Head pivot

Keyword:

MOVE_HEAD_PIVOT

Move code:

5

Status:

core (but almost always set to 0)

How it works

A head pivot is a pivot (Chain pivot) restricted to a single terminal bead: one of the two chain ends is chosen and that terminus is rotated about its neighbour. Only the end bead moves, so the conformational change is tiny - much smaller than a normal pivot, and largely redundant with what the crankshaft already does at the chain ends.

Why detailed balance holds

As for the other rigid moves, the choice of terminus and rotation is symmetric between the forward and reverse proposals,

\[g(x\to y) = g(y\to x),\]

so the plain Metropolis acceptance \(A = \min(1, e^{-\Delta E/T})\) preserves detailed balance (see the primer).

Configuration

MOVE_HEAD_PIVOTfloat

Probability of selecting a head-pivot step (all MOVE_* must sum to 1.0).

In practice this move adds little over the crankshaft and we recommend leaving it at 0. It is retained mainly for completeness.