Computationally Designed Crystal Structures of the Supertetrahedral Ga4C and Ga4Si Solids.

The structural, mechanical, electrical, and optical properties of new supertetrahedral structures cF-Ga4X (X = C, Si) were studied by using a solid state DFT calculation. The crystal structures of cF-Ga4X are built based on a diamond crystal lattice, in which pairs of adjacent carbon atoms are replaced by Ga4X fragments, where Ga4 is a tetrahedron of gallium atoms. Calculations have shown that new mixed-type supertetrahedral structures are dynamically stable, have densities of 3.49 g/cm3 (X = C) and 2.65 g/cm3 (X = Si), and are narrow band gap semiconductors. From the performed molecular dynamics calculations, it follows that the homogeneous melting temperature of the gallium-carbon structure is in the range from 600 to 700 K and that of the gallium-silicon structure is in the range from 400 to 500 K.

Molecular dynamics study of a new metastable allotropic crystalline form of gallium-supertetrahedral gallium.

A new metastable crystalline form of gallium has been computationally designed using density functional calculations with imposing periodic boundary conditions. The geometric and electronic structures of the predicted new allotrope were calculated on the basis of a diamond lattice in which all carbon atoms are replaced by gallium Ga4 tetrahedra. This form does not have any imaginary phonons, thus it is a metastable crystalline form of gallium. The new form of gallium is a metal and shows high plasticity and low-melting temperature. Molecular dynamics simulations show that this form of gallium will melt at about 273 K with a sharp increase in temperature in the system during the melting process from 273 to 1800 K. This melting process is very different from conventional melting, where temperature stays the same until complete melting. That unusual melting can be explained by the fact that supertetrahedral gallium is a metastable structure that has an excess of strain energy released during melting. If made this new material may find many useful applications as a new low density metal with stored internal energy. © 2019 Wiley Periodicals, Inc.

Computationally Designed Crystal Structures of the Supertetrahedral Al4X (X = B, C, Al, Si) Solids.

New metastable crystalline forms of the supertetrahedral Al4X (X = B, C, Al, Si) solids have been computationally designed using density functional theory calculations with imposing of periodic boundary conditions. The geometric and electronic structures of the predicted new systems were calculated on the basis of the diamond lattice in which all carbon atoms are replaced by the Al4X structural units, where X is boron, carbon, aluminum, and silicon atoms. The calculations showed that the dynamic stability of the Al4X crystal structures critically depends on the nature of the bridging atom X: supertetrahedral Al4C and Al4Si solids are dynamically stable, whereas Al4B and Al4Al ones are unstable.

From Two- to Three-Dimensional Structures of a Supertetrahedral Boran Using Density Functional Calculations.

With help of the DFT calculations and imposing of periodic boundary conditions the geometrical and electronic structures were investigated of two- and three-dimensional boron systems designed on the basis of graphane and diamond lattices in which carbons were replaced with boron tetrahedrons. The consequent studies of two- and three-layer systems resulted in the construction of a three-dimensional supertetrahedral borane crystal structure. The two-dimensional supertetrahedral borane structures with less than seven layers are dynamically unstable. At the same time the three-dimensional superborane systems were found to be dynamically stable. Lack of the forbidden electronic zone for the studied boron systems testifies that these structures can behave as good conductors. The low density of the supertetrahedral borane crystal structures (0.9 g cm-3 ) is close to that of water, which offers the perspective for their application as aerospace and cosmic materials.

A quantum chemical study of bis-(iminoquinonephenolate) Zn(II) complexes.

A computational DFT B3LYP*/6-311++G(d,p) study performed on bis-(iminoquinonephenolate) Zn(II) complex [Zn(II)(C(12)H(8)NO(2))(2)] has revealed a previously unexplored mechanism for valence tautomerism inherent in transition metal complexes with redox active (noninnocent) ligands. The occurrence of energy-close isomeric forms of the complex and their low energy barrier interconversion is caused not by the intramolecular electron transfer (IET) between the metal and ligand frontier orbitals, but the intersystem conversion within a redox active ligand without involvement of a metal center. This mechanism gives a new insight into the origin of the previously experimentally studied isomeric forms of bis-(iminoquinonephenolate) Zn(II) complexes that must be assigned to [Zn(II)((1)L(-1))(2)] (8) and [Zn(II)((1)L(-1))((3)L(-1))] (9) structures. The spin-forbidden transition between the two forms of the complex proceeds via a minimal energy crossing point (MECP) corresponding to the energy barrier of 8.9 kcal mol(-1) for the 9 --> 8 transformation in the gas phase.