Metastable atomic-ordered configurations for AlGaN predicted by Monte-Carlo method based on first-principles calculations.

Metastability of AlGaN (= 2-10: integer) with the 1-2 monolayer (ML) in-plane configuration towards the[0001] direction has been demonstrated recently. To theoretically explain the existence of these metastable structures, relatively large calculation cells are needed. However, previous calculations were limited to the use of small calculation cell sizes to estimate the local potential depth (Δ) of ordered AlGaN models.

Accelerated Data-Driven Accurate Positioning of the Band Edges of MXenes.

Functionalized MXene has emerged a promising class of two-dimensional materials having more than tens of thousands of compounds, whose uses may range from electronics to energy applications. Other than the band gap, these properties rely on the accurate position of the band edges. Hence, to synthesize MXenes for various applications, a prior knowledge of the accurate position of their band edges at an absolute scale is essential; computing these with conventional methods would take years for all the MXenes.

Correction: New carbon allotropes in sp + sp bonding networks consisting of C cubes.

Correction for 'New carbon allotropes in sp + sp3 bonding networks consisting of C8 cubes' by Jian-Tao Wang et al., Phys. Chem.

New carbon allotropes in sp + sp bonding networks consisting of C cubes.

We identify using ab initio calculations new types of three-dimensional carbon allotrope constructed by inserting acetylenic or diacetylenic bonds into a body-centered cubic C lattice. The resulting sp + sp-hybridized cubane-yne and cubane-diyne structures consisting of C cubes can be characterized as a cubic crystalline modification of linear carbon chains, but energetically more favorable than the simplest linear carbyne chain and the cubic tetrahedral diamond and yne-diamond consisting of C tetrahedrons. Electronic band calculations indicate that these new carbon allotropes are semiconductors with an indirect band gap of 3.

Mechanistic Insight into the Chemical Exfoliation and Functionalization of Ti3C2 MXene.

MXene, a two-dimensional layer of transition metal carbides/nitrides, showed great promise for energy storage, sensing, and electronic applications. MXene are chemically exfoliated from the bulk MAX phase; however, mechanistic understanding of exfoliation and subsequent functionalization of these technologically important materials is still lacking. Here, using density-functional theory we show that exfoliation of Ti3C2 MXene proceeds via HF insertion through edges of Ti3AlC2 MAX phase.

Three-Dimensional Carbon Allotropes Comprising Phenyl Rings and Acetylenic Chains in sp+sp(2) Hybrid Networks.

We here identify by ab initio calculations a new type of three-dimensional (3D) carbon allotropes that consist of phenyl rings connected by linear acetylenic chains in sp+sp(2) bonding networks. These structures are constructed by inserting acetylenic or diacetylenic bonds into an all sp(2)-hybridized rhombohedral polybenzene lattice, and the resulting 3D phenylacetylene and phenyldiacetylene nets comprise a 12-atom and 18-atom rhombohedral primitive unit cells in the symmetry, which are characterized as the 3D chiral crystalline modification of 2D graphyne and graphdiyne, respectively. Simulated phonon spectra reveal that these structures are dynamically stable.

Isolation of pristine MXene from Nb₄AlC₃ MAX phase: a first-principles study.

Synthesis of pristine MXene sheets from MAX phase is one of the foremost challenges in getting a complete understanding of the properties of this new technologically important 2D-material. Efforts to exfoliate Nb4AlC3 MAX phase always lead to Nb4C3 MXene sheets, which are functionalized and have several Al atoms attached. Using the first-principles calculations, we perform an intensive study on the chemical transformation of MAX phase into MXene sheets by inserting HF, alkali atoms and LiF in Nb4AlC3 MAX phase.

Kinetic origin of divergent decompression pathways in silicon and germanium.

