scholarly journals Structure variations within RSi2 and R 2 TSi3 silicides. Part I. Structure overview

2020 ◽  
Vol 76 (2) ◽  
pp. 177-200 ◽  
Author(s):  
M. Nentwich ◽  
M. Zschornak ◽  
M. Sonntag ◽  
R. Gumeniuk ◽  
S. Gemming ◽  
...  
Keyword(s):  
Density Functional ◽  
Alkaline Earth ◽  
Structural Parameters ◽  
Earth Metal ◽  
Structure Type ◽  
Underlying Structure ◽  
Alkaline Earth Metal ◽  
Formula Unit ◽  
Functional Theory ◽  
Subgroup Scheme

Here, structural parameters of various structure reports on RSi2 and R 2 TSi3 compounds [where R is an alkaline earth metal, a rare earth metal (i.e. an element of the Sc group or a lathanide), or an actinide and T is a transition metal] are summarized. The parameters comprising composition, lattice parameters a and c, ratio c/a, formula unit per unit cell and structure type are tabulated. The relationships between the underlying structure types are presented within a group–subgroup scheme (Bärnighausen diagram). Additionally, unexpectedly missing compounds within the R 2 TSi3 compounds were examined with density functional theory and compounds that are promising candidates for synthesis are listed. Furthermore, a correlation was detected between the orthorhombic AlB2-like lattices of, for example, Ca2AgSi3 and the divalence of R and the monovalence of T. Finally, a potential tetragonal structure with ordered Si/T sites is proposed.

Structure, stability and intramolecular interaction of M(N5)2(M = Mg, Ca, Sr and Ba) : a theoretical study

RSC Advances ◽  
2015 ◽  
Vol 5 (28) ◽  
pp. 21823-21830 ◽  
Author(s):  
Xueli Zhang ◽  
Junqing Yang ◽  
Ming Lu ◽  
Xuedong Gong
Keyword(s):  
Energetic Materials ◽  
Density Functional ◽  
Alkaline Earth ◽  
Theoretical Study ◽  
Intramolecular Interaction ◽  
Earth Metal ◽  
Structure Stability ◽  
Alkaline Earth Metal ◽  
Functional Theory ◽  
The Density Functional Theory

The potential energetic materials, alkaline earth metal complexes of the pentazole anion (M(N5)2, M = Mg2+, Ca2+, Sr2+and Ba2+), were studied using the density functional theory.

Activation of Cellulose with Alkaline Earth Metals

2021 ◽  
Author(s):  
Gregory Facas ◽  
Vineet Maliekkal ◽  
Matthew Neurock ◽  
Paul Dauenhauer
Keyword(s):  
Density Functional ◽  
Alkaline Earth ◽  
Earth Metal ◽  
Density Functional Theory Calculations ◽  
Alkaline Earth Metal ◽  
Magnesium Ions ◽  
Functional Theory ◽  
Naturally Occurring ◽  
Alkaline Earth Metal Ions ◽  
And Control

Alkaline earth metal ions accelerate the breaking of cellulose bonds and control the distribution of products in the pyrolysis of lignocellulose to biofuels and chemicals. Here, the activation of cellulose via magnesium ions was measured over a range of temperatures from 370 to 430 ⁰C for 20 to 2000 milliseconds and compared with activation of cellulose via calcium, another naturally-occurring alkaline earth metal in lignocellulose materials. The experimental approach of pulse heated analysis of solid/surface reactions (PHASR) showed that magnesium significantly catalyzes cellulose activation with a second order rate dependence on the catalyst concentration. An experimental barrier of 45.6 ± 2.1 kcal mol-1 and a pre-factor of 1.18 x 1016 (mmol Mg2+ / g CD)-2 * s-1 was obtained for the activation of α-cyclodextrin (CD), a cellulose surrogate, for catalyst concentrations of 0.1 to 0.5 mmol Mg+2 per gram of CD. First principles density functional theory calculations showed that magnesium ions play a dual role in catalyzing the reaction by breaking the hydrogen bonds with hydroxymethyl groups and destabilizing the reacting cellulose chain, thus making it more active. The calculated barrier of 47 kcal mol-1 is in agreement with the experimentally measured barriers and similar to that for calcium ion catalysts (~50 kcal mol-1).

Regulating the NLO response of anthraquinone-supported thiourea-linked crown ether macrocycle by introducing metal cations: A DFT study

2020 ◽  
Vol 19 (05) ◽  
pp. 2050017
Author(s):  
Yao Yao ◽  
Jin-Ting Ye ◽  
Xiang Li ◽  
Yuan Zhang ◽  
Si-Nan Zhu ◽  
...  
Keyword(s):  
Density Functional ◽  
Alkaline Earth ◽  
Earth Metal ◽  
Metal Cations ◽  
Alkaline Earth Metal ◽  
Functional Theory ◽  
Nlo Properties ◽  
Thiourea Group ◽  
Nlo Materials ◽  
The Subject

Recently, an anthraquinone-supported thiourea group linking a 1-aza-18-crown-6 macrocycle L has been the subject of extensive attention due to the perfect affinity towards metal cations. This work systematically researched the effects of different metal cations ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]) on the second-order nonlinear optical (NLO) properties of macrocycle L by density functional theory (DFT). DFT calculations revealed that the values of first hyperpolarizabilities ([Formula: see text] decrease significantly when alkaline earth metal cations ([Formula: see text] and [Formula: see text]) were injected into macrocycle L due to the smaller charge transfer (CT) transition and larger transition energy. Conversely, the variations of [Formula: see text] values in alkali metal cations ([Formula: see text] and [Formula: see text] and transition metal cations ([Formula: see text] and [Formula: see text]) derivatives are not obvious compared to the [Formula: see text] value of macrocycle L. Therefore, the NLO properties of macrocycle can be effectively regulated by alkaline earth metal cations. Furthermore, we found that the [Formula: see text] value of anion-controlled complex Na(L)(ClO4) is larger than that of L*Na+ complex because the anion [Formula: see text] improves the planarity of anthraquinone-supported thiourea group leading to the enhancement of the CT ability. In addition, the influence of frequency-dependent on the first hyperpolarizabilities is weak for the current systems. Hence, we look forward to the conception of this work will offer a fundamental guideline and reference for further research for novel NLO materials.

A first-principles study on alkaline earth metal atom substituted monolayer boron nitride (BN)

2017 ◽  
Vol 5 (32) ◽  
pp. 8112-8127 ◽  
Author(s):  
Rafique Muhammad ◽  
Yong Shuai ◽  
He-Ping Tan
Keyword(s):  
Density Functional Theory ◽  
Optical Properties ◽  
Boron Nitride ◽  
Dft Calculations ◽  
First Principles ◽  
Density Functional ◽  
Alkaline Earth ◽  
Earth Metal ◽  
Alkaline Earth Metal ◽  
Functional Theory

This paper presents first-principles density functional theory (DFT) calculations for the structural, electronic, magnetic and optical properties of monolayer boron nitride (BN) doped with different alkaline earth metal (AEM) atoms.

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