3,108 research outputs found
How Important is Metal-Carbon Back-Bonding for the Stability of Fullerene-Transition Metal Complexes? Role of Cage Sizes, Encapsulated Ions and Metal Ligands
A density functional study of {Ī·2-(X@Cn)}ML2 complexes with various cage sizes (C60, C70, C76, C84, C90, C96), encapsulated ions (X = Fā, 0, Li+) and metal fragments (M = Pt, Pd) is performed, using M06/LANL2DZ levels of theory. The importance of Ļ back-bonding to the thermodynamic stability of fullerene-transition metal complexes ({Ī·2-(X@Cn)}ML2) and the effect of encapsulated ions, metal fragments and cage sizes on the Ļ back-bonding are determined in this study. The theoretical computations suggest that Ļ back-bonding plays an essential role in the formation of fullerene-transition metal complexes. The theoretical evidence also suggests that there is no linear correlation between cage sizes and Ļ back-bonding, but the encapsulated Li+ ion enhances Ļ back-bonding and Fā ion results in its deterioration. These computations also show that a platinum center produces stronger Ļ back-bonding than a palladium center. It is hoped that the conclusions that are provided by this study can be used in the design, synthesis and growth of novel fullerene-transition complexes
The Triply Bonded Alā°Sb Molecules: A Theoretical Prediction
The effect of substitution on the potential energy surfaces of RAlā°SbR (RĀ =Ā F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2, Tbt, and Ar*) is investigated using density functional theories (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZĀ +Ā dp). The theoretical results demonstrated that all the triply bonded RAlā°SbR compounds with small substituents are unstable and can spontaneously rearrange to other doubly bonded isomers. That is, the smaller groups, such as RĀ =Ā F, OH, H, CH3 and SiH3, neither kinetically nor thermodynamically stabilize the triply bonded RAlā°SbR compounds. However, the triply bonded RāAlā°SbRĀ“ molecules that feature bulkier substituents (RĀ“Ā =Ā SiMe(SitBu3)2, SiiPrDis2, Tbt, and Ar*) are found to possess the global minimum on the singlet potential energy surface and are both kinetically and thermodynamically stable. In particular, the bonding characters of the RāAlā°SbRĀ“ species agree well with the valence-electron bonding model (model) as well as several theoretical analyses (the natural bond orbital, the natural resonance theory, and the charge decomposition analysis). That is to say, RāAlā°SbRĀ“ molecules that feature groups are regarded as Rā²āAl
SbāRā². Their theoretical evidence shows that both the electronic and the steric effects of bulkier substituent groups play a decisive role in making triply bonded Rā²Alā°SbRā² species synthetically accessible and isolable in a stable form
Simulations Suggest Possible Triply Bonded Phosphorusā”E13 Molecules (E13Ā =Ā B, Al, Ga, In, and Tl)
The effect of substitution on the potential energy surfaces of RE13Ā ā°Ā PR (E13Ā =Ā B, Al, Ga, In, Tl; RĀ =Ā F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2, Tbt, and Ar* is studied using density functional theory (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP and B3LYP/LANL2DZĀ +Ā dp). The theoretical results demonstrate that all triply bonded RE13Ā ā°Ā PR compounds with small substituents are unstable and spontaneously rearrange to other doubly bonded isomers. That is, the smaller groups, such as RĀ ćĀ F, OH, H, CH3 and SiH3, neither kinetically nor thermodynamically stabilize the triply bonded RE13Ā ā°Ā PR compounds. However, the triply bonded RāE13ā°PRĀ“ molecules, possessing bulkier substituents (RĀ“Ā =Ā SiMe(SitBu3)2, SiiPrDis2, Tbt and Ar*), are found to have a global minimum on the singlet potential energy surface. In particular, the bonding character of the RāE13ā°PRĀ“ species is well defined by the valence-electron bonding model (model [II]). That is to say, RāE13ā°PRĀ“ molecules that feature groups are regarded as Rā²-E13P-Rā². The theoretical evidence shows that both the electronic and the steric effects of bulkier substituent groups play a prominent role in rendering triply bonded Rā²E13ā°PRā² species synthetically accessible and isolable in a stable form
The Effect of Substituent on Molecules That Contain a Triple Bond Between Arsenic and Group 13 Elements: Theoretical Designs and Characterizations