Silicon and germanium transform from diamond to β-tin structure under compression, but upon decompression they turn into metastable BC8 Si and ST12 Ge phases, respectively, instead of returning to the lowest-enthalpy diamond structure. Here we explore by first-principles calculations the atomistic mechanism underlying this intriguing phenomenon. We identify a body-centered tetragonal structure in I4(1)/a (C(4h)(6)) symmetry as a precursory state of the BC8 Si phase formed via a double cell bond-rotation mechanism with a low kinetic barrier.

Theoretical prediction of the complexation behaviors of antitumor platinum drugs with cucurbiturils.

The inclusion complex formation ability between CB[n] (n = 6-9) and Pt-drugs (oxaliplatin, nedaplatin, carboplatin, and cisplatin) in gas phase as well as water phases has been investigated using the using density functional theory. The results reveal the existence of several stable inclusion complexes in aqueous solution with high solvation energies compared to the guest and host molecule. It has been shown that the formation of complexes between CB[6] and Pt-drugs resulted in structural change in the CB[6], with the calculated deformation energies being higher for the inclusion complexes.

Band gap engineering of silicene zigzag nanoribbons with perpendicular electric fields: a theoretical study.

The electronic properties of silicene zigzag nanoribbons with the presence of perpendicular fields are studied by using first-principles calculations and the generalized nearest neighboring approximation method. In contrast to the planar graphene, in silicene the Si atoms are not coplanar. As a result, by applying perpendicular fields to the two-dimensional silicene sheet, the on-site energy can be modulated and the band gap at the Dirac point is open.

A first-principles study on water flow through single-walled carbon nanotubes using artificial neural network method.

Ab initio molecular dynamics simulations are done to elucidate the electronic structure and properties of water/single-walled carbon nanotubes (SWCNTs) systems. The artificial neural network (ANN) approach and statistical methods are then used to model and analyze these properties. The ANN method substantially speeds up the ab initio electronic structure calculations and has superior accuracy in mimicking the results of such calculations.

Electron transport characteristics of organic molecule encapsulated carbon nanotubes.

One-dimensional carbon nanotube (CNT) junctions with interesting device characteristics have been designed by encapsulating p- and n-type organic molecules into CNTs with electrophilic tetracyano-p-quinodimethane (TCNQ) and nucleophilic tetrakis(dimethylamino)ethylene (TDAE) molecules in order to explore the effect of encapsulation of organic molecules and rectifying behaviors of the designed one-dimensional CNT p-n junctions. Our results show that p- and n-type doping of CNTs and their associated charge transfer play an important role in determining the electron transport characteristics and lead to materials with unique properties, p-n junction diode, i.e.

On the kinetics of the capillary imbibition of a simple fluid through a designed nanochannel using the molecular dynamics simulation approach.

A molecular dynamics (MD) approach was employed to simulate the imbibition of a designed nanopore by a simple fluid (i.e., a Lennard-Jones (LJ) fluid).

Electron transport characteristics of one-dimensional heterojunctions with multi-nitrogen-doped capped carbon nanotubes.

We present a systematic analysis of electron transport characteristics for one-dimensional heterojunctions with two multi-nitrogen-doped (multi-N-doped) capped carbon nanotubes (CNTs) facing one another at different numbers of nitrogen atoms and conformations. Our results show that the modification of the molecular orbitals by the nitrogen dopants generates conducting channels in the designed heterojunctions inducing multi-switching behavior with sequential negative differential resistance (NDR). The NDR behavior significantly depends on the doping site and conformation of doped nitrogen atoms.

Modular, homochiral, porous coordination polymers: rational design, enantioselective guest exchange sorption and ab initio calculations of host-guest interactions.

