Shugo Suzuki

Bio: Shugo Suzuki is an academic researcher from University of Tsukuba. The author has contributed to research in topics: Density functional theory & Electronic structure. The author has an hindex of 13, co-authored 53 publications receiving 1088 citations.

Optimized geometries and electronic structures of graphyne and its family

Abstract: The optimized geometries of carbon allotropes related to graphite, called graphyne, graphdiyne, graphyne-3, and graphyne-4, as well as their electronic band structures were calculated using a full-potential linear combination of atomic orbitals method in the local-density approximation. These carbon allotropes consist of hexagons connected by linear carbon chains. The bond length of a hexagon is a little longer than that of the bond that links a hexagon to the outside carbon. Furthermore, part of the linear carbon chain is composed of acetylenic linkages (---C\ensuremath{\equiv}C---) rather than cumulative linkages (=C=C=). The binding energies are 7.95 eV/atom for graphyne and 7.78 eV/atom for graphdiyne, and the optimized lattice lengths are 6.86 \AA{} for graphyne and 9.44 \AA{} for graphdiyne. These materials are semiconductors with moderate band gaps. The band gap occurs at the M point or \ensuremath{\Gamma} point depending on the number of acetylenic linkages that are contained between the nearest-neighboring hexagons. The effective masses are very small for both conduction and valence bands.

Electronic structure of three-dimensional graphyne

Abstract: Graphyne is a hypothetical carbon allotrope with a layered structure. We calculated the optimized geometries and electronic structures of three-dimensional graphyne in some possible stacking arrangements from symmetry considerations. The optimized lattice constants and the binding energy of graphyne are given in comparison with graphite. The binding energy of graphyne is about 90% of that of graphite, and graphyne will be stable when it is synthesized. The electronic structures are classified into two types, metallic and semiconducting, according to the stacking arrangements. The most stable graphyne is expected to be a semiconductor with a moderate band gap.

Potassium intercalated graphyne

Abstract: Graphyne intercalation compounds are expected to function as layered organic conductors and as storage of atoms and molecules, because graphyne as a host material is highly stable and has large voids. We have performed optimization of the geometry and calculation of the electronic structures for five hypothetical stacking arrangements of the stage-1 potassium-intercalated graphyne by use of the first-principles method. The results are compared with the values of the typical graphite-intercalation compound, C 8 K. The stability of potassium-intercalated graphyne is strongly dependent on the position of intercalated atoms relative to the characteristic voids in the pristine graphyne. It is found that some stacking arrangements are stable, and are expected to intercalate potassium easily since the estimated values of the heat of reaction are larger than that of C 8 K. For the optimized crystal structures the electronic structures show that these materials are metallic. Further, we show the relationship between the amount of charge transfer and each bond length in graphyne.

Two-Dimensional σ-Hole Systems in Boron Layers: A First-Principles Study on Mg1-xNaxB2 and Mg1-xAlxB2

Abstract: We study two-dimensional σ-hole systems in boron layers by calculating the electronic structures of Mg 1- x Na x B 2 and Mg 1- x Al x B 2 . In Mg 1- x Na x B 2 , it is found that the concentration of σ holes is approximately described by ( 0.8 + 0.8 x ) ×10 22 cm -3 and the largest attainable concentration is about 1.6 ×10 22 cm -3 in NaB 2 . In Mg 1- x Al x B 2 , on the other hand, it is found that the concentration of σ holes is approximately described by ( 0.8 - 1.4 x ) ×10 22 cm -3 and σ holes disappear at x of about 0.6. These relationships can be used for experimental studies on σ-hole systems in these materials.

A Fully Relativistic Full-Potential LCAO Method for Solids

Abstract: We present a fully relativistic full-potential linear-combination-of-atomic-orbitals method for solids based on the density-functional theory within the local-density approximation. We solve the Dirac-Kohn-Sham equations directly, handling not only the indirect relativistic effect but also the effect due to the spin-orbit coupling self-consistently. We apply the present method to Au and InSb and compare the results with those of experimental and other theoretical studies. Consequently, we show that the agreement is good and the present method is capable of obtaining reliable results in studying the structural and electronic properties of solids.

