The coronavirus severe acute respiratory syndrome 2 (SARS-CoV-2), which is responsible for the disease 2019 pandemic, and closely related SARS-CoV enter cells by binding at human angiotensin converting enzyme (hACE2). stronger hACE2 affinity of SARS-CoV-2 has been connected with its higher infectivity. In this work, we study complexes receptor-binding domains (RBDs) viruses, using all-atom mole...