Two new, homochiral, porous metal-organic coordination polymers [Zn(2)(ndc){(R)-man}(dmf)]⋅3DMF and [Zn(2)(bpdc){(R)-man}(dmf)]⋅2DMF (ndc=2,6-naphthalenedicarboxylate; bpdc=4,4'-biphenyldicarboxylate; man=mandelate; dmf=N,N'-dimethylformamide) have been synthesized by heating Zn(II) nitrate, H(2)ndc or H(2)bpdc and chiral (R)-mandelic acid (H(2)man) in DMF. The colorless crystals were obtained and their structures were established by single-crystal X-ray diffraction. These isoreticular structures share the same topological features as the previously reported zinc(II) terephthalate lactate [Zn(2)(bdc){(S)-lac}(dmf)]⋅DMF framework, but have larger pores and opposite absolute configuration of the chiral centers.

Rigid adamantane tripod linkage for well-defined conductance of a single-molecule junction.

We present a systematic analysis of molecular level alignments and electron transport characteristics based on the non-equilibrium Green's function (NEGF) approach combined with density functional theory (DFT) for phenyl dithiol (PDT) derivatives with two different linkages, simple thiol (ST) and tripod-shaped adamantane trithiol (ATT). The substantial adamantane-metal bonds afford a rigid contact structure and well-defined conductance of a single-molecule junction irrespective of interfacial phenomena, which accordingly allows us to utilize the intrinsic nature of the molecule for designing molecular devices with prescribed transport characteristics. We suggest a feasible application of the ATT linkage embedded single-molecule junction to a molecular transistor based on the practical feature of the ATT linkage, which is the unsusceptible behavior of transmission under the applied bias voltage.

The origin of the halogen effect on the phthalocyanine green pigments.

The structure and the electronic and optical properties of halogenated copper-phthalocyanine (nalpha,mbeta(Hal)-CuPc) molecules are investigated, according to the variation in the substituted halogen-atom species (Hal=Cl or Br) at the alpha and beta positions of isoindole ring with different numbers (n and m=0, 4, 8, or 16). Our results show that the halogen effect mainly results from a structural deformation rather than caused by electronic effects. A nonplanar deformation of the phthalocyanine chromophore of the nalpha,mbeta(Hal)-CuPc molecule causes a significant change only in the HOMO and HOMO-1 levels, rather than in the LUMO levels, which leads to the appearance of a green color arising from the large red-shifts of the Soret and Q bands.

Titanium-doped nickel clusters TiNi(n) (n = 1-12): geometry, electronic, magnetic, and hydrogen adsorption properties.

Using the first principles method, we study the growth behavior and electronic and magnetic properties of TiNi(n) (n = 1-12) clusters to clarify the effect of Ti modulation on the nickel nanostructures. Furthermore, chemisorption of H(2) was studied to understand the chemical reactivity of H(2) on the small Ni- and Ti-doped Ni clusters. The calculations are performed using the plane wave pseudopotential approach under the density functional theory and generalized gradient approximation for the exchange and correlation functional.

Atomistic nucleation and growth mechanism for single-wall carbon nanotubes on catalytic nanoparticle surfaces.

We demonstrate an atomistic nucleation and growth mechanism for single-wall carbon nanotubes (SWNTs) on catalytic nanoparticle surfaces based on a core-shell model. We show by ab initio calculations that strain relief between the metal core and carbon shell plays a crucial role in facilitating the hexagonal tubular growth. The incipient nucleation begins with the formation of a hemispherical fullerene cap by a size-selected core-shell bonding process which is followed by a repeated phase-separating growth mode with increasing energetic stability via periodic pulsatile strain relief along the tubular growth pathway.

Accurate description of phase diagram of clathrate hydrates at the molecular level.

In order to accurately estimate the thermodynamic properties of hydrogen clathrate hydrates, we developed a method based on the solid solution theory of van der Waals and Platteeuw. This model allows one to take into account the influence of guest molecules on the host lattice and guest-guest interactions--especially when more than one guest molecule occupies a cage. The free energies, equations of state, and chemical potentials of hydrogen and mixed propane-hydrogen clathrate hydrates of cubic structure II with different cage fillings have been estimated using this approach.