The effect of substitution on the potential energy surfaces of RE13ā”AsR (E13 = group 13 elements; R = F, OH, H, CH3, and SiH3) is determined using density functional theory (M06ā2X/Def2āTZVP, B3PW91/Def2āTZVP, and B3LYP/LANL2DZ+dp). The computational studies demonstrate that all triply bonded RE13ā”AsR species prefer to adopt a bent geometry that is consistent with the valence electron model. The theoretical studies also demonstrate that RE13ā”AsR molecules with smaller substituents are kinetically unstable, with respect to the intramolecular rearrangements. However, triply bonded Rā²E13ā”AsRā² species with bulkier substituents (Rā² = SiMe(SitBu3)2, SiiPrDis2, and NHC) are found to occupy the lowest minimum on the singlet potential energy surface, and they are both kinetically and thermodynamically stable. That is to say, the electronic and steric effects of bulky substituents play an important role in making molecules that feature an E13ā”As triple bond as viable synthetic target
An Efficient Fitness Function in Genetic Algorithm Classifier for Landuse Recognition on Satellite Images
Genetic algorithm (GA) is designed to search the optimal solution via weeding out the worse gene strings based on a fitness function. GA had demonstrated effectiveness in solving the problems of unsupervised image classification, one of the optimization problems in a large domain. Many indices or hybrid algorithms as a fitness function in a GA classifier are built to improve the classification accuracy. This paper proposes a new index, DBFCMI, by integrating two common indices, DBI and FCMI, in a GA classifier to improve the accuracy and robustness of classification. For the purpose of testing and verifying DBFCMI, well-known indices such as DBI, FCMI, and PASI are employed as well for comparison. A SPOT-5 satellite image in a partial watershed of Shihmen reservoir is adopted as the examined material for landuse classification. As a result, DBFCMI acquires higher overall accuracy and robustness than the rest indices in unsupervised classification
Triple Bonds between Bismuth and Group 13 Elements: Theoretical Designs and Characterization
The effect of substitution on the potential energy surfaces of RE13ā”BiR (E13 = B, Al, Ga, In, and Tl; R = F, OH, H, CH3, SiH3, Tbt, Ar*, SiMe(SitBu3)2, and SiiPrDis2) is investigated using density functional theories (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp). The theoretical results suggest that all of the triply bonded RE13ā”BiR molecules prefer to adopt a bent geometry (i.e., ā RE13Bi ā 180Ā° and ā E13BiR ā 90Ā°), which agrees well with the bonding model (model (B)). It is also demonstrated that the smaller groups, such as R = F, OH, H, CH3, and SiH3, neither kinetically nor thermodynamically stabilize the triply bonded RE13ā”BiR compounds, except for the case of H3SiBā”BiSiH3. Nevertheless, the triply bonded RŹ¹E13ā”BiRŹ¹ molecules that feature bulkier substituents (RŹ¹ = Tbt, Ar*, SiMe(SitBu3)2, and SiiPrDis2) are found to have the global minimum on the singlet potential energy surface and are both kinetically and thermodynamically stable. In other words, both the electronic and the steric effects of bulkier substituent groups play an important role in making triply bonded RE13ā”BiR (Group 13āGroup 15) species synthetically accessible and isolable in a stable form
Number Sense Performance of Gifted and General Fourth Graders in Taiwan
The study was designed to enable researchers the opportunities to investigate the number sense performance and methods used by both the gifted and general students. A mixed-method design was used, and 48 gifted students and 95 general students in fourth grade from two elementary schools in Southern Taiwan were selected. The sample was chosen using a convenience sampling method. Nine students in each group were randomly selected and interviewed. The results showed that the gifted students performed significantly higher than the general students on the whole test and in each component of number sense. The contributions of this study based on the findings are discussed
Optical Properties and Enhanced Photothermal Conversion Efficiency of SiO2/A-Dlc Selective Absorber Films for A Solar Energy Collector Fabricated by Unbalance Sputter
AbstractSolar energy could become the most attractive alternative energy source. In this study we test an attractive new candidate material for solar energy collectors. It can be found that the higher the gas pressure is, the higher the sp2/sp3 area ratio, the greater the sputtering rate and the greater the optical absorption. The photothermal conversion efficiency of a SiO2 coating on the amorphous diamond-like carbon (a-DLC) selective absorber films deposited on the Cr/mirror like Al substrate is 93.2% as the film thickness of a SiO2 coating is 105nm. The coatings also increase the protective properties for a longer service life. This makes the SiO2 coated a-DLC film a promising new candidate material for solar selective absorber films. The SiO2/a-DLC selective absorber films also were deposited on the Al extrusion substrates
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