Cluster rotate

Keyword:

MOVE_CLUSTER_ROTATE

Move code:

8

Status:

core

How it works

The rotational counterpart of Cluster translate. PIMMS identifies the connected cluster of chains containing the selected chain and rotates the whole cluster as a rigid body (a cardinal 90/180/270° rotation about the cluster’s centre of mass). This reorients an entire aggregate at once - a degree of freedom (whole-cluster tumbling) that single-chain rotations cannot capture.

Why detailed balance holds

As with cluster translation, two conditions hold:

1. Symmetric rotation. The rotation is drawn uniformly from the cardinal rotations, whose inverses are equally likely for the reverse move.

2. Cluster preservation. The connected component is required to be unchanged by the move, so the reverse move selects and rotates the same cluster.

Together these make the proposal symmetric (\(g(x\to y)=g(y\to x)\)), and only the cluster-environment interface contributes to \(\Delta E\) (intra-cluster contacts are preserved by the rigid rotation). The plain Metropolis acceptance \(A = \min(1, e^{-\Delta E/T})\) then satisfies detailed balance (see the primer).

Configuration

MOVE_CLUSTER_ROTATEfloat

Probability of selecting a cluster-rotation step (all MOVE_* must sum to 1.0). Like cluster translation, keep this small (e.g. 0.01-0.05).