A systematic study on the structures and electronic properties of copper clusters has been performed using the density functional theory. In the calculation, there are many isomers near the ground state for small copp...A systematic study on the structures and electronic properties of copper clusters has been performed using the density functional theory. In the calculation, there are many isomers near the ground state for small copper clusters. Our results show that the three-dimensional isomers of copper clusters start from Cu7 cluster and then show a tendency to form more compact structures. The results of the formation energy and the second derivative of binding energy with duster size show that besides N = 8, N =11 is also a magic number. Furthermore, it is the first time to find that the ground state of 11-atom clusters is a biplanar structure as same as the 13-atom cluster. The clear odd-even alternation as cluster size for the formation energy indicates the stability of electronic close shell existed in the range studied.展开更多
Gold（I） thiolate compounds （i.e. AuLSR） are important precursors for the synthesis of atom- ically precise Aun（SR）m nanoclusters. However, the nature of the AuI-SR precursor remains elusive. Here, we report that...Gold（I） thiolate compounds （i.e. AuLSR） are important precursors for the synthesis of atom- ically precise Aun（SR）m nanoclusters. However, the nature of the AuI-SR precursor remains elusive. Here, we report that the Aul0（TBBT）10 complex is a universal precursor for the synthesis of Aun（TBBT）m nanoclusters （where TBBT 4-tertbutylbenzenethiol/thiolate）. Interestingly, the Aul0（TBBT）10 complex is also found to be re-generated through extended etching of the Aun（SR）m nanoclusters with excess of TBBT thiol and O2. The formation of well-defined Aul0（TBBT）10 complex, instead of polymeric AuKSR, is attributed to the bulkiness of the TBBT thiol. Through 1D and 2D NMR charcteriztions, the structure of Aul0（TBBT）10 is correlated with the previously reported X-ray structure, which contains two inter-penetrated Aus（TBBT）5 rings. The photophysical property of Au10（TBBT）10 complex is further probed by femtosecond transient absorption spectroscopy. The acces- sibility of the precise Au10（TBBT）10 precursor improves the efficiency of the synthesis of the Aun（TBBT）m nanoclusters and is expected to further facilitate excellent control and understanding of the reaction mechanisms of nanocluster synthesis.展开更多
The association of organic carbon with secondary particles （aggregates） results in its storage and retention in soil. A study was carried out at a catchment covering about 92 km2 to predict spatial variability of so...The association of organic carbon with secondary particles （aggregates） results in its storage and retention in soil. A study was carried out at a catchment covering about 92 km2 to predict spatial variability of soil water-stable aggregates （WSA）, mean weight diameter （MWD） of aggregates and organic carbon （OC） content in macro.- （〉 2 mm）, meso- （1-2 mm）, and micro-aggregate （〈 1 mm） fractions, using geostatistical methods. One hundred and eleven soil samples were eSlleeted at the 0 10cm depth and fractionated into macro-, meso-, and mlcro-aggregates by wet sieving. The OC content was determined for each fraction. A greater percentage of water-stable aggregates was found for micro-aggregates, followed by meso-aggregates. Aggregate OC content was greatest in meso-aggregates （9 g kg-1）, followed by micro-aggregates （7 g kg-1）, while the least OC content was found in macro-aggregates （3 g kg-1）. Although a significant effect （P = 0.000） of aggregate size on aggregate OC content was found, however, our findings did not support the model of aggregate hierarchy. Land use had a significant effect （P = 0.073） on aggregate OC content. The coefficients of variation （CVs） for OC contents associated with each aggregate fraction indicated macro-aggregates as the most variable （CV = 71%）. Among the aggregate fractions, the micro-aggregate fraction had a lower CV value of 27%. macro-aggregates to 84% for micro-aggregates. Geostatistical analysis differences in their spatial patterns in both magnitude and space at variance for most aggregate-associated properties was lower than 45%. The mean content of WSA ranged from 15% for showed that the measured soil variables exhibited each aggregate size fraction. The relative nugget The range value for the variogram of water-stable aggregates was almost similar （about 3 km） for the three studied aggregate size classes. The range value for the variogram of aggregate-associated OC contents ranged from about 3 km for macro-aggregates to about 6.5 km for meso-aggregates. Kriged maps of predicted WSA, OC and MWD for the three studied aggregate size fractions showed clear spatial patterns. However, a close spatial similarity （co-regionalization） was observed between WSA and MWD.展开更多
文摘A systematic study on the structures and electronic properties of copper clusters has been performed using the density functional theory. In the calculation, there are many isomers near the ground state for small copper clusters. Our results show that the three-dimensional isomers of copper clusters start from Cu7 cluster and then show a tendency to form more compact structures. The results of the formation energy and the second derivative of binding energy with duster size show that besides N = 8, N =11 is also a magic number. Furthermore, it is the first time to find that the ground state of 11-atom clusters is a biplanar structure as same as the 13-atom cluster. The clear odd-even alternation as cluster size for the formation energy indicates the stability of electronic close shell existed in the range studied.
