Action: DUMPFORCES

Module	generic
Description	Usage
Dump the force acting on one of a values in a file.
This action outputs data to a file. You can read more about how PLUMED manages output files here

Input

The arguments that serve as the input for this action are specified using one or more of the keywords in the following table.

Further details and examples

Dump the force acting on one of a values in a file.

Consider the following PLUMED input:

Click on the labels of the actions for more information on what each action computes

rThe DISTANCE action with label r calculates the following quantities:
 Quantity   
 Type   
 Description  
r
scalar
the DISTANCE between this pair of atoms: DISTANCECalculate the distance/s between pairs of atoms. More details ATOMSthe pair of atom that we are calculating the distance between=1,2
VThe RESTRAINT action with label V calculates the following quantities:
 Quantity   
 Type   
 Description  
V.bias
scalar
the instantaneous value of the bias potential
V.force2
scalar
the instantaneous value of the squared force due to this bias potential: RESTRAINTAdds harmonic and/or linear restraints on one or more variables. This action has hidden defaults. More details ARGthe values the harmonic restraint acts upon=r ATthe position of the restraint=0.2 KAPPA specifies that the restraint is harmonic and what the values of the force constants on each of the variables are=100
V: RESTRAINTAdds harmonic and/or linear restraints on one or more variables. This action uses the defaults shown here. More details ARGthe values the harmonic restraint acts upon=r ATthe position of the restraint=0.2 KAPPA specifies that the restraint is harmonic and what the values of the force constants on each of the variables are=100  SLOPE specifies that the restraint is linear and what the values of the force constants on each of the variables are=0.0

This input will ultimately apply forces on the $x$, $y$ and $z$ components of two atoms as well as the 9 cell vectors. The force on the $i$th of these 15 quantities is given by:

$$F_i = - \frac{\textrm{d}V}{\textrm{d}r}\frac{\partial r}{\partial x_i}$$

where $x_i$ is the $x$, $y$ or $z$ component of the position of one of the two atoms or one of the cell vectors. If we modify the input above by adding the DUMPFORCES command as shown below:

Click on the labels of the actions for more information on what each action computes

rThe DISTANCE action with label r calculates the following quantities:
 Quantity   
 Type   
 Description  
r
scalar
the DISTANCE between this pair of atoms: DISTANCECalculate the distance/s between pairs of atoms. More details ATOMSthe pair of atom that we are calculating the distance between=1,2
VThe RESTRAINT action with label V calculates the following quantities:
 Quantity   
 Type   
 Description  
V.bias
scalar
the instantaneous value of the bias potential
V.force2
scalar
the instantaneous value of the squared force due to this bias potential: RESTRAINTAdds harmonic and/or linear restraints on one or more variables. This action has hidden defaults. More details ARGthe values the harmonic restraint acts upon=r ATthe position of the restraint=0.2 KAPPA specifies that the restraint is harmonic and what the values of the force constants on each of the variables are=100
V: RESTRAINTAdds harmonic and/or linear restraints on one or more variables. This action uses the defaults shown here. More details ARGthe values the harmonic restraint acts upon=r ATthe position of the restraint=0.2 KAPPA specifies that the restraint is harmonic and what the values of the force constants on each of the variables are=100  SLOPE specifies that the restraint is linear and what the values of the force constants on each of the variables are=0.0
DUMPFORCESDump the force acting on one of a values in a file. More details ARGthe labels of the values whose forces should be output=r FILEthe name of the file on which to output the forces=forces

we can then monitor the value of $-\frac{\textrm{d}V}{\textrm{d}r}\frac{\partial r}$ in the output file forces. As explained by the equation above to get the forces on the atom this 'input force' needs to be multiplied by $\frac{\partial r}{\partial x_i}$. To view the various components of the $\frac{\partial r}{\partial x_i}$ you would use the DUMPDERIVATIVES command. To control the buffering of output you use the FLUSH command.

Syntax

The following table describes the keywords and options that can be used with this action