets (SMMs), in order to investigate the role of ligands in controlling these features, as well as in developing new SMMs and single-chain magnets (SCMs). Our results show that the peripheral ligands play an important role in controlling the magnetic ground-state of Mn4 SMMs. A new model is proposed to explain the spin state of manganese ions in Mn4 molecules. This model shows that the saving energy from distortion, which can be controlled by peripheral-ligand substitutions, plays a crucial role in determining the spin state of manganese ions in Mn4 molecules. The mechanism of strong exchange couplings between manganese ions in Mn4 SMMs is revealed. The strength of exchange-couplings between manganese ions in Mn4 SMMs as a function of their charge and spin state can be also controlled by substituting peripheral-ligands. The results demonstrate the possibilities of developing new Mn4-based SMMs. In addition, strong spin polarizations on peripheral ligands containing sp2-hybridized carbon sites show that using ligands containing sp2-hybridized carbon sites can enhance exchange couplings between Mn4 building blocks to develop new SMMs and SCMs which operate at high temperatures.

Bonding nature and structural phase transition in fullerene based nanomaterials.

Rare-earth-metal-doped fullerides with a nominal composition of R3C70 (R = Sm, Eu, Yb) adopt a pseudomonoclinic structure in which C70 dimers glued with rare-earth ions are involved. High-temperature powder X-ray diffraction experiments revealed that the dimers undergo reversible first-order structural phase transitions, associated with reduction of the unit cell volume, similar to the results observed in previous high-pressure experiments. Structural analyses showed that C70 molecules are realigned to form closely packed structures, causing a reduction of volume at high temperature. The derived charge density map indicates that the transitions can be regarded as reversible structural changes from fullerene dimers to monomers. These features are ascribed to the unique bonding nature of rare-earth C70 compounds.