FRET
This is part of the isdb module

Calculates the FRET efficiency between a pair of atoms. The efficiency is calculated using the Forster relation:

\[ E=\frac{1}{1+(R/R_0)^6} \]

where \(R\) is the distance and \(R_0\) is the Forster radius.

By default the distance is computed taking into account periodic boundary conditions. This behavior can be changed with the NOPBC flag.

Examples

The following input tells plumed to print the FRET efficiencies calculated as a function of the distance between atoms 3 and 5 and the distance between atoms 2 and 4.

Click on the labels of the actions for more information on what each action computes
tested on master
fe1: FRET 
ATOMS
the pair of atom that we are calculating the distance between.
=3,5
R0
could not find this keyword
=5.5 fe2: FRET
ATOMS
the pair of atom that we are calculating the distance between.
=2,4
R0
could not find this keyword
=5.5 PRINT
ARG
compulsory keyword the labels of the values that you would like to print to the file
=fe1,fe2

The following input computes the FRET efficiency calculated on the terminal atoms of a polymer of 100 atoms and keeps it at a value around 0.5.

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




Notice that NOPBC is used to be sure that if the distance is larger than half the simulation box the distance is compute properly. Also notice that, since many MD codes break molecules across cell boundary, it might be necessary to use the WHOLEMOLECULES keyword (also notice that it should be before FRET). Just be sure that the ordered list provide to WHOLEMOLECULES has the following properties:

  • Consecutive atoms should be closer than half-cell throughout the entire simulation.
  • Atoms required later for the distance (e.g. 1 and 100) should be included in the list
Glossary of keywords and components
Description of components

By default the value of the calculated quantity can be referenced elsewhere in the input file by using the label of the action. Alternatively this Action can be used to calculate the following quantities by employing the keywords listed below. These quantities can be referenced elsewhere in the input by using this Action's label followed by a dot and the name of the quantity required from the list below.

Quantity Description
.#!value the fret efficiency between the input pair of atoms
The atoms involved can be specified using
ATOMS the pair of atom that we are calculating the distance between. For more information on how to specify lists of atoms see Groups and Virtual Atoms
Compulsory keywords
R0 The value of the Forster radius.
Options
NUMERICAL_DERIVATIVES ( default=off ) calculate the derivatives for these quantities numerically
NOPBC

( default=off ) ignore the periodic boundary conditions when calculating distances