LOWER_WALLS
 This is part of the bias module

Defines a wall for the value of one or more collective variables, which limits the region of the phase space accessible during the simulation.

The restraining potential starts acting on the system when the value of the CV is greater (in the case of UPPER_WALLS) or lower (in the case of LOWER_WALLS) than a certain limit $$a_i$$ (AT) minus an offset $$o_i$$ (OFFSET). The expression for the bias due to the wall is given by:

$$\sum_i {k_i}((x_i-a_i+o_i)/s_i)^e_i$$

$$k_i$$ (KAPPA) is an energy constant in internal unit of the code, $$s_i$$ (EPS) a rescaling factor and $$e_i$$ (EXP) the exponent determining the power law. By default: EXP = 2, EPS = 1.0, OFFSET = 0.

Examples

The following input tells plumed to add both a lower and an upper walls on the distance between atoms 3 and 5 and the distance between atoms 2 and 4. The lower and upper limits are defined at different values. The strength of the walls is the same for the four cases. It also tells plumed to print the energy of the walls.

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. =3,5
d2: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =2,4
uwall: UPPER_WALLS ARGthe input for this action is the scalar output from one or more other actions. =d1,d2 ATcompulsory keyword
the positions of the wall. =1.0,1.5 KAPPAcompulsory keyword
the force constant for the wall. =150.0,150.0 EXPcompulsory keyword ( default=2.0 )
the powers for the walls. =2,2 EPScompulsory keyword ( default=1.0 )
the values for s_i in the expression for a wall =1,1 OFFSETcompulsory keyword ( default=0.0 )
the offset for the start of the wall. =0,0
lwall: LOWER_WALLS ARGthe input for this action is the scalar output from one or more other actions. =d1,d2 ATcompulsory keyword
the positions of the wall. =0.0,1.0 KAPPAcompulsory keyword
the force constant for the wall. =150.0,150.0 EXPcompulsory keyword ( default=2.0 )
the powers for the walls. =2,2 EPScompulsory keyword ( default=1.0 )
the values for s_i in the expression for a wall =1,1 OFFSETcompulsory keyword ( default=0.0 )
the offset for the start of the wall. =0,0
PRINT ARGthe input for this action is the scalar output from one or more other actions. =uwall.bias,lwall.bias