Strain controlled switching effects in phosphorene and GeS.

By performing first principles calculations within the combined approach of density functional theory and nonequilibrium Green's function technique, we have designed some nanoelectronic devices to explore the ferroelastic switching of phosphorene and phosphorene analogs GeS. With the structure swapping along the zigzag direction and armchair direction, band gap transformed at different states due to their anisotropic phosphorene-like structure. From the initial state to the middle state, the band gap becomes progressively smaller, after that, it becomes wide. By analyzing transmission coefficients, it is found that the transport properties of phosphorene and GeS can be controlled by a uniaxial strain. The results also manifest that GeS has great potential to fabricate ferroic nonvolatile memory devices, because its relatively high on/off transmission coefficient ratio (∼1000) between the two stable ferroelastic states.

A new method to induce molecular low bias negative differential resistance with multi-peaks.

According to a first-principles study of the transport properties of two thiolated anthracene-9,10-diono molecules sandwiching ethyl, a new method to induce molecular low bias negative differential resistance with multi-peaks for strong n- or p-type molecules is proposed. The anthracene-9,10-diono molecule shows strong n-type characteristics when in contact with Au and Ag electrodes via a thiolate. The multiple negative differential resistance effect originated from the molecule-electrode couple is different between Ag and Au electrodes. Our investigations may promise potential for applications in molecular devices with low power dissipation and multifunction in the future.

The integrated spintronic functionalities of an individual high-spin state spin-crossover molecule between graphene nanoribbon electrodes.

The spin-polarized transport properties of a high-spin-state spin-crossover molecular junction with zigzag-edge graphene nanoribbon electrodes have been studied using density functional theory combined with the nonequilibrium Green's-function formalism. The molecular junction presents integrated spintronic functionalities such as negative differential resistance behavior, spin filter and the spin rectifying effect, associated with the giant magnetoresistance effect by tuning the external magnetic field. Furthermore, the transport properties are almost unaffected by the electrode temperature. The microscopic mechanism of these functionalities is discussed. These results represent a step toward multifunctional molecular spintronic devices on the level of the individual spin-crossover molecule.

Preserving the half-metallicity at the surfaces of rocksalt CaN and SrN and the interfaces of CaN/InN and SrN/GaP: a density functional study.

Recent theoretical studies indicate that metastable rocksalt CaN, SrN, and BaN exhibit half-metallic ferromagnetism (Volnianska and Boguslawski 2007 Phys. Rev. B 75 224418; Gao et al 2008 Phys. Lett. A 372 1512), and further experiments confirm the existence of self-assembled metastable CaN nanostructures (Liu et al 2008 Surf. Sci. 602 1844). We here use the first-principles method based on density functional theory to investigate the structural, electronic, and magnetic properties of the (111) surfaces of CaN and SrN and the interfaces of CaN/InN(111) and SrN/GaP(111). The surface stability from the calculated surface energy indicates that the N-terminated (111) surface is more stable than the Ca (Sr)-terminated (111) surface in the N-rich environment. For CaN and SrN, both anion- and cation-terminated (111) surfaces preserve the half-metallic characteristics of the bulk. Interfacial studies indicate that the half-metallicity of bulk CaN is retained in two of the four possible configurations of the CaN/InN(111) interface, while for the interface of SrN/GaP(111) only one interfacial configuration shows half-metallicity. Furthermore, we assess the interfacial adhesive strength for all the possible different configurations of the interfaces studied here by calculating the interface adhesion energies.

Field-controlled magnetic order with insulator-metal transitions in a periodic Anderson-like organic polymer.

The zero- and low-temperature behaviors of a quasi-one-dimensional organic polymer proposed as a symmetrical periodic Anderson-like chain model, in which the localized f orbitals hybridize with the conduction orbitals at even sites, are investigated by means of many-body Green's function theory. In the absence of magnetic field, the ground state of the system turns out to be ferrimagnetic. The temperature-induced phase diagrams have been explored, where the competition between the Hubbard repulsion U on the localized f orbital and the hybridization strength V makes an important impact on the transition temperature. In a magnetic field, it is found that a 1/3 magnetization plateau appears and two critical fields indicating the insulator-metal transitions at zero temperature emerge, which are closely related to the energy bands. Furthermore, the single-site entanglement entropy is a good indicator of quantum phase transitions. The temperature-field-induced phase diagram has also been attained, wherein the magnetization plateau state, the gapless phase and the spin polarized state are revealed. The temperature dependence of thermodynamic quantities such as the magnetization, susceptibility and specific heat are calculated to characterize the corresponding phases. It is also found that the up-spin and down-spin hole excitations are responsible for the thermodynamic properties.

