HarmonicCoupling

class openxps.couplings.HarmonicCoupling(collective_variable, dynamical_variable, force_constant)

A harmonic coupling between a dynamical variable and a collective variable.

The coupling energy is given by:

\[U = \frac{1}{2} \kappa \left(s - q({\bf r})\right)^2\]

where \(s\) is an extended dynamical variable, \(q({\bf r})\) is a physical collective variable, and \(\kappa\) is a coupling constant.

Parameters:

• collective_variable (CollectiveVariable) – The collective variable used in the coupling.

• dynamical_variable (DynamicalVariable) – The dynamical variable used in the coupling.

• force_constant (Quantity) – The force constant for the coupling.

Examples

>>> from copy import copy
>>> import cvpack
>>> import openxps as xps
>>> from openmm import unit
>>> dvmass = 3 * unit.dalton * (unit.nanometer / unit.radian)**2
>>> phi = cvpack.Torsion(6, 8, 14, 16, name="phi")
>>> phi_s = xps.DynamicalVariable(
...     "phi_s", unit.radian, dvmass, xps.CircularBounds()
... )
>>> kappa = 1000 * unit.kilojoule_per_mole / unit.radian**2
>>> xps.HarmonicCoupling(phi, phi_s, kappa)
HarmonicCoupling("0.5*kappa_phi_phi_s*((phi-phi_s-6.28...*floor(...))^2)")