Spin-dependent Optical Excitations in LiFeO.

The three-dimensional ternary LiFeO compound presents various unusual properties. The main features are thoroughly explored by using many-body perturbation theory. The concise physical/chemical picture, the critical spin polarizations, and orbital hybridizations in the Li-O and Fe-O bonds are clearly examined through geometric optimization, quasi-particle energy spectra, spin-polarized density of states, spatial charge densities, spin-density distributions, and strong optical responses.

Rich -type-doping phenomena in boron-substituted silicene systems.

The essential properties of monolayer silicene greatly enriched by boron substitutions are thoroughly explored through first-principles calculations. Delicate analyses are conducted on the highly non-uniform Moire superlattices, atom-dominated band structures, charge density distributions and atom- and orbital-decomposed van Hove singularities. The hybridized 2 -3 and [2s, 2 , 2 ]-[3s, 3 , 3 ] bondings, with orthogonal relations, are obtained from the developed theoretical framework.

Unusual features of nitrogen substitutions in silicene.

The quasiparticle properties resulting from charge and spin are clearly identified in nitrogen-substituted silicenes, for which a theoretical framework is successfully developed from first-principles calculations. Such systems create extremely non-uniform chemical and physical environments through the distribution of the guest atoms. They present unusual geometric, electronic, and magnetic properties, which can be identified from the optimal honeycomb lattices, the atom- and spin-dominated energy spectra, the spatial charge density distributions, and the atom-, orbital- and spin-projected van Hove singularities [the net magnetic moments].

First-principles studies of electronic properties in lithium metasilicate (LiSiO).

Lithium metasilicate (LiSiO), which could serve as the electrolyte material in Li-based batteries, exhibits unique lattice symmetry (an orthorhombic crystal), valence and conduction bands, charge density distribution, and van Hove singularities. Delicate analyses, based on reliable first-principles calculations, are utilized to identify the critical multi-orbital hybridizations in Li-O and Si-O bonds, 2s-(2s, 2p , 2p , 2p ) and (3s, 3p , 3p , 3p )-(2s, 2p , 2p , 2p ), respectively. This system shows a huge indirect gap of 5.

Anomalous magneto-transport properties of bilayer phosphorene.

The magneto-transport properties of phosphorene are investigated by employing the generalized tight-binding model to calculate the energy bands. For bilayer phosphorene, a composite magnetic and electric field is shown to induce a feature-rich Landau level (LL) spectrum which includes two subgroups of low-lying LLs. The two subgroups possess distinct features in level spacings, quantum numbers, as well as field dependencies.

The diverse magneto-optical selection rules in bilayer black phosphorus.

The magneto-optical properties of bilayer phosphorene is investigated by the generalized tight-binding model and the gradient approximation. The vertical inter-Landau-level transitions, being sensitive to the polarization directions, are mainly determined by the spatial symmetries of sub-envelope functions on the distinct sublattices. The anisotropic excitations strongly depend on the electric and magnetic fields.

Improving the convergence rate of a hybrid input-output phasing algorithm by varying the reflection data weight.

In an iterative projection algorithm proposed for ab initio phasing, the error metrics typically exhibit little improvement until a sharp decrease takes place as the iteration converges to the correct high-resolution structure. Related to that is the small convergence probability for certain structures. As a remedy, a variable weighting scheme on the diffraction data is proposed.

Improving the efficiency of molecular replacement by utilizing a new iterative transform phasing algorithm.

An iterative transform method proposed previously for direct phasing of high-solvent-content protein crystals is employed for enhancing the molecular-replacement (MR) algorithm in protein crystallography. Target structures that are resistant to conventional MR due to insufficient similarity between the template and target structures might be tractable with this modified phasing method. Trial calculations involving three different structures are described to test and illustrate the methodology.

Direct phasing of protein crystals with high solvent content.

An iterative transform method is proposed for solving the phase problem in protein crystallography. In each iteration, a weighted average electron-density map is constructed to define an estimated protein mask. Solvent flattening is then imposed through the hybrid input-output algorithm [Fienup (1982).

Electric-field-induced destruction of quasi-Landau levels in bilayer graphene nanoribbons.

The magneto-electronic properties of bilayer zigzag graphene nanoribbons are investigated by the Peierls tight-binding method. In the presence of magnetic fields, Landau quantization leads to the formation of Landau subbands. For the bilayer nanoribbons, these subbands are partially dispersionless in k-space and are called quasi-Landau levels (QLLs).

Model of vortex states in hole-doped iron-pnictide superconductors.

Based on a phenomenological model with competing spin-density-wave (SDW) and extended s-wave superconductivity, the vortex states in Ba(1-x)K(x)Fe2As2 are investigated by solving Bogoliubov-de Gennes equations. Our result for the optimally doped compound without induced SDW is in qualitative agreement with recent scanning tunneling microscopy experiment. We also propose that the main effect of the SDW on the vortex states is to reduce the intensity of the in-gap peak in the local density of states and transfer the spectral weight to form additional peaks outside the gap.

Multiresolution phase extension of a trypsin inhibitor structure from 5 A to 2 A based on diffraction amplitudes alone.

For a specific structure of trypsin inhibitor, starting from a 5 A phase set, about 80% of the 2 A phases are correctly determined within an error of 18 degrees by applying a multiresolution refinement procedure. The refinement proceeds both in real and reciprocal spaces. In extending the structure from 5 to 2 A, the amplitudes of the reflections are the only requirements for this procedure.

Dielectric screening in a layered lattice electron gas.

We study the dielectric screening of an external point charge by a layered lattice electron gas in the random phase approximation. The screened potential at the neighboring sites of the point charge is found to be attractive under certain circumstances. We also investigate the impact of band structure on the screened potential.

Retrieving low- and medium-resolution structural features of macromolecules directly from the diffraction intensities--a real-space approach to the X-ray phase problem.

A simple mathematical algorithm is proposed to generate electron-density functions whose Fourier amplitudes match the diffraction intensities. The function is by construction everywhere positive. Using appropriate averaging procedures, the high-density regions of such functions could yield important structural information about macromolecular crystals.

Solving the Sayre equations for centrosymmetric structures with a genetic algorithm.

Sayre's equations give a set of relationships that exist among the structure factors of an equal-atom structure. In order to obtain the correct phases of the structure factors, a genetic algorithm is used to minimize a least-squares residual of Sayre's equations. In the genetic algorithm, a phase is treated as a gene and the whole set of phases is considered as a chromosome.