Quasi-nonergodicity

One reason for the inefficiencies of constraint methods is that they may prevent an efficient sampling of the set (x) = . This is illustrated by Fig. 4.2. It is common that many pathways separated by high energy barriers exist to go from A to B. In constrained simulation, the system can get trapped in one of the pathways. In the most serious cases, this leads to quasi-nonergodic effect where only a part of the set (x) is effectively explored. In less serious cases, the convergence is quite slow. 

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