Predicting novel atomic structure of the lowest-energy Fe_(n)P_(13-n)(n=0-13)clusters:A new parameter for characterizing chemical stability

A series of novel atomic structure of lowest-energy Fe_(n)P_(13-n)(n=0-13)clusters via density functional theory(DFT)calculations and an unbiased structure search using Crystal structure AnaLYsis by Particle Swarm Optimization(CALYPSO)code.Our research results show that the global minimum geometry structure of neutral Fe_(13-n)P_(n)(n=0-6)clusters tend to form cage structures but the lowest-energy Fe_(13-n)P_(n)(n=7-13)clusters are gradually evolution from a cage structure to a chain shape geometric structure.Their geometric structure should responsible for the raise of binding energy from Fe_7P_(6)to P_(13)clusters rather than chemical components.This is completely different from a linear relation of the binding energy with chemical components in our previous research for Cu_(n)Zr_(13-n)(n=3-10)clusters(J.Mol.Liq.343117603(2021)).Hence,in order to characterize the global chemical stability of target cluster,we proposed a new parameter(jyq=η/χ)that the chemical hardness of isolated cluster is used to be divided by its electronegativity.One of the biggest advantages of this parameter is successful coupling the ability of a resistance to redistribution of electrons and the ability to attract electrons from other system(such as atom,molecular or metallic clusters).Moreover,it is found that the P_(13)cluster shows typical insulator characteristics but the Fe_(12)P_(1)shows typical conductor characteristics,which phenomena can be attributed to the remarkable delocalized and localized electrons in Fe_(12)P_(1)and P_(13),respectively.In terms of nearly-free-electron mode,we also found that the number of electrons on Femi level(N(E_F))are obviously tended to toward a lower value when Fe was replaced gradually with P from Fe_(13)to P_(13),and a non-magnetic can be observed in Fe_(13),Fe_(2)P_(11),Fe_(1)P_(12),and P_(13)that mainly because their perfect symmetrical between spin-up and spin-down of density of states of electrons.

Suppression of fluctuation on the angle of arrival for freespace optical communication

In order to increase the coupling efficiency and suppress the random angular jitter induced by atmosphere turbulent, the fine tracking system with fast steering mirror （FSM） is demonstrated. The field experiment results of free-space optical communication link across 16 km show that when there is no tracking, the range of the x-axis coordinates＇ fluctuation achieves 46 pixels, corresponding to the incident angle of 73.6 μrad, and its mean square deviation is 6.5 pixels, corre- sponding to the incident angle of 10.4/.trad. When there is tracking, the range of fiuctuation is suppressed to 10 pixels and 16 ktrad, and the mean square deviation reduces to 1.5 pixels and 2.6 brad for the spot＇s centroid and the incident angle, respectively. Significantly, the coupling efficiency increases by 6 times, and the fluctuation of received light power decreases obviously.

Optical Properties and Thermal Stability of a Cubic Sulfate Rb_(2)Ca_(2)(SO_(4))_(3)

In this paper,a non-centrosymmetric compound of Rb_(2)Ca_(2)(SO_(4))_(3)has been synthesized by a high temperature solid-state reaction and high temperature melting method.Single-crystal X-ray diffraction analysis shows that Rb_(2)Ca_(2)(SO_(4))_(3)crystallizes in the cubic space group of P2_(1)3,and its cell parameters are a=b=c=10.5569(6)Å,Z=4 and V=1176.55(12)Å^(3),respectively.In the crystal structure,SO4 tetrahedra and CaO6 octahedra are connected with each other by a corner-sharing mode to construct the three-dimensional framework of Rb_(2)Ca_(2)(SO_(4))_(3).Optical measurements show that the title compound has a short ultraviolet absorption edge and a moderate second-harmonic generation response.The optical origin is illustrated by the electron band structure calculation.In addition,thermal stability is also studied by virtue of differential thermal/thermogravimetric analysis and powder XRD technique.