 The conformation equilibrium between open (up) and closed (down) conformations of receptor binding domain (RBD)  is studied from the first-principle.
<meaning-changed>  The conformation equilibrium between open (up) and closed (down) conformations of receptor binding domain (RBD)  is studied from the first-principle.
 The conformation equilibrium between open (up) and closed (down) conformations of receptor binding domain (RBD) of the spike is studied from the first-principle.