Tongwei Li

Theoretical prediction of low-density nanoporous frameworks of zinc sulfide based on ZnnSn (n = 12, 16) nanocaged clusters

Using density functional theory calculations, the possibility of the formation of different low-density framework materials based on highly stable ZnnSn (n = 12, 16) clusters is systematically investigated. Our cluster building blocks, which have high symmetries and large HOMO–LUMO gaps, are predicted to be strongly energetically preferred. Via the coalescence of ZnnSn (n = 12, 16) building blocks, many kinds of low-density ZnS framework materials of varying porosity are thus proposed. All the frameworks differ from known synthesized materials and are predicted to be energetically stable at room temperature. These new materials are found to be semiconductors with wide bandgaps, indicating that they may have promise for optoelectronic applications. Because of their nanoporous structure, they could be used for gas storage, heterogeneous catalysis, and filtration and so on. The insights we obtained here will be helpful for extending the range of properties and applications of ZnS materials.

Pressure induced variation of second harmonic efficiency of K 3 B 6 O 10 Cl

K3B6O10Cl is a perovskite-like nonlinear optical (NLO) crystal, which exhibits large second harmonic generation (SHG) response. Based on density-functional theory, we investigate the influence of pressure on SHG tensor of K3B6O10Cl. At zero pressure, the non-centrosymmetric distortion of K3B6O10Cl from BO4 tetrahedron results in the similar SHG tensor to β-BaB2O4 (BBO). At 50 GPa, the ClK6 octahedron distortion of K3B6O10Cl becomes the main source of SHG and give similar SHG tensor to LiNbO3. Therefore, pressure induces K3B6O10Cl from a BBO-like NLO material to a LiNbO3-like NLO material.

W@Si12 cluster as a potential sensor for CO and NO detection

The adsorption of several common gas molecules on the W@Si12 cluster was investigated using density functional theory calculations in terms of geometric, energetic, and electronic properties to exploit its potential applications as gas sensors. It is found that the CO and NO molecules can be chemisorbed on the W@Si12 cluster with exothermic adsorption energy ( to ), and can lead to finite charge transfer. The electronic properties of the W@Si12 cluster present dramatic changes after the adsorption of the CO and NO molecules, especially its electric conductivity. However, the HCN, CO2, N2, O2, and H2O molecules are weakly physisorbed on the cluster, and do not induce significant change in electronic properties of the W@Si12 cluster. Thus, the W@Si12 cluster is expected to be a promising gas sensor for CO and NO detection.

A first-principles study on the defective properties of MAX phase Cr2AlC: the magnetic ordering and strong correlation effect

Our first-principles calculations indicate the defective properties of Cr2AlC are very different from the commonly studied Ti-based MAX phases. Al vacancies are predicted to have high formation energies while Cr vacancies have low formation energies in Cr2AlC. Compared with previously reported results of MAX phases, the formation energy of the anion antisite defect pair in Cr2AlC is the lowest (∼1.9 eV), predicting a good irradiation-resistance property. The reduction in the formation energy of the Cr–Al antisite defect is attributed to the magnetic ordering and strong correlation effect of Cr atoms. Analysis suggests that the majority spin state of the dz2 orbital of Cr is lowered in energy while the minority spin states become empty, which makes the Cr more ionic in character.

C54Si6 heterofullerene as a potential gas sensor for CO, NO, and HCN detection

The adsorption of CO, NO, and HCN molecules on the C54Si6 heterofullerene is investigated on the basis of density functional theory calculations to exploit its potential applications as a gas sensor. The C54Si6 heterofullerene has two highly stable isomers (named isomer-1 and isomer-2). We find that the toxic CO, NO, and HCN molecules are chemically adsorbed on isomer-1 with moderate adsorption energies and apparent charge transfer. The electronic properties of isomer-1 are significantly influenced by the CO, NO, and HCN adsorption, especially its electric conductivity. The recovery time of the isomer-1 sensor for CO, NO, and HCN at room temperature is estimated to be short due to the medium (optimal) adsorption energies, indicating that isomer-1 (i.e. the most stable configuration) of C54Si6 heterofullerene should be a good CO, NO, and HCN sensor. Similar analysis indicates that the isomer-2 of C54Si6 heterofullerene is a potential efficient gas sensor for NO detection.