First-principles study of strong rectification and negative differential resistance induced by charge distribution in single molecule.

For molecule-scale transport systems, a mechanism that the charge distribution of molecule under the various bias voltages can induce strong effect of rectification and negative differential resistance is proposed. Based on nonequilibrium Green's function combined with density functional theory, the proposal is testified by performing the first-principles calculations of transport characteristics of 2-(4(')-thiolate-butyl)-6-thiol-anthrecene molecule sandwiched in two gold electrodes. The strong effect of rectification and negative differential resistance is obtained. The rectification effect is as large as 16.

First-principles study of the ferroelectric and nonlinear optical properties of the LiNbO3-type ZnSnO3.

Electronic structures, spontaneous polarization, dynamical and nonlinear optical (NLO) properties of polar oxide ZnSnO(3) with LiNbO(3) (LN)-type structure have been investigated in the framework of density functional theory. By analyzing the Born effectives of LN-type ZnSnO(3), we find that Z* of Zn atoms show relatively large anomalous behavior. The spontaneous polarization is attributed to the large displacement of Zn atoms because of the mixed ionic-covalent character between the Zn-O bonds. The optical dielectric tensor is nearly the same; however the static dielectric tensor shows strongly anisotropy. Furthermore, the nonlinear optical properties are calculated by using 2n + 1 theorem applied to an electric-field dependent energy functional. The large dielectric constants and NLO susceptibilities indicate that the LN-type ZnSnO(3) would be a candidate as a high-performance dielectric and nonlinear optical material.

Spin-polarized transport and the electronic structure of the metallic antiferromagnet Fe(thiazole)(2)Cl(2).

We theoretically investigate the electron density of states, band structure, spin polarization, spin filter effect, and current-voltage curve of Fe(thiazole)(2)Cl(2) nanocrystal. The results show that Fe(thiazole)(2)Cl(2) is a metallic antiferromagnet with half-metallic ferromagnetic metastable state. The spin current for the ferromagnetic metastable state shows that Fe(thiazole)(2)Cl(2) has spin-filter property. Moreover, the current-voltage curve exhibits negative differential resistance, which is due to the narrow feature in the density of states of Fe(thiazole)(2)Cl(2). The perfect negative magnetoresistance is also obtained.

Spin-Peierls transition in low-dimensional quantum spin systems: a Green's function approach.

We study the spin-Peierls (SP) transition of one-dimensional chain polymeric complexes coupled to lattice by means of many-body Green's function theory. The chain effective elastic constant is an intrinsic factor that determines the order of SP transition. It is found that the SP transition temperature T(SP) and the susceptibility-maximum temperature T(max) are in agreement with the experimental results. When an external magnetic field is applied to the chain, it makes T(SP) and T(max) decrease, and drives the SP transition from the second order to the first order. Besides, we show that the two-site thermal entanglement entropy is a good indicator of SP transition. Further considering the effect of interchain coupling on SP transition, with weak coupling of double-chain, the theoretical values are closer to the experimental results. We also calculate the density of states and spectral functions, which show that the energy gap vanishes at a critical temperature lower than T(SP), indicating a gapless SP phase lies in the gapped dimerized phase. The interchain coupling can drive the SP transition from the second order to the first order, while the SP dimerization may collapse for large interchain couplings.

First-principles calculations: half-metallic Au-V(Cr) quantum wires as spin filters.

The half-metallic behavior of Au-V(Cr) quantum wires adsorbed on an armchair (5, 5) boron nitride nanotube is obtained by performing spin-polarized density functional calculations. The density of states shows a metallic property at the Fermi level for the majority spin channel and a semiconductor gap in the minority spin channel. The half-metallic behavior of the quantum wire/nanotube complex originates from the half-metallic behavior of the free-standing Au-V(Cr) quantum wires. The calculations of spin-polarized transport indicate that such a one-dimensional half-metallic magnet can be used as a spin filter.

First-principles studies of the atomic reconstructions of CdSe (001) and (111) surfaces.

We have performed the first-principles total-energy calculations to investigate (2 × 1), (1 × 2), (2 × 2), (4 × 2) and (2 × 4) reconstructions of Cd- and Se-terminated CdSe(001) and (111) surfaces as a function of the surface stoichiometry and the Cd chemical potential. We find that there exist Cd dimers on the (001) surface and Se tetramers on the (111) surface. Comparing surface formation energies as a function of the Cd chemical potential µ(Cd), we find the Cd-vacancy and Se-vacancy (2 × 2) structures to be energetically favorable for the Cd-terminated (001) surface at high µ(Cd) and Se-terminated (001) surface at low µ(Cd), respectively. In contrast, an Se-tetramer (2 × 4) structure is more favorable than the vacancy structure for the Se-terminated CdSe(111) surface almost in the whole region of allowed µ(Cd).

