scholarly journals Exploring charge density analysis in crystals at high pressure: data collection, data analysis and advanced modelling

Author(s):  
Nicola Casati ◽  
Alessandro Genoni ◽  
Benjamin Meyer ◽  
Anna Krawczuk ◽  
Piero Macchi

The possibility to determine electron-density distribution in crystals has been an enormous breakthrough, stimulated by a favourable combination of equipment for X-ray and neutron diffraction at low temperature, by the development of simplified, though accurate, electron-density models refined from the experimental data and by the progress in charge density analysis often in combination with theoretical work. Many years after the first successful charge density determination and analysis, scientists face new challenges, for example: (i) determination of the finer details of the electron-density distribution in the atomic cores, (ii) simultaneous refinement of electron charge and spin density or (iii) measuring crystals under perturbation. In this context, the possibility of obtaining experimental charge density at high pressure has recently been demonstrated [Casatiet al.(2016).Nat. Commun.7, 10901]. This paper reports on the necessities and pitfalls of this new challenge, focusing on the speciessyn-1,6:8,13-biscarbonyl[14]annulene. The experimental requirements, the expected data quality and data corrections are discussed in detail, including warnings about possible shortcomings. At the same time, new modelling techniques are proposed, which could enable specific information to be extracted, from the limited and less accurate observations, like the degree of localization of double bonds, which is fundamental to the scientific case under examination.

2001 ◽  
Vol 70 (4) ◽  
pp. 1162-1163 ◽  
Author(s):  
Takahisa Shobu ◽  
Yukio Noda ◽  
Kazuaki Iwasa ◽  
Abdul Hannan ◽  
Masahumi Kohgi ◽  
...  

2014 ◽  
Vol 68 (6) ◽  
Author(s):  
Subramanian Saravanakumar ◽  
Ramachandran Saravanan ◽  
Subramanian Sasikumar

AbstractPhase pure nano nickel oxide was synthesized by the chemical precipitation method and sintered at 200°C, 400°C and 600°C, respectively, to study the effect of sintering on the charge distribution and magnetism. The samples were analyzed by X-ray diffraction for electron density distribution studies, vibrating sample magnetometry for magnetic behavior and by UV-VIS spectrophotometry for optical characteristics. Rearrangement of charge density distribution with respect to sintering temperature was analyzed through the maximum entropy method employed using powder X-ray diffraction data. The observed magnetic transition with respect to the temperature/size effect was analyzed and correlated with electron density distribution studies.


2006 ◽  
Vol 987 ◽  
Author(s):  
Takamitsu Yamanaka ◽  
Taku Okada ◽  
Yuki Nakamoto ◽  
Kenji Ohi

AbstractSingle-crystal structure analysis of KNbO3 has been executed under high pressure through diamond anvil cell installed in the four-circle diffractometer using synchrotron radiation at Photon Factory, KEK in order to clarify the dielectric property. KNbO3 has three structural transitions with increasing pressure at ambient temperature: from orthorhombic structure with the space group Cm2m (Amm2) to tetragonal structure (P4mm) at about 7.0 GPa, to cubic structure (Pm3m) at about 10.0 GPa. The highest-pressure cubic phase is paraelectric, and the other two phases are ferroelectric. The dielectric changes in KNbO3 are clarified by the successive pressure-change of the electron density distribution observed by maximum entropy method (MEM) using high-pressure diffraction data. The MEM electron density maps suggest that the tetragonal phase designates the largest polarization among three polymorphs. The maps also indicate that the localization of the valence electron around the cation position is more enhanced under higher pressure.


2015 ◽  
Vol 1084 ◽  
pp. 241-245 ◽  
Author(s):  
Oksana V. Lopatina ◽  
Leonid A. Svyatkin ◽  
Yury M. Koroteev ◽  
Ivan P. Chernov

Ab initio calculations of electronic structures of Zr–H and Zr–He systems have been done. The influence of hydrogen or helium impurities on the electron density distribution of the host metal has been considered. Extremely inhomogeneous redistribution of the metal valence charge density within the first coordination sphere of the impurity was found. The character of the observed anisotropy depends on the impurity type.


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