   MOVINGRESTRAINT
 This is part of the bias module

Add a time-dependent, harmonic restraint on one or more variables.

This form of bias can be used to performed steered MD  and Jarzynski sampling .

The harmonic restraint on your system is given by:

$V(\vec{s},t) = \frac{1}{2} \kappa(t) ( \vec{s} - \vec{s}_0(t) )^2$

The time dependence of $$\kappa$$ and $$\vec{s}_0$$ are specified by a list of STEP, KAPPA and AT keywords. These keywords tell plumed what values $$\kappa$$ and $$\vec{s}_0$$ should have at the time specified by the corresponding STEP keyword. In between these times the values of $$\kappa$$ and $$\vec{s}_0$$ are linearly interpolated.

Additional material and examples can be also found in the tutorial Belfast tutorial: Out of equilibrium dynamics

Examples

The following input is dragging the distance between atoms 2 and 4 from 1 to 2 in the first 1000 steps, then back in the next 1000 steps. In the following 500 steps the restraint is progressively switched off.

Click on the labels of the actions for more information on what each action computes d: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =2,4
MOVINGRESTRAINT ...
ARGthe input for this action is the scalar output from one or more other actions. =d
STEP0compulsory keyword
This keyword appears multiple times as STEP\f$x\f$ with x=0,1,2,...,n. =0 AT0compulsory keyword
AT\f$x\f$ is equal to the position of the restraint at time STEP\f$x\f$. =1.0 KAPPA0compulsory keyword
KAPPA\f$x\f$ is equal to the value of the force constants at time STEP\f$x\f$. =100.0
STEP1compulsory keyword
This keyword appears multiple times as STEP\f$x\f$ with x=0,1,2,...,n. =1000 AT1compulsory keyword
AT\f$x\f$ is equal to the position of the restraint at time STEP\f$x\f$. =2.0
STEP2compulsory keyword
This keyword appears multiple times as STEP\f$x\f$ with x=0,1,2,...,n. =2000 AT2compulsory keyword
AT\f$x\f$ is equal to the position of the restraint at time STEP\f$x\f$. =1.0
STEP3compulsory keyword
This keyword appears multiple times as STEP\f$x\f$ with x=0,1,2,...,n. =2500 KAPPA3compulsory keyword
KAPPA\f$x\f$ is equal to the value of the force constants at time STEP\f$x\f$. =0.0
...


The following input is progressively building restraints distances between atoms 1 and 5 and between atoms 2 and 4 in the first 1000 steps. Afterwards, the restraint is kept static.

Click on the labels of the actions for more information on what each action computes d1: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =1,5
d2: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =2,4
MOVINGRESTRAINT ...
ARGthe input for this action is the scalar output from one or more other actions. =d1,d2
STEP0compulsory keyword
This keyword appears multiple times as STEP\f$x\f$ with x=0,1,2,...,n. =0 AT0compulsory keyword
AT\f$x\f$ is equal to the position of the restraint at time STEP\f$x\f$. =1.0,1.5 KAPPA0compulsory keyword
KAPPA\f$x\f$ is equal to the value of the force constants at time STEP\f$x\f$. =0.0,0.0
STEP1compulsory keyword
This keyword appears multiple times as STEP\f$x\f$ with x=0,1,2,...,n. =1000 AT1compulsory keyword
AT\f$x\f$ is equal to the position of the restraint at time STEP\f$x\f$. =1.0,1.5 KAPPA1compulsory keyword
KAPPA\f$x\f$ is equal to the value of the force constants at time STEP\f$x\f$. =1.0,1.0
...


The following input is progressively bringing atoms 1 and 2 close to each other with an upper wall

Click on the labels of the actions for more information on what each action computes d1: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =1,2
MOVINGRESTRAINT ...
ARGthe input for this action is the scalar output from one or more other actions. =d1
VERSEcompulsory keyword ( default=B )
Tells plumed whether the restraint is only acting for CV larger (U) or smaller (L)
than the restraint or whether it is acting on both sides (B) =U
STEP0compulsory keyword
This keyword appears multiple times as STEP\f$x\f$ with x=0,1,2,...,n. =0 AT0compulsory keyword
AT\f$x\f$ is equal to the position of the restraint at time STEP\f$x\f$. =1.0 KAPPA0compulsory keyword
KAPPA\f$x\f$ is equal to the value of the force constants at time STEP\f$x\f$. =10.0
STEP1compulsory keyword
This keyword appears multiple times as STEP\f$x\f$ with x=0,1,2,...,n. =1000 AT1compulsory keyword
AT\f$x\f$ is equal to the position of the restraint at time STEP\f$x\f$. =0.0
...


By default the Action is issuing some values which are the work on each degree of freedom, the center of the harmonic potential, the total bias deposited

 VERSE ( default=B ) Tells plumed whether the restraint is only acting for CV larger (U) or smaller (L) than the restraint or whether it is acting on both sides (B) STEP This keyword appears multiple times as STEP $$x$$ with x=0,1,2,...,n. Each value given represents the MD step at which the restraint parameters take the values KAPPA $$x$$ and AT $$x$$. You can use multiple instances of this keyword i.e. STEP1, STEP2, STEP3... AT AT $$x$$ is equal to the position of the restraint at time STEP $$x$$. For intermediate times this parameter is linearly interpolated. If no AT $$x$$ is specified for STEP $$x$$ then the values of AT are kept constant during the interval of time between STEP $$x-1$$ and STEP $$x$$. You can use multiple instances of this keyword i.e. AT1, AT2, AT3... KAPPA KAPPA $$x$$ is equal to the value of the force constants at time STEP $$x$$. For intermediate times this parameter is linearly interpolated. If no KAPPA $$x$$ is specified for STEP $$x$$ then the values of KAPPA $$x$$ are kept constant during the interval of time between STEP $$x-1$$ and STEP $$x$$. You can use multiple instances of this keyword i.e. KAPPA1, KAPPA2, KAPPA3...