Photoelectron spectroscopy revealed that a 20-atom gold cluster has an extremely large energy gap, which is even greater than that of C60, and an electron affinity comparable with that of C60. This observation suggests that the Au20 cluster should be highly stable and chemically inert. Using relativistic density functional calculations, we found that Au20 possesses a tetrahedral structure, which is a fragment of the face-centered cubic lattice of bulk gold with a small structural relaxation. Au20 is thus a unique molecule with atomic packing similar to that of bulk gold but with very different properties.

China has made remarkable progress in strengthening its primary health-care system. Nevertheless, the system still faces challenges in structural characteristics, incentives and policies, and quality of care, all of which diminish its preparedness to care for a fifth of the world's population, which is ageing and which has a growing prevalence of chronic non-communicable disease. These challenges include inadequate education and qualifications of its workforce, ageing and turnover of village doctors, fragmented health information technology systems, a paucity of digital data on everyday clinical practice, financial subsidies and incentives that do not encourage cost savings and good performance, insurance policies that hamper the efficiency of care delivery, an insufficient quality measurement and improvement system, and poor performance in the control of risk factors (such as hypertension and diabetes). As China deepens its health-care reform, it has the opportunity to build an integrated, cooperative primary health-care system, generating knowledge from practice that can support improvements, and bolstered by evidence-based performance indicators and incentives.