基金supported by the U.S.National Science Foundation(DMR-1808675)
文摘Gold（I） thiolate compounds （i.e. AuLSR） are important precursors for the synthesis of atom- ically precise Aun（SR）m nanoclusters. However, the nature of the AuI-SR precursor remains elusive. Here, we report that the Aul0（TBBT）10 complex is a universal precursor for the synthesis of Aun（TBBT）m nanoclusters （where TBBT 4-tertbutylbenzenethiol/thiolate）. Interestingly, the Aul0（TBBT）10 complex is also found to be re-generated through extended etching of the Aun（SR）m nanoclusters with excess of TBBT thiol and O2. The formation of well-defined Aul0（TBBT）10 complex, instead of polymeric AuKSR, is attributed to the bulkiness of the TBBT thiol. Through 1D and 2D NMR charcteriztions, the structure of Aul0（TBBT）10 is correlated with the previously reported X-ray structure, which contains two inter-penetrated Aus（TBBT）5 rings. The photophysical property of Au10（TBBT）10 complex is further probed by femtosecond transient absorption spectroscopy. The acces- sibility of the precise Au10（TBBT）10 precursor improves the efficiency of the synthesis of the Aun（TBBT）m nanoclusters and is expected to further facilitate excellent control and understanding of the reaction mechanisms of nanocluster synthesis.
基金Supported by Shahrekord University, Shahrekord, Iran
文摘The association of organic carbon with secondary particles （aggregates） results in its storage and retention in soil. A study was carried out at a catchment covering about 92 km2 to predict spatial variability of soil water-stable aggregates （WSA）, mean weight diameter （MWD） of aggregates and organic carbon （OC） content in macro.- （〉 2 mm）, meso- （1-2 mm）, and micro-aggregate （〈 1 mm） fractions, using geostatistical methods. One hundred and eleven soil samples were eSlleeted at the 0 10cm depth and fractionated into macro-, meso-, and mlcro-aggregates by wet sieving. The OC content was determined for each fraction. A greater percentage of water-stable aggregates was found for micro-aggregates, followed by meso-aggregates. Aggregate OC content was greatest in meso-aggregates （9 g kg-1）, followed by micro-aggregates （7 g kg-1）, while the least OC content was found in macro-aggregates （3 g kg-1）. Although a significant effect （P = 0.000） of aggregate size on aggregate OC content was found, however, our findings did not support the model of aggregate hierarchy. Land use had a significant effect （P = 0.073） on aggregate OC content. The coefficients of variation （CVs） for OC contents associated with each aggregate fraction indicated macro-aggregates as the most variable （CV = 71%）. Among the aggregate fractions, the micro-aggregate fraction had a lower CV value of 27%. macro-aggregates to 84% for micro-aggregates. Geostatistical analysis differences in their spatial patterns in both magnitude and space at variance for most aggregate-associated properties was lower than 45%. The mean content of WSA ranged from 15% for showed that the measured soil variables exhibited each aggregate size fraction. The relative nugget The range value for the variogram of water-stable aggregates was almost similar （about 3 km） for the three studied aggregate size classes. The range value for the variogram of aggregate-associated OC contents ranged from about 3 km for macro-aggregates to about 6.5 km for meso-aggregates. Kriged maps of predicted WSA, OC and MWD for the three studied aggregate size fractions showed clear spatial patterns. However, a close spatial similarity （co-regionalization） was observed between WSA and MWD.
