The performance of the three-layer ONIOM method was systematically investigated by comparing the optimized geometries and calculated deprotonation energy of a zwitterionic peptide molecule, NH3(+)-CH(n)Bu-CO-NH-CH2-CO-NH-CH(n)Bu-COO(-), using all possible combinations of B3LYP/6-31G* as the high-level quantum (HQ), AM1 as the low-level quantum (LQ), and Amber as the MM method. Results show that the three-layer ONIOM(HQ:LQ:MM) method, which includes a medium-level quantum method in the middle system to take into account the electronic effects of the middle layer and to keep the problematic QM-MM boundary away from the action region, is more reliable and more stable than the QM:MM:MM or generic QM/MM method and is the best compromise between accuracy and computational cost.
Previous research suggests that entrepreneurship can provide ethnic minorities a springboard for economic advancement and social integration. However, self-employment rates vary significantly among ethnic groups, between men and women, and in different places. The prevailing literature suggests that personal characteristics, including human capital attributes, ethnic networking, institutional regulations, societal structures and discrimination, all contribute to the differential ethnic entrepreneurship rates. However, very few recent studies have analyzed how different urban socio-economic contexts influence this process. Using the 2000 Public Usable Microdata Samples (PUMS), this study examines how Hispanic entrepreneurs perform in three different metropolitan areas in the US South. The results show that the ethnic diversity, history of immigration, and the economic structure in each local area have provided different opportunities and challenges for Hispanics to start up and maintain their own businesses. This study suggests that the process of economic incorporation of ethnic minorities and immigrants depends significantly on the institutional capacity and social, cultural and political resources of local communities.
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