Bulk and surface sp half-metallic ferromagnetism in alkali metal pnictides with rocksalt structure: a first-principles calculation.

Recently, sp half-metallic ferromagnetism in alkali metal/alkaline earth pnictides (I/II-V) with zinc blende structure was predicted by first-principles calculations (Sieberer et al 2006 Phys. Rev. B 73 024404). To search for half-metallic ferromagnets with a more stable structure in alkali metal pnictides MX (M  = Li, Na, K; X =  N, P, As), we apply here first-principles all-electron and pseudopotential-method-based density functional theory to investigate the electronic and magnetic properties of these compounds with rocksalt structure. Five rocksalt compounds are found to be half-metallic ferromagnets with a magnetic moment of 2.00 µ(B)/f.u., and they are more stable energetically than the ones with zinc blende structure, which makes them more promising candidates for the possible growth of half-metallic films or ultrathin films on suitable semiconductor substrates. Furthermore, we show that both lithium- and nitrogen-terminated (111) surfaces of rocksalt lithium nitride retain the bulk half-metallic characteristic, and the surface atomic magnetic moments are enhanced compared to the bulk values.

Search for new half-metallic ferromagnets in zinc blende CaSi and CaGe by first-principles calculations.

We present an investigation on the electronic structure and ferromagnetism for the hypothetical zinc blende (ZB) CaSi and CaGe by using first-principles full-potential linearized augmented plane-wave (FP-LAPW) calculations. It is found that ZB CaSi and CaGe are half-metallic (HM) ferromagnets without any transition-metal component; they have a magnetic moment of 2.000 µ(B) per formula unit. Analysis of the density of states and magnetic moment indicates that their magnetism mainly originates from the spin polarization of anion p states and the hybridization between the anion p states and the Ca d states. We also find that the half-metallicity can be maintained even when the lattice constant of ZB CaSi and CaGe is compressed up to 8% and 5%, respectively. The absence of the transition-metal atoms makes ZB CaSi and CaGe attractive not only as materials for possible spintronics devices but also as model objects for the study of new mechanisms of the formation of half-metallic ferromagnetism in s-p electron systems.

Spin distribution and hydrogen-bond effect in ferromagnetic alpha-phase crystal of 2-(2',5'-dihydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide.

The ferromagnetic phenyl nitronyl nitroxide derivate alpha-phase 2-(2('),5(')-dihydroxyphenyl)- 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide has been studied by the electronic structure calculation based on the density functional theory. The result shows that the spin delocalization due to hyperconjugation effect plays an important role in the spin distribution and ferromagnetic coupling of the crystal.

Two ferromagnetic azido-bridged copper(ll) complexes studied by first-principle electronic-structure calculation.

The electronic structures of two ferromagnetic polynuclear copper(II) complexes, derived from end-to-end azido ligand and tridentate (NNN donor) Schiff base ligand, have been studied using the full-potential linearized augmented plane-wave method based on the density-functional theory. They are [Cu(L1)(micro-1,3-N3)]n(ClO4)n (1) and [Cu(L2)(micro-1,3-N3)]n(ClO4)n (2). The result shows that the spin populations in these two complexes are mainly distributed on the equatorial planes of a square pyramidal that surround the copper(II) ions. There are large and positive spin populations on copper(II) ions, small and positive spin populations on the three nitrogen atoms of tridentate Schiff base ligand, and the two terminal nitrogen atoms of asymmetrical end-to-end azido ligand, while weak and negative spin populations on the central nitrogen atoms of asymmetrical end-to-end azido ligand. Ferromagnetic coupling through the asymmetrical azido ligand in these two complexes has been mainly attributed to the spin delocalization, also with weak spin-polarization effect.

Examination of the DNA methylation properties in nontumorigenic and tumorigenic breast epithelial cell lines.