Molecular structure, vibrational spectra, NBO analysis and molecular packing prediction of 3-nitroacetanilide by ab initio HF and density functional theory

Quantum chemical calculations of geometries and vibrational wavenumbers of 3-nitroacetanilide (C8H8N2O3) in the ground state were carried out by using ab initio HF and density functional theory (DFT/B3LYP) methods with 6-31+G(*) basis set. The -311++G(**) basis set is also used for B3LYP level. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR spectra. Theoretical vibrational spectra of the title compound were interpreted by means of potential energies distributions (PEDs) using MOLVIB program. The theoretical spectrograms for IR spectra of the title compound have been constructed. The shortening of C-H bond length and the elongation of N-H bond length suggest the existence of weak C-H⋯O and N-H⋯O hydrogen bonds, which is confirmed by the natural bond orbital analysis. In addition, the crystal structure obtained by molecular mechanics belongs to the P2(1) space group, with lattice parameters Z=4, a=14.9989 Å, b=4.0367 Å, c=12.9913 Å, ρ=0.998 g cm(-3).

Exotic d0 magnetism in partial hydrogenated silicene

The intriguing d0 magnetic properties of partially hydrogenated silicene are investigated via first-principles calculations. H atoms are assembled along the diagonal line of 4 × 4 supercell. The magnetism can be engineered through transforming the adsorption sites of H atoms. With odd number of H atoms, the systems demonstrate stable magnetism, and the total magnetic moment of each system is 1 μB. No magnetism is found in those systems with equal number of H atoms for sublattice A and sublattice B. Molecular dynamics simulations show the configurations and magnetism of the systems are stable at room temperature. Our work motivates promising applications for silicene in spintronics device.

Lattice vibrational spectra of double-helix LiP

The LiP infinite double-helix chain gives us the unique opportunity to investigate the double-helix structure at atomic level. Based on density-functional theory, we investigate the characteristic vibrational modes of this peculiar structure. Differently from single-wall carbon nanotubes, a dipole mode in LiP gives rise to high infrared intensity. Owing to the peculiar double-helix structure of LiP, the frequency of the out-of-phase radical breathing mode is lower than that of the in-phase one. It is similar to the condition of DNA. Furthermore, the out-of-phase breathing mode in LiP, instead of the in-phase one, has the highest Raman intensity. Most importantly, our finding is generally applicable to other double-helix structures. Copyright (C) EPLA, 2014

First-principles investigation of the lattice vibrational properties of inorganic double helical XY (X = Li, Na, K, Rb, Cs; Y = P, As, Sb)

Inorganic double helical XY (X = Li, Na, K, Rb, Cs; Y = P, As, Sb) materials are newly discovered compounds. Their structures are so simple that we can study their properties with first-principles calculations. Our calculation results show that their structures and lattice vibrational frequencies are sensitive to the cation (Li, Na, K, Rb, Cs) and anion (P, As, Sb). At the Γ point, there are 15 optical vibrational modes, in which the in-phase and out-of-phase breathing modes, dipole mode, and out-of-phase rotating mode are characteristic modes. Owing to the special double helical structure, the frequency of the in-phase breathing mode is always higher than that of the out-of-phase breathing mode. Furthermore, the frequencies of these two breathing modes evolve differently with cation and anion. The dipole mode and out-of-phase rotating mode are A2 modes. The frequency of the former decreases continuously from LiY to CsY, while the frequency of the latter firstly decreases, then increases, and finally approaches a stable value. Besides these characteristic modes, other modes are sensitive to ions, too. Our systematic calculation and analysis not only give much valuable insight into these newly discovered inorganic double helical XY, but also apply to other double helical compounds.

Density functional studies of small silicon clusters adsorbed on graphene

The structural and electronic properties of small Sin clusters (n = 1–6, 10) adsorbed on graphene are studied by use of density functional theory within periodic boundary conditions. Our results show that the structural properties of the deposited Sin clusters and graphene are weakly affected by their interaction. The adsorption energy difference of different adsorption sites for the same size Si cluster on graphene is very small, indicating the Sin-cluster–graphene system will be obtained easily. There is a little charge transfer from Sin clusters to graphene when the cluster size is larger. The adsorption of Sin clusters will be an effective method to open of an energy gap for graphene, which is useful for the applications of graphene to electrical and optical devices. Especially, the adsorption of Sin cluster with large size (n ≥ 5) would have a band gap with a constant energy value.