Penta-graphene: A new carbon allotrope

Abstract: A 2D metastable carbon allotrope, penta-graphene, composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling, is proposed. State-of-the-art theoretical calculations confirm that the new carbon polymorph is not only dynamically and mechanically stable, but also can withstand temperatures as high as 1000 K. Due to its unique atomic configuration, penta-graphene has an unusual negative Poisson’s ratio and ultrahigh ideal strength that can even outperform graphene. Furthermore, unlike graphene that needs to be functionalized for opening a band gap, penta-graphene possesses an intrinsic quasi-direct band gap as large as 3.25 eV, close to that of ZnO and GaN. Equally important, penta-graphene can be exfoliated from T12-carbon. When rolled up, it can form pentagon-based nanotubes which are semiconducting, regardless of their chirality. When stacked in different patterns, stable 3D twin structures of T12-carbon are generated with band gaps even larger than that of T12-carbon. The versatility of penta-graphene and its derivatives are expected to have broad applications in nanoelectronics and nanomechanics.

Review of the superconducting properties of MgB2

Abstract: This review paper illustrates the main normal and superconducting state properties of magnesium diboride, a material known since the early 1950s but only recently discovered to be superconductive at a remarkably high critical temperature Tc = 40 K for a binary compound. What makes MgB2 so special? Its high Tc, simple crystal structure, large coherence lengths, high critical current densities and fields, and transparency of grain boundaries to current promise that MgB2 will be a good material for both large-scale applications and electronic devices. During the last seven months, MgB2 has been fabricated in various forms: bulk, single crystals, thin films, tapes and wires. The largest critical current densities, greater than 10 MA cm−2, and critical fields, 40 T, are achieved for thin films. The anisotropy ratio inferred from upper critical field measurements is yet to be resolved as a wide range of values have been reported, γ = 1.2–9. Also, there is no consensus on the existence of a single anisotropic or double energy gap. One central issue is whether or not MgB2 represents a new class of superconductors, which is the tip of an iceberg awaiting to be discovered. To date MgB2 holds the record for the highest Tc among simple binary compounds. However, the discovery of superconductivity in MgB2 revived the interest in non-oxides and initiated a search for superconductivity in related materialss; several compounds have since been announced to be superconductive: TaB2, BeB2.75, C–S composites, and the elemental B under pressure.

Review of superconducting properties of MgB2

Abstract: This review paper illustrates the main normal and superconducting state properties of magnesium diboride, a material known since early 1950's, but recently discovered to be superconductive at a remarkably high critical temperature Tc=40K for a binary compound. What makes MgB2 so special? Its high Tc, simple crystal structure, large coherence lengths, high critical current densities and fields, transparency of grain boundaries to current promises that MgB2 will be a good material for both large scale applications and electronic devices. During the last seven month, MgB2 has been fabricated in various forms, bulk, single crystals, thin films, tapes and wires. The largest critical current densities >10MA/cm2 and critical fields 40T are achieved for thin films. The anisotropy ratio inferred from upper critical field measurements is still to be resolved, a wide range of values being reported, between 1.2 and 9. Also there is no consensus about the existence of a single anisotropic or double energy gap. One central issue is whether or not MgB2 represents a new class of superconductors, being the tip of an iceberg who awaits to be discovered. Up to date MgB2 holds the record of the highest Tc in its class. However, the discovery of superconductivity in MgB2 revived the interest in non-oxides and initiated a search for superconductivity in related materials, several compounds being already announced to become superconductive: TaB2, BeB2.75, C-S composites, and the elemental B under pressure.

Graphdiyne and graphyne: from theoretical predictions to practical construction

Abstract: Flat carbon (sp(2) and sp) networks endow the graphdiyne and graphyne families with high degrees of π-conjunction, uniformly distributed pores, and tunable electronic properties; therefore, these materials are attracting much attention from structural, theoretical, and synthetic scientists wishing to take advantage of their promising electronic, optical, and mechanical properties. In this Review, we summarize a state-of-the-art research into graphdiynes and graphynes, with a focus on the latest theoretical and experimental results. In addition to the many theoretical predictions of the potential properties of graphdiynes and graphynes, we also discuss experimental attempts to synthesize and apply graphdiynes in the areas of electronics, photovoltaics, and catalysis.

Electronic structure and carrier mobility in graphdiyne sheet and nanoribbons: theoretical predictions

Abstract: Using density functional theory coupled with Boltzmann transport equation with relaxation time approximation, we investigate the electronic structure and predict the charge mobility for a new carbon allotrope, the graphdiyne for both the sheet and nanoribbons. It is shown that the graphdiyne sheet is a semiconductor with a band gap of 0.46 eV. The calculated in-plane intrinsic electron mobility can reach the order of 10(5) cm(2)/(V s) at room temperature, while the hole mobility is about an order of magnitude lower.