ADD_STR_BENDS

NAME
ADD_STR_BENDS - Add a bending potential between three target atoms.

SYNOPSIS
ADD_STR_BENDS    iat1    iat2    iat2    k    $\alpha_0$    [ $alpha_{\tau}$]

DESCRIPTION
This command can be used to impose an additional bending constraint between atom iat1, iat2 and iat3 of the solute. The numeric order of the solute atom indices iat1, iat2 is that specified in the topology file (see Sec. 10.3). The central atom of the bending is ita2. The added bending potential has force constant k (in Kcal/mol/rad$^{2}$) and equilibrium bending angle $\alpha_0$ (in degrees). If $\alpha_\tau$ is also specified, then the added bending potential is time dependent and $alpha_{\tau}$ is the equilibrium bending angle after the steering time $\tau$ (see STEER(&RUN)) command for the definition of the steering time in a SMD simulation)

WARNINGS
If the chosen $\alpha_0$ is very different from the actual value of the bending angle at time 0, a very large force is experienced by the atoms in involved in the added bending and the simulation may catastrophically diverge after few steps.

EXAMPLES

• Example 1.
  

   
  ADD_STR_BENDS  1 50 104  400.  180.0
  

• Example 2.
  

   
  &POTENTIAL 
    ...
    ADD_STR_BENDS  1 50 104  400.  180.0 90.0
   ..
  &END
  ....
  ...
  &RUN
     ...
     STEER 10000.  50000. 
     ...
  &END
  

In the first example a bending constraint is imposed between atom 1, atom 50, and atom 104 of the solute. In the second example a time-dependent driving potential is applied to the same atoms of the solute. The equilibrium bending angle of such harmonic driving potential move at constant velocity in $\tau=40$ ps (starting at t=10 ps ) between $\alpha_0=180.0$ and $\alpha_\tau=90.0$.