We have investigated, by means of ab initio calculations, the electronic and magnetic structures of zigzag edge phosphorene nanoribbons (ZPNRs) with various widths. The stable magnetic state was found in pristine ZPNRs by allowing the systems to be spin-polarized. The ground state of pristine ZPNRs prefers ferromagnetic order in the same edge but antiferromagnetic order between two opposite edges. The magnetism arises from the dangling bond states as well as edge localized π-orbital states. The presence of a dangling bond is crucial to the formation of the magnetism of ZPNRs. The hydrogenated ZPNRs get nonmagnetic semiconductors with a direct band gap. While, the O-saturated ZPNRs show magnetic ground states due to the weak P-O bond in the ribbon plane between the pz-orbitals of the edge O and P atoms.
The control of thermal expansion of solid compounds is intriguing but remains challenging. The effect of guests on the thermal expansion of open-framework structures was investigated. Notably, the presence of guest ions (K ) and molecules (H O) can substantially switch thermal expansion of YFe(CN) from negative (α =-33.67×10 K ) to positive (α =+42.72×10 K )-a range that covers the thermal expansion of most inorganic compounds. The mechanism of such substantial thermal expansion switching is revealed by joint studies with synchrotron X-ray diffraction, X-ray absorption fine structure, neutron powder diffraction, and density functional theory calculations. The presence of guest ions or molecules plays a critical damping effect on transverse vibrations, thus inhibiting negative thermal expansion. An effective method is demonstrated to control the thermal expansion in open-framework materials by adjusting the presence of guests.
The geometric structure and electronic properties of Bi2X2Y (X, Y = O, S, Se, and Te) ternary compound have been studied by means of first-principles density functional theory.
Negative thermal expansion (NTE) is an abnormal physical behavior that has promising applications for high precision thermal control. Since Prussian blue analogues have the two central linking atoms of -C≡N-, they have large structure exibility and are suitable to explore new NTE materials. However, understanding the nature of structure exibility from the point of view of chemical bonding is important and urgent. Here, we adopt for the rst time rst-principles calculations to predict that the cubic TiCo(CN) 6 and ScCo(CN) 6 have NTE behavior. The calculated results for M in MCo(CN) 6 (M = Fe, Ti and Co) indicated that the Sc-N bond is the strongest, but with the weakest direction dependence among the M-N bonds in the three systems. The lattice dynamics calculations results revealed that the low-frequency phonon vibration modes for NTE in MCo(CN) 6 have much stronger relationship with the M-N bond feature. The present work reveals the important role of the related bond in the NTE open-framework materials.
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