Can P3S and C3S monolayers be used as anode materials in metal-ion batteries? An answer from first-principles study.

With the urgent need for efficient energy storage devices, significant attention has been directed to researching and developing promising anode materials for metal-ion batteries. Through density functional study, we successfully predicted the electrochemical performance of P3S and C3S monolayers for the first time, which could be used in alkali metal (Li, Na, and K)-ion batteries. Our study examines the energetic, dynamic, and thermal stabilities of pristine monolayers. The electronic structures of the pristine nanosheets are wide-gap semiconductors. After single metalation on the monolayers, the composite systems become metallic. Charge-density difference (CDD) analysis indicates that charge transfer occurs from alkali metal atoms to the P3S and C3S monolayers, and Bader charge analysis quantifies the amount of charge transfer. We analyzed how readily a single adatom diffuses within the 2D structures. One example is the diffusion of K on C3S, which has a low barrier value of 0.06 eV and seems practically barrierless. Our predicted composite systems report considerable theoretical storage capacity (C); for example, hexalayer K-adsorbed C3S shows a storage capacity of 1182.79 mA h g-1. The estimated open-circuit voltage (OCV) values suggest that the C3S monolayer is a promising anode material for Li-, Na-, and K-ion batteries, whereas the P3S monolayer is suitable as a cathode material for Li-, Na-, and K-ion batteries.

Ground state charge transfer complex formation of some metalloporphyrins with aromatic solvents: Further theoretical and experimental investigations.

In our earlier work (Chem. Phys. Letts. 592 (2014) 149-154), a new broad band was observed in the near infrared region (700-900nm) of the steady state absorption spectra of some metalloporphyrins (zinc tetraphenylporphyrin, zinc octaethylporphyrin and magnesium octaethylporphyrin) in aromatic solvents (chlorobenzene, 1,2-dichlorobenzene, benzonitrile, benzene and toluene) at high concentrations (~10-4molL-1). The band was ascribed to be due to ground state charge transfer complexation between solute and solvent molecules. In the present work, density functional theory calculations are carried out to study the possibility of such ground state charge transfer complex formation between zinc tetraphenylporphyrin and four aromatic solvents viz., benzene, toluene, chlorobenzene and benzonitrile with 1:1 and 2:1 solvent-solute stoichiometries. Also, we determined the association constants for the ground state charge transfer complex formation of zinc tetraphenylporphyrin and zinc octaethylporphyrin with two aromatic solvents (benzene and benzonitrile) by Benesi-Hildebrand method.

Electronic and magnetic properties of pristine and transition metal doped ZnTe nanowires.

We have carried out density functional theory based calculations for understanding the structural, electronic and magnetic properties of pristine and transition metal (TM) doped ZnTe nanowires. Pristine ZnTe nanowires (NWs) turn out to be semiconducting in nature, with the band gap varying with the diameter of the NWs. In Mn-doped ZnTe NWs, the Mn atoms retain a magnetic moment of 5 µB each and couple anti-ferromagnetically. A half metallic ferromagnetic state, although energetically not favorable, is observed arising from a strong hybridization between the d-states of Mn atoms and p-states of Te atoms. Further studies of V- and Sc-doped ZnTe NWs reveal the systems to be anti-ferromagnetic.

Usefulness of p-wave duration to identify myocardial ischemia during exercise testing.

It is well recognized that ST-segment depression is due to subendocardial ischemia secondary to an increase in left ventricular end-diastolic pressure. The increase in left ventricular end-diastolic pressure is associated with increased left atrial pressure, resulting in left atrial wall distension that contributes to increasing P-wave duration (PWD). The objective of this study was to determine if PWD measured in leads II and V(5) during maximum exercise stress testing could be a reliable predictor of myocardial ischemia. Patients with suspected coronary disease underwent maximum exercise stress testing with myocardial perfusion imaging. PWD was measured using leads II and V(5) at rest and after exercise, with electrocardiographic complexes magnified 4 times (100 mm/s, 40 mm/mV). The change in PWD was calculated as Delta = PWD(recovery) - PWD(rest). DeltaPWD and ST-segment changes were related to the absence or presence of ischemia (localized reversible perfusion abnormalities) on myocardial perfusion imaging scans. DeltaPWD had sensitivity of 72%, specificity of 82%, negative predictive power (NPP) of 90%, and positive predictive power of 57%. ST-segment change had sensitivity of 34%, specificity of 87%, NPP of 80%, and positive predictive power of 47%. When DeltaPWD and ST changes were combined, sensitivity increased to 79% and NPP increased to 91%. In conclusion, DeltaPWD outperformed ST-segment changes in predicting myocardial ischemia on myocardial perfusion imaging scans. Furthermore, when DeltaPWD and ST-segment changes were combined, sensitivity and NPP were also significantly increased. In this study population, measuring DeltaPWD substantially increased the diagnostic value of maximum exercise stress testing.

Structural evolution due to Zn and Te adsorption on As-exposed Si(211): density functional calculation.

Systematic theoretical investigations are carried out under the density functional formalism in an effort to understand the initial structural evolution due to the adsorption of ZnTe on As-exposed Si(211). Our calculations indicate that after the adsorption of Zn and Te on the As-exposed Si(211), the stable atomic structure qualitatively follows the ideal atomic structure of Si(211) with alteration of various bond lengths. Since the basic symmetry of the Si(211) is preserved after the adsorption of ZnTe, the deposition of ZnTe on the As terminated Si(211) prior to the deposition of CdTe and HgCdTe is useful for obtaining an ultimate quality layer of HgCdTe on Si(211). Some of our results are compared with the available experimental results, and they are found to agree with each other qualitatively.

Propagation inhibition and localization of electromagnetic waves in two-dimensional random dielectric systems.

We rigorously calculate the propagation and scattering of electromagnetic waves by rectangular and random arrays of dielectric cylinders in a uniform medium. For regular arrays, the band structures are computed and complete bandgaps are discovered. For random arrays, the phenomenon of wave transmission and scattering is investigated and compared in two scenarios: (1) Wave propagating through the array of cylinders; this is the scenario which has been commonly considered in the literature, and (2) wave transmitted from a source located inside the ensemble. We show that within complete band gaps, results from the two scenarios are similar. Outside the gaps, however, there could be a distinct difference, that is, wave transmission can be inhibited by disorders in the first scenario, but such an inhibition may not prevail in the second scenario.

Theoretical analysis of the focusing of acoustic waves by two-dimensional sonic crystals.

Motivated by a recent experiment on acoustic lenses, we perform numerical calculations based on a multiple scattering technique to investigate the focusing of acoustic waves with sonic crystals formed by rigid cylinders in air. The focusing effects for crystals of various shapes are examined. The dependence of the focusing length on the filling factor is also studied. It is observed that both the shape and filling factor play a crucial role in controlling the focusing. Furthermore, the robustness of the focusing against disorders is studied. The results show that the sensitivity of the focusing behavior depends on the strength of positional disorders. The theoretical results compare favorably with the experimental observations, reported by Cervera, et al. [Phys. Rev. Lett. 88, 023902 (2002)].

Localization of classical waves in two-dimensional random media: a comparison between the analytic theory and exact numerical simulation.

The localization length of classical waves in two-dimensional random media is calculated exactly, and is compared with the theoretical prediction from the current analytic theory. Significant discrepancies are observed. It is also shown that as the frequency varies, critical changes in the localization behavior can occur. However, by a rescaling of parameters the two results tend to match each other for weak scattering. Possible reasons for the discrepancies are discussed.