Molecular changes in the progressive state of tumorigenesis often include altered patterns of DNA methylation. Utilizing a series of breast epithelial cell lines, the overall 5-methylcytosine content in genomic DNA demonstrated an overall decrease when comparing two malignant cell lines (MCF-7 and T47D) with a mortal cell line (MCF 1 2M) and several derivative cell lines of the immortalized MCF10 cultures (MCF10A,-2A, -5A, A1neoT2, and 139B6). Further investigation on the methylation status of these cells lines indicated no difference in DNA methyltransferase activity, both at a protein and mRNA levels, in the nontumorigenic cell lines examined while activity was 3-10 fold higher in the tumorigenic lines (MCF7, T47D, SkBr3, MB-MDA-231, -468). Examination of the CpG island in the 5' promoter region of the estrogen receptor gene indicates that this region is unmethylated in the mortal and immortal nontumorigenic lines as well as the tumorigenic lines examined, with the exception of the estrogen receptor negative breast cell line MB-MDA-468 which appears to be partially methylated at this site. These results indicate methylation of this CpG island does not account for the inactivation of the estrogen receptor gene in immortalized nontumorigenic breast cells, suggesting another mechanism of transcriptional inactivation of ER in this environment.

[Study on the synthesis and antibacterial activity of Mannich bases containing alpha, beta-unsaturated ketone].

Twelve Mannich bases containing alpha, beta-unsaturated ketone were synthesized and characterized by elemental analysis, IR, 1HNMR, UV and MS spectra. All of the title compounds were unreported in the literature, some of these compounds showed marked antibacterial activity.

A universal method for the mutational analysis of K-ras and p53 gene in non-small-cell lung cancer using formalin-fixed paraffin-embedded tissue.

The p53 tumor suppressor gene has been found to be altered in almost all human solid tumors, whereas K-ras gene mutations have been observed in a limited number of human cancers (adenocarcinoma of colon, pancreas, and lung). Studies of mutational inactivation for both genes in the same patient's sample on non-small-cell lung cancer have been limited. In an effort to perform such an analysis, we developed and compared methods (for the mutational detection of p53 and K-ras gene) that represent a modified and universal protocol, in terms of DNA extraction, polymerase chain reaction (PCR) amplification, and nonradioisotopic PCR-single-strand conformation polymorphism (PCR-SSCP) analysis, which is readily applicable to either formalin-fixed, paraffin-embedded tissues or frozen tumor specimens. We applied this method to the evaluation of p53 (exons 5-8) and K-ras (codon 12 and 13) gene mutations in 55 cases of non-small-cell lung cancer. The mutational status in the p53 gene was evaluated by radioisotopic PCR-SSCP and compared with PCR-SSCP utilizing our standardized nonradioisotopic detection system using a single 6-microns tissue section. The mutational patterns observed by PCR-SSCP were subsequently confirmed by PCR-DNA sequencing. The mutational status in the K-ras gene was similarly evaluated by PCR-SSCP, and the specific mutation was confirmed by Southern slot-blot hybridization using 32P-labeled sequence-specific oligonucleotide probes for codons 12 and 13. Mutational changes in K-ras (codon 12) were found in 10 of 55 (18%) of non-small-cell lung cancers. Whereas adenocarcinoma showed K-ras mutation in 33% of the cases at codon 12, only one mutation was found at codon 13. As expected, squamous cell carcinoma samples (25 cases) did not show K-ras mutations. Mutations at exons 5-8 of the p53 gene were documented in 19 of 55 (34.5%) cases. Ten of the 19 mutations were single nucleotide point mutations, leading to amino acid substitution. Six showed insertional mutation, and three showed deletion mutations. Only three samples showed mutations of both K-ras and p53 genes. We conclude that although K-ras and p53 gene mutations are frequent in non-small-cell lung cancer, mutations of both genes in the same patient's samples are not common. We also conclude that this universal nonradioisotopic method is superior to other similar methods and is readily applicable to the rapid screening of large numbers of formalin-fixed, paraffin-embedded or frozen samples for the mutational analysis of multiple genes.

BCR/ABL fusion located on chromosome 9 in chronic myeloid leukemia with a masked Ph chromosome.

A reciprocal translocation, t(10;22)(q22;q11), resulting in a masked Ph chromosome was identified in a patient diagnosed with chronic myeloid leukemia (CML). Both homologs of chromosome 9 were of the normal pattern. Two signals for the ABL probe, both of them hybridized to chromosome 9, were demonstrated via fluorescence in situ hybridization (FISH). Furthermore, cohybridization with two differently labeled BCR/ABL translocation DNA probes indicated a BCR/ABL fusion apparently located on 9q34. Molecular studies revealed a rearrangement of the BCR region and expression of a chimeric BCR/ABL mRNA of CML configuration. These findings indicate that the BCR/ABL fusion resulted from an unusual relocation of the BCR gene from its normal position on 22q11 to 9q34 adjacent to the ABL gene.